FACT SHEET FOR NPDES PERMIT WA-002958-1 

KING COUNTY SOUTH WASTEWATER TREATMENT PLANT 

September 30, 2009 

PURPOSE of this Fact Sheet 

This fact sheet explains and documents the decisions Ecology made in drafting the proposed 

National Pollutant Discharge Elimination System (NPDES) permit for King County’s South 

Wastewater Treatment Plant (South WWTP). 

This fact sheet complies with Section 173-220-060 of the Washington Administrative Code 

(WAC), which requires Ecology to prepare a draft permit and accompanying fact sheet for 

public evaluation before issuing an NPDES permit. 

Ecology makes the draft permit and fact sheet available for public review and comment at least 

thirty (30) days before issuing the final permit. Copies of the fact sheet and draft permit for King 

County’s South WWTP NPDES permit WA-002958-1, were available for public review and 

comment from July 31, 2009, until September 18, 2009. For more details on preparing and filing 

comments about these documents, please see Appendix A—Public Involvement Information.

King County (County) reviewed the draft permit and fact sheet for factual accuracy. Ecology 

corrected any errors or omissions regarding the facility’s location, history, discharges, or 

receiving water. 

After the public comment period closed, Ecology included all comments received and provided 

responses to them. Ecology included the summary and responses to comments in this fact sheet 

as Appendix J—Response to Comments, and published it when issuing the final NPDES 

permit. Ecology will not revise the rest of the fact sheet, but the full document will become part 

of the legal history contained in the facility’s permit file. 

Mark Henley, P.E., municipal permit manager, prepared the permit and this fact sheet. 
Fact Sheet for NPDES Permit WA-002958-1 Page 2 of 101 

King County South Wastewater Treatment Plant 

TABLE OF CONTENTS

I. EXECUTIVE SUMMARY .................................................................................................5

Dilution Factors ...................................................................................................................5

Effluent Limits .....................................................................................................................5

Sediment Monitoring ...........................................................................................................6

Source Tracking ...................................................................................................................6

Priority Pollutant Testing .....................................................................................................7 

Receiving Water Characterization................................................................. 7 

Nitrogen Reduction Study....................................................................................................7 

INTRODUCTION.................................................................................... 8 

II. BACKGROUND INFORMATION ....................................................................................9

Table 1. General Facility Information ...................................................................9

Figure 1. Vicinity Map - King County South WWTP ..........................................9

Figure 2. Aerial Photograph - King County South WWTP ................................10

A. Facility Description ................................................................................................10

History............................................................................................................10

Collection System Status .......................................................................................11

Table 2. Agencies Tributary to South WWTP ....................................................11

Figure 3. Average Monthly Flow and Total Monthly Rainfall ...........................12

Figure 4. Average Monthly Influent BOD and TSS Mass Loadings ..................13

Table 3. Current and Projected (2009-2014) Influent Flow and Loadings .........13

Treatment Processes ...............................................................................................14

Figure 5. South WWTP – Simplified Process Flow Schematic ..........................14

Table 4. South WWTP Staffing ..........................................................................17

Discharge Outfalls .................................................................................................17

Residual Solids.......................................................................................................19

Reuse - Secondary Treated Effluent ......................................................................19

B. Permit Status ..........................................................................................................19

Table 5. Previous Permit’s Effluent Limits .........................................................20

C. Summary of Compliance With Previous Permit Issued on September 30, 2004 ..20

Table 6. Compliance With Effluent Permit Limits .............................................21

D. Wastewater Effluent, Whole Effluent Toxicity, and Sediment 

Characterizations ....................................................................................................21

Table 7. Wastewater Effluent Characterization ..................................................22

Whole Effluent Toxicity Testing ...........................................................................22

Table 8. Detected Chemicals Above or Approaching SQS Criteria ...................24

Figure 6. Sediment Sampling Locations from 1994-2001 .................................24

E. SEPA Compliance .................................................................................................25

III. PROPOSED PERMIT LIMITS .........................................................................................25

A. Design Criteria .......................................................................................................25 

Table 9. Design Standards for King County South WWTP........................ 26 

B. Technology-Based Effluent Limits ........................................................................26

Table 10. Technology-Based Limits. ..................................................................26
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King County South Wastewater Treatment Plant 

C. Surface Water Quality-Based Effluent Limits .......................................................27

Numerical Criteria for the Protection of Aquatic Life and Recreation ..................27

Numerical Criteria for the Protection of Human Health ........................................27

Narrative Criteria ...................................................................................................27

Antidegradation ......................................................................................................28

Mixing Zones.................................................................................. 29

D. Designated Uses and Surface Water Quality Criteria ............................................33

Table 11. Aquatic Life Uses and Associated Criteria .........................................34

Table 12. Recreational Uses ................................................................................34

Table 13. Aquatic Life Uses & Associated Criteria ............................................35

Table 14. Recreational Uses and Associated Criteria .........................................35

E. Evaluation of Surface Water Quality-Based Effluent Limits for Numeric 

Criteria ...................................................................................................................35

Puget Sound Outfall No. 001 .................................................................................35

Chronic Mixing Zone (Outfall 001) .......................................................................36

Acute Mixing Zone (Outfall 001) ..........................................................................36

Dilution Factors .....................................................................................................36

Table 15. Comparison of Dilution Ratios ...........................................................36

Table 16. Dilution Ratio for Outfall No. 001 ......................................................37

Table 17. Dilution Ratio - Green River Outfall No. 002 .....................................41

F. Whole Effluent Toxicity ........................................................................................42

G. Human Health ........................................................................................................43

H. Sediment Quality ...................................................................................................44

I. Ground Water Quality Limits ................................................................................45

J. Comparison of Effluent Limits With the Previous Permit Issued on 

September 30, 2004 ...............................................................................................45

Table 18. Comparison of Effluent Limits ...........................................................45

IV. MONITORING REQUIREMENTS ..................................................................................46

A. Lab Accreditation ...................................................................................................46

V. OTHER PERMIT CONDITIONS .....................................................................................47

A. Reporting and Record Keeping ..............................................................................47

B. Prevention of Facility Overloading ........................................................................47

C. Operation and Maintenance (O&M) ......................................................................47

D. Pretreatment ...........................................................................................................47

Duty to Enforce Discharge Prohibitions ................................................................47

E. Solid Waste Control ...............................................................................................48

F. Spill Plan ................................................................................................................48

G. Outfall Evaluation ..................................................................................................48

H. General Conditions ................................................................................................49

VI. PERMIT ISSUANCE PROCEDURES .............................................................................49

A. Permit Modifications .............................................................................................49

B. Proposed Permit Issuance ......................................................................................49

VII. REFERENCES FOR TEXT AND APPENDICES............................................................50 
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King County South Wastewater Treatment Plant 

APPENDIX A—PUBLIC INVOLVEMENT INFORMATION ...................................................51 

APPENDIX B—GLOSSARY .......................................................................................................52

APPENDIX C—SOUTH WWTP APPLICATION PRIORITY POLLUTANT DATA 

SUMMARY .......................................................................................................................56

APPENDIX D—SOUTH WWTP DISCHARGE MONITORING REPORT SUMMARY 

TABLES ............................................................................................................................60

APPENDIX E—SOUTH WWTP DISCHARGE MONITORING REPORT GRAPHS ..............63

APPENDIX F—OUTFALL DIAGRAMS ....................................................................................69

APPENDIX G—WHOLE EFFLUENT TOXICITY (WET) TESTING RESULTS .....................73

APPENDIX H—TECHNICAL CALCULATIONS ......................................................................74

Table H-1: South WWTP – Water Quality Criteria for Detected Pollutants ...............75

Table H-2: South WWTP – Ammonia Calculation Spreadsheet .................................76

Table H-3: South WWTP – Reasonable Potential to Exceed the Water Quality 

Standards ....................................................................................................77

Table H-4: South WWTP – Chlorine Limit to Meet Water Quality Limit ..................78

Table H-5: South WWTP – Reasonable Potential to Exceed Human Health 

Criteria .......................................................................................................79

Table H-6: South WWTP – Ambient Monitoring Data Summary ...............................81

Table H-7: South WWTP – Dilution Assessment for Temperature .............................82

Table H-8: South WWTP – Dilution Assessment for Fecal Coliform Bacteria ..........83

Table H-9: South WWTP – Assessment for Impacts to Dissolved Oxygen ................84

Table H-10: South WWTP – Assessment for pH ...........................................................85

APPENDIX I—INDUSTRIAL DISCHARGERS TO COUNTY’S SOUTH WWTP ..................86

APPENDIX J—RESPONSE TO COMMENTS ............................................................................87

 
Fact Sheet for NPDES Permit WA-002958-1 Page 5 of 101 

King County South Wastewater Treatment Plant 

I. EXECUTIVE SUMMARY 

Washington State rules require that the owner of a municipal wastewater treatment plant 

(WWTP) obtain a National Pollutant Discharge Elimination System (NPDES) permit prior to 

discharging wastewater to State waters. Statutes, rules, and guidance are used to establish the 

discharge limitation for pollutants and other permit requirements. Most NPDES permits are 

effective for five years and may be administratively extended. 

King County’s Wastewater Treatment Division owns and operates the South WWTP. King 

County applied for the renewal of their NPDES permit for the South WWTP on March 30, 2009. 

Ecology prepared a draft permit and accompanying fact sheet and made it available for public 

comment on July 31, 2009. 

The information below describes major changes from the previous permit (October 1, 2004 to 

September 30, 2009) to the proposed, renewed permit (November 1, 2009 to September 30, 

2014). 

Dilution Factors 

Ecology provided a thorough review of the County’s data, dilution factors, and modeling in June 

2009. Ecology verified that the County used conservative assumptions and provided rigorous 

modeling to obtain dilution factors. The dilution ratios predicted from the current modeling 

effort are substantially different (lower) from those predicted in the previous analysis, and are 

described in the table below. Ecology revised the dilution factors because the County 1) used 

new and improved computer models, 2) collected additional density profile data; and 3) updated 

plant flow rates. Ecology considers the dilution factors in the proposed permit more up-to-date 

and representative than the factors in the previous permit. Note that all of the dilution factors 

decreased (more restrictive) from the previous permit. 

Comparison of Dilution Ratio 

Outfall Chronic 

Mixing Zone 

Radius 

(feet) a

Zone of Acute 

Criteria 

Exceedance 

(feet) a

Proposed 

Chronic 

Dilution 

Ratio

Current 

Chronic 

Dilution 

Ratio

Proposed 

Acute 

Dilution 

Ratio

Current 

Acute 

Dilution 

Ratio

South WWTP 825 82.5 225:1 429:1 186:1 233:1 

a

 – as measured horizontally from each port 

Effluent Limits 

The following table compares the effluent limits from the previous permit to this final permit. 

The effluent limits for the South Wastewater Treatment Plant are unchanged from the previous 

permit because: 

1. Washington State’s rule requiring secondary treatment limits for municipal WWTPs has not 

changed. 
Fact Sheet for NPDES Permit WA-002958-1 Page 6 of 101 

King County South Wastewater Treatment Plant 

2. South WWTP did not violate any of its effluent parameters in the last 5 years. 

3. The reasonable potential analysis did not indicate that any priority pollutant or toxic 

pollutant in the South WWTP’s discharge had a reasonable potential to violate the water 

quality standards. 

4. The whole effluent toxicity (WET) testing on fish indicated that the South WWTP’s 

discharge is unlikely to cause fish toxicity problems in Puget Sound. 

For more specific information, please refer to the additional fact sheet information that follows. 

Comparison of Effluent Limits (South WWTP – Outfall 001) 

Parameter Basis of Limit Previous Effluent Limits: 

Outfall # 001 

Proposed Effluent Limits: 

Outfall # 001 

Average 

Monthly 

Average 

Weekly 

Average 

Monthly 

Average 

Weekly 

Biochemical Oxygen 

Demand (5-day) 

Technology 30 mg/L, 

36,000 lbs/day, 

85% removal of 

influent BOD 

45 mg/L, 

54,000 lbs/day 

30 mg/L, 

36,000 lbs/day, 

85% removal 

of influent BOD 

45 mg/L, 

54,000 lbs/day 

Total Suspended Solids Technology 30 mg/L, 

36,000 lbs/day, 

85% removal of 

influent BOD 

45 mg/L, 

54,000 lbs/day 

30 mg/L, 

36,000 lbs/day, 

85% removal 

of influent BOD 

45 mg/L, 

54,000 lbs/day 

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

pH Technology Daily Minimum is equal to or 

greater than 6.0 and the daily 

maximum is less than or equal to 

9.0 

Daily Minimum is equal to or 

greater than 6.0 and the daily 

maximum is less than or equal to 

9.0 

Parameter Basis of Limit Previous Effluent Limits: 

Outfall # 001 

Proposed Effluent Limits: 

Outfall # 001

Average 

Monthly

Maximum 

Daily

Average 

Monthly

Maximum 

Daily

Total Residual Chlorine Guidance/ 

TechnologyBased 

0.5 mg/L 0.75 mg/L 0.5 mg/L 0.75 mg/L 

Sediment Monitoring 

The proposed permit requires King County to test more extensively for sediment toxicity in the 

vicinity of the South WWTP outfall than the previous permit. The proposed permit includes 

bioassays to be performed, if the chemical concentrations are near or above the numeric chemical 

criteria in the Sediment Management Standards. 

Source Tracking 

In order to more fully characterize industrial discharges into the County’s conveyance system 

and ultimately to South WWTP, the County must conduct pollutant analysis for metals, cyanide, 

phenols, volatile compounds, acid compounds, and base/neutral compounds of at least one 

industry in each of the metal-finishing/electroplating, centralized waste treatment, plastic 

products, coil coating, and food processing categories. 
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King County South Wastewater Treatment Plant 

Priority Pollutant Testing 

The previous permit included priority pollutant sampling once per year for the South WWTP 

effluent. This permit includes priority pollutant sampling twice per year. 

Receiving Water Characterization 

In the vicinity of the South WWTP outfall, the Permittee must provide data via ambient monitoring 

stations or collect receiving water information via field sampling necessary to determine if the 

effluent has a reasonable potential to cause a violation of the water quality standards. 

Nitrogen Reduction Study 

Ecology has two studies underway to inform on the impacts of nutrient-laden discharges to Puget 

Sound. Ecology expects to complete the South Sound Dissolved Oxygen Study along with the 

Puget Sound Hydrodynamic Modeling by December 2010. 

Upon completion of both the South Puget Sound Dissolved Oxygen Study and Hydrodynamic 

Modeling, Ecology will determine whether the discharge from King County’s South WWTP is 

significantly and quantifiably impacting dissolved oxygen levels in South Puget Sound. If 

Ecology concludes that there is a significant and quantifiable adverse impact from the South 

WWTP discharge on dissolved oxygen in South Puget Sound, then Ecology will require King 

County to submit a Nitrogen Reduction Study to evaluate feasible alternatives to reduce nitrogen 

contributions from the South WWTP discharge. 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 8 of 101 

King County South Wastewater Treatment Plant 

INTRODUCTION 

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

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

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

Elimination System (NPDES), administered by the federal Environmental Protection Agency 

(EPA). The EPA authorized the State of Washington to manage the NPDES permit program in 

our state. Our state legislature accepted the delegation and assigned the power and duty for 

conducting NPDES permitting and enforcement to Ecology. The legislature defined Ecology's 

authority and obligations for the wastewater discharge permit program in 90.48 RCW (Revised 

Code of Washington). 

The following regulations apply to municipal NPDES permits: 

• Procedures Ecology follows for issuing NPDES permits (Chapter 173-220 WAC) 

• Technical criteria for discharges from municipal wastewater treatment facilities (Chapter 

173-221 WAC) 

• Water quality criteria for surface waters (Chapter 173-201A WAC) and for ground waters 

(Chapter 173-200 WAC) 

• Sediment management standards (Chapter 173-204 WAC) 

• Submission of Plans and Reports for Construction of Wastewater Facilities (Chapter 

173-240 WAC) 

These rules require any treatment facility operator to obtain an NPDES permit before discharging 

wastewater to state waters. They also help define the basis for limits on each discharge and for 

requirements imposed by the permit. 

Under the NPDES permit program and in response to a complete and accepted permit application, 

Ecology must prepare a draft permit and accompanying fact sheet, and make them available for 

public review before final issuance. Ecology must also publish an announcement (public notice) 

telling people where they can read the draft permit, and where to send their comments, during a 

period of thirty days (WAC 173-220-050). (See Appendix A—Public Involvement Information

for more detail about the public notice and comment procedures). After the public comment period 

ends, Ecology may make changes to the draft NPDES permit. Ecology will summarize the 

responses to comments and any changes to the permit in Appendix J. 

 
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King County South Wastewater Treatment Plant 

II. BACKGROUND INFORMATION 

Table 1. General Facility Information 

Applicant: King County Department of Natural Resources and Parks 

Wastewater Treatment Division 

201 S. Jackson Street, MS KSC-NR-0500 

Seattle, WA 98104-3855 

Facility Name and Address: King County South Wastewater Treatment Plant 

1200 Monster Road SW 

Renton, WA 98057

Type of Treatment: Secondary Treatment, Activated Sludge

Discharge Location: Puget Sound North Diffuser South Diffuser 

Latitude: 47° 36' 10" N 47° 35' 59" N 

Longitude: 122° 25' 44.4" W 122° 25' 44.5" W 

Emergency/Maintenance (Green River) 

Latitude: 47° 28' 03" N 

Longitude: 122° 14' 39" W 

Figure 1. Vicinity Map - King County South Wastewater Treatment Plant 
Fact Sheet for NPDES Permit WA-002958-1 Page 10 of 101 

King County South Wastewater Treatment Plant 

Figure 2. Aerial Photograph - King County South Wastewater Treatment Plant 

A. Facility Description 

History 

In 1958, voters in Seattle and King County created Metro, an agency charged with creating 

a regional wastewater conveyance and treatment system. The South Wastewater Treatment 

Plant (South WWTP) located in Renton is often referred to by County staff as the South 

Treatment Plant (STP). Metro completed construction of the plant in 1965. The original 

plant had the capacity to treat 24 million gallons per day (MGD) of wastewater to secondary 

treatment levels using an activated sludge biological process. The third, and latest, 

expansion of the plant began in 1991 and was considered complete in 2000-2001. This last 

upgrade brings the plant design capacity to 144 MGD maximum month flow (MMF). In 

2003, the County replaced the 90-ton railcar chlorine system with an interim sodium 

hypochlorite (12.5% NaOCl solution) disinfection facility. The City of Renton required the 

County to remove gaseous chlorine from the South WWTP site. The County is currently 

constructing a permanent sodium hypochlorite disinfection facility and plans completion in 

2010. In 2005, the solids dewatering facility was expanded by replacing eight belt filter 

presses (50-gpm each) with three high-solids centrifuges (350-gpm capacity each). 

The South Wastewater Treatment Plant is designated as an EPA major facility due to the 

magnitude of its daily discharge volume. 
Fact Sheet for NPDES Permit WA-002958-1 Page 11 of 101 

King County South Wastewater Treatment Plant 

Collection System Status 

The South Wastewater Treatment Plant serves an area of 152 square miles. King County owns 

and operates the major sewer interceptors and pump stations that carry the wastewater to the 

treatment plant. The component agencies (tabulated below) individually own, operate, and 

maintain the pipelines and other conveyance facilities that carry wastewater to the County’s 

interceptors. Wastewater is conveyed to the treatment plant via three interceptors, the Tukwila 

Interceptor, the South Interceptor, and the Eastside Interceptor and by the 26 pump stations in the 

system. The County monitors and controls the collection system using a SCADA (Supervisory 

Control and Data Acquisition) system located at the South Wastewater Treatment Plant. 

The South Wastewater Treatment Plant serves 25 jurisdictions and utility districts as noted in 

the County’s 2009 NPDES permit application and as listed below. 

Table 2. Agencies Tributary to South WWTP 

Agencies 

Cities Sewer/Utility Districts Other 

Algona Cedar River Water And Sewer District Muckleshoot Indian Tribe

Auburn Coal Creek Utility District Shorewood Apartments

Bellevue Lakehaven Utility District

Black Diamond Northeast Sammamish Sewer And Water District

Issaquah Northshore Utility District

Kent Sammamish Plateau Water And Sewer District

Kirkland Seattle Public Utilities

Mercer Island Skyway Water And Sewer District

Pacific Soos Creek Water And Sewer District

Redmond Valley View Sewer District

Renton 

Tukwila 

CSO Status 

All component agencies that provide flow to the South Wastewater Treatment Plant are separated 

sanitary systems with the exception of a small portion (approximately 4%) of the Seattle system 

that is a combined system. The South Wastewater Treatment Plant will continue to treat a 

portion of the flow from the Henderson CSO and Martin Luther King (MLK) diversion structure 

combined systems during the term of this permit. During heavy rain events, King County’s West 

Point Treatment Plant treats some of the flow. The MLK/Henderson/Norfolk project provides a 

tunnel for the storage and primary sedimentation of flows from Henderson, Martin Luther King, 

and Norfolk CSOs. During small rain events, the tunnel stores CSO flows for transfer to the 

South Wastewater Treatment Plant for secondary treatment. During the largest storms and when 

the tunnel fills, any flows that exceed the capacity of the tunnel storage will be treated and 

disinfected and discharged through the existing Norfolk CSO (which is included in King 

County’s West Point Treatment Plant Permit). 

Flow Blending 

During the previous permit cycle, Ecology authorized King County’s South Wastewater 

Treatment Plant to utilize flow blending to manage peak flow events. The South WWTP had 

twelve blending events between October 2004 and February 2009. In all of the twelve blending 
Fact Sheet for NPDES Permit WA-002958-1 Page 12 of 101 

King County South Wastewater Treatment Plant 

events, the County initiated blending only after solids started to wash out of the secondary 

process or when secondary flows were notably above 190-200 MGD. According to King 

County staff, blending proved successful at reducing the washout of secondary solids from the 

secondary clarifiers. There is no formally-adopted policy for flow blending in federal or state 

regulations at the writing of this permit. This permit does not authorize the use of flow 

blending, but rather relies on the bypass provision in Special Condition S5 of the permit to 

address any bypassing of treatment units. 

Inflow and Infiltration 

The King County Council has approved the Regional Infiltration/Inflow (I/I) Control Program 

as part of its Regional Wastewater Services Plan (RWSP). It is the first comprehensive 

investigation of I/I in the local agency service areas and is based on a cooperative partnership 

between King County and the 34 local agencies serving the Seattle Metropolitan area. 

Flow and Waste Load 

King County submitted, with the application for permit renewal and as required by the 

previous permit, a Flow and Waste Load Assessment. The graphs below show the hydraulic 

and organic loading to the South Wastewater Treatment Plant from October 2004 through 

December 2008 as based on data submitted in the DMRs. 

Figure 3. Average Monthly Flow and Total Monthly Rainfall 

Per Figure 3, the highest average monthly flow for the time period October 2004 – December 

2008 was 133 MGD in January 2006. It was the result of the second wettest January on record 

(11.65-inches) which followed a very wet second half of December 2005. The 133 MGD 

monthly flow is the highest monthly flow ever recorded at South WWTP. In fact, the 30-day 

running average reached 138 MGD (on January 22, 2006). This 30-day running average is only 

6-mgd short of South WWTP’s maximum monthly flow capacity of 144-mgd. South WWTP met 

all of its effluent limits in January 2006 in spite of the heavy rainfall. 

South Plant Flow and Rain

2004 - 2008

40

60

80

100

120

140

160

180

200

220

240

Jan-04Jan-05Jan-06Jan-07Jan-08Jan-09

Flow, MGD

0

4

8

12

16

20

24

28

32

36

40

Rainfall, inches (month total)

Flow, month avg

Flow, max-day

Rain, month total
Fact Sheet for NPDES Permit WA-002958-1 Page 13 of 101 

King County South Wastewater Treatment Plant 

Figure 4. Average Monthly Influent BOD and TSS Mass Loadings 

The maximum-month average TSS load during the last five years was 208,000 TSS lbs/day, 

which occurred in December 2004 and January 2005. The maximum month average TSS load 

of 208,000 lbs/day is 88% of the design maximum month loading. The maximum month 

BOD loading of 214,000 lbs/day occurred in January 2009, when the treatment plant received 

a large amount of deicer waste. 

Capacity Analysis 

Table 3 summarizes South WWTP’s design capacity and its current and projected flow and 

loadings through 2014. The County projected that all of the flows and loads between 2009 and 

2014 will be below South WWTP’s current design capacity assuming an average growth rate of 

1.5% to 1.8% per annum. Brightwater Wastewater Treatment Plant is scheduled to start operations 

in 2011, which will reduce South WWTP’s annual flow and loads by about 8%, and its wet weather 

flow and loads by 15%. Thus, the largest flows and loads over the next five years are projected to 

occur in 2010 and 2011 (i.e., just before the Brightwater Plant starts operation in 2011). 

Table 3. Current and Projected (2009-2014) Influent Flow and Loadings 

Parameter Design 

Capacity 

2004-09 

Max 

Projected 

2010-11 

Projected 

2014 

Flow Average Wet Weather, MGD 115 102 105 93 

Flow Max Month, MGD 144 133 138 121 

BOD Max Month Load, lbs/day 251,000 214,000 221,500 188,000 

TSS Max Month Load, lbs/day 235,000 208,000 215,100 182,000 

South WWTP Influent Loads

Monthly Avg. BOD and TSS

75,000

100,000

125,000

150,000

175,000

200,000

225,000

Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09

Influent Loads, lbs/day

TSS

BOD
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King County South Wastewater Treatment Plant 

 Treatment Processes 

Figure 5. South Wastewater Treatment Plant – Simplified Process Flow Schematic 
Fact Sheet for NPDES Permit WA-002958-1 Page 15 of 101 

King County South Wastewater Treatment Plant 

 Headworks 

The raw sewage can flow through eight bar screens to remove rags and plastics. The 

screenings are conveyed down a trough to the grinder pumps. The ground screenings are 

cleaned and dewatered in preparation for disposal at a landfill. The raw (influent) pumps lift 

the wastewater 40 feet to a division channel providing for gravity flow through the 

remaining treatment processes. The wastewater flows through the aerated grit channels to 

allow for grit to settle out. The grit is pumped to the cyclones, discharged to the classifiers, 

and then into dumpsters. 

