NC0083658_Draft Permit_20220503

ROY COOPER
Governor
ELIZABETH BISER
Secretary
RICHARD E. ROGERS, Jr.
Director
NORTH CAROLINA
fnvrronmerrfii rtatr�y
May 3, 2022
Daikin Applied Americas, Inc. (DAA)
13600 Industrial Park Blvd
Minneapolis, Minnesota 55441
c/o CORR Environmental Resources, Inc.
Raymond Roblin, P.G., Principal Hydrogeologist
4609 Candlestick
Garland, Texas 75043
Subject:
Mr. Roblin:
NPDES Permit - DRAFT Review
Permit NC0083658
former HeatCraft Site GW-REM
WPCS Grade PC-1
602 Sunnyvale Drive, Wilmington
New Hanover County
In response to your request to renew the subject NPDES permit, received June 21, 2021, the
Division of Water Resources (DWR or the Division) hereby transmits this draft for your review
and comment. Please review this document carefully to assure your understanding of the permit
limits and monitoring conditions, and to correct errors, if any.
Concurrent with this notification, the Division will solicit public comment on this draft by
publishing a notice in newspapers having circulation in the general New Hanover County area,
as required by the NPDES Program. Please provide your written comments, if any, to me via
email [[e-mail]], or write to my attention care of NCDEQ / DWR / NPDES
Program no later than June 5, 2022, approximately 30 days after receiving this letter. Your
written comments are welcome but are not mandatory.
SUMMARY OF RENEWAL CHANGES
• Updated permit format and vicinity map
• Added TCA monitoring - no limits
• Revised treatment facility description
• Considering stated parameters of concern (POCs) believed
present (volatile and semi -volatile compounds)
• Added EPA 624/625, monitor Quarterly
• Updated text for eDMR reporting
D_EC)
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 --
919.707.3616

Raymond Roblin, P.G.
Renewal - Draft Permit Review
April 2022
Page 2
The NPDES standard conditions (Parts II, III, and IV), are part of this permit but are not included
in this draft document (cover, map, and Part I). The latest version of Parts II, III, and IV are
available at https://bit.ly/2BZ4xxx and can be viewed online or downloaded as a PDF file.
Following the mandatory 45-day public comment period, the Division will review all pertinent
comments, if any, and take appropriate action prior to issuing an NPDES permit final. If you have
questions, please email the undersigned at [ioe.corporon(a,ncdenr.gov]. In support of mandated
emergency response to Covid 19, most of NC State Government may currently function remotely,
therefore correspondence via email is preferred.
Resetfully,
Joe R. Corp on, P.C.
DEQ / D /NPDES
Enclosure: NPDES Permit NC0083658 (renewal Dt AFT)
ec: NPDES Program Files / Laserfiche [draft permit and Fact Sheet]
WiRO/SWPS, Morella S. King, Supervisor
OCU, Maureen Kinney
ATB, Cindy Moore; Zachary Thomas
DAA: Donald Rooks[[e-mail]]
CORR: Raymond Roblin [[e-mail]]

Permit NC0083658
is hereby authoriz
HeatCr
to receiving waters designa
River Basin in accordance wi
conditions set forth in Parts I, I
STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENTAL QUALITY
DIVISION OF WATER RESOURCES
PERMIT
TO DISCHARGE WASTEWATER UNDER THE
NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM
(NPDES)
In compliance with the provisions of North Carolina Gener
standards and regulations promulgated and adopted by
Commission, and the Federal Water Pollutj
tatute 143-215.1, other lawful
orth Carolina Water Quality
trol Act, as amended,
Daikin Applied mericas
13600 I ► ustri # Blvd
Minneapo nn Qto 55441
fr • � .. ac
ility located at the former
undemediation (GW- REM)
ale ive, Wilmington
anover County
named tributary to Barnard's Creek within the Cape Fear
discharge limitations, monitoring requirements, and other
III, and IV hereof.
This permit shall become effective
, 2022.
This permit and the authorization to discharge shall expire at midnight on December 31, 2026.
