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- Permits \ SC0046175 2013

- Aug issued rationale.doc date printed 11/16/2015

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- 23

- 09



## South Carolina Generating Company (SCGENCO)
A.M. Williams Station

- Highway 52 Ash Disposal Facility

NPDES Permit No. SC00 46175

Permitting Engineer: Byron M Amick August 29, 2013

Facility Rating: Major Minor

Issuance (New) Reissuance Modification Minor Modification

If any part of this application is for a new facility or expansion of an existing facility or increase in permitted limits, a n antidegr adation review may be required per the requirements of R.61

- 68.D. If required, the antidegradation review will be included as part of the permit application.

Site Address: 2300 Block, US Highw ay 52, Station 445, Moncks Corner, SC 29461 County: Berkeley

Watershed: Basin 03 (Catawba-Santee River Basin)

Facility Description (include SIC code): This facility is a landfill for the disposal of coal ash and gypsum from the SCGENCO/AM Williams Station in Goose Creek, SC. SIC Code is 4952; Refuse Systems

Receiving Waters and Cl assification by outfall: 001

- Wappoola Swamp to Molly Branch to the West Branch of the Cooper River (FW) Is any discharge to Impaired Waters? Yes (see State 303(d) list for impaired waters) If Yes, list the monitoring station number(s) and parameter(s) causing impairment: The entire West Branch Cooper River from the Lake Moultrie Dam to the "T" is listed as impaired for mercury in the 2010 South Carolina Fish Consumption Advisory.

Is any discharge to a waterbody or for a parameter listed in an approved TMDL? Yes If Yes, list the parameter(s) for which t he TMDL is written and the waterbody segments impacted: Dissolved Oxygen for the Charleston Harbor, Cooper River and Wando River

Does any discharge have the potential to affect a threatened or endangered species? Yes (endangered species information from SCDNR Heritage Trust, 2008) If Yes, list the species and the waterbody in which the species resides: Sh ortnose Sturgeon

- Cooper River (including the West Branch)

Outfalls are discussed in Section I of this rationale with a general description of the discharge, treatment system, stream flows and other pertinent information about each outfall.

EPA review of the draft permit is required if any box below is checked (Mark all that apply) Permits with discharges which may adversely affect the waters of another State (Coordination with the other State is also required) List State and name of waterbody(ies) that reach affected state: NA Major permits Permits with any discharge subject to any of the prim ary industrial categories (see R.61

- 9.122, Appendix A) Permits with any discharge with an average flow exceeding 0.5 MGD Permits for federal facilities with a daily average discharge exceeding 0.05 MGD Priority permits Modification(s) to any permit listed above or a mod that changes a permit to put it into one of the above categories (where it previously was not) Modification to any permit where the schedule of complia nce interim dates are extended more than once 

## F ACT 

## S HEET

AND 

## P ERMIT 

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ATIONALERationale Page 2 of 30

Permit No. SC00 46175

List of Attachments to this Rationale:

Attachment 1 Permit Application

Attachment 2 Water Quality Spreadsheets

Attachment 3 Map of Drinking Water Intake/Source Water Protection Area Relative to Discharge

I

. PERMIT LIMITATIONS AND MONITORING REQUIREMENTS

Outfall 001 Description of outfall, receiving water and wastewater treatment system: The Williams Highway 52 Ash Disposal Facility is a landfill for the disposal of coal ash from SCGENCO’s Williams Station in Goose Creek, SC. This landfill has a sedimentation pond for the collection of ash landfill runoff, ash landfill leachate, and truck wash water. The discharge from the pond will flow to Wappoola Swamp to Molly Branch, then to the west branch of the Coo per River (Class FW). This facility began operation in July 2010 and will eventually replace the Williams Highway 17A Ash Disposal Facility. Since this facility began discharging in August 2010, the actually DMR data collected since that date and the follo w

- up 2C application will be used to determine permit limitations. The sanitary wastewater at the site is collected and hauled off

- site for disposal, and therefore is not considered part of this discharge.

Operator requirements: Based on the treatment sys tem described above and the Pollution Control Act (PCA), the treatment system is classified as Group I

- Physical/Chemical . The Environmental Certification Board Rules require that a Grade D

Physical/Chemical operator be assigned to operate this facility. Th is is a passive treatment system that requires little to no supervision. Therefore, inspections of the sediment pond system will be required once per week and anytime that discharge occurs, per Regulation 61

- 9.122.41(e)(3)(ii)(C) due to the sites ability t o stop the discharge for an appropriate period when necessary. The wastewater treatment system was permitted under the follow Permit to Construct: #19,330

- IW issued November 20, 2009.

Information for this outfall is based on NPDES Permit Application: 2D dated 3/26/10 and the follow

- up 2C dated 5/6/11

Data from Discharge Monitoring Reports (DMRs) and NPDES permit application (including all subsequent data presented)

from 8/1/10

- 2/28/11 has been used to evaluate permit limitations.

This outfall is outside a state

- approved source water protection area (SWPA) for a surface water drinking water intake, but has the potential to affect the inta ke. The affected intake (Intake # S10104 ) is owned by the Charleston Water System. The 7Q10 and AAF to be used for permitting MCL and water/organism criteria are given on the spreadsheet. Additional information on source water protection is provided in sec tions III.B and G of this rationale.

Previous permit limits are based on the permit (or modification) effective date of April 1, 2009

.

All waterbody data is provided on the attached Water Quality Spreadsheets. This data i ncludes 7Q10, annual average flow, dilution factors, hardness, TSS and other information as explained in this rationale. Additional information as necessary to explain the values used will be provided below.

A. Flow

1. Previous permit limits: Monthly Av erage: MR, MGD Daily Maximum: MR, MGD Sampling Frequency: 1/month Sample Type: instantaneous

2. NPDES Application: (No. of flow analyses: 7) Long Term Average Value: 0.698 MGD

Maximum 30

- day Value: 1.331 mg/l Maximum Daily Value: 1.331 MGDRationale Page 3 of 30

Permit No. SC00 46175

3. DMR Data: T he highest flow was reported in 9/10 as 1.331 MGD

4. Actual long

- term average flow (from DMR): 0.6678 MGD

5. Conclusion: Due to the large flows and variable nature of the discharge, flow monitoring shall continue as previously permitted. Since the nature o f the discharge is very dependent upon storm activity, the Department needs to document how often discharge occurs, therefore the permit will include a requirement to report the number of days the discharge occurs each month. Monthly Average: MR, MGD

Dai ly Maximum: MR, MGD Sampling Frequency: 1/month Sample Type: instantaneous

B. Dissolved Oxygen (DO)

1. Previous permit limits: not limited

2. NPDES Application: reporting not required

3. DMR Data: not limited

4. Water Quality Modeling Recommendation (Wa steload Allocation): not modeled

5. Stream Background Information: The Charleston Harbor, Cooper River and Wando River basins have a TMDL for Dissolved Oxygen (DO).

6. S.C. Water Classifications and Standards (S.C. Reg. 61

- 68) : This discharge is to an uncl assified tributary of the Cooper River, the Regulation states in section C.8; “ Where surface waters are not classified by name (unlisted) in

R.61

- 69, Classified Waters, the water quality standards of the class of the stream to which they are tributary shal l apply, disregarding any site specific numeric criteria for the named waterbody.” The Cooper River in this area is a

listed Class Freshwaters (FW) stream with an instream standard for DO of “daily average not less than 5.0 mg/l with a low of 4.0 mg/l”.

7. Conclusion: Non

- continuous stormwater discharges do not contribute to the DO deficit as identified in the Charleston Harbor TMDL; therefore no limit will be established for DO.

C. pH

1. Previous permit limits: Minimum

- 6.0 standard units; Maximum

- 8.5 st andard units. Sampling Frequency: 1/month Sample Type: grab

2. NPDES Application: (No. of pH analyses: 6)

minimum: 7.8 standard unit

maximum: 8.4 standard units

3. DMR Data: The lowest and highest values were reported as 7.8 in 9/10 and 8.4 in 10/10, respe ctively.

4. S.C. Water Classifications and Standards (S.C. Reg. 61

- 68) : This discharge is to an unclassified tributary of the Cooper River, the Regulation states in section C.8; “ Where surface waters are not classified by name (unlisted) in

R.61

- 69, Classi fied Waters, the water quality standards of the class of the stream to which they are tributary shall apply, disregarding any site specific numeric criteria for the named waterbody.” The Cooper River in this area is a

listed Class Freshwaters (FW) stream w ith an instream standard for pH of “between 6.0 and 8.5”

. 5. Conclusion: The pH limit will remain as previously permitted. pH shall be between 6.0 and 8.5 Sampling Frequency: 1/month Sample Type: grabRationale Page 4 of 30

Permit No. SC00 46175

D. Total Suspended Solids (TSS)

1. Previous perm it limits: Monthly Average: MR, mg/l Daily Maximum: 50 mg/l Sampling Frequency: 1/month Sample Type: grab

2. NPDES Application: (No. of TSS analyses: 6) Long Term Average Value: 5.4 mg/l

Maximum 30

- day Value: 9.0 mg/l Maximum Daily Value: 9.0 mg/l

3. DMR Data: The highest value was reported as 9 mg/l in 1/11.

4. NPDES General Permit for Storm Water Discharges Associated with Industrial Activity Part 4.1. Coal Pile

Runoff

- Any discharge composed of coal pile runoff shall not exceed a maximum concentration for any time of 50 mg/l total suspended solids.

