SW3191201_AddInfoRequest_20191211

ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
S. DANIEL SMITH
Director
Kai Burk, PE
Bowman Consulting
950 North Point Parkway, Suite 200
Alpharetta, GA 30004
NORTH CAROLINA
Environmental Quality
December 11, 2019
Subject: Request for Additional Information
Stormwater Permit No. SW3191201
Circle K Denver (Unity Church Rd)
Lincoln County
Dear Mr. Burk:
The Division of Energy, Mineral and Land Resources (DEMLR), received a Stormwater
Management Permit Application for the subject project on December 3, 2019. A review of that
information has determined that the application is not complete. The following information is
needed to continue the stormwater review:
1. The built -upon area measurements used in the calculations and the Supplement EZ form
do not match those listed in the application. Based on measurements taken off the
submitted plans it appears that those in the application are more accurate.
2. Please delineate all wetlands on site or add a note that none exist as well as the name of
the person/entity that made the determination [15A NCAC 02H .1042(2)(g)(iii)].
3. Based on the proposed contours on the grading plan, a significant amount of new BUA
on the west side of the project will bypass the bioretention cell and drain freely to NC-16
Business. The stormwater runoff generated from all of the built -upon area during the
design storm must be treated in a Primary SCM [15A NCAC 02H .1002(43)].
4. The post -development drainage basin map includes areas draining to structure A3-Y1
(Sheet C3.0) in Drainage Area C. However, runoff from areas collected by this inlet drain
to the sand filter and should thus be considered part of Drainage Area A.
5. Please provide calculations to show that the inlets to all SCMs and the outlets to all pipes
are designed to prevent erosion during the 10-year storm event (General MDC 4).
D EQ �� North Carolina Department of Environmental Quality Division of Energy, Mineral and Land Resources
512 North Salisbury Street 1 1612 Mail Service Center Raleigh, North Carolina 27699-1612
NORTH CAROLINA
Depadm.mofEnmmnm.maaualfty /� 919.707.9200

6. Please add a note to the details plan stating that each SCM impacted by sedimentation
and erosion control during the construction phase shall be cleaned out and converted to is
approved design state (General MDC 7).
7. Please address the following comments with respect to the proposed bioretention system:
a. Please provide a geotechnical report to verify that the bottom of the bioretention
system is at least 2 feet above the seasonal high water table (Bioretention MDC
1).
b. The bioretention detail on Sheet C3.3 shows the internal water storage 6" below
the surface of the bioretention system. The internal water storage must be a
minimum of 18" below the surface (Bioretention MDC 4).
c. The bioretention detail shows the depth of the bioretention media as 18". The
minimum depth of media for a bioretention system with sod and internal water
storage is 30" (Bioretention MDC 5).
d. Please specify on the bioretention detail that the media P-index shall not exceed
50 (Bioretention MDC 7).
e. Please add a note to the bioretention detail to not mechanically compact the
bioretention media. It is recommended to either water it or walk on it as it is
placed (Bioretention MDC 8).
f. Please add a note to the bioretention detail specifying that the sod shall be a non -
clumping, deep-rooted species that has not been grown in soil that has an
impermeable layer, such as clay (Bioretention MDC 10).
g. Mulch is typically only required for bioretention cells with vegetation other than
sod (Bioretention MDC 11). It is recommended to not use mulch when using sod
as the vegetation in the bioretention system.
h. The bioretention cell must have sufficient storage below the first outlet (weir at el.
845.6) to store the entire runoff volume from the I" storm. Please provide
calculations showing the storage volume in the bioretention cell below elevation
845.6.
i. Please extend the SCM maintenance easement to the nearest public right-of-way
(General MDC 9).
j. The outlet control structure detail (Sheet C3.3, Detail P6-CS) shows that the
invert of the outlet pipe from the outlet control structure is el. 843. The grading
plan (Sheet 3.0) shows the pipe drains to a flared end section (P.5-FES) at a
higher elevation (843.28). Please revise the plans to ensure the bioretention
system drains properly.
k. The bioretention details specifies that the outlet pipe diameter is 15", while the
outlet control structure specifies 18". Please correct the discrepancy.
1. The Supplement EZ form specifies that the method for dewater the SCM for
maintenance is a drawdown orifice. Please show the drawdown orifice on the
detail sheet.
in. Please provide calculations to show that the underdrain design is sufficient to
convey runoff from the bioretention cell. Guidance on these calculations can be
found in Chapter A-5 of the Stormwater Design Manual.
n. What is the intended purpose of the half round perforated pipe in the bioretention
design?

