Conservation Commission Agenda (linked)

STORMWATER
MANAGEMENT REPORT
Crystal Mall Adaptive Reuse
850 Hartford Turnpike (CT Route 85)
Waterford, Connecticut 06385
Prepared For:
GENERAL DYNAMICS
Electric Boat
January 26, 2026
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Kyle Haubert, P.E.

January 26, 2026
1.0 Narrative
The proposed project is the adaptive reuse of the former Crytal Mall (Mall) complex located at 850 Hartford
Turnpike (CT Route 85), Waterford, Connecticut for use by the Electric Boat Corporation. The Location
of the property in reference to the USGS Quad Map is attached as Figure 1. A location map is included on
the Site Improvement Plans (Plans).
The Electric Boat adaptive reuse of the property includes the conversion of the existing retail mall building
for office, work force development, and research and development use. The existing restaurant pad sites
(currently Olive Garden and Longhorn Steakhouse) located along the Hartford Turnpike (CT Route 85)
frontage will remain.
Proposed modifications to the site are depicted on the Plans. The existing bituminous concrete parking lots
will be reconfigured and rehabilitated to accommodate the parking necessary for Electric Boats adaptive
reuse of the facility. The entirety of the parking lots and parking spaces are necessary for Electric Boat’s
employee operations and the reuse of the property.
Stormwater management improvements have been proposed to the maximum extent practicable. The
improvements have been proposed to meet the goals of the Waterford Zoning Regulations Section 25, and
the 2024 CTDEEP Connecticut Stormwater Quality Manual (SQM).
2.0 Existing Conditions
The existing property is approximately 77.8 acres in total along the southwest side of Hartford Turnpike
(CT Route 85) as shown on Figure | and the location map included on the Plans. The Crystal Mall was
constructed on the property circa 1983-1984. The property is comprised primarily of commercially
developed land containing the Crystal Mall Building, two restaurant pad sites, and approximately 46 acres
of paved parking lots. The total impervious area on the site is 54.6 acres. The western portion of the
property is approximately 22 acres of undeveloped woodland that includes a detention basin (referred to as
the stormwater management basin herein) for the facility and the surrounding area. The property is
bordered by Hartford Turnpike (CT Route 85) to the northeast, additional commercial development to the
southeast (currently Home Depot) and northwest (currently Target), and undeveloped woodland to the
southwest. An aerial view of the existing property and surrounding area as they currently exist is included
in the Plans.
The existing topography of the site generally runs from the high points along Hartford Turnpike
southwesterly toward the low point along the undeveloped woodlands. The elevations range between 196
along Hartford Turnpike and 78 along the southwest property line.
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Crystal Mall Adaptive Reuse
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January 26, 2026
CTDEEP classifies Nevins Brook as Streamflow Classification is Class 3 indicating it is moderately altered,
and has intermediate balance points between ecological and human uses. The CTDEEP Surface Water
Quality Classification is A.
DISCHARGE FROM
HOME DEPOT
PARKING LOT 
CHARGE FROM
ROUTE 85
, NEVINS BROOK
DISCHARGE FROM,
oRYSTAL MALL
PARKING LOT
STORMWATER WANAGEVENT
[BAS OUTLET CONTROL
STRUCTURE
Picture 1 - Aerial View of the Existing Stormwater Management Basin (A.K.A. Trading Cove Pond)
Stormwater Management Basin
Stormwater runoff from the Mall, Home Depot, and CT Route 85 (Nevins Brook) is discharged into the
existing Stormwater management Basin. The basin is sometimes referred to as Trading Cove Pond in
publicly available mapping.
It appears that the basin was constructed with the development of the Mall around 1983-1984. It was
modified to its current configuration with the development of the adjacent Home Depot around 1995. Our
understanding is that the intent of this detention basin was to mitigate peak stormwater runoff from the
commercial developments at that time.
The Stormwater Management Basin is currently heavily vegetated and in good stable condition.
Water flow through the detention basin is controlled via a concrete outlet control structure with a 30” RCP
culvert discharge. A view of the ouilet control structure is shown in Picture 2.
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Crystal Mall Adaptive Reuse :
850 Hartford Tumpike, Waterford, CT 3 sf Civil * Structural + Survey

