Fact Sheet for NPDES Permit WA0029181

West Point Wastewater Treatment Plant (WWTP)

and

Combined Sewer Overflow (CSO) System

December 19, 2014

Purpose of this fact sheet

This fact sheet explains and documents the decisions the Department of Ecology (Ecology) made 

in drafting the proposed National Pollutant Discharge Elimination System (NPDES) permit for 

King County’s West Point WWTP, CSO treatment plants, and associated CSO outfalls.

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 West Point WWTP and CSO system, NPDES permit WA0029181, were available for 

public review and comment from October 30, 2014 until November 29, 2014. 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. Based on 

this review, Ecology provided additional clarification and corrected any errors or omissions 

regarding the facility’s location, history, or wastewater discharges prior to publishing this draft 

fact sheet for public notice. Significant comments from King County and Ecology’s responses 

are listed in Appendix I – Response to Comments.

After the public comment period closes, Ecology will summarize substantive comments and 

provide responses to them. Ecology will include the summary and responses to comments in this 

fact sheet as Appendix I - Response to Comments, and publish 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.

Summary

The proposed permit provides coverage for King County’s West Point WWTP, four CSO 

treatment facilities (Alki, Carkeek, Elliott West, and Henderson/MLK), and 38 CSO outfalls. 

The West Point WWTP treats domestic, commercial, and industrial wastewater and CSO 

stormwater from the greater Seattle area using a high rate oxygenated activated sludge biological 

treatment process with chlorine disinfection before discharging the treated effluent to central 

Puget Sound. For West Point WWTP, the proposed permit contains the same effluent limits for 

CBOD5, total suspended solids, fecal coliform, pH, and total residual chlorine as the permit 

issued in 2009. 

This permit proposes a few changes for the four CSO treatment plants. For all four facilities, 

compliance with settleable solids standards will be assessed annually instead of on an annual and 

per-event basis as in the previous permit. This is consistent with the legal basis in regulation 

(WAC 173-245). For the Alki and Carkeek CSO treatment facilities the proposed permit includes 

the same limits and monitoring requirements as the previous permit. For Elliott West and 

Henderson/MLK facilities, the following changes are being proposed:
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Elliott West CSO treatment plant - Due to a change in mixing dilution, the limits for total 

residual chlorine increased slightly from a maximum daily average of 104 to 109 μg/L. Fecal 

coliform limits became more stringent as they changed from a monthly limit of 154 (with 

non-discharge days calculated in the monthly geomean as ‘1’) to a guidance-based monthly limit 

of 400 counts/100 mL. Also, the proposed permit includes additional monitoring for dissolved 

oxygen, copper and cyanide, and requires a study to evaluate options for reducing copper and 

settleable solids concentrations.

Henderson/MLK CSO treatment plant – For this facility effluent limits remain the same. Copper 

monitoring is required for each event and PCB monitoring is required using EPA method 1668 

with a method detection limit of 0.0001 ug/L. 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table of Contents

I. Introduction............................................................................................................................ 7

II. Background Information ...................................................................................................... 8

A. Facility description......................................................................................................... 10

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

Background .................................................................................................................................10

Collection system status..............................................................................................................13

Treatment processes....................................................................................................................16

Solid wastes/Residual solids .......................................................................................................19

Discharge outfalls........................................................................................................................20

B. Description of the receiving water................................................................................. 26

C. Wastewater influent characterization............................................................................. 29

D. Wastewater effluent characterization............................................................................. 30

E. Sediment characterization.............................................................................................. 36

F. Summary of compliance with previous permit issued .................................................... 46

G. State environmental policy act (SEPA) compliance ....................................................... 50

III. Proposed Permit Limits ...................................................................................................... 51

A. Design criteria................................................................................................................ 51

B. Technology-based effluent limits.................................................................................... 53

C. Surface water quality-based effluent limits.................................................................... 56

Numerical criteria for the protection of aquatic life and recreation ............................................56

Numerical criteria for the protection of human health ................................................................56

Narrative criteria .........................................................................................................................57

Antidegradation...........................................................................................................................57

Combined Sewer Overflows .......................................................................................................58

Mixing zones...............................................................................................................................58

D. Designated uses and surface water quality criteria ....................................................... 66

Puget Sound Discharges:.............................................................................................................66

Duwamish River Discharge (Henderson/MLK):.........................................................................67

E. Water quality and sediment impairments....................................................................... 68

F. Evaluation of surface water quality-based effluent limits for numeric criteria ............. 69

Estuarine Mixing Zones (West Point WWTP, Alki, Carkeek, and Elliott West)........................69

Freshwater Mixing Zone (Henderson/MLK) ..............................................................................70

Dilution Factors...........................................................................................................................70

G. Human health ................................................................................................................. 79

H. Sediment quality ............................................................................................................. 79

I. Whole effluent toxicity .................................................................................................... 80

J. Groundwater quality limits............................................................................................. 81

K. Comparison of effluent limits with the previous permit ................................................. 81

IV. Monitoring Requirements................................................................................................... 83

A. Wastewater monitoring .................................................................................................. 83

B. Lab accreditation............................................................................................................ 83

V. Other Permit Conditions..................................................................................................... 84

A. Reporting and record keeping ........................................................................................ 84

B. Prevention of facility overloading .................................................................................. 84

C. Operation and maintenance ........................................................................................... 85
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

D. Pretreatment................................................................................................................... 85

Duty to enforce discharge prohibitions.......................................................................................85

E. Solid wastes.................................................................................................................... 86

F. Spill plan......................................................................................................................... 86

G. Combined sewer overflows............................................................................................. 86

CSO Reduction Plan/Long-Term Control Plan and CSO Reduction Plan Amendments............87

Nine Minimum Controls .............................................................................................................87

CSO Monitoring..........................................................................................................................88

Annual CSO Report ....................................................................................................................88

Post-Construction Monitoring Program......................................................................................88

H. Outfall evaluation........................................................................................................... 88

I. Elliott West CSO treatment plant – copper reduction assessment................................. 88

J. Elliott West CSO treatment plant – settleable solids removal assessment..................... 89

K. General conditions ......................................................................................................... 89

VI. Permit Issuance Procedures................................................................................................ 89

A. Permit modifications ...................................................................................................... 89

B. Proposed permit issuance............................................................................................... 89

VII.References for Text and Appendices.................................................................................. 89

Appendix A — Public Involvement Information..................................................................... 92

Appendix B — Your Right to Appeal ....................................................................................... 93

Appendix C — Glossary............................................................................................................. 94

Appendix D — Receiving Water Data .................................................................................... 101

Appendix E — Facility Data .................................................................................................... 102

Appendix F — Technical Calculations ................................................................................... 127

Appendix G — Significant Industrial Users........................................................................... 163

Appendix H — Process Flow Diagrams.................................................................................. 164

Appendix I — Response to Comments ................................................................................... 168
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

List of Tables

Table 1. General Facility Information .............................................................................................8

Table 2. Summary of West Point WWTP’s Flow, BOD, and TSS Projections ............................11

Table 3. Future CSO Projects ........................................................................................................15

Table 4. Combined Sewer Overflow Outfalls (38)........................................................................24

Table 5. West Point Ambient Background Data 1.........................................................................26

Table 6. Alki Ambient Background Data 1....................................................................................27

Table 7. Carkeek Ambient Background Data 1..............................................................................27

Table 8. Elliott West Ambient Background Data ..........................................................................28

Table 9. Henderson/MLK Ambient Background Data 1................................................................29

Table 10. Influent Characterization - West Point WWTP .............................................................29

Table 11. Influent Characterization - Alki.....................................................................................29

Table 12. Influent Characterization - Carkeek...............................................................................30

Table 13. Influent Characterization - Elliott West.........................................................................30

Table 14. Influent Characterization - Henderson/MLK.................................................................30

Table 15. Effluent Characterization – West Point WWTP............................................................31

Table 16. Effluent Characterization – Alki CSO TP .....................................................................32

Table 17. Effluent Characterization – Carkeek CSO TP ...............................................................33

Table 18. Effluent Characterization – Elliott West CSO TP .........................................................34

Table 19. Effluent Characterization – Henderson/MLK CSO TP .................................................35

Table 20. West Point WWTP – Sediment Test Results.................................................................36

Table 21. Elliott West CSO treatment plant outfall – sediment remediation activity7..................39

Table 22. Henderson/MLK CSO treatment plant outfall – sediment remediation activity ...........40

Table 23. Untreated CSO outfalls – sediment remediation activity ..............................................42

Table 24. Sediment testing priorities for CSO outfalls & sampling results from 2011 & 2013....43

Table 25. CSO outfalls scheduled to be controlled during this permit term..................................45

Table 26. Alki CSO Treatment Plant – Permit Violations.............................................................46

Table 27. Carkeek CSO Treatment Plant – Permit Violations ......................................................47

Table 28. Elliott West CSO Treatment Plant – Permit Violations and Permit Triggers ...............48

Table 29. Henderson/MLK CSO Treatment Plant – Permit Violations and Permit Triggers .......50

Table 30. West Point WWTP Design Criteria ...............................................................................51

Table 31. Alki CSO Treatment Plant – Design Criteria ................................................................52

Table 32. Carkeek CSO Treatment Plant – Design Criteria ..........................................................53

Table 33. EWCSO Treatment Plant – Design Criteria ..................................................................53

Table 34. Henderson/MLK CSO Treatment Plant – Design Criteria ............................................53

Table 35 Technology-based Limits (West Point WWTP)............................................................54

Table 36 Technology-based Mass Limits.....................................................................................54

Table 37. Technology & Guidance-based Limits for CSO Treatment Plants ...............................55

Table 38. Metal Translators Used in Reasonable Potential Analyses ...........................................57

Table 39. West Point WWTP - Critical Conditions Used to Model the Discharge.......................60
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 40. CSO discharge flows used in dilution calculations .......................................................60

Table 41. Alki CSO TP: Critical Conditions Used to Model the Discharge. ................................61

Table 42. Carkeek CSO TP: Critical Conditions Used to Model the Discharge. ..........................61

Table 43. Elliott West CSO TP: Critical Conditions Used to Model the Discharge. ....................61

Table 44. Henderson/MLK CSO TP: Critical Conditions Used to Model the Discharge. ............62

Table 45. Marine Aquatic Life Uses and Criteria - West Point WWTP, Alki, and Carkeek ........67

Table 46. Marine Aquatic Life Uses and Associated Criteria - Elliott West.................................67

Table 47. Recreational Uses - West Point WWTP, Alki, Carkeek, and Elliott West....................67

Table 48. Receiving Water Criteria Comparison for Henderson/MLK.........................................68

Table 49. Comparison of Dilution Factors ....................................................................................71

Table 50. Comparison of Previous and Proposed Effluent Limits - West Point WWTP..............81

Table 51. Comparison of Previous and Proposed Effluent Limits - Alki CSO TP .......................81

Table 52. Comparison of Previous and Proposed Effluent Limits - Carkeek CSO TP .................82

Table 53. Comparison of Previous and Proposed Effluent Limits - Elliott West CSO TP ...........82

Table 54. Comparison of Previous and Proposed Effluent Limits – Henderson/MLK TP ...........82

Table 55. Lab Accredited Parameters............................................................................................84

List of Figures

Figure 1. Facility Location...............................................................................................................9

Figure 2. West Point WWTP outfall location................................................................................21

Figure 3. Alki CSO treatment plant outfall location......................................................................22

Figure 4. Carkeek CSO treatment plant outfall location................................................................22

Figure 5. Elliott West CSO treatment plant outfall location..........................................................23

Figure 6. Henderson/MLK CSO treatment plant outfall location..................................................24

Figure 7. Sediment sampling locations for West Pt WWTP outfall. .............................................37

Figure 8. Fecal Coliform data for Elliott West CSO TP................................................................49

Figure 9. Residual chlorine data for Elliott West CSO TP.............................................49

Figure 10. West Point’s WWTP’s Mixing Zone ...........................................................................64

Figure 11. Alki’s Mixing Zone ......................................................................................................64

Figure 12. Carkeek’s Mixing Zone Zone.......................................................................................65

Figure 13. Elliott West Mixing Zone.............................................................................................65

Figure 14. Henderson/MLK Mixing Zones...................................................................................66
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

I. 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 domestic wastewater 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) 

 Water quality criteria for groundwaters (chapter 173-200 WAC)

 Whole effluent toxicity testing and limits (chapter 173-205 WAC)

 Sediment management standards (chapter 173-204 WAC)

 Submission of plans and reports for construction of wastewater facilities (chapter 173-240 

WAC)

The following additional regulations apply to communities operating collection systems with 

Combined Sewer Overflows (CSOs):

 Submission of plans and reports for construction and operation of CSO reduction facilities 

(chapter 173-245 WAC)

 US EPA CSO control policy (59 FR 18688)

These rules require any treatment facility owner/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 in 

response to comments. Ecology will summarize the responses to comments and any changes to 

the permit in Appendix I.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

II. Background Information

Table 1. General Facility Information

Facility Information

Applicant King County Wastewater Treatment Division (WTD), Department of Natural 

Resources and Parks (DNRP)

Facility Names and Addresses West Point Wastewater Treatment Plant (WWTP):

1400 Discovery Park Blvd, Seattle, WA 98199

Alki Storage and CSO Treatment Plant:

3380 Beach Drive SW, Seattle, WA 98116-2616

Carkeek Storage and CSO Treatment Plant:

1201 NW Carkeek Park Road, Seattle, WA 98177-4640

Denny/Elliott West Storage and CSO Treatment Plant:

545 Elliott Avenue West, Seattle, WA 98119

Henderson/MLK Storage and CSO Treatment Plant:

9829 42nd Avenue South, Seattle, WA 98118

Responsible Official Christie True

Director, King County DNRP

201 S. Jackson Street, Seattle, WA 98104

Type of Treatment West Point WWTP: Secondary (High-rate oxygenated activated sludge)

Alki, Carkeek, Denny/Elliott West, and Henderson/MLK CSO Treatment 

Plants: Primary with Disinfection

Facility Location

(NAD83/WGS84 reference datum)

West Point WWTP: Puget Sound

Lat: 47.661465 ̊, Long: -122.430693 ̊

Alki CSO Treatment Plant: Puget Sound

Lat: 47.574605 ̊, Long: -122.417348 ̊

Carkeek CSO Treatment Plant: Puget Sound

Lat: 47.710869 ̊, Long: -122.370723 ̊

Elliott West CSO Storage & Treatment Facility: Elliott Bay

Lat: 47.624603 ̊, Long: -122.366339 ̊

Henderson/MLK CSO Storage & Treatment Facility: Duwamish River

Lat: 47.514003 ̊, Long: -122.280776 ̊

Discharge Waterbody Name and Location

(NAD83/WGS84 reference datum)

West Point WWTP: Puget Sound

Lat: 47.661111 ̊, Long: -122.446389 ̊

Alki CSO Treatment Plant: Puget Sound

Lat: 47.57025 ̊, Long: -122.4225 ̊

Carkeek CSO Treatment Plant: Puget Sound

Lat: 47.71264 ̊, Long: -122.38789 ̊

Elliott West CSO Storage & Treatment Facility: Elliott Bay

Lat: 47.61755 ̊, Long: -122.36186 ̊

Henderson/MLK CSO Storage & Treatment Facility: Duwamish River

Lat: 47.51194 ̊, Long: -122.29736 ̊

Permit Status

Issuance Date of Previous Permit June 22, 2009

Application for Permit Renewal Submittal Date June 27, 2013

Date of Ecology Acceptance of Application September 13, 2013

Inspection Status

Date of Last Sampling Inspection December 17-18, 2007

Date of Last Non-sampling Inspection Date June 2, 2014
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Figure 1. Facility Location
Fact Sheet for NPDES Permit WA0029181 Page 10 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

A. Facility description

History

Metro (Municipality of Metropolitan Seattle) constructed the West Point Wastewater 

Treatment Plant (WWTP) in 1965 as a primary treatment plant. In 1972, the amended 

Federal Water Pollution Control Act (PL 92-500) established the National Pollutant 

Discharge Elimination System (NPDES) and pretreatment programs. Federal law provided 

that all sewage treatment plants were to meet secondary treatment requirements by July 1, 

1977. During the period 1976-1977, Metro, the agency having ownership of the plant at the 

time, prepared a draft facility plan and Environmental Impact Statement (EIS) and submitted 

a request for federal funding through EPA Grant No C0530816-01 to meet secondary 

treatment requirements at West Point. In 1979, Metro applied to the USEPA for a Clean 

Water Act Section 301(h) Waiver from secondary treatment at West Point, Richmond Beach, 

and Carkeek. Metro also planned to apply for a waiver for the Alki treatment plant. Metro 

withdrew from the 301(h) waiver process on September 7, 1984, which resolved this process. 

On September 24, 1984, Ecology issued Metro an Administrative Order, Docket No. DE 

84-577. The Order directed Metro to proceed with planning for secondary treatment at West 

Point and set a schedule for attaining secondary treatment no later than February 1, 1991. In 

November 1987, Ecology amended the Order by Consent Decree No. 87-2-05395-4 

changing, among other things, the final compliance date to December 31, 1995. On 

January 1, 1994, King County assumed control of Metro's assets and obligations under the 

existing NPDES permits issued by the Ecology.

On December 8, 1995, Ecology certified that the West Point WWTP achieved the secondary 

treatment level.

Background

West Point WWTP

King County’s Wastewater Treatment Division (WTD) owns and operates the West Point 

WWTP and associated regional facilities. Figure 1 shows the location of the West Point 

WWTP along with the four CSO treatment plants and 38 CSO outfalls that are also regulated 

by the proposed permit. The West Point WWTP is part of King County’s regional system 

that collects and treats wastewater from homes, businesses, and industries surrounding the 

Lake Washington area. King County’s other secondary wastewater treatment plants include 

South Plant (Renton), Brightwater (outside of Woodinville), Vashon, and Carnation.

King County provides wholesale wastewater treatment services to 17 cities, 16 local sewer 

utilities, and one Indian tribe. The county's WTD serves about 1.4 million people within a 

420-square-mile service area, which includes most urban areas of King County and parts of 

south Snohomish County and northeast Pierce County. The local agencies own and operate 

independent collection systems, which include pipelines and pump stations to collect and 

convey wastewater flows in their service area to King County's regional system for treatment 

and disposal. The local agencies have long-term agreements with King County for this 

service. King County owns and operates the regional treatment plants, pipelines, pump 

stations, and other related facilities. The following is a list of the municipalities, sewer 

districts, and water districts that contribute wastewater to this facility: Bothell, Brier, Lake 

Forest Park, Redmond, Seattle, Woodway, Alderwood Water District, Highlands Sewer 

District, North Shore Utilities, NE Sammamish Sewer & Water District, Valley View, 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Ronald Wastewater District, Sammamish Plateau Sewer & Water District, Skyway Water & 

Sewer District, and Olympic Water & Sewer District.

In addition to the domestic and commercial wastewater, nearly all of Seattle’s industrial areas 

discharge to the West Point WWTP. 48 significant industrial users discharge industrial flows 

to the West Point system. Based on King County’s permit application, West Point receives an 

estimated daily flow of 9.6 MGD from significant industrial sources. 

Table 2 presents a summary of the flow, BOD, and TSS projections, as described in the 

County’s NPDES permit application and waste load assessment analysis. The population 

projections take into account planned changes in apportionment of flows between the West 

Point, South Plant, and Brightwater WWTPs.

Table 2. Summary of West Point WWTP’s Flow, BOD, and TSS Projections

Year Res. Population

+ Employment

Percent 

Increase

Average Annual

Flow (MGD)*

Influent BOD 

Loading

(lb/day)

Influent TSS 

Loading

(lb/day)

2014 1,251,888 95 140,000 157,900

2015 1,274,230 1.78% 96 142,500 160,400

2016 1,296,572 1.75% 97 145,000 162,800

2017 1,318,913 1.72% 98 147,500 165,300

2018 1,341,255 1.69% 99 150,000 167,800

2019 1,363,597 1.67% 100 152,500 169,800

Design 1,251,888 215 254,000 274,000

*Annual flow projections are based on average rainfall.

The West Point WWTP is located on the Puget Sound at the western tip of Discovery Park 

between Shilshole Bay and Elliott Bay. King County owns approximately 80 acres of land at 

the West Point site; twenty of these acres are considered subtidal. The current facilities 

occupy approximately 25 acres of land. The West Point WWTP serves mostly a combined 

sewer system area and therefore this NPDES permit contains additional permit requirements 

related specifically to combined sewer systems. Currently, the West Point WWTP provides

secondary treatment for flows up to 300 MGD and provides primary treatment and 

disinfection for flows exceeding 300 MGD. The plants hydraulic capacity is 440 MGD. The 

West Point WWTP is rated as a Class IV treatment plant, according to regulation.

In addition to the West Point WWTP, the proposed permit authorizes discharges from four 

CSO storage and treatment facilities (Alki, Carkeek, Elliott West, and Henderson/MLK) and 

38 individual CSO outfalls.

Alki CSO Treatment Plant

Metro constructed the Alki treatment plant in 1958 as a primary treatment plant to serve the 

Alki Basin, an area of 4,095 acres. It is located in West Seattle at the intersection of Beach 

Drive and Benton Place on 2.8 acres. The service area is largely residential with a projected 

saturation population of 43,700. Commercial activity is concentrated along portions of 

California Avenue and SW Alaska Street. Metro overhauled the facility’s mechanical and 

electrical systems in 1987 and added architectural enclosures. In 1998, the County remodeled 

the facility to operate as a near-fully automated CSO treatment plant, and added flow transfer 

components such as the West Seattle Pump Station and the West Seattle Tunnel. In 1999, 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Ecology incorporated the Alki CSO treatment plant into the West Point WWTP NPDES 

Permit. 

Hydraulic capacity at Alki CSO treatment plant is 45to 65 MGD, depending on tide level. 

During dry-weather operation, the County sends all flows to the West Point WWTP for 

secondary treatment. During wet-weather operation, the Alki CSO treatment plant provides 

primary treatment, chlorine disinfection, and dechlorination to flows that exceed downstream 

collection system capacity. Downstream capacity is limited to 18.9 MGD of flow and 7.1 

MG of storage in the Alki/West Seattle tunnel. To protect the Alki plant, the County 

discharges excess flows at the 63rd Avenue Pump Station outfall, a permitted CSO location. 

According to the County’s 2013 wasteload analysis report, the Alki basin is considered 

substantially built out. The county expects increased flows due to expected densification in 

the basin to be offset by a reduction in per capita water use due to conservation efforts. The 

County expects no net changes in base or average flows in the next 5 years.

The two pump stations upstream of the 63rd Pump Station (Murray & Barton) are undergoing 

construction upgrades. These projects will increase the storage upstream of the 63rd Pump 

Station, helping to reduce untreated combined sewer overflows. These projects will also tend 

to increase the volume treated at Alki. The County will review operational strategies at the 

63rd PS, the inlet regulator gate, and the West Seattle Pump Station/Tunnel as these projects 

move forward.

Carkeek CSO Treatment Plant

Metro constructed the Carkeek treatment plant in 1962 as a primary treatment plant to serve 

the Carkeek Basin. It is located at 1201 NW Carkeek Park Road. In 1994, the County 

constructed a pumping station and converted the plant to a CSO treatment facility. The 

facility began operation as a CSO treatment facility on November 1, 1994, under its thenexisting NPDES Carkeek permit. The current West Point permit contains permit limits for 

the Carkeek CSO treatment plant.

During dry-weather operation the facility operates as a pump station only and King County’s 

West Section off-site crew services the facility three times a week. During wet-weather 

events, operators staff the plant during start up and shut down, as well as provide 

preventative maintenance and operational checks.

According to the County’s 2013 wasteload analysis report, the Carkeek basin is considered 

substantially built out. The county expects increased flows due to expected densification in 

the basin to be offset by a reduction in per capita water use due to conservation efforts. The 

County expects no net changes in base or average flows in the next 5 years.

Elliot West CSO Treatment Facilities

Ecology modified the West Point NPDES Permit in 2005 to include the Elliott West CSO 

storage and treatment facility. The County constructed the Elliott West CSO treatment plant 

as part of the Denny Way/Lake Union CSO Control project. The Denny Way/Lake Union 

CSO Control project consists of several CSO facilities that store and treat CSOs from the 

County’s Dexter and Denny Regulators, and the City of Seattle’s CSOs around Lake Union. 

King County completed construction of the project in May 2005. The project consisted of 

four major elements: the East Portal, which captures flow from a number of sewer lines in 

the South Lake Union area; the 14-foot-diameter Mercer Street Storage and Treatment 

Tunnel; and the Elliott West CSO treatment facility located on Elliott Bay; and the transition 

and dechlorination facilities adjacent to the Denny Way regulator station. Two new CSO 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

outfalls were built in Elliott Bay—one outfall to replace the outfall structure at the Denny 

Way Regulator and another outfall for the Elliott West CSO treatment facility. The Mercer 

Tunnel provides storage for up to 7.2 MG and primary clarification for all flows entering the 

tunnel. The County designed the Elliott West treatment facility to provide final treatment 

(screening, disinfection, and dechlorination) to settled flows that exceed the capacity of the 

tunnel. After storm events, the tunnel and wet well are emptied by pumping these stored 

flows to West Point WWTP. 

King County considers the Elliott West basin as already substantially developed. They expect 

to see continued significant redevelopment in the South Lake Union area over the next 5 

years. Based on their 2013 wasteload analysis, the County estimates base flows and average 

wet weather flows will increase by about 5 to 7% over the next 5 years due to densification in

the basin; these values are partially offset by a reduction in per capita water use due to water 

conservation efforts. 

Henderson/MLK CSO Facilities

Ecology modified the West Point NPDES Permit in 2005 to include the Henderson/MLK 

CSO storage and treatment facility. The County implemented the Henderson/Norfolk CSO 

control project to control the Henderson and Martin Luther King (MLK) CSOs into Lake 

Washington and Norfolk CSOs into the Duwamish River. King County upgraded the 

Henderson/MLK Pump Station and constructed a large storage and treatment tunnel between 

Henderson Street and Norfolk Street in the Rainier Valley. The County designed the facilities 

to provide final treatment (screening, disinfection, and dechlorination) to settled flows that 

exceed the capacity of the storage and treatment tunnel, and to discharge treated flows 

through the Norfolk CSO outfall in the Duwamish Waterway. The County transfers base 

flows, settled solids, and stored flows from the tunnel to the South Plant at Renton or to the 

West Point WWTP, depending on capacity in the Elliot Bay Interceptor, for secondary 

treatment. 

According to the County’s 2013 wasteload analysis report, the Henderson/MLK basin is 

considered substantially built out. The county expects increased flows due to expected 

densification in the basin to be offset by a reduction in per capita water use due to 

conservation efforts. The City of Seattle is starting construction on their Henderson South

CSO project that will increase conveyance and pumping capacity to the Henderson/MLK 

basin, resulting in increased volumes and peak flows. The City and the County signed an 

agreement on the South Henderson Projects in January 2014 to address any impacts of these 

new flows. Increased volumes are expected from the City’s CSO basins 44, 45, 46, 47b/171, 

and 47c. Peak flow volume increases are expected from basins 46, 47b/171, and 47c. It is 

unknown at this time if flow changes are expected from basin 49 since that project is still 

under review. The County expects that the increased flows from the City will not result in 

violating the CSO control standard at the Henderson Pump station CSO outfall or the 

Henderson/MLK CSO storage and treatment facility. The County and City will monitor 

changes with flow monitoring and modeling.

Collection system status

The King County wastewater service area is divided into the East and West Sections. 

Wastewater from the East Section is conveyed to the South Treatment Plant; West Section 

wastewater flows to the West Point WWTP. The West Section service area includes areas 

north and west of Lake Washington and the City of Seattle. Developments within the north 

Lake Washington area were constructed with separate sanitary and storm sewers. Within the 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

City of Seattle, approximately 42,000 acres or 75 percent of the total area is constructed with 

combined sewers. Sanitary and combined flows from Seattle are merged prior to arriving at 

the West Point WWTP.

West Point WWTP receives wastewater from the west division collection system, a series of 

pump and regulator stations and related trunks and interceptors. Sewage flows by gravity via 

two influent tunnels (Ft. Lawton 144” Diameter and the Old Ft. Lawton Tunnel 84” 

Diameter) and enters the WWTP site at the influent control structure. The County’s 

supervisory control and data acquisition (SCADA) computer systems automatically monitor 

and control the flow through the west division collection system. The control system 

minimizes surges, maximizes flow to the plant, and maximizes use of collection system 

storage to limit combined sewer overflows.

Combined Sewer Overflows

King County has 38 combined sewer overflow outfalls which discharge untreated sewage 

and stormwater during periods of heavy precipitation, within the city of Seattle. The 

collection system, as configured in 1983, discharged nearly 2.3 billion gallons per year of 

untreated sewage and stormwater from a total of 431 overflow events. Since 1988, the 

Metro/County has completed a number of projects to reduce the volume and frequency of 

CSOs. Based on data from 2006-2012, King County’s average annual untreated CSO volume 

has been approximately 811 million gallons per year.

Between 1995 and 2005, King County constructed the Elliott West and Henderson/MLK

projects, in addition to other CSO projects, to reduce CSO overflows. The County also

implemented a real-time, web-based notification system that the public can use to assess 

when CSOs are discharging. The website can be found at:

http://www.kingcounty.gov/environment/wastewater/CSO/RealTime/SeattleOverview.aspx.

The County’s 2008 CSO Reduction Plan Update identified priority projects at locations near 

beach areas. Consequently, King County began construction on four CSO control projects 

near beach areas in late 2013. These projects include CSO storage tanks in South Magnolia, 

North Beach, and at the Murray pump station, and neighborhood green stormwater 

infrastructure in the Barton neighborhood of West Seattle. 

In 2012, the King County Council adopted the 2012 CSO Long Term Control Plan 

Amendment, and in 2013 the County entered a CSO consent decree with Ecology, EPA, and 

the DOJ. Both the LTCP and CD include nine CSO control projects to reduce CSOs to no 

more than one untreated event per year on average at each CSO location by 2030. Table 3

outlines future CSO control projects as presented in the County’s 2012 CSO Long Term 

Control Plan Amendment and 2013 consent decree.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 3. Future CSO Projects

Project Name Project Description Project 

Completion Water Body

Hanford #1 (DSN 031) 0.34 MG storage and new conveyance 2019 Duwamish River

Brandon Street / South 

Michigan Street (DSN 041/039)

66 MG peak-flow CSO treatment facility 

and new conveyance

2022 Duwamish River

Chelan Avenue (DSN 036) 3.85 MG storage tank 2023 Duwamish River

3

rd Avenue W (DSN 008) Joint City-County 7.23 MG storage tank

or

County-only 4.18 MG storage tank

2023 West Ship Canal

West Michigan Street / 

Terminal 115 (DSN 042/038)

0.32 MG storage pipe 2025 Duwamish River

University/Montlake

(DSN 015)

Joint City-County 5.23 MG storage tank

or

County-only 2.94 MG storage tank

2028 Lake Union/

East Ship Canal

Montlake (DSN 014) Joint City-County 7.87 MG storage tank

or

County-only 6.6 MG storage tank

2028 West Ship Canal

Hanford #2/ Lander Street/ King 

Street/ Kingdome (DSN 

032/030/028/029)

151 MG peak-flow CSO treatment 

facility

2030 Duwamish River

11th Avenue NW Increased conveyance providing 3,200 

feet of 84-inch diameter pipe

2030 West Ship Canal

Inflow and Infiltration

King County created a Regional Infiltration and Inflow (I/I) Control Program in 1999 as part 

of the Regional Wastewater Services Plan (RWSP) to explore the feasibility of regional I/I 

control. The purpose of the program is to reduce the amount of peak wet weather flow 

entering the County's wastewater conveyance system when it is cost-effective to do so. 

Reduction of I/I in the system may prevent sanitary sewer overflows and decrease the costs 

of conveying and treating extraneous flows.

In response to the RWSP I/I Control Program policies, County staff, working in a 

consensus-based approach with the local sewer agencies, conducted a comprehensive 6-year, 

$41 million, I/I control study. The study began in 2000 and culminated with the County 

Executive’s recommendation for a regional I/I control program. The following work was 

completed as part of this study:

 Levels of I/I for each local agency tributary to the regional system were defined

through extensive flow monitoring and modeling program (2001-2002).

 10 pilot projects were selected and constructed in 12 local agency jurisdictions to 

demonstrate the effectiveness of collection system rehabilitation projects and to test 

various technologies and gain cost information (2003-2004).

 Final draft model standards, procedures, policies, and guidelines were developed 

(October 2004) for use by local agencies to reduce I/I in their systems. 

 A thorough benefit-cost analysis was conducted to determine the cost-effectiveness of 

I/I reduction (November 2005).

 A long-term regional I/I control plan was developed; approved by the King County 

Council in May 2006.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

 King County worked with the local sewer agencies to conduct an I/I reduction 

feasibility analysis and selected three initial I/I reduction project areas (2007-2009). 

 The Skyway Water and Sewer District I/I reduction project (2010-2014).

The County is currently analyzing the effectiveness of the Skyway Initial I/I Reduction 

Project (“Demonstration Project”). The project set out to rehabilitate close to 350 side sewers 

on private property, aiming to reduce flows by at least 60%, or about 1 MGD, in a Skyway 

Water and Sewer District basin. This reduction prediction was based conservatively on the 

reduction achieved in a similar, adjacent pilot project completed in 2003/4, in which I/I peak 

flow was reduced by 88.5%. For the Skyway Project, a 60% flow reduction would eliminate 

the need for the downstream 0.27 MG Bryn Mawr Storage Project. Project results fell short 

of the goal, with peak flows reduced by only 19% in the project basin. There are many 

complex reasons for this lower than expected flow reduction, most of which are contributed 

to basin-specific characteristics and conditions encountered during construction. One unique 

challenge was the discovery of a previously unrecognized flow diversion that sent flows from 

an adjacent basin into the project basin, diluting flow reduction results when flow monitoring 

was conducted. Other challenges include the effects of sump pumps and foundation drains, 

groundwater entering unrehabilitated side sewers downslope in the basin, and a higher than 

anticipated number of sewers being left out of the project for replacement due to field 

conditions. While the full reduction target was not met, it is still estimated that the sizing or 

timing of the storage project were beneficially affected by the Skyway project. Continued 

flow monitoring and modeling will determine the ultimate storage requirements, at which 

point the resulting benefit of the I/I reduction can be determined. For more information see 

the full report on the County’s I/I Program website.

Treatment processes

West Point WWTP

The West Point WWTP is a 215-million-gallon per day (maximum month design flow) high 

rate oxygen activated sludge secondary plant. Metro designed the plant to provide secondary 

treatment of flows up to 300 MGD. The liquid treatment process includes screening, grit 

removal, primary clarification, biological treatment using high rate oxygenated activated 

sludge, secondary clarification, chlorine disinfection, and dechlorination. The disinfected 

effluent discharges to Puget Sound through a multi-port diffuser located about 3,600 feet 

offshore at a depth of about 240 feet below mean lower low water. For flows above 300 

MGD and up to 440 MGD, the treatment process consists of screening, de-gritting, primary 

sedimentation in clarifiers, disinfection with sodium hypochlorite in a chlorine contact 

channel, and dechlorination. As for solids treatment, the primary and waste activated solids 

are blended in a tank and co-thickened via gravity belt thickeners. The thickened sludge is 

anaerobically digested, and dewatered by centrifuges. The plant produces several products 

including biosolids used in agriculture and forestry, reclaimed water used for in-plant 

processes and irrigation, and methane that fuels the raw sewage pump engines and power 

generation system. A schematic of the treatment process is presented in Appendix H.

King County indicated in their permit application that 29 non-categorical significant

industrial users (SIUs) and 19 categorical SIUs contribute to the collection system. These 

numbers are down from five years ago when King County reported 33 non-categorical SIUs 

and 31 categorical SIUs. See Appendix G for a listing of the significant users.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

The West Point WWTP is rated as a Class IV plant. The West Section employs personnel in 

operations, maintenance, facilities, process control, laboratory analysis, administration, and

off-site operations and maintenance. The section consists of approximately 156 FTEs with 10 

to 15 vacancies at any given time. Operations staff consists of about 70 employees, where 21 

employees have Group IV certifications, 21 have Group III certifications, 13 have Group II 

certifications, and 11 have Group I certifications. 

Wet Weather Operation - The proposed permit authorizes CSO-related bypasses of the 

secondary treatment portion of the West Point WWTP when the instantaneous flows to the 

WWTP exceed 300 MGD as a result of precipitation. The wastewater that bypasses 

secondary treatment must receive floatables removal, primary clarification, and disinfection, 

and must at all times meet the effluent limits listed in S1. See Section III.A of this fact sheet 

for more information on wet weather authorization.

Alki CSO Treatment Plant

The Alki CSO treatment plant operates only when flows in the Alki service area exceed 18.9 

MGD or when the storage in the tunnel has been filled. The County diverts the base flow to 

the West Seattle Pump Station, then directly to the West Point WWTP for secondary 

treatment. The County diverts wet weather flows in excess of 18.9 MGD or 7.1 million 

gallons of storage (West Seattle Tunnel) to the Alki CSO treatment plant for treatment. 

Treatment consists of disinfection using sodium hypochlorite, screening, and primary 

sedimentation followed by dechlorination with sodium bisulfite. Treated flows discharge to 

the Puget Sound through the existing outfall.

Flows in excess of the Alki CSO treatment plant capacity discharge through the 63rd Avenue 

pump station outfall, which is a permitted CSO located upstream of the treatment plant. King 

County is already meeting the Ecology standard of no more than one untreated overflow per 

year at this location.

Treatment plant solids and grit are conveyed to the Alki Trunk for transfer to the West

Seattle Tunnel and further conveyance to West Point WWTP. Screenings are collected, 

stored on-site, and disposed of as solid waste.

Carkeek CSO Treatment Plant

During dry weather and normal flows, the facility operates as a pump station only, pumping 

wastewater to the West Point WWTP. The Carkeek CSO treatment plant operates only 

during storm events when the combined sanitary/stormwater flows exceed the Carkeek Pump 

Station capacity (9.2 MGD), or when the downstream interceptor is full. The plant stores 

excess flows, solids, and grit, and then automatically returns them to the pump station wet 

well when there is capacity available at the pump station, or at the end of the storm. The 

pump station then pumps flow to the West Point WWTP.

If flows exceed the storage capacity of the treatment tanks, treated flows discharge to Puget 

Sound through a 4,200-foot long outfall. After the storm event, or when there is capacity 

available at the pump station, any wastewater in the plant is pumped to the West Point WWTP.

The treatment process consists of bar screens, a grit chamber, primary sedimentation, 

disinfection with sodium hypochlorite, and dechlorination with sodium bisulfite. When 

pumping capacity is exceeded wastewater spills over the pump wet well weir into the vault 

where hypochlorite is added to control odors and provide disinfection. From the vault 

wastewater flows into the grit tank that is equipped with aerators; settled grit is pumped to the 

solids storage tanks. From the grit tanks, the wastewater flows into two primary sedimentation 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

tanks. Solids settled in the primary sedimentation tanks are also pumped to the solids storage 

tanks. When both sedimentation tanks are full, wastewater flows into the contact tank for 

dechlorination, and from there over a weir to the outfall in Puget Sound.

Elliott West CSO Storage and Treatment Facility

The Elliott West CSO storage and treatment facility and associated conveyance facilities 

work to reduce CSOs to south, east, and west Lake Union and to Elliott Bay at the Denny 

Way Regulator Station. King County operates the facility in five modes depending on the 

magnitude of the rain event. The operating modes are as follows1:

Standby Mode (Dry Weather Operation) - Under dry weather conditions, the facility does not 

divert flow. Wastewater continues to flow through the Lake Union Tunnel and other conveyance 

facilities to the Elliott Bay Interceptor (EBI) to be treated at the West Point WWTP. The Mercer 

Tunnel is empty so that the storage capacity is maintained for storm events.

Tunnel Storage Mode - During storm conditions, when water levels rise to established levels 

in the Lake Union Tunnel Regulator, Central Trunk Diversion Structure, and/or Denny Way 

Diversion Structure, the County diverts flow from these structures to the Mercer Street 

Tunnel for storage. After the storm, or whenever the EBI has capacity, stored wastewater is 

pumped to West Point. Wastewater that previously discharged into Elliott Bay or Lake Union 

CSOs now is captured in the Mercer tunnel.

CSO Pumping and Treatment Mode - When tunnel storage and the EBI reach capacity, 

Elliott West treatment begins. Flow is pumped from the downstream end of the Mercer 

Tunnel into the floatable-control channel. The wastewater flows through mechanical screens 

to remove floatable materials, then into the effluent channel for injection with sodium 

hypochlorite for disinfection. Prior to discharge into Elliott Bay, the treated wastewater is 

treated with sodium bisulfite to neutralize residual chlorine. Throughout this pump and 

treatment mode, the County pumps solids from the base of tunnel to the EBI, reducing the 

discharge of solids to the Puget Sound.

Pumping and Treatment Extreme Event Mode – The County designed the CSO treatment 

plant with a capacity of 250 MGD, for the one-event-per-year storm. When flows exceed 250 

MGD untreated wastewater discharges from the Denny Way Regulator Station via the 

extended Denny Way CSO outfall. Flows entering the Mercer Street Tunnel in excess of 250 

MGD can overflow with no floatables control or disinfection. Meanwhile, 250 MGD of 

treated effluent continues to discharge through the Elliott West outfall.

Dewatering Mode (Tunnel Drawdown) - Following a CSO event, when capacity is available 

in the EBI, wastewater stored in the tunnel is pumped to the EBI and conveyed to the West 

Point WWTP for secondary treatment. Solids that settled in the tunnel during the event are 

also flushed to West Point WWTP. 

Henderson/MLK CSO Treatment and Storage Facility

King County’s East Section operates and maintains the Henderson/MLK CSO storage and 

treatment facility. The facility reduces CSO discharges to Lake Washington and the 

Duwamish River. The Henderson/MLK tunnel is 14’8” in diameter and 3100 feet long and 

holds 3.5 million gallons of combined wastewater. The different operating modes for the 

facility depend on the rain event magnitude as follows:

 

1 King County and City of Seattle, Denny Way/Lake Union CSO Control Facilities Plan, July 1998.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Inlet Regulator Operation - The Henderson/MLK tunnel inlet regulator accepts flows from 

the Henderson pump station and the Empire Way Trunk. Under typical, non-storm-event 

flow conditions wastewater flows through the Henderson tunnel inlet regulator, to the 

Henderson Street Trunk on Martin Luther King Way, to the Henderson Diversion structure, 

and then on to South Plant for treatment. When the conveyance line reaches capacity, the 

MLK regulator gate closes, filling the regulator station until combined sewage flows over a 

weir into the Henderson/MLK tunnel. 

Storage Mode - The tunnel stores combined sewage during peak flow events, and as long as 

the tunnel capacity is not exceeded, the combined sewage is returned to the collection system 

for additional treatment at a WWTP. Hypochlorite is injected automatically upon flow 

overtopping the tunnel’s inlet weir. The hypochlorite feed rate is controlled automatically 

based on the quantity of combined sewage entering the tunnel. After a filling event, when the 

trunk line returns to a specified level, the modulating drain valve opens and slowly drains the 

tunnel. The tunnel is drained such that the stored flows can be diverted at the Henderson 

Diversion Structure to either South Plant or West Point. After draining, the County has the 

ability to flush settled solids from the tunnel into the Henderson Trunk to convey them to a 

WWTP for treatment.

Treated CSO - In the event that the tunnel reaches capacity and wastewater continues to flow 

into the tunnel, the combined sewage flows over the discharge weir and discharges by gravity 

through two bar screens, where it is dechlorinated, then flows to the Norfolk outfall (044) on 

the Duwamish River at river km 10.5. After the storm event, combined sewage remaining in 

the tunnel is drained into the Henderson Trunk and conveyed to a WWTP for treatment. 

Solid wastes/Residual solids

West Point WWTP

The treatment facilities remove solids during the treatment of the wastewater at the headworks 

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

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

equipment. The plant generates approximately 3,500 tons of grit annually. Grit, rags, and 

screenings are drained and recycled or disposed of as solid waste. The County installed new 

influent screens with 3/8 inch openings in 2014. As a result of these new screens, the capture of 

screenings, rags, and debris is expected to increase.

Primary sludge and waste-activated sludge are blended together and thickened by gravity belt 

thickeners. The thickened sludge is then pumped to one-of-six anaerobic, mesophilic digesters. From 

the digesters, the digested sludge is withdrawn and dewatered by one-of-four centrifuges. Polymers 

are used in the gravity belt thickeners and centrifuges to aid sludge thickening/dewatering. The 

digestion process produces nutrient-rich, organic byproducts called biosolids.

According to the County’s 2012 Biosolids Quality Report, biosolids contain water, sand, 

organic matter, microorganisms, trace metals, and other chemicals. The report states, “because 

of their moisture content, humus-like characteristics, essential nutrients for plants, and very low 

levels of pollutants, biosolids are beneficial and safe to use as a soil conditioner, fertilizer for 

forest trees and agricultural crops, and as an ingredient of composts for landscaping.”
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

King County Wastewater Treatment Division began recycling biosolids on land in 1973. The 

program has grown to beneficially recycle more than 110,000 wet tons (or approximately 

27,000 dry tons) annually in forestry, agriculture, soil reclamation and compost.

Biosolids are regulated under both state and federal regulations (WAC 173-308 and 40 CFR 

Part 503). King County routinely monitors its biosolids for physical, chemical, and microbial 

characteristics, to examine changes over time, and to determine appropriate application rates 

for biosolids at reuse sites. The County’s West Point biosolids continue to meet quality 

standards for metals, pathogen reduction (Class B), and vector attraction reduction, which 

means it is safe for all land application projects.

The 2012 data report indicates that King County’s biosolids quality is excellent when 

compared with all relevant criteria. Concentrations of regulated metals in biosolids were 

consistently below the most stringent state and federal standards for land application. While 

not required by federal or state biosolids regulations, King County analyzes its biosolids for 

135 trace organic compounds listed on the EPA Priority Pollutant List (40 CFR 423, 

Appendix A) and the Hazardous Substances List (40 CFR 116.4 A & B). Less than 

15 percent of these compounds were detected in biosolids during 2007. The County detected 

twenty priority pollutants at very low concentrations in the West Point biosolids. These 

compounds included polynuclear aromatic hydrocarbons (PAHs), phthalates, polychlorinated 

biphenyls (PCBs), and solvents.

CSO Treatment Plants

For the Alki and Carkeek CSO facilities, grit and primary sludge settle in the storage tanks. 

After the storm subsides, the storage tank contents, solids and liquids, are pumped to the 

West Point WWTP for treatment.

For the Elliott West and Henderson/MLK facilities, solids settle in the storage tunnels. 

Following each storm event, solids in the Mercer Tunnel are automatically flushed and

pumped to the West Point WWTP and solids in the Henderson/MLK Tunnel are flushed and 

pumped to the South Plant or West Point WWTP for treatment.

Discharge outfalls

West Point WWTP Outfall

The plant discharges treated effluent to the Puget Sound via an eight-foot diameter, 

reinforced concrete pipe. The diffuser section consists of 600 feet of pipeline with 200 ports 

that run on the north and south sides of the pipe. The 4.5- to 5.75-inch diameter ports are 

located about one foot above the spring line. The diffuser terminates about 3,600 feet 

offshore at a depth of approximately 230 feet below mean lower low water.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Figure 2. West Point WWTP outfall location

A 2004 outfall inspection revealed that all external components of the outfall appeared to be 

in good condition with no physical damage or lack of flow coming from the diffusers. The 

inspectors found minimal marine growth along the outfall alignment with slightly more 

located in the diffuser area.

King County inspected the West Point outfall and diffuser again on September 14, 2011, and 

provided Ecology with a report with video. The inspectors observed that the outfall line was 

completely buried from a rock pile at 196 feet of water to the shoreline. The inspectors found

gaps in the pipeline around station 30 but they noted that no effluent appeared to be 

discharging from these gaps. Overall they found the outfall pipe in good condition with 

heavy sea anemone growth along the deeper sections. No remedial actions were 

recommended. The proposed permit requires another inspection during the permit term.

Alki CSO Treatment Plant Outfall

The Alki CSO treatment plant discharges primary treated and disinfected CSO effluent to the

Puget Sound via a 42-inch diameter pipe, which extends approximately 2,000 feet offshore 

and terminates at a depth of approximately 143 feet below mean lower low water. The 

diffuser is fitted with eight 12 inch diameter risers/ports, with rubber check valves, spaced 20 

feet apart in alternating directions. The two end ports discharge at an angle of 135 with 

respect to the other risers/ports. Engineers rated the outfall capacity at 45 MGD at mean 

higher high water and 65 MGD at mean lower low water. Flows in excess of these values 

discharge via the 63rd Avenue Pump Station outfall, a permitted CSO location.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Figure 3. Alki CSO treatment plant outfall location

Carkeek CSO Treatment Plant Outfall

The Carkeek CSO treatment plant discharges primary treated and disinfected CSO effluent to

the Puget Sound via a 33-inch diameter 4,200-foot outfall, which extends approximately 

2,200 feet offshore and terminates at a depth of 195 feet below mean lower low water. The

outfall consists of a 50 foot diffuser with 13 ports.

