FACT SHEET FOR NPDES PERMIT WA-002277-2 

SOUTHWEST SUBURAN SEWER DISTRICT 

SALMON CREEK WASTEWATER TREATMENT PLANT 

Summary 

• The monitoring frequency for both BOD5 and TSS was increased from 1/week to 2/week to 

comply more closely with the guideline of 3/week as written in the Department’s Permit 

Writer’s Manual and to align with the facility’s actual sample frequency during the previous 

permit cycle. 

• Mixing Zone remained the same as in previous permit. 

• Mass discharge limitations for BOD5 and TSS remained the same from the previous permit. 

• The design criteria for the facility (reference Table 7) were corrected to match most recent 

Engineering Report approved by the Department of Ecology. Reference the 1985 Secondary 

Treatment Project Engineering Report by Pool Engineering, Incorporated. 

• Acute WET limit was removed from permit based on previous permit results. 

• Waste characterization, according to the NPDES application Part D requirements, is due in 

the fourth year of the permit cycle in order to provide information on compliance with human 

health criteria for the future permit. Refer to Appendix D for a complete list of these testing 

requirements. 

• The Department requires that the Operations and Maintenance Manual be reviewed and 

updated within two (2) years of permit issuance. 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

DRAFT 

TABLE OF CONTENTS 

INTRODUCTION ...........................................................................................................................4 

BACKGROUND INFORMATION ................................................................................................6 

DESCRIPTION OF THE FACILITY .................................................................................6 

History......................................................................................................................6 

Collection System Status .........................................................................................7 

Treatment Processes.................................................................................................8 

Discharge Outfall.....................................................................................................9 

Residual Solids.........................................................................................................9 

PERMIT STATUS.............................................................................................................11 

SUMMARY OF COMPLIANCE WITH THE PREVIOUS PERMIT .............................11 

WASTEWATER CHARACTERIZATION ......................................................................12 

DMR 5-Year Summary..........................................................................................12 

Priority Pollutants ..................................................................................................15 

Whole Effluent Toxicity Testing ...........................................................................15 

PROPOSED PERMIT LIMITATIONS.........................................................................................17 

DESIGN CRITERIA .........................................................................................................17 

TECHNOLOGY-BASED EFFLUENT LIMITATIONS..................................................18 

SURFACE WATER QUALITY-BASED EFFLUENT LIMITATIONS .........................19 

Numerical Criteria for the Protection of Aquatic Life...........................................19 

Numerical Criteria for the Protection of Human Health........................................19 

Narrative Criteria ...................................................................................................19 

Antidegradation......................................................................................................20 

Critical Conditions.................................................................................................20 

Mixing Zones.........................................................................................................20 

Description of the Receiving Water.......................................................................20 

Surface Water Quality Criteria ..............................................................................21 

Consideration of Surface Water Quality-based Limits for Numeric Criteria........21 

Whole Effluent Toxicity ........................................................................................23 

Human Health ........................................................................................................24 

Sediment Quality ...................................................................................................25 

GROUND WATER QUALITY LIMITATIONS..............................................................25 

COMPARISON OF EFFLUENT LIMITS WITH THE EXISTING PERMIT 

ISSUED JUNE 23, 1997........................................................................................25 

MONITORING REQUIREMENTS..............................................................................................26 

LAB ACCREDITATION ..................................................................................................26 

OTHER PERMIT CONDITIONS .................................................................................................27 

REPORTING AND RECORDKEEPING .........................................................................27 

PREVENTION OF FACILITY OVERLOADING...........................................................27 

OPERATIONS AND MAINTENANCE (O&M) .............................................................27 

RESIDUAL SOLIDS HANDLING...................................................................................27 

PRETREATMENT............................................................................................................27 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

DRAFT 

Federal and State Pretreatment Program Requirements ....................................................27 

Wastewater Permit Required .............................................................................................28 

Requirements for Routine Identification and Reporting of Industrial Users.....................28 

Annual Submittal of List of Industrial Users.....................................................................29 

Duty to Enforce Discharge Prohibitions............................................................................29 

Support by the Department for Developing Partial Pretreatment Program by 

POTW ....................................................................................................................29 

GENERAL CONDITIONS ...............................................................................................29 

PERMIT ISSUANCE PROCEDURES .........................................................................................30 

PERMIT MODIFICATIONS ............................................................................................30 

RECOMMENDATION FOR PERMIT ISSUANCE ........................................................30 

REFERENCES FOR TEXT AND APPENDICES........................................................................31 

APPENDIX A—PUBLIC INVOLVEMENT INFORMATION...................................................32 

APPENDIX B—GLOSSARY.......................................................................................................33 

APPENDIX C—TECHNICAL CALCULATIONS......................................................................38 

APPENDIX D—EPA NPDES APPLICATION (PART D) TESTING REQUIREMENTS ........39 

APPENDIX E—RESPONSE TO COMMENTS ..........................................................................40 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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INTRODUCTION 

The Federal Clean Water Act (FCWA, 1972, and later modifications, 1977, 1981, and 1987) 

established water quality goals for the navigable (surface) waters of the United States. One of the 

mechanisms for achieving the goals of the Clean Water Act is the National Pollutant Discharge 

Elimination System of permits (NPDES permits), which is administered by the Environmental 

Protection Agency (EPA). The EPA has delegated responsibility to administer the NPDES permit 

program to the State of Washington on the basis of chapter 90.48 RCW which defines the Department 

of Ecology's authority and obligations in administering the wastewater discharge permit program. 

The regulations adopted by the State include procedures for issuing permits (chapter 173-220 WAC), 

technical criteria for discharges from municipal wastewater treatment facilities (chapter 173-221 

WAC), water quality criteria for surface and ground waters (chapters 173-201A and 200 WAC), and 

sediment management standards (chapter 173-204 WAC). These regulations require that a permit be 

issued before discharge of wastewater to waters of the state is allowed. The regulations also 

establish the basis for effluent limitations and other requirements which are to be included in the 

permit. One of the requirements (WAC 173-220-060) for issuing a permit under the NPDES permit 

program is the preparation of a draft permit and an accompanying fact sheet. Public notice of the 

availability of the draft permit is required at least thirty (30) days before the permit is issued (WAC 

173-220-050). The fact sheet and draft permit are available for review (see Appendix A—Public 

Involvement of the fact sheet for more detail on the public notice procedures). 

The fact sheet and draft permit have been reviewed by the Permittee. Errors and omissions 

identified in this review have been corrected before going to public notice. After the public 

comment period has closed, the Department will summarize the substantive comments and the 

response to each comment. The summary and response to comments will become part of the file on 

the permit and parties submitting comments will receive a copy of the Department's response. The 

fact sheet will not be revised. Comments and the resultant changes to the permit will be summarized 

in Appendix D—Response to Comments. 

GENERAL INFORMATION 

Applicant Information: Southwest Suburban Sewer District 

431 Ambaum Boulevard SW 

Burien, WA 98166 

Contact Person: William T. Skahan, General Manager 

(206) 244-9575 

Facility Name and Address: Salmon Creek Wastewater Treatment Plant 

12550 Shorewood Drive SW 

Burien, WA 98146 

Facility Contact: Tim Berge, Senior Operator 

(206) 243-7770 

Type of Treatment: Secondary Biological Treatment – Rotating Biological Contactors

Discharge Location: Puget Sound – East Passage 

Latitude: 47o 29' 14" N 

Longitude: 122o 22' 04" W 

Water Body ID Number: WA-PS-0270 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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Figure 1: Vicinity map showing location of Salmon Creek WWTP 

in Burien, WA 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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Figure 2: Facility Layout - Salmon Creek WWTP and 

Effluent Discharge Pipe to Puget Sound 

BACKGROUND INFORMATION 

DESCRIPTION OF THE FACILITY 

Salmon Creek Wastewater Treatment Plant (WWTP) provides secondary treatment to 

wastewater using rotating biological contactors (RBC). The treatment process purifies 

wastewater to meet water quality regulations before discharging into Puget Sound. 

HISTORY

Salmon Creek WWTP is operated by Southwest Suburban Sewer District (SWSSD) which was 

established in 1945 to serve the region of southwest King County. The original plant was built in 

1955. The secondary treatment system using RBC technology was installed in 1989, and odor 

control and scrubbing system became operational in 1991. Additional upgrades occurred in 1998 

with the addition of an Anoxic Gas Floatation (AGF) tank and Pasteurization Tank to the sludge 

handling system. The AGF and Pasteurization Tanks were taken out of service in late 2002 and 

there are no plans to resume operation at this time. In 2002, the headworks were improved with 

the addition of 1⁄4-inch fine step screens. Screenings were removed and disposed of in a landfill. 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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It currently serves a population of 27,126 in the communities of White Center, Shorewood, 

Fauntleroy, Arbor Heights, Delridge, Highland Park, Seahurst, and Burien.1

 The service area is 

mostly residential with little industrial or commercial activity. The facility lists no industrial 

discharges to the sewer system at this time. Salmon Creek WWTP is an EPA designated major 

facility. 

COLLECTION SYSTEM STATUS

The Salmon Creek drainage basin is approximately 3350 acres. The collector/interceptor system 

includes 129 miles of piping ranging from 4 inches to 36 inches in diameter.2

 Portions of the 

collection system date to the 1940’s. SWSSD has 11 pump stations of which 5 pump to Salmon 

Creek WWTP. Pump capacity has been deemed sufficient and adequately designed as outlined 

in the Comprehensive Sewer Plan 1999 (“CSP”).3

The CSP details flow projections in SWSSD over the next nearly twenty years based on expected 

demographic changes in the district. CSP projects Salmon Creek WWTP to see a flow (mean 

annual, MGD) increase of approximately 14.6% from basis year 1996 to year 2020.4

 Plant 

improvements in 2002 and other continuous improvement projects will accommodate the 

anticipated flows. 

The CSP used flow data from 1991 to 1996 to evaluate inflow and infiltration (I/I) attributed to 

direct storm runoff. I/I flow for Salmon Creek basin is 48% which equates to 1.72 gallons per 

day per foot of sewer line.5

 The District has applied for and received Public Works Trust Fund 

(PWTF) approval for a major rehabilitation program for the Salmon Creek basin. A list of 

collection system rehabilitation projects has been identified in the CSP to address I/I. Salmon 

Creek WWTP does not have a combined sewer overflow (CSO). 

