SW6200404_Email_20230216

Peck, Kaitlin
From:Farkas, Jim J
Sent:Thursday, February 16, 2023 4:30 PM
To:[e-mail]; Ward, Lee P CIV USARMY ID-READINESS (USA);
[e-mail]; Mason Manhertz
Cc:Lawyer, Mike
Subject:RE: SW6200404 Special Operations Forces (SOF) Group Support Battalion (GSB) TEMF
- PN79453
Attachments:Capture.PNG; Capture1.PNG; Capture2.PNG; Capture3.PNG; Capture4.PNG
While reviewing the originally approved design as part of this major modification request that we received on November
18, 2022, some issues were noted with the original design:
- The approved design indicates that the invert of the drawdown orifice/the permanent pool surface elevation is
at elevation 242.5’ whereas the provided state-storage table calculates the permanent pool volume up to an
elevation of 243.0’. This impacts the HRT calculation, as required per Wet Pond MDC 1a, since the actual main
pool volume provided below the permanent pool surface elevation (@242.5’) is approximately 106,000 cf which
is less than the minimum required per the revised HRT calculation (114,602 cf).
- The originally approved forebay state-storage table indicates that the volume of the forebay at elevation 243.0’
is 17,682 cf (the Supplement-EZ Form indicates 18,930 cf) which is less than the minimum of 15% of the main
pool volume (118,621 cf @243.0’) as required per Wet Pond MDC 5a (a similar issue also exists when the
elevation of 242.5’ is used).
- Please check the orifice sizing calculations as the originally provided one does not appear to be correct and
appears to result in a drawdown time of less than 2 days. Rearranging the orifice equation \[Q = CD * A * (2g *
Ho)^0.5\] to solve for Ho given the information (Q = 0.47 cfs, CD = 0.6, & A=0.196 sf (for a 6” diameter hole))
results in a Ho value of approximately 0.24’ which is significantly less than Ho value that should have been used
based on the actual driving head (an Ho value of 1.0’ would be appropriate based on the provided stage-storage
table, however, the stage-storage table shows the permanent pool surface elevation @242.5’). The orifice
discharge rate calculation was not provided in the original submittal items and appears to have been taken from
Hydraflow (but I am not entirely sure where this value came from).

Since our office has already approved this design (the configuration of the wet pond is not being modified as part of this
major modification) and it has already been constructed (per satellite imagery dated 4/19/2022), we ask that the
following changes be made as part of this major modification to bring the wet pond design into compliance:
- Increase the permanent pool surface elevation to 243.0’ so that the pond is adequately sized per the HRT
method (and so that the bottom of the vegetated shelf is at the permanent pool surface elevation). Increasing
the permanent pool surface elevation can be accomplished by either replacing the drawdown orifice with one at
the correct elevation or by adding an upturned elbow with the corrected invert to the drawdown orifice pipe on
the inside of the outlet structure (I can provide a picture if my explanation is unclear).
- Revise the orifice diameter so that the design volume (volume stored in the wet pond above the permanent
pool and below the lowest bypass elevation (top of riser @245.5’)) draws down within 2-5 days.
- Provide revised plans/calculations showing that the above two items have been incorporated into the project.
- While the forebay volume is not technically within 15%-20% of the main pool volume, we can approve a
variance for this project since the wet pond has already been graded/constructed and no further
grading/changes to the wet pond are proposed as part of this modification (The forebay is approximately 110 cf,
or 0.6% of the forebay volume, shy of being within the acceptable range per the MDC).

No other issues with the major modification were noted during review. Please resubmit the requested information
within 30 calendar days.

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Hard copies should be mailed to me at the following address:
For FedEx/UPS:
Jim Farkas
512 N. Salisbury Street, Office 640M
Raleigh, NC 27604

For USPS:
Jim Farkas
1612 Mail Service Center
Raleigh, NC 27699-1612

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.

Electronic copies should be uploaded at the following location:
https://edocs.deq.nc.gov/Forms/SW-Supplemental-Upload

Let me know if you have any questions.

Jim Farkas
State Stormwater Engineer
North Carolina Department of Environmental Quality
Office: [phone]
[e-mail]

From: DeBerry, Margie <[e-mail]>
Sent: Friday, November 18, 2022 11:34 AM
To: [e-mail]; Ward, Lee P CIV USARMY ID-READINESS (USA) <[e-mail]>;
[e-mail]; Mason Manhertz <[e-mail]>
Cc: Lawyer, Mike <[e-mail]>; Farkas, Jim J <[e-mail]>
Subject: SW6200404 Special Operations Forces (SOF) Group Support Battalion (GSB) TEMF - PN79453

Good morning,

We received your post-construction stormwater permit major modification application for the above mentioned project
on 11/18/2022. Reviews under the standard permitting process generally take 75 calendar days, but can take up to 90
calendar days per statute (our other reviewer, Corey Anen, no longer works for the State, so this review may exceed 75
days). Please upload all documents that you mailed into our office through the link provided below. Be sure to choose
the Central Office as the Primary Contact office.
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https://edocs.deq.nc.gov/Forms/SW-Supplemental-Upload

IMPORTANT NOTE: Please ensure that each file is uploaded under its appropriate file type. Additional file types can be
entered into the electronic form by clicking on the “Add Another Post-Construction File Upload” link directly below the
“State Stormwater Information Uploads” section of the form. Please do not upload entire plan sets through this form,
but rather upload the relevant individual sheets under the appropriate file type. Selecting the correct file type ensures
that the files are properly named in the electronic repository and it helps expedite the review process.

Please type in permit #: SW6200404

If you have any questions, please contact Jim Farkas [e-mail] 919-707-3646.

Thank you,

Margie DeBerry
Environmental Specialist, Division of Energy, Mineral, and Land Resources
North Carolina Department of Environmental Quality
Office: [phone]
[e-mail]

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