SW3221101_Add Info_20230227

Ft`STATE.
o.
ROY COOPER A
Governor
ELIZABETH S.BISER
Secretary
DOUGLAS R.ANSEL NORTH CAROLINA
Interim Director Environmental Quality
February 27, 2023
Pike Engineering
Attn: Joe Ervin, PE
123 N. White Street
Fort Mill, SC 29715
AND
Union Electric Membership Corporation
Attn: Gregory S. Andress, Executive VP & General Manager
1525 N. Rocky River Road
Monroe, NC 28110
Subject: Request for Additional Information
Stormwater Permit No. SW3221101
Parkwood Electrical Substation
Union County
Dear Mr. Ervin and Mr. Andress:
The Division of Energy, Mineral and Land Resources (DEMLR), received a Stormwater
Management Permit Application for the subject project on November 29, 2022. A review of that
information has determined that the application is not complete. The following information is
needed to continue the stormwater review:
1. General:
a. Please QA/QC the submission as there are a number of inconsistencies. Some noted
examples include the Project Area (shown as 21.2 ac in the Application, Section IV,
7, 20.3 ac in the Supplement-EZ Form, Cover Page, Line 2, and 15.55 ac in the
Supplement-EZ Form, Drainage Areas Page, Entire Site Column, Line 5), bottom of
the sand surface (shown as 652.65' in the sand filter plan view and 652.32' in the
profile view), general issues with the BUA accounting (see later comments), etc...
b. Please ensure that all of the electronic files submitted for this project are uploaded at
the following address: https://edocs.deg.nc.gov/Forms/SW-Supplemental-Upload.
The only files that appear to have been uploaded are the plan sheets and the report
that were uploaded on 2/17/2023. The other submittal items (such as the Application,
O&M Agreement Form, property deed, etc...) have not been uploaded.
D E Q�� North Carolina Department of Environmental Quality I Division of Energy,Mineral and Land Resources
512 North Salisbury Street 1 1612 Mail Service Center I Raleigh,North Carolina 27699-1612
NORTH CAROLINA _
uepn ,t 0 E,,im W a.ar\ r 919.707.9200

c. The Goose Creek Rules referenced in the stormwater narrative do not appear to be the
latest version of the rules. For example, removal of an average of 85% TSS and a
drawdown time between 48 & 120 hours are no longer requirements and the
requirement to, "implement stormwater management measures that promote
infiltration of flows and groundwater recharge for the purpose of maintaining stream
base flow" is not included. Please revise the narrative as needed and ensure that the
design promotes infiltration and groundwater recharge (which a lined sand filter does
not). If it is not practical to use an SCM that infiltrates stormwater runoff, please
provide an explanation for why it is not practical. See link to current version of the
Goose Creek Rules:
http://reports.oah.state.nc.us/ncac/title%2015 a%20-%20environmental%20qualit.
apter%2002%20-%20environmental%20management/subchapter%20b/15 a%20ncac
%2002b%20.0602.pdf
2. Sand Filter Design:
a. General MDC 3 —Please show the proposed side slopes of the sand filter on the sand
filter detail. Per the MDC, side slopes of the vegetated portion of the sand filter must
be 3:1 or flatter (steeper vegetated slopes are allowable on a case-by-case basis in
certain situations).
b. Sand Filter MDC 2—Please revise the location of the berm separating the two
chambers of the sand filter so that the storage volume in each is equivalent. NOTE:
The storage volume provided in the sediment chamber is provided above the
excavated bottom of the sediment chamber and below the bypass elevation (655.4').
The storage volume provided in the sand chamber is provided above the top of the
sand layer and below the bypass elevation. Storage provided within the sand layer
cannot be used towards providing the required treatment volume.
c. Please provide a stage-storage table for both the sediment chamber and sand chamber
(with cross-sectional areas) so that Sand Filter MDC 3 and the SCM sizing may be
verified. There appears to be an issue with the provided stage-storage table. Using the
provided cross-sectional area information from the Supplement-EZ Form (sand
chamber cross-sectional area=4,500 sf& sediment chamber cross-sectional area=
1,075 sf) results in a total cross-sectional area of the sand filter at elevation 654.4' of
5,575 sf. The provided stage-storage table shows an incremental storage volume
between this elevation, 654.4', and elevation 655.0' of 5,215 cf which would require
the cross-sectional area @ elevation 655.0' to be in excess of 20,000 sf which does
not seem correct based on the provided geometry. Please revise as needed.
d. While not required, it is recommended to reduce the pervious drainage area to the
Sand Filter as pervious areas generate fine particles that may clog the sand filter and
result in the need for more frequent maintenance of the SCM (submittal items
indicate that the %BUA of the sand filter drainage area is 35%).
3. Vegetated Conveyance (Swale) Design:
a. Please provide a detail for the vegetated conveyance in the main set of plans. The
detail should include a cross-sectional view of the vegetated conveyance that shows

