20240477 Ver 1_ParkMercerWetland_BufferAuthorization_DiffuseFlow_20240325

Stormwater Engineering Group
Vinicius Taguchi, Ph.D.
1 Department of Biological and Agricultural Engineering
Stormwater Extension Associate
North Carolina State University
Campus Box 7625
https://stormwater.bae.ncsu.edu/
Raleigh, NC 27695-7625
EXTENSION
P: 919.345.0886
[e-mail]
Dear Reviewer,
I imagine this application is rather unconventional in that it is for a standalone stormwater control method
(SCM) designed as an offline, pump -fed constructed stormwater wetland that has no sizeable drainage area
and does not treat any new land development. Moreover, the majority of the stormwater wetland footprint is
outside of the Buffer Zone, and a small portion is located in Buffer Zone 2. No portion of the project
extends into Buffer Zone 1, nor does the project result in increased flow being routed onto or through
Buffer Zone 1. As such, it is my judgement that there is no additional diffuse flow to mitigate. Furthermore,
as this entire project is a standalone SCM, any diffuse flow flowing onto the project is already being treated
by such. This SCM will withdraw urban stormwater runoff from an adjacent non jurisdictional ditch for
which the requisite permissions have been obtained from the US Army Corps of Engineers and uploaded as
part of this application. Treated water will then flow via gravity to return to the very same non -
jurisdictional ditch. At no point are additional flows routed directly onto or through the Buffer Zone.
I hope that the below project narrative will give you a clear understanding of our project and the
construction that is to occur. We also uploaded a full set of design plans for the project. Unfortunately, the
link provided with instructions on what information to call out seems to be broken:
htt2://edocs.deg.nc.gov/WaterResources/0/doc/402224/Pagel.aspx. In the event that any information is
missing from what we submitted, or if at any point during your review of this application you have
questions or concerns, please do not hesitate to contact me using any of the contact information in the above
letterhead. I would be more than happy to walk you through what we have in mind and accept any
recommendations or feedback you have. I appreciate your time and attention during the review.
Kindest regards,
Vinicius Taguchi
Vinicius J. Taguchi, Ph.D.
Stormwater Extension Associate
11ni R

PROJECT NARRATIVE
NC State University's (hereafter referred to as University), College of Agricultural and Life
Sciences' (CALS), Department of Biological and Agricultural Engineering (BAE), in
partnership with the City of Wilson, NC, has hired an experienced, qualified contractor,
Dragonfly Pond Works, LLC (hereafter referred to as the contractor), to construct an offline
pump -fed flow -through stormwater wetland (hereafter referred to as wetland) on a City -owned
parcel located at 208 Banks St. SW in Wilson, NC 27893 (35.752972N 77.919611W) with
1.44 acres of disturbed area proposed. Disposal of excess sediment shall occur at 3649 Ward
Blvd, Wilson, NC 27893, which has an approved erosion control plan issued by the City of
Wilson, permitted for 1.5 acres of disturbed area for a project total of 2.95 acres disturbed area.
As an offline, standalone stormwater wetland, the site has no direct drainage area and all
stormwater inflows shall be drawn from the adjacent unnamed tributary (non jurisdictional).
According to the USDA Web Soil Survey, the site soil is of type Bibb loam, 0 to 2 percent
slopes, frequently flooded, hydrologic soil group A/D. The site is located within the Neuse
River basin.
The purpose of the proposed project is to treat stormwater runoff from the adjacent unnamed
tributary (non jurisdictional), as part of a watershed improvement project and for use in
research trials for the North Carolina Department of Environmental Quality (NC DEQ).
Protection of 6 on -site trees is a secondary objective of this project but not a requirement,
therefore minor grading may encroach on tree protection radii where necessary. Silt fencing
shall be implemented along extent of proposed land disturbance with the exception of land
disturbance within the unnamed tributary (non jurisdictional) along the southeast boundary of
the project site. Erosion and sediment loss in and along the unnamed tributary channel shall be
minimized according to the requirements of the provided US Army Corps of Engineers permit.
