Representative Town Meeting (RTM) Regular Meeting (linked)

p
y
Waterford, CT 06385
Re: Stormwater Management Report
Oswegatchie Fire Station
441 Boston Post Road
Waterford, Connecticut
Langan Project No.: 140286501
Dear Mr. Mullen,
This report provides an analysis of the proposed peak runoff discharges and the engineering
design for the proposed stormwater conveyance system at 441 Boston Post Road.
PROJECT DESPCRIPTION
Existing Conditions
The project site is located at 441 Boston Post Road in Waterford CT; see Figure 1. The overall
approximately 2.0-acre parcel is currently occupied by the existing Oswegatchie Fire Station,
including impervious and grass areas. The parcel is located within the Niantic River sub regional
drainage basin. The parcel area does not contain any known locations of State and Federal Listed
Species and Critical Habitats per the CT Natural Diversity Data Base Areas map of Waterford, CT
dated June 2024. The project site is located on the western part of the parcel within the limits of
the existing fire station site. To the west the project site is bordered by a garden shop. To the
south, the project site is bordered by Boston Post Road. To the east the project site is bordered
by residential properties on Boston Post Road. To the north the site is bordered by lightly wooded
wetland areas. The existing project site is mostly impervious areas with the majority of
stormwater running overland towards the wetlands in the north.
Based upon a topographic survey prepared by Langan, dated June 28, 2024, the site grades slope
downward from the southern corner of the property towards the northern property line, with
elevations ranging from approximately 35 feet to about 30 feet.
555 Long Wharf Orwve New Haven, CY 06571 T: 203.562.5771 F: 203 789.6142 ww langan com
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considered a Low-Risk Area and described by FEMA as areas outside the 0.2-percent-annual-
chance chance flood. No base flood elevations or base flood depths are shown within these
zones.
According to the USDA Natural Resources Conservation Service Web Soil Survey, the site's soit
type varies throughout. The site is mostly classified as Hinckley Loamy Sand with an A hydrologic
rating and slopes between 3 and 15 percent. Additionally, the eastern corner of the site is
classified as Walpole Sandy Loam with a D hydrologic rating and slopes between 0 and 3 percent.
There are wetland areas to the east and north of the site. While some of the site work is proposed
within the 100-foot upland review area, no direct wetland impacts are proposed.
Proposed Project
The proposed project consists of the demolition of the existing fire station and the construction
of a new fire station building with new landscaped areas, driveways, and parking areas. Additional
improvements include new stormwater and utility infrastructure. A summary of the change in
impervious is shown below.
Project Site Impervious Cover [SF]
Existing Conditions | Proposed Conditions Net Decrease
£52,200 431,500 £20,700
The proposed stormwater system has been designed to maintain existing site hydrology to the
maximum extent practicable. The majority of runoff from the new development will be conveyed
to various stormwater management systerns before discharging to either the existing
stormwater network in Boston Post Road or overland towards the existing offsite wetlands.
Water quality improvements include yard drains with sumps, a pretreatment swale and a rain
garden. These water quality improvements have been designed to retain 100% of the proposed
project's water quality volume onsite. This achieves the average annual pollutant load reduction
requirements as per the recommendations of the 2024 CT Stormwater Quality Manual.
Details of the size and location of the stormwater network can be found on the Grading &
LANGAN

The stormwater management system is designed to control the rate of runoff from the site’s
watersheds to be equal or less than existing conditions up to, and including, a 100-year design
storm event.
The peak runoff discharges for the existing and proposed conditions were analyzed using Soil
Conservation Service (SCS) methodology which outlines procedures for calculating peak rates of
runoff resulting from precipitation events as well as procedures for developing runoff
hydrographs. The entire site was included in the analysis; see Figures EXWS and PRWS. Values
for area, curve number (CN), and a time of concentration were calculated for the existing and
proposed conditions.
The curve number is a land sensitive coefficient that dictates the relationship between total
rainfall depth and direct storm runoff. The soils within the watershed are divided into hydrologic
soil groups (A, B, C, and D). The SCS classification system evaluates the runoff potential of a soil
according to its infiltration and transmission rates. “A” soils have the lowest runoff potential,
while “D" soils have the greatest runoff potential.
The time of concentration (Tc) is defined as the time for runoff to travel from the hydraulically
most distant point in the watershed to a point of interest. Values of time of concentration were
determined for existing and proposed conditions based on land cover and slope of the flow path
using methods outlined in TR-55.
For this study, a 24-hour SCS Type III standard rainfall distribution was used to determine the
peak flow rate and volume to all points of discharge from the site. Precipitation data used for the
various storm events is based on the "NOAA Atlas 14 Point Precipitation Frequency Estimates:
CT" for Lake Konomoc Station. Lake Konomoc Station was chosen for rainfall data because it is
the station located within the closest proximity of the project location as shown in Graphic 1. A
summary of all rainfall data utilized in the analysis for this site is provided below and a complete
compilation of data provided by NOAA for this location is included in Appendix C.
LANGAN

eS .' j @ Stow stations on map
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| : * 4 |Lacation information:
Name: tote of Waterton,
} Bone Ranch 4 ? {i | Station name: LAKE KONOMOC
Nltary #4 } | Sito 10: 06-3989
Rorarvation ro a | Latitude: 41.9562"
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NOAA Precipitation Depth per Average Recurrence Interval [in]
Duration 2-Year 10-Year 25-Year 100-Year
24-hour 3.45 5.13 6.17 7.79
Existing Condition (See Appendix A)
The project area’s existing drainage conditions were analyzed as Watersheds A, B, and C (See
Drawing EXWS).
Existing Watershed A is approximately 0.26 acres and comprises grassy areas, driveway aprons
onto the site and the southwestern portion of the existing building. Stormwater runoff from this
watershed either flows into the existing storm drainage network or overland and offsite towards
Boston Post Road.
Existing Watershed B is approximately 0,08 acres and consists of grass a
east of the site. Stormwater runoff from this watershed flows overland to t
east of the site.
nd brush areas at the
he wetlands #2 to the
LANGAN