Primary Treatment 

The division channel splits flow between a north set of 4 primary clarifiers and south set of 8 

primary clarifiers. The north clarifiers use return flights and tipping troughs to capture and 

remove scum and grease. The south clarifiers use surface water spray to move scum and 

grease to a helical screw located at the upstream end of the tank; the return flights stay 

submerged on the south primaries. The primary clarifier effluent overflows via launders with 

submerged orifices. The launders saw-tooth weirs allow it to handle higher flows. Primary 

effluent flows by gravity to the aeration tanks. Primary sludge is continuously pumped from 

the bottom of the clarifiers to the dissolved air floatation tanks (DAFTs) for further treatment. 

Secondary Treatment 

Secondary treatment is accomplished using an activated sludge process. There are 4 aeration 

basins with fine bubble diffusers used for air distribution. The first part of each aeration 

basin is anaerobic when operating in the selector mode. Operators adjust the dissolved 

oxygen and sludge age to achieve a settable sludge. The aeration basin effluent flows from 

the aeration basins to the mixed liquor channel before distribution to the secondary clarifiers. 

There are 6 secondary clarifier pods each with 4 clarifiers for a total of 24 secondary 

clarifiers. Each pod has an effluent control center (ECC) where flow and turbidity are 

monitored. Pumps return the solids that settle out in the secondary clarifiers back to the 

aeration basins as return activated sludge (RAS) or pump them to solids handling as waste 

activated sludge (WAS). 

 Disinfection and Effluent 

Beginning in June 2003, the facility converted to sodium hypochlorite for disinfection in 

order to eliminate handling of chlorine gas. Hypochlorite is added at several locations along 

the chlorine contact channels. The chlorinated effluent flows through the chlorine contact 

channel to the forebay tank located before the effluent pumps. The effluent pumps 

discharge the treated wastewater from the forebay to the plant’s Puget Sound outfall located 

12 miles away off a point of land north of Alki. The outfall terminates 10,000 feet off shore 

and is 625 feet deep (refer to Appendix F). Additionally, the effluent can flow by gravity to 

the outfall during low flow conditions. 

 Water Reclamation 

This facility produces Class A water for reuse from a small portion of the plant’s flow. Plant 

operators use the chlorinated effluent water, referred to as C3 water, internally throughout the 

process in addition to feeding the water reclamation process. The Class A water treatment 
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King County South Wastewater Treatment Plant 

process includes the required treatment steps of coagulation and filtration. The coagulant, 

currently a polyaluminum chlorhydrate product (PAC), is added to C3 water and mixed via an 

inline static mixer. The water then flows through Parkson DynaSand ® continuously back 

flushing sand filters. The filtered effluent is disinfected with hypochlorite through a series of 

three contact tanks. 

The plant designers set up the control logic for the reuse facility so that high turbidity (>3 

NTU) or low total residual chlorine detected in the water will automatically valve the 

off-specification water back to the treatment plant headworks. Only water meeting the Class A 

specifications flows into the 500,000-gallon reuse water storage tank. In addition to supplying 

the off-site customers by pipeline, the facility allows customers to load reuse water in truck 

mounted storage tanks for off-site use. Ecology permits water distribution from the 

reclamation facilities under a separate Reclaimed Water Permit. 

Solids Handling 

Solids from the primary clarifiers, WAS from the secondary clarifiers, and scum are pumped 

to the DAFTs. The DAFTs (4 older tanks, 2 new larger tanks) thicken the sludge. Inside 

these tanks, a mixture of sludge, polymer, and air form a thick layer of sludge that floats to the 

surface. A scraper arm controls the thickness of the floating sludge blanket and moves solids 

out of the DAFT to the Thickened Sludge Blending Tank. The water layer below the sludge 

blanket in the DAFT is pumped to the aeration tanks. The thin sludge layer that forms on the 

bottom of the DAFT is pumped to grit cyclones for degritting and sent back to the DAFTS for 

reprocessing. 

The contents of the thickened sludge blending tank are pumped on level control to 1 of 4 

anaerobic digesters. Operators collect daily process control samples of the digester sludge. The 

digested sludge is transferred to the 5th digester that serves as the blended sludge storage tank. 

Polymer is added as a coagulant to the sludge as it is pumped from the blended sludge storage 

tanks to the centrifuges. The centrifuges produce a biosolids product that is about 20-25% 

solids. The biosolids are hauled to beneficial reuse sites in Eastern Washington (agriculture 

applications), and Western Washington (forest applications and commercial composting). 

Odor Control 

Odor control consists of a couple different air scrubbing systems. Chemical scrubbers use 

caustic and hypochlorite solutions to control odors from the secondary treatment area, the 

primary treatment area, the sludge thickeners, and the dewatering area. Carbon scrubbers 

control odors in the sludge thickening and dewatering areas. In addition, the facility 

maintains a biofilter to control odors on the influent interceptor collection system. 

Emergency Backup Power 

The facility’s two independent power feeders to the plant provide redundancy. In addition, an 

emergency generator powers essential services, for example, lighting, alarms, security, etc., 

although it is not sufficient to power the influent pumps or other plant processes. An 8-Mega 

Watt (MW) cogeneration facility is also located on-site. It consists of two 3.5-MW gas 

turbine generators and a 1-MW steam turbine generator. The cogeneration facility is fueled 

by pipeline natural gas or scrubbed digester gas produced at the South WWTP. 
Fact Sheet for NPDES Permit WA-002958-1 Page 17 of 101 

King County South Wastewater Treatment Plant 

Industrial and Commercial Users 

Ecology delegated King County the authority to run a Pretreatment Program. The South 

Wastewater Treatment Plant’s application for permit renewal lists a total of 65 industrial 

user discharges received by the treatment plant. There are 27 Significant Industrial Users 

(SIUs) and 38 Categorical Industrial Users (CIUs). Please refer to Appendix I for a list of 

the industrial users. 

Staffing 

Currently, the South WWTP employs 142 full-time employees (FTEs). The 142 FTEs 

provide service to not only the South WWTP and its off-site pump stations, but also to the 

treatment facilities for the City of Carnation, Vashon Island, and Buelah Cove and Park. 

The plant is staffed 24 hours per day with 12-hour shifts. Operators monitor and control 

critical plant operations from a central control room using a distributed control system 

(DCS). A supervisory control and data acquisition (SCADA) system is used to monitor 

off-site pump stations and facilities. 

Table 4. South WWTP Staffing 

Work Group Est. FTEs Responsibilities

Shift Crew (4 shifts, 6 FTE 

per shift) 

24 Operations 

Day Operations Crew 14 Assist with plant operations, training, special projects, 

and backfill for shift crews. 

Process Control Crew 11 Permit compliance issues, sampling, lab analysis, 

reporting, data handling, process setpoints, etc. 

Pump-run crew 11 Operation of off-site pump stations and treatment 

systems. 

Maintenance Staff 36 Electricians and Instrument Technicians and 

Mechanics. 

Other 37 Administration, Purchasing & Inventory, Building and 

Grounds Maintenance, Engineering & As-Builts, 

Technical Publications, etc. 

Future Construction Plans 

The facility is currently converting a temporary sodium hypochlorite system to a permanent 

system. The County is not planning any other major projects at the plant during the upcoming 

permit cycle. 

Discharge Outfalls 

Puget Sound Outfall 001 

Secondary treated and disinfected effluent is discharged from the facility via a 12-mile long 

8-foot diameter transfer line. The outfall consists of two pipelines, each extending over 

10,000 feet northwest into Elliot Bay from Duwamish Head. For nearshore protection, the 

initial portion is supported by legs and the remainder of the outfall rests along the seafloor in 

a shallow trench. An outfall junction structure is located at the end of the effluent transfer 
Fact Sheet for NPDES Permit WA-002958-1 Page 18 of 101 

King County South Wastewater Treatment Plant 

system (ETS) force main just west of Luna Park in West Seattle. The structure contains a 

64-inch diameter manifold connecting the 96-inch ETS to the two 64-inch outfall lines. The 

diffuser sections are on the final 500-ft of each leg. Each diffuser has 168-sweep radius 

diffuser ports, each 14 inches long and 4 inches in diameter. (This a total of 336 diffuser 

ports with a total diffuser opening of 336 * 0.087 ft2/port = 29.32 ft2.) The diffusers are 

staggered side-to-side every 3 feet. Each diffuser port is made of a copper-nickel alloy to 

inhibit bio-fouling. The diffusers are about 625 feet deep. 

The County inspected the marine outfall in 2004-2005. The extensive inspection concluded 

that all external components of the outfalls and associated structures appeared in good 

condition with no evidence of damage. However, the inspection report noted that many 

spans of the pipeline were unsupported, particularly in the steep sloping areas. Also, the 

report noted that sediments have buried significant portions of both pipelines since its 

installation. King County submitted video footage of the inspection along with the 

inspection report. Appendix F diagrams show the location of the marine outfall and the 

emergency outfall described in the next section. 

Green River Outfall (Maintenance & Emergency Purposes Only) 

The Green River outfall was the South WWTP’s sole discharge point prior to the 

construction of the marine outfall in 1987. The County increased the firm capacity (total 

capacity with one pump out of service) of the effluent transfer system (ETS), which carries 

flow to the marine outfall, to 325 MGD with the pumping system upgrade in 1999. With all 

pumps running, the predicted capacity is 340-360 MGD (depending on the tide). The 

proposed permit authorizes the treatment plant to discharge to the Green River during 

emergencies and for maintenance purposes only. 

An emergency discharge is an unplanned and unavoidable discharge which is necessary to 

prevent sewage overflows or damage to the plant. Emergency discharges may occur during 

a severe, heavy rain event when the flow exceeds the capacity of the ETS, or in the extreme 

event that the ETS loses significant capacity due to multiple equipment failures or power 

failure. 

Maintenance discharges are performed periodically to ensure that the outfall will function 

normally during an emergency event. During a maintenance discharge, the County uses a 

sufficient flow rate of disinfected and dechlorinated effluent to flush sediment from the 

diffuser ports. The proposed permit specifically authorizes discharges to the Green River 

for maintenance purposes. 

The diffuser is a 12-foot by 12-foot structure that is 44 feet long extending into the river. 

There are 8 discharge ports located on the downstream side of the diffuser. The top of each 

port is at the elevation of the river bottom. 

During the last permit cycle, no maintenance activities were performed on the Green River 

Outfall and therefore, no effluent was discharged to the Green River. 
Fact Sheet for NPDES Permit WA-002958-1 Page 19 of 101 

King County South Wastewater Treatment Plant 

Residual Solids 

The treatment facilities remove 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 a landfill. Primary and waste secondary sludge are co-thickened in the Dissolved 

Air Floatation Tanks. The thickened sludge is fed to the anaerobic, mesophilic digesters, 

which are maintained at 35-38 °C. The County blends and stores digested sludge in a tank 

followed by dewatering with centrifuges to produce biosolids. The biosolids are applied to 

forest and agriculture lands under a permit from the King County Health Department. 

The County periodically analyzes the biosolids for various chemical contaminants. 

Regulatory and compliance issues regarding biosolids are managed by the Department of 

Ecology’s Biosolids Program. 

Reuse - Secondary Treated Effluent 

A separate state Reclaimed Water Permit covers the existing water reclamation facility, the 

distribution of the Class A water it produces, and any future secondary effluent that is not 

returned to the ETS (effluent transfer system). The proposed NPDES permit regulates all 

direct discharges of treated secondary effluent that ultimately return the treated secondary 

effluent back to the ETS for discharge via the Puget Sound outfall. 

The proposed NPDES permit (Conditions S16) authorizes the County to distribute effluent 

from the ETS to Boeing for a specifically-identified use and allows it to distribute effluent 

for similar uses provided it receives written approval from both Ecology and the Department 

of Health. Following use the effluent discharges back to the ETS. Departmental approval is 

required for each application of direct reuse to ensure that such use does not cause a 

violation of the state water quality standards. The intent of the NPDES permit is to allow 

the Permittee flexibility to provide noncontact reuse water to customers with sufficient 

safeguards to ensure that the water quality standards are not violated. 

At the time of the writing of the permit, King County had one customer using treated 

secondary effluent in this manner. The Boeing Company uses secondary treated effluent in 

a closed-loop chiller system primarily during the summer months at the Boeing Training 

Center located in Renton, Washington. King County is permitted to enlist other customers 

located along the ETS corridor for noncontact use of the secondary treated effluent with 

return to the ETS for discharge at the Puget Sound Outfall. 

B. Permit Status 

Ecology issued the previous permit for this facility on September 30, 2004. The previous 

permit placed effluent limits on 5-day Biochemical Oxygen Demand (BOD5), Total 

Suspended Solids (TSS), pH, Fecal Coliform Bacteria, and Total Residual Chlorine. 

King County submitted an application for permit renewal on March 31, 2009. Ecology 

accepted it as complete on April 14, 2009. 
Fact Sheet for NPDES Permit WA-002958-1 Page 20 of 101 

King County South Wastewater Treatment Plant 

The effluent limits in the previous permit are as follows. 

Table 5. Previous Permit’s Effluent Limits 

EFFLUENT LIMITS a: OUTFALL # 1

Parameter Average Monthly Average Weekly

Biochemical Oxygen Demand b (BOD5) 30 mg/L, 36,000 lb/day 

85% minimum removal 

45 mg/L, 54,000 lb/day 

Total Suspended Solids b 30 mg/L, 36,000 lb/day 

85% minimum removal 

45 mg/L, 54,000 lb/day 

Fecal Coliform Bacteria 200/100 mL 400/100 mL 

pHc Daily minimum is equal to or greater than 6.0 and the 

daily maximum is less than or equal to 9.0. 

Parameter Average Monthly Maximum Daily d

Total Residual Chlorine 0.5 mg/L, 600 lb/day 0.75 mg/L 

Footnotes: 

a The average monthly and weekly effluent limits 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 shall not exceed 30 mg/L or 15 percent of the 

respective monthly average influent concentrations, whichever is more stringent. 

 The average monthly effluent concentration for TSS shall not exceed 30 mg/L or 15 percent of the 

respective monthly average influent concentrations, whichever is more stringent.

c Indicates the range of permitted values. When pH is continuously monitored, excursions between 

5.0 and 6.0, or 9.0 and 10.0 shall not be considered violations provided no single excursion exceeds 

60 minutes in length and total excursions do not exceed 7 hours and 30 minutes per month. Any 

excursions below 5.0 and above 10.0 are violations. The instantaneous maximum and minimum pH 

shall be reported monthly. 

d The maximum daily effluent concentration determined from a continuous measurement is calculated 

as the average of the pollutant concentrations measured over the day. 

C. Summary of Compliance With Previous Permit Issued on September 30, 2004 

Ecology staff last conducted a sampling compliance inspection on April 14-15, 2008. A 

compliance inspection report was issued on May 21, 2008. The inspectors found the facility 

to be operating in accordance with the permit and found no violations. 

King County has complied with the effluent limits throughout the duration of the permit 

issued on September 30, 2004. Ecology assessed compliance based on its review of the 

facility’s discharge monitoring reports (DMRs) and on inspections conducted by Ecology. 

The County submits two discharge monitoring reports (DMRs) each month, one for the 

treatment plant discharge and one for the reclaimed water discharge during months in which 

off-site use occurs. The following table summarizes the effluent DMR data (discharge No. 

001) submitted from September 2004 to December 2008. Ecology permits the reclaimed 

water system under Reclaimed Water Permit ST-7445 and its compliance record is described 

in the associated fact sheet. Appendix D provides a complete summary of monthly DMR data 

submitted by the Permittee from September 2004 to April 2009. 
Fact Sheet for NPDES Permit WA-002958-1 Page 21 of 101 

King County South Wastewater Treatment Plant 

Table 6. Compliance With Effluent Permit Limits 

September 2004 – December 2008 

Parameters Average Max Min Permit Limits 

BOD5 – lbs/d, Monthly Avg. 10,397 19,843 4,293 ≤ 36,000 

BOD5 – lbs/d, Max. Weekly Avg. 13,114 29,360 4,800 ≤ 54,000 

BOD5 – mg/L, Monthly Avg. 16 25 9 ≤ 30 

BOD5 – mg/L, Max. Weekly Avg. 19 30 10 ≤ 45 

TSS – lbs/d, Monthly Avg. TSS 11,360 32,357 4,388 ≤ 36,000 

TSS – lbs/d, Max. Weekly Avg. 15,157 50,971 4,999 ≤ 54,000 

TSS – mg/L, Monthly Avg. 17 30 8 ≤ 30 

TSS – mg/L, Max. Weekly Avg. 21 41 9 ≤ 45 

Fecal Coliforms, no./100 mL, 

Monthly 74 170 17 ≤ 200 

pH - Daily Low 6.7 7.4 6.0 ≥ 6.0 

pH - Daily High 7.4 9.8a 6.8 ≤ 9.0 

Cl2 Residual – mg/L, Monthly Avg. 0.04 0.29 0.00 ≤ 0.5 

Cl2 Residual – mg/L, Max. Daily 0.09 0.75 0.00 ≤ 0.75 

Cl2 Residual – lb/d, Monthly Avg. 20 231 0 ≤ 600 

BOD Removal - %, Monthly Avg. 93 96 86 ≥ 85 

TSS Removal - %, Monthly Avg. 93 97 85 ≥ 85 

Flow - mgd, Monthly Avg. 76 133 45b NA 

Source: NPDES Permit Application. 

a

 The County reports that the pH value of 9.8 is an artifact of hypochlorite dosing the final effluent 

sample line. The County believes that the maximum pH value is likely closer to pH 7.5. The 

hypochlorite dosing is necessary to keep nitrifying bacteria from growing and seeding the final 

effluent sample. Their presence in the sample will artificially increase the effluent BOD result. 

b

 The County reports that the minimum flow of 45-mgd is artificially low by 6-10 mgd. This low flow 

occurred during the summer of 2008 when calibration of the flow meters was changed. 

On November 7, 2008, the wastewater treatment plant had an unauthorized, secondary 

bypass of approximately 1,000 to 2,000 gallons. Primary effluent was unintentionally 

conveyed to the chlorine contact channel during preventative maintenance activities on the 

diversion gates. The County has since modified operational procedures to prevent this 

incident from reoccurring. 

D. Wastewater Effluent, Whole Effluent Toxicity, and Sediment Characterizations 

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

in discharge monitoring reports. Table 7 summarizes those pollutants that the County found 

in detectable quantities as reported in the NPDES form 2A application. Calculations show 

that none of these pollutants have the potential to exceed the state water quality standard at 

the edge of the chronic mixing zone based on the reasonable potential calculations provided 

in Appendix H. 
Fact Sheet for NPDES Permit WA-002958-1 Page 22 of 101 

King County South Wastewater Treatment Plant 

Table 7. Wastewater Effluent Characterization 

Max. Daily Discharge Average Daily Discharge 

POLLUTANT Conc. Units Mass Units Conc. Units Mass Units # of 

Samples

ML/ 

MDL 

Antimony 0.67 ug/L 0.45 lbs/d <0.51 ug/L <0.30 lbs/d 32 0.5 

Arsenic 1.60 ug/L 1.17 lbs/d 1.26 ug/L 0.76 lbs/d 34 0.5 

Cadmium 0.30 ug/L 0.17 lbs/d <0.11 ug/L <0.064 lbs/d 32 0.1 

Chromium 4.07 ug/L 2.28 lbs/d 0.87 ug/L 0.51 lbs/d 32 0.4 

Copper 42.4 ug/L 24.01 lbs/d 16.5 ug/L 9.51 lbs/d 32 0.4 

Lead 2.00 ug/L 1.12 lbs/d 0.66 ug/L 0.38 lbs/d 32 0.2 

Mercury 0.058 ug/L 0.045 lbs/d <0.05 ug/L <0.03 lbs/d 33 0.05 

Nickel 4.45 ug/L 2.34 lbs/d 2.99 ug/L 1.78 lbs/d 33 0.3 

Silver 0.84 ug/L 0.48 lbs/d <0.35 ug/L <0.21 lbs/d 32 0.2 

Zinc 68.0 ug/L 38.5 lbs/d 29.0 ug/L 17.4 lbs/d 33 0.5 

Cyanide 0.028 mg/L 14.61 lbs/d <0.008 mg/L <5.09 lbs/d 33 0.005 

Total Phenolic 

Compounds 

0.080 mg/L 47.2 lbs/d <0.011 mg/L <6.55 lbs/d 24 0.005-

0.02 

Chloroform 2.18 ug/L 1,565 lbs/d <1.32 ug/L <0.802 lbs/d 23 1.32 

Methylene Chloride 7 ug/L 4.16 lbs/d <4.74 ug/L <2.74 lbs/d 23 5 

Toluene 3.86 ug/L 1.845 lbs/d <1.45 ug/L <0.78 lbs/d 23 4 

1,4-dichlorobenzene 3.93 ug/L 2.82 lbs/d <1.21 ug/L <1.21 lbs/d 15 0.57-

0.6 

Whole Effluent Toxicity Testing 

The County conducted acute and chronic toxicity tests in February 2008, April 2008, July 2008, 

August 2008, and October 2008. Acute toxicity tests were conducted with Daphnia pulex 

(water flea) and Pimephales promelas (fathead minnow). Chronic toxicity tests were conducted 

with Atherinops affinis (topsmelt) and Mysidopsis bahia (Mysid Shrimp). Please refer to 

Appendix G for toxicity test results. 

For acute toxicity, the performance standard is the median survival in 100% effluent being equal 

to or greater than 80% and no individual test result showing less than 65% survival in 100% 

effluent. For the above tests, the median survival in 100% effluent was 90%. No individual test 

resulted in less than 65% survival in 100% effluent. Since the discharge met the performance 

standard for acute toxicity in the previous permit cycle, the proposed permit does not include an 

acute WET limit and instead includes another effluent characterization for acute WET to ensure 

that toxicity has not increased. 

For chronic toxicity, the performance standard is no chronic toxicity test demonstrating a 

statistically-significant difference in response between the control and a test concentration 

equal to the acute critical effluent concentration (ACEC). South WWTP had no chronic 

toxicity near the previous ACEC of 0.43% effluent in any recent test. No chronic WET 

limit is needed. The proposed permit includes the same set of chronic tests at the end of the 

new permit term for submission with the application. 
Fact Sheet for NPDES Permit WA-002958-1 Page 23 of 101 

King County South Wastewater Treatment Plant 

Sediment Characterization 

Ecology has promulgated sediment management standards under Chapter 173-204 WAC. 

The sediment management standards contain numeric chemical and biological criteria that 

protect benthic organisms that live in the sediment of the marine waters of Puget Sound. 

These standards state that Ecology may require permitted facilities to evaluate the potential 

for the discharge to cause a violation of applicable standards. 

In November 2001, King County performed sediment sampling from 0 to 2 cm depth at 13 

sample locations near the two marine outfalls. Sediment samples were analyzed for the 47 

chemicals with numeric criteria in the sediment management standards. All samples met the 

sediment quality standards (SQS) numeric criteria. One sample (RT625SD) had a 

bis(2-ethylhexyl) phthalate concentration of 43 ppm, compared to the SQS criteria of 47 

ppm. All other samples had bis(2-ethylhexyl) phthalate concentrations below 10 ppm. Five 

samples had detection limits for 2-methylphenol that were slightly above the sediment 

quality standards criteria, but were not detected in the sediment nor in the effluent. Most of 

the 47 chemicals were not present at detectable levels. The County measured low 

concentrations of PAH, phthalates and metals in the sediment, but they were below the 

numeric criteria for benthic toxicity.1

In October 1999, King County performed sediment sampling from 0 to 2 cm depth at 13 

sample locations near the two outfalls. Sediment samples were analyzed for the 47 

chemicals with numeric criteria in the sediment management standards. The County did not 

detect the following four chemicals (2,4-dimethyl phenol, 2-methylphenol, benzyl alcohol, 

and hexachlorobutadiene), but most of the samples had reported detection limits above the 

sediment quality standards numeric criteria. Most of the other 47 chemicals were not 

present at detectable levels below the SQS numeric criteria. The County measured low 

concentrations of PAHs, PCBs, phthalates, and metals in the sediment, but they were below 

the numeric criteria for benthic toxicity.2

Between 1994 and 1997, King County performed annual sediment sampling from 0 to 2 cm 

depth at locations near the two outfalls.3

 In October 1997, the County measured 

concentrations of hexachlorobenzene at three locations (RT700NS, RT625ND, RT625SD) 

that exceeded the sediment quality standards numeric criteria. In October 1995, one location 

(LSDS02) exceeded CSL numeric criteria for benzoic acid. One sample, RT625SD, had 

bis(2-ethylhexyl) phthalate concentration of 42 ppm, compared to the SQS criteria of 47 

ppm.

4

 For four chemicals (1,2,4-trichlorobenzene, benzyl alcohol, hexachlorobenzene, and 

hexachlorobutadiene) many of the samples had non-detect concentrations with reported 

detection limits above the sediment quality standard numeric criteria. 

Table 8 shows chemicals detected in sediment samples that approach or exceed the SQS 

criteria. Figure 6 shows the locations of the sampling stations. 

