SW4210701_O&M Agreement/Plan_20211008 (2)

G PT S ROYAL DESIGN GROUp
i'r €LE UIU I 0 S-11 ` i ININ STOR_1 VAVEll l'
PO BOX 1070,1UNG, NC 27021
Office Phone (336) 985 — 6519
Secondary Phone (336) 705 - 0633
WET DETENTION POND
OPERATION & MAINTENANCE PLAN
King's Crossing, King, N.C.
I. GENERAL INFORMATION and PURPOSE:
Wet detention ponds or basins have a permanent pool of standing water maintained by the
elevated outlet of the riser structure. Water in this permanent pool mixes with and dilutes the
initial runoff from rain storms. Wet detention ponds/basins fill with stormwater runoff from the
site and release most of the mixed and diluted water over a period of days slowly returning to the
pre -storm normal depth. Runoff generated during the first phases of a storm event usually
contains the highest amounts of sediment and pollutants. Since a wet detention pond/basin
mixes, dilutes, and settles pollutants in the initial runoff, the concentration of pollutants and
sediment in the runoff released downstream is reduced. Plants, algae, and bacteria in the water
consume some of the pollutants but require some maintenance and the periodic removal of
sediment.
This Operation & Maintenance Plan includes the inspection and maintenance provisions required
to ensure the proper functioning of the Wet Detention Pond/Basin. This document refers to
specific maintenance procedures and tasks that are common to wet detention pond/basins.
IL MAINTENANCE PROCEDURES:
lmmediately after the wet detention basin is established, the plants on the vegetated shelf and
perimeter of the basin should be watered twice a week, if needed, until the plants become
established (usually about six weeks).
No portion of the wet detention pond should be fertilized after the first initial fertilization that is
required to establish the plants on the vegetated shelf.
Stable groundcover should be maintained in the drainage area to reduce the sediment load to the
wet detention basin.
If the basin must be drained for an emergency or to perform maintenance, the flushing of
sediment through the emergency drain should be minimized to the maximum extent possible.
On— a year, a dam 3af"y expen should inspect the el7lbanKmellt.
1of10

After the wet detention pond is established, it should be inspected once a month and within 24
hours after every storm event greater than 1.0 inches. Records of inspection and maintenance
should be kept by the owner(s) and should be available upon request.
III. DAM SAFETY;
There are about five major problems concerning dam safety that require diligent and specific
attention: (1) the materials used to construct the dam; (2) water seepage and leakage; (3) tree and
vegetation growth on the dam embankments; (4) varmint and animal burrows in the
embankments; and (5) downstream hazard potential changes due to development.
Dam Material Problems
For earthen dams, pronounced cracks on the embankment surface indicate the first stages of
potential dam failure. Transverse cracks (running perpendicular to the embankment face)
generally indicating differential settlement of the dam, can provide pathways for excessive
seepage. Longitudinal cracks (running parallel to the embankment face) may be due to
inadequate compaction of the dam during construction or shrinkage of the clay (desiccation) in
the top of the embankment during prolonged dry conditions. These cracks may eventually lead to
slope failure, such as sliding or sloughing. For reinforced concrete dams, the concrete should be
checked for pronounced cracking, leakage from the joints, and displacement (noticeable leaning
or bulging). Also, excessive seepage, leakage, or springs just downstream of the concrete dam
could be indicative of potential seepage -related "piping" problems under the dam. If such
problems or other structural problems are observed, professional engineering advice should be
sought.
Seepage and Leakage
The downstream side of the dam should be inspected regularly for evidence of significant
seepage and leakage. Seepage can emerge anywhere below the normal pool elevation, including
the downstream slope of earth dams, areas beyond the toe of the dam, and around the spillway or
pond outlet conduit. Indications of significant seepage include areas where the soil is saturated or
where there is a flowing "spring" or leak. If "sinkholes" in the dam embankment are noticed, or
if constant flowing water is noticed on the downstream side of the dam, then seepage has become
excessive and professional engineering advice should be sought immediately to avert a major
structural problem or a catastrophic failure of the dam.
Tree and Vegetative Growth
Trees and other woody vegetation are not permitted on the top, slopes, or embankments of
earthen dams. Large root systems from woody vegetation can weaken the dam structure and
provide seepage pathways. Mowing of the dam embankments should occur, at a minimum, once
every 6 months to prevent woody vegetation from becoming established or a maximum grass
height of 6 inches.
Varmint and Animal Burrows
Thick vegetative cover can also provide a haven for burrowing animals such as groundhogs and
muskrats. These animals can create a network of burrows in the dam embankments that can
significantly weaken the dam, by creating seepage paths, which may eventually lead to dam
failure.
Downstream Hazard Potentials
2of10

