HomeMy WebLinkAbout20210755 269 Broadway Site Plan Review Public Comment-Attachment to Sara Mantas Submission Sheet C-130 identifies a stormwater detention system and corresponds to details 3, 4 and 5 on Sheet C-
503. Detail 4 on Sheet C-503 shows the proposed stormwater management practice as an underground
infiltration system rather than detention system.The system proposed will collect stormwater runoff,
allow it to temporarily impound and then discharge via infiltration through the .98' of crushed stone.
Based on the geotechnical report, the groundwater surface elevation is in the range of 289 to 292 feet,
however the geotechnical report does not provide a boring location map to identify where the borings
performed were. Although the project proposes disturbance less than 1 acre and the project is not
subject to the NYSDEC SPDES General Permit for Stormwater Discharges from Construction Activity(GP-
0-20-001), Section 242-7 of the City of Saratoga Code requires a Full Stormwater Pollution Prevention
Plan (soil and sediment control and post-construction controls)for nonresidential activities disturbing
0.1 acre or more that is designed to the technical standards of the New York State Stormwater
Management Design Manual (Code Section 242-8). Section 6.3.1 of the Design Manual requires that to
be suitable for infiltration, underlying soils shall have an infiltration rate of at least 0.5 inches per hour,
as confirmed by geotechnical tests taken at 24 inches below the bottom of the proposed practice.The
geotechnical report does not indicate infiltration testing was performed or, if it was performed, the
depths of the tests performed and the corresponding infiltration rates. Also, Detail 4 identifies the
bottom of the practice at elevation 292. Section 6.3.1 requires the bottom of the infiltration facility be
separated by at least three feet vertically from the seasonally high-water table, as documented by on-
site soil testing.The geotechnical report and plans do not identify the location of the borings performed
to demonstrate adequate separation. In addition, based on Detail 4, it does not appear that there is a
means of pretreatment for the infiltration system that meets the requirements of Section 6.3.3 of the
Design Manual. Based on the infiltration rate of the underlying soils,the required infiltration rate is
between 25%and 100%of the required water quality volume, as calculated by Chapter 4 of the Design
Manual. Finally, Sheet C-120 identifies an ADA compliant ramp with handrails overtop the underground
infiltration system and it should be detailed how the ramp foundation would be constructed without
impacting the underground system.