The wetland shall be constructed to occupy an area of approximately 46,500 square feet within
a total project site of approximately 63,900 square feet. The grading of the wetland shall
require approximately 1,400 cubic yards of excavation and approximately 260 cubic yards. of
on -site fill for a net volume of approximately 1,130 cu. yards. Coarse excavation shall be
completed by the contractor. Hauling of excess sediment shall be completed by the City of
Wilson. Final grading shall be the responsibility of the contractor. Absolutely no fill shall
occur within the FEMA 100-Year Floodplain; cut only. Absolutely no disturbance shall occur
within the Stream Buffer Zone 1 (extending 30 feet from top of bank) of Hominy Swamp
Creek, which runs along the southwest boundary of the project site. Specific design
specifications and construction guidance are provided in the attached drawing set.
Inlet and outlet infrastructure shall be fabricated to the specifications provided in the attached
drawing set and shall be composed of hydraulic cement and materials suitable for perpetual
inundation unless otherwise specified. The inlet shall draw water from the unnamed tributary
(non jurisdictional) from a point near the Eastern corner of the project site in coordination with
the pump vendor to accommodate the required pumps, pump housings, and intake stilling
wells with input from NC State. The outlet shall return water from the wetland to the unnamed
tributary (non jurisdictional) at a point near the Southern corner of the project site as indicated
in the attached drawing set. All inlet and outlet culvert outfalls shall be armored to prevent
erosion using suitable methods as provided in the attached drawing set.
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The contractor is responsible for full clean-up and proper offsite disposal of any construction
debris and residual material. All trash shall be cleaned up daily. While unforeseen, excess earth
shall be wasted and stabilized with seeding (temporary and permanent) and mulching within
the proposed disturbed area of the project site prior to demobilization and final acceptance by
the University. There shall be no stockpiling of soil onsite. Excavated soil shall be loaded
immediately onto trucks and hauled to the identified disposal site. No external topsoil is
anticipated to be brought in. If external topsoil is determined to be necessary for vegetation
establishment, it shall be applied immediately from trucks without stockpiling onsite.
As an offline, standalone stormwater wetland bounded by stream channels and roadways with
curbs and gutters, the site has no contributing drainage area beyond the footprint of the
excavated basin. Therefore, only occasional, small-scale dewatering is anticipated as every
reasonable effort shall be made to complete excavation and grading in as short a period as
possible to minimize exposure to rainfall. For reference, a one -inch rainfall event over the
46,500-ft2 basin footprint would generate 3,875 ft3 of stormwater, which would be slowly
dewatered through silt bags as needed. Dewatering shall also be undertaken using silt bags if at
any time the capacity of the excavated basin reaches 50%. Sediment shall be prevented from
being transported off site by stormwater runoff through the use of silt fences (see drawing set).
Only direct rainfall onto the excavated basin footprint is expected to accumulate. The
contractor is also responsible for the successful establishment of all planted vegetation. The
contractor shall replace any vegetation that is not alive and in good health one year after
planting.
The construction sequence shall be as follows:
1. Coordinate equipment/access/schedule with the University.
2. If necessary, arrange for and complete utility marking. Call NC 811.
3. Complete survey stakeout.
4. Install erosion control and tree protection measures.
5. Coarse excavation.
a. Excavated soil shall be loaded immediately onto trucks and hauled to the
identified disposal site. Sediment stockpiles are not allowed unless waiting on a
truck. Stockpiles shall not be allowed overnight.
6. Install inlet and outlet infrastructure.
7. Complete final grading.
8. Remove all trash and debris from the site.
9. Remove excess earth and stabilize disturbed non -wetland areas with seeding
(temporary and permanent) and mulching.
10. Coordinate installation of pump system.
11. Repair and or replace any damaged existing features and utilities.
12. Prepare wetland soil surface for planting.
13. Plant wetland areas as specified.
14. Coordinate activation of the pump system to ensure survival of plantings.
15. Demobilize from site after final acceptance of work by the University.
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Figure 1. View of project site (grassed City -owned parcel) facing North toward Mercer Street
and Banks Street.
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Figure 2. View of project site (grassed City -owned parcel) facing West away from Banks
Street with the unnamed tributary (non jurisdictional) visible.
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Figure 3. USGS quadrangle map of project site location (indicated by black dot).
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Figure 4. USGS quadrangle map of permitted sediment disposal location (indicated by black dot).
Figure 5. USDA Web Soil Survey map of site location (see uploaded soils report).
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