Proposed Condition (See Appendix B)
In the proposed condition, site hydrology attempts to mimic existing conditions and all watershed
outlets remain the same.
Proposed Watershed A is about 0.37 acres and consists of grassy areas and the proposed
driveway aprons. Stormwater wil! continue to flow overland to Boston Post Road. The proposed
site within this watershed has been designed to significantly reduce impervious area as
compared with the existing condition.
Proposed Watershed B is about 0.09 acres and includes grass and brush areas to the east of the
site. This watershed will remain generally unchanged, and stormwater collected within this
watershed will flow overland to the wetlands #2 offside to the east.
Proposed Watershed C is divided into two sub-watersheds: Sub-watershed C1 and Sub-
watershed C2. Sub-watershed C1 is about 1.04 acres and consists of the proposed building and
parking areas along with grassy areas; stormwater within this watershed will flow either through
a pretreatment swale conveyance feature or directly into a rain garden before flowing to the
wetlands #2 offsite to the north, Sub-watershed C2 is about 0.12 acres and consists of grassy
and brush areas; stormwater within this watershed will continue to flow overland to the wetlands
#2 offsite to the north.
Details of the sizes and locations of the stormwater collection systems can be found on drawings
CG101. A conservative design infiltration rate for the rain garden is 1 inch per hour. The design
infiltration rate will be confirmed with on-site testing prior to construction. Please refer to
Appendix F for boring log data within the vicinity of the proposed rain garden. This testing was
performed by Barton & Loguidice as a part of a Limited Phase |} Environmental Site Assessment
report, dated 08/27/2024. According to the boring log data, groundwater was encountered
between 6' and 13' below existing grade, and existing site soils within the rain gardens consist
of a mainly sandy material.
LANGAN

| 25-Year 1,04 0,71 -0,33 31.73%
100-Year | 1.46 1.20 -0.26 17.81%
Site Discharge Peak Flow Comparison for WS-B (CF)
Storm | Current | Proposed | Delta | % Reduction.
2-Year 0.02 0.01 -0,01 50,00%
10-Year 0.09 0.09 0.00 0.00%
25-Year 0.15 0.19 0.00 0.00%
100-Year | 0.26 0.26 0.00 0.00%
__Site Discharge Peak Flow Comparison eee
"Storm | Current | Proposed | Delta | % Reduction |
2-Year 3,77 0.32 -3.45 91.51%
10-Year 5,91 2,04 -3.87 65.48%
25-Year 7.22 3.73 ~3.49 48.34%
100-Year 9.24 5.62 ~3.62 39.18%
Site Discharge Peak Flow Comparison for Total Site (CF)
_Storm | Current | Proposed | Delta | % Reduction |
2-Year 4,15 0.38 -3.77 90.84%
10-Year 6.76 2.39 -4,37 64.65%
25-Year 8.39 4.44 -3.95 47.08%
100-Year | 10.95 6.93 -4,02 36.71%
As can be seen from the tables above, runoff from each watershed and the total site will be
attenuated for the storms up to and including the 100-year storm. Additionally, per the 2024 CT
Stormwater Quality Manual requirements, runoff from each watershed that includes proposed
site development will be attenuated by 50% for the 2-year storm event.
STORMWATER CONVEYANCE SYSTEM (See Appendix D)
The stormwater conveyance system was sized using the Rational Method for the 10-year storm
event as per the CTDEEP Stormwater Quality Manual. Values for area, runoff coefficient, C, and
LANGAN

Roof/Pavernent/Impervious 0.9
Rainfall intensities were taken from the “NOAA Atlas 14 Point Precipitation Frequency Estimates:
CT” for Lake Konomoc. Stormwater pipes were then sized based upon the Manning’s Equation
for full flow pipe capacity and solving for the hydraulic grade line. The computer program
Hydraflow Storm Sewers 2011 by Intellisolve was used in the analysis.
Each proposed storm sewer system has been analyzed sing a starting HGL elevation equal to
the outlet pipe’s crown elevation. This mimics a tailwater elevation equal to the outlet pipe’s
diameter or a scenario where a proposed pipe is entering an existing pipe flow at full capacity.
STORMWATER QUALITY {See Appendix E)
The proposed stormwater management system has been designed to incorporate stormwater
quality measures including a significant decrease in site imperviousness, yard drains with sumps,
a pretreatment swale conveyance feature, and a rain garden. These measures will be
implemented to increase water quality and minimize the passage of pollutants to the existing
stormwater systems as compared to current conditions.
Under current conditions, the entirety of the site impervious cover (£52,200 SF) is considered
directly connected impervious area (DCIA). This project proposes to decrease DCIA by over 90%,
which will decrease surface runoff and increase infiltration of rainfall into the soil.
Per Table 4.1 of the CT Stormwater Quality Manual, the site is considered a redevelopment with
existing DCIA of 40% or more. As such, the Required Retention Volume (RRV) is 50% of the
site's Water Quality Volume (WQV). Through coordination with the town of Waterford
Environmental Planner, this project occurs within the Stony Brook watershed area. Stormwater
discharge from the site contributes to an intermittent watercourse and wetland system located
north of the parcel. The receiving portion of Stony Brook south of Route 1 has been designated
as an impaired waterbody by CTDEEP. Because of this information, the stormwater system has
LANGAN

load reductions for Total Suspended Solids (TSS), Total Phosphorus (TP) and Total Nitrogen (TN).
Per the manual, “a proposed stormwater management system meets or exceeds these average
pollutant load reductions when the RRV is retained on-site using suitable stormwater retention
practices, Achieving these minimum required load reductions for sediment and nutrients is
assumed to provide adequate reductions of other stormwater pollutants including floatable
materials." Through the use of the proposed rain garden, the stormwater system designed
exceeds our RRV and will retain 100% of the WQV, thereby also exceeding the required average
annual pollutant load reductions.
CONCLUSION
The proposed stormwater management system has been designed in general accordance with
the 2024 CTDEEP Stormwater Quality Manual and the 2000 CTDOT Drainage Manual. It has
been designed to maintain existing site hydrology to the maximum extent practicable with
attenuated peak flows and multiple water quality improvements.
This Langan report shows that the proposed stormwater management system, as designed, will
effectively manage quality and quantity of stormwater runoff for the proposed development.
Please refer to the Drawings for additional drainage information.
Sincerely,
Langan CT, Inc.
en
Brian Phillips, P.E.
Senior Project Manager
Jang \Wata\NHVidatab\i 4028650 1\Project Data\_Discipline'\Site CivihRapons\StormwatenOswegatchie Fire Station Stormwater Report.docx
LANGAN

