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^3. 

DEQ 

State of Oregon 

Department of 

Environmental 

Quality 

National Pollutant Discharge Elimination System 

PERMIT EVALUATION AND FACT SHEET 

Oregon Department of Environmental Quality 

Northwest Region 

2020 SW 4th Ave., Suite 400 

Portland, OR 97201 

(503) 229-5263 

Permittee: 

Existing Permit 

Information: 

Source Contact: 

Source Location: 

LLID 

Receiving Stream 

Proposed Action: 

Source Category 

Permit Writer: 

Tri-City Service District 

150 Beavercreek Rd, Suite 430, 

Oregon City, OR 97045 

File Number: 89700 

PermitNumber:101168 

Expiration Date: 4/15/2016 

EPA Reference Number: OR-0031259 

Doug Harbaugh (503) 557-2802 

Wastewater Quality Manager 

15941 Agnes Avenue 

Oregon City, Oregon 97045 

1227618456580-25.5D 

Willamette River 

Permit Renewal 

Application Number: 991528 

Date Received: 1/29/1998 

NPDES Major Domestic 

Etsegenet Belete 

Water Quality Specialist 
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Table of Contents 

1.0 Introduction 3 

2.0 Facility description 3 

2.1 General 3 

2.2 Wastewater Treatment 5 

2.3 Changes in Operation 7 

2.4 Groundwater Issues 8 

2.5 Storm Water 8 

2.6 Outfalls 8 

2.7 Industrial Pretreatment 8 

2.8Biosolids 9 

2.9 Inflow and Infiltration (I/I) 10 

3.0 Permit History 10 

3.1 Compliance history 11 

4.0 Receiving Water 12 

4.1 Receiving Stream Water Quality 13 

4.2 Mixing Zone Analysis 14 

4.3 Environmental Mapping 15 

5.0 Permit limitations 15 

5.1 Permit Limits 15 

5.2 Water Quality-Based Effluent Limits 16 

5.3 Whole Effluent Toxicity : 21 

5.4 Antidegradation 21 

6.0 Permit Draft Discussion 22 

6.1 Face Page 22 

6.2 Schedule A, Waste Discharge Limitations. 22 

6.3 Schedule B —Minimum Monitoring and Reporting Requirements 22 

6.4 Schedule C-Compliance Schedules and Conditions 22 

6.5 Schedule D - Special Conditions ..23 

6.6 Schedule E, Pretreatment Program Activities ..23 

6.7 Schedule F,NPDES General Conditions 23 

6.8 Permit Processing/Public Comment/Appeal Process -.,24 

Appendix A- Anti-degradation worksheet 25 

Appendix B (1&2)-Reasonable Potential Analyses 26 
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1.0 INTRODUCTION 

The existing National Pollutant Discharge Elimination System (NPDES) Permit expired on July 

31, 1998. The Department received renewal application number 991528 from Tri-City Service 

District for the Tri-City Waste Pollution Control Plant (Tri-City WPCP) on January 29, 1998. As 

this renewal application was submitted to the Department in a timely manner prior to the 

expiration date of the permit, the permit has been administratively extended until final action is 

taken on the renewal application to issue the new permit as per OAR 340-045-0040. 

This permit evaluation report describes the basis and methodology used in developing the permit. 

The permit is divided into several sections: 

Schedule A - Waste discharge limitations 

Schedule B - Minimum monitoring and report requirements 

Schedule C - Compliance Schedule 

Schedule D - Special conditions 

Schedule E - Pretreatment conditions 

Schedule F - General conditions 

The Federal Water Pollution Control Act of 1972 and subsequent amendments require a NPDES 

permit for the discharge of wastewater to surface waters. Furthermore, Oregon Revised Statutes 

(ORS) 468B.050 also require a discharger be granted a permit for the discharge of wastewater to 

surface waters. This proposed permit action by the Department complies with both federal and 

state requirements. 

The proposed permit contains the following substantive changes from the previous permit. 

• Schedule A includes more stringent effluent limits for CBOD5 and TSS, and an interim 

limit for ammonia. It also includes conditions and limitations regarding Recycled Water 

Use. 

• Schedule B has Priority Pollutant Scan and Bioassay testing requirements which are part 

of requirements of EPA Permit application form 2A. It also contains temperature 

monitoring, and UV intensity monitoring for the Membrane Bio-Reactor (MBR) 

treatment system. 

• Schedule D includes Whole Effluent Toxicity Testing conditions that have been revised 

since the last permit, Biosolids management conditions and Recycled Water Use 

conditions. 

• Schedule E has Pretreatment condition that has been revised since the last permit. 

• Schedule F of the proposed permit includes the latest edition, edited by the Department in 

September 2009. 

2.0 FACILITY DESCRIPTION 

2.1 General 

Tri-City Service District operates the Tri-City WPCP located in Oregon City, Oregon. Wastewater is 

treated and discharged to the Willamette River in accordance with National Pollutant Discharge 

Elimination System (NPDES) Permit No. 101168. The most recent Permit for the facility is a 

modification that was issued on August 1,1997. The permit modification expired on July 31, 1998. 
Figure 1: Facility Location 
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This proposed permit is a renewal that includes new requirements for the wet weather design of 

the existing facility. The Tri-City Service District is partnered with Clackamas County Service 

District No 1 to expand the liquid treatment capacity. The secondary treatment process expansion 

was needed to serve current growth and regional capacity needs. The permit provides for the diy 

and wet weather design of the expanded liquid treatment capacity. The mass load limits that are 

established for the existing seasonal flows are not increased for the expanded treatment capacity. 

A renewal permit is necessary to discharge to state waters pursuant to provisions of ORS 468B.050 

and the Federal Clean Water Act. The Department proposes to modify and renew the permit. 

2.2 Wastewater Treatment 

The Tri-City Service District owns and operates the Tri-City WPCP which is located at 15941 S 

Agnes Avenue on the east side of the Willamette River in the city of Oregon City. This is an 

activated sludge secondary treatment plant that treats the wastewater from Oregon City, West 

Linn, Gladstone and several unincorporated areas of the county. The facility began operation in 

1986. Most of the equipment placed in service around that time is still in use today. Various 

pumps were added around the facility to improve solids handling. 

The plant was operating at 95 to 100 percent of its design capacity on average with maximum day 

loadings reaching design capacity. The actual average wet weather flow (November 1 through 

April 30), for the years 2006-2009 was 11.13 MGD. The current actual average diy weather flow 

(May 1 through October 31) for 2006-2009 was 7.01 MGD. 

The secondary treatment process expansion is leased space for CCSD # 1 to serve current growth 

and regional capacity needs. This capacity increase was accomplished by the addition of a new 

parallel Membrane Bio-Reactor (MBR) system. The dry season design capacity increased to 17.1 

MGD. The District completed startup and operation of the expanded facility in Spring, 2011. 

This proposed permit incorporates the expansion of the liquid treatment capacity. The permit 

provides for the dry and wet weather design of the expanded liquid treatment capacity. For this 

expansion, the summer and winter design flow will increase but the mass load limits remain the 

same. The concentration of BOD5, CBOD5 equivalent and TSS are reduced from 20 mg/L to 10 

mg/L. These new limits reflect the Willamette basin treatment standards prescribed in Oregon 

Administrative Rules for periods of low stream flow (OAR 340-041-0345(3)(a)(A)). Percent 

removal is dependent upon the average monthly influent concentration. Mass load limits are waived 

when the influent flows exceed twice the expanded dry weather design flow. 

The current treatment plant consists of the pre-existing activated sludge treatment and the new 

MBR treatment system. The two treatment systems function independently and effluent from the 

two treatments is mixed before discharge to the receiving stream. 

Conventional Activated Sludge (CAS) Treatment System: 

The CAS treatment plant is made up of a series of unit processes. Each unit process performs a 

specific function to aid in the treatment of the wastewater. 

Influent Pump Station 

The wastewater enters the facility through the influent pump station. In the influent pump station, 

there are two 5,000 gpm (7.2 MGD) and three 12,500 gpm (18 MGD), variable frequency speed 

pumps. 

Headworks 

Primary treatment includes the headworks and primary ciariflers. The headworks provide 

screening and grit removal where the influent is screened to remove materials with four bar 
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screens: one 4ft wide (10.4 MGD) mechanically cleaned bar screen, two 7 ft wide (25 MGD), 

mechanically cleaned bar screens and one 7 ft wide (25 MGD) manually cleaned bar screen. The 

mechanical bar screens prevent rags, plastic, and medium and large debris from entering the 

treatment process. The screened material is conveyed to a hopper where it is collected for 

disposal to a solid waste landfill. 