Signed this day , 2022.
for Richard Rogers, Jr., Director
Division of Water Resources
By the Authority of the Environmental Management Commission
Page 1 of 7

Permit NC0083658
SUPPLEMENT TO PERMIT COVER SHEET
All previous NPDES Permits issued to this facility, whether for operation or discharge are hereby
revoked. As of this permit issuance, any previously issued permit bearing this number is no longer
effective. Therefore, the exclusive authority to operate and discharge from this facility arises under
the permit conditions, requirements, terms, and provisions included herein.
Daikin Applied AmericaAInc.
is hereby authorized to:
1. continue to operate remediation facilities t
hydrocarbon fuel products and ch1 ated
limited to,
• eight (8) each G -x : ction
• oil/water sepa
• secondary sur
• two (2
located at the f
Hanover County,
t at a o ndwate
so s, ' is system c
EW #8]
es
pers [MAX flow each 125 gpm]
ow meters
outfall
uent containing
isting of, but not
GW-REM, 602 Sunnyvale Drive, Wilmington, New
2. discharge from said treatment works via Outfall 001, a location specified on the attached
map, into an unnamed tributary (UT) to Barnards Creek [stream segment 18-88], a
waterbody currently classified C; Swamp within hydrological unit 03-06-17 [HUC:
030300000504] of the Cape Fear River Basin.
Page 2 of 7

Permit NC0083658
PART I
A. (1.) EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS
[15A NCAC 02B .0400 et seq., 02B .0500 et seq.; WPCS Grade PC-1 [15A NCAC 08G .0302]
During the period beginning on the effective date of the permit and lasting until expiration, the
Permittee is authorized to discharge treated, remediated groundwater via Outfall 001. Such
discharges shall be limited, monitored, and reported 1 by the Permittee as specified below:
EFFLUENT
CHARACTERISTICS
[Parameter Codes]
MONITORING REQUIREMENTS
Monthly
Average
Daily
Maximum
Measurement
Frequency
Sample
Type
Sample
Location
Flow (MGD)50050
0.360
Conti ous<
Recordin g
Influent or
Effluent
Trichloroethylene
(TCE)
78391
3.0 µg/L
3.0 µg/L
2/ onthly
Grab
Effluent
Trichloroethane
(TCA)
81853
on
a
Effluent
pH Standard Units
00400
Not < 6.0 or > ' u.
hly
Grab
Effluent
1, 4 Dioxane
82388
► art 1
Grab
Effluent
WET Testing 2
THP3B
Qua -r►-
Grab
Effluent
Forgeable Organics —
VOCs (EPA 624)
60
1 uarterly 3
Grab
Effluent
Base Neutrals
&Acids semi-VOCs
EPA 625 -
28
Quarterly 3
Grab
Effluent
Total Volatile
Organics
EPA 6
Semi -Annually
Grab
Effluent
Footnotes:
1. Beginning on the effective date, the Permittee shall submit discharge Monitoring Reports electronically using
DWR's eDMR submittal system [See Section A. (3.)].
2. Whole Effluent Toxicity (WET) Testing; Chronic (Ceriodaphnia dubia) P/F at 90%: during the months of
February, May, August, and November [see A. (2.)].
3. Sampling and analyses shall be conducted in the first month of the calendar quarter. For eDMR reporting of
this test method, the Permittee shall enter "1" [Yes (Y) =1] if detected, and "0" [NO (N) = 0] if not detected.
Parameters detected by this method shall be recorded in the "Comments" section, to include the compound and
its reported concentration. Laboratory reports shall be kept on file in accordance with records retention
requirements, Part II. Section D. 6.
\Z
Condition: The Permittee shall discharge no floating solids or foam visible in other than trace amounts.
Page 3 of 7

Permit NC0083658
A. (2.) CHRONIC TOXICITY - PERMIT LIMIT (QUARTERLY)
[15A NCAC 02B .0500 et seq.]
The effluent discharge shall at no time exhibit observable inhibition of reproduction or significant mortality
to Ceriodaphnia dubia at an effluent concentration of 90%. The permit holder shall perform at a minimum,
quarterly monitoring using test procedures outlined in the "North Carolina Ceriodaphnia Chronic Effluent
Bioassay Procedure," Revised February 1998, or subsequent versions or, "North Carolina Phase II Chronic
Whole Effluent Toxicity Test Procedure" (Revised -February 1998) or subsequent versions. The tests will be
performed during the months of January, April, July, and October. Effluent sampling for this testing shall
be performed at the NPDES permitted final effluent discharge below all treatment processes.