5. Due to wastewater characteristic similarities the following guidance is used as a basis for the historical engineering judgment limitations.

40 CFR Part 411

- Cement Manufacturing Point Source Category Subp art C

- Materials Storage Piles Runoff Subcategory Sections: § 411.32, § 411.35 and § 411.37, “TSS.......Not to exceed 50 mg/l.”

40 CFR Part 423

- Steam Electric Power Generating Point Sources Category Sections: § 423.12 and § 423.15, “... the following effluent limitations shall apply to the point source discharge of coal pile runoff:” Maximum concentration for any time of TSS will be 50 mg/l

6. PQL: 1.0 mg/l (Method SM2540D)

7. Conclusion: This facility does not have coal pile runoff or cement storage pile run off, though fly ash is a raw material in the cement manufacturing industry and is a likely material stored at such sites. The Department has used these industry sources as guidance and applied this limit based on engineering judgment. Therefore based on

th e historical engineering judgment and anti

- backsliding regulations the limit will remain as previously permitted. Monthly Average: MR mg/l Daily Maximum: 50 mg/l Sampling Frequency: 1/month Sample Type: grab

E. Oil and Grease

1. Previous permit limits:

M onthly Average: 10 mg/l Daily Maximum: 15 mg/l Sampling Frequency: 1/month Sample Type: grab

2. NPDES Application: (No. of analyses: 6) Long Term Average Value: <5.0 mg/l

Maximum 30

- day Value: <5.0 mg/l Maximum Daily Value: <5.0 mg/l

3. DMR Data: All resul ts were reported as 0.0 mg/l

4. S.C. Water Classifications and Standards (S.C. Reg. 61

- 68) : Section E.5.b. states that all ground waters and surface waters of the State shall at all times, regardless of flow, be free from floating debris, oil, grease, scum , and other floating material attributable to sewage, industrial waste, or other water in amounts sufficient to be unsightly to such a degree as to create a nuisance or interfere with classified water uses or existing water uses.

5. PQL: 5.0 mg/l (Method 1664A)Rationale Page 5 of 30

Permit No. SC00 46175

6. Conclusion: Due to the truck wash contributing water to the ash leachate/runoff sedimentation pond the discharge limitations must be consistent with other vehicle wash activities, therefore the Oil and Grease limit will remain as previously per mitted. Monthly Average: 10 mg/l Daily Maximum: 15 mg/l Sampling Frequency: 1/quarter Sample Type: grab

F. Mercury, total

1. Previous permit limits: not limited

2. NPDES Application: (No. of analyses: 1) Long Term Average Value:

-- mg/l

Maximum 30

- day Va lue:

-- mg/l Maximum Daily Value: 0.00000182 mg/l

3. DMR Data: not limited

4. Water Quality Criteria: See Spreadsheet in Appendix 2.

5. Does the discharge cause, have the Reasonable Potential to Cause or Contribute: No

6. PQL: 0.0005 μg/l

7. Conclusio n: Due to the impairment for mercury in the West Branch of the Cooper River the reasonable potential

calculation was run with zero dilution. Based on the adjusted reasonable potential and the 2008 edition of S.C. Water Classifications and Standards (S.C. R eg. 61

- 68) , this parameter will not be in the permit.

G. Thallium, total

1. Previous permit limits: not limited

2. NPDES Application: (No. of analyses: 1) Long Term Average Value:

-- mg/l

Maximum 30

- day Value:

-- mg/l Maximum Daily Value: 0.703  g/l

3. D MR Data: not limited

4. Water Quality Criteria: See Spreadsheet in Appendix 2.

5. Does the discharge cause, have the Reasonable Potential to Cause or Contribute (based on the 2C): Yes

6. Other information: The facility believes the result reported on the 2C was the result of a lab error, and submitted new sample results that showed less than the PQL. Lab data was submitted from both the original sampling and

the follow

- up sampling, which has been reviewed by the Department’s Office of Laboratory Certific ation. The Laboratory Certification Officer has agreed that the sample result reported on the 2C can be attributed to carryover from the LCS analyzed prior to the sample used on the 2C. The Officer also agrees that the follow

- up results are

accurate.

7. Does the discharge cause, have the Reasonable Potential to Cause or Contribute (based on follow

- up results): No

8. PQL: 0.5 μg/l

9. Conclusion: Based on the conclusions made in the Department’s review of the Laboratory data, the follow

- up results will be used to determine reasonable potential. Based on the adjusted reasonable potential , this parameter will not be in the permit

.

H. Other Parameters

All other parameters reported on the 2C show no reasonable potential to cause or contribute to a water quality violation. Therefore no additional limits will be placed in the permit.Rationale Page 6 of 30

Permit No. SC00 46175

I. Floating Materials

1. Previous permit limi ts: Part V.D.6 states “The permittee shall report all visible discharges of floating materials, such as ash or an oil sheen, to SCDHEC when submitting DMR’s.”

2. Conclusion: This visual observation is to be reported on the DMR monthly, and will be separa ted into a visual report of floating solids, such as ash, and another report for oil and grease to account for the potential oil sheen.

Whole Effluent Toxicity (WET)

1. Previous permit requirements: Chronic whole effluent toxicity testing at a CTC = 100% using the dilution series 0%(control) 50%, 60%, 71%, 84%, 100% Quarterly Average: 25% effect (total, reproduction, & mortality) Maximum: 40% effect (total, reproduction, & mortality) Sampling Frequency: 1/quarter Sample Type: grab

2. NPDES Applica tion: No mixing requested

3. DMR Data: The maximum percent effect was reported in the last quarter of 2010 as 14.7%.

4. Mixing Zone and Zone of Initial Dilution (ZID) Information: discharge to a zero (0) 7Q10 stream, therefore no mixing

zone or dilution is allowed.

5. Conclusion: This is a complex wastewater with metals; therefore the WET limits will remain as previously permitted.

The limitations are Monthly average* = 25% Daily Maximum = 40% Chronic whole effluent toxicity testing shall be perf ormed at a CTC = 100% using the dilution series 0%(control) 50%, 60%, 71%, 84%, 100% Sampling Frequency: 1/month Sample Type: grab

* Please note that monthly average is being used per the requirements of R.61

- 9.122.45.d. This may be

different than was included in previous permits issued to this facility.

Groundwater Monitoring Requirements

Based on the facility’s comments on the draft permit reissuance, the Department’s Groundwater Management Section

reviewed the current information on the site made the following recommendations:

The permittee shall monitor and report results semi

- annually from four (4) groundwater monitoring wells (MW

- 16, MW

17, MW

- 18 and MW

- 19) for the following parameters:

Water Table Elevation Arsenic Depth to the Water Tab le Cadmium Field pH Chromium Field Specific Conductance Selenium Field Turbidity MercuryRationale Page 7 of 30

Permit No. SC00 46175

Threatened and Endangered Species Information

Both the federal and state authorities have listed the shortnose sturgeon as legally Endangered.

The Atlantic and shortnose sturgeons are identified with rankings of G3 and S3 (NatureServe 2005), meaning that populations for both species are “vulnerable,” both globally and in South Carolina. In general, populations of both species of sturgeon along the entire Atlantic Coast are reduced from historical levels for at least the past half

- century (ASMFC 1990; ASMFC 1998; NMFS 1998). The Atlantic sturgeon was considered for listing under the Endangered Species Act (ESA) in 1998, but the National Marine F isheries Service (NMFS) determined that listing was unwarranted. However, the gulf sturgeon (

Acipenser oxyrinchus desotoi ), a subspecies of the Atlantic sturgeon restricted to rivers and adjacent waters of the Gulf of Mexico, remains on the candidate list and is currently listed as “threatened” under the ESA. The shortnose sturgeon has been listed as “endangered” under the ESA since 1967 and the American Fisheries Society deemed it

“threatened” in 1989.

Previously SC DNR was contacted concerning the shortn ose sturgeon in the Cooper River. It is known that shortnose sturgeons, particularly juveniles, are sensitive to low dissolved oxygen levels. As stated earlier in this rationale when developing the Charleston Harbor TMDL for DO, it was determined that this facility does not contribute to the DO deficit. Aside from DO, there is no information showing that the shortnose sturgeon is more sensitive than the established Saltwater Aquatic Life criteria used to evaluate the permit limitations. Therefore based on k nown information this permit is protective of the shortnose sturgeon.

Within a 5

- mile radius of the site there are plant species that are “of concern”, the plants, with their global and state rankings are as follows:

Species Ranking Species Ranking

Nutm eg Hickory G4, S2 Virginia Bunchflower G5, S2

Reclined Meadow

- Rue G1G2Q, S1S2 Bottom

- Land Post Oak G4, S1

Long

- Horn Orchid G4G5, S1 Southeastern Tickseed G4G5, SNR

Biltmore Greenbrier G4?, S2 Coastal

- Plain Water

- Hyssop G3G5, S1

Slender

- Leaved Dragon

- H ead G4?, SNR Southern Twayblade G4, S2

There is also one vertebrate animal listed within the 5

- mile radius, which has both a global and state ranking and a State legal status. This animal is:

Species Ranking Legal Status

Bald Eagle G5, S2 SE

– Endanger ed, State

Global rankings:

G1

- Critically imperiled globally because of extreme rarity or because of some factor(s) making it especially vulnerable to extin ction

G2

- Imperiled globally because of rarity or factor(s) making it vulnerable

G3

- Either v ery rare throughout its range or found locally in a restricted range, or having factors making it vulnerable

G4

- Apparently secure globally, though it may be rare in parts of its range

G5

- Demonstrably secure globally, though it may be rare in parts of i ts range
G?

