NC0024945_approval_19970122

State of North Carolina
Department of Environment,
Health and Natural Resources
Division of Water Quality
James B. Hunt, Jr., Governor
Jonathan B. Howes, Secretary
A. Preston Howard, Jr., P.E., Director
January 22, 1997
Mr. Eric F. Davidson, P.E.
Project Manager
HDR Engineering, Inc.
Suite 1400
128 S. Tryon Street
Charlotte, North Carolina 28202-5001
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�EHNR
Subject: Aeration System Improvements
NPDES Permit No.: NC0024945
CMUD Irwin Creek WWTP
Mecklenburg County
Dear Mr. Davidson:
This letter is to acknowledge receipt of information concerning proposed aeration systems
improvements at the Irwin Creek WWTP on January 10, 1997. The proposed modifications
pertained to the following:
• Providing instrumentation/control to automatically monitor and maintain preselected DO
concentrations in 11 aeration basins.
• Modification of the existing air supply to provide discreet air supply control to specialized
zones of the aeration tanks.
• Replacement of existing porous tube -type diffusers in the 10 existing basins with
membrane diffusers for improved oxygen transfer.
Based on the information you provided, the Division of Water Quality (DWQ) does not
deem the issuance of an authorization to construct permit necessary to complete the proposed
modifications and installations.
A copy of the plans and specifications for the proposed modifications shall be kept on file
by the Permittee for the life of the facility.
If you have questions regarding this facility modification, you may contact me at (919) 733-
5083, extension 516.
Sincerely„
Steven D. Pellei
Environmental Engineer
cc: Mooresville Regional Office
Permits and Engineering Unit/Permit File
P.O. Box 29535, Raleigh, North Carolina 27626-0535 Telephone [phone] FAX [phone]
An Equal Opportunity Affirmative Action Employer 50% recycled/ 10% post -consumer paper

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January 9, 1997
North Carolina Department of Environment,
Health, and Natural Resources 1` JC —
Division of Water Quality Cnl� VJ/ ors
Permits and Engineering Unit apt 0 4 / q
P. O. Box 29535et�t ��
Raleigh, NC 27626-0535� hN �,�� C1�4L
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Attention: Mr. David A. Goodrich lr14i2 • ` t6-fr
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Re: Irwin Creek WWTP 6F 11411
Charlotte -Mecklenburg Utility Department 'S�
NPDES Permit No. NC0024945
Aeration System Improvements
HDR Project No. 00121-207-018
Dear Mr, Goodrich:
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HDR Engineering, Inc. of North Carolina (HDR), on behalf of the Charlotte -Mecklenburg Utility
Department (CMUD), is transmitting herewith information concerning proposed aeration system
improvements at the Irwin Creek WWTP.
The proposed modifications to the existing aeration system are as follows:
• Provide instrumentation/control to automatically monitor and maintain
preselected dissolved oxygen concentration in each of 11 aeration basins.
• Modify the existing air supply to provide discreet air supply control to the
carbon oxidation zone and the nitrification zone of the aeration tanks.
• Replace existing porous tube -type diffusers in 10 existing basins with
membrane disc diffusers.
CMUD has recently performed optimization studies for the Irwin Creek WWTP to
determine strategies to reduce operation and maintenance costs. The above indicated
improvements will provide CMUD significant plant operations cost savings by reducing
HDR Engineering, Inc.
of North Carolina
Suite 1400
128 S. Tryon Street
Charlotte, North Carolina
28202-5001
Telephone
704 338-6700
Fax
704 338-6760
Engineering

North Carolina Department of Environment,
Health, and Natural Resources
January 9, 1997
Page 2
gross electrical energy consumption and using electrical energy in a more efficient
manner. The instrumentation/control work will reduce the occurrence of over -aeration of
the activated sludge, and the conversion of fine bubble membrane diffusers will improve
the ability to transfer oxygen to the wastewater.
We have attached one set of 1 1x17 drawings to provide NCDEHNR Division of Water
Quality documentation of the proposed operational improvement work at the Irwin Creek
WWTP. We have also provided the technical specification Section 11088, "Fine Bubble
Membrane Type Diffusers," so that DWQ has documentation as to the type of diffusers
being installed.
It is HDR's understanding that a permit to construct from DWQ is not required for the
work that CMUD desires to perform. Currently, CMUD's project schedule is to advertise
and open bids for the aeration system improvements on February 27, 1997.
Please advise this office if any additional documentation is required and if there are any
objections by DWQ to CMUD's time schedule to proceed with the work.
Very truly yours,
HDR Engineering, Inc. of North Carolina
A. Vow r`
Eric F. Davison, P.E.
Project Manager
EFD/nct
EFD01091.DOC