820125_Lagoon Closure Specifications_20240210

LAGOON CLOSURE SPECIFICATIONS
Circle L Nursery Facility #82-125
/ Site Location: Warren Mill Rd
Newton Grove, NC 28365
Sampson County
Prepared By
R. Gregory Swain, P.E.
305 Wendover Lane
Wilmington, NC 28411
[phone]
NC PE License No. 016415
February 12, 2024

1.0 INTRODUCTION
Circle L Nursery (Mr. Freddy Langston) Facility ID 82-125, is a former swine farm in Sampson County that
has had no animals populated for considerable time. The purpose of this report is to provide
specifications for closure of the current impoundment for the purposes of animal waste treatment and
storage. The owner wishes to convert the impoundment to fresh water storage.
The information regarding lagoon specifications and cleanout have been provided by Barwick Ag
Services (BAS), certified Technical Specialist.'Topographic information was gathered on 2/10/24 during
on -site review of conditions with BAS.
2.0 DESCRIPTION
The impoundment, or lagoon to be closed is formerly aprimary treatment/storage lagoon. See attached
aerial view. According to provided dimensions from certified lagoon design document provided, along
with aerial GIS data, surface area is approximately 28,800 sq. ft.
GENERAL CRITERIA
All processes and specifications unless otherwise noted shall conform to NRCS Conservation Practice
Standard Code 360 revised October 2023, "WASTE FACILITY CLOSURE". Specifically for the purposes of
this closure, note the following requirements:
1. No additional conveyance of waste into the structure is allowed.
2. Liquid and slurry wastes shall be agitated and pumped according to nutrient and hydraulic
allowable limits established by BAS utilizing the sludge application plan.
3. Agitated slurry must be removed to the maximum extent practicable, adding water as necessary
to facilitate. No more than 12" depth shall be left remaining in bottom.
NOTE: Based on site evaluation of the structure and water table, it is not recommended to
scrape sludge from sides or bottom. As shown on the attached design drawing, both seasonal
high water table (SHWT) and water level on site visit are considerably above lagoon bottom
elevation, limiting the use of earth -moving equipment.
4. Final sludge survey must be conducted and recorded by a technical specialist to document
acceptable removal.
5. Disturbed areas (primarily constructed overflow spillway area) shall be vegetated and mulched
to minimize erosion, and shall maintain permanent vegetation post -construction.
6. Once the impoundment is converted to a fresh -water pond, it must not be used for fish
production, swimming, or livestock watering until the water quality is adequate for these
purposes.

4.0 DESIGN CONSIDERATIONS
As noted, the structure is to be converted to afresh water pond. A new overflow spillway shall be
constructed along the south side near southwest corner of the lagoon. This location is adjacent to an
existing drainage outlet. The aerial view utilized was sourced from Sampson County GIS. Spillway
overflow was determined to be the most economical and maintenance -free means of impoundment
protection. The area chosen to excavate the spillway is based on limiting the slope and length of slope
for outflow to existing outlets.
As shown in the plan, depth of cut should be based on establishing a bottom elevation in the cut area of
approximately 2.0' below the top of existing berm elevation. This provides spillway depth of 12" below
the design 12" freeboard of the structure. As shown in cross-section detail, the spillway shall be cut to
approximately 15' width at bottom, and side slopes minimum 3:1 to reach existing top of berm.
Additional disturbance of existing berms shall be limited as much as possible.
All disturbed area as well as constructed spillway cut shall be immediately seeded and mulched to
establish permanent vegetation and minimize erosion. The back slope of berm shall be lined with riprap
to original undisturbed grade for all disturbed area, extending minimally 5' in each side beyond the
width of excavated spillway. Riprap shall serve as energy dissipation from fresh water outflow during
storms and further minimizing potential erosion.
Based on previously estimated surface area of the impoundment, and utilizing accepted 25 year-24 hour
storm events, estimated outflow estimates are as follows:
28,800 sq.ft. x 7.0" storm event=16,800 ft' in storm event =17.6 ft3/min outflow (assuming structure
was at full capacity at start of event). 17.6 ft3/min / 15 ft wide spillway / 0.2 ft flow depth = 5.9 ft/min =
0.1 ft/sec flow velocity. This flow is acceptable to minimize the potential for destructive velocities in the
outflow area with appreciable safety factor.

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R. GREGORY SWAIN, P.E.
305 Wendover Ln. Wilmington, NC 28411
910-590-5179
CIRCLE L NURSERY
LAGOON CLOSURE
DATE: 2/ 12/2024 SCALE: 1 " = 80'