Updated 10/18/07

South Carolina Generating Company (SCGENCO)

A.M. Williams Station-Highway 52 Ash Disposal Facility

NPDES Permit No. SC0046175

 

Permitting Engineer: Byron M Amick Revised: February 27, 2009

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, an 

antidegradation 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: US Highway 52, Moncks Corner, SC 29461

County: Berkeley

Watershed: Basin 03 (Catawba-Santee River Basin)

Facility Description (include SIC code): The Highway 52 Ash Disposal Facility is a proposed landfill for the disposal of 

coal ash from SCGENCO/Williams Station in Goose Creek, SC with one (1) outfall for runoff and leachate. SIC Code is 

4953; Refuse Systems

Receiving Waters and Classification by outfall: Wappoola Swamp to Molly Branch to the Cooper River

Is any discharge to Impaired Waters? No (see State 303(d) list for impaired waters)

If Yes, list the monitoring station number(s) and parameter(s) causing impairment: None

Does any discharge have the potential to affect a threatened or endangered species? No (endangered species information 

from SCDNR Heritage Trust, 2006)

If Yes, list the species and the waterbody in which the species resides: 

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 primary 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

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 compliance interim dates are extended more than once

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

FACT SHEET 

AND 

PERMIT RATIONALE
Rationale

Page 2 of 32

Permit No. SC0046175

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 proposed landfill for the disposal of coal ash from SCGENCO’s Williams Station in Goose Creek, SC. This landfill 

will have 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 Cooper River 

(Class FW). This facility will eventually replace the Williams Highway 17A Ash Disposal Facility, therefore NPDES 

permit #SC0039535 may be used as guidance to determine limitations. Since this facility has not begun operation no plans 

have yet been developed for the disposal of sanitary wastewater.

Operator requirements: Based on the proposed treatment system described above and the Pollution Control Act (PCA), the 

treatment system may be classified as Group I-Physical/Chemical. The Environmental Certification Board Rules require 

that a Grade D-Physical/Chemical operator be assigned to operate the proposed facility. Inspections of the facility will be 

required on a daily basis per Regulation 61-9.122.41(e).

Information for this outfall is based on NPDES Permit Application: 2D dated 3/3/05

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

from 1/1/03 - 9/30/05 has been used to evaluate permit limitations.

Previous permit limits are based on the permit (or modification) effective date of January 1, 2003.

All waterbody data is provided on the attached Water Quality Spreadsheets. This data includes 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 (effective January 1, 2003):

Monthly Average: MR, MGD

Daily Maximum: MR, MGD

Sampling Frequency: 1/month

Sample Type: Instantaneous

2. NPDES Application 2D (dated 3/3/05):

Average Flow: 0.053 MGD

3. NPDES Application 2D (dated 9/25/98):

Average Flow: 0.040 MGD

4. Construction Permit Application for Permit #19,188-IW (dated 3/19/08):

Average Flow: 0.388 MGD

5. DMR Data: Discharge has not begun.

6. Conclusion: Flow monitoring will continue as previously permitted.

Monthly Average: MR, MGD

Daily Maximum: MR, MGD

Sampling Frequency: 1/month

Sample Type: Instantaneous

B. Total Suspended Solids (TSS)

1. Previous permit limits (effective January 1, 2003):

Monthly Average: MR, mg/l

Daily Maximum: 50 mg/l

Sampling Frequency: 1/month

Sample Type: Grab

2. NPDES Application 2D (dated 3/3/05): not reported
Rationale

Page 3 of 32

Permit No. SC0046175

3. NPDES Application 2D (dated 9/25/98):

Monthly Average: 20 mg/l

Daily Maximum: 100 mg/l

4. DMR Data: Discharge has not begun.

5. Other information: The existing limit has been applied based on engineering judgment.

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

7. Conclusion: The limit will remain as previously permitted. 

Monthly Average: MR, mg/l

Daily Maximum: 50 mg/l

Sampling Frequency: 1/month

Sample Type: Grab

C. pH

1. Previous Permit Limits (effective January 1, 2003): 6.0 – 8.5 standard units.

Sampling Frequency: 1/month

Sample Type: Grab

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98):

Monthly Average: 8.5 su

Daily Maximum: 9.0 su

4. DMR Data: Discharge has not begun.

5. Water Classification & Standards: SC Reg. 61-68 (2004), Section G.10.f. states that the Class Fresh Waters 

standards for pH shall always be “Between 6.0 and 8.5”.

6. Conclusion: pH shall be between 6.0 and 8.5, based on Water Classification & Standards.

Sampling Frequency: 1/month

Sample Type: Grab

D. Oil and Grease

1. Previous permit limits (effective January 1, 2003):

Monthly Average: 10 mg/l

Daily Maximum: 15 mg/l

Sampling Frequency: 1/month

Sample Type: Grab

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98):

Monthly Average: 10 mg/l

Daily Maximum: 20 mg/l

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A

6. Water Classification & Standards: SC Reg. 61-68 (2004), 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.

7. Other Information: Historically, using engineering judgment, the Department has determined that in order to 

achieve the narrative limit, as stated in Regulation 61-68, a limit is required for Oil & Grease of 10 mg/l 

monthly average, and 15 mg/l daily maximum.

8. PQL: 5.0 mg/l (Method 1664A)

9. Conclusion: Since truck washing activities contribute oil and grease to this discharge, the limit will remain as 

previously permitted. 

