NC0001422_Fact Sheet_20200616

DEQ/DWR
FACT SHEET FOR NPDES PERMIT DEVELOPMENT
Major Modification
NPDES No. NC0001422
Facility Information
Applicant/Facility Name:
Duke Energy Progress, LLC/ L.V. Sutton Energy Complex
Applicant Address:
801 Sutton Steam Plant Road, Wilmington, NC 28401
Facility Address:
same
Permitted Flow
N/A
Type of Waste:
100 % Industrial
Facility/Permit Status:
Major Modification P Class
County:
New Hanover
Miscellaneous
Receiving Stream:
Cape Fear River
(001), Sutton Lake
(002, 004, 008)
Regional Office:
WiRO
Stream Classification:
C Sw (001)
C (002, 004, 008)
SI: 18-(63)
Quad
J27SW
Castle Hayne
303(d) Listed?:
Yes
Impaired for D.O.
(Cape Fear River
Permit Writer:
Sergei Chernikov, Ph.D.
Subbasin:
030617 (CPF)
Date:
March 10, 2020
Drainage Area (mi2):
Summer 7Q10 (cfs)
Tidally influenced
(Outfall 001);
Lake (Outfalls
002, 004, and 008)
30Q2 (cfs):
See above
Average Flow (cfs):
See above
IWC (%):
100 (Outfall 8)
22 (Outfall 001)
based on
CORMIX model
Primary SIC Code:
SUMMARY
This is a Major Modification of the NPDES wastewater permit for L.V. Sutton Energy Complex.
Duke Energy Progress Sutton Plant is a natural gas -fired 620 MW combined cycle generation facility.
The power block consists of two combustion turbine generators (each with a HRSG — heat recovery
steam generator) and one steam turbine generator. Historically, the facility operated 3 coal-fired units.
The coal-fired units were shut -down in the fourth quarter of 2013. The facility is regulated by federal
effluent guidelines (40 CFR Part 423 — Steam Electric Power Generating Point Source Category) —
BPT/BAT.
On February 11, 2015 the Wilmington Regional Office delineated the Effluent Channel at the Sutton
Energy Complex in accordance with the requirements of 15A NCAC 02B .0228. The new Outfall 008
was established to accommodate discharge from this effluent channel.
The permit is being Modified to incorporate following changes.
• Copper and Nickel Compliance Schedule for Outfall 001 /004 was eliminated. The facility
submitted a CORMIX model and limits for Copper (limit was eliminated), Nickel, Arsenic,
and Selenium were recalculated.
Page 1 of 11

• Special conditions for continuous pH and TSS monitoring were removed from the permit
since the facility completed excavation of the ash.
• Copper compliance schedule for Outfall 008 was extended by 2 years to allow the facility to
conduct a Water Effect Ratio study.
• Wastewater from the Lay of the Land Ares (LOLA) was added to Outfall 001 to facility
excavation of coal ash from LOLA.
• Whole Effluent Toxicity monitoring frequency was reduced to Quarterly from Monthly due
to the completion of the coal ash excavation.
• Internal Outfalls 005, 006, 007, and 009 were removed from the permit since all the wastewater
from these Outfalls is monitored at Outfall 008.
• Outfalls 002 and 004 were removed from the permit since both ash ponds have been
completely excavated.
• Limit for Copper (Outfall 001) was removed from the permit based on the results of the
Reasonable Potential Analysis that considered a new dilution derived from the CORMIX
model.
• Limits for Arsenic, Selenium, and Nickel (Outfall 001) have been recalculated based on the
results of the Reasonable Potential Analysis that considered a new dilution derived from the
CORMIX model.
• Acute toxicity testing requirements have been changed to Chronic Quarterly testing
requirements at 22% based on the CORMIX model.
The remaining conditions of the permit have not been changed and remain intact until the
renewal.
Wastewater outfalls:
Outfall 001 — cooling pond discharge, recirculated cooling water, non -contact cooling water,
groundwater, landfill leachate, and treated wastewater from Outfall 004 (new ash pond). The new ash
pond can discharge directly to Sutton Lake through Outfall 004 or to Cape Fear River through Outfall
001. The Outfall 001 is discharging through the mixing box that was set-up to concurrently discharge
ash pond wastewater and water from Sutton Lake. The compliance point for Outfall 001 is located
within the mixing box.
Outfall 002 — wastewater associated with the old ash pond. May consist of low volume waste, yard
drains, oily waste treatment. Wastewater can be discharged to Sutton Lake or to Cape Fear River
through Outfall 001.
Outfall 004 — wastewater associated with the new ash pond. May consist of low volume waste, yard
drains, oily waste treatment. Wastewater can be discharged to Sutton Lake or to Cape Fear River
through Outfall 001.
Outfall 008- Primarily consists of recirculating cooling water from the Combined Cycle generation
unit, contains flows from internal outfalls 005, 006, 007, 009, and stormwater outfalls.
Internal Outfall 005 — wastewater from the Combined Cycle generation unit.
Internal Outfall 006 - wastewater from the Combined Cycle generation unit.
Internal Outfall 007 — stormwater/wastewater flows from the closure activities for coal-fired units.
Internal Outfall 009 — low volume wastes from a new simple cycle combustion turbine expected to
be online in 2017.
Page 2 of 11