Figure 4. Carkeek CSO treatment plant outfall location

Elliott West CSO Storage and Treatment Outfall

The Elliott West CSO treatment plant discharges primary treated and disinfected CSO effluent to 

Elliott Bay via a 96-inch diameter outfall, which extends 400 feet offshore and terminates at a 

depth of 60 feet below mean lower low water. 

During large storm events when the Mercer tunnel and Elliott West facility capacities are 

exceeded, the Denny Regulator Station discharges untreated CSO water to Elliott Bay via the 

Denny CSO outfall. The 120-inch Denny CSO outfall extends 100 feet offshore and terminates 

at a depth of 20 feet below mean lower low water.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Figure 5. Elliott West CSO treatment plant outfall location

Henderson/MLK CSO Treatment and Storage Outfall

The Henderson/MLK CSO facility discharges primary treated and disinfected CSO effluent

to the Duwamish River through the existing Norfolk outfall. The Norfolk outfall is located on 

the north bank of the Duwamish River at approximately river km 10.5. The 84-inch diameter 

outfall approaches the river bank at a 90-degree angle to the river flow and is flush with the 

bank. The outfall terminates with a flap gate that is assumed to be completely open during 

discharge events.2

Combined Sewer Overflow Outfalls

Table 4 lists King County’s 38 combined sewer overflows outfalls (not including the CSO 

treatment plant outfalls), which have the potential to discharge untreated sewage and 

stormwater during precipitation events. Based on monitoring data in King County’s 2012 

Annual CSO Report and King County’s 2012 Long Term Control Plan Amendment, 16 of the 

38 CSO outfalls meet the controlled performance standard of “greatest reasonable reduction” 

as defined in chapter WAC 173-245-020(22). Table 4 provides project status for the 

uncontrolled outfalls as described in King County’s 2012 Long Term Control Plan 

Amendment.

 

2 King County, Department of Natural Resources, Wastewater Treatment Division, Henderson/M.L. King CSO Control 

Facilities Plan, February 2002. Chapter 22, pg. 2.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Figure 6. Henderson/MLK CSO treatment plant outfall location

Table 4. Combined Sewer Overflow Outfalls (38)

Outfall

No. Outfall Name Receiving Water Control Status Project Status

003 Ballard Siphon Regulator Lake Washington 

Ship Canal

Uncontrolled Control project completed in 

December 2013.

004 11th Avenue NW (East Ballard 

Overflow)

Lake Washington 

Ship Canal

Uncontrolled Overflow reduction project 

underway.

006 Magnolia South Overflow Elliott Bay/Puget 

Sound

Uncontrolled Control project underway.

007 Canal Street Overflow Lake Washington 

Ship Canal

Controlled

008 3

rd Avenue West Overflow Lake Washington 

Ship Canal

Uncontrolled Control project in KC’s 

Recommended CSO Control Plan.

009 Dexter Avenue Regulator Lake Union Uncontrolled Control project completed. Full 

control being achieved by 

operational adjustments and 

upstream GSI.

011 E. Pine Street PS Emergency 

Overflow

Lake Washington Controlled

012 Belvoir PS Emergency Overflow Lake Washington 

(Union Bay)

Controlled

013 Martin Luther King Way 

Trunkline Overflow

Lake Washington Controlled

014 Montlake Overflow Lake Washington 

Ship Canal

Uncontrolled Control project in KC’s 

Recommended CSO Control Plan.

015 University Regulator Lake Wash Ship 

Canal (Portage Bay)

Uncontrolled Overflow reduction project 

completed in 1994. Control project 

in KC’s Recommended CSO 

Control Plan.

018 Matthews Park PS Emergency 

Overflow

Lake Washington Controlled

027a Denny Way Regulator Elliott Bay/Puget 

Sound

Uncontrolled Control project completed. Full 

control being achieved by 

operational adjustment and facility 

mods.
Fact Sheet for NPDES Permit WA0029181 Page 25 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 4. Combined Sewer Overflow Outfalls (38)

Outfall

No. Outfall Name Receiving Water Control Status Project Status

028 King Street Regulator Elliott Bay/Puget 

Sound

Uncontrolled Control project in KC’s 

Recommended CSO Control Plan.

029 Kingdome (Connecticut St

Regulator)

Elliott Bay/Puget 

Sound

Uncontrolled Installation of a storage pipeline in 

1994. Partial separation in 1999.

Control project in KC’s 

Recommended CSO Control Plan.

030 Lander Street Regulator Duwamish River –

East Waterway

Uncontrolled Control project in KC’s 

Recommended CSO Control Plan.

031a,b

,c

Hanford #1 Regulator Duwamish River –

East Waterway

Uncontrolled Overflow reduction project 

completed in 1992. Final control 

project included in KC’s 

Recommended CSO Control Plan.

032 Hanford #2 Regulator Duwamish River –

East Waterway

Uncontrolled Control project in KC’s 

Recommended CSO Control Plan.

033 Rainier Avenue PS Emergency 

Overflow

Lake Washington Controlled

034 E. Duwamish Siphon/Duwamish 

PS Emergency Overflow

Duwamish River Controlled

035 W. Duwamish 

Siphon/Duwamish PS 

Emergency Overflow

Duwamish River Controlled

036 Chelan Avenue Regulator Duwamish River –

West Waterway

Uncontrolled Control project in KC’s 

Recommended CSO Control Plan.

037 Harbor Avenue Regulator Duwamish River –

West Waterway

Uncontrolled Control project completed.

CSO site appears controlled –

Modeling confirmation underway.

038 Terminal 115 Overflow Duwamish River Uncontrolled Control project in KC’s 

Recommended CSO Control Plan.

039 Michigan S. Regulator Duwamish River Uncontrolled Control project in KC’s 

Recommended CSO Control Plan.

040 8

th Avenue South Regulator 

(West Marginal Way PS 

Emergency Overflow)

Duwamish River Controlled

041 Brandon Street Regulator Duwamish River Uncontrolled Overflow reduction project 

completed in 2003. Final control 

project included in KC’s 

Recommended CSO Control Plan.

042 Michigan W. Regulator Duwamish River Uncontrolled Control project in KC’s 

Recommended CSO Control Plan.

043 East Marginal Way PS 

Emergency Overflow

Duwamish River Controlled

044a Norfolk Street Regulator Duwamish River Controlled

045 Henderson Street Pump Station 

Emergency Overflow

Lake Washington Controlled

048 North Beach PS Emergency

Overflow 

Puget Sound Uncontrolled Control project underway

049 30th Avenue N.E. PS 

Emergency Overflow

L. Wash. Ship Canal

(Union Bay)

Controlled

053 53rd St SW PS Emerg. Overflow Puget Sound Controlled

054 63rd St SW PS Emerg. Overflow Puget Sound Controlled

055 S.W. Alaska Street Overflow Puget Sound Controlled

056 Murray St PS Emerg. Overflow Puget Sound Uncontrolled Control project underway

057 Barton St PS Emerg. Overflow Puget Sound Uncontrolled Control project underway
Fact Sheet for NPDES Permit WA0029181 Page 26 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

B. Description of the receiving water

King County submitted ambient background data with their permit application in a report 

called Receiving Water Characterization Study (June 2013). This report presented results of a 

characterization study of ambient receiving water in central Puget Sound, Elliott Bay, and the 

Duwamish River. 

West Point WWTP

The West Point WWTP outfall discharges to central Puget Sound. Other nearby point source 

outfalls include King County’s South Plant outfall and Bainbridge Island’s WWTP outfall.

Significant nearby non-point sources of pollutants include stormwater runoff, industrial 

runoff, and maritime uses. Water quality impairments for this waterbody are discussed in 

Section III.E of this fact sheet.

Ecology used ambient data from sampling station KSBP01 in King County's receiving water 

study to assess compliance with water quality standards. This sampling station is located six 

miles north of the West Point outfall (47.743960 ̊, -121.428169 ̊). 

Table 5. West Point Ambient Background Data 1

Parameter Value 

Temperature (highest annual 1-DADMax) 14.0o C (at 1.3 m below surface)

pH (Minimum / Maximum) 7.5 / 8.0 std units

Salinity (minimum) 26.1 pss

Dissolved Oxygen (10th percentile) 6.1 mg/L

Total Ammonia (max) 0.085 mg/L as N (from LSNT01)

Fecal Coliform (max) 4 / 100 mL

TSS (max) 7 mg/L

Arsenic (90th percentile), Dissolved / Total 21.390 / 1.360 μg/L

Cadmium (90th percentile), Dissolved / Total 0.073 / 0.081 μg/L

Chromium (90th percentile), Dissolved / Total 0.148 / 0.159 μg/L

Copper (90th percentile), Dissolved / Total 0.363 / 0.410 μg/L

Lead (90th percentile), Dissolved / Total 0.005 / 0.044 μg/L

Mercury (90th percentile), Dissolved / Total 0.00020 / 0.00048 μg/L

Nickel (90th percentile), Dissolved / Total 0.424 / 0.437 μg/L

Silver (90th percentile), Dissolved / Total 0.027 / 0.028 μg/L

Zinc (90th percentile), Dissolved / Total 0.643 / 0.685 μg/L

1 Data source: King County Receiving Water Characterization Study - Final Report, June 2013.

2 Data reported in 2013 report shows 90th percentile of dissolved fraction as slightly larger than total

concentration. This discrepancy is likely within the precision of the analytical method.

Alki CSO Treatment Plant

The Alki CSO treatment plant discharges to the Puget Sound. Another nearby point source 

outfall includes King County’s South Plant outfall. Significant nearby non-point sources of 

pollutants include stormwater runoff.

Ecology used ambient data from sampling station LSNT01 in King County's receiving water 

study to assess compliance with water quality standards. This sampling station is located 

three miles south of the Alki outfall (47.533333 ̊, -121.433333 ̊). 
Fact Sheet for NPDES Permit WA0029181 Page 27 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 6. Alki Ambient Background Data 1

Parameter Value 

Temperature (highest annual 1-DADMax) 12.7o C (at 1.3 m below surface)

pH (Minimum / Maximum) 7.4 / 8.0 std units

Salinity (minimum) 27.7 pss

Alkalinity (10th percentile) 97.5 mg/L CaCO3

Dissolved Oxygen (10th percentile) 5.8 mg/L

Total Ammonia (max) 0.085 mg/L as N

Fecal Coliform (max) 1 / 100 mL

TSS (max) 7.5 mg/L

Antimony (90th percentile), Dissolved / Total 0.172 / 0.178 μg/L

Arsenic (90th percentile), Dissolved / Total 1.450 / 1.450 μg/L

Cadmium (90th percentile), Dissolved / Total 0.073 / 0.081 μg/L

Chromium (90th percentile), Dissolved / Total 20.150 / 0.145 μg/L

Copper (90th percentile), Dissolved / Total 0.354 / 0.428 μg/L

Lead (90th percentile), Dissolved / Total 0.006 / 0.045 μg/L

Mercury (90th percentile), Dissolved / Total 0.00020 / 0.00038 μg/L

Nickel (90th percentile), Dissolved / Total 0.427 / 0.476 μg/L

Silver (90th percentile), Dissolved / Total 0.026 / 0.029 μg/L

Zinc (90th percentile), Dissolved / Total 20.605 / 0.538 μg/L

1 Data source: King County Receiving Water Characterization Study - Final Report, June 2013. 2 Data reported in 2013 report shows 90th percentile of dissolved fraction as slightly larger than total 

concentration. This discrepancy is likely within the precision of the analytical method.

Carkeek CSO Treatment Plant

The Carkeek CSO treatment plant discharges to Puget Sound. Pipers Creek also discharges to 

Puget Sound and affects water quality in this area. Significant nearby non-point sources of 

pollutants include stormwater runoff.

Ecology used ambient data from sampling station KSBP01 in King County's receiving water 

study to assess compliance with water quality standards. This sampling station is located two 

miles northwest of the Carkeek outfall (47.743960 ̊, -121.428169 ̊). 

Table 7. Carkeek Ambient Background Data 1

Parameter Value 

Temperature (highest annual 1-DADMax) 14.0o C (at 1.3 m below surface)

pH (Minimum / Maximum) 7.5 / 8.0 std units

Salinity (minimum) 26.1 pss

Dissolved Oxygen (10th percentile) 6.1 mg/L

Total Ammonia (max) 0.085 mg/L as N

Fecal Coliform (max) 4 / 100 mL

TSS (max) 7 mg/L

Arsenic (90th percentile), Dissolved / Total 21.390 / 1.360 μg/L

Cadmium (90th percentile), Dissolved / Total 0.073 / 0.081 μg/L

Chromium (90th percentile), Dissolved / Total 0.148 / 0.159 μg/L

Copper (90th percentile), Dissolved / Total 0.363 / 0.410 μg/L

Lead (90th percentile), Dissolved / Total 0.005 / 0.044 μg/L

Mercury (90th percentile), Dissolved / Total 0.00020 / 0.00048 μg/L

Nickel (90th percentile), Dissolved / Total 0.424 / 0.437 μg/L

Silver (90th percentile), Dissolved / Total 0.027 / 0.028 μg/L

Zinc (90th percentile), Dissolved / Total 0.643 / 0.685 μg/L

1 Data source: King County Receiving Water Characterization Study - Final Report, June 2013. 2 Data reported in 2013 report shows 90th percentile of dissolved fraction as slightly larger than total 

concentration. This discrepancy is likely within the precision of the analytical method.
Fact Sheet for NPDES Permit WA0029181 Page 28 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Elliott West CSO Treatment Plant

The Elliott West CSO treatment plant outfall discharges to Elliott Bay. Significant nearby 

non-point sources of pollutants include stormwater runoff and maritime uses.

Ecology used ambient data from sampling station LTED04 in King County's receiving water 

study to assess compliance with water quality standards. This sampling station is located one 

mile west of the Elliott West outfall (47.603642 ̊, -121.356514 ̊). 

Table 8. Elliott West Ambient Background Data

Parameter Value 

Temperature (highest annual 1-DADMax) 13.4

o C (at 1 m below surface)

pH (Minimum / Maximum) 7.4 / 8.0 std units

Salinity (minimum) 24.0 pss

Dissolved Oxygen (10th percentile) 5.7 mg/L

Total Ammonia (max) 0.085 mg/L as N (from LSNT01)

Fecal Coliform (geometric mean) 2 / 100 mL

TSS (max) 8.1 mg/L

Arsenic (90th percentile), Dissolved / Total 1.388 / 1.407 μg/L

Cadmium (90th percentile), Dissolved / Total 0.072 / 0.079 μg/L

Chromium (90th percentile), Dissolved / Total 0.139 / 0.167 μg/L

Copper (90th percentile), Dissolved / Total 0.487 / 0.696 μg/L

Lead (90th percentile), Dissolved / Total 0.005 / 0.066 μg/L

Mercury (90th percentile), Dissolved / Total 0.00020 / 0.00039 μg/L

Nickel (90th percentile), Dissolved / Total 0.432 / 0.464 μg/L

Silver (90th percentile), Dissolved / Total 0.028 / 0.032 μg/L

Zinc (90th percentile), Dissolved / Total 0.995 / 0.903 μg/L

Data source: King County Receiving Water Characterization Study - Final Report, June 2013.

Henderson/MLK CSO Treatment Plant

The Henderson/MLK CSO treatment plant outfall discharges to the Duwamish waterway. 

This discharge shares an outfall with Seattle’s Norfolk stormwater outfall. Another 

significant nearby source of pollutants is Boeing’s industrial stormwater outfall.

Ecology used ambient data from sampling station LTXQ01 in King County's receiving water 

study to assess compliance with water quality standards. This sampling station is located 

approximately 600 feet downstream of the Henderson/MLK outfall (47.512269 ̊, 

-121.29970 ̊). 
Fact Sheet for NPDES Permit WA0029181 Page 29 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 9. Henderson/MLK Ambient Background Data 1

Parameter Value 

Temperature (highest annual 1-DADMax) 18.7o C (at 1 m below surface)

pH (Minimum / Maximum) 6.8 / 7.3 std units

Salinity (minimum, 1⁄2 of DL) 1.0 pss

Dissolved Oxygen (10th percentile) 7.5 mg/L

Fecal Coliform (max, minus outlier) 110 / 100 mL

TSS (90th percentile) 20 mg/L

Arsenic (90th percentile), Dissolved / Total 0.555 / 0.796 μg/L

Cadmium (90th percentile), Dissolved / Total 20.020 / 0.018 μg/L

Chromium (90th percentile), Dissolved / Total 0.084 / 0.215 μg/L

Copper (90th percentile), Dissolved / Total 0.551 / 1.195 μg/L

Lead (90th percentile), Dissolved / Total 0.025 / 0.243 μg/L

Mercury (90th percentile), Dissolved / Total 0.00076 / 0.00175 μg/L

Nickel (90th percentile), Dissolved / Total 20.966 / 0.934 μg/L

Silver (90th percentile), Dissolved / Total 0.021 / 0.044 μg/L

Zinc (90th percentile), Dissolved / Total 1.135 / 1.810 μg/L

1 Data source: King County Receiving Water Characterization Study - Final Report, June 2013.

2 Data reported in 2013 report shows 90th percentile of dissolved fraction as slightly larger than total 

concentration. This discrepancy is likely within the precision of the analytical method.

C. Wastewater influent characterization

King County reports influent pollutant concentrations in discharge monitoring reports. The 

following tables summarize influent wastewater quality for each facility for the period 

between July 2009 and October 2013.

Table 10. Influent Characterization - West Point WWTP

Parameter Units # of Samples Average Monthly 

Average

Maximum Monthly 

Average

BOD5 mg/L ≈260 193 270

lbs/day ≈260 137,112 168,700

CBOD5 mg/L ≈1800 165 227

lbs/day ≈1800 117,115 147,500

TSS mg/L ≈1800 221 293

lbs/day ≈1800 161,975 191,645

Table 11. Influent Characterization - Alki

Parameter Units # of Samples Average Maximum

Volume MG 19 13.7 50.7

Average Monthly 

Average

Maximum Monthly 

Average

BOD5 mg/L ≈20 36 93

TSS mg/L ≈20 89 213
Fact Sheet for NPDES Permit WA0029181 Page 30 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 12. Influent Characterization - Carkeek

Parameter Units # of Samples Average Maximum

Volume MG 23 3.8 18.5

Average Monthly 

Average

Maximum Monthly 

Average

BOD5 mg/L ≈25 147 658

TSS mg/L ≈25 208 1,016

Table 13. Influent Characterization - Elliott West

Parameter Units # of Samples Average Maximum

Volume MG 41 42.5 200

Average Monthly 

Average

Maximum Monthly 

Average

BOD5 mg/L ≈41 77 391

TSS mg/L ≈41 150 706

Table 14. Influent Characterization - Henderson/MLK

Parameter Units # of Samples Average Maximum

Volume MG 11 4.7 20.8

Average Monthly 

Average

Maximum Monthly 

Average

BOD5 mg/L ≈11 23 45

TSS mg/L ≈11 55 104

D. Wastewater effluent characterization

King County reported the concentration of pollutants in the discharge in the permit

application and in discharge monitoring reports. The following tables summarize effluent

quality for each facility from 2009-2013. The priority pollutant data presented contains only 

detectable compounds and elements with existing water quality criteria. More data is 

available in Appendix E.
Fact Sheet for NPDES Permit WA0029181 Page 31 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 15. Effluent Characterization – West Point WWTP

Parameter Units # of Samples Maximum Average

Monthly

Maximum Average 

Weekly

CBOD5 mg/L ≈200 14 27

lbs/day ≈200 13,000 33,200

TSS mg/L ≈200 21 45

lbs/day ≈200 21,500 61,300

Maximum Monthly 

Geometric Mean

Maximum Weekly 

Geometric Mean

Fecal Coliform cfu/100 mL ≈200 16 45

Minimum Maximum

pH Std Units continuous 6.0 7.8

Maximum Monthly 

Average

Maximum Daily 

Maximum

Chlorine, Total Residual μg/L continuous 139 340

Ammonia, as N mg/L ≈60 29 32

lbs/day ≈60 19,867 27,700

Total Kjeldahl Nitrogen, as N mg/L ≈60 31 33

Nitrate + Nitrite, as N mg/L ≈60 10 10

Phosphorus, total, as P mg/L ≈60 3.4 3.4

Phosphate, ortho, as P mg/L ≈60 4.0 4.9

Dissolved Oxygen Mg/L 3 8.4 10.6

Minimum Maximum

1,4-Dichlorobenzene ug/L 9 1.0 10.2

2,4-Dichlorophenol ug/L 9 0.12 0.96

2,4-Dimethylphenol ug/L 9 0.24 0.48

Antimony, Total ug/L 15 0.30 0.63

Arsenic, Total ug/L 15 0.27 2.28

Bis(2-Ethylhexyl)Phthalate ug/L 9 0.41 10.20

Boron, Total ug/L 8 110 200

Cadmium, Total ug/L 15 0.05 0.18

Chloroform ug/L 9 1.00 5.68

Chromium, Total ug/L 15 0.20 1.34

Copper, Total ug/L 15 0.40 16.30

Cyanide, weak acid diss. mg/L 15 0.005 0.006

Diethyl Phthalate ug/L 9 0.120 0.850

Di-N-Octyl Phthalate ug/L 9 0.071 0.360

Iron, Total ug/L 8 110 661

Lead, Total ug/L 15 0.10 2.51

Magnesium, Total ug/L 8 6,040 10,300

Manganese, Total ug/L 8 8.7 71.1

Mercury, Total ug/L 27 0.002 0.016

Methylene Chloride ug/L 9 5.0 5.3

Molybdenum, Total ug/L 8 3.0 7.4

Naphthalene ug/L 9 0.14 0.76

Nickel, Total ug/L 23 0.1 6.5

Phenolics, Total mg/L 15 0.040 0.090

Potassium, Total ug/L 8 5,770 11,700

Pyrene ug/L 9 0.071 0.290

Selenium, Total ug/L 15 0.50 1.30

Silver, Total ug/L 15 0.04 0.15

Sodium, Total ug/L 8 34,200 54,700

Strontium, Total ug/L 8 107 277

Sulfur, Total ug/L 8 6,370 9,840

Thallium, Total ug/L 15 0.040 0.130

Titanium, Total ug/L 8 4.0 31.9

Toluene ug/L 9 1.0 1.1

Zinc, Total ug/L 23 10.7 54.2

Value

Temperature – 95th percentile

1-DADMAX

°C continuous 21.0
Fact Sheet for NPDES Permit WA0029181 Page 32 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 16. Effluent Characterization – Alki CSO TP

Parameter Units # of Samples Average Maximum

Volume MG 19 9.8 41.7

Average Monthly 

Average

Maximum Monthly 

Average

BOD5 mg/L ≈16 23 40

TSS mg/L ≈16 34 65

Maximum Monthly 

Geometric Mean

Maximum

Fecal Coliform cfu/100 mL 16 1 20,000

Minimum Maximum

pH Std Units continuous 5.8 8.4

Chlorine, Total Residual μg/L continuous 0 1708

Ammonia, as N mg/L 1 2.18 2.18

Total Kjeldahl Nitrogen, as N mg/L 1 6.3 6.3

Nitrate + Nitrite, as N mg/L 1 0.8 0.8

Phosphorus, total, as P mg/L 1 0.84 0.84

Phosphate, ortho, as P mg/L 1 0.6 0.6

Dissolved Oxygen mg/L 4 10.2 10.6

Hardness, calc mg CaCO3/L 1 35.6 35.6

Alkalinity, total mg CaCO3/L 1 40.2 40.2

Antimony, Total, ICP-MS ug/L 7 0.48 0.7

Arsenic, Total, ICP-MS ug/L 7 1.85 2.28

Benzyl Butyl Phthalate ug/L 7 0.071 0.43

Bis(2-Ethylhexyl)Phthalate ug/L 7 0.46 3.65

Cadmium, Total, ICP-MS ug/L 7 0.052 0.13

Chloroform ug/L 7 1.5 14

Chromium, Total, ICP-MS ug/L 7 1.47 2.2

Copper, Total, ICP-MS ug/L 7 8.93 12.3

Cyanide, weak acid diss. ug/L 6 5.0 18.3

Diethyl Phthalate ug/L 7 0.51 3.69

Lead, Total, ICP-MS ug/L 7 2.55 4.7

Mercury, Total ug/L 7 0.021 0.025

Nickel, Total, ICP-MS ug/L 7 2.83 3.37

Silver, Total, ICP-MS ug/L 7 0.04 0.1

Zinc, Total, ICP-MS ug/L 7 32.1 42.9

Value

Temperature – 95th

percentile 1-DADMAX

°C continuous No temp data available, used value from West 

Pt WWTP effluent: 21.0
Fact Sheet for NPDES Permit WA0029181 Page 33 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 17. Effluent Characterization – Carkeek CSO TP

Parameter Units # of Samples Average Maximum

Volume MG 23 3.2 17.4

Average Monthly 

Average

Maximum Monthly 

Average

BOD5 mg/L ≈12 38 132

TSS mg/L ≈12 46 132

Minimum Monthly 

Geometric Mean

Maximum

Fecal Coliform cfu/100 mL 11 0 80,000

Minimum Maximum

pH Std Units continuous 5.1 7.9

Chlorine, Total Residual μg/L continuous 8 1370

Ammonia, as N mg/L 4 1.66 3.35

Total Kjeldahl Nitrogen, as N mg/L 4 4.57 9.44

Nitrate + Nitrite, as N mg/L 4 1.18 2.15

Phosphorus, total, as P mg/L 4 0.67 1.18

Phosphate, ortho, as P mg/L 4 0.51 0.90

Dissolved Oxygen mg/L 3 8.6 10.1

Hardness, calc mg CaCO3/L 4 35 48

Alkalinity, total mg CaCO3/L 4 27.5 49.3

2,4-Dichlorophenol ug/L 9 0.12 0.89

Antimony, Total ug/L 10 0.47 1.03

Arsenic, Total ug/L 10 1.83 4.84

Benzo(b)fluoranthene ug/L 5 0.75 2.91

Benzo(k)fluoranthene ug/L 5 0.75 0.81

Benzyl Butyl Phthalate ug/L 9 0.14 4.46

Bis(2-Ethylhexyl)Phthalate ug/L 9 0.41 3.65

Cadmium, Total ug/L 10 0.05 0.2

Chloroform ug/L 8 1.5 64.3

Chloromethane ug/L 8 1 1

Chromium, Total ug/L 10 0.91 5.68

Copper, Total ug/L 10 9.83 27.7

Cyanide, weak acid diss. ug/L 17 5.0 20.1

Di-N-Butyl Phthalate ug/L 9 0.12 0.63

Diethyl Phthalate ug/L 9 0.28 1.54

Lead, Total ug/L 10 1.55 11.3

Mercury, Total ug/L 10 0.05 0.051

Nickel, Total ug/L 10 1.71 4.63

Silver, Total ug/L 10 0.04 0.3

Toluene ug/L 8 1 3.52

Zinc, Total ug/L 10 34 85

Value

Temperature – 95th

percentile 1-DADMAX

°C continuous No temp data available, used value from West 

Pt WWTP effluent: 21.0
Fact Sheet for NPDES Permit WA0029181 Page 34 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 18. Effluent Characterization – Elliott West CSO TP

Parameter Units # of Samples Average Maximum

Volume MG 27 20.1 97.4

Average Monthly 

Average

Maximum Monthly 

Average

BOD5 mg/L ≈27 69 191

TSS mg/L ≈27 144 708

Maximum Monthly 

Geometric Mean

Maximum Weekly 

Geometric Mean

Fecal Coliform cfu/100 mL ≈26 400,000 412,500

Minimum Maximum

pH Std Units continuous 5.5 8.5

Chlorine, Total Residual μg/L continuous 607 860

Ammonia, as N mg/L 2 2.54 2.68

Total Kjeldahl Nitrogen, as N mg/L 2 7.65 9.07

Nitrate + Nitrite, as N mg/L 2 0.35 0.45

Phosphorus, total, as P mg/L 2 1.04 1.14

Phosphate, ortho, as P mg/L 2 0.04 0.64

Dissolved Oxygen mg/L 2 0.1 5.2

Alkalinity, total mg CaCO3/L 2 32.7 38.6

Hardness, calc mg CaCO3/L 1 31.9 31.9

1,4-Dichlorobenzene ug/L 8 1 8.16

2,4-Dichlorophenol ug/L 9 0.24 1

Antimony, Total, ICP-MS ug/L 20 0.3 1.71

Arsenic, Total, ICP-MS ug/L 20 0.46 2.66

Benzo(b)fluoranthene ug/L 8 0.75 2.93

Benzo(k)fluoranthene ug/L 8 0.75 1.6

Benzyl Butyl Phthalate ug/L 9 0.41 1.42

Bis(2-Ethylhexyl)Phthalate ug/L 9 2.05 6.85

Bromodichloromethane ug/L 8 1 2

Cadmium, Total, ICP-MS ug/L 20 0.05 0.617

Chloroform ug/L 8 5.41 35.8

Chloromethane ug/L 8 1 1.3

Chromium, Total, ICP-MS ug/L 20 0.23 7.33

Copper, Total, ICP-MS ug/L 20 23 86.7

Cyanide, weak acid diss. ug/L 11 5.0 19.3

Diethyl Phthalate ug/L 9 0.47 5.47

Dimethyl Phthalate ug/L 9 0.179 0.4

Fluoranthene ug/L 9 0.16 0.6

Lead, Total, ICP-MS ug/L 20 0.39 26.8

Mercury, Total, CVAA ug/L 9 0.05 0.088

Mercury, Total, CVAF ug/L 1 0.0272 0.0272

Nickel, Total, ICP-MS ug/L 20 0.1 6.34

Pentachlorophenol ug/L 9 0.47 1.91

Pyrene ug/L 9 0.18 0.6

Selenium, Total, ICP-MS ug/L 20 0.5 0.61

Silver, Total, ICP-MS ug/L 20 0.05 1.9

Thallium, Total, ICP-MS ug/L 20 0.04 0.268

Toluene ug/L 8 1 32.8

Zinc, Total, ICP-MS ug/L 20 2.8 162

Value

Temperature – 95th

percentile 1-DADMAX

°C continuous No temp data available, used value from West 

Pt WWTP effluent: 21.0
Fact Sheet for NPDES Permit WA0029181 Page 35 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 19. Effluent Characterization – Henderson/MLK CSO TP

Parameter Units # of Samples Average Maximum

Volume MG 11 2.3 16.6

Minimum Maximum

BOD5 mg/L ≈4 5 16

TSS mg/L ≈4 31 45

Fecal Coliform cfu/100 mL ≈4 1 302,667

pH Std Units ≈4 6.7 7.0

Chlorine, Total Residual μg/L ≈4 13 218

Ammonia, as N mg/L 1 0.73 0.73

Total Kjeldahl Nitrogen, as N mg/L 1 3.86 3.86

Nitrate + Nitrite, as N mg/L 1 2.21 2.21

Phosphorus, total, as P mg/L 1 0.54 0.54

Phosphate, ortho, as P mg/L 1 0.27 0.27

Dissolved Oxygen, mg/L mg/L 3 8.4 10.6

Hardness, calc mg CaCO3/L 1 48.3 48.3

Alkalinity, total mg CaCO3/L 1 33.5 33.5

2,4-Dichlorophenol ug/L 3 0.24 2.54

Antimony, Total ug/L 3 0.77 0.89

Arsenic, Total ug/L 3 1.81 2.08

Bis(2-Ethylhexyl)Phthalate ug/L 3 0.732 1.33

Bromodichloromethane ug/L 3 1 1.5

Cadmium, Total ug/L 3 0.05 0.073

Chloroform ug/L 3 1 50.1

Chromium, Total ug/L 3 1.56 2.4

Copper, Total ug/L 3 10.1 12.3

Cyanide, weak acid diss. ug/L 6 5.0 6.5

Di-N-Butyl Phthalate ug/L 3 0.24 1.49

Diethyl Phthalate ug/L 3 0.34 0.47

Dimethyl Phthalate ug/L 3 0.11 0.2

Lead, Total ug/L 3 3.02 4.23

Mercury, Total ug/L 3 0.05 0.05

Nickel, Total ug/L 3 1.92 3.31

Phenol ug/L 3 1.9 6.72

Zinc, Total ug/L 3 30.1 40.2

Value

Temperature - 7-DADMAX °C continuous No temp data available, used value from West 

Pt WWTP effluent: 21.0

Whole Effluent Toxicity Testing - West Point WWTP

King County conducted acute and chronic toxicity testing in January 2012, April 2012, July 

2012, and October 2012. Acute toxicity tests were conducted with Daphnia pulex and fathead 

minnow. Chronic toxicity tests were conducted with Atlantic mysid and topsmelt. See

Appendix E for toxicity test results. 
Fact Sheet for NPDES Permit WA0029181 Page 36 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

For acute toxicity, the performance standard requires median survival in 100% effluent at 

levels equal to or greater than 80%, and no individual test result showing less than 65% 

survival in 100% effluent. All toxicity tests performed in 2012 met these performance 

standards. 

For chronic toxicity, the performance standard requires that no chronic toxicity test 

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

concentration equal to the acute critical effluent concentration (ACEC). West Point had no 

chronic toxicity anywhere near the ACEC of 3.1% effluent in any recent test. 

No WET limits are required. The proposed permit includes the same set of WET tests at the 

end of the next permit term to meet the application submission requirements.

E. Sediment characterization

West Point WWTP Outfall

Sediment testing in 19983, 20004, 20065, and 20116occurred at 12 to 19 stations and included 

chemistry, bioassays, and benthic surveys as shown in Table 20. The results are compared to 

the Sediment Quality Standards (SQS) criteria for marine water. The sediment sampling 

stations for the 2011 sampling report are shown in Figure 7. 

Table 20. West Point WWTP – Sediment Test Results

Year Chemistry

# of stations

Bioassays

# of stations

Benthic

Surveys*

SQS Hits Stations

2011-July 1 8 –Larval 

echinoderm 

only

0 Bioassays WP430S (no chemistry hits to 

support toxicity, and TIE conducted 

by King County indicates toxicity

was likely due to sample turbidity 

and not chemically induced)

2011- April 8 8 0 Chemistry & 

Bioassays

WP230P: Total PCB

WP420NW: Total PCB

WP215N: Dimethyl Phthalate

2006 19 10 10 Bioassays WP280W

WP230P

WP215N

2000 12 2 6 Bioassays WP230P

WP430N

1998 12 2 5 Chemistry & 

Bioassays

WP230P

WP430N

* Unable to determine compliance with Sediment Management Standards for the benthic surveys due to lack of 

reference station.

 

3

 King County 1998. SEDQUAL data WPNT98.

4

 King County 2000. SEDQUAL data WPNT00.

5 King County 2006. West Point Wastewater Treatment Plant 2006 Outfall Sediment Sampling Event Final Report. 

6

 King County, letters to Ecology (Henley) dated July 12, 2011 and February 16, 2012. EIM data WPNT00
Fact Sheet for NPDES Permit WA0029181 Page 37 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Figure 7. Sediment sampling locations for West Pt WWTP outfall

All detected concentrations have met the SQS chemical numeric standards (1988 Lowest 

Apparent Effects Threshold - LAET) except for one station in 1998 and 3 stations in April 

2011. Due to low organic carbon content, chemical concentrations were compared to the 

1988 LAET dry weight thresholds that are the basis for the organic carbon-normalized 

criteria in the Sediment Management Standards. Testing in April 2011 resulted in total PCB 

exceedances at stations WP230P and WP420NW, and a dimethyl phthalate exceedance at 

station WP215N. Although a few stations had elevated levels of Polycyclic Aromatic 

Hydrocarbons (PAH), all met the chemical criteria in 2006. In 2000, some samples had

Method Detection Limits (MDL) above SQS for Hexachlorobutadiene, but it also was not 

detected in the influent or effluent. In 1998, there were 42 non-detects and 5 detected 

concentrations above SQS. The five detected exceedances all occurred at one station, 

WP230P, and included benzo(g,h,i)perylene, fluoranthene, indeno(c,d)pyrene, phenanthrene, 

and pyrene (all PAH compounds).

Bioassay test results have shown toxicity at several stations over the years. The following 

stations have failed one or more bioassay test: WP280W, WP230P, WP215N, and 

WP430N. Some of these stations coincide with elevated concentrations of PAH 

compounds. The sediments at Station WP280W failed all three bioassay tests in 2006, but 

no elevated chemicals were detected. The sediments at station WP230P failed bioassay 

tests in 1998, 2000, and 2006, but passed in 2011. In April 2011, Station WP430S showed 

a bioassay hit but again toxicity was not supported with elevated chemical concentrations, 

and a TIE (toxics identification evaluation) conducted by King County showed that the 

toxicity was likely a result of physical characteristics (i.e., sample turbidity) and not 

chemically induced.

In 1998 and 2000, benthic surveys showed benthic abundance and diversity were reduced at 

two stations (WP230P, WP430N) compared to the other sites near the outfall. These two 

stations also had bioassay toxicity. In 2006, no differences were evident between the stations. 

Ecology cannot compare benthic data to the SQS criteria because no reference station data 

was collected. Benthic surveys were not conducted in 2011.

In summary, King County has conducted sediment analyses near the West Point WWTP 

outfall five times in the past sixteen years (1998, 2000, 2006, April 2011, and July 2011). 

Many of the stations have consistently shown no indication of chemical or biological effects. 
Fact Sheet for NPDES Permit WA0029181 Page 38 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Except for one station in 1998 and three stations in 2011, all detected concentrations met the 

SQS chemical numeric standards. Bioassay test results have consistently shown apparent 

sediment toxicity at a few stations, but cause of toxicity is unclear based on chemistry results

and on the TIE conducted by King County in 2011. Benthic surveys showed that in 1998 and 

2000, benthic abundance and diversity were reduced at the two stations that also had 

bioassay toxicity (WP230P, WP430N), but this was not evident in 2006. Sediment 

monitoring will continue in the vicinity of the outfall with more focus on investigating the 

area which has shown some evidence of sediment impacts.

Alki CSO Treatment Plant Outfall 

King County has sampled sediments near the Alki CSO treatment plant on several occasions, 

most recently in October 2001. The study evaluated sediments at six stations; five of the 

stations formed a transect perpendicular to the end of the outfall and the sixth station was 

located approximately 1,500 feet from the outfall. All detected chemical concentrations were 

less than their respective SQS criteria or LAET values. Data from this sampling event can be 

found in EIM under User Study ID ALKI01.7 No additional sediment monitoring is planned 

at this outfall because there were no SMS exceedances in the last round of sampling and 

source conditions have not changed

Carkeek CSO Treatment Plant Outfall

King County has sampled sediments near the Carkeek CSO treatment plant on several 

occasions, most recently in October 2000. The study evaluated sediments at six stations; five 

of the stations formed a transect perpendicular to the end of the outfall and the sixth station 

was located approximately 1,500 feet from the outfall in the direction of the prevailing 

current. All detected chemical concentrations were less than their respective SQS criteria or 

LAET values. Data from this sampling event can be found in EIM under User Study ID 

CARKEK00.

7 No additional sediment monitoring is planned at this outfall because there 

were no SMS exceedances in the last round of sampling and source conditions have not 

changed.

Elliott West CSO Treatment Plant Outfall 

King County has sampled sediments near the Elliott West CSO treatment plant and the Denny Way 

CSO extensively. The most recent sediment monitoring program has been in effect since 2001 as 

part of the Denny Way/Lake Union CSO Control Project long-term sediment monitoring program. 

The County collected samples from 16 locations near the two outfalls in 2001, 2003, 2004, 2006, 

2007, 2008, and 20097. Several chemicals exceeded either SQS and/or Clean-up Screening Level 

(CSL) chemical criteria at one or more locations. These include total PCBs, benzo(a)anthracene, 

benzo(a)pyrene, benzo(g,h,i)perylene, benzyl butyl phthalate, bis(2-ethylhexyl) phthalate, chrysene,

dibenzo(a,h)anthracene, fluroanthene, indeno(1,2,3-c,d)pyrene, and mercury. Sediment

characterization is ongoing and an interim cleanup plan has been developed for this outfall and the 

Denny Way Regulator.

8

Since sediment characterization is on-going and an interim cleanup plan 

has been developed as part of cleanup efforts, additional sediment monitoring requirements have 

not been imposed in this permit. Table 21 details King County’s sediment remediation activity in 

the vicinity of the Elliott West CSO treatment plant outfall.

 

7 King County, Comprehensive Sediment Quality Summary Report for CSO Discharge Locations, 2009.

8 King County, Post Construction Monitoring Plan for King County CSO Controls, Sept 2012.
Fact Sheet for NPDES Permit WA0029181 Page 39 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 21. Elliott West CSO treatment plant outfall – sediment remediation activity 7

1986 Metro began a trial program to identify and reduce toxicant inputs to the sewer system discharging 

through the Denny Way CSO.

1990 King County and the U.S. Army Corps of Engineers (Corps) sponsored the Denny Way CSO capping

project to test the feasibility of capping contaminated sediments in Elliott Bay with clean dredged 

material from the Duwamish Waterway. A 3-foot layer of clean sand, dredged from the upper Duwamish 

Waterway during routine maintenance, was placed over a 3-acre area in water depths ranging from 

approximately -25 to -60 feet mean lower low water (MLLW). Monitoring results show that the cap was 

stable, was not eroding, and had successfully isolated the underlying contaminated sediments9. 

However, chemical concentrations on the cap surface layer (offshore of the Denny Way CSO) increased 

after cap construction, suggesting possible recontamination from the continued CSO discharges from 

Denny Way or potential redistribution of remaining contaminated sediments from the intertidal area and 

the inshore edge of the cap.

1997 King County characterized the nature and extent of surface and subsurface sediment contamination in 

the outfall area and in areas inshore and offshore of the existing sediment cap10. Follow-up sediment 

sampling conducted by King County in 2005 demonstrated that chemical concentrations in the offshore 

areas declined over time due to a combination of natural processes, including biodegradation of 

chemicals, accumulation and mixing of clean sediment, and reduction of contaminant sources9. Thus, 

monitored natural recovery is a prospective cleanup remedy for the offshore areas. 

Sediments sampled within inshore areas of the site contained concentrations of cadmium, copper, lead, 

mercury, silver, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), bis(2-

ethylhexyl)phthalate, and butyl benzyl phthalate that exceeded SQS chemical criteria. Contaminant 

concentrations above SQS chemical criteria were present to a depth of approximately 10 feet below the 

existing mudline. Unlike offshore areas of the site, natural recovery rates in the inshore sediment areas 

appeared to be progressing relatively slowly. In order to accelerate cleanup of the site and minimize the 

risk of future recontamination to other site areas, including the offshore cap, an interim sediment cleanup 

action plan for the site was developed by King County and Ecology in 2007 that included dredging to the 

maximum extent practicable to remove contaminated sediments and backfilling to restore the grade to 

close to pre-project conditions.

2002 The County constructed a new outfall to extend CSO discharge location further offshore.

2006 Primary treatment and disinfection began for most of the discharges from this CSO (Elliott West CSO).

2007-

2008

Under an Ecology Agreed Order, the County completed an interim action to clean up contaminated 

sediments in two near-shore areas in the immediate vicinity of the former Denny Way CSO outfall. A 

combination of dredging, backfilling, and armoring was employed to remediate the near-shore areas.

King County dredged approximately 13,700 cubic yards of contaminated sediments and associated side 

slopes. The dredged area was backfilled and armored with an average thickness of more than 8 feet of 

material. Approximately 11,886 cy of well-graded clean sand was armored with approximately 4,821 cy 

of sandy-gravel habitat mix and with large cobbles and boulders. An additional 1,540 cy of well-graded 

clean sand was placed in an approximate 6-inch-thick layer around the perimeter of the dredge prism to 

address any residuals that may have resulted from the dredging. Sediment monitoring continued until 

2012 to satisfy the National Marine Fisheries Service Biological Opinion.11

Henderson/MLK CSO Treatment Plant Outfall 

Table 22 summarizes sediment remediation activity for the Henderson/MLK outfall area. 

Sediment sampling in this part of the Duwamish River has been characterized by 

Windward12 as part of the ongoing Lower Duwamish Waterway Superfund action. Sediment 

sampling off the Norfolk CSO/storm drain was conducted over three rounds from 1994 

 

9 King County. 2005. The Denny Way sediment cap – 2000 data – final monitoring report.

10 King County. 1999. Sediment remediation plan, Denny Way/Lake Union CSO Control Project.

11 King County 2008. Denny Way CSO and Elliott West CSO Treatment Facility, Post-Construction Sediment 

Monitoring Sampling and Analysis Plan. 

12 Windward Environmental LLC. 2008. Lower Duwamish Waterway remedial investigation, remedial 

investigation report, draft final (internal).
Fact Sheet for NPDES Permit WA0029181 Page 40 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

through 1995 under the Elliott Bay/Duwamish Restoration Program13. Both surface and 

subsurface sampling was extensively conducted within several hundred feet of the outfall to 

determine the remediation boundaries. SMS exceedances included mercury, total PCBs, 1,4 

dichlorobenzene, and bis(2-ethylhexyl)phthalate. The SQS was used to set the remediation 

boundaries. Data from this study may be found in EIM under User Study ID NRFK9495.

7

The 1999 remediation project was monitored for a period of five years to evaluate possible 

recontamination of the backfill sediment as a result of continuing CSO discharges. The 

monitoring was completed in 2005. The site is now under evaluation as part of the early 

action sites in the Superfund area. More information on Norfolk CSO sediment remediation 

can be found on King County’s website at: 

http://www.kingcounty.gov/environment/wastewater/SedimentManagement/Projects/Norfolk/Library.aspx.

Ecology does not expect significant recontamination from the CSO discharges during this 

permit term for the following reasons:

 The Henderson/MLK CSO facility discharges infrequently, only 1-3 times each year,

 The basin that feeds the facility is largely residential with few industrial users, 

therefore toxic pollutant loads are expected to be smaller,

 The facility provides some settling therefore fewer solids are discharged,

 The facility often retains ‘first flush’ stormwater (when the tunnel fills but does not 

discharge) and sends these more contaminated flows to a wastewater treatment plant 

for additional treatment.

Since the site is under sediment evaluations as part of Superfund cleanup efforts, additional 

sediment monitoring at the Norfolk CSO outfall is not required in this permit. Additional 

sediment concerns from other contaminant sources will be addressed through Lower 

Duwamish Waterway sediment cleanup projects.

Table 22. Henderson/MLK CSO treatment plant outfall – sediment remediation activity7

1991 To implement the requirements of a 1991 Consent Decree defining the terms of a natural resources 

damage agreement, the Elliott Bay/Duwamish Restoration Program (EBDRP) was established. Program 

oversight is provided by the EBDRP Panel, which is composed of federal, state, and tribal natural 

resource trustees, the Municipality of Metropolitan Seattle (which subsequently became part of King

County government and is now the King County Department of Natural Resources and Parks

(KCDNRP), and the City of Seattle (City). The goals of the EBDRP include remediation of contaminated 

sediments associated with KCDNRP and City CSOs and storm drains, restoration of habitat in Elliott 

Bay and the Duwamish River, and control of potential sources of contaminants from the outfalls.

1992 A Sediment Remediation Technical Working Group (SRTWG) was established by the EBDRP Panel to 

address contaminated sediment issues. The SRTWG identified 24 potential sediment remediation sites 

associated with KCDNRP and City CSOs and storm drains. These sites were evaluated against several 

criteria, which included extent of contamination, degree of source control near sites, and public input, as 

reported in the Final Concept Document. 

Ultimately, the SRTWG selected three sites (the Duwamish Pump Station CSO and Diagonal Way 

CSO/storm drain, the Norfolk CSO, and the Seattle Waterfront) for further investigation.

1994 A plan to investigate the extent of contamination at the Norfolk CSO was prepared by KCDNRP (then 

Metro) on behalf of the EBDRP Panel. KCDNRP implemented field data collection activities between 

August 1994 and December 1995. The primary goals were to determine the extent of sediment 

contamination around the Norfolk CSO outfall, based on comparison to SMS criteria and to determine a 

preferred remedial alternative for the site.

 

13 King County. 1996. Norfolk CSO cleanup study report. 
Fact Sheet for NPDES Permit WA0029181 Page 41 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1999 Site remediation began in February 1999 and was completed in March 1999. Activities consisted of 

dredging approximately 2 acres of contaminated sediment and backfilling the dredged area to original 

grade with clean sediment. A dredging dept of 3-9 feet resulted in 5,190 cubic yards of sediment 

removal.

2003 Elevated PCB concentrations (greater than the SQS criterion or LAET) indicated that cap 

recontamination was occurring. In response, Boeing conducted a cleanup of river sediments at a 

stormwater outfall adjacent to the Norfolk CSO outfall using a specialized vacuum excavator; 

approximately 100 cubic yards of sediment were removed.

2004 King County completed post-remedial monitoring at the Norfolk outfall, and reported (King County, June 

2005) sporadic SMS exceedances on the sediment cap without a consistent upward trend. The five-year 

monitoring period did not show surface recontamination from CSO discharges to levels approaching 

SQS chemical criteria. 

Untreated CSO Outfalls

Sediment monitoring at CSO locations is a complex situation at many locations, some in 

different stages of cleanup under different authorities. Several CSOs discharge into 

Superfund cleanup sites so King County is coordinating with other agencies on source 

control and cleanup of larger areas. Cleanups done under CERCLA and MTCA may have 

short-term monitoring, but rely on other authorities, such as NPDES permits under the Clean 

Water Act to address long-term monitoring. This NPDES permit has a role in assuring 

discharges are in compliance with the Sediment Management Standards, but it is necessary to 

coordinate these efforts with cleanup investigations and actions under state and federal 

authorities.

