SW4190901_Narrative_9/30/2019

Project Description and Purpose
Existing Site
The O'Reilly Auto Parts site is part of larger development. The master development has two phases.
Phase 1 of the development was a Family Dollar commercial retail store at the northwest corner of
Welcome Arcadia Rd. and Old U.S. Hwy 52. The Family Dollar site consists of 1.33 acres. The Family
Dollar site was preceded by a vacant building, home and parking lot that totaled 0.52 acres of
impervious. The Family Dollar site is currently built with a total impervious area of 0.87 acres. The
Family Dollar site has an existing State Stormwater Permit. Their pond is located on Phase II of this
development which will become the O'Reilly Auto Parts Site.
Phase II of the project is the O'Reilly Auto Parts proposed store and parking lot. The existing site is
completely vacant except for the stormwater pond that is currently used by the Family Dollar. There is
no assumed existing impervious area for the O'Reilly Auto Parts site.
Developed Site
Phase 1 and Phase 2 of this project will now be joined for the stormwater design. Water Quality and
Detention is part of the new proposed design. The Family Dollar site drains onto the proposed O'Reilly
Auto Parts site via stormwater piping. The current impervious area for the Family Dollar site is 0.87
acres with a total site area of 1.33 acres.
The Phase 2 portion of the site is the proposed O'Reilly Auto Parts site. The total project area is 1.29
acres and a disturbed area of 1.25 acres. The proposed impervious area for Phase 2 is 0.62 acres. The
O'Reilly project is split into two drainage areas. The first is the parking lot east of the proposed building
and the second includes the building and western parking lot.
Both Phase 1 and Phase 2 will be treated via an underground sand filter and sedimentation basin.
Storms larger than the water quality volume will bypass the system and flow into the proposed
underground detention system. Both underground systems are manufactured products by StormTrap.
The design sheets for the underground system are located on the Civil design sheets.
All storm events up to the 100-year storm will be reduced to below existing conditions. A detention
outlet structure in the underground detention basin will control the storm events. The development will
discharge to northwest corner of the property which is similar to existing drainage patterns.
Water Quality Information
The total area for Phase 1 and Phase 2 of this project is 2.62 acres with a total impervious area of 1.48
acres. The required WQv for the 1-inch storm is 5,392 cu.ft. This was calculated used the Simple
Method which takes into account the entire area and the proposed impervious surface. A 25%
reduction is included per the NCDEQ design manual for sand filters resulting in a required WQv of 4,044
cu.ft.
The Water Quality volume shall be captured in the underground Sand and Sedimentation basin and
discharged into the underground detention system.