NOTE: If the test procedure, performed as the first test of any single quarter, results in a failure or ChV
below the permit limit, then multiple -concentration testing shall be • = f. ed at a minimum, in each of the
two following months, as described in "North Carolina Phase II is Whole Effluent Toxicity Test
Procedure" (Revised -February 1998) or subsequent versions.
The chronic value for multiple concentration tests will
highest concentration having no detectable impairme
concentration that does have a detectable impairment o
"detectable impairment," collection methods,
in the "North Carolina Phase II Chronic Whol
or subsequent versions.
All toxicity testing results requi
Monitoring Form (MR-1) for t
for the pass/fail results and THP
sent to the following
rmined us : the geometric mean of the
reproduction or ival and the lowest
roduc ' ► or s v.. The definition of
further sta.'s 'cal methods are specified
Test Procedure (Revised -February 1998)
be entered on the Effluent Discharge
ere p ' i' ed, using the parameter code TGP3B
e. Additionally, DWQ Form AT-3 (original) is to be
olina Division of Water Quality
Env .nmental Sciences Section
1621 Mail Service Center
Raleigh, North Carolina 27699-1621
Completed Aquatic Toxicity e F shall be filed with the Environmental Sciences Section no later than
30 days after the end of the rep g . eriod for which the report is made. Test data shall be complete,
accurate, include all supporting c - ical/physical measurements and all concentration/response data, and be
certified by laboratory supervisor and ORC or approved designate signature. Total residual chlorine of the
effluent toxicity sample must be measured and reported if chlorine is employed for disinfection of the waste
stream.
Should there be no discharge of flow from the facility during a month in which toxicity monitoring is
required, the Permittee will complete the information located at the top of the aquatic toxicity (AT) test form
indicating the facility name, permit number, pipe number, county, and the month/year of the report with the
notation of "No Flow" in the comment area of the form. The report shall be submitted to the Environmental
Sciences Section at the address cited above. Should the Permittee fail to monitor during a month in which
toxicity monitoring is required, monitoring will be required during the following month.
Should any test data from this monitoring requirement or tests performed by the North Carolina Division of
Water Quality indicate potential impacts to the receiving stream, this permit may be re -opened and modified
to include alternate monitoring requirements or limits.
NOTE: Failure to achieve test conditions as specified in the cited document, such as minimum control
organism survival, minimum control organism reproduction, and appropriate environmental controls, shall
constitute an invalid test and will require immediate follow-up testing to be completed no later than the last
day of the month following the month of the initial monitoring.
Page 4 of 7

Permit NC0083658
A. (3.) ELECTRONIC REPORTING - DISCHARGE MONITORING REPORTS
[G.S. 143-215.1(b)]
Federal regulations require electronic submittal of all discharge monitoring reports (DMRs) and
program reports and specify that, if a state does not establish a system to receive such submittals,
then permittees must submit monitoring data and reports electronically to the Environmental
Protection Agency (EPA). The final NPDES Electronic Reporting Rule was adopted and became
effective on December 21, 2015.
NOTE: This special condition supplements or supersedes the following sections within Part II of
this permit (Standard Conditions for NPDES Permits):
• Section B. (11.)
• Section D. (2.)
• Section D. (6.)
• Section E. (5.)
Signatory Requirements
Reporting
Records Retention
Monitoring Reports
1. Reporting Requirements [Supersedes Section D. 2 and Section E. (5.) (a)1
Effective December 21, 2016
electronically using the N
application.
