Conservation Commission Agenda (linked)

DRAINAGE & STORMWATER
MANAGEMENT REPORT
Prepared for
PROPOSED CONTRACTOR’S BUILDING
152 CROSS ROAD
WATERFORD, CT
August 2025
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Prepared for
Eagle AAM, LLC
Dba Eagle Electric Services
Prepared by
Killingly Engineering Associates 4
Civil Engineering & Surveying
AUG 2 6 2025 Normand Thibeault Jr., P.E.
CT License #22834

Introduction
Eagle Electric Services LLC has submitted a proposal to the Town of Waterford to construct a
3,600 square foot commercial building with associated paved access and drainage improvements
ona 1.447-acre parcel . The property currently houses a 2-level commercial building on the
Cross Road frontage and Eagle Electric Services utilizes an office on the lower level. The
proposed building will serve as the location for the business to park company vans in a controlled
environment, store tools and supplies, and provide a dedicated office area for the company.
A good portion of the property is steeply sloped to a wetlands system to the west and there are
approximately only % of an acre of developable area; the proposed project will not result in the
disturbance of wetlands nor the clearing of any steeply sloped areas. Drainage from the site
currently flows to the west to the wetlands system and the design will maintain the existing
drainage patterns incorporating pre-treatment of stormwater runoff.
Summary
According to the USDA-SCS Soil Survey, the soils on the proposed development area on site
consist predominantly Canton and Charlton fine sandy loams and are very rocky. According to
the NRCS Web Soil Survey, these soils are associated with hydrologic soil group B. The project
strives to maintain the existing drainage patterns for post development conditions but curbing and
catch basins will be utilized to collect stormwater from paved areas and convey it to the proposed
on site stormwater basin prior to discharge off site.
The calculations utilized HydroCAD Stormwater Modeling System, a computer model, to
analyze pre-and post-development drainage conditions. The model used the NOAA Type D 24-
hour rainfall to calculate the runoff. The 2, 10 and 100-year frequency storms were analyzed to
evaluate peak runoff for pre-and post-construction conditions. Tables 1-2 summarize our findings
for pre and post construction flows toward the wetlands and to the adjacent property to the north:
Table 1. Existing & Proposed Peak Flows to Wetlands
1.50 CFS
2-Year 3.45 0.80 CFS -0.70 CFS
10-Year 5.13 2.45 CFS 1.92 CFS -0.53 CFS
100-Year 7.80 3.96 CFS 3.92 CFS -0.04 CFS
As shown by the computations, the post development peak runoff rates slightly reduced from pre-
construction rates. This is accomplished with the construction of a proposed stormwater
detention basin with a low-level outlet. Flows from this basin will discharge to the west and
overland before ultimately finishing in the on-site wetlands. Table 2 summarizes peak discharge
rates to the west toward the adjacent developed property:
Table 2. Existin
0.49 CFS
& Proposed Peak Flows West
2-Year 3.45 0.07 CFS -0.42 CFS
10-Year 5.13 1.03 CFS 0.15 CFS -0.88 CFS
100-Year 7.80 1.95 CFS 0.33 CFS -1.62 CFS

As shown by the summary, there are decreases in peak runoff rates to the west. This is
accomplished by re-routing drainage that previously flowed in that direction and conveying it to
the proposed stormwater basin.
The water quality is addressed by the installation of sumps in the proposed catch basins and water
quality volume (WQV) in the basin for the first 1.3” of rain as required by the CTDEEP
Stormwater Quality Manual. Water Quality Volume is as follows:
Drainage Area = 0.53 acres
Impervious area (I) = 49.17% (pavement, no roof)
WOQV = (1.3”) RA/12
R= 0.05+0,009(1) = 0.05+0.009(49.7) = 0.4973
WOV = (1.3)(0.4973)(0.53)/12 = 0.037 ac-ft = 1,478 c.f.
We have determined that a WQV of 1,478 cubic feet is required to meet the recommended
requirements of the Stormwater Quality Manual (SWQM). The stormwater basin will provide
1,878 cubic feet of WQV below the weir outlet.

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——-100——— EXISTING CONTOURS 
Civil Engineering & Surveying
114 Wescott Road
PROPOSED CONTOURS
INLAND WETLANDS FLAG
BUILDING SETBACK LINE
ELECTRIC LINE
SANITARY SEWER LINE
GAS LINE
WATER LINE
SILT FENCE
PO. Box 421
Killingly, Connecticut 06241
(860) 779-7299.
wowkillinglyenginecring com
DATE: 8/3/2025 DRAWN: RCS
SCALE: 1" = 20° DESI
SHEET: 2 OF 2 CHK BY:
DWC, No: CUENT FILE 408 No: 24032