Monthly Average: 10 mg/l

Daily Maximum: 15 mg/l

Sampling Frequency: 1/month

Sample Type: Grab
Rationale

Page 4 of 32

Permit No. SC0046175

E. Aluminum, total

1. Previous permit limits (effective January 1, 2003): not limited

2. NPDES Application 2D (dated 3/3/05): not reported

3. DMR Data: Discharge has not begun.

4. Effluent limitations guidelines: N/A

5. Water Quality Criteria for Protection of freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2004): 

CCC: monthly average = none

CMC: daily maximum = none

6. Water Quality Criteria for Protection of Human Health:

- from SC Reg. 61-68, Appendix 1(2004):

(1) Water & Organism Consumption: none

(2) Organism Consumption: none

(3) Drinking Water MCL (Maximum Contaminant Level): none

7. Other Information: Freshwater Aquatic Life

- from 53 FR 33178 (Aug. 30, 1988):

CCC: monthly average = 0.087 mg/l

CMC: daily maximum = 0.750 mg/l

8. Practical Quantitation Limit: 50 g/l (EPA Methods 200.7 or 200.8)

9. Conclusion: This facility is not involved in the production of aluminum or aluminum products. Since there is 

no State Standard for aluminum, no limit for aluminum will be established in this permit.

F. Arsenic, total

1. Previous permit limits (effective January 1, 2003):

Monthly Average: 0.827 g/l

Daily Maximum: 1.21 g/l

Sampling Frequency: 1/month

Sample Type: Grab

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98):

Monthly Average: 0.03 mg/l Daily Maximum: 0.19 mg/l

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A

6. Water Quality Criteria for Protection of Freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2008):

CCC: monthly average = 0.150 mg/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CaCO3 the derived monthly average is 0.3582 mg/l

CMC: daily maximum = 0.340 mg/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CaCO3 the derived daily maximum is 0.8119 mg/l

7. Water Quality Criteria for Protection of Human Health: CARCINOGEN

- from SC Reg. 61-68, Appendix 1(2008):

(1) Water & Organism Consumption: none

(2) Organism Consumption: none

(3) Drinking Water MCL (Maximum Contaminant Level): 10 g/l

monthly average = 10 g/l x 19486 (DF4) = 195 mg/l

daily maximum = 1.86(194.86 mg/l) = 362 mg/l

8. Practical Quantitation Limit: 5 g/l (EPA Methods 200.8, 200.9, or SM3113B)

9. Conclusion: Using the Highway 17A ash disposal facility as guidance, arsenic was not shown to have a 

reasonable potential to cause or contribute to a violation of the state standard. Therefore no limit will be 

established at this time. The permittee will be required to submit a complete EPA Application Form 2C within 

eighteen (18) months of the start of discharge from this facility. Based on the results reported in the EPA 

Application Form 2C the permit will be modified to add parameters and limitations, if necessary.
Rationale

Page 5 of 32

Permit No. SC0046175

G. Cadmium, total

1. Previous permit limits (effective January 1, 2003): not limited

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98): not reported

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A

6. Water Quality Criteria for Protection of freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2004):

CCC: monthly average = 0.10 g/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CaCO3 the derived monthly average is 0.000329 mg/l

CMC: daily maximum = 0.53 g/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CaCO3 the derived daily maximum is 0.001805 mg/l

7. Water Quality Criteria for Protection of Human Health: NONCARCINOGEN

- from SC Reg. 61-68, Appendix 1(2004):

(1) Water & Organism Consumption: none

(2) Organism Consumption: none

(3) Drinking Water MCL (Maximum Contaminant Level): 5 g/l

monthly average = 5 g/l x 13034 (DF3) = 65.2 mg/l

daily maximum = 1.46(65.2 mg/l) = 95.2 mg/l

8. Practical Quantitation Limit: 0.1 g/l (EPA Methods 200.8, 200.9, or SM3113B)

9. Conclusion: Using the Highway 17A ash disposal facility as guidance, cadmium was not shown to have a 

reasonable potential to cause or contribute to a violation of the state standard. Therefore no limit will be 

established at this time. The permittee will be required to submit a complete EPA Application Form 2C within 

eighteen (18) months of the start of discharge from this facility. Based on the results reported in the EPA 

Application Form 2C the permit will be modified to add parameters and limitations, if necessary.

H. Copper, total

1. Previous permit limits (effective January 1, 2003):

Monthly Average: ---

Daily Maximum: MR, mg/l

Sampling Frequency: 1/year

Sample Type: Grab

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98): not reported

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A

6. Water Quality Criteria for Protection of freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2004): 

CCC: monthly average = 2.9 g/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CACO3 the standard is 0.01068 mg/l

CMC: daily maximum = 3.8 g/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CACO3 the standard is 0.01399 mg/l

7. Water Quality Criteria for Protection of Human Health: NONCARCINOGEN

- from SC Reg. 61-68, Appendix 1(2004):

(1) Water & Organism Consumption: 1300 g/l =1.3 mg/l

monthly average = 1.300 mg/l x 13034 (DF3) = 16,944 mg/l

daily maximum = 1.46(16,944 mg/l) = 24,738 mg/l

(2) Organism Consumption: none

(3) Drinking Water MCL (Maximum Contaminant Level): none

8. Practical Quantitation Limit: 10 g/l (EPA Methods 200.7, 200.8, 200.9, or SM3113B)
Rationale

Page 6 of 32

Permit No. SC0046175

9. Conclusion: Using the Highway 17A ash disposal facility as guidance, cooper was not shown to have a 

reasonable potential to cause or contribute to a violation of the state standard. Therefore no limit will be 

established at this time. The permittee will be required to submit a complete EPA Application Form 2C within 

eighteen (18) months of the start of discharge from this facility. Based on the results reported in the EPA 

Application Form 2C the permit will be modified to add parameters and limitations, if necessary.