Monitoring resu
and submitte
enter monitori
the state's eDMR
Regulation (CRO
the state electronicall
printing, signing, and su
to the following address:
onic
ata and s
lication
), Pe
'ng e
ischarge monitoring data
nitoring Report (eDMR) internet
onth(s) shall be summarized for each month
MR system allows permitted facilities to
Rs eleconically using the internet. Until such time that
ant with EPA's Cross -Media Electronic Reporting
ee *F1 be required to submit all discharge monitoring data to
R and will be required to complete the eDMR submission by
one signed original and a copy of the computer printed eDMR
NC DENR / Division of Water Resources / Water Quality Permitting Section
ATTENTION: Central Files
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
If a Permittee is unable to use the eDMR system due to a demonstrated hardship or due to the
facility being physically located in an area where less than 10 percent of the households have
broadband access, then a temporary waiver from the NPDES electronic reporting requirements
may be granted and discharge monitoring data may be submitted on paper DMR forms (MR 1,
1.1, 2, 3) or alternative forms approved by the Director. Duplicate signed copies shall be
submitted to the mailing address above. See "How to Request a Waiver from Electronic
Reporting" section below.
Regardless of the submission method, the first DMR is due on the last day of the month
following the issuance of the permit or in the case of a new facility, on the last day of the month
following the commencement of discharge.
Page 5 of 7

Permit NC0083658
Starting on December 21, 2020, the Permittee must electronically report the following
compliance monitoring data and reports, when applicable:
• Sewer Overflow/Bypass Event Reports;
• Pretreatment Program Annual Reports; and
• Clean Water Act (CWA) Section 316(b) Annual Reports.
The Permittee may seek an electronic reporting waiver from the Division (see "How to Request
a Waiver from Electronic Reporting" section below).
How to Request a Waiver from Electronic Reporting
The Permittee may seek a temporary electronic reporting waiver from the Division. To obtain
an electronic reporting waiver, a Permittee must first submi . 1 electronic reporting waiver
request to the Division. Requests for temporary electro - . orting waivers must be submitted
in writing to the Division for written approval at leas 0) days prior to the date the
facility would be required under this permit to be ' imit' : monitoring data and reports.
The duration of a temporary waiver shall not e ce 5 years a all thereupon expire. At
such time, monitoring data and reports shall bmitted electro lly to the Division unless
the Permittee re -applies for and is granted a ne t p electro eporting waiver by the
Division. Approved electronic report aivers no ransferrable. my permittees with an
approved reporting waiver request ma
Division for the period that th- :. Trove
Information on eDMR a
on the following web pag
http://portal.n . e
2. Signatory Refill'
(d)1
ng data and reports on paper to the
request is effective.
ectronic reporting waiver are found
leme is Section B. (11.) (b) and Supersedes Section B. (11.)
All eDMRs submitted s e . r it issuing authority shall be signed by a person described in
Part II, Section B. (11.)(a a duly authorized representative of that person as described in
Part II, Section B. (11.)(b). person, and not a position, must be delegated signatory authority
for eDMR reporting purposes.
For eDMR submissions, the person signing and submitting the DMR must obtain an eDMR user
account and login credentials to access the eDMR system. For more information on North
Carolina's eDMR system, registering for eDMR and obtaining an eDMR user account, please
visit the following web page:
http://portal.ncdenr.org/web/wq/admin/bog/ipu/edmr
Page 6 of 7

Permit NC0083658
Certification. Any person submitting an electronic DMR using the state's eDMR system shall
make the following certification [40 CFR 122.22]. NO OTHER STATEMENTS OF
CERTIFICATION WILL BE ACCEPTED:
"I certify, under penalty of law, that this document and all attachments were prepared under my
direction or supervision in accordance with a system designed to assure that qualified personnel
properly gather and evaluate the information submitted. Based on my inquiry of the person or
persons who manage the system, or those persons directly responsible for gathering the
information, the information submitted is, to the best of my knowledge and belief true, accurate,
and complete. I am aware that there are significant penalties for submitting false information,
including the possibility of fines and imprisonment for knowing violations."
Records Retention [Supplements Section D. (6.)1
The Permittee shall retain records of all Discharge
submissions. These records or copies shall be
the date of the report. This period may be ex
CFR 122.41].
on �,' eports, including eDMR
ned for : -riod of at least 3 years from
by request o'. t ' e Director at any time [40
Page 7 of 7

HWY 421
.•
• ea Tan .�
UT to Barnard's
Creek (flows S)
River Road
Daikin Applied Americas, Inc.
