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20240614 Lexington Road Subdivision Area Variances SWPPP
Unauthorized alteration or addition to this document is a violation of the NYS Education Law. © 202 1 BASIC STORMWATER POLLUTION PREVENTION PLAN (SWPPP) FOR THE DEVELOPMENT OF BEMIS POINT CITY OF SARATOGA SPRINGS SARATOGA COUNTY, NEW YORK PREPARED FOR: AAADMC VENTURES, LLC 1 NADEAU DRIVE CLIFTON PARK, NEW YORK 12065 JUNE 2025 PREPARED BY: Arico Associates 1407 Route 9, Bld.2, Suite 6 Clifton Park, New York 12065 ARICO ASSOCIATES PROJECT ID: 21.32 Arico Associates Bemis Point Engineers, Land Planners & Consultants SWPPP Narrative Report Page 1 of 7 Introduction and Background In 1972, Congress passed the Federal Water Pollution Control Act (FWPCA), also known as the Clean Water Act (CWA), to restore and maintain the quality of the nation’s waterways. The ultimate goal was to ensure that rivers and streams were fishable, swimmable, and drinkable. In 1987, the Water Quality Act (WQA) added provisions to the CWA that allowed the United States Environmental Protection Agency (EPA) to govern stormwater discharges from construction sites. In 1998, EPA published the final notice for General Permits for Stormwater Discharges from Construction Activities Disturbing 5 Acres or Greater (63 Federal Register 7898, February 14, 1998). The general permit includes provisions for development of a SWPPP to maximize the potential benefits of pollution prevention and sediment and erosion control measures at construction sites. Development, implementation, and maintenance of the SWPPP will provide the General Contractor with the framework for reducing soil erosion and minimizing pollutants in stormwater during site work construction of the Bemis Point residential development (Project). To accommodate the proposed development, it will be necessary to modify the existing drainage patterns from runoff from roofs, pavement and other impervious and open/landscaped areas. Since there is more than 1.0 acres and less than 5.0 acres of land disturbance, a Full Stormwater Pollution Prevention Plan (SWPPP) is not required. Instead, only a Basic Stormwater Pollution Prevention Plan for erosion and sediment controls will be developed and presented for review. All erosion and sediment control measures will be implemented prior to commencing excavation or grading as shown on the plans and will remain in operation until the projects’ end. Disturbed areas will be stabilized by seeding and mulching per the Basic Stormwater Pollution Prevention Plan (SWPPP) details and specifications. In general, the existing drainage patterns will remain the same based on pre-developed conditions vs. post-developed improvements. As depicted on the existing conditions plan, the drainage predominantly drains to the southeast. The drainage patterns will remain primarily as sheet flow, except for the proposed access road and portions of the development lots that will be collected by means of a stormwater collection system. Stormwater collection will be directed to the northern and southern portions of the property prior to discharging to erosion and sediment basins. SWPPP Content This SWPPP Narrative has been prepared in summary and is based on the current level of design, in accordance with the regulations, guidelines, and conditions set forth in the Construction Stormwater General Permit, NYS Stormwater Pollution Prevention Plan (SWPPP) Design Manual, January 2024 and NYSDEC GP-0-25-001 Permit Requirements, in addition to the NYS Standard and Specifications for Erosion and Sediment Control November 2016. The following documentation is to provide the accreditation that the stormwater management plan being proposed. Upon review by City of Saratoga Springs and other agencies having jurisdiction, the management plan will be updated for permitting and construction. Arico Associates Bemis Point Engineers, Land Planners & Consultants SWPPP Narrative Report Page 2 of 7 Applicant and Existing Site The project applicant, AAADMC Ventures LLC, c/o Arthur Curto, located at 1 Nadeau Drive, Clifton Park, New York is pursuing approvals for a 14-lot residential single-family subdivision on approximately 21.7± acre parcel. The newly constructed homes will be accessed via an extension of Lexington Road with the single home on Bemis Heights Road accessed via Concord Drive and/or Bemis Heights Road and Lexington Road. The existing neighborhood consists of 68 single family homes and was also known as Independence Square under the original subdivision approvals. Initially, the 21.7± acre was considered Phase 3 and consisted of 39 single-family building lots, though never constructed. Over the years the land has remained undeveloped and the proposal is to modify the 39-lot subdivision into 14-lots. The Project parcel is a wooded area with surrounding land use that includes low-density residential developments, educational facility and undeveloped wooded areas. The parcel is bounded by Lots 2, 4, 6 and 8 Bemis Height Road; Lands N/F of Board of Cooperative Educational Services to the west; Lands N/F of Thomas Deveno to the south; and NYS 87 to the east. The parcel is identified as Tax Map Parcels 166.15- 2-34, -35, 166.19-1-1 through -41 (NYSDEC Stormwater Mapper Coordinates: LAT 43.078, LONG -73.752). Stormwater Management & Drainage The proposed land use will modify the existing site by increasing impervious area with the construction of the access road, roof tops and driveways. Accordingly, 1.29± acres, or 5.9% of the entire project parcel area of the 21.7± acres will contain impervious area. Of the remaining 20.4± acres, 1.96± acres will consist of grassed area for lawns and landscaping totaling and 18.45± acres will be undisturbed woods and wetlands. Though not a requirement under the general permit, a series of Green Infrastructure Practices (GIP) are planned for this project for removal of stormwater pollutants to aide in the reduction for stormwater quality control. The intended GIP include sedimentation areas at storm collection discharge points and disconnection of roof tops along the rear yards. All or nearly all the new impervious area from roofs, pavement and other impervious areas will be directed to the storm sewer collection system and management areas. The remaining area will sheet drain maintain the present runoff flow towards the wooded and wetland areas. As noted above, since there is more than 1.0 acres and less than 5.0 acres of land disturbance, a Full Stormwater Pollution Prevention Plan (SWPPP) is not required. Instead, only a Basic Stormwater Pollution Prevention Plan for erosion and sediment controls and are presented below. Erosion and Sediment Controls During construction, the Operator will comply with the measures provided in this SWPPP and conduct construction activities in such a manner that is in accordance with GP-0-20-001 conditions. It is the Operator’s responsibility not to undertake more than that magnitude of work that can be safely and adequately controlled by the methods at their disposal. The Operator’s approach must emphasize preventing erosion before it occurs as opposed to treating sediment- laden storm water runoff. Arico Associates Bemis Point Engineers, Land Planners & Consultants SWPPP Narrative Report Page 3 of 7 The Erosion Control Plan proposed will represent the suggested best management practices proposed for the project. The Contractor's approach to controlling storm water runoff from the site may vary; however, they must update this SWPPP to reflect the changes and appropriate corresponding erosio n control measures using the Progress Maps and the SWPPP Amendment form. The use of erosion and sedimentation controls is mandatory and must be employed to minimize impacts to adjacent areas during the construction. If sediment escapes the construction site, off- site accumulations of sediment must be removed at a frequency sufficient to minimize off-site impacts. The control practices which are required to control storm water pollution during construction must remain functional until disturbed areas have been stabilized. Erosion control products are to be installed and maintained in accordance with manufacturer's specifications and good engineering practices. During all phases, the Erosion and Sediment Control BMPs outlined in the following sections must be inspected based the inspection frequency discussed. In addition, stabilization measures must be instituted on disturbed areas as soon as practicable, but no more than 14 days after construction activity has temporarily or permanently ceased on any portion of the site. Construction Phasing and Best Management Practices (BMPS) Construction activities will be sequenced in order to minimize site disturbance, protect sensitive natural features, and prevent soil erosion and sediment transport. The intended construction sequence and timing of major activities are identified below. Stabilized Construction Exit: At the beginning a stabilized construction exit must be installed at the location where vehicles are expected to enter and/or exit the site in order to prevent the off-site tracking of sediment onto adjacent public roadways. The stabilized construction entrances will consist of compacted two to three inch (2"-4" thickness) crushed stone, placed over a layer of geotextile fabric (to provide separation from the underlying soil and prevent the stone from being ground down into the soil). The stabilized construction entrance must be wide enough to cover the entire width of the entrance/exit and allow two vehicles to pass comfortably, and it should be flared where it meets the public roadway to accommodate longer construction vehicles. The stabilized construction entrance must be long enough to allow mud and sediment to become dislodged from vehicle tires, and/or a minimum of fifty (50’) in length. Over the course of construction, the stabilized construction entrance will become filled with accumulated sediment. The Contractor must inspect the stabilized construction entrance and adjacent public roadways for off-site sediment tracking and repair the entrance as necessary (remove accumulated sediment and add new stone as necessary). If tracking onto public roadways does occur, the streets in the vicinity of the stabilized construction entrance shall be swept immediately. The stabilized construction entrance shall not be removed until just prior to project completion. Mulch Tube/Silt Fence: At the beginning a combination of mulch tube and silt fence or just silt fence shall be installed to prevent sediment laden runoff from leaving the site. In addition, silt fence will be used on the down gradient sides of material stockpile areas. Arico Associates Bemis Point Engineers, Land Planners & Consultants SWPPP Narrative Report Page 4 of 7 The mulch tubes consist of a tube of mulch placed along a contour if possible. The tubes intercept and slow sheet flow runoff. Mulch tubes shall be firmly staked. Accumulated sediment must be removed from the tubes when it reaches ½ of the height of the tube. Silt fence is a sediment control BMP consisting of a length of geotextile fabric stretched between anchoring posts spaced at regular intervals along the site at low/down-slope areas. The geotextile fabric must be entrenched in the ground between the support posts. Silt fence is effective in treating low velo sheet flow and is not intended for use in areas of concentrated or channelized flow. Silt fence must be inspected for rips, tears, and gaps between the fence and the ground. An adequate reserve of silt fence must be kept on site at all times for emergency and/or routine replacement. Silt fence shall be entirely removed only after exposed soils in the contributing drainage area are stabilized. Silt fence can also be used as an effective perimeter control to contain stockpiles of topsoil or other erodible material. Stockpile Management: Stockpiles of erodible material, including any topsoil salvaged during construction, must be surrounded by a perimeter sediment control such as silt fence to prevent storm water runoff from being contaminated by eroded sediment. Stockpiles of erodible material must be stabilized utilizing a temporary stabilization technique if they remain inactive for more than fourteen (14) days. Stockpiles must be located at least 100 feet from wetland resource areas (i.e. bordering vegetated wetlands and Buffer zone). Stockpile locations must be tracked using the Site Maps included in Appendix A. Dust Control: Dust control BMPs are various means and methods of preventing soil erosion by wind. During all stages of the project generation of dust must be minimized to prevent air and water pollution as well as minimize risks to human health. Earthmoving activities are the primary source of dust 'generation during construction, but traffic on un-stabilized access roads and sediment transport by wind blowing across exposed soil surfaces can also be contributing factors. The most effective dust control BMPs for preventing wind erosion involve stabilizing (temporary or permanent) exposed soils. However, where soil stabilization is not practical techniques that increase soil moisture and encourage the formation of soil clods or reduce wind velo at the soil surface are also effective. The following dust control BMPs are typically used on construction sites: • Watering/Irrigation: Sprinkling the ground surface with water until it is moist. • Soil Stabilization: Vegetative cover, mulch, riprap or any method that covers the soil surface reduces the potential for soil particles to become airborne. • Wind Breaks: Wind breaks are barriers (either natural or constructed) that reduce wind velo across exposed soil surfaces and reduces the potential for soil particles become airborne. Wind breaks can be trees or shrubs left in place during site clearing or constructed barriers such as a wind fence. • Soil Roughening: Deep tillage in large areas of exposed soil brings soil clods to the surface preventing soil particles from becoming airborne. Temporary Sediment Basins/Traps: If temporary sediment basins/traps/swales are needed at the beginning, basins must provide 3,600 cubic feet of storage per acre drained and disturbed. Temporary sediment basins are a sediment control BMP that consist of an excavated or natural depression that detains/retains storm water runoff allowing sediments to settle out of suspension prior to discharge via a suitably stabilized outlet. They also provide an opportunity for storm water infiltration. The temporary Arico Associates Bemis Point Engineers, Land Planners & Consultants SWPPP Narrative Report Page 5 of 7 sediment basin's side-slopes and bottom must be appropriately stabilized prior to directing runoff to it. Accumulated sediment must be removed when it reaches 33% of the design volume capacity of the basin in order to maximize sediment settling potential and minimize the possibility of sediment washout during high intensity/long duration storm events. The basins will include a controlled outlet structure consisting of a perforated riser pipe packed in gravel which allow for further reduction of sediment prior to discharge. Traps will include a rip rap spillway. Temporary Stabilization: Stabilization measures must be initiated as soon as practicable on portions of the site where construction activities have temporarily or permanently ceased, but in no case more than 14 days after the construction activity in that portion of the site has temporarily or permanently ceased. Temporary stabilization refers to a variety of erosion control BMPs that protect exposed soils from the erosive forces of precipitation (raindrop and sheet erosion) and/or prevent the formation of channelized flow (rill, gully and channel erosion). The Contractor must inspect temporarily stabilized areas to assess the effectiveness of temporary stabilization BMPs and replace/repair then as necessary. The following temporary stabilization BMPs are typically used on construction sites and may be used by the Contractor for this project: Erosion Control Blankets: Erosion control blankets are erosion control BMPs consisting of natural or synthetic geotextile fabrics formed into long sheets or mats that are rolled out over exposed soils and fastened with stakes, pegs or staples. They are used in areas where high runoff velo makes traditional mulching ineffective. Blankets are highly effective at stabilizing steep slopes (3:1or greater) and can be used to stabilize areas of concentrated flow such as swales. Soil Roughening: Soil roughening is an erosion control BMP that involves creating grooves or impressions in exposed soil surfaces with tracked construction equipment (bulldozer, excavator, etc.). Slopes that are not fine graded or smoothed but left in a roughened condition reduce erosion by decreasing slope length and runoff velo, increasing infiltration, trapping sediment, and allowing seed to take hold and grow. It is critically important that the impressions be made perpendicular to the slope contours (never parallel to the contour); improper use of this technique can actually accelerate erosion. Soil roughening shall be used as a last resort. Temporary Seeding: Temporary seeding is an erosion control BMP that consists of using select varieties of grasses to establish vegetative cover. Temporary seeding utilizes annual species that establish quickly, are not persistent or invasive, but provide long term temporary cover (as opposed to the perennial species used in permanent seeding for final stabilization). Temporary Diversion Ditches: Temporary diversion ditches are an option to divert runoff away from construction area. Temporary drainage ditches are a runoff control BMP consisting of a ditch or excavation installed as a means of conveying storm water runoff to temporary sediment basins/traps (or other sediment control BMPs) while soil disturbing construction activities are ongoing. The temporary drainage ditch side-slopes and bottom must be appropriately stabilized prior to directing runoff to it. The temporary ditches will include stone check dams (see below). Temporary drainage ditches may be constructed as needed at locations determined by the Operator. This is done to account for unanticipated on-site field conditions. Arico Associates Bemis Point Engineers, Land Planners & Consultants SWPPP Narrative Report Page 6 of 7 Concrete Washout Area: Concrete washout areas consist of a prefabricated or site-built impermeable containment area sized to hold concrete wastes and wash water (including one (1) foot freeboard). Concrete washouts are used to contain concrete and liquids when the chutes of concrete mixers and hoppers of concrete pumps are rinsed out after delivery. The washout facility consolidates solids for easier disposal and prevent runoff of liquids. The wash water is alkaline and contains high levels of chromium, which can leach into the ground and contaminate groundwater. It can also migrate to a storm drain, which can increase the pH of area waters and harm aquatic life. Solids that are improperly disposed of can clog storm drain pipes and cause flooding. The concrete washouts must be constructed prior to placement of concrete on-site. The concrete washout area must be located in an area where its likelihood of contributing to storm water discharges is negligible. Washouts shall be located outside of any wetland resource are and 100’ from buffer zones to wetlands. These specially designated areas should be properly signed, and onsite personnel instructed in their proper use. The hardened residue from the concrete wash out area will be disposed of in the same manner as other non-hazardous construction waste materials or may be broken up and used onsite as appropriate. It is the responsibility of the Contractor to ensure that these procedures are followed. The Contractor must track concrete washout locations on the Progress Map if they are moved or if additional concrete washouts need to be constructed. Permanent Stabilization: Permanent stabilization refers to a variety of erosion control BMPs that allow a construction project to achieve "final stabilization." Final stabilization is defined in Appendix A of GP- 0-25-001 as: a uniform, perennial vegetative cover with a density of eighty percent (80%) over the entire pervious surface has been established, or other equivalent permanent stabilization measures have been employed. Construction Sequencing and Phasing Soil disturbing activities associated with the site development will be phased according to the construction schedule. The sequence of major activities will show on Erosion and Sedimentation Control Plans found in Appendix A and is expected to be as follows: Site Preparation. The limits of disturbance shall be identified. Erosion and sedimentation control systems shall be placed in accordance with the plans and/or where erosion and sedimentation may occur. Erosion and sediment control systems will be placed as dictated by site conditions in order to maintain the intent of the specifications of the SWPPP and/or contract documents. Clearing and grubbing and removal of any trees, other vegetation and/or excavation from areas to be disturbed may begin only when erosion and sediment control systems are in place and fully functional. Place construction trailers (if any) and portable toilets. Erosion & Sediment Control Systems. A number of stormwater controls are proposed for both construction and permanent/long-term measures. During construction, stormwater management areas will be used in conjunction with silt fence, staked hay bales, silt bags and stone check dams. Detention/Sedimentation basins will be installed as a permanent water quality measure. For dust and debris control, construction traffic must enter and exit the site at the stabilized construction entrance(s). Arico Associates Bemis Point Engineers, Land Planners & Consultants SWPPP Narrative Report Page 7 of 7 Excavation & Rough Grading. Large scale earth moving will occur in this stage in order to construct the proposed roadway, proposed stormwater management areas, underground utilities, and building pad locations. The topsoil stripping and stockpiling will occur during this phase. The topsoil will be used later in landscaped areas. Erosion and sediment controls including, but not limited to, silt fencing will be installed prior to, during and after earthwork activities. The stormwater detention basins and the storm sewer drainage system shall be constructed and be fully operational. Material(s) resulting from clearing, grubbing and excavation activities shall be stockpiled and protected up-slope from erosion and sediment control systems. Excavation and rough grading for lots will not be started prior to the completion of the road construction. A phasing plan has been developed in order to limit the disturbance to less than five (5) acres at one time. Decompaction of Existing Soils. Upon removal of any existing pavement areas, heavily traveled areas and/or areas that appear to be over compacted shall undergo a de-compaction application to restore soil porosity and permeability. Installation of Utilities. Utilities will be installed once rough grading activities are completed and all exposed slopes are temporarily stabilized. Fill areas shall be compacted and stabilized. Foundation Site Preparation. The building pad locations will be final graded to establish the finished floor elevation. Road Construction & Pavement Preparation. Finished subgrade elevation and subbase course grades will be established and verified before any roadway asphalt courses are installed. Landscaping. Topsoil shall be spread on areas to be landscaped and disturbed areas will be planted/seeded in accordance with approved