The County’s 1999 Sediment Management Plan14 developed remedial strategies for 

correcting short- and long-term hazards associated with contaminated sediments near King 

County CSO sites. In 2011 and 2013 the County collected sediment data at several CSO 

outfall locations to update their Sediment Management Plan (SMP). King County is using

this data to calibrate and validate a near-field sediment model that will be used to evaluate 

recontamination potential for CSOs following control and sediment remediation projects. An 

updated SMP is expected in 2015.

In 2009 King County provided Ecology with a Comprehensive Sediment Quality Summary 

Report that summarizes sediment data collected up until 2009 for all of King County’s CSO

outfalls. The County has conducted sediment monitoring at most CSO outfalls to assess CSO 

impacts and to determine if remediation is needed. King County’s 2012 Post Construction 

Monitoring Plan also provides a brief summary of the sediment samples that have been 

collected near each CSO discharge location.

King County outlined their post construction monitoring program for sediments in their 2012

Post Construction Monitoring Plan (PCMP). Post construction sediment monitoring requires

site characterization using modeling and/or sediment quality samples. King County, in 

consultation with Ecology, will determine what comprises an adequate site characterization 

on a site specific basis. Based on the site characterization, certain CSO discharge locations 

may exceed Sediment Management Standards (SMS). For these locations, King County will 

develop site-specific sediment clean-up plans. Clean-up plans will contain actions required to 

meet the SMS as well as a sampling program to ensure the outcome has been achieved and 

recontamination is not occurring.

 

14 King County, 1999.
Fact Sheet for NPDES Permit WA0029181 Page 42 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

For untreated CSOs discharging to the Puget Sound, sediment data show either no

exceedances of SQS or a single exceedance of a phthalate compound, except for the Barton 

CSO site. For the Barton CSO outfall, the 2011 sediment monitoring results show multiple 

exceedances of SQS and CSL for several parameters (likely contributed to by other sources).

For untreated CSOs discharging to Elliott Bay and the Duwamish River, sediment quality data 

show multiple exceedances of SQS, often including PAHs, total PCBs, phthalate compounds, 

and some metals. CSOs discharging into Lake Washington and the Ship Canal have multiple 

exceedances of the freshwater sediment guidelines for metals, total PCBs, PAHs, phthalate 

compounds, and other organic compounds.

Table 23 lists sediment remediation activities King County has undertaken to improve sediment 

quality near untreated CSO outfall locations.

Based on the County’s 2009 Sediment Quality Summary Report, Ecology prioritized sampling at 

the County’s 38 untreated CSO locations into categories of high, medium, or low (Ecology 

memo, Podger, 2010). Ecology based prioritization on discharge characteristics (volume and 

frequency, treatment), past sediment data results, and impact of other activities (cleanups 

pending or completed, construction pending, monitoring under other authorities). However the 

predominant metric used for ranking was average discharge flow from 2001-2007, in which 

discharges less than 1 million gallons (MG) average per year were rated low, 1-10 MG/year were 

rated as medium, and >10 MG/year were rated as high priority. Locations with primary treatment 

and with diffusers were also rated lower than untreated single-pipe discharges. CSOs ranked with 

high and medium priorities are listed in Table 24 along with sampling results from 2011 and 

2013. The table also lists low priority CSOs that were tested in 2011/2013. 

Table 23. Untreated CSO outfalls – sediment remediation activity

1999 King County developed a Sediment Management Plan that identified seven contaminated sediment sites 

near CSO discharges.15 Four of those sites have cleanup actions planned or completed including Denny 

Way, Norfolk, Diagonal/Duwamish, and Hanford/Landers.

2000 King County, the Boeing Company, the City of Seattle (the City), and the Port (the Lower Duwamish 

Waterway Group or LDWG) completed a voluntary agreement to begin investigation of the LDW 

sediments, toward an ultimate waterway cleanup plan.

2003 The Diagonal/Duwamish cleanup included dredging and capping of seven acres of contaminated 

sediment along the Lower Duwamish River. Post-cleanup monitoring continued for five years.16

2003-

2006

The County and City, as operators of the local sanitary sewer and stormwater drainage systems, worked 

together to inspect more than 1,000 Lower Duwamish Waterway businesses to reduce pollutants 

discharged to the Lower Duwamish. 

2003-

present

The County worked in partnership with the Port on the Harbor Island Superfund project. The project will 

remediate sediments at the County’s Lander St and Hanford St CSOs.

2004 The County participated in two early action sites—the Diagonal/Duwamish CSO/Storm Drain and Slip 4 

CSO. King County removed 66,000 cubic yards of contaminated sediment at the Duwamish CSO outfall 

and Diagonal storm drain.

2005 King County placed a thin sand layer over four acres adjacent to the Duwamish CSO outfall and 

Diagonal storm drain cleanup site to control residuals from the dredging and to compare enhanced 

natural recovery to monitored natural recovery in that portion of the LDW.

2007-

present

The County’s Industrial Waste Program works with other agencies to conduct pollution source control 

inspections at Lower Duwamish Waterway businesses as part of the Urban Waters Initiative, an 

interagency coordination effort of Ecology. The initiative provides increased resources to speed up 

pollution reduction efforts to benefit the waters, sediments, and human and marine inhabitants of the 

Lower Duwamish Waterway.

 

15 King County 1999. King County Department of Natural Resources Year 2000 CSO Plan Update Project, 

Sediment Management Plan. 

16 Ecology 2002. Final Sediment Management Standards Cleanup Action Decision Duwamish/Diagonal CSO/SD. 
Fact Sheet for NPDES Permit WA0029181 Page 43 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

2008-

2009

As part of the Duwamish East Waterway Superfund site, the County removed approximately 20,000 

cubic yards of sediment in front of the Lander CSO. 

2012 WTD partnered with the City, the Port, and Boeing under a consent agreement with EPA and Ecology to 

prepare a remedial investigation and feasibility study for the Lower Duwamish Waterway Superfund Site. 

The feasibility study described 11 cleanup alternatives. In 2012 EPA proposed a cleanup plan based on 

the 2010 Lower Duwamish Waterway Draft Final Feasibility Study.

2012 King County developed a sediment transport model to better assess impacts from CSO discharges.

present Ecology leads the Source Control Work Group that includes EPA, Seattle Public Utilities (SPU), the King 

County Industrial Waste Program, the Port of Seattle, the Puget Sound Clean Air Agency, and the City 

of Tukwila. This group meets monthly to coordinate source control efforts and make it easier for 

businesses to identify and control pollutant sources. The group’s first priority is to address the early 

action areas identified for sediment cleanup. The group is working on controlling sources of 

contaminants that may pose health or environmental problems if they accumulate in waterway 

sediments. More information is available on the group’s website at: http://www.ldwg.org/ and at 

http://www.ecy.wa.gov/programs/tcp/sites_brochure/lower_duwamish/lower_duwamish_hp.html.

present The County is in the process of updating its 1999 Sediment Management Plan in coordination with new 

requirements for characterization and Post- Construction Monitoring.

present The Wastewater Division's Sediment Management Program is coordinating expanded source control to 

identify and control the sources of pollution that may pose health or environmental problems if they 

accumulate in Duwamish Waterway sediments or re contaminate cleanup areas. The Industrial Waste 

Program, Water and Land Resources Division and KC Airport are some of the groups involved with the 

current expanded source control efforts in King County.

Table 24. Sediment testing priorities for CSO outfalls & sampling results from 2011 & 2013

CSO Outfall 2010 Comments from 

Ecology 1

2011 & 2013 Sampling Results 2Future Monitoring / 

Cleanup

High Priority

028-King Street 15+ year old sediment data 

with multiple hits, not 

cleanup site.

Not tested. Treatment plant constructed 

in 2026. Sediments to be 

sampled prior to construction.

029-Kingdome

036 - Chelan Harbor Island superfund 

site. Sediment impairment in 

1996 samples but EPA 

signed a ‘No Further Action’ 

on the site. No additional 

monitoring planned.

2011: 5 of the 6 sites exceeded SQS for 2 to 

several chemicals, 1 site exceeded CSL for 1 

chemical (many NDs exceeded criteria).

2013: 1 site had dimethyl phthalate SQS 

exceedance, many NDs exceed criteria. 

HPAHs, PCBs, phthalates

Storage tank constructed in 

2023. Sediments to be 

sampled post-construction.

037 - Harbor 

Avenue

Not tested. Area-wide cleanup in 

progress. To be sampled 

when complete or when CSO 

controlled.

041- Brandon 

Street

Large discharge with high 

metals concentrations, little 

sediment data available.

2011: 4 of the 6 sites exceeded SQS for 1 to 

several chemicals, 3 sites exceeded CSL for 

1 to several chemicals.

HPAHs, LPAH, PCBs, phthalate

Treatment plant constructed 

by 2022. Sediments to be 

sampled prior to construction 

or with area-wide clean-up 

effort.

015- University Large discharge with no 

recent sediment data

2011: 5 of the 7 sites had SCO or CSL 

exceedances.

2013: 3 of the 5 sites had SCO or CSL 

exceedances.

Phthalates, mercury, lead, nickel, silver, PCBs

Storage tank constructed in 

2028. Sediments to be 

sampled post-construction or 

with area-wide clean-up 

effort.

014- Montlake Medium discharges and 10-

20 year old sediment data 

show elevated PAH and 

other chemicals. [Last 

sampled in 2001, single site 

(KC 2009)].

2011: 2 of the 7 sites had SCO exceedances, 

no sites had CSL exceedances. 

Arsenic, lead

Storage tank constructed in 

2028. Sediments to be 

sampled post-construction or 

with area-wide effort.

008- 3

rd Ave 

West

2011: 6 of the 7 sites exceeded SQS levels 

for 3 to 5 chemicals, 6 sites exceeded CSL 

for 2-5 chemicals.

Phthalates, nickel, silver, PCBs, phenol, total 

PAHs, mercury

Storage tank constructed in 

2023. Sediments to be 

sampled post-construction or 

with area-wide effort.
Fact Sheet for NPDES Permit WA0029181 Page 44 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

CSO Outfall 2010 Comments from 

Ecology 1

2011 & 2013 Sampling Results 2Future Monitoring / 

Cleanup

009- Dexter Ave Not tested. Area-wide cleanup projects 

expected. CSO projects 

completed but not yet 

deemed controlled.

Sediments to be sampled 

after outfalls deemed 

controlled or area-wide 

cleanup projects completed.

003- Ballard

013/045- MLK

and Henderson 

PS

CSO controlled since 2005 

but had medium discharges 

in the past. Sediment data 

from 2005 had high PAH, 

phthalates, zinc.

Not tested. Sediments characterized 

during this permit term.

Medium Priority

044- Norfolk Sediment data with hits or 

increasing trends.

Not tested. CSO treatment plant outfall. 

Area-wide clean-up and 

monitoring complete. See 

discussion for Henderson/ 

MLK TP above. 

038- Terminal 

115

Not tested. Storage pipe constructed by

2025. Sediments to be 

sampled prior to construction 

or with area-wide clean-up

effort.

039- S Michigan Not tested. Treatment plant constructed 

by 2022. Sediments to be 

sampled prior to construction 

or with area-wide clean-up 

effort.

Low Priority (does not include all outfalls, only sites tested in 2011/2013 and those with proposed monitoring)

048- North 

Beach

2011: No SMS exceedances at 6 sites.

2013: No SMS exceedances at 5 sites.

CSO project in progress. No 

further action.

006- South 

Magnolia

2011: No SMS exceedances at 6 sites.

2013: No SMS exceedances at 1 site.

CSO project in progress. No 

further action.

056- Murray 

Avenue 

2011: Benzyl Butyl Phthalate exceeded SQS 

at 1 site, no exceedances at remaining 6 

sites.

2013: 1 site had SQS and CSL exceedances, 

no exceedances at remaining 5 sites.

Phthalate, LPAHs, HPAHs

CSO project in progress. Site 

evaluation and possible 

clean-up plan as required by 

PCMP.

057- Barton 

Street

2011: 6 of 6 sites exceeded several SQS and 

CSL criteria.

HPAHs, LPAHs, phthalates, dibenzofuran

CSO project in progress. Site 

evaluation and possible 

clean-up plan as required by 

PCMP.

052- 53rd 

Avenue 

2011: No SMS exceedances at 6 sites. CSO controlled. No further 

action.

012/049-

Belvoir & 30th

Ave NE PS

2013: 1 site tested; 2 SCO and no CSL 

exceedances.

Total DDEs, bis(2-ethylhexyl)phthalate

CSO controlled. Sediments to 

be characterized during this 

permit term due to SMS 

exceedances.

011- E. Pine 

Street PS 

Emergency 

Overflow

Not tested. CSOs controlled. Low volume 

discharges with no recent 

data. Sediments to be 

characterized during this 

permit term to confirm meet 

water quality standards, 

consistent with County’s 2012 

018 - Matthews 

Park PS 

Emergency 

Overflow 

Not tested.
Fact Sheet for NPDES Permit WA0029181 Page 45 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

CSO Outfall 2010 Comments from 

Ecology 1

2011 & 2013 Sampling Results 2Future Monitoring / 

Cleanup

033-Rainier 

Avenue PS 

Emergency 

Overflow

Not tested. PCMP.

1

Source: Ecology TCP memo on review of KC’s 2009 Sediment Quality Report (Podger), 2010.

2 Sampling performed according to Ecology-approved KC CSO Sediment Quality Characterization Final Sampling and Analysis 

Plan, August 2011.

King County must model and/or sample sediments in accordance with the approved 2012 

Post Construction Monitoring Plan or any approved plan revisions. Post construction 

monitoring of sediments is required with the completion of CSO projects once the CSO has 

been deemed controlled. If an area-wide cleanup project is planned, sediment samples must 

be collected once the project is complete. 

During this permit term, the CSOs listed in Table 25 are scheduled to be controlled. The 

proposed permit requires submittal of a Post-Construction Summary Report that summarizes 

post construction sediment data and any clean-up actions performed. Anticipated monitoring 

is also described in the table.

Table 25. CSO outfalls scheduled to be controlled during this permit term

CSO Outfall Anticipated Sediment Monitoring / Cleanup

Dexter Avenue Regulator (DSN 009) Area-wide clean-up anticipated. 

Denny Way Regulator (DSN 027a) Area-wide clean-up in progress. 

Harbor Avenue Regulator (DSN 037) Area-wide clean-up in progress. 

Ballard Siphon Regulator (DSN 003) Area-wide clean-up anticipated.

Barton (DSN 057) Post Construction monitoring and clean-up plan 

Murray (DSN 056) required by PCMP.

South Magnolia (DSN 006) No additional sediment monitoring; pre-project 

North Beach (DSN 048) monitoring showed no SMS exceedances. 

Hanford #1 - Construction of the Hanford #1 CSO project will begin during this permit term

and must be completed by December 31, 2019 according to the County’s consent decree.

Since the project does not include in-water work the County will not perform pre-project 

sediment monitoring according to their PCMP (King County, September 2012). An areawide cleanup effort is in progress in the vicinity of the diagonal stormwater drain outfall 

through which the Hanford #1 CSO discharges. According to the PCMP, the County will 

assess sediment quality in the vicinity of the outfall following completion of the CSO control 

project or cleanup project. This assessment will be conducted by modeling, collecting

sediment samples, and/or assessing recent sediment data. No pre-project monitoring is 

required with the proposed permit. A post-construction monitoring report will be required in 

the next permit term.
Fact Sheet for NPDES Permit WA0029181 Page 46 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

F. Summary of compliance with previous permit issued

Ecology assessed compliance based the facilities’ discharge monitoring reports (DMRs), 

annual CSO reports, and inspections. 

West Point WWTP 

The West Point WWTP consistently complied with the effluent limits and permit conditions 

throughout the duration of the permit term. The County reported no effluent limit violations 

for CBOD5, TSS, pH, total residual chlorine, or fecal coliform for the period July 1, 2009 to 

October 2013.

Alki CSO Treatment Plant

For the Alki CSO treatment plant, the previous permit placed effluent limits on TSS, fecal 

coliform, settleable solids, pH, and chlorine. Table 26 summarizes the violations and permit 

triggers that occurred from July 2009 through September 2013. 

Table 26. Alki CSO Treatment Plant – Permit Violations 

Date Parameter Statistical Base Units Value Limit

10/1/2009 Fecal Coliform Geometric Mean #/100ml 20000 400

11/1/2009 Chlorine, Total residual Daily Maximum μg/L 684 234

1/1/2010 Chlorine, Total residual Daily Maximum μg/L 1708 234

11/1/2010 Chlorine, Total residual Daily Maximum μg/L 513 234

12/1/2010 Chlorine, Total residual Daily Maximum μg/L 503 234

3/1/2011 pH, Daily Min Minimum Std Units 5.8 6.0-9.0

11/1/2011 Fecal Coliform Geometric Mean #/100ml 18150 400

1/1/2012 Fecal Coliform Geometric Mean #/100ml 2157 400

9/1/2013 pH, Daily Min Minimum Std Units 5.8 6.0-9.0

In 2009 and 2010 the facility struggled to meet chlorine limits, as shown in Table 26. The 

facility exceeded chlorine limits by a wide margin four times during this period. King 

County responded to these violations by correcting a PLC programming error and by 

increasing SBS dosing capacity. 

The facility continues to experience occasional fecal coliform exceedances. During this 

compliance period the facility exceeded the fecal limit three times. In response to these 

permit violations the County increased chlorine residual levels. They also lowered the 

hypochlorite solution concentration from 4% to 2% to allow for finer control, minimizing 

the risk of overdosing. The County also improved sample collection procedures to 

minimize cross-contamination.
Fact Sheet for NPDES Permit WA0029181 Page 47 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Twice during the compliance period effluent pH dropped below 6.0 due to sodium bisulfate 

feed rates and low-alkalinity stormwater. The County is currently improving the sodium 

bisulfate feet system to prevent these violations.

The County is in the process of upgrading three pump stations upstream of the 63rd Avenue 

PS (53rd, Murray, and Barton). These projects will increase the storage upstream of the 63rd

Avenue Pump Station, helping to reduce untreated combined sewer overflows. It may also 

tend to increase the volume treated at Alki. The County will need to review operational 

strategies at 63rd Avenue PS, the inlet regulator gate, and the West Seattle PS/Tunnel as these 

projects move forward.

Annual Limits - Between 2009 and 2012 there were 27 filling events and 19 discharge events, 

and the Alki facility met all annual permit limits for settleable solids and TSS removal. 

During this time period, the CSO facility prevented 67 million gallons of combined sewage 

from discharging into the Puget Sound. 

5-Year Limits - The long-term average (i.e. permit cycle length) effluent discharge volume 

and number of events is limited to 108 million gallons (MG) and 29 discharge events, 

respectively. During the current permit cycle the Alki CSO treatment plant met these limits 

with an average annual discharge volume of 52 MG and average of 5 discharge events per 

year. 

Carkeek CSO Treatment Plant 

For the Carkeek CSO treatment plant, the previous permit placed effluent limits on TSS, 

fecal coliform, settleable solids, pH, and chlorine. Table 27 summarizes the violations and 

permit triggers that occurred from July 2009 through September 2013. 

Table 27. Carkeek CSO Treatment Plant – Permit Violations

Date Parameter Statistical Base Units Value Limit

1/1/2010 Fecal Coliform Geometric Mean #/100ml 755 400

12/1/2010 Chlorine, Total residual Maximum μg/L 1370 490

12/1/2010 Fecal Coliform Geometric Mean #/100ml 752 400

11/1/2012 Chlorine, Total residual Maximum μg/L 723 490

12/1/2012 pH, Daily Min Minimum Std Units 5.1 6

From 2009 to 2013, the Carkeek CSO plant exceeded fecal coliform and chlorine limits each 

twice. In 2011 King County retrofitted their sampling procedures and installed new autosamplers that are capable of notifying the SCADA system when the sampling system fails. In 

2013 the County upgraded the hypochlorite feed pump system with a pump upgrade, line 

flushing improvements, and a new hypochlorite flow meter.

Annual Limits - Between 2009 and 2012 there were 50 filling events and 23 discharge events, 

and the Carkeek facility met all annual permit limits for settleable solids and TSS removal. 

During this time period, the CSO facility prevented 17 million gallons of combined sewage 

from discharging into the Puget Sound. 

5-Year Limits - The long-term average (i.e. permit cycle length) effluent discharge volume 

and number of events is limited to 46 million gallons (MG) and 10 discharge events, 

respectively. During the current permit cycle the Carkeek CSO treatment plant met these 

limits averaging 6 discharge events per year with an average annual discharge volume of 

19 MG. 
Fact Sheet for NPDES Permit WA0029181 Page 48 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Elliott West CSO Treatment Plant 

For the Elliott West CSO treatment plant, the previous permit placed effluent limits on TSS, 

fecal coliform, settleable solids, pH, and chlorine.

Table 28 summarizes the violations and permit triggers that occurred from July 2009 through 

September 2013. 

Table 28. Elliott West CSO Treatment Plant – Permit Violations and Permit Triggers

Date Parameter Statistical Base Units Value Limit

10/1/09 Fecal Coliform Geometric Mean #/100ml 5889 400

10/1/09 Settleable Solids Maximum mL/L 6 1.9

11/1/09 Settleable Solids Maximum mL/L 10 1.9

2009 TSS, Annual % removal Annual Ave % 41.6 >50

2009 Settleable Solids Annual Ave mL/L 2.3 0.3

1/1/10 Settleable Solids Maximum mL/L 9 1.9

4/1/10 Settleable Solids Maximum mL/L 2 1.9

9/1/10 Fecal Coliform Geometric Mean #/100ml 5,099 400

9/1/10 Settleable Solids Maximum mL/L 2 1.9

11/1/10 Fecal Coliform Geometric Mean #/100ml 2,439 400

11/1/10 Settleable Solids Maximum mL/L 2.5 1.9

12/1/10 Chlorine, Total residual Maximum μg/L 158 104

2010 Settleable Solids Annual Ave mL/L 1.5 0.3

3/1/11 Fecal Coliform Geometric Mean #/100ml 553 400

4/1/11 pH, Daily Min Minimum Std Units 5.5 6

4/1/11 Settleable Solids Maximum mL/L 4.5 1.9

5/1/11 Fecal Coliform Geometric Mean #/100ml 400,000 400

12/1/11 Chlorine, Total residual Maximum μg/L 259 104

12/1/11 Fecal Coliform Geometric Mean #/100ml 17000 400

2011 Settleable Solids Annual Ave mL/L 0.8 0.3

1/1/12 Chlorine, Total residual Maximum μg/L 231 104

1/1/12 Settleable Solids Average mL/L 1 0.3

7/1/12 Settleable Solids Maximum mL/L 5.5 1.9

10/1/12 pH, Daily Min Minimum Std Units 5.7 6

11/1/12 pH, Daily Min Minimum Std Units 5.7 6

12/1/12 Chlorine, Total residual Maximum μg/L 407 104

12/1/12 pH, Daily Min Minimum Std Units 5.76 6

12/1/12 Settleable Solids Maximum mL/L 3.7 1.9

2012 Settleable Solids Annual Ave mL/L 1.2 0.3

1/1/13 pH, Daily Min Minimum Std Units 5.9 6

3/1/13 Chlorine, Total residual Maximum μg/L 435 104

3/1/13 pH, Daily Min Minimum Std Units 5.95 6

3/1/13 Settleable Solids Maximum mL/L 2 1.9

4/1/13 pH, Daily Min Minimum Std Units 5.93 6

9/1/13 Chlorine, Total residual Maximum μg/L 860 104

9/1/13 Fecal Coliform Geometric Mean #/100ml 700 400
Fact Sheet for NPDES Permit WA0029181 Page 49 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Figure 8. Fecal Coliform data for Elliott West CSO TP.

Figure 9. Residual chlorine data for Elliott West CSO TP.

Several contributory factors affected 

permit compliance, including 

equipment performance (auto 

samplers, sampling pumps, 

dewatering pumps, flap gate failure, 

drain gate failure), poor mixing of 

chemicals, and hydraulic gradient 

issues that were causing surcharging 

at the dechlorination and outfall 

transition structures. The County 

has hired consultant engineers and 

implemented many projects to 

address the performance concerns. 

Fecal Coliform - As shown in

Table 28 and Figure 8 the facility exceeded 

fecal coliform limits seven times between 

October 2009 and October 2013. In 

2011 the County rebuilt all three

hypochlorite pumps, modified the 

hypo system plumbing, and started 

exercising the pumps on a regular 

schedule. In 2012 the County added 

new chemical flowmeters, increased 

chlorine contact time by moving the 

hypo injection point upstream, 

added an initial chlorine-demand 

analyzer, and converted the 

hypochlorite and bisulfite dosing 

control programs to compound loop 

controls. These improvements have 

resulted in somewhat lower fecal 

coliform levels and improved 

compliance, as can be seen in Figure 8.

Residual Chlorine - As shown in 

Table 28 and Figure 9 the facility exceeded chlorine limits six times between October 2009 

and October 2013. To address this, in 2011 the County improved the sodium bisulfite system

plumbing and initiated a standard procedure to manually flush the lines periodically to 

prevent freezing. The County also installed a pressure gauge to monitor for line constrictions.

In 2012 the County converted the hypochlorite and bisulfite dosing controls as discussed 

above. 

pH - Prior to 2011 pH fluctuated around 6.5. Since 2011, however, low pH has plagued this 

facility with the effluent frequently dropping below 6.0. These drops are likely a result of 

sodium bisulfate feed rates, but the situation is compounded by the lack of alkalinity in 

Seattle’s stormwater.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Settleable Solids - The facility also has difficulty meeting settleable solids limits. Table 28

shows 11 monthly exceedances and 4 annual exceedances. In 2013 the County repaired the 

discharge line drain gate through which marine water was entering the effluent line and 

sampling well. Automated tunnel flushing schedules implemented in 2013 will hopefully 

send more solids to West Point treatment plant after each CSO event. In addition, the County 

started turning on the tunnel’s dewatering pumps sooner and leaving them on during a 

discharge event to enhance settled solids transfer to the West Point Treatment Plant. Also, the 

marine transition flap gate repair in December 2013 will keep marine water and solids out of 

the effluent tunnel and sampling well.

Additionally, the County installed a new effluent sample pump in 2010 and implemented 

procedures to make sure the pump is regularly inspected and tested. In February 2013 the 

County completed an effluent sampling improvement project and the County continues to 

provide annual sampling refresher training courses for operators.

The facility met the annual TSS removal requirement every year except 2009 in which the 

facility only achieved 42% removal.

Between 2009 and 2012 the Elliott West facility experienced 158 filling events and 45

discharge events. During this period, the CSO facility prevented 889 million gallons of 

combined sewage from discharging into Elliott Bay. However, the Elliott West CSO 

treatment plant continues its struggle to meet permit limits for fecal coliform, pH, chlorine, 

and settleable solids. 

Henderson/MLK CSO Treatment Plant 

For the Henderson/MLK CSO treatment plant, the previous permit placed effluent limits on 

TSS, fecal coliform, settleable solids, pH, and chlorine. Table 29 summarizes the violations 

and permit triggers that occurred from July 2009 through September 2013. 

Table 29. Henderson/MLK CSO Treatment Plant – Permit Violations and Permit Triggers

Date Parameter Statistical Base Units Value Limit Violation

10/1/2010 Fecal Coliform Geometric Mean #/100ml 302,667 400 Numeric effluent 

violation

11/1/2012 Chlorine, Total residual Maximum μg/L 218 39 Numeric effluent 

violation

Annual Limits - Between 2009 and 2012 there were twelve filling events and four discharge 

events, and the Henderson/MLK facility met all annual permit limits for settleable solids and 

TSS removal. During this time period, the CSO facility prevented 24 million gallons of 

combined sewage from discharging into the Duwamish River. 

G. State environmental policy act (SEPA) compliance

State law exempts the issuance, reissuance or modification of any wastewater discharge 

permit from the SEPA process as long as the permit contains conditions are no less stringent 

than federal and state rules and regulations (RCW 43.21C.0383). The exemption applies only 

to existing discharges, not to new discharges.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

III. Proposed Permit Limits

Federal and state regulations require that effluent limits in an NPDES permit 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. 

Ecology does not usually develop limits for pollutants not reported in the permit application but 

may be present in the discharge. The permit does not authorize discharge of the non-reported 

pollutants. During the five-year permit term, the facility’s effluent discharge conditions may change 

from those conditions reported in the permit application. The facility must notify Ecology if 

significant changes occur in any constituent [40 CFR 122.42(a)]. Until Ecology modifies the permit 

to reflect additional discharge of pollutants, a permitted facility could be violating its permit.

A. Design criteria

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

criteria. 

West Point WWTP

The design criteria for the West Point WWTP listed in Table 30 are taken from the 1991 Plans 

titled West Point Treatment Plant Secondary Treatment Facilities, Liquids Stream, prepared by 

CH2M Hill, KCM, and others. Ecology erroneously put the wrong design criteria in the previous

permit; the values were taken from the same document but for the ‘saturation/future’ loading 

levels instead of the actual ‘design’ levels. The proposed permit corrects this mistake by 

reducing the TSS and BOD5 design loadings to those listed in Table 30.

Table 30. West Point WWTP Design Criteria

Parameter Design Quantity

Monthly average flow (maximum month) 215 MGD

Average wet weather flow (non-storm) 133 MGD

Instantaneous peak flow (combined) 440 MGD

BOD5 influent loading (maximum month) 201,000 lbs/day

TSS influent loading (maximum month) 218,000 lbs/day
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Permit Condition S10 authorizes CSO-related bypasses of the secondary treatment portion of 

the West Point WWTP when the instantaneous flows to the WWTP exceed 300 MGD as a 

result of precipitation. The wastewater that bypasses secondary treatment must receive solids 

and floatables removal, primary clarification, and disinfection. The final combined discharge 

must at all times meet the effluent limits listed in S1. EPA’s 1994 CSO Control Policy allows 

for “CSO-related bypass” under certain conditions. 

EPA's CSO Guidance for Permit Writers (EPA-832-B-95-08) states that a "CSO-related 

bypass" at the wastewater treatment plant can only occur if there is no feasible alternative 

and the no feasible alternatives analysis is part of the administrative record. The no feasible 

alternative requirement can be met if “the record shows that the secondary treatment system 

is properly operated and maintained, that the system has been designed to meet secondary 

limits for flows greater than the peak dry weather flow, plus an appropriate quantity of wet 

weather flow, and that it is either technically or financially infeasible to provide secondary 

treatment at the existing facilities for greater amounts of wet weather flow.” 

Ecology is confident the West Point WWTP is well operated and maintained based on 

monthly DMR and annual CSO reporting, frequent meetings, and inspections. As 

recommended by EPA’s guidance, the West Point WWTP “meets secondary limits for flows 

greater than the peak dry weather flow plus an appropriate wet weather flow” (i.e., the 

facility provides secondary treatment to flows up to 300 MGD, which is greater than the 

maximum month wet weather flow of 215 MGD and meets secondary limits under all CSO 

conditions). When Metro designed the facility it was deemed infeasible to provide secondary 

treatment to peak wet weather flows from the combined system due to concerns that peak 

flows would wash out the secondary process. 

King County submitted to Ecology a no feasibility alternatives analysis in 2009 (King 

County, 2009) per the CSO Control Policy requirements. As part of this permit development 

process Ecology reviewed this document again and concluded it still applies since there have 

been no major capacity changes at the facility. The document provides adequate justification 

to continue to authorize the CSO-related bypass for this permit cycle. Additionally, the 

collection system storage projects planned and in progress will likely result in fewer bypass 

events allowing the West Point facility to provide secondary treatment to more CSO flows 

than previously assessed in the 2009 analysis. Ecology will likely require an update to the no 

feasible alternatives analysis in the next permit which will be issued in 2019-2020.

Alki CSO Treatment Plant

Ecology obtained the design criteria the Alki facility, listed in Table 31, from the Facilities

Plan for Alki Transfer/CSO Project prepared by HDR Engineering, Inc. and dated October 

1992.

Table 31. Alki CSO Treatment Plant – Design Criteria

Parameter Design 

Peak storm water flow to treatment plant 65 MGD

TSS influent loading (average annual) 9,580 lbs/day

Carkeek CSO Treatment Plant

Ecology obtained the design criteria for the Carkeek Storage and CSO Treatment Plant, listed 

in Table 32, from the Facility Plan for the Carkeek Transfer/CSO Facilities Project prepared 

by Brown and Caldwell Consulting Engineers and dated December 1988.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 32. Carkeek CSO Treatment Plant – Design Criteria

Parameter Design Quantity

Peak wet weather flow 20 MGD

TSS influent loading 5,100 lbs/day

EWCSO CSO Treatment Plant

Ecology obtained the design criteria for the EWCSO Satellite CSO Treatment Plant, listed in 

Table 33, from the Denny Way/Lake Union CSO Control Facilities Plan, dated July 1988.

Table 33. EWCSO Treatment Plant – Design Criteria

Parameter Design

Tunnel Diameter 14’ 8”

Tunnel Length 6,200’

Total Volume 7.2 MG

Henderson/MLK CSO Treatment Plant

Ecology obtained the design criteria for the Henderson/MLK CSO treatment plant, listed in 

Table 34, from the Henderson/ML King CSO Control Facilities Plan (approved March 5, 

2002).

Table 34. Henderson/MLK CSO Treatment Plant – Design Criteria

Parameter Design

Tunnel Diameter 14’ 8”

Tunnel Length 3,100’

Total Volume 4 MG

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.

The federal CSO Control Policy (59 FR 18688) also requires entities with Combined Sewer 

Overflows to implement “Nine Minimum Controls” as technology-based performance 

standards for CSO discharges. Nine Minimum Controls are discussed in more detail in 

Section V.G of this fact sheet.

West Point WWTP

The table below identifies technology-based limits for pH, fecal coliform, CBOD5, and TSS, 

as listed in chapter 173-221 WAC for secondary wastewater treatment plants. Section III.F of

this fact sheet describes the potential for water quality-based limits.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 35 Technology-based Limits (West Point WWTP)

Parameter Average Monthly Limit Average Weekly Limit

CBOD5 25 mg/L 40 mg/L

In addition, the CBOD5 effluent concentration must not exceed:

15% of the average influent concentration from May-October, and

20% of the average influent concentration from November-April.

TSS 30 mg/L 45 mg/L

In addition, the TSS effluent concentration must not exceed:

15% of the average influent concentration from May-October, and

20% of the average influent concentration from November-April.

Chlorine 0.5 mg/L 0.75 mg/L

Parameter Monthly Geometric Mean Limit Weekly Geometric Mean Limit

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

Parameter Daily Minimum Daily Maximum

pH 6.0 standard units 9.0 standard units

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, 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.

Technology-based mass limits are based on WAC 173-220-130(3)(b) and 173-221-030(11)(b). 

Ecology calculated the monthly and weekly average mass limits for CBOD5 and Total 

Suspended Solids as follows:

Mass Limit = CL x DF x CF

where:

CL = Technology-based concentration limits listed in the above table

DF = Maximum Monthly Average Design flow (MGD)

CF = Conversion factor of 8.34

Table 36. Technology-based Mass Limits

Parameter Concentration Limit (mg/L) Mass Limit (lbs/day)

CBOD5 Monthly Average 25 44,800

CBOD5 Weekly Average 40 71,700

TSS Monthly Average 30 53,800

TSS Weekly Average 45 80,700

WAC 173-221-050 subsection (3) states that, “for domestic wastewater facilities which 

receive flows from combined sewer, Ecology shall decide on a case-by-case basis whether 

any attainable percent removal can be defined during wet weather.” The West Point WWTP 

receives a more dilute influent during wet weather due to a collection system that combines 
Fact Sheet for NPDES Permit WA0029181 Page 55 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

both sanitary sewage and storm water. A dilute influent can make the 85% removal criteria 

for CBOD5 and TSS difficult to achieve.

Calculations show that due to dilute influent at West Point during wet weather months, 

effluent TSS and CBOD5 average monthly effluent concentrations would have to be 13% and 

19% lower, on average, than their respective discharge limits (30/25 mg/L) 36 and 49 percent 

of the time, respectively, to meet the 85% removal requirement. Ecology calculated these 

values using average monthly influent concentrations over the past 5 years. According to the 

EPA Permit Writer's Manual (page 5-11), this criteria qualifies the West Point facility for 

less stringent percent removal requirements, consistent with 40 CFR 133.103(a). Ecology has 

assessed historical data and concluded that the West Point facility can consistently achieve 

80% TSS and CBOD5 removal during the wet weather months of November through April; 

the 85% removal requirement applies during the remaining months.

Federal CSO statute requires as one of the Nine Minimum Controls (9MC No. 4) that King 

County maximizes flows to the plant during the wet season in order to minimize CSO 

discharges. Ecology recognizes that increased flows and more dilute flows to the treatment 

plant over time may impact the achievable removal efficiency during wet weather conditions.

In accordance with the EPA CSO guidance document, Ecology will re-evaluate wet season 

percent removal requirements each permit cycle based on recent plant performance data.

CSO Treatment Plants

The specific technology-based limits that apply to CSOs are the nine minimum controls. 

Also, CSO treatment plants must provide “primary treatment” which is defined in WAC 

173-245-020(16) as “any process which removes at least 50% of the total suspended solids 

from the waste stream, and discharges less that 0.3 ml/L/hr of settleable solids.” 

Additionally, Ecology’s Criteria for Sewage Works Design clarifies that the 50% removal is 

to be assessed on an annual average basis.

Table 37. Technology & Guidance-based Limits for CSO Treatment Plants

Parameter Limit

TSS a50% removal, annual average

Settleable Solids a0.3 ml/L/hr, annual average

Fecal Coliform Bacteria b400 /100 mL

a WAC 173-245-020(16)

b Washington State Department of Ecology, Criteria for Sewage Works Design, December 1998, p C3-21.

Total Suspended Solids: The County’s four CSO treatment plants provide primary treatment 

which consists of sedimentation of solids and disinfection of the effluent prior to discharge. 

In order to comply with Washington State regulation, the limit for all CSO treatment plants is 

based on overall percent removal of total suspended solids of 50% or greater. The overall 

percent removal on an annual basis includes the removal achieved at the CSO treatment plant 

and that achieved at the West Point WWTP.

Settleable Solids: Ecology evaluates compliance of the CSO treatment plant effluent with the 

0.3 ml/l/hr of settleable solids limit based on a yearly average due to the intermittent and 

highly variable operation of the CSOs. Ecology removed the settleable solids event 

maximum limit of 1.9 ml/l/hr because there is no basis in regulation for an event maximum

settleable solids limit.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Fecal Coliform: Ecology’s technical guidance document (Criteria for Sewage Works Design, 

C3-3.3.8) states that an appropriate performance criterion for end-of-the-pipe CSO treatment for 

fecal coliform is 400 cfu/100 mL. Ecology believes this criterion is appropriate and achievable 

for the Alki, Carkeek, and Henderson/MLK facilities based on data collected between 

September 2009 and September 2013. During this time, Alki met the fecal coliform criteria 13 

of the 16 months in which discharges occurred, the Carkeek facility met the criteria 9 of the 11 

months in which discharges occurred, and the Henderson/MLK facility met the criteria 3 of the 

4 months in which discharges occurred. Additionally, King County has recently upgraded 

equipment and improved SOPs at these facilities to improve future performance. 

For Elliott West, the technical guidance-based limit is applied as Ecology views this limit as 

more appropriate and protective of water quality than the previous final limit. For further 

discussion, refer to sub-section F below and Appendix F.

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.

Federal regulation (40 CFR 122.45(c)) requires Ecology to express effluent limits for metals

in the form of total recoverable. However, the 1992 revision of the Washington Water 

Quality Standards express metals criteria in the dissolved form. Ecology therefore uses metal 

translators to predict the dissolved to total recoverable fraction in the receiving water. For 

marine waters, these translators are provided in WAC 173-201A-240(3). However, 

Ecology’s Permit Writer’s Manual recommends using the fraction of dissolved to total 

recoverable measured in the receiving water during the critical condition if data is available. 

King County provided both the dissolved and total recoverable fractions of several metals in 

their 2013 Receiving Water Study and Ecology chose to use these ratios where applicable, as 

summarized in Table 38.

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.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 38. Metal Translators Used in Reasonable Potential Analyses

Metal Ecology Translatorsa

Wt Point & 

Carkeek Alki Elliott West

Henderson 

/ MLKb

Acute Chronic

Arsenic 1.000 1.000 1.000 0.980 1.000 1.000

Cadmium 0.994 0.994 0.980 0.950 0.960 0.994

Chromium 0.993 0.993 0.960 0.993 0.993 0.993

Copper 0.830 0.830 0.790 0.920 0.790 0.830

Lead 0.951 0.951 0.951 0.951 0.951 0.951

Mercury 0.850 n/a 0.850 0.850 0.850 0.850

Nickel 0.990 0.990 1.000 0.950 0.970 0.990

Silver 0.850 n/a 0.850 0.850 0.850 0.850

Zinc 0.946 0.946 0.946 0.946 0.946 0.946

a

From WAC 173-201A-240(3)

b Used Ecology's marine translators for all metals for this outfall because critical condition was not fully 

characterized with receiving water data (e.g., unclear how partitioning is affected by salinity fluctuations).

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:

• 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 

Description--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 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

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.

Facility Specific Requirements--The facilities covered by this permit 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. 

Ecology’s analysis described in this section of the fact sheet demonstrates that the proposed 

permit conditions will protect existing and designated uses of the receiving water.

Combined Sewer Overflows

Chapter 173-245 WAC requires that “all CSO sites shall achieve and at least maintain the 

greatest reasonable reduction, and neither cause violations of applicable water quality 

standards, nor restrictions to the characteristic uses of the receiving water, nor accumulation 

of deposits which: (a) exceed sediment criteria or standards; or (b) have an adverse biological 

effect.” The greatest reasonable reduction means control of each CSO outfall such that an 

average of no more than one untreated discharge may occur per year. Ecology includes 

specific conditions in the proposed permit to ensure that the Permittee continues to make 

progress towards meeting water quality goals for each CSO outfall in its system. Section V of 

this fact sheet contains more detailed information on these CSO requirements.

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 doesn’t 

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 must not use more than 25% of the available width of the 

water body for dilution [WAC 173-201A-400 (7)(a)(ii-iii)]. 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

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 derives 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. 

Most of the aquatic life acute criteria are 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. Most of the aquatic life chronic criteria are 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. 

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 acute mixing zones for each outfall, surrounded by chronic mixing 

zones around each point of discharge (WAC 173-201A-400). The water quality standards 

impose certain conditions before allowing dischargers a mixing zone: 

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

The proposed permit specifies the sizes and locations of the allowed mixing zones (as 

specified below).

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

control and treatment” (AKART) to its discharges.

Ecology has determined that the treatment provided meets the requirements of AKART.

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 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

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.

West Point WWTP

King County modeled the West Point WWTP discharge using the critical conditions listed in 

Table 39.

Table 39. West Point WWTP - Critical Conditions Used to Model the Discharge.

Critical Condition Value

Water depth at MLLW 230 feet

Number of diffuser ports 200

Diffuser port diameter 4.5” - 5.75“

Acute Condition:

Density profile with a difference of 0.1 sigma-t units between246 feet and the surface (Dec)

10th or 90th percentile current speeds 0.428-0.49 m/sec

Maximum daily effluent flow 404 MGD

Chronic and Human Health Conditions:

Density profile with a difference of 1.5 sigma-t units between246 feet and the surface (July)

50th percentile current speeds for chronic and human health mixing zones 0.252-0.264 m/sec

Maximum ave monthly effluent flow for chronic and human health non-carcinogen 87 MGD

Annual average flow for human health carcinogen (design average annual flow) 142 MGD

Source: King County’s 2013 Effluent Dilution Modeling Report for the West Point WWTP Outfall

CSO Treatment Plants

King County derived the chronic and acute dilution factors for the intermittent CSO 

discharges using effluent flow rates calculated according to guidance in Ecology’s Permit 

Writer’s Manual, Appendix 6. Table 40 summarizes the very conservative methodology 

King County used to assess treatment plant flows for these intermittent discharges.

Table 40. CSO discharge flows used in dilution calculations

Acute Equivalent 24-hour Average Flow = total event volume divided by total event duration. King 

County used the event with the highest equivalent 24-hr flow for each assessment.

Chronic Equivalent Monthly Average Flow = Total volume of all discharge events in a month divided by 

the total hours of discharge in that month. King County used the highest equivalent monthly 

average flow from the previous 3 years of operation for each assessment.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

King County modeled the Alki, Carkeek, Elliott West, and Henderson/MLK CSO treatment 

plant discharges using the critical conditions listed in Table 41 through Table 44.

Table 41. Alki CSO TP: Critical Conditions Used to Model the Discharge

Critical Condition Value

Water depth at MLLW 143 feet

Number of diffuser ports 8

Diffuser port diameter 12”

Acute Condition:

Density profile with a difference of 0.7 sigma-t units between147 feet and the surface

10th or 90th percentile current speeds 0.05 m/sec

Maximum equivalent 24-hour flow 52 MGD

Chronic Condition:

Density profile with a difference of 0.04 sigma-t units between147 feet and the surface

50th percentile current speeds 0.16 m/sec

Maximum equivalent monthly average effluent flow 33 MGD

Source: King County’s 2013 Effluent Dilution Modeling Report for the Alki CSO TP Outfall

Table 42. Carkeek CSO TP: Critical Conditions Used to Model the Discharge

Critical Condition Value

Water depth at MLLW 195 feet

Number of diffuser ports 13

Diffuser port diameter 5.5 - 10”

Acute Condition:

Density profile with a difference of 0.25 sigma-t units between195 feet and the surface

10th or 90th percentile current speeds 0.02 & 0.15 m/sec

Maximum equivalent 24-hour flow 9.5 MGD

Chronic Condition:

Density profile with a difference of 0.5 sigma-t units between195 feet and the surface

50th percentile current speeds 0.05 m/sec

Maximum equivalent monthly average effluent flow 9.3 MGD

Source: King County’s 2013 Effluent Dilution Modeling Report for the Carkeek CSO TP Outfall

Table 43. Elliott West CSO TP: Critical Conditions Used to Model the Discharge

Critical Condition Value

Water depth at MLLW 60 feet

Number of diffuser ports 1

Diffuser port diameter 90”

Acute Condition:

Density profile with a difference of 0.9 sigma-t units between 60 feet and the surface

10th or 90th percentile current speeds 0.025 & 0.1 m/sec

Maximum equivalent 24-hour flow 67 MGD

Chronic Condition:

Density profile with a difference of 1.4 sigma-t units between 60 feet and the surface

50th percentile current speeds 0.05 m/sec

Maximum equivalent monthly average effluent flow 58 MGD

Source: King County’s 2013 Effluent Dilution Modeling Report for the Elliott West CSO TP Outfall
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 44. Henderson/MLK CSO TP: Critical Conditions Used to Model the Discharge

Critical Condition Value

Number of diffuser ports 1

Port diameter 84”

50th percentile current speed for chronic mixing zone 0.21 m/s

10th & 90th percentile current speeds for acute mixing zone 0.078 & 0.39 m/s

Maximum average monthly effluent flow for chronic = used chronic facility design flow 25 MGD

Maximum daily flow for acute mixing zone – used acute facility design flow 77 MGD

Source: King County’s 2013 Effluent Dilution Modeling Report for the Henderson/MLK CSO TP Outfall. 

Ambient data at critical conditions in the vicinity of the outfall were taken from the Henderson/MLK 

Pre-design Report.

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. 

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. 

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.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

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 

mixes as it rises through the water column 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 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 sizes of the mixing 

zones authorized in the proposed permit.

7. Maximum size of mixing zone.

The authorized mixing zones do not exceed the maximum size restrictions. Mixing zone 

dimensions are depicted in Figure 10 through Figure 14.

8. Acute mixing zone.

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

point of discharge as practicably attainable.

For each outfall, Ecology determined whether the acute criteria would be met at 10% 

of the distance or volume fraction of the chronic mixing zone.

• 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.

The mixing zones authorized in this permit do not overlap other mixing zones.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Diffuser: Diameter = 42”, Length = 120’ 

with 8 (12”) Ports, 2,000’ offshore

Plan View 806 ft

Side View

-143 ft MLLW

0 ft MLLW

Acute Mixing 

Zone Boundary

189 ft 

188.6ft

Chronic Mixing 

Zone Boundary

68.6 ft 686 ft

188.6 ft

Not to Scale

Figure 10. West Point’s WWTP’s Mixing Zone

Figure 11. Alki’s Mixing Zone

Diffuser: Diameter = 96”, Length = 600’ 

with 200 Ports.

Plan View 1,460 ft

Side View

-230 ft MLLW

0 ft MLLW

Acute Mixing 

Zone Boundary

686 ft

Chronic Mixing 

Zone Boundary

860

ft

86

ft

686 ft

Not to Scale
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Figure 12. Carkeek’s Mixing Zone Zone

Figure 13. Elliott West Mixing Zone

96 inch Outfall Pipe w/ open end port

Plan View 520 ft

Chronic Mixing 

Zone 

Boundary

Side View

-60 ft MLLW

52 ft

0 ft MLLW

Acute Mixing 

Zone 

Boundary

Diffuser length = 50 ft. Diffuser Dia. = 

33in. 13 ports, 5-10 inches in diameter.