 

1

 NPDES Permit Application. 

2

 Horton, Dennis and Associates, Kirkland, WA, Southwest Suburban Sewer District, 1999 Comprehensive Sewer 

Plan, February 1999, p. 48. 3

 Horton, CSP, p. 68. 4

 Horton, CSP, p. 50. 5

 Horton, CSP, p. 42. 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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TREATMENT PROCESSES

Figure 3. Process Flow Diagram – Salmon Creek WWTP6

Refer to Figure 3. The plant wastewater influent enters the facility via a main truck line and 

several inverted siphon lines. The headworks include 1⁄4-inch fine step screens and grit collectors 

to remove debris from the wastewater. The debris is washed and compacted in preparation for 

disposal at a landfill. The wastewater flows from the headworks to the primary clarifiers. The 

facility operates two or all three clarifiers depending on total flow of wastewater requiring 

treatment. Secondary treatment is done using rotating biological contactor (RBC) technology. 

There are three RBC trains; each train has seven shafts for a total of twenty-one air-driven 

rotating shafts. The wastewater flows from the RBCs to the secondary clarifiers. As with the 

primary clarifiers, the facility is able to operate with one secondary clarifier on line during low 

 

6

 NPDES Permit Application 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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flow conditions. Disinfection is the final treatment step for the wastewater overflowing from the 

secondary clarifiers. Sodium Hypochlorite is injected into the wastewater just upstream of the 

contact tanks. The contact tanks allow sufficient residence time for disinfection of the plant 

effluent prior to discharge into Puget Sound. 

Sludge handling is discussed under the section titled “Residual Solids.” 

The Permittee lists no industrial users in the permit application and has not received any 

industrial wastewater during the previous permit. It does not foresee receiving any industrial 

wastewater during this permit cycle. 

Salmon Creek WWTP is designated as a Class 3 WWTP under State operator certification 

regulations, WAC 173-230. The permit requires that the sewage treatment plant operator in 

charge of operations be Class 3 certified. The plant is staffed by four operators in a 10-hour 

daily shift. The plant is staffed seven days per week. 

Emergency operating procedures are adequately outlined in the Operations and Maintenance 

Manual, and all operators are appropriately trained in those procedures. 

Improvement plans for 2002 and 2003 are funded by a loan from the Public Works Trust Fund. 

The plans for 2002 include improvements to screening of and grit removal from the wastewater. 

DISCHARGE OUTFALL

The treated and disinfected secondary effluent is discharged from the facility via the effluent 

pipe into Puget Sound. The existing outfall pipe was installed in 1969. It consists of 1200 lineal 

feet (lf) of 36-inch diameter concrete pipe underwater and 1580 lf of 36-inch concrete pipe to the 

facility for a total of 2780 lf of pipe. The outfall has a 100 lf multiple port diffuser assembly 

which has twelve discharge ports, the deepest discharging at -200 feet mean lower low water 

(MLLW).7 The CSP indicates that the dilution rate is adequate for current and future conditions 

based on the existing water quality standards. According to the CSP, the facility plans to 

continue to periodically monitor the condition of the outfall pipe for signs of deterioration. The 

last video inspection of the outfall was done in July 1995. 

RESIDUAL SOLIDS

Refer to Figure 3. The treatment facility removes solids during the treatment of the wastewater 

at the headworks (grit and screenings), and at the primary and secondary clarifiers, in addition to 

incidental solids (rags, scum, and other debris) removed as part of the routine maintenance of the 

equipment. Grit, rags, scum, and screenings are drained and disposed of as solid waste at the 

local landfill. 

 

7

 Gary R. Bourne, P.E., Poole Engineering, Inc., Secondary Treatment Project Engineering Report, August 1985, p. 7-7. 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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Solids removed from the primary and secondary clarifiers are treated first by pumping to a 

gravity thickener to increase the percent of solids and thereby improve filterability of the solids. 

The sludge is pumped to a primary anaerobic mesophilic digester. The digested sludge is 

dewatered using a Parkson® belt filter press. All the filtrate and other liquid waste streams from 

the facility are returned to the headworks for treatment. 

The solids collected from the belt filter are trucked batchwise to the District’s Miller Creek 

WWTP. The majority of the filter solids (Class B biosolids) are land applied under permit 

number BA-002277-2. In addition, a portion of the dewatered biosolids are mixed with tree 

chippings and composted in aerated static piles for Class A biosolids which are screened and 

sold to the public.8

The monitoring results for pollutant metals in sludge as required by 40 CFR 503 are shown in 

Table 1. The sludge generated at the facility meets the exceptional quality standards set forth by 

federal regulations. 

Table 1. Biosolids Pollutant Concentrations (mg/kg) 

 Pollutant Analytical 

Method 

DL 

11-Jan-00 

11-Apr-00 

11-Jul-00 

17-Oct-00 

24-Jan-01 

26-Jul-01 

18-Oct-01 

Ave. Standard 

Arsenic SW-846 

7060A 

0.1 6.1 3.8 4 5.8 0.3 1.6 2 3.4 41 

Cadmium SW-846 

6010 

0.05 1.8 2.9 6.9 1.6 3.9 2.7 3.4 3.3 39 

Chromium SW-846 

6010 

0.1 18 14 28 19 18 20 24 20 

Copper SW-846 

6010 

0.1 430 430 560 420 380 410 360 427 1500 

Lead SW-846 

6010 

1 81 74 81 55 72 54 71 70 300 

Mercury SW-84 

7471A 

0.01 0.5 0.76 2 1.4 1.2 1.3 1.4 1.2 17 

Molybdenum SW-846 

6010 

0.5 4.6 6.1 9.8 7.1 3.8 5.3 5.7 6.1 18 

Nickel SW-846 

6010 

0.5 20 15 30 13 18 19 16 19 420 

Selenium SW-846 

7740 

0.1 1.4 5.6 4.1 2 4.8 0.1 2.4 2.9 100 

Zinc SW-846 

6010 

0.1 1200 1000 1200 910 1000 1100 790 1029 2800 

TolsI Kjel. N EPA 351.3 5 62500 56500 40700 58100 61000 67000 52000 56829 

Ammonia SM 

4500NH3 

5 16300 15300 12900 13800 16000 15000 13000 14614 

N02+N03 EPA 351.2 0.05 2.5 3.2 1 2.5 0.3 0.3 3.1 1.8 

 

8

 NPDES Form 2S Application Overview 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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PERMIT STATUS 

The previous permit for this facility was issued on June 23, 1997, and became effective on 

July 1, 1997. The previous permit placed effluent limitations on 5-day Biochemical Oxygen 

Demand (BOD5), Total Suspended Solids (TSS), pH, Fecal Coliform bacteria, and Total Residual 

Chlorine (TRC). 

An application for permit renewal was submitted to the Department on April 4, 2002, and 

accepted by the Department on April 29, 2002. An extension of the previous permit was granted 

as of June 23, 2002, and will remain in effect until the effective date of this permit. 

Table 2. Previous Permit Limits 

EFFLUENT LIMITATIONSa: OUTFALL # 001 

Parameter Average Monthly Average Weekly

Biochemical Oxygen Demandb (5-day) 30 mg/L, 2025 lb/day 45 mg/L, 3040 lb/day 

Total Suspended Solidsb 30 mg/L, 2025 lb/day 45 mg/L, 3040 lb/day 

Fecal Coliform Bacteria 200 cfu /100 mL 400 cfu /100 mL 

pH shall not be outside the range 6.0 to 9.0 

Total Residual Chlorine 0.5 mg/L, 33.8 lb/day 0.75 mg/L 

Acute Whole Effluent Toxicity No statistically significant difference in survival between 

the control (0% effluent) and the ACEC of 0.625%. 

a The average monthly and weekly effluent limitations are based on the arithmetic mean of the samples 

taken with the exception of fecal coliform, which is based on the geometric mean. 

b The average monthly effluent concentration for BOD5 and Total Suspended Solids shall not exceed 30 

mg/L or 15 percent of the respective monthly average influent concentrations, whichever is more 

stringent. 

SUMMARY OF COMPLIANCE WITH THE PREVIOUS PERMIT 

Salmon Creek WWTP received two (2) Class I inspections by the Department during the previous 

permit on the dates of June 26, 1998, and May 3, 2001. The last inspection showed the facility to 

be in good order. The inspector recommended that staffing should be reviewed to ensure that it is 

adequate based on EPA criteria.9

During the history of the previous permit, the Permittee has remained in good compliance, based 

on Discharge Monitoring Reports (DMRs) submitted to the Department and inspections 

conducted by the Department. All reported effluent and influent data were reviewed for the 

5-year period from July 1997 to July 2002. Two (2) violations occurred during the 5-year 

period. The first violation occurred in October 1997 when the pH was below 6.0. The second 

violation occurred in September 1998 when the BOD exceeded 30 mg/L. An additional 

compliance-related concern occurred in 1997 and 1998 when the facility exceeded 85% of the 

design criteria for BOD and TSS for three (3) consecutive months. This may indicate that the 

facility needs to investigate the need for expansion. The 1999 CSP addresses this concern. 

 

9

 Water Compliance Inspection Report, 5/3/02, Ed Abassi 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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Refer to Table 3: 5-Year Summary of Noncompliance. A complete 5-year summary of DMR 

data is listed in Appendix C. Table 2: Summary of DMR Effluent Data and Summary of DMR 

Influent Data. 

Table 3: Compliance History July 1997 to July 2002 

Date Parameter Limit Reported 

Value 

Comment 

Oct.-1997 Effluent pH 6.0 5.9 

Sept.-1998 Fecal Coliform, 

monthly average 

200 cfu/100 mL 241 Temperature related nitrification 

problems resulted in higher than 

normal chlorine demand. 

Disinfection pump delivered only 

1⁄2 of rated capacity. Venturi 

injection was installed to 

accommodate high chlorine 

demand situations.10

July-1997 

Aug.-1997 

Sept.-1997 

Influent Flow 

exceeded 85% of 

design BOD and 

TSS loading for 

three (3) consecutive 

months. 

7650 lb/day 

average for BOD 

and TSS 

12338 BOD,

13264 TSS

9985 BOD,

10425 TSS

10411 BOD, 

11423 TSS 

Due in part to influent sampling 

related problem which the facility 

is working to resolve. 