plans. Temporary Seeding. Within 7-days after construction activity ceases on any particular area, all disturbed ground where there will not be construction for longer than 21-days must be seeded with fast-germinating temporary seed and protected with mulch. Permanent Seeding. All areas at final grade must be seeded within 7-days after completion of the major construction activity. Except for small level spots, seeded areas should generally be protected with mulch. Permanently seed and mulch cut slopes as excavation proceeds to extent considered desirable and practicable. Slopes exposed by the Road Construction are deemed fully stabilized and complete when turf grass cover provides permanent stabilization for at least 80% of the disturbed soil surface, exclusive of pavement areas. Conclusions In conclusion, based on drainage patterns and peak flows compared relatively to pre-developed and post- developed conditions, it is believed that the improvements being proposed will not affect present or future downstream conditions relative to flow or sedimentation. APP E N D I X A DEPARTMENT OF ENVIRONMENTAL CONSERVA TIONNew York State Better Site Design New York State Department of Environmental Conservation Division of Wa ter April 2008 Document Prepared by: Horsley Witten Group with assistance from the Center for Watershed Protection Better Site Design 1 BETTER SITE DESIGN 1 INTRODUCTION 1.1 Purpose The purpose of this document is to provide guidance to developers and designers to plan for and implement better site-design practices for new development and redevelopment projects. While reducing the effects of stormwater runoff may be achieved through both regulatory and non- regulatory techniques, this document focuses on the site-level planning and design tools available to the development community. As research, technology and information transfer have improved over recent years, alternative approaches are being sought by the public and regulatory boards to reduce the effects of stormwater runoff from new development and redevelopment. Developers and designers also are seeking alternatives to expedite permitting processes, reduce construction costs, reduce long- term operation and maintenance costs and increase property values. What is better site design, and how does it differ from conventional design? Better site design incorporates non-structural and natural approaches to new and redevelopment projects to reduce effects on watersheds by conserving natural areas, reducing impervious cover and better integrating stormwater treatment. For the purposes of this document, conventional design can be viewed as the style of suburban development that has evolved during the past 50 years and generally involves larger lot development, clearing and grading of significant portions of a site, wider streets and larger cul-de-sacs, enclosed drainage systems for stormwater conveyance and large “hole-in-the-ground” detention basins. The aim of better site design is to reduce the environmental-impact “footprint” of the site while retaining and enhancing the owner/developer’s purpose and vision for the site. Many of the better site-design concepts employ non-structural on-site treatment that can reduce the cost of infrastructure while maintaining or even increasing the value of the property relative to conventional designed developments. The goals of better site design include: • Prevention of stormwater effects rather than having to mitigate for them • Management of stormwater (quantity and quality) as close to the source as possible and minimization of the use of large or regional collection and conveyance • Preservation of natural areas, native vegetation and reduction of the effect of on watershed hydrology • Usage of natural drainage pathways as a framework for site design • Utilization of simple, non-structural methods for stormwater management that are lower cost and lower maintenance than structural controls • Creation of a multifunctional landscape Better Site Design 2 1.2 Scope and Context/How to Use this Document The scope and context of this document is to present developers and site designers with a series of alternatives to conventional stormwater management practices to reduce the effect development has on the watershed (e.g., peak stream flow, stormwater runoff, habitat, etc.). The information presented is intended to provide guidance during the site-planning process on how to “re-think” the traditional site layout and design approach for both new and redevelopment projects. This document provides an overview of the broad categories of better site design, the specific practices under each category, guidance on evaluating appropriate practices by weighing the benefits and risks of each practice and further guidance on each individual practice. Two case studies are also presented, one for a residential development and one for a commercial development, that illustrate conventional site designs versus “better” site designs. This document provides general guidance on how to choose the appropriate design technique but does not provide detailed design requirements and specifications for each of these practices. A list of resources on where to find this information is provided in the profile sheets in Section 2.4. 1.3 Key Terminology Better site design - Incorporates non-structural and natural approaches to new and redevelopment projects to reduce effects on watersheds by conserving natural areas, reducing impervious cover and better integrating stormwater treatment. Conservation design - Includes laying out the elements of a development project in such a way that the site design takes advantage of a site’s natural features, preserves the more sensitive areas and identifies any site constraints and opportunities to prevent effects. Conventional site design - For the purposes of this document, conventional design can be viewed as the style of suburban development that has evolved during the past 50 years and generally involves larger lot development, clearing and grading of significant portions of a site, wider streets and larger cul-de-sacs, enclosed drainage systems for stormwater conveyance and large “hole-in-the-ground” detention basins. Total impervious area - This is the total area within a watershed of all materials or structures on or above the ground surface that prevents water from infiltrating into the underlying soils. Impervious surfaces include, without limitation: paved parking lots, sidewalks, rooftops, patios, and paved, gravel and compacted-dirt surfaced roads. Gravel parking lots and/or compacted urban soils are often not included in total impervious area but may have hydrologic characteristics that closely resemble paved areas. Natural areas - This is undisturbed land or previously disturbed land that has recovered and that retains pre-development hydrologic and water quality characteristics. Better Site Design 3 New development – Any construction or disturbance of a parcel of land that is currently undisturbed or unaltered by human activities and in a natural state. Non-structural stormwater control – Natural measures that reduce pollution levels, do not require extensive construction or engineering efforts and/or promote pollutant reduction by eliminating the pollutant source. Redevelopment – Any land disturbance for construction, alteration or improvement where the existing land use is commercial, industrial, institutional or multi-family residential. Structural stormwater control – Devices that are engineered and constructed to provide temporary storage and treatment of stormwater runoff. 1.4 The Benefits of Better Site Design The use of better site design can have a number of benefits that extend beyond improving water quality and stormwater runoff management, including: • Reduced construction costs • Reduced long-term operation and maintenance costs • Increased property values • Easier compliance with wetland and other resource protection regulations • More open space for recreation • More pedestrian-friendly neighborhoods • Protection of sensitive forests, wetlands and habitats • More aesthetically pleasing and naturally attractive landscape 1.5 The Obstacles of Better Site Design Some obstacles exist or are perceived in the implementation of better site-design practices. Such as: • Public perception of a particular practice may not be favorable • Local codes may not allow for particular design elements • Capital costs and/or operation and maintenance costs for some practices may not always be less expensive than conventional designs. Typical perceived obstacles and realities specific to each practice are presented in the individual practice profile sheets in Section 2.4. Better Site Design 4 2 STORMWATER BETTER SITE DESIGN PRACTICES 2.1 Better Site-Design Categories and Listing of Practices Stormwater better site-design practices and techniques covered in this document are grouped into the following three categories: Preservation of Natural Features and Conservation Design: Preservation of natural features includes techniques to foster the identification and preservation of natural areas that can be used in the protection of water resources. Conservation design includes laying out the elements of a development project in such a way that the site design takes advantage of a site’s natural features, preserves the more sensitive areas and identifies any site constraints and opportunities to prevent or reduce effects. Reduction of Impervious Cover: Reduction of impervious cover includes methods to reduce the amount of rooftops, parking lots, roadways, sidewalks and other surfaces that do not allow rainfall to infiltrate into the soil, in order to reduce the volume of stormwater runoff, increase groundwater recharge, and reduce pollutant loadings that are generated from a site. Use of Natural Features and Source Control for Stormwater Management: Use of natural features for stormwater management includes design strategies rather than structural stormwater controls to help manage and mitigate runoff. Source control for stormwater management includes elements to mitigate or manage stormwater in a natural or lower-impact manner. Table 1 lists the specific better site-design practices and techniques presented in this document for each of the three categories. An evaluation of each practice is presented in Table 2, and further detail on each site-design practice is provided in the profile sheets in section 2.4. Table 1: Better Site-Design General Categories and Specific Practices Preservation of Natural Features and Conservation Design 1. Preservation of Undisturbed Areas 2. Preservation of Buffers 3. Reduction of Clearing and Grading 4. Locating Sites in Less Sensitive Areas 5. Open Space Design Reduction of Impervious Cover 6. Roadway Reduction 7. Sidewalk Reduction 8. Driveway Reduction 9. Cul-de-sac Reduction 10. Building Footprint Reduction 11. Parking Reduction Use of Natural Features and Source Control for Stormwater Management 12. Vegetated Buffer/Filter Strips 13. Open Vegetated Channels 14. Bioretention and Raingardens 15. Infiltration 16. Rooftop Runoff Reduction Mitigation 17. Stream Daylighting for Redevelopment Projects 18. Tree Planting Better Site Design 5 2.2 Better Site-Design Planning Process Site design should be done in unison with the design and layout of stormwater infrastructure in attaining stormwater management and land use goals. The stormwater better site-design process used a three-step process as follows: 1. Avoiding the Impacts – Preserving natural features and use conservation design techniques 2. Reducing the Impacts – Reducing impervious cover. 3. Managing the Impacts – Using natural features and natural low-impact techniques to manage stormwater The first step in the planning and design process is to avoid or minimize disturbance by preserving natural areas or strategically locating development based on the location of resource areas and physical conditions at a site. Once sensitive resource areas and site constraints have been avoided, the next step is to minimize the impact of land alteration by reducing impervious areas. Finally, for the areas that must be impervious, alternative and natural stormwater management techniques are chosen as opposed to the more routine structural, “pipe-to-pond,” approach. 2.3 Evaluating and Selecting Better Site Design Practices Part of the planning process for better site design includes choosing the appropriate practice or practices for a given site. Table 2 illustrates the various criteria and factors used to evaluate the feasibility of a particular design practice and are ranked as either good, fair or poor, or as often, sometimes or rarely. The factors presented in Table 2 that will help a developer decide which practices to choose include: How the Practice Applies To Meeting New York State Stormwater Criteria – Does the practice help meet the water quality volume (WQv) criteria? Does the practice help provide the quantity controls such as channel protection (Cpv), overbank flood (Qp), and extreme flooding (Qf)? For descriptions of the criteria, see the New York State Stormwater Management Design Manual. (www.dec.state.ny.us/website/dow/toolbox/swmanual/#Downloads) Economics – Does the practice decrease capital construction/infrastructure costs and decrease long-term operation and maintenance costs? Does the practice increase property values? Public Perception – Is the practice well received by the public and something people will want to live with? Local Codes – Do local codes, ordinances and regulations typically allow implementation of the practice? Better Site Design 6 Table 2: Better Site Design Practice Evaluation Applies To SW Criteria1 Economics Category Technique WQv Cpv, Qp, Qf How Applies To Criteria Lowers Capital Costs2 Lowers O&M3 Costs Raises Property Value Public Per- ception Allowed by Local Codes4 1. Preservation of Undisturbed Areas Increases times of concentration, reduces CN5 z z 2. Preservation of Buffers Increases times of concentration, reduces CN z z z 3. Reduction of Clearing and Grading Increases times of concentration, reduces CN z z z z 4. Locating Sites in Less Sensitive Areas Increases times of concentration, reduces CN z z Preservation of Natural Features and Conservation Design 5. Open-Space Design Increases times of concentration, reduces CN z z | 6. Roadway Reduction z z Reduces impervious area, which reduces WQv & flows z z z | 7. Sidewalk Reduction z z Reduces impervious area, which reduces WQv & flows z z | 8. Driveway Reduction z z Reduces impervious area, which reduces WQv & flows z z 9. Cul-de-sac Reduction z z Reduces impervious area, which reduces WQv & flows z z | 10. Building-Footprint Reduction z z Reduces impervious area, which reduces WQv & flows z z z z Reduction of Impervious Cover 11. Parking Reduction z z Reduces impervious area, which reduces WQv & flows z z 12. Vegetated Buffer/Filter Strips Increases times of concentration, reduces CN z z z 13. Open Vegetated Channels z z Stores WQv & Peak Flows z z 14. Bioretention z z Stores WQv & Peak Flows z z z 15. Infiltration z z Stores WQv & Peak Flows z z z 16. Rooftop Runoff Reduction Mitigation z z Stores WQv & Peak Flows z z z 17. Stream Daylighting for Redevelopment Projects | | Increases travel times, decreases peak flows | z z z Use of Natural Features and Source Control for Stormwater Management 18. Tree Planting Reduces volume of runoff, reduces CN z z z Key: z = good/often = fair/sometimes | = poor/rarely 1 - WQv = Water Quality Volume, Cpv = Channel Protection, Qp = Overbank Flood, Qf = Extreme Flood 2 - “Lowers Capital Costs” is intended for general purposes. Capital costs may vary on a site-by-site basis. 3 - Operation and Maintenance 4 - “Allowed by Local Code” is intended for general purposes. User should consult with actual local planning codes. 5 - CN = Runoff Coefficient “Curve Number” Better Site Design 7 2.4 Better Site Design Practice Profile Sheets 2.4.1 Preservation of Natural Features and Conservation Design Preservation of natural features includes the techniques to foster the identification and preservation of natural areas that can be used in the protection of water resources by reducing stormwater runoff, providing runoff storage, reducing flooding, preventing soil erosion, promoting infiltration and removing stormwater pollutants. Conservation Design includes laying out the elements of a development project in such a way that the site design takes advantage of a site’s natural features, including areas to be protected as conservation areas, preserves the more sensitive areas and identifies any site constraints and opportunities (e.g., topography, soils, natural vegetation, wetlands, floodplains, shallow bedrock, high water table, etc.) to prevent both on-site and downstream stormwater effects. 2.4.2 Reduction of Impervious Cover Reduction of impervious cover includes methods to reduce the amount of rooftops, parking lots, roadways, sidewalks and other surfaces that do not allow rainfall to infiltrate into the soil, in order to reduce the volume of stormwater runoff, increase groundwater recharge and reduce pollutant loadings that are generated from a site. 2.4.3 Utilization of Natural Features and Source Control for Stormwater Management Use of natural features for stormwater management includes design strategies that use existing or recreate natural features to help manage and mitigate runoff, rather than structural stormwater controls. Source control for stormwater management includes elements to mitigate or manage stormwater in a natural or lower-impact manner. Better Site Design 8 Better Site Design Practice #1: Preservation of Undisturbed Description: Important natural features and areas such as undisturbed forested and native vegetated areas, natural terrain, riparian corridors, wetlands and other important site features should be delineated and placed into permanent conservation areas. Key Benefits Typical Perceived Obstacles and Realities • Helps to preserve a site’s natural hydrology and water balance • Can act as a non-structural stormwater feature to promote additional filtration and infiltration • Can help to preserve a site’s natural character, habitat and aesthetic appeal • Has been shown to increase property values for adjacent parcels • Can reduce structural stormwater management storage requirement and may be used as a “stormwater credit • Preserved conservation areas may limit the development potential of a site – With clustering and other development incentives, development yield can be maintained. • Preserved habitats may harbor undesirable wildlife and insects – Most people enjoy viewing wildlife; native vegetation does not provide a food source for most vermin; continued education is necessary to show that humans and wildlife can co-exist, even at the neighborhood level. • Preserved areas may represent a fire hazard – Clearing setbacks and target vegetation around residential structures can reduce property damage potential. USING THIS PRACTICE • Delineate and define natural conservation areas before performing site layout and design. • Ensure that conservation areas and native vegetation are protected in an undisturbed state through the design, construction and occupancy stages. Discussion Conservation of natural areas such as undisturbed forested and native-vegetated areas, natural terrain, riparian corridors and wetlands on a development project can help to preserve pre- development hydrology of the site and aid in reducing stormwater runoff and pollutant load. Undisturbed vegetated areas also promote soil stabilization and provide for filtering and infiltration of runoff. Natural conservation areas are typically identified through a site-analysis stage using mapping and field-reconnaissance assessments. Areas proposed for protection should be delineated early in the planning stage, long before any site design, clearing or construction begins. When done before the concept-plan phase, the planned conservation areas can be used to guide the layout of a project. Figure 1 shows components of a natural resources inventory map with proposed conservation areas delineated. Preservation of Natural Features and Conservation Better Site Design 9 Preservation areas should then be incorporated into site-development plans and clearly marked on all construction and grading plans to ensure that construction activities are kept out of these areas and that native vegetation is undisturbed. The boundaries of each conservation area should be mapped by carefully determining the limit which should not be crossed by construction activity. Once established, natural conservation areas must be protected during construction and managed after occupancy by a responsible party able to maintain the areas in a natural state in perpetuity. Typically, conservation areas are protected by legally enforceable deed restrictions, conservation easements and a maintenance agreement. When all of these measures are applied, a permanently protected natural area can be applied as a “stormwater credit” to reduce the structural stormwater management measures (see Figure 2 for a representative project illustrating natural resource area protection). Additional Guidance Arendt, Randall. 