[former] HeatCraft Site GW-REM
Receiving Stream:
USGS Ouad/State Grid:
Latitude:
Longitude:
Drainage Basin:
Barnards Creek [stream segment 18-80]
Wilmington, NC / K27NW
N 34° 10' 33" Sub -Basin: 03-06-17
W 77° 56' 14" HUC: 030300000504
Cape Fear River Basin Stream Class: C; Swamp
Outfall 001
(flows south)
Barnard's Creek
(flows W)
Cape Fear River
Facility
Location
[not to scale]
North
NPDES Permit NC0083658
New Hanover County

DENR / DWR / NPDES
COMPLEX - EXPIDITED FACT SHEET
FOR NPDES PERMIT RENEWAL
NPDES NC0083658
Facility Information
Applicant/
Facility Name:
Daikin Applied Americas, Inc. (DAA)
[former] HeatCraft Site — Groundwater Remediation (GW-REM)
Applicant Address:
13600 Industrial Park Blvd, Minneapolis, Minnesota 55441
Facility Address:
602 Sunnyvale Drive, Wilmington 25412
Consultant Contact:
Raymond Roblin, PG, Principal Hydrogeologist
972-523-0487 / [[e-mail]]
Facility Contact:
Donald Rooks[[e-mail]] 763-553-5005
Flow — Permitted / MA Flow
design flow => 0.360 MGD
max. flow => 0.230 MGD (Aug2018); ave. flow => 0.120 MGD
Type of Waste:
GW treated for fuel hydrocarbons and chlorinated solvents — TCE, TCA
Facility Class / Permit Status:
Class PC-1 / Renewal
County:
New Hanover
Miscellaneous
Receiving Stream:
UT to Barnards Creek
Regional Office:
Wilmington (WiRO)
Stream Classification:
C; Sw
State Grid / USGS Quad:
K27NW / Wilmington
303(d) Listed?
No [Supporting]
Permit Writer:
Joe R. Corporon. P.G.
Subbasin:
03-06-17
Date:
02May2022
HUC:
030300000504
Outfall: Lat. N 34° 10' 33" / Long. W 77° 56' 14"
--Ner-
i
Drainage Area (min):
Summer 7Q10 (cfs)
0.0
Winter 7Q10 (cfs):
0.0
30Q2 (cfs)
0.0
Average Flow (cfs):
0.0
IWC (%):
100%
Primary SIC Code
Site Background — Groundwater remediation (GW-REM) at the former HeatCraft plant was approved in
1994 with DWR's first discharge permit and Authorizations to Construct (ATCs). While there have been
multiple property owners (at least six) since that time, GW-REM continues. HeatCraft stored chlorinated
solvents used to degrease parts during the manufacture of refrigeration coils. Historically, an accidental
release of 400 to 500 gallons of trichloroethylene (TCE) caused the first adverse environmental impacts
in 1983 with a second release 1987 of 55 gallons of Trichloroethane (TCA).
Treatment System Components —
• eight (8) each GW extraction wells [EW #1 thru EW #8]
• oil/water separator / primary surge tank
• secondary surge tanks [2 each in series]
• two (2) each QED EZ-24 6SS air strippers [MAX flow each 125 gpm]
• appurtenant valves, sample ports, and flow meters
• discharge line to a concrete ditch @ outfall
Fact Sheet
NPDES NC0083658 - Renewal May2022
Page 1

Receiving Stream — Barnards Creek [segment 18-80], classified C; Swamp, supporting/ not impaired
[not 303d listed, 2010]. Outfall 001 discharges to a UT draining southeast for about 1.8 creek miles of
swampland before reaching mainstem Barnards Creek, draining ultimately another —1.4 creek miles
before reaching the Cape Fear River, Impaired for aquatic life (see attached map).
Parameters of Concern (POCs) — Previous monitoring requirements include Flow (limited by design,
0.360 MGD), pH, WET testing, and the POC, trichloroethylene (TCE). Effluent TCE was reported in
April and in May 2018 [respectively 14.6 ug/L and 1.0 ug/L]. The permittee reported this as an
operational equipment error, and asserts that, if the existing treatment system is properly maintained and
operated, it has proven successful in removing TCE to 1.0 ug/L, in compliance the permit limits of 3.0
ug/L. All other TCE samples were reported below the laboratory PQL (106 samples, Sep2017 to
Feb2022),
Reasonable Potential Analysis (RPA) — However, the TCE database shows reasonable potential. To
exceed its surface water -quality standard. Therefore, TCE monitoring and limits, are hereby continued.