Once the influent flow passes the screens it flows through parshall flumes. The parshall flumes 

measure the amount of influent flow. From there a common channel directs the flow to the 

aerated grit basins. The grit basins remove inert particulate matter from the screened raw sewage 

to reduce abrasive wear on downstream pumps and equipment and reduce the amount of material 

that settles in the primary, secondary and solids processing tanks. Grit is removed in two 55,023 

gallon aerated grit chambers. The grit settles to the bottom of the grit chambers where is it 

pumped as slurry to hydrocyclone de-gritters and classifiers for separation from the water. The 

grit is washed in the grit washers and removed for disposal to a solid waste landfill. 

A septage receiving station is also located in the headworks screening building. Septage haulers 

discharge septage into a receiving vault equipped with a bar rack. Septage is contained in the 

10,000 gallon septage storage tank. The septage storage tank is located next to the grit chambers 

building complex. Septage tank waste enters the treatment system after the influent pump station 

prior to screening in the screening approach channel. 

The screening headworks building is completely enclosed and ducted to odor control equipment. 

Primary Clarifiers 

After screenings and grit removal, the influent flows to the primary clarifiers. Influent sluice 

gates to the primary clarifiers were put under automatic operation this past summer to manage 

flows to the primary clarifiers. The primary clarifiers concentrate the "settleable" portion of the 

suspended solids in the wastewater. Six primary clarifiers provide conditions which allow solids 

in the wastewater either to settle or to float. Settled solids also called "sludge" is collected in the 

primary basin's deep sludge collection hoppers, which is then pumped to the anaerobic digesters 

for further processing. The scum that floats on the top is collected with a skimmer and removed 

to the anaerobic digesters as well. 

Secondary Treatment 

The activated sludge process provides secondary treatment to plant flows below 25 MGD. The 

activated sludge process removes suspended and dissolved organics that were not removed in the 

primary treatment process by creating an environment for micro-organisms to metabolize the 

food in the wastewater. The secondary treatment system consists of four 639,000 gallon aeration 

basins with fine pore diffusers and an anoxic zone at the front end of each basin. In September 

2001, a $1 million dollar project was approved for improving the efficiency and effectiveness in 

all four aeration basins of treatment facility. The anoxic zone of the aeration basin was further 

divided into 3 chambers while keeping the aeration zone to further improve biological nutrient 

removal. Dissolved Oxygen probes with motorized butterfly valves were also added to provide 

automatic oxygen control. 

The aeration basin creates an environment for biological treatment of the wastewater. The result 

is sludge that settles out for separation and removal in the secondary clarifiers. There are two 120 

ft diameter secondary clarifiers each with side water depths of 18 feet. Floating scum from the 

secondary clarifiers is collected with a skimmer and removed to the anaerobic digesters. A 

hydrogen peroxide solution that feeds directly to the return activated sludge line to control 

filamentous bacteria was installed in April 2003. 
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Disinfection 

The secondary effluent is disinfected prior to discharge. Chlorine dosage is controlled by the 

effluent flow meter prior to the chlorine contact basin. Contact time is provided in the two 

274,500 gallon chlorine contact basins, hi 1995, a sodium bisulfite dechlorination system was 

added. The treated effluent is dechlorinated with sodium bisulfite prior to discharge. 

Membrane Bio-Reactor (MBR) Treatment System: 

The MBR facility is designed to provide treatment of the flows entering the treatment plant in 

conjunction with the CAS system. All flow from the MBR system is combined with the CAS 

system prior to discharge. This combined flow is required to meet the discharge criteria of the 

NPDES permit. In addition, the MBR treatment system treats to a level that will allow the 

distribution of reclaimed water that meets the current reuse requirements in OAR 340-055. 

The MBR treatment system includes Fine Screenings Building, Aeration Basins, Blower 

Building, Membrane Filtration Building and Ultraviolet (UV) Disinfection Building. Primary 

effluent feed to the two aeration basins is by gravity from the fine screen building and flow is 

split evenly between the two basins. Mixed liquor from the aeration basins is then transferred into 

the submerged MBR basins. Treated effluent from the MBR is conveyed to the UV disinfection 

area before discharge. 

2,3 Changes in Operation 

hi January 2000, the Tri-City WPCP started accepting flow from the Kellogg Creek wastewater 

treatment plant in order to reduce loading to the Kellogg treatment plant, but there is no direct 

connection between the two facilities. Planning and construction schedules for the Tri-City 

WPCP is discussed as part of the Kellogg Creek Mutual Agreement and Order (MAO) No. 

WQ/M-MWR-08-067. 

The Tri-City WPCP put diversion into place to reduce loads for the Kellogg Creek wastewater 

plant. On average, 0.6 MGD during dry weather with peak wet weather flow of about 1.5 MGD 

was pumped from Kellogg. In 2009, following an upgrade to the Clackamas Pump Station, the 

phase I diversion project was placed on line. With this diversion, flow increased to an average 1.5 

MGD with a peak of 2.5 MGD during wet weather. 

Upon startup of the MBR system, wastewater from the Kellogg Creek treatment facility can be 

diverted to the MBR facility. At that time, upgrades to the conventional activated sludge system 

will begin. Upgrades will include installation of new Mixed Liquor Suspended Solids (MLSS) 

recirculation pumps, new aeration diffusers and new process air blowers to help the system with 

increased energy efficiency and improved nitrification/de-nitrification. In July 2012, the new 

diversion pump station with the capacity of 2-4 MGD diy weather flow and 10 MGD of peak 

flow will be completed. Upon completion of the MBR facility and the diversion systems, the total 

increased flow from the Kellogg plant will be about 6-8 MGD of diy weather flow with peak 

flow of 17.5 MGD during wet weather. 

Tri-City upgraded the redundancy power to the facility after the power outage on November 22, 

2009. During that time, the 115kV transmission line fell into the 13kV primary lines causing both 

feeders to become de-energized. Following the incident, PGE removed the double circuit to 

eliminate the preferred and alternate circuits being taken out by a single source event. There 

remains two common tie points between both the preferred and alternate feed (source) to TriCity. One of the common tie points is down stream of fuses thus if a fault occurs between the 

switch and upstream fuses, the preferred and alternate sources to Try-City will remain in service. 
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In addition, the expanded MBR facility includes a stand alone generator that will provide power 

to the main influent pump and to the MBR part of the treatment. This will provide treatment 

without discharge of untreated effluent if the two main power sources to the facility fail. 

2.4 Groundwater Issues 

Based on the Department's current information, this facility has a low potential for adversely 

impacting groundwater quality. Therefore, Schedule D of the proposed permit states that no 

groundwater evaluations will be required during this permit cycle. The permit also includes a 

condition in Schedule A that prohibits any adverse impact on groundwater quality. 

2.5 Storm Water 

Stormwater discharge from the facility is covered under the District's NPDES Industrial 

Stormwater Discharge 1200Z Permit (File no. 110122). 

2.6 Outfalls 

The existing outfall conveys the final plant effluent through 1.1 miles of piping to the Willamette 

River. There is approximately 3,142 feet of 72- inch pipe between the chlorine contact basins and 

the flow control structure for the outfall. From the discharge distribution box there are three 40-feet 

long, 42-inch diameter lines that discharge the final effluent to the Willamette River at river mile 

25.5 using the LLID reference point (or 25.2 when using a USGS topographic map). The outfall 

diffuser consists of three (3) 42-inch diameter discharge ports that discharge below the surface during 

diy weather (low river flow) conditions at a depth of approximately 7 feet. The diffuser axis is 

aligned parallel to the river flow, with the diffuser ports discharging at 45° relative to the direction of 

the river flow. 

Outfall inspection was conducted in August 2010 by Advanced American Construction, Inc., and all 

three pipes were free of upsets and abnormalities. There was no accumulation inside the pipes. 

2.7 Industrial Pretreatment 

The Tri-City Service District implements an industrial pretreatment program originally approved and 

incorporated into the permit on December 21,1983. Federal and state pretreatment requirements 

were included in the NPDES permit for this facility when the previous permit was issued. 