I. Iron, total

1. Previous permit limits (effective January 1, 2003): not limited

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98):

Monthly Average: 1.15 mg/l

Daily Maximum: 5.00 mg/l

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A

6. Water Quality Criteria for Protection of freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2008): 

CCC: monthly average = none

CMC: daily maximum = none

7. Water Quality Criteria for Protection of Human Health:

- from SC Reg. 61-68, Appendix 1(2008):

(1) Water & Organism Consumption: none

(2) Organism Consumption: none

(3) Drinking Water MCL (Maximum Contaminant Level): none

8. Practical Quantitation Limit: 20 g/l (EPA Methods 200.7 or 200.8)

9. Conclusion: Since there is no State Standard for iron, no limit for iron will be established in this permit.

J. Manganese, total

1. Previous permit limits (effective January 1, 2003): not limited

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98): not reported

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A

6. Water Quality Criteria for Protection of freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2008): 

CCC: monthly average = none

CMC: daily maximum = none

7. Water Quality Criteria for Protection of Human Health:

- from SC Reg. 61-68, Appendix 1(2008):

(1) Water & Organism Consumption: none

(2) Organism Consumption: none

(3) Drinking Water MCL (Maximum Contaminant Level): none

8. Practical Quantitation Limit: 10 g/l (EPA Methods 200.7 or 200.8)

9. Conclusion: Since there is no State Standard for manganese, no limit will be established in this permit.

K. Mercury, total

1. Previous permit limits (effective January 1, 2003): not limited

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98): not reported

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A
Rationale

Page 7 of 32

Permit No. SC0046175

6. Water Quality Criteria for Protection of freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2004): 

CCC: monthly average = 0.91 g/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CACO3 the standard is 0.0021 mg/l

CMC: daily maximum = 1.6 g/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CACO3 the standard is 0.0037 mg/l

7. Water Quality Criteria for Protection of Human Health: NONCARCINOGEN

- from SC Reg. 61-68, Appendix 1(2004):

(1) Water & Organism Consumption: 0.050 g/l

monthly average = 0.050 g/l x 13034 (DF3) = 0.6517 mg/l

daily maximum = 1.46(0.6517 mg/l) = 0.9515 mg/l

(2) Organism Consumption: 0.051 g/l

monthly average = 0.051 g/l x 1.0 (DF1) = 0.000051 mg/l

daily maximum = 1.46(0.000051 mg/l) = 0.000074 mg/l

(3) Drinking Water MCL (Maximum Contaminant Level): 2 g/l

monthly average = 2 g/l x 13034 (DF3) = 26.07 mg/l

daily maximum = 1.46(26.07 mg/l) = 38.06 mg/l

8. Practical Quantitation Limit: 0.0005 g/l (EPA Methods 1669(sampling)/1631E (analysis))

9. Conclusion: Using the Highway 17A ash disposal facility as guidance, mercury was not shown to have a 

reasonable potential to cause or contribute to a violation of the state standard. Therefore no limit will be 

established at this time. The permittee will be required to submit a complete EPA Application Form 2C within 

eighteen (18) months of the start of discharge from this facility. Based on the results reported in the EPA 

Application Form 2C the permit will be modified to add parameters and limitations, if necessary.

L. Nickel, total

1. Previous permit limits (effective January 1, 2003):

Monthly Average: ---

Daily Maximum: MR, mg/l

Sampling Frequency: 1/year

Sample Type: Grab

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98): not reported

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A

6. Water Quality Criteria for Protection of freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2004): 

CCC: monthly average = 16 g/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CACO3 the standard is 0.05767 mg/l

CMC: daily maximum = 150 g/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CACO3 the standard is 0.5412 mg/l

7. Water Quality Criteria for Protection of Human Health: NONCARCINOGEN

- from SC Reg. 61-68, Appendix 1(2004):

(1) Water & Organism Consumption: 610 g/l = 0.61 mg/l

monthly average = 0.61 mg/l x 13034 (DF3) = 7,950 mg/l

daily maximum = 1.46(7,950 mg/l) = 11,607 mg/l

(2) Organism Consumption: 4600 g/l = 4.60 mg/l

monthly average = 4.60 mg/l x 1.0 (DF1) = 4.60 mg/l

daily maximum = 1.46(4.60 mg/l) = 6.716 mg/l

(3) Drinking Water MCL (Maximum Contaminant Level): none

8. Practical Quantitation Limit: 10 g/l (EPA Methods 200.8, 200.9, or SM3113B)
Rationale

Page 8 of 32

Permit No. SC0046175

9. Conclusion: Using the Highway 17A ash disposal facility as guidance, nickel was not shown to have a 

reasonable potential to cause or contribute to a violation of the state standard. Therefore no limit will be 

established at this time. The permittee will be required to submit a complete EPA Application Form 2C within 

eighteen (18) months of the start of discharge from this facility. Based on the results reported in the EPA 

Application Form 2C the permit will be modified to add parameters and limitations, if necessary.

M. Selenium, total

1. Previous permit limits (effective January 1, 2003): not limited

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98): not reported

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A

6. Water Quality Criteria for Protection of Freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2004):

CCC: monthly average = 5.0 g/l

CMC: daily maximum = none

- since there is no CMC the daily maximum will be twice the monthly average, or 10.0 g/l

7. Water Quality Criteria for Protection of Human Health: NONCARCINOGEN

- from SC Reg. 61-68, Appendix 1(2004):

(1) Water & Organism Consumption: 170 g/l

monthly average = 170 g/l x 13034 (DF3) = 2,216 mg/l

daily maximum = 1.46(2,216 mg/l) = 3,235 mg/l

(2) Organism Consumption: 4,200 g/l

monthly average = 4,200 g/l x 1.0 (DF1) = 4.2 mg/l

daily maximum = 1.46(4.2 mg/l) = 6.13 mg/l

(3) Drinking Water MCL (Maximum Contaminant Level): 50 g/l

monthly average = 50 g/l x 13034 (DF3) = 652 mg/l

daily maximum = 1.46(652 mg/l) = 952 mg/l

8. Practical Quantitation Limit: 5 g/l (EPA Methods 200.8, 200.9, or SM3113B)

9. Conclusion: Using the Highway 17A ash disposal facility as guidance, it was unclear if selenium would have a 

reasonable potential to cause or contribute to a violation of the state standard. However, having no data 

reported for this site, we have added a requirement to monitor and report. The permittee will be required to 

submit a complete EPA Application Form 2C within eighteen (18) months of the start of discharge from this 

facility. Based on the results reported in the EPA Application Form 2C the permit will be modified to add 

parameters and limitations, if necessary.

