SW3221007_Response To Comments_20230203

� X REC
February 3, 2023
NCDEQ
Jim Farkas
RE: Dollar General — Store #24556
Stormwater Permit No. SW3221007
The following responses are pertaining to the review letter dated January 18, 2023.
1. C) Please clarify what type of SCM will be used for this project. Certain aspects of this
submittal refer to the SCM as a sand filter while others refer to infiltration. For the
purposed of this review, it is assumed that the SCM is designed as an infiltration
trench. If this is incorrect, please let me know as it will impact the comments.
R) The SCM is intended to function as an infiltration trench. The sand filter
references were oversights that have been removed.
2. C) Please check the emergency spillway and top of embankment elevation values
provided in the SCM detail on plan sheet C903. They appear to be approximately
200 feet higher than the SCM. Please revise as needed.
R) Embankment and spillway elevations have been revised on the detail sheet C903.
3. C) Please provide the outlet sizing and design calculations in accordance with
General MDC 4. It is noted that the stormwater outlets have riprap protection
however no design calculations appear to have been provided. Please revise as
needed.
R) Stormwater report has been revised to include outlet design calculations.
C) Please show the stormwater maintenance access and easement in the main set of
plan in accordance with he General MDC's 8&9. The stormwater maintenance
access & easement must include the entire footprint of the SCM system and an
additional 10 or so feet around the SCM footprint to facilitate the completion of
the maintenance tasks. This maintenance access & easement must also extend to
the nearest public right-of-way.
1520 Meadowview Drive [e-mail] 336.844.4088 t
Wilkesboro NC 28697 www.brec.biz C' `+

R) Maintenance easement has been shown on C100 & C200.
5. C) Please correct the following issues with the Supplement-EZ Form:
a. Cover Page:
i. Line 7 — Please include the width of the vegetated setback from surface
water (per 15A NCAC 02H .1003(4) & .1017(10)). It is noted that there are
no surface waters located on -site, however we ask that this value be
included on this form (Lines 8 &9 may be left as "N/a" since there are no
surface waters located on -site).
b. Drainage Area Page:
i. Entire Site Column:
1. The Entire Site Column is an accounting of the entire project area
(similar to how the Drainage Area Column is an accounting
of the drainage area to the SCM). All of the BUA located
within the project area should be included in this column
whether it drains to the SCM or not. The "drainage area" for
this column is equal to the project area as shown in Section
IV, 7 of the Application(in square feet).
2. Line 18 — This item is the percent BUA of the entire project area
and should correspond to the value shown in Section IV, 8
of the Application.
3. Lines 4, & 19-21—These items are not required for this column.
c. Infiltration System Page:
i. Line 30 — This item refers to the ponding elevation of the design volume.
It may be the same as Line 31 or lower than Line 31.
ii. Line 31— Per the provided detail on plan sheet C903, the invert elevation
of the upturned underdrain (lowest bypass elevation) is at
elevation 816.75'. Please revise. NOTE: This cell may round a
decimal number to the nearest whole number, in this case, please
include the actual bypass elevation in the additional information
section (Line 46). NOTE: Bypass, in this case, refers to and
stormwater that is not required to infiltrate into the soil so the
upturned underdrain elbow would be the lowest bypass device.
ines 32-43 —This SCM configuration appears to be that of an infiltration
trench instead of an infiltration basin (The main difference
between the two being that trenches contain stone or some other
material in the storage area while basins do not). Please complete
Lines 34-43. NOTE: Lines 34 & 35 refer to the dimensions of the
stone reservoir, not the overall SCM.
ine 44—The design volume of the SCM must be able to be stored in
the SCM below the lowest bypass device. The provided stage -
storage table does not indicate that 3,376 cf of storage is provided
below the upturned underdrain elbow (elevation 816.75'). Please
revise as needed.

v. Line 45 — This item is the amount of time that it would take the
design volume to drawdown to the bottom of the SCM
(813.0') based on the design of the SCM. The minimum
surface area equation (Equation 2 in Part C-1 of the Manual)
can be rearranged to solve for time given the actual surface
area of the bottom of the infiltration trench, design volume,
and infiltration rate of the soils.
R) Supplement form has been revised. Thank you for the clarifications. It cleared up
some long standing confusion with the supplement form for me.
6. C) Please revise the 0&M Agreement form to indicate an Infiltration Trench instead
of an Infiltration Basin (If I recall correctly, the maintenance requirements are
slightly different for the two different facilities. The revised form will require a new
original signature. While not required, you may wish to get a second copy signed
for the Applicant's records (as on original copy will be needed to record with the
Register of Deeds).
R) Revised 0&M included in resubmission.
Thanks,
BREC, PA