Waterford, CT 06385
RE: Stormwater Management Report
Oswegatchie Fire Station
441 Boston Post Road
Waterford, Connecticut
Langan Project No.: 140286501
Dear Mr. Mullen,
This report provides an analysis of the proposed peak runoff discharges and the engineering
design for the proposed stormwater conveyance system at 441 Boston Post Road.
PROJECT DESPCRIPTION
Existing Conditions
The project site is located at 441 Boston Post Road in Waterford CT; see Figure 1. The overall
approximately 2.0-acre parcel is currently occupied by the existing Oswegatchie Fire Station,
including impervious and grass areas. The parcel is located within the Niantic River sub regional
drainage basin. The parcel area does not contain any known locations of State and Federal Listed
Species and Critical Habitats per the CT Natural Diversity Data Base Areas map of Waterford, CT
dated June 2024. The project site is iocated on the western part of the parcel within the limits of
the existing fire station site. To the west the project site is bordered by a garden shop. To the
south, the project site is bordered by Boston Post Road. To the east the project site is bordered
by residential properties on Boston Post Road. To the north the site is bordered by lightly wooded
wetland areas. The existing project site is mostly impervious areas with the majority of
stormwater running overland towards the wetlands in the north.
Based upon a topographic survey prepared by Langan, dated June 28, 2024, the site grades slope
downward from the southern corner of the property towards the northern property line, with
elevations ranging from approximately 35 feet to about 30 feet.
555 Long Wharf Drive New Haven, CT 06511 1; 203.562.5773 F: 203 789.6142 www. langan.com
New detsey ¢ Naw Yok oo Virgina ¢ Cavfupea a Piepiana 9 Caeteteal @ ovnuli @ Bea SRAls @ ava a Uae lief @ teiadtad

considered a Low-Risk Area and described by FEMA as areas outside the 0.2-percent-annual-
chance chance flood, No base flood elevations or base flood depths are shown within these
zones.
According to the USDA Natural Resources Conservation Service Web Soil Survey, the site's soil
type varies throughout. The site is mostly classified as Hinckley Loamy Sand with an A hydrologic
rating and slopes between 3 and 15 percent. Additionally, the eastern corner of the site is
classified as Walpole Sandy Loam with a D hydrologic rating and slopes between 0 and 3 percent.
There are wetland areas to the east and north of the site. While some of the site work is proposed
within the 100-foot upland review area, no direct wetland impacts are proposed.
Proposed Project
The proposed project consists of the demolition of the existing fire station and the construction
of a new fire station building with new landscaped areas, driveways, and parking areas. Additional
improvements include new stormwater and utility infrastructure. A summary of the change in
impervious is shown below.
Project Site impervious Cover [SF]
Existing Conditions Proposed Conditions Net Decrease
£52,200 £31,500 £20,700
The proposed stormwater system has been designed to maintain existing site hydrology to the
maximum extent practicable. The majority of runoff from the new development will be conveyed
to various stormwater management systems before discharging to either the existing
stormwater network in Boston Post Road or overland towards the existing offsite wetlands.
Water quality improvements include yard drains with sumps, a pretreatment swale and a rain
garden, These water quality improvements have been designed to retain 100% of the proposed
project's water quality volume onsite. This achieves the average annual pollutant load reduction
requirements as per the recommendations of the 2024 CT Stormwater Quality Manual.
Details of the size and location of the stormwater network can be found on the Grading &
LANGAN

The stormwater management system is designed to control the rate of runoff from the site s
watersheds to be equal or less than existing conditions up to, and including, a 100-year design
storm event.
The peak runoff discharges for the existing and proposed conditions were analyzed using Soil
Conservation Service (SCS} methodology which outlines procedures for calculating peak rates of
runoff resulting from precipitation events as well as procedures for developing runoff
hydrographs. The entire site was included in the analysis; see Figures EXWS and PRWS. Values
for area, curve number (CN), and a time of concentration were calculated for the existing and
proposed conditions.
The curve number is a land sensitive coefficient that dictates the relationship between total
rainfall depth and direct storm runoff. The soils within the watershed are divided into hydrologic
soil groups (A, B, C, and D). The SCS classification system evaluates the runoff potential of a soil
according to its infiltration and transmission rates. “A" soils have the lowest runoff potential,
while “D" soils have the greatest runoff potential.
The time of concentration (Tc) is defined as the time for runoff to travel from the hydraulically
most distant point in the watershed to a point of interest. Values of time of concentration were
determined for existing and proposed conditions based on land cover and slope of the flow path
using methods outlined in TR-55.
For this study, a 24-hour SCS Type II! standard rainfall distribution was used to determine the
peak flow rate and volume to all points of discharge from the site. Precipitation data used for the
various storm events is based on the “NOAA Atlas 14 Point Precipitation Frequency Estimates:
CT” for Lake Konomoc Station. Lake Konomoc Station was chosen for rainfall data because it is
the station located within the closest proximity of the project location as shown in Graphic 1. A
summary of all rainfall data utilized in the analysis for this site is provided below and a complete
compilation of data provided by NOAA for this location is included in Appendix C.
LANGAN

a” | fh Show stations on map
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Location Information:
Sent, 2 g_|| Name: Town of Waterford,
Connecticut, USA®
i Stati : LAKE KONOMOC
2 pamnaton on i eh Latitude: 41.9582"
# pte, Ey be Longitude: -72.1728°
A | ‘* New Landon | Groton, Blevation: 1800
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NOAA Precipitation Depth per Average Recurrence Interval [in]
Duration 2-Year 10-Year 25-Year 100-Year
24-hour 3.45 5.13 6.17 7.79
Existing Condition (See Appendix A)
The project area's existing drainage conditions were analyzed as Watersheds A, B, and C (See
Drawing EXWS).
Existing Watershed A is approximately 0.26 acres and comprises grassy areas, driveway aprons
onto the site and the southwestern portion of the existing building. Stormwater runoff from this
watershed either flows into the existing storm drainage network or overland and offsite towards
Boston Post Road.
Existing Watershed B is approximately 0.08 acres and consists of grass and brush areas at the
east of the site. Stormwater runoff from this watershed flows overland to the wetlands #2 to the
east of the site.
LANGAN