Monthly Average: MR, mg/l

Daily Maximum: MR, mg/l

Sampling Frequency: 1/month

Sample Type: Grab

N. Zinc, total

1. Previous permit limits (effective January 1, 2003):

Monthly Average: ---

Daily Maximum: MR, mg/l

Sampling Frequency: 1/year

Sample Type: Grab

2. NPDES Application 2D (dated 3/3/05): not reported

3. NPDES Application 2D (dated 9/25/98): not reported

4. DMR Data: Discharge has not begun.

5. Effluent limitations guidelines: N/A
Rationale

Page 9 of 32

Permit No. SC0046175

6. Water Quality Criteria for Protection of freshwater Aquatic Life

- from SC Reg. 61-68, Appendix 1(2004):

CCC: monthly average = none

CMC: daily maximum = 37 g/l

- using a stream TSS of 1 mg/l and hardness 25 mg/l as CACO3 the standard is 0.1803 mg/l

7. Water Quality Criteria for Protection of Human Health: NONCARCINOGEN

- from SC Reg. 61-68, Appendix 1(2004):

(1) Water & Organism Consumption: 7,400 g/l

monthly average = 7400 g/l x 13034 (DF3) = 96,450 mg/l

daily maximum = 1.46(96,450 mg/l) = 140,800 mg/l

(2) Organism Consumption: 26,000 g/l

monthly average = 26,000 g/l x 1.0 (DF1) = 26 mg/l

daily maximum = 1.46(26 mg/l) = 37.96 mg/l

(3) Drinking Water MCL (Maximum Contaminant Level): none

8. Practical Quantitation Limit: 10 g/l (EPA Methods 200.7, 200.8, 200.9, 289.1, SM3113B or SM3111B)

9. Conclusion: Using the Highway 17A ash disposal facility as guidance, zinc was not shown to have a 

reasonable potential to cause or contribute to a violation of the state standard. Therefore no limit will be 

established at this time. The permittee will be required to submit a complete EPA Application Form 2C within 

eighteen (18) months of the start of discharge from this facility. Based on the results reported in the EPA 

Application Form 2C the permit will be modified to add parameters and limitations, if necessary.

Whole Effluent Toxicity (WET)

Previous permit requirements (effective January 1, 2003): chronic toxicity 

CTC: 100% expressed as a maximum of 40% effect and an average of 25% effect.

- Monitor and report for reproduction and mortality at the CTC

Species: Ceriodaphnia dubia

Dilution Series:0%, 50%, 60%, 71%, 84%, 100%

Sampling frequency: 1/quarter

Sample type: Grab

DMR Data: Discharge has not begun.

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

zone or dilution allowed.

Other information: Due to the fact that the discharge is complex, quarterly toxicity testing will continue to be 

required.

From the information described above, using the procedures in Regulation 61-9.122.44(d)(1)(ii), the Department 

has determined that this discharge causes, has the reasonable potential to cause or contributes to an excursion of the 

narrative water quality standards in Regulation 61-68.A.4, which says that “It is the goal of the Department...to 

provide for the survival and propogation of a balanced indigenous aquatic community of flora and fauna” and 

“free-from” criterion in R.61-68.E.5. Therefore, limitations on WET are needed.

Testing Requirements for this permit: 

Your permit requirements are expressed as a maximum of 40% effect and an average of 25% effect. These 

limitations are designed to protect to the narrative water quality criterion for toxicity of “no toxics in toxic 

amounts.” For a monitoring period where a single test is performed, the Department has determined that an 

average 25% effect closely corresponds to 0.05 alpha level and a maximum 40% effect is close to 0.01 alpha level 

under current test design and methods. This approach mirrors EPA’s use of IC25, the Inhibition Concentration or 

concentration at which 25% effect exists.
Rationale

Page 10 of 32

Permit No. SC0046175

Dilution Factor = 7Q10 + Flow of Discharge = 0.0 MGD + 0.053 MGD = 1.0

Flow of Discharge 0.053

Instream Waste Concentration = 1/IWC x 100 = 1/1 x 100 = 100%

Chronic toxicity testing will be performed at the chronic test concentration (CTC) of 100%. 

The following calculation, as explained in the Bureau’s guidance document Options for Data Analysis of Whole 

Effluent Toxicity Testing Required by NPDES Permits, September 2001, shows how the multiple concentrations 

are derived. To determine a geometric series of effluent concentrations given a low concentration L, a high 

concentration H, and n concentrations, the concentration factor is

 

F = (H/L)1/(n-1) and the ith concentration is Ci = L * F i - 1

Where, F is the concentration factor and n is the number of concentrations:

For n = 5, L = 50, and H = 100, F = 100 1/(5-1) = 21/4 = 1.19

50

After determining the concentration factor the following formula is used to determine the test concentrations:

Ci = L x F(I-1) where, I is the number of concentrations

Determining the four concentrations: Note; I = 1,2, 3, 4, 5

C1 = 50 x 1.19(1-1) = 50%

C2 = 50 x 1.19(2-1) = 60%

C3 = 50 x 1.19(3-1) = 71%

C4 = 50 x 1.19(4-1) = 84%

For this discharge situation, the concentrations are 0%, 50%, 60%, 71%, 84% and 100% for each multiple 

concentration test.

Groundwater Monitoring

Based on the recommendations of the Department’s Groundwater Quality Section, the permittee shall continue to 

monitor and report each of the two (2) groundwater monitoring wells (MW-1A and MW-5) semi-annually for the 

following parameters:

Water Table Elevation Arsenic Lead

Depth to the Water Table Cadmium Mercury

Field pH Chlorides Nickel

Field Specific Conductance Chromium Zinc

Field Turbidity Copper Selenium

Total Dissolved Solids (TDS) Iron Sulfate as SO4
Rationale

Page 11 of 32

Permit No. SC0046175

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 accordance 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 NPDES 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 wide-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 Limitations, Standards and other 

permit conditions) and other appropriate sections of R.61-9.

