Planning & Zoning Commission (linked)

STORMWATER MANAGEMENT REPORT 
WATERFORD CENTRAL APARTMENTS 
61 & 61A MYROCK AVENUE EXT 
WATERFORD, CT 
PREPARED FOR 
SIG CON ASSOCIATES, LLC 
606 POST ROAD EAST #320 
WESTPORT, CT 06880 
DATE: 
MARCH 20, 2023 
REVISED: 


 
 
 
WATERFORD CENTRAL APARTMENTS 
 
61 & 61A MYROCK AVENUE 
 
WATERFORD, CONNECTICUT 
 
 
 
 
 
 
TOC 
TABLE OF CONTENTS 
 
PROJECT DESCRIPTION ........................................................................................................................ 1 
EXISTING SITE DESCRIPTION ............................................................................................................. 2 
PEAK FLOW CONTROL & FLOOD PROTECTION ............................................................................. 2 
 
PRE-DEVELOPED CONDITIONS ................................................................................................. 2 
 
POST-DEVELOPED CONDITIONS .............................................................................................. 3 
 
COMPARISON ................................................................................................................................ 3 
 
DETENTION .................................................................................................................................... 4 
STORMWATER QUALITY AND TREATMENT ................................................................................... 4 
 
WATER QUALITY VOLUME & FLOW ....................................................................................... 5 
 
GROUNDWATER RECHARGE VOLUME ................................................................................... 5 
CONCLUSION .......................................................................................................................................... 6 
APPENDICES 
A. DRAINAGE MAPS 
B. HYDROLOGIC COMPUTATIONS (Hydrograph Summary Report) 
C. STORMWATER TREATMENT COMPUTATIONS 
D. SUPPLEMENTAL DATA 
TABLES 
1. PEAK FLOW COMPARISON – EXISTING VS. PROPOSED (NO DETENTION) ................. 3 
2. PEAK FLOW COMPARISON – EXISTING VS. PROPOSED (WITH DETENTION) ............. 4 
3. PROPOSED TREATMENT SUMMARY .................................................................................... 5 


 
WATERFORD CENTRAL APARTMENTS 
 
61 & 61A MYROCK AVENUE 
 
WATERFORD, CONNECTICUT 
1 
PROJECT DESCRIPTION 
 
Sig Con Associates, LLC is proposing Waterford Central Apartments, a residential multi-family 
development on two parcels of land.  61 & 61A Myrock Avenue total 27.62 acres and are located to 
the south of Willetts Avenue Ext. and west of Myrock Avenue. The parcels are identified as Lots 5002 
and 5005 on the Waterford Tax Assessors Map 140. The combined parcels are hereinafter referred to 
as the Site. 
The Site is in the Commercial Multi-Family District (C-MF). Per Section 16.1.2 of the Zoning 
Regulations multi-family developments are listed as a permitted use within the district, which requires 
a Site Plan approval per Section 18.1.a. 
The new development will consist of the construction of six (6) apartment buildings with a total of 
216 units and a mix of 144 one-bedroom and 72 two-bedroom dwelling units. Main access to the new 
development will utilize the existing driveway constructed as part of the Waterford Woods multi-
family development on the adjacent parcel at 394 Willetts Avenue Extension. The full site 
development will include: 
• Clearing and grubbing of brush 
• Construction of Buildings G, H, I, J, K, and L with an additional 216 residential units. 
• Construction of 24’ wide internal access drives with looped intersection to the existing 
driveway network serving the adjacent Waterford Woods development on 394 Willetts Avenue 
Extension. 
• Outdoor recreation areas including community spaces. 
• Parking situated near the apartment buildings and site amenities with a total of 325 spaces, 
including 8 handicapped accessible. 
• Minor road widening with additional northbound lane at intersection of Willetts Avenue with 
Boston Post Road. 
• Concrete pedestrian sidewalks connecting the apartment buildings to the adjacent parking areas 
and amenities. 
• Drainage improvements including a stormwater collection network, treatment, recharge, and 
attenuation. 
• Extension of private water, sewer, electric, gas and telecom mains. 
• Landscaping including a mixture of street trees, shrubs, foundation plantings and planting beds. 
• Front and side yard screening and buffers. 
• Building and street lighting. 
• Erosion and sedimentation control measures. 
To support the new site plan application for Waterford Central Apartments, the following stormwater 
management report was prepared by a professional engineer and provides a comprehensive evaluation 
of the fully developed Site. The report concludes that there will be zero net increase in peak flow rates 
discharging to downgradient wetlands or private properties, general drainage patterns will be 
maintained, and stormwater will be treated in accordance with the CT DEEP 2004 Stormwater Quality 
Manual. 
 

