SW5180301_Resubmittal Letter_20180424

© 2018 FLM Engineering, Inc. Page 1 of 2 April 24, 2018

PO Box 91727, Raleigh, NC 27675 p | 919.610.1051

April 24, 2018

Cory Anen
Environmental Engineer
North Carolina Department of Environmental Quality
Division of Energy, Mineral and Land Resources
1612 Mail Service Center
Raleigh, NC 27699-1612

Reference: Crawford Townes
Stormwater Permit No. SW5180301
Request for Additional Information

Dear Mr. Anen:

In response to your April 11, 2018 request for additional information, enclosed you will find the
revised drawings with your comments addressed as follows.

1. Please provide a signed and notarized Operation and Maintenance Agreement.

A signed and notarized Operation and Maintenance Agreement is included with this
resubmittal. Please see Appendix M of the stormwater report.

2. Please provide a detail depicting the forebay, including the forebay depth
and elevations of the forebay inlet and outlet.

The forebays have been called out on sheet C-9 in both plan view and cross section view.

3. Please provide calculations demonstrating that the proposed riprap apron is
sufficient to prevent erosion as a result of discharges from the SCM.

Dissipator calculations for the SCM outlet have been provided with this submittal.

4. Please revise the SCM design to address the following deficiencies:
a. The detail on sheet C-9 shows that the forebay comprises approximately half
the surface area noted in the Supplement Form. Therefore, it comprises less
than 10 percent of the wetland surface area. The forebay must comprise 10
to 15 percent of the wetland surface area.

Per our email correspondence, the two forebays shown on sheet C-9 provide the
10 to 15 percent of the wetland surface area.

b. The drawdown time calculations do not accurately calculate the drawdown
time from the SCM. The actual drawdown time under the proposed
conditions is below the minimum of two days. Please revise the design to
ensure the design volume will drain to the permanent pool level in between
two to five days.
© 2018 FLM Engineering, Inc. Page 2 of 2 April 24, 2018
The drawdown orifice calculations have been revised and are in the revised
stormwater report.

5. Please provide a landscape plan that shows the delineation of planting zones and
the plant layout with species names and locations.

The delineations of planting zones and plant species names is shown on sheet C-9.

6. Please 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://edocs.deq.nc.gov/Forms/SW_Project_Submittal

Two copies of the plan set and one hardcopy of other documents have been provided
alongside this comment response letter. The revisions have been clouded as necessary.
Pdfs have been uploaded per the link above.

Please let me know if you have any questions or need any additional information.

Sincerely,

T. Chase Massey, PE
Principal
919.423.8975
[e-mail]