1996. Conservation Design for Subdivisions: A Practical Guide to Creating Open Space Networks. American Planning Association. Chicago, IL. Available from the American Planning Association at www.planning.org Figure 2: Aerial Photograph of Development Project Illustrating Preservation of Undisturbed Natural Areas (Source: Arendt, 1996) Figure 1: Example of Natural Resource Inventory Plan (Source: Georgia Stormwater Manual, 2001) Stream Wetland Undisturbed Forest Proposed Conservation Area Better Site Design 10 Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies: An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Available from www.epa.gov Better Site Design 11 Better Site Design Practice #2: Preservation of Natural Features Preservation of Buffers and Conservation Design Description: Naturally vegetated buffers should be defined, delineated and preserved along perennial streams, rivers, shorelines and wetlands. Key Benefits Typical Perceived Obstacles and Realities • Riparian buffers treat stormwater and improve water quality • Can be used as nonstructural stormwater infiltration zones • Keep structures out of the floodplain and provide a right-of-way for large flood events • Help to preserve riparian ecosystems and habitats • Can serve as recreational areas • A buffer credit can be taken if allowed by the local review authority. • Buffers may result in a potential loss of developable land – Regulatory tools or other incentives may be available to protect the interests of property owners • Private landowners may be required to provide public access to privately held stream buffers – Effective buffers can be maintained in private ownership through deed restrictions and conservation easements • Excessive nuisance species will be present due to the natural buffer area - Forested buffers do not encourage nuisance vegetative species, and animal habitation can be controlled at the outer zone of the buffer. USING THIS PRACTICE • Delineate and preserve naturally vegetated riparian buffers (define the width, identify the target vegetation, designate methods to preserve the buffer indefinitely) • Ensure that buffers and native vegetation are protected throughout planning, design, construction and occupancy • Consult local planning authority for minimum buffer width and/or recommended width. Discussion A riparian buffer is a special type of natural conservation area along a stream, wetland or shoreline where development is restricted or prohibited. The primary function of buffers is to protect and physically separate a stream, lake, coastal shoreline or wetland from future disturbance or encroachment. If properly designed, a buffer can provide stormwater management functions, can act as a right-of-way during floods, and can sustain the integrity of water-resource ecosystems and habitats. An example of a riparian stream buffer is shown in Figure 3. Better Site Design 12 Forested riparian buffers should be maintained and reforestation should be encouraged where no wooded buffer exists. Proper restoration should include all layers of the forest plant community, including understory, shrubs and groundcover, not just trees. A riparian buffer can be of fixed or variable width but should be continuous and not interrupted by impervious areas that would allow stormwater to concentrate and flow into the stream without first flowing through the buffer. Ideally, riparian buffers should be sized to include the 100-year floodplain as well as steep banks and freshwater wetlands. The buffer depth needed to perform properly will depend on the size of the stream and the surrounding conditions, but a minimum 25-foot undisturbed vegetative buffer is needed for even the smallest perennial streams, and a 50-foot or larger undisturbed buffer is ideal. Even with a 25-foot undisturbed buffer, additional zones can be added to extend the total buffer to at least 75 feet from the edge of the stream. The three distinct zones within the 75-foot depth are shown in Figure 4. The function, vegetative target and allowable uses vary by zone as described in Table 3. These recommendations are minimum standards for most streams. Some streams and watersheds may benefit from additional measures to ensure adequate protection. In some areas, specific state laws or local ordinances already require stricter buffers than are described here. The buffer widths discussed are not intended to modify or supersede wider or more restrictive buffer requirements that are already in place. Table 3: Riparian Buffer Management Zones (Source: Adapted from Schueler, 1995) Streamside Zone Middle Zone Outer Zone Width Minimum 25 feet plus wetlands and critical habitat Variable, depending on stream order, slope, and 100-year floodplain (min. 25 ft.) 25-foot minimum setback from structures Vegetative Target Undisturbed mature forest. Reforest if necessary. Managed forest, some clearing allowed. Forest encouraged, but usually turfgrass. Allowable Uses Very restricted (e.g., flood control, utility easements, footpaths) Restricted (e.g., some recreational uses, some stormwater controls, bike paths) Unrestricted (e.g., residential uses, including lawn, garden, most stormwater controls) Figure 3: Riparian Stream Buffer (Source: Georgia Stormwater Manual, 2001) Better Site Design 13 As stated above, the streamside or inner zone should consist of a minimum of 25 feet of undisturbed mature forest. In addition to runoff protection, this zone provides bank stabilization as well as shading and protection for the stream. This zone should also include wetlands and any critical habitats, and its width should be adjusted accordingly. The middle zone provides a transition between upland development and the inner zone and should consist of managed woodland that allows for infiltration and filtration of runoff. An outer zone allows more clearing and acts as a further setback for impervious surfaces. It also functions to prevent encroachment and filter runoff. It is here that flow into the buffer should be transformed from concentrated flow into sheet flow to maximize ground contact with the runoff. Development within the riparian buffer should be limited only to those structures and facilities that are absolutely necessary. Such limited development should be specifically identified in any codes or ordinances enabling the buffers. When construction activities do occur within the riparian corridor, specific mitigation measures should be required, such as deeper buffers or riparian buffer improvements. Generally, the riparian buffer should remain in its natural state. However, some maintenance is periodically necessary, such as planting to minimize concentrated flow, removal of exotic plant species when these species are detrimental to the vegetated buffer and removal of diseased or damaged trees. Additional Guidance Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Berkshire Regional Planning Commission. 2003. The Massachusetts Buffer Manual: Using Vegetated Buffers to Protect our Lakes and Rivers. Prepared for the Massachusetts Department of Environmental Protection. Boston, MA. Available from www.berkshireplanning.org Figure 4: Three-Zone Stream Buffer System (Source: Adapted from Schueler, 1995) STREAMSIDE ZONE MIDDLE ZONE OUTER ZONESTREAM Better Site Design 14 Maine Department of Environmental Protection. 1998. The Buffer Handbook: A Guide to Creating Vegetated Buffers for Lakefront Properties. Maine DEP. Augusta, ME. Available from http://www.state.me.us/dep/blwq/doclake/publake.htm Schueler, T. 1995. Site Planning for Urban Stream Protection. Prepared for: Metropolitan Washington Council of Governments. Washington, DC. Center for Watershed Protection, Ellicott City, MD. Available from www.cwp.org Better Site Design 15 Better Site Design Practice #3: Preservation of Natural Features Reduction of Clearing and Grading and Conservation Design Description: Clearing and grading of the site should be limited to the minimum amount needed for the development function road access and infrastructure (e.g., utilities, wastewater disposal, stormwater management). Site foot-printing should be used to disturb the smallest possible land area on a site. Key Benefits Typical Perceived Obstacles and Realities • Preserves more undisturbed natural areas on a development site • Areas of a site that are conserved in their natural state retain their natural hydrology and do not contribute to construction erosion • Native trees, shrubs and grasses are important contributors to the overall quality and viability of the environment. • Preserving trees during construction is expensive – Minimizing clearing during construction can reduce earth movement and erosion and sediment control costs • People prefer large lawns – Lots with trees tend to have a higher value than those without • Vegetation near homes can be a fire risk – Even if clearing is required near homes, this can be accommodated while minimizing clearing on the entire site • Native vegetation may harbor undesirable wildlife or insects - Most people enjoy viewing wildlife; native vegetation does not provide a food source for most vermin; continued education is necessary to show that humans and wildlife can co-exist, even at the neighborhood level. USING THIS PRACTICE • Restrict clearing to the minimum area required for building footprints, construction access, and safety setbacks • Establish limits of disturbance for all development activities • Use site foot-printing to minimize clearing and land disturbance • Limit site mass grading approach. • Use alternative site designs that use open-space or “cluster” developments. Discussion Minimal disturbance methods should be used to limit the amount of clearing and grading that takes place on a development site, preserving more of the undisturbed vegetation and natural hydrology of a site. A limit of disturbance (LOD) should be established based on the maximum disturbance zone. These maximum distances should reflect reasonable construction techniques and equipment needs, together with the physical situation of the development site, such as slopes or soils. LOD Better Site Design 16 distances may vary by type of development, size of lot or site and by the specific development feature involved. Site "foot-printing" should be used which maps all of the limits of disturbance to identify the smallest possible land area on a site which requires clearing or land disturbance. An example of site foot-printing is illustrated in figures 5 and 6. Sites should be designed so that they fit the terrain (see practice #4). During construction, special procedures and equipment that reduce land disturbance should be used. Alternative site designs should be considered to minimize limits of clearing, such as “cluster” developments (see practice #5). Additional Guidance Arendt, Randall. 1996. Conservation Design for Subdivisions: A Practical Guide to Creating Open Space Networks. American Planning Association. Chicago, IL. Available from the American Planning Association at www.planning.org Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Schueler, T. 1995. Site Planning for Urban Stream Protection. Prepared for: Metropolitan Washington Council of Governments. Washington, DC. Center for Watershed Protection, Ellicott City, MD. Available from www.cwp.org Figure 5: Establishing Limits of Clearing (Source: DDNREC, 1997) Figure 6: Example of Site Foot-Printing (Source: Georgia Stormwater Manual, 2001) Better Site Design 17 Better Site Design Practice #4: Preservation of Natural Features Locating Sites in Less Sensitive Areas and Conservation Design Description: Development sites should be located to avoid sensitive resource areas such as floodplains, steep slopes, erodible soils, wetlands, mature forests and critical habitat areas. Buildings, roadways and parking areas should be located to fit the terrain and in areas that will create the least impact. Key Benefits Typical Perceived Obstacles and Realities • Preserving floodplains provides a natural right-of-way and temporary storage for large flood events; keeps people and structures out of harm's way and helps to preserve riparian ecosystems and habitats. • Preserving steep slopes and building on flatter areas helps to prevent soil erosion and minimizes stormwater runoff; helps to stabilize hillsides and soils and reduces the need for cut-and-fill and grading. • Avoiding development on erodible soils can prevent sedimentation problems and water-quality degradation. Areas with highly permeable soils can be used as nonstructural stormwater infiltration zones • Fitting the design to the terrain and in less sensitive areas helps to preserve the natural hydrology and drainageways of a site; reduces the need for grading and land disturbance, and provides a framework for site design and layout. • Costs will be higher for developments due to increased planning and design, localized construction and less developable land - Developments that protect sensitive areas will likely have higher market value, less liability for potential natural disasters, such as flooding or slope failures and lower construction costs for areas that require less earthwork or difficult terrain, such as steep slopes or wetland areas to work around. USING THIS PRACTICE • Ensure all development activities do not encroach on designated floodplain and/or wetland areas • Avoid development on steep slope areas and minimize grading and flattening of hills and ridges • Leave areas of porous or highly erodible soils as undisturbed conservation areas Better Site Design 18 • Develop roadway patterns to fit the site terrain, and locate buildings and impervious surfaces away from steep slopes, drainageways and floodplains • Locate site in areas that are less sensitive to disturbance or have a lower value in terms of hydrologic function. Discussion Development in floodplain areas can reduce the ability of the floodplain to convey stormwater, potentially causing safety problems or significant damage to the site in question, as well as to both upstream and downstream properties. Ideally, the entire 100-year full-buildout floodplain should be avoided for clearing or building activities and should be preserved in a natural, undisturbed state where possible. Development on slopes with a grade of 15% or greater should be avoided, if possible, to limit soil loss, erosion, excessive stormwater runoff and the degradation of surface water. Excessive grading should be avoided on all slopes, as should the flattening of hills and ridges. Steep slopes should be kept in an undisturbed natural condition to help stabilize hillsides and soils. On slopes greater than 25%, no development, regarding or stripping of vegetation should be considered. Areas of a site with hydrologic soil group A and B soils, such as sands and sandy loam soils, should be conserved as much as possible, and these areas should ideally be incorporated into undisturbed natural or open-space areas (Figure 8). Conversely, buildings and other impervious surfaces should be located on those portions of the site with the least permeable soils. Similarly, areas on a site with highly erodible or unstable soils should be avoided for land-disturbing activities and buildings to prevent erosion and sedimentation problems as well as potential structural problems. These areas should be left in an undisturbed and vegetated condition. Figure 7: Grading that Creates Large Construction “Pads” Effects more Land than Contoured Grading on Smaller Areas at Flatter Slopes (Source: MPCA, 1989) Large Impact Area Small Impact Area Figure 8: Soil Mapping Can Be Used to Guide Development (Source: Georgia Stormwater Manual, 2001) A A A A B B B C C C D “A” and “B” soils are more porous – preserve undisturbed if possible “C” and “D” soils should be used for impervious surfaces and buildings Area with erodible soils A A A A B B B C C C D “A” and “B” soils are more porous – preserve undisturbed if possible “C” and “D” soils should be used for impervious surfaces and buildings Area with erodible soils Better Site Design 19 The layout of roadways and buildings on a site should generally conform to the landforms on a site (Figure 9). Natural drainageways and stream buffer areas should be preserved by designing road layouts around them. Buildings should be sited to use the natural grading and drainage system and avoid the unnecessary disturbance of vegetation and soils. Roadway patterns on a site should be chosen to provide access schemes which match the terrain. In rolling or hilly terrain, streets should be designed to follow natural contours to reduce clearing and grading. In flatter areas, a traditional grid pattern of streets or "fluid" grids which bend and may be interrupted by natural drainageways may be more appropriate. In much the same way that a development should be designed to conform to the terrain of the site, layout should also be designed so that the areas of development are placed in the locations of the site that minimize the hydrologic impact of the project. This is accomplished by steering development to areas of the site that are less sensitive to land disturbance or have a lower value in terms of hydrologic function. Figure 10 shows a development site where the natural features have been mapped in order to delineate the hydrologically sensitive areas. Through careful site planning, sensitive areas can be set aside as natural open space areas. In many cases, such areas can be used as buffer spaces between land uses on the site or between adjacent sites. Additional Guidance Figure 9: Preserving the Natural Topography of a Site (Source: Adapted from Prince George’s County, 1999) Roads on ridge lines or upland areas Vegetated drainage swales Natural drainageways preserved Houses located on “brow” of ridge Undisturbed vegetation on slopes Roads on ridge lines or upland areas Vegetated drainage swales Natural drainageways preserved Houses located on “brow” of ridge Undisturbed vegetation on slopes Figure 10: Guiding Development to Less Sensitive Areas of a Site (Source: Adapted from Prince George’s County, 1999) Better Site Design 20 Arendt, Randall. 1996. Conservation Design for Subdivisions: A Practical Guide to Creating Open Space Networks. American Planning Association. Chicago, IL. Available from the American Planning Association at www.planning.org Environmental Protection Agency (EPA) site on smart growth including a focus on community-based approaches to reducing sprawl. www.epa.gov/ebtpages/envismartgrowth.html Hart, Leslie. 1994. Guiding Principles of Sustainable Design. Prepared for the U.S Department of the Interior and the National Parks Service. Available from http://www.nps.gov/dsc/dsgncnstr/gpsd/ Better Site Design 21 Better Site Design Practice #5: Preservation of Natural Features Open-Space Design and Conservation Design Description: Open-space site designs (also referred to as conservation development or clustering) incorporate smaller lot sizes to reduce overall impervious cover while providing more undisturbed open space and protection of water resources. Key Benefits Typical Perceived Obstacles and Realities • Preserves conservation areas on a development site • Can be used to preserve natural hydrology and drainageways • Can be used to help protect natural conservation areas and other site features • Reduces the need for grading and land disturbance • Reduces infrastructure needs and overall development costs • Allows flexibility for developers to implement creative site designs, including better stormwater management practices • Smaller lot sizes and compact development may be perceived by developers as less marketable – Open space designs are in fact highly desirable and have economic advantages such as cost savings and higher market appreciation • Lack of speed and certainty in the review process may be of concern – Consult with the local review authority to review requirements; some communities are moving toward open- space design as a “by right” form of subdivision • Prospective homebuyers may be reluctant to purchase homes due to concerns regarding management of the community open space – Proper methods and implementation of maintenance agreements are available; natural open space reduces maintenance costs and can help keep association fees down • Open-space developments appear incompatible with adjacent land uses and are equated with increased noise and traffic – Open-space design allows preservation of natural areas, using less space for streets, sidewalks, parking lots and driveways; incorporating buffers into the design can help alleviate incompatibility with other competing land uses. USING THIS PRACTICE • Use a site design which concentrates development and preserves open space and natural areas of the site • Locate the developed portion of the cluster areas in the least sensitive areas of the site (see practice #4). • Use reduced setbacks and frontages and narrower right-of-way widths to design non- traditional lot layouts within the cluster. Better Site Design 22 Discussion Open-space development, also known as “open space residential design” (OSRD), or conservation development or clustering, is a better site-design technique that concentrates structures and impervious surfaces in a compact area in one portion of the development site in exchange for providing open space and natural areas elsewhere on the site. Typically smaller lots and/or nontraditional lot designs are used to cluster development and create more conservation areas on the site. Open-space developments have many benefits compared with conventional commercial developments or residential subdivisions: they can reduce impervious cover, stormwater pollution, construction costand the need for grading and landscaping, while providing for the conservation of natural areas. Figures 11 and 12 show examples of open space developments. Along with reduced imperviousness, open-space designs provide a host of other environmental benefits lacking in most conventional designs. These developments reduce potential pressure to encroach on conservation and buffer areas because enough open space is usually reserved to accommodate these protection areas. As less land is cleared during the construction process, alteration of the natural hydrology and the potential for soil erosion are also greatly diminished. Perhaps most importantly open space design reserves 25 to 50 percent of the development site in conservation areas that would not otherwise be protected. Open-space developments can also be significantly less expensive to build than conventional projects. Most of the cost savings are due to reduced infrastructure cost for roads and stormwater management controls and conveyances. While open-space developments are frequently less expensive to build, developers find that these properties often command higher prices than those in more conventional developments. Several studies estimate that residential properties in open- space developments garner premiums that are higher than conventional subdivisions and moreover, sell or lease at increased rates. Once established, common open-space and natural conservation areas must be managed by a responsible party able to maintain the areas in a natural state in perpetuity. Typically, the conservation areas are protected by legally enforceable deed restrictions, conservation easements and maintenance agreements. Figure 11: Example of an Open Space or “Cluster” Subdivision (Source: Georgia Stormwater Manual, 2001) Figure 12: Aerial View of an Open Space or “Cluster” Subdivision (Source: Georgia Stormwater Manual, 2001) Better Site Design 23 Flexible lot shapes and setback and frontage distances allow site designers to create attractive and unique lots that provide homeowners with enough space while allowing for the preservation of natural areas in a residential subdivision. A narrower right-of-way will consume less land that may be better used for housing lots and allow for a more compact site design. Figure 13 illustrates various nontraditional lot designs, and Figure 14 illustrates reduced front and side setbacks. Additional Guidance Arendt, Randall. 1994. Designing Open Space Subdivisions: A Practical Step-by-Step Approach. Natural Lands Trust, Inc. Media, PA. Available from www.natlands.org or www.greenerprospects.com Figure 13: Nontraditional Lot Designs (Source: ULI, 1992) Figure 14: Lots with Reduced Front and Side Setbacks (Source: Georgia Stormwater Manual, 2001) Better Site Design 24 Arendt, Randall. 1996. Conservation Design for Subdivisions: A Practical Guide to Creating Open Space Networks. American Planning Association. Chicago, IL. Available from the American Planning Association at www.planning.org Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org A non-profit Massachusetts organization dedicated to educating people about OSRD development and implementation. http://www.greenneighborhoods.org/site/Index.htm University of Michigan study finds homebuyers want view of woods, not large lawns. www.umich.edu/news/index.html?Releases/2004/Jun04/r062904a Environmental Protection Agency (EPA) site on smart growth including a focus on community based approaches to reducing sprawl. www.epa.gov/ebtpages/envismartgrowth.html Better Site Design 25 Better Site Design Practice #6: Roadway Reduction Reduction of Impervious Cover Description: Roadway lengths and widths should be minimized on a development site where possible to reduce overall imperviousness. Key Benefits Typical Perceived Obstacles and Realities • Reduces the amount of impervious cover and associated runoff and pollutants generated • Reduces the costs associated with road construction and maintenance • Local codes may not permit shorter or narrower roads – Meet with local officials to discuss waivers for alternative designs that will address concerns of access, snow stockpiling, and parking. • The public may view narrow roads as unsafe – Narrower roads in fact reduce the speeds at which vehicles drive; many maintenance and emergency vehicles can in fact access narrow roads • Narrow and shorter roads do not have enough parking – Provisions can be made in the design of a site to accommodate off-street parking. USING THIS PRACTICE • Consider different site and road layouts that reduce overall street length • Minimize street width by using narrower street designs that are a function of land use, density and traffic demand. • Use smaller side-yard setbacks to reduce total road length. Discussion The use of alternative road layouts that reduce the total linear length of roadways can significantly reduce overall imperviousness of a development site. Site designers are encouraged to analyze different site and roadway layouts to see if they can reduce overall street length. In addition, residential streets and private streets within commercial and other development should be designed for the minimum required pavement width needed to support travel lanes, on-street parking and emergency access. Figure 15 shows options for narrower street designs. In many instances, on-street parking can be reduced to one lane or eliminated on local access roads with less than 200 average daily trips (ADT) and on short cul-de-sacs street. One-way, single- lane, loop roads are another way to reduce the width of lower-traffic streets. Further, reducing side yard setbacks and using narrower frontages can reduce total street length, which is especially important in cluster and open-space designs. Better Site Design 26 Additional Guidance Arendt, Randall. 