Other POCs were not detected above their laboratory practical quantitation level (PQL), but
monitoring remains in the permit as they are as established POCs in influent groundwater. Likewise,
trichloroethane (TCA) and related break -down daughter products of chlorinated solvents are considered
primary POCs in the influent prompting Simi -Annual monitoring to include EPA 624 and 625 (see
Permittee's APP page 2).
Whole Effluent Toxicity (WET) Testing — This facility has "passed" all quarterly WET tests since July
2017 (18 Quarterly tests). No changers recommended.
SUMMARY OF RENEWAL CHANGES
• Updated permit format and vicinity map
• Added TCA monitoring - no limits
• Revised treatment facility description
• Considering stated parameters of concern (POCs)
believed present (volatile and semi -volatile compounds)
• Added EPA 624/625, monitor Quarterly
• Updated text for eDMR reporting
PROPOSED SCHEDULE FOR PERMIT ISSUANCE
Draft Permit to Public Notice:
Permit Scheduled to Issue [estimated]:
Effective Date [estimated]
NPDES UNIT CONTACT
May 03, 2022
July 10, 2022
August 1, 2022
If you have questions regarding any of the above information or on the attached permit, please contact
Joe Corporon [[e-mail]].
NAME:
DATE: 02MAY2022
Fact Sheet
NPDES NC0083658 - Renewal May2022
Page 2

NPDES Implementation of Instream Dissolved Metals Standards - Freshwater
The NC 2007-2015 Water Quality Standard (WQS) Triennial Review was approved by the NC Environmental
Management Commission (EMC) on November 13, 2014. The US EPA subsequently approved the WQS revisions
on April 6, 2016, with some exceptions. Therefore, metal limits in draft permits out to public notice after April 6,
2016 must be calculated to protect the new standards - as approved.
Table 1 Notes:
1. FW= Freshwater, SW= Saltwater
2. Calculatiol = Hardness dependent standard
3. Only the aquatic life standards listed above are expressed in dissolved form. Aquatic life standards for
Mercury and selenium are still expressed as Total Recoverable Metals due to bioaccumulative concerns (as
are all human health standards for all metals). It is still necessary to evaluate total recoverable aquatic life
and human health standards listed in 15A NCAC 2B.0200 (e.g., arsenic at 10 µg/1 for human health
protection; cyanide at 5 µg/L and fluoride at 1.8 mg/L for aquatic life protection).
Table 2. Dissolved Freshwater Standards for Hardness -Dependent Metals
The Water Effects Ratio (WER) is equal to one unless determined otherwise under 15A NCAC 02B
.0211 Subparagraph (11)(d)
Metal
NC Dissolved Standard, µg/1
Cadmium, Acute
WER*{1.136672-[ln hardness](0.041838)} • e^{0.9151 [ln hardness]-
3.1485}
Cadmium, Acute Trout
waters
WER*{1.136672-[ln hardness](0.041838)} • e^{0.9151[ln hardness] -
3.6236}
Cadmium, Chronic
WER*{1.101672-[ln hardness](0.041838)} • e^{0.7998[ln hardness]-
4.4451 }
Chromium III, Acute
WER*0.316 • e^{0.8190[ln hardness]+3.7256}
Chromium III, Chronic
WER*0.860 • e^{0.8190[ln hardness]+0.6848}
Copper, Acute
WER*0.960 • e^{0.9422[ln hardness]-1.700}
Copper, Chronic
WER*0.960 • e^{0.8545[ln hardness]-1.702}
Lead, Acute
WER*{1.46203-[ln hardness](0.145712)} • e^{1.273[ln hardness]-
1.460}
Lead, Chronic
WER* { 1.46203-[ln hardness](0.145712)} • e^ {1 .27 3[ln hardness]-
4.705}
Nickel, Acute
WER*0.998 • e^{0.8460[ln hardness]+2.255}
Nickel, Chronic
WER*0.997 • e^{0.8460[1n hardness]+0.0584}
Silver, Acute
WER*0.85 • e^{1.72[In hardness]-6.59}
Silver, Chronic
Not applicable
Zinc, Acute
WER*0.978 • e^{0.8473[ln hardness]+0.884}
Zinc, Chronic
WER*0.986 • e^{0.8473[ln hardness]+0.884}
General Information on the Reasonable Potential Analysis (RPA)
Fact Sheet
NPDES NC0083658 - Renewal May2022
Page 3

The RPA process itself did not change as the result of the new metals standards. However, application of the
dissolved and hardness -dependent standards requires additional consideration in order to establish the numeric
standard for each metal of concern of each individual discharge.
