NC0074772_Fact Sheet_20180424

NCDEQ / DWR / NPDES
COMPLEX -EXPEDITED FACT SHEET - NPDES PERMIT RENEWAL
NPDES Permit NCO074772
Joe R. Corporon, L.G., Compliance & Expedited Permitting Unit / 919-807-6394 02May2017
Facility Summary — This facility is a privately owned minor WWTP (flow <1 MGD) receiving 100%
domestic wastewater, plus a proposed uranium -filter generated backwash from ion -exchange (IE) treatment
of potable -water. The WWTP's extended -aeration treatment system is currently designed for a maximum
capacity of 0.0731 MGD, but is permitted to expand to a 2' phase not -to -exceed 0.100 MGD. Expansion
requires the Division's Authorization to Construct (ATC). This WWTP utilizes the following treatment
units:
• influent includes trucked -in filter backwash from potable -water treatment [ion -
exchange technology] from Subdivision wells
• influent bar screen
• V -notch weir
• flow -equalization tank
duel (2) aeration basins
dual (2) clarifiers
• aerated sludge holding tank
• tertiary filters
• tablet chlorination / tablet de -chlorination
• post aeration
• flow recorder
• effluent pump station
• standby power generator
Fact Sheet for Permit Renewal
May2017 -- NPDES Permit NCO074772 - Page 1
Table I - Facility Information
Applicant/Facility Name
AQUA North Carolina, Inc.
Diamond Head Subdivision WWTP, Class 2
Applicant Address
202 Mackenan Court, Cary, NC 27511
Facility Address
799 Williamson Road, Mooresville
Permitted Flow (MGD)
Phase 1: 0.0731 MGD, and Phase 2: 0.100 MGD
Type of Waste
Discharging 100% domestic < 1MGD
Facility Class
WW -2
County
Iredell
Permit Status
Renewal
Regional Office
MRO
Stream Characteristics
Receiving Stream
Lake Norman
[Reeds Creek Arm]
Stream
Classification
WS -IV; B; CA
Stream Segment
ll -(75)
Drainage basin
Catawba
Summer 7Q10 (cfs)
—
Subbasin
03-08-32
Winter 7QI0 (cfs)
—
Use Support
Statewide advisory for Hg
[HH for fish consumption]
30Q2 (cfs)
—
303(d) Listed
Average Flow (cfs)
—
State Grid
E15SE
IWC (%) Phase 1 & 2
Lake discharge
USGS Quad
Mooresville, NC
Facility Summary — This facility is a privately owned minor WWTP (flow <1 MGD) receiving 100%
domestic wastewater, plus a proposed uranium -filter generated backwash from ion -exchange (IE) treatment
of potable -water. The WWTP's extended -aeration treatment system is currently designed for a maximum
capacity of 0.0731 MGD, but is permitted to expand to a 2' phase not -to -exceed 0.100 MGD. Expansion
requires the Division's Authorization to Construct (ATC). This WWTP utilizes the following treatment
units:
• influent includes trucked -in filter backwash from potable -water treatment [ion -
exchange technology] from Subdivision wells
• influent bar screen
• V -notch weir
• flow -equalization tank
duel (2) aeration basins
dual (2) clarifiers
• aerated sludge holding tank
• tertiary filters
• tablet chlorination / tablet de -chlorination
• post aeration
• flow recorder
• effluent pump station
• standby power generator
Fact Sheet for Permit Renewal
May2017 -- NPDES Permit NCO074772 - Page 1