On December 30, 1996, Tri-City Service District submitted to the Department proposed 

modifications to their industrial pretreatment program procedures in response to findings of the 

Department's April 4, 1996, pretreatment compliance inspection. On December 4,1998, the TriCity Service District provided public notice of the proposed modifications of the Procedures 

Manual in accordance with requirements of 40 CFR 403.18 and 403.11. Tri-City Service District 

notified the Department on January 11,1999, that no comments and no requests for public 

hearing were received regarding these modifications. In accordance with 40 CFR 403.11(d), EPA 

was given 30 days to review the modification. The final DEQ approval was granted on March 1, 

1999. The Agency also approved pretreatment program modifications that include RCRA 

notification procedures and forms on August 6, 1999, and revisions to the Enforcement Response 

Guidance on November 13,2002. These modifications to the pretreatment program are hereby 

incorporated into the NPDES permit by reference. 

On June 15,2001, Tri-City Service District received a Notice of Noncompliance SWM/NWRWQ-01 -066 for failure to furnish the Department requested information within a reasonable time, 

and failure to enforce its pretreatment program as approved by the Department. On November 

30,2001, the Audit Report indicated that the items in the Notice of Noncompliance were 

satisfactorily addressed. On February 2009, the Department approved the District's request for 
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Pretreatment Program Non-Substantial Modification, responding to August 2008 pretreatment 

compliance audit. 

The District will be conducting an evaluation of the need to revise their technically-based local limits 

within 18 months after the re-issuance of this NPDES permit. The local limits evaluation will 

include an evaluation of the headworks loading criteria and possible sources of the various pollutants 

being evaluated. 

The USEPA revised the federal pretreatment streamlining rules (40 CFR § 403) effective November 

14,2005. The District will be implementing program modifications to reflect the voluntary and 

mandatory changes during 2006 which will result in modifications to Schedule E, Pretreatment 

Activities, in the future to incorporate streamlining-related changes. 

2.8 Biosolids 

Solids generated in the primary clarifiers and secondary clarifier treatment are processed and then 

stabilized in two anaerobic digesters. The initial processes thicken the solids. The primary solids are 

thickened in deep hoppers in the primary clarifiers and the secondary solids are thickened using 

gravity belt thickeners prior to pumping to the digesters. Polymers are used in the thickening 

process. Thickening reduces the volume of the sludge added to the digesters. Two fixed cover 

65-ft diameter digesters and associated equipment provide for the stabilization and digestion of 

the solids generated in the treatment plant. The contents of the digesters are mixed with pump 

mixers. Digester gas that is produced is utilized in an engine generator producing up to 250kW of 

electrical power. It is anticipated that with the facility expansion solids handling will change. Waste 

Activated Sludge (WAS) streams of the MBR and the conventional activated sludge systems will 

be conveyed to the gravity belt thickeners for thickening. The two existing gravity belt thickeners 

will be dedicated to each process stream. This permit requires monitoring of the methods used to 

comply with vector attraction and pathogen reduction requirements. It also requires the submittal 

of an annual summary. 

Biosolids must be managed in accordance with the Department approved Biosolids Management 

Plan to ensure compliance with the Oregon and federal biosolids regulations (40 CFR Part 503). 

The Tri-City Service District will submit a revised biosolids management plan as part of a 

requirement of this permit. Once the biosolids management plan has been reviewed and approved 

the management plan will be placed on public notice. 

Monitoring results for metals content in the final product to be land applied are noted below. All 

metals concentrations appear to be well below EPA pollutant concentration limits. 

Parameter 

Arsenic 

Cadmium 

Copper 

Lead 

Mercury 

Molybdenum 

Nickel 

Selenium 

Zinc 

Concentration 

(mefks) 2/2/2010 

2.83 

<9.30 

480 

19.17 

1.16 

<9.20 

< 13.9 

4.3 

893 

Concentration 

(me/ke) 8/10/2009 

4.10 

< 13.40 

535 

<26.85 

0.95 

< 13.42 

<20.1 

<6.6 

1000 

EPA Pollutant 

Concentration Limits 

dne/ke) 

41 

39 

1500 

300 

17 

75 

420 

100 

2800 
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2.9 Inflow and Infiltration (I/I) 

Tri-City is a regional sewerage agency; the local collection facilities are owned, operated and 

maintained individually by the cities of Gladstone, Oregon City and West Linn. Between 1986 and 

1992 Tri-City, Gladstone, Oregon City and West Liim went though a major combined sewer 

separation program to disconnect street storm water inlets from the sewer system. This program 

reduced the peak flow to the wastewater treatment facility; however inflow and infiltration (I/I) are 

still problems. 

Wet Weather Mass Load Increase 

Tri-City submitted the Tri-City Service District Sewerage Master Plan prepared by WES and 

CH2MHH1, (Oct 1998) which contained technical memoranda describing and supporting the 

design average wet weather flow and percent removals. The Department approved the 

engineering study which supported the change in the wet weather mass load increase and percent 

removal requirements. 

In addition, the wet weather mass load increase is allowed provided the facility follows an 

approved program and time schedule for identifying and reducing inflow. The approved program 

and time schedule is usually begun after a permit modification for the mass load increase has 

been issued; however, for a number of years, the Tri-City Service District has been actively 

pursuing the reduction of infiltration and inflow (I/I) to the Tri-City WPCP. Between 1986 and 

1992, twelve combined sewer overflows were plugged as part of a major combined sewer 

separation project. 

The 1998 Tri-City Service District Sewerage Master Plan conducted analysis to identify sewerage 

basins which are large contributors to I/I. This analysis is also presented in Appendix C in the 

Master Plan technical report submitted to DEQ in March 1999. This analysis resulted in 

recommendations for selective smoke testing and televised inspections in local basins where I/I 

problems have been identified. This permit renewal includes the same requirement in Schedule C in 

order to receive an updated program with a look at where the program and time schedule is for 

continuing to identify and address reducing inflow. 

The proposed permit wet weather mass load for the facility is calculated based on the existing plant 

design capacity; average design wet weather flow of 13.5 MGD. 

3.0 PERMIT HISTORY 

The permit that was issued in June 28,1991, was for a permit renewal that was administratively 

extended from July 31, 1988. The permit was issued with an expiration date of May 31,1996. The 

permit contained concentration, mass load and percent removal limits of BOD5 and TSS as well as 

permit limits for fecal coliform, pH and chlorine residual. The 1.5 mg/L permit limit for chlorine 

residual was subject to modification based upon the results of a mixing zone study. The size of the 

mixing zone was described as a 150 foot radius from the point of discharge. The permit also 

contained a condition with higher mass load limits for BOD and TSS when the combined sewer 

systems caused the monthly average flow going into the treatment facility to go above the average 

design dry weather flow of 8.4 MGD. The permit was issued along with a Stipulation and Final 

Order (SFO) No. WQ-NWR-91-80. The SFO contained a requirement to complete the separation of 

the remaining combined portions of the Oregon City and Gladstone sewage collection systems. The 

1991 permit was appealed after issuance; the appeal for Tri-City Service District and six other parties 

was settled in November 1993. An outcome of the appeal was a rule change in OAR 340-041-0120 

(now OAR 340-041-0061(10)) to recognize that mass load limits could be based on a wet weather 

design flow of the treatment facility. On December 10,1993, the permit was issued with an 
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expiration date of July 31,1998 and SFO No. WQ-NWR-91-80 was superseded by SFO No. 

WQMW-NWR-93-108. 

On September 13,1994, the permit was modified, to incorporate the results of the mixing zone study 

and include revised permit limits for chlorine residual. The chlorine residual permit limits are a daily 

maximum limit of 0.05 mg/L and a monthly average limit of 0.02 mg/L. The mixing zone was 

redefined as 300 feet downstream of the point of discharge with a zone of initial dilution of 30 feet 

downstream. The diy season BOD5 was changed to the equivalent of CBOD5. The CBOD5 

concentration limits are considered equivalent to the minimum design criteria for BOD5 specified 

in OAR 340-041. The permit allowed for the percent removal requirements to be changed upon 

request and based on the approval of an engineering evaluation. The permit expiration remained July 

31,1998. 

Two pretreatment Permit Action Letters were issued. A permit action letter was issued in August 14, 

1995, to incorporate approved local limits into the pretreatment program. A permit action letter was 

issued in September 22, 1995, to incorporate approved changes in the rules and regulations of the 

pretreatment program. 