Aug.-1998 

Sept.-1998 

Oct.-1998 

Influent Flow 

exceeded 85% of 

design BOD loading 

for three (3) 

consecutive months. 

7650 lb/day 

average for BOD 

8256 BOD 

8567 BOD 

8237 BOD 

Due in part to influent sampling 

related problem which the facility 

is working to resolve. 

WASTEWATER CHARACTERIZATION 

DMR 5-YEAR SUMMARY

The concentration of pollutants in the discharge was reported in the NPDES application and in 

Discharge Monitoring Reports. The effluent is characterized as follows, as summarized from 

Discharge Monitoring Report Data (Appendix C): 

 

10 Discharge Monitor Report Salmon Creek, September 1998. 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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Table 4: Wastewater Characterization (5-year Summary) 

Pollutant/ 

Analysis 

Units Design 

Criteria 

Permit 

Limit or 

85% of 

Design* 

5-yr. 

Average 

Minimum Maximum 

BOD, 5 LB/DAY AVG 2025 255.6 98 744 

BOD, 5 LB/DAY AVW 3040 351.5 151.0 1303.0 

BOD, 5 MG/L AVG 30 11.3 5.9 21.3 

BOD, 5 MG/L AVW 45 14.1 7.1 24.6 

BOD, 5 % PERCENT AVG 85 96.3 87.0 99.0 

CL LB/DAY AVG 33.8 5.6 2.8 15.3 

CL MG/L AVG 0.5 0.3 0.15 0.43 

CL MG/L MAX 0.75 0.3 0 0 

COLI. FECAL #/100 ML GEM 200 28.0 4 241 

COLI. FECAL #/100 ML GM7 400 59.8 6.0 352.0 

FLOW, IN MGD AVG 8.1 6.89* 2.6 1.9 4.8 

FLOW, IN MGD MAX NA 3.9 2.11 9.70 

PH S.U. MAX 9 7.3 6.8 7.9 

PH S.U. MIN 6 6.6 5.9 7.0 

TSS % PERCENT AVG 85 96.6 91.0 99.0 

TSS LB/DAY AVG 2025 176.0 69 483 

TSS LB/DAY AVW 3040 229.2 80 691 

TSS MG/L AVG 30 7.7 4.2 13.4 

TSS MG/L AVW 45 9.2 4.7 17.9 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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Salmon Creek 5-year Organic Loading

0

2000

4000

6000

8000

10000

12000

14000

1-Jul-97

1-Oct-97

1-Jan-98

1-Apr-98

1-Jul-98

1-Oct-98

1-Jan-99

1-Apr-99

1-Jul-99

1-Oct-99

1-Jan-00

1-Apr-00

1-Jul-00

1-Oct-00

1-Jan-01

1-Apr-01

1-Jul-01

1-Oct-01

1-Jan-02

1-Apr-02

Day/Year

loading (lb/day)

BOD (lb/day) TSS (lb/day) Design TSS Loading (lb/day) Design BOD Loading (lb/day)

Permit BOD and TSS loading = 9,200 lb/day

Salmon Creek 5-year Hydraulic Loading

0

2

4

6

8

10

12

1-Jul-97

1-Oct-97

1-Jan-98

1-Apr-98

1-Jul-98

1-Oct-98

1-Jan-99

1-Apr-99

1-Jul-99

1-Oct-99

1-Jan-00

1-Apr-00

1-Jul-00

1-Oct-00

1-Jan-01

1-Apr-01

1-Jul-01

1-Oct-01

1-Jan-02

1-Apr-02

Date/Year

Flow (GMD)

Max. Monthly Ave. Daily Flow Ave. Daily Flow Average Flow Max. Month

Permit Design Criteria = 8.1 MGD

Figure 4: Salmon Creek Organic and Hydraulic Loading January 1997 to January 

2002 vs. Approved Design Criteria 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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Hydraulic loading has remained consistent over the term of the pervious permit. The organics 

and solids loading have remained within the design limits of this permit with the exception of a 

few explained excursions (reference Table 3). Both of the above graphs display the Permittees 

ability to operate the facility within the design criteria upon which this permit is based. 

PRIORITY POLLUTANTS

The Permittee characterized the effluent for priority pollutant metals during the last permit cycle. 

The data was analyzed to determine if there is a reasonable potential to violate state water quality 

standards for any of the pollutants listed in Table 5. Calculations for Reasonable Potential are 

shown in Appendix C, Table 5. Based on these calculations, none of the pollutants listed below 

have a reasonable potential to exceed water quality standards. 

Table 5: Priority Pollutants Analysis (all units in mg/l) 

Parameter Method DL 5/31/2001 8/29/2001 10/18/2001 1/29/2002 Average 

Antimony 200.7 0.01 0.01 0.02 0.01 0.01 <0.0125 

Arsenic 206.2 0.001 0.001 0.001 0.001 0.001 0.001

Beryllium 200.7 0.0005 0.0005 0.0005 0.0005 0.0005 <0.00005 

Cadmium 200.7 0.0005 0.0005 0.0005 0.0005 0.0005 <0.0005 

Chromium 200.7 0.001 0.001 0.001 0.001 0.002 <0.00125 

Copper 200.7 0.001 0.003 0.015 0.013 0.005 0.009

Lead 239.2 0.001 0.001 0.001 0.016 0.001 0.00475

Mercury 245.1 0.0002 0.0002 0.0002 0.0002 0.0002 <0.0002 

Nickel 200.7 0.005 0.005 0.005 0.005 0.005 <0.005 

Selenium 270.2 0.001 0.001 0.001 0.001 0.002 <0.00125 

Silver 200.7 0.01 0.01 0.01 0.01 0.01 <0.01 

Thallium 279.2 0.001 0.001 0.001 0.001 0.001 <0.001 

Zinc 200.7 0.001 0.037 0.05 0.054 0.035 0.044

italics – Indicates pollutant found in a detectable quantity in effluent. 

bold – Indicates maximum effluent concentration measured for pollutants found in a detectable quantity. 

WHOLE EFFLUENT TOXICITY TESTING

The Permittee performed two (2) chronic Whole Effluent Toxicity (WET) tests for the purpose 

of characterization of the effluent in August 2000 and March 2001 as required by the previous 

permit. They performed nine (9) acute WET tests at the rate of one test every six (6) months as 

required by the previous permit. The results of these tests are shown in Table 6. The WET tests 

results were reviewed by the Department’s WET Coordinator who concluded that no WET limits 

are required in this permit. The Permittee is required to perform WET testing for 

characterization purposes at the times specified in the permit Sections S8 and S9 of this permit. 
FACT SHEET FOR NPDES PERMIT WA-002277-2 

Salmon Creek Wastewater Treatment Plant 

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Table 6: Whole Effluent Toxicity (WET) Testing 

Date 

Report 

Submitted 

Type of 

Test 

Sample Dates 

 (24-hour composite 

samples) 

Summary of 

Results 

Oct. 15, 1997 Acute September 3, 1997 Daphnia pulex LC50 = >100% 

Mar. 15, 1998 Acute February 9, 1998 Fathead minnow LC50 = >100% 

Sep. 15, 1998 Acute August 25, 1998 Daphnia pulex LC50 = >100% 

Mar. 15, 1999 Acute February 9, 1999 Fathead minnow LC50 = >100% 

Sept. 15, 1999 Acute August 9, 1999 Daphnia pulex LC50 = >100% 

Mar. 15, 2000 Acute February 15, 2000 Fathead minnow LC50 = >100% 

Aug. 15, 2000 Chronic July 10, 12, and 14, 2000 Topsmelt: 

 Survival NOEC = 100% 

 LOEC = >100% 

 Growth NOEC = 100% 

 LOEC = >100% 

 Mysidopsis bahia: 

 Survival NOEC = 50% 

 LOEC = 100% 

 Growth NOEC = 25% 

 LOEC = 50% 

Aug. 15, 2000 Acute Jul 10, 2000 Daphnia pulex LC50 = >100% 

Mar. 15, 2001 Chronic Jan. 24, 26, and 29, 2001 Topsmelt: 

 Survival NOEC = 100% 

 LOEC = >100% 

 Growth NOEC = 100% 

 LOEC = >100% 

 Mysidopsis bahia: 

 Survival NOEC = 50% 

 LOEC = 100% 

 Growth NOEC = 25% 

 LOEC = 50% 

Mar. 15, 2001 Acute Jan. 24, 2001 Fathead minnow NOEC = 100% 

 LC50 = >100% 

Jan. 15, 2002 Acute December 12, 2001 Daphnia pulex: LC50 = >100% 
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PROPOSED PERMIT LIMITATIONS 

Federal and state regulations require that effluent limitations set forth in an NPDES permit must be 

either technology- or water quality-based. Technology-based limitations for municipal discharges 

are set by regulation (40 CFR 133, and chapters 173-220 and 173-221 WAC). Water quality-based 

limitations are based upon compliance with the surface water quality standards (chapter 173-201A 

WAC), ground water standards (chapter 173-200 WAC), sediment quality standards (chapter 173-

204 WAC), or the National Toxics Rule (Federal Register, Volume 57, No. 246, Tuesday, 

December 22, 1992.) The most stringent of these types of limits must be chosen for each of the 

parameters of concern. Each of these types of limits is described in more detail below. 

The limits in this permit are based in part on information received in the application. The effluent 

constituents in the application were evaluated on a technology- and water quality-basis. The limits 

necessary to meet the rules and regulations of the State of Washington were determined and 

included in this permit. Ecology does not develop effluent limits for all pollutants that may be 

reported on the application as present in the effluent. Some pollutants are not treatable at the 

concentrations reported, are not controllable at the source, are not listed in regulation, and do not 

have a reasonable potential to cause a water quality violation. Effluent limits are not always 

developed for pollutants that may be in the discharge but not reported as present in the application. 

In those circumstances the permit does not authorize discharge of the non-reported pollutants. 

Effluent discharge conditions may change from the conditions reported in the permit application. If 

significant changes occur in any constituent, as described in 40 CFR 122.42(a), the Permittee is 

required to notify the Department of Ecology. The Permittee may be in violation of the permit until 

the permit is modified to reflect additional discharge of pollutants. 