 
WATERFORD CENTRAL APARTMENTS 
 
61 & 61A MYROCK AVENUE 
 
WATERFORD, CONNECTICUT 
2 
EXISTING SITE DESCRIPTION  
The subject Site is a partially developed commercial site with the former Atlantic Broadband building 
and site improvements located at the southeast corner with access from Myrock Avenue. The land to 
the south of the commercial development pad consists of wooded and wetland areas, which will not 
be disturbed as part of the development. The land to the east and north of the commercial pad consist 
of shrub and brush growth over historically disturbed areas, with visible evidence of stripping, 
stockpiling, and landfilling. The new development has been sited within the historically disturbed 
areas while the existing commercial development will remain. 
TOPOGRAPHY – The existing topography generally consists of gentle to moderately sloping terrain 
from the northeast corner along Willetts Avenue to the southwest toward inland wetland areas. 
Existing slopes within the upland development area range from 5% to 10% with steeper slopes along 
the westerly boundary. 
SOILS – The USDA NRCS Web Soil Survey indicates that the upland area of the Site contains 
Udorthents – Urban Land Complex (306) soils, which have a hydrologic soil group classification 
(HSG) of B. This classification correlates with the limits of the historical land disturbance activities 
visible on the site. Deep observation test holes were performed at the site, which generally confirmed 
the NRCS soil types within upland areas. Inland wetland areas are designed as Ridgebury, Leicester, 
and Whitman and Tamakwa and Natchaug which have an HSG of D.  
DRAINAGE – The Site drains from the northeast along Willetts Avenue towards wetland systems to 
the south and southwest. One (1) existing drainage area was delineated based upon topography and 
field observation terminating at the delineated limit of the wetlands. 
• SITE-EX-01 is 21.882 acres and consists of the portions of the site to the north of the wetland 
delineation. 
Based upon CTDEEP mapping, the entire Site lies within the Southeast Shoreline subregional drainage 
basin 2000, which is part of the Southeast Coast major basin 2. However, based upon the “Jordan 
Brook Watershed Management Plan Final Report, Town of Waterford, Connecticut”, dated February 
2000, prepared by Fuss & O’Neill, Inc., the Site is included within the Jordan Brook subregional basin 
2201 (hereinafter JBWMP). A detailed review of the hydrologic conditions of the subregional 
watershed was not performed as part of this review; however, the recommendations of the JBWMP 
were followed as a conservative measure. 
PEAK FLOW CONTROL & FLOOD PROTECTION 
 
Stormwater runoff from the proposed multi-family development will be collected through a series of 
rain gardens, swales, yard drains, catch basins, and drainage piping and discharged to a series of 
treatment, retention, and detention areas on the Site.  
Peak flow rates for pre-development and post-development conditions were calculated using SCS TR-
55 methodology. Hydrology Studio 2022 v.3.0.0.27 was used to generate peak flows from the 
watershed with the following parameters: 
PRE-DEVELOPED CONDITIONS (Drainage Area Map DA-01A) 
• DRAINAGE AREAS:  As described above, the Site has one (1) existing drainage area. 