Before any dam is constructed, the design engineer is responsible for notifying the NC State
Dam Safety Office of the proposed dam. If the dam falls under State Dam Safety jurisdiction, the
dam must be constructed, maintained, and operated according to departments design and
construction guidelines. Even if the dam does not fall under the NC Dam Safety Office's
jurisdiction, the dam should be designed and constructed in accordance with current proper
engineering practices. As new development occurs downstream of the pond, the chance of
significant property damage or danger to human life may increase if catastrophic failure of the
dam occurs. Although the dam may be initially exempt from regulation by the State, the owner is
responsible for reporting to the State Dam Safety Office any downstream development that may
affect the hazard classification of the dam.
IV. SITE POLLUTION PREVENTION:
Every effort should be made to reduce the pollutant load entering the pond system.
Fertilizers and pesticides should be used conservatively on the site grounds. Excessive amounts
of these chemicals can be washed away with stormwater runoff, increasing the nutrient load to
the pond.
Outside trash dumpsters should be kept covered, and the area around the dumpsters should be
kept neat and clean.
Chemicals, petroleum products, and other pollution sources (such as machinery) should be stored
in a covered area away from possible stormwater contact. Spent chemicals are to be properly
disposed or recycled.
Chemicals such as copper sulfate used to inhibit algal growth in the pond degrade water quality
and should not be used. Rather, reducing the amount of fertilizer applications and ensuring that
the pond outlets are properly functioning so the pool is flushed periodically will help to deter
algal growth.
Trash and vegetative floating debris (grass clippings, leaves, limbs, etc.) should be cleaned from
the pond surface and surrounding banks periodically to promote a healthy, aesthetically pleasing
environment, and to prevent blockage of the pond outlets. Studies have shown that people are
less likely to litter ponds that are aesthetically pleasing and support wildlife.
V. STABILIZATION of WET DETENTION POND DRAINAGE AREA:
The area draining to the wet detention pond should be stabilized to prevent excessive sediment
from entering the pond. When bare soil is directly exposed to rain, the sediment contained in the
runoff is much higher than for soil that is covered and stabilized. A stabilized area is covered by
impervious surfaces (pavement, buildings), grass cover, landscaping (mulch, pine straw), etc. It
is in the best interest of the pond owner to reduce onsite sediment into the pond, as this will
reduce the life span of the pond and result in the need for more frequent and expensive dredging.
If pond embankments are not kept well vegetated with grasses, erosion may occur. Erosion can
be repaired by filling the small channels and gullies with suitable soil, compacting, and seeding.
It may be necessary to install temporary erosion control devices along heavily eroded areas to
allow the repaired areas to stabilize. It is especially important to inspect for and immediately
repair any erosion on the dam embankments.
3 of 10

VI. PIPE INLETS and OUTLETS:
Where erosion causes the undercutting of the downstream end of pipe, the undercut should be
stabilized immediately to prevent the end pipe section from "breaking" off. Eroded areas should
be filled with good compactable soil and covered with geotextile fabric and rip -rap.
Wet detention ponds are designed for the water to exit the pond through the low flow orifice(s),
the principal spillway, and the emergency spillway. It is important to check all three outlets for
blockage that would impede the pond's hydraulic functions and water quality.
Low Flow Orifice(s)
Unless an inverted orifice is used, some type of trash guard is to be maintained over the low flow
orifice(s) to prevent clogging. When the orifice becomes clogged the water level rises to the
principal spillway elevation and the benefits associated with temporary storage and its gradual
release are lost. To preserve "extended detention" the low flow orifice should be inspected for
blockage monthly, and within 24 hours after every storm event greater than 1.0 inches.
Principal and Emergency Spillway
Principal and emergency spillways are designed to safely convey greater than one -inch rainfall
events, and those larger storms that produce runoff which exceed the water quality volume of the
wet detention pond. If these spillways are blocked so they do not operate at full capacity, the risk
of dam overtopping or other uncontrolled releases may result. To ensure the hydraulic capacity
of the spillways, the spillways should be inspected for blockage monthly, and within. 24 hours
after every storm event greater than 1.0 inches. If a riseribarrel is used for the principal spillway,
a trash rack is to be maintained on the riser. Vegetative growth in the riser should be removed
promptly so that the design capacity of the spillway is maintained. The emergency spillway and
outlet area where the barrel projects from the fill slope should be clear of woody vegetation, tree
limbs, sediment accumulation, etc.
VII. SEDIMENT ACCUMULATION:
To preserve the wet detention pond's pollutant removal capability, sediment must be removed in
areas where the capacity of the design sediment storage volume has been exceeded. The pond
forebay helps to improve the removal efficiency of the pond system by trapping the majority of
coarser suspended solids behind a rock baffle. When sediment deposits in the forebay exceed the
designed sediment storage capacity for the forebay, the forebay must be dredged. Typically,
forebays will need to be dredged every 5 to 10 years. Depth measurements relative to the normal
surface elevation (bottom of water quality orifice) should be taken at several locations around the
pond. The sediment is to be removed when the measured depth is less than the design permanent
water depth. Most wet detention ponds are designed for three to four foot permanent water
depths. As sediment accumulates in the pond, the permanent water depth is reduced along with
the pond's ability to treat pollutants in the runoff. If a forebay is used at the inlet area of the pond
and m regularly dredged, the frequency of dredging the entire pond could be greatly reduced.
Check water depth at various points in the pond semi-annually. If depth is reduced to 75 % of
the original design depth, sediment must be removed to at least the original design depth.
4of10