January 26, 2026
Channel Located tinmedic tely
Picture 5 - Nevins Brook N, ral Channel Downstream of the Detention Basin Disch age Loi
Toward [-95
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Stormwater Management Repoyi
CLA Engineers, Inc.
Crystal Mall Adaptive Reuse [| CA Bngincors, Ine,
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Civil + Structural + Survey

January 26, 2026
3.0 Post Development Conditions
The proposed project is the adaptive reuse of the existing Crystal Mall Building. The existing Mall building
will remain in place as it currently exists. The reuse includes the interior conversion of the building for
office, work force development, and research and development. The existing restaurant pad sites (currently
Olive Garden and Longhorn Steakhouse) located along the Hartford Turnpike (CT Route 85) frontage will
remain.
Proposed modifications to the site are depicted on the Plans. The existing bituminous concrete parking lots
will be reconfigured and rehabilitated to accommodate the parking necessary for Electric Boats adaptive
reuse of the facility. The entirety of the parking lots and parking spaces are necessary for Electric Boat’s
employee operations and reuse of the property.
The reconfigured parking lot has reduced the amount of impervious surface onsite by approximately 1.2
Acres.
The existing stormwater infrastructure will remain in place. Existing tops, frames, and grates will be
replaced with new structures. Due to the parking lot reconfiguration and landscape island relocations,
additional stormwater infrastructure will be added to supplement the existing system. The new
infrastructure was located to capture runoff and direct it to the existing system to prevent excessive gutter
flow and ponding within the parking lots and generally includes the following improvements.
- All new drainage structures will be constructed with a 2-foot deep sump.
- All new drainage structures will include a hood on the discharge pipe.
- Permanent inlet filters are proposed within existing catch basin tops at strategic locations to filter
runoff prior to entering the system.
- Four hydrodynamic separators are proposed where new piping runs are proposed to further cleanse
the stormwater in the drainage system.
Zoning Considerations
The proposed project is considered a redevelopment project based on the Waterford Zoning Regulation and
the CTDEEP 2024 Stormwater Quality Manual (SQM). Section 25.6.8 of the Waterford Zoning
Regulations requires the redevelopment project comply with one of three objectives
1. Reduce the total impervious cover by 40% from the existing conditions; or
2. Where site conditions prevent a reduction in impervious cover, implement stormwater controls for
at least 40% of the site’s impervious cover; or
3. Implement a combination of impervious cover reduction and area treated with stormwater controls
that shall equal or exceed 40% of the site’s impervious cover.
The reduction in impervious cover to meet the 40% is not practical due to Electric Boat’s need to utilize all
of the available parking for their employees and visitors. Therefore, an approach to implement a
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Crystal Mall Adaptive Reuse
850 Hartford Tumpike, Waterford, CT 7 y Civil + Structural * Survey

January 26, 2026
development. A copy of the soil mapping is included in Appendix B. The runoff curve numbers for the
site are based on the ground cover and hydrologic soil group and are included in Table 1.
Table | — Curve Numbers
Runoff curve numbers for the existing and post development conditions were compiled from Table 2-2 of
the USDA/NRCS TR-55 manual a portion is included in Appendix A. The following curve numbers were
used for the calculations:
Existing Conditions
Watershed EX 1 CN Area
Impervious (roofs, pavement, rock outcrop, etc.) 98 55.35
Open space (lawns), HSG D, Good Condition 80 5.15
Watershed EX 2 CN Area
Impervious (roofs, pavement, rock outcrop, etc.) 98 3:35
Open space (lawns), HSG D, Good Condition 80 0.75
Watershed EX 3 CN Area
Impervious (roofs, pavement, rock outcrop, etc.) 98 0.05
Open space (lawns), HSG D, Good Condition 80 0.08
Watershed EX 4 CN Area
Impervious (roofs, pavement, rock outcrop, etc.) 98 0.32
Open space (lawns), HSG D, Good Condition 80 0.23
Post Development Conditions
Watershed PD 1 CN Area
Impervious (roofs, pavement, rock outcrop, etc.) 98 54.05
Open space (lawns), HSG D, Good Condition 80 6.80
Pervious Surface w/ Silva Cell Subsurface Storage 60 0.25
Watershed PD 2 CN Area
Impervious (roofs, pavement, rock outcrop, etc.) 98 3.35
Open space (lawns), HSG D, Good Condition 80 0.75
Watershed PD 3 CN Area
Impervious (roofs, pavement, rock outcrop, etc.) 98 0.05
Open space (lawns), HSG D, Good Condition 80 0.08
Watershed PD 4 CN Area
Impervious (roofs, pavement, rock outcrop, etc.) 98 0.32
Open space (lawns), HSG D, Good Condition 80 0.23
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Crystal Mall Adaptive Reuse
850 Hartford Tumpike, Waterford, CT 9 V Civil * Structural * Survey