DESIGN CRITERIA 

In accordance with WAC 173-220-150 (1)(g), flows or waste loadings shall not exceed approved 

design criteria. The design criteria for this treatment facility are taken from the 1985 Secondary 

Treatment Project Engineering Report by Pool Engineering, Inc., and are as follows: 

Table 7: Design Standards for Salmon Creek WWTP11

Criteria Design Year 2010 Design Year 2040 85% of Design 

Sewered Population 26,000 33,000 

Flow (MGD) 

 annual average 4.0 5.1 

 dry weather average 3.3 4.1 

 wet weather average 4.7 6.0 

 maximum month 6.4 8.1 6.89 

 maximum day 16.0 20.4 

 peak hour 20.0 25.5 

Maximum flow to secondary 10.0 10.0 

Loadings (pounds/day) 

 BOD annual average 5,500 7,100 

 BOD maximum month 7,200 9,200 7,820 

 SS annual average 5,500 7,100 

 SS maximum month 7,200 9,200 7,820 

 

11 Borne, p. 3-9 
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The design criteria listed in the previous permit was incorrect. The above table was updated to 

show the correct design criteria. The plant was designed for an ultimate maximum month flow 

of 8.1 MGD. When the flow reaches 6.4 MGD around the year 2010, the only necessary change 

will be to restage the RBCs by removing the baffles between the 2nd and 3rd stages. As this is an 

operational change only, the design values in the permit will be the 2040 values. Construction of 

additional facilities will be necessary when those loadings are approached. 

TECHNOLOGY-BASED EFFLUENT LIMITATIONS 

Municipal wastewater treatment plants are a category of discharger for which technology-based 

effluent limits have been promulgated by federal and state regulations. These effluent limitations 

are given in the Code of Federal Regulations (CFR) 40 CFR Part 133 (federal) and in chapter 

173-221 WAC (state). These regulations are performance standards that constitute all known 

available and reasonable methods of prevention, control, and treatment for municipal 

wastewater. 

The following technology-based limits for pH, fecal coliform, BOD5, and TSS are taken from 

chapter 173-221 WAC: 

Table 8: Technology-based Limits 

Parameter Limit 

pH: shall be within the range of 6 to 9 standard units. 

Fecal Coliform Bacteria Monthly Geometric Mean = 200 organisms/100 mL 

Weekly Geometric Mean = 400 organisms/100 mL 

BOD5 

(concentration) 

Average Monthly Limit is the most stringent of the following: 

 - 30 mg/L 

 - may not exceed fifteen percent (15%) of the average influent concentration 

Average Weekly Limit = 45 mg/L 

TSS 

(concentration) 

Average Monthly Limit is the most stringent of the following: 

 - 30 mg/L 

 - may not exceed fifteen percent (15%) of the average influent concentration

Average Weekly Limit = 45 mg/L 

Chlorine Average Monthly Limit = 0.5 mg/L 

Average Weekly Limit = 0.75 mg/L 

The technology-based monthly average limitation for chlorine is derived from standard operating 

practices. The Water Pollution Control Federation's Chlorination of Wastewater (1976) states 

that a properly designed and maintained wastewater treatment plant can achieve adequate 

disinfection if a 0.5 mg/liter chlorine residual is maintained after fifteen minutes of contact time. 

See also Metcalf and Eddy, Wastewater Engineering, Treatment, Disposal and Reuse, Third 

Edition, 1991. A treatment plant that provides adequate chlorination contact time can meet the 

0.5 mg/liter chlorine limit on a monthly average basis. According to WAC 173-221-030(11)(b), 

the corresponding weekly average is 0.75 mg/liter. 

The following technology-based mass limits are based on WAC 173-220-130(3)(b) and 

173-221-030(11)(b). 
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For BOD5 and TSS: 

Monthly effluent mass loadings (lb/day) were calculated as the maximum monthly design flow 

(8.1 MGD) x Concentration limit (30 mg/L) x 8.34 (conversion factor) = mass limit 2027 lb/day 

(rounded to 2025 lb/day for the permit limit). 

The weekly average effluent mass loading is calculated as 1.5 x monthly loading = 3040 lb/day. 

Chlorine: 

Monthly effluent mass loadings (lb/day) were calculated as the maximum monthly design flow 

(8.1 MGD) x Concentration limit (0.5 mg/L) x 8.34 (conversion factor) = mass limit 33.8 lb/day. 

The weekly average effluent mass loading is omitted. Maximum mass chlorine limits conflict 

with requirements to provide disinfection during extremely high flow episodes. Such flow 

episodes have occurred at least once in each of the last two years. These rare events affect the 

weekly output more drastically than the monthly outputs. 

SURFACE WATER QUALITY-BASED EFFLUENT LIMITATIONS 

In order to protect existing water quality and preserve the designated beneficial uses of 

Washington's surface waters, WAC 173-201A-060 states that waste discharge permits shall be 

conditioned such that the discharge will meet established surface water quality standards. The 

Washington State surface water quality standards (chapter 173-201A WAC) is a state regulation 

designed to protect the beneficial uses of the surface waters of the state. Water quality-based 

effluent limitations may be based on an individual waste load allocation (WLA) or on a WLA 

developed during a basin-wide total maximum daily loading study (TMDL). 

NUMERICAL CRITERIA FOR THE PROTECTION OF AQUATIC LIFE

"Numerical" water quality criteria are numerical values set forth in the Washington State’s water 

quality standards for surface waters (chapter 173-201A WAC). They specify the levels of 

pollutants allowed in receiving water while remaining protective of aquatic life. Numerical 

criteria set forth in the water quality standards are used along with chemical and physical data for 

the wastewater and receiving water to derive the effluent limits in the discharge permit. When 

surface water quality-based limits are more stringent or potentially more stringent than 

technology-based limitations, they must be used in a permit. 

NUMERICAL CRITERIA FOR THE PROTECTION OF HUMAN HEALTH 

The state was issued 91 numeric water quality criteria for the protection of human health by the U.S. 

EPA (EPA, 1992). These criteria are designed to protect humans from cancer and other diseases and 

are primarily applicable to fish and shellfish consumption and drinking water from surface waters. 

NARRATIVE CRITERIA

In addition to numerical criteria, "narrative" water quality criteria (WAC 173-201A-030) limit 

toxic, radioactive, or deleterious material concentrations below those which have the potential to 

adversely affect characteristic water uses, cause acute or chronic toxicity to biota, impair aesthetic 

values, or adversely affect human health. Narrative criteria protect the specific beneficial uses of all 

fresh (WAC 173-201A-130) and marine (WAC 173-201A-140) waters in the state of Washington. 
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ANTIDEGRADATION 

The State of Washington's Antidegradation Policy requires that discharges into receiving water 

shall not further degrade the existing water quality of the water body. In cases where the natural 

conditions of receiving water are of lower quality than the criteria assigned, the natural 

conditions shall constitute the water quality criteria. Similarly, when the natural conditions of 

receiving water are of higher quality than the criteria assigned, the natural conditions shall 

constitute the water quality criteria. More information on the State Antidegradation Policy can 

be obtained by referring to WAC 173-201A-070. 

The Department has reviewed existing records and is unable to determine if ambient water 

quality is either higher or lower than the designated classification criteria given in chapter 

173-201A WAC; therefore, the Department will use the designated classification criteria for this 

water body in the proposed permit. The discharges authorized by this proposed permit should 

not cause a loss of beneficial uses. 

CRITICAL CONDITIONS

Surface water quality-based limits are derived for the water body's critical condition, which 

represents the receiving water and waste discharge condition with the highest potential for 

adverse impact on the aquatic biota, human health, and existing or characteristic water body 

uses. 

MIXING ZONES

The water quality standards allow the Department of Ecology to authorize mixing zones around a 

point of discharge in establishing surface water quality-based effluent limits. Both "acute" and 

"chronic" mixing zones may be authorized for pollutants that can have a toxic effect on the 

aquatic environment near the point of discharge. The concentration of pollutants at the boundary 

of these mixing zones may not exceed the numerical criteria for that type of zone. Mixing zones 

can only be authorized for discharges that are receiving all known, available, and reasonable 

methods of prevention, control and treatment (AKART) and in accordance with other mixing 

zone requirements of WAC 173-201A-100. 

The National Toxics Rule (EPA, 1992) allows the chronic mixing zone to be used to meet human 

health criteria. 

DESCRIPTION OF THE RECEIVING WATER

The facility discharges to Puget Sound which is designated as a Class AA receiving water in the 

vicinity of the outfall. Characteristic uses include the following: 

water supply (domestic, industrial, agricultural); stock watering; fish migration; fish and 

shellfish rearing, spawning and harvesting; wildlife habitat; primary contact recreation; 

sport fishing; boating and aesthetic enjoyment; commerce and navigation. 

Water quality of this class shall markedly and uniformly exceed the requirements for all or 

substantially all uses. 
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SURFACE WATER QUALITY CRITERIA

Applicable criteria are defined in chapter 173-201A WAC for aquatic biota. In addition, U.S. 

EPA has promulgated human health criteria for toxic pollutants (EPA, 1992). Criteria for this 

discharge are summarized below: 

Fecal Coliforms 14 organisms/100 mL maximum geometric mean 

Dissolved Oxygen 7 mg/L minimum 

Temperature 13 degrees Celsius maximum or incremental increases above background 

pH 7.0 to 8.5 standard units 

Turbidity Less than 5 NTUs above background 

Toxics No toxics in toxic amounts (see Appendix C for numeric criteria for toxics 

of concern for this discharge) 

CONSIDERATION OF SURFACE WATER QUALITY-BASED LIMITS FOR NUMERIC CRITERIA

Pollutant concentrations in the proposed discharge exceed water quality criteria with 

technology-based controls which the Department has determined to be AKART. A mixing zone 

is authorized in accordance with the geometric configuration, flow restriction, and other 

restrictions for mixing zones in chapter 173-201A WAC. The regulation requires that the mixing 

zone not extend in any horizontal direction from the discharge port for a distance greater than 

two hundred feet plus the depth of water over the discharge port. The depth of the outfall is 200 

feet at MLLW. The dimensions of the mixing zone are shown in the diagram below. 

Figure 5: Schematic diagram of the mixing zone. 