On February 27,1997, after discussions with the DEQ, Tri-City Service District applied for a 

modification of the permit to put the remaining requirement from SFO No. WQMW-NWR-94-047 

into the permit. On August 1, 1997, the permit was modified to include a schedule for completing a 

basin-wide evaluation of alternatives, and to provide capacity at the Bolton pump station adequate to 

accommodate estimated flows under a one in five-year storm event. Tri-City Service District 

completed the other requirements in SFO No. WQMW-NWR-94-047. The remaining requirements 

relating to the Bolton pump station were transferred to the compliance schedule in Schedule C and 

SFO No. WQMW-NWR-94-047 was terminated. The permit limits remained the same as the 

previous permit issued on September 13,1994. The permit allowed for the percent removal 

requirements to be changed upon request and based on the approval of an engineering evaluation. 

The permit expiration remained July 31,1998. 

This permit action is a renewal of the permit that was issued on August 1,1997. The proposed 

permit regulates CBOD5 and TSS concentrations year round. The proposed permit includes 

modifications for the diy weather concentration of CBOD5 and TSS based on Basin Standard. 

Percent removal efficiencies to reflect the dilute wet weather flows are proposed. Mass load limits 

will be waived when influent flows exceed twice the design average diy weather flow. The bacteria 

standard was changed in 1996 from fecal coliform to __. coli. This permit renewal includes bacteria 

limits for E. coli. 

The proposed permit incorporates the expansion of the liquid treatment capacity. The secondary 

treatment process expansion is needed to serve current growth and regional capacity needs. The 

necessary capacity increase is accommodated through addition of the MBR facility operating in 

parallel to the conventional activated sludge system. The permit provides for the dry and wet 

weather design of the expanded liquid treatment capacity. For this expansion, the summer and 

winter design flow will increase but the mass load limits remain the same. 

3.1 Compliance history 

The permit that was issued on August 1, 1997 contained the remaining requirements of Stipulated 

Final Order No. WQMW-NWR-94-047. The remaining requirements were placed into Schedule 

C condition No. 3.a. through c. in the permit. 
Page 12 of 29 

• Condition Nos. 3.a. and 3.b. were satisfied upon the receipt of the Bolton Pump Station 

report on September 1, 1998. A November 30, 1998 letter from DEQ to Tri-City Service 

District refers to the review of the report. 

• Condition No. 3.c. was satisfied when a new gravity interceptor was placed in operation 

on December 14,2001. The preliminary design report dated March 29,2001, contains 

the detailed design calculations for the project to show that the pump station is adequate 

to accommodate estimated flows under a one in five-year, 24 hour storm event. 

Notice of Noncompliance (WQ/D-NWR-02-053) was issued on September 3,2002, for 

exceeding the mass load limits for TSS and CBOD5. 

Notice of Violation and Assessment of Civil Penalty No. (WQ/M-NWR-02-172) was written for 

sewage spills that occurred on August 2,2002, and November 6,2002. 

Notice of Noncompliance (WQ/D NWR-03-0048) was written for exceeding the weekly fecal 

coliform geometric mean in January 2003. 

Notice of Noncompliance (WQ/D NWR-04-0080) was written on June 28, 2004, for exceeding 

the mass load limit for TSS. 

Warning Letter (WL-NWR-WQ-2005-0070) was written on August 24,2005, for a late 

stormwater sampling annual report. 

Notice of Violation (NWR-WQ-06-169) was written because during the week of October 8, 2006, 

the facility failed to monitor for total kejldahl nitrogen and total phosphorus. 

Warning Letter (WL-NWR-WQ-08-0107) was written on October 9,2009, for construction 

commencing without Department approval in the spring of 2009. 

Notice of Violation and Assessment of Civil Penalty No. (WQ/M-NWR-09-041) was issued on 

March 31,2009, for multiple exceedances of CBOD5 and TSS values between December 28, 

2008 and January 3, 2009. 

Warning Letter (NWR-WQ-09-0147) was written for sewage spills that occurred on November 

22, 2009, due to primary and secondary power failure. This problem has since been corrected and 

the facility currently has triple power redundancy. 

Notice of Noncompliance (NWR- WQ-10-0067) was issued on May 10,2010, for exceeding the 

mass load limits for CBOD5. 

4.0 RECEIVING WATER 

The Tri-City WPCP discharges to the Willamette River. The water quality standards for all water 

bodies (Oregon Administrative Rules 340-41) and specifically the Willamette Basin (Oregon 

Administrative Rules 340-41 -0345) were developed to protect the beneficial uses for the basin. The 

designated beneficial uses of the Willamette River Basin from the mouth to Willamette Falls are 

listed below: 

• Private Domestic Water Supply 

• Public Domestic Water Supply 

« Industrial Water Supply 
Page 13 of 29 

Irrigation 

Livestock Watering 

Fish & Aquatic Life 

Wildlife & Hunting 

Fishing 

Boating 

Water Contact Recreation 

Aesthetic Quality 

Hydro Power 

Commercial Navigation & Transportation 

4.1 Receiving Stream Water Quality 

The Department is required by the Federal Clean Water Act, Section 303(d) to identify all water 

bodies in Oregon that do not meet water quality standards. Once identified, the stream segments are 

placed on the DEQ's "303(d) list". This listing means that the standards that protect the most 

sensitive beneficial uses of the water are not being met and the Department is required to establish a 

plan with goals and pollution control targets for improving water quality. 

The "303(d) list" provides a way to identify and prioritize water quality problems. The list also 

serves as a guide for developing and implementing watershed pollution reduction plans to achieve 

water quality standards and protect beneficial uses. 

From river mile 24.8 to 54.8, the Willamette River is listed for the following parameter's: 

Parameter 

Toxics 

Iron 

Biological Criteria 

C riteria/Stand a rd 

Fish Tissue-DDT 

and DDT'Metabolite (DDE) 

Fish Tissue-PCB 

Fish Tissue —Aldrin 

Fish Tissue -Dieldrin 

RM 34 and 48 Table 20 > 300 ug/L drinking water 

Skeletal deformities in squawfish 

Season 

Year Round 

Year Round 

Year Round 

Year Round 

Year Round 

NA 

A Total Maximum Daily Load (TMDL) for the Willamette River for temperature, bacteria and 

mercury was approved by both DEQ and EPA in September 2006. hi the TMDL for bacteria, 

individual municipal discharges are required to comply with the water quality standard for E. coli. A 

permit limit for E. coli bacteria has been set and meets this requirement. A separate Department 

Order will be written for mercury sampling. The facilities included in the Department Order will 

be required to follow those sampling and analysis requirements. The temperature thermal load 

limits are included as part of this permit. 

Toxics such as Aldrin, Dieldrin, PCB, DDE and DDT are not known to be introduced to the 

domestic wastewater treatment facility through production or manufacturing processes. They are 

not considered to be present above trace background levels. 

Skeletal deformities in fish is a separate study, this source has not been evaluated for its 

contribution to skeletal deformities in squawfish. A recent study entitled Environmental Stresses 

and Fish Deformities in the Willamette River Project Status Report (December 2003) conducted 

by Departments of Environmental and Molecular Toxicology, Microbiology, and Fisheries and 

Wildlife, Oregon State University, Corvallis, Oregon, indicates that parasites are major 

contributors to high prevalence of skeletal deformities in fish from the Newberg Pool section of 

the Willamette River. 
Page 14 of 29 

Iron is listed as exceeding the drinking water standards because iron and manganese can be 

aesthetically unappealing in drinking water. RPA shows that there is no reasonable potential for 

iron in the Tri-City effluent discharge. 

4.2 Mixing Zone Analysis 

Federal regulations (40 CFR 131.13) allow for the use of mixing zones, also known as "allocated 

impact zones". These are small areas around a discharge where water quality standards may be 

suspended. Application of mixing zones must ensure acute toxicity to drifting organisms is 

prevented and the integrity of the waterbody as a whole is not impaired. EPA does not have 

specific regulations pertaining to mixing zones. Each state may adopt its own mixing zone 

regulations that are subject to review and approval by EPA. In States that lack approved mixing 

zone regulations, ambient water quality standards must be met at the end of the pipe. OAR 340-

041-0053(1) provides that the Department may suspend all or part of the water quality standards 

in a designated portion of the receiving water to serve as a zone of dilution for wastes and 

receiving waters to mix thoroughly. 

