NC0020648_Review of CORMIX Modeling Plan_20240202

DocuSign Envelope ID: 5AF8F8D7-FFC3-452E-99E6-538190010F3D
ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
RICHAR) E. ROGERS, JR.
Director
NORTH CAROLINA
Environmental Quality
February 2, 2024
CERTIFIED MAIL 7019 1120 0001 4877 6079
RETURN RECEIPT REQUESTED
Mr. Jonathan Russell, City Manager
City of Washington
PO Box 1988
Washington, NC 27889-1988
Subject: Review of CORMIX Modeling Plan
NPDES Permit No. NCO020648
Washington WWTP
Beaufort County
Dear Mr. Russell:
The Division of Water Resources (DWR) reviewed the "Dilution Study Plan of Effluent Mixing for
Wastewater Treatment Plant Discharge City of Washington, Beaufort County, North Carolina" submitted
to the NPDES Permitting Branch on November 6, 2023. The report was submitted by Groundwater
Management Associates, Inc. on behalf of the City of Washington to develop and apply a mixing zone
model to evaluate the potential for an expansion from 3.65 MGD to 4.95 MGD based on observed and
modeled dilution at the point of discharge. Based on our review of the plan, the Division has the following
comments and requests for additional information:
1. For additional clarity for dilution calculations, please identify what you believe will be the near -
field and far -field and what would be the distance upstream and downstream.
2. For evaluation of the model, please submit CORMIX runs and underlying files. Please include a
CORMIX lab data preparation sheet (see the attached example).
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 (919)
707-3618 / [e-mail] or Doug Dowden at [phone] / [e-mail].
Respectfully,
Ctxcuaanw e,,:
AS v6W�
�...
Doug Dowden
Supervisor, NPDES Industrial Permitting Unit
ec: NPDES Files [Laserfiche]
City of Washington / Jonathan Russell [e-mail]]; Hope Woolard [[e-mail]]
Groundwater Management Associates, Inc. / Cody J. Shell, P.G., 4300 Sapphire Court, Suite 100, Greenville, NC 27834
DWR / Nick Coco [[e-mail]]; Doug Dowden [[e-mail]];
Kristin Litzenberger[[e-mail]]; Derek Denard [[e-mail]]
WARO / Robert Tankard [[e-mail]]; Robbie Bullock [[e-mail]]
North Carolina Department of Environmental Quality I Division of W ater Resources
RE Q 512 North Salisbury Street 1 1617 Mail Service Center I Raleigh, North Carolina 27699-1617
TH 1n 919.707.9000

CORMIX Data Input
Chapter 4
CORMIX Checklist for Data Preparation — Version v5.0
PROJECTLEGEND
Project File Name: Design Case:
Site Name: Prepared By: Date:
EFFLUENT DATA
❑ Non -Fresh Water Effluent Density ❑ Fresh Water Effluent Density
Density po:......................................kg/m3 ❑ Temperature To: ................. °C ❑ Density po:................................ kg/m3
Discharge Excess Concentration: .................. ❑ Effluent Flowrate Qo .........m3/s ❑ Effluent Velocity Uo:................. mis
Pollutant Types
❑ Conservative ❑ Non Conservative: ............................ . /day ❑ Heated — Heat Loss Coefficient: ................................... W/m2/°C
❑ Brine ❑ Sediment: Chunks .......... % Sand:........... % Coarse Silt:.......... % Fine Silt:........ % Clay ........... %
Total Sediment Concentration: ............ kg/m3
AMBIENT GEOMETRY / FLOW FIELD DATA
Average Depth H.: .................................. m ❑ Unbounded ❑ Bounded: Width BS:.................... m
Depth at Discharge Hd:........................... m Appearance: ❑ Uniform ❑ Slight Meander ❑ Highly Irregular
❑ Steady ❑ Unsteady
❑ Ambient Flowrate Qa............................ m3/s ` Period ............. hr Max Velocity Um .......... m/s Tidal Velocity at this Time Ua:............ m/s
❑ Ambient Velocity Ua ............................. m/s ' ❑ At Time:.... hr Before Slack ❑ At Slack — A Time:..... hr ❑ At Time: .... hr After Slack
❑ Single Slope ❑ Near & Far Slope
Slope S:.................................................... % ❑ Near Shore Slope S1 ............................% ❑ Far Slope S2:.................................. %
Near Shore Velocity: ................................. m/s ❑ Near Shore Velocity Ua1........................ m/s ❑ Far Shore Velocity Ua2..................... m/s
Near Shore Darcy-Weisbach f:.................... ❑ Near Shore Darcy-Weisbach f1:............... ❑ Far Shore Darcy-Weisbach f2:............
❑ Breakpoint: ........................................... m
❑ Mannin 's n:........................................ Wind Speed: ................................ m/s
AMBIENT DENSITY DATA
Water Body: ❑ Fresh Water ❑ Non -Fresh Water
❑ Uniform Fresh: El Temperature: ......... °C El Density pa..... .......... kg/ m3 Non -Fresh: Density pa :. ................. kg/ m3
El Stratified
El Type A El Type B: Pycnocline Height: ............ m ❑ Type C: Pycnocline Height:.......... m Jump: ........ kg/ m3 / °C Density p: At Surface pas .................. kg/m3/ °C At Bottom pab:.................................. kg/ m3/ °C
❑ Brine & Sediment Only Level 1 Density p1:.. kg/ m3 Sub 1:............m; Level 2 Density3
P2:....... kg/ m Sub 2:........... m
DISCHARGE GEOMETRY DATA
CORMIX 1 — Single Port CORMIX 2 — Multiport CORMIX 3 — Surface Discharge
Nearest Bank: ❑ Left ❑ Right Nearest Bank: ❑ Left ❑ Right Discharge Located: ❑ Left ❑ Right
Dist. to Nearest Bank: ............................ m ❑ Unidirectional ❑ Staged ❑ Altem./ Vert. Horiz. Angle Q: ..........................0
Vert. Angle Go:...... °; Horiz. Angle vo:..... ° °1 No of openings:.........; Diffuser Length:.......... m Local Depth at Discharge Outlet: ................. m
❑ Port Diameter Do: .............. m Dist. to 1no end -point YB1:.................. m ❑ Flush ❑ Co -flowing
❑ Port Area Ao:....................m2 Dist. to 2s' far end -point Y62:.............. m ❑ Protruding: Distance from Bank:.......... m
Submerged Port Height ho: .......... m; Port Diameter Do:.... m Discharge Outlet
Port Height above Bottom ho.. ................ m Contraction Ratio:........... ❑ Channel: Width: ........ m; Depth bo:..... m
Above Surface Angles (degrees)
Pipe: Diameter Do: ................................ m
Port Height above Surface ...................... m Vert. Angle A:........ °; Horiz. Angle I7:................ ° El
Bottom Invert Depth: ..................................... m
❑ Jet -like ❑ Spray ❑ Area Align. Angle y:...... °; Relat.Orient. Angle R:...... ° Local Bottom Sloe at Chanel Ent °
Deflector Plate:. El With or ❑ Without Nozzle Direction: ❑ Same or ❑ Fanned Out P Entry:
MIXING ZONE DATA
❑ Non -Toxic Effluent ❑ Toxic Effluent
❑ WQ Standard: .......................... ❑ No WQ Standard CMC :............................ CCC:...................................
❑ Mixing Zone Specified ❑ No Mixing Zone Specified
❑ Trajectory: ............ m ❑ Downstream Distance:............ m ❑ Width:..................... % / m ❑ Area:.............................. %
Region of Interest: .................... rn Grid Intervals for Display: ...................................................
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