Current through Register Vol. 41, No. 3, September 23, 2024
An erosion and sediment control plan consistent with the
following criteria, techniques, and methods shall be submitted to the VESMP
authority or VESCP authority for review and approval:
1. Permanent or temporary soil stabilization
shall be applied to denuded areas within seven days after final grade is
reached on any portion of the site. Temporary soil stabilization shall be
applied within seven days to denuded areas that may not be at final grade but
will remain dormant for longer than 14 days. Permanent stabilization shall be
applied to areas that are to be left dormant for more than one year.
2. During construction of the project, soil
stockpiles and borrow areas shall be stabilized or protected with sediment
trapping measures. The applicant is responsible for the temporary protection
and permanent stabilization of all soil stockpiles on site as well as borrow
areas and soil intentionally transported from the project site.
3. A permanent vegetative cover shall be
established on denuded areas not otherwise permanently stabilized. Permanent
vegetation shall not be considered established until a ground cover is achieved
that is uniform, is mature enough to survive, and will inhibit
erosion.
4. Sediment basins and
traps, perimeter dikes, sediment barriers, and other measures intended to trap
sediment shall be constructed as a first step in any land-disturbing activity
and shall be made functional before upslope land disturbance takes
place.
5. Stabilization measures
shall be applied to earthen structures such as dams, dikes, and diversions
immediately after installation.
6.
Sediment traps and sediment basins shall be designed and constructed based upon
the total drainage area to be served by the trap or basin.
a. The minimum storage capacity of a sediment
trap shall be 134 cubic yards per acre of drainage area and the trap shall only
control drainage areas less than three acres.
b. Surface runoff from disturbed areas that
is comprised of flow from drainage areas greater than or equal to three acres
shall be controlled by a sediment basin. The minimum storage capacity of a
sediment basin shall be 134 cubic yards per acre of drainage area. The outfall
system shall, at a minimum, maintain the structural integrity of the basin
during a 25-year storm of 24-hour duration. Runoff coefficients used in runoff
calculations shall correspond to a bare earth condition or those conditions
expected to exist while the sediment basin is utilized.
7. Cut and fill slopes shall be designed and
constructed in a manner that will minimize erosion. Slopes that are found to be
eroding excessively within one year of permanent stabilization shall be
provided with additional slope stabilizing measures until the problem is
corrected.
8. Concentrated runoff
shall not flow down cut or fill slopes unless contained within an adequate
temporary or permanent channel, flume, or slope drain structure.
9. Whenever water seeps from a slope face,
adequate drainage or other protection shall be provided.
10. All storm sewer inlets that are made
operable during construction shall be protected so that sediment-laden water
cannot enter the conveyance system without first being filtered or otherwise
treated to remove sediment.
11.
Before newly constructed stormwater conveyance channels or pipes are made
operational, adequate outlet protection and any required temporary or permanent
channel lining shall be installed in both the conveyance channel and receiving
channel.
12. When work in a live
watercourse is performed, precautions shall be taken to minimize encroachment,
control sediment transport, and stabilize the work area to the greatest extent
possible during construction. Nonerodible material shall be used for the
construction of causeways and cofferdams. Earthen fill may be used for these
structures if armored by nonerodible cover materials.
13. When a live watercourse must be crossed
by construction vehicles more than twice in any six-month period, a temporary
vehicular stream crossing constructed of nonerodible material shall be
provided.
14. All applicable
federal, state, and local requirements pertaining to working in or crossing
live watercourses shall be met.
15.
The bed and banks of a watercourse shall be stabilized immediately after work
in the watercourse is completed.
16. Underground utility lines shall be
installed in accordance with the following standards in addition to other
applicable criteria:
a. No more than 500
linear feet of trench may be opened at one time.
b. Excavated material shall be placed on the
uphill side of trenches.
c.
Effluent from dewatering operations shall be filtered or passed through an
approved sediment trapping device, or both and discharged in a manner that does
not adversely affect flowing streams or off-site property.
d. Material used for backfilling trenches
shall be properly compacted in order to minimize erosion and promote
stabilization.
e. Restabilization
shall be accomplished in accordance with this chapter.
f. Applicable safety requirements shall be
complied with.
17. Where
construction vehicle access routes intersect paved or public roads, provisions
shall be made to minimize the transport of sediment by vehicular tracking onto
the paved surface. Where sediment is transported onto a paved or public road
surface, the road surface shall be cleaned thoroughly at the end of each day.
Sediment shall be removed from the roads by shoveling or sweeping and
transported to a sediment control disposal area. Street washing shall be
allowed only after sediment is removed in this manner. This provision shall
apply to individual development lots as well as to larger land-disturbing
activities.
18. All temporary
erosion and sediment control measures shall be removed within 30 days after
final site stabilization or after the temporary measures are no longer needed,
unless otherwise authorized by the VESCP or VESMP authority. Trapped sediment
and the disturbed soil areas resulting from the disposition of temporary
measures shall be permanently stabilized to prevent further erosion and
sedimentation.