- Status unknown Q

- Questionable taxonomy that may reduce conservation priority

- Distinctiveness of this entity as a taxon or ecosystem type at the current level is questionable; resolution of this uncertainty may result in change from a sp ecies to a subspecies or hybrid, or inclusion of this taxon or type in another taxon or type, with the resulting taxon having a lower

- priority (numerically higher) conservation status rank. The “Q” modifier is only used at a global level and not at a natio nal or subnational level.Rationale Page 8 of 30

Permit No. SC00 46175

State rankings:

S1

- Critically imperiled state

- wide because of extreme rarity or because of some factor(s) making it especially vulnerable to extirpation

S2

- Imperiled state

- wide because of rarity or factor(s) making it vulner able

S3

- Rare or uncommon in state

S4

- Apparently secure in state

S5

- Demonstrably secure in state

SNR

- State Not Ranked

There does not appear to be any limitations that could be placed in this permit, which will have any impact on any of the species listed above.

Coal Ash Basins Operation and Maintenance (Part V.D.6)

Coal ash basins are used to treat or store wastewater and thus are included in the permit’s operation and maintenance requirements. Regulation 61

- 9.122.41(e) requires the permittee t o properly operate and maintain all facilities of treatment and control used to achieve compliance with their permits.

The permit includes new requirements to address coal ash basin operation and maintenance. The permit requires monthly inspections by trained personnel. Increased monitoring is required after large precipitation events, when there is an increased stress to impoundments and a greater potential for impacts on integrity. In addition, annual inspections by a qualified professional engineer are required. In response to any changes, such as cracks, erosion, bulges, and changes in seepage that may compromise the structural integrity, the permittee is also required to respond in a timely manner. The permit requires annual reporting of inspect ion and remedial activities as well as timely reporting of changes to integrity and associated corrective actions. These new requirements are intended to increase the permittee’s focus on operation and maintenance to reduce future risks of basin compromis e. Inspections which are required by some other agency may be used to meet the permit requirements as long as they meet all the requirements of this permit.

II. GENERAL INFORMATION

A. The effluent from this facility may be subject to the requirements of any of the following regulations: R.61

- 68,

R.61

- 69, R.61

- 9.122, 124, 125, 129, 133, and 403; 40 CFR Part 136; Subchapter N (40 CFR Parts 400 through 402 and 404 through 471); and R.61

- 9.503, 504 and 505.

B. Authority: This permit is written in accord ance with applicable laws and regulations including, but not limited to, Regulation 61

- 9, Regulation 61

- 68, Pollution Control Act and Clean Water Act.

C. Under R.61

- 9.124.8 (Fact Sheet), a fact sheet shall be prepared for every draft permit for a major NP DES facility or activity, for every Class I sludge management facility, for every NPDES draft permit that incorporates a variance or requires an explanation under section 124.56(b), and for every draft permit which the Department finds is the subject

of wi de

- spread public interest or raises major issues.

D. The conclusions noted in the Rationale establish proposed effluent limitations and permit requirements addressed

in R.61

- 9.122.43 (Establishing Permit Conditions), R.61

- 9.122.44 (Establishing Limitati ons, Standards and other permit conditions) and other appropriate sections of R.61

- 9.Rationale Page 9 of 30

Permit No. SC00 46175

III. BACKGROUND AND PROCEDURES FOR PERMIT LIMIT DEVELOPMENT

A. The receiving waterbody 7Q10, annual average flow or other critical flow condition at the discharge point, and 7Q10, annual average flow, or other critical flow condition for source water protection are determined by the SCDHEC’s Wasteload Allocation Section. The 7Q10, Annual Average Flow or other critical flow conditions are based on information publis hed or verified by the USGS, an estimate extrapolation from published or verified USGS data or from data provided by the permittee. These flows may be adjusted by the Wasteload Allocation Section to account for existing water withdrawals that impact the f low. The 7Q10 (or 30Q5 if provided by the applicant), annual average flow at the discharge point, or other critical flow condition or 7Q10 (or 30Q5 if provided by the applicant), annual average flow or other critical flow condition for source water protec tion for a proposed or existing surface water drinking water intake will be used to determine dilution factors, as appropriate,

in accordance with R.61

- 68.C.4.a & 4.b for aquatic life, human health, and organoleptic effects respectively.

B. Water and orga nism consumption and drinking water MCL criteria will be evaluated for protection of human health when calculating dilution factors. “The Department may, after Notice of Intent included in a notice of a proposed NPDES permit in accordance with Regulation 61

- 9.124.10, determine that drinking water MCLs or W/O shall not apply to discharges to those waterbodies where there is: no potential to affect an existing or proposed drinking water source and no state

- approved source water protection area.” For permitt ing purposes, “a proposed drinking water source is one for which a complete permit application, including plans and specifications for the intake, is on file with the Department at the time of consideration of an NPDES permit application for a discharge

th at will affect or has the potential to affect the drinking water source” (R.61

- 68.E.14.c(5)).

The Department will implement this protection in NPDES permits using the source water protection program already developed for the drinking water program. A so urce water protection program was developed originally in 1999 to define the source water protection areas for each drinking water intake. The program was designed to identify source water protection areas (SWPAs) to aid drinking water systems in identify ing sources of potential contamination that could affect their intakes. In September 2009, this program was modified to redefine the SWPAs as smaller, more manageable areas. The revised document developed in September 2009 is entitled
“South Carolina Dri nking Water Source Assessment and Protection Program.” For the purposes of NPDES permitting, the SWPA referred to in Regulation 61

- 68.E.14.c(5) is the Primary Protection Area defined in the revised assessment and protection document. More information rega rding the use of these protection areas is provided later in this rationale with the discussion of the procedure for establishing permit limits in Section G.2.

C. Application of numeric criteria to protect human health: If separate numeric criteria are g iven for organism consumption, water and organism consumption (W/O), and drinking water Maximum Contaminant Levels (MCLs), they shall be applied as appropriate. The most stringent of the criteria shall be applied to protect the existing and classified use s of the waters of the State (R.61

- 68.E.14.b(1)).

D. Numeric criteria have been established in R.61

- 68 based on organoleptic data (prevention of undesirable taste and odor). For those substances which have aquatic life and/or human health numeric criteria and organoleptic numeric criteria, the most stringent of the three shall be used for derivation of permit effluent limitations. See R.61

- 68.E.13.

E. Sampling Frequency: Samples and measurements taken for the purpose of monitoring shall be representative of the monitored activity. Monitoring results must be conducted according to test procedures approved under 40 CFR Part 136, unless other test procedures have been specified in the permit (R.61

- 9.122.41(j)(4)). Typically, requirements to report monitoring results shall be established on a case

- by

- case basis with a frequency dependent on the nature and effect of the discharge but in no case less than once a year (R.61

- 9.122.44(i)(2)).Rationale Page 10 of 30

Permit No. SC00 46175

F. Compliance Schedules:

1. A person issued an NPDES permit by the D epartment who is not in compliance with applicable effluent standards and limitations or other requirements contained therein at the time the permit is issued, shall be required to achieve compliance within a period of time as set forth by the Department, with effluent standards and limitations, with water quality standards, or with specific requirements or conditions set by the Department. The Department shall require compliance with terms and conditions of the permit in the shortest reasonable period of time as determined thereby or within a time schedule for compliance which shall be specified in the issued permit. (R.61

- 9.122.47(c)(1))

2. If a time schedule for compliance specified in an NPDES permit which is established by the Department, exceeds

nin e (9) months, the time schedule shall provide for interim dates of achievement for compliance with certain applicable terms and conditions of the permit. (R.61

- 9.122.47(c)(2))

G. Procedure for establishing effluent limitations:

1. Effluent limits (mass and concentration) for Five day Biochemical Oxygen Demand (BOD 5 ), Ultimate Oxygen Demand (UOD), Dissolved Oxygen (DO), Total Ammonia Nitrogen (as N), and Nutrients (e.g., nitrogen and phosphorus) are established by the Wasteload Allocation (WLA) Section, with consideration given to technology

- based limitations.

a. Five day Biochemical Oxygen Demand BOD 5 , Ultimate Oxygen Demand (UOD), Dissolved Oxygen (DO):

Effluent limits for conventional oxygen demanding constituents (BOD 5 , UOD and DO) are established to
prote ct in

- stream water quality, while utilizing a portion of the assimilative capacity of the receiving water. The ability of a water body to assimilate oxygen

- demanding substances is a function of its physical and

chemical characteristics above and below the discharge point. Various mathematical techniques, called models, have been developed to estimate this capacity. The Department follows the procedures as outlined in the “State/EPA Region IV Agreement on the Development of Wasteload Allocations/Total Maxi mum Daily Loads and NPDES Permit Limitations” dated October 30, 1991 (as updated) for determining the assimilative capacity of a given water body. Mathematical models such as QUAL2E and QUAL2E

UNCAS are used in accordance with “Enhanced Stream Water Quali ty Models QUAL2E and QUAL2E

UNCAS: Documentation and Users Manual” (EPA/600/3

- 87/007; dated May 1987) as updated. BOD 5 and UOD values determined from modeling results will be used in permitting as monthly average derived limits (C wla ). Daily maximum deri ved limits will typically be determined by multiplying the monthly average value by two.