Sediment from most sources is usually not hazardous or contaminated; however, it is very
"soupy" and is difficult to manage. It is a good idea to provide a storage area near the wet
detention pond to place sediment once it is dredged to allow it to dry. If desired and approved by
the local authority, sediment may be land applied and seeded, while following all pertinent soil
and erosion control regulations. If land applied on -site, it should be within the drainage area to
the pond so sediment that runs off can be recaptured.
VIR WET DETENTION POND MAINTENANCE PROCEDURES:
Routine Maintenance
Routine maintenance shall include minor upkeep such as the following: mowing, trash and debris
removal, minor slope repair and stabilization, periodic structural inspections of the valves, gates,
dam, etc., and tree and brush removal from the dam, spillway, inlet(s), and outlet. These
maintenance items may be performed by the owner without review of a Professional Engineer.
Non -Routine Maintenance
Non -routine maintenance shall include such items as the following: sediment clean -out
(dredging), channel stabilization, and problems regarding the principal spillway conduits,
emergency spillway, dam failure, and seepage. These items require a Licensed Professional
Engineer to prepare a plan and/or details and to certify completion of the maintenance. All
revisions and repairs to permanent runoff control structures shall be done in accordance with
Division of Water Resources guidelines and specifications, and in all cases meet or exceed the
original design specifications.
IX. MAINTENANCE SCHEDULE GUIDELINES:
I. Monthly, and within 24 hours after every storm event greater than 1.0 inches.
A. Remove trash and debris from the trash rack.
B. Check and clear the orifice of any obstructions.
C. Check the pond side slopes for erosion and remove trash from around the pond.
D. Inspect principal and emergency spillways for blockage.
2. Quarterly — Four Times a Year.
A. Inspect the collection system (e.g. catch basins, piping, grassed swales) for proper
functioning. If erosion is occurring in the swale, re -grade the swale if necessary to
smooth it over and provide erosion control devices such as reinforced turf matting or
riprap to avoid future problems with erosion. Clear accumulated trash from basin
grates and basin bottoms, and check piping for obstructions or damages.
B. Check pond inlet pipes for undercutting, replace rip -rap that is choked with sediment,
and repair broken pipes.
C. Check the operation of the gate valve. All valves should be operated from the fully
closed to the fully open position.
D. Remove woody vegetation, trees and brush, from dam embankment surfaces and
spillway(s). Consult a dam safety specialist to remove the trees if those can weaken
the dam structure. Also, in the vegetated shelf remove the weeds, preferably by hand.
If pesticide is used, wipe it on the plants rather than spraying.
3. Semi -Annually — Twice a Year.
5of10