100 foot long, 12 port diffuser 
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The Department has estimated dilution factors of effluent to receiving water that occur within 

these zones at the critical conditions by the use of EPA PLUMES model, third edition, August 

1995. Inputs for the model are taken from ambient data collected by Ecology at monitoring 

station EAP001 (East Passage) and ambient current data supplied by the National Oceanic Data 

Center for a station within one mile of the outfall. The estimated dilution factors are as follows: 

Acute Chronic 

Aquatic Life 160 770 

Human Health, Carcinogen NA 1225 

Human Health, Non-carcinogen NA 1025 

Pollutants in an effluent may affect the aquatic environment near the point of discharge 

(near-field) or at a considerable distance from the point of discharge (far-field). Toxic pollutants, 

for example, are near-field pollutants—their adverse effects diminish rapidly with mixing in the 

receiving water. Conversely, a pollutant such as BOD is a far-field pollutant whose adverse 

effect occurs away from the discharge even after dilution has occurred. Thus, the method of 

calculating water quality-based effluent limits varies with the point at which the pollutant has its 

maximum effect. 

The derivation of water quality-based limits also takes into account the variability of the 

pollutant concentrations in both the effluent and the receiving water. 

BOD5--Under critical conditions there is no predicted violation of the water quality standards for 

surface waters. Therefore, the technology-based effluent limitation for BOD5 was placed in the 

permit. 

Temperature--The impact of the discharge on the temperature of the receiving water was 

modeled by simple mixing analysis at critical condition. The receiving water varies from 8o C to 

12.5o C and the effluent temperature 10o C to 20o C. The discharge of 20o C effluent into the 

marine water at 8o C results in a temperature change of less than 0.1o C. Under critical conditions 

there is no predicted violation of the water quality standards for surface waters. Therefore, no 

effluent limitation for temperature was placed in the proposed permit. 

pH--Because of the high buffering capacity of marine water, compliance with the 

technology-based limits of 6 to 9 will assure compliance with the water quality standard of 7 to 

8.5 in the receiving water. 

Fecal Coliform--The numbers of fecal coliform were modeled by simple mixing analysis using 

the technology-based limit of 400 organisms per 100 ml and a dilution factor of 770. The 

dilution reduces the bacteria to less than 1 (400/770). Under critical conditions there is no 

predicted violation of the water quality standards for surface waters with the technology-based 

limit. Therefore, the technology-based effluent limitation for fecal coliform bacteria was placed 

in the proposed permit. 
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Toxic Pollutants--Federal regulations (40 CFR 122.44) require NPDES permits to contain 

effluent limits for toxic chemicals in an effluent whenever there is a reasonable potential for 

those chemicals to exceed the surface water quality criteria. This process occurs concurrently 

with the derivation of technology-based effluent limits. Facilities with technology-based effluent 

limits defined in regulation are not exempted from meeting the water quality standards for 

surface waters or from having surface water quality-based effluent limits. 

The following toxics were determined to be present in the discharge: chlorine, ammonia, and 

heavy metals, arsenic, copper, lead, and zinc. A reasonable potential analysis (see Appendix C, 

Table 5) was conducted on these parameters to determine whether or not effluent limitations would 

be required in this permit. 

The determination of the reasonable potential for the pollutants listed in the previous paragraph 

to exceed the water quality criteria was evaluated with procedures given in EPA, 1991 

(Appendix C) using the acute and chronic dilution factors calculated for aquatic life. 

No valid ambient background data was available for above-listed pollutants. A determination of 

reasonable potential using zero for background resulted in no reasonable potential. 

Water quality criteria for metals in chapter 173-201A WAC are based on the dissolved fraction 

of the metal. 

The Permittee may provide data clearly demonstrating the seasonal partitioning of the dissolved 

metal in the ambient water in relation to an effluent discharge. Metals criteria may be adjusted 

on a site-specific basis when data is available clearly demonstrating the seasonal partitioning in 

the ambient water in relation to an effluent discharge. 

Metals criteria may also be adjusted using the water effects ratio approach established by 

USEPA, as generally guided by the procedures in USEPA Water Quality Standards Handbook, 

December 1983, as supplemented or replaced. 

WHOLE EFFLUENT TOXICITY

The water quality standards for surface waters require that the effluent not cause toxic effects in 

the receiving waters. Many toxic pollutants cannot be detected by commonly available detection 

methods. However, toxicity can be measured directly by exposing living organisms to the 

wastewater in laboratory tests and measuring the response of the organisms. Toxicity tests 

measure the aggregate toxicity of the whole effluent, and therefore this approach is called whole 

effluent toxicity (WET) testing. Some WET tests measure acute toxicity and other WET tests 

measure chronic toxicity. 

Acute toxicity tests measure mortality as the significant response to the toxicity of the effluent. 

Dischargers who monitor their wastewater with acute toxicity tests are providing an indication of 

the potential lethal effect of the effluent to organisms in the receiving environment. 

Chronic toxicity tests measure various sublethal toxic responses such as retarded growth or 

reduced reproduction. Chronic toxicity tests often involve either a complete life cycle test of an 

organism with an extremely short life cycle or a partial life cycle test on a critical stage of one of 

a test organism's life cycles. Organism survival is also measured in some chronic toxicity tests. 
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Accredited WET testing laboratories have the proper WET testing protocols, data requirements, 

and reporting format. Accredited laboratories are knowledgeable about WET testing and capable 

of calculating an NOEC, LC50, EC50, IC25, etc. All accredited labs have been provided the most 

recent version of the Department of Ecology Publication # WQ-R-95-80, Laboratory Guidance 

and Whole Effluent Toxicity Test Review Criteria which is referenced in the permit. Any 

Permittee interested in receiving a copy of this publication may call the Ecology Publications 

Distribution Center (360-407-7472) for a copy. Ecology recommends that Permittees send a 

copy of the acute or chronic toxicity sections(s) of their permits to their laboratory of choice. 

The WET tests during effluent characterization indicate that no reasonable potential exists to 

cause receiving water acute toxicity, and the Permittee will not be given an acute WET limit 

and will only be required to retest the effluent prior to application for permit renewal in order to 

demonstrate that acute toxicity has not increased in the effluent. 

The WET tests during effluent characterization indicate that no reasonable potential exists to 

cause receiving water chronic toxicity, and the Permittee will not be given a chronic WET 

limit and will only be required to retest the effluent prior to application for permit renewal in 

order to demonstrate that chronic toxicity has not increased in the effluent. 

If the Permittee makes process or material changes which, in the Department's opinion, results in 

an increased potential for effluent toxicity, then the Department may require additional effluent 

characterization in a regulatory order, by permit modification, or in the permit renewal. Toxicity 

is assumed to have increased if WET testing conducted for submission with a permit application 

fails to meet the performance standards in WAC 173-205-020, "whole effluent toxicity 

performance standard." The Permittee may demonstrate to the Department that changes have not 

increased effluent toxicity by performing additional WET testing after the time the process or 

material changes have been made. 

HUMAN HEALTH

Washington’s water quality standards now include 91 numeric health-based criteria that must be 

considered in NPDES permits. These criteria were promulgated for the state by the U.S. EPA in 

its National Toxics Rule (Federal Register, Volume 57, No. 246, Tuesday, December 22, 1992). 

The Department has determined that the effluent is likely to have chemicals of concern for 

human health. The discharger's high priority status is based on: (1) the discharger’s status as a 

major discharger, and (2) knowledge of data or process information indicating regulated 

chemicals occur in the discharge. 

A determination of the discharge's potential to cause an exceedance of the water quality 

standards was conducted as required by 40 CFR 122.44(d). The reasonable potential 

determination was evaluated with procedures given in the Technical Support Document for 

Water Quality-Based Toxics Control (EPA/505/2-90-001) and the Department's Permit Writer's 

Manual (Ecology Publication 92-109, July 2002). The determination indicated that the discharge 

has no reasonable potential to cause a violation of water quality standards, thus an effluent limit 

is not warranted. 
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SEDIMENT QUALITY

The Department has promulgated aquatic sediment standards (chapter 173-204 WAC) to protect 

aquatic biota and human health. These standards state that the Department may require 

Permittees to evaluate the potential for the discharge to cause a violation of applicable standards 

(WAC 173-204-400). 

The Department has determined through a review of the discharger characteristics and effluent 

characteristics that this discharge has a reasonable potential to violate the sediment management 

standards for Arsenic, Copper, Lead and Zinc, Appendix C, Table 7: Potential for Sediment 

Contamination. However, the Permittee conducted a Sediment Baseline Analysis (February 1997) 

which showed no pattern of sediment contamination. No additional sediment analysis is required 

by this permit. 

GROUND WATER QUALITY LIMITATIONS 

The Department has promulgated ground water quality standards (chapter 173-200 WAC) to 

protect uses of ground water. Permits issued by the Department shall be conditioned in such a 

manner so as not to allow violations of those standards (WAC 173-200-100). 

This Permittee has no discharge to ground and therefore no limitations are required based on 

potential effects to ground water. 

COMPARISON OF EFFLUENT LIMITS WITH THE EXISTING PERMIT ISSUED JUNE 23, 1997 

Parameter Existing Limits Proposed Limits 

BOD5 monthly average

30 mg/L, 2025 lb/day 

weekly maximum

45 mg/L, 3040 lb/day 

monthly average

30 mg/L, 2025 lb/day 

weekly maximum

45 mg/L, 3040 lb/day 

TSS monthly average

30 mg/L, 2025 lb/day 

weekly maximum

45 mg/L, 3040 lb/day 

monthly average

30 mg/L, 2025 lb/day 

weekly maximum

45 mg/L, 3040 lb/day 

pH Shall be within the range 

of 6 to 9 standard units 

Shall be within the range 

of 6 to 9 standard units 

Fecal Coliform Bacteria monthly average

200/100 mL 

weekly maximum

400/100 mL 

monthly average

200/100 mL 

weekly maximum

400/100 mL 

Total Residual Chlorine 0.5 mg/L monthly average 

0.75 mg/L daily maximum 

0.5 mg/L monthly average 

0.75 mg/L daily maximum 

Acute WET Testing No statistically significant 

difference in survival between 

the control (0% effluent) and 

ACEC (0.625% effluent) 

None 
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MONITORING REQUIREMENTS 

Monitoring, recording, and reporting are required (WAC 173-220-210 and 40 CFR 122.41) to 

verify that the treatment process is functioning correctly and the effluent limitations are being 

achieved. 