For facilities subject to effluent guidelines limitations or other technology

- based limitations, BOD 5 will also be evaluated in accordance with the applicable industr ial categorical guidelines. These guidelines will be identified in Part I of this rationale when they are applicable to the permit.

b. Total Ammonia Nitrogen (as N):

Ammonia limitations based on oxygen demand will be determined from modeling information as described above. These values will be used as monthly average derived limits and a daily maximum will typically be determined by multiplying the monthly average derived limit by two. These values will be compared with the ammonia water quality criteria f or protection of aquatic life from Regulation 61

- 68, Attachment 3 and any categorical limitations. The more stringent of the limitations will be imposed. Calculations for aquatic

life criteria and other wasteload recommendations are shown in Part I of thi s rationale when ammonia is a pollutant of concern.Rationale Page 1 1 of 30

Permit No. SC00 46175

c. Discharges of Nutrients:

In order to protect and maintain lakes and other waters of the State, consideration is given to the control of nutrients reaching the waters of the State. Therefore, in accordan ce with regulation R.61

- 68.E.11
, the Department controls the nutrients as prescribed below. Nutrient limitations will be determined from the best available information and/or modeling performed by the Wasteload Allocation Section to meet these water quali ty standards.

i. Discharges of nutrients from all sources, including point and nonpoint, to waters of the State shall be prohibited or limited if the discharge would result in or if the waters experience growths of microscopic or macroscopic vegetation su ch that the water quality standards would be violated or the existing or classified uses of the waters would be impaired. Loading of nutrients shall be addressed on an individual basis as necessary to ensure compliance with the narrative and numeric crite ria.

ii. Numeric nutrient criteria for lakes are based on an ecoregional approach which takes into account the geographic location of the lakes within the State and are listed below. These numeric criteria are applicable to lakes of 40 acres or more. La kes of less than 40 acres will continue to be protected by

the narrative criteria.

1. For the Blue Ridge Mountains ecoregion of the State, total phosphorus shall not exceed 0.02 mg/l, chlorophyll a shall not exceed 10 ug/l, and total nitrogen shall not excee d 0.35 mg/l

2. For the Piedmont and Southeastern Plains ecoregions of the State, total phosphorus shall not exceed 0.06 mg/l, chlorophyll a shall not exceed 40 ug/l, and total nitrogen shall not exceed 1.50 mg/l

3. For the Middle Atlantic Coastal Plains ecoreg ion of the State, total phosphorus shall not exceed 0.09 mg/l, chlorophyll a shall not exceed 40 ug/l, and total nitrogen shall not exceed 1.50 mg/l.

iii. In evaluating the effects of nutrients upon the quality of lakes and other waters of the State, the Department may consider, but not be limited to, such factors as the hydrology and morphometry of the waterbody, the existing and projected trophic state, characteristics of the loadings, and other control mechanisms in order to protect the existing and cla ssified uses of the waters.

iv. The Department shall take appropriate action, to include, but not limited to: establishing numeric effluent limitations in permits, establishing Total Maximum Daily Loads, establishing waste load allocations, and establishi ng load allocations for nutrients to ensure that the lakes attain and maintain the narrative and numeric criteria and other applicable water quality standards.

v. The criteria specific to lakes shall be applicable to all portions of the lake. For this pu rpose, the Department shall define the applicable area to be that area covered when measured at full pool

elevation.

2. Effluent concentration limits ( C efflim ) for parameters other than the parameters listed in G.1.a

- c (except ammonia toxicity calculation s) above are established using the following procedures:

Q 7Q10 7Q10 or other critical flow condition of the receiving water at the discharge point in mgd.

(may require adjustment for withdrawals)

AAF

d Average Annual Flow (AAF) or other critical flow c ondition of the receiving water at the discharge point in mgd. (may require adjustment for withdrawals) Q 7Q10i 7Q10 or other critical flow condition of the receiving water at either the SWP Area 15

- river

mile boundary or at the intake, as appropriate, i n mgd.Rationale Page 12 of 30

Permit No. SC00 46175

AAF

i Average Annual Flow (AAF) of the receiving water at either the SWP Area 15

- river mile boundary or at the intake, as appropriate, in mgd. Q d Long term average discharge flow in mgd.

a. Determine dilution factors: The following information is to be used (where applicable) for establishing effluent concentration limits:

DF 1 : This dilution factor is based on 7Q10 or other critical flow condition of the receiving water at the discharge point ( Q 7Q10 ). This dilution factor is used to determine the derived limits for protection of the following aquatic life and human health concerns for the reasons indicated:

i. Aquatic Life (see R.61

- 68.C.4.a(1)). Protection of aquatic life on a short

- term basis is needed at the point where aquatic organisms become exposed to the discharge.

ii. Human Health

– Organism Consumption for parameters identified as non

- carcinogens per

R.61

- 68.C.4.b(1). Protection for human health on a short

- term basis for consumption of aquatic organisms is needed at the point the a quatic organisms become exposed to the discharge.

DF 2 : This dilution factor is based on the Average Annual Flow or other critical flow of the receiving water at the discharge point ( AAF d ) . This dilution factor is used to determine the derived limits for protection of the following human health and organoleptic concerns for the reasons indicated:

i. Human Health

– Organism Consumption for parameters identified as carcinogens per R.61

- 68.C.4.b(1). Protection for human health on a lon g

- term basis to prevent cancer due to consumption of aquatic organisms is needed at the point the aquatic organisms become exposed to the discharge.

ii. Organoleptic effects per R.61

- 68.C.4.b(1). Protection for taste and odor issues related to the

discha rge is needed at the point where the discharge enters the receiving water.

DF 3 : This dilution factor is based on the 7Q10 or other critical flow condition ( Q 7Q10i ) for protection of a proposed or existing surface water drinking w ater intake that the discharge has the potential to affect. This dilution factor is used to determine the derived limits for protection of the following

human health concerns for the reasons indicated:

i. Human Health

– Water and Organism (W/O) Consumption for parameters identified as non

carcinogens per R.61

- 68.C.4.b(1) and E.14.c(5) to protect for short

- term health effects when the discharge has the potential to affect a surface water drinking water intake. Protection of human health relative to drinking the water from the waterbody and consuming aquatic organisms from the same waterbody is provided by this criterion, but drinking the water withdrawn from the waterbody may require a higher level of protection in terms of applicable dilution than consumptio n of organisms.Rationale Page 13 of 30

Permit No. SC00 46175

ii. Human Health

- Drinking Water Maximum Contaminant Level (MCL) for parameters

identified as non

- carcinogens per R.61

- 68.C.4.b(1) and E.14.c(5) to protect for short

- term health effects when the discharge has the potential to affect a surfac e water drinking water intake. Protection of human health relative to drinking the water from the waterbody after conventional treatment per R.61

- 68.G is provided by this criterion.

DF 4 : This dilution factor is based on the Aver age Annual Flow or other critical flow condition ( AAF i ) for protection of a proposed or existing surface water drinking water intake that the discharge has the potential to affect. This dilution factor is used to determine the derived limits for protectio n of the following human health concerns for the reasons indicated:

i. Human Health

– Water and Organism Consumption for parameters identified as carcinogens per R.61

- 68.C.4.b(1) and E.14.c(5) to protect for long

- term health effects due to cancer when

the d ischarge has the potential to affect a surface water drinking water intake. Protection of human health relative to drinking the water from the waterbody and consuming aquatic organisms from the same waterbody is provided by this criterion, but drinking th e water withdrawn from the waterbody may require a higher level of protection in terms of applicable dilution than consumption of organisms.

ii. Human Health

- Drinking Water Maximum Contaminant Level (MCL) for parameters identified as carcinogens per R .61

- 68.C.4.b(1) and E.14.c(5) to protect for long

- term health effects due to cancer when the discharge has the potential to affect a surface water drinking water intake. Protection of human health relative to drinking the water from the waterbody

after co nventional treatment per R.61

- 68.G is provided by this criterion.

For both DF

3 and DF

4 , to satisfy the mixing zone requirements of R.61

- 68.C.10(a) for both W/O and MCL criteria, the Department will use the following flows to deter mine dilution:

1. The following applies to discharges and intakes in flowing rivers:

a. Where the discharge is within the SWPA (15 river miles) of the intake, the flow at the 15

- river mile boundary of the tributary with the largest applicable critical flow will be used.

b. Where the discharge is outside the SWPA (15 river miles) of the intake, the applicable critical

flow at the intake will be used.

2. When the discharge is either in the tributary to a lake or in a lake and the intake is in the same lake that

does not behave as a run

- of

- river impoundment*, the flow is determined using the sum of the applicable critical flows of all tributaries entering the lake.

