Conservation Commission - 1222 (02/26/2026)

agenda center attachment

Board/Commission	Conservation Commission
Meeting Date	February 26, 2026
Pages	26
File Size	6.1 MB
OCR Status	Searchable (OCR processed)
Source URL	Original

Download PDF

Document Preview

Full Text (OCR Extracted)

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
Prepared By:
CLA Engineers, Inc.
.
Consulting Engineers
é
j
317 Main Street
4
p
Norwich, CT 06360
SOW) - ae
Ph: 860-886-1966 F: 860-886-9165
USS ROS
www.claengineers.com
My ONAL So
Kyle Haubert, P.E.

January 26, 2026
STORMWATER MANAGEMENT REPORT
Crystal Mall Adaptive Reuse
850 Hartford Turnpike
Waterford, Connecticut 06385
Prepared for
GENERAL DYNAMICS
Electric Boat
TABLE OF CONTENTS
1.0
Narrative ....
2.0
Existing Conditions
3.0
Post Development Conditions....
4.0
Analysis
5.0
CT DEEP 2024 Stormwater Quality Manual Compliance .....c.ccscssssesessssessestesseseseeseaneseensseeseeess 12
om!
Standard 1 — Runoff Volume and Pollutant Retention.......ccccccesssesseseeesteseeseetesseneseeseeeeeesesteeeeees 12.
5.2
Standard 2 — Stormwater Runoff Quantity Control oo... cececesesseesesseeseeseeseeseeseesneseseeesneeneeneeaeeaeens 17
53
Standard 3 — Construction Soil Erosion and Sediment Control ........cccccescsssesessesseseeteseeeeteseeteeeenees 17
5.4
Standard 4 — Post Construction Operation and Maintenance........ccessccsseeseseeseeseeneeseeseeereeneenenees 17
5.5
Standard 5 — Stormwater Management Plam.....c.ccccccsecssssesssesseseesesessesesssseesesscsvesesseseescseeseaeseessavess 19
LIST OF FIGURES
Figure 1:
Location Map
(USGS)
Figure 2:
Watershed Map: Existing Condition
Figure 3:
Watershed Map: Post Development
Figure 4:
Watershed Map: Hydrodynamic Separators
CALCULATIONS
Hydrograph Reports - 2, 10, 25, 50, and 100-Year Frequencies
APPENDICES
Appendix A:
Support Data
Appendix B:
— Soil Resource Report
Appendix C:
Stormwater Sample Lab Reports
Appendix D: | Hydrodynamic Separator Information
Stormwater Management Report
A CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
i
|
Civil * Structural * Survey

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.
Stormwater Management Report
\ CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
1
y
Civil + Structural + Survey

January 26, 2026
The site soils are generally comprised of Urban Land (307). Rock outcrops are present along the eastern
side of the property along the CT Route 85 frontage. A USDA Soil Resource Report is included in
Appendix B. Inland wetlands are present at the stormwater management basin and along the western edge
of the site.
Stormwater from the facility is collected in a standard catch basin and culvert system. Inlets are typically
cast iron 2’ diameter or 2’x2’ grates located throughout the parking areas as depicted on the Plans. The
culverts are primarily reinforced concrete pipe (RCP) ranging in size from 12” through 72” diameter. It
appears that the stormwater infrastructure was constructed with the Mall in the 1983-1984 era. Spot repairs
and grate replacements have been performed as needed.
The stormwater discharge is to a vegetated stormwater management (detention) basin located at the
southwest corner of the property, sometimes referred to as Trading Cove Pond on public mapping. The
basin is located on a separate parcel under the same ownership. The basin location is shown on the Plans.
This basin is sometimes referred to as the detention basin in previous applications; it is referred to as the
stormwater management basin herein. The basin collects runoff from the mall property, the adjacent Home
Depot property, and the State of CT Route 85 drainage system (Nevins Brook). 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.
Nevins Brook
The stormwater management basin was constructed over Nevins Brook. Nevins Brook traverses the site in
a closed catch basin and culvert system. The headwater of the brook appears to be a wetland system located
northeast of the property; to the south of Dayton Road and flows behind the former Cohanzie School. The
brook is collected at a 30” RCP inlet near the Dayton Place and Hartford Turnpike intersection and is
conveyed across Hartford Turnpike in the State of Connecticut drainage system. At the time of the Mall
construction a drainage manhole was constructed over the cross-culvert discharge and the flow was
conveyed through the developed portion of the property by RCP culvert. Several catch basin inlets are
located along the routing that collect stormwater runoff from CT Route 85. Stormwater from the Mall
property is collected separately in a segregated collection system onsite. There is a portion of the Mall
property in the Longhorn Steakhouse area that is collected in a drainage system and combines with the
Nevins Brook system offsite in the Home Depot Parking lot.
The brook discharges into the existing
stormwater management basin where it combines with other discharge from the Mall and the Home Depot.
The stormwater management basin is depicted on the Plans and in Picture 1.
Stormwater Management Report
\ CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
2
|
Civil * Structural * Survey