1994. Designing Open Space Subdivisions: A Practical Step-by-Step Approach. Natural Lands Trust, Inc. Media, PA. Available from www.natlands.org or www.greenerprospects.com Arendt, Randall. 1996. Conservation Design for Subdivisions: A Practical Guide to Creating Open Space Networks. American Planning Association. Chicago, IL. Available from the American Planning Association at www.planning.org Institute of Traffic Engineers (ITE). 2001. Residential Streets, Third Edition. Institute of Traffic Engineers, Publication No. LP-630. Available from www.ite.org Institute of Traffic Engineers (ITE). 1999. Traditional Neighborhood Development Street Design Guidelines. Institute of Traffic Engineers, Publication No. RP-027A. Available from www.ite.org Institute of Traffic Engineers (ITE). 1997. Designing Neighborhood Streets. Institute of Traffic Engineers, Publication No. VHS-027. Available from www.ite.org Figure 15: Potential Design Options for Narrower Roadway Widths (Source: Georgia Stormwater Manual, 2001) 26’ PAVE WIDTH 10’ DRAINAGE SWALE 4’ SIDEWALK 3’ UTILITY 60’ RIGHT OF WAY 18’ PAVE WIDTH 6’ DRAINAGE SWALE 3’ UTILITY 36’ RIGHT OF WAY Better Site Design 27 Better Site Design Practice #7: Sidewalk Reduction Reduction of Impervious Cover Description: Sidewalk lengths and widths should be minimized on a development site where possible to reduce overall imperviousness. Key Benefits Typical Perceived Obstacles and Realities • Reduces the amount of impervious cover and associated runoff and pollutants generated • Reduces the costs associated with construction and maintenance • Reduces the individual homeowner’s responsibility for maintenance, such as snow clearance • Sidewalks on only one side of the street may be perceived as unsafe – Accident research shows sidewalks on one side are nearly as safe as sidewalks on both • Homebuyers are perceived to want sidewalks on both sides – Some actually prefer not to have a sidewalk in front of their home, and there is no market difference between homes with and without sidewalks directly in front. • Local codes may not permit narrower, alternative, or the elimination of a sidewalk – Meet with local officials to discuss waivers for alternative designs that will address concerns of accessibility and safety issues. USING THIS PRACTICE • Locate sidewalks on only one side of the street. • Provide common walkways linking pedestrian areas. • Use alternative sidewalk and walkway surfaces. • Shorten front setbacks to reduce walkway lengths. Discussion Most codes require that sidewalks be placed on both sides of residential streets (e.g., double sidewalks) and be constructed of impervious concrete or asphalt. Many subdivision codes also require sidewalks to be 4 to 6 feet wide and 2 to 10 feet from the street. These codes are enforced to provide sidewalks as a safety measure. Developers may wish to consider allowing sidewalks on only one side of the street or eliminating them where they don't make sense. Sidewalks should be designed with the goal of improving pedestrian movement and diverting it away from the street. Developers may also consider reducing sidewalk widths and placing them farther from the street. In addition, sidewalks should be graded to drain to front yards rather than the street. Alternative surfaces for sidewalks and walkways should be considered to reduce impervious cover (figures 16 and 17). In addition, building and home setbacks should be shortened to reduce the amount of impervious cover from entry walks. Better Site Design 28 Additional Guidance Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Website for Walkable Communities, Inc. www.walkablecommunities.org Litman, Todd Alexander. 2004. The Economic Value of Walkability. Victoria Transport Policy Institute. Victoria, British Columbia. Available from http://www.vtpi.org/walkability.pdf Figure 16: Sidewalk with a permeable paver surface (Source: MA EOEA, 2005) Figure 17: Sidewalk with Common Walkways Linking Pedestrian Areas (Source: MA EOEA, 2005) Better Site Design 29 Better Site Design Practice #8: Driveway Reduction Reduction of Impervious Cover Description: Where driveway lengths and widths should be minimized on a development site possible, to reduce overall imperviousness. Key Benefits Typical Perceived Obstacles and Realities • Reduces the amount of impervious cover and associated runoff and pollutants generated • Alternative driveway surfaces make snow removal more difficult – Careful site design, material selection and homeowner education can help alleviate the concern • Developers perceive alternative surfaces as less marketable – “Green” development projects are increasingly being sought by consumers. • Homeowners have concerns regarding access with shared driveways – Proper site design and homeowner education will alleviate access issues. • Local codes may not permit shorter or narrower driveways or driveways with porous surfaces – Meet with local officials to discuss waivers for alternative designs. USING THIS PRACTICE • Use shared driveways that connect two or more homes. • Use alternative driveway surfaces. • Use smaller lot front building setbacks to reduce total driveway length. Discussion Most local subdivision codes are not very explicit as to how driveways must be designed. Most simply require a standard apron to connect the street to the driveway but do not specify width or surface material for driveways. Typical residential driveways range from 12 feet wide for one- car driveways to 20 feet for two. Shared driveways are discouraged or prohibited by many communities. Shared driveways can reduce impervious cover and should be encouraged with enforceable maintenance agreements and easements. Secondly, the typical 400-800 square feet of impervious cover per driveway can be minimized by using narrower driveway widths, reducing the length of driveways, or using alternative surfaces such as double-tracks, reinforced grass or permeable paving materials. Better Site Design 30 Building and home setbacks should be shortened to reduce the amount of impervious cover from driveways and entry walks. A setback of 20 feet is more than sufficient to allow a car to park in a driveway without encroaching into the public right of way and reduces driveway and walk pavement by more than 30 percent compared with a setback of 30 feet (see Figure 18). Figure 18: Reduced Driveway and Walkway Lengths by Using Reduced Setbacks (Adapted from: MPCA, 1989) Typical 30 ft Setback 20 ft Setback Reduction in Impervious Surfaces Typical 30 ft Setback 20 ft Setback Reduction in Impervious Surfaces Figure 19: Reduced Driveway Lengths by Using Shared Driveways (Source: MA EOEA, 2005) Figure 20: Permeable Pavers as an Alternative Driveway Surface (Source: MA EOEA, 2005) Better Site Design 31 Additional Guidance Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies: An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Available from www.epa.gov Massachusetts Executive Office of Environmental Affairs (EOEA). 2005. Smart Growth Toolkit. Boston, MA. Available from http://www.mass.gov/envir/ Better Site Design 32 Better Site Design Practice #9: Cul-de-sac Reduction Reduction of Impervious Cover Description: Minimize the number of cul-de-sacs and incorporate landscaped areas to reduce their impervious cover. The radius of a cul-de-sac should be the minimum required to accommodate emergency and maintenance vehicles. Alternative turnarounds should also be considered. Key Benefits Typical Perceived Obstacles and Realities • Reduces the amount of impervious cover, associated runoff and pollutants generated • Increases aesthetics by allowing for natural or landscaped areas rather than pavement • Emergency and maintenance vehicles require a large turning radius – Many newer vehicles are available with small turning radii. • School buses require a large turning radius - Verify school bus pick-up plans. Not every cul- de-sac will need to accommodate school bus turning radii. • Homeowners like the “end of the road” appeal of cul-de-sacs – This appeal can be accommodated using loop roads or lots that back onto open space areas. • Local codes may not permit smaller or alternative cul-de-sac designs – Meet with local officials to discuss waivers for alternative designs that will address concerns of access. USING THIS PRACTICE • Reduce the radius of the turnaround bulb or consider alternative cul-de-sac design, such as “tee” turn-a-rounds or looping lanes. • Apply site design strategies that minimize dead-end streets. • Create a pervious island or a stormwater bioretention area in the middle of the cul-de-sac to reduce impervious area. Discussion Alternative turnarounds are end of the street designs that replace fully-paved cul-de-sacs and reduce the amount of impervious cover created in developments. Cul-de-sacs are local access streets with a closed circular end that allows for vehicle turnarounds. Many of these cul-de-sacs can have a radius of more than 40 feet. From a stormwater perspective, cul-de-sacs create a huge bulb of impervious cover, increasing the amount of runoff. For this reason, reducing the size of cul-de-sacs through the use of alternative turnarounds or eliminating them altogether can reduce the amount of impervious cover created at a site. Better Site Design 33 Numerous alternatives create less impervious cover than the traditional 40-foot cul-de-sac. These alternatives include reducing cul-de-sacs to a 30-foot radius and creating hammerheads, loop roads and pervious islands in the cul-de-sac center (see figures 21, 22 and 23 below). Sufficient turnaround area is a significant factor to consider in the design of cul-de-sacs. In particular, the types of vehicles entering the cul-de-sac should be considered. Firetrucks, service vehicles and schoolbuses are often cited as needing large turning radii. However, some firetrucks are designed for smaller turning radii. In addition, many newer largeservice vehicles are designed with a tri-axle (requiring a smaller turning radius), and many school buses usually do not enter individual cul-de-sacs. Another option for designing cul-de-sacs involves the placement of a pervious island in the center. Vehicles only travel along the outside of the cul-de-sac when turning, leaving an unused “island” of pavement in the center. These islands can be attractively landscaped and also designed as bioretention areas to treat stormwater (see practice #14). 40 ft cul-de sac with landscaped island 30 ft radius cul-de-sac 60 by 20 ft T-shaped turnaround Loop road 40’ 30’60’ 20’ Figure 21: Turnaround Options for Residential Streets (Source: Adapted from Schueler, 1995) Figure 23: T-Shaped Turnaround Option (Source: Center for Watershed Protection, 2005) Figure 22: Loop Road Option (Source: Center for Watershed Protection, 2005) Better Site Design 34 Additional Guidance Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Schueler, T. 1995. Site Planning for Urban Stream Protection. Prepared for: Metropolitan Washington Council of Governments. Washington, DC. Center for Watershed Protection, Ellicott City, MD. Available from www.cwp.org Massachusetts Executive Office of Environmental Affairs (EOEA). 2005. Smart Growth Toolkit. Boston, MA. Available from http://www.mass.gov/envir/ Better Site Design 35 Better Site Design Practice #10: Building Footprint Reduction Reduction of Impervious Cover Description: The impervious footprint of residences and commercial buildings can be reduced by using alternate or taller buildings while maintaining the same floor to area ratio. Key Benefits Typical Perceived Obstacles and Realities • Reduces the amount of impervious cover and associated runoff and pollutants generated • Taller buildings are perceived to have higher construction and maintenance costs – Costs for taller buildings and associated parking may be offset by land costs. • Local codes may not permit taller buildings – Consider alternative locations that do allow taller buildings, or meet with local officials to discuss waivers for alternative designs. USING THIS PRACTICE • Use alternate or taller building designs to reduce the impervious footprint of buildings. • Consolidate functions and buildings or segment facilities to reduce footprints of structures. • Reduce directly connected impervious areas. Discussion In order to reduce the imperviousness associated with the footprint and rooftops of buildings and other structures, alternative and/or vertical (taller) building designs should be considered. Consolidate functions and buildings, as required, or segment facilities to reduce the footprint of individual structures. Figure 24 shows the reduction in impervious footprint by using a taller building design, and figures 25 and 26 show residential examples of reduced footprints. Figure 24: Reduction of Impervious Cover by Building Up Rather than Out (Source: Georgia Stormwater Manual, 2001) Single Story Building Four Story Building (75% Less Impervious Cover) Better Site Design 36 Additional Guidance Environmental Protection Agency (EPA) site on smart growth including a focus on community based approaches to reducing sprawl. www.epa.gov/ebtpages/envismartgrowth.html Hart, Leslie. 1994. Guiding Principles of Sustainable Design. Prepared for the U.S Department of the Interior and the National Parks Service. Available from http://www.nps.gov/dsc/dsgncnstr/gpsd Figure 26: Taller Apartments Create a Smaller Impervious Footprint (Source: City of Portland, OR, 2001) Figure 25: Taller Houses Create a Smaller Impervious Footprint (Source: Center for Watershed Protection, 2005) Better Site Design 37 Better Site Design Practice #11: Parking Reduction Reduction of Impervious Cover Description: Reduce the overall imperviousness associated with parking lots by eliminating unneeded spaces, providing compact car spaces, minimizing stall dimensions, incorporating efficient parking lanes, using multi-storied parking decks and using porous paver surfaces or porous concrete in overflow parking areas where feasible. Key Benefits Typical Perceived Obstacles and Realities • Reduces the amount of impervious cover, associated runoff and pollutants generated • Reduces construction costs, long- term operation and maintenance costs, and the need for larger stormwater facilities • Improves aesthetics of an area by increasing vegetative surfaces and reducing the feeling a large, paved urban area • Developers desire excess parking and fear losing customers during peaks – The potential loss of customers due to reduced parking is unknown however, often times parking areas are not full during peak periods. • Parking may spill over into residential or commercial areas when full – Include preferential parking provisions for residents or parking enforcement with meters. • Trend to larger vehicles such as SUVs – Stall width requirements in most local parking codes are much larger than the widest SUVs. • Structured parking is more expensive than surface lots – Costs for structured parking may be offset by land costs or by constructing garages above or below an actual building. • Porous pavement surfaces are more expensive to install and maintain – Alternative surfaces may alleviate the need for larger stormwater treatment elsewhere on the site. USING THIS PRACTICE • Reduce the number of unnecessary parking spaces by examining minimum parking ratio requirements, and set a maximum number of spaces. • Reduce the number of un-needed parking spaces by examining the site’s accessibility to mass transit. • Minimize individual parking stall dimensions. • Examine the traffic flow of the parking lot design to eliminate un-needed lanes / drive aisles • Consider parking structures and shared parking arrangements between non-competing uses • Use alternative porous surface for overflow areas or main parking areas if not a high-traffic parking lot. • Use landscaping or vegetated stormwater practices in parking lot islands. • Provide incentives for compact and hybrid cars. Better Site Design 38 Discussion Setting maximums for parking spaces, minimizing stall dimensions, using structured parking, encouraging shared parking and using alternative porous surfaces can all reduce the overall parking footprint and site imperviousness. Many parking lot designs result in far more spaces than actually required. This problem is exacerbated by a common practice of setting parking ratios to accommodate the highest hourly parking during the peak season. By determining average parking demand instead, a lower maximum number of parking spaces can be set to accommodate most of the demand. Table 4 provides examples of conventional parking requirements and compares them to average parking demand. In addition, the number of parking spaces needed may be reduced by a site’s accessibility to public transportation. Table 4: Conventional Minimum Parking Ratios (Source: CWP, 1998) Parking Requirement Land Use Parking Ratio Typical Range Actual Average Parking Demand Single family homes 2 spaces per dwelling unit 1.5–2.5 1.11 spaces per dwelling unit Shopping center 5 spaces per 1000 ft2 GFA 4.0–6.5 3.97 per 1000 ft2 GFA Convenience store 3.3 spaces per 1000 ft2 GFA 2.0–10.0 -- Industrial 1 space per 1000 ft2 GFA 0.5–2.0 1.48 per 1000 ft2 GFA Medical/dental office 5.7 spaces per 1000 ft2 GFA 4.5–10.0 4.11 per 1000 ft2 GFA GFA = Gross floor area of a building without storage or utility spaces Another technique to reduce the parking footprint is to minimize the dimensions of the parking spaces. This can be accomplished by reducing both the length and width of the parking stall. Parking stall dimensions can be further reduced if compact spaces are provided. Another method to reduce the parking area is to incorporate efficient parking lanes such as using one-way drive aisles with angled parking rather than the traditional two-way aisles. Structured parking decks are another method for significantly reducing the overall parking footprint by minimizing surface parking. Figure 27 shows a parking deck used for a commercial development. Shared parking in mixed-use areas and structured parking are techniques that can further reduce the conversion of land to impervious cover. A shared parking arrangement could include usage of the same parking lot by an office space that experiences peak parking demand during the weekday with a church that experiences parking demands during the weekends and evenings. Figure 27: Structured Parking at an Office Park (Source: Georgia Stormwater Manual, 2001) Better Site Design 39 Using alternative surfaces such as porous pavers or porous concrete is an effective way to reduce the amount of runoff generated by parking lots. They can replace conventional asphalt or concrete in both new developments and redevelopment projects. Figure 28 is an example of porous pavers used at an overflow lot. Alternative pavers can also capture and treat runoff from other sites area. When possible, expanses of parking should be broken up with landscaped islands which could include shade trees and shrubs (see Figure 29) or landscaped stormwater management “islands” such as filter strips, swales and bioretention areas (see practice #s 12, 13 & 14) Additional Guidance Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies: An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Available from www.epa.gov Massachusetts Executive Office of Environmental Affairs (EOEA). 2005. Smart Growth Toolkit. Boston, MA. Available from http://www.mass.gov/envir/ Institute of Traffic Engineers (ITE). 1997. The Aesthetics of Parking. Institute of Traffic Engineers, Publication No. LP-090A. Available from www.ite.org Institute of Traffic Engineers (ITE). 1994. Guidelines for Parking Facility Location and Design. Institute of Traffic Engineers, Publication No. RP-022A. Available from www.ite.org U.S. Environmental Protection Agency. 