A. Remove accumulated sediment from the bottom of the outlet structure.
B. Check for presence of rip -rap at inlet pipes and replace if necessary.
C. Grassed swales and vegetated filters, if applicable, will be reseeded twice a year as
necessary.
D. Check riser and barrel for improper alignment, elongation and displacement of joints,
cracks, leaks, loss of protective coating, corrosion, and blockage. Repair as necessary.
4. Annually — Once a Year
A. Once a year, a dam safety expert will inspect the embankment. If the inspection shows
that the embankment needs repair, make all needed repairs.
B. Check pond depth at various points in the pond. If mean depth is reduced to 75 % of
the original design depth, sediment will be removed to at least the original design
depth and will be disposed in a location where it will not cause impacts to streams or
the BMP.
5. General
A. Mow side slopes according to the season. Grass height should be six (6) inches.
B. Riparian and aquatic vegetation are encouraged along the perimeter of the pond at the
water's edge. However, the dam, emergency spillway, inlet(s), and water control
structure should be kept clear of all woody vegetation. If Cattails, phragmites or other
invasive plants cover 50% of the basin surface, remove the plants by wiping them with
pesticide (do not spray).
C. If algal growth in the main treatment area covers over 50% of the area, consult a
professional to remove and control the algal growth.
D. If evidence of muskrat or beaver activity is observed, use traps to remove muskrats
and consult a professional to remove beavers.
E. Excessive plant growth or dead, diseased and dying plants, odors, discoloration,
perceived animal pests, etc. should be addressed with the Stormwater Administrator
on an as -needed basis. Solutions to these problems should be non -chemical and
deemed safe to our drinking water supply.
F. Best professional practices show that pruning is needed to maintain optimal plant
health. Prune according to best professional practices.
G. If areas of bare soil and/or erosive gullies have formed in the perimeter of the wet
detention basin, re -grade the soil if necessary to remove the gully, and then plant a
ground cover and water until it is established. Use erosion control matting if necessary
and provide lime and a one-time fertilizer application.
H. In case the ownership of the pond should change, the current owner should, within
thirty (30) days of transfer of ownership, notify the Division of Water Resources
officer, of the ownership transfer.
6of10

This Wet Detention Pond Operation and Maintenance Plan for King's Crossing is hereby
approved and accepted by Kin 's Cross Properties, LLC.
Any and all amendments to this Operation and Maintenance Plan shall first be submitted to and
approved by the North Carolina Department of Environmental Quality, Division of Water
Resources officer.
Samuel G. Hooker
Type or print name
i1
Signature
Memember/Manager
Title or Authority
Date
1,a Notary Public of the County of
State of North Carolina, hereby certify that M m L Gam'.
appeared personally before me this day and being duly sworn acknowledged that the above form
was executed by him.
Witness my hand and notarial seal, this day of _ oO5 ,20
MARSHAL DEE EDDLEMAN
Notary Public, North Carolina
Yadkin County
MY Commission Expires
June 21qwm�, 2023 Notary
Seal
My commission expires
7of10

WET POND INSPECTION CHECKLIST
Date: Monthly Quarterly Semi-annually Annually
Time:
Project Name: Wet Detention Pond #
BMP Owner:
SPILLWAYS — DRAINS — OUTLETS
Inspected By:
Check/Circle Condition Noted
Observations
Action —
Repair
Action —
Monitor
Action --
Investigative
Principal Spillway
Type:
Trash Racks/Debris/
Rust/Deterioration
Cracks/Deterioration
Joint Deterioration
Improper Alignment
Cracks/Deterioration
Seepage/Piping
Undercutting
Erosion
Debris
Pond Drain/Other Outlets
Type:
Gates/Valves
Operability
Rip Rap
General Comments, Sketches & Field Measurements
8of10

Date:
Time:
Project Name:
BMP Owner:
WET POND INSPECTION CHECKLIST
Monthly Quarterly Semi-annually Annually
EMBANKMENT — POOL
Wet Detention Pond #
Inspected By:
Check/Circle Condition Noted
Observations
Action —
Repair
Action —
Monitor
Action --
Investigative
U/S Sloe
..-Type:
Vegetation/Riprap
Beaching/Slides/Cracks
Undermining/erosion
Rodent burrows
Crest
Type:
Ruts/Erosion
Cracks/Settlement
Poor Alignment
D/S Sloe
Type:
Vegetation/Erosion
Rodent burrows
Sloughs/Slides/Cracks
Seepage/Wetness
Pool
Type:
Erosion
Sedimentation
Water Quality
Aquatic Plants
Mosquito Controls
Abutment
Type:
Vegetation/erosion
Slough/Slides/Cracks
Seepage/Wetness
General Comments, Sketches & Field Measurements
9of10

WET POND INSPECTION CHECKLIST
Date: Monthly Quarterly
Time:
Project Name:
BMP Owner:
Semi-annually Annually
ANNUAL BUDGET AND REPLACEMENT FUND
Wet Detention Pond #
Inspected By:
Item
Yearly Cost
Budget
Actual
Mowing
1,800
Seeding
100
Fertilizer/Lime
150
Embankment Repair
150
Trash Removal
1,300
Sediment Removal
100
Outlet Structure Maintenance (includes Rip
Ply)
200
Pest Control
100
Deposit in Capital Reserve Fund
200
Inspector Fee
8Q0
Total Annual Budget
$ 4,900
Date:
M.
Report Prepared By:
Balance in Capital Reserve Fund:
Deposit in Capital Reserve Fund
10 of 10