SW3221003_Response To Comments_20230117

Summey Engineering Associates, PLLC
PO Box 968., Asheboro, NC 27204
Phone: [phone] Fax: [phone]
Email: [e-mail]
NCDEQ Stormwater - Comment Response Letter
SW3221003 — Request for Additional Information
This letter is to provide a point -by -point response to comments received
from the NCDEQ following the review of the Rockwell ABC Plans. Comments
received are listed below followed by our responses noted in bold.
Per 15A NCAC 02H .1003(3)(b), any off -site areas that are not bypassed around the
SCM must be accounted for at their full build -out potential. This can be accomplished by
either assuming that the off -site area is 100% impervious (its full build out potential) or
by having the permittee and off -site property owner enter into a legal agreement limiting
the amount of BUA and area that can be directed from the off -site area to the SCM (see
more information after the comments). Please revise the submittal materials as needed.
Acknowledged. Offsite area is now bypassed with a permanent diversion ditch.
2. Similar to the prior comment (and per the same rule), the off -site portions of the drainage
area to the SCM should be used to determine the SCM sizing. The provided calculations
only use the on -site portion of the drainage area to the SCM to calculate the design
volume whereas the entire drainage area to the SCM should be used in this calculation.
Please revise as needed. NOTE: This results in the SCM not providing a sufficient
treatment volume so the design will need to be modified.
Acknowledged. Offsite area is now bypassed with a permanent diversion ditch.
3. The project overview (in the Stormwater Management Report) lists the project area as
1.09 ac while the other submittal items list the project area as 1.52 ac. Please revise as
needed.
Acknowledged. Revised SW Narrative with updated project area.
4. Please provide the calculations showing that the riprap apron is adequately sized in
accordance with General MDC 4.
Acknowledged. Updated Rip Rap Calculations included in stormwater report.

5. Please correct the following issues with the Supplement-EZ Form:
a. Cover Page:
i. i. Line 7 — It is noted that there are no surface waters located on -site, however
we ask that the required vegetated setback width (30 ft per 15A NCAC
02H .1017(10)) be included on this form (Lines 8 & 9 may be left as "N/a"
since there are no surface waters located on -site).
Acknowledged. 30 ft added on cover sheet #7.
b. Drainage Area Page:
The entire site column is an accounting of the entire project area, not just a
summation of the drainage area columns. Any BUA that is located within the
project area but does not drain to one of the SCMs should be accounted for in
the Entire Site Column. The value shown on Line 5 (42,633 sf) does not
correspond to the total proposed BUA for the project (43,101 sf). Please revise
as needed.
Acknowledged. Areas have been revised for offsite are to bypass BMP.
ii. Line 12, Parking — This value (36,825 sf) does not correspond to the new parking
area value shown in other submittal items (33,714 sf). Off -site areas should not
be included on Line 12.
Acknowledged. Areas have been revised for offsite are to bypass BMP.
iii. Line 16 —The 3,111 sf of off -site parking area does not appear to be already
permitted (The most recent version of this form has a line for off -site
impervious areas).
Acknowledged. Areas have been revised for offsite are to bypass BMP.
iv. Revise the drainage area information and design volume as needed in
accordance with earlier comments.
Acknowledged. Areas have been revised for offsite are to bypass BMP.
Sand Filter Page:
i. Lines 2, 23, 30, and possibly others — Revise as needed in accordance with
earlier comments
Acknowledged. Areas have been revised for offsite are to bypass BMP.
ii. Line 9 —There does not appear to be a drawdown orifice capable of drawing
down the permanent pool in the sediment chamber. Please revise as needed.
Acknowledged. Dewatering method revised.
iii. Line 18 — Per the provided SHWT boring information, the SHWT was not
encountered to a depth of elevation 745'. Please revise or clarify.
Acknowledged. SHWT elevation revised.
iv. Line 27 —The physical depth of the sediment chamber is the distance from the
bottom of the sediment chamber (752.17') to the invert of the bypass device
(758.5')
Acknowledged. This has been revised per comments.
v. Line 28 —The ponding depth in the sediment chamber is the distance from the
permanent pool surface elevation (754.0') to the invert of the bypass device
(758.5')
Acknowledged. This has been revised per comments.

vi. Line 33 —The physical depth of the sand chamber is the distance from the
bottom of the sand chamber (752.17') to the invert of the bypass device (758.5')
Acknowledged. This has been revised per comments.
vii. Line 34 —The ponding depth in the sand chamber is the distance from the top of
the sand layer (753.67") to the invert of the bypass device (758.5')
Acknowledged. This has been revised per comments.
viii. Line 39 —This item refers to the depth of sand above the underdrain pipe (12").
Acknowledged. This has been revised per comments.
While not required, it is recommended, per the guidance in the Manual under Sand Filter
MDC 4, to limit the maximum ponding depth for peak flows to no more than 6 feet above
the top of the sand layer (The distance between the top of the sand layer, 753.66',and the
inside top of the chamber, 761.0', is approximately 7.3'). NOTE: The MDC only
requires the maximum ponding depth from the top of the sand layer to the bypass device
(invert at 758.5') to be limited to 6' (so the provided design meets the MDC) however
peak flow ponding depths in excess of 6' can negatively impact the functionality of the
sand filter.
Acknowledged. The ponding depth in excess of 6' has been considered and should have
minimal impact on the sand chamber since a ponding depth of over 6 ft will be for a very short
period of time and the frequency of ponding depths above 6 ft will not be often and only
during intense storm events.
While not required, it is recommended to ensure that the access to the underground sand
filter meets the applicable OSHA requirements for confined spaces as it will be necessary
to enter the sand filter to perform maintenance.
Acknowledged. Note has been added to plan sheet C-7 to provide adequate OSHA approved
inspection and maintenance measures.
Provide PDFs of all revisions, 2 hardcopies of revised plan sheets, 1 hardcopy of other
documents, and a response to comments letter briefly describing how the comments have
been addressed.
a. PDFs must be uploaded using the form at:
https://edocs.deq.nc.gov/Forms/SW-Supplemental-Upload
b. Hard copies must be mailed or delivered to the following address:
i. For Fed Ex/UPS:
Jim Farkas
512 N. Salisbury Street, Office 640M
Raleigh, NC 27604
ii. For USPS:
Jim Farkas
1612 Mail Service Center
Raleigh, NC 27699-1612
iii. Hand Delivery:
Please reach out to me prior to hand delivering a submission to make sure that I
(or someone else in my group) will be able to receive the submission. Do not
leave the package in the foyer with the security guard.
Acknowledged.

NOTE: Hard copies should not be sent to a Regional Office. Doing so will delay
the review process and the submission package may be lost while being sent from
the Regional Office to me in the Central Office.
While it is not required, it is recommended that the off -site drainage from upstream properties
be
diverted around the SCM since the Applicant cannot maintain control over the development of
property that they do not own. If the Applicant elects to account for off -site drainage, it must
either be accounted for as 100% BUA (its full build out potential, or there must be a recorded
legal agreement in place between the Applicant and the Owner of the upstream property in
which
the Owner of the upstream property agrees to record a deed restriction limiting the
minimum/maximum amount of BUA on the upstream property that will be treated in the
Applicant's SCM, the locations and sizes of access and drainage easements, how construction
and/or ongoing maintenance costs will be handled, maintenance responsibility, a list of legal
recourses available to each party should one party fail to hold up their end of the agreement,
and
any other related legal issues.
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 February 4, 2023, 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 SW3221003 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
[e-mail] or [phone].