SW6130203_Stormwater Narrative_20240116

O'Reilly Area Auto Parts
Storm Water Management Statement
Harnett County, NC
Owner/Developer: Allied Development, Inc.
350 Wagoner Drive
Fayetteville, NC 28303
Consultant:
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HILLIARD - s Ei•
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ENGINEERING = 1,35: •
Contact: Jarrod E. Hilliard, PE, CFM a•F.�GINEF::•••
PO Box 249 Sanford, NC 27331 E. N
[phone]
NC License No. P-0836 Date: 5/15/23

A. Oreilly Auto Parts Area Infiltration Basin, Spout Springs, NC, Harnett County
B. Developer/Owner: Allied Development, Inc; Consultant: Hilliard Engineering, PLLC (contact
information on cover)
C. The existing project site currently has a Dollar Tree on it and the remaining portion of the
property is vacant
1. A vicinity map is included with this Statement
2. A USGS map is included with this Statement along with a Soil Survey for the project area
3. This project contains an existing infiltration basin which is planned to be replaced by the
proposed infiltration basin. Water from this project flows into Barbeque Creek. The
stream classification is as follows:
Stream Index: 18-20-13
Stream Name: Barbeque Creek
Classification: C
D. The site is not located within a conservation zoning nor a watershed district
E. Impervious Area Calculations:
Reference stormwater management permit application
F. The project site is subject to Phase II Post Construction Storm Water regulations.
1. The project is greater than 24% impervious area, therefore it is considered high density.
2. Off-site storm water is being diverted from the site via low-velocity swales.
3. Infiltration Basin:
Q10 pre: 8.46 cfs
Q10 post: 50.10 cfs
Q10 outflow: 4.00 cfs
Q25 pre: 9.40 cfs
Q25 post: 55.64 cfs
Q25 wet pond: 4.31 cfs

G. Downstream Analysis, if required:
1. See drainage map within the plan set for drainage areas
2. Significant increases in velocity and flooding are not anticipated from this project based
upon the use of the infiltration basin for mitigation, which is designed to contain the 25-
year storm.
3. A driveway culvert is not proposed for this project.
4. The total drainage area in which proposed impervious area exists for this project is 8.60
acres. The point where the development becomes less than 10% of the total watershed is
at the property line for the project.
5. If erosion control measures are maintained prior to permanent stabilization, and the
infiltration basin is properly constructed and maintained, no adverse impacts are
anticipated from this project.
6. Detention is proposed for this project in the form of an infiltration basin.