Outfall 010 - non -contact stormwater from North Pond Emergency Spillway, the pond will receive
stormwater from the coal ash landfill after landfill is capped.
Outfall 0 11 - non -contact stormwater from South Pond Emergency Spillway, the pond will receive
stormwater from the coal ash landfill after landfill is capped.
Stormwater outfalls discharging to the effluent channel and then to Sutton Lake via Outfall 008:
Internal Outfall SWO01 - Runoff from the temporary laydown area and the parking lot.
Internal Outfall SWO02 - Runoff from the parking lot and Peaker Combustion Turbine area.
Internal Outfall SWO03 - Runoff from the parking lot.
Internal Outfall SWO04 - Pumped stormwater from the 115 Electrical Switchyard area.
Internal Outfall SWO05 - Discharge from the south wet detention basin.
Internal Outfall SWO06 - Discharge from the rip rap armored emergency spillway for the north
infiltration basin that treats stormwater from a parking lot and surrounding areas.
Internal Outfall SWO07 - Runoff from the potential rail loading yard, rail spur, and truck roads
installed to transport coal ash from the site.
ASH POND DAMS
Seepage through earthen dams is common and is an expected consequence of impounding water
with an earthen embankment. Even the tightest, best -compacted clays cannot prevent some water
from seeping through them. Seepage is not necessarily an indication that a dam has structural
problems, but should be kept in check through various engineering controls and regularly monitored
for changes in quantity or quality which, over time, may result in dam failure.
Currently, no seeps have been detected at the site.
DILUTION MODEL
Geosyntec Consultants of NC has submitted a CORMIX model on behalf Duke Energy Progress,
LLC for the discharge of Sutton Lake water to the Cape Fear River (classified C, Swamp, PNA) at
0.35 and 3.5 MGD.
The CORMIX model was used in conjunction with a previously calibrated Environmental Fluid
Dynamics Code (EFDC) model to determine tidal inputs to the model. The outfall configuration
was updated with the latest changes to the outfall following the separation of the Cooling Pond
wastewater discharge to Sutton Lake. The model was completed in two parts. The first, the
embayment stage, is a roughly uniform channel to the main river. The plume characteristics at the
end of the embayment model run are used as inputs to the river hydrodynamics portion of the
model. For reasons discussed below, mixing zone considerations were reserved to the embayment
channel.
The model results show a buoyant plume undergoing near -field mixing for approximately three
meters before contacting the surface of the water. Near -field mixing occurs along the surface
contact for another half meter before moving into passive ambient diffusion. The plume continues
with passive diffusion and contacts the nearest bank at 14 meters eventually ending approximately 8
meters wide and 0.25 meters deep from the surface. EPA guidance for sizing acute mixings zones
(section 4.3.3 of the Tecbnical Support Document for ilaterQuality-based Toxics Control, 1991) were
reviewed with the criteria of 50 times the discharge length scale (square root of the port cross -
Page 3 of 11