Proposed Condition (See Appendix B)
In the proposed condition, site hydrology attempts to mimic existing conditions and all watershed
outlets remain the same.
Proposed Watershed A is about 0.37 acres and consists of grassy areas and the proposed
driveway aprons. Stormwater will continue to flow overland to Boston Post Road. The proposed
site within this watershed has been designed to significantly reduce impervious area as
compared with the existing condition.
Proposed Watershed B is about 0.09 acres and includes grass and brush areas to the east of the
site. This watershed will remain generally unchanged, and stormwater collected within this
watershed will flow overland to the wetlands #2 offside to the east.
Proposed Watershed C is divided into two sub-watersheds: Sub-watershed C1 and Sub-
watershed C2. Sub-watershed C1 is about 1.04 acres and consists of the proposed building and
parking areas along with grassy areas; stormwater within this watershed will flow either through
a pretreatment swale conveyance feature or directly into a rain garden before flowing to the
wetlands #2 offsite to the north. Sub-watershed C2 is about 0.12 acres and consists of grassy
and brush areas; stormwater within this watershed will continue to flow overland to the wetlands
#2 offsite to the north.
Details of the sizes and locations of the stormwater collection systems can be found on drawings
CG101. A conservative design infiltration rate for the rain garden is 1 inch per hour. The design
infiltration rate will be confirmed with on-site testing prior to construction. Please refer to
Appendix F for boring log data within the vicinity of the proposed rain garden. This testing was
performed by Barton & Loguidice as a part of a Limited Phase II Environmental Site Assessment
report, dated 08/27/2024. According to the boring log data, groundwater was encountered
between 6’ and 13' below existing grade, and existing site soils within the rain gardens consist
of a mainly sandy material.
LANGAN

25-Year 1.04 0.71 -0,33 31.73%
100-Year 1.46 1.20 -0.26 17.81%
Storm | Current | Proposed | Delta % Reduction
2-Year 0.02 0.01 “0,01 50.00%
10-Year 0.09 0,09 0.00 0.00%
25-Year 0.15 ' 0,19 0.00 0.00%
100-Year | 0.26 0,26 0.00 0.00%
Site Discharge Peak Flow Comparison for WS-C (CF)
Storm | Current Proposed | Delta | % Reduction
2-Year 3.77 0.32 3.45 91.51%
10-Year 5.91 2,04 3.87 65.48%
25-Year 7.22 3.73 -3.49 48.34%
100-Year | 9.24 5.62 3.62 39.18%
Site Discharge Peak Flow Comparison for Total Site (CF)
Storm | Current | Proposed | Delta | % Reduction
2-Year 4.15 0,38 3.77 90.84%
10-Year 6.76 2,39 -4,37 64.65%
25-Year 8.39 4.44 -3.95 47,08%
100-Year | 10.95 6.93 -4.02 36.71%
As can be seen from the tables above, runoff from each watershed and the total site will be
attenuated for the storms up to and including the 100-year storm. Additionally, per the 2024 CT
Stormwater Quality Manual requirements, runoff from each watershed that includes proposed
site development will be attenuated by 50% for the 2-year storm event.
STORMWATER CONVEYANCE SYSTEM (See Appendix D)
The stormwater conveyance system was sized using the Rational Method for the 10-year storm
event as per the CTDEEP Stormwater Quality Manual. Values for area, runoff coefficient, C, and
LANGAN

Roof/Pavement/Impervious 0.9
Rainfall intensities were taken from the “NOAA Atlas 14 Point Precipitation Frequency Estimates:
CT" for Lake Konomoc. Stormwater pipes were then sized based upon the Manning’s Equation
for full flow pipe capacity and solving for the hydraulic grade line. The computer program
Hydraflow Storm Sewers 2011 by Intellisolve was used in the analysis.
Each proposed storm sewer system has been analyzed sing a starting HGL elevation equal to
the outlet pipe’s crown elevation. This mimics a tailwater elevation equal to the outlet pipe’s
diameter or a scenario where a proposed pipe is entering an existing pipe flow at full capacity.
STORMWATER QUALITY (See Appendix E)
The proposed stormwater management system has been designed to incorporate stormwater
quality measures including a significant decrease in site imperviousness, yard drains with sumps,
a pretreatment swale conveyance feature, and a rain garden. These measures will be
implemented to increase water quality and minimize the passage of pollutants to the existing
stormwater systems as compared to current conditions.
Under current conditions, the entirety of the site impervious cover (452,200 SF) is considered
directly connected impervious area (DCIA). This project proposes to decrease DCIA by over 90%,
which will decrease surface runoff and increase infiltration of rainfall into the soil.
Per Table 4.1 of the CT Stormwater Quality Manual, the site is considered a redevelopment with
existing DCIA of 40% or more. As such, the Required Retention Volume (RRV) is 50% of the
site's Water Quality Volume (WQV). Through coordination with the town of Waterford
Environmental Planner, this project occurs within the Stony Brook watershed area. Stormwater
discharge from the site contributes to an intermittent watercourse and wetland system located
north of the parcel. The receiving portion of Stony Brook south of Route 1 has been designated
as an impaired waterbody by CTDEEP. Because of this information, the stormwater system has
LANGAN

load reductions for Total Suspended Solids (TSS), Total Phosphorus (TP) and Total Nitrogen (TN).
Per the manual, “a proposed stormwater management system meets or exceeds these average
pollutant load reductions when the RRV is retained on-site using suitable stormwater retention
practices. Achieving these minimum required load reductions for sediment and nutrients is
assumed to provide adequate reductions of other stormwater pollutants including floatable
materials.” Through the use of the proposed rain garden, the stormwater system designed
exceeds our RRV and will retain 100% of the WOV, thereby also exceeding the required average
annual pollutant load reductions.
CONCLUSION
The proposed stormwater management system has been designed in general accordance with
the 2024 CTDEEP Stormwater Quality Manual and the 2000 CTDOT Drainage Manual. It has
been designed to maintain existing site hydrology to the maximum extent practicable with
attenuated peak flows and multiple water quality improvements.
This Langan report shows that the proposed stormwater management system, as designed, will
effectively manage quality and quantity of stormwater runoff for the proposed development.
Please refer to the Drawings for additional drainage information.
Sincerely,
Langan CT, Inc.
a
Brian Phillips, P.E.
Senior Project Manager
Wangan.com\data\NHVidatab\i 4028650 1\Project Data\_Discipline\Site CivihReporis\S tormwateNOswagatchie Fre Station Stormwater Report.docx
LANGAN

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p
Fig. 2 FEMA Flood Map
Fig. 3 NRCS Soil Map
LIST OF DRAWINGS
EXWS Existing Watershed Map
PRWS Proposed Watershed Map
DACB Drainage Area Catchment Basin Map
REFERENCE DRAWINGS
CG101 Grading & Drainage Plan
CG501 Grading & Drainage Details
LIST OF
APPENDICES
Appendix A Existing Stormwater Discharge Calculations
Appendix B Proposed Stormwater Discharge Calculations
Appendix C NOAA Rainfall! Data
Appendix D Stormwater Collection System Calculations
Appendix E Supporting Calculations
Appendix F Boring Logs (by others)
Appendix G Stormwater Management System Operation and
Maintenance Plan
LANGAN