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
DISCHARGE FROM.
CRYSTAL MALL
JPARKING LOT
ISTCRUWATER WANAGEVENT
ISASIN 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 outlet control structure is shown in Picture 2.
Stormwater Management Report
\ CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
3
|
Civil + Structural + Survey

January 26, 2026
Picture 3 - Detention Basin Discharge Culvert
Stormwater Management Report
CLA Engineers, Inc.
Crystal Mall Adaptive Reuse
CLA Engineers, Ine,
850 Hartford Turnpike, Waterford, CT
4
y
Civil
Structural - Survey

January 26, 2026
Picture 5 - Nevins Brook Natural Channel Downstream of the Detention Basin Discharge Looking Toward 1-95
Stormwater Management Report
CLA Engineers, Inc.
Crystal Mall Adaptive Reuse
CLA Engineers, Ine.
850 Hartford Turnpike, Waterford, CT
5
y
Civil « Structural
Survey

January 26, 2026
Stormwater Quality
It appears that the intent of this detention basin construction was to mitigate peak stormwater runoff from
the commercial developments at that time. Stormwater runoff pollutant renovation is also provided as a
byproduct of the detention basin storage, stormwater flow path through the basin, and vegetation.
Robert Russo and Kyle Lynch of CLA performed grab samples of the stormwater discharge from the basin
on two occasions: December 3, 2025 (CU86796) and December 19, 2025 (CU99833). A summary of the
lab testing results is below. Full lab testing results are included in Appendix C.
CU86796
CU99833
CTDEEP
12/3/2025
12/19/2025
Ms4
CM BASIN
CM BASIN
Outfall
Storm Water
Storm Water
Screening
Units
RL
Result
Result
Limits
Miscellaneous/Inorganics
B.0.D./5 day
mg/L
4.0
<4.0
5:2
Chlorine Residual
mg/L
0.02
< 0.02
< 0.02
Conductivity
umhos/cm
5.00
136
750
Escherichia Coli
MPN/100 mls
10
2,490
197
410.0
MBAS
mg/L
0.10
<0.05
< 0.10
Ammonia as Nitrogen
mg/L
0.10
0.13
0.38
Nitrite-N
mg/L
0.010
< 0.010
0.012
Nitrate-N
me/L
0.02
0.07
0.15
pH
pH Units
1.00
6.1
6.26
Nitrogen Tot Kjeldahl
me/L
0.20
0.63
0.98
Total Nitrogen
mg/L
0.10
0.7
1.14
2.5
Phosphorus, as P
mg/L
0.010
0.077
0.3
Turbidity
NTU
0.200
12
1.2
Metals, Total
Cadmium
mg/L
0.001
< 0.001
< 0.001
Copper
mg/L
0.005
< 0.005
< 0.005
Lead
mg/L
0.001
0.002
0.002
Zinc
mg/L
0.004
0.016
0.046
The samples were taken during a rain event to capture the first flush conditions. The December 19, 2025
sample also captured snow melt from a previous snow storm event. The results show that the water leaving
the stormwater management basin has values below the CTDEEP MS4 General Permit standards set forth,
with the exception of Escherichia Coli in the December 3, 2025.
In our opinion the high levels of
Escherichia Coli in the December 3, 2025 sample would be an anomaly and would not be typical of parking
lot stormwater runoff, but may be from a source elsewhere in the contributing watershed.
Stormwater Management Report
Y CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
6
|
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
Stormwater Management Report
k CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
i
| |
Civil * Structural + Survey