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 at the boundary of the source water protection area 

above a proposed or existing drinking water intake (if applicable) are determined by the SCDHEC’s Wasteload 

Allocation Section. The 7Q10, Annual Average Flow or other critical flow conditions are based on information 

published 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 flow. 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 at the boundary of the SWP area for a proposed or existing 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 organism consumption and drinking water MCL data will be evaluated as human health values 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 permitting 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 that will 

affect or has the potential to affect the drinking water source (R.61-68.E.14.c(5)). The Department defines the 

source water protection (SWP) area to be the primary SWP area delineated by the Source-Water Assessment and 

Protection (SWAP) Program initiated by the EPA and required by the states to identify SWP areas to protect 

drinking water sources. Using the procedure described in the document entitled, “Determination of the Primary 

and Secondary Source-Water Protection Areas for Selected Surface-Water Public-Supply Systems in South 

Carolina, 1999,” USGS Water Resource Investigations Report 00-4097, the primary SWP area for a drinking water 

intake is the area which encompasses all 14-digit Hydrologic Unit Code (HUC) basins that adjoin streams, 

tributaries, and reservoirs between an intake and the upstream 10-percent exceedance, 24-hour travel distance 

(TOT10). The entire basin above a drinking water intake has been designated as the SWP area where the drainage 

area is equal to or less than one HUC basin or is estimated to have less than 24-hours of instream travel time 

between the intake and the HUC basin in the headwaters of the drainage basin.

C. Application of numeric criteria to protect human health: If separate numeric criteria are given 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 uses of the waters of the State (R.61-68.E.14.b(1)).
Rationale

Page 12 of 32

Permit No. SC0046175

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)).

F. Compliance Schedules:

1. A person issued an NPDES permit by the Department 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 

nine (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 (BOD5), 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 BOD5, Ultimate Oxygen Demand (UOD), Dissolved Oxygen 

(DO):

Effluent limits for conventional oxygen demanding constituents (BOD5, UOD and DO) are established to 

protect 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 Maximum 

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 QUAL2EUNCAS are used in accordance with “Enhanced Stream Water Quality Models QUAL2E and QUAL2EUNCAS: Documentation and Users Manual” (EPA/600/3-87/007; dated May 1987) as updated. BOD5

and UOD values determined from modeling results will be used in permitting as monthly average derived 

limits (Cwla). Daily maximum derived 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, BOD5 will 

also be evaluated in accordance with the applicable industrial categorical guidelines. These guidelines will

be identified in Part I of this rationale when they are applicable to the permit.
Rationale

Page 13 of 32

Permit No. SC0046175

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 for 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 this rationale when ammonia is a 

pollutant of concern.

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 accordance 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 quality 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 such 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 criteria.

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. Lakes 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 exceed 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 ecoregion 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 classified 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 establishing 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 purpose, the 

Department shall define the applicable area to be that area covered when measured at full pool 

elevation.
Rationale

Page 14 of 32

Permit No. SC0046175

2. Effluent concentration limits (Cefflim) for parameters other than the parameters listed in G.1.a-c (except 

ammonia toxicity calculations) above are established using the following procedures:

Q7Q10 7Q10 or other critical flow condition of the receiving water at the discharge point in mgd. 

(may require adjustment for withdrawals) 

AAFd Average Annual Flow (AAF) or other critical flow condition of the receiving water at the 

discharge point in mgd. (may require adjustment for withdrawals) 

Q7Q10i 7Q10 or other critical flow condition of the receiving water at the SWP Area boundary in mgd.

AAFi Average Annual Flow (AAF) of the receiving water at the SWP Area boundary in mgd.

Qd 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:

DF1: Dilution factor based on 7Q10 or other critical flow condition of the receiving water at the 

discharge point (Q7Q10). 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 aquatic organisms become exposed to the 

discharge.















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

d

Q d

Q

Q Q

DF 7 10

1

DF2: Dilution factor, at the discharge point, based on the Average Annual Flow of the receiving water at 

the discharge point (AAFd). 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 long-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 

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















 



d

d d

Q

AAF Q

DF2

DF3: Dilution factor based on the 7Q10 or other critical flow condition at the source water protection 

area boundary for protection of a proposed or existing water intake downstream of the discharge 

(Q7Q10i). This dilution factor is used to determine the derived limits for protection of the following 

human health concerns for the reasons indicated:
Rationale

Page 15 of 32

Permit No. SC0046175

i. Human Health – Water and Organism Consumption for parameters identified as noncarcinogens per R.61-68.C.4.b(1) and E.14.c(5) to protect for short-term health effects when 

the discharge is above any 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 potentially higher level of protection in terms of applicable dilution than 

consumption of organisms. In addition, to satisfy the requirements of R.61-68.C.10(a), the 

Department has determined that dilution at the boundary of the Source Water Protection area 

will protect the source water protection area and drinking water intake to meet this 

requirement. 

For discharges except those to lakes affecting the primary source water protection (SWP) area, 

dilution will be determined using the largest flow (7Q10 or annual average flow, as 

appropriate) associated with any TOT10 point along the SWP area boundary upstream of the 

drinking water intake of concern. For discharges to lakes affecting the primary SWP area, 

dilution will be determined using the sum of the flows (7Q10 or average annual flow, as 

appropriate) associated with all TOT10 point(s) along the SWP area boundary upstream of the 

drinking water intake of concern. If multiple drinking water intakes are present below the 

discharge, the SWP area of the intake closest to the discharge will be protected. If the entire 

basin is designated as the SWP area, the boundary will be the TOT10 at the beginning of the 

basin, even if it is outside the State boundaries (e.g. North Carolina).

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 is above any 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. In addition, to satisfy the requirements of R.61-68.C.10(a), 

the Department has determined that dilution at the boundary of the Source Water Protection 

area will protect the source water protection area and drinking water intake to meet this 

requirement. 