The Department has developed mixing zone regulations and policy based in part on the acute and 

chronic aquatic life criteria. Based on EPA guidance and the Department's mixing zone 

regulations, two mixing zones may be developed for each discharge that reflect acute and chronic 

effects: 1) The acute mixing zone, also known as the "zone of initial dilution" (ZID), and 2) the 

chronic mixing zone, usually referred to as "the mixing zone". Acute criteria are suspended 

within the ZID but it is designed to prevent lethality to organisms passing through the ZID. 

Chronic criteria are suspended within the mixing zone and are designed to protect the integrity of 

the entire water body as a whole. The allowable size of the mixing zone should be based upon 

the relative size of the discharge to the receiving stream, the beneficial uses of the receiving 

stream, location of other discharges nearby, location of drinking water intakes, and other 

considerations. More specific guidance is available from EPA regarding criteria used in 

appropriately sizing a ZID. Primarily the ZID must be designed to prevent lethality to drifting 

organisms. 

The first mixing zone study entitled 'Mixing Zone Evaluation for TCSD Outfall of the Tri-City 

WPCP' was conducted for Tri-City Service District by Liberie Environmental Associates in October 

2001. The CORMDC2 model was used to simulate 7Q10 critical low river flow of 5430 CFS based 

on the USGS statistical flow data from Wilsonville. The modeling was refined using data from the 

Tri-City WPCP Mixing Zone Field Study (Volume 2 of 3). The field study includes data that was 

collected during low river flows in August 2001. The field study results were adjusted to critical 

conditions to simulate the mixing zone. 

hi October of 2007 the District provided additional velocity measurement at the Tri-City outfall site 

in a Teciniical Memo titled "Current Velocity Measurement at the Tri-City and Kellogg Creek 

WPCP Outfall Sites-CIackamas WES". 

hi May 2010, this data was used in conjunction with the 2001 data in CORMIX v6.0 modeling to 

predict plume trajectory and dilution. A full level 3 study will be completed in late summer or early 

fall of 2010. The allowable mixing zone (RMZ) is that portion of the Willamette River which 

extends 300 feet downstream of the point of discharge. The zone of initial dilution (ZID) is that 

portion of the Willamette River which extends 30 feet downstream of the discharge point. At the 

zone of initial dilution and at the edge of the mixing zone, a dilution was derived for the facility 

expansion from the mixing zone study data. A facility flow of 17.1 was substituted in the equations. 

Dilution at the edge of mixing zone is 13.9 and the dilution at the zone of initial dilution is 3.3. 
Page 15 of 29 

4.3 Environmental Mapping 

Environmental Mapping was completed as part of the mixing zone study completed in July of 

2010. The study indicates that the Willamette River outfall structure is located adjacent to the 

Willamette River at approximately river mile 25 on the right shoreline, just upstream from where 

Clackamas River joins. There are no commercial / recreational shellfish or cold water refugia 

areas near the Tri-City outfall location. Fish use for the area, including at the Clackamas 

confluence are Summer Steelhead and Coho Salmon migration; Winter Steelhead rearing and 

Chinook Salmon rearing and spawning. Bald Eagle and N. Spotted Owl are the two possible 

threatened or endangered species that may have presence, habitat or migration pathways near the 

outfall location. 

Fishing occurs in the Willamette and Clackamas River. Oregon Department of Human Services 

fishing advisories for the main stem of the Willamette River continue. The Department of 

Human Services recommends that consumers limit their consumption of resident fish from the 

Willamette River. This advisory does not relate to migrating ocean fish such as salmon, steelhead, 

shad or lampreys. Fish use the mouth of the Clackamas River as a holding area. The fish are 

present there for a longer period of time before continuing their migration. There is a fishing spot 

that is dubbed 'the garbage hole' which is located above the outfall. The 'garbage hole' is a 

deeper area (slightly deeper than 15 feet) in the Willamette River that fish tend to hold up in. The 

side of the river that the outfall is located has been altered by rip rap and as such is faster moving 

the area that fish tend to move right through. 

5.0 PERMIT LIMITATIONS 

Two categories of effluent limitations exist for NPDES permits: 1) Technology based effluent 

limits, and 2) Water quality based effluent limits. Technology based effluent limits are developed 

by applying the national effluent limitation guidelines (ELGs) established by EPA for specific 

industrial categories. Technology based effluent limits were established to require a minimum 

level of treatment for industrial or municipal sources using available technology. Water quality 

based effluent limits are designed to be protective of the beneficial uses of the receiving water 

and are independent of the available treatment technology. In addition, when performing a permit 

renewal, there are existing permit limits. These may be technology-based limits, water qualitybased limits, or limits based on best professional judgment. When renewing a permit, the most 

stringent of technology based or water quality based limits apply. 

5.1 Permit Limits 

Treated Effluent Outfall 001 (Wastewater treatment facility discharge) 

(1) May 1 - October 31: 

Parameter 

CBOD5 

TSS 

Average Effluent 

Concentrations 

Monthly Weekly 

10 mg/L 15 mg/L 

10 mg/L 15 mg/L 

Monthly* 

Average 

lb/day 

1050 

1400 

Weekly* 

Average 

ib/day 

1750 

2100 

Daily* 

Maximum 

lbs 

2100 

2800 

(2) November 1-April 30: 

Parameter 

CBOD5 

TSS 

Average Effluent 

Concentrations 

Monthly Weekly 

25 mg/L 40 mg/L 

30 mg/L 45 mg/L 

Monthly* 

Average 

lb/day 

2800 

3400 

Weekly* 

Average 

Ib/day 

4500 

5100 

Daily* 

Maximum 

lbs 

5600 

6800 
Page 16 of 29 

* The winter mass load limits are based upon average wet weather design flow prior to expansion 

(13.5 MGD). The daily mass load limit is suspended on any day in which the flow into the 

treatment facility exceeds 23.8 MGD (twice the design average diy weather flow). 

(_i 

Other parameters (year-round) 

E. coli Bacteria 

pH 

BOD5 and TSS Removal Efficiency 

Total Chlorine Residual 

Ammonia (Interim limit) 

Limitations 

Shall not exceed 126 organisms per 100 mL monthly 

geometric mean. No single sample shall exceed 406 

organisms per 100 mL. 

Shall be within the range of 6.0 - 9.0 

Shall not be less than 85% based on a monthly 

average for BOD5) and shall not be less than 85% 

based on a monthly average for TSS. 

Shall not exceed an average monthly concentration 

of 0.02 mg/L and a maximum daily concentration of 

0.04 mg/L 

Shall not exceed a monthly average of 15 mg/L 

BOD^/CBODsand TSS concentration and mass limits for secondary treatment expansion 

After the expansion, the facility will have of average diy weather design flow of 11.9 MGD and 

wet weather design flow of 17.1 MGD. The BOD5 and TSS mass load limits will remain the same 

as the previous permit. The monthly concentration limit of BOD5 and CBOD5 which is the 

equivalent of BOD5 will be reduced to 10 mg/L; and the TSS monthly concentration limit will be 

reduced to 10 mg/L based on the Willamette basin standard. 

BOD and TSS Percent Removal Efficiency 

BOD is required to meet 85 percent removal efficiency. The federal secondary treatment 

regulations allow for exceptions to the 85 percent removal efficiency limitation for wastewater 

treatment facilities with a separate sewer system under 40 CFR Part 133.103(d). To qualify for 

this exception, there are three conditions to meet. DEQ determined that the Tri-City WPCP 

qualified for exceptions based upon information provided to the department in 1998. Upon 

further consideration, DEQ determined that the Tri-City WPCP does not meet the three 

conditions necessary to allow exceptions to the BOD and TSS percent removal efficiency. 

Namely, the Tri-City WPCP has consistently met the 85% removal requirement in recent years. 

Therefore, the proposed permit requires 85% removal of BOD and TSS. 

5.2 Water Quality-Based Effluent Limits 

Reasonable Potential Analysis 

The Department performs an analysis to determine if there is a reasonable potential to cause or 

contribute to violations of instream water quality criteria. The Department has adopted EPA's 

recommended methodology for performing a reasonable potential analysis (RPA). This 

methodology was developed primarily for acute and chronic criteria but can be adapted to other 

criteria based on different frequencies and durations. This RPA takes into account effluent 

variability, available dilution (if applicable), and receiving stream water quality. The RPA for 

specific parameters are discussed below. 