By APPROXIMATE
"ISITE LOCATION, >
id [_] Site Boundary
‘Copyright© 2013 Netonal Society, Loubed; © 2013 Geographic Society, Hebi
LANGAN [Oswegatchie Fire
300 Kimboal Drive 4th Floor
Pereippony NJ O7054-2172 Station
Tt 973-500-4900 =F: 973-600-4901 wew.langen.com
Langen Engineering & Environmental Servicas, Inc,
a pees triage sorta al_— Site Analyzer
Langan Intemational WATERFORD
Collectively known os Langan CONNECTICUT Submission Date
SOUTHEASTERN CT | 41/3/2025 Sheet 1 of 2
Disclaimer: This information is produced by an eutometed sryalem end may nol be eompiele. eee eee ree eet re m8 promt at Is In tha public domein and unless noted has
on beeen eld ie Dy prone Joc aty apetic une. Users ure diay cautioned to ‘confirm the Ja puitable fos their
Spatiel Raterance: NAD 1983 StatePlene Connecticul FIPS 0600 Feat
© 2025 Langan

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LANGAN |}* EFF
Oswegatchie Fire EFFECTIVE FEMA
900 Kimbalt
Parsippany NI 07054-2172 Station FIRM
‘TR 873-660-4900 F; 973-560-4901 wwwtengan.com
Langan a Sarvioaa, Inc,
{Langan yng, L
Architecture and Geology, D.P.C.
Langan Intemational WATERFORD
Collectively known ea Langan CONNECTICUT
SOUTHEASTERN ct 7
Thi t by system end may notbe complete. The abeance of o feature It not a confirmation that the feature lb nol present et the subject location, Information produced & in the pub: domain sad wilass noted hes
Not been field verified or provided for any use. Usern 210 also Cautaned to confirm the information shown ts eultabla for their intended use.
Spatial Rederence: NAD 1983 StatePisne
FIPS 0600 Feet
By
Site Analyzer
bmission Date
—__ 1/3/2025
Sheet 2 of 2
©2025 Langan

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SYMBOL | NAME GROUP
Z 13 WALPOLE SANDY LOAM, 0 TO 3 PERCENT SLOPES B/D
38C HINCKLEY LOAMY SAND, 3 TO 15 PERCENT SLOPES A
REFERENCE: WEB SOIL SURVEY BY THE UNITED STATES DEPARTMENT OF
AGRICULTURAL AND NATURAL RESOURCES CONSERVATION SERVICE.
L A N G A N Project rawing Title [Project No. Drawing No. .
Langan CT, Inc. alten FIRE NRCS SOl LS ian 17/2025 3 e
555 Long Wharf Drive, 9th Floor rawn By
New Haven, CT 08511 MAP = “ft q
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T: 203.662.5774 F: 203.769.6142 www Jangan.com ee &
Date: 1/3/2025 Time: 10:67 User: afay Style Table: Langan,stb Layout: Layout? Document Code: 140286601-0202-CS101-0104

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APPENDIX A
Existing Stormwater Discharge Calculations

eo @ &
EXWS- EXWS-B XWS-C
Total Site
Gunea = rN Routing Diagram for EX Hydro
Prepared by Langan Engineering, Printed 11/12/2024
HydroCAD® 10.20-3f s/n 08223 © 2023 HydroCAD Software Solutions LLC

13,021 49 50-75% Grass cover, Fair, HSG A (15S, 2S, 3S)
4,022 84 50-75% Grass cover, Fair, HSG D (2S, 3S)
1,432 7 Brush, Fair, HSG D (28, 38)
52,049 98 Paved parking, HSG A (1S, 3S)
36 98 Paved parking, HSG D (28)
70,560 88 TOTAL AREA

Flow Length=137' Tc=6.0 min CN=75 Runoff=0.37 cfs 1,211 of
Subcatchment 2S: EXWS-B Runoff Area=3,749 sf 0.96% impervious Runoff Depth=0.36"
Flow Length=68' Slope=0.0250 ' Tc=6.4 min CN=56 Runoff=0.02 cfs 113 cf
Subcatchment 3S: EXWS-C Runoff Area=55,336 sf 83.12% Impervious Runoff Depth=2.69"
Flow Length=248' Slope=0.0200‘/' Tc=6.0 min CN=93 Runoff=3.77 cfs 12,389 cf
Link SITE: Total Site Inflow=4.15 cfs 13,7413 cf
Primary=4.15 cfs 13,713 ef
Total Runoff Area = 70,560 sf Runoff Volume = 13,713 cf Average Runoff Depth = 2.33"
26.18% Pervious = 18,475 sf 73.82% Impervious = 52,085 sf

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type lil 24-hr 2-yr Rainfall=3.45"
Area (sf) CN Description
5,423, 49 50-75% Grass cover, Fair, HSGA
6,052.98 Paved parking, HSGA
11,475 75 Weighted Average
5,423 47.26% Pervious Area
6,052 52.74% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) __ (feet) (fUft) (ft/sec) (cfs)
1.1 54 0.0075 0.85 Sheet Flow, Segment 1
Smooth surfaces n=0.011 P2= 3.43”
0.3 83 0.0100 4,50 1.57 Pipe Channel, Segment 2
8.0" Round Area= 0.3 sf Perim=2.1' r= 0.17'
n= 0.010
1.4 137 Total, Increased to minimum Tc = 6.0 min
——“Sgnrrent-d—_. N
: EXWS-A