Plan View 840 ft

Side View

-195 ft MLLW

0 ft MLLW

Acute Mixing 

Zone 

Boundary

129 ft

Chronic Mixing 

Zone 

Boundary

79 ft 790 ft

129 ft

Not to Scale
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Figure 14. Henderson/MLK Mixing Zones

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). The descriptions and tables below summarize the criteria applicable to the 

receiving water’s designated uses.

Puget Sound Discharges:

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.

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 West Point WWTP, Alki CSO TP, and the Carkeek CSO TP discharge to Extraordinary

Marine waters. The Aquatic Life Uses and the associated criteria for this receiving water are 

identified in Table 45.

Plan View - not to scale

Dilution Zone = 300 ft + diffuser depth = 312 ft

Width of plume = 

74 feet (from 

CORMIX model)

Max. = 100 ft.

50th% current = 0.21 m/s

10th and 90th % currents = 0.078 & 0.39 m/s

River width = 

300 ft

Outfall is located at bank.

Pipe is 8” diameter cast iron.

Acute Zone 

= 31 ft
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Table 45. Marine Aquatic Life Uses and Criteria - West Point WWTP, Alki, and Carkeek

Extraordinary Quality

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

Dissolved Oxygen Criteria – Lowest 1-Day Min 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.

The Elliott West CSO TP discharges to Excellent Marine waters. The Aquatic Life Uses and 

the associated criteria for this receiving water are identified in Table 46.

Table 46. Marine Aquatic Life Uses and Associated Criteria - Elliott West

Excellent Quality

Temperature Criteria – Highest 1D MAX 16°C (60.8°F)

Dissolved Oxygen Criteria – Lowest 1-Day Min 6.0 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 0.5 units.

To protect shellfish harvesting in the receiving waters around the West Point WWTP, Alki, 

Carkeek, and Denny/Elliott West CSO treatment plants, 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.

Recreational uses include primary contact and secondary contact recreation. The recreational 

use for receiving waters around the West Point WWTP, Alki, Carkeek, and Elliott West CSO 

treatment plant outfalls is primary contact as identified in Table 47.

Miscellaneous marine water uses include wildlife habitat, harvesting, commerce and 

navigation, boating, and aesthetics.

Table 47. Recreational Uses - West Point WWTP, Alki, Carkeek, and Elliott West 

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.

Duwamish River Discharge (Henderson/MLK):

The Henderson/MLK CSO TP discharges to the Duwamish River. Ecology designated this

portion of the river with an Aquatic Life Use of rearing and migration only and a Recreation 

Use of secondary contact. However, salinity data from King County’s 2012 Receiving Water 

Study and other sources indicates that the receiving water in the vicinity of the 

Henderson/MLK outfall is tidally influenced and meets the salinity requirements of WAC 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

173-201a-260. This means that the marine criteria apply to this waterbody for all parameters 

except for fecal coliform. The criteria for Excellent Aquatic Life Uses are listed in Table 48.

Table 48. Receiving Water Criteria Comparison for Henderson/MLK

Aquatic Life Uses Marine Criteria: Excellent

Temperature 16°C (60.8°F) – Highest 1D MAX

Dissolved Oxygen 6.0 mg/L – Lowest 1-Day Minimum

Turbidity • 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 pH must be within the range of 7.0 to 8.5 with a human-caused variation within the 

above range of less than 0.5 units.

Recreational Use Freshwater Criteria: Secondary Contact

Fecal Coliform Fecal coliform organism levels must not exceed a geometric mean value of 200 

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 400 colonies /100 mL.

For fecal coliform, WAC 173-201a-260 states that freshwater criteria must be applied when 

ninety-five percent of the salinity values are less than ten parts per thousand (based on 

vertically averaged daily maximum salinity values). Ecology placed freshwater criteria in the 

proposed permit, consistent with the existing permit. This decision is supported by the fact 

that this treatment facility only discharges once or twice each year and during very large 

storm events when the river flow is likely high from significant storm runoff. Under these 

circumstances the salinity component of the receiving water is most likely quite insignificant. 

As discharges from the facility increase with future CSO correction projects, Ecology may 

require future ambient salinity testing to support this decision.

The miscellaneous freshwater uses for the Henderson/MLK receiving water are wildlife 

habitat, harvesting, commerce and navigation, boating, and aesthetics.

E. Water quality and sediment impairments

Central Puget Sound, South Puget Sound, and Elliott Bay are listed on Ecology’s 2012

303(d) list as impaired for fecal coliform in the vicinities of the West Point WWTP, Alki, 

Carkeek, and Elliott West CSO outfalls. Ecology is not currently conducting a fecal coliform 

Total Maximum Daily Load (TMDL) analysis for these areas. Instead, Ecology is focusing 

on the South Puget Sound Dissolved Oxygen study; this study should be finalized in the next 

few years.

The Duwamish River is listed as impaired for high pH in the vicinity of the Henderson/MLK 

CSO outfall. Downstream of the outfall in the lower Duwamish, sediments and fish tissue are 

listed as impaired for a wide range of contaminants due to decades of industrial activity and 

run off from industrial areas. These contaminants include PCBs (polychlorinated biphenyls), 

PAHs (polycyclic aromatic hydrocarbons), chlorinated dioxins & furans, arsenic and other 

metals, pesticides and phthalates. EPA is leading the sediment contamination investigation 

for the Lower Duwamish Waterway site with support from Ecology. In 2001, EPA added the 

Lower Duwamish Waterway site to the Superfund National Priorities List; Ecology added the 

site to the Washington Hazardous Sites list in 2002. More information on the Lower 

Duwamish Waterway Superfund site can be found on EPA’s web page: Lower Duwamish 

Waterway site. More information on the sediment contamination clean-up can be found on 
Fact Sheet for NPDES Permit WA0029181 Page 69 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

the following sites: Duwamish River Cleanup Coalition (http://www.duwamishcleanup.org) 

the Lower Duwamish Work Group (http://www.ldwg.org), and Ecology’s LDW webpage

(http://www.ecy.wa.gov/programs/tcp/sites_brochure/lower_duwamish/lower_duwamish_hp.html).

In 1992 Ecology issued an ammonia-nitrogen TMDL in the Green/Duwamish system that 

identified a zero ammonia-nitrogen wasteload allocation for King County’s Renton South 

WWTP (except during emergencies and planned short-term maintenance). King County 

responded to this TMDL by relocating their South Plant WWTP outfall to the Puget Sound.

F. Evaluation of surface water quality-based effluent limits for numeric criteria

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 biochemical 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.

With technology-based controls (AKART), predicted pollutant concentrations in the 

discharge 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.

Estuarine Mixing Zones (West Point WWTP, Alki, Carkeek, and Elliott West)

Chronic --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 mixing zone extends from 

the top of the discharge ports to the water surface.

Acute - 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. 

West Point WWTP

The diffuser at outfall 001 is 600 feet long with 200 ports spaced equally on alternating sides 

with diameters ranging between 4.5 and 5.75-inches. The mean lower low water (MLLW) 

diffuser depth is 230 feet. Ecology obtained this information from King County’s 2013

Effluent Dilution Modeling for West Point Treatment Plant Outfall Report.

The horizontal distance of the chronic mixing zone is 430 feet from any discharge port. The 

acute mixing zone extends 43 feet in any direction from any discharge port.

Alki CSO 

The Alki outfall ends in a multi-port diffuser at a depth of 43.6m (143 ft) MLLW. The 

diffuser is 120 feet long with eight 12-inch diameter diffuser ports. The first six ports are 

directed to alternating sides of the outfall. The two end ports formed a ‘Y’ at the end of the 

diffuser. Ecology obtained this information from King County’s 2013 Effluent Dilution 

Modeling-Alki CSO Treatment Facility Marine Outfall Report.

The horizontal distance of the chronic mixing zone is 340 feet. The acute mixing zone 

extends 34 feet in any direction from any discharge port.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Carkeek CSO Outfall

The Carkeek outfall ends in a multi-port diffuser at a depth of 59.5m (195 ft) MLLW. The 

diffuser is 50 feet long with 13 diffuser ports varying between 5.5-inches and 10.0-inches in 

diameter. The ports are equally spaced on alternating sides. A port diameter of 6.57 inches 

corresponds to the average port area. Ecology obtained this information from King County’s 

2013 Effluent Dilution Modeling-Carkeek CSO Treatment Facility Marine Outfall Report.

The horizontal distance of the chronic mixing zone is 395 feet from any discharge port. The 

acute mixing zone extends 39.5 feet in any direction from any discharge port.

Elliott West CSO Outfall

The Elliott West outfall ends with a single 90 inch diameter port at a depth of 60 ft MLLW, 

approximately 490 ft offshore. Several years ago King County removed a duckbill valve 

from the end of the port to reduce back pressure caused by the valve. Ecology obtained this 

information from King County’s 2013 Effluent Dilution Modeling-Elliott West CSO 

Treatment Facility Marine Outfall Report.

The horizontal distance of the chronic mixing zone is 260 feet from any discharge port. The 

acute mixing zone extends 26 feet in any direction from any discharge port.

Freshwater Mixing Zone (Henderson/MLK)

While the marine water quality criteria apply for the Henderson/MLK discharge, Ecology 

applied the freshwater mixing zone sizing criteria to the Henderson/MLK outfall because

WAC 173-201A-400(8)(a) states that riverine size criteria “may also be applied to estuaries 

having flow characteristics resembling rivers”.

Chronic --WAC 173-201A-400(7)(a) specifies that mixing zones must not extend in a 

downstream direction from the discharge ports for a distance greater than 300 feet plus the 

depth of water over the discharge ports or extend upstream for a distance of over 100 feet, 

not utilize greater than 25% of the flow, and not occupy greater than 25% of the width of the 

water body.

Acute --WAC 173-201A-400(8)(a) specifies that in rivers and streams a zone where acute 

toxics criteria may be exceeded must not extend beyond 10% of the distance towards the 

upstream and downstream boundaries of the chronic zone, not use greater than 2.5% of the 

flow and not occupy greater than 25% of the width of the water body. 

The Henderson/MLK effluent discharges through an 84-inch, single-port pipe, located at the 

Norfolk outfall. The Norfolk outfall is located on the north bank of the Duwamish River 

approximately at river km 10.5. The 84-inch diameter outfall approaches the river bank at a 

90-degree angle to the river flow and is flush with the bank. There is a flap gate on the end of 

the pipe that is assumed to be completely open during discharge events.

For the Henderson/MLK CSO treatment plant outfall, the chronic mixing zone is 312 feet

long (downstream) and 74 feet wide. The acute mixing zone is 31.2 feet long. Both mixing 

zones extend from the river bottom to the top of the water surface. The dilution factors are

based on dilution at the downstream distance or where the plume width reaches 25% of the 

river width, whichever is more conservative.

Dilution Factors

King County calculated the dilution factors that occur within these zones at the critical 

conditions using Visual Plumes (UM3 and RSB model components) for all outfalls except 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Henderson/MLK, for which the County used the CORMIX model. Table 49 compares the 

proposed dilution factors to the dilution factors in the current permit.

Ecology reviewed the County’s data, dilution factors, and modeling in November 2013.

Ecology verified that the County used conservative assumptions and provided rigorous 

modeling to obtain dilution factors. There are differences between the dilution factors used in 

the previous permit and the dilution factors used in the proposed permit as described below. 

Ecology revised the dilution factors because calculations were performed with 1) updated

receiving water current and density data, and 2) updated effluent flow data obtained during 

the previous permit cycle. Ecology considers the dilution factors in the proposed permit to be 

more up-to-date and representative than the factors in the previous permit. Ecology notes that 

three of the dilution factors increased and four dilution factors decreased from the previous 

permit.

Table 49. Comparison of Dilution Factors 

Chronic Dilution 

Factor

Acute Dilution 

Factor

Human Health, 

Carcinogen

Human Health, 

Non-carcinogen

Current 

Permit

Proposed 

Permit

Current 

Permit

Proposed 

Permit

Current 

Permit

Proposed 

Permit

Current 

Permit

Proposed 

Permit

West Point WWTP 181 188 28 28 330 324 330 324

Alki CSO 61 99 17.5 20 * * * *

Carkeek CSO 146 104 93 75 * * * *

Elliott West CSO 11 9.7 7.8 8.4 * * * *

Henderson/MLK 10.3 10.3 1.9 1.9 * * * *

* Human Health dilution factors not assessed for CSO treatment plants. Ecology used chronic dilution factors for 

reasonable potential assessments.

Changes in the proposed dilution factors can be explained as follows:

1. West Point WWTP – Updated effluent and receiving water data resulted in a larger

chronic dilution factor compared to the previous analysis. In the recent analysis, receiving 

water density data show that the receiving water is most stratified in July. This 

stratification results in reduced plume mixing and therefore lower dilution factors than 

those calculated during winter months. As a result, the maximum average monthly flow 

used in the dilution calculation decreased from 204 MGD in the previous analysis to 87 

MGD (max flow during July in past 3 years). This in combination with the updated 

receiving water density profile resulted in a slightly higher dilution factor. No change is

proposed for the acute dilution factor.

2. Alki CSO – Updated effluent and receiving water data resulted in larger chronic and acute 

dilution factors compared to the previous analysis. 

3. Carkeek CSO – Updated effluent and receiving water data resulted in reduced chronic 

and acute dilution factors compared to the previous analysis.

4. Elliott West CSO – Updated effluent and receiving water data resulted in a reduced 

chronic and a slightly larger acute dilution factor compared to the previous analysis.

5. Henderson/MLK CSO – No dilution factors changes are proposed.

Ecology assessed the impacts of the treatment plant discharges on receiving water dissolved 

oxygen deficiency, pH, fecal coliform, turbidity, toxics (ammonia, chlorine, metals, and other 

priority pollutants), and temperature using the dilution factors listed in Table 49. The 
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

following tables describe this assessment for each treatment plant. The derivation of any 

surface water quality-based limits also takes into account the variability of pollutant 

concentrations in both the effluent and the receiving water.

West Point Wastewater Treatment Plant

Dissolved 

Oxygen -

BOD5 and 

Ammonia 

Effects

Natural decomposition of organic material in wastewater effluent impacts dissolved 

oxygen (DO) in the receiving water at distances far outside of the regulated mixing 

zone. The 5-day Biochemical Oxygen Demand (BOD5) of an effluent sample indicates 

the amount of biodegradable material in the wastewater and estimates the magnitude 

of oxygen consumption the wastewater will generate in the receiving water. The 

amount of ammonia-based nitrogen in the wastewater also provides an indication of 

oxygen demand potential in the receiving water.

Ecology modeled the impact of BOD5 on the receiving water using a simple mixing

model and an estimated oxidation rate at critical conditions (see Appendix F). Based 

on King County’s receiving water study, dissolved oxygen in the vicinity of the outfall is 

frequently below the water quality criteria of 7 mg/L. King County’s data shows the 10th

percentile dissolved oxygen value as 6.1 mg/L. Under critical conditions, assuming a 

typical technology-based weekly average effluent limit of 45 mg/L, the mixing model 

shows that dissolved oxygen decreases by 0.07 mg/L at the chronic mixing zone.

Ecology is in the process of modeling the impacts of nutrient discharges from

wastewater treatment plants and non-point sources on dissolved oxygen levels in the 

south Puget Sound. Ecology plans to publish the results of this study in the next 

several years. The results may impact nutrient control in future permits but since the 

study is not yet complete, the proposed permit does not include nutrient limits. The 

proposed permit requires nutrient monitoring to provide data to better inform future 

permitting decisions.

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. For calculations see Appendix F.

Fecal 

Coliform

Ecology modeled receiving water fecal coliform by simple mixing analysis and ambient 

data from King County’s 2013 Receiving Water Characterization Study. With a dilution 

factor of 188, a technology-based limit of 400/100 mL, and an ambient fecal 

concentration of 4/100 mL, Ecology calculated a fecal coliform concentration at the 

edge of the mixing zone boundary of 6/100 mL, well below the water quality standard 

of 14 colonies/100 mL (for primary contact recreation). Therefore, the proposed permit 

includes the technology-based effluent limits for fecal coliform bacteria.

Turbidity Ecology evaluated the impact of turbidity based on the range of total suspended solids 

in the effluent and turbidity of the receiving water. Ecology expects no violations of the 

turbidity criteria outside the designated mixing zone provided the facility meets its 

technology-based total suspended solids permit limits.

Toxics 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 were detected in West Point WWTP’s discharge: 

ammonia, 1,4 dichlorobenzene, 2,4 dichlorophenol, 2,4 dimethylphenol, antimony, 

arsenic, bis(2-ethylhexyl)phthalate, cadmium, chromium (hex), copper, cyanide, 

diethylphthalate, lead, manganese, methylene chloride, mercury, nickel, phenol, 

pyrene, selenium, silver, thallium, toluene, zinc, chlorine. Ecology conducted a 

reasonable potential analysis (see Appendix F) on these parameters to assess whether 

effluent limits would be required.
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West Point Wastewater Treatment Plant

King County provided ambient data in their 2013 receiving water study and the 

following parameters were detected in the receiving water: ammonia, arsenic, 

cadmium, chromium (hex), copper, lead, mercury, nickel, silver, and zinc. Ecology 

used the 90% concentrations for these pollutants in the reasonable potential analysis 

and assumed zero for ambient concentrations if data was not available.

Ecology determined that none of the toxics detected in the effluent pose a reasonable 

potential to exceed the water quality criteria at the critical condition using procedures 

given in EPA, 1991. Ecology’s determination assumes that this facility meets the other 

effluent limits of this permit.

Ecology derived effluent limits for chlorine using methods from EPA, 1991 as shown in 

Appendix F. 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 28 

and a chronic dilution factor of 188. The proposed effluent limits are 139 μg/L (average 

monthly limit) and 364 μg/L (maximum daily limit).

Temperature The state temperature standards (WAC 173-201A-200-210 and 600-612) include 

multiple elements: annual summer maximum threshold criteria, supplemental spawning 

and rearing season criteria, incremental warming restrictions, and 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 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). 

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.

Protections for 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 
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West Point Wastewater Treatment Plant

temperatures will not exceed 33°C two 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. 

Reasonable Potential Analysis for Annual summer maximum and incremental 

warming criteria: Ecology calculated the reasonable potential for the discharge to 

exceed the annual summer maximum and the incremental warming criteria at the edge 

of the chronic mixing zone during critical conditions (see Appendix F). No reasonable 

potential exists to exceed the temperature criterion where: 

(Criterion + 0.3) > [Criterion + (Teffluent95 – Criterion)/DF].

(13 + 0.3) > (13 + (21.0 – 13.0)/188)

13.3 > 13.04

Therefore, the proposed permit does not include a temperature limit. 

King County reported temperature data with their monthly discharge monitoring reports; 

Ecology used the 95th percentile of the 1DADmax value reported. Using a dilution factor

of 188 and maximum daily temperature of 14.0°C for the receiving water, the predicted 

maximum daily temperature inside the dilution zone is 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.

Alki CSO Treatment Plant

Dissolved 

Oxygen -

BOD5

Calculations show there is no reasonable potential for the Alki CSO treatment plant to 

violate DO water quality standards. For calculations see Appendix F.

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. For calculations see Appendix F.

Fecal 

Coliform

With the dilution factor of 99, the guidance-based limit of 400/100mL, and an ambient 

fecal concentration of 1/100 mL (from KC’s 2013 receiving water study), Ecology 

calculated a fecal coliform concentration at the edge of the mixing zone boundary of 

5/100 mL, which is below the water quality standard of 14 colonies/100 mL (see 

Appendix F). Therefore, the proposed permit includes the technology-based effluent 

limit for fecal coliform bacteria, on a monthly basis, since it is protective of water quality 

and more stringent than the water-quality based limit.

For CSO treatment plants that have technology/guidance-based limits for fecal coliform, 

the calculation method only includes discharge days. Non-discharge days are not 

included in the calculation, as the technology/guidance-based limit applies only when 

discharges are occurring with the reasoning that the plant is capable of achieving the 

technology/guidance limit on any given day. 

Toxics The following toxic pollutants are present in the Alki CSO treatment plant’s discharge:

ammonia, antimony, arsenic, bis(2-ethylhexyl)phthalate, butylbenzyl phthalate, 

cadmium, chlorine, chloroform, chromium (hex), copper, diethylphthalate, lead, mercury, 

nickel, silver, and zinc. Ecology conducted a reasonable potential analysis (see 

Appendix F) on these parameters to assess whether effluent limits would be required.

King County provided ambient data in their 2013 receiving water study and the following 

parameters were detected in the receiving water: ammonia, antimony, arsenic, 

cadmium, chlorine, chromium (hex), copper, lead, mercury, nickel, silver, and zinc. 

Ecology used the 90% concentrations for these pollutants in the reasonable potential 

analysis and assumed zero for ambient concentrations if data was not available.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Alki CSO Treatment Plant

Ecology determined that none of the toxics detected in the effluent, except chlorine, 

pose a reasonable potential to exceed the water quality criteria at the critical condition 

using procedures given in EPA, 1991. Ecology’s determination assumes that this facility 

meets the other effluent limits of this permit.

Ecology derived effluent limits for the toxic pollutant chlorine using methods from EPA, 

1991 as shown in Appendix F. The calculated maximum daily water-quality-based limit 

for chlorine based on the revised dilution factors is 260 μg/L. The previous permit 

included a water-quality based limit of 234 μg/L based the dilution factor in the 2009 

permit. 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.

Temperature The County was not required to collect temperature data for this facility so Ecology 

used West Point data for this assessment. Using the 95th percentile of West Point’s

1DADmax (21.0°C) and a dilution factor of 99, no reasonable potential exists to exceed 

the temperature criterion where: 

0.3 > (Teffluent95 – Tambient90)/DF

0.3 > (21.0 – 12.7)/99

0.3 > 0.08

Under these assumptions, the effluent discharge from this facility results in warming of 

the ambient temperature by 0.08°C, which is less than the allowable warming 

temperature of 0.3°C. Therefore, the proposed permit does not include a temperature 

limit.

Carkeek CSO Treatment Plant

Dissolved 

Oxygen -BOD5

Calculations show there is no reasonable potential for the Carkeek CSO treatment plant 

to violate DO water quality standards. For calculations see Appendix F.

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. For calculations see Appendix F.

Fecal Coliform With the dilution factor of 104, the guidance-based limit of 400/100mL, and an ambient 

fecal concentration of 4/100 mL (obtained from King County’s 2013 ambient monitoring 

report), Ecology calculated a fecal coliform concentration at the edge of the mixing zone 

boundary of 8/100mL, which is below the water quality standard of 14 colonies/100 mL

(see Appendix F). Therefore, the proposed permit includes the guidance-based effluent 

limit for fecal coliform bacteria, on a monthly basis, since it is protective of water quality 

and more stringent than the water quality-based limit.

For CSO treatment plants that have technology/guidance-based limits for fecal coliform, 

the calculation method only includes discharge days. Non-discharge days are not 

included in the calculation, as the technology/guidance-based limit applies only when 

discharges are occurring with the reasoning that the plant is capable of achieving the 

technology/guidance limit on any given day. 

Toxics The following toxic pollutants were detected in Carkeek CSO treatment plant’s 

discharge: ammonia, antimony, arsenic, benzo(b)fluoranthene, benzo(k)fluoranthene, 

bis(2-ethylhexyl)phthalate, butybenzyl phthalate, cadmium, chloroform, chromium (hex), 

copper, 2-4 dichlorophenol, diethylphthalate, di-n-butyl phthalate, lead, mercury, nickel, 

silver, toluene, zinc, and chlorine. Ecology conducted a reasonable potential analysis 

(see Appendix F) on these parameters to assess whether effluent limits would be 

required.

King County provided ambient data in their 2013 receiving water study and the following 

parameters were detected in the receiving water: ammonia, arsenic, cadmium, 

chromium (hex), copper, lead, mercury, nickel, silver, and zinc. Ecology used the 90% 

concentrations for these pollutants in the reasonable potential analysis and assumed 

zero for ambient concentrations if data was not available.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Carkeek CSO Treatment Plant

Ecology determined that none of the toxics detected in the effluent, except chlorine, 

pose a reasonable potential to exceed the water quality criteria at the critical condition 

using procedures given in EPA, 1991. 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 F. The 

calculated maximum daily water-quality-based limit for chlorine based on the revised 

mixing zone is 975 μg/L. The technology-based maximum daily limit for chlorine is more 

stringent than the water-quality-based limit at 750 μg/L. The previous permit included a 

water-quality based limit of 490 μg/L based on the dilution factor in the 2004 permit. The 

anti-backsliding provision under the federal regulations [CFR 122.44(l)] requires that the 

more stringent limit established in the previous permit be applied since it has been 

shown to be technologically achievable.

Temperature The County was not required to collect temperature data for this facility so Ecology used 

West Point data for this assessment. Using the 95th percentile of West Point’s 

1DADmax (21.0°C) and a dilution factor of 104, no reasonable potential exists to exceed 

the temperature criterion where: 

0.3 > (Teffluent95 – Tambient90)/DF

0.3 > (21.0 – 14.0)/104

0.3 > 0.07

Under these assumptions, the effluent discharge from this facility results in warming of 

the ambient temperature by 0.07°C, which is less than the allowable warming

temperature of 0.3°C. Therefore, the proposed permit does not include a temperature 

limit.

Elliott West CSO Treatment Plant

Dissolved 

Oxygen -

BOD5

Preliminary calculations show there could be a reasonable potential for the effluent 

from the Elliott West CSO treatment plant to violate DO water quality standards (see 

Appendix F). Ecology could not make a reliable assessment due to very limited DO 

data for this facility. The proposed permit requires additional DO monitoring so Ecology 

can better assess the impacts of BOD on dissolved oxygen in the receiving water at 

the next permit issuance. The Elliott West CSO treatment plant was originally designed 

for CSO treatment and not designed to remove BOD. Ecology is addressing the impact 

of effluent nutrients on Puget Sound DO in the ongoing South Puget Sound DO Study.

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. For calculations see Appendix F.

Fecal 

Coliform

With the chronic dilution factor of 9.7, the guidance-based limit of 400/100mL, an 

ambient fecal concentration of 2/100 mL (obtained from King County’s 2013 ambient 

monitoring report), and an assumption that the facility discharges three times each 

month for a period of 24 hours, Ecology calculated a monthly geometric mean for fecal 

coliform at the edge of the mixing zone boundary of 2.4/100mL. This easily meets the 

water quality standard of 14 colonies/100 mL (see Appendix F for calculations). 

Therefore, the proposed permit includes the guidance-based effluent limit for fecal 

coliform bacteria, on a monthly basis, since it is protective of water quality and more 

stringent than the water quality-based limit. The previous permit included this same 

guidance-based limit for an interim period followed by a less stringent WQ-based limit 

that included non-discharge days in the calculation. Ecology now believes this 

guidance-based limit is more appropriate and more protective of the water quality in 

Elliott Bay and therefore proposes this limit in the proposed permit.

For CSO treatment plants that have technology/guidance-based limits for fecal 

coliform, the calculation method only includes discharge days. Non-discharge days are 

not included in the calculation, as the technology/guidance-based limit applies only 
Fact Sheet for NPDES Permit WA0029181 Page 77 of 175

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Elliott West CSO Treatment Plant

when discharges are occurring with the reasoning that the plant is capable of achieving 

the technology/guidance limit on any given day. Compliance with this limit must be 

calculated using the geometric mean of all fecal coliform samples taken during each

calendar month a discharge occurs.

Toxics The following toxic pollutants were detected in Elliott West CSO treatment plant’s 

discharge: ammonia, antimony, arsenic, bis(2-ethylhexyl)phthalate, butylbenzyl 

phthalate, cadmium, chloroform, chromium (hex), copper, 1-4 dichlorobenzene, 

dichlorobromomethane, 2-4 dichlorophenol, diethylphthalate, dimethylphthalate, 

fluoranthene, lead, mercury, nickel, pentachlorophenol, pyrene, selenium, silver, 

thallium, toluene, zinc, chlorine, and cyanide (weak acid dissociable).

King County provided ambient data in their 2013 receiving water study and the 

following parameters were detected in the receiving water: ammonia, arsenic, 

cadmium, chromium (hex), copper, lead, mercury, nickel, silver, and zinc. Ecology 

used the 90% concentrations for these pollutants in the reasonable potential analysis 

and assumed zero for ambient concentrations if data was not available.

Ecology conducted a reasonable potential analysis (see Appendix F) on these 

parameters to determine if they pose a reasonable potential to exceed the water quality 

criteria at the critical condition using procedures given in EPA, 1991. Ecology 

determined that the only toxics detected in the effluent that pose a reasonable potential 

are chlorine, copper, and cyanide. Ecology’s determination assumes that this facility 

meets the other effluent limits of the permit.

Ecology derived an effluent limit for chlorine using methods from EPA, 1991 as shown 

in Appendix F. The proposed chlorine effluent limit is based on the revised dilution 

factors King County calculated using recent effluent flow data. The resultant maximum 

daily effluent limit for chlorine is 109 μg/L.

Calculations also showed a reasonable potential for copper. The copper levels in the 

Elliott West effluent are consistently five to six times higher than those from other King 

County outfalls. The County suspects this is a sampling anomaly caused by 

contamination within the sampling collection system. The proposed permit requires

additional copper monitoring using an improved sampling technique, along with a study 

to evaluate copper reduction strategies including source control options, copper 

removal at the facility, and improved outfall mixing.

Cyanide (weak acid dissociable) concentrations in the effluent were below detection 

(<5 μg/L) for 8 out of 11 samples; the three detected samples measured 7.3 (estimate), 

11.8, and 19.3 μg/L. The proposed permit requires additional monitoring to better 

assessment cyanide concentrations in the Elliott West effluent. 

Temperature The County was not required to collect temperature data for this facility so Ecology 

used West Point data for this assessment. Using the 95th percentile of West Point’s 

1DADmax (21.0°C) and a dilution factor of 9, no reasonable potential exists to exceed 

the temperature criterion where:

Max Incremental increase= 12 / (T - 2) where T = ambient temp

= 12 / (13.4 - 2) 

= 1.05° 

Max Incremental increase > (Teffluent95 – Tambient90)/DF

1.05° > (21.0 – 13.4) / 9.7

1.05° > 0.78°

This calculation is based on the requirements of WAC 173-201a-210(1)(c)(ii)(A)]. 

Under these assumptions, the effluent discharge from this facility results in warming of 

the ambient temperature by 0.78°C, which is less than the allowable warming 

temperature of 1.05°C. Therefore, the proposed permit does not include a temperature 

limit.
Fact Sheet for NPDES Permit WA0029181 Page 78 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Henderson/MLK CSO Treatment Plant

Dissolved 

Oxygen -

BOD5

Calculations show there is no reasonable potential for the Henderson/MLK CSO 

treatment plant to violate DO water quality standards. For calculations see Appendix F.

pH Ecology modeled the impact of the effluent pH on the receiving water using the 

calculations from EPA, 1988, and the chronic dilution factor of 10.3 (see Appendix F). 

The receiving water input variables used were obtained from King County’s 2013 

receiving water study and the effluent characteristics were obtained from DMRs. Using 

the assumed values, Ecology predicts no violation of the pH criteria under critical 

conditions. Therefore, the proposed permit includes technology-based effluent limits for 

pH.

Fecal 

Coliform

Ecology modeled the numbers of fecal coliform by simple mixing analysis. With the 

dilution factor of 10.3, the guidance-based limit of 400/100mL, and an ambient fecal 

concentration of 110/100 mL obtained from King County’s 2013 receiving water study, 

Ecology calculated a fecal coliform concentration at the edge of the mixing zone 

boundary of 138/100mL, which is below the water quality standard of 200 colonies/100 

mL (for freshwater recreational secondary contact). Therefore, the proposed permit 

includes the guidance-based effluent limit for fecal coliform bacteria, on a monthly 

basis, since it is protective of water quality and more stringent than the water qualitybased limit. 

Toxics Based on three sampling events, the following toxic pollutants were detected in the 

Henderson/MLK CSO treatment plant’s discharge: ammonia, antimony, arsenic, bis(2-

ethylhexyl)phthalate, cadmium, chlorine, chloroform, chromium (hex), chromium (tri), 

copper, dichlorobromomethane, 2-4 dichlorophenol, diethylphthalate, 

dimethylphthalate, di-n-butyl phthalate, lead, mercury, nickel, phenol, zinc, and 

cyanide.

Ecology did not conduct a reasonable potential analysis on these parameters because 

it would not be prudent to set a limit based on three data points. Instead, Ecology is 

requiring the County to sample for priority pollutants during the next permit cycle for reassessment with the next permit issuance.

Ecology derived an effluent limit for chlorine using methods from EPA, 1991 as shown 

in Appendix F. The proposed chlorine effluent limit is based on the dilution factors King 

County calculated using recent effluent flow data. The resultant maximum daily 

average effluent limit for chlorine is 25 μg/L, but since the chlorine analyzers cannot

accurately measure in this range the limit was kept at 39 μg/L. This limit will be 

protective of the maximum daily water quality criteria since additional chlorine decay 

occurs in the 5000 foot outfall line. Also, the Henderson/MLK facility typically 

discharges for less than 24 hours, therefore, if the proposed limit is met, the daily 

average concentration will be less than 25 μg/L.

Temperature The County was not required to collect temperature data for this facility so Ecology 

used West Point data for this assessment. Using the 95th percentile of West Point’s 

1DADmax (21.0°C) and a dilution factor of 10.3, no reasonable potential exists to 

exceed the temperature criterion where: 

0.3 > (Teffluent95 – Tambient90)/DF

0.3 > (21.0 – 18.7)/10.3

0.3 > 0.2

Under these assumptions, the effluent discharge from this facility results in warming of 

the ambient temperature by 0.22°C, which is less than the allowable warming 

temperature of 0.3°C. Therefore, the proposed permit does not include a temperature 

limit.
Fact Sheet for NPDES Permit WA0029181 Page 79 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

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 effluents for the West Point WWTP, Alki CSO TP, Carkeek CSO 

TP, Elliott West CSO TP, and the Henderson/MLK CSO TP may contain chemicals of 

concern for human health, based on (1) the facilities’ status as EPA major dischargers, or (2) 

data or information indicating regulated chemicals occur in the discharges. Ecology 

evaluated the discharges’ 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 reasonable potential determinations (Appendix F). For all facilities listed 

above, the evaluations showed that the discharges have no reasonable potential to cause

violation of the human health water quality standards and effluent limits are 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 West Point WWTP discharge has potential to cause a violation 

of the sediment quality standards because:

 Past sediment testing near the outfall has shown some inconclusive evidence of 

toxicity to benthic organisms (refer to Section II.E for more information).

 Past sediment testing near CSO locations has shown exceedances of the Sediment 

Management Standard.

The proposed permit includes a condition requiring King County to: 

 Continue sediment and effluent testing to investigate the source and extent of 

toxicity at the West Point WWTP outfall. 

 Provide an update to the 2009 CSO sediment report that summarizes activities and 

existing data for sediment quality at the CSO locations.

 Submit a post-construction monitoring summary report for CSO outfalls that will be 

controlled during this permit term.

 Model or sample sediments at five controlled CSO outfall locations: E. Pine Street 

Pump Station Emergency Overflow (011), Belvoir (012)/30th Ave NE Pump Station 

(049), Martin Luther King (013)/Henderson Pump Station (045), Matthews Park 

Pump Station Emergency Overflow (018), and Rainier Avenue Pump Station 

Emergency Overflow (033).
Fact Sheet for NPDES Permit WA0029181 Page 80 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

I. Whole effluent toxicity

The water quality standards for surface waters forbid discharge of effluent that has the 

potential to cause 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 reduced growth 

or 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.

Laboratories accredited by Ecology for WET testing know how to use the proper WET 

testing protocols, fulfill the data requirements, and submit results in the correct reporting 

format. Accredited laboratory staff know 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 (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

of its NPDES permit to the laboratory.

WET testing conducted during effluent characterization at the West Point WWTP showed no 

reasonable potential to cause receiving water acute or chronic toxicity, therefore the proposed 

permit does not include WET limits. King County must retest the West Point WWTP 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. King County may demonstrate to Ecology that effluent toxicity has not 

increased by performing additional WET testing and/or chemical analyses after the 

process or material changes have been made. Ecology recommends that the Permittee 

check first to make sure that Ecology will consider the demonstration adequate to support 

a decision to not require an 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.
Fact Sheet for NPDES Permit WA0029181 Page 81 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

J. Groundwater quality limits

The groundwater quality standards (chapter 173-200 WAC) protect beneficial uses of 

groundwater. Permits issued by Ecology must not allow violations of those standards (WAC 

173-200-100). King County does not discharge wastewater to the ground. No permit limits

are required to protect groundwater.

K. Comparison of effluent limits with the previous permit

The proposed limits are compared to those of the current permit in Table 50 through Table 

54. For the CSO treatment plants, Ecology evaluates settleable solids compliance using the 

0.3 ml/l/hr yearly average limit due to the intermittent and highly variable operation of the 

CSOs. Ecology removed the settleable solids event maximum limit of 1.9 ml/l/hr because 

there is no basis in regulation for an event maximum limit.

Table 50. Comparison of Previous and Proposed Effluent Limits - West Point WWTP

Parameter Basis of Limit Previous Effluent Limits Proposed Effluent Limits

Average 

Monthly

Average 

Weekly

Average 

Monthly

Average 

Weekly

CBOD (5-day) Technology 25 mg/L, 

44,800 lb/day

80% removal 

(Nov-April)

85% removal 

(May-Oct)

40 mg/L, 

71,700 lb/day

25 mg/L, 

44,800 lb/day

80% removal 

(Nov-April)

85% removal 

(May-Oct)

40 mg/L, 

71,700 lb/day

TSS Technology 30 mg/L, 

53,800 lb/day

80% removal

(Nov-April)

85% removal 

(May- Oct)

45 mg/L, 

80,700 lb/day

30 mg/L, 

53,800 lb/day

80% removal

(Nov-April)

85% removal 

(May- Oct)

45 mg/L, 

80,700 lb/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

Average 

Monthly

Maximum 

Daily

Average 

Monthly

Maximum 

Daily

Total Residual 

Chlorine

Water QualityBased139 μg/L 364 μg/L 139 μg/L 364 μg/L

Table 51. Comparison of Previous and Proposed Effluent Limits - Alki CSO TP

Previous Effluent Limits Proposed Effluent Limits

Parameter Monthly 

Average

Annual 

Average

Long-Term 

Average

Monthly 

Average

Annual 

Average

Long-Term 

Average

TSS Removal 

Efficiency, %

NA 50% NA NA 50% NA

Settleable Solids

(mL/L/hr)

1.9 Maximum

per event

0.3 NA no limit 0.3 NA

Fecal Coliform 

Bacteria

400/100mL NA NA 400/100mL NA NA

Number of 

events per year

NA NA 29/yr NA NA 29/yr

Average Vol. per 

yr, MG

NA NA 108 MG/yr NA NA 108 MG/yr

pH Daily Minimum is equal to or greater than 6.0 and the daily maximum is less than or equal to 9.0

Average 

Monthly

Maximum 

Daily

Average 

Monthly

Maximum 

Daily 

Total Residual 

Chlorine

NA 234 μg/L NA 234 μg/L
Fact Sheet for NPDES Permit WA0029181 Page 82 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 52. Comparison of Previous and Proposed Effluent Limits - Carkeek CSO TP

Previous Effluent Limits Proposed Effluent Limits

Parameter Monthly 

Average

Annual 

Average

Long-Term 

Average

Monthly 

Average

Annual 

Average

Long-Term 

Average

TSS Removal 

Efficiency, %

NA 50% NA NA 50% NA

Settleable Solids

(mL/L/hr)

1.9 Maximum

per event

0.3 NA no limit 0.3 NA

Fecal Coliform 

Bacteria

400/100mL NA NA 400/100mL NA NA

Number of 

events per year

NA NA 10/yr NA NA 10/yr

Average Vol. per 

yr, MG

NA NA 46 MG/yr NA NA 46 MG/yr

pH Daily Minimum is equal to or greater than 6.0 and the daily maximum is less than or equal to 9.0

Average 

Monthly

Maximum 

Daily 

Average 

Monthly

Maximum 

Daily 

Total Residual 

Chlorine

NA 490 μg/L NA 490 μg/L

Table 53. Comparison of Previous and Proposed Effluent Limits - Elliott West CSO TP

Previous Effluent Limits Proposed Effluent Limits

Parameter Monthly 

Average

Annual 

Average

Long-Term 

Average

Monthly 

Average

Annual 

Average

Long-Term 

Average

TSS Removal 

Efficiency, %

Report 50% NA Report 50% NA

Settleable Solids

(mL/L/hr)

1.9 Maximum

per event

0.3 NA no limit 0.3 NA

Fecal Coliform 

Bacteria

Interim 

400/100 mL

Final 154/100 

mL (calculated 

w/ ‘1’ for nondischarge days)

NA NA 400/100 mL

(not calculated 

w/ ‘1’ for nondischarge days)

NA NA

Number of 

events per year

NA Report NA NA Report NA

Average Vol. per 

yr, MG

NA Report NA NA Report NA

pH Daily Minimum is equal to or greater than 6.0 and the daily maximum is less than or equal to 9.0

Average 

Monthly

Maximum 

Daily 

Average 

Monthly

Maximum 

Daily 

Total Residual 

Chlorine

NA 104 μg/L NA 109 μg/L

Table 54. Comparison of Previous and Proposed Effluent Limits – Henderson/MLK TP

Previous Effluent Limits Proposed Effluent Limits

Parameter Monthly 

Average

Annual 

Average

Long-Term 

Average

Monthly 

Average

Annual 

Average

Long-Term 

Average

TSS Removal 

Efficiency, %

NA 50% NA NA 50% NA

Settleable Solids

(mL/L/hr)

1.9 Maximum

per event 

0.3 NA no limit 0.3 NA

Fecal Coliform 

Bacteria

400/100 mL Report NA 400/100 mL Report NA

Number of 

events per year

NA Report NA NA Report NA

Average Vol. per 

yr, MG

NA Report NA NA Report NA

pH Daily Minimum is equal to or greater than 6.0 and the daily maximum is less than or equal to 9.0

Average 

Monthly

Maximum 

Daily 

Average 

Monthly

Maximum 

Daily

Total Residual 

Chlorine

NA 39 μg/L NA 39 μg/L
Fact Sheet for NPDES Permit WA0029181 Page 83 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

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.

If a facility uses a contract laboratory to monitor wastewater, it must ensure that the laboratory 

uses the methods and meets or exceeds the method detection levels required by the permit. The 

permit describes when facilities may use alternative methods. It also describes what to do in 

certain situations when the laboratory encounters matrix effects. When a facility uses an 

alternative method as allowed by the permit, it must report the test method, DL, and QL on the 

discharge monitoring report or in the required report.

A. Wastewater monitoring

The monitoring schedule is detailed in the proposed permit under Special Condition S2. 

Specified monitoring frequencies take into account the quantity and variability of the 

discharges, the treatment methods, past compliance, significance of pollutants, and cost of 

monitoring. The required monitoring frequency for the West Point WWTP is consistent with 

or more conservative than agency guidance given in Ecology’s Permit Writer's Manual

(Publication Number 92-09) for municipal activated sludge facilities with design flows 

greater than 5 MGD. 

Ecology has included some additional monitoring of nutrients in the proposed permit to 

establish a baseline for this discharger. Ecology will use this data if TMDLs for dissolved 

oxygen are developed and waste load allocations for nutrients are established. 

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

the biosolids. 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, primary clarifier effluent, 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 sludge 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 sediments, whole effluent toxicity, 

and priority pollutants to further characterize the discharges. These pollutants could have a 

significant impact on the quality of the surface water. 

B. 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 the parameters listed in Table 55.
Fact Sheet for NPDES Permit WA0029181 Page 84 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Table 55. Lab Accredited Parameters

Parameter Name Analyte ID Method Name Method Code

Solids, Total Volatile 1970 EPA 160.4_1971 10010409

Chemical Oxygen Demand (COD) 1565 HACH 8000 90004005

Alkalinity 1505 SM 2320 B-97 20045607

Hardness, Total (as CaCO3) 1755 SM 2340 C-97 20047603

Specific Conductance 1610 SM 2510 B-97 20048606

Solids, Total 1950 SM 2540 B-97 20049405

Solids, Total Dissolved 1955 SM 2540 C-97 20050402

Solids, Total Suspended 1960 SM 2540 D-97 20051201

Solids, Settleable 1965 SM 2540 F-97 20052204

Chlorine (Residual), Total 1940 SM 4500-Cl D-00 20080108

Chlorine (Residual), Total 1940 SM 4500-Cl E-00 20080415

Chloride 1575 SM 4500-Cl ̄ C-97 20085205

pH 1900 SM 4500-H+ B-00 20105219

Ammonia 1515 SM 4500-NH3 E-97 20110605

Nitrogen, Total Kjeldahl 1795 SM 4500-Norg B-97 20119204

Dissolved Oxygen 1880 SM 4500-O G-01 20121408

Orthophosphate 1870 SM 4500-P E-99 20124214

Phosphorus, Total 1910 SM 4500-P E-99 20124214

Sulfate 2000 SM 4500-SO4 ̄ E-97 20132803

BOD, Carbonaceous BOD (CBOD) 1532 SM 5210 B-01 20135006

Fecal coliform-count 2530 SM 9221 E2 (A1) + C MPN 20196207

Total coliforms-count 2500 SM 9222 B (M-endo)-97 20203207

V. Other Permit Conditions

A. Reporting and record keeping

Ecology based Special Condition S3 on its 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 Special Condition S4.

• Design and construct expansions or modifications before the treatment plant reaches 

existing capacity.

• Report and correct conditions that could result in new or increased discharges of 

pollutants. 

Special Condition S4 restricts the amount of flow.
Fact Sheet for NPDES Permit WA0029181 Page 85 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

If a municipality intends to apply for Ecology-administered funding for the design or 

construction of a facility project, the plan must meet the standard of a Facility Plan, as 

defined in WAC 173-98-030. A complete Facility Plan includes all elements of an 

Engineering Report along with State Environmental Review Process (SERP) documentation 

to demonstrate compliance with 40 CFR 35.3140 and 40 CFR 35.3145, and a cost 

effectiveness analysis as required by WAC 173-98-730. The municipality should contact 

Ecology’s regional office as early as practical before planning a project that may include 

Ecology-administered funding.

C. Operation and maintenance 

The proposed permit contains Special Condition S5 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 C 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:

a. Are prohibited due to dangerous waste rules.

b. Are explosive or flammable. 

c. Have too high or low of a pH (too corrosive, acidic or basic). 

d. May cause a blockage such as grease, sand, rocks, or viscous materials. 

e. Are hot enough to cause a problem.

f. Are of sufficient strength or volume to interfere with treatment.

g. Contain too much petroleum-based oils, mineral oil, or cutting fluid. 

h. Create noxious or toxic gases at any point. 

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: 

a. Cooling water in significant volumes. 

b. Stormwater and other direct inflow sources. 
Fact Sheet for NPDES Permit WA0029181 Page 86 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

c. 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).

As sufficient data becomes available, King County must, in consultation with Ecology, 

reevaluate its local limits in order to prevent pass-through or interference. If any pollutant 

causes pass-through or interference, or exceeds established biosolids standards, King County

must establish new local limits or revise existing local limits as required by 40 CFR 403.5. In 

addition, Ecology may require revision or establishment of local limits for any pollutant that 

causes a violation of water quality standards or established effluent limits, or that causes 

whole effluent toxicity. 

E. Solid wastes

To prevent water quality problems the facility is required in permit Special 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 biosolids 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 Public Health - Seattle and King County.

Requirements for monitoring biosolids and record keeping are included in this permit. Ecology 

will use this information, required under 40 CFR 503, to develop or update local limits. 

F. Spill plan

The permitted facilities store 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]. 

King County developed a plan for preventing the accidental release of pollutants to state 

waters and for minimizing damages if such a spill occurs. The proposed permit requires the 

facility to review the plan annually and send revised plans to Ecology when significant 

changes are made.

G. Combined sewer overflows

Combined sewer systems are sewers that are designed to collect rainwater runoff, domestic 

sewage, and industrial wastewater in the same piping system. Most of the time, combined 

sewer systems transport all wastewater to a sewage treatment plant, where it is treated and 

then discharged to a water body. During periods of heavy rainfall or snowmelt, however, the 

wastewater volume in a combined sewer system can exceed the capacity of the combined 

sewer system or treatment plant. For this reason, combined sewer systems are designed to 

overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, or 
Fact Sheet for NPDES Permit WA0029181 Page 87 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

other water bodies. Chapter 173-245 WAC and EPA’s CSO control policy (59 FR 18688) 

identify the required measures for control of overflows from combined sewer systems. 

CSO Reduction Plan/Long-Term Control Plan and CSO Reduction Plan Amendments

Ecology requires municipalities to initially develop combined sewer overflow (CSO) reduction 

plans per chapter 173-245 WAC requirements. These plans are substantially equivalent to the 

long-term control plan (LTCP) as defined by EPA in its CSO control policy. Chapter 173-245 

WAC requires that “all CSO sites shall achieve and at least maintain the greatest reasonable 

reduction, and neither cause violations of applicable water quality standards, nor restrictions to 

the characteristic uses of the receiving water, nor accumulation of deposits which: (a) exceed 

sediment criteria or standards; or (b) have an adverse biological effect.” The greatest 

reasonable reduction means control of each CSO outfall such that an average of no more than 

one untreated discharge may occur per year. 