January 26, 2026
Peak Flow Rate (CFS)
2-Year | 10-Year | 25-Year | 50-Year | 100-Year
Existing Condition: EX 2 (Hyd. #2): | 13.480 | 20.620 25.050 28.320 31.800
Post Development: PD 1 (Hyd. #7): | 13.480 | 20.620 25.050 28.320 31.800
Change: | 0.000 0.000 0.000 0.000 0.000
WATERSHED 2 (AP 2)
Peak Flow Rate (CFS)
2-Year | 10-Year | 25-Year | 50-Year | 100-Year
Existing Condition: EX 3 (Hyd. #3): | 0.332 0.560 0.702 0.807 0.918
Post Development: PD 1 (Hyd. #8): | 0.332 0.560 0.702 0.807 0.918
Change : | 0.000 0.000 0.000 0.000 0.000
WATERSHED 3 (AP 3)
Peak Flow Rate (CFS)
2-Year | 10-Year | 25-Year | 50-Year | 100-Year
Existing Condition: EX 4 (Hyd. #4): | 1.552 2.512 3.106 3.545 4.011
Post Development: PD 1 (Hyd. #8): | 1.552 2512, 3.106 | 3.545 4.011
Change : | 0.000 0.000 0.000 | 0.000 0.000
WATERSHED 4 (AP 4)
Runoff Volume (CF)
2-Year | 10-Year | 25-Year | 50-Year | 100-Year
Existing Condition: EX 1 (Hyd. #1): | 685,232 | 1,066,260 | 1,305,249 | 1,483,001 | 1,672,285
Post Development: PD 1 (Hyd. #6) : | 685,232 | 1,066,260 | 1,305,249 | 1,483,001 | 1,672,285
WATERSHED 1 (AP 1)
Change:| 0 | 0 0 0 0
Runoff Volume (CF)
WATERSHED 2 (AP 2) | 2-Year | 10-Year | 25-Year | 50-Year | 100-Year
Existing Condition: EX 2 (Hyd. #2): | 45,438 | 71,511 87,894 | 100,088 113,078
Post Development: PD | (Hyd. #7) : | 45,438 | 71,511 87,894 | 100,088 113,078
Change : 0 0 0 | 0 0
| Runoff Volume (CF)
[ 2-Year | 10-Year | 25-Year | 50-Year | 100-Year
Existing Condition: EX 3 (Hyd. #3): | 1,040 1,796 2,282 | 2,648 3,039
Post Development: PD | (Hyd. #8): | 1,040 1,796 2,282 | 2,648 3,039
Change:| 0 | 0 0 | 0 0
WATERSHED 3 (AP 3)
Runoff Volume (CF)
2-Year | 10-Year | 25-Year | 50-Year | 100-Year
Existing Condition: EX 4 (Hyd. #4): | 4,944 8,239 10,338 | 11,909 13,586
Post Development: PD 1 (Hyd. #8): | 4,944 | 8,239 10,338 | 11,909 13,586
Change:| 0 | 0 0 | 0 0
WATERSHED 4 (AP 4)
RRR a SEE TY GT 2D
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Crystal Mall Adaptive Reuse
850 Hartford Tumpike, Waterford, CT il Pp Civil * Structural * Survey