the bottom width, side slopes, and proposed vegetation. This item is required per
Section VI, 81 of the Application.
4. Application:
a. Section IV, 8 —Please revise as needed, see later comment (This value appears to be
based off of a project area of 15.55 ac which does not correspond to the information
shown in Section IV, 7).
b. Section IV, 9—Please revise to "2" drainage areas (one for the sand filter and one
low-density drainage area).
c. Section IV, 10—Please include a column in this table for the drainage area to the
SCM and a column for the remaining low-density area. Since there are no off-site
components to the drainage area for the SCM, the sum of the drainage area to the
SCM and the low-density drainage area should equal the project area (all of the
portions of the project area that do not drain to the SCM will be included in the low-
density drainage area). For example, if the project area is 21.2 ac and the drainage
area to the SCM is 3.6 ac, the low-density drainage area would be 17.6 ac (21.2 ac—
3.6 ac). Please revise as needed. NOTE: The provided information shows a project
area of 15.55 ac (677,358 sf) which does not correspond to the information shown in
Section IV, 7.
5. Supplement-EZ Form:
a. Cover Page:
i. Line 2—This item, 20.3 ac, does not correspond to the information shown in the
Application (Section IV, 7). Please revise as needed.
ii. Line 7—It is noted that there are no surface waters located on-site, however,please
include this item on the form. Vegetated setback width information can be found in
15A NCAC 02H .1017(10). NOTE: Lines 8-10 may remain as they are since there
are no on-site surface waters.
b. Drainage Areas Page:
i. Entire Site Column:
1. The entire site column should be an accounting of the entire project area,
similar to how the SCM DA column is an accounting of the entire drainage
area to the SCM. The "drainage area" for this column is equal to the project
area, as shown in Section IV, 7 of the Application. Please revise Lines 5, 6, &
18 as needed.
ii. Sand Filter DA Column:
1. Lines 5 & 6—This value, 111,078 sf(2.55 ac) does not correspond to the
information shown in the design calculations and plan sheets (DA = 3.61 ac).
Please revise as needed.
2. Line 18—Please revise as needed.
3. Line 20—The design volume of this SCM is based on the difference between
the pre-development and post-development 1-year, 24-hour design storm. The
provided value (10,411 cf) does not correspond to the value shown in the
calculations. Please revise as needed.

iii. Low-Density DA Column:
1. Per earlier comments, the low-density drainage area for this project is equal to
the portion of the project area that does not drain to the SCM. The sum of this
column and the Sand Filter DA Column should add up to the Entire Site
Column. Please revise as needed.
iv. Line 22—The information shown in the additional information section appears to
have been cut off(everything after"This includes applications such as..." is
missing). Please ensure that all of the information entered is accounted for.
c. Low-Density Page:
i. Line 5 —Please include this value (If the cell either won't format properly or won't
let you enter a value in this cell, please include this information in the Additional
Information Section).
d. Sand Filter Page:
i. Line 2—This value (8,695 cf) does not correspond to the information as shown in
the calculations (9,552 cf). Please revise as needed.
ii. Lines 20 & 21 —Please answer these items. Since this is a non-typical closed
bottom design, you can elaborate on these items in the Additional Information
section. For Line 21, please indicate the highest elevation of the geomembrane
layer.
iii. Lines 23 & 30—The sum of the volumes that can be retained in each chamber
must be at least as large as the minimum required treatment volume and per Sand
Filter MDC 2, the storage volumes should be equivalent.
iv. Lines 26 & 32—These items refer to the cross-sectional area of the sand filter, of
either the sediment chamber or sand chamber, at the bottom elevation (654.4') of
the sand filter.
v. Line 27 - The physical depth of the sediment chamber is the distance from the
bottom of the sediment chamber(654.4') to the bypass elevation (655.4'),
expressed in inches.
vi. Line 31 —See earlier comment with regard to the bottom elevation of the sand
chamber. This value refers to the elevation of the bottom of the sand layer.
vii. Line 33 —The physical depth of the sand chamber is the distance from the bottom
of the sand layer to the bypass elevation, expressed in inches.
viii. Line 43 —The information shown in the additional information section appears to
have been cut off(everything after"in accordance with Goose Creek..." is
missing). Please ensure that all of the information entered is accounted for.
6. 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 FedEx/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.
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.
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 March 29, 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 SW3221101 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(919) 707-3646.
Sincerely,
Jim Farkas
State Stormwater Engineer
DEMLR Post-Construction Stormwater Program
cc: Mooresville Regional Office