January 26, 2026
combination of impervious cover reduction and area treated with stormwater controls that shall equal or
exceed 40% of the site’s impervious cover has been proposed.
The entire existing impervious area onsite is 54.6 acres. Implementing impervious coverage reduction and
stormwater controls for at least 40% of that area requires providing improvement and treatment for at least
22.4 acres of the site.
With the new parking lot reconfiguration, the impervious surface was reduced by approximately 1.2 Acres
and is the maximum achievable due to the need for employee parking.
The structural stormwater management improvements have been proposed to the maximum extent
achievable and generally include the following:
1.
Four hydrodynamic separators have been proposed within the new stormwater infrastructure. The
combined total watershed for these separators is 8.75 Acres.
2.
Permanent catch basin inlet filter pretreatment has been proposed at strategic locations within the
parking lots. The combined total watershed for these inlet filters is 22 Acres.
The proposed additional pervious surface and structural stormwater management improvements total 31.95
Acres. This equates to 58.5% of the existing impervious area, meeting the Zoning Regulation requirements.
Additionally, a large portion of the remaining impervious surface (approximately 12 Acres) is the building
roofs that have limited potential for pollutant loading to the stormwater runoff.
In addition to the structural stormwater management improvements, maintenance and operations
improvements have also been proposed that generally include the following:
1.
Snow storage will be primarily focused to the landscape areas, with limited storage in the parking
areas. Due to the need for employee parking, excess snow will be trucked offsite to a separate
facility as needed. This will reduce the amount of deicing materials within the stormwater runoff
from the site.
2.
Implement inspection and maintenance procedures for the facility as outlined in this document and
the Plans.
4.0
Analysis
The overall site stormwater analysis was performed for the 2-year, 10-year, 25-year, 50-year, and 100-year
frequency storms using the USDA/NRCS TR-55 method to determine the peak flow rates from the existing
and post development site. Precipitation data and rainfall were acquired from NOAA Atlas 14, Volume
10, Version 3 for the site, and are included in Appendix A. NRCS Type D regional rainfall distribution
was used in accordance with the 2024 CTDEEP Connecticut Stormwater Quality Manual. The soils within
the analyzed watersheds generally fall into the hydrologic soil group D due to the current level of
Stormwater Management Report
\ CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
8
|
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 1 — 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
5.75
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, ete.)
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
Stormwater Management Report
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
9
A CLA Engineers, Inc.
|
Civil * Structural + Survey

January 26, 2026
Watershed Descriptions
The existing and post development watersheds are depicted on Figures 2 and 3. The following is a general
description of each watershed.
EXI1/PD1
This is the major watershed on the property. The watershed surrounds the mall building
and includes the majority of the parking lots and mall roof. It is generally contained within
the parking lot curb line with sheet flow from a portion of CT Route 85 contributing. Is
approximately 61.1 Ac. Discharge is to Analysis Point 1 (AP 1) which is a 72” culvert
located within the existing Stormwater Management Basin.
EX2/PD2
This watershed generally surrounds the current Longhorn Steakhouse. It includes the
parking lot surrounding the building, a portion of the southern driveway and sheet flow
from a portion of CT Route 85. Discharge is to Analysis Point 2 (AP 2) which is a drainage
manhole located at the property boundary with Home Depot. The final discharge is into
the Stormwater Management Basin after passing through the Home Depot property.
EX3/PD3
This is an isolated watershed at the middle driveway near Olive Garden. A portion of the
vegetated property frontage and CT Route 85 flow to an 18” RCP culvert inlet.
EX4/PD4
This watershed includes the CT Route 85 frontage along the Olive Garden development.
It includes a portion of the front parking area, vegetated frontage and a portion of the
northern entrance drive. Stormwater is collected in catch basins and discharges to the north
through a 36” RCP culvert in a concrete wingwall.
Peak Flow Rates and Volumes
Peak stormwater flow rates and runoff volume for the existing conditions and post development conditions
are summarized in Tables 2 and 3 respectively. Supporting calculations are included in the Calculations
section.
The post development peak flow rates and runoff volume match the existing conditions.
Stormwater
improvements for water quality and impervious surface reduction have been made onsite 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.
Table 3 — Peak Flow Rates
Peak Flow Rate (CFS)
2-Year | 10-Year | 25-Year | 50-Year | 100-Year
Existing Condition: EX 1 (Hyd. #1): | 199.840 | 303.000 | 367.040 | 414.480 | 464.880
Post Development: PD 1 (Hyd. #6): | 199.840 | 303.000 | 367.040 | 414.480 | 464.880
Change: |
0.000
0.000
0.000
0.000
0.000
WATERSHED 1 (AP 1)
Stormwater Management Report
y
:
Crystal Mall Adaptive Reuse
Chas Engineer Ine,
850 Hartford Turnpike, Waterford, CT
10
y
Civil + Structural + Survey