sectional area) being the most restrictive of the three options, in this case 13.5 m with a dilution of
10.5. The Division believes that 13.5 m is too large of an acute mixing zone considering the
receiving water classification of Primary Nursery Area by the NC Division of Marine Fisheries, the
length of the passive buoyant plume, and that the dilution allowed at this distance too great to
protect downstream saltwater standards in accordance with 15A NCAC 2B .0203. To minimize the
mixing zone and the pollutant concentrations in the ambient spreading plume, the mixing zone will
be set where the plume contacts the water surface approximately 3 m from the outfall. The dilution
at this point is 4.5.
Dilution Chronic/Acute- 4.5:1
IWC%- 22%
Diffuser -Existing outfall structure.
Regulatory Mixing Zone- three meters downstream of outfall.
REASONABLE POTENTIAL ANALYSIS(RPA)-OUTFAL.001
The Division conducted EPA -recommended analyses to determine the reasonable potential for
toxicants to be discharged at levels exceeding water quality standards/EPA criteria by this facility.
For the purposes of the RPA, the background concentrations for all parameters were assumed to be
below detections level. The RPA uses 95% probability level and 95% confidence basis in accordance
with the EPA Guidance entitled "Technical Support Document for Water Quality -based Toxics
Control." The RPA included evaluation of dissolved metals' standards, utilizing a default hardness
value of 25 mg/L CaCO3 for hardness -dependent metals. The 2007-2014 Triennial Review
standards adopted by NC in Nov. 2014 and approved by EPA in April 2016 were used to develop
the acute and chronic limits. The RPA spreadsheets are attached to this Fact Sheet.
RPA for Outfall 001 have been re -calculated based on the results of the new CORMIX dilution model.
Calculations included: As, Be, Cd, Al, Cr, Cu, F, Pb, Hg, Mo, Ni, Se, Ag, Zn, Ba, Sb and Tl (please
see attached). The projected flow of 3.5 MGD was used in the analysis. The RPA indicated the need
for following the water -quality based limits: As, Ni, and Se.
The proposed permit requires that EPA methods 200.7 or 200.8 (or the most current versions) shall
be used for analyses of all metals except for total mercury.
MERCURY EVALUATION (Outfall 001)
The State of North Carolina has a state-wide mercury impairment. The TMDL has been developed
to address this issue in 2012. The TMDL included the implementation strategy, both documents were
approved by EPA in 2012.
The mercury evaluation was conducted in accordance with the Permitting Guidelines for Statewide
Mercury TMDL.
Year
2015
2016
Annual average
1.69
1.91
concentration n /L
Maximum sampling
3.43
9.8
result n /L
Allowable mercury concentration for this facility is 12.0 ng/L. All annual average mercury concentrations
are below the allowable level. All maximum sampling results are below the TBEL of 47.0 ng/L. Based on the
Permitting Guidelines for Statewide Mercury TMDL, the limits are not required.
INSTREAM MONITORING-OUTFALL 002
The permit required semi-annual upstream and downstream monitoring near the ash pond
discharge. These monitoring stations have been established through the Lower Cape Fear River
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Program. The monitored parameters are: total arsenic, total selenium, total mercury (method
1631E), total chromium, dissolved lead, dissolved cadmium, dissolved copper, and dissolved zinc.
The results for all parameters are below detection level upstream and downstream of the Outfall
001. It is required that the monitoring of the instream stations will continue during the next permit
cycle.
CWA SECTION 316(a)
Since the Sutton Lake has been reclassified to the "waters of the State" on November 5, 2014, the
facility has to develop a strategy to meet the state temperature standard in Sutton Lake. In order to
obtain thermal variance/mixing zone for Lake Sutton/Cape Fear River the facility shall develop and
conduct comprehensive 316(a) studies. The 316(a) studies shall be performed in accordance with the
Division of Water Resources approved plan. The temperature analysis and the balanced and
indigenous study plan shall conform to the specifications outlined in 40 CFR 125 Subpart H and the
EPA's Draft 316(a) Guidance Manual, dated 1977, and the Region 4 letter to NCDENR, dated June
3, 2010.
CWA SECTION 316(b)
The permittee shall comply with the Cooling Water Intake Structure Rule per 40 CFR 125.95. The
Division approved the facility request for an alternative schedule in accordance with 40 CFR
125.95(a)(2). The permittee shall submit all the materials required by the Rule with the next renewal
application.
TOXICITY TESTING-OUTFALL 001 AND OUTFALL 008
Current Requirement: Outfall 001, 008 — Acute P/F @ 90% using Pimepbales promelas
Recommended Requirement: Outfall 001 — Chronic P/F @ 22% using Ceriodapbnia dubia
'
Recommended Requirement: Outfall 008 — Acute P/F @ 90% using Pimepbales pmmelas
This facility has passed all toxicity tests during the previous permit cycle, please see attached.
COMPLIANCE SUMMARY
During the last 5 years, the facility has exceeded limit 3 times, please see attached. The limit violations were for
Oil and Grease (2 times - Outfall 005) and flow volume (Outfall 001), please see attached.
PERMIT LIMITS DEVELOPMENT
• The temperature limits (Outfall 001 and Outfall 008) are based on the North Carolina water
quality standards (15A NCAC 2B .0200).
• The limits for Oil and Grease and Total Suspended Solids (Outfall 001, Outfall 008, Outfall
010, and Outfall 011) are based on the requirements in 40 CFR 423.
• The pH limits (Outfall 001, Outfall 008, Outfall 010, and Outfall 011) are based on the North
Carolina water quality standards (15A NCAC 2B .0200).
• The Whole Effluent Toxicity limit (Outfall 001 and Outfall 008) is based on the
requirements of 15A NCAC 2B .0500.
• The Water Quality Based Effluent Limits for Total Arsenic, Total Selenium, and Total
Nickel (Outfall 001) are based on the results of the Reasonable Potential Analysis.
• The turbidity limit (Outfall 001) is based on North Carolina water quality standards (15A
NCAC 2B .0200).
• The Water Quality Based Effluent Limits for Total Arsenic, Total Selenium, and Total
Copper (Outfall 008) are based on the results of the Reasonable Potential Analysis.
Page 5 of 11