0.38 aes
0.36 ei 24-
0.34 2
0.32 425yi K °
0.2 9
0.26 p=1,21)
= 0.24
% 0.22 ul Tl
Boe all noath=137"
0.16 H
0.14 O-mnt Lu
0.1
0.1
0.08:
0.06
0.04
0.02
av) a
NI
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type Ill 24-hr 2-yr Rainfall=3.45"
Area (sf) CN Description
2,844 49 50-75% Grass cover, Fair, HSG A
770 =©77_~=«~Brush, Fair, HSG D
99 84 50-75% Grass cover, Fair, HSG D
36-98 ~— Paved parking, HSG D
3,749 56 Weighted Average
3,713 99.04% Pervious Area
36 0.96% Impervious Area
Te Length Slope Velocity Capacity Description
(min) (feet) _(ft/ft) _(ft/sec) (cfs)
6.4 68 0.0250 0.18 Sheet Flow, Segment 1
Grass: Short n=0.150 P2= 3.43"
Segment.
—~Gvboatchmnani 23: EXWS-B
Subcatchment 2S: EXWS-B
Hydrograph
0.0170.016 TT Ce)
Liar 4
0.015:0.014 Rainfalls3,45!"
0.013:0.012 5
0,011 unott ume=1138 cf
0.01 pth=0-p6r -
0.009 .
g
A
I
Flow (cfs)
0.008 Fle
0.0070,006: Sto
0.005 ics in
0,004
0.003
0.0020.001 |
0 Kombat
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type Ill 24-hr 2-yr Rainfall=3.45"
Area (sf) CN Description
4,754 49 50-75% Grass cover, Fair, HSGA
3,923 84 50-75% Grass cover, Fair, HSG D
662 77 Brush, Fair, HSG D
45,997 98 Paved parking, HSGA
55,336 93 Weighted Average
9,339 16.88% Pervious Area
45,997 83.12% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) _(ft/ft) _ (ft/sec) (cfs)
1.6 150 0.0200 1.54 Sheet Flow, Segtment 1
Smooth surfaces n=0.011 P2= 3.43"
0.5 86 0.0200 2.87 Shallow Concentrated Flow, Segment 2
Paved Kv= 20.3 fps
0.1 12 0.0200 2.12 Shallow Concentrated Flow, Segment 3
Grassed Waterway Kv= 15.0 fps
2.2 248 Total, Increased to minimum Tc = 6.0 min
~—“Segirent4. ,

Flow (cfs)
344
4
0-
377 cle
r faint i
Type IllLl
-hr
Ru nq
un
off
R
y,
ff
q
|
;
lu
*)
ea=55,336 sf
=12,389 af
Depth
Fl
Sle
DW Lengt
ppe=0.
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)
2
=248'
200
NF9

y
g
Primary outflow = Inflow, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Link SITE: Total Site
Hydrograph
Gi Inflow
1 REE | @ Primary
- ow Area=(70,560 s
Flow (cfs)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

f
,
pf
p
Flow Length=137' Tc=6.0 min CN=75 Runoff=0.77 cfs 2,443 cf
Subcatchment 2S: EXWS-B Runoff Area=3,749 sf 0.96% Impervious Runoff Depth=1.11"
Flow Length=68' Slope=0.0260 '/ Tc=6.4 min CN=56 Runoff=0.09 cfs 347 cf
Subcatchment 38: EXWS-C Runoff Area=55,336 sf 83.12% Impervious Runoff Depth=4.33"
Flow Length=248' Slope=0.0200 '" Tc=6.0 min GN*93 Runoff=5.91 cis 19,947 cf
Link SITE: Total Site Inflow=6.76 cfs 22,737 cf
Primary=6.76 cis 22,737 of
Total Runoff Area = 70,560 sf Runoff Volume = 22,737 cf Average Runoff Depth = 3.87"
26.18% Pervious = 18,475 sf 73.82% Impervious = 52,085 sf

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type Ill 24-hr 10-yr Rainfall=5.13"
Area (sf) CN Description
5,423 49 50-75% Grass cover, Fair, HSGA
6,052. 98 Paved parking, HSG A
11,475 75 Weighted Average
5,423 47.26% Pervious Area
6,052 52.74% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) _(feet) _(ft/ft) _ (ft/sec) (cfs)
1.1 54 0.0075 0.85 Sheet Flow, Segment 1
Smooth surfaces n=0.011 P2= 3.43"
0.3 83 0.0100 4.50 1.57 Pipe Channel, Segment 2
8.0" Round Area= 0.3 sf Perim=2.1' r=0.17'
n= 0.010
1.4 137 Total, Increased to minimum Tc = 6.0 min
“Segnrert +. r
~Swnneubletehnant is: EXWEA

0.8 A
0.75 ype 11/24-
0.7: H UJ
0.65 fore °
0.6 uno rea F
os ngft Volume 2ip4t f
0.50.45 una p «NO}
0.3:0. . j
0.25 GN+75
0,
0.15
0.1
0.0:
Flow (cfs)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type Ill 24-hr 10-yr Rainfall=5.13"
Area (sf) CN Description
2,844 49 50-75% Grass cover, Fair, HSG A
770 77 ~~ Brush, Fair, HSG D
99 84 50-75% Grass cover, Fair, HSG D
36-98 ~— Paved parking, HSG D
3,749 56 Weighted Average
3,713 99.04% Pervious Area
36 0.96% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) _(ft/ft) _(ft/sec) (cfs)
6.4 68 0.0250 0.18 Sheet Flow, Segment 1
Grass: Short n=0.150 P2= 3.43"
——““Segetti=l..
—Suboatchmant 28: EWS
Subcatchment 2S: EXWS-B
Hydrograph
0.
0,095: Jane os |
al
0.09 tt
0.0850.08 AYA t
0.0750.07 RUN re
0.085 A - : = 47
= 0.06 =
0.055 Ru 4.44"
0.05 U
| Pee IF 6
0.00.09 ‘FetG.4 in
» LJ
0.025:
0.02
0,015
0.01
0.005
=
i.
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type Ill 24-hr 10-yr Rainfall=5.13"
Area (sf) CN Description
4,754 49 50-75% Grass cover, Fair, HSG A
3,923 84 50-75% Grass cover, Fair, HSG D
662 77 ~—~« Brush, Fair, HSG D
45,997 98 Paved parking, HSGA
55,336 93 Weighted Average
9,339 16.88% Pervious Area
45,997 83.12% Impervious Area
Te Length Slope Velocity Capacity Description
(min) _(feet) _(ft/ft)__ (ft/sec) (cfs)
1.6 150 0.0200 1.54 Sheet Flow, Segtment 1
Smooth surfaces n=0.011 P2= 3.43"
0.5 86 0.0200 2.87 Shallow Concentrated Flow, Segment 2
Paved Kv= 20.3 fps
0.1 12 0.0200 2.12 Shallow Concentrated Flow, Segment 3
Grassed Waterway Kv= 15.0 fps
2.2 248 Total, Increased to minimum Tc = 6.0 min
———Segtrentt..