Monitoring of sludge quantity and quality is necessary to determine the appropriate uses of the 

sludge. Sludge monitoring is required by the current state and local solid waste management 

program and also by EPA under 40 CFR 503. 

The monitoring schedule is detailed in the proposed permit under Condition S.2. Specified 

monitoring frequencies take into account the quantity and variability of discharge, the treatment 

method, past compliance, significance of pollutants, and cost of monitoring. The required 

monitoring frequency is consistent with agency guidance given in the current version of 

Ecology’s Permit Writer's Manual (July 2002) for a rotating biological contactor (RBC) facility 

of greater than 2 MGD design with a partial reduction for exemplary performance. 

The reduced frequency is determined by the ratio of the long term average (LTA) to the average 

monthly limit (AML). The results of the analysis as shown are based on the DMR data 

submitted for the 2-year period from June 2000 to July 2002 for both BOD and TSS. 

Pollutant LTA 

(mg/L) 

AML 

(mg/L) 

Ratio 

(LTA/AML) 

Allowable Minimum Monitoring 

Frequency for Ratio12

 25%-49% <25%

BOD5 10.4 30 35% 1/week 1/week 

TSS 6.0 30 23% 1/week 1/week 

The monitoring requirement for both BOD5 and TSS is set at 2/week. This determination was 

made based on: (1) that it is more comparable to the requirement for other facilities of similar 

design and flow and (2) that it aligns with the sample frequency of the Permittee over the last 

year of the previous permit cycle. 

LAB ACCREDITATION 

With the exception of certain parameters, the permit requires all monitoring data to be prepared 

by a laboratory registered or accredited under the provisions of chapter 173-50 WAC, 

Accreditation of Environmental Laboratories. The laboratory at this facility is accredited for: 

Biological Oxygen Demand, Total Suspended Solids, Fecal Coliform, Dissolved Oxygen and pH. 

 

12 Ecology Permit Writer’s Manual, p. XIII-15. 
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OTHER PERMIT CONDITIONS 

REPORTING AND RECORDKEEPING 

The conditions of S3 are based on the authority to specify any appropriate reporting and 

recordkeeping requirements to prevent and control waste discharges (WAC 173-220-210). 

PREVENTION OF FACILITY OVERLOADING 

Overloading of the treatment plant is a violation of the terms and conditions of the permit. To 

prevent this from occurring, RCW 90.48.110 and WAC 173-220-150 require the Permittee to 

take the actions detailed in proposed permit requirement S.4 to plan expansions or modifications 

before existing capacity is reached and to report and correct conditions that could result in new 

or increased discharges of pollutants. Condition S.4 restricts the amount of flow. 

OPERATIONS AND MAINTENANCE (O&M) 

The proposed permit contains Condition S.5 as authorized under RCW 90.48.110, WAC 

173-220-150, chapter 173-230 WAC, and WAC 173-240-080. It is included to ensure proper 

operation and regular maintenance of equipment, and to ensure that adequate safeguards are 

taken so that constructed facilities are used to their optimum potential in terms of pollutant 

capture and treatment. The Department requires the Permittee to update the Operations and 

Maintenance Manual (current version 1988) to ensure that it provides accurate and up-to-date 

information. 

RESIDUAL SOLIDS HANDLING 

To prevent water quality problems, the Permittee is required in permit Condition S7 to store and 

handle all residual solids (grit, screenings, scum, sludge, and other solid waste) in accordance 

with the requirements of RCW 90.48.080 and state water quality standards. 

The final use and disposal of sewage sludge from this facility is regulated by U.S. EPA under 40 

CFR 503. The disposal of other solid waste is under the jurisdiction of the King County Health 

Department. 

PRETREATMENT 

Federal and State Pretreatment Program Requirements 

Under the terms of the addendum to the “Memorandum of Understanding between Washington 

Department of Ecology and the United States Environmental Protection Agency, Region 10” 

(1986), the Department of Ecology (Department) has been delegated authority to administer the 

Pretreatment Program [i.e., act as the Approval Authority for oversight of delegated Publicly 

Owned Treatment Works (POTWs)]. Under this delegation of authority, the Department has 

exercised the option of issuing wastewater discharge permits for significant industrial users 

discharging to POTWs which have not been delegated authority to issue wastewater discharge 

permits. 
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There are a number of functions required by the Pretreatment Program which the Department is 

delegating to such POTWs because they are in a better position to implement the requirements (e.g., 

tracking the number and general nature of industrial dischargers to the sewerage system). The 

requirements for a Pretreatment Program are contained in Title 40, Part 403 of the Code of Federal 

Regulations. Under the requirements of the Pretreatment Program [40 CFR 403.8(f)(1)(iii)], the 

Department is required to approve, condition, or deny new discharges or a significant increase in 

the discharge for existing significant industrial users (SIUs) [40 CFR 403.8 (f)(1)(i)]. 

The Department is responsible for issuing state waste discharge permits to SIUs and other 

industrial users of the Permittee's sewer system. Industrial dischargers must obtain these permits 

from the Department prior to the Permittee accepting the discharge [WAC 173-216-110(5)] 

(Industries discharging wastewater that is similar in character to domestic wastewater are not 

required to obtain a permit. Such dischargers should contact the Department to determine if a 

permit is required.). Industrial dischargers need to apply for a state waste discharge permit sixty 

(60) days prior to commencing discharge. The conditions contained in the permits will include 

any applicable conditions for categorical discharges, loading limitations included in contracts 

with the POTW, and other conditions necessary to assure compliance with state water quality 

standards and biosolids standards. 

The Department requires this POTW to fulfill some of the functions required for the 

Pretreatment Program in the NPDES permit (e.g., tracking the number and general nature of 

industrial dischargers to the sewage system). The POTW's NPDES permit will require that all 

SIUs currently discharging to the POTW be identified and notified of the requirement to apply 

for a wastewater discharge permit from the Department. None of the obligations imposed on the 

POTW relieve an industrial or commercial discharger of its primary responsibility for obtaining 

a wastewater discharge permit (if required), including submittal of engineering reports prior to 

construction or modification of facilities [40 CFR 403.12(j) and WAC 173-216-070 and WAC 

173-240-110, et seq.]. 

Wastewater Permit Required 

RCW 90.48 and WAC 173-216-040 require SIUs to obtain a permit prior to discharge of industrial 

waste to the Permittee's sewerage system. This provision prohibits the POTW from accepting 

industrial wastewater from any such dischargers without authorization from the Department.

Requirements for Routine Identification and Reporting of Industrial Users 

The NPDES permit requires nondelegated POTWs to "take continuous, routine measures to 

identify all existing, new, and proposed SIUs and potential significant industrial users (PSIUs) 

discharging to the Permittee's sewerage system." Examples of such routine measures include 

regular review of business tax licenses for existing businesses and review of water billing records 

and existing connection authorization records. System maintenance personnel can also be 

diligent during performance of their jobs in identifying and reporting as-yet unidentified 

industrial dischargers. Local newspapers, telephone directories, and word-of-mouth can also be 

important sources of information regarding new or existing discharges. The POTW is required 

to notify an industrial discharger, in writing, of their responsibilities regarding application for a 

state waste discharge permit and to send a copy of the written notification to the Department. 

The Department will then take steps to solicit a state waste discharge permit application. 
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Annual Submittal of List of Industrial Users 

This provision requires the POTW to submit annually a list of existing and proposed SIUs and 

PSIUs. This requirement is intended to update the Department as needed on the status of 

industrial users in the POTW's service area, without requiring the POTW to go through the 

process of performing a formal Industrial User Survey. This provision is normally applied to 

POTWs not serving industrial or commercial users. Although this permit does not require 

performance of an Industrial User Survey, the Permittee is nevertheless required under the 

previous section, to take adequate continuous routine measures to identify existing and new 

industrial discharges.

Duty to Enforce Discharge Prohibitions 

This provision prohibits the POTW from authorizing or permitting an industrial discharger to 

discharge certain types of waste into the sanitary sewer. The first portion of the provision 

prohibits acceptance of pollutants which cause pass through or interference. The definitions of 

pass through and interference are in Appendix B of the Fact Sheet. 

The second portion of this provision prohibits the POTW from accepting certain specific types of 

wastes, namely those which are explosive, flammable, excessively acidic, basic, otherwise 

corrosive, or obstructive to the system. In addition, wastes with excessive BOD, 

petroleum-based oils, or wastes which result in toxic gases are prohibited to be discharged. The 

regulatory basis for these prohibitions is 40 CFR Part 403, with the exception of the pH 

provisions which are based on WAC 173-216-060. 

The third portion of this provision prohibits certain types of discharges unless the POTW 

receives prior authorization from the Department. The discharges include cooling water in 

significant volumes, stormwater and other direct inflow sources, and wastewaters significantly 

affecting system hydraulic loading, which do not require treatment. 

Support by the Department for Developing Partial Pretreatment Program by POTW 

The Department has committed to providing technical and legal assistance to the Permittee in 

fulfilling these joint obligations, in particular, assistance with developing an adequate sewer use 

ordinance, notification procedures, enforcement guidelines, and developing local limits and 

inspection procedures. 

GENERAL CONDITIONS 

General Conditions are based directly on state and federal law and regulations and have been 

standardized for all individual municipal NPDES permits issued by the Department. 
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PERMIT ISSUANCE PROCEDURES 

PERMIT MODIFICATIONS 

The Department may modify this permit to impose numerical limitations, if necessary, to meet 

water quality standards, sediment quality standards, or ground water standards, based on new 

information obtained from sources such as inspections, effluent monitoring, outfall studies, and 

effluent mixing studies. 

The Department may also modify this permit as a result of new or amended state or federal 

regulations. 

RECOMMENDATION FOR PERMIT ISSUANCE 

This proposed permit meets all statutory requirements for authorizing a wastewater discharge, 

including those limitations and conditions believed necessary to protect human health, aquatic 

life, and the beneficial uses of waters of the state of Washington. The Department proposes that 

this permit be issued for five (5) years. 
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REFERENCES FOR TEXT AND APPENDICES 

Documents received by the Department from Southwest Suburban Sewer District 

EPA NPDES Form 2A Application 

Boure, Gary R. P.E., Pool Engineering Inc., Secondary Treatment Project Engineering 

Report, August 1985. 

Henke, Evan P.E, CHS Engineer, Inc., Miller Creek/Salmon Creek WWTP Improvements, 

May 2002. 