January 26, 2026
Conclusion:
In our opinion, the proposed redevelopment will have no negative impact to the peak stormwater runoff
rates and volumes leaving the site. Stormwater quality improvements and a reduction in impervious surface
on the site have been proposed that benefit the watersheds and the receiving Stormwater Management
Basin. As such, in our opinion, the proposed development will have no negative impact on the adjacent
State of CT infrastructure, Nevins Brook, or properties downstream of the site.
5.0
CT DEEP 2024 Stormwater Quality Manual Compliance
The proposed development meets the five performance standards of the Connecticut DEEP 2024
Stormwater Quality Manual to the Maximum Extent Achievable (MEA). The project is a redevelopment
of an existing facility; as such stormwater improvement have been incorporated into the proposed
improvements as much as possible given the site parameters and necessary use of the site. Low impact
development features have been incorporated into the site development plans including the addition of
impervious landscape surfaces, subsurface infiltration by way of Silva Cell underground storage, catch
basin inlet filters, and hydrodynamic separators. Low impact development features have been designed in
accordance with the 2024 Connecticut Stormwater Quality Manual to treat the proposed stormwater runoff.
5.1
Standard 1 — Runoff Volume and Pollutant Retention
The primary discharge form the site is to the Stormwater Management Basin. Stormwater runoff pollutant
renovation is provided in this basin as a byproduct of the detention basin storage, stormwater flow path
through the basin, and vegetation. As previously outlined under the Existing Conditions narrative herein,
the existing discharge from Stormwater Management Basin removes pollutants to levels meeting a CT
DEEP standards and Stormwater Quality Manual standards.
As an improvement to the existing site and watershed additional pervious surface has been incorporated
into the design amounting to approximately 1.2 Acres. Catch basin inlet filters have also been proposed to
pre-treat approximately 22 Acres of the site. Four hydrodynamic separators are proposed that will further
renovate the stormwater runoff. Hydrodynamic separator sizing is based on the water quality flow (WQF)
as required in the SQM.
Stormwater Management Report
A CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
12
|
Civil
Structural + Survey

Hydrodynamic Separator 1 (HDS-1)
January 26, 2026
The proposed watershed for HDS-1 is depicted on Figure 4. The required water quality volume is calculated
as follows:
Hydrodynamic Separator #1 (HDS-1)
Water Quality Volume (WQV)
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
Sizing in Accordance with Chapter 4 of the DEEP 2024 Storm Water Quality Manual
Total Watershed Area (Ac.) :
3.50
Watershed Impervious Area (Ac.) :
3.40
[=
97.1%
R=
0.924
Required WQV =
0.3505
15,266.0
Ac.-Ft
CF
Water Quality Flow (WQF)
Water Quality Flow (WQF) = (qu)(A)(Q)
qu = unit peak discharge (cfs/mi2/inch)
A=
watershed area (mi2)
Q=runoff depth (in watershed inches)
Sizing in Accordance with Appendix D of the DEEP 2024 Storm Water Quality Manual
P (1.3" for water quality flow) :
1.3
Q=
1.20
CN=
97
Ia (from Table 4-1) :
0.062
Ia/P=
0.048
Tc (Time of Concentration) :
0.167
qu (from Exhibit 4-IID) :
700
Total Watershed Area (Square Miles) =
0.00547
Required WQF =
4.600
2,064.5
in
Hr
esm/in
mi2
CFS
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
\ CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
13
Civil + Structural + Survey