For discharges except those to lakes affecting the primary source water protection (SWP) area, 

dilution will be determined using the largest flow (7Q10 or annual average flow, as 

appropriate) associated with any TOT10 point along the SWP area boundary upstream of the 

drinking water intake of concern. For discharges to lakes affecting the primary SWP area, 

dilution will be determined using the sum of the flows (7Q10 or average annual flow, as 

appropriate) associated with all TOT10 point(s) along the SWP area boundary upstream of the 

drinking water intake of concern. If multiple drinking water intakes are present below the 

discharge, the SWP area of the intake closest to the discharge will be protected. If the entire 

basin is designated as the SWP area, the boundary will be the TOT10 at the beginning of the 

basin, even if it is outside the State boundaries (e.g. North Carolina).















 



d

Q i d

Q

Q Q

DF 7 10

3

DF4: Dilution factor based on the Average Annual Flow at the source water protection area boundary 

for protection of a proposed or existing water intake downstream of the discharge (AAFi ).

This dilution factor is used to determine the derived limits for protection of the following human 

health concerns for the reasons indicated:
Rationale

Page 16 of 32

Permit No. SC0046175

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 discharge is above any 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 potentially higher level of protection in terms of applicable dilution than 

consumption of organisms. In addition, to satisfy the requirements of R.61-68.C.10(a), the 

Department has determined that dilution at the boundary of the Source Water Protection area 

will protect the source water protection area and drinking water intake to meet this 

requirement. 

For discharges except those to lakes affecting the primary source water protection (SWP) area, 

dilution will be determined using the largest flow (7Q10 or annual average flow, as 

appropriate) associated with any TOT10 point along the SWP area boundary upstream of the 

drinking water intake of concern. For discharges to lakes affecting the primary SWP area, 

dilution will be determined using the sum of the flows (7Q10 or average annual flow, as 

appropriate) associated with all TOT10 point(s) along the SWP area boundary upstream of the 

drinking water intake of concern. If multiple drinking water intakes are present below the 

discharge, the SWP area of the intake closest to the discharge will be protected. If the entire 

basin is designated as the SWP area, the boundary will be the TOT10 at the beginning of the 

basin, even if it is outside the State boundaries (e.g. North Carolina).

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 is above any 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 potentially higher level of protection in terms of 

applicable dilution than consumption of organisms. In addition, to satisfy the requirements of 

R.61-68.C.10(a), the Department has determined that dilution at the boundary of the Source 

Water Protection area will protect the source water protection area and drinking water intake 

to meet this requirement. 

For discharges except those to lakes affecting the primary source water protection (SWP) area, 

dilution will be determined using the largest flow (7Q10 or annual average flow, as 

appropriate) associated with any TOT10 point along the SWP area boundary upstream of the 

drinking water intake of concern. For discharges to lakes affecting the primary SWP area, 

dilution will be determined using the sum of the flows (7Q10 or average annual flow, as 

appropriate) associated with all TOT10 point(s) along the SWP area boundary upstream of the 

drinking water intake of concern. If multiple drinking water intakes are present below the 

discharge, the SWP area of the intake closest to the discharge will be protected. If the entire 

basin is designated as the SWP area, the boundary will be the TOT10 at the beginning of the 

basin, even if it is outside the State boundaries (e.g. North Carolina).















 



d

i d

Q

AAF Q

DF4

b. Determine derived limits using the following procedures:

WQSal Freshwater Standard (based on an established criteria or other published data per R.61-68) for 

protection of Aquatic Life; may be a CCC or CMC as defined below
Rationale

Page 17 of 32

Permit No. SC0046175

WQSorg Standard (based on an established criteria or other published data per R.61-68) for protection of 

Human Health – Organism Consumption

WQSwo Standard (based on an established criteria or other published data per R.61-68) for protection of 

Human Health – Water & Organism Consumption. 

WQSmcl Standard (based on an established criteria or other published data per R.61-68) for Drinking Water 

MCL (Maximum Contaminant Level). 

WQSol: Standard (based on an established criteria or other published data per R.61-68) based on 

Organoleptic Data.

Caqlife Concentration limit derived from aquatic life data

CHH Concentration limit derived from human health data as determined from organism (Corg), 

water/organism (Cwo)and MCL (Cmcl) data

Col Concentration limit derived from organoleptic data

Cb The background 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 discharge 

flows is not on the 303(d) list, the 90th 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 available 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 Quality 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 EPA 

recommendation.

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

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





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

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   

d

Q

aqlife a l b Q

Q

C DF WQS C

7 1 0

1

( )

a. Typically, the Criterion Maximum Concentration (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 Implementation 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 in this rationale.

monthly average = Caqlife using CCC as WQSal

daily maximum = Caqlife using CMC as WQSal

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 dilution 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 61-9.122.45(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 
Rationale

Page 18 of 32

Permit No. SC0046175

average derived limit and the daily maximum derived limit 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 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 = Caqlife using CCC as WQSal

daily maximum = 2 x Caqlife

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

are 

monthly average = Caqlife using CMC as WQSal

daily maximum = Caqlife using CMC as WQSal

c. If only an acute toxicity effect concentration for a number of species for a particular pollutant 

is given as a LC50, 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 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 = Caqlife using other data as WQSal

daily maximum = 2 x Caqlife

d. If a chronic toxicity effect concentration for 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 = Caqlife using other data as WQSal

daily maximum = 2 x Caqlife

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 monthly 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 recommended in Section 5.4.2 of the TSD.

monthly average = Caqlife using other data as WQSal

daily maximum = 2 x Caqlife
Rationale

Page 19 of 32

Permit No. SC0046175

f. Consider the background concentration (Cb) 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 (Caqlife) for that parameter is 

established equal to the standard (WQS) so that no additional amount of that pollutant is added 

to the waterbody. 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 (Cefflim) 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 Cb is not based on naturally occurring concentrations and

Cb  WQS

Then, generally,

Caqlife  WQS .

If Cb is based on naturally occurring concentrations and

Cb WQS

Then, generally,

Caqlife  Ceff lim  Cb

.

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-Dependent”. 

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 greater 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-weighted 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 below 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 Cd below changes the total metal to dissolved metal. From Technical Guidance 

Manual for Performing Waste Load Allocations Book II, Rivers and Streams, EPA/440/484/022. 
Rationale

Page 20 of 32

Permit No. SC0046175

S  CCC orCMC

(adjusted for hardness)

Cd  S CF

where Cd = 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 Cp using the equation for Cd above 

and the following equations. 

