HomeMy Public PortalAbout5 - Stormwater-Drainage SummarySTORMWATER/DRAINAGE SUMMARY
July 09, 2019
19 Coolidge Hill Road
Watertown, Massachusetts
CROWE
Landscape Architects and Civil Engineers
Winchester, Massachusetts
A Stormwater/Drainage Report was prepared to present the stormwater management plan and
drainage system design for the Redevelopment of the property at 19 Coolidge Hill Road, Watertown,
Massachusetts.
The stormwater management system has been designed to meet the MassDEP Stormwater
Management Standards and Watertown Stormwater Regulations. As a Redevelopment, the Project is
required to provide peak flow mitigation and provide water quality treatment and groundwater recharge
to the maximum extent practicable. The proposed design exceeds this requirement by achieving
standards set for a New Development including Watertown's requirement to retain all 24 -hour storm
events if possible. The project design meets this criterion.
The redevelopment objectives of the project's stormwater management design are:
1) to retain drainage on -site to the maximum extent practicable;
2) to detain drainage on -site to reduce peak rates of run-off from the site to the municipal property
(Filippello Park) and municipal drainage systems;
3) to reduce peak rates of run-off and run-off volume, thereby reducing the possibility of down -
gradient flooding of the municipal drainage systems; and
4) to improve the water quality of the stormwater leaving the site, thereby improving the quality of
Watertown's municipal discharge to the Charles River system.
The Project has been designed using environmentally -sensitive site design and LID techniques. This
design prevents the generation of stormwater and non -point source pollution by reducing impervious
surfaces, disconnecting undesirable flow paths, treating stormwater, and recreating the pre -
development natural process of infiltration.
The site hydrology was analyzed using HydroCAD computer software. The total drainage area includes
40,899 square feet (SF) of watershed. Geotechnical subsurface investigations provided evidence that
the existing soils are conducive to subsurface recharge (infiltration).
Stormwater run-off from vehicular pavement will be collected and receive pre-treatment (pollutant
removal) by proprietary structural BMPs which result in a high rate of Total Suspended Solids
(sediment) removal and also trap floatable petroleum products for collection and proper disposal
elsewhere.
100 percent of the treated vehicular pavement run-off and run-off from cleaner roof and pedestrian
pavement surfaces for all of the 24 -hour storms, including the 100 -year storm will be infiltrated into the
ground. This results in no stormwater run-off contribution to the municipal system, both in terms of
peak rates of run-off and volume.