 

1

 EIM Data User Study ID RENT01 

2

 EIM Data User Study ID RENT99 

3

 EIM Data User Study ID RENT9497 

4

 Total organic carbon normalized. Sediment Management Standards WAC 173-204-320. 
Fact Sheet for NPDES Permit WA-002958-1 Page 24 of 101 

King County South Wastewater Treatment Plant 

Table 8. Detected Chemicals Above or Approaching SQS Criteria 

Sampling 

Station 

Sampling 

Year 

Chemical Detected in 

Sediments 

Sediment 

Concentration 

Criteria 

RT625SD 2001 Bis(2-ethylhexyl)phthalate 43 ppm 

OC normalized 

47 ppm 

OC normalized 

RT625SD 1997 Bis(2-ethylhexyl)phthalate 42 ppm 

OC normalized 

RT625SD 1997 Hexachlorobenzene 1.9 ppm 

OC normalized 

0.38 ppm 

OC normalized 

RT700NS 1997 Hexachlorobenzene 2.5 ppm 

OC normalized 

RT625ND 1997 Hexachlorobenzene 0.95 ppm 

OC normalized 

LSDS02 1995 Benzoic acid 1500 ppb dry weight 650 ppb dry weight 

Figure 6. Sediment Sampling Locations from 1994-2001 
Fact Sheet for NPDES Permit WA-002958-1 Page 25 of 101 

King County South Wastewater Treatment Plant 

In summary, past sediment monitoring does not indicate sediment toxicity or a violation of 

the sediment management standards at this site. The proposed permit includes additional 

sediment monitoring to ensure continued compliance because of the large volume of 

discharge, some past instances of detection limits above the SQS numeric criteria, and 1997 

concentrations in the chemical analyses of sediments above SQS near the site. 

E. SEPA Compliance 

Regulation exempts reissuance or modification of any wastewater discharge permit from the 

SEPA process as long as the permit contains conditions that are no less stringent than state rules 

and regulations. The exemption applies only to existing discharges, not to new discharges. 

III. PROPOSED PERMIT LIMITS 

Federal and state regulations require that effluent limits in an NPDES permit must be either 

technology- or water quality-based. 

• Technology-based limits are based upon the treatment methods available to treat specific 

pollutants. Technology-based limits are set by the EPA and published as a regulation, or 

Ecology develops the limit on a case-by-case basis (40 CFR 125.3, and Chapter 173-220 WAC). 

• Water quality-based limits are calculated so that the effluent will comply 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 

(40 CFR 131.36). 

• Ecology must apply the most stringent of these limits to each parameter of concern. These 

limits are described below. 

The limits in this permit reflect information received in the application and from supporting reports 

(engineering, hydrogeology, etc.). Ecology evaluated the permit application and determined the 

limits needed to comply with the rules adopted by the state of Washington. Ecology does not 

develop effluent limits for all reported pollutants. 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. 

Nor does Ecology usually develop limits for pollutants that were not reported in the permit 

application but that may be present in the discharge. The permit does not authorize discharge of the 

non-reported pollutants. If significant changes occur in any constituent of the effluent discharge, 

King County is required to notify Ecology [40 CFR 122.42(a)]. King County may be in violation of 

the permit until Ecology modifies the permit to reflect additional discharge of pollutants. 

A. Design Criteria 

Under WAC 173-220-150 (1)(g), flows and waste loadings must not exceed approved design 

criteria. Ecology-approved design criteria for this facility’s treatment plant were obtained from 

the August 1991 Facilities Plan (Metro’s Regional Treatment Plant in Renton, Enlargement III 

Program) and the October 1997 East Division Reclamation Plant Stage 2 Liquid Stream 

Improvements – III2B.1. Both documents were prepared by Brown and Caldwell Consultants 

and associated firms. 
Fact Sheet for NPDES Permit WA-002958-1 Page 26 of 101 

King County South Wastewater Treatment Plant 

 Table 9: Design Standards for King County South Wastewater Treatment Plant 

Parameter Design Quantity 

Monthly average flow (max. month) 144 MGD 

Monthly average dry weather flow (AWDF) 96 MGD 

Monthly average wet weather flow (AWWF) 115 MGD 

Instantaneous peak flow 325 MGD 

Maximum Month BOD5 influent loading 251,000 lb/day 

Maximum Month TSS influent loading 235,000 lb/day 

Design population equivalent 1,298,000 

B. Technology-Based Effluent Limits 

Federal and state regulations define technology-based effluent limits for municipal wastewater 

treatment plants. These effluent limits are given in 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 (AKART) for 

municipal wastewater. 

Chapter 173-221 WAC lists the following technology-based limits for pH, fecal coliform, 

BOD5, and TSS: 

Table 10. Technology-Based Limits 

Parameter Limit 

pH The pH must measure 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 

Ecology derived the technology-based monthly average limit for chlorine 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/L chlorine residual is maintained after fifteen 

minutes of contact time. See also Metcalf and Eddy, Wastewater Engineering, Treatment, 
Fact Sheet for NPDES Permit WA-002958-1 Page 27 of 101 

King County South Wastewater Treatment Plant 

Disposal and Reuse, Third Edition, 1991. A treatment plant that provides adequate 

chlorination contact time can meet the 0.5 mg/L chlorine limit on a monthly average basis. 

According to WAC 173-221-030(11)(b), the corresponding weekly average is 0.75 mg/L. 

The existing permit has chlorine limits of 0.5 mg/L (average monthly) and 0.75 mg/L 

(maximum daily), and the facility is able to comply with it. The proposed permit includes 

the same limit. 

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

173-221-030(11)(b). 

Monthly effluent mass loadings (lbs/day) = maximum monthly design flow (144 MGD) x 

Concentration limit (30 mg/L) x 8.34 (conversion factor) = mass limit 36,000 lb/day. 

Average weekly effluent mass loadings (lbs/day) = maximum monthly design flow (144 MGD) x 

Concentration limit (45 mg/L) x 8.34 (conversion factor) = mass limit 54,000 lb/day. 

C. Surface Water Quality-Based Effluent Limits 

The Washington State surface water quality standards (Chapter 173-201A WAC) are 

designed to protect existing water quality and preserve the beneficial uses of Washington's 

surface waters. Waste discharge permits must include conditions that ensure the discharge 

will meet the surface water quality standards (WAC 173-201A-510). Water quality-based 

effluent limits may be based on an individual waste load allocation or on a waste load 

allocation developed during a basin wide total maximum daily load study (TMDL). 

Numerical Criteria for the Protection of Aquatic Life and Recreation 

Numerical water quality criteria are listed in the water quality standards for surface waters 

(Chapter 173-201A WAC). They specify the maximum levels of pollutants allowed in 

receiving water to protect aquatic life and recreation in and on the water. Ecology uses 

numerical criteria 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 

limits, the discharge must meet the water quality-based limits. 

Numerical Criteria for the Protection of Human Health 

The U.S. EPA has published 91 numeric water quality criteria for the protection of human 

health that are applicable to dischargers in Washington State (EPA, 1992). These criteria 

are designed to protect humans from exposure to pollutants linked to cancer and other 

diseases, based on consuming fish and shellfish and drinking contaminated surface waters. 

The water quality standards also include radionuclide criteria to protect humans from the 

effects of radioactive substances. 

Narrative Criteria 

Narrative water quality criteria (e.g., WAC 173-201A-240(1); 2006) limit the toxic, 

radioactive, or other deleterious material concentrations that the facility may discharge to 

levels below those which have the potential to: 
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King County South Wastewater Treatment Plant 

• Adversely affect designated water uses. 

• Cause acute or chronic toxicity to biota. 

• Impair aesthetic values. 

• Adversely affect human health. 

Narrative criteria protect the specific designated uses of all fresh waters (WAC 173-201A-200, 

2006) and of all marine waters (WAC 173-201A-210, 2006) in the state of Washington. 

Antidegradation 

The purpose of Washington's Antidegradation Policy (WAC 173-201A-300-330; 2006) is to: 

• Restore and maintain the highest possible quality of the surface waters of Washington. 

• Describe situations under which water quality may be lowered from its current condition. 

• Apply to human activities that are likely to have an impact on the water quality of 

surface water. 

• Ensure that all human activities likely to contribute to a lowering of water quality, at a 

minimum, apply all known, available, and reasonable methods of prevention, control, 

and treatment (AKART). 

• Apply three tiers of protection (described below) for surface waters of the state. 

Tier I ensures existing and designated uses are maintained and protected and applies to all waters 

and all sources of pollutions. Tier II ensures that waters of a higher quality than the criteria 

assigned are not degraded unless such lowering of water quality is necessary and in the 

overriding public interest. Tier II applies only to a specific list of polluting activities. Tier III 

prevents the degradation of waters formally listed as "outstanding resource waters," and applies 

to all sources of pollution. 

A facility must prepare a Tier II analysis when all three of the following conditions are met: 

• The facility is planning a new or expanded action. 

• Ecology regulates or authorizes the action. 

• The action has the potential to cause measurable degradation to existing water quality at 

the edge of a chronic mixing zone. 

This facility must meet Tier I requirements. 

• Dischargers must maintain and protect existing and designated uses. Ecology must not 

allow any degradation that will interfere with, or become injurious to, existing or 

designated uses, except as provided for in Chapter 173-201A WAC. 
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Ecology’s analysis described in this section of the fact sheet demonstrates that the existing 

and designated uses of the receiving water will be protected under the conditions of the 

proposed permit. 

Mixing Zones 

A mixing zone is the defined area in the receiving water surrounding the discharge port(s), 

where wastewater mixes with receiving water. Within mixing zones the pollutant 

concentrations may exceed water quality numeric standards, so long as the discharge does not 

interfere with designated uses of the receiving water body (for example, recreation, water 

supply, and aquatic life and wildlife habitat, etc.) The pollutant concentrations outside of the 

mixing zones must meet water quality numeric standards. 

State and federal rules allow mixing zones because the concentrations and effects of most 

pollutants diminish rapidly after discharge, due to dilution. Ecology defines mixing zone 

sizes to limit the amount of time any exposure to the end-of-pipe discharge could harm 

water quality, plants, or fish. 

The state’s water quality standards allow Ecology to authorize mixing zones for the facility’s 

permitted wastewater discharges only if those discharges already receive all known, available, 

and reasonable methods of prevention, control, and treatment (AKART). Mixing zones 

typically require compliance with water quality criteria within a specified distance from the 

point of discharge and use no more than 25% of the available width of the water body for 

dilution. Ecology uses modeling to estimate the amount of mixing within the mixing zone. 

Through modeling Ecology determines the potential for violating the water quality standards at 

the edge of the mixing zone and derive any necessary effluent limits. Steady-state models are 

the most frequently used tools for conducting mixing zone analyses. Ecology chooses values 

for each effluent and for receiving water variables that correspond to the time period when the 

most critical condition is likely to occur (see Ecology’s Permit Writer’s Manual). Each critical 

condition parameter, by itself, has a low probability of occurrence and the resulting dilution 

factor is conservative. The term “reasonable worst-case” applies to these values. 

The mixing zone analysis produces a numerical value called a dilution factor (DF). A dilution 

factor represents the amount of mixing of effluent and receiving water that occurs at the 

boundary of the mixing zone. For example, a dilution factor of 10 means the effluent is 10% 

and the receiving water is 90% of the total volume of water at the boundary of the mixing zone. 

Ecology uses dilution factors with the water quality criteria to calculate reasonable potentials 

and effluent limits. Water quality standards include both aquatic life-based criteria and human 

health-based criteria. The former are applied at both the acute and chronic mixing zone 

boundaries; the latter are applied only at the chronic boundary. The concentration of pollutants 

at the boundaries of any of these mixing zones may not exceed the numerical criteria for that 

zone. 

Each aquatic life acute criterion is based on the assumption that organisms are not exposed 

to that concentration for more than one hour and more often than one exposure in three 

years. Each aquatic life chronic criterion is based on the assumption that organisms are not 

exposed to that concentration for more than four consecutive days and more often than once 

in three years. 
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The two types of human health-based water quality criteria distinguish between those 

pollutants linked to non-cancer effects (non-carcinogenic) and those linked to cancer effects 

(carcinogenic). The human health-based water quality criteria incorporate several exposure 

and risk assumptions. These assumptions include: 

• A 70-year lifetime of daily exposures. 

• An ingestion rate for fish or shellfish measured in kg/day. 

• An ingestion rate of two liters/day for drinking water 

• A one-in-one-million cancer risk for carcinogenic chemicals. 

This permit authorizes an acute mixing zone, surrounded by a chronic mixing zone around 

the point of discharge (WAC 173-201A-400). The water quality standards impose certain 

conditions before allowing the discharger a mixing zone: 

1. Ecology must specify both the allowed size and location in a permit. 

The proposed permit specifies the size and location of the allowed mixing zone. 

2. The facility must fully apply “all known, available, and reasonable methods of 

prevention, control and treatment” (AKART) to its discharge. 

 Ecology has determined that the treatment provided at King County’s South WWTP

meets the requirements of AKART (see “Technology-Based Limits”). 

3. Ecology must consider critical discharge conditions. 

Surface water quality-based limits are derived for the waterbody’s critical condition (the 

receiving water and waste discharge condition with the highest potential for adverse impact 

on the aquatic biota, human health, and existing or designated waterbody uses). The 

critical discharge condition is often pollutant-specific or waterbody-specific. 

Critical discharge conditions are those conditions that result in reduced dilution or 

increased effect of the pollutant. Factors affecting dilution include the depth of water, 

the density stratification in the water column, the currents, and the rate of discharge. 

Density stratification is determined by the salinity and temperature of the receiving 

water. Temperatures are warmer in the surface waters in summer. Therefore, density 

stratification is generally greatest during the summer months. Density stratification 

affects how far up in the water column a freshwater plume may rise. The rate of 

mixing is greatest when an effluent is rising. The effluent stops rising when the mixed 

effluent is the same density as the surrounding water. After the effluent stops rising, 

the rate of mixing is much more gradual. Water depth can affect dilution when a plume 

might rise to the surface when there is little or no stratification. Ecology uses the water 

depth at mean lower low water (MLLW) for marine waters. Ecology’s Permit Writer’s 

Manual describes additional guidance on criteria/design conditions for determining 

dilution factors. The manual can be obtained from Ecology’s website at: 

http://www.ecy.wa.gov/biblio/92109.html. 
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Ecology used the following critical conditions to model the discharge: 

• Water depth at MLLW of 625 feet. 

• 50th percentile current speeds of 0.069 m/sec for chronic and human health mixing 

zones (at Station 46, depth = 191 m). 

• 10th or 90th percentile current speeds of 0.021 and 0.14 m/sec, respectively for 

acute mixing zone (at Station 46, depth = 191 m) 

• Maximum average monthly effluent flow of 144 MGD for chronic and human 

health non-carcinogen. 

• Annual average flow of 106 MGD for human health carcinogen. 

• Maximum daily flow of 235 million gallons per day (MGD) for acute mixing zone. 

• 1 DAD MAX Effluent temperature of 22.2 degrees C. 

Ambient data at critical conditions in the vicinity of the outfall was taken from Effluent 

Dilution Modeling for South Wastewater Treatment Plant Outfall study conducted in 

March 2009. 

4. Supporting information must clearly indicate the mixing zone would not: 

• Have a reasonable potential to cause the loss of sensitive or important habitat. 

• Substantially interfere with the existing or characteristic uses. 

• Result in damage to the ecosystem. 

• Adversely affect public health. 

Ecology established Washington State water quality criteria for toxic chemicals using 

EPA criteria. EPA developed the criteria using toxicity tests with numerous organisms 

and set the criteria to generally protect the species tested and to fully protect all 

commercially- and recreationally-important species. 

EPA sets acute criteria for toxic chemicals assuming organisms are exposed to the 

pollutant at the criteria concentration for one hour. They set chronic standards assuming 

organisms are exposed to the pollutant at the criteria concentration for four days. 

Dilution modeling under critical conditions generally shows that both acute and chronic 

criteria concentrations are reached within minutes of being discharged. 

The discharge plume does not impact drifting and non-strong swimming organisms 

because they cannot stay in the plume close to the outfall long enough to be affected. 

Strong swimming fish could maintain a position within the plume, but they can also 

avoid the discharge by swimming away. Mixing zones generally do not affect benthic 

organisms (bottom dwellers) because the buoyant plume rises in the water column. 

Ecology has additionally determined that the effluent will not exceed 33 degrees C for 

more than two seconds after discharge; and that the temperature of the water will not 

create lethal conditions or blockages to fish migration. 
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Ecology evaluates the cumulative toxicity of an effluent by testing the discharge with 

whole effluent toxicity (WET) testing. 

Ecology reviewed the above information, the specific information on the characteristics 

of the discharge, the receiving water characteristics, and the discharge location. Based 

on this review, Ecology concluded that the discharge does not have a reasonable 

potential to cause the loss of sensitive or important habitat, substantially interfere with 

existing or characteristics uses, result in damage to the ecosystem, or adversely affect 

public health if the permit limits are met. 

5. The discharge/receiving water mixture must not exceed water quality criteria 

outside the boundary of a mixing zone. 

Ecology conducted a reasonable potential analysis, using procedures established by the 

EPA and by Ecology, for each pollutant and concluded the discharge/receiving water 

mixture will not violate water quality criteria outside the boundary of the mixing zone 

if permit limits are met. 

6. The size of the mixing zone and the concentrations of the pollutants must be 

minimized. 

At any given time, the effluent plume uses only a portion of the acute and chronic 

mixing zone, which minimizes the volume of water involved in mixing. Because tidal 

currents change direction, the plume orientation within the mixing zone changes. The 

plume rises through the water column as it mixes, therefore much of the receiving water 

volume at lower depths in the mixing zone is not mixed with discharge. Similarly, 

because the discharge may stop rising at some depth due to density stratification, waters 

above that depth will not mix with the discharge. Ecology determined it is impractical 

to specify in the permit the actual, much more limited volume in which the dilution 

occurs as the plume rises and moves with the current. 

Ecology minimizes the size of mixing zones by requiring dischargers to install diffusers 

when they are appropriate to the discharge and the specific receiving waterbody. When 

a diffuser is installed, the discharge is more completely mixed with the receiving water 

in a shorter time. Ecology also minimizes the size of the mixing zone (in the form of 

the dilution factor) using design criteria with a low probability of occurrence. For 

example, Ecology uses the expected 95th percentile pollutant concentration, the 90th

percentile background concentration, the centerline dilution factor, and the lowest flow 

occurring once in every ten years to perform the reasonable potential analysis. 

Because of the above reasons, Ecology has effectively minimized the size of the mixing 

zone authorized in the proposed permit. 

7. Maximum size of mixing zone. 

The authorized mixing zone does not exceed the maximum size restriction. 
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King County South Wastewater Treatment Plant 

8. Acute Mixing Zone. 

• The discharge/receiving water mixture must comply with acute criteria as 

near to the point of discharge as practicably attainable.

Ecology determined the acute criteria will be met at 10% of the distance of the 

chronic mixing zone at the ten-year low flow. 

• The pollutant concentration, duration, and frequency of exposure to the 

discharge will not create a barrier to migration or translocation of indigenous 

organisms to a degree that has the potential to cause damage to the ecosystem. 

As described above, the toxicity of any pollutant depends upon the exposure, the 

pollutant concentration, and the time the organism is exposed to that concentration. 

Authorizing a limited acute mixing zone for this discharge assures that it will not 

create a barrier to migration. The effluent from this discharge will rise as it enters 

the receiving water, assuring that the rising effluent will not cause translocation of 

indigenous organisms near the point of discharge (below the rising effluent).

• Comply with size restrictions.

The mixing zone authorized for this discharge complies with the size restrictions 

published in Chapter 173-201A WAC. 

9. Overlap of Mixing Zones. 

For the marine discharge, please see Appendix F for acute and chronic mixing zones 

diagrams. South WWTP’s mixing zones do not overlap another discharger’s mixing zones.

For the Green River outfall, the mixing zone cannot extend more than 310 feet downstream 

and more than 100 feet upstream from the diffusers. The mixing zone cannot utilize 

greater than 25 percent of the flow and cannot occupy greater than 25 percent of the width 

of the river. 

D. Designated Uses and Surface Water Quality Criteria 

Applicable designated uses and surface water quality criteria are defined in Chapter 173-201A 

WAC. In addition, the U.S. EPA set human health criteria for toxic pollutants (EPA 1992). 

Criteria applicable to this facility’s discharge are summarized below in Tables 11 - 14. 

Marine Water Discharge (Outfall 001): 

• Aquatic life uses are designated using the following general categories. All indigenous 

fish and non-fish aquatic species must be protected in waters of the state. 

(a) Extraordinary quality salmonid and other fish migration, rearing, and spawning; 

clam, oyster, and mussel rearing and spawning; crustaceans and other shellfish 

(crabs, shrimp, crayfish, scallops, etc.) rearing and spawning. 
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(b) Excellent quality salmonid and other fish migration, rearing, and spawning; clam, 

oyster, and mussel rearing and spawning; crustaceans and other shellfish (crabs, 

shrimp, crayfish, scallops, etc.) rearing and spawning. 

(c) Good quality salmonid migration and rearing; other fish migration, rearing, and 

spawning; clam, oyster, and mussel rearing and spawning; crustaceans and other 

shellfish (crabs, shrimp, crayfish, scallops, etc.) rearing and spawning. 

(d) Fair quality salmonid and other fish migration. 

The South WWTP’s outfall discharges to Puget Sound at a location that is classified as 

extraordinary marine waters. The Aquatic Life Uses and associated criteria for 

extraordinary marine waters are identified below. 

Table 11. Aquatic Life Uses and Associated Criteria 

Extraordinary quality

Temperature Criteria – Highest 1D MAX 13°C (55.4°F) 

Dissolved Oxygen Criteria – Lowest 1-Day 

Minimum 

7.0 mg/L 

Turbidity Criteria • 5 NTU over background when the background is 

50 NTU or less; or 

• A 10 percent increase in turbidity when the 

background turbidity is more than 50 NTU. 

pH Criteria pH must be within the range of 7.0 to 8.5 with a 

human-caused variation within the above range of 

less than 0.2 units. 

• To protect shellfish harvesting, fecal coliform organism levels must not exceed a 

geometric mean value of 14 colonies/100 mL, and not have more than 10 percent of all 

samples (or any single sample when less than ten sample points exist) obtained for 

calculating the geometric mean value exceeding 43 colonies/100 mL. 

• The recreational uses are primary contact recreation and secondary contact recreation. 

For the South WWTP’s discharge to Puget Sound, the recreational uses for this receiving 

water are identified as primary contact, as shown below. 

Table 12. Recreational Uses 

Recreational use Criteria 

Primary Contact 

Recreation 

Fecal coliform organism levels must not exceed a geometric mean value of 14 

colonies/100 mL, with not more than 10 percent of all samples (or any single 

sample when less than ten sample points exist) obtained for calculating the 

geometric mean value exceeding 43 colonies/100 mL. 

• The miscellaneous marine water uses are wildlife habitat, harvesting, commerce and 

navigation, boating, and aesthetics. 
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Freshwater Discharge (Maintenance & Emergency Outfall): 

• Aquatic Life Uses are designated based on the presence of, or the intent to provide 

protection for, the key uses. All indigenous fish and non-fish aquatic species must be 

protected in waters of the state in addition to the key species. The Aquatic Life Uses 

for the Green River at the Emergency Outfall location are identified below. 

Table 13. Aquatic Life Uses & Associated Criteria 

Salmonid Spawning, Rearing, and Migration

Temperature Criteria – Highest 7DAD MAX 17.5°C (63.5°F) 

Dissolved Oxygen Criteria – Lowest 1-Day 

Minimum 

8.0 mg/L 

Turbidity Criteria • 5 NTU over background when the background is 

50 NTU or less; or 

• A 10 percent increase in turbidity when the 

background turbidity is more than 50 NTU. 

Total Dissolved Gas Criteria Total dissolved gas shall not exceed 110 percent 

of saturation at any point of sample collection. 

pH Criteria pH shall be within the range of 6.5 to 8.5 with a 

human-caused variation within the above range of 

less than 0.5 units. 

• The recreational uses are extraordinary primary contact recreation, primary contact 

recreation, and secondary contact recreation. The recreational uses for this receiving 

water are identified below. 

Table 14. Recreational Uses and Associated Criteria 

Recreational Use Criteria 

Primary Contact 

Recreation 

Fecal coliform organism levels must not exceed a geometric mean value of 100 

colonies /100 mL, with not more than 10 percent of all samples (or any single 

sample when less than ten sample points exist) obtained for calculating the 

geometric mean value exceeding 200 colonies/100 mL. 

• The water supply uses are domestic, agricultural, industrial, and stock watering. 

• The miscellaneous freshwater uses are wildlife habitat, harvesting, commerce and 

navigation, boating, and aesthetics. 

E. Evaluation of Surface Water Quality-Based Effluent Limits for Numeric Criteria 

Puget Sound Outfall No. 001 

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 biological oxygen demand 

(BOD) is a far-field pollutant whose adverse effect occurs away from the discharge even after 

dilution has occurred. Thus, the method of calculating surface water quality-based effluent 

limits varies with the point at which the pollutant has its maximum effect. 
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King County South Wastewater Treatment Plant 

With technology-based controls (AKART), predicted pollutant concentrations in the 

discharge may exceed water quality criteria. Ecology therefore authorizes a mixing zone in 

accordance with the geometric configuration, flow restriction, and other restrictions imposed 

on mixing zones by Chapter 173-201A WAC. 

Chronic Mixing Zone (Outfall No. 001) 

WAC 173-201A-400(7)(b) specifies that mixing zones must not extend in any horizontal 

direction from the discharge ports for a distance greater than 200 feet plus the depth of water 

over the discharge ports as measured during MLLW. 

The horizontal distance of the chronic mixing zone is 825 feet. The mixing zone extends 

from the seabed to the top of the water surface. 

Acute Mixing Zone (Outfall No. 001) 

WAC 173-201A-400(8)(b) specifies that in estuarine waters a zone where acute criteria may be 

exceeded must not extend beyond 10% of the distance established for the chronic zone. The 

acute mixing zone for Outfall 001 extends 82.5 feet in any direction from any discharge port. 