Permit Flow Conditions — Effluent flow is permitted as Phase 1 and Phase 2 (see Part I), and limited at
0.0731 MGD and 0.100 MGD [A. (1.)]. Upon reaching flow at 80% of Phase 1 design capacity, the
Permittee shall have submitted plans and specifications to the Division to upgrade the treatment system in
support of its application to expand to Phase 2. Expansion requires the Division's Authorization to
Construct (ATC) permit and subsequent submittal of an Engineer's Certification Form (see Supplement to
Permit Cover Sheet).
Table 2 - Effluent History / Summa — DMR Data Jan2012 throu h Feb2017
Parameter
Max
Min
Ave
n
Units / Comments
Flow
0.34
0.009
0.036
1885
MGD
Dissolved Oxygen
12.7
6.3
9.46
269
mg/L
Fecal Coliform
96
1
6.17
239
# / 100ml
TRC
48
2
21.4
538
µg/L
BOD 5
12.9
2
2.39
270
mg/L
pH
8.3
6.3
7.4
269
Standard Units
Ammonia
4.68
0.2
0.34
269
mg/L
TSS
18
2.5
5.04
269
mg/L
TP
5.94
1.89
4.39
22
mg/L
Renewal Summary —This renewal includes new parameters of concern (POCs) originating from potable -
water treatment systems utilizing ion -exchange (IE) technology including POCs governing radiological
uranium -filter backwash. Filter -backwash is generated by potable -water treatment of well water systems
owned and operated by AQUA. The Permittee proposes to introduce filter backwash episodically by tanker
truck into the WWTP's equalization basin for further treatment (rate: Igpm/60gph; proposed not -to -exceed
500 gpd).
Radiological POCs — Radiological POCs (see Table 3.) are added to Part I Section A. (1.) in accordance
with the Division's memo dated December 5, 2005 for Disposal Wastewater Associated with Private Water
Supply Wells (with potential radiology components). The Division applies permit limits to these POCs
without benefit of dilution (lake discharge). North Carolina Narrative Standards 15A NCAC 02B .0211
(17) for Radiological POCs address maximum contaminant levels (MCLs). The MCL of 30 gg//L for
Uranium is based on EPA Federal Criteria [40 CFR 141.66]; see federal guidance and rules EPA 816-F-01-
003 and 40 CFR Parts 9, 141, and 142.
Table 3: Radiological POCs
EFFLUENT
MONITORING REQUIREMENTS
CHARACTERISTICS
LIMITS
Measurement
Sample
Sample
[Parameter Codes]
__frequency
Type
Location
Combined radium -226 and radium -228
5 pCi/L
(pCi/L) 1, 2
11503
(report annual average)
Quarterly
Grab
Effluent
Alpha emitters, excluding radon and
15pCi/L
1 2
uranium (pCi/L)
82077
(report g
re ort annual average)
Quarterly
Grab
Effluent
Beta emitters, excluding potassium -40
and other naturallyoccurring
ocg
03520
50 pCi/L
Quarterly
Grab
Effluent
1 2
(report annual average)
radionuclides (pCi/L) '
Strontium -90 (pCi/L) 1, 2
13501
30 µg//L
(report weekly average)
Quarterly
Grab
Effluent
Tritium (pCi/L) 12
82126
20,000 pCi/L(report annual average)Quarterly
Grab
Effluent
Uranium (gg/L) 1, 3
22708
30 pg//L
(report weekly average)
Quarterly
Grab
Effluent
Fact Sheet for Permit Renewal
May2017 -- NPDES Permit NCO074772 - Page 2

Table 3 Footnotes:
1. All quarterly samples shall be taken 72 to 80 hours after the introduction of offsite
wastewater into the equalization tank. If an introduction of offsite wastewater does not
occur within a given quarter, a sample shall be taken of the effluent and noted on the DMR
as "No introduction of offsite wastewater occurred for this quarter."
2. If the quarterly value exceeds 4 times the annual average limit, then (a) the sampling
frequency shall increase to Monthly and (b), a written notification shall be sent to the
Water Quality Permitting Section and the Mooresville Regional Office (MRO).
3. A Weekly Average value can be determined from one quarterly sample, or it can be
determined from the average of multiple samples taken during a period not to exceed seven
(7) consecutive days during the quarter.
Adding Water Treatment Plant (WTP) Strategy —This renewal combines the Division's WTP
strategies (Oct2009, amended Jun2012) with WWTP strategies to accommodate a proposed complex
metals influent (Table 4). This includes monitoring only for dissolved metals with their newly
promulgated surface water standards for freshwater [see permit Part I, A. (1.)]. These metals are not
limited in the permit because their influent volume (max 500 gpd) was judged insignificant (< 0.01 %) to
the average WWTP flow. Likewise, other WTP POCs (Turbidity, Salinity and Conductivity) were deemed
insignificant to average inflow.
Table 4: POCs for Ion Exchange (IE) Technology - Phase I at 0.032 MGD /IWC=38.27%
EFFLUENT
CHARACTERISTICS
LIMITS
MONITORING REQUIREMENTS
Monthly
DailyMeasurement
Sample
Sample
[Parameter Codes]
Average
Maximum
Frequency
Type
Location
Total Hardness (mg/L)1'2
00900
Quarterly
Composite
Effluent &
Upstream
Total Copper (mg/L) 1,2
01042
7.88 gg/L
10.47 gg/L
Quarterly
Composite
Effluent
Total Chloride (mg/L) 1,2
00940
230 gg/L
250 gg/L
Quarterly
Composite
Effluent
Total Zinc (mg/L) 1,2
01092
125.7 gg/L
125.7 gg/L
Quarterly
Composite
Effluent
Chronic WET Testing 3
TGP3B
Quarterly
Grab
Effluent
Fnntnntec-
1. All test -method practical quantitation limits (PQL) must be sufficiently sensitive
considering the respective permit limit for each parameter of concern [see permit Part II.
Section D. (4.)].
2. All quarterly samples shall be taken 72 to 80 hours after the introduction of offsite
wastewater into the equalization tank. If an introduction of offsite wastewater does not
occur within a given quarter, a sample shall be taken of the effluent and noted on the DMR
as "No introduction of offsite wastewater occurred for this quarter".
3. Phase I flow - Chronic Toxicity (Ceriodaphnia dubia) test at 90% in January, April, July
and October [See A. (6.)].
Ouarterly Whole Effluent Toxicity (WET) Testing — In accordance with current strategies designating
this proposed new influent as a "complex waste stream," WET testing has been added to this permit as
fresh water Chronic [TGP3B] Quarterly monitoring [15A NCAC 02B .0200 et seq.].
Fact Sheet for Permit Renewal
May2017 -- NPDES Permit NCO074772 - Page 3

