NC0030210_Staff Report_19980202

NPDES DOCYNENT SCANNINU COVER SMEET
NPDES Permit:
NC0030210
Charlotte / Mallard Creek WWTP
Document Type:
Permit Issuance
Was teload Allocation
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Engineering Alternatives (EAA)
Staff Report
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Document Date:
February 2, 1998
This document is printed on reuse paper -ignore a aiy
content on the reverse bide

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SOC PRIORITY PROJECT: Yes No X
If Yes, SOC No.
To: Permits and Engineering Unit
Water Quality Section
Attention: Mary Cabe
Date: February 2, 1998
NPDES STAFF REPORT AND RECOMMENDATION
County: Mecklenburg
Permit No. ACB030210 pcc o 0&
ISE 4-/4a
PART I - GENERAL INFORMATION
1. Facility and Address: Mallard Creek WWTP
CMUD
5100 Brookshire Blvd.
Charlotte, NC 28216
2. Date of Investigation: August 13, 1997
3. Report Prepared By: Todd St. John
4. Persons Contacted and Telephone Number: David Parker, P.E. [phone]; Willie Porter
[phone]
5. Directions to Site: From the intersection of Highway 29 and Harris Boulevard travel north
two miles on Highway 29. The entrance to the W WTP is on the right.
6. Discharge Point(s). List for all discharge points:
Latitude: 35' 19' 52" Longitude: 80° 41' 54"
Attach a U.S.G.S. map extract and indicate treatment facility site and discharge point on
map.
U.S.G.S. Quad No.: F16SW U.S.G.S. Name: Harrisburg, NC
7. Site size and expansion are consistent with application?
Yes X No_ If No, explain:

8. Topography (relationship to flood plain included): The WWTP is located on a moderately
sloped site. The facilities appear to be protected from the 100 year flood.
9. Location of nearest dwelling: The nearest dwelling is approximately 500 feet.
10. Receiving stream or affected surface waters: Mallard Creek
a. Classification: C
b. River Basin and Subbasin No.: YAD711
C. Describe receiving stream features and pertinent downstream uses: The stream is
approximately 30 to 40 feet wide with sandy to gravel bottom. The uses appear to be
consistent with typical Class C uses.
PART II - DESCRIPTION OF DISCHARGE AND TREATMENT WORKS
Please provide a description of existing or substantially constructed wastewater treatment
facilities: The current facilities consist of an influent pump station, dual mechanical bar
screens, aerated grit chambers, 3 primary clarifiers, 2 trickling filters, 2 aeration basins
associated with four anaerobic chambers for BPR, two round aeration basins, two final
clarifiers, dual tertiary filters, UV disinfection, anaerobic digesters, centrifuge dewatering,
and sludge drying beds. The back-up chlorination system has been removed.
2. Please provide a description of proposed wastewater treatment facilities: The proposed
changes include the addition of a fourth primary clarifier, and a cover and mixing equipment
for an existing open digester (which is currently used only for storage) in order to increase
the treatment capability of the Mallard Creek W WTP from 6.0 MGD to 8.0 MGD.
Residuals handling and utilization/disposal scheme:
a. If residuals are being land applied, please specify DWQ permit no.: WQ000057
Residuals stabilization: PSRP
C. Landfill: Grit chamber residuals and bar screenings are hauled to a Mecklenburg
County landfill by BFI.
Treatment plant classification (attach completed rating sheet): Class IV (unchanged)
5. SIC Code(s): 4952
Wastewater Code(s) of actual wastewater, not particular facilities, i.e., non -contact cooling
water discharge from a metal plating company would be 14, not 56.
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Primary: 01 Secondary:
Main Treatment Unit Code: 01103 (current operation)
PART III - EVALUATION AND RECOMMENDATIONS
The Charlotte Mecklenburg Utilities Department is applying for an authorization to construct
permit for the addition of a fourth primary clarifier, and a cover and mixing equipment for an
existing open digester (which is currently used only for storage) in order to increase the treatment
capability of the Mallard Creek WWTP from 6.0 MGD to 8.0 MGD.
According to the application, during the period from July 1996 through January 1997, the
primary clarifiers removed TSS and BOD at average efficiency rates of approximately 72% and 50%,
respectively, at an average flow of 4.5 MGD (75% capacity). The calculations for TSS and BOD
removal for the current proposal (i.e. at 8 MGD flow with an additional primary clarifier) assumed
removal efficiencies of 66% and 45% for TSS and BOD, respectively. A review of "Figure 17"
reportedly from EPA document 430/9-78-001 reveals that predicted TSS removal efficiency is within
the range predicted by the figure at 100% capacity (i.e. 8 MGD). The predicted BOD removal
efficiency of 45% at 100% flow capacity is above the range of approximately 26% to 35% removal
efficiency predicted by the above mentioned "Figure 17". However, the measured (actual) BOD
efficiency, at 75% capacity, during the period from July 1996 through January 1997, was 50% which
is greater than the predicted removal efficiency of 31% to 40% at 75% flow capacity. Therefore, the
predicted BOD removal rate at 8 MGD with a total four primary clarifiers appears to be possible.
The permittee has not proposed the construction of any other additional wastewater treatment
capability (other than pumps and appurtenances). The permittee has proposed that the BNR process
be converted to a conventional process to provide the necessary treatment to increase the capacity
of the WWTP from 6 to 8 MGD. The permittee reports that the detention time will be approximately
1 hour anoxic and 9 hours oxic at 8 MGD. The current detention time is reportedly approximately
2 and % hours anoxic and 9 and % hours oxic.
The permittee has also proposed the addition of a sludge storage facility (no A to C required)
and mixing equipment for an existing open digester (which is currently used only for storage). The
purpose of the additional storage and digestion is to increase sludge treatment and handling
capability needed for expansion. The permittee has provided calculations to support its claim that
the proper amount of sludge treatment capability will exist.
The permittee has provided plans and calculations to support its plans to increase its
discharge from 6.0 to 8.0 MGD at the Mallard Creek WWTP. As part of the proposed changes, the
WWTP will no longer be used for BNR, as it is currently designed. Currently the WWTP does not
have any need for BNR because there are no limits for total nitrogen or phosphorous in place.
However, if, in the future, total nitrogen and phosphorus limits are added to the permit, the WWTP
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should be restricted to a flow capacity of 6.0 MGD, if the permittee desires to re -convert the WWTP
to the BNR treatment process. If the permittee desires to operate the WWTP using the BNR
capabilities at a flow above 6.0 MGD, it should be required to submit plans to upgrade the facility.
This Office has no objections to the proposed changes in operation and physical upgrades to
the Mallard Creek WWTP. This Office recommends issuing the Authorization to Construct.
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Signature of Repod Preparer
Water Quality Region upervisor
Date �
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