8. Please address the following comments with respect to the proposed sand filter:
a. Please provide a geotechnical report to verify that the bottom of the sand filter is
at least 2 feet above the seasonal high water table (Sand Filter MDC 1).
b. The sand filter must be designed with sufficient storage to hold 75% of the design
runoff volume below the first outlet (weir at el. 847.3) with at least 50% of that
volume in the sand chamber. Please provide the storage volumes in the sand
chamber and sediment chamber below el. 847.3 (Sand Filter MDC 2 & 3).
c. Sand Filter MDC 5 requires that incoming stormwater be evenly distributed over
the surface of the sand chamber. Please provide a method for distributing the
runoff evenly over the sand chamber surface.
d. Please add a note the sand filter detail stating that the sand filter shall be
maintained in a manner that results in a drawdown of at least two inches per hour
at the sand surface (Sand Filter MDC 8).
e. The sand filter clean -out shown on Sheet C3.0 is not connected to the underdrain
system. Please show at least one clean -out pipe at the low point of each
underdrain line (Sand Filter MDC 9).
f. The entire surface area of the sand chamber should contain the sand media.
g. Please provide calculations to show that the underdrain design is sufficient to
convey runoff from the sand filter. Guidance on these calculations can be found in
Chapter A-5 of the Stormwater Design Manual.
9. Please address the following comments with respect to the Supplement EZ form:
a. Cover Page
i. The width of the vegetated setbacks is listed as 10 feet. The minimum with
for vegetated setbacks from all perennial waterbodies, perennial streams,
and intermittent streams is 30 feet [15A NCAC 02H .017(10)].
b. Drainage Areas sheet:
i. Please complete the table for the entire site.
c. Bioretention sheet:
i. The ponding depth for the bioretention cell (Field 20) should be the
maximum depth of runoff in the bioretention cell from a 1" rainfall event.
ii. The peak attenuation depth in the bioretention cell (Field 24) should be
expressed as the depth in inches, not an elevation.
iii. Please add the diameter of the underdrain pipes in the bioretention cell
(Field 27).
iv. The Supplement EZ form states that the bioretention cell is designed
without internal water storage (Field 28). However, the bioretention detail
shows that the system is designed with internal water storage. Please
correct the discrepancy.
v. Please revise the bioretention media depth in accordance with above
comment 6.c (Field 32).
vi. Please add the P-index of the bioretention media (Field 37).
d. Sand Filter sheet:
i. Field 8 states that there is no bypass for flows in excess of the design
volume. The rim of the outlet structure would be considered a bypass for
this system. Please revise the form to correct Field 8 and complete Fields
35 and 36.

ii. The physical depth of the sediment chamber is listed as 48" (Field 27).
However, the sand filter detail on Sheet C3.3 shows that the depth is 5'
Please revise this field.
iii. Field 37 states that the mechanism for distributing flow over the sand
surface is the underdrain. This field should explain how flow from the
sediment chamber is distributed into the sand chamber.
10. Provide pdfs of all revisions, 2 hardcopies of revised plan sheets, and 1 hardcopy of other
documents. Pdfs must be uploaded using the form at:
https:Hedocs.deq.nc.gov/Forms/SW ProjectSubmittal
Please note that this request for additional information is in response to a preliminary review.
The requested information should be received by this Office prior to January 10, 2020, or
the application will be returned as incomplete. The return of a project will necessitate
resubmittal of all required items, including the application fee. Please reference the State
assigned project number SW3191201 on all correspondence.
If you need additional time to submit the information, please submit your request for a time
extension to the Division at the contact below. The request must indicate the date by which you
expect to submit the required information. The Division is allowed 90 days from the receipt of
a completed application to issue the permit.
The construction of any impervious surfaces, other than a construction entrance under an
approved Sedimentation Erosion Control Plan, is a violation of NCGS 143-215.1 and is subject
to enforcement action pursuant to NCGS 143-215.6A.
If you have any questions concerning this matter please feel free to contact me at
Corey. Anen(d),ncdenr. gov or [phone].
Sincerely,
Corey Anen
Environmental Engineer
Stormwater Program
cc: Mooresville Regional Office