NC0057533_Response to Comments_20190215

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540D Glenwood Avenue, Suite 400
Raleigh, North Carolina 27612
tel: [phone]
February 15,2019
Mr. David Hill
Environmental Specialist
NC DEQ/Division of Water Resources/Water Quality Permitting
NPDES Complex Permitting, Wastewater Branch
512 North Salisbury Street
Raleigh, North Carolina 27604
Subject: Brunswick County Public Utilities
Northwest WTP RO Concentrate Discharge NPDES Permit Application
Response to Comments on CORMIX Model
NPDES No.N00057533
Dear Mr. Hill:
On December 17, 2018, CDM Smith received an a -mail from Mr. David Hill of NC DEQ with the
following comments on the November 2018 draft of this report. Responses to the comments are
embedded below:
■ There are 16 scenarios modeled and summarized in Tables 6-5 through 6-7 but only four
prediction files were provided. Please provide the input and prediction files for all 16
modeled scenarios.
REPLY: For the revised draft report, we have provided a copy of a single CORMIX
output file in Appendix D; this and the remaining output files are enclosed on CD.
■ Please provide field data to justify the input assumption of unstratified conditions in the
receiving water for the modeled scenarios.
REPLY: Section 4.4.3 has been added to this report to describe the water quality data
collection program that indicated unstratified conditions at the project site. The field
data are documented in Appendix B.
■ Table 6-2 refers to Table 4-1 for ambient inputs, this seems to be in error and appears to
refer to Table 6-1, please clarify.
REPLY: The correct reference should have been Table 64 (now Table 74 in this draft).
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WATER +ENVIRONMENT +TRANSPORTATION + ENERGY + FACILITIES

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CDM
Smith
Mr. David Hill
February 15, 2019
Page 2
■ Section 3, page 3-7 has a footnote 3 in the Fish Consumption column header but there is no
associated footnote on the page, please clarify.
REPLY: This footnote reference should not have been included, and has been removed
from Table 3-3.
■ The receiving water was identified as C, Swamp waters. This area has also been classified by
the Division of Marine Fisheries as a Primary Nursery Area (PNA) under 15A NCAC 03R
.0103. According to 15A NCAC 02B .0301, all PNAs are classified as High Quality Waters
(HQW). HQWs have additional requirements listed under 15A NCAC 02B .0224. Please revise
your analysis and modeling taking into account these additional requirements.
REPLY: The revised draft report lras been updated to address the additional
requirements of the Primary Nursery Area regulations. Specifically:
• Section 2.3 was added to provide the additional requirements.
• Additional testing was conducted on the concentrate to obtain data on (1)
conventional parameters to address the oxygen consuming wastes and total
suspended criteria, and (2) acute whole effluent toxicity. The results of this testing
are included in Section 3.
• Section 3.3.2 describes the results of the acute WET testing, which showed that
there was no acute toxicity measured as a 48-hour LC50, as required by the
Primary Nursery Area/High Quality Water regulations.
• In Section 3.4, the required dilutions were increased by a factor of two, a required
by the Primary Nursery Area regulations.
• Section 6 was added to address the oxygen consuming waste, TSS and volume
requirements of the Primary Nursery Area/High Quality Water regulations.

�1.CDM
Smith
Mr. David Hill
February 1S, 2019
Page 3
■ Supplementary data were provided on the RO treatment of unregulated contaminants. Please
indicate bench test removal efficiencies and anticipated removal efficiencies under design
conditions. Also, please identify anywater quality standards or criteria associated with these
parameters, especially in light of the HQW requirements noted above.
REPLY: Section 3.2 provides an improved understanding of the design operating
conditions of the membrane facility based on additional pilot testing since the draft
report. The design operating condition is for the plant to produce permeate between
an 89 and 92% efficiency, the draft report assumed 92% efficiency. The revised draft
report has been updated to provide additional chemistry and acute and chronic WET
testing results for the concentrate from the 92% concentrate (conservative because
this concentrate has the lowest volume and hence the highest concentrations). As
described in the response to the previous comment, the required dilution was
increased to comply with the Primary Nursery Area/HQW requirements.
Please review the revised report and let us know if you have any questions.
Sinc ely,
Jonathan B. Tr Edway, P.E.
CUM Smith Inc.
cc: John Nichols, Brunswick County Public Utilities
Glenn Walker, Brunswick County Public Utilities
Bob Tweedy, Brunswick County Public Utilities
Greg Roy, CDM Smith
Bernadette Kolb, CDM Smith
Reed Barton, CDM Smith
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