SW6221006_Design Calculations_20230531

Stormwater Narrative and Calculations for the
NCDEMLR Post Construction Stormwater Management
Permit
for the
+/- 20,000-SF Distribution Facility Expansion for
CCBCC -Fayetteville
in
Cumberland County, North Carolina
Prepared For:
CCBCC Operations, LLC
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CONSOLIDATED
Prepared By:
Fitts and Goodwin, Inc.
120 Corporate Blvd.
West Columbia, SC 29169
NC License 051479
Initial Submittal: 09/09/2022
Resubmittal: 02/14/2023
Resubmittal: 05/25/2023
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Narrative
These calculations have been prepared to address NCDEMLR's post -construction
stormwater management requirements for the +/- 20,000-SF Distribution Facility
Expansion for CCBCC-Fayetteville. The site is located at 800 Tom Starling Rd.
Fayetteville, NC (34°57'8.21 "N, 78°53'37.76"W) which is an unincorporated area of
Cumberland County.
The current site totals +/- 13.7-acres and includes +/- 6.75-acres of existing built -upon
area (BUA). The existing BUA consists of a +/- 45,000-sf warehouse and a +/- 6,500-sf
maintenance facility with the remainder being parking and truck court space.
Stormwater runoff from this existing BUA is conveyed through a pipe network to an
existing wet detention pond located in the northwest quadrant of the site. The remaining
areas of the site are grassed, landscaped, and wooded and runoff from these areas
bypasses the existing detention pond.
The proposed development of the site will include a +/- 20,000-sf expansion to the
existing warehouse and expansion of the existing truck court which will result in a net
increase of +/- 0.73-ac of impervious area. The total proposed drainage area will be +/-
8.07-ac consisting of +/- 6.75-ac of existing BUA, +/- 0.73-ac of new BUA, and +/- 0.59-
ac of grassed area. The proposed drainage pattern will remain consistent with the
existing pattern and runoff from the new impervious area will be conveyed to the
existing wet detention pond through the existing pipe network. To meet water quality
requirements, two (2) Filterra units will be installed adjacent to the +/-1.04-ac existing
employee parking lot off of Tom Starling Rd. The units will treat +/- 0.49-ac of existing
BUA each, totaling +/- 0.98-ac of existing BUA, which exceeds the area of new BUA.
The USGS Soil Survey indicates the site consists of Torhunta (HSG A/D) and Kalmia
(HSG B) soils. FEMA Flood Panel 3720043300J indicates the site is located in Zone X —
Area of Minimal Flood Hazard.
CCBCC Fayetteville 2 September 2022 r ti-U ff„ 2 May2023

Drainage Area and Runoff Calculations
CCBCC Fayetteville 15 SepteFnber 2022 r br-UGry 2 May2023

Drainage Area and Runoff Calculations
for
+/-20,000-SF Distribution Facility Expansion for CCBCC-Fayetteville
Drainage Area: Drainage Area to Filterra Unit 1
Runoff Calculation Method: Discrete
Drainage Area Characteristics:
CN
Total Drainage Area =
0.52
ac
Directly Connected Impervious Area =
0.49
ac
98
Other Area =
0.03
ac
61
Design Storm Depth =
1.0
in
Drainage Area: Drainage Area to Filterra Unit 2
Runoff Calculation Method: Discrete
Drainage Area Characteristics:
CN
Total Drainage Area =
0.52
ac
Directly Connected Impervious Area =
0.49
ac
98
Other Area =
0.03
ac
61
Design Storm Depth =
1.0
in
NRCS Curve Number Method for Runoff Volume:
5 =
1000 - 10
CN
Where:
S =
Maximum retention after rainfall begins (in)
CN =
Curve number (unitiess)
Q*
(P + 0 8s)
Where:
Q' =
Runoff depth (in)
P -
Rainfall depth (in)
Drainage Area 1
CN =
S =
P=
Q* =
DA 1 Total Q* (ft3) =
Directly
Connected Imp.
Area
Other Area
98.0
61
0.20
0
1
0
0.7909
0
1407
Drainage Area
CN =
S =
P=
Q* =
DA 2 Total Q* (ft3) =
2
Directly
Connected Imp.
Area
Other Area
98.0
61
0.20
0
1
0
0.7909
0
1407
Minimum Treatment Volume Required = 2,814 cu ft
Minimum Treatment Volume Provided = (See Contech-Filterra Calculations Attached)
Project No.: 22000-0600
Date: September 2022 Revised May 2023