Dilution Factors 

Ecology provided a thorough review of the County’s data, dilution factors, and modeling in 

June 2009. Ecology verified that the County used conservative assumptions and provided 

rigorous modeling to obtain dilution factors. The dilution ratios predicted from the current 

modeling effort are substantially different (lower) from those predicted in the previous 

analysis, and are described in the table below. Ecology revised the dilution factors because 

the County 1) used new and improved computer models, 2) collected additional density 

profile data; and 3) updated plant flow rates. Ecology considers the dilution factors in the 

proposed permit more up-to-date and representative than the factors in the previous permit. 

Note that all of the dilution factors decreased from the previous permit. 

Table 15. Comparison of Dilution Ratios 

Outfall Chronic 

Mixing Zone 

Radius 

(feet) a

Zone of Acute 

Criteria 

Exceedance 

(feet) a

Proposed 

Chronic 

Dilution 

Ratio

Current 

Chronic 

Dilution 

Ratio

Proposed 

Acute 

Dilution 

Ratio

Current 

Acute 

Dilution 

Ratio

South 

WWTP

825 82.5 225:1 429:1 186:1 233:1 

a

 – as measured horizontally from each port 

Ecology determined the dilution factors that occur within these zones at the critical 

condition using UM3 and NRFIELD/RSB model components. The dilution ratio for this 

permit is listed in Table 16: 
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Table 16. Dilution Ratio for Outfall No. 001 

Criteria Acute Chronic 

Aquatic Life 186:1 225:1 

Human Health, Carcinogen 428:1 

Human Health, Non-carcinogen 428:1 

Ecology determined the impacts of dissolved oxygen deficiency, temperature, pH, fecal 

coliform, chlorine, ammonia, metals, nutrients and other toxics as described below, using the 

dilution ratios in the above tables. The derivation of surface water quality-based limits also 

takes into account the variability of pollutant concentrations in both the effluent and the 

receiving water. 

BOD5—With technology-based limits, this discharge results in a small amount of BOD loading 

relative to the large amount of dilution in the receiving water at critical conditions. 

Technology-based limits will ensure that dissolved oxygen criteria are met in the receiving water. 

Temperature—The state temperature standards (WAC 173-201A-200-210 and 600-612) 

include multiple elements: 

• Annual summer maximum threshold criteria (June 15 to September 15). 

• Supplemental spawning and rearing season criteria (September 15 to June 15). 

• Incremental warming restrictions. 

• Protections against acute effects. 

Ecology evaluates each criterion independently to determine reasonable potential and 

derive permit limits. 

• Annual summer maximum and supplementary spawning/rearing criteria. 

Each water body has an annual maximum temperature criterion [WAC 

173-201A-200(1)(c), 210(1)(c), and Table 602]. These threshold criteria (for 

example, 12, 16, 17.5, 20°C) protect specific categories of aquatic life by 

controlling the effect of human actions on summer temperatures. 

Some waters have an additional threshold criterion to protect the spawning and 

incubation of salmonids (9°C for char and 13°C for salmon and trout) [WAC 

173-201A-602, Table 602]. These criteria apply during specific date-windows. 

The threshold criteria apply at the edge of the chronic mixing zone. Criteria for 

most fresh waters are expressed as the highest 7-Day average of daily maximum 

temperature (7-DADMax). The 7-DADMax temperature is the arithmetic average 

of seven consecutive measures of daily maximum temperatures. Criteria for 

marine waters and some fresh waters are expressed as the highest 1-Day annual 

maximum temperature (1-DMax). 
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King County South Wastewater Treatment Plant 

• Incremental warming criteria. 

The water quality standards limit the amount of warming human sources can cause 

under specific situations [WAC 173-201A-200(1)(c)(i)-(ii), 210(1)(c)(i)-(ii)]. The 

incremental warming criteria apply at the edge of the chronic mixing zone. 

At locations and times when background temperatures are cooler than the assigned 

threshold criterion, point sources are permitted to warm the water by only a 

defined increment. These increments are permitted only to the extent doing so 

does not cause temperatures to exceed either the annual maximum or supplemental 

spawning criteria. 

At locations and times when a threshold criterion is being exceeded due to natural 

conditions, all human sources, considered cumulatively, must not warm the water 

more than 0.3°C above the naturally warm condition. 

When Ecology has not yet completed a TMDL, our policy allows each point 

source to warm water at the edge of the chronic mixing zone by 0.3°C. This is true 

regardless of the background temperature and even if doing so would cause the 

temperature at the edge of a standard mixing zone to exceed the numeric threshold 

criteria. Allowing a 0.3°C warming for each point source is reasonable and 

protective where the dilution factor is based on 25% or less of the critical flow. 

This is because the fully mixed effect on temperature will only be a fraction of the 

0.3°C cumulative allowance (0.075°C or less) for all human sources combined. 

• Temperature Acute Effects. 

Instantaneous lethality to passing fish: The upper 99th percentile daily 

maximum effluent temperature must not exceed 33°C; unless a dilution analysis 

indicates ambient temperatures will not exceed 33°C 2-seconds after discharge. 

General lethality and migration blockage: Measurable (0.3°C) increases in 

temperature at the edge of a chronic mixing zone are not allowed when the 

receiving water temperature exceeds either a 1DMax of 23°C or a 7DADMax of 

22°C. 

Lethality to incubating fish: Human actions must not cause a measurable (0.3°C) 

warming above 17.5°C at locations where eggs are incubating. 

• Temperature Chronic Effects. 

1. Annual summer maximum. 

Ecology calculated the reasonable potential for the discharge to exceed the 

annual summer maximum, the supplementary spawning criterion, and the 

incremental warming criteria at the edge of the chronic mixing zone during 

critical condition(s). No reasonable potential exists to exceed the temperature 

criterion where: 
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King County South Wastewater Treatment Plant 

(Criterion + 0.3) > Criterion + [(Teffluent95 – Criterion)/DF]. 

(13 + 0.3) > 13 + [(22.5 – 13)/225]. 

13.3 > 13.04 

Therefore, the proposed permit does not include a temperature limit. The permit 

requires additional monitoring of effluent and ambient temperatures. Ecology 

will reevaluate the reasonable potential during the next permit renewal. 

2. Incremental warming criteria.

Some waters are naturally incapable of meeting their assigned threshold 

temperature criteria. At locations and times when a threshold criterion is being 

exceeded due to natural conditions, all human sources, considered cumulatively, 

must not warm the water more than 0.3°C above the naturally warm condition. 

When Ecology has not yet completed a TMDL, our policy allows each point 

source to warm water at the edge of the chronic mixing zone by 0.3°C. This is 

true regardless of the background temperature and even if doing so would cause 

the temperature at the edge of a standard mixing zone to exceed the numeric 

threshold criteria. Allowing a 0.3°C warming for each point source is reasonable 

and protective where the dilution factor is based on 25 percent or less of the 

critical flow. This is because the fully mixed effect on temperature will be only a 

fraction (0.075°C or less) of the 0.3°C cumulative allowance for all human 

sources combined. 

South WWTP reported a maximum effluent temperature of 22.2°C on their 

NPDES application. Using the dilution ratio of 225:1 (receiving water : effluent) 

and maximum daily temperature of 14.0°C for the receiving water and 22.2°C 

for the effluent, the predicted maximum daily temperature inside the dilution 

zone is ((225x14.0)+(1x22.2))/(225+1) = 14.04°C. Thus, under the worst case 

scenario, the effluent discharge from this facility results in warming of the 

ambient temperature by 0.04°C, which is less than the allowable warming 

temperature of 0.3°C. 

Since the discharge does not have a potential to violate the water quality standards 

for temperature in the receiving water, Ecology placed no limits in the permit for 

effluent temperature. To acquire ambient temperature and effluent temperature 

data, the proposed permit requires the South WWTP to continue to monitor these 

temperatures. The need for a limit will be evaluated during the next permit cycle. 

pH—Compliance with the technology-based limits of 6.0 to 9.0 will assure compliance with the 

water quality standards of surface waters because of the high buffering capacity of marine water. 

Fecal Coliform—Ecology modeled the numbers of fecal coliform by simple mixing analysis 

using the maximum day discharge (years 2004-2008) of 2,075 organisms per 100 ml and a 

dilution factor of 225. 
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King County South Wastewater Treatment Plant 

Under critical conditions, modeling predicts no violation of the water quality criterion for 

fecal coliform. Therefore, the proposed permit includes the technology-based effluent limit 

for fecal coliform bacteria. 

Toxic Pollutants—Federal regulations (40 CFR 122.44) require Ecology to place limits in 

NPDES permits on toxic chemicals in an effluent whenever there is a reasonable potential for 

those chemicals to exceed the surface water quality criteria. Ecology does not exempt facilities 

with technology-based effluent limits from meeting the surface water quality standards. 

The following toxic pollutants are present in the discharge: chlorine, ammonia, and heavy 

metals. Ecology conducted a reasonable potential analysis (see Appendix H) on these 

parameters to determine whether it would require effluent limits in this permit. 

Ammonia's toxicity depends on that portion which is available in the unionized form. The 

amount of unionized ammonia depends on the temperature, pH, and salinity of the receiving 

marine water. To evaluate ammonia toxicity, Ecology used the available receiving water 

information for ambient station LSTN01 and Ecology spreadsheet tools. 

Valid ambient background data was available for arsenic, cadmium, chromium, copper, lead, 

mercury, nickel, and zinc (see Appendix H). Ecology used all applicable data to evaluate 

reasonable potential for this discharge to cause a violation of water quality standards. 

Ecology determined that ammonia, arsenic, cadmium, chromium, copper, cyanide, lead, 

mercury, nickel, silver, and zinc pose no reasonable potential to exceed the water quality 

criteria at the critical condition using procedures given in EPA, 1991 (Appendix H) and as 

described above. Ecology’s determination assumes that this facility meets the other effluent 

limits of this permit. 

Ecology derived effluent limits for the toxic pollutant chlorine, determined to have a 

reasonable potential to cause a violation of the water quality standards. Ecology calculated 

effluent limits using methods from EPA, 1991 as shown in Appendix H. 

Ecology used new dilution modeling results (more restrictive) to determine new total residual 

chlorine limits for the proposed permit. Ecology derived the new limits based on the state water 

quality standards of 13 μg/L for acute and 7.5 μg/L for chronic along with an acute dilution 

factor of 186:1 and a chronic dilution factor of 225:1 (refer to Appendix H—Technical 

Calculations). The resulting permit limits would be an average monthly total residual chlorine 

limit of 924 μg/L and a maximum daily total residual chlorine limit of 2,418 μg/L. However, 

the technology, guidance-based limit for chlorine is more stringent than the water quality-based 

limit at 500 μg/L (Average Monthly Limit) and 750 μg/L (Maximum Daily Limit). The 

anti-backsliding provision under the federal regulations [CFR 122.44(l)] requires that the 

chlorine limit be based on the more stringent limit established in the previous permit since it has 

been shown to be technologically achievable.

The resultant effluent limits are as follows: 

Chlorine 0.5 mg/L (average monthly) and 0.75 mg/L (average weekly) 
Fact Sheet for NPDES Permit WA-002958-1 Page 41 of 101 

King County South Wastewater Treatment Plant 

Freshwater Dilution Factors – Green River Outfall No. 002 (Maintenance Only) 

Ecology determined the dilution ratio of effluent to receiving water that occurs within the 

freshwater zones based on bulk dilution. The resultant dilution ratio is: 

Table 17. Dilution Ratio - Green River Outfall No. 002 

Green River Outfall Acute Chronic 

Aquatic Life – Maintenance 9:1 Not Applicable

Aquatic Life – Emergency Permitted Under S5.F Not Applicable 

Ecology determined the acute dilution ratio based on bulk dilution achieved under the 

conditions expected during use of the outfall for maintenance purposes. King County may 

discharge only when the river flow is at least 1000 cfs (cubic feet per second). The rate of 

discharge anticipated during a maintenance event is limited to no more than an average of 

28 cfs. Ecology used these assumptions for the previous permit and verified them for this 

permit. Based on these assumptions, the bulk dilution using the entire river is 36:1 

(1000/28=36). The regulation permits only 25% of the river width to be utilized; therefore, 

the effective acute dilution ratio is 9:1 during a maintenance event. Ecology expects that 

maintenance discharges will only occur for short periods of time and therefore chronic water 

quality standards would not apply. 

Ecology did not determine a mixing zone for the emergency use of the Green River outfall. 

The Green River outfall is implicitly permitted under Special Condition S5.F and explicitly 

permitted under Special Condition S1.B for emergency use. Effluent limits were not 

imposed for emergency use because it is assumed that such use will occur under extreme 

and unpredictable circumstances. 

BOD5—Ecology predicts a violation of the dissolved oxygen criterion for the receiving 

water under critical conditions with the technology-based limit. Ecology determined the 

impact of BOD on the receiving water based on a discharge limit of 15 mg/L and a dilution 

of 9:1. This discharge limit could produce a drop in dissolved oxygen in the river by as 

much as 1.67 mg/L based on worst case assumptions. Based on the short duration of this 

discharge, Ecology believes this limit will protect the receiving water. 

Temperature and pH—The impact of pH and temperature were modeled using the 

calculations from EPA, 1988. The input variables were dilution factor 9, upstream temperature 

17.2o

C, upstream pH 7.5, upstream alkalinity 50(as mg CaCO3/L), effluent temperature 20oC, 

effluent pH of 6, and effluent alkalinity 68.8 (as mg CaCO3/L). (Refer to Appendix H.) 

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

surface waters. Therefore, the no technology-based limit was placed in the permit for 

temperature. A technology-based effluent limit for pH was placed in the permit. 

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

using the technology-based limit of 200 organisms per 100 ml and a dilution factor of 9. 

The resulting fecal coliform at the edge of the dilution zone would be 22.1 organisms per 

100 ml. 
Fact Sheet for NPDES Permit WA-002958-1 Page 42 of 101 

King County South Wastewater Treatment Plant 

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 

limit for fecal coliform bacteria was placed in the proposed permit. 

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. 

Due to the infrequency and short duration of discharges to the Green River, the only toxicant 

considered was chlorine. Ecology conducted a reasonable potential analysis (see Appendix H) 

on chlorine to determine whether or not it would require effluent limits in this permit. 

Ecology derived effluent limits for chlorine, which showed a reasonable potential to cause a 

violation of the water quality standards. Effluent limits were calculated using methods from 

EPA, 1991 as shown in Appendix H. 

The resultant effluent limits are as follows: 

 Chlorine 171 μg/L. 

F. Whole Effluent Toxicity 

The water quality standards for surface waters forbid discharge of effluent that causes toxic 

effects in the receiving waters. Many toxic pollutants cannot be measured by commonly 

available detection methods. However, laboratory tests can measure toxicity directly by 

exposing living organisms to the wastewater and measuring their responses. These tests 

measure the aggregate toxicity of the whole effluent, so 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 find early 

indications of any potential lethal effect of the effluent on organisms in the receiving 

water. 

• 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 on an organism with an extremely short life cycle, or a partial life cycle 

test during a critical stage of a test organism's life. Some chronic toxicity tests also 

measure organism survival. 

Ecology-accredited WET testing laboratories use the proper WET testing protocols, fulfill 

the data requirements, and submit results in the correct reporting format. Accredited 

laboratory staff knows about WET testing and how to calculate an NOEC, LC50, EC50, IC25, 

etc. Ecology gives all accredited labs the most recent version of Ecology Publication No. 

WQ-R-95-80, Laboratory Guidance and Whole Effluent Toxicity Test Review Criteria
Fact Sheet for NPDES Permit WA-002958-1 Page 43 of 101 

King County South Wastewater Treatment Plant 

(http://www.ecy.wa.gov/biblio/9580.html), which is referenced in the permit. Ecology 

recommends that King County send a copy of the acute or chronic toxicity sections(s) of its 

NPDES permit to the laboratory. 

WET testing conducted during effluent characterization showed no reasonable potential for 

effluent discharges to cause receiving water acute toxicity. All individual acute WET tests 

had greater than 65% survival in 100% effluent, and the median survival in 100% effluent 

was 90%. Since the acute toxicity tests passed the performance standard, the proposed 

permit will not impose an acute WET limit. King County must retest the effluent before 

submitting an application for permit renewal. 

• If this facility makes process or material changes which, in Ecology's opinion, increase 

the potential for effluent toxicity, then Ecology may (in a regulatory order, by permit 

modification, or in the permit renewal) require the facility to conduct additional effluent 

characterization. 

• If WET testing conducted for submittal with a permit application fails to meet the 

performance standards in WAC 173-205-020, Ecology will assume that effluent 

toxicity has increased. King County may demonstrate to Ecology that effluent toxicity 

has not increased, by performing additional WET testing after the process or material 

changes have been made. 

WET testing conducted during effluent characterization showed no reasonable potential for 

effluent discharges to cause receiving water chronic toxicity. The proposed permit will not 

impose a chronic WET limit. King County must retest the effluent before submitting an 

application for permit renewal. 

• If this facility makes process or material changes which, in Ecology's opinion, increase 

the potential for effluent toxicity, then Ecology may (in a regulatory order, by permit 

modification, or in the permit renewal) require the facility to conduct additional effluent 

characterization 

• If WET testing conducted for submittal with a permit application fails to meet the 

performance standards in WAC 173-205-020, Ecology will assume that effluent 

toxicity has increased. King County may demonstrate to Ecology that effluent toxicity 

has not increased by performing additional WET testing after the process or material 

changes have been made. 

G. Human Health 

Washington’s water quality standards include 91 numeric human health-based criteria that 

Ecology must consider when writing NPDES permits. These criteria were established in 

1992 by the U.S. EPA in its National Toxics Rule (40 CFR 131.36). The National Toxics 

Rule allows states to use mixing zones to evaluate whether discharges comply with human 

health criteria. 

Ecology determined the effluent may contain chemicals of concern for human health, based 

on (1) the facility’s status as an EPA major discharger, and (2) data or information 

indicating regulated chemicals occur in the discharge. 
Fact Sheet for NPDES Permit WA-002958-1 Page 44 of 101 

King County South Wastewater Treatment Plant 

Ecology evaluated the discharge's potential to violate the water quality standards as required by 

40 CFR 122.44(d) by following the procedures published in the Technical Support Document for 

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

to make a reasonable potential determination. The evaluation showed that the discharge has no 

reasonable potential to cause a violation of water quality standards, and an effluent limit is not 

needed. 

H. Sediment Quality 

The aquatic sediment standards (Chapter 173-204 WAC) protect aquatic biota and human 

health. Under these standards Ecology may require a facility to evaluate the potential for its 

discharge to cause a violation of sediment standards (WAC 173-204-400). You can obtain 

additional information about sediments at the Aquatic Lands Cleanup Unit website. 

http://www.ecy.wa.gov/programs/tcp/smu/sediment.html 

Ecology determined that the South WWTP discharge may have the potential to cause a 

violation of the sediment quality standards because: 

• In some of the past testing, detection limits were above the SQS numeric criteria. 

• In 1997, three locations had detected concentrations of hexachlorobenzene above the SQS 

numeric criteria for benthic toxicity. 

• King County has previously collected sediment samples from the top 2 centimeters of 

sediment in accordance with past permit requirements. Ecology now bases compliance 

on the top 10 centimeters of sediment, which is the biologically active zone. 

• King County has not performed sediment chemical analysis since 2001, and has not been 

required to conduct biological tests at locations near the outfalls. 

The proposed permit includes a condition requiring King County to: 

• Sample and analyze sediments in the vicinity of South WWTP’s outfall to characterize

sediment quality (the nature and extent of chemical contamination and biological toxicity) 

in the vicinity of the Permittee’s discharge locations. Specifically, sediment sampling will 

be required for 0 to 10 cm depth at 8 locations near the two outfalls. Chemical analysis of 

the 47 chemicals in the sediment management standards plus conventional analytes will be 

required at all 8 sites. Bioassays will be performed, if the chemical concentrations are near 

or above the sediment management standards numeric chemical criteria. 

• The Permittee must develop a Sampling and Analysis Plan in accordance with the 

Sediment Sampling and Analysis Plan Appendix. The Sampling and Analysis Plan must 

be approved by the Department of Ecology before performing sediment sampling. After 

the sediment sampling is completed, the Permittee must submit a Sediment Data Report 

and Environmental Information Management (EIM) templates to the Department of 

Ecology for review and approval. 

• If the sediment evaluation shows toxicity at any station, the Permittee must perform 

additional testing to investigate the source of sediment toxicity. 
Fact Sheet for NPDES Permit WA-002958-1 Page 45 of 101 

King County South Wastewater Treatment Plant 

I. Ground Water Quality Limits 

The ground water quality standards (Chapter 173-200 WAC) protect beneficial uses of 

ground water. Permits issued by Ecology must not allow violations of those standards 

(WAC 173-200-100). 

King County South WWTP does not discharge wastewater to the ground. No permit limits 

are required to protect ground water. 

J. Comparison of Effluent Limits With the Previous Permit Issued on September 30, 2004 

There were no changes in effluent limits from the permit issued in 2004. 

Table 18. Comparison of Effluent Limits 

Basis of 

Limit 

Previous Effluent Limits: Puget 

Sound Outfall #001 

Proposed Effluent Limits: 

Puget Sound Outfall #001 

Average 

Monthly

Average 

Weekly

Average 

Monthly

Average 

Weekly

Biochemical 

Oxygen 

Demand (5-day) 

Technology 30 mg/L, 

36,000 lbs/day, 

85% min. removal

45 mg/L, 

54,000 lbs/day

30 mg/L, 

36,000 lbs/day, 

85% min. removal 

45 mg/L, 

54,000 lbs/day

Total 

Suspended 

Solids 

Technology 30 mg/L, 

36,000 lbs/day, 

85% min. removal

45 mg/L, 

54,000 lbs/day

30 mg/L, 

36,000 lbs/day, 

85% min. removal 

45 mg/L, 

54,000 lbs/day

Fecal Coliform 

Bacteria 

Technology 200/100 mL 400/100 mL 200/100 mL 400/100 mL 

pH Technology 6.0-9.0 6.0-9.0 6.0-9.0 6.0-9.0 

Total Residual 

Chlorine 

Technology 0.5 mg/L, 

600 lbs/day 

0.75 mg/L 1 0.5 mg/L 0.75 mg/L 1

 Previous Effluent Limits: 

Green River-Maintenance

Proposed Effluent Limits2: 

Green River-Maintenance

Parameter Average 

Monthly

Maximum 

Daily

Average 

Monthly

Maximum 

Daily

BOD5 daily 

maximum 

 NA 20 mg/L NA 20 mg/L 

TSS, daily 

maximum 

 NA 20 mg/L NA 20 mg/L 

Fecal Coliform 

Bacteria, 

daily max. 

 NA 200/100 mL NA 200/100 mL 

pH NA 6.0-9.0 NA 6.0-9.0 

Parameter Average 

Monthly

Maximum 

Daily

Average 

Monthly

Maximum 

Daily

Total Residual 

Chlorine 

NA 171 ug/L NA 171 ug/L 

1

 Represents a Maximum Daily Limit 

2

 No limits are proposed for an emergency discharge to the Green River. 
Fact Sheet for NPDES Permit WA-002958-1 Page 46 of 101 

King County South Wastewater Treatment Plant 

IV. MONITORING REQUIREMENTS 

Ecology requires monitoring, recording, and reporting (WAC 173-220-210 and 40 CFR 122.41) 

to verify that the treatment process is functioning correctly and that the discharge complies with 

the permit’s effluent limits. 

The monitoring schedule is detailed in the proposed permit under Condition S2. Specified 

monitoring frequencies take into account the quantity and variability of the 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 (Publication Number 92-09) for an activated sludge secondary treatment 

plant. 

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

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

program and also by EPA under 40 CFR 503. 

As a pretreatment publicly-owned treatment works (POTW), King County is required to sample 

influent, final effluent, and sludge for toxic pollutants in order to characterize the industrial input. 

Sampling is also done to determine if pollutants interfere with the treatment process or pass through 

the plant to the biosolids or the receiving water. King County will use the monitoring data to 

develop local limits which commercial and industrial users must meet. 

The proposed permit requires King County to monitor for sediment toxicity to further characterize 

the sediments near the outfall. 

A. Lab Accreditation 

Ecology requires that facilities must use a laboratory registered or accredited under the 

provisions of Chapter 173-50 WAC, Accreditation of Environmental Laboratories, to prepare 

all monitoring data (with the exception of certain parameters). Ecology accredited the 

laboratory at this facility for General Chemistry and Microbiology. The County’s 

environmental lab at W. Ewing Street is additionally accredited for trace metals by ICP-OES 

and ICP-MS, mercury, inorganics, organics by GC and GC-MS, bioassays, and microbiology in 

matrices, including liquids, sediments, and tissues.
Fact Sheet for NPDES Permit WA-002958-1 Page 47 of 101 

King County South Wastewater Treatment Plant 

V. OTHER PERMIT CONDITIONS 

A. Reporting and Record Keeping 

Ecology based permit Condition S3 on our authority to specify any appropriate reporting and 

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

B. 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 King County to 

take the actions detailed in proposed permit Requirement S4 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 S4 restricts the amount of flow. 

C. Operation 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. Ecology included it to ensure 

proper operation and regular maintenance of equipment, and to ensure that King County takes 

adequate safeguards so that it uses constructed facilities to their optimum potential in terms of 

pollutant capture and treatment. 

D. Pretreatment 

Duty to Enforce Discharge Prohibitions 

This provision prohibits the publicly-owned treatment works (POTW) from authorizing or 

permitting an industrial discharger to discharge certain types of waste into the sanitary sewer. 