Hydrodynamic Separator 2 (HDS-2)
January 26, 2026
The proposed watershed for HDS-2 is depicted on Figure 4. The required water quality volume is calculated
as follows:
Hydrodynamic Separator #2 (HDS-2)
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.) :
2.20
Watershed Impervious Area (Ac.) :
2.20
I=
100.0%
R=
0.950
Required WQV =
0.2264
9,862.7
Ac.-Ft
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=runoff depth (in watershed inches)
P (1.3" for water quality flow) :
1.3
Q=
1.24
CN=
98
Ta (from Table 4-1) :
0.041
la/P=
0.032
Tc (Time of Concentration) :
0.167
qu (from Exhibit 4-III) :
700
Total Watershed Area (Square Miles) =
0.00344
Required WQF =
2.972
1,333.8
in
Hr
cesm/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
\ CLA Engineers, Inc.
|
Civil + 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)
P= 1.3"
R=0.05 + 0,009(1)
I= percent of impervious cover
A = watershed area
Sizing in Accordance with Chapter 4 of the DEEP 2024 Storm Water Quality Manual
Water Quality Volume (WQV) = (1”)(R)(A) / 12
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
CF
Water Quality Flow (WQF
Water Quality Flow (WQF) = (qu)(A)(Q)
qu = unit peak discharge (cfs/mi2/inch)
A = watershed area (mi2)
Q= runoff depth (in watershed inches)
Sizing in Accordance with Appendix D of the DEEP 2024 Storm Water Quality Manual
P (1.3" for water quality flow) :
1.3
Q=
1.15
CN=
98
Ia (from Table 4-1) :
0.041
Ia/P=
0.032
Tc (Time of Concentration) :
0.167
qu (from Exhibit 4-II1) :
700
Total Watershed Area (Square Miles) =
0.00320
Required WQF =
2.577
1,156.7
in
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
\ CLA Engineers, Inc.
|
Civil * Structural * Survey

Hydrodynamic Separator 4 (HDS-4)
January 26, 2026
The proposed watershed for HDS-4 is depicted on Figure 4. The required water quality volume is calculated
as follows:
Hydrodynamic Separator #4 (HDS-4)
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= 13"
R= 0.05 + 0.009(1)
I= percent of impervious cover
A=
watershed area
Total Watershed Area (Ac.) :
1.00
Watershed Impervious Area (Ac.) :
1.00
I=
100.0%
R=
0.950
Required WQV =
0.1029
Ac.-Ft
4,483.1
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 = runoff depth (in watershed inches)
P (1.3" for water quality flow) :
1.3
in
Q=
1.24
CN =
98
la (from Table 4-1) :
0.041
in
Ia/P=
0.032
Te (Time of Concentration) :
0.167
Hr
qu (from Exhibit 4-III) :
700
esm/in
Total Watershed Area (Square Miles) =
0.00156
mi2
Required WQF =
1.351
CFS
606.3
GPM
A Contech Cascade CS-4 unit has been proposed that is capable of treating up to 1.8 CFS in accordance
with the CTDOT Guidelines for the Use of Hydrodynamic Separators on CTDOT Projects.
may select an alternate separator capable of treating the minimum water quality flow rate
Appendix D.
The Contractor
s as outlined in
Stormwater Management Report
h CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
16
||
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 volume 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
Schedule
e
Clean out sediment from catch basin
e
Between November
15" and December
15" (after leaf fall)
e
During April (after
snow melt)
Stormwater Management Report
A CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
17
|
Civil Structural + Survey

