SW3230605_Response To Comments_20240129

A AMERICAN
Engineering
January 26, 2024
North Carolina Department of Environmental Quality
Division of Energy, Mineral & Land Resources
Stormwater Program
512 North Sailsbury Street
Raleigh, NC 27699
Subject: Request for Additional Information
Stormwater Permit No.SW3230605
Rogers Pond
Union County
Dear Ms. Holland,
Please find below the original review comments provided by the NCDEQ and each subsequent response:
1) Design Requirements for High Density Projects
a.The project does not appear to meet the requirement of Runoff Treatment (15ANCAC 02H
.1002(43)). For a project to meet Runoff Treatment, the net increase in BUA must be captured
and treated in one or more primary SCMs. Per Sheet C4.7, it appears that approximately 1.67 ac
of BUA are not treated (northern portion of area labeled "Undetained Area" on Drainage Area
Plan, see snip below for clarification). If it is not practicable to capture and treat all of the
required BUA,the bypassed areas can be permitted as a low-density area (provided that the
bypass area meets the low-density requirements). Occasionally,there are situations where it is
not practicable to capture all of the required BUA in an SCM and it is not possible to permit the
bypass areas as a low-density area,these situations require a variance/waiver in accordance
with 15A NCAC 02H .1003(6). Revise the package as necessary and indicate which of the options
is being pursued.
Response: The "Undetained Area"has been added to the permit as a low-density area. The
supplement EZ cover page and drainage areas have been revised to include the low-density.
The supplement EZ low density form has been included with this resubmittal.
2)Sand Filter:
a. In the previous submittal, the storage volume in the sediment chamber was much larger than
the sand chamber, in this submittal,the sand chamber is much larger than the sediment
chamber. Per Sand Filter MDC 2, storage volume in the sediment chamber and sand chamber
shall be equivalent. Guidance provided in the Design Manual states: "The sediment chamber
may be designed to have a permanent pool of water or with orifices that allow it to drain
between storm events. If the sediment chamber has a permanent pool,then the volume
American Engineering Associates—Southeast, PA
8008 Corporate Center Drive, Suite 110, Charlotte, NC 28226 •704-375-2438 •www.American-EA.com

contained by the permanent pool shall not be considered to be storage volume.The sediment
chamber can be oversized to provide detention when peak flow mitigation is required for a
site." With the revised design, the sediment chamber is relatively undersized to the sand
chamber, which can result in clogging and maintenance issues.
Response: The riprap berm separating the sand filter and sediment chamber has been
revised so that the volumes are nearly equal. The calculation book and supplement EZ form
for sand filter has been corrected for the sand filter volume to be 23,882 cf and the sediment
chamber volume to be 25,283 cf.
3)Supplement-EZ
1x hard copy of the complete, original Supplement-EZ Form and lxscanned copy is required per
Sections V& VI, 3 of the Application.
a. Drainage Areas: The entire site column is not the total of the drainage area columns.
It is for the entire site (-60.01 acres).
i. Drainage Areas, Line 8: Ensure this item includes the total BUA, as it appears
that not all of the BUA is directed to the SCM per Comment 1.
Response: The drainage area supplement EZ form has been revised to include the total
BUA for the project.
Sincerely,
American Engineering Associates—Southeast, PA
e-75/714. (—
Blake Estridge, PE
Project Engineer
[e-mail]
American Engineering Associates—Southeast, PA
8008 Corporate Center Drive, Suite 110, Charlotte, NC 28226 •704-375-2438 •www.American-EA.com