• The first section of the pretreatment requirements prohibits the POTW from accepting 

pollutants which causes “pass-through” or “interference.” This general prohibition is 

from 40 CFR §403.5(a). Appendix B of this fact sheet defines these terms. 

• The second section reinforces a number of specific state and federal pretreatment 

prohibitions found in WAC 173-216-060 and 40 CFR §403.5(b). These reinforce that 

the POTW may not accept certain wastes, which: 

• Are prohibited due to dangerous waste rules. 

• Are explosive or flammable. 

• Have too high or low of a pH (too corrosive, acidic or basic). 

• May cause a blockage such as grease, sand, rocks, or viscous materials. 

• Are hot enough to cause a problem. 

• Are of sufficient strength or volume to interfere with treatment. 

• Contain too much petroleum-based oils, mineral oil, or cutting fluid. 

• Create noxious or toxic gases at any point. 
Fact Sheet for NPDES Permit WA-002958-1 Page 48 of 101 

King County South Wastewater Treatment Plant 

40 CFR Part 403 contains the regulatory basis for these prohibitions, with the exception 

of the pH provisions which are based on WAC 173-216-060. 

• The third section of pretreatment conditions reflects state prohibitions on the POTW 

accepting certain types of discharges unless the discharge has received prior written 

authorization from Ecology. These discharges include: 

• Cooling water in significant volumes. 

• Stormwater and other direct inflow sources. 

• Wastewaters significantly affecting system hydraulic loading, which do not 

require treatment. 

Ecology delegated authority to King County for permitting, monitoring, and enforcement over 

industrial users discharging to their treatment system to provide more direct and effective 

control of pollutants. Ecology oversees the delegated Industrial Pretreatment Program to 

assure compliance with federal pretreatment regulations (40 CFR Part 403) and categorical 

standards and state regulations (Chapter 90.48 RCW and Chapter 173-216 WAC). 

E. Solid Waste Control 

To prevent water quality problems, the facility 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, and by Ecology under Chapter 70.95J RCW, Chapter 173-308 WAC “Biosolids 

Management,” and Chapter 173-350 WAC “Solid Waste Handling Standards.” The disposal 

of other solid waste is under the jurisdiction of the King County Health Department. 

F. Spill Plan 

This facility stores a quantity of chemicals on-site that have the potential to cause water 

pollution if accidentally released. Ecology can require a facility to develop best 

management plans to prevent this accidental release [Section 402(a)(1) of the Federal Water 

Pollution Control Act (FWPCA) and RCW 90.48.080]. 

The proposed permit requires this facility to develop and implement a plan for preventing 

the accidental release of pollutants to state waters and for minimizing damages if such a 

spill occurs. 

G. Outfall Evaluation 

The proposed permit requires King County to conduct an outfall inspection and submit a 

report detailing the findings of that inspection (Condition S13). The inspection must 

evaluate the physical condition of the discharge pipe and diffusers, and evaluate the extent 

of sediment accumulations in the vicinity of the outfall. 
Fact Sheet for NPDES Permit WA-002958-1 Page 49 of 101 

King County South Wastewater Treatment Plant 

H. General Conditions 

Ecology bases the standardized General Conditions on state and federal law and regulations. 

They are included in all individual municipal NPDES permits issued by Ecology. 

VI. PERMIT ISSUANCE PROCEDURES 

A. Permit Modifications 

Ecology may modify this permit to impose numerical limits, if necessary, to comply with 

water quality standards for surface waters, with sediment quality standards, or with water 

quality standards for ground waters, based on new information from sources such as 

inspections, effluent monitoring, outfall studies, and effluent mixing studies. 

Ecology may also modify this permit to comply with new or amended state or federal 

regulations. 

B. Proposed Permit Issuance 

This proposed permit meets all statutory requirements for Ecology to authorize a wastewater 

discharge. The permit includes limits and conditions to protect human health and aquatic 

life, and the beneficial uses of waters of the state of Washington. Ecology proposes to issue 

this permit for a term of five years. 
Fact Sheet for NPDES Permit WA-002958-1 Page 50 of 101 

King County South Wastewater Treatment Plant 

VII. REFERENCES FOR TEXT AND APPENDICES 

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. 

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. 

2006. Permit Writer’s Manual. Publication Number 92-109 

(http://www.ecy.wa.gov/biblio/92109.html) 

 Laws and Regulations (http://www.ecy.wa.gov/laws-rules/index.html) 

 Permit and Wastewater Related Information 

(http://www.ecy.wa.gov/programs/wq/wastewater/index.html) 

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.) 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 51 of 101 

King County South Wastewater Treatment Plant 

APPENDIX A—PUBLIC INVOLVEMENT INFORMATION 

Ecology proposes to reissue a permit to King County’s South WWTP. The permit includes 

wastewater discharge limits and other conditions. This fact sheet describes the facility and 

Ecology’s reasons for requiring permit conditions. 

Ecology placed a Public Notice of Application on April 16, 2009, and April 23, 2009, in The 

Seattle Times to inform the public about the submitted application and to invite comments on the 

reissuance of this permit. 

Ecology placed a Public Notice of Draft on July 31, 2009, in The Seattle Times to inform the 

public and to invite comments on the proposed draft National Pollutant Discharge Elimination 

System permit and fact sheet. 

The notice – 

• Told where copies of the draft permit and fact sheet were available for public evaluation (a 

local public library, the closest regional or field office, posted on our website). 

• Offered to provide the documents in an alternate format to accommodate special needs. 

• Asked people to tell us how well the proposed permit would protect the receiving water. 

• Invited people to suggest fairer conditions, limits, and requirements for the permit. 

• Invited comments on Ecology’s determination of compliance with antidegradation rules. 

• Urged people to submit their comments, in writing, before the end of the comment period. 

• Explained the next step(s) in the permitting process. 

Ecology held an informal public meeting and a formal hearing on September 3, 2009, at King 

County’s regional Bellevue Library to obtain additional comments regarding the South WWTP 

NPDES Permit. 

Ecology has published a document entitled Frequently Asked Questions about Effective Public 

Commenting which is available on our website at http://www.ecy.wa.gov/biblio/0307023.html. 

You may obtain further information from Ecology by telephone, 425-649-7201, or by writing to 

the address listed below. 

Water Quality Permit Coordinator 

Department of Ecology 

Northwest Regional Office 

3190 160th Avenue SE 

Bellevue, WA 98008-5452 

The author of this permit and fact sheet is Mark Henley, P.E. 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 52 of 101 

King County South Wastewater Treatment Plant 

APPENDIX B—GLOSSARY 

1-DMax or 1-day maximum temperature—The highest water temperature reached on any 

given day. This measure can be obtained using calibrated maximum/minimum thermometers 

or continuous monitoring probes having sampling intervals of thirty minutes or less. 

7-DADMax or 7-day average of the daily maximum temperatures—The arithmetic average 

of seven consecutive measures of daily maximum temperatures. The 7-DADMax for any 

individual day is calculated by averaging that day's daily maximum temperature with the 

daily maximum temperatures of the three days prior and the three days after that date.

Acute Toxicity—The lethal effect of a compound on an organism that occurs in a short period of 

time, usually 48 to 96 hours. 

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

and treatment.” AKART is a technology-based approach to limiting pollutants from 

wastewater discharges which requires an engineering judgment and an economic judgment. 

AKART must be applied to all wastes and contaminants prior to entry into waters of the state 

in accordance with RCW 90.48.010 and 520, WAC 173-200-030(2)(c)(ii), and WAC 

173-216-110(1)(a). 

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. 

Annual Average Design Flow (AADF)—The average of the daily flow volumes anticipated to 

occur over a calendar year. 

Average Monthly Discharge Limit—The average of the measured values obtained over a 

calendar month's time.

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 receiving 

waters 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. 

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

also extremely toxic to aquatic life. 
Fact Sheet for NPDES Permit WA-002958-1 Page 53 of 101 

King County South Wastewater Treatment Plant 

Chronic Toxicity—The effect of a compound 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. 

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 for the purpose of determining the 

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

and regulations. In addition it includes 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 85 percent removal 

requirement. Ecology may conduct additional sampling. 

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

different times, formed either by continuous sampling or by mixing 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 (DF)—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 percent effluent 

fraction, for example, 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 

must contain the appropriate information required in WAC 173-240-060 or 173-240-130. 

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. 
Fact Sheet for NPDES Permit WA-002958-1 Page 54 of 101 

King County South Wastewater Treatment Plant 

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

period of time as is feasible. 

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. 

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 Limit—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. 

Maximum Day Design Flow (MDDF)—The largest volume of flow anticipated to occur during 

a one-day period, expressed as a daily average. 

Maximum Month Design Flow (MMDF)—The largest volume of flow anticipated to occur 

during a continuous 30-day period, expressed as a daily average. 

Maximum Week Design Flow (MWDF)—The largest volume of flow anticipated to occur 

during a continuous 7-day period, expressed as a daily average. 

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

measured and reported with 99 percent confidence that the pollutant concentration is above 

zero and is determined from analysis of a sample in a given matrix containing the pollutant. 

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—An area 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. 

pH—The pH of a liquid measures its acidity or alkalinity. It is the negative logarithm of the 

hydrogen ion concentration. A pH of 7 is defined as neutral, and large variations above or 

below this value are considered harmful to most aquatic life. 

Peak Hour Design Flow (PHDF)—The largest volume of flow anticipated to occur during a 

one-hour period, expressed as a daily or hourly average. 

Peak Instantaneous Design Flow (PIDF)—The maximum anticipated instantaneous flow. 
Fact Sheet for NPDES Permit WA-002958-1 Page 55 of 101 

King County South Wastewater Treatment Plant 

Quantitation Level (QL)—The smallest detectable concentration of analyte greater than the 

Method Detection Limit (MDL) where the accuracy (precision &bias) achieves the 

objectives of the intended purpose. 

Reasonable Potential—A reasonable potential to cause a water quality violation, or loss of 

sensitive and/or important habitat. 

Responsible Corporate Officer—A president, secretary, treasurer, or vice-president of the 

corporation in charge of a principal business function, or any other person who performs 

similar policy- or decision-making functions for the corporation, or the manager of one or 

more manufacturing, production, or operating facilities employing more than 250 persons or 

have gross annual sales or expenditures exceeding $25 million (in second quarter 1980 

dollars), if authority to sign documents has been assigned or delegated to the manager in 

accordance with corporate procedures (40 CFR 122.22). 

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 is the particulate material in an effluent. 

Large quantities of TSS discharged to receiving waters 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. 

Solid Waste—All putrescible and non-putrescible solid and semisolid wastes including, but not 

limited to, garbage, rubbish, ashes, industrial wastes, swill, sewage sludge, demolition and 

construction wastes, abandoned vehicles or parts thereof, contaminated soils and 

contaminated dredged material, and recyclable materials. 

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

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. 

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

with technology-based permit effluent limits 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 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 receiving waters. 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 56 of 101 

King County South Wastewater Treatment Plant 

APPENDIX C—SOUTH WWTP APPLICATION PRIORITY POLLUTANT DATA SUMMARY 

 

POLLUTANT 

MAXIMUM DAILY 

DISCHARGE 

AVERAGE DAILY DISCHARGE

ANALYTICAL 

METHOD Conc. Units Mass Units Conc. Units Mass Units Number ML/MDL 

of 

Samples 

METALS (TOTAL RECOVERABLE), CYANIDE, PHENOLS, AND HARDNESS. 

ANTIMONY 0.67 μg/L 0.45 lbs/d <0.51 μg/L <0.30 lbs/d 32 EPA200.8 0.5 

ARSENIC 1.60 μg/L 1.17 lbs/d 1.26 μg/L 0.76 lbs/d 34 EPA200.8 0.5 

BERYLLIUM <MDL μg/L <0.18 lbs/d <MDL μg/L <0.12 lbs/d 32 EPA200.8 0.2 

CADMIUM 0.30 μg/L 0.17 lbs/d <0.11 μg/L <0.064 lbs/d 32 EPA200.8 0.1 

CHROMIUM 4.07 μg/L 2.28 lbs/d 0.87 μg/L 0.51 lbs/d 32 EPA200.8 0.4 

COPPER 42.40 μg/L 24.01 lbs/d 16.5 μg/L 9.51 lbs/d 32 EPA200.8 0.4 

LEAD 2.00 μg/L 1.12 lbs/d 0.66 μg/L 0.38 lbs/d 32 EPA200.8 0.2 

MERCURY 0.058 μg/L 0.045 lbs/d <0.05 μg/L <0.03 lbs/d 33 CVAA 

EPA245.1 0.05 

NICKEL 4.45 μg/L 2.34 lbs/d 2.99 μg/L 1.78 lbs/d 33 EPA200.8 0.3 

SELENIUM <MDL μg/L <1.35 lbs/d <MDL μg/L <0.89 lbs/d 33 EPA200.8 1.5 

SILVER 0.84 μg/L 0.48 lbs/d <0.35 μg/L <0.21 lbs/d 32 EPA200.8 0.2 

THALLIUM <MDL μg/L 0.18 lbs/d <MDL μg/L <0.117 lbs/d 33 EPA200.8 0.04-0.2 

ZINC 68.0 μg/L 38.5 lbs/d 29.0 μg/L 17.4 lbs/d 33 EPA200.8 0.5 

CYANIDE 0.028 mg/L 14.61 lbs/d <0.008 mg/L <5.09 lbs/d 33 SM4500-CN-I,E 0.005 

TOTAL PHENOLIC 

COMPOUNDS 0.080 mg/L 47.2 lbs/d <0.011 mg/L <6.55 lbs/d 24 EPA 420.1 & 

420.2 

0.005-

0.02 

HARDNESS (AS 

CaCO3) 99.4 mg/L 105,50

0 lbs/d 64.8 mg/L 44,632 lbs/d 75 SM2340C 0.1 

Use this space (or a separate sheet) to provide information on other metals requested by the permit writer 

 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 57 of 101 

King County South Wastewater Treatment Plant 

POLLUTANT 

MAXIMUM DAILY 

DISCHARGE 

AVERAGE DAILY DISCHARGE

ANALYTICAL 

METHOD Conc. Units Mass Units Conc. Units Mass Units Number ML/MDL 

of 

Samples 

VOLATILE ORGANIC COMPOUNDS 

ACROLEIN <MDL μg/L <3.886 lbs/d <MDL μg/L <2.902 lbs/d 23 EPA 624 5 

ACRYLONITRILE <MDL μg/L <3.886 lbs/d <MDL μg/L <2.902 lbs/d 23 EPA 624 5 

BENZENE <MDL μg/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

BROMOFORM <MDL μg/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

CARBON 

TETRACHLORIDE <MDL μg/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

COLORBENZENE <MDL μg/L <0.777 lbs/d <MDL μg/L <0.580 lbs/d 23 EPA 624 1 

CHLOROBIDBROMOMETHANE <MDL μg/L <0.777 lbs/d <MDL μg/L <0.58 lbs/d 23 EPA 624 1 

CHLOROETHANE <MDL μg/L <0.777 lbs/d <MDL μg/L <0.580 lbs/d 23 EPA 624 1 

2-CHLOROETHYLVINYL ETHER <MDL μg/L <0.777 lbs/d <MDL μg/L <0.580 lbs/d 23 EPA 624 1 

CHOLOROFORM 2.18 μg/L 1.565 lbs/d <1.32 μg/L <0.802 lbs/d 23 EPA 624 1.32 

DICHLOROBROMOMETHANE <MDL μg/L <0.777 lbs/d <MDL μg/L <0.58 lbs/d 23 EPA 624 1 

1,1-

DICHLOROETHANE <MDL ug/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

TRANS-1,2-

DICHLOROETHYLENE 

<MDL ug/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

1,1-

DICHLOROPROPANE <MDL μg/L <0.777 lbs/d <MDL μg/L <0.58 lbs/d 23 EPA 624 1 

ETHYLBENZENE <MDL ug/L <0.777 lbs/d <MDL ug/L <0.58 lbs/d 23 EPA 624 1 

METHYL BROMIDE <MDL ug/L <3.49 lbs/d <MDL ug/L <1.92 lbs/d 23 EPA 624 5 

METHYL 

CHLORIDE <MDL ug/L <0.78 lbs/d <MDL ug/L <0.58 lbs/d 23 EPA 624 1 

METHYLENE 

CHLORIDE 7 ug/L 4.164 lbs/d <4.74 ug/L <2.74 lbs/d 23 EPA 624 5 

1,1,2,2-

TETRACHLOROETHANE 

<MDL ug/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

TETRACHLOROETHYLENE <MDL μg/L <0.777 lbs/d <MDL μg/L <0.58 lbs/d 23 EPA 624 1 

TOLUENE 3.86 ug/L 1.845 lbs/d <1.45 ug/L <0.78 lbs/d 23 EPA 624 4 
Fact Sheet for NPDES Permit WA-002958-1 Page 58 of 101 

King County South Wastewater Treatment Plant 

POLLUTANT 

MAXIMUM DAILY 

DISCHARGE 

AVERAGE DAILY DISCHARGE

ANALYTICAL 

METHOD Conc. Units Mass Units Conc. Units Mass Units Number ML/MDL 

of 

Samples 

1,1,1-

TRICHLOROETHANE <MDL ug/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

1,1,2-

TRICHLOROETHANE <MDL ug/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

TRICHLOROETHYL

ENE <MDL ug/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

VINYL CHLORIDE <MDL ug/L <0.777 lbs/d <MDL ug/L <0.580 lbs/d 23 EPA 624 1 

Use this space (or a separate sheet) to provide information on other metals requested by the permit writer 

 

ACID-EXTRACTABLE COMPOUNDS 

P-CHLORO-MCRESOL <MDL μg/L <1.48 lbs/d <MDL μg/L <1.14 lbs/d 24 EPA 

3520C/625 1.9-2.4 

2-CHLOROPHENOL <MDL μg/L <1.48 lbs/d <MDL μg/L <1.14 lbs/d 24 EPA 

3520C/625 1.9-2.4 

2,4-

DIMETHYLPHENOL <MDL μg/L <0.74 lbs/d <MDL μg/L <0.56 lbs/d 24 EPA 

3520C/625 0.94-1.2 

4,6-DINITRO-OCRESOL <MDL μg/L <1.48 lbs/d <MDL μg/L <1.14 lbs/d 24 EPA 

3520C/625 1.9-2.4 

2,4-

DINITROPHENOL <MDL μg/L <1.48 lbs/d <MDL μg/L <1.14 lbs/d 24 EPA 

3520C/625 1.9-2.4 

2-NITROPHENOL <MDL μg/L <0.74 lbs/d <MDL μg/L <0.56 lbs/d 24 EPA 

3520C/625 0.94-1.2 

4-NITROPHENOL <MDL μg/L <1.48 lbs/d <MDL μg/L <1.14 lbs/d 24 EPA 

3520C/625 1.9-2.4 

PENTA 

CHLOROPHENOL <MDL μg/L <0.74 lbs/d <MDL μg/L <0.56 lbs/d 24 EPA 

3520C/625 0.94-1.2 

PHENOL <MDL μg/L <2.95 lbs/d <MDL μg/L <2.27 lbs/d 24 EPA 

3520C/625 3.9 

2,4,6-TRICHLORO 

PHENOL <MDL μg/L <2.95 lbs/d <MDL μg/L <2.27 lbs/d 24 EPA 

3520C/625 3.8-4.7 

Use this space (or a separate sheet) to provide information on other metals requested by the permit writer 

 

BASE-NEUTRAL COMPOUNDS 

ACENAPHTHENE <MDL μg/L <0.30 lbs/d <MDL μg/L <0.23 lbs/d 24 EPA 

3520C/625 0.38-0.47 

ACENAPHTYLENE <MDL μg/L <0.44 lbs/d <MDL μg/L <0.34 lbs/d 24 EPA 

3520C/625 0.57-0.71 

ANTHRACENE <MDL μg/L <0.44 lbs/d <MDL μg/L <0.34 lbs/d 24 EPA 

3520C/625 0.57-0.71 

BENZIDINE <MDL μg/L <17.88 lbs/d <MDL μg/L <13.72 lbs/d 24 EPA 

3520C/625 23-28 

BENZO(A) 

ANTHRACENE <MDL μg/L <0.44 lbs/d <MDL μg/L <0.34 lbs/d 24 EPA 

3520C/625 0.57-0.71 
Fact Sheet for NPDES Permit WA-002958-1 Page 59 of 101 

King County South Wastewater Treatment Plant 

 

POLLUTANT 

MAXIMUM DAILY 

DISCHARGE 

AVERAGE DAILY DISCHARGE

ANALYTICAL 

METHOD Conc. Units Mass Units Conc. Units Mass Units Number ML/MDL 

of 

Samples 

FLUORANTHENE <MDL μg/L <0.44 lbs/d <MDL μg/L <0.34 lbs/d 24 EPA 

3520C/625 0.57-0.71 

FLUORENE <MDL μg/L <0.44 lbs/d <MDL μg/L <0.34 lbs/d 24 EPA 

3520C/625 0.57-0.71 

HEXACHLORO 

BENZENE <MDL μg/L <0.44 lbs/d <MDL μg/L <0.34 lbs/d 24 EPA 

3520C/625 0.57-0.71 

HEXACHLOROBUT

ADIENE <MDL μg/L <0.74 lbs/d <MDL μg/L <0.57 lbs/d 24 EPA 

3520C/625 0.94-1.2 

HEXACHLOROCYCLOPENTADIENE <MDL μg/L <0.74 lbs/d <MDL μg/L <0.57 lbs/d 24 EPA 

3520C/625 0.94-1.2 

HEXA 

CHLOROETHANE <MDL μg/L <0.74 lbs/d <MDL μg/L <0.57 lbs/d 24 EPA 

3520C/625 0.94-1.2 

INDENO(1,2,3-CD) 

PYRENE <MDL μg/L <0.74 lbs/d <MDL μg/L <0.57 lbs/d 24 EPA 

3520C/625 0.94-1.2 

ISOPHORONE <MDL μg/L <0.74 lbs/d <MDL μg/L <0.57 lbs/d 24 EPA 

3520C/625 0.94-1.2 

NAPHTHALENE <MDL μg/L <1.17 lbs/d <MDL μg/L <0.90 lbs/d 24 EPA 

3520C/625 1.5-1.9 

NITROBENZENE <MDL μg/L <0.74 lbs/d <MDL μg/L <0.57 lbs/d 24 EPA 

3520C/625 0.94-1.2 

N-NITROSODI-NPROPYLAMINE <MDL μg/L <0.74 lbs/d <MDL μg/L <0.57 lbs/d 24 EPA 

3520C/625 0.94-1.2 

N-NITROSODIMETHYLAMINE <MDL μg/L <2.95 lbs/d <MDL μg/L <2.72 lbs/d 24 EPA 

3520C/625 3.8-4.7 

N-NITROSODIPHENYLAMINE <MDL μg/L <0.74 lbs/d <MDL μg/L <0.97 lbs/d 24 EPA 

3520C/625 0.94-1.2 

PHENANTHRENE <MDL μg/L <0.44 lbs/d <MDL μg/L <0.34 lbs/d 24 EPA 

3520C/625 0.57-0.71 

PYRENE <MDL μg/L <0.44 lbs/d <MDL μg/L <0.34 lbs/d 24 EPA 

3520C/625 0.57-0.71 

1,2,4-

TRICHLOROBENZENE <MDL μg/L <0.44 lbs/d <MDL μg/L <0.44 lbs/d 24 EPA 

3520C/625 0.57-0.71 

Use this space (or a separate sheet) to provide information on other metals requested by the permit writer 

 

Use this space (or a separate sheet) to provide information on other metals requested by the permit writer 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 60 of 101 

King County South Wastewater Treatment Plant 

APPENDIX D—SOUTH WWTP DISCHARGE MONITORING REPORT SUMMARY TABLES 

Discharge Monitoring Data – October 2004 to April 2009 
Fact Sheet for NPDES Permit WA-002958-1 Page 61 of 101 