1999. Parking Alternatives: Making Way for Urban Infill and Brownfields Redevelopment. U.S. EPA Urban and Economic Development Division. Washington, DC. Available from http://www.epa.gov/smartgrowth/publications.htm#articles Figure 28: Grass Paver Used for Parking (Source: Georgia Stormwater Manual, 2001) Figure 29: Expanses of Parking Area “Broken-Up” with Landscape Features (Source: MA EOEA, 2005) Better Site Design 40 Better Site Design Practice #12: Use of Natural Features and Source Vegetated Buffer/Filter Strips Control for Stormwater Management Description: Undisturbed natural areas such as forested conservation areas and stream buffers or vegetated filter strips can be used to treat and control stormwater runoff from some areas of a development project. Key Benefits Typical Perceived Obstacles and Realities • Riparian buffers and undisturbed vegetated areas can be used to filter and infiltrate stormwater runoff • Natural depressions can provide inexpensive storage and detention of stormwater flows • A stormwater site design credit can be taken if allowed by the local review authority. • Require space – Use in areas where land is available and land costs are not significantly high. • May be inappropriate in areas of higher pollutant loading due to direct infiltration of pollutants– Integrate with other practices to ensure adequate treatment prior to discharge. • Channelization and premature failure can occur – This can be alleviated with proper design, construction and maintenance. USING THIS PRACTICE • Direct runoff towards buffers and undisturbed areas using sheet flow or a level spreader to ensure sheet flow. • Use natural depressions for runoff storage. • Direct runoff and nature of runoff (sheet flow versus shallow concentrated flow) to buffer/filter strip areas. • Examine the slope, soils and vegetative cover of the buffer/filter strip. • Disconnect impervious areas to these areas. Discussion Runoff can be directed towards riparian buffers and other undisturbed natural areas delineated in the initial stages of site planning to infiltrate runoff, reduce runoff velocity and remove pollutants. Natural depressions can be used to temporarily store (detain) and infiltrate water, particularly in areas with more permeable (hydrologic soil groups A and B) soils. The objective in using natural areas for stormwater infiltration is to intercept runoff before it has become substantially concentrated and then distribute this flow evenly (as sheet flow) to the buffer or natural area. This can typically be accomplished using a level spreader, as seen in Figure 30. A mechanism for the bypass of higher-flow events should be provided to reduce erosion or damage to a buffer or undisturbed natural area. Better Site Design 41 Carefully constructed berms can be placed around natural depressions and below undisturbed vegetated areas with porous soils to provide for additional runoff storage and/or infiltration of flows. Additional Guidance Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies: An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Available from www.epa.gov Figure 30: Use of a Level Spreader with a Riparian Buffer (Source: Georgia Stormwater Manual, 2001) LEVEL SPREADER UNDISTURBED BUFFER Figure 32: Use of a Vegetated Filter Strip (Source: MA EOEA, 2005) Figure 31: Use of a Grassed Filter Strip (Source: MA EOEA, 2005) Better Site Design 42 City of Portland, Oregon. September 2004. Stormwater Management Manual. Bureau of Environmental Services, Portland, OR. Available from http://www.portlandonline.com/bes/ Better Site Design 43 Better Site Design Practice #13: Use of Natural Features and Source Open Vegetated Channels Control for Stormwater Management Description: The natural drainage paths of a site, or properly designed and constructed vegetated channels can be used instead of constructing underground storm sewers or concrete open channels. Where density, topography, soils, slope and safety issues permit, vegetated open channels can be used in the street right-of-way to convey and treat stormwater runoff from roadways. Key Benefits Typical Perceived Obstacles and Realities • Reduces the cost of road and storm sewer construction • Provides for some runoff storage and infiltration, as well as treatment of stormwater • A stormwater site design credit can be taken if allowed by the local review authority. • Increases stormwater travel times and lowers peak discharges. • Local codes may not allow swales instead of curb and gutter or closed drainage pipes – Meet with local officials to discuss waivers for alternative designs. • There is a strong perception that swales require more maintenance than curb and gutter or closed drainage pipes – With the proper design, swales require less maintenance and are less prone to failure. • Lack of curbing may increase potential for failure of the pavement at the grass interface – The potential for failure can be alleviated by hardening the interface by installing grass pavers, geosynthetics or placing a low-rising concrete strip along the pavement edge. USING THIS PRACTICE • Preserve natural flow paths in the site design. • Direct runoff to natural drainage ways, ensuring that peak flows and velocities will not cause channel erosion. • Use vegetated open channels (enhanced wet or dry swales or grass channels) and pipes in place of curb and gutter, to convey and treat stormwater runoff. • Ensure runoff volumes and velocities provide adequate residence times and non-erosive conditions (i.e., use of check dams). Discussion Open vegetated channels (see figures 33 and 34) remove pollutants by allowing infiltration and filtration to occur, unlike curb-and-gutter systems or closed piping systems which move water with virtually no treatment. Curb-and-gutter and storm drain systems allow for the quick transport of stormwater, which results in increased peak flow and flood volumes and reduced runoff infiltration. Curb-and-gutter systems also do not provide treatment of stormwater that is often polluted from vehicle emissions, pet waste, lawn runoff and litter. Engineering techniques have advanced the roadside ditches of the past, which suffered from erosion, standing water and Better Site Design 44 breakup of the road edge. Grass channels and enhanced dry swales are two such alternatives, and with proper installation under the right site conditions, they are excellent methods for treating stormwater on site. In addition, open vegetated channels can be less expensive to install than curb-and-gutter systems. Complete descriptions and design criteria for open channels are included in the New York State Stormwater Management Manual. Figure 33: Examples of Open Vegetated Channels (Source: Georgia Stormwater Manual, 2001) Figure 34: Another Example of an Open Vegetated Channel (Source: MA EOEA, 2005) Better Site Design 45 Additional Guidance Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Center for Watershed Protection. August 2003. New York State Stormwater Management Design Manual. Prepared for New York State Department of Environmental Conservation, Albany, NY. http://www.dec.state.ny.us/website/dow/toolbox/swmanual/#Downloads Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies: An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Available from www.epa.gov City of Portland, Oregon. September 2004. Stormwater Management Manual. Bureau of Environmental Services, Portland, OR. Available from http://www.portlandonline.com/bes/ Massachusetts Executive Office of Environmental Affairs (EOEA). 2005. Smart Growth Toolkit. Boston, MA. Available from http://www.mass.gov/envir/ Better Site Design 46 Better Site Design Practice #14: Use of Natural Features and Source Bioretention and Rain Gardens Control for Stormwater Management Description: Provide stormwater treatment for runoff from impervious surfaces using bioretention areas or rain gardens that can be integrated into required landscaping areas and traffic islands. Key Benefits Typical Perceived Obstacles and Realities • Breaks up impervious cover, thus allowing for better infiltration and treatment from smaller drainage areas. • Combines landscaping with stormwater treatment. • Improves aesthetics. • Reduces thermal impacts. • Bioretention areas require regular maintenance – Regular maintenance amounts to general landscaping duties such as trash removal, mulching, weeding and irrigation. • Bioretention areas may be expensive – Using bioretention and other on-site treatment can significantly reduce the need for storm drain,s thus reducing stormwater infrastructure costs USING THIS PRACTICE • Integrate bioretention into a parking lot or roadway design. • Integrate bioretention, or raingardens, into on-lot residential designs. • Closely examine runoff volumes and velocities to ensure runoff enters bioretention in a distributed manner and in a non-erosive condition. • Ensure the bioretention has proper pre-treatment. • Carefully select the landscaping materials required. • Use as a retrofit or in redevelopment projects. Discussion Bioretention areas are naturally vegetated, structural, stormwater-treatment practices that offer an aesthetically pleasing alternative to pavement or traditional detention stormwater facilities. Bioretention areas resemble landscaped depressions and can contain grasses, wildflowers or trees, depending on the size of the facility. Stormwater runoff is routed by slopes, curb cuts or piping into these depressions, where it is allowed to pond temporarily. Eventually, the retained runoff will seep through an organic underground filter system before discharging to an underdrain or infiltrating to the underlying soils. Treatment of stormwater includes attenuation of sediment, metals, bacteria and nutrients. Complete descriptions and design criteria for bioretention are included in the New York State Stormwater Management Manual (http://www.dec.state.ny.us/website/dow/toolbox/swmanual/#Downloads) Bioretention facilities can receive runoff from areas as small as residential lawns or as large as commercial parking areas. These facilities are often used to replace conventional landscaping in parking areas or along roadways. Site limitations include steep slopes, high water tables or Better Site Design 47 excessively cold climates. Where unusually high sediment loading is expected, proper pretreatment, such as a sediment forebay designed for settling sediments, should be used to reduce the probability of clogging the subsurface filter. Parking lots should be designed with landscaped stormwater management “islands” which reduce the connected impervious cover of the lot as well as provide for runoff treatment and control in stormwater facilities. Bioretention can be incorporated into roadway design as well, such as in the center of a cul-de-sac or within roadway rights-of-way or easements following sheet flow from the road surface. Rain gardens are smaller versions of bioretention, typically considered for on-lot residential designs. Rain gardens can be landscaped depressions on the lot used to mitigate rooftop runoff, or can be designed as the low point of a lot to treat on-site stormwater. Rain gardens are constructed as shallow depressions where stormwater runoff will collect during and shortly after a rain event. These areas are vegetated with plants that are both aesthetically pleasing and well suited to an environment periodically inundated with water. Rain gardens can be designed at different scales to suit different levels of runoff. Adequate sizing of these gardens will allow for infiltration of the most common rain events, while runoff from larger events will overflow into other stormwater infrastructure or a receiving water body. Rain gardens are an appropriate practice as long as certain potential site constraints have been considered. Drainage areas cannot be too extensive for rain gardens, and slopes leading to them cannot be too steep because large volumes of rain or runoff moving at excessive velocities will simply overwhelm these facilities. Also, where subsurface soils do not naturally allow for good drainage, these soils should be replaced or mixed with sandier varieties. Figure 36: Example of a Bioretention Facility Along Roadway Figure 35: Example of a Bioretention Facility in a Parking Lot Island Better Site Design 48 Additional Guidance Center for Watershed Protection. August 2003. New York State Stormwater Management Design Manual. Prepared for New York State Department of Environmental Conservation, Albany, NY. http://www.dec.state.ny.us/website/dow/toolbox/swmanual/#Downloads Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies: An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Available from www.epa.gov City of Portland, Oregon. September 2004. Stormwater Management Manual. Bureau of Environmental Services, Portland, OR. Available from http://www.portlandonline.com/bes/ Massachusetts Executive Office of Environmental Affairs (EOEA). 2005. Smart Growth Toolkit. Boston, MA. Available from http://www.mass.gov/envir/ Low Impact Development (LID) Center website: http://www.lowimpactdevelopment.org/ Figure 37: Example of an On-Lot Rain Garden Source (MA EOEA, 2005) Better Site Design 49 Better Site Design Practice #15: Use of Natural Features and Source Infiltration Control for Stormwater Management Description: Use infiltration trenches, basins or leaching chambers to provide groundwater recharge, mimic existing hydrologic conditions and reduce runoff and pollutant export. Permeable paving surfaces may also be used where site conditions are appropriate. Key Benefits Typical Perceived Obstacles and Realities • Increases recharge to the groundwater. • Reduces stormwater runoff volume and peak runoff rates; therefore, pipes and basins are smaller. • Can increase effective developable area on a site because portions of the stormwater system are located underneath the paved areas. • Grass pavers can improve site appearance by providing vegetation where there would otherwise be only pavement. • Infiltration trenches and dry wells cannot receive untreated stormwater runoff, except rooftop runoff – Provide proper pretreatment such as grass swales or filter strip. • Rehabilitation of failed infiltration trenches and dry wells requires complete reconstruction – Proper system design, construction and ongoing operation and maintenance will prevent failure. • Permeable paving can be prone to clogging from sand and fine sediments that fill void spaces and the joints between pavers – Avoid permeable paving in high traffic areas where frequent winter sanding is necessary; provide periodic maintenance. • Snow plows can catch the edge of grass pavers and some paving stones – Avoid using in high traffic areas; and attach rollers to the bottom edge of a snowplow to prevent this problem. USING THIS PRACTICE • May be used for roadway or parking impervious areas if adequate pre-treatment is. provided;Rooftop runoff may discharge directly to drywells or infiltration chambers. • The site must have soils with moderate to high infiltration capacities and must have adequate depth to groundwater. • Certain sites (i.e., pollutant hotspots) require additional pretreatment prior to infiltration. • Use porous pavers only in low-traffic areas or for pedestrian walkways/plazas. • Poor soils may preclude aggressive infiltration. Better Site Design 50 Discussion Infiltration trenches, dry wells and chambers are standard stormwater management structures that can play an important role in lower-impact site design. Dispersed around the site, these infiltration structures can recharge groundwater and help to maintain or restore the site’s natural hydrology. Dry wells, infiltration trenches, and chambers all store water in the void between crushed stone or gravel; the water slowly percolates downward into the subsoil. An overflow outlet is needed for runoff from large storms that cannot be fully infiltrated by the trench or dry well. Complete descriptions and design criteria for infiltration trenches, basins, and drywells are included in the New York State Stormwater Management Manual. (http://www.dec.state.ny.us/website/dow/toolbox/swmanual/#Downloads) Because impervious pavement is the primary source of stormwater runoff, better site-design strategies offer permeable paving as an option for parking areas and other hard surfaces. Permeable paving allows rainwater to percolate through the paving and into the ground before it runs off. This approach reduces stormwater runoff volumes and minimizes the pollutants introduced into stormwater runoff from parking areas. All permeable paving systems consist of a durable, load bearing, pervious surface overlying a crushed-stone base that stores rainwater before it infiltrates into the underlying soil. Permeable paving techniques include porous asphalt, pervious concrete, paving stones and manufactured “grass pavers” made of concrete or plastic. Permeable paving may be used for walkways, patios, plazas, driveways, parking stalls and overflow parking areas. Figure 38: Dry Well (Source: MA EOEA, 2005) Figure 40: Infiltration Chambers (Source: MA EOEA, 2005) Figure 39: Infiltration Trench (Source: MA EOEA, 2005) Better Site Design 51 Permeable paving is appropriate for pedestrian-only areas and for low-volume, low-speed areas such as overflow parking areas, residential driveways, alleys and parking stalls. It can be constructed where the underlying soils have a permeability of at least 0.5 inch per hour. Permeable paving is an excellent technique for dense urban areas because it does not require any additional land. With proper design, cold climates are not a major limitation; porous pavement has been used successfully in Norway, incorporating design features to reduce frost heave. Additional Guidance Center for Watershed Protection. August 2003. New York State Stormwater Management Design Manual. Prepared for New York State Department of Environmental Conservation, Albany, NY. http://www.dec.state.ny.us/website/dow/toolbox/swmanual/#Downloads Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies: An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Available from www.epa.gov Low Impact Development (LID) Center website: http://www.lowimpactdevelopment.org/ Metropolitan Area Planning Council (MAPC). 2005. Massachusetts Low Impact Development Toolkit Fact Sheets. Metropolitan Area Planning Council. Boston, MA. Available from www.mapc.org/lid Figure 41: Examples of Permeable Pavers (Source: MA EOEA, 2005) Better Site Design 52 Better Site Design Practice #16: Use of Natural Features and Source Rooftop Runoff Reduction Mitigation Control for Stormwater Management Description: Direct runoff from residential rooftop areas to pervious areas, lower-impact practices or use “green-roof” (specially designed vegetated rooftops) strategies to reduce rooftop runoff volumes and rates. Key Benefits Typical Perceived Obstacles and Realities • Sending runoff to pervious areas, lower-impact practices or using green roofs increases overland flow time and reduces peak flows. • Vegetated and pervious areas can filter and infiltrate stormwater runoff, thus increasing water quality. • A stormwater site design credit can be taken if allowed by the local review authority. • Wet basements will result from re-directing rooftop runoff – Careful design and construction inspection will minimize this condition. • Re-directed rooftop runoff may increase a property owner’s maintenance burden – When designed properly, on-lot rain gardens do not require supplemental water. • Alternative rooftop runoff mitigation may be costly – Rain barrels, in fact, are inexpensive and will reduce water-use costs; green roofs reduce heating and cooling costs and roof replacement costs. USING THIS PRACTICE • Direct rooftop runoff to pervious areas such as yards, open channels or vegetated areas. • Direct rooftop runoff to lower-impact practices such as rain barrels, cisterns, drywells, rain gardens, or stormwater planters. • Use “green roofs” to reduce stormwater runoff from rooftops. Discussion Stormwater quantity and quality benefits can be achieved by routing the runoff from rooftop areas to pervious areas such as lawns, landscaping, filter strips and vegetated channels. Much like the use of undisturbed buffers and natural areas (see practices #1 & 2), revegetated areas such as lawns and engineered filter strips and vegetated channels can act as biofilters for stormwater runoff and provide for infiltration in more permeable soils (hydrologic groups A and B). Cisterns and rain barrels are designed to retain water that runs off of roofs for an extended period. Rain barrels are smaller structures ranging generally from 20 to 100 gallons, while cisterns can store thousands of gallons, depending on the design. Construction material for rain barrels is generally plastic although other materials such as wooden barrels have been used. Cisterns can be constructed of metal, wood, concrete or plastic. Stormwater stored in these structures is generally used for irrigation, Better Site Design 53 although more complex designs incorporate that water into everyday uses such as toilet and shower water. Rain barrels and cisterns have historically been used in more arid climates where water is scarce for much of the year. More recently, however, these technologies have been applied in less arid climates because of the savings in water costs and overall increases in water demands. Drywells, as described under practice #15, are underground chambers surrounded by crushed stone, typically used to infiltrate runoff from rooftops. Drywells are well suited for residential applications or small buildings. Rain gardens, as described under practice #14, are constructed as shallow depressions where stormwater runoff will collect during and shortly after a rain event. These areas are vegetated with plantings that are both aesthetically pleasing and well suited to an environment periodically inundated with water. Rain gardens are well suited for small drainage areas such as residential building rooftops. Stormwater planters are a small-scale engineered management strategy designed to treat limited volumes of stormwater runoff in discrete areas. Planters generally look like large vaulted plant boxes and can contain anything from basic wildflower communities to complex arrangements of trees and flowering shrubs. Other stormwater planters, known as “tree boxes,” are simply modified side tree enclosures that are installed below the surface of the sidewalk. Stormwater is generally routed into these systems from roofs via downspouts, where it runs through various filtering media and is also subject to uptake from vegetation. Because of the compact and self- contained nature of these practices, they are best suited to handling rooftop runoff. Multiple units can be used to treat large-scale commercial developments. Green rooftops are rooftop areas that have been landscaped with grasses, shrubs and, in some cases, trees. “Intensive” rooftops are designed with pedestrian access and deep soil layers to provide for complex planting schemes. “Extensive” rooftops are designed with a more shallow soil foundation and generally do not incorporate pedestrian access. Stormwater runoff is either retained until uptake can occur, or eventually runs off the roof with considerably less pollution than would be contained in runoff from a standard impervious rooftop. Beyond stormwater pretreatment, benefits of green rooftops include reduction of the “heat island” effect, extended life of the rooftop, aesthetic appeal and increased useable area. Green rooftops are best suited for Figure 42: Rain Barrel (Source: MA EOEA, 2005) Figure 43: Stormwater Planters (Source: MA EOEA, 2005) Better Site Design 54 the construction of new buildings because the special structural considerations necessary for these applications can be incorporated early in the design phase. Retrofits to older buildings are often possible, however, owing to the fact that the rooftops were designed well beyond the minimum necessary support capacity. Additional Guidance Prince George’s County, MD. June 1999. Low- Impact Development Design Strategies: An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Available from www.epa.gov Rhode Island Department of Environmental Management. January 2005. The Urban Environmental Design Manual. Rhode Island Department of Environmental Management, Providence, Rhode Island. Available from http://www.dem.state.ri.us/programs/bpoladm/suswshed/pubs.htm City of Portland, Oregon. September 2004. Stormwater Management Manual. Bureau of Environmental Services, Portland, OR. Available from http://www.portlandonline.com/bes/ Green Roofs for Healthy Cities website - www.greenroofs.org The international greenroof industry’s resource and online information portal. www.greenroofs.com Figure 44: Green Roof (Source: MA EOEA, 2005) Better Site Design 55 Better Site Design Practice #17: Stream Daylighting for Utilization of Natural Features and Source Redevelopment Projects Control for Stormwater Management Description: Stream Daylight previously-culverted/piped streams to restore natural habitats, better attenuate runoff and help reduce pollutant loads where feasible and practical. Key Benefits Typical Perceived Obstacles and Realities • The aesthetic appeal of daylighted streams can be expected to add appeal to neighborhoods or urban areas. • Improves water quality. • Prevents flooding by increasing storage and reducing peak flows. • Increases habitat and wildlife value. • Increases pedestrian traffic and general public use. • Increases property values. • Daylighting a stream can be expensive - Costs for daylighting streams are often comparable to costs for replacing culverts. • Maintenance of daylighted stream areas can be intensive during the first years the stream is established – Once the banks are well established, regular maintenance is similar to that required in any public green spac,e such as trash removal, mowing and general housekeeping. • Finding the original stream channel may be difficult – examine historic records, soils, and up and downstream channel characteristics. • Political backing and public support is more difficult for daylighting streams than for surface restoration because the culvert is not seen – Provide proper public education and outreach about the benefits and how safety issues will be addressed. USING THIS PRACTICE • Daylighting should be considered