Horton, Dennis and Associates, Southwest Suburban Sewer District 1999 Comprehensive 

Sewer Plan, February 1999. 

Standard Reference Documents 

Environmental Protection Agency (EPA) 

1992. National Toxics Rule. Federal Register, V. 57, No. 246, Tuesday, December 22, 1992. 

1991. Technical Support Document for Water Quality-based Toxics Control. EPA/505/2-90-001. 

1988. Technical Guidance on Supplementary Stream Design Conditions for Steady State 

Modeling. USEPA Office of Water, Washington, D.C. 

1985. Water Quality Assessment: A Screening Procedure for Toxic and Conventional 

Pollutants in Surface and Ground Water. EPA/600/6-85/002a. 

1983. Water Quality Standards Handbook. USEPA Office of Water, Washington, D.C. 

Metcalf and Eddy. 

1991. Wastewater Engineering, Treatment, Disposal, and Reuse. Third Edition, 

Tsivoglou, E.C., and J.R. Wallace. 

1972. Characterization of Stream Reaeration Capacity. EPA-R3-72-012. (Cited in EPA 1985 

op.cit.) 

Washington State Department of Ecology. 

 2002. Permit Writer’s Manual. Publication Number 92-109. 

Water Pollution Control Federation. 

1976. Chlorination of Wastewater. 

Wright, R.M., and A.J. McDonnell. 

1979. In-stream Deoxygenation Rate Prediction. Journal Environmental Engineering 

Division, ASCE. 105(EE2). (Cited in EPA 1985 op.cit.) 
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APPENDIX A—PUBLIC INVOLVEMENT INFORMATION 

The Department has tentatively determined to reissue a permit to the applicant listed on page one 

of this fact sheet. The permit contains conditions and effluent limitations which are described in 

the rest of this fact sheet. 

Public Notice of Application (PNOA) was published on September 4, 2001, and September 11, 

2002, in the Seattle Times to inform the public that an application had been submitted and to 

invite comment on the reissuance of this permit. 

The Department published a Public Notice of Draft (PNOD) on March 17, 2003, in the Seattle 

Times to inform the public that a draft permit and fact sheet were available for review. Interested 

persons were invited to submit written comments regarding the draft permit. The draft permit, 

fact sheet, and related documents were available for inspection and copying between the hours of 

8:00 a.m. and 5:00 p.m. weekdays, by appointment, at the regional office listed below. Written 

comments were mailed to: 

Water Quality Permit Coordinator 

Department of Ecology 

Northwest Regional Office 

3190 160th Avenue SE 

Bellevue, WA 98008 

Any interested party may comment on the draft permit or request a public hearing on this draft 

permit within the thirty (30)-day comment period to the address above. The request for a hearing 

shall indicate the interest of the party and the reasons why the hearing is warranted. The 

Department will hold a hearing if it determines there is a significant public interest in the draft 

permit (WAC 173-220-090). Public notice regarding any hearing will be circulated at least thirty 

(30) days in advance of the hearing. People expressing an interest in this permit will be mailed 

an individual notice of hearing (WAC 173-220-100). 

Comments should reference specific text followed by proposed modification or concern when 

possible. Comments may address technical issues, accuracy and completeness of information, 

the scope of the facility’s proposed coverage, adequacy of environmental protection, permit 

conditions, or any other concern that would result from issuance of this permit. 

The Department will consider all comments received within thirty (30) days from the date of 

public notice of draft indicated above, in formulating a final determination to issue, revise, or 

deny the permit. The Department's response to all significant comments is available upon 

request and will be mailed directly to people expressing an interest in this permit. 

Further information may be obtained from the Department by telephone, 425-649-7201, or by 

writing to the address listed above. 

This permit and fact sheet were written by Karen Burgess. 
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APPENDIX B—GLOSSARY 

Acute Toxicity—The lethal effect of a pollutant on an organism that occurs within a short period 

of time, usually 48 to 96 hours. 

AKART—An acronym for “all known, available, and reasonable methods of prevention, 

control, and treatment.” 

Ambient Water Quality—The existing environmental condition of the water in a receiving 

water body. 

Ammonia—Ammonia is produced by the breakdown of nitrogenous materials in wastewater. 

Ammonia is toxic to aquatic organisms, exerts an oxygen demand, and contributes to 

eutrophication. It also increases the amount of chlorine needed to disinfect wastewater. 

Average Monthly Discharge Limitation—The highest allowable average of daily discharges 

over a calendar month, calculated as the sum of all daily discharges measured during a 

calendar month divided by the number of daily discharges measured during that month 

(except in the case of fecal coliform). The daily discharge is calculated as the average 

measurement of the pollutant over the day.

Average Weekly Discharge Limitation—The highest allowable average of daily discharges 

over a calendar week, calculated as the sum of all daily discharges measured during a 

calendar week divided by the number of daily discharges measured during that week. The 

daily discharge is calculated as the average measurement of the pollutant over the day.

Best Management Practices (BMPs)—Schedules of activities; prohibitions of practices; 

maintenance procedures; and other physical, structural and/or managerial practices to prevent 

or reduce the pollution of waters of the state. BMPs include treatment systems, operating 

procedures, and practices to control: plant site runoff, spillage or leaks, sludge or waste 

disposal, or drainage from raw material storage. BMPs may be further categorized as 

operational, source control, erosion and sediment control, and treatment BMPs. 

BOD5—Determining the Biochemical Oxygen Demand of an effluent is an indirect way of 

measuring the quantity of organic material present in an effluent that is utilized by bacteria. 

The BOD5 is used in modeling to measure the reduction of dissolved oxygen in a receiving 

water after effluent is discharged. Stress caused by reduced dissolved oxygen levels makes 

organisms less competitive and less able to sustain their species in the aquatic environment. 

Although BOD is not a specific compound, it is defined as a conventional pollutant under the 

federal Clean Water Act. 

Bypass—The intentional diversion of waste streams from any portion of a treatment facility. 

CBOD5—The quantity of oxygen utilized by a mixed population of microorganisms acting on 

the nutrients in the sample in an aerobic oxidation for five days at a controlled temperature of 

20 degrees Celsius, with an inhibitory agent added to prevent the oxidation of nitrogen 

compounds. The method for determining CBOD5 is given in 40 CFR, Part 136. 

Chlorine—Chlorine is used to disinfect wastewaters of pathogens harmful to human health. It is 

also extremely toxic to aquatic life. 
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Chronic Toxicity—The effect of a pollutant on an organism over a relatively long time, often 

1/10 of an organism's lifespan or more. Chronic toxicity can measure survival, reproduction 

or growth rates, or other parameters to measure the toxic effects of a compound or 

combination of compounds. 

Clean Water Act (CWA)—The Federal Water Pollution Control Act enacted by Public Law 

92-500, as amended by Public Laws 95-217, 95-576, 96-483, 97-117; USC 1251 et seq. 

Combined Sewer Overflow (CSO)—The event during which excess combined sewage flow 

caused by inflow is discharged from a combined sewer, rather than conveyed to the sewage 

treatment plant because either the capacity of the treatment plant or the combined sewer is 

exceeded. 

Compliance Inspection - Without Sampling—A site visit for the purpose of determining the 

compliance of a facility with the terms and conditions of its permit or with applicable statutes 

and regulations. 

Compliance Inspection - With Sampling—A site visit to accomplish the purpose of a 

Compliance Inspection - Without Sampling and as a minimum, sampling and analysis for all 

parameters with limits in the permit to ascertain compliance with those limits; and, for 

municipal facilities, sampling of influent to ascertain compliance with the percent removal 

requirement. Additional sampling may be conducted. 

Composite Sample—A mixture of grab samples collected at the same sampling point at 

different times, formed either by continuous sampling or by mixing a minimum of four 

discrete samples. May be "time-composite" (collected at constant time intervals) or 

"flow-proportional" (collected either as a constant sample volume at time intervals 

proportional to stream flow, or collected by increasing the volume of each aliquot as the flow 

increased while maintaining a constant time interval between the aliquots). 

Construction Activity—Clearing, grading, excavation, and any other activity which disturbs the 

surface of the land. Such activities may include road building; construction of residential 

houses, office buildings, or industrial buildings; and demolition activity. 

Continuous Monitoring—Uninterrupted, unless otherwise noted in the permit. 

Critical Condition—The time during which the combination of receiving water and waste 

discharge conditions have the highest potential for causing toxicity in the receiving water 

environment. This situation usually occurs when the flow within a water body is low, thus, 

its ability to dilute effluent is reduced. 

Dilution Factor—A measure of the amount of mixing of effluent and receiving water that 

occurs at the boundary of the mixing zone. Expressed as the inverse of the effluent fraction 

e.g., a dilution factor of 10 means the effluent comprises 10% by volume and the receiving 

water 90%. 

Engineering Report—A document which thoroughly examines the engineering and 

administrative aspects of a particular domestic or industrial wastewater facility. The report 

shall contain the appropriate information required in WAC 173-240-060 or 173-240-130. 
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Fecal Coliform Bacteria—Fecal coliform bacteria are used as indicators of pathogenic bacteria 

in the effluent that are harmful to humans. Pathogenic bacteria in wastewater discharges are 

controlled by disinfecting the wastewater. The presence of high numbers of fecal coliform 

bacteria in a water body can indicate the recent release of untreated wastewater and/or the 

presence of animal feces. 

Grab Sample—A single sample or measurement taken at a specific time or over as short period 

of time as is feasible. 

Industrial User—A discharger of wastewater to the sanitary sewer which is not sanitary 

wastewater or is not equivalent to sanitary wastewater in character. 

Industrial Wastewater—Water or liquid-carried waste from industrial or commercial processes, 

as distinct from domestic wastewater. These wastes may result from any process or activity 

of industry, manufacture, trade or business, from the development of any natural resource, or 

from animal operations such as feed lots, poultry houses, or dairies. The term includes 

contaminated storm water and, also, leachate from solid waste facilities. 

Infiltration and Inflow (I/I)—"Infiltration" means the addition of ground water into a sewer 

through joints, the sewer pipe material, cracks, and other defects. "Inflow" means the 

addition of precipitation-caused drainage from roof drains, yard drains, basement drains, 

street catch basins, etc., into a sewer. 

