NC0023973_Pretreatment_HWA_Letter_20190807

ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
LINDA CULPEPPER
Director
NORTH CAROLINA
Environmental Quality
August 7, 2019
Via Electronic Mail ([e-mail])
William Roy
Community Compliance Supervisor
Cape Fear Public Utility Authority
235 Government Center Drive
Wilmington, NC 28403
Subject: Pretreatment Review of Headworks Analysis (HWA)
Program: Cape Fear Public Utility Authority, New Hanover County
NPDES #: NCO023973 / M'Kean Maffitt WWTP
Dear Mr. Roy:
The Pretreatment, Emergency Response and Collection Systems Unit (PERCS) of the Division of
Water Resources has reviewed the Headworks Analysis (HWA) submitted by the Cape Fear Public
Utility Authority. This HWA was received by the Division on June 27, 2019. Additional information
was requested and was received on August 2, 2019.
The Division concurs with the headworks calculations of the Maximum Allowable Headworks
Loadings (MAHL) for all pollutants of concern with the following corrections and comments. All
changes were highlighted in the attached HWA spreadsheet.
1. Plant Removal Rate: was updated for Cd, Cr, CN, Pb, Ni, Ag to reflect the literature removal
rates for trickling filter.
2. Stream standards: the 2017 NPDES reasonable potential analysis were used to reference
the stream standards. The standard for Cu was removed as the NPDES limit had already
taken stream standards into consideration. The standards for CN was updated to 0.001
mg/L, for Ba was updated 25 mg/L for salt water. The standards for Hg, Mo, Se and Al
were doubled as % WQS would not apply before the expansion.
3. CBOD MAHL: In reviewing the current POTW data, there is a CBOD: BOD ratio of
approximately 96%. Therefore, we allow applying the BOD design value of 200 mg/L to
CBOD, which gives CBOD a design criteria loading of 20,016 Ibs/day. The Division suggests
using the design criteria as CBOD MAHL to prevent the POTW from potentially exceeding
its capacity.
4. Inhibition concentration: were updated for Cr and CN to reflect the literature inhibition
values for trickling filter.
NORTH CAROLINAD Q�
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North Carolina Department of Environmental Quality I Division of Water Resources
512 North Salisbury Street 11617 Mail Service Center I Raleigh, North Carolina 27699-1617
919.707.9000

5. Sludge site area: Was updated to 1324 acres using total permitted area 2962.8 acres
multiply 44.7%.
6. Uncontrollable concentration:
a. Was updated for CN to 0 to resolve over allocation as all influent and effluent data
was below detection level of 0.008 mg/L.
b. Was updated for Ag to 0.00022 mg/L to free up some allowable industrial loading, as
all data except for the December 2018 data were below the detection level of 0.002
mg/L and the December 2018's influent data should be protective as the
uncontrollable concentration.
7. Allocation table: Cu, Hg and Ag are over allocated. Looking at the uncontrollable mass
balance sheet, New Hanover Regional Medical Center on average discharges about
0.1343 Ibs/day of Cu, 0.00016 Ibs/day of Hg and 0.0044 Ibs/day of Ag. IUP revision would
likely to resolve the over allocation for Cu and Hg. It is highly recommended to use the
lowest available detection level for all future silver samples to obtain a site specific
removal rate as well as uncontrollable concentration.
8. LTMP and IUP: with the new HWA, it is a good time to reevaluate the LTMP and IUP. It is
recommended to develop two different monitoring plans for north side and south side as
their pollutants of concern varies depending on the SIUs. It appears that several
parameters in the LTMP are not required to be included, the POTW should make a
decision whether to keep them to obtain more data or to remove them to save on
sampling costs. It is also highly recommended to review the SIU's historical data and
reevaluate the necessity of certain parameters and limits. For example, parameters never
had a hit in the past could be eliminated from the IUP.
River modeling studies is undergoing to determine the 7Q10 status and revision can be made
when the 7Q10 is finalized. The next HWA will be due June 30, 2024, unless circumstances
warrant an earlier submission.
Thank you for your continued support of the Pretreatment Program. If you have any questions
or comments, please contact me at [phone] (email: [e-mail]) or
Deborah Gore, Unit Supervisor at [phone] (email: [e-mail]).
Enclosures: HWA and AT spreadsheets
vz/CF P UA_H WA_SS_2019
Ec: Central Files (LF), w/out enclosures
PERCS Unit file
Tom Tharrington, WIRO
Sincerely,
DocuSigned by:
Vivien Zhong, PERCS Unit
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