In accordance with DEQ's "Internal Management Directive for Reasonable Potential Analysis for 

Toxic Pollutants" (September 2005), domestic sources like Tri-City Service District with a diy 

weather design flow greater than 1.0 MGD must be characterized for chlorine and ammonia as 

well as other potentially toxic parameters identified in their renewal application. A summary of 

the RPA results based on the most recent mixing zone study is provided as an attachment. The 
Page 17 of 29 

RPA spreadsheet using data from the most recent permit cycle indicates that there is no 

reasonable potential for toxic pollutants to cause or contribute to an excursion above State water 

quality standards. However, the reasonable potential analysis indicates that the existing facility 

has the potential to cause or contribute to a violation of water quality standards for ammonia. 

Expansion of the liquid treatment capacity: The same data was used to evaluate the expanded 

treatment capacity using a dilution of 3.3 at the zone of initial dilution and 13.9 at the edge of the 

mixing zone. The reasonable potential analysis indicates that the existing facility has the 

reasonable potential to cause or contribute to a violation of water quality standards for ammonia. 

Ammonia 

The Reasonable Potential Analyses shows that the facility's discharge ammonia concentration 

exceeds the chronic water quality standard and has a reasonable potential to pollute. The previous 

permit had no permit limit for ammonia in the discharge, and the Tri-City WPCP cannot 

immediately comply with the effluent limit that was calculated based on the RPA. Therefore, a 

Mutual Agreement and Order (MAO) has been developed that includes a requirement for Tri-City 

WPCP to reduce the ammonia concentration to the level of compliance by providing additional 

treatment through process, or re-designing the outfall to improve the dilution in the receiving 

stream. The MAO includes compliance dates for an administrative and engineering feasibility 

study, completion of construction/start up, and interim effluent limit for ammonia in the effluent. 

If the facility chooses to redesign the outfall, with outfall improvement and better diffusion, the 

dilution associated with the mixing that occurs within the zone of initial dilution and edge of the 

mixing zone may change. The reasonable potential analysis will be re-evaluated after the 

requirement is addressed. 

Chlorine Residual 

Water quality standards for chlorine are based on preventing both acute and chronic toxicity. The 

acute chlorine standard in 0.019 mg/L and chronic chlorine standard is 0.011 mg/L. The facility 

used chlorine gas for the disinfection of effluent to comply with the effluent limits for bacteria. 

Sodium bisuffate is used for dechlorination. Effluent is reflective of the use of the dechlorination 

system and effluent values have typically been in the 0.003 mg/L range. A permit limit remains 

in the permit to indicate the amount of chlorine residual that would cause a water quality violation 

if the equipment were not operating properly. 

The pH is a measure of how acidic or basic a solution is. At a pH of 7.0 s.u. the solution is 

considered neutral. The purpose of an in-stream water quality pH standard is generally the protection 

of aquatic life since most aquatic organisms can only tolerate a fairly narrow range around 7.0 s.u. 

The Willamette Basin Water Quality Standard for pH is found in OAR 340-041-0290(l)(a). The 

allowed range is 6.5 to 8.5 s.u. The proposed permit limits pH to the range 6.0 to 9.0 s.u. This limit 

is based on Federal secondary treatment standards for wastewater treatment facilities (40 CFR Part 

133.102), and is applied to the majority of domestic NPDES permittees in the state. Within the 

permittee's mixing zone, the water quality standard for pH does not have to be met. The Department 

evaluated pH using a spreadsheet that derives the pH at the mixing zone boundary using the table 

below. 

Figurel. Dilution analyses for pH 

Calculation of pH of a mixture of two flows. 

Based on the procedure in EPA's DESCON program (EPA, 1988. Technical 

Guidance on Supplementary Stream Design Conditions for Steady State 
Page 18 of 29 

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

INPUT 

1. DILUTION FACTOR AT MZ BOUNDARY - (Qe+Qr)/Qe 

2. UPSTREAM/BACKGROUND CHARACTERISTICS 

Temperature (deg C): 

pH: 

Alkalinity (mgCaC03/L}: 

3. EFFLUENT CHARACTERISTICS 

Temperature (deg C): 

pH: 

Alkalinity (mg CaC03/L): 

4. APPLICABLE PH CRITERIA 

OUTPUT 

1. IONIZATION CONSTANTS 

Upstream/Background pKa: 

Effluent pKa: 

2. IONIZATION FRACTIONS 

Upstream/Background Ionization Fraction: 

Effluent ionization Fraction: 

3. TOTAL INORGANIC CARBON 

Upstream/Background Total Inorganic Carbon (mg CaC03/L): 

Effluent Total Inorganic Carbon (mg CaC03/L): 

4. CONDITIONS AT MIXING ZONE BOUNDARY 

Temperature (deg C): 

Alkalinity (mg CaC03/L): 

Total Inorganic Carbon (mg CaC03/L): 

pKa: 

pH at Mixing Zone Boundary: 

Is there Reasonable Potential? 

RPAt 

Lower pH 

Criteria 

12 

22.0 

6.8 

25.0 

25.0 

6.0 

75.0 

6.5 

6.37 

6.35 

0.73 

0.31 

34.26 

242.90 

22.26 

29.35 

52.40 

6.37 

6.5 

No 

orpH 

Upper pH 

Criteria 

12 

22.0 

7.9 

25.0 

25.0 

9.0 

75.0 

8.5 

6.37 

6.35 

0.97 

1.00 

25.74 

75.17 

22.26 

29.35 

30.03 

6.37 

8.0 

No 

Bacteria 

The proposed permit limits are based on the E. coli standard contained in OAR 340-041-0009(5). 

The proposed limits are a monthly geometric mean of 126 E. coli per 100 mL, with no single 

sample exceeding 406 E. coli per 100 mL. If a single sample exceeds 406 E. coli per 100 mL, 

then the permittee may take five consecutive re-samples. If the log mean of the five re-samples is 
Page 19 of 29 

less than or equal to 126, a violation is not triggered. The re-sampling must be taken at four hour 

intervals beginning within 28 hours after the original sample was taken. 

The proposed limits are taken directly from the Oregon bacteria rule which is found in OAR 340-

041-0009. This rule establishes numeric in-stream water quality standards (OAR 340-041-

0009(1)) and establishes effluent limitations and the methodology for establishing a violation 

(OAR 340-041-0009(5)). 

Regarding the general condition 6 found in Section B of Schedule F in this permit which prohibits 

overflows from wastewater conveyance systems, the Environmental Quality Commission (EQC) 

recognizes that it is impossible to design and construct a conveyance system that will prevent 

overflows under all storm conditions. The applicant is not seeking permit coverage for overflows 

and the permit does not authorize such discharges. The State of Oregon has determined that all 

wastewater conveyance systems should be designed to transport storm events up to a specific size 

to the treatment facility. Therefore, in exercising its enforcement discretion regarding Sanitary 

Sewer Overflows, the Department will consider the following: 

(1) Whether the permittee has conveyance and treatment facilities adequate to prevent 

overflows except during a storm event greater than the one-in-five-year, 24-hour duration 

storm from November 1 through May 21 and except during a storm event greater than the 

one-in-ten-year, 24-hour duration storm from May 22 through October 31. In addition, 

DEQ will also consider using enforcement discretion for overflows that occur during a 

storm event less than the one-in-five-year, 24-hour duration storm from November 1 

through May 21 if the permittee had separate sanitaty and storm sewers on January 10, 

1996, had experienced sanitary sewer overflows due to inflow and infiltration problems, 

and has submitted an acceptable plan to the Department to address these sanitaiy sewer 

overflows by January 1, 2010; 

(2) Whether the permittee has provided the highest and best practicable treatment and/or 

control of wastes, activities, and flows and has properly operated the conveyance and 

treatment facilities; 

(3) Whether the permittee has minimized the potential environmental and public health 

impacts from the overflow; and 

(4) Whether the permittee has properly maintained the capacity of the conveyance system. 

DEQ will review the permittee's determination of the one-in-five-year, 24-hour duration winter 

storm and the one-in-ten year, 24-hour duration summer storm as described above in the 

permittee's facilities plan. In the event that a permittee reports an overflow event associated with 

a storm event and DEQ does not have information from the permittee sufficient to determine 

whether or not the storm event exceeds storm events as specified in OAR 340-041-0009(6) & (7), 

DEQ will perform the determination using the information contained in Figure 26 of the 1973 

NOAA Atlas 2 entitled "Precipitation-Frequency Atlas of the Western United States, Volume X -

Oregon". This figure is entitled "Isopluvials of 5-yr 24-hr precipitation in tenths of an inch". The 

Atlas can be obtained on line at http://hdsc.nws.noaa.gov/hdsc/pfds/other/or pfds.html. however 

the file is very large. A scanned version of Figure 26 is available at: 

http://www.wrcc.dri.edu/pcpnfreq/or5y24.gif. DEQ will compare the information in this figure 

with rainfall data available from the National Weather Service, or other sources as necessary. 