Interference—A discharge which, alone or in conjunction with a discharge or discharges from 

other sources, both: 

• Inhibits or disrupts the POTW, its treatment processes or operations, or its sludge 

processes, use or disposal; and 

• Therefore is a cause of a violation of any requirement of the POTW's NPDES permit 

(including an increase in the magnitude or duration of a violation) or of the 

prevention of sewage sludge use or disposal in compliance with the following 

statutory provisions and regulations or permits issued thereunder (or more stringent 

state or local regulations): Section 405 of the Clean Water Act, the Solid Waste 

Disposal Act (SWDA) [including Title II, more commonly referred to as the 

Resource Conservation and Recovery Act (RCRA), and including state regulations 

contained in any state sludge management plan prepared pursuant to Subtitle D of the 

SWDA], sludge regulations appearing in 40 CFR, Part 507; the Clean Air Act; the 

Toxic Substances Control Act; and the Marine Protection, Research, and Sanctuaries 

Act. 

Major Facility—A facility discharging to surface water with an EPA rating score of >80 points 

based on such factors as flow volume, toxic pollutant potential, and public health impact. 

Maximum Daily Discharge Limitation—The highest allowable daily discharge of a pollutant 

measured during a calendar day or any 24-hour period that reasonably represents the calendar 

day for purposes of sampling. The daily discharge is calculated as the average measurement 

of the pollutant over the day.

Method Detection Level (MDL)—The minimum concentration of a substance that can be 

measured and reported with 99% confidence that the analyte concentration is above zero and 

is determined from analysis of a sample in a given matrix containing the analyte. 
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Minor Facility—A facility discharging to surface water with an EPA rating score of <80 points 

based on such factors as flow volume, toxic pollutant potential, and public health impact.

Mixing Zone—A volume that surrounds an effluent discharge within which water quality 

criteria may be exceeded. The area of the authorized mixing zone is specified in a facility's 

permit and follows procedures outlined in state regulations (chapter 173-201A WAC). 

National Pollutant Discharge Elimination System (NPDES)—The NPDES (Section 402 of 

the Clean Water Act) is the federal wastewater permitting system for discharges to navigable 

waters of the United States. Many states, including the state of Washington, have been 

delegated the authority to issue these permits. NPDES permits issued by Washington State 

permit writers are joint NPDES/state permits issued under both state and federal laws. 

Pass Through—A discharge which exits the POTW into waters of the state in quantities or 

concentrations which, alone or in conjunction with a discharge or discharges from other 

sources, is a cause of a violation of any requirement of the POTW's NPDES permit 

(including an increase in the magnitude or duration of a violation), or which is a cause of a 

violation of state water quality standards. 

pH—The pH of a liquid measures its acidity or alkalinity. A pH of 7 is defined as neutral, and 

large variations above or below this value are considered harmful to most aquatic life. 

Potential Significant Industrial User—A potential significant industrial user is defined as an 

industrial user which does not meet the criteria for a significant industrial user, but which 

discharges wastewater meeting one or more of the following criteria: 

a. Exceeds 0.5 % of treatment plant design capacity criteria and discharges <25,000 gallons 

per day; or 

b. Is a member of a group of similar industrial users which, taken together, have the 

potential to cause pass through or interference at the POTW (e.g., facilities which 

develop photographic film or paper, and car washes). 

 The Department may determine that a discharger initially classified as a potential significant 

industrial user should be managed as a significant industrial user. 

Quantitation Level (QL)—A calculated value five times the MDL (method detection level). 

Significant Industrial User (SIU)— 

1. All industrial users subject to Categorical Pretreatment Standards under 40 CFR 403.6 and 40 

CFR chapter I, subchapter N; and 

2. Any other industrial user that: discharges an average of 25,000 gallons per day or more of 

process wastewater to the POTW (excluding sanitary, noncontact cooling, and boiler 

blow-down wastewater); contributes a process wastestream that makes up 5 percent or more 

of the average dry weather hydraulic or organic capacity of the POTW treatment plant; or is 

designated as such by the Control Authority* on the basis that the industrial user has a 

reasonable potential for adversely affecting the POTW's operation or for violating any 

pretreatment standard or requirement [in accordance with 40 CFR 403.8(f)(6)]. 
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 Upon finding that the industrial user meeting the criteria in paragraph 2, above, has no 

reasonable potential for adversely affecting the POTW's operation or for violating any 

pretreatment standard or requirement, the Control Authority* may at any time, on its own 

initiative or in response to a petition received from an industrial user or POTW, and in 

accordance with 40 CFR 403.8(f)(6), determine that such industrial user is not a significant 

industrial user. 

 *The term "Control Authority" refers to the Washington State Department of Ecology in the 

case of nondelegated POTWs or to the POTW in the case of delegated POTWs. 

State Waters—Lakes, rivers, ponds, streams, inland waters, underground waters, salt waters, 

wetlands, and all other surface waters and watercourses within the jurisdiction of the state of 

Washington. 

Stormwater—That portion of precipitation that does not naturally percolate into the ground or 

evaporate, but flows via overland flow, interflow, pipes, and other features of a storm water 

drainage system into a defined surface water body, or a constructed infiltration facility. 

Technology-based Effluent Limit—A permit limit that is based on the ability of a treatment 

method to reduce the pollutant. 

Total Suspended Solids (TSS)—Total suspended solids are the particulate materials in an 

effluent. Large quantities of TSS discharged to a receiving water may result in solids 

accumulation. Apart from any toxic effects attributable to substances leached out by water, 

suspended solids may kill fish, shellfish, and other aquatic organisms by causing abrasive 

injuries and by clogging the gills and respiratory passages of various aquatic fauna. 

Indirectly, suspended solids can screen out light and can promote and maintain the 

development of noxious conditions through oxygen depletion. 

Upset—An exceptional incident in which there is unintentional and temporary noncompliance 

with technology-based permit effluent limitations because of factors beyond the reasonable 

control of the Permittee. An upset does not include noncompliance to the extent caused by 

operational error, improperly designed treatment facilities, lack of preventative maintenance, 

or careless or improper operation. 

Water Quality-based Effluent Limit—A limit on the concentration or mass of an effluent 

parameter that is intended to prevent the concentration of that parameter from exceeding its 

water quality criterion after it is discharged into a receiving water. 

Week—For the purposes of the permit, the week is defined at Sunday through Saturday. 
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APPENDIX C—TECHNICAL CALCULATIONS 

Several of the Excel® spreadsheet tools used to evaluate a discharger’s ability to meet 

Washington State’s water quality standards can be found on the Department’s homepage at 

http://www.ecy.wa.gov. 

List of Tables 

Table 1: Salmon Creek WWTP Influent DMR Data for 7/1/97 to 7/1/02 

Table 2: Salmon Creek WWTP Effluent DMR Data for 7/1/97 to 7/1/02 

Table 3: Water Quality Criteria Worksheet 

Table 4: Ammonia Conversion Spreadsheet 

Table 5: Reasonable Potential Calculation 

Table 6: Water Quality-based Human Health Calculation 

Table 7: Potential for Sediment Contamination 
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APPENDIX D—EPA NPDES APPLICATION (PART D) TESTING REQUIREMENTS 

The following pollutant scan data are required at the time of NPDES permit application for 

municipal treatment facilities with design flow greater than 1.0 mgd. At least three scans are 

required, conducted during the term of the previous permit. 

METALS & MISC. VOL. ORGANICS (Cont.) BASE NEUTRALS (Cont.)

Antimony Ethylbenzene Bis (2-Chloroethyl)-Ether 

Arsenic Methyl Bromide Bis (2-Chloroiso-Propyl) Ether 

Beryllium Methyl Chloride Bis (2-Ethylhexyl) Phthalate 

Cadmium Methylene Chloride 4-Bromophenyl Phenyl Ether 

Chromium 1,1,2,2-Tetrachloro-Ethane Butyl Benzyl Phthalate 

Copper Tetrachloro-Ethylene 2-Chloronaphthalene 

Lead Toluene 4-Chlorphenyl Phenyl Ether 

Mercury 1,1,1-Trichloroethane Chrysene 

Nickel 1,1,2-Trichloroethane Di-N-Butyl Phthalate 

Selenium Trichlorethylene Di-N-Octyl Phthalate 

Silver Vinyl Chloride Dibenzo(A,H) Anthracene 

Thallium 1,2-Dichlorobenzene 

Zinc ACID EXTRACTABLES 1,3-Dichlorobenzene 

Cyanide P-Chloro-M-Cresol 1,4-Dichlorobenzene 

Total Phenolic Compounds 2-Chlorophenol 3,3-Dichlorobenzidine 

Hardness (As CaCO3) 2,4-Dichlorophenol Diethyl Phthalate 

2,4-Dimethylphenol Dimethyl Phthalate 

VOLATILE ORGANICS 4,6-Dinitro-O-Cresol 2,4-Dinitrotoluene 

Acrolein 2,4-Dinitrophenol 2,6-Dinitrotoluene 

Acrylonitrile 2-Nitrophenol Fluoranthene 

Benzene 4-Nitrophenol Fluorene 

Bromoform Pentachlorophenol Hexachlorobenzene 

Carbon Tetrachloride Phenol Hexachlorobutadiene 

Clorobenzene 2,4,6-Trichlorophenol Hexachlorocyclo-Pentadiene 

Chlorodibromo-Methane Hexachloroethane 

Chloroethane BASE NEUTRALS Indeno(1,2,3-CD)Pyrene 

2-Chloro-Ethylvinyl Ether Acenaphthene Isophorone 

Chloroform Acenaphthylene Naphthalene 

Dichlorobromo-Methane Anthracene Nitrobenzene 

1,1-Dichloroethane Benzidine N-Nitrosodi-N-Propylamine 

1,2-Dichloroethane Benzo(A)Anthracene N-Nitrosodi-Methylamine 

Trans-1,2-Dichloro Ethylene 3,4 Benzo-Fluoranthene N-Nitrosodi-Phenylamine 

1,1-Dichloroethylene Benzo(Ghi)Perylene Phenanthrene 

1,2-Dichloropropane Benzo(K)Fluoranthene Pyrene 

1,3-Dichloro-Propylene Bis (2-Chloroethoxy) Methane 1,2,4-Trichlorobenzene 
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APPENDIX E—RESPONSE TO COMMENTS 

No comments were received during the public comment period.