when a culvert replacement is scheduled. • Restore historic drainage patterns by removing closed drainage systems and constructing stabilized, vegetated streams. • Carefully examine flooding potential, utility impacts and/or prior contaminated sites. • Consider runoff pretreatment and erosion potential of restored streams/rivers. Discussion Stream daylighting involves uncovering a stream or a section of a stream that had been artificially enclosed in the past to accommodate development. The original enclosure of rivers and streams often took place in urbanized areas through the use of large culvert operations that often integrated the stormsewer system and combined sanitary sewers. The daylighting operation, therefore, often requires overhauls or updating of storm-drain systems and re- Better Site Design 56 establishing stream banks where culverts once existed. When the operation is complete, what was once a linear pipe of heavily polluted water can become a meandering stream with dramatic improvements to both aesthetics and water quality. In some cases, instead of creating a natural channel for the daylighted stream, the culvert is simply replaced with a concrete channel. Where combined sewer overflow (CSO) separation and other upgrades to storm-sewer systems are part of a daylighting project, significant water-quality improvements can be expected during wet-weather events. Also, as ultraviolet radiation is one of the most effective ways to eliminate pathogens in water, exposing these streams to sunlight could significantly decrease pathogen counts in the surface water. Stream daylighting can play an integral role in neighborhood restoration and site redevelopment efforts. Aside from improvements to infrastructure, stream daylighting can restore floodplain and aquatic habitat areas, reduce runoff velocities and be integrated into pedestrian walkway or bike- path design. Stream daylighting can generally be applied most successfully to sites with considerable open or otherwise vacant space. This space is required to: 1) Potentially reposition the stream in its natural stream bed; 2) Accommodate the meandering that will be required if a natural channel is being designed and 3) Provide adjacent floodplain area to store water in large storm-flow situations. However, where a concrete channel will replace a culverted stream, these projects require significantly less space than those designed for a natural streambed. Figure 45: Before and After Daylighting Blackberry Creek in Berkeley, CA (Source: Stormwater Magazine, Nov/Dec 2001) Better Site Design 57 Additional Guidance Rhode Island Department of Environmental Management. January 2005. The Urban Environmental Design Manual. Rhode Island Department of Environmental Management, Providence, Rhode Island. Available from http://www.dem.state.ri.us/programs/bpoladm/suswshed/pubs.htm Blankinship, Donna Gordon. Jan/Feb 2005. Creeks are Coming Back into the Light. Article from Stormwater Magazine Vol. 6, No. 1. Forester Communications. Caledonia, MI. Available from www.stormh2o.com Pinkham, Richard. Nov/Dec 2001. Daylighting: New Life for Buried Streams. Article from Stormwater Magazine Vol. 2, No. 6. Forester Communications. Caledonia, MI. Available from www.stormh2o.com Figure 46: Daylighting Arcadia Creek in an Urban Area in Kalamazoo, MI (Source: Stormwater Magazine, Nov/Dec 2001) Better Site Design 58 Better Site Design Practice #18: Tree Planting Description: Plant or conserve trees at new or redevelopment sites to reduce stormwater runoff, increase nutrient uptake, provide bank stabilization, provide shading and provide wildlife habitat. Trees can be used for applications such as landscaping, stormwater management practice areas, conservation areas and erosion and sediment control. Key Benefits Typical Perceived Obstacles and Realities • Reduces construction and maintenance costs. • Increases property values. • Reduces urban heat island, decreases heating and cooling costs, blocks UV radiation. • Buffers wind and noise. • Planting trees in stormwater management practices can increase nutrient uptake, reduce runoff through rainfall interception and evapotranspiration (ET), aid infiltration, provide wildlife habitat, provide shading, discourage geese and reduce mowing costs. • Tree planting can be applied to stormwater credit #6, “Riparian Reforestation.” • Local codes may restrict trees in certain areas – Consult with local officials to discuss waivers for alternative designs. • Trees may not survive through construction or in certain urban environments – Trees will survive with proper tree selection, landscape design and protection during construction. • Planting or preserving trees may be expensive – Conserving or planting trees increases property values. • Native vegetation may harbor undesirable wildlife and insects - Most people enjoy viewing wildlife; native vegetation does not provide a food source for most vermin; continued education is necessary to show that humans and wildlife can co-exist, even at the neighborhood level. USING THIS PRACTICE • Conserve existing trees during construction by performing an inventory of the existing forest and identifying trees to protect. • Design the development with tree conservation in mind, protect trees during construction and protect trees after construction. • Plant trees at development sites by first selecting the planting sites and then evaluate and improve the planting sites. Trees should be planted in stormwater-management practices and other open spaces. • Tree types and locations should be chosen to withstand the constraints of an urban setting. Better Site Design 59 Discussion Few communities require that trees and native vegetation be conserved during the development process. However, native trees, shrubs, and grasses are important contributors to the overall quality and viability of the environment. Some tools that can be used for tree conservation include open space development practices, planting of vegetation in street, clearing and grading restrictions that include preservation of trees and native vegetation and the addition of vegetation to parking-lot islands. Developers, engineers or landscape architects can incorporate more trees into a development site, using a three-prong approach: Conserving existing trees during construction; planting trees in stormwater management practices; and Planting trees in other open spaces. Trees can be conserved and planted at both new development and redevelopment or infill projects. On currently forested development sites, it is most important to conserve existing trees, particularly high-quality stands or large, mature trees (Figure 47). To conserve existing trees, developers should inventory existing forest at the site to identify the best trees and forest to protect, design the development around these trees and take measures to ensure the protection of trees both during and after construction. Where tree conservation is not an option, urban development sites provide many opportunities to plant new trees, such as in stormwater management practices (SMPs) and other pervious areas of the site. Some SMPs are not traditionally considered appropriate for tree planting; however, planting trees and shrubs in certain areas of specific SMPs can enhance the aesthetic appeal and even improve their performance. The remaining pervious areas of the site that make good candidates for tree planting and are often overlooked and include local road rights-of-way, landscaped islands in cul-de-sacs or traffic circles and parking lots. Private lawns may also constitute a significant portion of green space at the site, and the developer should certainly strive to conserve or plant trees in these areas Figure 47: Mature Trees Conserved During Development (Photo Sources: Randall Arendt and Ed Gilman) Better Site Design 60 as well. These urban planting sites may have harsh soil and environmental conditions that should be addressed through appropriate species selection or proper site preparation prior to planting. Conserving or planting trees at development sites can be done to meet forest conservation, landscaping or other site-design requirements to enhance the appeal of the development and, therefore, increase land and housing values, to reduce costs of construction and stormwater management and to provide many additional benefits summarized above. Additional Guidance Cappiella, K., T. Schueler, T. Wright. 2004. Urban Watershed Forestry Manual. Available from www.cwp.org American Forests website: www.americanforests.org City of Toronto Tree Advocacy Planting Program website: http://www.city.toronto.on.ca/parks/treeadvocacy.htm Better Site Design 61 2.3 BETTER SITE DESIGN CASE STUDIES The following case studies illustrate how better site-design practices can be successfully incorporated into site planning. A comparison to a conventional design approach illustrates the opportunities presented by better site-design practices to meet stormwater management criteria in addition to identifying the obstacles for implementing such practices. 2.3.1 Medium Density Residential Subdivision Case Study A conventional residential subdivision design on a parcel is shown in Figure 48. The entire parcel, except for the subdivision amenity area (clubhouse and tennis courts), is used for lots. The entire site is cleared and mass graded, and no attempt is made to fit the road layout to the existing topography. Because of the clearing and grading, all of the existing tree cover and vegetation and topsoil are removed, dramatically altering both the natural hydrology and drainage of the site. The wide residential streets create unnecessary impervious cover and a curb- and-gutter system that carries stormwater flows to the storm sewersystem. No provision for non- structural stormwater treatment is provided on the subdivision site. A residential subdivision employing stormwater better site design practices is presented in Figure 49. This subdivision configuration preserves a quarter of the property as undisturbed open space and vegetation. The road layout is designed to fit the topography of the parcel, following the high points and ridgelines. The natural drainage patterns of the site are preserved and are used to provide natural stormwater treatment and conveyance. Narrower streets reduce impervious cover, and open vegetated channels provide for treatment and conveyance of roadway and driveway runoff. Bioretention islands at the ends of cul-de-sacs also reduce impervious cover and provide stormwater treatment functions. When constructing and building homes, only the building envelopes of the individual lots are cleared and graded, further preserving the natural hydrology of the site. 2.3.2 Commercial Development Case Study Figure 50 shows a conventional commercial development containing a supermarket, drugstore, smaller shops and a restaurant on an adjacent lot. The majority of the parcel is a concentrated parking-lot area. The only pervious area is a small, replanted vegetation area acting as a buffer between the shopping center and adjacent land uses. Stormwater quality and quantity control are provided by a wet, extended-detention pond in the corner of the parcel. A better site-design commercial development can be seen in Figure 51. Here the retail buildings are dispersed on the property, providing more of an “urban village” feel, with pedestrian access between the buildings. The parking is broken up, and bioretention areas for stormwater treatment are built into parking-lot islands. A large bioretention area which serves as open green space is located at the main entrance to the shopping center. A larger undisturbed buffer has been preserved on the site. Because the bioretention areas and buffer provide water-quality treatment, only a dry, extended-detention basin is needed for water-quantity control. Better Site Design 62 Figure 48: Residential Subdivision - Conventional Design (Source: Georgia Stormwater Manual, 2001) Figure 49: Residential Subdivision - Better Site Design (Source: Georgia Stormwater Manual, 2001) Site is Mass Graded Natural Drainage Patterns Destroyed Existing Tree Cover Removed Character of Site is Destroyed Extensive Storm Drain System Required Amenity Center is Only Open Space Cul-de-Sac with Bioretention Undisturbed Vegetation Open Vegetated Channel Instead of Curb and Gutter Undisturbed Vegetation Natural Drainage Preserved Natural Drainage Patterns Guide Layout Only Building Envelopes are Graded Character of Site is Preserved No Storm Drain System Required Impervious Cover Reduced Provides Open Space for Community Narrower Streets Narrower Streets Better Site Design 63 Figure 50: Commercial Development - Conventional Design (Source: Georgia Stormwater Manual, 2001) Figure 51: Commercial Development - Better Site Design (Source: Georgia Stormwater Manual, 2001) Concentrated Parking Area Concentrated Parking Area Revegetated (Disturbed) Area Revegetated (Disturbed) Area Wet Extended Detention Pond Wet Extended Detention Pond Drugstore Shops Supermarket Shops Restaurant Revegetated (Disturbed) Area Revegetated (Disturbed) Area Extended Detention Pond Dry Extended Detention Pond Bioretention Area Bioretention Area Undisturbed Buffer Undisturbed Buffer Undisturbed Buffer Undisturbed Buffer Bioretention Islands Bioretention Islands Dispersed Parking Dispersed Parking Drugstore Shops SupermarketRestaurant Shops Shops Better Site Design 64 4 REFERENCES Arendt, Randall. 1994. Rural by Design: Maintaining Small Town Character. Planners Press, American Planning Association. Chicago, IL. Arendt, Randall. 1994. Designing Open Space Subdivisions: A Practical Step-by-Step Approach. Natural Lands Trust, Inc. Media, PA. Arendt, Randall. 1996. Conservation Design for Subdivisions: A Practical Guide to Creating Open Space Networks. American Planning Association. Chicago, IL. Atlanta Regional Commission. August 2001. Georgia Stormwater Management Manual. Atlanta, GA. Berkshire Regional Planning Commission. 2003. The Massachusetts Buffer Manual: Using Vegetated Buffers to Protect our Lakes and Rivers. Prepared for the Massachusetts Department of Environmental Protection. Boston, MA. Blankinship, Donna Gordon. Jan/Feb 2005. Creeks are Coming Back into the Light. Article from Stormwater Magazine Vol. 6, No. 1. Forester Communications. Caledonia, MI. Cappiella, K., T. Schueler, T. Wright. 2004. Urban Watershed Forestry Manual. Center for Watershed Protection. August 2003. New York State Stormwater Management Design Manual. Prepared for New York State Department of Environmental Conservation, Albany, NY. http://www.dec.state.ny.us/website/dow/toolbox/swmanual/#Downloads Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Center for Watershed Protection, Ellicott City, MD. Center for Watershed Protection. July 1998. Nutrient Loading from Conventional and Innovative Site Development. Prepared for: Chesapeake Research Consortium. Center for Watershed Protection, Ellicott City, MD. Center for Watershed Protection. 1998. Better Site Design: An Assessment of the Better Site Design Principles for Communities Implementing the Chesapeake Bay Preservation Act.. Center for Watershed Protection, Ellicott City, MD. Center for Watershed Protection. 2000. Introduction to Better Site Design Slideshow. Available from www.stormwatercenter.net Center for Watershed Protection. October 2001. Redevelopment Roundtable Consensus Agreement: Smart Site Practices for Redevelopment and Infill Practices. Center for Watershed Protection, Ellicott City, MD. Better Site Design 65 Center for Watershed Protection. 2005. Better Site Design and Changing the Development Rules Slideshow. Presented at New Windsor, New York, June 21-22, 2005. DDNREC. 1997. Conservation Design for Stormwater Management. Delaware Department of Natural Resources and Environmental Control and the Environmental Management Centre of the Bradywine Conservancy. Green Roofs for Healthy Cities website: www.greenroofs.org Green Roofs.com website: www.greenroofs.com - The international greenroof industry’s resource and online information portal. Hart, Leslie. 1994. Guiding Principles of Sustainable Design. Prepared for the U.S Department of the Interior and the National Parks Service. Institute of Traffic Engineers (ITE). 2001. Residential Streets, Third Edition. Institute of Traffic Engineers, Publication No. LP-630. Institute of Traffic Engineers (ITE). 1999. Traditional Neighborhood Development Street Design Guidelines. Institute of Traffic Engineers, Publication No. RP-027A. Institute of Traffic Engineers (ITE). 1997. The Aesthetics of Parking. Institute of Traffic Engineers, Publication No. LP-090A. Institute of Traffic Engineers (ITE). 1997. Designing Neighborhood Streets. Institute of Traffic Engineers, Publication No. VHS-027. Institute of Traffic Engineers (ITE). 1994. Guidelines for Parking Facility Location and Design. Institute of Traffic Engineers, Publication No. RP-022A. Litman, Todd Alexander. 2004. The Economic Value of Walkability. Victoria Transport Policy Institute. Victoria, British Columbia. Low Impact Development (LID) Center website: http://www.lowimpactdevelopment.org/ Maine Department of Environmental Protection. 1998. The Buffer Handbook: A Guide to Creating Vegetated Buffers for Lakefront Properties. Maine DEP. Augusta, ME. Massachusetts Executive Office of Environmental Affairs (EOEA). 2005. Smart Growth Toolkit. Boston, MA. Metropolitan Area Planning Council (MAPC). 2005. Massachusetts Low Impact Development Toolkit Fact Sheets. Metropolitan Area Planning Council. Boston, MA. MPCA. 1989. Best Management Practices for Minnesota. Minnesota Pollution Control Agency. Minneapolis, MN. Better Site Design 66 Pinkham, Richard. Nov/Dec 2001. Daylighting: New Life for Buried Streams. Article from Stormwater Magazine Vol. 2, No. 6. Forester Communications. Caledonia, MI. City of Portland, Oregon. September 2004. Stormwater Management Manual. Bureau of Environmental Services, Portland, OR. Prince George’s County, MD. June 1999. Low-Impact Development Design Strategies: An Integrated Design Approach. Prince George’s County, Maryland, Department of Environmental Resources, Largo, Maryland. Rhode Island Department of Environmental Management. January 2005. The Urban Environmental Design Manual. Rhode Island Department of Environmental Management, Providence, Rhode Island. Schueler, T. 1995. Site Planning for Urban Stream Protection. Prepared for: Metropolitan Washington Council of Governments. Washington, DC. Center for Watershed Protection, Ellicott City, MD. Urban Land Institute (ULI). 1992. Density by Design. James W. Wetling and Lloyd W. Bookout, editors. Urban Land Institute, Washington, DC. U.S. Environmental Protection Agency. 1999. Parking Alternatives: Making Way for Urban Infill and Brownfields Redevelopment. U.S. EPA Urban and Economic Development Division. Washington, DC. August 2005 Page 5A.75 New York Standards and Specifications For Erosion and Sediment Control STANDARD AND SPECIFICATIONS FOR STABILIZED CONSTRUCTION ENTRANCE Criteria for Geotextile The geotextile shall be woven or nonwoven fabric consisting only of continuous chain polymeric filaments or yarns of polyester. The fabric shall be inert to commonly encountered chemicals, hydro-carbons, mildew, rot resistant, and conform to the fabric properties as shown: Light Duty1 Heavy Duty2 Roads Haul Roads Fabric Grade Rough Test Properties3 Subgrade Graded Method Grab Tensile Strength (lbs) 200 220 ASTM D1682 Elongation at Failure (%) 50 60 ASTM D1682 Mullen Brust Strength (lbs) 190 430 ASTM D3786 Puncture Strength (lbs) 40 125 ASTM D751 modified Equivalent 40-80 40-80 US Std Sieve Opening Size CW-02215 Aggregate Depth 6 10 -- 1Light Duty Road: Area sites that have been graded to subgrade and where most travel would be single axle vehicles and an occasional multi- axle truck. Acceptable materials are Trevira Spunbond 1115, Mirafi 100X, Typar 3401, or equivalent. 2Heavy Duty Road: Area sites with only rough grading, and where most travel would be multi-axle vehicles. Acceptable materials are Trevira Spunbond 1135, Mirafi 600X, or equivalent. 3Fabrics not meeting these specifications may be used only when design procedure and supporting documentation are supplied to determine aggregate depth and fabric strength. Maintenance The entrance shall be maintained in a condition which will prevent tracking of sediment onto public rights-of-way or streets. This may require periodic top dressing with additional aggregate. All sediment spilled, dropped, or washed onto public rights-of-way must be removed immediately. When necessary, wheels must be cleaned to remove sediment prior to entrance onto public rights-of-way. When washing is required, it shall be done on an area stabilized with aggregate, which drains into an approved sediment-trapping device. All sediment shall be prevented from entering storm drains, ditches, or watercourses. Definition A stabilized pad of aggregate underlain with geotextile located at any point where traffic will be entering or leaving a construction site to or from a public right-of-way, street, alley, sidewalk, or parking area. Purpose The purpose of stabilized construction entrance is to reduce or eliminate the tracking of sediment onto public rights-of- way or streets. Conditions Where Practice Applies A stabilized construction entrance shall be used at all points of construction ingress and egress. Design Criteria See Figure 5A.35 on page 5A.76 for details. Aggregate Size: Use a matrix of 1-4 inch stone, or reclaimed or recycled concrete equivalent. Thickness: Not less than six (6) inches. Width: 12-foot minimum but not less than the full width of points where ingress or egress occurs. 24-foot minimum if there is only one access to the site. Length: As required, but not less than 50 feet (except on a single residence lot where a 30 foot minimum would apply). Geotextile: To be placed over the entire area to be covered with aggregate. Filter cloth will not be required on a single- family residence lot. Piping of surface water under entrance shall be provided as required. If piping is impossible, a mountable berm with 5:1 slopes will be permitted. New York Standards and Specifications Page 5A.76 August 2005 For Erosion and Sediment Control Figure 5A.35 Stabilized Construction Entrance August 2005 Page 5A.77 New York Standards and Specifications For Erosion and Sediment Control Road Width – 14 foot minimum for one-way traffic or 24 foot minimum for two-way traffic. Side Slope of Road Embankment – 2:1 or flatter. Ditch Capacity – On-site roadside ditch and culvert capacities shall be the 10 yr. peak runoff. Composition – Use a 6-inch layer of NYS DOT sub-base Types 1,2,3, 4 or equivalent as specified in NYS – Standards and Specifications for Highways. Construction Specifications 1. Clear and strip roadbed and parking areas of all vegetation, roots, and other objectionable material. 2. Locate parking areas on naturally flat areas as available. Keep grades sufficient for drainage, but not more than 2 to 3 percent. 3. Provide surface drainage and divert excess runoff to stabilized areas. 4. Maintain cut and fill slopes to 2:1 or flatter and stabilized with vegetation as soon as grading is accomplished. 5. Spread 6-inch layer of sub-base material evenly over the full width of the road and smooth to avoid depressions. 