King County South Wastewater Treatment Plant 

Date

BOD, mg/LBOD, mg/LBOD, ppdBOD, ppdTSS, mg/LTSS, mg/LTSS, ppdTSS, ppd

Mnthly 

Ave

Max 

day

Mnthly 

Ave Max day

Mnthly 

Ave Max Day

Mnthly 

Ave Max day

1-Oct-04 205 213 115655 123429 231 259 132103 152714

1-Nov-04 217 237 141967 153571 286 300 186667 2000714

1-Dec-04 209 245 157385 166000 277 297 207933 222000

1-Jan-05 236 288 167407 184000 289 351 207500 224000

1-Feb-05 258 293 163100 18000 238 261 150929 179000

1-Mar-05 257 301 167458 182000 251 293 161700 181000

1-Apr-05 217 275 144286 172000 234 247 157310 164000

1-May-05 208 217 123214 131000 248 261 146069 165000

1-Jun-05 271 289 155267 165000 284 307 162800 172000

1-Jul-05 266 285 140500 15100 293 308 154710 162000

1-Aug-05 259 284 133586 147000 255 295 131194 15000

1-Sep-05 217 231 111000 117000 243 266 123862 139000

1-Oct-05 203 238 104083 125000 241 276 124500 145000

1-Nov-05 195 217 130737 142000 228 242 155519 175000

1-Dec-05 178 207 121667 128000 213 251 153484 173000

1-Jan-06 106 134 114095 120000 145 163 157033 167000

1-Feb-06 149 191 117684 125000 195 217 149808 160000

1-Mar-06 166 179 113789 121000 197 212 134310 145000

1-Apr-06 131 150 73125 87000 210 246 114733 126000

1-May-06 178 200 88643 98000 234 274 117600 135000

1-Jun-06 159 184 88517 101000 251 292 139533 159000

1-Jul-06 167 179 82161 88000 233 241 114839 123000

1-Aug-06 171 18 77750 85000 234 263 107033 121000

1-Sep-06 163 187 76400 90000 239 258 112615 121000

1-Oct-06 183 203 91037 108000 271 302 135000 161000

1-Nov-06 119 176 115760 128000 198 299 190667 209000

1-Dec-06 125 154 114791 130000 188 211 170516 185000

1-Jan-07 194 254 171936 207273 202 234 181675 194047

1-Feb-07 228 260 175349 189959 214 258 163499 188819

1-Mar-07 200 222 173264 188278 190 210 163790 172649

1-Apr-07 223 248 161646 177289 236 300 171296 217415

1-May-07 261 291 169684 183530 284 314 184373 206998

1-Jun-07 266 305 155759 185908 280 302 163794 184306

1-Jul-07 266 281 154919 165367 274 288 159404 162066

1-Aug-07 267 304 150752 178668 279 297 157276 174574

1-Sep-07 258 287 143860 157492 265 279 149373 159556

1-Oct-07 245 286 153475 181750 248 306 155068 193760

1-Nov-07 251 258 167336 175401 252 287 166792 195538

1-Dec-07 208 233 187630 212502 205 218 183212 197848

1-Jan-08 230 253 185376 194462 222 255 179970 207100

1-Feb-08 246 261 180033 182851 234 255 172707 179393

1-Mar-08 251 276 195478 206004 248 265 190174 196611

1-Apr-08 250 275 173840 187373 249 258 176737 187316

1-May-08 272 285 155043 164240 280 304 160027 174982

1-Jun-08 270 317 157417 175848 267 300 156557 166613

1-Jul-08 291 308 128112 139850 284 309 125001 131251

1-Aug-08 276 302 132284 146017 263 279 128507 151526

1-Sep-08 271 287 142891 149496 259 272 136316 141808

1-Oct-08 285 300 152221 161913 264 292 140785 150531

1-Nov-08 253 289 178953 191857 257 284 184084 216825

1-Dec-08 266 305 191900 240824 216 250 155366 173750

1-Jan-09 252 301 214073 225037 216 233 185616 232900

1-Feb-09 290 305 196211 207194 260 278 175071 184177

1-Mar-09 266 302 207950 222730 242 251 189248 191276

1-Apr-09 242 283 159607 206371 259 348 170167 225204

AVE: 223 248 144231 152763 243 270 156587 203983

MIN: 106 18 73125 15100 145 163 107033 15000

MAX: 291 317 214073 240824 293 351 207933 2000714

Limit 251000 235000

85% 213350 199750

Influent
Fact Sheet for NPDES Permit WA-002958-1 Page 62 of 101 

King County South Wastewater Treatment Plant 

Date

Flow, MGDFlow, MGDBOD, mg/LBOD, mg/LBOD, ppdBOD, ppdBOD, % RemovalTSS, mg/LTSS, mg/LTSS, ppdTSS, ppdTSS, % RemovalPHPHFecal Coliform, Fecal Coliform, Cl, mg/LCl, mg/LCal. Cl, ppd

Mnthly 

Ave Max day

Mnthly 

Ave

Wkly 

Ave

Mnthly 

Ave

Wkly 

Ave

Mnthly 

Ave

Mnthly 

Ave

Wkly 

Ave

Mnthly 

Ave

Wkly 

Ave

Mnthly 

Ave

Day 

Min

Day 

Max GEM GM7

Ave 

Monthly

Max 

day

Monthly 

Ave

1-Oct-04 67.9 76.9 14.8 15.3 8371 8543 93 13.9 16.1 8013 10143 94 7 9.8 33 80 0.003 0.02 1.5

1-Nov-04 78 106.9 14 15 9117 9800 93 18 20 11910 14300 94 7 8.2 153 208 0 0.01 0

1-Dec-04 91.3 109.6 15.6 17 12074 15100 93 17 20.3 12910 15400 94 6.4 8.9 67 83 0 0.01 3

1-Jan-05 91 118 15 17 11118 13100 94 17 22 12603 15000 94 6.8 8.3 107 320 0.02 0.19 22

1-Feb-05 75 82 16 19 10315 13000 94 21 24 13425 16300 91 6.9 7.5 64 99 0 0 0

1-Mar-05 78 100 20.5 23.5 13483 15180 92 15.4 17.7 9952 11500 94 6.9 7.3 48 206 0 0 0

1-Apr-05 81 82 15 18 10369 12200 93 13.5 14 9160 9400 94 6.8 8.5 17 22 0 0 0

1-May-05 70 73 10.9 12 6397 7000 95 13.7 18 8100 11000 94 6.8 7.3 37 88 0 0 0

1-Jun-05 68 70 14 18 7787 10000 95 12.5 18 7117 9900 96 6.7 7.2 121 196 0 0 0

1-Jul-05 63 63.7 20.7 23 10924 12000 92 17.3 19 9126 10100 94 6.8 7.4 75 265 0 0 0

1-Aug-05 61.3 61.9 16 18 8155 9100 94 13 14 6687 7500 95 6.4 7.2 108 148 0 0 0

1-Sep-05 61 62.2 14 17 7155 8600 94 15.8 16.6 8043 8400 93 6.8 7.2 95 180 0 0 0

1-Oct-05 62 62.4 12.2 13 6321 6700 94 14.7 17 7703 9000 94 6.8 7.3 50 70 0 0 0

1-Nov-05 81 86.2 14 15 8891 9500 93 20.8 22 14030 14900 91 6.9 7.1 59 134 0 0 0

1-Dec-05 91 133.4 14.4 20 10867 21600 92 25.3 36 20645 40500 88 6.6 7.3 54 115 0 0 0

1-Jan-06 133 158 14.7 23 16855 24700 86 20.4 34 23097 36700 86 6 7.3 66 125 0 0 0

1-Feb-06 96 148 11 11 8835 12400 93 14 15 11311 18200 93 6.5 7 48 76 0 0 0

1-Mar-06 81 90 13.8 16 9333 10500 92 16.4 18.4 11090 11900 92 6.6 7 130 329 0 0.01 0

1-Apr-06 65 78 10 13.7 5720 7900 92 14.2 19 7853 11000 93 6 7.4 88 197 0.01 0.05 3

1-May-06 60 70 14.4 20 7161 9700 92 12.9 14.8 6448 7400 94 6.4 7.8 51 67 0 0.03 2

1-Jun-06 66 77 12 15 6514 8000 93 9.9 11 5480 6200 96 6.5 7.2 86 100 0 0.02 2

1-Jul-06 59 65 11.9 13.4 5835 6600 93 16.1 18.9 7865 8700 93 6.8 7.1 134 294 0 0.03 0

1-Aug-06 55 58 9.7 11 4426 5000 94 11.7 16 5345 7000 95 6.1 7.5 42 108 0 0.05 2

1-Sep-06 56 62 9 10 4293 4800 94 14.5 17 6803 8300 94 6.6 7.4 79 156 0 0.03 1

1-Oct-06 59 74 11.4 14.1 5664 7500 94 11.7 13.9 5794 7300 96 6.5 8.6 40 44 0 0 0

1-Nov-06 119 183 15 18 15569 22157 88 30 41 32357 50971 85 6.3 7 56 135 0 0.03 2

1-Dec-06 111 193 14 18 14133 21700 89 23 30 22455 35000 88 6.3 6.9 41 86 0 0 0

1-Jan-07 104 142.7 22 26 18777 21394 89 25 34 22760 36308 87 6.3 7.1 110 249 0.05 0.05 43.5

1-Feb-07 89.1 115.2 20 21 15262 17447 91 17 18 12850 14838 92 6.7 7.2 49 105 0.05 0.05 37.2

1-Mar-07 100.7 131.5 18 19 15154 17003 91 18 21 15494 18647 91 6.6 7 32 116 0.05 0.05 42

1-Apr-07 82.9 95.8 25 30 16969 20271 89 22 25 15192 16891 91 6.6 8.8 96 300 0.05 0.05 34.6

1-May-07 72.8 81 18 29 10918 19169 94 17 22 10587 13766 94 6.6 7.8 57 85 0.05 0.05 30.4

1-Jun-07 66.5 70.3 18 21 10191 11651 93 13 15 7296 8111 95 6.6 7.2 110 355 0.05 0.05 27.7

1-Jul-07 67.3 77.2 12 14 6595 8178 96 8 9 4651 5108 97 6.2 6.8 56 173 0.05 0.08 28.6

1-Aug-07 64.7 70 15 19 8072 9890 95 12 15 6430 7847 96 6.5 6.9 85 241 0.06 0.17 30

1-Sep-07 62.7 84.2 15 17 7906 8987 94 16 18 8302 9642 94 6.5 7.2 105 247 0.05 0.14 27.8

1-Oct-07 70.4 82.8 15 17 9063 10124 94 13 19 7615 11394 95 6 7.3 150 308 0.05 0.05 29.4

1-Nov-07 74.4 95.8 17 21 10934 12993 93 15 21 9411 13286 94 6.6 7.2 170 254 0.05 0.15 34.2

1-Dec-07 99.4 234.9 23 24 19843 29360 90 25 27 21218 32134 89 6.6 7.3 141 363 0.29 0.75 231.3

1-Jan-08 89.7 116.6 22 26 16617 18282 91 24 29 17989 20585 90 6.7 7.2 35 39 0.07 0.17 49.2

1-Feb-08 79.9 104.1 23 28 15193 20311 92 24 30 16590 21710 90 6.7 7.4 35 62 0.05 0.05 33.3

1-Mar-08 81.6 106.5 20 21 13795 15267 93 23 25 15653 18520 92 6.9 7.3 37 78 0.06 0.16 44.8

1-Apr-08 75.6 89.1 17 22 10405 17768 94 21 28 13513 21306 92 7 7.4 135 259 0.05 0.05 31.5

1-May-08 60.4 65.8 19 21 9811 10519 94 16 18 8214 9073 95 7.1 7.5 106 145 0.05 0.07 25.6

1-Jun-08 62.4 74.2 18 20 9145 10226 94 13 14 6962 8126 95 7.1 7.5 84 171 0.05 0.12 28

1-Jul-08 45.2 55.1 17 19 6547 7584 95 17 20 6578 8192 95 7.3 7.5 48 66 0.05 0.07 19.1

1-Aug-08 52.1 76.7 17 18 7143 8777 95 15 19 6731 9291 95 7.2 7.5 20 23 0.05 0.07 22

1-Sep-08 57.7 64.6 13 13 6151 6578 96 9 11 4388 4999 97 6.8 8.4 25 43 0.05 0.11 25.1

1-Oct-08 59.2 65.3 16 25 8188 12753 16 22 7908 11281 6.9 7.6 34 53 0.06 0.22 28.7

1-Nov-08 80.5 144.4 22 25 15108 19881 18 20 12195 15558 6.8 6.9 85 185 0.06 0.18 39.3

1-Dec-08 81.6 132.6 23 27 15799 21514 23 26 15517 24360 6.7 6.9 38 56 0.06 0.17 39.9

1-Jan-09 100.8 200.7 23 26 20186 29891 27 30 23121 32420 6.3 6.9 35 104 0.06 0.19 53.4

1-Feb-09 73.5 84.4 19 24 11865 14750 19 20 11405 13378 6.5 6.9 23 56 0.05 0.05 30.6

1-Mar-09 87.7 105.8 20 22 14582 18491 24 30 17672 24443 6.5 6.8 94 145 0.05 0.05 36.6

1-Apr-09 75 124.4 18 20 11231 15467 19 24 11958 16810 6.3 6.9 43 80 0.05 0.05 31.3

AVE: 76.34 98.36 16 19 10665 13545 93 17 21 11696 15615 93 6.6 7.4 73 152 0 0 8

MIN: 45.20 55.10 9 10 4293 4800 86 8 9 4388 4999 85 6.0 6.8 17 22 0 0 0

MAX: 133.00 234.90 25 30 20186 29891 96 30 41 32357 50971 97 7.3 9.8 170 363 0 0 44

Limit 144.00 30 45 36000 54000 85 30 45 36000 54000 85 6.0 9.0 200 400 0.5 0.75

85% 122.40

Effluent
Fact Sheet for NPDES Permit WA-002958-1 Page 63 of 101 

King County South Wastewater Treatment Plant 

APPENDIX E—SOUTH WWTP DISCHARGE MONITORING REPORT GRAPHS 

South WWTP – Influent TSS (Mass Basis) 

South WWTP – Influent TSS (Concentration Basis) 

0

50,000

100,000

150,000

200,000

250,000

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Apr-09

Influent TSS, lbs/day

Monthly Avg

85% of Design Loading

100% Design Loading

0

50

100

150

200

250

300

350

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Monthly Average Influent TSS, mg/L
Fact Sheet for NPDES Permit WA-002958-1 Page 64 of 101 

King County South Wastewater Treatment Plant 

South WWTP – Influent BOD5 (Mass Basis) 

South WWTP – Influent BOD5 (Concentration Basis) 

 

0

50,000

100,000

150,000

200,000

250,000

300,000

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Influent BOD5, lbs/day

Monthly Avg

85% of Design Loading

100% Design Loading

0

50

100

150

200

250

300

350

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Monthly Average Influent BOD5, mg/L
Fact Sheet for NPDES Permit WA-002958-1 Page 65 of 101 

King County South Wastewater Treatment Plant 

South WWTP – Influent Flow 

South WWTP – Effluent pH 

 

0

20

40

60

80

100

120

140

160

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Influent 

Flow, MGD

Average Monthly Flow

85% of Max Month Flow

100% of Max Month Flow

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

Jan-04

Aug-04

Feb-05

Sep-05

Mar-06

Oct-06Apr-07

Nov-07

Jun-08

Dec-08

Jul-09

Effluent pH, Std. Units

Day Min

permit range: 6.0 - 9.0 Day Max
Fact Sheet for NPDES Permit WA-002958-1 Page 66 of 101 

King County South Wastewater Treatment Plant 

South WWTP – Effluent TSS (Mass Basis) 

South WWTP – Effluent TSS (Concentration Basis) 

 

0

10000

20000

30000

40000

50000

60000

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Effluent TSS, ppd

Monthly Avg

Weekly Avg

Monthly Avg permit limit

Weekly Avg permit limit

0

5

10

15

20

25

30

35

40

45

50

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Effluent TSS, mg/L

Monthly Avg

Weekly Avg

Monthly Avg permit limit

Weekly Avg permit limit
Fact Sheet for NPDES Permit WA-002958-1 Page 67 of 101 

King County South Wastewater Treatment Plant 

South WWTP – Effluent BOD5 (Mass Basis) 

South WWTP – Effluent BOD5 (Concentration Basis) 

 

0

10000

20000

30000

40000

50000

60000

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Effluent 

BOD5, ppd

Monthly Avg

Weekly Avg

Monthly Avg permit limit

Weekly Avg permit limit

0

5

10

15

20

25

30

35

40

45

50

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Effluent 

BOD5, mg/L

Monthly Avg

Weekly Avg

Monthly Avg permit limit

Weekly Avg permit limit
Fact Sheet for NPDES Permit WA-002958-1 Page 68 of 101 

King County South Wastewater Treatment Plant 

South WWTP – Effluent Fecal Coliform Bacteria 

0

50

100

150

200

250

300

350

400

450

Oct-04

Dec-04

Feb-05

Apr-05

Jun-05

Aug-05

Oct-05

Dec-05

Feb-06

Apr-06

Jun-06

Aug-06

Oct-06

Dec-06

Feb-07

Apr-07

Jun-07

Aug-07

Oct-07

Dec-07

Feb-08

Apr-08

Jun-08

Aug-08

Oct-08

Dec-08

Feb-09

Effluent Fecal Coliform, #/100 mL

GEM

GM7

GEM permit limit

GM7 permit limit
Fact Sheet for NPDES Permit WA-002958-1 Page 69 of 101 

King County South Wastewater Treatment Plant 

APPENDIX F—OUTFALL DIAGRAMS 
Fact Sheet for NPDES Permit WA-002958-1 Page 70 of 101 

King County South Wastewater Treatment Plant 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 71 of 101 

King County South Wastewater Treatment Plant 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 72 of 101 

King County South Wastewater Treatment Plant 

Pipe length=10,000 ft. Pipe Dia. = 8 ft. 

Diffuser length = 500 ft. Diffuser Dia. = 

64in. with 168 - 4in. Diameter Ports. 

Plan View 2,150 ft 

Side View

-625 ft MLLW 

0 ft MLLW 

Acute Mixing 

Zone Boundary 

South WWTP Marine Outfall Mixing Zones – North Diffuser. 

665 ft 

Chronic Mixing 

Zone Boundary 

1,650 ft 165 ft 

665 ft 

Not to Scale 

Pipe length=10,000 ft. Pipe Dia. = 8 ft. 

Diffuser length = 500 ft. Diffuser Dia. = 

64in. with 168 - 4in. Diameter Ports. 

Plan View 2,150 ft 

Side View

-625 ft MLLW 

0 ft MLLW 

Acute Mixing 

Zone Boundary 

South WWTP Marine Outfall Mixing Zones – South Diffuser. 

665 ft 

Chronic Mixing 

Zone Boundary 

1,650 ft 165 ft 

665 ft 

Not to Scale 
Fact Sheet for NPDES Permit WA-002958-1 Page 73 of 101 

King County South Wastewater Treatment Plant 

APPENDIX G—WHOLE EFFLUENT TOXICITY (WET) TESTING RESULTS 

ACUTE TEST

King County South Plant Acute WET Test Results as % Survival in 100% Effluent

Test Code Collected Start Date Organism Endpoint % Survival

RMAR1177 2/8/2008 2/8/2008 Daphnia pulex 48-hour Survival 75%

RMAR1178 2/11/2008 2/11/2008 Fathead Minnow 96-hour Survival 88%

RMAR1210 4/2/2008 4/2/2008 Daphnia pulex 48-hour Survival 100%

RMAR1208 4/7/2008 4/7/2008 Fathead Minnow 96-hour Survival 78%

RMAR1298 7/9/2008 7/9/2008 Daphnia pulex 48-hour Survival 100%

RMAR1296 8/18/2008 8/18/2008 Fathead Minnow 96-hour Survival 85%

RMAR1327 10/8/2008 10/8/2008 Daphnia pulex 48-hour Survival 100%

RMAR1325 10/13/2008 10/13/2008 Fathead Minnow 96-hour Survival 93%

Median = 90%

CHRONIC TEST

King County South Plant Chronic WET Test Results as NOEC/LOEC in % Effluent

Test Code Collected Start Date Organism Endpoint NOEC LOEC PMSD

RMAR1180 2/6/2008 2/6/2008 Atlantic Mysid 7-day Survival 12.5 25 15.43%

Biomass 0.43 12.5 15.46%

Weight 0.43 12.5 14.99%

RMAR1179 2/6/2008 2/7/2008 Topsmelt 7-day Survival 12.5 25 12.80%

Biomass 0.43 12.5 16.27%

Weight 0.43 12.5 11.28%

RMAR1209 4/2/2008 4/2/2008 Topsmelt 7-day Survival 25 50 11.96%

Biomass 12.5 25 15.36%

Weight 12.5 25 13.46%

RMAR1207 4/2/2008 4/2/2008 Atlantic Mysid 7-day Survival 50 100 11.63%

Biomass 12.5 25 13.90%

Weight 0.43 12.5 12.22%

RMAR1299 7/9/2008 7/9/2008 Atlantic Mysid 7-day Survival 50 100 12.88%

Biomass 12.5 25 12.92%

Weight 12.5 25 11.83%

RMAR1297 7/9/2008 7/9/2008 Topsmelt 7-day Survival 50 100 14.56%

Biomass 25 50 22.16%

Weight 25 50 18.74%

RMAR1326 10/8/2008 10/8/2008 Topsmelt 7-day Survival 50 100 7.29%

Biomass 50 100 20.18%

Weight 50 > 50 18.53%

RMAR1328 10/8/2008 10/8/2008 Atlantic Mysid 7-day Survival 50 100 15.90%

Biomass 25 50 15.32%

Weight 25 50 12.41%

For Acute toxicity, the performance standard is the median survuval in 100% effluent being equal to or 

greater than 80% and no individual test result showing less than 65% survival in 100% effluent.

Median survival in 100% effluent = 90%. All Acute WET Tests had greater than 65% survival in 100% 

effluent. Therefore, no Acute WET limit required. Permit requires another effluent characterization for acute 

WET (WAC 173-245). 

For Chronic toxicity, the performance standard is no chronic toxicity test demonstrating a statistically 

significant difference in response between the control and a test concentration equal to the acute critical 

effluent concentration (ACEC). For the tests below, the previous ACEC of 0.43% effluent was used.

The proposed permit includes lower (more restrictive) dilution factors than the previous permit. This results in a new ACEC of 

0.54% and CCEC of 0.44%, which will be used in the proposed permit for WET testing.

If there is no chronic toxicity at the acute mixing zone boundary, then there is no reasonable potential for chronic toxicity at the 

edge of the chronic mixing zone boundary. 

To review, Ecology compares the Lowest Observed Effects Concentration (LOEC) to the ACEC. If the LOEC is always above the 

ACEC, we can assume that there is no chronic toxicity. Based on the above data, the LOEC is always greater than the ACEC 

(0.43 %). Therefore, no chronic WET limit is needed.
Fact Sheet for NPDES Permit WA-002958-1 Page 74 of 101 

King County South Wastewater Treatment Plant 

APPENDIX H—TECHNICAL CALCULATIONS 

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

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

http://www.ecy.wa.gov/programs/eap/pwspread/pwspread.html. 
Fact Sheet for NPDES Permit WA-002958-1 Page 75 of 101 

King County South Wastewater Treatment Plant 

Table H-1: South WWTP – Water Quality Criteria for Detected Pollutants 

 

FACILITY: South Plant WWTP

FILENAME: 

RUN DATE:4/17/2009

PREPARED BY: M. Henley

Red font = National Toxics Rule (40 CFR 131.36)

Blue font = EPA National Recommended Water Quality Criteria:2002 (EPA 822-R-02-47)

Green font = Other source - see comment

Black font = WAC 173-201A (Nov. 1997)

Input Required Data Units

0 mg/L 

S

99.4 mg/L at CaCO 3

WATER QUALITY CRITERIA (in ug/L unless otherwise noted)

Pollutant 

Detected 

input "y"

Pollutant CAS No. NPDES 

Application 

Reference No.

Hardness or 

pH dependent

Conversion 

Factor

Conversion 

Factor 

Chronic

Priority 

Pollutants

Carcinogen Water Quality 

Criteria - Marine - 

Acute

Water Quality 

Criteria - Marine 

- Chronic

Human Health 

Criteria - Marine

48.70 AMMONIA mg/L N N 233 35

0.67 ANTIMONY (INORGANIC) 7440360 1M Y N 4300 

1.60 ARSENIC (dissolved) 7440382 2M Y Y 69 36 

0.30 CADMIUM 7440439 4M 50.0 0.97 0.94 Y N 42.00 9.3

750.00 CHLORINE (Total Residual) 7782506 N N 13 7.50

2.18 CHLOROFORM 67663 11V Y Y 470

4.07 CHROMIUM(HEX) 18540300 Y N 1100 50

42.40 COPPER 744058 6M 50.0 Y N 4.80 3.10

28.00 CYANIDE 57125 14M Y N 1.00 1.00 220000 

3.93 1,4 DICHLOROBENZENE 106467 22B Y N 2600 

2.00 LEAD 7439921 7M 50.0 0.89 Y N 210.00 8.10

7.00 METHYLENE CHLORIDE 75092 22V Y Y 1600 

0.058 MERCURY 7439976 8M Y N 1.80 0.0250 0.15 

4.45 NICKEL 7440020 9M 50.0 Y N 74.00 8.20 4600

0.84 SILVER 7740224 11M 50.0 Y N 1.90 NA

1.40 TETRACHLOROETHYLENE 127184 24V Y Y 8.85 

3.86 TOLUENE 108883 25V Y N 200000 

68.00 ZINC 7440666 13M 50.0 Y N 90.00 81.00

VALUE PRESENTED IS TH L.O.E.LENTER RECEIVING WATER TSS (IF 

IF RECEIVING WATER TSS IS ANNUAL 

HARDNESS VALUE USED FOR 

HARDNESS DEPENDENT LIMITS>>>> * = INSUFFICIENT DATA TO DEVELOP 
Fact Sheet for NPDES Permit WA-002958-1 Page 76 of 101 

King County South Wastewater Treatment Plant 

Table H-2: South WWTP – Ammonia Calculation Spreadsheet 

 

Ammonia Calculation Spreadsheet

Calculation of seawater fraction of un-ionized ammonia

 from Hampson (1977). Un-ionized ammonia criteria for 

 salt water are from EPA 440/5-88-004. Revised 19-Oct-93.