The hardness -based standards require some knowledge of the effluent and instream (upstream) hardness and so
must be calculated case -by -case for each discharge.
Metals limits must be expressed as `total recoverable' metals in accordance with 40 CFR 122.45(c). The discharge -
specific standards must be converted to the equivalent total values for use in the RPA calculations. We will
generally rely on default translator values developed for each metal (more on that below), but it is also possible to
consider case -specific translators developed in accordance with established methodology.
RPA Permitting Guidance/WQBELs for Hardness -Dependent Metals - Freshwater
The RPA is designed to predict the maximum likely effluent concentrations for each metal of concern, based on
recent effluent data, and calculate the allowable effluent concentrations, based on applicable standards and the
critical low -flow values for the receiving stream.
If the maximum predicted value is greater than the maximum allowed value (chronic or acute), the discharge has
reasonable potential to exceed the standard, which warrants a permit limit in most cases. If monitoring for a
particular pollutant indicates that the pollutant is not present (i.e. consistently below detection level), then the
Division may remove the monitoring requirement in the reissued permit.
1. To perform a RPA on the Freshwater hardness -dependent metals the Permit Writer compiles the following
information:
• Critical low flow of the receiving stream, 7Q10 (the spreadsheet automatically calculates the 1Q10
using the formula 1Q10 = 0.843 (s7Q10, cfs) 0.993
• Effluent hardness and upstream hardness, site -specific data is preferred
• Permitted flow
• Receiving stream classification
2. In order to establish the numeric standard for each hardness -dependent metal of concern and for each
individual discharge, the Permit Writer must first determine what effluent and instream (upstream)
hardness values to use in the equations.
The permit writer reviews DMR's, Effluent Pollutant Scans, and Toxicity Test results for any hardness
data and contacts the Permittee to see if any additional data is available for instream hardness values,
upstream of the discharge.
If no hardness data is available, the permit writer may choose to do an initial evaluation using a default
hardness of 25 mg/L (CaCO3 or (Ca + Mg)). Minimum and maximum limits on the hardness value used
for water quality calculations are 25 mg/L and 400 mg/L, respectively.
If the use of a default hardness value results in a hardness -dependent metal showing reasonable potential,
the permit writer contacts the Permittee and requests 5 site -specific effluent and upstream hardness
samples over a period of one week. The RPA is rerun using the new data.
The overall hardness value used in the water quality calculations is calculated as follows:
Combined Hardness (chronic)
= (Permitted Flow, cfs *Avg. Effluent Hardness, mg/L) x (s7Q10, cfs *Avg. Upstream Hardness, mg/L)
(Permitted Flow, cfs + s7Q10, cfs)
The Combined Hardness for acute is the same but the calculation uses the 1Q10 flow.
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3. The permit writer converts the numeric standard for each metal of concern to a total recoverable metal,
using the EPA Default Partition Coefficients (DPCs) or site -specific translators, if any have been
developed using federally approved methodology.
EPA default partition coefficients or the "Fraction Dissolved" converts the
value for dissolved metal at laboratory conditions to total recoverable metal
at in -stream ambient conditions. This factor is calculated using the linear
partition coefficients found in The Metals Translator: Guidance for
Calculating a Total Recoverable Permit Limit from a Dissolved Criterion
(EPA 823-B-96-007, June 1996) and the equation:
Cdiss =
Ctotal
1
1 + { [Kpo] [ss(1+a)] [10-6] }
Where:
ss = in -stream suspended solids concentration [mg/1], minimum of 10 mg/L
used, and
Kpo and a = constants that express the equilibrium relationship between
dissolved and adsorbed forms of metals. A list of constants used for each
hardness -dependent metal can also be found in the RPA program under a
-1- - 1_1-_1.,,1 1-1Te1..
