NC0020648_More Information (Received)_20240214

2/20/24,2:23 PM Mail-Denard, Derek-Outlook
Re: [External] Re: Review of CORMIX Modeling Plan - City of Washington WWTP -
NPDES Permit No. NCO020648
Cody Shell <[e-mail]>
Wed 2/14/2024 1:52 PM
To:Denard, Derek <[e-mail]>
Cc:Jay Holley <[e-mail]>
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Hi Derek,
I have discussed possible estimates of what the nearfield and farfield might be with a few
people here in the office. I also looked back to the CORMIX study (by Black and Veatch) for the
original permit to get an idea of what these values might be. Although they didn't include
nearfield and farfield terms in their report, Black and Veatch did give estimates of the RMZ
based on a 10:1 dilution.
Depending on whether the model (Black and Veatch) used a multi-port versus a single-port,
the RMZ ranged from less than five feet to approximately 20 ft downstream. Although the City of
Washington is seeking an increase in volume of discharge, the dilution requirements should
remain approximately the same indicating an RMZ similar to Black and Veatch CORMIX model.
Another CORMIX model that GMA performed further downstream (Chocowinity Bay) resulted
in a nearfield ranging between 10 and 25 feet. The water depth was much shallower at that
location, however, and full vertical mixing of the water column is what defined the edge of the
nearfield. In the deeper waters at the field study location for the City of Washington WWTP, it is
likely that full vertical mixing would occur at a greater distance. It is our estimate that the
nearfield would likely extend to between 20 and 40 ft downstream.
An estimate of the farfield is more difficult to quantify. The width of the river at this location is
significant, and the model is likely to be considered unbounded with little chance of bank
attachment. This would default the farfield to be defined by the tidal reversals that occur at this
location. An estimated velocity from the field study of 0.15 ft/s indicates the edge of the farfield
could be several thousand feet (2, 000 - 3,500 ft) downstream.
Once GMA starts the CORMIX modeling and optimizes the port geometries, we will have a
much better idea of what the nearfield and farfield will be. We will begin the modeling within the
next few weeks and can give better estimates at that time. If you have any further questions or
need any other additional information, please do not hesitate to ask.
Thank you,
Cody Shell, PG
Project Hydrogeologist
Groundwater Management Associates, Inc.
4300 Sapphire Court, Suite 100
Greenville, NC 27834
Phone: [phone]
Email: [e-mail]
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2/20/24,2:23 PM Mail-Denard, Derek-Outlook
GMA
From: Denard, Derek<[e-mail]>
Sent: Wednesday, February 7, 2024 10:29 AM
To: Cody Shell <[e-mail]>
Subject: Re: [External] Re: Review of CORMIX Modeling Plan -City of Washington WWTP- NPDES Permit No.
NCO020648
Cody,
We wanted estimates of what the nearfield/farfield might be.
Thanks,
Derek C. Denard
Environmental Program Consultant, Division of Water Resources
North Carolina Department of Environmental Quality
Office: [phone]
[e-mail]
From: Cody Shell <[e-mail]>
Sent:Tuesday, February 6, 2024 1:43 PM
To: Denard, Derek<[e-mail]>
Subject: [External] Re: Review of CORMIX Modeling Plan -City of Washington WWTP- NPDES Permit No.
NCO020648
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Hi Derek,
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2/20/24,2:23 PM Mail-Denard, Derek-Outlook
My name is Cody Shell (GMA) and I will be doing the CORMIX modeling for the City of Washington
WWTP. I saw the response to the dilution study plan and I was a little confused by it. The information
you requested (nearfield/farfield and CORMIX files) are the end results of the CORMIX modeling. Did
you want estimates of what those values might be, or were these comments about what should be
included with the modeling report? Please let me know what information (if any) you need before I start
the modeling process
Thank you,
Cody Shell
Project Hydrogeologist
Groundwater Management Associates, Inc.
4300 Sapphire Court,Suite 100
Greenville, NC 27834
Phone: [phone]
Email: [e-mail]
From: Denard, Derek<[e-mail]>
Sent: Friday, February 2, 2024 3:48 PM
To: Russell,Jonathan <[e-mail]>; [e-mail]
<[e-mail]>; Cody Shell <[e-mail]>;Jay Holley<[e-mail]>;
[e-mail] <[e-mail]>; Blaine Humphrey
<[e-mail]>
Cc: Coco, Nick A<[e-mail]>; Dowden, Doug<[e-mail]>; Litzenberger, Kristin S
<[e-mail]>;Tankard, Robert<[e-mail]>; Bullock, Robert
<[e-mail]>; Montebello, Michael J <[e-mail]>; Orlando, Anjali
<[e-mail]>
Subject: Review of CORMIX Modeling Plan -City of Washington WWTP- NPDES Permit No. NCO020648
Dear Mr. Russell:
Please find the attached review comments for the CORMIX Modeling Plan submitted for the City of
Washington WWTP NPDES Permit No. NC. Also attached is the CORMIX Checklist for Data Preparation.
Please let us know if you have any questions regarding these comments and we will schedule a meeting
to discuss them accordingly. Should you have any questions, please feel free to contact Derek Denard at
[phone]/[e-mail] or Doug Dowden at [phone] /
[e-mail].
Sincerely,
Derek C. Denard
Environmental Program Consultant, Division of Water Resources
North Carolina Department of Environmental Quality
Office: [phone]
[e-mail]
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2/20/24,2:23 PM Mail-Denard, Derek-Outlook
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