5
")
Flow (cfs)
17>
0 2 4 6 6 10 12 14 16 18 20 22 24 26 28 30 32 34 36 368 40 42 44 46 48
Time (hours)

Primary 
 6.76 cfs @ 12.09 hrs, Volume
 22,737 cf, Atten  0%, Lag  0.0 min
Primary outflow = Inflow, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Link SITE: Total Site
Hydrograph
@ Inflow
i Prima
Flow (cfs)
10 12 14 16 18 20 22 24 26 28 30 32 4 36 38 40 42 44 46 48
Time (hours)

Flow Length=137' Tc=6.0 min CN=75 Runoff=1.04 cfs 3,277 cf
Subcatchment 28: EXWS-B Runoff Area=3,749 sf 0.96% Impervious Runoff Depth=1.70"
Flow Length=68’ Slope=0.0250 ') Tc=6.4 min CN=56 Runoff=0.15 cfs 530 cf
Subcatchment 3S: EXWS-C Runoff Area=55,336 sf 83.12% Impervious Runoff Depth=5.35"
Flow Length=248' Slope=0.0200 '* Tc=6.0 min CN=93 Runoff=7.22 cfs 24,673 cf
Link SITE: Total Site inflow=8.40 cfs 28,480 cf
Primary=8.40 cfs 28,480 cf
Total Runoff Area = 70,560 sf Runoff Volume = 28,480 cf Average Runoff Depth = 4.84"
26.18% Pervious = 18,475 sf 73.82% Impervious = 52,085 sf

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type Ill 24-hr 25-yr Rainfall=6.17"
Area (sf) CN Description
5,423 49 50-75% Grass cover, Fair, HSGA
6,052.98 Paved parking, HSGA
11,475 75 Weighted Average
§,423 47.26% Pervious Area
6,052 52.74% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) _(feet) (ft/ft} (ft/sec) (cfs)
1.1 54 0.0075 0.85 Sheet Flow, Segment 1
Smooth surfaces n= 0.011 P2= 3.43"
0.3 83 0.0100 4.50 1.57 Pipe Channel, Segment 2
8.0" Round Area= 0.3 sf Perim= 2.1' r=0.17'
n= 0.010
1.4 137 Total, Increased to minimum Tc = 6.0 min
~ Srureurbdeichmant 1S: EXWS:A

#4 ype |iil| 24-nr
5-yn Riainfall=6.1 7)"
Runoff Area=1/1,475 sf
_ Runoff/Volume=3,277 cf
3 Runoff Depth+3.43"
: Flaw |Length=137"
c+6,0 mi
N=7
60 2 4 6 B 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type (Il 24-hr 25-yr Rainfall=6.17"
Area (sf) CN Description
2,844 49 50-75% Grass cover, Fair, HSG A
770 77 Brush, Fair, HSG D
99 84 50-75% Grass cover, Fair, HSG D
36-98 ~—~ Paved parking, HSG D
3,749 56 Weighted Average
3,713 99,04% Pervious Area
36 0.96% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) _(feet) (ft/ft) _ (ft/sec) (cfs)
6.4 68 0.0250 0.18 Sheet Flow, Segment 1
Grass: Short n=0.150 P2= 3.43"
~—“Seyrient-t...
—Swosatchinant 2S: EXWS-B
Subcatchment 2S: EXWS-B
Hydrograph
0.170.15 y. va
0.140.13 Bory "
0.12 R
0.14
— 0.4 Fur ~~
8 o0 _Ruhaff Depth=1,70"
& 0.08 Fin, 0
TM 0.070.06 lope=0.0250 *
” 1A
0.04 ; .
0.03 U
0.0
0.01
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 3% 36 38 40 42 44 46 48
Time (hours)

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type Ill 24-hr 25-yr Rainfall=6.17"
Area (sf) CN Description
4,754 49 50-75% Grass cover, Fair, HSG A
3,923 84 50-75% Grass cover, Fair, HSG D
662 77 ~~ Brush, Fair, HSG D
45,997, 98 Paved parking, HSGA
55,336 93 Weighted Average
9,339 16.88% Pervious Area
45,997 83.12% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) _(feet) (ft/ft) _(ft/sec) (cfs)
1.6 150 0.0200 1.54 Sheet Flow, Segtment 1
Smooth surfaces n=0.011 P2= 3.43"
0.5 86 0.0200 2.87 Shallow Concentrated Flow, Segment 2
Paved Kv= 20.3 fps
0.1 12 0.0200 2.12 Shallow Concentrated Flow, Segment 3
Grassed Waterway Kv= 15.0 fps
2.2 248 Total, Increased to minimum Tc = 6.0 min
“=Segtrrentt.
==

Z22 os
7 Typ 24-
25- i Wd
Flow (cfs)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Primary outflow = Inflow, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Link SITE: Total Site
Hydrograph
B Inflow
9 ba0ds. @ Prima
a Inffo =/0,560 sf
Flow {cfs}
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 36 40 42 44 46 48
Time (hours)

f
pf
p
Flow Length=137' Tc=6.0 min CN=75 Runoff=1.46 cfs 4,640 cf
Subcatchment 2S: EXWS-B Runoff Area=3,749 sf 0.96% Impervious Runoff Depth=2.75"
Flow Length=68' Slope=0.0250 '/ Tc=6.4 min CN=56 Runoff=0.26 cfs 858 cf
Subcatchment 3S: EXWS-C Runoff Area=55,336 sf 83.12% Impervious Runoff Depth=6.95"
Flow Length=248' Slope=0.0200 ' Tc=6.0 min CN293 Runoff=9.24 cfs 32,069 cf
Link SITE: Total Site Inflow=10.96 cfs 37,567 of
Primary=10.96 cfs 37,567 cf
Total Runoff Area = 70,560 sf Runoff Volume = 37,567 cf Average Runoff Depth = 6.39"
26.18% Pervious = 18,475 sf 73.82% Impervious = 52,085 sf .