Temperature 

For existing and expanded facility: 

An evaluation of effluent temperature data collected through 2008 and 2009 for the existing 

facility indicates that temperature criteria is met at the edge of the mixing zone. The 2010 mixing 

zone study predicted dilutions using the results of a CORMIX v6.0 modeling study of mixing 
Page 20 of 29 

zone dilution for the Tri-city outfall for 2015 projected and current 2010 discharge rates of 17.1 

and 8.4 MGD, respectively. The study indicates that thermal impacts from Tri-City may be 

significant for a summer discharge. Since critical ambient temperature is assumed to be Ta= 

20°C, a temperature rise of less than 5°C would meet the standard. 

This segment of the Willamette River serves as a migration corridor for sahnonids. OAR 340-

041 -0028(4)(d) states that the 7-day maximum temperature of a stream identified as a migration 

corridor may not exceed 20°C(68°F). In addition, for streams that do not meet water quality 

standards, OAR-041-0028(12)(b)(A) states that prior to the completion of a temperature TMDL or 

other cumulative effects analysis, no single NPDES point source that discharges into temperature 

water quality limited water may cause the temperature of the water body to increase more than 0.3°C 

above the applicable criteria after mixing with either twenty-five percent of the stream flow or the 

temperature mixing zone whichever is more restrictive. A temperature TMDL has been completed 

for the Willamette River, therefore the above provision from OAR 340-041-0028(12)(b)(A) does 

not apply. The proposed permit includes Excess Thermal Load (ETL) limitation for the facility 

based on the September 2006 Willamette Basin TMDL for temperature. 

Temperature Thermal Plume Limitations 

The Department's water quality standards also include the temperature thermal plume limitations 

in OAR 340-041-0053(2)(d). This section of the rules contains criteria to prevent potential 

adverse impacts that may result from thermal plumes within the mixing zone. 

[OAR 340-041-0053(d)(A)]: The impairment of an active salmonid spawning area where 

spawning redds are located or likely to be located. This segment of the Willamette River is a 

migration corridor for sahnonids. Based on Figure 304B in OAR 340-041-0028, spawning in this 

segment of the river does not occur. 

[OAR 340-041-0053(d)(B)]: Acute impairment or instantaneous lethality is prevented or 

minimized by limiting potential fish exposure to temperatures of 32°C or higher to less than 2 

seconds. Based on temperature data (2008/2009) collected using a continuous recording device, 

the maximum effluent temperature of 23.7°C is less than 32°C. 

[OAR 340-041-0053(d)(C)]: Thermal shock caused by a sudden increase in water temperature is 

prevented or minimized by limiting potential fish exposure to effluent temperatures of 25°C or higher 

to less than 5% of the cross-section of the 7Q10 flow of the water body. The maximum effluent 

temperature recorded in 2008 and 2009 was 23.0°C and 23.7°C, respectively. The Cormix modeling 

data (Mixing Zone Evaluation for TCSD Outfall of the Tri-City WPCP Volume 1 of 3 and 

Volume 3 of 3) indicates the cross section of the Willamette River in the area of the outfall is 

approximately 2500 square feet. Based on a maximum temperature of 23.7°C, a temperature of 

25°C will be met prior to the edge of the zone of initial dilution. Effluent temperatures will be 

reduced to 25°C in less than 5% of the cross section of the 7Q10 of the water body. 

[OAR 340-041-0053(d)(D)]: Unless ambient temperature is 21°C or greater, migration blockage 

is prevented or minimized by limiting potential fish exposure to temperatures of 21°C or higher to 

less than 25% of the cross-section of the 7Q10 flow of the water body. The maximum effluent 

temperature recorded in 2003 and 2004 was 23.0°C and 23.7°C, respectively. The Cormix modeling 

data (Mixing Zone Evaluation for TCSD Outfall of the Tri-City WPCP Volume 1 of 3 and 

Volume 3 of 3) indicates the cross section of the Willamette River in the area of the outfall is 

approximately 2500 square feet. A 25% cross section would be 625 square feet. Based on a 

maximum temperature of 23.7°C, a temperature of 21°C will be met prior to the edge of the zone 

of initial dilution. The cross section is less than 25% ((225/2500) x 100 = 9%). 
Page 21 of 29 

5.3 Whole Effluent Toxicity 

In addition to analyzing the effluent for individual pollutants, the effluent is also tested to 

determine its aggregate effect on aquatic organisms. These tests are known as whole effluent 

toxicity (WET) tests. Effluent samples are collected and aquatic organisms are subjected to 

various effluent concentrations in controlled laboratory experiments. EPA has developed WET 

test protocols using both freshwater and marine and estuarine test species. EPA recommends 

running tests using an invertebrate, a vertebrate and a plant. Organisms used in WET tests are 

indicators or surrogates for the aquatic community to be protected, and a measure of the real 

biological impact from exposure to the toxic pollutants. To protect water quality, EPA 

recommends that WET tests be used in NPDES permits together with requirements based on 

chemical-specific water quality criteria. 

WET tests are used to determine the percentage of effluent that produces an adverse effect on a 

group of test organisms. The measured effect may be fertilization, growth, reproduction, or 

survival. EPA's methodology includes both an acute test and a chronic test. An acute WET test 

is considered to show toxicity if adverse affects occur at effluent concentrations less than that 

which is found at the edge of the zone of immediate dilution (ZID). A chronic WET test is 

considered to show toxicity if adverse affects occur at effluent concentration less than that which 

is known to occur at the edge of the mixing zone. 

Two WET tests were conducted for the existing facility in 2008/2009, after application submittal. 

No acute toxicity was noted in any of these tests for 100% effluent. In addition, no chronic 

toxicity was observed at worst case effluent concentrations expected to be found at the edge of 

the mixing zone. The Department recommends that a point estimate (IC25) be used to assess the 

likelihood of chronic toxicity. The table that follows demonstrates the effluent concentrations 

that caused a 25% reduction in a biological measurement (i.e. growth, reproduction) and the 

corresponding dilution in which chronic toxicity would be anticipated from the effluent. For 

example: A significant reduction was estimated in reproduction for P. promelas at an effluent 

concentration of 40.3%. The corresponding dilution (2.5:1) can be compared to the demonstrated 

dilution (18.6:1) which occurs at the mixing zone boundary. The mixing zone study demonstrated 

dilution is much greater than the dilutions at which chronic toxicity was estimated and thus these 

adverse effects noted do not occur at concentrations less than the 2.4% worst case effluent 

concentration expected to be found at the mixing zone boundary. The WET test results indicate 

the effluent is not causing either an adverse acute or chronic aggregate effect on the aquatic 

community. 

Sampling 

month/year 

March 2008 

March 2009 

Pimephales promelas 

(Fathead Minnow) 

Concentration 

40.3% 

>50% 

Dilution 

2.5:1 

2:1 

Ceriodaphni 

(Water F 

Concentration 

37.6% 

>50% 

a dubia 

ea) 

Dilution 

2.7:1 

2:1 

Raphidocelius subcapitata 

(Algae) 

Concentration 

34.3% 

>50% 

Dilution 

2.9:1 

2:1 

Bioassay study for the expanded facility will be based on the mixing zone dilutions for the 

projected discharge rate of 17.1 MGD. The proposed permit includes WET dilution numbers for 

the expanded facility. 

5.4 Antidegradation 

An Antidegradation Review was performed for this discharge. The permit is being renewed 

without any increase in discharge loadings. Permit renewals with the same discharge loadings as 

the previous permit are not considered to lower water quality from the existing condition. Based 
Page 22 of 29 

on the antidegradation review, the Department determined the proposed discharge complies with 

the Antidegradation Policy for Surface Waters found in OAR 340-041-0026 (see Appendix A). 

6.0 PERMIT DRAFT DISCUSSION 

6.1 Face Page 

The face page provides information about the permittee, description of the wastewater, outfall 

locations, receiving stream information, permit approval authority, and a description of permitted 

activities. The permittee is authorized to construct, install, modify, or operate a wastewater 

collection, treatment, control, and disposal system. The permit allows discharge to the 

Willamette River within limits set by the following schedules. All other discharges are 

prohibited. 