Under EPA’s CSO Control Policy’s presumption approach, CSO controls are presumed to 

attain WQS if certain performance criteria are met. Ecology presumes that a program that meets 

the criteria specified in WAC 173-245 and EPA’s CSO control policy provides an adequate 

level of control to meet the water quality-based requirements of the Clean Water Act. This 

presumption must be verified via a post-construction monitoring program by characterization, 

monitoring, and modeling of the system, including consideration of sensitive areas.

King County submitted a CSO reduction plan amendment in 2012 (King County’s 2012 Long 

Term CSO Control Plan Amendment). The proposed permit requires King County to submit an 

amendment of its CSO reduction plan in conjunction with its application for permit renewal. The 

amendment must include an assessment of the effectiveness of the CSO reduction plan, a reevaluation of CSO project priorities, and a list of projects to be completed in the next five years. 

In addition, King County must identify newly corrected or controlled CSOs that meet the state’s 

one untreated discharge per year per CSO standard in the CSO Reduction Plan Amendment.

Nine Minimum Controls

Municipalities with combined sewer overflow outfalls must implement nine minimum controls as 

technology-based standards for CSO discharges. The nine minimum controls are largely 

programmatic policies and practices designed to minimize the impacts untreated CSOs have on 

human health and the environment. It is not possible with current knowledge and technology to 

calculate numeric water quality-based effluent limits for CSOs. 

The nine minimum controls include:

1. Use proper operations and maintenance practices within the combined collection system 

to reduce the magnitude, frequency and duration of CSOs.

2. Implement procedures that maximize storage capacity of the combined collection system.

3. Minimize pollution from non-domestic wastewater sources through close management of 

a pretreatment program.

4. Maximize treatable flow to the wastewater treatment plant during wet weather.

5. Prevent CSO discharges during dry weather and properly report any dry weather CSO 

discharges immediately to Ecology.

6. Implement procedures to control solid and floatable materials in CSOs.

7. Implement and maintain a pollution prevention program designed to keep pollutants from 

entering the combined sewer system.
Fact Sheet for NPDES Permit WA0029181 Page 88 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

8. Establish a process to notify the public when and where CSOs occur.

9. Monitor CSO outfalls to characterize CSO impacts and the efficacy of CSO controls, 

including event-based monitoring of all CSO flow quantity, frequency and duration.

CSO Monitoring 

The proposed permit requires King County to monitor the volume, duration, and precipitation 

associated with each CSO discharge event at each identified outfall. 

Annual CSO Report

King County must submit annual reports according to the requirements of WAC 173-245-090(1). 

This report: (a) details the past year’s frequency and volume of combined sewage discharge from 

each CSO site, (b) explains the previous year’s CSO reduction accomplishments, and (c) lists the 

projects planned for the next year. The report must indicate whether a CSO site has increased 

over the baseline annual condition. The report must document implementation of the nine 

minimum controls, and wet weather operation (flow blending) at the West Point WWTP.

King County must also assess in its annual reports and CSO reduction plan amendment whether 

identified outfalls meet the state standard of one untreated discharge per year per CSO. 

Assessment may be based on a long-term average, which is defined as a 20-year averaging period.

King County may choose to indicate in the annual report which CSO events were exacerbated. 

For this purposes, exacerbated CSO shall mean any overflow at a CSO outfall that, while already 

discharging as a result of precipitation, is worsened by mechanical failures, blockages, power 

outages, and/or human error.

Post-Construction Monitoring Program

The federal CSO control policy (59 FR 18688) requires post-construction monitoring to verify 

implemented CSO control strategies comply with water quality standards. Post-construction 

monitoring applies to any CSO outfall that is controlled to meet the “greatest reasonable 

reduction” of combined sewer overflows, as defined in chapter 173-245 WAC. Implementation 

requires development of a monitoring plan and completion of a data report that documents 

compliance. The proposed permit requires King County to implement their 2012 Post 

Construction Monitoring Plan and to submit any plan modifications to Ecology for review and 

approval.

H. Outfall evaluation

The proposed permit requires King County to conduct outfall inspections of the West Point 

WWTP and CSO treatment plant outfalls and submit a report detailing the findings of those 

inspections (Special Condition S14). The inspections must evaluate the physical condition of 

the discharge pipes and diffusers, and evaluate the extent of sediment accumulations in the 

vicinity of the outfalls.

I. Elliott West CSO treatment plant – copper reduction assessment

King County must assess copper discharges from the Elliott West CSO treatment plant and 

submit a Copper Reduction Assessment Report to Ecology. The County has consistently 

measured copper concentrations from the facility at five times higher than other CSO 

facilities. The proposed permit requires the County to determine if these measurements 
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accurately reflect copper concentrations in the effluent or if there is sample interference. The 

study also requires the County to evaluate various copper reduction strategies.

J. Elliott West CSO treatment plant – settleable solids removal assessment

The Elliott West CSO treatment facility has difficulty meeting its annual settleable solids 

limit. The proposed permit requires the County to assess ways to reduce settleable solids 

from its discharge. 

K. General conditions

Ecology bases the standardized General Conditions on state and federal law and regulations. 

They are included in all individual domestic wastewater 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 groundwaters, 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 5 years.

VII. References for Text and Appendices

Ecology. Laws and Regulations (http://www.ecy.wa.gov/laws-rules/index.html)

Ecology. Permit and Wastewater Related Information 

(http://www.ecy.wa.gov/programs/wq/permits/guidance.html)

Ecology 1995. Sediment Management Standards. Chapter 173-204 WAC. Amended December 1995. 

http://www.ecy.wa.gov/programs/tcp/smu/sed_standards.htm

Ecology 1998. Chapter E-1, Criteria For Sewage Works Design, Ecology Publication # 98-37. 

Ecology 2002. Final Sediment Management Standards Cleanup Action Decision 

Duwamish/Diagonal CSO/SD. Department of Ecology NWRO TCP. July 25, 2002.

Environmental Protection Agency (EPA). 1983. Water Quality Standards Handbook. USEPA 

Office of Water, Washington, D.C.

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

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

EPA, 1991. Technical Support Document for Water Quality-based Toxics Control. EPA/505/2-90-001. 
Fact Sheet for NPDES Permit WA0029181 Page 90 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

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

EPA, 1995. Combined Sewer Overflow Guidance for Permit Writers, EPA, August 1995.

King County. 1996. Norfolk CSO cleanup study report. Prepared for Elliott Bay/Duwamish Restoration 

Program Panel. Panel Publication 13. King County Department of Natural Resources, Seattle, WA.

(http://www.kingcounty.gov/environment/wastewater/SedimentManagement/Projects/Norfolk/Library.aspx)

King County, 1999. King County Department of Natural Resources Year 2000 CSO Plan Update 

Project, Sediment Management Plan. Prepared by Anchor Environmental and Herrera 

Environmental Consultants in collaboration with King County. June 1999.

King County, 1999. Sediment remediation plan, Denny Way/Lake Union CSO Control Project. 

Prepared for King County and Black and Veatch. Seattle, Washington.

King County. 2005. The Denny Way sediment cap – 2000 data – final monitoring report. King 

County Department of Natural Resources. Seattle, Washington.

King County. June 2005. Norfolk CSO Sediment Remediation Project Five-Year Monitoring Program, 

Final Monitoring Report, Year Five. Prepared for the Elliott Bay/Duwamish Restoration Program 

Panel, Panel Publication 38. King County Department of Natural Resources. Seattle, Washington.

King County 2006. West Point Wastewater Treatment Plant 2006 Outfall Sediment Sampling Event 

Final Report. King County Department of Natural Resources and Parks, Marine and Sediment 

Assessment Group, September 2007. SEDQUAL data WPNT06.

King County 2008. Denny Way CSO and Elliott West CSO Treatment Facility, Post-Construction 

Sediment Monitoring Sampling and Analysis Plan. Prepared by King County Department of Natural 

Resources and Parks Marine and Sediment Assessment Group. March 2008.

King County, CSO Sediment Quality Characterization Final Sampling and Analysis Plan, Aug 2011.

King County, Technical Memorandum - Feasible Alternatives Analysis for CSO-Related 

Secondary Process Diversion at West Point Treatment Plant, May 21, 2009.

King County, 2009 Comprehensive Sediment Quality Summary Report for CSO Discharge Locations, 

Dec 2009.

King County, CSO Sediment Quality Characterization Final Sampling and Analysis Plan, Aug 2011.

King County, Post Construction Monitoring Plan for King County CSO Controls, Sept 2012.

King County, 2012 Long Term CSO Control Plan Amendment, October 2012.

King County, CSO Sediment Quality Characterization, 2011 Sediment Sampling Event, Dec 2012.

King County, 2013 Receiving Water Characterization Study, King County NPDES Monitoring 

Program, Final Report for Brightwater, South, Vashon, and West Point Treatment Plants and Alki, 

Carkeek, Elliott West, and Henderson/MLK CSO Storage and Treatment Facilities, June 2013.

King County, Effluent Dilution Modeling Report for the West Point WWTP Outfall, 2013.

King County, Effluent Dilution Modeling Report for the Alki CSO Treatment Plant Outfall, 2013.

King County, Effluent Dilution Modeling Report for the Carkeek CSO Treatment Plant Outfall, 2013.

King County, Effluent Dilution Modeling Report for the Elliott West CSO Treatment Plant Outfall, 2013.

King County, Effluent Dilution Modeling Report for the Henderson/MLK CSO Treatment Plant 

Outfall, 2013.
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West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Washington State Department of Ecology. Permit Writer’s Manual. Publication Number 92-109, 

December 2011. (http://www.ecy.wa.gov/biblio/92109.html)

Washington State Department of Health, 1994. Design Criteria for Municipal Wastewater Land 

Treatment.

Water Pollution Control Federation, Chlorination of Wastewater, 1976.

Windward Environmental LLC. 2008. Lower Duwamish Waterway remedial investigation, 

remedial investigation report, draft final (internal). Prepared for submittal to EPA and Ecology. 

(http://yosemite.epa.gov/r10/CLEANUP.NSF/LDW/Lower+Duwamish+Waterway+Draft+Phase+II+

Remedial+Investigation+Report/$FILE/draft_riII.pdf)
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Appendix A — Public Involvement Information

Ecology proposes to reissue a permit to King County. 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 Draft on October 30, 2014, in the Seattle Times to inform the 

public and to invite comment 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.

• Told how to request a public hearing about the proposed NPDES permit.

• Explained the next step(s) in the permitting process.

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 primary author of this permit and fact sheet is Alison Evans, PE.
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Appendix B — Your Right to Appeal

You have a right to appeal this permit to the Pollution Control Hearing Board (PCHB) within 30 

days of the date of receipt of the final permit. The appeal process is governed by chapter 43.21B 

RCW and chapter 371-08 WAC. “Date of receipt” is defined in RCW 43.21B.001(2) (see 

glossary).

To appeal you must do the following within 30 days of the date of receipt of this permit:

 File your appeal and a copy of this permit with the PCHB (see addresses below). Filing 

means actual receipt by the PCHB during regular business hours.

 Serve a copy of your appeal and this permit on Ecology in paper form - by mail or in person. 

(See addresses below.) E-mail is not accepted.

You must also comply with other applicable requirements in chapter 43.21B RCW and chapter 

371-08 WAC.

Street Addresses Mailing Addresses

Department of Ecology

Attn: Appeals Processing Desk

300 Desmond Drive SE

Lacey, WA 98503

Department of Ecology

Attn: Appeals Processing Desk

PO Box 47608

Olympia, WA 98504-7608

Pollution Control Hearings Board 

1111 Israel RD SW

STE 301

Tumwater, WA 98501

Pollution Control Hearings Board

PO Box 40903

Olympia, WA 98504-0903
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Appendix C — 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 time 

period, 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).

Alternate point of compliance -- An alternative location in the groundwater from the point of 

compliance where compliance with the groundwater standards is measured. It may be 

established in the groundwater at locations some distance from the discharge source, up to, 

but not exceeding the property boundary and is determined on a site specific basis following 

an AKART analysis. An “early warning value” must be used when an alternate point is 

established. An alternate point of compliance must be determined and approved in 

accordance with WAC 173-200-060(2).

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 (intermittent) discharge limit -- The average of the measured values 

obtained over a calendar months time taking into account zero discharge days. 

Average monthly discharge limit -- The average of the measured values obtained over a 

calendar month's time.

Background water quality -- The concentrations of chemical, physical, biological or radiological 

constituents or other characteristics in or of groundwater at a particular point in time upgradient 

of an activity that has not been affected by that activity [WAC 173-200-020(3)]. Background 

water quality for any parameter is statistically defined as the 95% upper tolerance interval with 

a 95% confidence based on at least eight hydraulically upgradient water quality samples. The 

eight samples are collected over a period of at least one year, with no more than one sample 

collected during any month in a single calendar year.

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 
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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 five-day 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 BOD5 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.

Categorical pretreatment standards -- National pretreatment standards specifying quantities or 

concentrations of pollutants or pollutant properties, which may be discharged to a POTW by 

existing or new industrial users in specific industrial subcategories.

Chlorine -- A chemical used to disinfect wastewaters of pathogens harmful to human health. It is 

also extremely toxic to aquatic life. 

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

ability to dilute effluent is reduced.

Date of receipt – This is defined in RCW 43.21B.001(2) as five business days after the date of 

mailing; or the date of actual receipt, when the actual receipt date can be proven by a 

preponderance of the evidence. The recipient's sworn affidavit or declaration indicating the 

date of receipt, which is unchallenged by the agency, constitutes sufficient evidence of actual 

receipt. The date of actual receipt, however, may not exceed forty-five days from the date of 

mailing.

Detection limit -- 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.

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%.

Distribution uniformity -- The uniformity of infiltration (or application in the case of sprinkle 

or trickle irrigation) throughout the field expressed as a percent relating to the average depth 

infiltrated in the lowest one-quarter of the area to the average depth of water infiltrated.

Enforcement limit -- The concentration assigned to a contaminant in the groundwater at the 

point of compliance for the purpose of regulation, [WAC 173-200-020(11)]. This limit 

assures that a groundwater criterion will not be exceeded and that background water quality 

will be protected.

Engineering report -- A document that 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.

Exacerbated CSO -- Any overflow at a CSO outfall that, while already discharging as a result 

of precipitation, is worsened by mechanical failures, blockages, power outages, and/or 

human error.

Fecal coliform bacteria -- Fecal coliform bacteria are used as indicators of pathogenic bacteria 

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

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

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

presence of animal feces.

Grab sample -- A single sample or measurement taken at a specific time or over as short a 

period of time as is feasible.

Groundwater -- Water in a saturated zone or stratum beneath the surface of land or below a 

surface water body.

Industrial user -- A discharger of wastewater to the sanitary sewer that is not sanitary 

wastewater or is not equivalent to sanitary wastewater in character.

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

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

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

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

contaminated storm water and, also, leachate from solid waste facilities.
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Interference -- A discharge which, alone or in conjunction with a discharge or discharges from 

other sources, both:

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

processes, use or disposal; and

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

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

sewage sludge use or disposal in compliance with the following statutory provisions and 

regulations or permits issued thereunder (or more stringent State or local regulations): 

Section 405 of the Clean Water Act, the Solid Waste Disposal Act (SWDA) (including 

title II, more commonly referred to as the Resource Conservation and Recovery Act 

(RCRA), and including State regulations contained in any State sludge management plan 

prepared pursuant to subtitle D of the SWDA), sludge regulations appearing in 40 CFR 

Part 507, the Clean Air Act, the Toxic Substances Control Act, and the Marine 

Protection, Research and Sanctuaries Act.

Local limits -- Specific prohibitions or limits on pollutants or pollutant parameters developed by 

a POTW.

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.

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 permit specifies the area of the authorized mixing zone that Ecology 

defines following 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.

Pass-through -- A discharge which exits the POTW into waters of the State in quantities or 

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

sources, is a cause of a violation of any requirement of the POTW's NPDES permit 
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(including an increase in the magnitude or duration of a violation), or which is a cause of a 

violation of State water quality standards.

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.

Point of compliance -- The location in the groundwater where the enforcement limit must not be 

exceeded and a facility must comply with the Ground Water Quality Standards. Ecology 

determines this limit on a site-specific basis. Ecology locates the point of compliance in the 

groundwater as near and directly downgradient from the pollutant source as technically, 

hydrogeologically, and geographically feasible, unless it approves an alternative point of 

compliance.

Potential significant industrial user (PSIU) --A potential significant industrial user is defined 

as an Industrial User that does not meet the criteria for a Significant Industrial User, but 

which discharges wastewater meeting one or more of the following criteria:

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

per day; or

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

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

photographic film or paper, and car washes).

Ecology may determine that a discharger initially classified as a potential significant 

industrial user should be managed as a significant industrial user.

Quantitation level (QL) -- Also known as Minimum Level of Quantitation (ML) – The lowest level 

at which the entire analytical system must give a recognizable signal and acceptable calibration 

point for the analyte. It is equivalent to the concentration of the lowest calibration standard, 

assuming that the lab has used all method-specified sample weights, volumes, and cleanup 

procedures. The QL is calculated by multiplying the MDL by 3.18 and rounding the result to the 

number nearest to (1,2,or 5) x 10n, where n is an integer (64 FR 30417). 

ALSO GIVEN AS: 

The smallest detectable concentration of analyte greater than the Detection Limit (DL) where the 

accuracy (precision & bias) achieves the objectives of the intended purpose. (Report of the 

Federal Advisory Committee on Detection and Quantitation Approaches and Uses in Clean 

Water Act Programs Submitted to the US Environmental Protection Agency, December 2007).

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).

Significant industrial user (SIU) --

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

and 40 CFR Chapter I, Subchapter N; and 
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2) Any other industrial user that: discharges an average of 25,000 gallons per day or more of 

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

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

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

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

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

pretreatment standard or requirement [in accordance with 40 CFR 403.8(f)(6)].

Upon finding that the industrial user meeting the criteria in paragraph 2, above, has no 

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

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

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

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

significant industrial user.

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

the case of non-delegated POTWs or to the POTW in the case of delegated POTWs.

Slug discharge -- Any discharge of a non-routine, episodic nature, including but not limited to 

an accidental spill or a non-customary batch discharge to the POTW. This may include any 

pollutant released at a flow rate that may cause interference or pass through with the POTW 

or in any way violate the permit conditions or the POTW’s regulations and local limits.

Solid waste -- All putrescible and non-putrescible solid and semisolid wastes including, but not 

limited to, garbage, rubbish, ashes, industrial wastes, swill, sewage sludge, biosolids, 

demolition and construction wastes, abandoned vehicles or parts thereof, contaminated soils 

and contaminated dredged material, and recyclable materials.

Soluble BOD5 -- Determining the soluble fraction of Biochemical Oxygen Demand of an 

effluent is an indirect way of measuring the quantity of soluble organic material present in an 

effluent that is utilized by bacteria. Although the soluble BOD5 test is not specifically 

described in Standard Methods, filtering the raw sample through at least a 1.2 um filter prior 

to running the standard BOD5 test is sufficient to remove the particulate organic fraction.

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.

Technology-based effluent limit -- A permit limit based on the ability of a treatment method to 

reduce the pollutant.

Total coliform bacteria--A microbiological test, which detects and enumerates the total 

coliform group of bacteria in water samples.

Total dissolved solids--That portion of total solids in water or wastewater that passes through a 

specific filter.

Total maximum daily load (TMDL) -- A determination of the amount of pollutant that a water 

body can receive and still meet water quality standards.

Total suspended solids (TSS) -- Total suspended solids is the particulate material in an effluent. 

Large quantities of TSS discharged to a receiving water may result in solids accumulation. 
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Apart from any toxic effects attributable to substances leached out by water, suspended solids 

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

clogging the gills and respiratory passages of various aquatic fauna. Indirectly, suspended 

solids can screen out light and can promote and maintain the development of noxious 

conditions through oxygen depletion. 

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

with technology-based permit effluent 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 imposed on the concentration of an effluent 

parameter to prevent the concentration of that parameter from exceeding its water quality 

criterion after discharge into receiving waters.
Fact Sheet for NPDES Permit WA0029181 Page 101 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Appendix D — Receiving Water Data

Parameter Min Ave Max StdDev Count C V Min Ave Max StdDev Count C V

Antimony (μg/L) 0.1430 0.1631 0.1830 0.0102 32

Arsenic (μg/L) 1.1100 1.3075 1.4300 0.0968 24 0.07 1.2200 1.3788 1.4900 0.0765 32 0.06

Cadmium (μg/L) 0.05200 0.06978 0.08640 0.00731 24 0.10 0.06110 0.07178 0.08300 0.00510 32 0.07

Chromium (μg/L) 0.08800 0.11700 0.19000 0.02531 24 0.22 0.08800 0.11638 0.18000 0.02417 32 0.21

Copper (μg/L) 0.2340 0.3795 1.2200 0.1955 24 0.52 0.2310 0.3749 1.9900 0.2996 32 0.80

Cyanide (μg/L) 0.005 0.005 0.005 0.000 16 0.00

Lead (μg/L) 0.0050 0.0127 0.0460 0.0127 24 0.99 0.0050 0.0159 0.0492 0.0139 32 0.88

Mercury (μg/L) 0.000200 0.000251 0.000550 0.000099 24 0.39 0.000200 0.000238 0.000400 0.000060 32 0.25

Nickel (μg/L) 0.387 0.422 0.593 0.039 24 0.09 0.390 0.424 0.511 0.027 32 0.06

Silver (μg/L) 0.01000 0.01642 0.03000 0.00754 24 0.46 0.01000 0.01625 0.03000 0.00733 32 0.45

Zinc (μg/L) 0.170 0.476 0.890 0.171 24 0.36 0.270 0.465 0.707 0.106 32 0.23

Parameter Min Ave Max StdDev Count C V Min Ave Max StdDev Count C V

Antimony (μg/L)

Arsenic (μg/L) 1.1200 1.3079 1.4500 0.0888 24 0.07 0.3910 0.5423 0.8570 0.1287 32 0.24

Cadmium (μg/L) 0.05520 0.06990 0.07990 0.00608 24 0.09 0.00500 0.01008 0.02300 0.00614 32 0.61

Chromium (μg/L) 0.07700 0.11158 0.18000 0.02653 24 0.24 0.05000 0.12138 0.22000 0.05548 32 0.46

Copper (μg/L) 0.2770 0.4292 0.8150 0.1457 24 0.34 0.3060 0.6721 1.3700 0.2892 32 0.43

Cyanide (μg/L)

Lead (μg/L) 0.0050 0.0208 0.0842 0.0227 24 1.09 0.0050 0.0763 0.3270 0.0847 32 1.11

Mercury (μg/L) 0.000200 0.000241 0.000517 0.000082 24 0.34 0.000240 0.000843 0.001990 0.000508 32 0.60

Nickel (μg/L) 0.383 0.418 0.501 0.026 24 0.06 0.156 0.479 1.090 0.299 32 0.62

Silver (μg/L) 0.01000 0.01700 0.03300 0.00846 24 0.50 0.01000 0.01634 0.05240 0.01141 32 0.70

Zinc (μg/L) 0.300 0.631 1.020 0.235 24 0.37 0.460 1.029 2.160 0.407 32 0.40

KSBP01 (Carkeek, West Pt) LSNT01 (Alki)

LTED04 (Elliott West) LTXQ01 (Henderson)

Receiving Water Metals Data

Parameter Min Ave Max Count Min Ave Max Count Min Ave Max Count Min Ave Max Count

Alkalinity, Total (mg CaCO3/L) 97 100 103 16

Ammonia (mg/L as N) 0.0050 0.0188 0.0853 191

Fecal Coliform (#/100 mL) 1 1 

(geomean)

4 24 1 1 

(geomean)

1 24 1 2 

(geomean)

29 24 5 33 

(geomean)

600 24

Total Suspended Solids (mg/L) 0.5 2.4 7.0 136 0.5 2.4 7.5 134 0.5 2.7 8.1 102 2.5 16 116 22

pH 7.5 7.7 8.0 108 7.4 7.6 8.0 112 7.4 7.6 8.0 84 6.8 7.1 7.3 16

KSBP01 (Carkeek, West Pt) LSNT01 (Alki) LTED04 (Elliott West) LTXQ01 (Henderson)
Fact Sheet for NPDES Permit WA0029181 Page 102 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Appendix E — Facility Data

0

100,000,000

200,000,000

300,000,000

400,000,000

500,000,000

600,000,000

Alki CSO Treatment 

Facility

Carkeek CSO 

Treatment Facility 

Elliott West CSO 

Treatment Facility

Henderson/MLK CSO 

Treatment Facility

West Point 

Wastewater 

Treatment Plant Gallons

Volume Discharged per Year

2009

2010

2011

2012

0

5

1 0

1 5

2 0

2 5

3 0

Alki CSO Treatment 

Facility

Carkeek CSO 

Treatment Facility

Elliott West CSO 

Treatment Facility

Henderson/MLK CSO 

Treatment Facility

West Point 

Wastewater 

Treatment Plant # of Events

Number of Events per Year

2009

2010

2011

2012
Fact Sheet for NPDES Permit WA0029181 Page 103 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System 05

1 0

1 5

2 0

2 5

3 0

3 5

Alki CSO 

Treatment Facility 

Carkeek CSO 

Treatment Facility 

Elliott West CSO 

Treatment Facility

Henderson/MLK 

CSO Treatment 

Facility

West Point 

Wastewater 

Treatment Plant

# of Events: 2009 - 2012

Event Duration profile 2009-2012

< 1hr 1-4 hrs 4-8 hrs 8-12 hrs

1 2-24 hrs

2 4-48 hrs

48hrs-4 days

> 4 days
Fact Sheet for NPDES Permit WA0029181 Page 104 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

West Point WWTP – Plant Data

Test Code Collected Start Date Organism Endpoint NOEC LOEC PMSD

RMAR2559 4/11/2012 4/11/2012 Atlantic mysid 7-day Survival 5 0 100 28.87%

Biomass 2 5 5 0 27.44%

Weight 2 5 5 0 21.92%

RMAR2558 4/11/2012 4/11/2012 topsmelt 7-day Survival 5 0 100 13.50%

Biomass 2 5 5 0 16.35%

Weight 2 5 5 0 18.23%

RMAR2761 10/3/2012 10/3/2012 Atlantic mysid 7-day Survival 5 0 100 16.14%

Biomass 2 5 5 0 21.62%

Weight 2 5 5 0 15.99%

RMAR2762 10/3/2012 10/3/2012 topsmelt 7-day Survival 5 0 100 8.20%

Biomass 2 5 5 0 15.36%

Weight 5 0 > 50 14.59%

Test Code Collected Start Date Organism Endpoint NOEC LOEC PMSD

RMAR2431 1/10/2012 1/10/2012 Daphnia pulex 48-hour Survival 100 > 100 5.00% 100%

RMAR2430 1/10/2012 1/10/2012 fathead minnow 96-hour Survival 100 > 100 4.57% 100%

RMAR2615 7/17/2012 7/18/2012 Daphnia pulex 48-hour Survival 100 > 100 5.00% 100%

RMAR2616 7/17/2012 7/18/2012 fathead minnow 96-hour Survival 100 > 100 6.45% 98%

% 

Survival 

King County West Point Acute WET Test Results

 NOEC/LOEC in % Effluent

King County West Point Chronic WET Test Results

NOEC/LOEC in % 

Effluent
Fact Sheet for NPDES Permit WA0029181 Page 105 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

West Point 

WWTP

CBOD5, lbs/dayCBOD5, lbs/dayCBOD5, mg/LCBOD5, mg/LBOD5, lbs/dayBOD5, lbs/dayBOD5, mg/LBOD5, mg/LTSS, lbs/dayTSS, lbs/dayTSS, mg/LTSS, mg/L

Ave Max Day Ave

Max 

Day Ave Max Day Ave

Max 

Day Ave Max Day Ave

Max 

Day

1-Jul-09 115,800 152,600 208 277 131,100 157,100 237 279 148,500 193,700 268 344

1-Aug-09 133,100 287,100 221 328 154,400 359,200 257 409 169,700 419,000 281 457

1-Sep-09 125,500 173,000 208 292 162,000 318,300 270 535 162,700 350,900 263 342

1-Oct-09 117,800 184,600 181 302 136,400 261,600 211 504 163,500 310,500 239 451

1-Nov-09 116,300 178,700 105 220 143,400 249,900 131 241 174,500 301,000 150 267

1-Dec-09 105,700 155,400 140 202 130,300 192,400 172 247 145,200 234,500 188 291

1-Jan-10 103,500 168,400 93 148 126,500 207,700 118 188 172,300 307,700 148 267

1-Feb-10 109,800 159,200 125 171 129,900 201,500 146 205 163,500 298,800 180 246

1-Mar-10 108,300 171,900 143 226 131,000 225,700 172 253 153,600 427,900 195 342

1-Apr-10 118,500 151,500 149 198 141,700 237,600 176 265 159,700 266,800 198 340

1-May-10 124,300 156,200 164 220 146,100 204,300 194 301 166,000 270,800 216 306

1-Jun-10 127,800 204,100 169 262 147,200 208,200 196 273 169,300 298,500 222 346

1-Jul-10 114,900 149,600 196 240 139,400 229,200 238 406 143,500 188,100 245 343

1-Aug-10 118,000 150,400 201 263 132,900 175,000 227 304 147,900 229,800 251 305

1-Sep-10 112,900 151,300 167 238 134,000 186,800 198 260 158,000 268,100 225 289

1-Oct-10 129,000 319,100 189 323 152,300 240,000 223 314 185,400 346,400 263 350

1-Nov-10 118,900 169,500 147 186 143,900 243,200 179 300 183,700 292,700 223 295

1-Dec-10 102,200 158,200 95 176 113,700 175,000 106 206 154,600 282,900 137 245

1-Jan-11 113,500 156,900 117 179 125,900 192,500 132 216 155,000 259,300 158 266

1-Feb-11 110,300 162,100 134 209 130,400 208,100 157 227 158,500 315,100 187 274

1-Mar-11 111,700 154,700 102 147 133,700 225,900 120 167 171,600 468,100 149 230

1-Apr-11 136,200 226,000 156 236 152,800 240,000 176 265 168,800 275,500 191 287

1-May-11 131,700 208,300 159 210 161,900 427,300 194 535 174,000 254,500 208 280

1-Jun-11 147,500 200,300 193 246 163,000 211,200 214 270 189,700 284,000 248 312

1-Jul-11 146,600 200,000 217 285 168,700 234,400 250 348 183,800 293,300 271 360

1-Aug-11 138,000 228,000 218 351 157,700 274,400 250 417 176,300 269,800 279 410

1-Sep-11 110,400 131,700 197 244 128,200 157,600 230 261 152,200 217,600 270 304

1-Oct-11 111,000 159,700 182 257 130,300 209,600 213 274 156,300 319,000 250 301

1-Nov-11 106,800 152,100 156 236 129,900 170,600 188 268 154,500 303,000 210 298

1-Dec-11 113,200 175,600 185 235 133,300 207,100 217 293 148,200 299,600 237 301

1-Jan-12 111,700 174,200 123 192 136,500 219,700 151 237 160,300 246,700 173 221

1-Feb-12 106,700 163,000 135 173 128,400 192,900 162 203 151,400 302,600 187 273

1-Mar-12 103,000 147,000 109 186 127,000 158,300 136 251 159,300 275,000 163 252

1-Apr-12 107,500 140,300 143 190 135,400 184,400 180 254 155,900 229,500 204 248

1-May-12 117,900 155,100 168 220 140,800 219,300 200 256 167,200 325,400 232 304

1-Jun-12 119,000 192,400 173 265 137,700 213,300 201 267 171,100 328,500 245 339

1-Jul-12 107,000 151,700 174 225 121,700 156,600 198 261 150,500 269,300 240 331

1-Aug-12 112,800 160,000 208 291 124,000 179,800 229 327 144,800 233,200 267 424

1-Sep-12 107,800 142,411 211 274 119,500 146,446 234 290 143,600 228,689 281 440

1-Oct-12 117,300 157,988 179 260 139,000 218,503 208 352 177,700 323,338 259 354

1-Nov-12 111,700 183,015 117 197 129,500 189,031 136 228 178,700 316,723 176 248

1-Dec-12 107,600 133,912 85 120 121,000 151,413 100 143 165,500 271,055 125 242

1-Jan-13 113,900 149,835 129 198 132,300 179,760 150 259 156,200 273,931 173 236

1-Feb-13 113,700 139,612 160 216 134,500 215,798 189 271 147,100 206,864 206 251

1-Mar-13 111,900 146,135 155 212 147,600 307,607 202 297 148,600 253,424 203 277

1-Apr-13 112,400 145,654 134 180 135,500 189,917 162 230 169,700 297,440 194 257

1-May-13 121,000 157,126 190 251 136,300 183,141 214 302 154,900 244,937 240 278

1-May-13 121,000 157,126 190 251 136,300 183,141 214 302 154,900 244,937 240 278

1-Jun-13 121,800 156,917 202 252 143,300 427,634 228 500 157,300 269,805 252 294

1-Jul-13 122,889 185,681 227 341 140,376 264,636 259 486 158,998 438,882 293 806

1-Aug-13 120,287 178,230 212 339 128,263 181,287 227 326 156,170 289,289 272 363

1-Sep-13 126,469 178,499 200 302 139,492 222,914 221 373 191,645 381,933 292 602

1-Oct-13 112,553 217,970 199 411 120,499 197,817 212 373 152,658 316,083 268 596

AVE: 117,115 171,887 165 239 137,112 219,146 193 298 161,975 290,838 221 328

MIN: 102,200 131,700 85 120 113,700 146,446 100 143 143,500 188,100 125 221

MAX: 147,500 319,100 227 411 168,700 427,634 270 535 191,645 468,100 293 806

Limits 201,000 218,000

Nov-April

Influent
Fact Sheet for NPDES Permit WA0029181 Page 106 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

West Point 

WWTP

Flow, MGDFlow, MGDCBOD, lbs/dayCBOD, lbs/dayCBOD, mg/LCBOD, mg/LCBOD, % RemovalTSS, lbs/dayTSS, lbs/dayTSS, mg/LTSS, mg/LTSS, % RemovalFecal Coliform, #/100 mlFecal Coliform, #/100 mlp Hp H

Ave

Max 

Day

Mnth 

Ave Wk Ave

Mnth 

Ave

Wkly 

Ave Ave

Mnth 

Ave Wk Ave

Mnth 

Ave

Wk 

Ave Ave GEM GM7 max min

1-Jul-09 6 6 7 4 2700 3200 5 6 9 8 3500 3900 6.0 7.0 9 8 3 1 2 7.2 6.8

1-Aug-09 7 1 110 3700 4600 6 7 9 7 4300 5200 7.0 9.0 9 7 4 1 4 7.2 6.8

1-Sep-09 7 5 155 3400 4000 5 6 9 8 3600 4200 5.0 6.0 9 8 7 1 2 7.3 6.7

1-Oct-09 9 0 239 4800 7000 7 8 9 6 5600 10000 7.0 10.0 9 7 5 1 4 7.5 6.5

1-Nov-09 157 323 7310 11100 5 6 9 5 10800 16500 7.0 9.0 9 5 6 1 6 7.1 6.5

1-Dec-09 9 5 198 3790 5330 4 5 9 7 5550 7910 6.0 7.0 9 7 6 1 7 7.5 6.5

1-Jan-10 156 316 6360 12600 5 6 9 5 9750 18400 7.0 8.0 9 5 4 1 7 7.2 6.4

1-Feb-10 112 237 5490 6280 5 6 9 6 9430 11600 9.0 11.0 9 5 2 4 7.0 6.5

1-Mar-10 9 6 225 4350 6150 5 6 9 6 6820 9840 8.0 10.0 9 6 1 3 2 7.5 6.5

1-Apr-10 9 9 199 4110 5510 5 5 9 7 5890 6960 7.0 7.0 9 7 5 8 7.4 6.6

1-May-10 9 4 164 4310 5100 6 7 9 7 5550 6060 7.0 8.0 9 7 6 1 3 7.1 6.6

1-Jun-10 9 2 166 4610 5160 6 7 9 7 6030 7090 8.0 8.0 9 7 1 1 2 5 7.3 6.5

1-Jul-10 7 0 8 6 3800 3960 7 7 9 7 4050 4400 7.0 7.0 9 7 2 4 7.2 6.7

1-Aug-10 7 1 116 3450 3710 6 6 9 7 4100 4230 7.0 7.0 9 7 2 2 7.1 6.7

1-Sep-10 8 7 216 4560 6940 6 8 9 6 5210 7740 6.0 8.0 9 7 7 9 7.2 6.8

1-Oct-10 9 0 243 13000 33200 1 4 2 7 9 2 21500 61300 21.0 45.0 9 2 7 4 2 7.3 6.6

1-Nov-10 103 239 9130 17100 9 1 2 9 4 13300 26400 13.0 17.0 9 4 1 6 4 5 7.4 6.8

1-Dec-10 153 404 7000 9540 5 7 9 5 13800 21800 9.0 12.0 9 3 6 1 5 7.2 6.3

1-Jan-11 127 296 5520 9210 5 6 9 6 8560 14400 7.0 8.0 9 5 2 6 6.9 6.4

1-Feb-11 107 240 5380 10200 5 8 9 6 7620 13400 8.0 10.0 9 6 2 4 7.8 6.6

1-Mar-11 149 335 7900 14600 5 7 9 5 13700 30900 8.0 15.0 9 4 3 6 7.6 6.3

1-Apr-11 108 200 5740 8970 6 9 9 6 6960 9070 8.0 9.0 9 6 2 3 7.5 6.3

1-May-11 104 276 5150 6960 6 8 9 6 7040 9270 8.0 9.0 9 6 4 4 7.2 6.3

1-Jun-11 9 2 131 4270 4830 6 6 9 7 5830 6860 8.0 9.0 9 7 9 2 4 7.2 6.6

1-Jul-11 8 1 106 5540 6710 8 1 0 9 6 6240 7160 9.0 11.0 9 7 1 3 4 0 7.3 6.7

1-Aug-11 7 6 8 1 4340 6300 7 1 0 9 7 5370 8200 8.0 13.0 9 7 1 4 2 6 7.6 6.8

1-Sep-11 6 8 115 2750 3510 5 6 9 8 3080 4230 5.0 7.0 9 8 4 7 7.3 6.7

1-Oct-11 7 6 171 5030 7090 8 1 0 9 6 7140 11000 11.0 18.0 9 6 6 3 3 7.3 6.5

1-Nov-11 101 319 4670 9040 5 5 9 7 7770 17100 8.0 10.0 9 6 4 1 2 7.5 6.1

1-Dec-11 7 7 176 5640 9610 9 1 2 9 5 8250 14500 12.0 18.0 9 5 5 1 9 7.6 6.5

1-Jan-12 120 295 7340 12000 7 1 1 9 4 9870 13900 9.0 14.0 9 5 3 1 1 7.8 6.3

1-Feb-12 9 8 186 5610 7340 7 8 9 5 8850 12600 10.0 14.0 9 4 2 4 7.0 6.2

1-Mar-12 131 266 9770 16300 7 1 0 9 3 19400 36600 14.0 20.0 9 1 4 1 3 7.1 6.2

1-Apr-12 9 2 135 4420 5070 6 7 9 6 5330 5790 7.0 8.0 9 7 2 2 7.1 6.4

1-May-12 8 8 193 4570 5530 6 9 9 6 6220 7560 9.0 12.0 9 6 2 3 7.2 6.3

1-Jun-12 8 6 166 7250 9910 1 0 1 1 9 5 8750 13000 12.0 14.0 9 5 3 4 7.7 6.6

1-Jul-12 7 6 152 4310 5290 6 7 9 6 5480 6440 8.0 10.0 9 7 5 2 6 7.4 6.3

1-Aug-12 6 5 7 9 3080 3810 6 6 9 7 3980 4810 7.0 9.0 9 7 1 4 2 9 7.5 6.7

1-Sep-12 6 1 7 1 3510 4090 7 8 9 7 3130 3880 6.0 8.0 9 8 3 6 7.2 6.6

1-Oct-12 9 3 299 6750 11500 8 1 0 9 6 8610 22100 9.0 14.0 9 7 1 0 4 3 7.3 6.1

1-Nov-12 140 339 7100 12300 6 6 9 5 13500 27200 10.0 14.0 9 4 1 2 2 4 7.7 6.3

1-Dec-12 175 340 7040 11400 4 6 9 5 13600 22100 8.0 11.0 9 4 8 2 5 7.3 6.1

1-Jan-13 115 336 6370 8350 6 9 9 5 8600 11700 8.0 11.0 9 5 2 4 7.0 6.0

1-Feb-13 8 6 121 3980 4970 5 6 9 7 5120 6050 7.0 8.0 9 7 2 4 7.1 6.5

1-Mar-13 9 1 222 4210 5710 5 6 9 7 5340 6890 7.0 8.0 9 7 2 5 6.8 6.2

1-Apr-13 108 247 4290 5640 5 5 9 7 6650 9650 7.0 7.0 9 6 2 2 6.9 6.2

1-May-13 7 7 135 5130 6050 8 1 0 9 6 6200 7930 10.0 12.0 9 6 3 1 3 6.6 7.4

1-May-13 7 7 135 5130 6050 8 1 0 9 6 6200 7930 10.0 12.0 9 6 3 1 3 6.6 7.4

1-Jun-13 7 5 126 5270 6080 8 9 9 6 5520 8470 8.0 11.0 9 7 2 3 6.5 7.7

1-Jul-13 6 5 6 9 3925 4693 7 9 9 7 3649 4409 7.0 8.0 9 8 4 7 7.3 6.7

1-Aug-13 6 9 120 5855 7393 1 0 1 1 9 5 7622 11606 13.0 18.0 9 5 4 1 0 7.5 6.5

1-Sep-13 8 5 220 4898 6353 7 9 9 6 9602 14987 12.0 14.0 9 6 7 2 6 7.3 6.6

1-Oct-13 6 9 102 3414 5173 6 8 9 7 4188 7631 7.0 10.0 9 7 4 1 8 7.1 6.7

AVE: 9 6 198 5302 7896 6 8 9 6 7580 12318 8.5 11.3 9 6 5 1 4 7.3 6.5

MIN: 6 1 6 9 2700 3200 4 5 9 2 3080 3880 5.0 6.0 9 1 2 2 6.5 6.0

MAX: 175 404 13000 33200 1 4 2 7 9 8 21500 61300 21.0 4 5 9 8 1 6 4 5 7.8 7.7

Limits 215 44800 71700 2 5 4 0 8 5 53800 80700 3 0 4 5 8 5 200 400 6.0 9.0

Nov-April 8 0 8 0

Effluent - page 1
Fact Sheet for NPDES Permit WA0029181 Page 107 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

West Point 

WWTP Res. Chlorine - BEFORE Disinfect., μg/L Res. Chlorine - BEFORE Disinfect., μg/L Res. Chlorine - AFTER Disinfect., μg/L Res. Chlorine - AFTER Disinfect., μg/L

TKN, mg/L as NTKN, mg/L as NAmmonia, lbs/dayAmmonia, lbs/dayAmmonia, mg/LAmmonia, mg/LNitrate+Nitrite, mg/L as N Nitrate+Nitrite, mg/L as N Ortho Phos, mg/L as POrtho Phos, mg/L as PTotal Phos, mg/L as PTotal Phos, mg/L as PTemp, deg CTemp, deg C

Mnth Ave Max Day

Mnth 

Ave

Max 

Day

Mnth 

Ave

Max 

Day

Mnth 

Ave Max Day

Mnth 

Ave

Max 

Day

Mnth 

Ave

Max 

Day

Mnth 

Ave

Max 

Day

Mnth 

Ave

Max 

Day Ave Max

1-Jul-09 757 973 5 7 142 2 4 2 6 11,550 12,900 2 3 2 6 6.2 6.2 4.0 4.2 E E 2 1 2 2

1-Aug-09 714 832 6 4 131 2 6 3 1 14,225 16,900 2 5 2 9 2.1 2.1 3.7 4.4 3.0 3.0 2 2 2 2

1-Sep-09 811 1017 8 6 190 3 1 3 3 16,200 19,000 2 9 3 2 2.4 3.1 2.6 2.6 2 1 2 2

1-Oct-09 799 1057 9 4 135 1 9 2 4 16,550 19,400 1 8 2 3 8.0 8.0 2.7 2.9 1.8 1.8 2 0 2 1

1-Nov-09 724 910 9 5 140 1 6 2 1 13,900 20,900 1 4 1 9 4.8 4.8 2.7 3.4 2.0 2.0 1 6 1 9

1-Dec-09 654 903 103 141 1 7 1 7 10,850 12,900 1 5 1 7 6.7 6.7 2.9 3.1 1.5 1.5 1 6 1 7

1-Jan-10 692 934 103 164 1 0 1 3 15,875 22,800 1 0 1 2 4.0 4.0 1.3 2.2 2.1 2.1 1 4 1 5

1-Feb-10 642 822 110 151 1 4 1 5 9,800 10,100 1 3 1 4 4.9 4.9 2.2 2.2 1.9 1.9 1 5 1 6

1-Mar-10 775 662 9 1 154 1 5 1 7 12,825 19,600 1 4 1 7 4.5 4.5 2.3 2.9 1.5 1.5 1 5 1 6

1-Apr-10 658 961 100 177 1 7 1 8 12,200 12,400 1 6 1 8 6.2 6.2 2.9 2.9 2.3 2.3 1 6 1 7

1-May-10 654 830 9 2 5 0 2 0 2 3 13,500 17,100 1 8 2 1 1.1 1.1 3.2 3.6 2.5 2.5 1 7 1 8

1-Jun-10 632 830 102 140 2 3 3 0 14,300 17,200 2 1 2 7 6.9 6.9 3.0 3.5 c c 1 8 1 9

1-Jul-10 622 800 120 170 2 6 2 6 13,100 13,100 2 4 2 4 3.6 3.6 3.9 3.9 2.8 2.8 2 0 2 1

1-Aug-10 655 810 107 170 2 6 2 9 14,800 16,600 2 5 2 7 5.7 5.7 3.9 4.1 2.9 2.9 2 1 2 2

1-Sep-10 656 740 9 8 150 1 9 2 1 12,250 13,200 1 8 1 9 3.0 3.0 2.2 2.8 1.7 1.7 2 1 2 1

1-Oct-10 639 900 107 140 1 9 3 0 12,725 15,000 1 7 2 7 6.5 6.5 2.4 3.8 2.6 2.6 2 0 2 1

1-Nov-10 676 800 9 4 340 2 1 2 2 19,867 27,700 1 9 2 2 0.5 0.5 2.0 2.3 2.4 2.4 1 8 1 9

1-Dec-10 665 1030 101 160 1 2 2 2 12,850 14,800 1 6 2 1 4.1 4.1 1.4 2.7 1.9 1.9 1 4 1 7

1-Jan-11 646 940 9 3 120 1 4 1 5 10,175 12,500 1 3 1 4 6.0 6.0 1.9 2.2 1.9 1.9 1 4 1 5

1-Feb-11 636 790 9 3 130 1 4 1 9 15,125 20,900 1 3 8 6.5 6.5 1.4 2.0 1.5 1.5 1 4 1 6

1-Mar-11 661 980 100 140 1 2 1 8 11,600 13,800 1 2 1 7 2.3 2.3 1.1 2.1 1.9 1.9 1 4 1 5

1-Apr-11 618 740 114 150 1 5 1 7 12,975 17,700 1 3 1 5 7.2 7.2 2.1 2.7 1.4 1.4 1 5 1 6

1-May-11 679 930 111 160 1 7 2 1 14,667 18,200 1 6 1 9 6.1 6.1 2.0 2.9 1.1 1.1 1 6 1 7

1-Jun-11 689 780 9 0 150 2 6 2 6 17,900 18,500 2 4 2 5 3.2 3.2 3.1 3.3 2.3 2.3 1 8 1 9

1-Jul-11 635 740 9 5 140 2 6 2 6 17,100 17,100 2 5 2 6 4.3 4.3 3.2 3.4 1.9 2.0 2 0 2 0

1-Aug-11 626 860 9 6 160 3 1 3 2 18,700 19,700 2 9 3 1 4.2 4.2 3.4 3.7 2.0 2.0 2 1 2 1

1-Sep-11 664 840 9 1 160 2 7 3 2 14,200 16,900 2 7 3 2 2.3 2.3 3.4 4.1 1.7 1.7 2 1 2 2

1-Oct-11 650 800 8 6 140 2 7 3 1 16,800 21,100 2 6 3 1 4.7 4.7 3.2 3.7 2.5 2.5 2 0 2 1

1-Nov-11 679 920 8 8 150 2 2 2 3 10,900 11,300 2 1 2 2 5.2 5.2 3.1 3.4 2.9 2.9 1 7 1 9

1-Dec-11 639 750 8 9 130 2 1 2 2 10,600 11,700 1 9 2 1 9.0 9.0 3.1 3.3 3.4 3.4 1 6 1 7

1-Jan-12 679 990 102 140 1 6 2 7 13,500 18,400 1 5 2 6 1.8 1.8 1.5 2.8 2.6 2.6 1 4 1 7

1-Feb-12 636 790 113 190 2 0 2 1 14,500 17,700 1 8 1 9 5.8 5.8 2.6 2.8 2.5 2.5 1 4 1 5