  

6

1 10 Cp Cd   Kpb TSSb 

a

po b b

Kp K (TSS )

where Cp = Particulate sorbed metal concentration (μg/l). This value represents the 

revised water quality criterion for the metal to be used for ambient data 

comparison. 

Kpb= Linear partition coefficient using the stream TSS (liters/mg)

Kpo = Metal-specific equilibrium constant (liters/mg)

a = Metal-specific constant 

TSSb = Background or in-stream Total Suspended Solids (TSS) concentration 

(mg/l). The background 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 (Caqlife), use the following equations to translate the limits into a 

total recoverable metal concentration. 

 

7 1 0

7 1 0 ( )

d Q

d e Q b

avg Q Q

Q TSS Q TSS

TSS



  



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

from actual long-term average data or proposed permit limits if no data 

available.

TSSavg = Average in-stream (mixed) TSS concentration (mg/l)

  

6

1 10 Ct Cd   KpTSSavg

a Kp Kpo TSSavg

 ( )

where Ct = Total metal concentration (μg/l)

Kp = Linear partition coefficient (liters/mg). This is the distribution of metal at 

equilibrium between the particulate and dissolved forms.

Once Ct has been calculated, it is multiplied by DF1 and background concentrations are accounted 

for to obtain the derived limit (max or avg) (Caqlife):
Rationale

Page 21 of 32

Permit No. SC0046175

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   

d

Q

aqlife t b Q

Q

C C DF C

7 1 0

1

( )

monthly average = Caqlife based on CCC

daily maximum = Caqlife based on CMC

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

aquatic life criterion (Caqlife-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 approved 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. 

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 Caqlife value that will be used 

to determine derived limits:

monthly average = Caqlife-adj based on CCC

daily maximum = Caqlife-adj based on CMC

b. For other parameters, use the appropriate equation in #1 above to derive an adjusted Caqlife

value. The monthly average will be calculated as follows using the appropriate WQSal and the 

daily maximum calculated using the appropriate equations in #1 above.

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

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     

d

Q

aqlife adj a l b Q

Q

C DF WQS WER C

7 1 0

1

( )

4. Where the Recalculation Procedure is used to adjust a criterion, derived limits for the adjusted 

aquatic life criterion (Caqlife-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 develop 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 columns 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.
Rationale

Page 22 of 32

Permit No. SC0046175

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



    

d

Q

aqlife adj b Q

Q

C DF SS C

7 1 0

1

(

monthly average = Caqlife-adj based on CCC

daily maximum = Caqlife-adj based on CMC

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

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

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     

d

Q

aqlife adj b Q

Q

C DF SS WER C

7 1 0

1

( )

monthly average = Caqlife-adj based on CCC

daily maximum = Caqlife-adj based on CMC

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 for 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 concentrations (CHH-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 existing or proposed drinking water intake and no 

state-approved source water protection area (i.e., if there is no intake downstream of the

discharge) 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 multiplier (M) determined using a statistical procedure recommended in Section 

5.5 using average = 95th 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. 

( 0.5 )

( 0.5 )

2

2

a n n

m

Z

Z

e

e M

 

 







where:

















 ln 1

2

2

n

CV

 n

ln 1

2 2   CV 

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 evaluated. 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.
Rationale

Page 23 of 32

Permit No. SC0046175

n = the number of effluent samples per month (where frequency is less than 

1/month, n =1) 

zm = the percentile exceedance probability for the daily maximum permit limit 

(=2.326 for 99th percentile basis)

za = the percentile exceedance probability for the monthly average permit limit 

(=1.645 for 95th percentile basis)

CHH-max = M * CHH-avg

c. Consider the background concentration (Cb) 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 (CHHe) 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 derived 

permit effluent limitation. In those situations, the Department may establish permit effluent 

limitations (Cefflim) 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 (See R.61-68.E.14.c(3)). 

If Cb is not based on naturally occurring concentrations and

Cb  WQS

Then, generally,

CHH WQS .

If Cb is based on naturally occurring concentrations and

Cb WQS

Then, generally,

CHH  Ceff lim  Cb

.

2. Human Health – Organism Consumption (Corg).

a. For Carcinogens 

The Monthly Average is calculated as follows:

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

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   

d

d

org org b Q

AAF C (DF2 WQS ) C

The Daily Maximum is calculated as

Corg-max = M * Corg

b. For Non-carcinogens

The Monthly Average is calculated as follows:

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   

d

Q

org org b Q

Q

C DF WQS C

7 1 0

1

( )

The Daily Maximum is calculated as
Rationale

Page 24 of 32

Permit No. SC0046175

Corg-max = M * Corg

3. Human Health – Water and Organism Consumption (Cwo) 

a. For Carcinogens 

The Monthly Average is calculated as follows:

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

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   

d

i

wo wo b Q

AAF C (DF4 WQS ) C

The Daily Maximum is calculated as

Cwo-max = M * Cwo

b. For Non-carcinogens 

The Monthly Average is calculated as follows:

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   

d

Q i

wo wo b Q

Q

C DF WQS C

7 1 0

3

( )

The Daily Maximum is calculated as

Cwo-max = M * Cwo

4. Human Health – Drinking Water Maximum Contaminant Level (MCL) (Cmcl).

a. For Carcinogens 

The Monthly Average is calculated as follows:

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   

d

i

mcl mcl b Q

AAF C (DF4 WQS ) C

The Daily Maximum is calculated as

Cmcl-max = M * Cmcl

b. For Non-carcinogens 

The Monthly Average is calculated as follows:

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   

d

Q i

mcl mcl b Q

Q

C DF WQS C

7 1 0

3

( )

The Daily Maximum is calculated as

Cmcl-max = M * Cmcl
Rationale

Page 25 of 32

Permit No. SC0046175

5. Organoleptic criteria (Col).

The Monthly Average is calculated as follows:

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   

d

d

o l o l b Q

AAF C (DF2 WQS ) C

The Daily Maximum is calculated as

Col-max = M * Col

iii. Parameters given in a wasteload allocation for oxygen-demanding pollutants and nutrients will be 

limited as

monthly average = Cwla

daily maximum = 2 x Cwla

c. Determine the most stringent of applicable water quality data using the monthly average derived limits 

determined above:

monthly average Cefflim = minimum of derived monthly averages (Caqlife, Corg, Cwo, Cmcl, Col , Cwla) 

daily maximum Cefflim = minimum of derived daily maximums (Caqlife, Corg-max, Cwo-max, Cmcl-max, Col-max , Cwla-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 the 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 proposed 

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 Department 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.
Rationale

Page 26 of 32

Permit No. SC0046175

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 pollutant 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 

waterbody, 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.

