SW8030720_Stormwater Narrative_20210825

P1312 MARINE CORPS ENGINEERING SCHOOL
HORN ROAD, COURTHOUSE BAY,
MARINE CORPS BASE CAMP LEJEUNE, NC
STORMWATER NARRATIVE
The P1312 Marine Corps Engineering School (MCES) project site is located on the east side of
Horn Road in the Courthouse Bay region of Marine Corps Base Camp Lejeune (MCBCQ, in
Onslow County North Carolina. Latitude and Longitude are 34.581085N, -77.363062W
respectively. The project site is the former location of a water treatment plant that has since been
demolished. The site is undeveloped and includes a gravel access road from Horn Road to the
Marine Mini Mart (MCX). There is an active State Stormwater Permit (SW8 030720) for this site
that includes the Courthouse Bay Regional Pond.
This project will construct a new two-story MCES Applied Instruction Facility that will include
outdoor covered classrooms/lab space, hazardous material storage building, covered lumber
storage, and a 3,000-gallon JP-8 aboveground fuel storage tank.
Site improvements will consist of grading, surface parking for 125 vehicles, bus drop-off lane
along Horn Road, roadways, curbs, sidewalks, landscaping, fencing, and pedestrian and bicycling
features.
The project site is located within the White Oak River basin. Based on available information,
stormwater runoff from this site drains to the Courthouse Bay Regional Pond. According to the
design branch of the Base Public Works Department, the pond outfall is likely captured along
Munro Road and discharges into New River. This portion of the New River (New River Restricted
Areas #2, Stream Index 19-37) has been classified by the State as SC waters.
The site is generally flat with elevations ranging from 9' to 14' per the vertical NAVD 1988 datum.
The project site is located within the 100-year flood per Flood Insurance Rate Maps (FIRM)
3720438000K effective 6/19/2020. Base flood elevation (BFE) is 10.0. In accordance with UFC
3-201-01, Change 3, the MCES is considered a critical structure, and therefore, the proposed
building's finished floor elevation has been set at elevation 13.00, 3 feet higher than the BFE.
There are no wetlands within the proposed project limits. The site is located within an existing
developed urban area in the Courthouse Bay region of MCB Camp Lejeune.
The US Department of Agriculture (USDA) Natural Resource Conservation Services soil mapping
indicates that the site consists of Wando fine sand and Urban land. Depth to seasonal high-water
table is generally 2 to 4 feet below ground surface. Based on the results of the geotechnical

investigation performed in January 2021, the depth to shallow groundwater table at the MCES
project site is approximately 2.9 to 7.4 feet below land surface (BLS). The seasonal high water
table ranges from 26 inches to 72 inches BLS.
The existing Courthouse Bay Regional Stormwater Pond was constructed for the original dining
hall. The pond was permitted in 2007 for 34.6% BUA (SW8 030720) and revised July 27, 2010
with a potential build out condition that is not proposed with this project. According to a
modification to the permit in July 2020, the future BUA allowance under the existing permit with
no build out of the pond is 190,962 sf. Maximum BUA threshold for the current pond (without build
out) is 43.6% or 960,509 sf of impervious area.
A modification to the existing State Stormwater Permit SW8 030720 is requested for this project.
67,382 sf of impervious areas within the drainage area of the permit will be removed. Proposed
impervious consists of 59,707 sf of buildings, 78,572 sf of parking, 19,055 sf of sidewalks, and
2,816 sf of asphalt pavement for the bus drop-off along Horn Road. Again, no build out of the
existing pond is requested. The project will remove 67,382 sf of existing permitted impervious
area and add 160,150 sf of new buildings, parking, and sidewalks for a total of 92,768 sf of new
impervious. Therefore, this modification will reduce the future impervious from 190,962 sf to
98,194 sf, while staying below the 43.6% maximum BUA for the permit.