Hydrodynamic Separator 1 (HDS-1)
January 26, 2026
The proposed watershed for HDS-| is depicted on Figure 4. The required water quality volume is calculated
as follows:
Hydrodynamic Separator #1 (HDS-1)
Water Quality Volume (WOQOV)
Sizing in Accordance with Chapter 4 of the DEEP 2024 Storm Water Quality Manual
Water Quality Volume (WQV) = (1”)(R)(A) / 12
P= 13"
R=0.05 + 0.009(1)
I= percent of impervious cover
A= watershed area
Total Watershed Area (Ac.) : 3.50
Watershed Impervious Area (Ac.) : 3.40
I= 97.1%
R= 0.924
Required WQV = 0.3505 Ac.-Ft
15.266.0 CF
Water Quality Flow (WQF)
Sizing in Accordance with Appendix D of the DEEP 2024 Storm Water Quality Manual
Water Quality Flow (WQF) = (qu)(A)(Q)
qu = unit peak discharge (cfs/mi2/inch)
A = watershed area (mi2)
Q=tunoff depth (in watershed inches)
P (1.3" for water quality flow) : 1.3 in
Q= 1.20
CN= 97
la (from Table 4-1) : 0.062 in
Ia/P= 0.048
Tc (Time of Concentration) : 0.167 Hr
qu (from Exhibit 4-1) : 700 csin/in
Total Watershed Area (Square Miles) = 0.00547 mi2
Required WQF = 4.600 CFS
2,064.5 GPM
A Contech Cascade CS-8 unit has been proposed that is capable of treating up to 7.2 CFS in accordance
with the CTDOT Guidelines for the Use of Hydrodynamic Separators on CTDOT Projects. The Contractor
may select an alternate separator capable of treating the minimum water quality flow rates as outlined in
Appendix D.
Stormwater Management Report
Crystal Mall Adaptive Reuse
850 Hartford Tumpike, Waterford, CT
\ CLA Engineers, Inc.
Vo civa- Structural * Survey

Hydrodynamic Separator 3 (HDS-3)
January 26, 2026
The proposed watershed for HDS-3 is depicted on Figure 4. The required water quality volume is calculated
as follows:
Hydrodynamic Separator #3 (HDS-3)
Water Quality Volume (WQV)
Sizing in Accordance with Chapter 4 of the DEEP 2024 Storm Water Quality Manual
Water Quality Volume (WQV) = (1”)(R)(A) / 12
P=1,3"
R=0.05 + 0.009(1)
I= percent of impervious cover
A= watershed area
Total Watershed Area (Ac.) : 2.05
Watershed Impervious Area (Ac.) : 1.90
I= 92.7%
R= 0.884
Required WQV = 0.1964
8,553.2
Ac.-Ft
Water Quality Flow (WQF)
Sizing in Accordance with Appendix D of the DEEP 2024 Storm Water Quality Manual
Water Quality Flow (WQF) = (qu)(A)(Q)
qu = unit peak discharge (cfs/mi2/inch)
A= watershed area (mi2)
Q=runoff depth (in watershed inches)
P (1.3" for water quality flow) : 1.3
Q= 1.15
CN= 98
Ia (from Table 4-1) : 0,041
la/P= 0.032
Tc (Time of Concentration) : 0.167
qu (from Exhibit 4-ITI) : 700
Total Watershed Area (Square Miles) = 0.00320
Required WQF = 2371
1,156.7
Hr
esm/in
mi2
CFS
GPM
A Contech Cascade CS-6 unit has been proposed that is capable of treating up to 4.0 CFS in accordance
with the CTDOT Guidelines for the Use of Hydrodynamic Separators on CTDOT Projects. The Contractor
may select an alternate separator capable of treating the minimum water quality flow rates as outlined in
Appendix D.
Stormwater Management Report
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT 1
wn
\ CLA Engineers, Inc.
/ Civil * Structural + Survey