1-Mar-12 686 860 9 4 160 1 8 2 4 15,100 17,200 1 6 2 1 3.2 3.2 1.8 2.8 1.6 1.8 1 4 1 5

1-Apr-12 648 760 103 280 2 1 2 3 15,500 18,000 2 0 2 2 3.8 3.8 2.0 2.7 1.8 1.8 1 6 1 7

1-May-12 663 1130 9 0 120 2 2 2 4 16,400 25,400 2 1 2 3 4.4 4.4 2.8 3.3 2.0 2.0 1 7 1 8

1-Jun-12 657 750 8 7 180 2 5 2 9 14,900 17,600 2 3 2 7 3.3 3.3 3.4 4.9 2.9 2.9 1 8 2 0

1-Jul-12 638 740 103 160 2 3 2 6 13,200 14,700 2 2 2 6 6.6 6.6 3.3 3.7 2.5 2.5 2 0 2 1

1-Aug-12 632 760 9 6 130 2 9 3 0 13,800 15,100 2 7 2 8 3.0 3.0 3.5 3.6 3.0 3.0 2 1 2 2

1-Sep-12 637 800 8 8 140 2 6 2 7 12,400 13,233 2 3 2 6 5.8 5.8 3.6 3.7 2.4 2.4 2 1 2 2

1-Oct-12 681 890 105 240 2 0 2 4 14,300 22,615 1 8 2 2 3.5 3.5 2.1 3.2 1.9 1.9 2 0 2 1

1-Nov-12 658 860 118 340 1 5 1 7 13,200 15,488 1 3 1 6 2.6 2.6 1.4 1.5 1.8 1.8 1 7 1 9

1-Dec-12 690 930 102 150 9 1 2 10,400 10,472 9 1 2 5.0 5.0 1.2 1.9 1.6 1.6 1 4 1 6

1-Jan-13 663 890 139 180 1 7 2 2 13,300 17,882 1 5 1 8 5.8 5.8 2.0 2.3 1.9 1.9 1 4 1 6

1-Feb-13 654 1020 104 210 2 0 2 3 12,500 13,675 1 7 2 0 4.9 4.9 2.0 2.1 2.0 2.1 1 5 1 6

1-Mar-13 650 970 9 5 180 1 5 1 8 8,920 10,590 1 4 1 7 9.8 9.8 2.2 2.4 2.0 2.0 1 5 1 6

1-Apr-13 585 730 9 3 140 9 1 4 6,740 7,849 9 1 3 9.7 9.7 1.1 2.5 0.9 0.9 1 5 1 7

1-May-13 622 730 9 6 260 2 6 2 6 17,700 19,676 2 5 2 6 3.1 3.1 2.7 2.8 2.9 2.9 1 8 1 8

1-May-13 622 730 9 6 260 2 6 2 6 17,700 19,676 2 5 2 6 3.1 3.1 2.7 2.8 2.9 2.9 1 8 1 8

1-Jun-13 633 730 9 5 210 2 7 3 1 15,200 17,605 2 7 3 1 2.6 2.6 2.8 3.3 2.6 2.6 1 9 2 0

1-Jul-13 610 760 9 3 170 2 7 3 0 14,430 15,677 2 6 2 9 4.1 4.1 3.0 3.3 2.4 2.4 2 1 2 2

1-Aug-13 625 830 9 8 170 2 5 2 5 12,004 12,004 2 3 2 3 4.6 4.6 2.8 2.8 2.8 2.8 2 2 2 2

1-Sep-13 680 1090 110 230 2 2 2 5 13,116 14,377 2 0 2 1 2.1 2.1 2.8 e 2.1 2.1 2 1 2 2

1-Oct-13 638 850 118 320 2 5 2 8 13,143 14,483 2 4 2 7 4.7 4.7 2.6 3.0 2.3 2.3 2 0 2 0

AVE: 663 858 9 8 172 2 1 2 4 13,775 16,423 1 9 2 2 4.7 4.7 2.6 3.1 2.2 2.2 1 8 1 9

MIN: 585 662 5 7 5 0 9 1 2 6,740 7,849 9 8 0.5 0.5 1.1 1.5 0.9 0.9 1 4 1 5

MAX: 811 1130 139 340 3 1 3 3 19,867 27,700 2 9 3 2 1 0 1 0 4.0 4.9 3.4 3.4 2 2 2 2

Limits 139 364

Nov-April

Effluent - page 2
Fact Sheet for NPDES Permit WA0029181 Page 108 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

West Point WWTP - Influent Data

0

50

300250200150100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Influent BOD5, Average Monthly, mg/L

0

50,000

250,000200,000150,000100,000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Influent BOD5, Average Monthly, lb/day Monthly Average

85 % of Max Month Design FlowMax Month Design Flow

0

50

350300250200150100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Influent TSS, Average Monthly, mg/L

0

50,000

250,000200,000150,000100,000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Influent TSS, Average Monthly, lb/day Monthly Average

85 % of Max Month Design FlowMax Month Design Flow
Fact Sheet for NPDES Permit WA0029181 Page 109 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

West Point WWTP - Effluent Data

0

50

250200150100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Flow, Average Monthly, MGD

Monthly Average85% of Max Month Design FlowMax Month Design Flow

9.59.08.58.07.57.06.5

6.05.55.0

10.0 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan pH, standard units

monthly minimummonthly maximum

0

50

450400350300250200150100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Flow, Maximum Daily, MGD

Maximum DayCSO-related Bypass Threshold

0

50

450400350300250200150100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Fecal Coliform, #/100 mLGEM

GEM limitGM7GM7 limit
Fact Sheet for NPDES Permit WA0029181 Page 110 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

West Point WWTP - Effluent Data (continued)

50

504540353025201510 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent CBOD5, Average Monthly, mg/L

Monthly AveragePermit Limit-Monthly Average

50

504540353025201510 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent CBOD5, Average Weekly, mg/L Weekly Average

Permit Limit-Weekly Average

50

504540353025201510 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent TSS, Average Monthly, mg/L

Monthly AveragePermit Limit-Monthly Average

50

504540353025201510 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent TSS, Average Weekly, mg/L Weekly Average

Permit Limit-Weekly Average
Fact Sheet for NPDES Permit WA0029181 Page 111 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

West Point WWTP - Effluent Data (continued)

0

50

100

150

200

250

300

350

400

Apr-09 Jul-09 Oct-09 Jan-10 Apr-10 Jul-10 Oct-10 Jan-11 Apr-11 Jul-11 Oct-11 Jan-12 Apr-12 Jul-12 Oct-12 Jan-13 Apr-13 Jul-13 Oct-13 Jan-14 Effluent Residual Chlorine, μg/L

Monthly Average

Monthly Ave Limit

Max Day

Max Day Limit
Fact Sheet for NPDES Permit WA0029181 Page 112 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Alki CSO Treatment Plant – Plant Data

Alki CSO Volume, MG BOD, mg/L BOD, mg/L TSS, mg/L TSS, mg/L Volume, MG BOD, mg/L BOD, mg/L TSS, mg/L TSS, mg/L TSS, % Removal Fecal Coliform, #/100 ml Fecal Coliform, #/100 ml pHpHRes. Chlorine, 

μg/L Res. Chlorine, μg/L Settleable Solies, mL/L Settleable Solies, mL/L

Total Ave Max Ave Max Total

Mnth 

Ave Max

Mnth 

Ave Max Ave GEM Max max min

Mnth 

Ave

Max 

Day

Mnth 

Ave

Max 

Event

1-Sep-09 0.2 E E 213 213 0.0 n d n d n d n d 9 4 n d n d n d n d n d n d n d n d

1-Oct-09 1.4 4 1 4 1 122 122 0.0 2 4 2 4 4 1 4 1 9 7 20,000 20,000 8.4 8.4 100 100 0.1 0.1

1-Nov-09 6.4 1 3 2 2 5 1 8 2 1.8 1 4 1 4 2 6 3 2 8 4 1 1 7.4 7.2 684 684 0.1 0.1

1-Jan-10 14.5 3 9 5 1 5 6 6 1 8.4 2 6 2 8 2 7 2 7 6 7 1 1 7.3 7.0 1092 1708 0.2 0.2

1-Mar-10 0.2 2 8 2 8 4 0 4 0 0.0 n d n d n d n d 9 6 n d n d n d n d n d n d n d n d

1-Sep-10 3.8 3 4 3 8 115 156 1.0 1 6 1 7 3 1 4 8 8 9 1 0 1 8 7.2 6.8 3 9 5 0 0.3 0.3

1-Oct-10 2.5 2 8 2 8 100 100 0.9 2 4 2 4 2 5 2 5 8 7 1 7 1 7 6.9 6.9 3 1 3 1 0.1 0.1

1-Nov-10 8.8 1 2 1 2 6 6 6 6 6.9 2 4 2 4 1 5 1 5 4 5 1 0 1 0 7.1 7.1 513 513 0.1 0.1

1-Dec-10 45.5 2 2 3 5 126 167 41.7 2 1 3 2 4 6 5 2 1 9 7 5 0 7.3 7.1 254 503 0.2 0.4

1-Jan-11 11.3 3 6 4 2 6 5 8 2 7.9 2 2 2 2 5 7 8 2 3 7 2 2 235 7.4 7.1 158 213 0.3 0.3

1-Mar-11 9.0 1 1 1 1 6 2 6 2 6.4 1 2 1 2 3 7 3 7 5 2 1 1 7.2 7.2 227 227 0.3 0.3

1-May-11 2.1 7 0 7 0 9 7 9 7 0.0 n d n d n d n d 8 6 n d n d n d n d n d n d n d n d

1-Nov-11 21.3 5 1 7 2 125 166 16.7 2 7 2 9 2 5 2 8 6 1 18,150 18,150 7.3 7.3 3 8 3 8 0.1 0.1

1-Jan-12 16.1 4 5 5 1 3 2 3 6 12.7 2 2 2 8 2 4 2 6 3 1 2157 2157 7.4 7.4 2 8 2 8 0.1 0.1

1-Oct-12 9.3 2 7 2 7 5 4 5 4 6.7 1 4 1 8 1 3 2 0 6 5 5 6 5 6 6.2 6.2 3 4 3 4 0.2 0.2

1-Nov-12 50.7 >28 5 7 9 1 188 41.6 1 7 2 9 3 0 6 0 6 0 3 5 7 7 6.3 6.3 6 6 8 7 0.2 0.6

1-Dec-12 32.3 3 7 6 1 101 214 20.4 3 5 5 1 4 0 8 2 5 9 9 9 800 6.7 6.0 1 7 4 9 0.2 0.4

1-Jan-13 12.9 9 3 9 3 6 0 6 0 5.7 4 0 4 0 4 4 4 4 5 1 4 5 4 5 7.4 6.0 0 0 0.2 0.2

1-Sep-13 12.2 2 8 4 2 108 142 7.4 2 5 3 6 6 5 6 8 5 6 173 30,000 6.8 5.8 3 0 4 0 0.6 0.7

AVE: 13.7 3 6 4 3 8 9 111 9.8 2 3 2 7 3 4 4 3 6 5 2,549 4,476 7.1 6.9 207 269 0.2 0.3

MIN: 0.2 1 1 1 1 3 2 3 6 0.0 1 2 1 2 1 3 1 5 1 9 1 1 6.2 5.8 0 0 0.1 0.1

MAX: 50.7 9 3 9 3 213 214 41.7 4 0 5 1 6 5 8 2 9 7 20,000 30,000 8.4 8.4 1092 1708 0.6 0.7

5th %tile:

95th %tile: 3 6 4 3

85%

Limits thru 

June 09 1,700 - - 290 1.9

Limits 7/09-

present 400 9.0 6.0 234 1.9

nd - No Discharge

Exceeds Permit Limit

Influent Effluent

Alki CSO Treatment Plant DMR Data

Year Number of 

Inflow Events

Inflow Volume, 

Annual Total, 

MG

Number of 

Discharge 

Events

Discharge 

Volume, Annual 

Total, MG

Settleable 

Solids, Annual 

Average, mL/L

TSS, Annual 

Average % 

Removal

2009 1 0 4 9 4 3 7 0.3 6 2

2010 6 7 5 5 5 9 0.3 68*

2011 4 4 4 3 3 1 0.3 5 5

2012 7 108 7 8 1 0.2 5 7

Total 2 7 276 1 9 209

Average 5 5 2

Limits - - 2 9 108 0.3 > 50%

Volume Diverted, MG 6 7

Annual Reporting for the Alki CSO Treatment Facility

* Omits 1 event from calculation
Fact Sheet for NPDES Permit WA0029181 Page 113 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Alki CSO Treatment Plant - Influent vs. Effluent 

0

80604020

200180160140120100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct Flow Volume, total MG

Influent VolumeEffluent Volume

0

50

250200150100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct BOD5, mg/L

InfluentEffluent

0

50

250200150100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct TSS, mg/L

InfluentEffluent
Fact Sheet for NPDES Permit WA0029181 Page 114 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Alki CSO Treatment Plant - Effluent Data

9.59.08.58.07.5

7.06.56.05.55.0

10.0 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan pH, standard units

monthly minimummonthly maximumLimit-minLimit-max

1

10

100

1,000

10,000

100,000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Fecal Coliform, #/100 mL

GEMGEM limit

0

800600400200

1,2001,000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Residual Chlorine, μg/L

Monthly AverageMonthly Ave Limit

2.01.81.61.41.21.00.80.6

0.40.20.0 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Settleable Solids, mL/L

Max EventMax Event Limit
Fact Sheet for NPDES Permit WA0029181 Page 115 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Carkeek CSO Treatment Plant – Plant Data

Carkeek 

CSO Volume, MG BOD, mg/L BOD, mg/L TSS, mg/L TSS, mg/L Volume, MG BOD, mg/L BOD, mg/L TSS, mg/L TSS, mg/L TSS, % Removal Fecal Coliform, #/100 ml Fecal Coliform, #/100 ml p Hp HRes. Chlorine, 

μg/L Res. Chlorine, μg/L Settleable Solies, mL/L Settleable Solies, mL/L

Total Ave Max Ave Max Total

Mnth 

Ave Max

Mnth 

Ave Max Ave GEM Max max min

Mnth 

Ave

Max 

Day

Mnth 

Ave

Max 

Event

1-Sep-09 0.4 9 7 132 215 297 0.1 132 132 132 132 8 4 n d n d n d n d n d n d n d n d

1-Oct-09 0.6 7 5 8 7 154 195 0.0 n d n d n d n d 9 4 n d n d n d n d n d n d n d n d

1-Nov-09 8.6 5 2 8 6 7 5 201 5.7 3 8 6 1 3 6 124 6 5 2 7 17,000 7.9 6.9 344 448 0 0.5

1-Jan-10 2.6 9 7 128 130 184 4.8 3 1 3 2 2 2 2 4 7 0 755 13,000 7.1 6.9 2 6 5 3 0 0.1

1-Mar-10 0.0 9 9 9 9 117 117 0.0 n d n d n d n d 9 6 n d n d n d n d n d n d n d n d

1-May-10 0.1 148 148 251 251 0.0 n d n d n d n d 9 6 n d n d n d n d n d n d n d n d

1-Sep-10 0.0 392 392 603 603 0.0 n d n d n d n d 9 1 n d n d n d n d n d n d n d n d

1-Nov-10 1.0 658 658 1,016 1,016 0.0 n d n d n d n d 5 5 n d n d n d n d n d n d n d n d

1-Dec-10 18.3 5 2 116 108 368 16.1 2 0 3 7 4 6 156 1 3 752 80,000 7.5 6.6 374 1370 0 1.4

1-Jan-11 1.9 7 6 100 6 8 111 1.3 4 0 4 8 5 6 8 1 2 4 1 1 6.9 6.9 1 8 2 2 0 0.1

1-Feb-11 0.1 4 3 4 3 141 141 0.0 n d n d n d n d 8 6 n d n d n d n d n d n d n d n d

1-Mar-11 16.3 3 9 6 2 5 9 121 15.1 1 8 3 7 3 0 4 8 3 7 8 5,000 7.7 6.0 233 475 0 0.5

1-Jul-11 0.1 264 264 620 620 0.0 n d n d n d n d 9 7 n d n d n d n d n d n d n d n d

1-Nov-11 2.6 7 6 103 9 2 114 2.0 2 3 2 7 1 9 2 4 6 6 1 1 6.7 6.7 102 130 0 0.1

1-Jan-12 0.2 8 1 121 101 141 0.0 n d n d n d n d 9 0 n d n d n d n d n d n d n d n d

1-Mar-12 0.5 113 172 325 551 0.0 n d n d n d n d 4 3 n d n d n d n d n d n d n d n d

1-Jul-12 0.1 9 9 104 150 152 0.0 n d n d n d n d 9 3 n d n d n d n d n d n d n d n d

1-Oct-12 1.0 9 8 124 148 180 0.2 1 1 1 1 2 2 2 2 8 1 1 1 7.1 6.3 9 4 9 4 0.1 0.1

1-Nov-12 18.5 511 2 0 8 2 180 17.4 1 7 3 3 2 1 5 1 4 4 1 1 6.9 6.3 178 723 0 0

1-Dec-12 11.0 5 7 9 0 7 1 9 9 9.2 2 4 4 1 1 8 2 7 5 9 2 0 2 0 7.9 5.1 159 474 0 0

1-Jan-13 1.0 9 4 9 4 109 109 0.7 4 7 4 7 3 0 3 0 6 4 5 5 5 5 7.7 6.2 8 8 0 0

1-Apr-13 0.2 3 9 4 4 9 5 133 0.0 n d n d n d n d 9 7 n d n d n d n d n d n d n d n d

1-Sep-13 1.4 124 220 225 447 0.9 4 9 4 9 123 123 4 9 0 1 7.9 7.7 7 0 7 0 0.5 0.5

AVE: 3.8 147 148 215 275 3.2 3 8 4 6 4 6 7 0 6 9 147 10,462 7.4 6.5 146 352 0 0

MIN: 0.0 3 9 2 0 5 9 9 9 0.0 1 1 1 1 1 8 2 2 1 3 0 1 6.7 5.1 8 8 0 0

MAX: 18.5 658 658 1,016 1,016 17.4 132 132 132 156 9 7 755 80,000 7.9 7.7 374 1370 1 1.4

5th %tile:

95th %tile:

85%

Limits thru 

June 09 2,800 - - 490 1.9

Limits 7/09-

present 400 9.0 6.0 490 1.9

nd - No Discharge

Exceeds Permit Limit

Influent Effluent

Carkeek CSO Treatment Plant DMR Data

Year Number of 

Inflow Events

Inflow Volume, 

Annual Total, 

MG

Number of 

Discharge 

Events

Discharge 

Volume, Annual 

Total, MG

Settleable 

Solids, Annual 

Average, mL/L

TSS, Annual 

Average % 

Removal

2009 1 4 1 4 9 8.1 0.2 75.8

2010 1 1 2 5 4 2 1 0.2 67.8*

2011 8 2 1 4 1 8 0.1 65.7*

2012 1 7 3 1 6 2 7 0.1 50.1*

Total 5 0 9 1 2 3 7 4

Average 6 1 9

Limits - 1 0 4 6 0.3 > 50%

Volume Diverted, MG 1 7

Annual Reporting for the Carkeek CSO Treatment Facility

* Omits 1 event from calculation
Fact Sheet for NPDES Permit WA0029181 Page 116 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Carkeek CSO Treatment Plant - Influent vs. Effluent

50

25201510 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct Flow Volume, total MG

Influent VolumeEffluent Volume

0

800600400200

12001000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct BOD5, mg/L

InfluentEffluent

0

800600400200

12001000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct TSS, mg/L

InfluentEffluent
Fact Sheet for NPDES Permit WA0029181 Page 117 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Carkeek CSO Treatment Plant - Effluent Data

9.59.08.58.07.57.06.56.05.55.0

10.0 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan pH, standard units

monthly minimummonthly maximumLimit-minLimit-max

1

10

100

1,000

10,000

100,000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Fecal Coliform, #/100 mL

GEMGEM limitMax

0

600500400300200100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Residual Chlorine, μg/L Monthly Average

Monthly Ave Limit

2.01.81.61.41.21.00.80.60.40.20.0 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Settleable Solids, mL/L

Max EventMax Event Limit
Fact Sheet for NPDES Permit WA0029181 Page 118 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Elliott West CSO Treatment Plant – Plant Data

Elliott West 

CSO TP Volume, MG BOD, mg/L BOD, mg/L TSS, mg/L TSS, mg/L Volume, MG BOD, mg/L BOD, mg/L TSS, mg/L TSS, mg/L TSS, % Removal Fecal Coliform, #/100 ml Fecal Coliform, #/100 ml p Hp HRes. Chlorine, 

μg/L Res. Chlorine, μg/L Settleable Solies, mL/L Settleable Solies, mL/L

Total Ave Max Ave Max Day Total

Mnth 

Ave Max

Mnth 

Ave Max Ave GEM Max max min

Mnth 

Ave

Max 

Day

Mnth 

Ave

Max 

Event

1-Oct-09 90.5 1 6 159 1 5 171 29.1 9 9 187 6 9 171 3 7 5,889 412,510 6.7 6.4 6 1 6 9 4.0 6.0

1-Nov-09 141 3 0 135 5 2 397 87.5 3 8 5 9 6 7 151 2 8 5 1 150,250 e e e e 5.0 10.0

1-Dec-09 14.6 1 8 170 2 2 201 14.6 7 1 170 8 4 201 9 3 n d n d n d n d n d n d n d n d

1-Jan-10 103 3 4 365 4 9 494 58.9 5 2 9 9 7 3 131 3 7 220 2,875 7.5 6.9 2 1 5 3 4.0 9.0

1-Feb-10 12.3 4 4 327 6 4 488 0.0 n d n d n d n d n d n d n d n d n d n d n d n d n d

1-Mar-10 27.1 112 294 288 890 21.4 110 294 286 890 7 3 339 115,085 6.6 6.6 2 8 2 8 0.6 0.9

1-Apr-10 25.1 5 4 710 154 2,035 16.4 122 710 342 2035 7 1 0 0 6.7 6.7 1 8 1 8 2.0 2.0

1-May-10 9.1 2 3 126 6 3 467 0.0 n d n d n d n d 9 7 n d n d n d n d n d n d n d n d

1-Jun-10 4.5 8 7 273 170 660 0.0 n d n d n d n d 9 6 n d n d n d n d n d n d n d n d

1-Aug-10 1.8 107 107 6 6 6 6 0.0 n d n d n d n d 9 5 n d n d n d n d n d n d n d n d

1-Sep-10 57.3 5 2 122 189 675 38.3 3 7 8 0 9 0 159 1 5 5,099 400,000 7.2 6.9 1 2 1.4 2.0

1-Oct-10 51.8 151 845 394 2,250 27.9 3 4 3 7 6 0 9 6 4 7 316 2,500 6.9 6.6 3 8 0.8 1.5

1-Nov-10 54.5 9 2 244 186 778 26.2 5 7 5 7 8 1 9 6 5 4 2,439 7,000 6.9 6.6 8 1 6 1.4 2.5

1-Dec-10 200 7 7 636 143 1,945 32.7 191 654 342 1945 6 0 4 1 5,000 7.0 6.6 2 5 158 0.2 0.5

1-Jan-11 57.5 4 8 8 6 7 0 242 24.7 5 8 185 9 8 496 6 1 0 0 6.9 6.7 0 0 0.1 0.1

1-Feb-11 42.4 139 403 143 453 38.3 141 403 151 453 9 2 4 5 4 5 6.7 6.7 2 2 0.1 0.1

1-Mar-11 71.7 134 627 706 4,320 41.4 139 627 708 4320 8 0 553 1,300 6.5 6.5 3 8 0.2 0.5

1-Apr-11 17.5 119 267 126 372 14.4 120 267 129 372 8 0 2 0 2 0 5.5 5.5 2 2 0.1 4.5

1-May-11 29.8 6 0 175 7 7 161 15.3 6 4 175 8 8 271 6 7 400,000 400,000 6.4 6.2 1 2 1.2 1.7

1-Jul-11 0.6 6 2 112 171 322 0.0 n d n d n d n d 9 7 n d n d n d n d n d n d n d n d

1-Sep-11 1.8 107 107 6 6 6 6 0.0 n d n d n d n d n d n d n d n d n d n d n d n d

1-Oct-11 3.1 5 8 132 246 726 0.0 n d n d n d n d 9 5 n d n d n d n d n d n d n d n d

1-Nov-11 110 7 7 214 164 435 83.7 2 0 2 2 9 4 124 2 8 1 1 0 6.8 6.7 9 4 9 4 0.8 0.9

1-Dec-11 18.4 6 6 7 4 7 2 104 1.7 7 4 7 4 104 104 7 8 17,000 17,000 7.9 7.9 259 259 0.1 0.1

1-Jan-12 68.9 5 1 104 152 760 30.3 4 7 7 3 4 4 5 6 6 4 2 30,000 6.7 6.6 7 7 231 0.4 0.9

1-Feb-12 9.7 165 492 353 1,006 0.0 n d n d n d n d 9 2 n d n d n d n d n d n d n d n d

1-Mar-12 63.9 391 4,418 313 3,058 18.0 3 1 3 2 100 110 5 6 1 1,100 6.8 6.5 3 3 7 6 1.2 1.4

1-Apr-12 1.6 134 219 189 348 0.0 n d n d n d n d 9 7 n d n d n d n d n d n d n d n d

1-May-12 15.9 5 8 9 0 108 262 0.0 n d n d n d n d 9 6 n d n d n d n d n d n d n d n d

1-Jun-12 11.9 6 6 114 9 5 169 0.0 n d n d n d n d 9 1 n d n d n d n d n d n d n d n d

1-Jul-12 20.5 102 132 295 535 7.8 110 110 315 315 5 5 1 4 0 6.5 6.5 5 9 5 9 5.5 5.5

1-Oct-12 54.7 3 4 6 6 7 1 187 27.0 3 0 4 2 3 1 4 3 6 2 1 1 6.1 5.7 6 9 103 0.1 0.2

1-Nov-12 135 6 4 478 172 1,195 97.4 2 2 3 6 8 6 203 3 1 6 4 335 6.3 5.7 4 0 102 0.2 0.3

1-Dec-12 66.6 4 0 202 6 2 206 18.4 3 2 4 3 5 9 121 5 7 4 0 5 0 7.6 5.8 165 407 1.3 3.7

1-Jan-13 30.6 3 9 128 5 5 104 18.4 3 9 4 2 3 5 3 8 3 1 4 0 4 0 6.4 5.9 0 0 1.4 1.4

1-Mar-13 20.5 4 6 113 102 274 10.1 3 0 3 0 5 4 5 4 5 2 2 0 4 0 8.0 6.0 280 435 1.4 2.0

1-Apr-13 21.9 2 6 8 1 6 5 282 5.2 8 8 1 0 1 0 9 2 7 0 7 0 8.0 5.9 5 0 5 0 0.1 0.1

1-May-13 3.2 3 7 6 2 229 574 0.0 n d n d n d n d 9 6 n d n d n d n d n d n d n d n d

1-Jun-13 10.0 9 8 107 8 6 133 0.0 n d n d n d n d 9 3 n d n d n d n d n d n d n d n d

1-Sep-13 58.4 3 0 6 3 8 8 189 37.4 3 6 4 3 9 0 108 4 1 2 6 700 8.5 6.1 607 860 1.2 2.5

1-Oct-13 2.1 4 4 2 5 2 5 0.0 n d n d n d n d 9 6 n d n d n d n d n d n d n d n d

AVE: 42.5 7 7 331 150 684 20.5 6 7 169 137 484 6 9 16,626 59,460 6.9 6.4 7 6 122 1.3 2.3

MIN: 0.6 4 4 1 5 2 5 0.0 8 8 1 0 1 0 1 5 0 0 5.5 5.5 0 0 0.1 0.1

MAX: 200 391 4,418 706 4,320 97.4 191 710 708 4320 9 7 400,000 412,510 8.5 7.9 607 860 5.5 10.0

5th %tile:

95th %tile: 140 646 429

85%

Limits thru 

June 09 400 - - 4 4 1.9

Limits 7/09-

5/11 400 9.0 6.0 104 1.9

Limits 6/11-

present 154 9.0 6.0 104 1.9

nd - No Discharge

Exceeds Permit Limit

Influent Effluent

Elliott West CSO Treatment Plant DMR Data
Fact Sheet for NPDES Permit WA0029181 Page 119 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Elliott West CSO Treatment Plant - Influent vs. Effluent

0

80604020

200180160140120100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct Flow Volume, total MG

Influent VolumeEffluent Volume

0

800700600500400300200100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct BOD5, mg/L

Influent Effluent

0

800700600500400300200100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct TSS, mg/L

Influent Effluent
Fact Sheet for NPDES Permit WA0029181 Page 120 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Elliott West CSO Treatment Plant - Effluent Data

9.59.08.58.07.5

7.06.56.05.55.0

10.0 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan pH, standard units

monthly minimummonthly maximumLimit-minLimit-max

1

10

100

1,000

10,000

100,000

1,000,000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Fecal Coliform, #/100 mL

GEMGEM limit

0

900800700600500400300200100

1,000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Residual Chlorine, μg/L

Max DayMax Daily Average Limit
Fact Sheet for NPDES Permit WA0029181 Page 121 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Year Number of 

Inflow Events

Inflow Volume, 

Annual Total, 

MG

Number of 

Discharge 

Events

Discharge 

Volume, Annual 

Total, MG

Settleable 

Solids, Annual 

Average, mL/L

TSS, Annual 

Average % 

Removal

2009 2 4 371 1 0 196 2.3 41.6*

2010 4 7 547 1 5 333 1.5 53.3

2011 4 1 357 8 170 0.8 62.4

2012 4 6 512 1 2 199 1.15 64.5*

Total 158 1787 4 5 898

Limits - - - - 0.3 > 50%

Exceeds Permit Limit

Volume Diverted, MG 889

Annual Reporting for the Elliott West CSO Treatment Facility

* Omits 1 event from calculation
Fact Sheet for NPDES Permit WA0029181 Page 122 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Henderson / MLK CSO Treatment Plant – Plant Data

Henders

on CSO Volume, MG BOD, mg/L BOD, mg/L TSS, mg/L TSS, mg/L Volume, MG BOD, mg/L BOD, mg/L TSS, mg/L TSS, mg/L TSS, % Removal Fecal Coliform, #/100 ml Fecal Coliform, #/100 ml pHpHRes. Chlorine, 

μg/L Res. Chlorine, μg/L Settleable Solies, mL/L Settleable Solies, mL/L

Total Ave Max Ave Max Total

Mnth 

Ave Max

Mnth 

Ave Max Ave GEM Max max min

Mnth 

Ave

Max 

Day

Mnth 

Ave

Max 

Event

1-Jan-09 5.3 3 2 3 2 3 8 3 8 1.6 5 5 4 5 4 5 6 1 1 6 4 4 6.8 6.7 3 5 3 5 0.1 0.1

1-Jan-10 0.3 3 0 3 0 3 7 3 7 0.0 n d n d n d n d 9 5 n d n d n d n d n d n d n d n d

1-Oct-10 5.9 2 4 2 4 4 0 4 0 2.1 1 6 1 6 4 0 4 0 9 0 302,667 302,667 6.7 6.7 2 0 2 0 0.1 0.1

1-Nov-10 1.4 4 5 4 5 104 104 0.0 n d n d n d n d 5 5 n d n d n d n d n d n d n d n d

1-Dec-10 20.8 1 7 2 1 7 0 8 4 16.6 8 8 3 1 3 9 4 1 1 1 7.0 7.0 1 3 1 3 0.1 0.1

1-Mar-11 1.8 2 0 2 0 7 8 7 8 0.0 n d n d n d n d 9 1 n d n d n d n d n d n d n d n d

1-Jan-12 0.5 3 2 3 2 3 0 3 0 0.0 n d n d n d n d 7 5 n d n d n d n d n d n d n d n d

1-Mar-12 1.6 2 4 2 4 8 4 8 4 0.0 n d n d n d n d 8 9 n d n d n d n d n d n d n d n d

1-Nov-12 12.0 3 2 8 3 6 7 3 5.2 1 6 1 6 3 7 3 7 5 9 2 2 6.8 6.8 218 218 0.1 0.1

1-Jan-13 2.6 2 1 2 1 5 1 5 1 0.0 n d n d n d n d 7 9 n d n d n d n d n d n d n d n d

1-Sep-13 0.1 9 9 3 6 3 6 0.0 n d n d n d n d 9 5 n d n d n d n d n d n d n d n d

AVE: 4.7 2 3 2 6 5 5 6 0 2.3 1 1 1 1 3 8 4 0 7 5 75,672 75,679 6.8 6.8 7 2 7 2 0.1 0.1

MIN: 0.1 3 9 3 0 3 0 0.0 5 5 3 1 3 7 4 1 1 1 6.7 6.7 1 3 1 3 0.1 0.1

MAX: 20.8 4 5 4 5 104 104 16.6 1 6 1 6 4 5 4 5 9 5 302,667 302,667 7.0 7.0 218 218 0.1 0.1

5th %tile:

95th %tile:

85%

Limits thru 

June 09 400 - - 3 9 1.9

Limits 7/09-

present 400 9.0 6.0 3 9 1.9

nd - No Discharge

Exceeds Permit Limit

Influent Effluent

Henderson CSO Treatment Plant DMR Data

Year Number of 

Inflow Events

Inflow Volume, 

Annual Total, 

MG

Number of 

Discharge 

Events

Discharge 

Volume, Annual 

Total, MG

Settleable 

Solids, Annual 

Average, mL/L

TSS, Annual 

Average % 

Removal

2009 2 5.4 1 1.6 0.1 6 1

2010 4 2 8 2 1 9 0.1 59*

2011 1 1.8 0 0 - 9 1

2012 5 1 4 1 5.2 0.1 6 4

Total 1 2 5 0 4 2 6

Limits - - - - 0.3 > 50%

Volume Diverted, MG 2 4

* Omits 1 event from calculation

Annual Reporting for the Henderson / MLK CSO Treatment Facility
Fact Sheet for NPDES Permit WA0029181 Page 123 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Henderson/MLK CSO Treatment Plant - Influent vs. Effluent

50

25201510 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct Flow Volume, total MG

Influent VolumeEffluent Volume

0

80604020

120100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct BOD5, mg/L

InfluentEffluent

0

80604020

120100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct TSS, mg/L

InfluentEffluent
Fact Sheet for NPDES Permit WA0029181 Page 124 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Henderson/MLK CSO Treatment Plant - Effluent Data

9.59.08.58.07.57.06.56.05.55.0

10.0 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan pH, standard units

monthly minimummonthly maximumLimit-minLimit-max

1

10

100

1,000

10,000

100,000

1,000,000 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Fecal Coliform, #/100 mL

GEMGEM limit

0

50

250200150100 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Effluent Residual Chlorine, μg/L

Monthly AverageMonthly Ave Limit

2.01.81.61.41.21.00.80.60.40.20.0 09 - Apr 09 - Jul 09 - Oct 10 - Jan 10 - Apr 10 - Jul 10 - Oct 11 - Jan 11 - Apr 11 - Jul 11 - Oct 12 - Jan 12 - Apr 12 - Jul 12 - Oct 13 - Jan 13 - Apr 13 - Jul 13 - Oct 14 - Jan Settleable Solids, mL/L

Max EventMax Event Limit
Fact Sheet for NPDES Permit WA0029181 Page 125 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Untreated CSO Discharges - Data

1983Baseline 2006 2007 2008 2009 2010 2011 2012

CSO Outfall Name006 - Magnolia Overflow 25 18 22 26 25 38 22 36030 - Lander St Regulator 26 18 8 6 19 17 15 25032 - Hanford #2 Regulator 28 16 12 8 17 18 15 23004 - East Ballard (AKA 11th Ave NW) 16 14 10 7 16 19 16 20048a - North Beach Pump Station (wet well) 18 9 4 4 14 10 15 20048b - North Beach Pump Station (inlet structure) 11 6 3 13 6 8 13031a - Hanford #1 (Hanford @ Rainier) 30 13 13 18031b - Hanford #1 (Bayview S.) 1031c - Hanford #1 (Bayview N.) 5 2 7031 - Hanford #1 Overflow 16 3 6 14014 - Montlake Overflow 6 1 3 9 8 18039 - Michigan Regulator (AKA S. Michigan Regulator) 34 9 6 3 10 12 14 16003 - Ballard Siphon Regulator via Seattle Storm Drain 13 3 2 1 8 6 7 13009 - Dexter Ave Regulator 15 12 9 3 11 13 8 13008 - 3rd Ave W and Ewing St 17 6 6 3 9 8 7 13036 - Chelan Ave. Regulator 7 2 2 3 4 13015 - University Regulator 13 7 5 3 9 8 6 13028 - King Street Regulator 16 17 7 3 15 18 15 13041 - Brandon Street Regulator 36 3 16 11 7 12029 - Connecticut St. Regulator (AKA Kingdome) 29 4 5 1 8 6 2 11056 - Murray Street Pump Station 5 7 4 3 11 9 3 5042 - West Michigan (AKA SW Michigan St regulator) 5 6 4 8 11 3 5057 - Barton Street Pump Station 9 5 3 2 2 4 1 4054 - 63rd Avenue SW Pump Station 2 1 1 3037 - Harbor Avenue Regulator 30 3 2 1 1 3012 - Belvoir Pump Station Emergency Overflow 1 1 1 2 1052 - 53rd Avenue SW Pump Station 1 2 1 1 1055 - SW Alaska Street Overflow 1 1 1 1 1 1038 - Terminal 115 Overflow 4 5 4 3 3 1007 - Canal Street Overflow 1 1 1 1 1027a - Denny Way Regulator 32 7 1 2 4 2 2 1035 - W. Duwamish Pump Station 1 1 1040 - 8th Ave South Regulator (AKA W. Marginal Way Pump Station) 6 1018 - Matthews Park Pump Station Emergency Overflows 1 1034 - E. Duwamish Pump Station 1 1 1Total Number of Untreated Events 429 199 131 89 236 259 196 324Annual Precipitation, inches 42.8 31.1 24.9 31.46 40.30 32.20 42.57

Number of CSO Events per CSO Outfall - King County
Fact Sheet for NPDES Permit WA0029181 Page 126 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

2006 2007 2008 2009 2010 2011 2012

CSO Outfall Name030 - Lander St Regulator 128,641,103 120,537,575 33,623,696 355,927,868 502,565,171 223,304,825 524,435,439032 - Hanford #2 Regulator 111,251,187 65,598,493 23,939,993 36,341,949 138,189,415 215,148,888 333,413,251015 - University Regulator 56,040,237 198,223,235 6,545,240 61,898,794 135,381,902 48,815,940 105,058,388031a - Hanford #1 (Hanford @ Rainier) 76,674,809 25,588,985 89,941,019039 - Michigan Regulator (AKA S. Michigan Regulator) 6,660,296 98,799,925 105,226 12,434,895 126,186,674 32,703,434 75,982,142014 - Montlake Overflow 407,251 8,716,113 65,427,370 22,015,836 51,843,559041 - Brandon Street Regulator 1,898,700 24,149,925 38,715,418 9,821,972 47,750,378029 - Connecticut St. Regulator (AKA Kingdome) 17,595,651 28,557,622 229,293 3,544,686 9,991,516 418,810 47,429,418

004 - East Ballard (AKA 11th Ave NW) 10,265,362 23,489,433 903,054 8,914,906 13,179,721 8,548,291 18,486,212037 - Harbor Avenue Regulator 8,814,345 28,053,235 21,288,198 5,961,131 16,678,543036 - Chelan Ave. Regulator 67,675 4,505,684 13,211,184 7,330,397 12,016,886048a - North Beach Pump Station (wet well) 679,242 7,327,646 6,531 283,130 163,806 22,589,128 11,208,348054 - 63rd Avenue SW Pump Station 4,627,555 1,554,706 11,018,376006 - Magnolia Overflow 56,893,112 56,564,669 17,435,792 6,061,884 12,250,169 8,840,437 9,755,097

009 - Dexter Ave Regulator 8,252,560 28,999,995 3,598,264 8,124,651 15,109,389 967,316 9,146,016056 - Murray Street Pump Station 11,077,241 107,410,187 10,311,939 50,497,793 54,917,734 5,761,039 8,613,011028 - King Street Regulator 28,095,389 25,375,911 815,653 56,238,166 32,775,036 16,053,502 7,865,932031c - Hanford #1 (Bayview N.) 6,624,140 310,862 4,586,194008 - 3rd Ave W and Ewing St 913,746 42,074,066 1,743,583 10,578,307 25,025,932 5,795,081 4,381,473048b - North Beach Pump Station (inlet structure) 208,237 576,388 112,078 682,846 3,902,200 2,887,006 4,338,033042 - West Michigan (AKA SW Michigan St regulator) 1,809,606 3,186,749 474,681 2,664,881 684,735 3,390,864057 - Barton Street Pump Station 24,188,105 12,620,362 779,492 157,392 965,905 129,652 1,985,628038 - Terminal 115 Overflow 3,927,165 5,364,475 1,146,469 3,900,369 1,937,500003 - Ballard Siphon Regulator via Seattle Storm Drain 465,296 910,538 32,518 660,812 1,433,199 1,118,148 1,668,118012 - Belvoir Pump Station Emergency Overflow 148,476 4,089,303 4,778,145 864,797031b - Hanford #1 (Bayview S.) 667,100052 - 53rd Avenue SW Pump Station 36,804 1,274,529 99,965 558,004007 - Canal Street Overflow 1,019,018 418,355 1,123,622 18,819055 - SW Alaska Street Overflow 55,114 2,285 23,495 19,148 8,063027a - Denny Way Regulator 57,562,597 29,065,200 81,495 953,306 11,125 50,613 580034 - E. Duwamish Pump Station 10,096,325 6,067,408018 - Matthews Park Pump Station Emergency Overflows 6,600,000035 - W. Duwamish Pump Station 6,268,539 35,911

040 - 8th Ave South Regulator (AKA W. Marginal Way Pump Station) 18031 - Hanford #1 Overflow 36,100,125 5,782,035 3,254,230 42,011,528Total Annual Volume, gallons 569,748,670 915,773,422 105,923,993 690,218,456 1,323,811,418 666,419,882 1,405,047,188Annual Precipitation, inches 42.8 31.1 24.9 31.5 40.3 32.2 42.6

Annual Discharge Volume (gallons) per CSO Outfall - King County
Fact Sheet for NPDES Permit WA0029181 Page 127 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Appendix F — 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.

Simple Mixing:

Ecology uses simple mixing calculations to assess the impacts of certain conservative pollutants, such as the 

expected increase in fecal coliform bacteria at the edge of the chronic mixing zone boundary. Simple mixing 

uses a mass balance approach to proportionally distribute a pollutant load from a discharge into the authorized 

mixing zone. The approach assumes no decay or generation of the pollutant of concern within the mixing zone. 

The predicted concentration at the edge of a mixing zone (MC) is based on the following calculation:

MC = [EC + (AC x DF)]/(1 + DF)

where:

EC = Effluent Concentration

AC = Ambient Concentration

DF = Dilution Factor

Reasonable Potential Analysis:

The process and formulas for determining reasonable potential and effluent limits are taken directly from the 

Technical Support Document for Water Quality-based Toxics Control, (EPA 505/2-90-001). The adjustment for 

autocorrelation is from EPA (1996a), and EPA (1996b).

Calculation of Water Quality-Based Effluent Limits:

Water quality-based effluent limits are calculated by the two-value wasteload allocation process as described on 

page 100 of the TSD (EPA, 1991) and shown below. 

1. Calculate the acute wasteload allocation WLAa by multiplying the acute criteria by the acute dilution factor 

and subtracting the background factor. Calculate the chronic wasteload allocation (WLAc) by multiplying 

the chronic criteria by the chronic dilution factor and subtracting the background factor.

WLAa = (acute criteria x DFa) – [(background conc.x (DFa - 1)]

WLAc = (chronic criteria x DFc) – [(background conc. x (DFc -1)]

where: DFa = Acute Dilution Factor

DFc = Chronic Dilution Factor

2. Calculate the long term averages (LTAa and LTAc) which will comply with the wasteload allocations WLAa

and WLAc. 

LTAa = WLAa  e

[0.52 - z] where: 2 = ln[CV2 + 1]

z = 2.326

CV = coefficient of variation = std. dev./mean

LTAc = WLAc  e

[0.52 - z] where: 2 = ln[(CV2  4) + 1]

z = 2.326
Fact Sheet for NPDES Permit WA0029181 Page 128 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

3. Use the smallest LTA of the LTAa or LTAc to calculate the maximum daily effluent limit and the monthly 

average effluent limit.

Maximum Daily Limit = MDL

MDL = LTA x e[Zσ - 0.5σ2] where: 2 = ln[CV2

+ 1]

z = 2.326 (99th percentile occurrence)

LTA = Limiting long term average

Average Monthly Limit = AML

AML = LTA x e[Zσ

n

- 0.5σ

n

2] where: n2 = ln[(CV2  n) + 1]

n = number of samples/month

z = 1.645 (95th percentile occurrence)

LTA = Limiting long term average

West Point WWTP - Calculations

Notes

Effluent BOD5 (mg/L) 4 5 Tech-based permitted max w eekly value

Effluent Dissolved Oxygen (DO) (mg/L) 2.0 Conservative estimate, small impact on results

Receiving Water Temperature (deg C) 1 4 1 DADMax value from KC's ambient study

Receiving Water DO (mg/L) 6.10 10% value from KC's ambient study

DO WQ Standards (mg/L) 7

Chronic Mixing Dilution Factor 188

Time for effluent to travel from outfall to chronic mixing boundary (days) 0.758 Small impact, so approximate-->Mixing document 

show s min current = 0.2 cm/s, therefore to 

reach chronic boundary at 430' (131 m) w ould 

take approx 0.758 days.

Oxidation rate of BOD, base e at 20 deg C, k1 (day^-1)* 0.23 *k1

 = 0.12-0.23 day-1 for effluent from biological 

treatment process (Metcalf and Eddy 

Wastewater Engineering Treatment and 

Reuse. Fourth edition , page 86. 2003.)

Effluent Ultimate BOD (mg/L) 65.85

Oxidation rate of BOD at ambient temperature, base e (day^-1) 0.17

BOD oxidized between outfall and chronic mixing zone (mg/L) 8.16

DO at chronic mixing zone 6.03

Difference between ambient DO and DO at chronic mixing boundary 0.07

Calculation of BOD5 Oxidation with Temperature Adjustment

There is no reasonable potential of not meeting the DO criteria under these conditions.

INPUT - West Point WWTP

OUTPUT

RESULTS
Fact Sheet for NPDES Permit WA0029181 Page 129 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. MIXING ZONE BOUNDARY CHARACTERISTICS

 Dilution factor at mixing zone boundary 188

 Depth at plume trapping level (m) 1.000

2. BACKGROUND RECEIVING WATER CHARACTERISTICS

 Temperature (deg C): 14.00

 pH: 8.00

 Salinity (psu): 26.10

 Total alkalinity (meq/L) 1.90

3. EFFLUENT CHARACTERISTICS

 Temperature (deg C): 21.00

 pH: 7.80

 Salinity (psu) 12.00

 Total alkalinity (meq/L): 0.55

4. CLICK THE 'Calculate" BUTTON TO UPDATE OUTPUT RESULTS -->

CONDITIONS AT THE MIXING ZONE BOUNDARY

 Temperature (deg C): 14.04

 Salinity (psu) 26.03

 Density (kg/m^3) 1019

 Alkalinity (mmol/kg-SW): 122.13

 Total Inorganic Carbon (mmol/kg-SW): 117

 pH at Mixing Zone Boundary: 8.00

Based on the CO2SYS program (Lewis and Wallace, 1998), 

http://cdiac.esd.ornl.gov/oceans/co2rprt.html

INPUT - West Point WWTP

OUTPUT

Calculation of pH of a Mixture in Marine Water

Calculate

Chronic Dilution Factor 188

Receiving Water Fecal Coliform, #/100 ml 4 Maximum value from KC's ambient study

Effluent Fecal Coliform - worst case, #/100 ml 400 Maximum permitted limit

Surface Water Criteria, #/100 ml 1 4

Fecal Coliform at Mixing Zone Boundary, #/100 ml 6 <14

Difference between mixed and ambient, #/100 ml 2

Calculation of Fecal Coliform at Chronic Mixing Zone 

INPUT - West Point WWTP

OUTPUT
Fact Sheet for NPDES Permit WA0029181 Page 130 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. Receiving Water Temperature, deg C (1 DADmax): 14.0

2. Receiving Water pH, (max): 8.0

3. Receiving Water Salinity, g/kg (min): 26.1

4. Pressure, atm (EPA criteria assumes 1 atm): 1.0

5. Unionized ammonia criteria (mg un-ionized NH3 per liter) 

from EPA 440/5-88-004:

 Acute: 0.233

 Chronic: 0.035

Using mixed temp and pH at mixing zone boundaries? N o

1. Molal Ionic Strength (not valid if >0.85): 0.534

2. pKa8 at 25 deg C (Whitfield model "B"): 9.307

3. Percent of Total Ammonia Present as Unionized: 2.1%

4. Total Ammonia Criteria (mg/L as N H3):

 Acute: 10.85

 Chronic: 1.63

Total Ammonia Criteria (mg/L as N)

 Acute: 8.92

 Chronic: 1.34

INPUT

OUTPUT

RESULTS

Calculation of seawater fraction of un-ionized ammonia from Hampson (1977). Unionized ammonia criteria for salt water are from EPA 440/5-88-004. Revised 19-Oct93.