6.2 Schedule A, Waste Discharge Limitations 

The proposed permit contains limitations for the existing facility and for the expanded facility. 

Summer time CBOD5/TSS concentrations are based on the basin limit while mass load limits stay 

the same as the previous permit. Percent removal efficiency limit is dependent on influent 

BOD/TSS concentration while ETL limitation includes three options of calculating thermal load 

for the facility. The bacteria standard was changed in 1996 from fecal coliform to E. coli. This 

permit renewal includes bacteria limits fori?, coli. This schedule also includes UV dosage limitation 

and language regarding Recycled Water Use and Biosolids. Other permit limits remain the same as 

the previous permit. 

6.3 Schedule B - Minimum Monitoring and Reporting Requirements 

Due to the types of treatment processes utilized to treat domestic wastewater, DEQ developed 

recommended monitoring frequencies for parameters based on the size and type of treatment 

facility. Wastewater discharge permit monitoring frequencies of similar type facilities were 

reviewed for specific parameters in relation to the facility design flow. Similar monitoring 

frequencies for parameters allow for statewide consistency based on facility design flow and type. 

The monitoring and reporting requirements in this permit are in accordance with the DEQ's 

monitoring matrix for an activated sludge and MBR facility with a design flow greater than 10 

MGD. 

Additional sampling requirements have been added to this permit to meet the effluent testing for 

the EPA Form 2A renewal application dated January 1999 and the monitoring requirements 

prescribed in the DEQ Internal Management Directive for the Reasonable Potential Analysis for 

Toxic Pollutants dated September 2005. 

6.4 Schedule C - Compliance Schedules and Conditions 

This permit does not include a compliance schedule. Rather, a Mutual Agreement and Order 

(MAO) has been developed to address ammonia concentration and the need for capital 

improvements or additional treatment of ammonia in order reduce its concentration in the effluent 

discharge. The District is given milestones for completion of the necessary improvements. The 

MAO also includes ammonia interim effluent limit that is as stringent as practicable; based on the 

discharge monitoring report data from the last three years. Upon completion of requirements, the 

Permittee is expected to meet the water quality standards for ammonia; RPA for ammonia will be 

re-evaluated at that time. 
Page 23 of 29 

6.5 Schedule D - Special Conditions 

The permit includes eight special conditions. 

Conditions L2&3 are related to the biosolids management practices that are to be followed and 

include a reopener condition should the standard biosolids practices be changed so that they 

become more stringent than the proposed permit under the Clean Water Act. 

Condition 4 relates to whole effluent toxicity (WET) testing or bioassay testing to look for the 

potential for toxic effects from this wastewater discharge. The condition specifies the organisms 

and protocols for acute and chronic testing, how those tests should be evaluated, the quality 

assurance and reporting specifics and reopener for the permit should it become appropriate based 

on the WET test results. 

Condition 5 defines the operator certification requirements that must be adhered to in accordance 

with Oregon Administrative Rules, Chapter 340, and Division 49. 

Condition 6 includes a requirement that notification be made to the Department for malfunctions 

at the treatment facility such that corrective actions can be coordinated if appropriate. 

Condition 7 requires that the permittee have in place a contingency plan that lays out prevention 

measures and a response plan for spills or unplanned discharges. 

Conditions 8 & 9 require the permittee to meet the requirements of OAR 340-055, "Recycled 

Water Use Rules". 

Condition 10 prohibits any adverse impact on groundwater quality. 

6.6 Schedule E, Pretreatment Program Activities 

This section includes conditions related to the proper implementation of a pretreatment program 

in accordance with 40 CFR § 403. 

6.7 Schedule F, NPDES General Conditions 

NPDES General Conditions are the same in all permits issued in the State of Oregon. These 

General Conditions have five sections. 

Section A-Standard Condition: contains compliance, penalty and assessment of violations, 

mitigation, permit renewal application, permit action, toxic pollutant discharges, property rights, 

referenced rules and permit fees. 

Section B- Operation and Maintenance of Pollution Controls: contains operation and maintenance 

of the facility which include operation and maintenance, need to halt or reduce activity in order to 

comply with the permit, bypass of treatment facility, upset conditions, treatment of single 

operational upset, overflows from wastewater conveyance systems and associated pump stations, 

public notification of effluent violation and overflow, emergency response and public notification 

plan, and disposal of removed substances. 

Section C- Monitoring and Records: contains monitoring and reporting requirements including 

representative sampling, flow measurements, monitoring procedures, penalties of tampering, 
Page 24 of 29 

reporting of monitoring results, any additional monitoring, averaging, record retention, records 

contents, inspection and entry, and confidentiality of information. 

Section D- Reporting Requirements: contains reporting requirements and includes reporting 

planned changes, anticipated noncompliance, transfers, compliance schedule, twenty-four hour 

reporting, other noncompliance, duty to provide information, signatory requirements, information 

falsification, and changes to indirect dischargers. 

Changes and modification to the General conditions can only occur statewide. The General 

Conditions included in the Schedule F of the permit are the latest edition, edited in September, 

2009.- The 2009 changes are summarized below. 

« There are additional citations to the federal Clean Water Act and CFR, including 

references to standards for sewage sludge use or disposal. 

• There is additional language regarding federal penalties. 

• Bypass language has been made consistent with the Code of Federal Regulations. 

• Overflow language has been modified. Formerly the language stated that 

overflows in response to the five or ten year event would not violate the permit. 

Now it states that overflows are prohibited. DEQ will continue to exercise 

enforcement discretion with respect to overflows consistent with the provisions 

of the Bacteria Rule (OAR 340-041-0009). 

« Reporting requirements regarding overflows have been made more explicit. 

• Requirements regarding emergency response and public notification plans have 

been made more explicit. 

» Language pertaining to duty to provide information has been made more explicit. 

• Confidentiality of information is addressed. 

6.8 Permit Processing/Public Comment/Appeal Process 

The beginning and end date of the public comment period to receive written comments regarding 

this permit, and the contact name and telephone number are included in the public notice (See 

Attachment G). The permittee is the only party having standing to file a permit appeal. If the 

Permittee is dissatisfied with the conditions of the permit when issued, they may request a hearing 

before the EQC or its designated hearing officer, within 20 days of the final permit being mailed. 

The request for hearing must be sent to the Director of the Department. Any hearing held shall be 

conducted pursuant to regulations of the Department. 
Page 25 of 29 

Appendix A: Antidegradation Review Sheet 

ANTIDEGRADATION REVIEW SHEET 

FOR A PROPOSED INDIVIDUAL NPDES DISCHARGE 

1. What is the name of Surface Water that receives the discharge? Willamette River 

Briefly describe the proposed activity: 

Is this review for a <genewaT_X>R new permit application? 

Go to Step 2. 

2. Is this surface water an Outstanding Resource Water or upstream from an Outstanding 

Resource Water? 

Yes. Go to Step 5. 

(No) Go to Step 3. 

3. Is this surface water a High Quality Water? 

Yes. Go to Step 8. 

(No) Go to Step 4. 

4. Is this surface water a Water Quality Limited Water? 

CjosT^) Go to Step 14. 

No. Go to Step 2. Note: The surface water must fall into one of three (3) 

categories: Outstanding Resource Water (Step 2), High Quality Water (Step 3), 

or Water Quality Limited Water (Step 4). 

14. Will the proposed activity result in a Lowering of Water Quality in the Water Quality 

Limited Water? [see OAR 340-041 -0004(3)-(5) for a description in rule of discharges that 

do not result in lowering of water quality or do not constitute a new and/or increased 

discharge or are otherwise exempt from antidegradation review; otherwise see "Is an 

Activity Likely to Lower Water Quality?" in Antidegradation Policy Implementation 

Internal Management Directive for NPDES Permits and Section 401 Water Quality 

Certifications.] 

Go to Step 15. 

Proceed with Permit Application. Applicant should provide basis for 

conclusion. Go to Step 21. 

21. On the basis of the Antidegradation Review, the following is recommended: 

X Proceed with Application to Interagency Coordination and Public Comment 

Phase. 

Deny Application; return to applicant and provide public notice. 

Action Approved 

Section: Northwest Region - WO Permitting_ 

Review Prepared By: _Etsegenet Belete 

Phone: 503-229-5349 

Date Prepared: Sept 23. 2010 
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