January 26, 2026
5.2 Standard 2 — Stormwater Runoff Quantity Control
As outlined under the Analysis section of this report the peak flow rates and voluine leaving the site match
the existing conditions. Stormwater improvements by impervious surface reduction and addition of
subsurface storage have been made onsite to the maximum extent achievable as outlined herein. However,
due to the order of magnitude of the existing watersheds and the impervious surfaces they contain, the
proposed improvements did not impact the weighted curve numbers used in the calculations or the
calculated peak flow rates and runoff volumes.
5.3 Standard 3 — Construction Soil Erosion and Sediment Control
The erosion and sedimentation control plan was designed in accordance with the 2024 Connecticut DEEP
Guidelines for Soil Erosion & Sediment Control. Erosion and sedimentation control measures are depicted
on the site development plans. Plans, construction details, and a narrative are included in the plan set.
5.4 Standard 4 — Post Construction Operation and Maintenance
The following is a general operations and maintenance schedule for the stormwater infrastructure and
project site. These provisions are also included on the project Plans.
Maintenance Schedule for Existing Stormwater Management Basins
Activity | Schedule
e Inspect for damage, undercut, or eroded area Semi-Annual inspection
Monitor for sediment accumulation
e Repair undercut or eroded areas. As needed maintenance
e Clean and remove debris & sediment from inlet and outlet
structures
e Inspect and clean debris & sediment in the basin | Semi-annual
e Clean and remove debris from inlets
Maintenance Schedule for Catch Basins
Activity cm Schedule
e Clean out sediment from catch basin 1® Between November
| 15" and December
| 15" (after leaf fall)
|
© During April (after
snow melt)
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Crystal Mall Adaptive Reuse
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January 26, 2026
5.5 Standard 5 — Stormwater Management Plan
During Construction
The stormwater pollution prevention plan and all erosion and sedimentation control measures have been
designed in accordance with the 2024 Connecticut DEEP Guidelines for Soil Erosion & Sediment Control.
The location of temporary erosion and sedimentation control measures for the proposed development are
included in the site development plan set. Construction details and an erosion and sedimentation control
narrative are also included in the plan set. The narrative and construction details outline the requirements
for stabilization of disturbed areas, slope stabilization requirements, and maintenance requirements.
Stormwater Management & Pollution Prevention:
Provisions for stormwater management and pollution prevention are outlined on the plans and are as
follows:
1. Pollution Prevention Team:
The General Contractor shall be responsible for carrying out the provisions of the plan.
2. Sweeping:
Parking lots, sidewalks, and other impervious surfaces beyond the work site shall be swept
clean of sand, silt, and litter daily at the end of the work day.
3. Outside Storage:
Accessories or equipment stored outside shall be covered or maintained to minimize the
possibility of these materials or their residue passing to stormwyater.
4. Washing:
No washing of vehicles, accessories, equipment, or appliances in the work site.
5. Maintenance and Inspection:
a. The Contractor shall inspect, repair, and/or replace erosion control measures every 7
days and immediately following any significant rainfall or snow melt.
b. Sediment deposits must be removed when deposits reach approximately one-half the
height of the barrier.
c. Daily dust control using water or approved equal shall be provided for all earth
stockpiles, earth piled along excavations, surfaces of backfilled trenches and gravel
surfaces.
6. Spills or Accidental Discharges:
a. Comply with State and Federal regulations to contain and clean up any spill or
discharge and dispose of materials at an approved facility.
b. Contact Connecticut DEEP oil and chemical spill response division 860-424-3338.
The following steps should be performed as soon as possible
- Stop the source of the spill
fe
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- Cover the spill with absorbent material such as kitty litter, saw dust, or oil
absorbent pads. Do not use straw.
Dispose of absorber in accordance with Local and State regulations
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Crystal Mall Adaptive Reuse hc 8 Z
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Civ. « St i . Suavaiuna Crystal Mall Adaptive Reuse FIGURE
850 Hartford Turnpike (CT Route 85)
317 Main Street Norwich, Connecticut Waterford, Connecticut ]
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