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type Ill 24-hr 100-yr Rainfall=7.79"
Area (sf) CN Description
5,423 49 50-75% Grass cover, Fair, HSGA
6,052 98 Paved parking, HSG A
11,475 75 Weighted Average
5,423 47.26% Pervious Area
6,052 52.74% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) _ (feet) (ft/ft) _ (ft/sec) (cfs)
1.1 54 0.0075 0.85 Sheet Flow, Segment 1
Smooth surfaces n=0.011 P2= 3.43"
0.3 83 0.0100 4.50 1.57 Pipe Channel, Segment 2
8.0" Round Area= 0.3 sf Perim=2.1' r= 0.17'
n= 0.010
1.4 137 Total, Increased to minimum Tc = 6.0 min
Segre. i
~Seonewbdetahsaant IS. EXWS-A

14
Flow (cfs)
me i |
at MN MPA rr sane am
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type tl! 24-hr 100-yr Rainfall=7.79"
Area (sf) CN Description
2,844 49 50-75% Grass cover, Fair, HSGA
770 #877 Brush, Fair, HSG D
99 84 50-75% Grass cover, Fair, HSG D
3698 ~——~ Paved parking, HSG D
3,749 56 Weighted Average
3,713 99.04% Pervious Area
36 0.96% Impervious Area
Te Length Slope Velocity Capacity Description
(min) _(feet) _(ft/ft) _ (ft/sec) (cfs)
6.4 68 0.0250 0.18 Sheet Flow, Segment 1
Grass: Short n=0.150 P2= 3.43"
g : EXWS-B
Subcatchment 2S: EXWS-B
0.28 7 aah {ai Runoff j
0.26 4 Wi24
0.24 4 . ’
0.22 tOGiyr : |
024 Runoff Area=3,749 sf |
0.18 Ruhoff Volum f
g 0.16 unatt ne
z 0.14 [ad | UJ
© 012 .s - .
0.1 wlope= °
0.08 Te in
0.06
0.04
0.02:
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Type II] 24-hr 100-yr Rainfall=7.79"
Area (sf) CN __ Description
4,754 49 50-75% Grass cover, Fair, HSG A
3,923 84 50-75% Grass cover, Fair, HSG D
662 77 _ Brush, Fair, HSG D
45,997 _ __98 Paved parking, HSG A
55,336 93 Weighted Average
9,339 16.88% Pervious Area
45,997 83.12% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) (feet) (ft/ft) _(ft/sec) (cfs)
1.6 150 0.0200 1.54 Sheet Flow, Segtment 1
Smooth surfaces n=0.011 P2= 3.43"
0.5 86 0.0200 2.87 Shallow Concentrated Flow, Segment 2
Paved Kv= 20.3 fps
0.1 12 0.0200 2.12 Shallow Concentrated Flow, Segment 3
Grassed Waterway Kv= 15.0 fps
2.2 248 Total, Increased to minimum Tc = 6.0 min
~—Segiment-d..

Type ill 24-hr
5 O0-yr Rai d
; Rut = II,
; Runoff! =
g R Depth+6/95"
Bs Flpw Length=248"
‘ lope=0.0.200 '/'
3 c=6/0 mi
J ¢C
,
o 2 4 6 & 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Primary = 10.96 cfs @ 12.09 hrs, Volume= 37,567 cf, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs
Link SITE: Total Site
Hydrograph
1B Inflow
. ior nflowAten=70,560.s aa
Flow (cfs)
0 2 4 6 8 10 12 146 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

APPENDIX B
Proposed Stormwater Discharge Calculations

liad PRWS-C2
PRWS-A PRWS-B C Total
Total Site
Reach Fon Routing Diagram for PR Hydro
Prepared by Langan Engineering, Printed 1/3/2025
HydroCAD® 10.20-6a s/n 08223 © 2024 HydroCAD Software Solutions LLC

0.652 39 >75% Grass cover, Good, HSG A {A, B, C1, C2)
0.206 80 »>75% Grass cover, Good, HSG D (B, G1, C2)
0.018 77 ~—«&Brush, Fair, HSG D (B)
0.013 73 ~~ Brush, Good, HSG D (C2)
0.114 98 Paved parking, HSG A (A, B)
0.617 98 Paved parking, HSG D (C1)
1.620 72, = TOTAL AREA

Flow Length=68' Slope=0.0440 7 Te=6.0 min CN=57 Runoff=0.09 cfs 0.012 af
Subcatchment B: PRWS-B Runoff Area=3,874 sf 3.02% Impervious Runoff Depth=0.33"
Flow Length=45' Slope=0.0389 '/ Tc=6.0 min CN=55 Runoff=0.01 cfs 0.002 af
Subcatchment C1: PRWS-C1 Runoff Area=45,321 sf 59.33% Impervious Runoff Depth=1.46"
Flow Length=205' Tc=6.8 min CN=78 Runoff=1.70 cfs 0.127 af
Subcatchment C2: PRWS-C2 Runoff Area=5,156 sf 0.00% Impervious Runoff Depth=1.21"
Flow Length=74' Slope=0.0610'/ Te=6.0 min CN=74 Runoff=0.16 cfs 0.012 af
Pond P-C: Pond C Peak Elev=32.09' Storage=2,079 cf Inflow=1.70 cfs 0.127 af
Discarded=0.09 cfs 0.102 af Primary=0.29 cfs 0.025 af Secondary=0.00 cfs 0.000 af Outflow=0.38 cfs 0.127 af
Link 2L: C Total 
Inflow=0,32 cfs 0.037 af
Primary=0.32 cfs 0.037 af
Link SITE: Total Site Inflow=0.38 cfs 0.052 af
Primary=0.38 cfs 0.052 af
Total Runoff Area = 1.620 ac Runoff Volume = 0.153 af Average Runoff Depth = 1,13"
§4.86% Pervious = 0.889 ac 45.14% Impervious = 0.731 ac

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.03 hrs
Type Il 24-hr 2-yr Rainfall=3.45"
Area (sf) CN Description
11,370 39 >75% Grass cover, Good, HSG A
4850 98 Paved parking, HSGA
16,220 57 Weighted Average
11,370 70.10% Pervious Area
4,850 29.90% Impervious Area
Tc Length Slope Velocity Capacity Description
(min) _(feet}) _(ft/ft) (ft/sec) (cfs)
5.1 68 0.0440 0.22 Sheet Fiow, Segment 1
Grass: Short_n= 0.150 P2= 3.43"
5.1 68 Total, Increased to minimum Tc = 6.0 min
ae a : PRWS-A
Subcatchment A: PRWS-A
Hydrograph oe ;
0.0950,09: ; :
0.085 L]
0.08 mn —
0.075 2ayt z
0.07 RY ;
0.0650.06 Ruhnaft =
Pp 0.0565:
: 0.06 RU :
0.04 :
& 0.04 7
0.035 lo!
0.03 ex 8
0.025 C70. !
0.02 g ‘
0.015
0.01
0.005
0 2 4 6 B 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Time (hours)

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.03 hrs
Type Ill 24-hr 2-yr Rainfall=3.45"
Area (sf) CN Description
2,337 39 >75% Grass cover, Good, HSG A
648 80 >75% Grass