 
WATERFORD CENTRAL APARTMENTS 
 
61 & 61A MYROCK AVENUE 
 
WATERFORD, CONNECTICUT 
3 
o SITE-EX-01 is 21.882 acres and consists of the portion of the site to the north of the wetland 
delineation. 
• RAINFALL: Precipitation frequency and depth estimates (rainfall data) were obtained from 
NOAA Atlas 14, Volume 10, Version 2 at Lat. 41.3376 Long. -72.1163, which corresponds with 
the geographic location of the Site. 
• RUNOFF COEFFICIENT: Composite Curve Numbers (CN) were calculated based on the land 
cover types for the site for HSG B. Land cover types consist of impervious buildings and pavement, 
meadow/brush, open space vegetated areas, woods, and wetlands. Wetland areas were excluded 
from the drainage areas and calculations.  
• TIME OF CONCENTRATION:   Time of concentration (Tc) was estimated for the basin based 
on the SCS method, with sheet and shallow concentrated flow from the hydraulically most distant 
point of the watershed to the discharge point.  
POST-DEVELOPED CONDITIONS (Drainage Area Map DA-02A) 
• DRAINAGE AREA:  For direct comparison with existing conditions, the same design point was 
evaluated. 
o SITE-PR-01 is 21.882 acres and consists of the portion of the site to the north of the wetland 
delineation, including the new multi-family development areas. 
• RAINFALL: Same as Pre-Developed Conditions. 
• CURVE NUMBER: Same methodology as Pre-Developed Conditions. Composite Curve 
Numbers (CN) were calculated based on the land cover types for the proposed multi-family 
residential development for HSG B. 
• TIME OF CONCENTRATION:   Same methodology as Pre-Developed Conditions. 
COMPARISON 
A summary of flows for existing and proposed conditions, without consideration of detention is 
provided below with a complete output provided in the enclosed Hydrology Studio Report. 
STORM 
EVENT 
AREA 01 
SITE-EX-01 
SITE-PR-01 
EX 
vs. 
PR 
2-yr 
4.34 
12.46 
8.12 
5-yr 
9.80 
21.18 
11.38 
10-yr 
15.31 
29.10 
13.79 
25-yr 
24.02 
40.85 
16.83 
50-yr 
30.99 
49.85 
18.86 
100-yr 
38.92 
59.79 
20.87 
TABLE 1: PEAK FLOW COMPARISON - NO DETENTION 
 

 
WATERFORD CENTRAL APARTMENTS 
 
61 & 61A MYROCK AVENUE 
 
WATERFORD, CONNECTICUT 
4 
As shown in the table above, the proposed multi-family development (SITE-PR) results in an increase 
in peak flow rates as compared to existing conditions (SITE-EX) without consideration of detention. 
To attenuate peak flow rates, a single detention pond is proposed, which will collect runoff from the 
collection network and attenuate peak flow rates and volumes. Further discussion is provided below. 
DETENTION (Drainage Area Map DA-03A) 
The proposed stormwater network consists of a series of treatment and detention methods to attenuate 
peak flow rates. 
PROPOSED AREA 01A (SITE-PR-01A) 
Stormwater runoff within PR-01A will discharge to the following: 
• POND-04A – Wet detention pond used for peak runoff attenuation with a deep wet pool, 
sediment forebay and filter bed to promote treatment and infiltration from contributing area. 
This area will discharge through outlet control structure 04A (OCS 04A) with staged outlets 
to regulate outflow, an emergency overflow weir, and riprap plunge pool to dissipate energy 
and velocity before flowing towards the downstream wetlands. 
The wet detention pond has been sized to attenuate peak flow rates as compared to pre-development 
conditions for the 2-, 5-, 10-, 25-, 50-, and 100-year storm events. 
STORM 
EVENT 
AREA 01 
SITE-EX-01 
SITE-PR-01-2 
EX 
vs. 
PR 
2-yr 
4.34 
4.13 
-0.21 
5-yr 
9.80 
9.84 
0.04 
10-yr 
15.31 
15.22 
-0.09 
25-yr 
24.02 
23.22 
-0.80 
50-yr 
30.99 
30.99 
0.00 
100-yr 
38.92 
38.03 
-0.89 
TABLE 2: PEAK FLOW COMPARISON - WITH DETENTION 
As shown in Table 2 above, incorporation of the detention system into the proposed development 
results in a minor decrease or balance of peak flow rates as compared to existing conditions for the 
entire Site. The plan provides for zero net increase in peak flow rates for all storms up to the 100-year 
event. 
STORMWATER QUALITY & TREATMENT  
 
The proposed development has been designed to reduce stormwater runoff and pollutant loads to the 
maximum extent possible and to treat the required water quality volume and flow per the CTDEEP 
2004 Stormwater Quality Manual (2004 DEEP Manual). The proposed measures incorporated into the 
plan include: 
• Maximize conservation and preservation of natural features: Impervious surfaces and buildings 
fall within historic limits of site disturbance activities. There are no features warranting 
preservation within the development footprint. 