Marine Un-ionized Ammonia Criteria Calculation
Fact Sheet for NPDES Permit WA0029181 Page 131 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 2 8 188

Water Body Type 324

Rec. Water Hardness 324 AMMONIA, Criteria as Total NH3 1,4 DICHLOROBENZENE 106467 22B 2,4 DICHLOROPHENOL 120832 2A 2,4 DIMETHYLPHENOL 105679 ANTIMONY (INORGANIC) 7440360 1M ARSENIC (dissolved) 7440382 2 MBIS(2-ETHYLHEXYL) PHTHALATE 117817 13B CADMIUM - 7440439 4M CHLOROFORM 67663 11V CHROMIUM(HEX) 18540299** COPPER - 744058 6M 

5 3 9 9 9 1 5 1 5 9 1 5 9 1 5 1 5

0.26 0.6 0.6 0.6 0.3 0.6 0.6 0.6 0.6 0.6 0.6

31,000 10.2 0.96 0.48 2.196 7.332 0.1233 5.68 1.235 16.3

0.44

8 5 1.388 0.072 0.139 0.487 0 0 0 0 0 0

Acute 8,923 - - - - 6 9 - 4 2 - 1100 4.8

Chronic 1,340 - - - - 3 6 - 9.3 - 5 0 3.1 - 2600 790 850 4300 - 5.9 - 470 - -

Acute - - - - - 1.000 - 0.980* - 0.960* 0.790*

Chronic - - - - - - - 0.980* - 0.960* 0.790* N N N N N Y Y N Y N N

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 s 0.256 0.555 0.555 0.555 0.275 0.555 0.555 0.555 0.555 0.555 0.555

Pn 0.945 0.717 0.717 0.717 0.819 0.819 0.717 0.819 0.717 0.819 0.819

1.00 1.81 1.81 1.81 1.22 1.50 1.81 1.50 1.81 1.50 1.50

Acute 1,189 0.660 0.062 0.031 0.000 1.456 0.474 0.076 0.367 0.198 1.160

Chronic 249 0.098 0.009 0.005 0.000 1.398 0.071 0.073 0.055 0.148 0.587

NO n/a n/a n/a n/a NO n/a NO n/a NO NO

Human Health Reasonable Potential s 0.256 0.5545 0.5545 0.5545 0.2747 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545

Pn 0.945 0.717 0.717 0.717 0.819 0.819 0.717 0.819 0.717 0.819 0.819

0.664 0.7276 0.7276 0.7276 0.7785 0.6033 0.7276 0.6033 0.7276 0.6033 0.6033

324 324 324 324 324 324 324 324 324 324 324

63.570 0.0229 0.0022 0.0011 0.0014 4.1E-03 1.6E-02 0.0002 0.0128 0.0023 0.0303

n/a NO NO NO NO n/a NO n/a NO n/a* n/a

Comments/Notes: *Translator derived from receiving w ater data. **Data only available for total chromium - conservative evaluation. 

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

West Point WWTP

Marine

 mg/L

Aquatic Life

Human Health Non-Carcinogenic

Human Health Carcinogenic

WQ Criteria for Protection of 

Human Health, ug/L

Multiplier

Max concentration (ug/L) at edge of...

Reasonable Potential?

Pn=(1-confidence level)1/n s2=ln(CV2+1)

Multiplier

Dilution Factor s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Effluent percentile value

Reasonable Potential Calculation

Effluent Data

# of Samples (n)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Aquatic Life Criteria, 

ug/L

Carcinogen?

Water Quality Criteria

Coeff of Variation (Cv)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Metal Criteria 

Translator, decimal

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential?
Fact Sheet for NPDES Permit WA0029181 Page 132 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 2 8 188

Water Body Type 324

Rec. Water Hardness 324 CYANIDE 57125 14M DIETHYLPHTHALATE 84662 24B LEAD - 7439921 7M MANGANESE 7439965 METHYLENE CHLORIDE 75092 22V MERCURY 7439976 8M NICKEL - 7440020 9M PHENOL 108952 10A PYRENE 129000 45B SELENIUM 7782492 10M SILVER - 7740224 11M

1 5 9 1 5 8 9 2 1 2 3 9 9 1 5 1 5

0.0001 0.6 0.6 0.6 0.6 0.63 0.48 0.6 0.6 0.373 0.6

0.57 0.85 2.475 71.1 5.3 0.0155 5.999 0.95 0.29 0.74 0.143

0.005 0.005 2.81 0.5 0 0.005 0.0002 0.432 0 0.028 0 0 0 0 0.0002 0.410 0 0 0

Acute 9.1 - 210 - - 1.8 7 4 - - 290 1.9

Chronic 2.8 - 8.1 - - 0.025 8.2 - - 7 1 -

220000 120000 - 100 1600 0.15 4600 5E+06 11000 4200 -

Acute - - 0.951 - - 0.85 1.000* - - - 0.85

Chronic - - 0.951 - - - 1.000* - - - - N N N N Y N N N N N N

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 s 0.000 0.555 0.555 0.555 0.555 0.578 0.455 0.555 0.555 0.361 0.555

Pn 0.819 0.717 0.819 0.688 0.717 0.867 0.878 0.717 0.717 0.819 0.819

1.00 1.81 1.50 1.90 1.81 1.00 1.00 1.81 1.81 1.30 1.50

Acute 0.020 0.055 0.131 4.820 0.343 0.001 0.631 0.061 0.019 0.034 0.034

Chronic 0.003 0.008 0.024 0.718 0.051 0.000 0.462 0.009 0.003 0.005 0.029

NO n/a NO n/a n/a NO NO n/a n/a NO NO

Human Health Reasonable Potential s 1E-04 0.5545 0.5545 0.5545 0.5545 0.5781 0.4553 0.5545 0.5545 0.3609 0.5545

Pn 0.819 0.717 0.819 0.688 0.717 0.867 0.878 0.717 0.717 0.819 0.819

0.9999 0.7276 0.6033 0.7624 0.7276 0.5256 0.5885 0.7276 0.7276 0.7197 0.6033

324 324 324 324 324 324 324 324 324 324 324

2E-05 0.0019 0.0046 0.167 0.012 2.1E-04 0.42 0.0021 0.0007 0.0015 0.0003

NO NO n/a NO NO NO NO NO NO NO n/a

Comments/Notes: *Translator derived from receiving w ater data.

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99 s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Multiplier

Dilution Factor

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential?

Reasonable Potential Calculation - Page 2

West Point WWTP Aquatic Life

Marine Human Health Carcinogenic

 mg/L Human Health Non-Carcinogenic

Pollutant, CAS No. & 

NPDES Application Ref. No.

Effluent Data

# of Samples (n)

Coeff of Variation (Cv)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Aquatic Life Criteria, 

ug/L

WQ Criteria for Protection of 

Human Health, ug/L

Carcinogen? s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Effluent percentile value

Multiplier

Max concentration (ug/L) at edge of...

Reasonable Potential?

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Water Quality Criteria

Metal Criteria 

Translator, decimal
Fact Sheet for NPDES Permit WA0029181 Page 133 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 2 8 188

Water Body Type 324

Rec. Water Hardness 324 THALLIUM 7440280 12M TOLUENE 108883 25V ZINC- 7440666 13M CHLORINE (Total Residual) 7782505

1 5 9 2 3 1825

0.478 0.6 0.226 0.32

1.1 50.78 296

0.040

0.995 0 0 0

Acute - - 9 0 1 3 #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic - - 8 1 7.5 #N/A #N/A #N/A #N/A #N/A #N/A #N/A

6.3 200000 - - #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Acute - - 0.946 - #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic - - 0.946 - #N/A #N/A #N/A #N/A #N/A #N/A #N/A N N N N #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 s 0.454 0.555 0.223 0.312 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Pn 0.819 0.717 0.878 0.998 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

1.39 1.81 1.00 1.00 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

Acute 0.000 0.071 2.7 10.6 #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 0.000 0.011 1.2 1.6 #N/A #N/A #N/A #N/A #N/A #N/A #N/A

n/a n/a NO NO #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Human Health Reasonable Potential s 0.4536 0.5545 0.2232 0.3122 0 0 0 0 0 0 0

Pn 0.819 0.717 0.878 0.998 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

0.6614 0.7276 0.7711 0.3993 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

324 324 324 324 #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.0001 0.0025 0.1209 0.3648 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

NO NO n/a n/a #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Comments/Notes:

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Multiplier

Reasonable Potential Calculation - Page 3

West Point WWTP Aquatic Life

Marine Human Health Carcinogenic

 mg/L Human Health Non-Carcinogenic

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Calculated 50th percentile 

Effluent Conc. (when n>10)

WQ Criteria for Protection of 

Human Health, ug/L s2=ln(CV2+1)

Pn=(1-confidence level)1/n s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Pollutant, CAS No. & 

NPDES Application Ref. No.

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential?

Dilution Factor

Effluent percentile value

Reasonable Potential?

Multiplier

Max concentration (ug/L) at edge of...

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Water Quality Criteria

Aquatic Life Criteria, 

ug/L

Metal Criteria 

Translator, decimal

Carcinogen?

Effluent Data

# of Samples (n)

Coeff of Variation (Cv)
Fact Sheet for NPDES Permit WA0029181 Page 134 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 2 8 188

Water Body Type 324

Rec. Water Hardness 324 CHLORINE (Total Residual) 7782505

Effluent Data 0.60

Acute 1 3 #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 7.5 #N/A #N/A #N/A #N/A #N/A #N/A - #N/A #N/A #N/A #N/A #N/A #N/A

Acute - #N/A #N/A #N/A #N/A #N/A #N/A

Chronic - #N/A #N/A #N/A #N/A #N/A #N/A N #N/A #N/A #N/A #N/A #N/A #N/A

Aquatic Life Limit Calculation

3 0

0.6 0 0 0 0 0 0

0.6 0 0 0 0 0 0

Acute 364 #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 1410 #N/A #N/A #N/A #N/A #N/A #N/A

Acute 117 #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 744 #N/A #N/A #N/A #N/A #N/A #N/A

117 #N/A #N/A #N/A #N/A #N/A #N/A

1.00 #N/A #N/A #N/A #N/A #N/A #N/A

139 #N/A #N/A #N/A #N/A #N/A #N/A

364 #N/A #N/A #N/A #N/A #N/A #N/A

Comments/Notes:

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Maximum Daily Limit (MDL), ug/L

Average Monthly Limit (AML), ug/L

Metal Translator or 1?

Limiting LTA, ug/L

Long Term Averages, ug/L

Waste Load Allocations, ug/L

Permit Limit Coeff. Var. (CV), decimal

LTA Coeff. Var. (CV), decimal

# of Compliance Samples Expected per month

Carcinogen?

Water Quality Criteria

Aquatic Life Criteria, 

ug/L

WQ Criteria for Protection of 

Human Health, ug/L

Metal Criteria 

Translator, decimal

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Coeff of Variation (Cv)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Chlorine Limit Calculation

 mg/L Human Health Non-Carcinogenic

Marine Human Health Carcinogenic

West Point WWTP Aquatic Life
Fact Sheet for NPDES Permit WA0029181 Page 135 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. Chronic Dilution Factor at Mixing Zone Boundary 188

2. Annual max 1DADMax Ambient Temperature 14.0 °C

3. 1DADMax Effluent Temperature (95th percentile) 21.0 °C

4. Aquatic Life Temperature WQ Criterion 13.0 °C

5. Temperature at Chronic Mixing Zone Boundary: 14.04 °C

6. Incremental Temperature Increase or decrease: 0.04 °C

7. Incremental Temperature Increase 12/(T-2) if T< crit: ---

8. Maximum Allowable Temperature at Mixing Zone Boundary: 14.3 °C

A. If ambient temp is warmer than WQ criterion

9. Does temp fall within this warmer temp range? YES

10. Temp increase allowed at mixing zone boundary, if required: NO LIMIT

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? ---

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? ---

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? ---

16. Temp increase allowed at mixing zone boundary, if required: ---

17. Do any of the above cells show a temp increase? NO

18. Temperature Limit if Required? NO LIMIT

Marine Temperature Reasonable Potential and Limit Calculation

Based on WAC 173-201A-200(1)(c)(i)--(ii) and Water Quality Program Guidance. All Data inputs must 

meet WQ guidelines. The Water Quality temperature guidance document may be found at: 

http://www.ecy.wa.gov/biblio/0610100.html

INPUT - West Pt WWTP

OUTPUT

RESULTS
Fact Sheet for NPDES Permit WA0029181 Page 136 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Alki CSO Treatment Plant - Calculations

Notes

Effluent BOD5 (mg/L) 5 1 Max month - DMR data

Effluent Dissolved Oxygen (DO) (mg/L) 5 Conservative estimate - small impact on results

Receiving Water Temperature (deg C) 12.7 KC's 2013 Receving Water Rpt -1 DADMax

Receiving Water DO (mg/L) 5.8 KC's 2013 Receving Water Rpt -10th percentile

DO WQ Standards (mg/L) 7

Chronic Mixing Dilution Factor 9 9

Time for effluent to travel from outfall to chronic mixing boundary (days) 0.008 (refer to mixing model if available)

Oxidation rate of BOD, base e at 20 deg C, k1 (day^-1)* 0.23 *k1

 = 0.12-0.23 day-1 for effluent from biological 

treatment process (Metcalf and Eddy Wastewater 

Engineering Treatment and Reuse. Fourth edition , 

page 86. 2003.)

Effluent Ultimate BOD (mg/L) 7 5

Oxidation rate of BOD at ambient temperature, base e (day^-1) 0.16

BOD oxidized between outfall and chronic mixing zone (mg/L) 0.10

DO at chronic mixing zone 5.79

Difference between ambient DO and DO at chronic mixing boundary 0.01

OUTPUT

RESULTS

There is no reasonable potential of not meeting the DO criteria under these conditions.

DO Drop at Chronic Mixing Zone 

INPUT - Alki CSO TP
Fact Sheet for NPDES Permit WA0029181 Page 137 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. MIXING ZONE BOUNDARY CHARACTERISTICS

 Dilution factor at mixing zone boundary 99

 Depth at plume trapping level (m) 1.000

2. BACKGROUND RECEIVING WATER CHARACTERISTICS

 Temperature (deg C): 12.70

 pH: 7.40

 Salinity (psu): 27.70

 Total alkalinity (meq/L) 1.98

3. EFFLUENT CHARACTERISTICS

 Temperature (deg C): 0.00

 pH: 5.80

 Salinity (psu) 12.00

 Total alkalinity (meq/L): 0.80

4. CLICK THE 'Calculate" BUTTON TO UPDATE OUTPUT RESULTS -->

CONDITIONS AT THE MIXING ZONE BOUNDARY

 Temperature (deg C): 12.57

 Salinity (psu) 27.54

 Density (kg/m^3) 1021

 Alkalinity (mmol/kg-SW): 1.93

 Total Inorganic Carbon (mmol/kg-SW): 2

 pH at Mixing Zone Boundary: 7.32

Based on the CO2SYS program (Lewis and Wallace, 1998), 

http://cdiac.esd.ornl.gov/oceans/co2rprt.html

INPUT - Alki CSO TP

OUTPUT

Calculation of pH of a Mixture in Marine Water

Calculate
Fact Sheet for NPDES Permit WA0029181 Page 138 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Chronic Dilution Factor 9 9

Receiving Water Fecal Coliform, #/100 ml 1 KC's 2013 Receving Water Rpt

Effluent Fecal Coliform - worst case, #/100 ml 400

Surface Water Criteria, #/100 ml 1 4

Fecal Coliform at Mixing Zone Boundary, #/100 ml 5 No Reasonable potential

Difference between mixed and ambient, #/100 ml 4

INPUT - Alki CSO TP

OUTPUT

Calculation of Fecal Coliform at Chronic Mixing Zone 

Conclusion: At design flow, the discharge has no reasonable potential to violate water quality standards for 

fecal coliform.

1. Receiving Water Temperature, deg C (max 1DADmax): 12.7

2. Receiving Water pH, (max): 8.0

3. Receiving Water Salinity, g/kg (min): 27.7

4. Pressure, atm (EPA criteria assumes 1 atm): 1.0

5. Unionized ammonia criteria (mg un-ionized NH3 per liter) 

from EPA 440/5-88-004:

 Acute: 0.233

 Chronic: 0.035

Using mixed temp and pH at mixing zone boundaries? N o

1. Molal Ionic Strength (not valid if >0.85): 0.568

2. pKa8 at 25 deg C (Whitfield model "B"): 9.311

3. Percent of Total Ammonia Present as Unionized: 1.9%

4. Total Ammonia Criteria (mg/L as N H3):

 Acute: 12.04

 Chronic: 1.81

Total Ammonia Criteria (mg/L as N)

 Acute: 9.90

 Chronic: 1.49

INPUT - Alki CSO TP

OUTPUT

RESULTS

Calculation of seawater fraction of un-ionized ammonia from Hampson (1977). Unionized ammonia criteria for salt water are from EPA 440/5-88-004. Revised 19-Oct93.

Marine Un-ionized Ammonia Criteria Calculation
Fact Sheet for NPDES Permit WA0029181 Page 139 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 20.0 9 9

Water Body Type 9 9

Rec. Water Hardness 9 9 AMMONIA, Criteria as Total NH3 ANTIMONY (INORGANIC) 7440360 1M ARSENIC (dissolved) 7440382 2 MBIS(2-ETHYLHEXYL) PHTHALATE 117817 13B BUTYLBENZYL PHTHALATE 85687 15B CADMIUM - 7440439 4M CHLORINE (Total Residual) 7782505 CHLOROFORM 67663 11V CHROMIUM(HEX) 18540299** COPPER - 744058 6M DIETHYLPHTHALATE 84662 24B 1 7 7 7 7 7 1 6 7 7 7 7

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

2,180 0.7 2.28 3.65 0.43 0.13 1708 1 4 2.2 12.3 3.69

8 5 1.45 0.073 0 0.15 0.354

0.172 0 0 0 0

Acute 38,840 - 6 9 - - 4 2 1 3 - 1100 4.8 -

Chronic 5,834 - 3 6 - - 9.3 7.5 - 5 0 3.1 - - 4300 - 5.9 1900 - - 470 - - 120000

Acute - - 0.980* - - 0.095* - - 0.993 0.920* -

Chronic - - 1.000 - - 0.095* - - 0.993 0.920* - N N Y Y N N N Y N N N

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 s 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555

Pn 0.050 0.652 0.652 0.652 0.652 0.652 0.829 0.652 0.652 0.652 0.652

6.20 2.01 2.01 2.01 2.01 2.01 1.47 2.01 2.01 2.01 2.01

Acute 756 0.070 1.602 0.366 0.043 0.071 125.459 1.404 0.362 1.471 0.370

Chronic 221 0.014 1.482 0.074 0.009 0.073 25.345 0.284 0.193 0.580 0.075

NO n/a NO n/a n/a NO YES n/a NO NO n/a

Human Health Reasonable Potential s 0.555 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545

Pn 0.050 0.652 0.652 0.652 0.652 0.652 0.829 0.652 0.652 0.652 0.652

2.490 0.8054 0.8054 0.8054 0.8054 0.8054 0.5901 0.8054 0.8054 0.8054 0.8054

9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9

54.820 0.176 0.0185 0.0297 0.0035 1.1E-03 1.0E+01 0.1139 0.0179 0.1001 0.03

n/a NO n/a NO NO n/a n/a NO n/a n/a* NO

Comments/Notes: *Translator derived from receiving w ater data. **Data only available for total chromium - conservative evaluation. 

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Reasonable Potential Calculation

Effluent Data

# of Samples (n)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Aquatic Life Criteria, 

ug/L

Carcinogen?

Water Quality Criteria

Coeff of Variation (Cv)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Metal Criteria 

Translator, decimal

Alki CSO TP

Marine

 mg/L

Aquatic Life

Human Health Non-Carcinogenic

Human Health Carcinogenic

Effluent percentile value

WQ Criteria for Protection of 

Human Health, ug/L

Multiplier

Max concentration (ug/L) at edge of...

Reasonable Potential?

Pn=(1-confidence level)1/n s2=ln(CV2+1)

Multiplier

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential?

Dilution Factor s2=ln(CV2+1)

Pn=(1-confidence level)1/n
Fact Sheet for NPDES Permit WA0029181 Page 140 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 20.0 9 9

Water Body Type 9 9

Rec. Water Hardness 9 9 LEAD - 7439921 7M MERCURY 7439976 8M NICKEL - 7440020 9M SILVER - 7740224 11M ZINC- 7440666 13M CYANIDE 57125 14M 7 7 7 7 7 6

0.6 0.6 0.6 0.6 0.6 0.6

4.7 0.025 3.37 0.1 42.9 18.3

0.006 0.0002 0.427 0.026 0.605 0

0.0002 0.411 0

Acute 210 1.8 7 4 1.9 9 0 9.1 #N/A #N/A #N/A #N/A #N/A

Chronic 8.1 0.025 8.2 - 8 1 2.8 #N/A #N/A #N/A #N/A #N/A - 0.15 4600 - - 220000 #N/A #N/A #N/A #N/A #N/A

Acute 0.951 0.850 0.950* 0.850* 0.946* - #N/A #N/A #N/A #N/A #N/A

Chronic 0.951 - 0.950* - 0.946* - #N/A #N/A #N/A #N/A #N/A N N N N N N #N/A #N/A #N/A #N/A #N/A

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 s 0.555 0.555 0.555 0.555 0.555 0.555 0.000 0.000 0.000 0.000 0.000

Pn 0.652 0.652 0.652 0.652 0.652 0.607 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

2.01 2.01 2.01 2.01 2.01 2.14 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

Acute 0.454 0.002 0.727 0.033 4.643 1.960 #N/A #N/A #N/A #N/A #N/A

Chronic 0.096 0.001 0.488 0.028 1.421 0.396 #N/A #N/A #N/A #N/A #N/A

NO NO NO NO NO NO #N/A #N/A #N/A #N/A #N/A

Human Health Reasonable Potential s 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0 0 0 0 0

Pn 0.652 0.652 0.652 0.652 0.652 0.607 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

0.8054 0.8054 0.8054 0.8054 0.8054 0.8603 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

9 9 9 9 9 9 9 9 9 9 9 9 #N/A #N/A #N/A #N/A #N/A

0.0382 0.0004 0.4343 0.0008 0.349 1.6E-01 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

n/a NO NO n/a n/a NO #N/A #N/A #N/A #N/A #N/A

Comments/Notes: *Translator derived from receiving w ater data.

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99 s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Multiplier

Dilution Factor

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential? Limit Required?

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Water Quality Criteria

Metal Criteria 

Translator, decimal

Multiplier

Max concentration (ug/L) at edge of...

Reasonable Potential? Limit Required?

Reasonable Potential Calculation - Page 2

Alki CSO TP Aquatic Life

Marine Human Health Carcinogenic

 mg/L Human Health Non-Carcinogenic

Pollutant, CAS No. & 

NPDES Application Ref. No.

Effluent Data

# of Samples (n)

Coeff of Variation (Cv)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Aquatic Life Criteria, 

ug/L

WQ Criteria for Protection of 

Human Health, ug/L

Carcinogen? s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Effluent percentile value
Fact Sheet for NPDES Permit WA0029181 Page 141 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 2 0 9 9

Water Body Type 9 9

Rec. Water Hardness 9 9 CHLORINE (Total Residual) 7782505 Chlorine Limit from 2009 permit

Acute Dilution Factor 2 0 1 8

Chronic Dilution Factor 9 9 6 1

Effluent Data 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0 0 0 0 0 0 0 0

Acute 1 3 1 3 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 7.5 7.5 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A - - #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Acute - - #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic - - #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A N N #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Aquatic Life Limit Calculation 4 4

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

Acute 260 234 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 743 458 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Acute 8 3 7 5 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 392 241 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

8 3 7 5 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

1.00 1.00 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

130 117 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

260 234 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Comments/Notes:

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Maximum Daily Limit (MDL), ug/L

Average Monthly Limit (AML), ug/L

Metal Translator or 1?

Limiting LTA, ug/L

Long Term Averages, ug/L

Waste Load Allocations, ug/L

Permit Limit Coeff. Var. (CV), decimal

LTA Coeff. Var. (CV), decimal

# of Compliance Samples Expected per month

Carcinogen?

Water Quality Criteria

Aquatic Life Criteria, 

ug/L

WQ Criteria for Protection of 

Human Health, ug/L

Metal Criteria 

Translator, decimal

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Coeff of Variation (Cv)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Aquatic Life and Human Health Limits Calculations

 mg/L Human Health Non-Carcinogenic

Marine Human Health Carcinogenic

Alki CSO TP Aquatic Life
Fact Sheet for NPDES Permit WA0029181 Page 142 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. Chronic Dilution Factor at Mixing Zone Boundary 9 9

2. Annual max 1DADMax Ambient Temperature (Background 90th percentile) 12.7 °C

3. 1DADMax Effluent Temperature (95th percentile) 21.0 °C

4. Aquatic Life Temperature WQ Criterion 13.0 °C

5. Temperature at Chronic Mixing Zone Boundary: 12.78 °C

6. Incremental Temperature Increase or decrease: 0.08 °C

7. Incremental Temperature Increase 12/(T-2) if T< crit: 1.12 °C

8. Maximum Allowable Temperature at Mixing Zone Boundary: 13.00 °C

A. If ambient temp is warmer than WQ criterion

9. Does temp fall within this warmer temp range? N O

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? N O

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? YES

14. Temp increase allowed at mixing zone boundary, if required: NO LIMIT

D. If ambient temp is cooler than (WQ criterion - 12/(Tamb-2))

15. Does temp fall within this Incremental temp. range? N O

16. Temp increase allowed at mixing zone boundary, if required: ---

17. Do any of the above cells show a temp increase? NO

18. Temperature Limit if Required? NO LIMIT

Marine Temperature Reasonable Potential and Limit Calculation

Based on WAC 173-201A-200(1)(c)(i)--(ii) and Water Quality Program Guidance. All Data inputs must 

meet WQ guidelines. The Water Quality temperature guidance document may be found at: 

http://www.ecy.wa.gov/biblio/0610100.html

INPUT - Alki CSO TP

OUTPUT

RESULTS
Fact Sheet for NPDES Permit WA0029181 Page 143 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Carkeek CSO Treatment Plant - Calculations

Notes

Effluent BOD5 (mg/L) 132 Max month - DMR data

Effluent Dissolved Oxygen (DO) (mg/L) 5 Conservative estimate - small impact on results

Receiving Water Temperature (deg C) 1 4 KC's 2013 Receving Water Rpt -1 DADMax

Receiving Water DO (mg/L) 6.1 KC's 2013 Receving Water Rpt -10th percentile

DO WQ Standards, Marine Extraordinary (mg/L) 7

Chronic Mixing Dilution Factor 104

Time for effluent to travel from outfall to chronic mixing boundary (days) 0.008 (refer to mixing model if available)

Oxidation rate of BOD, base e at 20 deg C, k1 (day^-1)* 0.23 *k1

 = 0.12-0.23 day-1 for effluent from biological 

treatment process (Metcalf and Eddy 

Wastewater Engineering Treatment and Reuse. 

Fourth edition , page 86. 2003.)

Effluent Ultimate BOD (mg/L) 193

Oxidation rate of BOD at ambient temperature, base e (day^-1) 0.17

BOD oxidized between outfall and chronic mixing zone (mg/L) 0.28

DO at chronic mixing zone 6.09

Difference between ambient DO and DO at chronic mixing boundary 0.01

There is no reasonable potential of not meeting the DO criteria under these conditions.

DO Drop at Chronic Mixing Zone 

INPUT - Carkeek CSO TP

OUTPUT

RESULTS
Fact Sheet for NPDES Permit WA0029181 Page 144 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. MIXING ZONE BOUNDARY CHARACTERISTICS

 Dilution factor at mixing zone boundary 104

 Depth at plume trapping level (m) 1.000

2. BACKGROUND RECEIVING WATER CHARACTERISTICS

 Temperature (deg C): 14.00

 pH: 7.50

 Salinity (psu): 26.10

 Total alkalinity (meq/L) 1.90

3. EFFLUENT CHARACTERISTICS

 Temperature (deg C): 0.00

 pH: 5.10

 Salinity (psu) 12.00

 Total alkalinity (meq/L): 0.55

4. CLICK THE 'Calculate" BUTTON TO UPDATE OUTPUT RESULTS -->

CONDITIONS AT THE MIXING ZONE BOUNDARY

 Temperature (deg C): 13.87

 Salinity (psu) 25.96

 Density (kg/m^3) 1019

 Alkalinity (mmol/kg-SW): 1.85

 Total Inorganic Carbon (mmol/kg-SW): 2

 pH at Mixing Zone Boundary: 7.22

Based on the CO2SYS program (Lewis and Wallace, 1998), 

http://cdiac.esd.ornl.gov/oceans/co2rprt.html

INPUT - Carkeek CSO TP

OUTPUT

Calculation of pH of a Mixture in Marine Water

Calculate
Fact Sheet for NPDES Permit WA0029181 Page 145 of 

175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Chronic Dilution Factor 104

Receiving Water Fecal Coliform, #/100 ml 4 KC 2013 receiving w ater study

Effluent Fecal Coliform - worst case, #/100 ml 400 Guidance-based limit

Surface Water Criteria, #/100 ml 1 4

Fecal Coliform at Mixing Zone Boundary, #/100 ml 8 < 14

Difference between mixed and ambient, #/100 ml 4

INPUT - Carkeek CSO TP

OUTPUT

Calculation of Fecal Coliform at Chronic Mixing Zone 

1. Receiving Water Temperature, deg C (max 1DADMax): 14.0

2. Receiving Water pH, (max): 8.0

3. Receiving Water Salinity, g/kg (min): 26.1

4. Pressure, atm (EPA criteria assumes 1 atm): 1.0

5. Unionized ammonia criteria (mg un-ionized NH3 per liter) 

from EPA 440/5-88-004:

 Acute: 0.233

 Chronic: 0.035

Using mixed temp and pH at mixing zone boundaries? N o

1. Molal Ionic Strength (not valid if >0.85): 0.534

2. pKa8 at 25 deg C (Whitfield model "B"): 9.307

3. Percent of Total Ammonia Present as Unionized: 2.1%

4. Total Ammonia Criteria (mg/L as N H3):

 Acute: 10.85

 Chronic: 1.63

Total Ammonia Criteria (mg/L as N)

 Acute: 8.92

 Chronic: 1.34

INPUT - Carkeek CSO TP

OUTPUT

RESULTS

Calculation of seawater fraction of un-ionized ammonia from Hampson (1977). Unionized ammonia criteria for salt water are from EPA 440/5-88-004. Revised 19-Oct93.

Marine Un-ionized Ammonia Criteria Calculation
Fact Sheet for NPDES Permit WA0029181 Page 146 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 75.0 104

Water Body Type 104

Rec. Water Hardness 104 AMMONIA, Criteria as Total NH3 ANTIMONY (INORGANIC) 7440360 1M ARSENIC (dissolved) 7440382 2 MBENZO(b)FLUORANTHENE 205992 7B BENZO(k) FLUORANTHENE 207089 9B BIS(2-ETHYLHEXYL) PHTHALATE 117817 13B BUTYLBENZYL PHTHALATE 85687 15B CADMIUM - 7440439 4M CHLORINE (Total Residual) 7782505** CHLOROFORM 67663 11V CHROMIUM(HEX) 18540299* 4 1 0 1 0 5 5 9 9 1 0 1 1 8 1 0

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

3,350 1.03 4.48 2.91 0.81 3.65 4.46 0.2 1370 64.3 5.68

8 5 1.39 0.073 0 0.148 0 0 0 0 0 0

Acute 27,804 - 6 9 - - - - 4 2 1 3 - 1100

Chronic 4,177 - 3 6 - - - - 9.3 7.5 - 5 0 - 4300 - 0.031 0.031 5.9 1900 - - 470 -

Acute - - 1.000 - - - - 0.980* - - 0.960*

Chronic - - - - - - - 0.980* - - 0.960* N N Y Y Y Y N N N Y N

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 s 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555

Pn 0.473 0.741 0.741 0.549 0.549 0.717 0.717 0.741 0.762 0.688 0.741

2.59 1.74 1.74 2.32 2.32 1.81 1.81 1.74 1.68 1.90 1.74

Acute 199 0.024 1.475 0.090 0.025 0.088 0.108 0.077 30.651 1.627 0.272

Chronic 167 0.017 1.452 0.065 0.018 0.064 0.078 0.076 22.104 1.173 0.238

NO n/a NO n/a n/a n/a n/a NO YES n/a NO

Human Health Reasonable Potential s 0.555 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545

Pn 0.473 0.741 0.741 0.549 0.549 0.717 0.717 0.741 0.762 0.688 0.741

1.038 0.6986 0.6986 0.9336 0.9336 0.7276 0.7276 0.6986 0.674 0.7624 0.6986

104 104 104 104 104 104 104 104 104 104 104

33.450 0.0069 0.0301 0.0261 0.0073 2.6E-02 3.1E-02 0.0013 8.8788 0.4714 0.0382

n/a NO n/a NO NO NO NO n/a n/a NO* n/a

Comments/Notes: *Translator derived from receiving w ater data. **Data only available for total chromium - conservative evaluation. 

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential?

Reasonable Potential Calculation

Effluent Data

# of Samples (n)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Aquatic Life Criteria, 

ug/L

Carcinogen?

Water Quality Criteria

Coeff of Variation (Cv)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Metal Criteria 

Translator, decimal

Carkeek CSO TP

Marine

 mg/L

Aquatic Life

Human Health Non-Carcinogenic

Human Health Carcinogenic

Dilution Factor s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Multiplier

Max concentration (ug/L) at edge of...

Reasonable Potential?

Pn=(1-confidence level)1/n s2=ln(CV2+1)

Effluent percentile value

Multiplier

WQ Criteria for Protection of 

Human Health, ug/L
Fact Sheet for NPDES Permit WA0029181 Page 147 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 75.0 104

Water Body Type 104

Rec. Water Hardness 104 COPPER - 744058 6M 2,4 DICHLOROPHENOL 120832 2A DIETHYLPHTHALATE 84662 24B DI-n-BUTYL PHTHALATE 84742 26B LEAD - 7439921 7M MERCURY 7439976 8M NICKEL - 7440020 9M SILVER - 7740224 11M TOLUENE 108883 25V ZINC- 7440666 13M CYANIDE 57125 14M

1 0 9 9 9 1 0 1 0 1 0 1 0 8 1 0 1 7

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

27.7 0.89 1.54 0.63 11.3 0.051 4.63 0.3 3.52 8 5 20.15

0.363 0.005 0.0002 0.424 0.027 0.643 0 0 0 0 0.0002 0.408 0 0

Acute 4.8 - - - 210 1.8 7 4 1.9 - 9 0 9.1

Chronic 3.1 - - - 8.1 0.025 8.2 - - 8 1 2.8 - 790 120000 12000 - 0.15 4600 - 200000 - 220000

Acute 0.790* - - - 0.951 0.85 1.000* 0.85 - 0.946 -

Chronic 0.790* - - - 0.951 - 1.000* - - 0.946 - N N N N N N N N N N N

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 s 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555 0.555

Pn 0.741 0.717 0.717 0.717 0.741 0.741 0.741 0.741 0.688 0.741 0.838

1.74 1.81 1.81 1.81 1.74 1.74 1.74 1.74 1.90 1.74 1.44

Acute 0.866 0.021 0.037 0.015 0.254 0.001 0.526 0.033 0.089 2.499 0.386

Chronic 0.725 0.016 0.027 0.011 0.185 0.001 0.497 0.032 0.064 1.981 0.278

NO n/a n/a n/a NO NO NO NO n/a NO NO

Human Health Reasonable Potential s 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545 0.5545

Pn 0.741 0.717 0.717 0.717 0.741 0.741 0.741 0.741 0.688 0.741 0.838

0.6986 0.7276 0.7276 0.7276 0.6986 0.6986 0.6986 0.6986 0.7624 0.6986 0.5782

104 104 104 104 104 104 104 104 104 104 104

0.1861 0.0062 0.0108 0.0044 0.0759 5.4E-04 4.4E-01 0.002 0.0258 0.571 0.0481

n/a NO NO NO n/a NO NO n/a NO n/a NO

Comments/Notes: *Translator derived from receiving w ater data.

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential?

Reasonable Potential Calculation - Page 2

Carkeek CSO TP Aquatic Life

Marine Human Health Carcinogenic

 mg/L Human Health Non-Carcinogenic

Pollutant, CAS No. & 

NPDES Application Ref. No.

Effluent Data

# of Samples (n)

Coeff of Variation (Cv)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Aquatic Life Criteria, 

ug/L

WQ Criteria for Protection of 

Human Health, ug/L

Carcinogen? s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Effluent percentile value

Reasonable Potential? s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Multiplier

Dilution Factor

Multiplier

Max concentration (ug/L) at edge of...

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Water Quality Criteria

Metal Criteria 

Translator, decimal
Fact Sheet for NPDES Permit WA0029181 Page 148 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 7 5 104

Water Body Type 104

Rec. Water Hardness 104 CHLORINE (Total Residual) 7782505 Chlorine Limit - 2004 Permit

Acute Dilution Factor 7 5 3 8

Chronic Dilution Factor 104 197

Effluent Data 0.6 0.6 0 0

Acute 1 3 1 3 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 7.5 7.5 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A - - #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Acute - - #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic - - #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A N N #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Aquatic Life Limit Calculation 4 4

0.6 0.6 0 0 0 0 0 0 0 0

0.6 0.6 0 0 0 0 0 0 0 0

Acute 975 494 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 780 1477.5 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Acute 313 159 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 411 779 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

313 159 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

1.00 1.00 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

486 246 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

975 494 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Comments/Notes:

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Maximum Daily Limit (MDL), ug/L

Average Monthly Limit (AML), ug/L

Metal Translator or 1?

Limiting LTA, ug/L

Long Term Averages, ug/L

Waste Load Allocations, ug/L

Permit Limit Coeff. Var. (CV), decimal

LTA Coeff. Var. (CV), decimal

# of Compliance Samples Expected per month

Carcinogen?

Water Quality Criteria

Aquatic Life Criteria, 

ug/L

WQ Criteria for Protection of 

Human Health, ug/L

Metal Criteria 

Translator, decimal

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Coeff of Variation (Cv)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Aquatic Life and Human Health Limits Calculations

 mg/L Human Health Non-Carcinogenic

Marine Human Health Carcinogenic

Carkeek CSO TP Aquatic Life
Fact Sheet for NPDES Permit WA0029181 Page 149 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. Chronic Dilution Factor at Mixing Zone Boundary 1 0

2. Annual max 1DADMax Ambient Temperature (Background 90th percentile) 18.7 °C

3. 1DADMax Effluent Temperature (95th percentile) 21.0 °C

4. Aquatic Life Temperature WQ Criterion 16.0 °C

5. Temperature at Chronic Mixing Zone Boundary: 18.92 °C

6. Incremental Temperature Increase or decrease: 0.22 °C

7. Incremental Temperature Increase 12/(T-2) if T< crit: ---

8. Maximum Allowable Temperature at Mixing Zone Boundary: 19.00 °C

A. If ambient temp is warmer than WQ criterion

9. Does temp fall within this warmer temp range? YES

10. Temp increase allowed at mixing zone boundary, if required: NO LIMIT

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? ---

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? ---

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? ---

16. Temp increase allowed at mixing zone boundary, if required: ---

17. Do any of the above cells show a temp increase? NO

18. Temperature Limit if Required? NO LIMIT

Marine Temperature Reasonable Potential and Limit Calculation

Based on WAC 173-201A-200(1)(c)(i)--(ii) and Water Quality Program Guidance. All Data inputs must 

meet WQ guidelines. The Water Quality temperature guidance document may be found at: 

http://www.ecy.wa.gov/biblio/0610100.html

INPUT - Carkeek CSO TP

OUTPUT

RESULTS
Fact Sheet for NPDES Permit WA0029181 Page 150 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Elliott West CSO Treatment Plant - Calculations

1. MIXING ZONE BOUNDARY CHARACTERISTICS

 Dilution factor at mixing zone boundary 9.7

 Depth at plume trapping level (m) 1.000

2. BACKGROUND RECEIVING WATER CHARACTERISTICS

 Temperature (deg C): 13.40

 pH: 7.40

 Salinity (psu): 24.00

 Total alkalinity (meq/L) 1.78

3. EFFLUENT CHARACTERISTICS

 Temperature (deg C): 21.00

 pH: 5.50

 Salinity (psu) 12.00

 Total alkalinity (meq/L): 0.65

CONDITIONS AT THE MIXING ZONE BOUNDARY

 Temperature (deg C): 11.91

 Salinity (psu) 22.67

 Density (kg/m^3) 1017

 Alkalinity (mmol/kg-SW): 1.63

 Total Inorganic Carbon (mmol/kg-SW): 2

 pH at Mixing Zone Boundary: 6.59

Based on the CO2SYS program (Lewis and Wallace, 1998), http://cdiac.esd.ornl.gov/oceans/co2rprt.html

INPUT - Elliott West CSO TP

OUTPUT

Calculation of pH of a Mixture in Marine Water
Fact Sheet for NPDES Permit WA0029181 Page 151 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Chronic Dilution Factor 9.7 

Receiving Water Fecal Coliform 2.0 #/100 mL

Effluent Fecal Coliform - worst case 400 #/100 mL Effluent Fecal Coliform - worst case 400 #/100 mL

Surface Water Criteria 14 #/100 mL

Day of Month Fecal Value Limit Day of Month Fecal - 

Effluent

Fecal - Receiving 

Water @ Chronic 

Mixing Boundary 1 400 1 400 43 2 400 2 400 43 3 400 3 400 43 4 4 0 2 5 5 0 2 6 6 0 2 7 7 0 2 8 8 0 2 9 9 0 2

10 10 0 2

11 11 0 2

12 12 0 2

13 13 0 2

14 14 0 2

15 15 0 2

16 16 0 2

17 17 0 2

18 18 0 2

19 19 0 2

20 20 0 2

21 21 0 2

22 22 0 2

23 23 0 2

24 24 0 2

25 25 0 2

26 26 0 2

27 27 0 2

28 28 0 2

29 29 0 2

30 30 0 2

31 31 0 2

Monthly Geomean = 400 400 Monthly Geomean = 2.4

Calculation of Fecal Coliform at Chronic Mixing Boundary - Elliott West CSO TP

Technology-based limits WQ-based limits

For WWTPs: 200/400 monthly/weekly geomean For WWTPs: 14/43 [+Dilution] monthly/daily geomean

For CSO TPs: 400 monthly geomean For CSO TPs: 14/43 [+Dilution] monthly/daily geomean. We typically 

compare monthly geomean limit (400) to 14 WQ Std. Since 14 is an 

assessment of the receiving water quality assessed on a 

monthlybasis, we should include non-discharge days in this 

calculation.
Fact Sheet for NPDES Permit WA0029181 Page 152 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. Receiving Water Temperature, deg C (90th percentile): 13.4

2. Receiving Water pH, (90th percentile): 8.0

3. Receiving Water Salinity, g/kg (10th percentile): 24.0

4. Pressure, atm (EPA criteria assumes 1 atm): 1.0

5. Unionized ammonia criteria (mg un-ionized NH3 per liter) 

from EPA 440/5-88-004:

 Acute: 0.233

 Chronic: 0.035

Using mixed temp and pH at mixing zone boundaries? N o

1. Molal Ionic Strength (not valid if >0.85): 0.490

2. pKa8 at 25 deg C (Whitfield model "B"): 9.302

3. Percent of Total Ammonia Present as Unionized: 2.1%

4. Total Ammonia Criteria (mg/L as N H3):

 Acute: 11.21

 Chronic: 1.68

Total Ammonia Criteria (mg/L as N)

 Acute: 9.22

 Chronic: 1.38

INPUT

OUTPUT

RESULTS

Calculation of seawater fraction of un-ionized ammonia from Hampson (1977). Unionized ammonia criteria for salt water are from EPA 440/5-88-004. Revised 19-Oct93.

Marine Un-ionized Ammonia Criteria Calculation
Fact Sheet for NPDES Permit WA0029181 Page 153 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 8.4 9.7

Water Body Type 9.7

Rec. Water Hardness 9.7 AMMONIA, Criteria as Total NH3 ANTIMONY (INORGANIC) 7440360 1 MARSENIC (dissolved) 7440382 2 MBIS(2-ETHYLHEXYL) PHTHALATE 117817 13B BUTYLBENZYL PHTHALATE 85687 15B CADMIUM - 7440439 4M CHLOROFORM 67663 11V CHROMIUM(HEX) 18540299** COPPER - 744058 6M 2 2 0 2 0 9 9 2 0 8 2 0 2 0

0.6 0.67 0.63 0.6 0.6 0.88 0.6 0.96 0.34

2,680 2.60 6.85 1.42 0.60 35.8 5.72 6 6

0.485

0.085 1.39 0.72 0.14 0.49 0 0 0 0

Acute 9,216 - 6 9 - - 4 2 - 1100 4.8

Chronic 1,384 - 3 6 - - 9.3 - 5 0 3.1 - 4300 - 5.9 1900 - 470 - -

Acute - - 1.000 - - 0.960* - 0.993 0.790*

Chronic - - - - - 0.960* - 0.993 0.790* N N Y Y N N Y N N

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 s 0.555 0.609 0.578 0.555 0.555 0.757 0.555 0.808 0.331

Pn 0.224 0.861 0.861 0.717 0.717 0.861 0.688 0.861 0.861

3.79 1.41 1.38 1.81 1.81 1.53 1.90 1.57 1.20

Acute 1,211 0.000 1.65 1.477 0.306 0.739 8.089 1.2 7.9

Chronic 1,048 0.000 1.62 1.279 0.265 0.737 7.005 1.0 6.9

NO n/a NO n/a n/a NO n/a NO YES

Human Health Reasonable Potential s 0.555 0.6089 0.5781 0.5545 0.5545 0.7573 0.5545 0.8082 0.3307

Pn 0.224 0.861 0.861 0.717 0.717 0.861 0.688 0.861 0.861

1.524 0.5167 0.5342 0.7276 0.7276 0.4399 0.7624 0.4163 0.6986

9.7 9.7 9.7 9.7 9.7 9.7 9.7 9.7 9.7

###### 0.05 0.1434 5.1E-01 0.11 0.0272 2.81 0.2453 4.7535

n/a NO n/a NO NO n/a NO n/a* n/a

Comments/Notes: *Translator derived from receiving w ater data. **Data only available for total chromium - conservative evaluation.

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential?

Effluent percentile value

Reasonable Potential Calculation

Effluent Data

# of Samples (n)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Aquatic Life Criteria, 

ug/L

Carcinogen?

Water Quality Criteria

Coeff of Variation (Cv)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Metal Criteria 

Translator, decimal

Multiplier

Max concentration (ug/L) at edge of...

Reasonable Potential?

Pn=(1-confidence level)1/n s2

=ln(CV2+1)

Multiplier

Dilution Factor s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Elliott West CSO TP

Marine

 mg/L

Aquatic Life

Human Health Non-Carcinogenic

Human Health Carcinogenic

WQ Criteria for Protection of 

Human Health, ug/L
Fact Sheet for NPDES Permit WA0029181 Page 154 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 8.4 9.7

Water Body Type 9.7

Rec. Water Hardness 9.7 1,4 DICHLOROBENZENE 106467 22B DICHLOROBROMOMETHANE 75274 12V 2,4 DICHLOROPHENOL 120832 2A DIETHYLPHTHALATE 84662 24B DIMETHYLPHTHALATE 131113 25B FLUORANTHENE 206440 31B LEAD - 7439921 7M MERCURY 7439976 8M NICKEL - 7440020 9M PENTACHLOROPHENOL 87865 9 A 8 8 9 9 9 9 2 0 1 0 2 0 9

0.6 0.6 0.6 0.6 0.6 0.6 1.14 0.301 0.88 0.6

8.16 2 1 5.47 0.4 0.6 23.6 0.088 4.887 1.91

0.05 2.16

0.005 0.0002 0.432 0 0 0 0 0 0 0 0.0002 0.410 0

Acute - - - - - - 210 1.8 7 4 1 3

Chronic - - - - - - 8.1 0.025 8.2 7.9

2600 2 2 790 120000 3E+06 370 - 0.15 4600 8.2

Acute - - - - - - 0.951 0.85 0.970* -

Chronic - - - - - - 0.951 - 0.970* - N Y N N N N N N N Y

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 0.950 s 0.555 0.555 0.555 0.555 0.555 0.555 0.913 0.294 0.757 0.555

Pn 0.688 0.688 0.717 0.717 0.717 0.717 0.861 0.741 0.861 0.717

1.90 1.90 1.81 1.81 1.81 1.81 1.67 1.34 1.53 1.81

Acute 1.844 0.452 0.216 1.179 0.086 0.129 4.455 0.012 1.243 0.412

Chronic 1.597 0.391 0.187 1.021 0.075 0.112 3.9 0.012 1.13 0.36

n/a n/a n/a n/a n/a n/a NO NO NO NO

Human Health Reasonable Potential s 0.5545 0.5545 0.5545 0.5545 0.5545 0.55451 0.9125 0.2945 0.7573 0.5545

Pn 0.688 0.688 0.717 0.717 0.717 0.717 0.861 0.741 0.861 0.717

0.7624 0.7624 0.7276 0.7276 0.7276 0.72756 0.3718 0.82655 0.4399 0.7276

9.7 9.7 9.7 9.7 9.7 9.7 9.7 9.7 9.7 9.7

0.64 0.16 0.08 0.41 0.03 0.045 9.0E-01 0.00533 0.5904 0.14

NO NO NO NO NO NO n/a NO NO NO

Comments/Notes: *Translator derived from receiving w ater data.