January 26, 2026
Maintenance Schedule for Catch Basin Inlet Filters
Activity
Schedule
e
Inspect inlet filters for accumulated sediment
Quarterly
e
Inspect oil skimmer pouches for solidification and color
e
Inspect the filter bag for punctures, tears, or other damage
e¢
Remove sediment when accumulation reaches % of the filter
As needed maintenance
volume. Use industrial vacuum or replace the filter bags
As observed at quarterly
e
Replace oil skimmer pads when they have solidified or turned black | inspections
©
Replace damaged filter bags
Maintenance Schedule for Hydrodynamic Separators
Activity
Schedule
e
Inspect sump for accumulated sediment
Semi-annual
e
Inspect oil skimmer pouches for solidification and color
e
Inspect the filter bag for punctures, tears, or other damage
e¢
Remove sediment when accumulation reaches 50% of the
As needed maintenance
maximum storage volume. Use industrial vacuum / Vac-all.
As observed at semi-
e
Replace oil skimmer pads when they have solidified or turned black | annual inspections
e
Replace damaged filter bags
Maintenance Schedule for Parking Areas
Activity
Schedule
e
Sweep parking lots & impervious areas
e
Between November
15" and December
15" (after leaf fall)
e
During April (after
snow melt)
e¢
Remove and dispose of trash and debris onsite
Daily - As needed
maintenance
Stormwater Management Report
A
tape
Crystal Mall Adaptive Reuse
Cha Rong ingens, Arc
850 Hartford Turnpike, Waterford, CT
18
|
Civil * Structural * Survey

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 stormwater.
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
Stormwater Management Report
A CLA
Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
19
|
Civil : Structural + Survey

January 26, 2026
-
Contain the spill
-
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.
Post Construction
Stormwater Management & Pollution Prevention:
Provisions for stormwater management and pollution prevention are outlined on the plans and are as
follows:
1.
6.
Pollution Prevention Team:
The Owner shall be responsible for carrying out the provisions of the plan.
Sweeping:
Parking lots, sidewalks, and other impervious surfaces shall be swept clean of sand and
litter and any other pollutants at least twice per year
a.
Between November 15" and December 15" (after leaf fall)
b.
During April (after snow melt)
Outside Storage:
Accessories or equipment stored outside shall be covered or maintained to minimize the
possibility of these materials or their residue passing to stormwater.
Washing:
No washing of vehicles, accessories, equipment, or appliances onsite.
Maintenance and Inspection:
a.
Inspect stormwater structures and outfalls twice per year.
b.
Clean sediment and debris from structures at least once per year during April.
c.
Stormwater Management Basin
-
Remove accumulated sediment, leaf litter, and trash from the inlets twice yearly.
Between November 15th and December 15th (after leaf fall) and During April
(after snow melt).
-
Perform yearly inspection for embankment erosion and restore as needed.
-
Review yearly for invasive species.
Spills or Accidental Discharges:
d.
Comply with State and Federal regulations to contain and clean up any spill or
discharge and dispose of materials at an approved facility.
e.
Contact Connecticut DEEP oil and chemical spill response division 860-424-3338.
f.
The following steps should be performed as soon as possible
-
Stop the source of the spill
-
Contain the spill
Stormwater Management Report
\ CLA Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Turnpike, Waterford, CT
20
Civil : Structural
Survey

January 26, 2026
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
Stormwate Management Report
f
CLA Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Tumpike, Waterford, CT
21
y
Civil * Structural « Survey

FIGURES
Stormwater Management Report
CLA Engineers, Inc.
Crystal Mall Adaptive Reuse
850 Hartford Tumpike, Waterford, CT
P
Civil - Structural - Survey

CLA Engineers, Inc.
Civit. + SrRuCTURAL + SURVEYING
LOCATION
MAP
J
317 Main Street
Norwich, Connecticut
860-886-1966
cluengineers.com
Crystal Mall Adaptive Reuse
850 Hartford Turnpike (CT Route 85)
Waterford, Connecticut
Montville Quad (#86)
DATE: 12/12/2025
SOURCE: USGS Quad
N
A
FIGURE
1