Piedmont Natural Gas Sutton Steam Plan Road Stormwater 2.15.2021NARRATIVE > PNG-20000
2905 Meridian Parkway, Durham, NC 27713 / 919. 361. 5000 creating experiences through experience
Wilmington CNG Station – Sutton Steam Plant Road
Stormwater Narrative GENERAL DESCRIPTION
Wilmington CNG Station – Sutton Steam Plant Road, is a fueling station that sits on a 3 acre piece of property on Sutton
Steam Plant Road and US Highway 421 in Wilmington, NC. This analysis covers the development of the lot into a fueling
station consisting of a driveway and pad with fueling equipment. The purpose of this analysis is to ensure the
stormwater runoff will be adequately infiltrated into existing soils.
According to the New Hanover County Stormwater, Infiltration facilities should be designed for the runoff of a 25-year
storm event, and checked for the 100-year storm. CALCULATION METHODOLOGY
Used New Hanover County GIS topo to determine ultimate endpoint for runoff from the project site, at ultimate endpoints of runoff assume water to infiltrate the existing soils at adequate rate. Will get actual infiltration rate of offsite soils for next submittal.
On-site and off-site soils were determined using the best available GIS data sources
Rainfall data for this area in the Wilmington, NC region is from NOAA Atlas 14. This data contains a depth-
duration-frequency (DDF) table describing rainfall depth versus time for varying return periods in the area.
These rainfall depths are input into the meteorological model within PondPack for peak flow rate calculations.
Please reference the precipitation information within the Miscellaneous Site Information section of this report
for additional information.
Soil Conservation Service Curve Numbers (SCS CN) were selected from Table 2 of the USDA TR-55 for the land use that is most similar to the zoning type or cover condition.
DISCUSSION OF RESULTS
PEAK RUNOFF CONTROL REQUIREMENTS
Shown below is a topo map taken from New Hanover County GIS, the two areas circled in blue are the ultimate
endpoints of the runoff from the site. These areas both contain Kureb sand, which is a “Group A” Soil as obtained
from Web Soil Survey USDA tool.
NARRATIVE > PNG-20000
creating experiences through experience 2 of 3
POLLUTANT AND NUTRIENT CONTROL REQUIREMENTS
CONCLUSION
If the development on this tract is built as proposed within this report, then the requirements set forth in New Hanover
County regulations will be met without additional stormwater management facilities. However, modifications to the
proposed development may require that this analysis be revised. Some modifications that would require this analysis
to be revised include:
1. The proposed site impervious surface exceeds the amount accounted for in this report.
2. The post-development watershed breaks change significantly from those used to prepare this report.
The above modifications may result in the assumptions within this report becoming invalid. The computations within
this report will need to be revisited if any of the above conditions become apparent as development of the proposed
site moves forward.
GRAPHIC SCALE
0 10 20 40
1 inch = 20 ft.
PROJECT AREA = 3.00 ACRES
IMPERVIOUS AREA = 0.00 ACRES
PERCENT IMPERVIOUS = 0%
The John R. McAdams Company, Inc.
2905 Meridian Parkway
Durham, NC 27713
phone 919. 361. 5000
fax 919. 361. 2269
license number: C-0293, C-187
www.mcadamsco.com
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PIEDMONT NATURAL GAS
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GRAPHIC SCALE
0 10 20 40
1 inch = 20 ft.
PROJECT AREA = 3.00 ACRES
IMPERVIOUS AREA = 0.70 ACRES
PERCENT IMPERVIOUS = 23%
The John R. McAdams Company, Inc.
2905 Meridian Parkway
Durham, NC 27713
phone 919. 361. 5000
fax 919. 361. 2269
license number: C-0293, C-187
www.mcadamsco.com
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PIEDMONT NATURAL GAS
Subsection: Master Network Summary
Catchments Summary
Peak Flow
(ft³/s)
Time to Peak
(min)
Hydrograph
Volume
(ac-ft)
Return
Event
(years)
ScenarioLabel
0.44753.0000.10125Pre-Development 25-
yr
Sub 2
1.81729.0000.295100Pre-Development 100
-yr
Sub 2
0.35753.0000.07625Pre-Development 25-yrSub 1
1.37729.0000.211100Pre-Development 100
-yr
Sub 1
Node Summary
Peak Flow
(ft³/s)
Time to Peak
(min)
Hydrograph
Volume
(ac-ft)
Return
Event
(years)
ScenarioLabel
0.44753.0000.10125Pre-Development 25-
yr
O-1
1.81729.0000.295100Pre-Development 100
-yr
O-1
0.35753.0000.07625Pre-Development 25-
yr
O-2
1.37729.0000.211100Pre-Development 100-yrO-2
Page 1 of 127 Siemon Company Drive Suite 200 W
Watertown, CT 06795 USA +1-203-755-1666
2/15/2021
PondPack CONNECT Edition
[10.02.00.01]
Bentley Systems, Inc. Haestad Methods Solution
CenterPNG-20000.ppc
Subsection: Master Network Summary
Catchments Summary
Peak Flow
(ft³/s)
Time to Peak
(min)
Hydrograph
Volume
(ac-ft)
Return
Event
(years)
ScenarioLabel
2.56726.0000.23825Post-Development 25
-yr
Sub 2
4.24726.0000.439100Post-Development
100-yr
Sub 2
4.87726.0000.44925Post-Development 25-yrSub 1
8.45726.0000.857100Post-Development
100-yr
Sub 1
Node Summary
Peak Flow
(ft³/s)
Time to Peak
(min)
Hydrograph
Volume
(ac-ft)
Return
Event
(years)
ScenarioLabel
2.56726.0000.23825Post-Development 25
-yr
O-1
4.24726.0000.439100Post-Development
100-yr
O-1
4.87726.0000.44925Post-Development 25
-yr
O-2
8.45726.0000.857100Post-Development 100-yrO-2
Page 1 of 127 Siemon Company Drive Suite 200 W
Watertown, CT 06795 USA +1-203-755-1666
2/15/2021
PondPack CONNECT Edition
[10.02.00.01]
Bentley Systems, Inc. Haestad Methods Solution
CenterPNG-20000.ppc