3. The following applies when both the discharge and the intake are in a lake arm that behav es as a run

of

- river impoundment*:Rationale Page 14 of 30

Permit No. SC00 46175

a. Where the discharge is within the SWPA (15

- mile buffer which may include both lake and river miles) of the intake, the flow at the 15

- mile boundary of the tributary with the largest applicable

critical flow will be used

.

b. Where the discharge is outside the SWPA (15

- mile buffer which may include both lake and river miles) of the intake, the applicable critical flow at the intake will be used.

4. Where the discharge is in the arm of a lake and the intake is in the upper reach of another arm of the lake, no protection of W/O or MCL criteria is needed because the discharge does not have the potential to affect the intake,

5. If the discharge has the potential to affect multiple intakes, the SWPA of the intake closest to t he discharge will be protected. However, the permittee may be required to provide notification to all potentially affected intakes.

* Run

- of

- river impoundment is defined as a lake or reservoir (or arm of a lake or reservoir) that is

narrow and/or shallow offering little dilution or delay in contaminant flow toward an intake.

b. Determine derived limits using the following procedures:

WQS al Freshwater Standard (based on an established criteria or other published data per R.61

- 68) for protection of Aquati c Life; may be a CCC or CMC as defined below WQS

org Standard (based on an established criteria or other published data per R.61

- 68) for protection of

Human Health

– Organism Consumption WQS

wo Standard (based on an established criteria or other published da ta per R.61

- 68) for protection of

Human Health

– Water & Organism Consumption. WQS mcl Standard (based on an established criteria or other published data per R.61

- 68) for Drinking Water MCL (Maximum Contaminant Level). WQS ol : Standard (based on an establ ished criteria or other published data per R.61

- 68) based on Organoleptic Data.

C aqlife Concentration limit derived from aquatic life data

C HH Concentration limit derived from human health data as determined from organism ( C org ), water/organism ( C

wo )and M CL ( C mcl ) data

C ol Concentration limit derived from organoleptic data

C b The b ackground concentration of the concerned parameter in mg/l is typically determined from ambient monitoring data or data provided by applicant. If the waterbody to which the di scharge flows is not on the 303(d) list, the 90 th percentile of ambient monitoring data for aquatic life protection for the parameters identified in the Appendix (Water Quality Numeric Criteria) to Regulation 61

- 68 from the last 3 years, or whatever is ava ilable if less than 3 years, will typically be used. If the waterbody to which the discharge flows is not on the 303(d) list, the median value of ambient monitoring data for human health protection for the parameters identified in the Appendix (Water Quali ty Numeric Criteria) to Regulation 61

- 68 from the last 3 years, or whatever is available if less than 3 years, will typically be used. The background concentration is assumed to be zero (0) in the absence of actual data based on Departmental guidance and E PA

recommendation.Rationale Page 15 of 30

Permit No. SC00 46175

i. Determine the derived limits for protection of Aquatic Life ( C aqlife )

1. The following guidelines apply to determining aquatic life limits using this basic equation:

a. Typically, the Criterion Maximum Concentr ation (CMC) is applied as a daily maximum derived limit and the Criterion Continuous Concentration (CCC) is applied as a monthly average derived limit, after consideration of dilution and background concentrations. The CMC and CCC for specific metals will be adjusted using the procedures in 60 FR 22229, “Water Quality Standards; Establishment of Numeric Criteria for Priority Toxic Pollutants; States’ Compliance

- Revision of Metals Criteria,” May 4, 1995 and the “Technical Guidance on Interpretation and Imple mentation of Aquatic Life Metals Criteria,” Oct. 1, 1993 and applied as a daily maximum and monthly average, respectively, after consideration of dilution and background concentrations. For specific metals, this calculation is explained in detail

later i n this rationale.

monthly average = C aqlife using CCC as WQS al daily maximum = C aqlife using CMC as WQS al

b. If only a CMC exists for a particular parameter, the daily maximum derived permit limit will be set using that value, after consideration of diluti on and background concentrations. If no other values (e.g., human health) exist for that parameter on which to base a monthly average limit and the discharge is continuous, the monthly average will be set equal to the daily maximum to satisfy Regulation 6 1

- 9.122.45(d). In no case shall the monthly average limit be set higher than the daily maximum limit. If only a CCC is given, it will be used as a monthly average derived limit and the daily maximum derived limit will be two (2) times the value

obtained f

or the monthly average based on a simplified statistical procedure for determining permit limits recommended in Section 5.4.2 of the US EPA’s “Technical Support Document for Water Quality

- based Toxics Control”, EPA/505/2

- 90

- 001, March 1991 (hereafter known as the TSD).

If a CCC exists and no CMC exists and no other acute or chronic data exists, the aquatic life

limits are

monthly average = C aqlife using CCC as WQS al daily maximum = 2 x C aqlife

If a CMC and no CCC exists, and no other acute or chron ic data exists, the aquatic life limits

are

monthly average = C aqlife using CMC as WQS al daily maximum = C aqlife using CMC as WQS alRationale Page 16 of 30

Permit No. SC00 46175

c. If only an acute toxicity effect concentration for a number of species for a particular pollutant is given as a LC 50 , the lowest concentration should be divided by an acute

- to

- chronic ratio (ACR) of 10 and a sensitivity factor of 3.3, for an acceptable instream concentration in order to protect against chronic toxicity effects (R.61

- 68.E.16.a(1)). Other acute toxicity d ata will be handled similarly. The value obtained from this calculation will be used as a monthly average derived limit after consideration of dilution and background concentrations. The daily maximum will be two (2) times the value obtained for the month ly average based on a simplified statistical procedure for determining permit limits recommended in Section 5.4.2 of

the TSD.

monthly average = C aqlife using other data as WQS al daily maximum = 2 x C aqlife

d. If a chronic toxicity effect concentration fo r a number of species for a particular pollutant is given as a no observed effect concentration (NOEC), the lowest concentration should be divided by a sensitivity factor of 3.3 in order to protect against chronic toxicity to the most sensitive species (R. 61

- 68.E.16.a(2)). Other chronic toxicity data will be handled similarly. The value obtained from this calculation will be used as a monthly average derived limit after consideration of dilution and background concentrations. The daily maximum will be two (2) times the value obtained for the monthly average based on a simplified statistical procedure for determining permit limits recommended in Section 5.4.2 of the TSD.

monthly average = C aqlife using other data as WQS al daily maximum = 2 x C aqlife

e. If both acute and chronic data are available for a particular pollutant, monthly average derived limit will be calculated as in c and d above for each acute and chronic, respectively. The more stringent of the monthly average derived limits will be the month ly average derived limit used after consideration of dilution and background concentrations. The daily maximum will be two (2) times the value obtained for the monthly average based on a simplified statistical procedure for determining permit limits recom mended in Section 5.4.2 of the TSD.

monthly average = C aqlife using other data as WQS al daily maximum = 2 x C aqlife

f. Consider the background concentration ( C b ) of the parameter of concern. If the background concentration is equal to or greater than the applicable standard ( WQS, as defined above) for the parameter of concern, then the derived concentration limit ( C aqlife ) for that parameter is established equal to the standard ( WQS ) so that no additional amount of that pollutant is added

to the waterb ody. An exception exists where the naturally occurring instream concentration for a substance is higher than the derived permit effluent limitation. In those situations, the Department may establish permit effluent limitations ( C efflim ) at a level higher than the derived limit, but no higher than the natural background concentration (i.e. a “rise above background” limit). In such cases, the Department may require biological instream monitoring and/or whole effluent toxicity (WET) testing (R.61

- 68.E.14.c(2) ).

If C b is not based on naturally occurring concentrations and

Then, generally,

.Rationale Page 17 of 30

Permit No. SC00 46175

If C b is based on naturally occurring concentrations and

Then, generally,

.

2. Metals: Regulation 61

- 9.122.45(c) requires that permit limits be expressed in terms of total recoverable metal (with limited exceptions). In order to translate from the water quality criterion to a total recoverable metal, Regulation R.61

- 68.E.14.c(4) provides for the use of the EPA Office of Water Policy and "Technical Guidance on Interpretation and Implementation of Aquatic Life Metals Criteria", October 1, 1993. A subsequent revision published in the Federal Register (60 FR 22229) on May 4, 1995 updated the data in the original report. See R.61

- 68 Appendix for CMC and CCC values and equations, Attachment 1 for “Conversion Factors for Dissolved Metals” and Attachment 2 “Parameters for Calculating Freshwater Dissolved Metals Criteria that

are Hardness

- Dependen t”.

Per R.61

- 68.E.14.a(3), the CMC and CCC are based on a hardness of 25 mg/l if the ambient or mixed stream hardness is equal to or less than 25 mg/l. Concentrations of hardness less than 400 mg/l may be based on the mixed stream hardness if it is gre ater than 25 mg/l and less than 400 mg/l and 400 mg/l if the ambient stream hardness is greater than 400 mg/l. The ambient stream hardness is assumed to be 25 mg/l in the absence of actual stream data. Mixed stream hardness may be determined using flow

- we ighted effluent hardness and stream hardness.