19. Properties and
waterways downstream from development sites shall be protected from sediment
deposition, erosion, and damage due to increases in volume, velocity, and peak
flow rate of stormwater runoff for the stated frequency storm of 24-hour
duration in accordance with the following standards and criteria. Stream
restoration and relocation projects that incorporate natural channel design
concepts are not manmade channels and shall be exempt from any flow rate
capacity and velocity requirements for natural or manmade channels:
a. Concentrated stormwater runoff leaving a
development site shall be discharged directly into an adequate natural or
manmade receiving channel, pipe, or storm sewer system. For those sites where
runoff is discharged into a pipe or pipe system, downstream stability analyses
at the outfall of the pipe or pipe system shall be performed.
b. Adequacy of all channels and pipes shall
be verified in the following manner:
(1) The
applicant shall demonstrate that the total drainage area to the point of
analysis within the channel is 100 times greater than the contributing drainage
area of the project in question; or
(2)
(a)
Natural channels shall be analyzed by the use of a two-year storm to verify
that stormwater will not overtop channel banks nor cause erosion of channel bed
or banks.
(b) All previously
constructed manmade channels shall be analyzed by the use of a 10-year storm to
verify that stormwater will not overtop the stormwater's banks and by the use
of a two-year storm to demonstrate that stormwater will not cause erosion of
channel bed or banks; and
(c) Pipes
and storm sewer systems shall be analyzed by the use of a 10-year storm to
verify that stormwater will be contained within the pipe or system.
c. If existing natural
receiving channels or previously constructed manmade channels or pipes are not
adequate, the applicant shall:
(1) Improve
the channels to a condition where a 10-year storm will not overtop the banks
and a two-year storm will not cause erosion to the channel, the bed, or the
banks;
(2) Improve the pipe or pipe
system to a condition where the 10-year storm is contained within the
appurtenances;
(3) Develop a site
design that will not cause the predevelopment peak runoff rate from a two-year
storm to increase when runoff outfalls into a natural channel or will not cause
the predevelopment peak runoff rate from a 10-year storm to increase when
runoff outfalls into a manmade channel; or
(4) Provide a combination of channel
improvement, stormwater detention, or other measures that is satisfactory to
the VESCP or VESMP authority to prevent downstream erosion.
d. The applicant shall provide
evidence of permission to make the improvements.
e. All hydrologic analyses shall be based on
the existing watershed characteristics and the ultimate development condition
of the subject project.
f. If the
applicant chooses an option that includes stormwater detention, the applicant
shall obtain approval from the VESCP or VESMP authority for a plan for
maintenance of the detention facilities. The plan shall set forth the
maintenance requirements of the facility and the person responsible for
performing the maintenance.
g.
Outfall from a detention facility shall be discharged to a receiving channel,
and energy dissipators shall be placed at the outfall of all detention
facilities as necessary to provide a stabilized transition from the facility to
the receiving channel.
h. All
on-site channels must be verified to be adequate.
i. Increased volumes of sheet flows that may
cause erosion or sedimentation on adjacent property shall be diverted to a
stable outlet, adequate channel, pipe, or pipe system or to a detention
facility.
j. In applying these
stormwater management criteria, individual lots or parcels in a residential,
commercial, or industrial development shall not be considered to be separate
development projects. Instead, the development, as a whole, shall be considered
to be a single development project. Hydrologic parameters that reflect the
ultimate development condition shall be used in all engineering
calculations.
k. All measures used
to protect properties and waterways shall be employed in a manner that
minimizes impacts on the physical, chemical, and biological integrity of
rivers, streams, and other waters of the state.
l. Any plan approved prior to July 1, 2014,
that provides for stormwater management that addresses any flow rate capacity
and velocity requirements for natural or manmade channels shall satisfy the
flow rate capacity and velocity requirements for natural or manmade channels if
the practices are designed to (i) detain the water quality volume and to
release it over 48 hours; (ii) detain and release over a 24-hour period the
expected rainfall resulting from the one year, 24-hour storm; and (iii) reduce
the allowable peak flow rate resulting from the 1.5-year, two-year, and 10-year
24-hour storms to a level that is less than or equal to the peak flow rate from
the site assuming the site was in a good forested condition, achieved through
multiplication of the forested peak flow rate by a reduction factor that is
equal to the runoff volume from the site when the site was in a good forested
condition divided by the runoff volume from the site in the site's proposed
condition, and shall be exempt from any flow rate capacity and velocity
requirements for natural or manmade channels as defined in any regulations
promulgated pursuant to §
62.1-44.15:28 of the Code of
Virginia (VESMA) or §
62.1-44.15:54 or
62.1-44.15:65 of the Code of
Virginia (ESCL).
m. For plans
approved on and after July 1, 2014, the flow rate capacity and velocity
requirements of §
62.1-44.15:52A
of the Code of Virginia (ESCL) and this subdivision 19 shall be satisfied by
compliance with water quantity requirements in the VESMA and attendant
regulations, unless such land-disturbing activities (i) are in accordance with
provisions for time limits on applicability of approved design criteria in
9VAC25-875-480 or grandfathering in
9VAC25-875-490, in which case the
flow rate capacity and velocity requirements of §
62.1-44.15:52A
of the Code of Virginia (ESCL) shall apply; or (ii) are exempt pursuant to
§
62.1-44.15:34G
2 of the Code of Virginia (VESMA).
n. Compliance with the water quantity minimum
standards set out in
9VAC25-875-600 shall be deemed to
satisfy the requirements of this subdivision 19.
Statutory Authority: §
62.1-44.15:28 of the Code of
Virginia; Chapters 68 and 758 of the 2016 Acts of
Assembly.