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99 s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Multiplier

Dilution Factor

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential?

Reasonable Potential Calculation - Page 2

Elliott West CSO TP Aquatic Life

Marine Human Health Carcinogenic

 mg/L Human Health Non-Carcinogenic

Pollutant, CAS No. & 

NPDES Application Ref. No.

Effluent Data

# of Samples (n)

Coeff of Variation (Cv)

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Calculated 50th percentile 

Effluent Conc. (when n>10)

Aquatic Life Criteria, 

ug/L

WQ Criteria for Protection of 

Human Health, ug/L

Carcinogen? s2

=ln(CV2+1)

Pn=(1-confidence level)1/n

Effluent percentile value

Multiplier

Max concentration (ug/L) at edge of...

Reasonable Potential?

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Water Quality Criteria

Metal Criteria 

Translator, decimal
Fact Sheet for NPDES Permit WA0029181 Page 155 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 8.4 9.7

Water Body Type 9.7

Rec. Water Hardness 9.7 PYRENE 129000 45B SELENIUM 7782492 10M SILVER - 7740224 11M THALLIUM 7440280 12M TOLUENE 108883 25V ZINC- 7440666 13M CHLORINE (Total Residual) 7782505 CYANIDE 57125 14M CYANIDE 57125 14M* 9 2 0 2 0 2 0 8 2 0 2 5 1 1 1 0

0.6 0.049 1.55 1.0 0.6 0.858 1.6 0.64 0.64

0.600 0.5055 0.7914 32.8 161.1 860 19.3 11.8

0.500 0.040 5.0 5.0 0 0.028 0.995 0 0 0 0 0 0 0 0 0

Acute - 290 1.9 0.00 - 9 0 1 3 9.1 9.1 #N/A #N/A

Chronic - 7 1 - - - 8 1 7.5 2.8 2.8 #N/A #N/A

11000 4200 - 6.3 200000 - - 220000 220000 #N/A #N/A

Acute - - 0.85 - - 0.946 - - - #N/A #N/A

Chronic - - - - - 0.946 - - - #N/A #N/A N N N N N N N N N #N/A #N/A

Aquatic Life Reasonable Potential

0.950 0.950 0.950 0.950 0.950 0.950 0.95 0.950 0.950 0.950 0.950 s 0.555 0.049 1.107 0.833 0.555 0.743 1.13 0.586 0.586 0.000 0.000

Pn 0.717 0.861 0.861 0.861 0.688 0.861 0.89 0.762 0.741 #DIV/0! #DIV/0!

1.81 1.03 1.86 1.59 1.90 1.52 1.00 1.73 1.79 #DIV/0! #DIV/0!

Acute 0.129 0.062 0.17 0.000 7.411 28.4 102 3.970 2.521 #N/A #N/A

Chronic 0.112 0.054 0.18 0.000 6.418 24.7 8 9 3.438 2.183 #N/A #N/A

n/a NO NO n/a n/a NO YES YES NO #N/A #N/A

Human Health Reasonable Potential s 0.5545 0.049 1.1066 0.8326 0.5545 0.7428 1.1268 0.5859 0.5859 0 0

Pn 0.717 0.861 0.861 0.861 0.688 0.861 0.887 0.762 0.741 #DIV/0! #DIV/0!

0.7276 0.9483 0.3012 0.4054 0.7624 0.4469 0.2555 0.6591 0.6845 #DIV/0! #DIV/0!

9.7 9.7 9.7 9.7 9.7 9.7 9.7 9.7 9.7 #N/A #N/A

0.045 0.052 0.0246 0.0041 2.6 7.4E+00 2.3E+01 0.5155 0.5155 #DIV/0! #DIV/0!

NO NO n/a NO NO n/a n/a NO NO #N/A #N/A

Comments/Notes: *Cyanide below detection limit in 8 of 11 samples. Second column show s RP w ith max value discarded as potential outlier.

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Multiplier

Reasonable Potential Calculation - Page 3

Elliott West CSO TP Aquatic Life

Marine Human Health Carcinogenic

 mg/L Human Health Non-Carcinogenic

Effluent Concentration, ug/L 

(Max. or 95th Percentile)

Calculated 50th percentile 

Effluent Conc. (when n>10)

WQ Criteria for Protection of 

Human Health, ug/L s2=ln(CV2+1)

Pn=(1-confidence level)1/n s2=ln(CV2+1)

Pn=(1-confidence level)1/n

Pollutant, CAS No. & 

NPDES Application Ref. No.

Max Conc. at edge of Chronic Zone, ug/L

Reasonable Potential?

Dilution Factor

Effluent percentile value

Reasonable Potential?

Multiplier

Max concentration (ug/L) at edge of...

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Water Quality Criteria

Aquatic Life Criteria, 

ug/L

Metal Criteria 

Translator, decimal

Carcinogen?

Effluent Data

# of Samples (n)

Coeff of Variation (Cv)
Fact Sheet for NPDES Permit WA0029181 Page 156 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 8.4 9.7

Water Body Type 9.7

Rec. Water Hardness 9.7 CHLORINE (Total Residual) 7782505

Effluent Data 1.600

Acute 1 3 #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 7.5 #N/A #N/A #N/A #N/A #N/A #N/A - #N/A #N/A #N/A #N/A #N/A #N/A

Acute - #N/A #N/A #N/A #N/A #N/A #N/A

Chronic - #N/A #N/A #N/A #N/A #N/A #N/A N #N/A #N/A #N/A #N/A #N/A #N/A

Aquatic Life Limit Calculation 4

1.6 0 0 0 0 0 0

1.6 0 0 0 0 0 0

Acute 109 #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 7 3 #N/A #N/A #N/A #N/A #N/A #N/A

Acute 1 5 #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 1 8 #N/A #N/A #N/A #N/A #N/A #N/A

1 5 #N/A #N/A #N/A #N/A #N/A #N/A 1 #N/A #N/A #N/A #N/A #N/A #N/A

3 7 #N/A #N/A #N/A #N/A #N/A #N/A

109 #N/A #N/A #N/A #N/A #N/A #N/A

Comments/Notes:

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Maximum Daily Limit (MDL), ug/L

Average Monthly Limit (AML), ug/L

Metal Translator or 1?

Limiting LTA, ug/L

Long Term Averages, ug/L

Waste Load Allocations, ug/L

Permit Limit Coeff. Var. (CV), decimal

LTA Coeff. Var. (CV), decimal

# of Compliance Samples Expected per month

Carcinogen?

Water Quality Criteria

Aquatic Life Criteria, 

ug/L

WQ Criteria for Protection of 

Human Health, ug/L

Metal Criteria 

Translator, decimal

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Coeff of Variation (Cv)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Chlorine Limit Calculation

 mg/L Human Health Non-Carcinogenic

Marine Human Health Carcinogenic

Elliott West CSO TP Aquatic Life
Fact Sheet for NPDES Permit WA0029181 Page 157 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. Chronic Dilution Factor at Mixing Zone Boundary 9.7

2. Annual max 1DADMax Ambient Temperature (Background 90th percentile) 13.4 °C

3. 1DADMax Effluent Temperature (95th percentile) 21.0 °C

4. Aquatic Life Temperature WQ Criterion 16.0 °C

5. Temperature at Chronic Mixing Zone Boundary: 14.18 °C

6. Incremental Temperature Increase or decrease: 0.78 °C

7. Incremental Temperature Increase 12/(T-2) if T< crit: 1.05 °C

8. Maximum Allowable Temperature at Mixing Zone Boundary: 14.45 °C

A. If ambient temp is warmer than WQ criterion

9. Does temp fall within this warmer temp range? N O

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? N O

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? N O

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

16. Temp increase allowed at mixing zone boundary, if required: NO LIMIT

17. Do any of the above cells show a temp increase? NO

18. Temperature Limit if Required? NO LIMIT

Marine Temperature Reasonable Potential and Limit Calculation

Based on WAC 173-201A-200(1)(c)(i)--(ii) and Water Quality Program Guidance. All Data inputs must 

meet WQ guidelines. The Water Quality temperature guidance document may be found at: 

http://www.ecy.wa.gov/biblio/0610100.html

INPUT - Elliott West CSO TP

OUTPUT

RESULTS
Fact Sheet for NPDES Permit WA0029181 Page 158 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Henderson/MLK CSO Treatment Plant - Calculations

Comments

1. EFFLUENT CHARACTERISTICS

 Discharge (mgd): 2 5 From KC's chronic mixing model.

 Discharge (cfs): 3 9

 CBOD5 (mg/L): 2 0 Conservative estimate - no permit limit - max BOD5 measured = 16 mg/L

 NBOD (mg/L): 3.3 Conservative estimate - max NH3 measured = 0.73 mg/L

 Dissolved Oxygen (mg/L): 8 Conservative estimate - min DO measured = 8.4 mg/L

 Temperature (deg C): 2 1 No data, used West Pt effluent data

2. RECEIVING WATER CHARACTERISTICS 

 Upstream Discharge (cfs): 309 Used 10th percentile of daily mean values from 1995-2004 from USGS 

data site. Likely conservative because CSOs usually discharge in w inter 

w hen flow s are higher. 

 Upstream CBOD5 (mg/L): 1.0 Conservative estimate - no data

 Upstream NBOD (mg/L): 0.2 Conservative estimate - no data

 Upstream Dissolved Oxygen (mg/L): 7.5 KC 2013 Receiving w ater data report, 10th percentile value.

 Upstream Temperature (deg C): 18.7 KC 2013 Receiving w ater data report, 1DADMax

 Elevation (ft NGVD): 1 0 Estimate - small impact on results betw een 0 and 100

 Downstream Average Channel Slope (ft/ft): 0.00088

 Downstream Average Channel Depth (ft): 1 2 USGS site: Duw amish River at Golf Course in tukw ila

 Downstream Average Channel Velocity (fps): 0.26 From KC mixing model, min current = 7.8 cm/s. 

3. REAERATION RATE (Base e) at 20 deg C (day- 1): 0.39

Applic. Applic. Suggested

 Reference Vel (fps) Dep (ft) Values

 Churchill 1.5 - 6 2 - 50 0.05

 O'Connor and Dobbins 0.1 - 1.5 2 - 50 0.16

 Owens 0.1 - 6 1 - 2 0.09

 Tsivoglou-Wallace 0.1 - 6 0.1 - 2 0.93

4. BOD DECAY RATE (Base e) AT 20 deg C (day- 1): 0.23

 (or use Wright and McDonnell eqn, 1979, for small rivers.) Enter this value --> 0.59

1. INITIAL MIXED RIVER CONDITION 

 CBOD5 (mg/L): 3.1

 NBOD (mg/L): 0.5

 Dissolved Oxygen (mg/L): 7.6

 Temperature (deg C): 19.0

2. TEMPERATURE ADJUSTED RATE CONSTANTS (Base e)

 Reaeration (day^-1): 0.38

 BOD Decay (day^-1): 0.22

3. CALCULATED INITIAL ULTIMATE CBODU AND TOTAL BODU 

 Initial Mixed CBODU (mg/L): 4.6

 Initial Mixed Total BODU (CBODU + NBOD, mg/L): 5.1

4. INITIAL DISSOLVED OXYGEN DEFICIT

 Saturation Dissolved Oxygen (mg/L): 9.281

 Initial Deficit (mg/L): 1.73

5. TRAVEL TIME TO CRITICAL DO CONCENTRATION (days): 1.64

6. DISTANCE TO CRITICAL DO CONCENTRATION (miles):6.86

7. CRITICAL DO DEFICIT (mg/L): 2.05

8. CRITICAL DO CONCENTRATION (mg/L): 7.23

INPUT

Streeter-Phelps Analysis of Critical Dissolved Oxygen Sag for the Henderson/MLK CSO TP

OUTPUT
Fact Sheet for NPDES Permit WA0029181 Page 159 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. Dilution Factor at Mixing Zone Boundary 10.3

2. Ambient/Upstream/Background Conditions

 Temperature (deg C): 18.70

 pH: 7.30

 Alkalinity (mg CaCO3/L): 25.29

3. Effluent Characteristics

 Temperature (deg C)*: 18.00

 pH: 7.00

 Alkalinity (mg CaCO3/L): 33.50

1. Ionization Constants

 Upstream/Background pKa: 6.39

 Effluent pKa: 6.40

2. Ionization Fractions

 Upstream/Background Ionization Fraction: 0.89

 Effluent Ionization Fraction: 0.80

3. Total Inorganic Carbon

 Upstream/Background Total Inorganic Carbon (mg CaCO3/L): 28

 Effluent Total Inorganic Carbon (mg CaCO3/L): 42

4. Condtions at Mixing Zone Boundary

 Temperature (deg C): 18.63

 Alkalinity (mg CaCO3/L): 26.09

 Total Inorganic Carbon (mg CaCO3/L): 29.72

 pKa: 6.39

 pH at Mixing Zone Boundary: 7.25

* estimated value, no data available, small imact on results

INPUT - Henderson / MLK CSO TP

OUTPUT

RESULTS

Based on the procedure in EPA's DESCON program (EPA, 1988. Technical 

Guidance on Supplementary Stream Design Conditions for Steady State 

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

Calculation of pH of a Mixture of Two Flows
Fact Sheet for NPDES Permit WA0029181 Page 160 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Chronic Dilution Factor 10.3

Receiving Water Fecal Coliform, #/100 ml 110 KC 2013 receiving water study (max minus outlier)

Effluent Fecal Coliform - worst case, #/100 ml 400 Guidance-based limit

Surface Water Criteria, #/100 ml 200 Freshwater secondary contact

Fecal Coliform at Mixing Zone Boundary, #/100 ml 138 <200

Difference between mixed and ambient, #/100 ml 2 8

OUTPUT

Calculation of Fecal Coliform at Chronic Mixing Zone 

INPUT - Henderson CSO TP
Fact Sheet for NPDES Permit WA0029181 Page 161 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Dilution Factors: Acute Chronic

Facility 1.9 10.3

Water Body Type 10.3

Rec. Water Hardness 10.3 CHLORINE (Total Residual) 7782505

Acute Dilution Factor 1.9

Chronic Dilution Factor 10.3

Effluent Data 0.60

Acute 1 3 #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 7.5 #N/A #N/A #N/A #N/A #N/A #N/A - #N/A #N/A #N/A #N/A #N/A #N/A

Acute - #N/A #N/A #N/A #N/A #N/A #N/A

Chronic - #N/A #N/A #N/A #N/A #N/A #N/A N #N/A #N/A #N/A #N/A #N/A #N/A

Aquatic Life Limit Calculation 4

0.6 0 0 0 0 0 0 0

0.6 1.0 0 0 0 0 0 0

Acute 24.7 0.0 #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 77.3 0.0 #N/A #N/A #N/A #N/A #N/A #N/A

Acute 7.9 0.0 #N/A #N/A #N/A #N/A #N/A #N/A

Chronic 40.7 0.0 #N/A #N/A #N/A #N/A #N/A #N/A

7.9 0.0 #N/A #N/A #N/A #N/A #N/A #N/A

1.00 1.00 #N/A #N/A #N/A #N/A #N/A #N/A

1 2 #DIV/0! #N/A #N/A #N/A #N/A #N/A #N/A

2 5 0.0 #N/A #N/A #N/A #N/A #N/A #N/A

Comments/Notes:

References: WAC 173-201A,

Technical Support Document for Water Quality-based Toxics Control, US EPA, March 1991, EPA/505/2-90-001, pages 56/99

Maximum Daily Limit (MDL), ug/L

Average Monthly Limit (AML), ug/L

Metal Translator or 1?

Limiting LTA, ug/L

Long Term Averages, ug/L

Waste Load Allocations, ug/L

Permit Limit Coeff. Var. (CV), decimal

LTA Coeff. Var. (CV), decimal

# of Compliance Samples Expected per month

Carcinogen?

Water Quality Criteria

Aquatic Life Criteria, 

ug/L

WQ Criteria for Protection of 

Human Health, ug/L

Metal Criteria 

Translator, decimal

Receiving Water Data

90th Percentile Conc., ug/L

Geo Mean, ug/L

Coeff of Variation (Cv)

Pollutant, CAS No. & 

NPDES Application Ref. No.

Aquatic Life and Human Health Limits Calculations

 mg/L Human Health Non-Carcinogenic

Marine Human Health Carcinogenic

Henderson CSO TP Aquatic Life
Fact Sheet for NPDES Permit WA0029181 Page 162 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

1. Chronic Dilution Factor at Mixing Zone Boundary 10.3

2. Annual max 1DADMax Ambient Temperature (Background 90th percentile) 18.7 °C

3. 1DADMax Effluent Temperature (95th percentile) 21.0 °C

4. Aquatic Life Temperature WQ Criterion 16.0 °C

5. Temperature at Chronic Mixing Zone Boundary: 18.92 °C

6. Incremental Temperature Increase or decrease: 0.22 °C

7. Incremental Temperature Increase 12/(T-2) if T< crit: ---

8. Maximum Allowable Temperature at Mixing Zone Boundary: 19.00 °C

A. If ambient temp is warmer than WQ criterion

9. Does temp fall within this warmer temp range? YES

10. Temp increase allowed at mixing zone boundary, if required: NO LIMIT

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? ---

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? ---

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? ---

16. Temp increase allowed at mixing zone boundary, if required: ---

17. Do any of the above cells show a temp increase? NO

18. Temperature Limit if Required? NO LIMIT

RESULTS

Marine Temperature Reasonable Potential and Limit Calculation

Based on WAC 173-201A-200(1)(c)(i)--(ii) and Water Quality Program Guidance. All Data inputs must 

meet WQ guidelines. The Water Quality temperature guidance document may be found at: 

http://www.ecy.wa.gov/biblio/0610100.html

INPUT - Henderson/MLK CSO TP

OUTPUT
Fact Sheet for NPDES Permit WA0029181 Page 163 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Appendix G — Significant Industrial Users

Company Name Permit 

Number

Local 

Limits

Categorical 

Limits

If categorical, which category and 

sub-category

Acu-Line Corporation 7231-04 No Yes Metal Finishing - CFR 433 PSNS

Alaskan Copper Works - 6th Ave. 7238-05 No Yes Metal Finishing - CFR 433

Alaskan Copper Works - Marginal Way 7201-04 No Yes Metal Finishing - CFR 433

Amgen Corporation (Seattle) 7785-02 Yes No

Art Brass Plating, Inc. 7722-04 No Yes Metal Finishing - CFR 433 PSNS

ASKO Processing Inc. 7728-03 No Yes Metal Finishing - CFR 433

BNSF Railway Co. - Interbay Facility 7872-01 Yes No

Boeing Commercial Airplane - North Field 7594-05 No Yes Metal Finishing - CFR 433

Boeing Company - Plant 2 Facility 7811-03 No Yes Metal Finishing - CFR 433 PSNS

BP West Coast Products, LLC 7592-04 Yes No

Carl Zapffe, Inc. 7654-03 No Yes Metal Finishing - CFR 433 PSNS

Ceradyne Inc. - Viox Glass Technology 7507-04 Yes No

Darigold, Inc. - Rainier Plant 7116-05 Yes No

Emerald Services Inc. - Airport Way Facility 7884-01 No Yes Centralized Waste Treatment 

437,ABC PSES

Emerald Services Inc. - Marginal Way Facility 7725-04 Yes No

Encore Oils, LLC 7751-04 Yes No

Foss Maritime Company 7703-04 Yes No

Glacier Northwest Inc. 7740-03 Yes No

GM Nameplate Inc. 7187-05 No Yes Metal Finishing - CFR 433

Industrial Container Services 7130-04 Yes No

IRIS Holdings LLC - 5th Ave. N. Ph 2 Construction Site 7871-01 Yes No

Kerry Food & Beverage 7854-01 Yes No

King County SWD - Shoreline Transfer Station 7587-05 Yes No

King County SWD - Vashon Transfer Station 7675-04 Yes No

King County WTD - Ballard Siphon Replacement Project 7849-01 Yes No

Magnetic and Penetrant Services Co. 7873-01 No Yes Metal Finishing - CFR 433 PSNS

Marel Seattle, Inc. 7821-02 No Yes Metal Finishing - CFR 433 PSNS

Marine Vacuum Service, Inc. 7676-05 No Yes Centralized Waste Treatment 437D 

PSES

Mastercraft Metal Finishing, Inc. 7233-03 No Yes Electroplating - CFR 413

National Products Inc. 7834-02 No Yes Metal Finishing - CFR 433 PSNS

Pacific Iron and Metal 7577-04 Yes No

Pepsi Beverages Company - Seattle Facility 7820-02 Yes No

Pioneer Industries 7723-04 No Yes Metal Finishing - CFR 433 PSNS

Rabanco Recycling Company 7595-05 Yes No

Seattle Barrel Company 7113-03 Yes No

Seattle, City of - SDOT - Mercer Corridor Improvements 7863-01 Yes No

Seattle, City of - SPU - South Transfer Station 7878-01 Yes No

Skills, Inc. - Ballard Facility 7552-03 No Yes Electroplating - CFR 413

Sound Transit - Capitol Hill Station Location 7860-02 Yes No

Sound Transit - U830 Tunneling Pine Street Location 7859-01 Yes No

Sound Transit - University of Washington Station Location 7861-02 Yes No

TOC Holdings Co. 7689-07 Yes No

U.S. Starcraft Corporation 9711-01 No Yes Metal Finishing - CFR 433

University of Washington Microfabrication Facility 7800-02 No Yes Electronic Components - CFR 469

University of Washington School of Dentistry 7797-03 Yes No

Vigor Shipyards, Inc. 7782-06 Yes No

WSDOT - Alaskan Way Viaduct Replacement Project, 

SR99 Bored Tunnel

7875-01 Yes No

WSDOT - Viaduct - S. Holgate St. to S. King St. Stage 3 

Atlantic Bypass Project

7877-01 Yes No
Fact Sheet for NPDES Permit WA0029181 Page 164 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Appendix H — Process Flow Diagrams

West Point WWTP
Fact Sheet for NPDES Permit WA0029181 Page 165 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Alki CSO Treatment Plant
Fact Sheet for NPDES Permit WA0029181 Page 166 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Carkeek CSO Treatment Plant
Fact Sheet for NPDES Permit WA0029181 Page 167 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Elliott West CSO Treatment Plant
Fact Sheet for NPDES Permit WA0029181 Page 168 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Number Page

Section/ 

permit or 

factsheet

KC Comments KC Suggested Resolution/Change

KC commenters name

Ecology Response

2 5 S1.A Request retention of the permit allowance that allows for a reduction in removal % 

during wet weather. During wet weather conditions, there are two forces that make compliance more difficult. With high flows, (1) the influent becomes more dilute and have demonstrated concentrations close to proposed limit in 2012/13 (examples listed below), the higher the flow is above 300 mgd, the higher the % of primary effluent in the blended effluent. Also the potential for the screenings project representing and new potential reduction in TSS in influent that could compound the effect of wet weather highly dilute flows. 

Retain the 80% removal during wet weather.Propose a "floor" to the effluent concentration limit, when the removal % is applied. 20 mg/L for both (a higher floor for cBOD, relative to its normal effluent limit - because cBOD removal is more difficult with primary treatment)

Eugene Sugita/ Betsy Cooper

3 5 S1.A (1) - Several times during this current permit period, the effluent limits were driven 

below the 30 mg/L for TSS and 25 for cBOD. If the 85% removal limit was in effect, the limits would have been even lower. For example, in December 2012 - the cBOD limit would 13 mg/L and the TSS limit 19 mg/L.

Eugene Sugita

4 5 S1.A (2) - At 350 MGD, the plant would be below 85%, with a 90% removal assumed for 

the secondary, and 55% for the primary treated flow. Also, although 50% removal is in the primary treatment definition, this should only apply to TSS. BOD removals are typically much lower with primary treatment - in the 25 to 35% range. 

Eugene Sugita

5 5 S1.A Anticipated changes during the upcoming permit period that would also impact the 

% removal.Screenings project - the improved screenings removes more material from the influent, and the influent sample is taken downstream of the screens.

Climate change / Seattle CSOs - anticipating higher flows (resulting in more dilute influent flows, and a higher % of treated CSO)

Eugene Sugita

6 6 thru 9 S1.B footnote c, consider adding the addition in green to this footnote - For the monthly 

geometric mean, calculate the geometric mean of all samples collected during the month; use a value of 1 for the geomean calc when fecal coliform results are 0. Do not include non-discharge days in the calculation. Ecology provides directions to calculate this value in publication No. 04-10-020, Information Manual for Treatment Plant Operators, available at: http://www.ecy.wa.gov/pubs/0410020.pdf

For the monthly geometric mean, calculate the geometric mean of all samples collected during the month; use a value of 1 for the geomean calc when fecal coliform results are 0. In this calculation include days in which influent samples are collected or discharge occurs. For influent only days, include a value of 1 for the geomean value. Do not include nondischarge days in the calculation. Ecology provides directions to calculate this value in publication No. 04-10-020, Information Manual for Treatment Plant Operators.

Karl Zimmer no - have 400 tech based limit

8 6 thru 9 S1.B Applies to each CSO facility.

Footnote d - report the instantaneous max and min pH monthly. The monthly limits for pH are 6 and 9. 

Propose the EPA language / previous permit language, which allowed for brief excurs ions .From previous permit - "Indicates the range of permitted values. When pH is continuously monitored, excursions between 5.0 and 6.0, or 9.0 and 10.00 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.

Eugene Sugita Cannot change - will set precedent, if allowed 7 hours of 

exceedance per month no need to monitor! Ecology will keep using enforcement descretion.

9 1 0 S2.A Intro 

Paragraph

Need to discuss the affect the revision of this paragraph has on the affect monitoring for this permit, Treatment Plant Effluent and CSO Effluent. KC believes there may be difficulty meeting some of the DLs and QLs for parameters in Appendix A for secondary effluent. Further the extension of these DLs and QLs to CSO effluent raises additional concerns that such DLs and QLs would not be applicable and that no one matrix-specific study could be expected to capture the variability of CSO effluent quality. While KC agrees that methods with sufficient sensitivity should always be applied all sample analyses and seek the best sensitivity to assure our Pre-treatment has the best data on which to base limit and so all our effluents are thoroughly characterized, we are concerned if the well executed laboratory testing done consistently at the KC Environmental Lab is considered in violation of our NPDES permit conditions. There are a number of ways to address these issues. One could be to adjust DLS and QLs to more realistic values; another, to modify the to section to consider the methods, or others alternate methods of sufficient sensitivity as required, but indicate the DLs and QLs as guidelines. We suggest this topic may warrant a more detailed discussion with several of Ecology's units and our Laboratory professional. We look forward to initiating any additional meetings to address this issue. 

The change from the Appendix A as "...the following table with analytical levels is to be used as guidance for effluent characterization NPDES permit applications and applications for permit renewal. "to "The Permittee must use the specified analytical methods, DLs and QLs in the following table for permit and applications requirements... If the permittee uses an alternative method, not specified in the permit ... If the permittee is unable to obtain the required DL and QL in its effluent due to matrix effects, the permittee must submit a matrix-specific DL and QLto Ecology with appropriate lab documentation." 

Betsy Cooper

Added the following to permit: Calculations show that due to dilute influent at West Point during wet weather, effluent TSS and CBOD5 average monthly effluent concentrations would have to be 13% and 19% lower, on average, than their respective discharge limits (30/25 mg/L) 36 and 49 percent of the time, respectively, to meet the 85% removal requirement. Ecology calculated these values using average monthly influent concentrations over the past 5 years. According to the EPA Permit Writer's Manual (page 5-11), this criteria qualifies the West Point facility for less stringent percent removal requirements, consistent with 40 CFR 133.103(a). Ecology has assessed, based on historical data, that the West Point facility can achieve 80% removal for TSS and CBOD5 during the wet weather months of November through April.Revised RDLs/MDLs according to KC's request.

Permit Comments

Appendix I — Response to Comments

King County Entity Review Comments

Significant comments are listed below; comments that provided clarification and/or corrections are not listed.
Fact Sheet for NPDES Permit WA0029181 Page 169 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Number Page

Section/ 

permit or 

factsheet

KC Comments KC Suggested Resolution/Change

KC commenters name

Ecology Response

1 5 1 5 S2.C - 3 the specific bullets under the requirement to calibrate consistent with 

manufacturer's recommendations create some unrealistic logistical challenges as written.

The current calibration measures used are consistent with the manufacturer's recommendations. The specifics listed in the bullets in thedraft permit are not fully compliant with Manufactures Specifications. Therefore we would request removing bullet a,b,c from the permit and just leaving the basic sentence. 

Eugene Sugita The following text was removed: a. May calibrate 

apparatus for continuous monitoring of dissolved oxygen by air calibration.b. Must calibrate continuous pH measurement instruments using a grab sample analyzed in the lab with a pH meter calibrated with standard buffers and analyzed within 15 minutes of sampling.c. Must calibrate continuous chlorine measurement instruments using a grab sample analyzed in the laboratory within 15 minutes of sampling.

1 6 1 6 S3.A-7 a. Submit monthly DMRs by the 15th - Preparing reports for the TP and four CSO 

facilities, by the 15th, is challenging.b. Submit annual DMRs by March 30th...First need to clarify if this is the CSO Treatment Plant DMRs? - can be done but would then be a separate submittal from the CSO annual report.

a. propose retaining the 20th as in the current permit.b. propose submitting the annual DMRs with the CSO annual reports, and their due date. 

Eugene Sugita 15th for monthly - changed annual DMR submittal to July 

31st, consistent with annual report.

2 9 3 0 S6.D. As sufficient data become available, the Permittee must, in consultation with 

Ecology, reevaluate their local limits in order to prevent pass through or interference. On a case-by-case basis, as applicable, the Permittee should consider the impacts of CSO discharges on the receiving waterbody when establishing limits for individual Permittees . If Ecology determines that any pollutant present causes pass through or interference, or exceeds established sludge standards, the Permittee must establish new local limits or revise existing local limits as required by 40 CFR 403.5. Ecology may also require the Permittee to revise or establish local limits for any pollutant discharged from the treatment works, including CSO outfalls (treated or untreated, controlled or uncontrolled), that has a reasonable potential to exceed the water quality standards, sediment standards, or established effluent limits, or causes whole effluent toxicity. Ecology makes this determination in the form of an Administrative Order.

We propose that Ecology remove reference to a requirement to apply local limits based on CSOs and revise the section to be clear that individual permits limits will include CSO considerations where applicable and only on a case -by case basis. The basis for local limits is for municipal wastewater treatment plants, not for CSO outfalls or for CSO treatment facilities. Therefore we suggest leaving the first added sentence as drafted but deleting 'including CSO outfalls(treated or untreated, controld or uncontrolled) '.

Despina Strong/Betsy Cooper 

Kept sentence that starts with "On a case-by-case basis.." since it refers to individual permits. Removed 'including CSO outfalls(treated or untreated, controld or uncontrolled)' because of the difficullty of assessing the individual discharges impacts to specific CSO discharges during large storm events. 

3 3 3 6 S11.B. #7 New text proposed for 9 MC #7 call for two new activities - they are: In the second 

paragraph (The first Annual CSO Report submitted under this permit cycle must include a detailed description of the pollution prevention program, appropriate BMPs, and the legal authority and administrative procedures that will be used to ensure the program is being implemented. If the legal authority and/or administrative procedures are not in place, the first Annual CSO Report must include a detailed description of the steps needed to establish such a program and the timeline for getting the program in place.) 1) the need to clarify the legal and administrative procedures in place to address stormwater BMP in combined areas. The third paragraph (In addition, every Annual CSO Report must contain a list of facilities that discharge, or have the potential to discharge, industrial stormwater into the combined sewer system.) 2) proposes new reporting of information on industrial discharge stormwater discharges. We would like to discuss each.

Regarding topic 1) it is our understanding that the term 'first annual CSO report submitted under this permit cycle' would mean the first full year under this permit so the report would be submitted in July 31 2016. While KC has committed to clarifying the regulatory and administrative authority for these SW source control in the Duwamish in the proposed KC Duwamish 5-year Source Control plan, we proposed clarifying the roles and responsibility by 2017 therefore we would request that the permit be consistent with that commitment. 

Betsy Cooper Added clarification that this requirement will start with the 

Annual Report submitted in 2016.

3 4 3 7 S11.B. #7 New text proposed for 9 MC #7 call for two new activities - they are: In the second 

paragraph (The first Annual CSO Report submitted under this permit cycle must include a detailed description of the pollution prevention program, appropriate BMPs, and the legal authority and administrative procedures that will be used to ensure the program is being implemented. If the legal authority and/or administrative procedures are not in place, the first Annual CSO Report must include a detailed description of the steps needed to establish such a program and the timeline for getting the program in place.) 1) the need to clarify the legal and administrative procedures in place to address stormwater BMP in combined areas. The third paragraph (In addition, every Annual CSO Report must contain a list of facilities that discharge, or have the potential to discharge, industrial stormwater into the combined sewer system.) 2) proposes new reporting of information on industrial discharge stormwater discharges. We would like to discuss each.

Regarding topic 2) to comply with such a requirement is complicated by conflicting definitions of "industrial uses" by various authorities (KC pretreatment program, Ecology SW manual and MS4 permit, Seattle SW code) and KC's limited ability to have knowledge of many facilities that might have stormwater discharges since KC does not have jurisdiction over stormwater or land use (building or occupancy permits) in the City limits. Other that providing basic information regarding the general zoning and land use types in the areas of the CSO basins, KC does not appear to be able to have the ability to provide this data sought in this condition. Therefore we request this proposed requirement be deleted from the permit.

Betsy cooper Removed second sentence ("in addition ...), due ot 

difficulty in tracking down individual industrial stormwater contributors (many and new ones every year). Start with first part of requirement now with thoughts on second for next permit.

3 5 3 7 S11.C. CSO 

Reporting

1. monthly reporting by the 15th of the month As requested for the full DMR, in recognition of the 4 

CSO treatment plants, as well as the data for 38 flow monitoring activities and additional control facilities coming on line during this permit cycle we request that having all report in, QCd and submitted by the 15th of the month would be extremely difficult and request the 20th date be maintained, as it has been in all previous permits. 

Betsy Cooper Must be consistent with all other permittees and have 

DMRs submitted by the 15th of each month.
Fact Sheet for NPDES Permit WA0029181 Page 170 of 175

West Point Wastewater Treatment Plant and Combined Sewer Overflow System

Number Page

Section/ 

permit or 

factsheet

KC Comments KC Suggested Resolution/Change

KC commenters name

Ecology Response

4 0 4 2 S13B The adopted Post-Construction Monitoring plans states "Post construction 

sediment monitoring comprises a combination of modeling and sediment quality samples that provide a site characterization. King County, in consultation with Ecology, will determine what comprises an adequate site characterization on a site specific basis. Based on the site characterization, certain CSO discharge locations may exceed Sediment Management Standards (SMS). For these locations, a sitespecific sediment cleanup plan will be developed. Cleanup plans will contain actions required to meet the Sediment Management Standards (SMS) as well as a sampling program to ensure the outcome has been achieved and recontamination is not occurring."

Clarify the language in the first paragraph of S13B on sediment characterization at controlled CSOs to indicate that sampling or modeling can be used (similar to the language used in the second paragraph on monitoring).

Jeff Stern Added text "model and/or collect sediment samples"

4 2 4 3 S13B.b Data reports are requested 8 months after sample collection. While this is 

possible, if there are competing projects or unexpected requests that compete for lab or staff time (other the norm), this timing will be extremely difficult to meet.

Please change report due date to 10 months after collection.

Jeff Stern Due date changed to 10 months after collection.

4 3 4 4 S15. EW 

Copper 

Reduction 

assessment

This new condition calls for KC to, among other things, Assess copper discharge patterns such as seasonal or first flush impacts, stormwater vs. domestic wastewater concentrations, etc. We would like to discuss what is expected and what we think is possible to address "stormwater vs domestic wastewater concentrations, etc." 

We believe the assessment could characterize, in the EW drainage basin sample areas with particular development patterns (predominantly industrial, industrial/commercial, residential) and look at copper concentrations during wet and dry periods, but we do not see a way to assess "stormwater vs domestic wastewater concentrations". We request a revision of that conditions.

Betsy cooper Thanks for the feedback. Language changed 

accordingly.

4 7 53-57 Appendix A As noted earlier, and supported by information provided regarding the methods 

currently and continuously years for years by our Process Control labs and Environmental Labs. There are a number of methods we use that are not in the Appendix A table. Also the DLs and QLs in some cases do not appear to be consistently achievable. 

We request a larger discussion about how to address are significant concerns with the changes to this section and how they would affect KC's ability to comply with this permit.

Betsy cooper

4 8 Appendix A 

5 3

Additional Ammonia 

Methodology

Please add Ammonia method "Kerouel & Aminot 1997" to the Recommended Analytical Protocol column in Appendix A. KCEL has received permission from EPA to use this fluorometric method for all ammonia samples analyzed at KCEL but it is not listed in 40 CFR 136.

for all Lab comments, suggested resolution is in Comment column

Brian Prosch

4 9 Appendix 

A53

Additional 

Fluoride 

methodology

For Fluoride, please add ion chromatography method SM4110B to the Recommended Analytical Protocol column in Appendix A. This method was in Appendix A from the previous West Point NPDES permit.

for all Lab comments, suggested resolution is in Comment column

Brian Prosch Fluoride deleted from table.

5 1 Appendix A 

5 4

Update Total 

Phosphorus 

DL & QL

For total phosphorus, the DL and QL values should be updated to 100 ug/L each, as in Appendix A from the previous West Point NPDES permit. These limits should be no lower than the soluble reactive phosphorus limits of 100 ug/L.

for all Lab comments, suggested resolution is in Comment column

Brian Prosch Updated table for this discharger since 0.1 mg/L 

provides sufficient sensitivity.

5 2 Appendix A 

5 4

Update 

Settleable 

Solids QL

For Settleable Solids, please update the QL to 1000 ug/L since 100 ug/L is too low to be detected by SM2540-F.

for all Lab comments, suggested resolution is in Comment column

Brian Prosch Updated table - permit specific

5 4 Appendix A 

5 4

Additional 

Total Cyanide 

Methodology

For Total Cyanide, please add method SM4500-CN-C,E to the Recommended Analytical Protocol column in Appendix A. It is an approved method under 40 CFR 136 and is the reference method used by KCEL.

for all Lab comments, suggested resolution is in Comment column

Brian Prosch Added.

5 7 Appendix A 

5 4

Iron, Total Please add 200.8 to the list of recommended protocols. for all Lab comments, suggested resolution is in 

Comment column

Diane McElhany Added.

5 8 Appendix A 

5 4

Magnesium, 

Total

Please add 200.8 to the list of recommended protocols. for all Lab comments, suggested resolution is in 

Comment column

Diane McElhany Added.

5 9 Appendix A 

5 6

1,2-

Diphenylhydra

zine (as 

Azobenzene) 

has only 

method 1625 listed. This is 

an isotope 

dilution 

method. 

Please add 625 to the list of protocols. for all Lab comments, suggested resolution is in 

Comment column

Diane McElhany Added.

6 1 Appendix A Appendix A (in 

general)

EPA is in the process of revamping many of the 40 CFR methods listed in Appendix A including 608, 624and 625. These methods have not been updated in over 25 years. I'd suggest that Appendix A reflective of the current EPA DLs and or be open to including the new detection limits when these methods are finally promulgated.

for all Lab comments, suggested resolution is in Comment column

Diane McElhany Addressed by line 50 above.

6 2 Appendix A 

5 3

Matrix specific 

MDL study 

when DL and 

QL if the 

DL/QL's are 

higher due to 

matrix effects.

Can you give more details in terms of exactly what types of documentation are you expecting to see? Are you asking for an MDL study in the exact matrix? Final treatment plant effluent is fairly consistent, however CSO effluent can be very inconsistent making the achievable DLs and QLs variable. We'd like to discuss how best to approach this issue with DOE prior to the new permit.

for all Lab comments, suggested resolution is in Comment column

Diane McElhany

Added following language to App A: "Alternative methods may be used if the Permittee knows that an alternate, less sensitive method (higher DL and QL) from those listed below is sufficient to produce measurable results in their effluent." Also: OK to use if EPA has granted the laboratory written permission to use the method". Addressed with specific statement about matrix problems for CSO influent/efluent.

also: 

"Appendix A methods required for parameters with Limits. For parameters w/o limits, use method with similar detection level."
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Number Page

Section/ 

permit or 

factsheet

KC Comments KC Suggested Resolution/Change

KC commenters name

Ecology Response

6 3 Appendix A 

5 4

Chromium 

(hex) 

dissolved was 

added under 

the Priority 

Pollutants 

(Metals, 

Cyanide and 

Total 

Phenols).

Hexavalent chromium is not listed in the EPA priority pollutant list (40 CFR, Part 423, Appendix A), just Total Chromium. If hexavalent chromium should be added to this Appendix A, could it be added to the NONCONVENTIONALS PARAMETERS grouping instead of the PRIORITY POLLUTANTS heading? 

for all Lab comments, suggested resolution is in Comment column

Diane McElhany removed Priority Pollutants title

6 4 Appendix A 

5 4

Clarification of 

Chromium 

(hex) 

dissolved 

methodology

I am not sure which method is meant by SM3500-Cr EC since there is no method E for SM3500. Do you mean SM3500-Cr C?

for all Lab comments, suggested resolution is in Comment column

Brian Prosch Chromium Hex changed to SM3500-CR C

6 5 Appendix A 

5 4

Additional 

Chromium 

(hex) 

dissolved 

methodology

Please add SM3500-Cr B to the Recommended Analytical Protocol column in Appendix A for Chromium (hex) dissolved. It is an approved method in 40 CRF 136 and KCEL is accredited for this method. The DL and QL for this method should be listed as 5 and 10 ug/L, respectively.

for all Lab comments, suggested resolution is in Comment column

Brian Prosch Added.

6 7 Permit 

Effective date

If we find that the effective date will fall somewhere in December, will Ecology consider making the date in January? This would allow a tidy reporting on annual reports, etc. avoiding requirement spanning the last month of the year. 

see comments Pedro De 

Arteaga/ Betsy Cooper

Will do.

1 5 3 5 Table 18 EW Copper Ecology value 86.7 KC value 71.4 in max column; Cadmium Ecology 

value 0.617 KC value 0.349 in max column; Weak Dissociable Cyanide Ecology value 11.8 KC value 19.3 in Max column all units ug/l

Fritz Grothkoff Copper: Sample collected 8/24/09 was reported as 86.7 

ug/L. Cadmium: Sample collected 8/24/09 was reported as 0.617 ug/L. Weak dissociable cyanide: Value should be 19.3 as pointed out, table and RP calc updated.

Fact Sheet Comments
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Public Review Comments

Ecology received two comments during the 30-day public review period: one from EPA Region 

10 and the other from Seattle Public Utilities.

Comment #1: EPA

The U.S. Environmental Protection Agency reviewed the above-referenced draft permit pursuant to the 

NPDES Memorandum of Agreement between the Washington Department of Ecology and United States 

Environmental Protection Agency Region 10 (MOA) and the EPA’s obligation to oversee implementation 

of the NPDES programs by delegated states. The EPA reviewed the draft permit for consistency with the 

Clean Water Act and NPDES implementing regulations and with the Department of Ecology’s (Ecology) 

regulations and permit writing guidance.

The EPA completed a screening-level review of the above-mentioned draft NDPES permit. Although our 

review was not comprehensive, the following concern must be addressed to ensure consistency with the 

CWA and NPDES regulations.

The proposed draft permit removes discharge event maximum settleable solids effluent limits of 1.9 

mL/L for all four CSO treatment plant discharges. Presumably these limits were developed in a previous 

version of the NPDES permit as a technology-based effluent limit based on best professional judgment 

(BPJ). CWA section 402(o) expressly prohibits backsliding from certain existing effluent limitations. The 

fact sheet must explain how removal of these effluent limits is consistent with CWA section 402(o) and 

exceptions to the general prohibition outlined in part (2) of that section or anti-backsliding regulation at 

40 CFR 122.44(l). Refer to EPA’s Permit Writers’ Manual 

(http://www.epa.gov/npdes/pubs/pwm_2010.pdf), section 7.2, for information about applying the antibacksliding provisions in NPDES permitting.

Please let me know if you have any questions regarding these comments. Sincerely, Karen

KAREN BURGESS, P.E.

NPDES Permits Unit - State Oversight Lead

EPA Region 10

206-553-1644 | Burgess.Karen@epa.gov

U.S. Environmental Protection Agency

Office of Water and Watersheds, M/S OWW-130

1200 Sixth Avenue, Suite 900

Seattle, Washington 98101

http://www.epa.gov

Ecology’s response to Comment #1:

Ecology proposes to regulate settleable solids discharges from the CSO treatment plants in King 

County’s collection system using the annual average limit of 0.3 mL/L/hr instead of both the per 

event limit of 1.9 mL/L/hr and annual average limit of 0.3 mL/L/hr, as instated in the previous 

permit. 

The Clean Water Act (CWA) section 402(o) expressly prohibits backsliding from certain 

existing effluent limits including:

1. To revise an existing technology-based effluent limit (TBEL) that was developed on a 

case-by-case basis using best professional judgment (BPJ) to reflect subsequently 

promulgated effluent limitations guidelines and standards (effluent guidelines) that would 

result in a less stringent effluent limitation, and
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2. Relaxation of an effluent limitation that is based on state standards, such as water quality 

standards or treatment standards, unless the change is consistent with CWA section 

303(d)(4). 

The discharge event maximum settleable solids limit that Ecology is proposing to remove is not 

a state standard (i.e. not in state regulation) and is not a guidance-based or a water quality-based 

limit, but instead a case-by-case limit developed using best professional judgment (BPJ). 

Therefore the exception allowances of 40 CFR 122.44(l) apply.

40 CFR 122.44(l)(2)(i)(B)(1) allows an exception to anti-backsliding policies when “information 

is available which was not available at the time of permit issuance (other than revised 

regulations, guidance, or test methods) and which would have justified the application of a less 

stringent effluent limitation at the time of permit issuance”. When Ecology originally issued the 

settleable solids per event limit of 1.9 mL/L/hr it was unaware of the extreme variability in 

volume and quality (physical and chemical characteristics) of CSO influent flows. In addition, 

the event maximum limit appears to have been developed with data for continuously operated 

facilities (i.e. Carkeek primary plant), which does not fit the intermittently operated CSO 

facilities. The CSO treatment plants cannot always meet the treatment demands of these highly 

fluctuating, intermittent influent flows when averaged over short periods such as 1 to 2 hours as 

is often the case for CSO events. This especially applies when “first flush” conditions occur and 

settleable solids levels are particularly high. Averaging treatment performance over a longer time 

period provides a more representative assessment of a facility’s performance capability under 

these instances. Therefore Ecology is proposing to require the annual average limit of 0.3 

mL/L/hr and not include the maximum per event limit.

This decision is consistent with Ecology’s regulation to require on-site treatment of CSOs to 

provide treatment equivalent to primary treatment which is defined in WAC 173-245-020(16) as 

”any process which removes at least 50% of the total suspended solids from the waste stream, 

and discharges less that 0.3 ml/L/hr of settleable solids”. The proposed permit restricts the 

facility to an annual average limit of 0.3 mL/L/hr to meet this design standard.

The removal of the discharge event maximum settleable solids limit for the four CSO satellite 

treatment plants is consistent with CWA section 402(o) and exceptions to the general prohibition 

outlined in anti-backsliding regulation at 40 CFR 122.44(l).
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Comment #2: Seattle Public Utilities
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Ecology’s response to Comment #2

Ecology has revised the sentence to indicate “appropriate BMPs” instead of “applicable 

BMPs”. Ecology did not intend to invoke the meaning of “applicable” as used in Volume IV 

of Ecology’s Stormwater Management Manual for Western Washington (2012).

Ecology agrees that stormwater management manuals approved by Ecology under a Phase 

I Municipal Stormwater Permit also contain appropriate BMPs. Such BMPs are determined 

to be functionally equivalent to the relevant portion of Ecology’s Stormwater Management 

Manual for Western Washington through a process associated with the Phase I Municipal 

Stormwater Permit. 

For this CSO-related permit requirement, Ecology agrees that use of Ecology’s Stormwater

Management Manual for Western Washington and/or use of functionally equivalent 

manuals approved by Ecology under a Phase I Municipal Stormwater Permit is acceptable 

for reference purposes in identifying “appropriate” BMPs. 

Ecology would also like to provide the following definitions of stormwater BMPs:

Stormwater Best Management Practices (BMPs) means schedules of activities, prohibitions 

of practices, maintenance procedures, and structural and/or managerial practices to 

prevent or reduce the release of pollutants. BMPs include treatment systems, operating 

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

disposal, or drainage from raw material storage. 

Equivalent BMPs means operational, source control, treatment or innovative BMPs which 

result in equal or better quality of stormwater discharge from a site than BMPs selected 

from the Ecology Stormwater Management Manual for Western Washington.