Facility: South Plant WWTP

Permit No: WA-002958-1

INPUT*

1. Temperature, deg C (90th percentile): 14.0 Max.

2. pH, (90th percentile): 8.0

3. Salinity, g/Kg (90th percentile): 31.1 Max.

OUTPUT

1. Pressure (atm; EPA criteria assumes 1 atm): 1.0

2. Molal Ionic Strength (not valid if >0.85): 0.640

3. pKa8 at 25 deg C (Whitfield model "B"): 9.319

4. Percent of Total Ammonia Present as Unionized: 2.066%

5. Unionized ammonia criteria (mg un-ionized NH3 per liter)

 from EPA 440/5-88-004

 Acute: 0.233

 Chronic: 0.035

6. Total Ammonia Criteria (mg/L as NH3)

 Acute: 11.28

 Chronic: 1.69

7. Total Ammonia Criteria (mg/L as NH3-N)

 Acute: 9.27 9269.35 ug/L

 Chronic: 1.39 1392.39 ug/L

* Data from ambient monitoring station LSNT01, South Plant Outfall

fn: TSDCalc10.cls
Fact Sheet for NPDES Permit WA-002958-1 Page 77 of 101 

King County South Wastewater Treatment Plant 

Table H-3: South WWTP – Reasonable Potential to Exceed the Water Quality Standards State Water Quality Standard Max concentration at edge of... Metal Criteria Translator as decimal Metal Criteria Translator as decimal Ambient Concentration (metals as dissolved) Acute Chronic Acute Mixing Zone Chronic Mixing Zone LIMIT REQ'D? Effluent percentile value 95th % effluent conc. measured (metals as total recoverable) Coeff Variation # of samples Multiplier Acute Dil'n Factor Chronic Dil'n Factor Parameter Acute Chronic ug/L ug/L ug/L ug/L ug/L Pn ug/L CV s n COMMENTS

Ammonia 11.0 9269 1392 212.55 177.62 NO 0.95 0.997 37500 0.210 0.21 934 1 186 225ARSENIC (dissolved) 1.00 1.4400 69.0 36.0 1.44 1.44 NO 0.95 0.916 1.516 0.101 0.10 34 1 186 225CADMIUM 0.994 0.994 0.0746 42.0 9.3 0.07 0.07 NO 0.95 0.911 0.077 0.756 0.67 32 1 186 225CHLORINE (Total Residual) 13.0 7.5 0.27 0.22 NO 0.95 0.998 50.000 0.751 0.67 1553 1 186 225CHROMIUM(HEX) 0.993 0.993 0.4510 1100.0 50.0 0.46 0.46 NO 0.95 0.911 1.480 0.723 0.65 32 1 186 225COPPER 0.83 0.83 0.5740 4.8 3.1 0.71 0.69 NO 0.95 0.911 31.340 0.475 0.45 32 1 186 225CYANIDE 1.0 1.0 0.00 0.00 NO 0.95 0.913 0.019 0.903 0.77 33 1 186 225LEAD 0.951 0.95 0.1630 210.0 8.1 0.17 0.17 NO 0.95 0.911 1.254 0.522 0.49 32 1 186 225MERCURY 0.85 0.000621 1.8 0.025 0.00 0.00 NO 0.95 0.913 0.051 0.306 0.30 33 1 186 225NICKEL 0.99 0.99 0.6830 74.0 8.20 0.70 0.70 NO 0.95 0.913 4.004 0.183 0.18 33 1 186 225SILVER 0.85 1.9 NA 0.00 0.00 NO 0.95 0.911 0.596 0.423 0.41 32 1 186 225ZINC 0.946 0.946 0.8880 90.0 81.0 1.13 1.09 NO 0.95 0.913 49.340 0.414 0.40 33 1 186 225

This spreadsheet calculates the reasonable potential to exceed state water quality standards for a small number of samples. The procedure and calculations are done per the procedure in Technical Support Document for Water Quality-based Toxics Control, U.S. EPA, March, 1991 (EPA/505/2-90-001) on page 56. 

User input columns are shown with red headings. Corrected formulas in col G and H on 5/98 (GB)
Fact Sheet for NPDES Permit WA-002958-1 Page 78 of 101 

King County South Wastewater Treatment Plant 

Table H-4: South WWTP – Chlorine Limit to Meet Water Quality Limit 

 

Permit Limit Calculation Summary

Acute 

Dil'n 

Factor

Chronic 

Dil'n 

Factor

Metal 

Criteria 

Translat

or 

Metal 

Criteria 

Translat

or 

Ambient 

Concentr

ation

Water 

Quality 

Standard 

Acute

Water 

Quality 

Standard 

Chronic

Average 

Monthly 

Limit (AML)

Maximum 

Daily Limit 

(MDL) Comments

PARAMETER Acute Chronic ug/L ug/L ug/L ug/L ug/L

Chlorine 186.00 225.00 13.00 7.50 923.7 2418.0 New DF

500.0 750.0 Technology-Based

Waste Load Allocation (WLA) and Long 

Term Average (LTA) Calculations

Statistical variables for permit limit 

calculation

WLA 

Acute

WLA 

Chronic

LTA 

Acute

LTA 

Chronic

LTA 

Coeff. 

Var. 

(CV)

LTA 

Prob'y 

Basis

Limiting 

LTA

Coeff. 

Var. 

(CV)

AML 

Prob'y 

Basis

MDL 

Prob'y 

Basis

# of 

Sample

s per 

Month

ug/L ug/L ug/L ug/L decimal decimal ug/L decimal decimal decimal n

2418 1687.50 776.4 890.0 0.60 0.99 776.4 0.60 0.95 0.99 30.00 1.00
Fact Sheet for NPDES Permit WA-002958-1 Page 79 of 101 

King County South Wastewater Treatment Plant 

Table H-5: South WWTP – Reasonable Potential to Exceed Human Health Criteria 
Fact Sheet for NPDES Permit WA-002958-1 Page 80 of 101 

King County South Wastewater Treatment Plant 

Table H-5 (Continued): South WWTP – Reasonable Potential to Exceed Human 

Health Criteria 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 81 of 101 

King County South Wastewater Treatment Plant 

Table H-6: South WWTP – Ambient Monitoring Data Summary 

King County Water Quality Data

Station LSNT01 - Central Basin

1999 through 2008 - Conventionals

Salinity Temperature Dissolved Oxygen Fecal Coliform Bacteria

(PSS) (°C) (mg/L) (# organisms/100 mL) 

Minimum 27.0 7.5 4.5 0.0 

Maximum 31.1 14.0 13.6 4.0 

Average 30.1 10.3 7.2 0.2 

90% 30.8 12.4 8.6 1.0 

95% 30.8 13.0 9.0 1.0 

 
Fact Sheet for NPDES Permit WA-002958-1 Page 82 of 101 

King County South Wastewater Treatment Plant 

Table H-7: South WWTP – Dilution Assessment for Temperature 

 

The Water Quality temperature guidance document may be found at: http:// www.ecy.wa.gov/ biblio/ 0610100.html

INPUT May-Sep Oct-Apr

1. Chronic Dilution Factor at Mixing Zone Boundary 225 225

2. Annual max 1DADMax Ambient Temperature (Background 90th percentile) 14.0 °C 12.5 °C Max.

3. 1DADMax Effluent Temperature (95th percentile) 22.2 °C 18.9 °C Max.

4. Aquatic Life Temperature WQ Criterion 16.0 °C 16.0 °C

OUTPUT

5. Temperature at Chronic Mixing Zone Boundary: 14.04 °C 12.53 °C

6. Incremental Temperature Increase or decrease: 0.04 °C 0.03 °C

7. Incremental Temperature Increase 12/(T-2) if T< crit: 1.00 °C 1.14 °C

8. Maximum Allowable Temperature at Mixing Zone Boundary: 15.00 °C 13.64 °C

A. If ambient temp is warmer than WQ criterion

9. Does temp fall within this warmer temp range? NO NO

10. Temp increase allowed at mixing zone boundary, if required: --- ---

B. If ambient temp is cooler than WQ criterion but within 12/(Tamb-2) and within 0.3 °C 

 of the criterion 

11. Does temp fall within this incremental temp. range? NO NO

12. Temp increase allowed at mixing zone boundary, if required: --- ---

C. If ambient temp is cooler than (WQ criterion-0.3) but within 12/(Tamb-2) of the criterion

13. Does temp fall within this Incremental temp. range? NO NO

14. Temp increase allowed at mixing zone boundary, if required: --- ---

D. If ambient temp is cooler than (WQ criterion - 12/(Tamb-2))

15. Does temp fall within this Incremental temp. range? YES YES

16. Temp increase allowed at mixing zone boundary, if required: NO LIMIT NO LIMIT

17. Do any of the above cells show a temp increase? NO NO

18. Temperature Limit if Required? NO LIMIT NO LIMIT

Marine T-mix

T-Mix is based on WAC 173-201A-200(1)(c)(i)--(ii) and Water Quality Program Guidance.

Notes: 

All Data inputs must meet WQ guidelines.
Fact Sheet for NPDES Permit WA-002958-1 Page 83 of 101 

King County South Wastewater Treatment Plant 

Table H-8: South WWTP – Dilution Assessment for Fecal Coliform Bacteria 

 

South Plant WWTP Receiving Water Calculations

Chronic Dilution Factor 225 1

Acute Dilution Factor 186

Facility Design Max Month Flow 144.00 mgd

222.82 cfs

Fecal Coliform Dilution Calculation

Receiving Water Fecal Coliform 4 #/100 ml Ambient Monitoring LSNT01

Effluent Fecal Coliform - worst case 2075 #/100 ml Max. Daily Discharge (2004-2008)

Downstream Fecal Coliform 13 #/100 ml

Difference between mixed and ambient 9 #/100 ml

Primary Contact and Shellfish Habitat Surface Water Criteria 14 #/100 ml Current state WAC designation

Conclusion: At design flow, the discharge has no reasonable potential for violation of water quality standards for fecal 

coliform.
Fact Sheet for NPDES Permit WA-002958-1 Page 84 of 101 

King County South Wastewater Treatment Plant 

Table H-9: South WWTP – Assessment for Impacts to Dissolved Oxygen 

 

South WWTP

Dissolved oxygen concentration following initial dilution.

References: EPA/600/6-85/002b and EPA/430/9-82-011

INPUT Source

1. Dilution Factor at Mixing Zone Boundary: 225 Chronic dilution factor

2. Ambient Dissolved Oxygen Concentration (mg/L): 4.5 Min. at LSNT01

3. Effluent Dissolved Oxygen Concentration (mg/L): 4.5 NPDES permit application - Min. value

4. Effluent Immediate Dissolved Oxygen Demand (mg/L): 45 DMR Data Max BOD 5-day

OUTPUT

Dissolved Oxygen at Mixing Zone Boundary (mg/L): 4.30

Decrease of 0.2 mg/L = No Measurable Change 0.20
Fact Sheet for NPDES Permit WA-002958-1 Page 85 of 101 

King County South Wastewater Treatment Plant 

Table H-10: South WWTP – Assessment for pH 

 

Calculation of pH of a mixture in seawater.

Based on the CO2SYS program (Lewis and Wallace, 1998)

http://cdiac.esd.ornl.gov/oceans/co2rprt.html

INPUT

1. MIXING ZONE BOUNDARY CHARACTERISTICS

 Dilution factor at mixing zone boundary 225.000

 Depth at plume trapping level (m) 2.000

2. BACKGROUND RECEIVING WATER CHARACTERISTICS

 Temperature (deg C): 14.00 Max

 pH: 7.80 Avg. 2007 EB Monit. Sta.

 Salinity (psu): 31.10 Max

 Total alkalinity (meq/L) 2.40

3. EFFLUENT CHARACTERISTICS

 Temperature (deg C): 22.20 Max

 pH: 8.80 Max

 Salinity (psu) 0.00

 Total alkalinity (meq/L): 3.00

4. CLICK THE 'calculate" BUTTON TO UPDATE OUTPUT RESULTS >>>

OUTPUT

CONDITIONS AT THE MIXING ZONE BOUNDARY

 Temperature (deg C): 14.04

 Salinity (psu) 30.96

 Density (kg/m^3) 1023.07

 Alkalinity (mmol/kg-SW): 2.35

 Total Inorganic Carbon (mmol/kg-SW): 2.25

 pH at Mixing Zone Boundary: 7.81
Fact Sheet for NPDES Permit WA-002958-1 Page 86 of 101 

King County South Wastewater Treatment Plant 

APPENDIX I—INDUSTRIAL DISCHARGERS TO COUNTY’S SOUTH WWTP 

 

F.1. Pretreatment program. Does the treatment works have, or is subject to, an approved pretreatment program? - Yes

F.2. Number of Significant Industrial Users (SIUs) and Categorical Industrial Users (CIUs). Provide number of each of the

 following types of industrial users that discharge to the treatment works.

 a. Number of non-categorical SIUs. 36

 b. Number of CSIUs. 29

F.3. Mailing Address F.7.

A. O. Smith Water Products Company 820 SW 41ST STREET RENTON 98057 METAL FINISHING - CFR 433

Aero Controls, Inc. 1602 PIKE STREET NW AUBURN 98001 METAL FINISHING - CFR 433

Aero Controls, Inc. 1610 20TH STREET NW AUBURN 98002-3459 METAL FINISHING - CFR 433

Aerojet-General Corporation 11441 WILLOWS ROAD NE REDMOND 98052 METAL FINISHING - CFR 433

Aramark Uniform & Career Apparel, LLC 7810 SOUTH 228TH STREET KENT 98032 LAUNDRY-INDUSTRIAL

B.S.B. Diversified Company Inc. S. 200 ST. AND 81ST ST. KENT 98032 GROUNDWATER REMEDIATION - ORGANICS

Baker Commodities Inc. 5795 S. 130TH PLACE SEATTLE 98178 RENDERING

Bakery Chef Company -Ralcorp Frozen 6320 S. 190TH STREET KENT 98032 FOOD PROCESSING

Black Oxide, LLC 131 30TH STREET NE, SUITE 25 AUBURN 98002 METAL FINISHING - CFR 433

Boeing Commercial Airplane - Auburn 700 15TH ST. SW AUBURN 98002 METAL FINISHING - CFR 433

Boeing Commercial Airplane - Renton 801 LOGAN AVE. N. RENTON 98055 METAL FINISHING - CFR 433

Boeing Electronics Center 616 SW 41ST STREET, BLDG.7-107 RENTON 98055 METAL FINISHING - CFR 433

Burlington Environmental, LLC 20245 77TH AVE. S. KENT 98032 CENTRALIZED WASTE TREATMENT 437B PSES

Cedar Grove Composting, Inc. 17825 CEDAR GROVE RD. SE MAPLE VALLEY 98038 COMPOSTING-YARD WASTE

Circuit Services WorldWide 13000 BEL-RED ROAD, NO. 105 BELLEVUE 98005 ELECTROPLATING - CFR 413

Coca-Cola Bottling Company of Washington 1150 124TH AVE NE BELLEVUE 98005 FOOD PROCESSING-SOFT DRINKS

Davis Wire Corporation 19411-80TH AVENUE SOUTH KENT 98032-1190 IRON AND STEEL MANF - CFR 420

Electrofinishing, Inc. 22630 88TH AVENUE S., UNIT A KENT 98031 METAL FINISHING - CFR 433

Exotic Metals Forming Company 5411 S. 226TH STREET KENT 98032 METAL FINISHING - CFR 433

Express Finishing 15046 NE 95TH STREET REDMOND 98052 METAL FINISHING - CFR 433

G & K Services 1001 SW 34TH ST. RENTON 98055 LAUNDRY-INDUSTRIAL

Genie Industries - Bld. 2 - Moosewerks 7140 180TH AVENUE NE REDMOND 98052 METAL FINISHING - CFR 433

Genie Industries - Bld. 3 & 4 18340 NE 76TH STREET REDMOND 98052 METAL FINISHING - CFR 433

Genie Industries - Bld. 6 & 7 - Scissors Plant 18700 & 18750 NE 65TH STREET REDMOND 98052 METAL FINISHING - CFR 433

GKN Aerospace Chem-tronics Inc. 20231 72ND AVENUE SOUTH KENT 98032 METAL FINISHING - CFR 433

Green Garden Food Products, Inc. 5851 S. 194TH ST. KENT 98032 FOOD PROCESSING

Hexcel Corporation 19819 84TH AVE. S. KENT 98032 GROUNDWATER REMEDIATION - ORGANICS

Honeywell International Inc. 15001 NE 36TH STREET REDMOND 98073 METAL FINISHING - CFR 433

Hytek Finishes Company 8127 S. 216TH STREET KENT 98032 METAL FINISHING - CFR 433

International Paper Company (fka Weyerhaeuser) 1899 120TH AVENUE NE BELLEVUE 98005 CORRUGATED CONTAINER

January Company 9844 40TH AVE. S. SEATTLE 98118 FOOD PROCESSING-MEATS

Kenworth Truck Company - Renton 1601 N. 8TH STREET RENTON 98057 METAL FINISHING - CFR 433

King County CIP - Juanita Bay Pump Station 9304 JUANITA DRIVE NE KIRKLAND 98034 CONSTRUCTION DEWATERING

King County DOT - Renton Decant Facility 155 MONROE AVE. NE RENTON 98056-4199 DECANT STATION

King County SWD - Cedar Hills Landfill 16645 228TH AVENUE SE MAPLE VALLEY 98038 SOLID WASTE - LANDFILL

King County SWD - Factoria Transfer Station 13800 SE 32ND ST. BELLEVUE 98005 SOLID WASTE - TRANSFER FAC

King County SWD - Houghton Transfer Station 11724 NE 60TH STREET KIRKLAND 98033 SOLID WASTE - TRANSFER FAC

King's Command Foods, Inc. 7622 S. 188TH ST. KENT 98032 FOOD PROCESSING-MEATS

Metro Transit South Base 12100 E MARGINAL WAY SOUTH TUKWILA 98168 TRANSPORTATION FACILITY

Mikron Industries 1034 SIXTH AVENUE NORTH KENT 98032 PLASTIC PRODUCTS MANF. 463

Oberto Sausage Company - Kent 7060 SOUTH 238TH STREET KENT 98032 FOOD PROCESSING-MEATS

Pacific Metallurgical Inc. 925 5TH AVENUE SOUTH KENT 98035 METAL FINISHING - CFR 433

Pacific Propeller International, LLC 5802 SOUTH 228TH STREET KENT 98032-1810 ELECTROPLATING - CFR 413

Port of Seattle, Seattle-Tacoma International Airport, BW 17025 AIR CARGO ROAD SEATAC 98188 CHEMICAL TOILET

Port of Seattle, Seattle-Tacoma International Airport, IWS 17801 INTERNATIONAL BOULEVARD SEA TAC 98188 GENERAL TYPE

Protective Coatings Inc. 1215 N. SECOND AVENUE KENT 98032 ELECTROPLATING - CFR 413

Prototron Circuits Inc. 15225 NE 95TH STREET REDMOND 98052 METAL FINISHING - CFR 433

Puget Sound Recycling 523 A STREET SE AUBURN 98002 CENTRALIZED WASTE TREATMENT 437 PSNS

Quala Systems, Inc. 19929 77TH AVENUE SOUTH KENT 98032 TRANSPORTATION FACILITY

Quality Finishing Inc. 12704 NE 124TH STREET, #42 KIRKLAND 98034 ELECTROPLATING - CFR 413

Rexam Beverage Can Company 1220 NORTH SECOND AVENUE KENT 98032 COIL COATING - CFR 465

Safeway, Inc. - Bellevue Beverage Plant 1500 124TH AVE NE BELLEVUE 98005 FOOD PROCESSING-SOFT DRINKS

Safeway, Inc. - Milk Plant 1723 124TH AVENUE NE BELLEVUE 98005 FOOD PROCESSING-DAIRY

Seattle, City of-SWD - Kent Highlands 23240 MILITARY ROAD S. KENT 98032 SOLID WASTE - LANDFILL

Shasta Beverages 1227 ANDOVER PARK EAST TUKWILA 98188 FOOD PROCESSING-SOFT DRINKS

Skills, Inc. - Auburn Facility 715 - 30TH STREET NE AUBURN 98002 METAL FINISHING - CFR 433

Smith Fabrication Inc. 1609 S. CENTRAL AVE. NO. 11 KENT 98032 METAL FINISHING - CFR 433

Stoller Metals, Inc. 22809 86TH AVENUE S KENT 98031 METAL FINISHING - CFR 433

Tri-Way Industries, Inc. (Auburn) 506 44TH STREET NW AUBURN 98001 METAL FINISHING - CFR 433

Truesoups Division of H.J. Heinz Company, L. P. 26401 79TH AVENUE SOUTH KENT 98032 FOOD PROCESSING-SOUPS

TTM Technologies, Inc. 17550 NE 67TH COURT REDMOND 98052 METAL FINISHING - CFR 433

Vectra Fitness Inc. Kent Facility 19021 80TH AVENUE SOUTH KENT 98032 METAL FINISHING - CFR 433

Western Metal Art and Sign 7042 SOUTH 188TH STREET KENT 98032 METAL FINISHING - CFR 433

Western Pneumatic Tube 835 6TH SOUTH KIRKLAND 98033 METAL FINISHING - CFR 433

WestFarm Foods/Darigold - Issaquah 611 FRONT STREET NORTH ISSAQUAH 98027 FOOD PROCESSING-DAIRY
Fact Sheet for NPDES Permit WA-002958-1 Page 87 of 101 

King County South Wastewater Treatment Plant 

APPENDIX J—RESPONSE TO COMMENTS 

Comments Received During Public Hearing – September 3, 2009 

Betsy Cooper, King County Wastewater Treatment Division 

My name is Betsy Cooper. I am the NPDES Permit Administrator for the Wastewater Treatment 

Division. King County’s address is 201 S Jackson Street in Seattle. I am pleased to give 

comments tonight in reference to the draft South Plant permit. 

I want to thank the Department of Ecology for running this public hearing. 

More than 40 years ago, the Metropolitan Sewer Authority and now King County began the 

process of helping to protect public health and the citizens and the environment by beginning 

wastewater treatment in this region. 

Before South Plant, basically there were, you know, wastewater from homes or industries was 

flowing directly into Lake Washington or into Puget Sound and the beaches were affected by 

those discharges and the people who used them and fishing and swimming was not necessarily 

the thing you wanted to do all the time in this area. However, the region decided to address that 

issue and in 1958, the region pulled together to create a regional government called METRO and 

that is now incorporated into King County’s Wastewater Treatment Division. 

In reference to the South Plant, South Plant began, as Mark noted earlier in his presentation, as a 

secondary treatment plant in 1965 and fairly soon after additional upgrades began to increase the 

capacity of that secondary treatment. Initially there was a discharge into the Green River of this 

effluent but in the late 80s a new 12 mile tunnel was built to Duwamish Head and then outfalls 

were built there approximately 10,000 feet long and they discharged our treated effluent into 

about 625 feet of water. 

 

The South Plant today treats approximately 94 million gallons of wastewater every day for the 

residents and businesses of the area and that treatment removes tons of pollutants and creates 

resources for our region. I’ll talk a little about both the treatment at the plant and those resources 

that we are involved in creating 

And we also at the plant, we treat septage, as well the materials that are removed from septic 

tanks and in 1998 about 20 million gallons of septage was also treated at the plant. 

So, South Plant as Mark mentioned, really does create a high quality effluent and in compliance 

with all the existing requirements of the permit and we consistently exceed those requirements. 

We also, as part of the wastewater treatment program, have an industrial wastewater program 

that is involved in trying to remove pollutants before they reach the influent to the plant. One 

example of that, a very successful example, is the dental waste program, were the County 

determined that it was important to remove mercury from the sources, the main sources of 

mercury to our system, which are dental offices. So that program, since 2003, has removed 
Fact Sheet for NPDES Permit WA-002958-1 Page 88 of 101 

King County South Wastewater Treatment Plant 

approximately 375 pounds of mercury, from what would have been in our influent and perhaps 

moving through our system and into our environment. 

One of the other major things that King County does to protect against pollution is vigorous 

environmental education programs that we try to invite people to the plant so that they 

understand where that water goes, as well we try to inform people about what kinds of choices 

they can make to improve the environment. 

One other component of King County’s efforts to try and protect Puget Sound, in addition to the 

way we operate the plant, really is to participate in a variety of different activities that Ecology 

and other organizations such as the Puget Sound Partnership are doing to try to protect Puget 

Sound. We feel that being a partner in regional efforts is important and we put substantial 

resources and effort to do that. 

But, the other large component that we mentioned, was we create resources from wastewater. It 

is a recycling plant as well. As we talked about the effluent leaving the outfall, we also generate 

about 6500 wet tons of biosolids every year and those are used as fertilizer for enriching soils 

and they alone represent a significant removal of nutrients and a reuse of those nutrients for 

beneficial use. 

Also the gas system that has been created at South Plant uses digester gas to run specific 

equipment in the plant as well as to send scrub gas back to Puget Sound Energy for its use. An 

example that has been given of the amount of gas we send back can typically light 2500 homes. 

The one other very important recycling program we have is the reclaimed water program where 

approximately 80-94 million gallons of reclaimed water is used in the plant every year or on-site 

and then 2-6 million gallons is sent off-site for irrigation uses and other uses. And the 

Wastewater Treatment Division is looking is looking to create a sort of larger vision for that 

reclaimed water program and our other plants will be participating in that and we are looking to 

expand that reclaimed water program so that there will be less flow to Puget Sound from our 

system. 

So in conclusion, we are very proud of our role that South Plant plays in the protection of Puget 

Sound and we are happy to give comments tonight. Thank you. 

End of Public Hearing Comments 

Ecology’s response to King County’s Oral Testimony: 

Comments noted. 
Fact Sheet for NPDES Permit WA-002958-1 Page 89 of 101 

King County South Wastewater Treatment Plant 

Comments from People For Puget Sound (via e-mail) 

September 18, 2009 

Karen Burgess 

Mark Henley 

Department of Ecology 

Northwest Regional Office 

3190 - 160th Avenue SE 

Bellevue, WA 98008-5452 

Via E-mail: kbur461@ecy.wa.gov, mahe461@ecy.wa.gov, tmil461@ecy.wa.gov 

RE: King County South Wastewater Treatment Plant draft NPDES Permit (No. WA-002958-1) 

To Karen and Mark, 

We are writing to comment on the King County South Wastewater Treatment Plant draft NPDES 

Permit (No. WA-002958-1), dated July 28, 2009. 

People For Puget Sound is a nonprofit, citizens’ organization whose mission is to protect and 

restore Puget Sound and the Northwest Straits. 

We are attaching our recent (February 13, 2009) West Point Permit comment letter because most 

of the background information and the comments apply to the South Plant as well. 

The King County South Plant is a major facility with potential adverse impacts to the health of 

Puget Sound. Together with the King County West Point facility, these two plants discharge 

about 50 percent of the treated sewage wastewater to the surface waters of the Puget Sound 

basin. 