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 below. 

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 results 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 PQL” 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 to 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 two 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 Limits (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 data and determine the highest value (Cmax) from that data 

set. For the monthly average comparison, the data set will include monthly average results 
Rationale

Page 27 of 32

Permit No. SC0046175

and n will be the number of months in which they sampled in the time period being 

evaluated. For the daily maximum 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 variation (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 uncertainty in the CV is too large to calculate a standard deviation or mean with 

sufficient confidence.

CV  0.6 for n 10 



CV  for 

n 10

where:



= Standard Deviation of the samples



= 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 the sample data.

n

pn Confidence Level 1/ (1 )

where: pn = 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 (Cp) and the selected upper bound of the lognormal effluent distribution, 

which in this case will be the 95th percentile (C95).

( 0.5 )

( 0.5 )

95

2

2

9 5

 

 





 

Z p

Z

p e

e

C

C

MF

where: Z95 is the standardized Z-score for the 95th percentile of the standardized 

normal distribution = 1.645

Zp 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 

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

ln( 1)

2 2   CV 

ln( 1)

2   CV 
Rationale

Page 28 of 32

Permit No. SC0046175

Step 5: Multiply the highest value from the data set (Cmax) by the multiplying factor (MF) 

determined in Step 4 to obtain the maximum receiving water concentration (RWC).

RWC  Cmax MF

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

RWC > Derived limit (Cefflim) implies that reasonable potential exists.

2. Reasonable potential for Whole Effluent 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 IC25, LC50 and/or NOEC 

values:

Step 1: Convert the given values to toxic units: TUa for acute data and TUc for chronic data, 

respectively, using the following formulae. Please note that an NOEC derived using the 

IC25 is approximately the analogue of an NOEC derived using hypothesis testing. The IC25

is the preferred statistical method for determining the NOEC (EPA TSD, March 1991, 

p.6). 

50

100

LC

TUa

NOEC

TUc

100

 or 

25

100

IC

TUc

if IC25 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 (TUa, 

max or TUc, 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 TUa, max or TUc, 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 = [TUa, max * MF * conc. at MZ boundary]

RWC for Chronic Toxicity = [TUc, max * MF * conc. at MZ boundary]

Step 6: RWC for Acute Toxicity ≤ 0.3TUa implies that a reasonable potential does not exist

RWC for Acute Toxicity > 0.3TUa implies that a reasonable potential exists

RWC for Chronic Toxicity ≤ 1.0TUc implies that a reasonable potential does not exist 

RWC for Chronic Toxicity >1.0TUc implies that a reasonable potential exists 
Rationale

Page 29 of 32

Permit No. SC0046175

b. When pass/fail effluent data only is available and all tests have passed, the Department may be 

able to determine reasonable potential in a manner similar to above assuming the test 

concentration of interest is greater than or equal to the concentration at which the permittee 

has tested. If the permittee has not tested at or above the test concentration of interest, the 

Department cannot say that reasonable potential does not exist, unless perhaps, circumstances 

related to the discharge have changed. If any failures exist in the data set, reasonable potential 

may be determined to exist. 

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

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

The more stringent of 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 due 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.

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

ELG lim  (ELGprod)(ELG)

where

ELGlim: 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  (ELGflow)(ELG)8.34 

ELGlim: 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 concentration 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 monitoring 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 

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 (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 evaluating other issues such as anti-backsliding and antidegradation.
Rationale

Page 30 of 32

Permit No. SC0046175

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 discharges 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 than 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).

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 special 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 Control

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 period beginning July 28, 2006 and ending on August 28, 2006 shall be 

considered in making the final decision and shall be answered as prescribed below. See Public Notice #06-187-R.

Per R.61-9.124.17, the Department is only required to issue a response to comments 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 the 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 public 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. 
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Permit No. SC0046175

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 Department 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 the 

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.

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 discretion 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 general 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 received 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 limits 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 comment 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 

inappropriate, 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 that 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 incorporated 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 

materials. 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 section. 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).
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Permit No. SC0046175

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 procedures 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; or

(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 issued 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 48-1-200 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 days after notice of the decision has been mailed to the applicant or respondent, unless 

a written request for final review is filed with the Department. 

An applicant, permittee, licensee, or affected person who wishes to appeal this decision must file a written request 

for final review with the Clerk of the Board at the following address or by facsimile at 803-898-3323:

Clerk of the Board

SC DHEC

2600 Bull Street

Columbia, SC 29201

The request for final review should include the following:

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

2. A statement of any significant issues or factors the Board should consider in deciding how to handle the matter, 

and 

3. A copy of the Department’s decision or action under review.

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. If a timely request for final review is filed with the Clerk of the Board, the Clerk will provide 

additional information regarding procedures. 

The Board of Health and Environmental Control has 60 days from the date of receipt of a request for final review 

to conduct a final review conference. The conference may be conducted by the Board, its designee, or a committee 

of three members of the Board appointed by the chair. 

If a final review conference is not conducted within 60 days, the Department decision becomes the final agency 

decision, and a party may request a contested case hearing before the Administrative Law Court within 30 days 

after the deadline for the 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 Carolina or by calling 803-898-3350.