PROPOSED CHANGES
• Copper and Nickel Compliance Schedule for Outfall 001 /004 was eliminated. The facility
submitted a CORMIX model and limits for Copper (limit was eliminated), Nickel, Arsenic,
and Selenium were recalculated.
• Special conditions for continuous pH and TSS monitoring were removed from the permit
since the facility completed excavation of the ash.
• Copper compliance schedule for Outfall 008 was extended by 2 years to allow the facility to
conduct a Water Effect Ratio study.
• Wastewater from the Lay of the Land Ares (LOLA) was added to Outfall 001 to facility
excavation of coal ash from LOLA.
• Whole Effluent Toxicity monitoring frequency was reduced to Quarterly from Monthly due
to the completion of the coal ash excavation.
• Internal Outfalls 005, 006, 007, and 009 were removed from the permit since all the wastewater
from these Outfalls is monitored at Outfall 008.
• Outfalls 002 and 004 were removed from the permit since both ash ponds have been
completely excavated.
• Limit for Copper (Outfall 001) was removed from the permit based on the results of the
Reasonable Potential Analysis that considered a new dilution derived from the CORMIX
model.
• Limits for Arsenic, Selenium, and Nickel (Outfall 001) have been recalculated based on the
results of the Reasonable Potential Analysis that considered a new dilution derived from the
CORMIX model.
PROPOSED SCHEDULE
Draft Permit to Public Notice: March 30, 2020 (est.)
Permit Scheduled to Issue: May 22, 2020 (est.)
STATE CONTACT
If you have any questions on any of the above information or on the attached permit, please contact
Sergei Chernikov at [phone] or [e-mail].
Page 6 of 11

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 1. NC Dissolved Metals Water Quality Standards/Aquatic Life Protection
Parameter
Acute FW, µg/l
(Dissolved)
Chronic FW,
µg/1
(Dissolved)
Acute SW, µg/l
(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 1 Notes:
1. FW= Freshwater, SW= Saltwater
2. Calculation = 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 213.0200 (e.g., arsenic at 10 µg/l 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, [t/1
Cadmium, Acute
WER*{1.136672-[ln hardness](0.041838)} e^{0.9151 [In hardness]-
3.1485}
Cadmium, Acute Trout
waters
WER*{1.136672-[ln hardness](0.041838)} e^{0.9151[ln hardness] -
3.62361
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}
Page 7 of 11

Chromium III, Chronic
WER*0.860 e^{0.8190[ln hardness]+0.6848}
Copper, Acute
WER*0.960 e^{0.9422[ln hardness]-1.7001
Copper, Chronic
WER*0.960 e^{0.8545[ln hardness]-1.7021
Lead, Acute
WER* { 1.46203- [ln hardness] (0.145712)1 • e^ { 1.273 [ln hardness] -
1.460}
Lead, Chronic
WER* { 1.46203- [ln hardness] (0.145712)1 • e^ { 1.273 [ln hardness] -
4.705 }
Nickel, Acute
WER*0.998 e^{0.8460[ln hardness]+2.255}
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 e^{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/WOBELs 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.��s
• Effluent hardness and upstream hardness, site -specific data is preferred
• Permitted flow
• Receiving stream classification
Page 8 of 11

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
mstream (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/" + (s7Q10, cfs *Avg. Upstream Hardness,
m L
(Permitted Flow, cfs + s7Q10, cfs)
The Combined Hardness for acute is the same but the calculation uses the 1Q10 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.
4. The
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 + 1 [Kpo] [ss(l+a)] [10-6] i
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
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
Page 9 of 11

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 + w) (C)ygs) — (s7 Q1W (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)
s7Q10 = 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:
1Q10 = 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.
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.
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10. 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+M ]
25.0
Default value
Average Upstream Hardness
(mg/L)
25.0
Default value
[Total as, CaCO3 or (Ca+Mg)]
7Q10 summer cfs
0
Lake or Tidal
1Q10 cfs
0
Lake or Tidal
Permitted Flow (MGD)
2.1
For dewatering
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