4. The numeric standard for each metal of concern is divided by the default partition coefficient (or site -
specific translator) to obtain a Total Recoverable Metal at ambient conditions.
In some cases, where an EPA default partition coefficient translator does not exist (ie. silver), the dissolved
numeric standard for each metal of concern is divided by the EPA conversion factor to obtain a Total
Recoverable Metal at ambient conditions. This method presumes that the metal is dissolved to the same
extent as it was during EPA's criteria development for metals. For more information on conversion factors
see the June 1996 EPA Translator Guidance Document.
5. The RPA spreadsheet uses a mass balance equation to determine the total allowable concentration (permit
limits) for each pollutant using the following equation:
Ca = (s7Q10 + Qw) (Cwqs) — (s7Q10) (Cb)
Qw
Where: Ca = allowable effluent concentration (µg/L or mg/L)
Cwqs = NC Water Quality Standard or federal criteria (µg/L or mg/L)
Cb = background concentration: assume zero for all toxicants except NH3* (µg/L or mg/L)
Qw = permitted effluent flow (cfs, match s7Q10)
s7Q 10 = summer low flow used to protect aquatic life from chronic toxicity and human health through
the consumption of water, fish, and shellfish from noncarcinogens (cfs)
* Discussions are on -going with EPA on how best to address background concentrations
Flows other than s7Q10 may be incorporated as applicable:
1 Q 10 = used in the equation to protect aquatic life from acute toxicity
QA = used in the equation to protect human health through the consumption of water, fish, and
shellfish from carcinogens
30Q2 = used in the equation to protect aesthetic quality
6. The permit writer enters the most recent 2-3 years of effluent data for each pollutant of concern. Data
entered must have been taken within four and one-half years prior to the date of the permit application (40
CFR 122.21). The RPA spreadsheet estimates the 95th percentile upper concentration of each pollutant.
The Predicted Max concentrations are compared to the Total allowable concentrations to determine if a
permit limit is necessary. If the predicted max exceeds the acute or chronic Total allowable concentrations,
the discharge is considered to show reasonable potential to violate the water quality standard, and a permit
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limit (Total allowable concentration) is included in the permit in accordance with the U.S. EPA Technical
Support Document for Water Quality -Based Toxics Control published in 1991.
7. When appropriate, permit writers develop facility specific compliance schedules in accordance with the
EPA Headquarters Memo dated May 10, 2007 from James Hanlon to Alexis Strauss on 40 CFR 122.47
Compliance Schedule Requirements.
8. The Total Chromium NC WQS was removed and replaced with trivalent chromium and hexavalent
chromium Water Quality Standards. As a cost savings measure, total chromium data results may be used as
a conservative surrogate in cases where there are no analytical results based on chromium III or VI. In
these cases, the projected maximum concentration (95th %) for total chromium will be compared against
water quality standards for chromium III and chromium VI.
9. Effluent hardness sampling and instream hardness sampling, upstream of the discharge, are inserted into all
permits with facilities monitoring for hardness -dependent metals to ensure the accuracy of the permit limits
and to build a more robust hardness dataset.
Hardness and flow values used in the Reasonable Potential Analysis for this permit included:
Parameter
Value
Comments (Data Source)
Average Effluent Hardness (mg/L)
[Total as, CaCO3 or (Ca + Mg)]
Metals not POCs; monitoring not required
Average Upstream Hardness (mg/L)
[Total as, CaCO3 or (Ca + Mg)]
Metals not POCs; monitoring not required
7Q10 summer (cfs)
0.0
UT discharge IWC = 100%
1 Q 10 (cfs)
0.0
UT discharge IWC = 100%
Permitted Flow (MGD)
0.360
BIMS: Highest monthly average [previous report
period] = Aug2018 (0.120 MGD; MAX=0.230
MGD).
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