The following equations and constants will be used to calculate aquatic life metals limits based on

these documents. The values of the terms referenced in this section and determined from the equations belo w are included in the Metals spreadsheet attached to this rationale. The following metals are subject to this section:

arsenic lead

cadmium mercury chromium (III & VI) nickel

copper zinc

The equation for C d below changes the tot al metal to dissolved metal. From Technical Guidance Manual for Performing Waste Load Allocations Book II, Rivers and Streams , EPA/440/484/022,

(adjusted for hardness)

where C

d = Dissolved metal concentration (μg/l)

S = a constant to represent the CCC or CMC (μg/l)

CF = Conversion factor considered most relevant in fresh water for aquatic life as defined by EPA for each metal

Once the dissolved metal concentration is known, determine C p using the equation f

or C d above and the following equations.Rationale Page 18 of 30

Permit No. SC00 46175

where C

p = Particulate sorbed metal concentration (μg/l). This value represents the revised water quality criterion for the metal to be used for ambient data compariso n.
K pb = Linear partition coefficient using the stream TSS (liters/mg)

K po = Metal

- specific equilibrium constant (liters/mg)

a = Metal

- specific constant

TSS b = Background or in

- stream Total Suspended Solids (TSS) concentration (mg/l). The backg round TSS is assumed to be 1 mg/l in the absence of actual instream data based on the 5th percentile of ambient TSS data on

South Carolina waterbodies from 1993

- 2000.

To determine the effluent limit ( C aqlife )

, use the following equations to translate the limits into a

total recoverable metal concentration.

where TSS

e = Effluent Total Suspended Solids (TSS) concentration (mg/l) determined

from actual long

- term average data or proposed permit limits if no data

available.

TSS avg = A verage in

- stream (mixed) TSS concentration (mg/l)

where C t = Total metal concentration (μg/l)

K p = Linear partition coefficient (liters/mg). This is the distribution of metal at equilibrium between the particul ate and dissolved forms.

Once C t has been calculated, it is multiplied by DF 1 and background concentrations are accounted for to obtain the derived limit (max or avg) ( C aqlife ):

monthly average = C aqlife based on CCC daily maximum = C aqlife based on CMC

3. Where a Water Effects Ratio (WER) is used to adjust a criterion, derived limits for the adjusted aquatic life criterion ( C aqlife

- adj ) are calculated as follows. The WER is a type of site

- specific permit effluent limit (as allowed by R.61

- 68.E.14.c(7)) derived using a ratio determined from EPA methodology. Both DHEC and EPA must approve the WER prior to implementation. See EPA's
1994 “Interim Guidance on the Determination and Use of Water

- Effect Ratios (WERs) for Metals.” The ap proved WER will be shown in the water quality spreadsheets on the Data sheet. The revised aquatic life value will be shown with the WER, hardness and dissolved metals adjustments, as appropriate, in the aquatic life columns on the Pollutant spreadsheet.Rationale Page 19 of 30

Permit No. SC00 46175

a. For metals identified in #2 above, revise the equation for S as follows:

S = [CCC or CMC (adjusted for hardness)] x WER

Follow the remaining calculations in #2 above to get an adjusted C aqlife value that will be used

to determine derived limits :

monthly average = C aqlife

- adj based on CCC daily maximum = C aqlife

- adj based on CMC

b. For other parameters, use the appropriate equation in #1 above to derive an adjusted C aqlife value. The monthly average will be calculated as follows using the appr opriate WQS al and the daily maximum calculated using the appropriate equations in #1 above.

4. Where the Recalculation Procedure is used to adjust a criterion, derived limits for the adjusted aquatic life criterion ( C aqlife

- adj ) are calculated as follows. The Recalculation Procedure is intended

to cause a site

- specific criterion to appropriately differ from the State

- adopted national aquatic life criterion if justified by demonstrated pertinent toxicological differences between the aquatic species that occur at the site and those that were used in the derivation of the criterion. It is important to note that the site (the portion of the waterbody or watershed being affected) must be clearly defined. This procedure is used to develo p site

- specific criteria in accordance with R.61

- 68.C.12. Both DHEC and EPA must approve the recalculated criterion prior to implementation. The recalculated criterion will require an update to the Water Classifications and Standards Regulations, R.61

- 68 and 61

- 69.

The approved recalculated aquatic life criteria ( SS

- CCC and SS

- CMC, as appropriate) will be shown adjusted for hardness on the Data spreadsheet. The additional dissolved metals adjustments, as appropriate, will be shown in the aquatic life col umns on the Pollutant spreadsheet. If the parameter being adjusted is one of the metals in #2 above, SS will include all the appropriate metals adjustments.

monthly average = C aqlife

- adj based on CCC daily maximum = C aqlife

- adj based on CMC

5. Where a WER and recalculation procedure are combined to adjust a criterion, derived limits ( C aqlife

- adj ) for aquatic life protection are calculated by combining the calculations in #3 and #4.

monthly average = C aqlife

- adj based on CCC daily maximum = C aqlife

- adj based on CMCRationale Page 20 of 30

Permit No. SC00 46175

6. Other scientifically defensible methods for developing site

- specific aquatic life effluent limits or

site

- specific criterion may be used on a case

- by

- case basis.

ii. Determine derived limits f or protection of Human Health

1. The following guidelines apply to determining human health limits:

a. The human health criterion given by Regulation 61

- 68 will be applied as a monthly average derived limit after consideration of dilution and background con centrations ( C HH

- avg ). Exceptions exist based on EPA criteria and are indicated for specific parameters. No limits on human health based on water and organism consumption or drinking water MCLs will be imposed if there is no potential to affect an existi ng or proposed surface water drinking water

intake and no state

- approved source water protection area in accordance with Regulation 61

- 68.E.14.c(5).

b. The daily maximum permit limit will be determined from the monthly average value from (a)

above and a mult iplier ( M) determined using a statistical procedure recommended in Section 5.5 using average = 95 th percentile from Table 5

- 3 in the TSD. The permitted or proposed number of samples per month (n) is used with the coefficient of variation (CV) to determine

M

.

where:

CV = coefficient of variation of the effluent concentration. For a data set where

n >10, the CV is calculated as standard deviation divided by mean for the data set being eva luated. For data set where n <10, the CV is estimated to equal 0.6. For less than 10 items of data, the uncertainty in the CV is too large to

calculate a standard deviation or mean with sufficient confidence.

n = the number of effluent samples per month ( where frequency is less than 1/month, n =1)

z
m = the percentile exceedance probability for the daily maximum permit limit (=2.326 for 99 th percentile basis)

z
a = the percentile exceedance probability for the monthly average permit limit (=1.645 for 95 th p ercentile basis)

C HH

- max = M * C HH

- avg

c. Consider the background concentration ( C b ) of the parameter of concern. If the background concentration is equal to or greater than the applicable standard ( WQS, as defined above) for the parameter of concern, t hen the derived concentration limit ( C HH e ) for that parameter and for the protection of that standard is established equal to the standard ( WQS ). An exception exists where the naturally occurring instream concentration for a substance is higher than the d erived permit effluent limitation. In those situations, the Department may establish permit effluentRationale Page 21 of 30

Permit No. SC00 46175

limitations ( C efflim ) at a level higher than the derived limit, but no higher than the natural background concentration (i.e. a “rise above background” li mit). In such cases, the Department may require biological instream monitoring and/or whole effluent toxicity (WET) testing (See R.61

- 68.E.14.c(3)).

If C b is not based on naturally occurring concentrations and

Then, generally,

.

If C b is based on naturally occurring concentrations and

Then, generally,

.

2. Human Health

– Organism Consumption ( C org ).

a. For Carcinogens The Monthly Average is calculated as follows:

The Daily Maximum is calculated as

C org

- max = M * C org

b. For Non

- carcinogens The Monthly Average is calculated as follows:

The Daily Maximum is calculated as

C org

- max = M * C org

3. Human Health

– Water an d Organism Consumption ( C

wo )

a. For Carcinogens The Monthly Average is calculated as follows:Rationale Page 22 of 30

Permit No. SC00 46175

The Daily Maximum is calculated as

C

wo

- max = M * C

wo

b. For Non

- carcinogens The Monthly Average is calculated as follows:

The Daily Maximum is calculated as

C

wo

- max = M * C

wo

4. Human Health

– Drinking Water Maximum Contaminant Level (MCL) ( C mcl ).

a. For Carcinogens The Monthly Average is calculated as follows:

The Daily Maximum is calc ulated as

C mcl

- max = M * C mcl

b. For Non

- carcinogens The Monthly Average is calculated as follows:

The Daily Maximum is calculated as

C mcl

- max = M * C mcl

5. Organoleptic criteria ( C ol ).

The Monthly Average is calculated as follows :

The Daily Maximum is calculated as

C ol

- max = M * C olRationale Page 23 of 30

Permit No. SC00 46175

iii. P arameters given in a wasteload allocation for oxygen

- demanding pollutants and nutrients will be

limited as monthly average = C
wla

daily maximum = 2 x C
wla

c. Determi ne the most stringent of applicable water quality data using the derived limits determined above:

monthly average C efflim = minimum of derived monthly averages ( C aqlife , C

org , C

wo , C mcl , C

ol , C wla ) daily maximum C efflim = minimum of derived daily maximu ms ( C aqlife , C

org

- max , C

wo

- max , C

mcl

- max , C

ol

- max , C

wla

- max )

d. Determine whether the discharge causes, has the reasonable potential to cause or contributes to a water quality violation.