6. Provide appropriate sediment control measures to prevent offsite sedimentation. Maintenance Inspect construction roads and parking areas periodically for condition of surface. Topdress with new gravel as needed. Check ditches for erosion and sedimentation after rainfall events. Maintain vegetation in a health, vigorous condition. Areas producing sediment should be treated immediately. STANDARD AND SPECIFICATIONS FOR CONSTRUCTION ROAD STABILIZATION Definition The stabilization of temporary construction access routes, on-site vehicle transportation routes, and construction parking areas. Purpose To control erosion on temporary construction routes and parking areas. Condition Where Practice Applies All traffic routes and parking areas for temporary use by construction traffic. Design Criteria Construction roads should be located to reduce erosion potential, minimize impact on existing site resources, and maintain operations in a safe manner. Highly erosive soils, wet or rocky areas, and steep slopes should be avoided. Roads should be routed where seasonal water tables are deeper than 18 inches. Surface runoff and control should be in accordance with other standards. Road Grade – A maximum grade of 12% is recommended, although grades up to 15% are possible for short distances. New York Standards and Specifications Page 5A.78 August 2005 For Erosion and Sediment Control August 2005 Page 5A.27 New York Standards and Specifications For Erosion and Sediment Control STANDARD AND SPECIFICATIONS FOR STORM DRAIN INLET PROTECTION Definition A temporary, somewhat permeable barrier, installed around inlets in the form of a fence, berm or excavation around an opening, trapping water and thereby reducing the sediment content of sediment laden water by settling. Purpose To prevent heavily sediment laden water from entering a storm drain system through inlets. Conditions Where Practice Applies This practice shall be used where the drainage area to an inlet is disturbed, it is not possible to temporarily divert the storm drain outfall into a trapping device, and watertight blocking of inlets is not advisable. It is not to be used in place of sediment trapping devices. This may be used in conjunction with storm drain diversion to help prevent siltation of pipes installed with low slope angle. Types of Storm Drain Inlet Practices There are four (4) specific types of storm drain inlet protection practices that vary according to their function, location, drainage area, and availability of materials: I. Excavated Drop Inlet Protection II. Fabric Drop Inlet Protection III. Stone & Block Drop Inlet Protection IV. Curb Drop Inlet Protection Design Criteria Drainage Area – The drainage area for storm drain inlets shall not exceed one acre. The crest elevations of these practices shall provide storage and minimize bypass flow. Type I – Excavated Drop Inlet Protection See details for Excavated Drop Inlet Protection in Figure 5A.11 on page 5A.29. Limit the drainage area to the inlet device to 1 acre. Excavated side slopes shall be no steeper than 2:1. The minimum depth shall be 1 foot and the maximum depth 2 feet as measured from the crest of the inlet structure. Shape the excavated basin to fit conditions with the longest dimension oriented toward the longest inflow area to provide maximum trap efficiency. The capacity of the excavated basin should be established to contain 900 cubic feet per acre of disturbed area. Weep holes, protected by fabric and stone, should be provided for draining the temporary pool. Inspect and clean the excavated basin after every storm. Sediment should be removed when 50 percent of the storage volume is achieved This material should be incorporated into the site in a stabilized manner. Type II – Fabric Drop Inlet Protection See Figure 5A.12 for details on Filter Fabric Drop Inlet Protection on page 5A.30. Limit the drainage area to 1 acre per inlet device. Land area slope immediately surrounding this device should not exceed 1 percent. The maximum height of the fabric above the inlet crest shall not exceed 1.5 feet unless reinforced. The top of the barrier should be maintained to allow overflow to drop into the drop inlet and not bypass the inlet to unprotected lower areas. Support stakes for fabric shall be a minimum of 3 feet long, spaced a maximum 3 feet apart. They should be driven close to the inlet so any overflow drops into the inlet and not on the unprotected soil. Improved performance and sediment storage volume can be obtained by excavating the area. Inspect the fabric barrier after each rain event and make repairs as needed. Remove sediment from the pool area as New York Standards and Specifications Page 5A.28 August 2005 For Erosion and Sediment Control necessary with care not to undercut or damage the filter fabric. Upon stabilization of the drainage area, remove all materials and unstable sediment and dispose of properly. Bring the adjacent area of the drop inlet to grade, smooth and compact and stabilize in the appropriate manner to the site. If straw bales are used in lieu of filter fabric, they should be placed tight with the cut edge adhering to the ground at least 3 inches below the elevation of the drop inlet. Two anchor stakes per bale shall be driven flush to bale surface. Straw bales will be replaced every 4 months until the area is stabilized. Type III – Stone and Block Drop Inlet Protection See Figure 5A.13 for details on Stone and Block Drop Inlet Protection on page 5A.31. Limit the drainage area to 1 acre at the drop inlet. The stone barrier should have a minimum height of 1 foot and a maximum height of 2 feet. Do not use mortar. The height should be limited to prevent excess ponding and bypass flow. Recess the first course of blocks at least 2 inches below the crest opening of the storm drain for lateral support. Subsequent courses can be supported laterally if needed by placing a 2x4 inch wood stud through the block openings perpendicular to the course. The bottom row should have a few blocks oriented so flow can drain through the block to dewater the basin area. The stone should be placed just below the top of the blocks on slopes of 2:1 or flatter. Place hardware cloth of wire mesh with ½ inch openings over all block openings to hold stone in place. As an optional design, the concrete blocks may be omitted and the entire structure constructed of stone, ringing the outlet (“doughnut”). The stone should be kept at a 3:1 slope toward the inlet to keep it from being washed into the inlet. A level area 1 foot wide and four inches below the crest will further prevent wash. Stone on the slope toward the inlet should be at least 3 inches in size for stability and 1 inch or smaller away from the inlet to control flow rate. The elevation of the top of the stone crest must be maintained 6 inches lower than the ground elevation down slope from the inlet to ensure that all storm flows pass over the stone into the storm drain and not past the structure. Temporary diking should be used as necessary to prevent bypass flow. The barrier should be inspected after each rain event and repairs made where needed. Remove sediment as necessary to provide for accurate storage volume for subsequent rains. Upon stabilization of contributing drainage area, remove all materials and any unstable soil and dispose of properly. Bring the disturbed area to proper grade, smooth, compact and stabilized in a manner appropriate to the site. Type IV – Curb Drop Inlet Protection See Figure 5A. 14 for details on Curb Drop Inlet Protection on page 5A.32. The drainage area should be limited to 1 acre at the drop inlet. The wire mesh must be of sufficient strength to support the filter fabric and stone with the water fully impounded against it. Stone is to be 2 inches in size and clean. The filter fabric must be of a type approved for this purpose with an equivalent opening size (EOS) of 40-85. The protective structure will be constructed to extend beyond the inlet 2 feet in both directions. Assure that storm flow does not bypass the inlet by installing temporary dikes (such as sand bags) directing flow into the inlet. Make sure that the overflow weir is stable. Traffic safety shall be integrated with the use of this practice. The structure should be inspected after every storm event. Any sediment should be removed and disposed of on the site. Any stone missing should be replaced. Check materials for proper anchorage and secure as necessary. August 2005 Page 5A.29 New York Standards and Specifications For Erosion and Sediment Control Figure 5A.11 Excavated Drop Inlet Protection New York Standards and Specifications Page 5A.30 August 2005 For Erosion and Sediment Control Figure 5A.12 Filter Fabric Drop Inlet Protection August 2005 Page 5A.31 New York Standards and Specifications For Erosion and Sediment Control Figure 5A.13 Stone & Block Drop Inlet Protection New York Standards and Specifications Page 5A.32 August 2005 For Erosion and Sediment Control Figure 5A.14 Curb Drop Inlet Protection August 2005 Page 5A.87 New York Standards and Specifications For Erosion and Sediment Control Vegetative Cover – For disturbed areas not subject to traffic, vegetation provides the most practical method of dust control (see Section 3). Mulch (including gravel mulch) – Mulch offers a fast effective means of controlling dust. This can also include rolled erosion control blankets. Spray adhesives – These are products generally composed of polymers in a liquid or solid form that are mixed with water to form an emulsion that is sprayed on the soil surface with typical hydroseeding equipment. The mixing ratios and application rates will be in accordance with the manufacturer’s recommendations for the specific soils on the site. In no case should the application of these adhesives be made on wet soils or if there is a probability of precipitation within 48 hours of its proposed use. Material Safety Data Sheets will be provided to all applicators and others working with the material. B. Driving Areas – These areas utilize water, polymer emulsions, and barriers to prevent dust movement from the traffic surface into the air. Sprinkling – The site may be sprayed with water until the surface is wet. This is especially effective on haul roads and access routes. Polymer Additives – These polymers are mixed with water and applied to the driving surface by a water truck with a gravity feed drip bar, spray bar or automated distributor truck. The mixing ratios and application rates will be in accordance with the manufacturer’s recommendations. Incorporation of the emulsion into the soil will be done to the appropriate depth based on expected traffic. Compaction after incorporation will be by vibratory roller to a minimum of 95%. The prepared surface shall be moist and no application of the polymer will be made if there is a probability of precipitation within 48 hours of its proposed use. Material Safety Data Sheets will be provided to all applicators working with the material. Barriers – Woven geotextiles can be placed on the driving surface to effectively reduce dust throw and particle migration on haul roads. Stone can also be used for construction roads for effective dust control. Windbreak – A silt fence or similar barrier can control air currents at intervals equal to ten times the barrier height. Preserve existing wind barrier vegetation as much as practical. STANDARD AND SPECIFICATIONS FOR DUST CONTROL Definition The control of dust resulting from land-disturbing activities. Purpose To prevent surface and air movement of dust from disturbed soil surfaces that may cause off-site damage, health hazards, and traffic safety problems. Conditions Where Practice Applies On construction roads, access points, and other disturbed areas subject to surface dust movement and dust blowing where off-site damage may occur if dust is not controlled. Design Criteria Construction operations should be scheduled to minimize the amount of area disturbed at one time. Buffer areas of vegetation should be left where practical. Temporary or permanent stabilization measures shall be installed. No specific design criteria is given; see construction specifications below for common methods of dust control. Water quality must be considered when materials are selected for dust control. Where there is a potential for the material to wash off to a stream, ingredient information must be provided to the local permitting authority. Construction Specifications A. Non-driving Areas – These areas use products and materials applied or placed on soil surfaces to prevent airborne migration of soil particles. New York Standards and Specifications Page 5A.88 August 2005 For Erosion and Sediment Control All Stormwater Pollution Prevention Plans must contain the NYS DEC issued “Conditions for Use” and “Application Instructions” for any polymers used on the site. This information can be obtained from the NYS DEC website. Maintenance Maintain dust control measures through dry weather periods until all disturbed areas are stabilized. August 2005 Page 3.29 New York Standards and Specifications For Erosion and Sediment Control Definition Applying coarse plant residue or chips, or other suitable materials, to cover the soil surface. Purpose The primary purpose is to provide initial erosion control while a seeding or shrub planting is establishing. Mulch will conserve moisture and modify the surface soil temperature and reduce fluctuation of both. Mulch will prevent soil surface crusting and aid in weed control. Mulch is also used alone for temporary stabilization in non- growing months. Conditions Where Practice Applies On soils subject to erosion and on new seedings and shrub plantings. Mulch is useful on soils with low infiltration rates by retarding runoff. Criteria Site preparation prior to mulching requires the installation of necessary erosion control or water management practices and drainage systems. Slope, grade and smooth the site to fit needs of selected mulch products. Remove all undesirable stones and other debris to meet the needs of the anticipated land use and maintenance required. Apply mulch after soil amendments and planting is accomplished or simultaneously if hydroseeding is used. Select appropriate mulch material and application rate or material needs. Determine local availability. Select appropriate mulch anchoring material. NOTE: The best combination for grass/legume establishment is straw (cereal grain) mulch applied at 2 ton/ acre (90 lbs./1000sq.ft.) and anchored with wood fiber mulch (hydromulch) at 500 – 750 lbs./acre (11 – 17 lbs./1000 sq. ft.). The wood fiber mulch must be applied through a hydroseeder immediately after mulching. STANDARD AND SPECIFICATIONS FOR MULCHING New York Standards and Specifications Page 3.30 August 2005 For Erosion and Sediment Control Table 3.7 Guide to Mulch Materials, Rates, and Uses Mu l c h Ma t e r i a l Qu a l i t y St a n d a r d s pe r 1 0 0 0 S q . F t . pe r A c r e De p t h o f Ap p l i c a t i o n Re m a r k s Wo o d c h i p s o r sh a v i n g s Ai r - d r i e d . F r e e o f ob j e c t i o n a b l e c o a r s e ma t e r i a l 50 0 - 9 0 0 l b s . 10 - 2 0 t o n s 2- 7 ” Us e d p r i m a r i l y a r o u n d s h r u b a n d t r e e pl a n t i n g s a n d r e c r e a t i on t r a i l s t o i n h i b i t we e d c o m p e t i t i o n . R e s i s t a n t t o w i n d bl o w i n g . D e c o m p o s e s s l o w l y . Wo o d f i b e r c e l l u l o s e (p a r t l y d i g e s t e d wo o d f i b e r s ) Ma d e f r o m n a t u r a l w o o d us u a l l y w i t h g r e e n d y e an d d i s p e r s i n g a g e n t 50 l b s . 2, 0 0 0 l b s . — Ap p l y w i t h h y d r o m u l c h e r . N o t i e d o w n re q u i r e d . L e s s e r o s i o n c o n t r o l p r o v i d e d th a n 2 t o n s o f h a y o r s t r a w . Gr a v e l , C r u s h e d St o n e o r S l a g Wa s h e d ; S i z e 2 B o r 3A — 1 1 / 2 ” 9 c u . y d s . 40 5 c u . y d s . 3” Ex c e l l e n t m u l c h f o r s h o r t s l o p e s a n d ar o u n d p l a n t s a n d o r n a m e n t a l s . U s e 2 B wh e r e s u b j e c t t o t r a f f i c . ( A p p r o x i m a t e l y 2, 0 0 0 l b s . / c u . y d . ) . F r e q u e n t l y u s e d o v e r fi l t e r f a b r i c f o r b e t t e r w e e d c o n t r o l . Ha y o r S t r a w Ai r - d r i e d ; f r e e o f un d e s i r a b l e s e e d s & co a r s e m a t e r i a l s 90 - 1 0 0 l b s . 2 - 3 b a l e s 2 t o n s ( 1 0 0 - 1 2 0 ba l e s ) co v e r a b o u t 9 0 % su r f a c e Us e s m a l l g r a i n s t r a w w h e r e m u l c h i s ma i n t a i n e d f o r m o r e t h a n t h r e e m o n t h s . Su b j e c t t o w i n d b l o w i n g u n l e s s a n c h o r e d . Mo s t c o m m o n l y u s e d m u l c h i n g m a t e r i a l . Pr o v i d e s t h e b e s t m i c r o - e n v i r o n m e n t f o r ge r m i n a t i n g s e e d s . Ju t e t w i s t e d y a r n Un d y e d , u n b l e a c h e d pl a i n w e a v e . W a r p 7 8 en d s / y d . , W e f t 4 1 e n d s / yd . 6 0 - 9 0 l b s . / r o l l 48 ” x 5 0 y d s . o r 4 8 ” x 7 5 y d s . — — Us e w i t h o u t a d d i t i o n a l m u l c h . T i e d o w n as p e r m a n u f a c t u r e r s s p e c i f i c a t i o n s . Go o d f o r c e n t e r l i n e of c o n c e n t r a t e d wa t e r f l o w . Ex c e l s i o r w o o d f i b e r ma t s In t e r l o c k i n g w e b o f ex c e l s i o r f i b e r s w i t h ph o t o d e g r a d a b l e p l a s t i c ne t t i n g 8” x 1 0 0 ” 2 - s i d e d pl a s t i c , 4 8 ” x 1 8 0 ” 1- s i d e d p l a s t i c — — Us e w i t h o u t a d d i t i o n a l m u l c h . E x c e l l e n t fo r s e e d i n g e s t a b l i s h m e n t . T i e d o w n a s pe r m a n u f a c t u r e r s s p e c i f i c a t i o n s . Ap p r o x i m a t e l y 7 2 l b s . / r o l l f o r e x c e l s i o r wi t h p l a s t i c o n b o t h s i d e s . U s e t w o s i d e d pl a s t i c f o r c e n t e r l i n e o f w a t e r w a y s . Co m p o s t Up t o 3 ” p i e c e s , mo d e r a t e l y t o h i g h l y st a b l e 3- 9 c u . y d s . 13 4 - 4 0 2 c u . y d s . 1- 3 ” Co a r s e r t e x t u r e d m u l c h e s m a y b e m o r e ef f e c t i v e i n r e d u c i n g w e e d g r o w t h a n d wi n d e r o s i o n . St r a w o r c o c o n u t fi b e r , o r c o m b i n a t i o n Ph o t o d e g r a d a b l e p l a s t i c ne t o n o n e o r t w o s i d e s Mo s t a r e 6 . 5 f t . x 3 . 5 ft . 81 r o l l s — De s i g n e d t o t o l e r a t e h i g h e r v e l o c i t y w a t e r fl o w , c e n t e r l i n e s o f w a t e r w a y s , 6 0 s q . yd s . p e r r o l l . August 2005 Page 3.31 New York Standards and Specifications For Erosion and Sediment Control Table 3.8 Mulch Anchoring Guide Anchoring Method or Material Kind of Mulch to be Anchored How to Apply 1. Peg and Twine Hay or straw After mulching, divide areas into blocks approximately 1 sq. yd. in size. Drive 4-6 pegs per block to within 2” to 3” of soil surface. Secure mulch to surface by stretching twine between pegs in criss-cross pattern on each block. Secure twine around each peg with 2 or more tight turns. Drive pegs flush with soil. Driving stakes into ground tightens the twine. 2. Mulch netting Hay or straw Staple the light-weight paper, jute, wood fiber, or plastic nettings to soil surface according to manufacturer’s recommendations. Should be biodegradable. Most products are not suitable for foot traffic. 3. Wood cellulose fiber Hay or straw Apply with hydroseeder immediately after mulching. Use 500 lbs. wood fiber per acre. Some products contain an adhesive material (“tackifier”), possibly advantageous. 4. Mulch anchoring tool Hay or straw Apply mulch and pull a mulch anchoring tool (blunt, straight discs) over mulch as near to the contour as possible. Mulch material should be “tucked” into soil surface about 3”. 5. Tackifier Hay or straw Mix and apply polymeric and gum tackifiers according to manufacturer’s instructions. Avoid application during rain. A 24-hour curing period and a soil temperature higher than 450 Fahrenheit are required. New York Standards and Specifications Page 3.32 August 2005 For Erosion and Sediment Control August 2005 Page 3.37 New York Standards and Specifications For Erosion and Sediment Control Definition The protection of trees, shrubs, ground cover and other vegetation from damage by construction equipment. Purpose To preserve existing vegetation determined to be important for soil erosion control, water quality protection, shade, screening, buffers, wildlife habitat, wetland protection, and other values. Condition Where Practice Applies On planned construction sites where valued vegetation exists and needs to be preserved. Design Criteria 1. Planning Considerations A. Inventory: 1) Property boundaries, topography, vegetation and soils information should be gathered. Identify potentially high erosion areas, areas with tree windthrow potential, etc. A vegetative cover type map should be made on a copy of a topographic map which shows other natural and manmade features. Vegetation that is desirable to preserve because of its value for screening, shade, critical erosion control, endangered species, aesthetics, etc., should be identified and marked on the map. 2) Based upon this data, general statements should be prepared about the present condition, potential problem areas, and unique features of the property. B. Planning: 1) After engineering plans (plot maps) are prepared, another field review should take place and recommendations made for the vegetation to be saved. Minor adjustments in location of roads, dwellings, and utilities may be needed. Construction on steep slopes, erodible soils, wetlands, and streams should be avoided. Clearing limits should be delineated (See Section 2). 2) Areas to be seeded and planted should be identified. Remaining vegetation should blend with their surroundings and/or provide special function such as a filter strip, buffer zone, or screen. 3) Trees and shrubs of special seasonal interest, such as flowering dogwood, red maple, striped maple, serviceberry, or shadbush, and valuable potential shade trees should be identified and marked for special protective treatment as appropriate. 4) Trees to be cut should be marked on the plans. If timber can be removed for salable products, a forester should be consulted for marketing advice. 5) Trees that may become a hazard to people, personal property, or utilities should be removed. These include trees that are weak-wooded, disease-prone, subject to windthrow, or those that have severely damaged root systems. 6) The vigor of remaining trees may be improved by a selective thinning. A forester should be consulted for implementing this practice. 