We are pleased that Ecology has incorporated into this draft permit many of the same 

requirements that have been included in the new West Point facility permit based on our and 

other stakeholder concerns. These requirements include improved industrial user monitoring, a 

trigger for a nutrient reduction feasibility analysis if the current Ecology-led Puget Sound 

dissolved oxygen studies show that South Plant is contributing to the nutrient loading problem, 

and improved water and sediment monitoring. 

In addition, we would like to express appreciation for the improved Fact Sheet. This Fact Sheet 

is well written, more detailed and overall is substantially improved over other Fact Sheets we 

have reviewed and also includes improved maps, photos, graphs, etc. The mixing zone diagrams 

are excellent. The changes in the permit and the justifications are well explained. The 

wastewater effluent characterization is the model that we hope all Ecology Fact Sheets will 

follow. 
Fact Sheet for NPDES Permit WA-002958-1 Page 90 of 101 

King County South Wastewater Treatment Plant 

Our comments follow:

1. Omission of relevant ongoing studies and reports. We recommend that the Fact Sheet 

should include mention of important studies being undertaken by Ecology that relate to 

the permit such as the toxic loadings studies. 

Ecology’s response: Generally, the fact sheet is used to provide information specific to the 

permit, and we do not typically include regional or statewide studies in individual fact sheets. 

The best source for information regarding broad studies is the Ecology webpage. These studies 

are ongoing and only the webpage provides the most up-to-date information. The web links to 

these studies was provided in the Public Notice as follows: 

Puget Sound Water Quality: 

http://www.ecy.wa.gov/puget_sound/index.html 

South Sound Dissolved Oxygen Study: 

http://www.ecy.wa.gov/puget_sound/dissolved_oxygen_study.html

Control of Toxic Chemicals in Puget Sound 

http://www.ecy.wa.gov/programs/wq/pstoxics/index.html

Special Condition S17 has been added to the permit to address possible outcomes of the South 

Sound Dissolved Oxygen Study and the Puget Sound Hydrodynamic Modeling. 

2. Endocrine disrupters. People For Puget Sound requests that Ecology include monitoring 

of emerging chemicals including pharmaceuticals (at a minimum, the chemicals currently 

being assessed in Ecology’s study), PBDEs and additional chemicals that were detected 

in King County’s surface water study in the new permit. A baseline is needed so that the 

success of future work on source reduction/pollution prevention can be assessed. 

Ecology’s response: At this time, Ecology is not putting requirements for EDC testing in 

individual permits. Ecology is awaiting the results of our current study on pharmaceuticals and 

personal care products (PPCPs) before making programmatic decisions concerning PPCPs. 

3. S6.E. Source Tracking Characterization. We are pleased that Ecology has included our 

request to require King County to begin the process of looking at sources of toxic chemicals 

in a more systematic way. At this point, King County does not have an inline characterization 

of the toxic chemical loads in each section of their system (i.e., areas in the system where 

lead, mercury, phthalates, etc. have higher concentrations) and so does not know where the 

problems are in terms of being able to reduce sources of toxic chemicals to the facility. 

Our concerns are:

a. One report is inadequate. We request that Ecology request that a source tracing plan 

be submitted by 6 months from the permit start date and that a yearly progress update 

be due by June 1 of each year of the permit cycle. Furthermore, the plan and progress 

reports should be sent to interested stakeholders, including People For Puget Sound 

by King County.
Fact Sheet for NPDES Permit WA-002958-1 Page 91 of 101 

King County South Wastewater Treatment Plant 

b. Our key goal in requesting this study in the first place was that the sewer line itself 

be tested, branch by branch. This proposed S6.E.study does not include that key 

requirement and we request that it do so.

Ecology’s response: At this time, Ecology believes that Special Condition S6.E is an appropriate 

requirement for source characterization. King County relies on their Industrial Waste Program 

(KCIW) to regulate permitted and authorized discharges from significant industrial users. Ecology 

has delegated pretreatment authority to King County and inspects their program annually. 

4. Pretreatment. The permit or the Fact Sheet should list in an appendix the name and type of 

industry for each pretreatment facility. 

Ecology’s response: The draft permit included Appendix I which listed the name and type of 

industries that discharge into the County’s South conveyance system. Appendix I is retained for 

the final fact sheet. 

5. Mailing list. Stakeholder and interested persons list for permit should be added as an appendix. 

Ecology’s response: In regard to the draft South Plant NPDES permit, comments were received 

by only three stakeholders: People For Puget Sound, City of Everett and King County. Ecology 

does not believe that a separate appendix is necessary as there was limited public participation in 

this draft permit. 

6. Public Participation. As a final note, we are concerned that the public hearing for this 

permit was held on the Thursday before the Labor Day holiday weekend. For future public 

hearings associated with major permits, we request that key stakeholders be contacted to 

help determine the optimal date for holding hearings. 

Ecology’s response: It is often difficult to select a date for the public hearing that works for 

everyone and that fits the timeline for the issuance of the permit. In an e-mail dated August 3, 

2009, we invited someone from your organization to attend the informal public meeting and to 

provide testimony on your behalf. No other stakeholders expressed reservations regarding the 

hearing date. 

Thank you for the opportunity to comment. Please contact me with questions at (206) 382-7007 

X215. 

Sincerely, 

Heather Trim 

Urban Bays and Toxics Program Manager 

Attachment 
Fact Sheet for NPDES Permit WA-002958-1 Page 92 of 101 

King County South Wastewater Treatment Plant 

Comments from King County (via e-mail and USPS letter) 

September 18, 2009 

Tricia Miller 

Water Quality Permit Coordinator 

Northwest Regional Office 

Dept. of Ecology 

3190 160th Avenue SE 

Bellevue, WA 98008-5452 

RE: Comments on the Draft South Plant NPDES Permit (No. WA-002958-1) Renewal 

Dear Ms. Miller: 

Thank you for the opportunity to comment on the South Plant Permit Renewal. King County’s 

comments are below. 

Permit Comments 

• Page 14 - S2.C – Sampling and Analytical Procedures - For consistency, after the reference to 

40 CFR 136 in the second paragraph of S2.C, please add: "Methods identified in Appendix A 

may be used." This is the same language that was added to section S6B. 

Ecology’s response: Additional requested language is not necessary. Special Conditions 

S2.A and S2.B explicitly allow for laboratory methods in Appendix A to be used. 

• Page 32 – S11.1 or 2 – Receiving Water Characterization - The analysis of Total and 

Dissolved Metals in a saltwater matrix will required methods and detection limits that are 

not in Appendix A. Therefore, please add, to either #1 or #2 of these sections: "Conduct 

all chemical analysis using the methods and detection levels identified in the approved 

SAP/QAPP". This will allow the methodologies to be specified and approved by Ecology 

through the SAP/QAPP, giving Ecology in either case, the final approval. 

Ecology’s response: Additional requested language is not necessary. S11.9 explicitly allows 

for chemical analyses using methods and detection levels identified in Appendix A, or as 

identified in the Sampling and Quality Assurance Plan. 

 

• Page 33 – S12C – Source of Sediment Toxicity Study - This section calls for King County 

to undertake an analysis of the source of sediment toxicity for which Ecology has no 

guidance. The absence of guidance on this issue is understandable as the relationship 

between sediment-bound and deposited chemicals and toxicity is not as well studied as 
Fact Sheet for NPDES Permit WA-002958-1 Page 93 of 101 

King County South Wastewater Treatment Plant 

water column relationships. The process and procedures used in traditional Toxicity 

Reduction Evaluation studies are not directly transferable or possibly even appropriate for 

sediments. Further, since there has not been any indication that there is a toxicity concern at 

this site, it is presumptive and premature to have such a requirement in the permit at this 

time; particularly so if there is no defined process to assess such a concern. Including this 

requirement in this permit, prior to any indication of toxicity concerns near South Plant’s 

outfall is unwarranted and we request this requirement be removed. 

A more appropriate approach to addressing this concern would be to work with the County if 

any toxicity was observed to determine what next steps would be appropriate. Next steps 

would likely vary dependant on the specific findings. They could range from verification 

and further characterization of the problem, to an attempt to identify the source of toxicity or 

even to determine if a sediment impact zone would be appropriate. In addition, guidance 

development and rule making to define such a toxicity evaluation program for sediments is 

needed so that such guidance would be available for those sites where sources of toxicity 

needed to be pursued. 

 

Ecology’s response: This permit requirement only applies if toxicity is found in the sediment. It 

is in the permit so that if toxicity is found, actions to investigate may be taken immediately 

without a permit revision. Ecology will work with the County to determine what next steps are 

appropriate, if toxicity is found in the sediments. We agree that the next steps may vary 

depending on the nature and severity of the problem. Ecology does not plan to develop specific 

guidance or rule revision to address this topic because this type of activity is varied, occurs very 

infrequently, and should be based on the most current science. USEPA has published a guidance 

document on Sediment Toxicity Identification Evaluation (EPA/600/R-07/080 September 2007) 

that can be used for this purpose. 

• Page 33 – S12.C – Source of Sediment Toxicity Study - If this section remains in the permit 

the 30-day period for commencement of toxicity source evaluation is much too short, 

especially if additional sampling needed to occur. We request, at a minimum, a 90-day 

period to allow adequate time for discussion of findings to determine that such a step is the 

appropriate action and a clarification that commencement means starting development of a 

sampling plan or starting further studies with existing materials, as appropriate. We further 

request that the clock would not run during the period of time required for development of 

what an appropriate sediment toxicity evaluation would comprise. Based on the timeframe 

for Ecology’s development of whole effluent toxicity identification procedures in the 1990’s, 

this could be a considerable period of up to one to two years. As the period of time is not 

discernable, the only implementable approach in the permit is to suspend the clock during 

this process. 

Ecology’s response: Conditions may change during the time that samples are stored, including 

loss of volatile constituents and changes in redox state. Toxicity evaluations should begin as 

soon as possible after toxicity is detected, or there is increased potential for inconclusive results. 

There are already existing Sediment Toxicity Identification Evaluation procedures published by 

the USEPA. Thirty days to begin toxicity identification is reasonable. 
Fact Sheet for NPDES Permit WA-002958-1 Page 94 of 101 

King County South Wastewater Treatment Plant 

• Page 33 – S12.C- Also, if this section remains in the permit, please change the final sentence 

of Section S12.C to read: "The Permittee must submit to Ecology the results of the sediment 

toxicity investigation within three months of completion of testing." 

Ecology’s response: The permit has been modified with the additional language. 

Fact Sheet Comments 

• Page 23 – Sediment Characterization - In the second paragraph, please correct the first 

sentence to read: "In November 2001, King County performed sediment sampling from 0 to 2 

cm depth at 13 (rather than 10) sample locations near the two marine outfalls." 

Ecology’s response: The fact sheet has been corrected. 

• Page 23 – In the second paragraph, it is not clear why a Bis(2-ethylhexyl)phthalate 

concentration of 43 ppm at Station RT625SD is presented in text here and in the Table 8 on 

page 24, since the reported concentration did not exceed the SMS chemical criterion and, the 

datum is further qualified with a "B" flag. Such data should be considered at best, an 

estimate. In addition, all other samples during that sampling period had Bis(2-

ethylhexyl)phthalate concentrations below 10 ppm. Therefore, it is requested that the fourth 

and fifth sentences be deleted from this paragraph. 

Ecology’s response: The table title is “Detected Chemicals Above or Approaching SQS 

Criteria.” This sample is close to the SQS criteria. Since it is qualified with a “B” flag, it is less 

precise than other measurements, and may actually be at a level that can cause effects. There is 

nothing incorrect in the representation of the facts in the fact sheet. 

• Page 23 – In the third paragraph, please correct the first sentence to read: "In October 

1999, King County performed sediment sampling from 0 to 2 cm depth at 13 (rather than 

12) sample locations near the two outfalls." 

Ecology’s response: The fact sheet has been corrected. 

• Page 23 – In the fourth paragraph, please correct the second sentence to read: "In October 

1997, the County measured concentrations of hexachlorobenzene at three locations 

(RT700NS, RT625ND, RT625SD) that exceeded the Sediment Quality Standards numeric 

criterion”. (There were no exceedances of benzoic acid in 1997. There was one exceedance 

of the SQS/CSL criterion for Benzoic Acid at one location (LSDSO2) in 1995 but 1997, 99, 

and 2001 data have shown no such exceedances.) Then, add the following sentence after 

the second sentence: "During both the 1999 and 2001 sediment monitoring events, 

hexachlorobenzene was not detected at these three locations, nor any of the other 10 

locations sampled and, the method detection limits were all below the associated Sediment 

Quality Standard chemical criterion." 
Fact Sheet for NPDES Permit WA-002958-1 Page 95 of 101 

King County South Wastewater Treatment Plant 

Ecology’s response: The fact sheet has been modified with the correct date for the benzoic acid 

exceedance. The requested additional sentence is not necessary and does not fit in this paragraph 

since this paragraph speaks to the timeframe of 1994-1997. 

• Page 24 – We do not feel that Table 8 should remain in the Fact Sheet. The three locations 

that exhibited some exceedances of Hexachlorobenzene in 1997, exhibited no exceedances in 

two subsequent sampling events. As mentioned above, the Benzoic acid datum mentioned 

was from 1995, not 1997, and data from 1997, 1999, and 2001 do not exhibit and exceedances 

for Benzoic acid. Finally, the Bis(2-ethylhexyl)phthalate data listed in the table are not 

exceedances of the standard. Therefore, we request the table be deleted from the Fact Sheet. 

Ecology’s response: Table 8 provides a historical summary of exceedances or chemicals 

approaching the criteria. Once the date is changed from 1997 to 1995 for benzoic acid, this is an 

accurate representation of the facts. The table will be retained in the fact sheet. 

• Page 44 – Sediment Quality – Please delete the second bullet under the second paragraph of 

this section as it is an incorrect statement. As mentioned above, Benzoic acid was not 

detected in any of the 8 sediment samples collected during the 1997 sediment-monitoring 

event. Dry-weight normalized detection limits for the 8 samples ranged from 338 to 368 

μg/Kg, which is well below the SQS/CSL criterion of 650 μg/Kg. Benzoic acid was not 

detected in any of the 13 samples collected during the 1999 monitoring event, at a similar 

range of dry-weight normalized detection limits. During the 2001 sediment monitoring event, 

analytical detection limits had improved significantly for benzoic acid and this compound was 

detected in all 13 samples at concentrations ranging from 342 to 553 μg/Kg, all below the 

SQS/CSL criterion. 

Ecology’s response: The draft fact sheet was intended to note hexachlorobenzene as an 

exceedance, and not benzoic acid, under the second bullet. The fact sheet has been corrected to 

mention hexachlorobenzene instead of benzoic acid. 

 

• King County certainly accepts the idea that Ecology would require additional sampling at the 

outfalls to check sediment conditions as these sites not been sampled for almost 10 years. 

However, as noted in earlier comments on this matter, it is incorrect and misleading to 

represent the current sediment dataset as indicating that there has been sediment 

contamination at these sites and we request that this section not present that impression 

because it is not supported by the data. 

Ecology’s response: This section is intended to provide a factual summary of existing data. 

There have been past exceedances of the chemical criteria. We also state in a summary on page 

23 that past sediment monitoring does not generally indicate sediment toxicity or violation of 

SMS criteria. 
Fact Sheet for NPDES Permit WA-002958-1 Page 96 of 101 

King County South Wastewater Treatment Plant 

• Page 44 – With regard to the fourth bullet under the second paragraph which describes the 

requirement for the sample to be of the top 10 centimeters rather than the top 

2 centimeters - this is a significant paradigm shift. The most-recent version of the Sediment 

Sampling and Analysis Plan Appendix (Ecology 2008) still recommends the 0- to 2-cm 

depth stratum when sampling sediment around permitted outfalls. It states: “In some cases, 

monitoring data may be used to interpret temporal changes in sediment conditions. Such 

cases may include, for example, ambient monitoring programs, monitoring of conditions in 

the vicinity of a permitted discharge, or monitoring of a cap placed over contaminated 

sediments as part of remediation. In such cases, it would be more appropriate to limit the 

sampling to the uppermost 2 cm of sediment, which would represent the most recently 

deposited particulate matter. If deeper (e.g., 10 cm) sediment samples were collected and 

analyzed, older sediment would be included in the samples, making it more difficult to 

detect temporal changes in sediment conditions.” (SAPA, Ecology 2008). 

If, as was suggested in discussions with Ecology staff, the purpose of 10 cm sampling is really 

a one-time assessment for compliance with water quality standards (the Sediment 

Management Standards), we recommend that this is clarified in the permit and fact sheet. It 

would also be helpful to identify that following a demonstration of compliance; future 

sampling will revert to the 2-cm depth consistent with existing guidance. This will provide a 

clearer demonstration of intent for the next permit. 

Ecology’s response: The top 10 centimeters of sediment is considered the biologically-active 

zone for Puget Sound and is used for compliance with the Sediment Management Standards. 

Sediment samples from the top 2 cm have been used in the past for trend analysis. In the past 

several years, we have been asking for 10 cm depth samples at NPDES outfalls so that we may 

evaluate compliance with the Sediment Management Standards. It is not just a one-time 

assessment of compliance. Ecology has discretion whether to request 10 cm or 2 cm samples 

depending on the purpose of the sampling study. 

The SAPA was updated in 2008 to add a new appendix with procedures for entering data into 

the EIM database. Other sections of the SAPA were not updated at that time. 

• Page 44 – Please add the following language to the fifth bullet under the second paragraph: 

"Although not required, King County has performed benthic community analysis during two 

previous sediment monitoring events. Analysis of the benthic data indicates a healthy 

benthic community, typical of deep, depositional environments in Puget Sound." 

The benthic community proximal to the South Treatment Plant outfalls was characterized in 

both 1999 and 2001, with triplicate samples collected from 5 stations proximal to the outfalls 

and one reference station, located 2,500 feet from the outfalls, at a similar depth. During 

both monitoring years, the benthic community showed no impact from the outfalls and no 

apparent gradient in benthic community indices exists, with respect to proximity to or 

distance from the outfalls. Tables of the benthic indices may be found at the following links: 

http://your.kingcounty.gov/dnrp/library/2001/kcr64/99sec3.pdf

http://your.kingcounty.gov/dnrp/library/2002/kcr64/Section3.pdf
Fact Sheet for NPDES Permit WA-002958-1 Page 97 of 101 

King County South Wastewater Treatment Plant 

Ecology’s response: Although the Sediment Management Standards require submittal of any 

existing sediment data (WAC 173-204-610), these benthic community data have not been 

submitted to Ecology’s EIM database. If King County wanted these data included in the fact 

sheet summary, the data should have been submitted to Ecology and brought to our attention 

with the permit renewal application or during entity review of the draft fact sheet and permit. 

Since we do not have this data, nor do we have adequate time to review it before permit issuance, 

we can not include the requested quote as it is not confirmed at this time. Please provide EIM 

benthic community data, summary report, and bench sheets to Ecology for review, verification, 

and approval. 

• Page 44 – We recognize that Ecology can require additional sediment testing above its 

regular tiered approach paradigm. However, to indicate that the Ecology will be expecting 

four bioassays analyses be undertaken without specific SMS exceedances is another 

significant paradigm shift and one that again does not seem warranted based on the existing 

data that has clearly demonstrated there is little indication of toxicity in the vicinity of the 

outfalls (as presented below): 

o Sediments in the vicinity of the South Plant outfalls have been tested for sediment 

contamination since the mid- 1990’s. Each sampling event have taken sediments from 

multiple sites – as many as 13 in the most recent sampling events, with an overall total 

of 48 samples. In the last two events, the benthic community was also sampled. In total 

these samples represent a significant data set. 

o The two most recent sampling events (2001 and 1999), had no detected sediment 

chemical concentrations that exceeded any Sediment Management Standards chemical 

criterion. During the 2001 monitoring event, analytical method detection limits had 

improved to the point that all method detection limits (MDLs) met SQS chemical 

criteria with one exception. The dry-weight normalized MDL for 2-Methylphenol 

exceeded the SQS of 63 ug/Kg DW in four of 13 samples, ranging from 64 to 67 ug/Kg 

DW. This is merely an artifact of slightly lower percent solids concentrations in these 

four samples as 2-Methylphenol was not detected in any of the 13 samples, 9 of which 

had MDLs that met the SQS criterion. 

o The only detected exceedances found in earlier sampling events are summarized below 

and do not indicate any pattern of exceedances or the existence of current toxicity 

concerns: 

 Hexachlorobenzene detected in samples collected from three stations proximal 

to the outfalls during the 1997 monitoring event. Two of these concentrations 

(0.954 and 1.87 mg/Kg OC exceeded the SQS chemical criterion of 0.38 

mg/Kg OC. The third concentration of 2.52 mg/Kg OC exceeded the CSL 

chemical criterion of 2.3 mg/Kg OC. All three of these stations were sampled 

again in both 1999 and 2001, during which hexachlorobenzene was not 

detected, with a method detection limit that met the SQS chemical criterion. 
Fact Sheet for NPDES Permit WA-002958-1 Page 98 of 101 

King County South Wastewater Treatment Plant 

 Benzoic acid was detected at a concentration of 1,480 ug/Kg DW in one sample 

collected during the 1994 monitoring event. This concentration exceeded the 

SQS/CSL chemical criterion of 650 ug/Kg DW. The station from which this 

sample was collected was located approximately 3,000 feet from the outfall. 

Benzoic acid was not detected at the station that was located equidistant between 

the two outfalls. 

o The benthic community proximal to the South Treatment Plant outfalls, characterized 

in both 1999 and 2001, showed no impact from the outfalls and no apparent gradient 

in benthic community indices exists, with respect to proximity to or distance from the 

outfalls (see comment above). 

o Whole Effluent Toxicity Testing has been performed consistently since 1986 on South 

Plant effluent. No concerns regarding effluent toxicity have been identified. No 

toxicity-based requirements have been determined to be needed in this permit. Limits 

earlier imposed on metals concentrations where removed in the 1990’s because metals 

data demonstrated they were no longer warranted. 

We contend that if such an significant and expensive bioassay requirement is being added to 

this permit that there needs to be a compelling case to suspect that sediment contamination, 

and thus toxicity, is present. We submit that no such case can be made and, in fact, that the 

data support a compelling case that toxicity is not indicated at this site. We therefore request 

that the expectation of bioassays should continue to be triggered only if a sediment quality 

exceedance is observed as has been typical for NPDES permits to date. 

Ecology’s response: The Sediment Management Standards provide Ecology with specific 

authority to evaluate NPDES discharges in consideration of multiple factors including discharge 

characteristics, receiving water characteristics, and cost mitigating factors. Ecology’s request for 

toxicity testing at this location was not based solely on past chemistry data, but also because of the 

size of the discharge and consistency with permits at other wastewater treatment plants of this size. 

The West Point Wastewater Treatment Plant, which has a similar size discharge, has had many 

bioassays performed near the outfall and has found toxicity, even when concentrations are below 

the chemical criteria. 

However, in this case Ecology has considered your request, and will only require bioassays to be 

performed if the chemical concentrations are near or above the numeric chemical criteria in the 

Sediment Management Standards. 

Thank you for consideration of our comments. If you have any questions regarding these comments, 

please contact me at 206-263-3728. 

Sincerely, 

Betsy Cooper 

NPDES Coordinator 

 

Cc: Mark Henley, Permit Manager, Dept of Ecology NWRO 
Fact Sheet for NPDES Permit WA-002958-1 Page 99 of 101 

King County South Wastewater Treatment Plant 

Comments from the City of Everett (via USPS letter) 
Fact Sheet for NPDES Permit WA-002958-1 Page 100 of 101 

King County South Wastewater Treatment Plant 
Fact Sheet for NPDES Permit WA-002958-1 Page 101 of 101 

King County South Wastewater Treatment Plant 

Ecology’s response to Issue #1: The Sediment Management Standards provide Ecology with 

specific authority to evaluate NPDES discharges in consideration of multiple factors including 

discharge characteristics, receiving water characteristics, and cost mitigating factors. Ecology’s 

request for toxicity testing at the South plant outfalls was not based solely on past chemistry data, 

but also because of the size of the discharge and consistency with permits at other wastewater 

treatment plants of this size. The West Point Wastewater Treatment Plant, which has a similar size 

discharge, has had many bioassays performed near the outfall and has found toxicity, even when 

concentrations are below the chemical criteria. 

However, in this case Ecology has considered the County’s request, and will only require bioassays 

to be performed if the chemical concentrations are near or above the numeric chemical criteria in the 

Sediment Management Standards. 

 

Ecology’s response to Issue #2: The top 10 centimeters of sediment is considered the 

biologically-active zone for Puget Sound and is used for compliance with the Sediment Management 

Standards. Sediment samples from the top 2 cm have been used in the past for trend analysis. In the 

past several years, we have been asking for 10 cm depth samples at NPDES outfalls so that we may 

evaluate compliance with the Sediment Management Standards. It is not just a one-time assessment 

of compliance. Ecology has discretion whether to request 10 cm or 2 cm samples depending on the 

purpose of the sampling study. 

The SAPA was updated in 2008 to add a new appendix with procedures for entering data into the 

EIM database. Other sections of the SAPA were not updated at that time. 

Ecology’s response to Issue #3: This permit requirement only applies if toxicity is found in the 

sediment. It is in the permit so that if toxicity is found, actions to investigate may be taken 

immediately without a permit revision. Ecology will work with the County to determine what next 

steps are appropriate, if toxicity is found in the sediments. Ecology acknowledges that the next steps 

may vary depending on the nature and severity of the problem. Ecology does not plan to develop 

specific guidance or rule revision to address this topic because this type of activity is varied, occurs 

very infrequently, and should be based on the most current science. USEPA has published a 

guidance document on Sediment Toxicity Identification Evaluation (EPA/600/R-07/080 September 

2007) that can be used for this purpose.