 
WATERFORD CENTRAL APARTMENTS 
 
61 & 61A MYROCK AVENUE 
 
WATERFORD, CONNECTICUT 
5 
• Minimize clearing and grubbing maintain native vegetation on site: There is no clearing of the 
mature tree vegetation to the south. All existing vegetation within 100’ of the delineated inland 
wetlands will be preserved exceeding the recommendations in the JBWMP. 
• Minimize building footprint: Buildings have been designed to accommodate site grades and 
unit areas were condensed to maximize the number of units in a limited footprint area. 
• Minimize impervious surfaces for roadways and parking: Curb cuts and access drives are the 
minimum required for adequate site access and the proposed parking quantity has been reduced 
to the minimum allowed per zoning requirements. Impervious area totals 23% of the total site, 
which is on the low end of the 18% to 30% impervious cover referenced in Section 3.1.2.3 of 
the JBWMP for “intermediate” level uses such as multi-family. The impervious totals include 
the existing commercial development. 
• Disconnect impervious areas where possible, such as sidewalks: Disconnected impervious 
areas were not subtracted from the treatment calculations as a conservative measure. 
• Collect, treat, and infiltrate to encourage groundwater recharge including the incorporation of 
base level and secondary controls to improve water quality as recommended by the JBWMP. 
WATER QUALITY VOLUME & FLOW (Drainage Area Map DA-03A) 
Water quality volumes and flows were calculated for all proposed impervious surfaces for the 
driveway, parking and building areas in accordance with the 2004 DEEP Manual. 
AREA 
DA 
IA 
WQV 
WQF 
WQF 
PROPOSED TREATMENT 
Label 
acre 
acre 
acre-ft 
cfs 
sf 
Method 
Vol 
Flow 
Area 
Note 
POND 04A 
13.289 
5.264 
0.450 
3.630 
2400 
Sediment Forebay 
0.06 
N/A 
N/A 
14% WQV 
POND 04A 
13.289 
5.264 
0.450 
3.630 
2400 
Filter Bed 
N/A 
N/A 
4300 
180% WQF 
POND 04A 
13.289 
5.264 
0.450 
3.630 
2400 
Forebay Retention 
0.56 
N/A 
N/A 
125% WQV 
TABLE 3: PROPOSED TREATMENT SUMMARY 
1. Rain Garden Volume not included in treatment calculations 
As shown in Table 3 above, the proposed treatment measures will adequately retain the calculated 
water quality volume and/or treat the calculated water quality flow, removing 80% or more of total 
suspended solids and floatable debris for the first inch of rainfall before discharging to the Site 
wetlands 
GROUNDWATER RECHARGE VOLUME  
Existing non-wetland soils are classified as Udorthents-Urban Land complex (HSG B) and the wetland 
soils as Ridgebury, Leicester, and Whitman and Tamakwa and Natchaug (HSG D). Required 
Groundwater Recharge Volumes (GRV) were calculated in accordance with 2004 DEEP Manual 
based upon the area of each Hydrologic Soil Group. 
GRV (required) 
= 0.072 acre-feet 
GRV (provided) = 0.356 acre-feet 
The combination of rain gardens, sediment areas, and filter beds provide adequate capacity to fully 
retain over 4 times the recommended groundwater recharge volume, thereby exceeding the GRV 
requirement. 

 
WATERFORD CENTRAL APARTMENTS 
 
61 & 61A MYROCK AVENUE 
 
WATERFORD, CONNECTICUT 
6 
CONCLUSION 
 
There will be no increase in peak flow rates discharging to the downgradient wetlands or adjacent 
properties. The stormwater network will maintain approved drainage patterns and utilize a 
combination of treatment and detention to regulate any increase in run-off on site. Stormwater will be 
treated in accordance with the CTDEEP 2004 Stormwater Quality Manual. 
No adverse impacts to the site, adjacent wetlands, or municipal systems are anticipated.