NPDES Implementation of Instream Dissolved Metals Standards - Freshwater Standards
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 5. NC Dissolved Metals Water ualit Standards/Aquatic Life Protection
Parameter
Acute FW, µg/1
(Dissolved)
Chronic FW, gg/1
(Dissolved)
Acute SW, gg/1
(Dissolved)
Chronic SW, µg/1
(Dissolved)
Arsenic
340
150
69
36
Beryllium
65
6.5
---
---
Cadmium
Calculation
Calculation
40
8.8
Chromium III
Calculation
Calculation
---
---
Chromium VI
16
11
1100
50
Copper
Calculation
Calculation
4.8
3.1
Lead
Calculation
Calculation
210
8.1
Nickel
Calculation
Calculation
74
8.2
Silver
Calculation
0.06
1.9
0.1
Zinc
Calculation
Calculation
90
81
Table 3 Notes:
1. FW= Freshwater, SW= Saltwater
2. Calculation = Hardness dependent standard
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 213.0200 (e.g., arsenic at
10 µg/1 for human health protection; cyanide at 5 gg/L and fluoride at 1.8 mg/L for aquatic life
protection).
Table 6. 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)} eA{0.9151 [In hardness] -3.1485}
Cadmium, Acute Trout waters
WER*{1.136672-[ln hardness] (0.041838)} eA{0.9151[ln hardness] -3.6236}
Cadmium, Chronic
WER*{1.101672-[1n hardness] (0.041838)} -e A {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^{1.273[In hardness] -4.705}
Nickel, Acute
WER*0.998 • e^{0.8460[ln hardness]+2.255}
Fact Sheet for Permit Renewal
May2017 -- NPDES Permit NC0074772 - Page 4

Nickel, Chronic
WER*0.997 • e^{0.8460[ln hardness]+0.0584}
Silver, Acute
WER*0.85 • e^{1.72[ln hardness] -6.59}
Silver, Chronic
Not applicable
Zinc, Acute
WER*0.978 e^{0.8473[ln hardness]+0.884}
Zinc, Chronic
WER*0.986 eA{0.8473[ln hardness]+0.884}
General Information on the Reasonable Potential Analysis (RPA)
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.
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 1 Q 10 using the formula 1 Q 10 = 0.843 (s7Q 10, 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.
Fact Sheet for Permit Renewal
May2017 -- NPDES Permit NC0074772 - Page 5

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)+(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 IQ 10 flow.
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 - 1
Ctotal 1 + { [Kpo] [ss('+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 sheet labeled DPCs.
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 (i.e. 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 = (s7Q 10 + Qw) (Cwgs) — (s7Q 10) (Cb)
Qw
Where: Ca = allowable effluent concentration (gg/L or mg/L)
Cwqs = NC Water Quality Standard or federal criteria (lag/L or mg/L)
Cb = background concentration: assume zero for all toxicants except NH3* (gg/L or mg/L)
Qw = permitted effluent flow (cfs, match s7Q 10)
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
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Flows other than s7Q 10 may be incorporated as applicable:
IQ 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 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.
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.
10. Table 7 - Hardness / Flow Values [in the absence of data] to be used in the Reasonable Potential
Analysis (RPA):
Parameter
Value
Comments (Data Source)
Average Effluent Hardness (mg/L)
25 mg/L
Assumed (no data to date); added
[Total as, CaCO3 or (Ca+Mg)]
monitoring to create database
Average Upstream Hardness (mg/L)
25mg/L
Assumed (no data to date); added
[Total as, CaCO3 or (Ca+Mg)]
monitoring to create database
7Q10 summer (cfs)
0.08 cfs
Phase 1 flow [Outfall 0011
0.034 cfs
Phase 2 flow [Outfall 002]
1 Q 10 (cfs)
Permitted Flow (MGD)
0.032 MGD
Phase 1 flow [Outfall 001 ]
0.185 MGD
Phase 2 flow [Outfall 002]
[original signed by Joe Corporon] Date:
NPDES Permit Writer: Joe R. Corporon, L.G.
Fact Sheet for Permit Renewal
May2017 -- NPDES Permit NC0074772 - Page 7