SW3190201_Comment Response Letter_20190429

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BOHLER
E N G I` E E R I
North Carolina Department
Of Environmental Quality
Mooresville Regional Office
610 East Center Avenue, Suite 301
Mooresville, NC 28115
Attn: Corey Anen
1927 S. Ryon St, Suite 310
Chadatte, NC 28203
PHONE [phone]
April 29, 2019
Via Electronical Mail
Re: Stormwater Permit No. SW3190201
Comment Response Letter
O'Reilly Auto Parts, Wingate, NC
BE 9 NCC182114
Bohler Engineering is pleased to submit on behalf of O'Reilly Auto Parts, the revised Stormwater Permit
Application for the O'Reilly Wingate project located in Wingate, North Carolina. The following is our
comment response letter addressing comments received from NCDEQ received March 27, 2019. Each
comment is addressed and responded to as follows:
Comment 1: The bioretention cell must be sized using a volume -based calculation rather than a
routing calculation. Information can be found in Part B of our Stormwater Design Manual
Response 1: Per email and phone correspondence, routing method to show no more than 1.0'
stage during 1" storm is acceptable, so long as exfiltration is no more than 1 in./hr.
Calculations have been revised to show 1 inJhr. exfiltration. Additionally, based on
concerns with permanent water in storm pipes based on inflow elevation being
below top of media elevation, the concrete pre-treatment manhole was extended 12"
below bottom of media elevation with rip -rap to allow exfiltration through in -situ
soils after rainfall events. Email correspondence included with this submission.
Comment 2: Please correct the following inaccuracies on the Supplement EZ form:
A. The side slopes of the SCM are listed as 2:1 rather than 3:1 as shown on the plan
and required by the MDCs.
B. The Supplement EZ form shows that the depth to the seasonal high-water table is
">1.5 feet." According to Bioretention MDC 1, the minimum separation is 2 feet
C. The surface area listed must be the area at the planted surface of the bioretention
cell.
D. The ponding depth is listed incorrectly.
E. Mulch is not an acceptable form of organic matter for the bioretention media mix.
Response 2: A. Revised to 3:1
B. SHWT analysis performed and is included in this submission. The testing shows
no indication of SHWT the full depth of the hand auger or 37" (3.1') below existing
grade (approximately 560' based on the boring map). 560' — IF = elevation 556.9',
which is >2' below bottom of system (559').

Comment Response Letter
Stormwater Permit No. SW3190201
NCC182114
April 5, 2019
Page 2 of 2
C. Area revised to 390 SF, which is the area at the media surface.
D. Ponding depth revised to 6" for the design storm (1" storm).
E. Pine Bark Fines will be the organic material in the media. Form revised.
Comment 3: Please submit a USGS map identifying the site location.
Response 3: USGS Site Map included in submission package.
Comment 4: Please provide calculations showing that the inlet protection for the bioretention cell is
sufficient to prevent erosion from the peak flow during the 10-year storm.
Response 4: Inflow pipe into bioretention cell enters 2' below media into 48" bottomless manhole
with 12" of rip -rap. Runoff stages 2' before spilling out of manhole ring into
bioretention media. Because of this configuration, runoff will slowly enter into the
media and erosion will not occur.
Comment 5: Please show a maintenance access and easement that meets the requirements of General
MDCs 8 and 9.
Response 5: Maintenance access will be off of Chaney Street entrance. Easement for access of the
bioretention cell added to Site Plan, sheet C2.1 and SWM/BMP Details, sheet C3.7
Comment 6: 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:
hitps://edocs.deg.nc.gov/Forins/SW ProjectSubmittal
Response 6. All are included in this set and PDFs uploaded.
Should you have any questions regarding this project or require additional information, please do not
hesitate to contact me at [phone].
Sincerely,
Bohler Engineering NC, PLLC
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Daniel Renckens, PE
Project Manager