Regulation 61

- 9.122.44(d)(1)(i) states: “Limitations must control all pollutants or pollutant parameters (either conventional, nonconventional, or toxic pollutants) which the Department determines are or may be discharged at a level which will cause, have the reasonable potential to cause, or contribute to an excursion above any State water quality standard, including State narrative criteria for water quality.”

When determining whether a discharge causes, has the reasonable potential to cause or contributes to an instream excursion, the Department will use procedures which account for controls on point and nonpoint sources of pollution, the variability of the pollutant in the effluent, the sensitivity of the species to toxicity testing (when evaluating whole effluent toxicity), and, where appropriate, the dilution of t he effluent in the receiving water (R.61

- 9.122.44(d)(1)(ii)).

Based on the above statements, there are three scenarios when limitations are required, as follows:

i. When data provided by the permit applicant indicates discharge values greater than the pr oposed limitation derived above, that discharge may cause an excursion above a narrative or numeric water quality criterion.

ii. A discharge may be determined to contribute to an excursion of a water quality criterion when the waterbody is impaired (e.g. , on the 303(d) list) for the parameter of concern and that parameter is also being discharged at levels above the water quality criterion.

iii. Reasonable potential to cause a water quality violation is determined using the following information:

The De partment will primarily use EPA’s Technical Support Document (TSD) for determining reasonable potential using effluent data. Other methods may be used as well to evaluate data sets. All pollutants given in a wasteload allocation or an effluent limitation guideline will be limited in the permit.

When effluent data consists of non

- quantifiable/non

- detectable values or when no effluent data is available, other factors and information are considered to determine reasonable potential. In situations where a p ollutant is known to be present in the wastestream (due to production data or other information), we know it is being discharged and has the potential to impact even though it may not be quantifiable. The fact that it is present will be enough information to say reasonable potential exists for that pollutant. Therefore, a reasonable potential decision is based on various data and information, and not just non

- quantifiable/non

- detectable data. Consideration is given to existing data, dilution in the

waterb ody, type of receiving water, designated use, type of industry/wastestream, ambient data, history of compliance, and history of toxic impact. If any source of information indicates reasonable potential

to cause or contribute to an exceedance of the water quality standard, a water quality limit will be

established.Rationale Page 24 of 30

Permit No. SC00 46175

Note: The result of the following calculations may indicate that reasonable potential does not exist. However, as stated above, other information may “override” this numerical determination to justify the

need for a limit.

1. The procedure for determining reasonable potential from actual effluent data is explained in Box

3

- 2 on page 53 of the TSD. Multiplying factors are determined from Table 3

- 2 at a 95% confidence level and 95% probability in Section 3.3.2. The following describes the procedures used for determining reasonable potential for chemical

- specific parameters and WET, under certain circumstances. More information on determining reasonable potential for WET is given in

Item 2 belo w.

Step 1: Data Analysis: The statistical calculations involved in the “Reasonable Potential” analysis require discrete numerical data. The following describes how the effluent data will be used in determining reasonable potential.

Actual analytical r esults should be used whenever possible. Results less than detection and quantification should be used as follows:

a. If the permittee reports results below the practical quantitation limit (PQL) (as defined by the permit), then the reported “less than PQ L” value for a given sample is generally

assumed to be zero.

b. If the permittee uses a detection/quantification level that is greater than the PQL, then the reported “less than” value for a given sample is generally assumed to be a discrete value equal t o the detection/quantification level used by the permittee.

c. If the reported data consists of both discrete and non

- discrete values and/or the data is reported using varying detection/quantification levels, then, generally, a combination of

the above tw o approaches is used, or the data is evaluated in a manner that is most appropriate for that data set.

Note: For information on the acceptable analytical methods and PQLs please refer to NPDES permit application attachment titled “Practical Quantitation L imits (PQL) and Approved Test Methods.”

Step 2: Using data from the permit application, other data supplied by the applicant and/or Discharge Monitoring Report (DMR) data, determine the total number of observations ( n ) for a particular set of effluent dat a and determine the highest value ( C

max ) from that data set. For the monthly average comparison, the data set will include monthly average results

and n will be the number of months in which they sampled in the time period being evaluated. For the daily m aximum comparison, the data set will include daily maximum

results and n will be the total number of samples in the time period being evaluated. Individual results may not necessarily be used in the calculation.

Step 3: Determine the coefficient of varia tion ( CV ) for the data set. For a data set where n >10, the

CV is calculated as standard deviation divided by mean for the data set being evaluated.

For data set where n <10, the CV is estimated to equal 0.6. For less than 10 items of data,

the uncertaint y in the CV is too large to calculate a standard deviation or mean with

sufficient confidence.

forRationale Page 25 of 30

Permit No. SC00 46175

for

where: = Standard Deviation of the sam ples

= Mean of the samples

Step 4: Determine the appropriate multiplying factor ( MF ) from either Table 3

- 2 or using the

formulae in Section 3.3.2 of the TSD.

a. Determine the percentile represented by the highest concentration in t he sample data.

where: p

n = Percentile represented by the highest concentration in the data

n = number of samples Confidence Level = 0.95 i.e. 95%

b. Determine the multiplying factor ( MF ), which is the relationship between the percentile described above ( C

p ) and the selected upper bound of the lognormal effluent distribution,

which in this case will be the 95 th percentile ( C 95 ).

where: Z

95 is the standardized Z

- score for the 95 th percentile of the standar dized

normal distribution = 1.645

Z

p is the standardized Z

- score for the p th percentile of the standardized normal distribution.(determined in (b) above)

Note: The values of Z

- scores are listed in tables for the normal distribution. If using

Microso ft® Excel, this can be calculated using the NORMSINV function.

Step 5: Multiply the highest value from the data set ( C

max ) by the multiplying factor ( MF ) determined in Step 4 to obtain the maximum receiving water concentration ( RWC ).

Step 6: RWC ≤ Derived limit ( C efflim ) implies that reasonable potential does not exist.

RWC > Derived limit ( C efflim ) implies that reasonable potential exists.Rationale Page 26 of 30

Permit No. SC00 46175

2. Reasonable potential for Whole Efflu ent Toxicity (WET) may be determined from numerical data using the following procedure:

a. When the effluent data is given in terms of percent effluent as an IC 25 , LC 50 and/or NOEC

values:

Step 1: Convert the given values to toxic units: TU

a for acute data and TU

c for chronic data, respectively, using the following formulae. Please note that an NOEC derived using the

IC 25 is approximately the analogue of an NOEC derived using hypothesis testing. The IC 25 is the preferred statistical method for determining t he NOEC (EPA TSD, March 1991, p.6).

or if IC 25 available

Step 2: Using DMR data or other data provided by the applicant, determine the total number of observations ( n ) for a particular set of effluent data and determine the highest value ( TU
a ,

max or TU

c , max ) from that data set.

Step 3: Determine the coefficient of variation ( CV ) for the data set. For a data set where n >10, the

CV is calculated as standard deviation divided by mean. For data set where n <10, the CV is estimated to equal 0.6. For less than 10 items of data, the uncertainty in the CV is too large to calculate a standard deviation or mean with sufficient confidence.

Step 4: Determine the appropriate multiplying factor ( MF ) from either Table 3

- 2 or using the formulae in Section 3.3.2. (see iii.1, Step 4 above).

Step 5: Multiply the highest value of TU

a , max or TU

c , max from the data set by the multiplying factor ( MF ) determined in Step 4 and the dilution at the edge of the mixing zone (the test concentration obtained from mixing zone modeling or demonstration) to obtain the maximum receiving water concentration ( RWC )

RWC for Acute Toxicity = [ TU

a , max * MF * conc. at MZ boundary]

RWC for Chronic Toxicity = [ TU

c , max * MF * conc. at MZ boundary ]

Step 6: RWC for Acute Toxicity ≤ 0.3TU

a implies that a reasonable potential does not exist

RWC for Acute Toxicity > 0.3TU

a implies that a reasonable potential exists

RWC for Chronic Toxicity ≤ 1.0TU

c implies that a reasonable potential does not exist

RWC for Chroni c Toxicity > 1.0TU

c implies that a reasonable potential exists

b. Other methods for determining reasonable potential may be used if appropriately justified.

e. Consider Effluent Limitations Guidelines (ELG or Categorical guidelines)

The more stringent o f the effluent limitations guidelines average and maximum derived limits and water quality

- derived average and maximum limits shall be used as permit limits, unless other information indicates more stringent limits are needed (e.g. previous permit limits d ue to backsliding). Categorical limitations based on mass may be converted to concentration using the long

- term average flow of the discharge for comparison to the monthly average and daily maximum derived limits.Rationale Page 27 of 30

Permit No. SC00 46175

1. For effluent guidelines based on produ ction, limits will be calculated as follows:

where

ELG lim : the mass limit, in lbs/day, for an applicable pollutant based on the production ELGprod: the production rate, in lbs, for the applicable guideline(s), usually based on long

- term average data

ELG: the effluent guideline limitation, given as a measure of production (e.g. lbs/1000 lbs), for an applicable pollutant

2. For effluent guidelines based on flow, limits will typically be calculated as follows:

ELG lim: the mass limit, in lbs/day, for the applicable pollutant based on the applicable flow ELGflow: the long

- term average process flow rate, in MGD, for the applicable guideline(s) (unless

otherwise specified in the guideline)

ELG: the concentrati on limitation, in mg/l, for the applicable pollutant from the applicable guideline(s)

H. Other considerations

1. When the derived permit effluent limitation based on aquatic life numeric criteria is below the practical quantitation limit for a substance , the derived permit effluent limitation shall include an accompanying statement in the permit that the practical quantitation limit using approved analytical methods shall be considered as being in compliance with the limit. Appropriate biological monito ring requirements shall be incorporated into the permit to determine compliance with appropriate water quality standards (R.61

- 68.E.14.c(2)).