2. Measures to Protect Vegetation A. Limit soil placement over existing tree and shrub roots to a maximum of 3 inches. Soils with loamy texture and good structure should be used. B. Use retaining walls and terraces to protect roots of trees and shrubs when grades are lowered. Lowered grades should start no closer than the dripline of the tree. For narrow-canopied trees and shrubs, the stem diameter in inches is converted to feet and doubled, such that a 10 inch tree should be protected to 20 feet. STANDARD AND SPECIFICATIONS FOR PROTECTING VEGETATION DURING CONSTRUCTION New York Standards and Specifications Page 3.38 August 2005 For Erosion and Sediment Control C. Trenching across tree root systems should be the same minimum distance from the trunk, as in “B”. Tunnels under root systems for underground utilities should start 18 inches or deeper below the normal grounds surface. Tree roots which must be severed should be cut clean. Backfill material that will be in contact with the roots should be topsoil or a prepared planting soil mixture. D. Construct sturdy fences, or barriers, of wood, steel, or other protective material around valuable vegetation for protection from construction equipment. Place barriers far enough away from trees, but not less than the specifications in "B", so that tall equipment such as backhoes and dump trucks do not contact tree branches. E. Construction limits should be identified and clearly marked to exclude equipment. F. Avoid spills of oil/gas and other contaminants. G. Obstructive and broken branches should be pruned properly. The branch collar on all branches whether living or dead should not be damaged. The 3 or 4 cut method should be used on all branches larger than two inches at the cut. First cut about one-third the way through the underside of the limb (about 6-12 inches from the tree trunk). Then (approximately an inch further out) make a second cut through the limb from the upper side. When the branch is removed, there is no splintering of the main tree trunk. Remove the stub. If the branch is larger than 5-6 inches in diameter, use the four cut system. Cuts 1 and 2 remain the same and cut 3 should be from the underside of the limb, on the outside of the branch collar. Cut 4 should be from the top and in alignment with the 3rd cut. Cut 3 should be 1/4 to 1/3 the way through the limb. This will prevent the bark from peeling down the trunk. Do not paint the cut surface. H. Penalties for damage to valuable trees, shrubs, and herbaceous plants should be clearly spelled out in the contract. August 2005 Page 5A.35 New York Standards and Specifications For Erosion and Sediment Control STANDARD AND SPECIFICATIONS FOR SEDIMENT TRAP Definition A temporary sediment control device formed by excavation and/or embankment to intercept sediment laden runoff and retain the sediment. Purpose The purpose of the structure is to intercept sediment-laden runoff and trap the sediment in order to protect drainage ways, properties, and rights-of-way below the sediment trap from sedimentation. Conditions Where Practice Applies A sediment trap is usually installed in a drainage way, at a storm drain inlet, or other points of collection from a disturbed area. Sediment traps should be used to artificially break up the natural drainage area into smaller sections where a larger device (sediment basin) would be less effective. Design Criteria If any of the design criteria presented here cannot be met, see Standard and Specification for Sediment Basin on page 5A.49. Drainage Area The drainage area for sediment traps shall be in accordance with the specific type of sediment trap used (Type I through V). Location Sediment traps shall be located so that they can be installed prior to grading or filling in the drainage area they are to protect. Traps must not be located any closer than 20 feet from a proposed building foundation if the trap is to function during building construction. Locate traps to obtain maximum storage benefit from the terrain and for ease of cleanout and disposal of the trapped sediment. Trap Size The volume of a sediment trap as measured at the elevation of the crest of the outlet shall be at least 3,600 cubic feet per acre of drainage area. The volume of a constructed trap shall be calculated using standard mathematical procedures. The volume of a natural sediment trap may be approximated by the equation: Volume (cu.ft.) = 0.4 x surface area (sq.ft.) x maximum depth (ft.). Trap Cleanout Sediment shall be removed and the trap restored to the original dimensions when the sediment has accumulated to ½ of the design depth of the trap. Sediment removed from the trap shall be deposited in a protected area and in such a manner that it will not erode. Embankment All embankments for sediment traps shall not exceed five (5) feet in height as measured at the low point of the original ground along the centerline of the embankment. Embankments shall have a minimum four (4) foot wide top and side slopes of 2:1 or flatter. The embankment shall be compacted by traversing with equipment while it is being constructed. The embankment shall be stabilized with seed and mulch as soon as it is completed The elevation of the top of any dike directing water to any sediment trap will equal or exceed the maximum height of the outlet structure along the entire length of the trap. Excavation All excavation operations shall be carried out in such a manner that erosion and water pollution shall be minimal. Excavated portions of sediment traps shall have 1:1 or flatter slopes. Outlet The outlet shall be designed, constructed, and maintained in such a manner that sediment does not leave the trap and that erosion at or below the outlet does not occur. New York Standards and Specifications Page 5A.36 August 2005 For Erosion and Sediment Control Sediment traps must outlet onto stabilized (preferable undisturbed) ground, into a watercourse, stabilized channel, or into a storm drain system. Distance between inlet and outlet should be maximized to the longest length practicable. Trap Details Needed on Erosion and Sediment Control Plans Each trap shall be delineated on the plans in such a manner that it will not be confused with any other features. Each trap on a plan shall indicate all the information necessary to properly construct and maintain the structure. If the drawings are such that this information cannot be delineated on the drawings, then a table shall be developed. If a table is developed, then each trap on a plan shall have a number and the numbers shall be consecutive. The following information shall be shown for each trap in a summary table format on the plans. 1. Trap number 2. Type of trap 3. Drainage area 4. Storage required 5. Storage provided (if applicable) 6. Outlet length or pipe sizes 7. Storage depth below outlet or cleanout elevation 8. Embankment height and elevation (if applicable) Type of Sediment Traps There are five (5) specific types of sediment traps which vary according to their function, location, or drainage area. I. Pipe Outlet Sediment Trap II. Grass Outlet Sediment Trap III. Catch Basin Sediment Trap IV. Stone Outlet Sediment Trap V. Riprap Outlet Sediment Trap I. Pipe Outlet Sediment Trap A Pipe Outlet Sediment Trap consists of a trap formed by embankment or excavation. The outlet for the trap is through a perforated riser and a pipe through the embankment. The outlet pipe and riser shall be made of steel, corrugated metal or other suitable material. The top of the embankment shall be at least 1 ½ feet above the crest of the riser. The top 2/3 of the riser shall be perforated with one (1) inch nominal diameter holes or slits spaced six (6) inches vertically and horizontally placed in the concave portion of the corrugated pipe. No holes or slits will be allowed within six (6) inches of the top of the horizontal barrel. All pipe connections shall be watertight. The riser shall be wrapped with ½ to ¼ inch hardware cloth wire then wrapped with filter cloth with a sieve size between #40-80 and secured with strapping or connecting band at the top and bottom of the cloth. The cloth shall cover an area at least six (6) inches above the highest hole and six (6) inches below the lowest hole. The top of the riser pipe shall not be covered with filter cloth. The riser shall have a base with sufficient weight to prevent flotation of the riser. Two approved bases are: 1. A concrete base 12 in. thick with the riser embedded 9 in. into the concrete base, or 2. One quarter inch, minimum, thick steel plate attached to the riser by a continuous weld around the circumference of the riser to form a watertight connection. The plate shall have 2.5 feet of stone, gravel, or earth placed on it to prevent flotation. In either case, each side of the square base measurement shall be the riser diameter plus 24 inches. Pipe outlet sediment traps shall be limited to a five (5) acre maximum drainage area. Pipe outlet sediment traps may be interchangeable in the field with stone outlet or riprap sediment traps provided that these sediment traps are constructed in accordance with the detail and specifications for that trap. Select pipe diameter from the following table: Minimum Sizes 1 Barrel diameter may be same size as riser diameter. See details for Pipe Outlet Sediment Trap ST-I in Figure 5A.16 (1) and 5A.16 (2) on pages 5A.38 and 5A.39. II. Grass Outlet Sediment Trap A Grass Outlet Sediment Trap consists of a trap formed by excavating the earth to create a holding area. The trap has a discharge point over natural existing grass. The outlet crest width (feet) shall be equal to four (4) times the drainage area (acres) with a minimum width of four (4) feet. The outlet shall be free of any restrictions to flow. The outlet lip must remain undisturbed and level. The volume of this trap shall be computed at the elevation of the crest of the outlet. Grass outlet sediment traps shall be limited to a five (5) acre maximum drainage area. Barrel Diameter1 (in.) Riser Diameter1 (in.) Maximum Drainage Area (ac.) 12 15 1 15 18 2 18 21 3 21 24 4 21 27 5 August 2005 Page 5A.37 New York Standards and Specifications For Erosion and Sediment Control See details for Grass Outlet Sediment Trap ST-II in Figure 5A.17 on page 5A.40. III. Catch Basin Sediment Trap A Catch Basin Sediment Trap consists of a basin formed by excavation on natural ground that discharges through an opening in a storm drain inlet structure. This opening can either be the inlet opening or a temporary opening made by omitting bricks or blocks in the inlet. A yard drain inlet or an inlet in the median strip of a dual highway could use the inlet opening for the type outlet. The trap should be out of the roadway so as not to interfere with future compaction or construction. Placing the trap on the opposite side of the opening and diverting water from the roadway to the trap is one means of doing this. Catch basin sediment traps shall be limited to a three (3) acre maximum drainage area. The volume of this trap is measured at the elevation of the crest of the outlet (invert of the inlet opening). See details for Catch Basin Sediment Trap ST-III in Figure 5A.18 on page 5A.41. IV. Stone Outlet Sediment Trap A Stone Outlet Sediment Trap consists of a trap formed by an embankment or excavation. The outlet of this trap is over a stone section placed on level ground. The minimum length (feet) of the outlet shall be equal to four (4) times the drainage area (acres). Required storage shall be 3,600 cubic feet per acre of drainage area. The outlet crest (top of stone in weir section) shall be level, at least one (1) foot below top of embankment and no more than one (1) foot above ground beneath the outlet. Stone used in the outlet shall be small riprap (4 in. x 8 in.). To provide more efficient trapping effect, a layer of filter cloth should be embedded one (1) foot back into the upstream face of the outlet stone or a one (1) foot thick layer of two (2) inch or finer aggregate shall be placed on the upstream face of the outlet. Stone Outlet Sediment Traps may be interchangeable in the field with pipe or riprap outlet sediment traps provided they are constructed in accordance with the detail and specifications for those traps. Stone outlet sediment traps shall be limited to a five (5) acre maximum drainage area. See details for Stone Outlet Sediment Trap ST-IV in Figure 5A.19 on page 5A.42. V. Riprap Outlet Sediment Trap A Riprap Outlet Sediment Trap consists of a trap formed by an excavation and embankment. The outlet for this trap shall be through a partially excavated channel lined with riprap. This outlet channel shall discharge onto a stabilized area or to a stable watercourse. The riprap outlet sediment trap may be used for drainage areas of up to a maximum of 15 acres. Design Criteria for Riprap Outlet Sediment Trap 1. The total contributing drainage area (disturbed or undisturbed either on or off the developing property) shall not exceed 15 acres. 2. The storage needs for this trap shall be computed using 3600 cubic feet of required storage for each acre of drainage area. The storage volume provided can be figured by computing the volume of storage area available behind the outlet structure up to an elevation of one (1) foot below the level weir crest. 3. The maximum height of embankment shall not exceed five (5) feet. 4. The elevation of the top of any dike directing water to a riprap outlet sediment trap will equal or exceed the minimum elevation of the embankment along the entire length of this trap. Riprap Outlet Sediment Trap ST-V (for Stone Lined Channel) Contributing Depth of Length of Drainage Area Channel (a) Weir (b) (ac.) (ft.) (ft.) 1 1.5 4.0 2 1.5 5.0 3 1.5 6.0 4 1.5 10.0 5 1.5 12.0 6 1.5 14.0 7 1.5 16.0 8 2.0 10.0 9 2.0 10.0 10 2.0 12.0 11 2.0 14.0 12 2.0 14.0 13 2.0 16.0 14 2.0 16.0 15 2.0 18.0 See details for Riprap Outlet Sediment Trap ST-V on Figures 5A.20(1) and 5A.20(2) on pages 5A.43 and 5A.44. Optional Dewatering Methods Optional dewatering devices may be designed for use with sediment traps. Included are two methods, which may be used. See Figure 5A.21 on page 5A.45 for details. New York Standards and Specifications Page 5A.38 August 2005 For Erosion and Sediment Control Figure 5A.16(1) Pipe Outlet Sediment Trap: ST-I August 2005 Page 5A.39 New York Standards and Specifications For Erosion and Sediment Control Figure 5A.16(2) Pipe Outlet Sediment Trap: ST-I—Construction Specifications New York Standards and Specifications Page 5A.40 August 2005 For Erosion and Sediment Control Figure 5A.17 Grass Outlet Sediment Trap: ST-II August 2005 Page 5A.41 New York Standards and Specifications For Erosion and Sediment Control Figure 5A.18 Catch Basin Sediment Trap: ST-III New York Standards and Specifications Page 5A.42 August 2005 For Erosion and Sediment Control Figure 5A.19 Stone Outlet Sediment Trap: ST-IV August 2005 Page 5A.43 New York Standards and Specifications For Erosion and Sediment Control Figure 5A.20(1) Riprap Outlet Sediment Trap: ST-V New York Standards and Specifications Page 5A.44 August 2005 For Erosion and Sediment Control Figure 5A.202) Riprap Outlet Sediment Trap: ST-V—Construction Specifications August 2005 Page 5A.45 New York Standards and Specifications For Erosion and Sediment Control Figure 5A.21 Optional Sediment Trap Dewatering Devices New York Standards and Specifications Page 5A.46 August 2005 For Erosion and Sediment Control August 2005 Page 5A.19 New York Standards and Specifications For Erosion and Sediment Control STANDARD AND SPECIFICATIONS FOR SILT FENCE Definition A temporary barrier of geotextile fabric installed on the contours across a slope used to intercept sediment laden runoff from small drainage areas of disturbed soil. Purpose The purpose of a silt fence is to reduce runoff velocity and effect deposition of transported sediment load. Limits imposed by ultraviolet stability of the fabric will dictate the maximum period the silt fence may be used (approximately one year). Conditions Where Practice Applies A silt fence may be used subject to the following conditions: 1. Maximum allowable slope lengths contributing runoff to a silt fence placed on a slope are: Slope Maximum Steepness Length (ft.) 2:1 25 3:1 50 4:1 75 5:1 or flatter 100 2. Maximum drainage area for overland flow to a silt fence shall not exceed ¼ acre per 100 feet of fence, with maximum ponding depth of 1.5 feet behind the fence; and 3. Erosion would occur in the form of sheet erosion; and 4. There is no concentration of water flowing to the barrier. Design Criteria Design computations are not required for installations of 1 month or less. Longer installation periods should be designed for expected runoff. All silt fences shall be placed as close to the areas as possible, but at least 10 feet from the toe of a slope to allow for maintenance and roll down. The area beyond the fence must be undisturbed or stabilized. Sensitive areas to be protected by silt fence may need to be reinforced by using heavy wire fencing for added support to prevent collapse. Where ends of filter cloth come together, they shall be overlapped, folded and stapled to prevent sediment bypass. A detail of the silt fence shall be shown on the plan. See Figure 5A.8 on page 5A.21 for details. Criteria for Silt Fence Materials 1. Silt Fence Fabric: The fabric shall meet the following specifications unless otherwise approved by the appropriate erosion and sediment control plan approval authority. Such approval shall not constitute statewide acceptance. Minimum Acceptable Fabric Properties Value Test Method Grab Tensile Strength (lbs) 90 ASTM D1682 Elongation at Failure (%) 50 ASTM D1682 New York Standards and Specifications Page 5A.20 August 2005 For Erosion and Sediment Control Mullen Burst Strength (PSI) 190 ASTM D3786 Puncture Strength (lbs) 40 ASTM D751 (modified) Slurry Flow Rate (gal/min/sf) 0.3 Equivalent Opening Size 40-80 US Std Sieve CW-02215 Ultraviolet Radiation Stability (%) 90 ASTM G-26 2. Fence Posts (for fabricated units): The length shall be a minimum of 36 inches long. Wood posts will be of sound quality hardwood with a minimum cross sectional area of 3.0 square inches. Steel posts will be standard T and U section weighing not less than 1.00 pound per linear foot. 3. Wire Fence (for fabricated units): Wire fencing shall be a minimum 14 gage with a maximum 6 in. mesh opening, or as approved. 4. Prefabricated Units: Envirofence, Geofab, or approved equal, may be used in lieu of the above method providing the unit is installed per details shown in Figure 5A.8. August 2005 Page 5A.21 New York Standards and Specifications For Erosion and Sediment Control Figure 5A.8 Silt Fence New York Standards and Specifications Page 5A.22 August 2005 For Erosion and Sediment Control August 2005 Page 3.27 New York Standards and Specifications For Erosion and Sediment Control Definition Spreading a specified quality and quantity of topsoil materials on graded or constructed subsoil areas. Purpose To provide acceptable plant cover growing conditions, thereby reducing erosion; to reduce irrigation water needs; and to reduce the need for nitrogen fertilizer application. Conditions Where Practice Applies Topsoil is applied to subsoils that are droughty (low available moisture for plants), stony, slowly permeable, salty or extremely acid. It is also used to backfill around shrub and tree transplants. This standard does not apply to wetland soils. Design Criteria 1. Preserve existing topsoil in place where possible, thereby reducing the need for added topsoil. 2. Conserve by stockpiling topsoil and friable fine textured subsoils that must be stripped from the excavated site and applied after final grading where vegetation will be established. 3. Refer to USDA Soil Conservation Service (presently Natural Resource Conservation Service) soil surveys or soil interpretation record sheets for further soil texture information for selecting appropriate design topsoil depths. Site Preparation 1. As needed, install erosion control practices such as diversions, channels, sediment traps, and stabilizing measures, or maintain if already installed. 2. Complete rough grading and final grade, allowing for depth of topsoil to be added. 3. Scarify all compact, slowly permeable, medium and fine textured subsoil areas. Scarify at approximately right angles to the slope direction in soil areas that are steeper than 5 percent. Areas that have been overly compacted shall be decompacted to a minimum depth of 12 inches with a deep ripper or chisel plow prior to topsoiling. 4. Remove refuse, woody plant parts, stones over 3 inches in diameter, and other litter. Topsoil Materials 1. Topsoil shall have at least 6 percent by weight of fine textured stable organic material, and no greater than 20 percent. Muck soil shall not be considered topsoil. 2. Topsoil shall have not less than 20 percent fine textured material (passing the NO. 200 sieve) and not more than 15 percent clay. 3. Topsoil treated with soil sterilants or herbicides shall be so identified to the purchaser. 4. Topsoil shall be relatively free of stones over 1 1/2 inches in diameter, trash, noxious weeds such as nut sedge and quackgrass, and will have less than 10 percent gravel. 5. Topsoil containing soluble salts greater than 500 parts per million shall not be used. Application and Grading 1. Topsoil shall be distributed to a uniform depth over the area. It shall not be placed when it is partly frozen, muddy, or on frozen slopes or over ice, snow, or standing water puddles. 2. Topsoil placed and graded on slopes steeper than 5 percent shall be promptly fertilized, seeded, mulched, and stabilized by “tracking” with suitable equipment. STANDARD AND SPECIFICATIONS FOR TOPSOILING New York Standards and Specifications Page 3.28 August 2005 For Erosion and Sediment Control 3. Apply topsoil in the following amounts: Site Conditions Intended Use Minimum Topsoil Depth 1. Deep sand or loamy sand Mowed lawn Tall legumes, unmowed Tall grass, unmowed 6 in. 2 in. 1 in. 2. Deep sandy loam Mowed lawn Tall legumes, unmowed Tall grass, unmowed 5 in. 2 in. none 3. Six inches or more: silt loam, loam, or silt Mowed lawn Tall legumes, unmowed Tall grass, unmowed 4 in. 1 in. 1 in. SITE INSPECTION REPORT REQUIREMENTS This information is to be provided on contracts covered by SPDES General Permit for Construction Activity (GP-0-20-001). The completed inspection form must be filed in the Engineer’s Field Office. 1. Describe the condition of the runoff at all points of discharge from the construction site. Include discharges from conveyance systems (i.e. pipes, culverts, ditches, etc.) and overland flow. 2. Describe condition of any waterbodies within or adjacent to the construction site. Identify any sediment discharges to the surface waterbody. 3. Identify all erosion and sediment control practices that need repair or maintenance. 4. Identify all erosion and sediment control practices that were not installed properly or are not functioning as designed and need to be reinstalled or replaced. 5. Description and sketch of areas that are disturbed at the time of the inspection and areas that have been stabilized (temporary and/or final) since the last inspection. 6. Identify current phase of construction of all post-construction stormwater management practices and identify all construction that is not in conformance with the SWPPP and technical standards. 7. Identify corrective action(s) that must be taken to install, repair, replace or maintain erosion and sediment control practices; and to correct deficiencies identified with the construction of the post-construction stormwater management practice(s). 8. Digital photographs, with date stamp, that show the condition of all practices that have been identified as needing corrective actions. a. Photographs must also be taken that show the practice(s) after the corrective action has been completed. b. Color paper copies of the photographs must be included in the inspection report within 7 calendar days. 9. Inspection Notification: Within One Business day of the inspection, the qualified inspector shall notify the owner or operator and appropriate contractor or subcontractor of any corrective actions required. . STORMWATER POLLUTION PREVENTION PLAN INSPECTION REPORT Project Name: Time: Weather Conditions: Soil Conditions: Reason for Visit: Codes for erosion and sedimentation controls to be inspected: Mon Tue Wed (13) Pipe inlet/outlet protection Inspector Name: Temperature: Project Number: Day of the Week: (14) Water bars Thur Fri Sat Sun □ Special (8) Sedimentation Basins (1) Mulch (2) Seeding and Mulch (11) Soil Stabilizers (12) Construction Entrance (3) Check Dams (15) Other Control Measures Inspector's Signature: (5) Silt Fence (6) Sediment Trap (7) Turbidity Curtains (9) Drain Structure Inlet Protection (10) Rolled Erosion Control Products (4) Triangular Silt Dike Comments: Approximate Sediment Accumulation (%) of Depth Describe structure integrity and any erosion Code # Remarks Location Disturbance Next 7 days Y or N Temp or Perm (T,P or NA) Measure Existing Y or N Maintenance Required Y or N (if Y describe) □ 5+ acres exposed □ Saturated□ Dry □ Wet Date of Inspection: □ Weekly STORMWATER POLLUTION PREVENTION PLAN INSPECTION REPORT