### 2. When the derived permit effluent limitation based on human health numeric criteria is below the practical

quan titation limit for a substance, the derived permit effluent limitation shall include an accompanying statement in the permit that the practical quantitation limit using approved analytical methods shall be considered as being in compliance with the limit ( R.61

- 68.E.14.c(3)).

3. The effluent concentration limits determined above may not necessarily be the NPDES permit limit. NPDES Permit limits are determined after a reasonable potential analysis is conducted using these derived limits and

also after evalu ating other issues such as anti

- backsliding and antidegradation.

4. When mass limits are calculated, the formula to be used is as follows.

Mass (lb/day) = Flow (mgd) * Concentration (mg/l) * 8.345

5. Per Regulation 61

- 9.122.45(d), for continuous disc harges all permit effluent limitations, standards, and prohibitions, including those necessary to achieve water quality standards, shall unless impracticable be stated as maximum daily and average monthly discharge limitations for all dischargers other tha n publicly owned

treatment works.

6. Antibacksliding: When a permit is reissued, the terms and conditions of the reissued permit must be at least as stringent as those final limits in the previous permit unless certain exceptions are met (see Regulation 61

- 9.122.44.l).Rationale Page 28 of 30

Permit No. SC00 46175

IV. PROCEDURES FOR REACHING A FINAL PERMIT DECISION

A. Comment Period (R.61

- 9.124.10 and 11)

The Department of Health and Environmental Control proposes to issue an NPDES permit to this applicant subject to the effluent limitations and sp ecial conditions outlined in this document. These determinations are tentative.

During the public comment period, any interested person may submit written comments on the draft permit to the following address:

SC Dept. of Health and Environmental Contro l Water Facilities Permitting Division

Bureau of Water

2600 Bull Street Columbia, South Carolina 29201

For additional information, interested persons may contact Byron M Amick at 803

- 898

- 4236

.

All written comments received during the public comment period shall be considered in making the final decision and shall be responded to as prescribed below.

Per R.61

- 9.124.17, the Department is only required to issue a response to comment s when a final permit is issued. This response shall:

1. Specify which provisions, if any, of the draft permit have been changed in the final permit decision, and the reasons for the change; and

2. Briefly describe and respond to all significant comments on t he draft permit raised during the public comment period, or during any hearing.

The response to comments shall be available to the public.

B. Public Hearings (R.61

- 9.124.11 and 12)

During the public comment period, any interested person may request a publi c hearing, if no hearing has already been scheduled. A request for a public hearing shall be in writing and shall state the nature of the issues proposed to be raised in the hearing.

Determinations and Scheduling.

1. Within the thirty (30) day comment period or other applicable comment period provided after posting or publishing of a public notice, an applicant, any affected state or interstate agency, the Regional Administrator or any other interested person or agency may file a petition with the Depar tment for a public hearing on an application for a permit. A petition for a public hearing shall indicate the specific reasons why a hearing is requested, the existing or proposed discharge identified therein and specifically indicate which portions of th e application or other permit form or information constitutes necessity for a public hearing. If the Department determines that a petition constitutes significant cause or that there is sufficient public interest in an application for a public hearing, it may direct the scheduling of a hearing thereon.Rationale Page 29 of 30

Permit No. SC00 46175

2. A hearing shall be scheduled not less than four (4) nor more than eight (8) weeks after the Department determines the necessity of the hearing in the geographical location of the applicant or, at the disc retion of the Department, at another appropriate location, and shall be noticed at least thirty (30) days before the hearing. The notice of public hearing shall be transmitted to the applicant and shall be published in at least one (1) newspaper of genera l circulation in the geographical area of the existing or proposed discharge identified on the permit application and shall be mailed to any person or group upon request thereof. Notice shall be mailed to all persons and governmental agencies which receiv ed a copy of the notice or the fact sheet for the permit application.

3. The Department may hold a single public hearing on related groups of permit applications.

4. The Department may also hold a public hearing at its discretion, whenever, for instance, such a hearing might clarify one or more issues involved in the permit decision;

5. Public notice of the hearing shall be given in accordance with R.61

- 9.124.10.

Any person may submit oral or written statements and data concerning the draft permit. Reasonable l imits may be set upon the time allowed for oral statements, and the submission of statements in writing may be required. The public comment period under R.61

- 9.124.10 shall automatically be extended to the close of any public hearing

under this section. The hearing officer may also extend the comment period by so stating at the hearing.

A tape recording or written transcript of the hearing shall be made available to the public.

C. Obligation to raise issues and provide information during the public co mment period. (R.61

- 9.124.13)

All persons, including applicants, who believe any condition of a draft permit is inappropriate or that the Department’s tentative decision to deny an application, terminate a permit, or prepare a draft permit is inappropri ate, must raise all reasonably ascertainable issues and submit all reasonably available arguments supporting their position by the close of the public comment period (including any public hearing). No issue shall be raised during an appeal by any party tha t was not submitted to the administrative record as part of the preparation and comment on a draft permit, unless good cause is shown for the failure to submit it. Any supporting materials which are submitted shall be included in full and may not be incorp orated by reference, unless they are already part of the administrative record in the same proceeding, or consist of State or Federal statutes and regulations, Department and EPA documents of general applicability, or other generally available reference

ma terials. Commenters shall make supporting materials not already included in the administrative record available. (A comment period longer than 30 days may be necessary to give commenters a reasonable opportunity to comply with the requirements of this se ction. Additional time shall be granted under R.61

- 9.124.10 to the extent that a commenter who requests additional time demonstrates the need for such time).

D. Issuance and Effective Date of the Permit

1. After the close of the public comment period on a draft permit, the Department shall issue a final permit decision. The Department shall notify the applicant and each person who has submitted written comments or requested notice of the final permit decision. This notice shall include reference to the pr ocedures for appealing a decision on a permit. For the purposes of this section, a final permit decision means a final decision to issue, deny, modify, revoke and reissue, or terminate a permit.

2. A final permit decision shall become effective 30 days after the service of notice of the decision unless:

(a) A later effective date is specified in the decision; orRationale Page 30 of 30

Permit No. SC00 46175

(b) No comments requested a change in the draft permit, in which case the permit shall become effective on

the effective date shown in the issue d permit.

3. Issuance or Denial of Permits. An appeal to a final determination of the Department or to a condition of a permit issued or the denial of a permit pursuant to the State law and Regulation 61

- 9, shall be in accordance with and subject to 48

- 1

- 20 0 of the SC Code (see E below).

E. Adjudicatory Hearings

The issuance of this permit by the S.C. Department of Health and Environmental Control (Department) becomes the final agency decision 15 calendar days after notice of the decision has been mailed or otherwise sent to the applicant, permittee, licensee and affected persons who have requested in writing to be notified, unless a written request for final review accompanied by a filing fee in the amount of $100 is filed with the Department by the appl icant, permittee, licensee, or affected person. This Department decision relies on the administrative record, which includes the permit rationale, and other supporting documentation contained in the permit file.

An applicant, permittee, licensee, or affe cted person who wishes to appeal this decision must file a timely written request for final review with the Clerk of the Board at the following address or by facsimile at 803

- 898

- 3393. A filing fee in the amount of $100 made payable to SC DHEC must also be received by the Clerk within the time allowed for filing a request for final review. However, if a request for final review is filed by facsimile, the filing fee may be mailed to the Clerk of the Board if the envelope is postmarked within the time allowed for filing a request for final review.

Clerk of the Board

SC DHEC

2600 Bull Street Columbia, SC 29201

In order to be timely, a request for final review must be received by the Clerk of the Board within 15 calendar days

after notice of the decision h as been mailed or otherwise sent to persons entitled to receive notice. If the 15th day occurs on a weekend or State holiday, the request is due to be received by the Clerk of the Board on the next working day. The request for final review must be received by the Clerk of the Board by 5:00 p.m. on the date it is due. A request for final review will be returned to the requestor if the filing fee is not received on time as described

above.

The request for final review should include the following:

a. The grounds on which the Department’s decision is challenged and the specific changes sought in the decision;

b. A statement of any significant issues or factors the Board should consider in deciding whether to conduct a final review conference; and

c. A co py of the Department’s decision for which review is requested.

If a timely request for final review is filed with the Clerk of the Board, the Clerk will provide additional information regarding procedures. If the Board declines in writing to schedule a fi nal review conference, the Department’s decision becomes the final agency decision and an applicant, permittee, licensee, or affected person may request a contested case hearing before the Administrative Law Court within 30 calendar days after notice is

ma iled that the Board declined to hold a final review conference.

Information pertaining to adjudicatory matters may be obtained by contacting the Legal Office of the Department of Health and Environmental Control, 2600 Bull Street, Columbia, South Carolin a or by calling 803

- 898

- 3350.