FACT SHEET 

And 

NPDES WASTEWATER DISCHARGE PERMIT EVALUATION 

Department of Environmental Quality 

Western Region - Salem Office 

750 Front Street NE, Suite 120, Salem, OR 97301-1039 

Telephone: (503) 378-8240 

PERMITTEE: City of Corvallis 

P.O. Box 1083 

Corvallis, OR 97339-1083 

File Number: 20151 

SOURCE LOCATION: P.O. Box 1083 

SOURCE CONTACT: 

DanHanthorn Telephone Number: 541754-1757 

PERMIT WRITER: 

Robert Dicksa Telephone Number: 503 378-5039 

PROPOSED ACTION: Renewal of a National Pollutant Discharge Elimination System (NPDES) 

wastewater discharge permit 

SOURCE CATEGORY: Major Domestic 

TREATMENT SYSTEM CLASS: Level IV 

COLLECTION SYSTEM CLASS: Level IV 

PERMIT APPLICATION DATE: December 31, 2003 

PERMIT APPLICATION NUMBER: 983793 

BACKGROUND 

Introduction 

City of Corvallis operates a wastewater treatment facility located in Corvallis, Oregon (see Figure 1). Wastewater 

is treated and discharged to Willamette River in accordance with National Pollutant Discharge Elimination System 

(NPDES) Permit number 101714. The Permit for the facility was issued on August 9,1999 and expired on June 30, 

2004. 
City of Corvallis Evaluation Report 

Page 2 

Figure 1 

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The Department received a renewal application on December 31,2003. The permit shall not be deemed to expire 

until final action has been taken on the renewal application as per Oregon Administrative Rules (OAR) 340-045-

0040. A renewal permit is necessaiy to discharge to state waters pursuant to provisions of Oregon Revised Statutes 

(ORS) 468B.050 and the Federal Clean Water Act. The Department proposes to renew the permit. This permit 

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

This permit is a joint federal and state permit and subject to federal and state regulations. The Clean Water Act, 

the Code of Federal Regulations, and numerous guidelines of the Environmental Protection Agency provide the 

federal permit requirements. The Oregon Revised Statutes, Oregon Administrative Rules, and policies and 

guidelines of the Department of Environmental Quality provide the state permitting requirements. 

FACILITY DESCRIPTION 

The current treatment facility consists of an influent pump station, primary screening and grit removal, primary 

settling, trickling filters with activated sludge biological secondary treatment and secondaiy clarification. After 

secondary treatment the wastewater is disinfected with chlorine and dechlorhlated with sodium bisulfite prior to 

discharge to the Willamette River through a submerged multi-port diffuser. 

The completion of the combined sewer overflow (CSO) project has added additional facilities to provide 

primary treatment, storage, and disinfection of combined sewage. In addition, the treated combined sewage is 

dechlorinated with sodium bisulfite to comply with chlorine residual requirements prior to its discharge to the 

Willamette River. The CSO remediation collection and facilities were placed into service in October 2000. 

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Community investment in the project was $30.1M. 

The proposed NPDES permit will cover a number of discharges, to waters of the State of Oregon. The various 

points of discharge are listed on the cover page of the proposed permit. Outfalls 001 and 002 consist of 

secondary treated wastewater. Outfall 001 is a diffuser located in the Willamette River. Treated effluent flows 

out through Outfall 001 by gravity. During periods of high river flow, the river elevation causes gravity flow 

through the diffuser to be impeded and the use of Outfall 002 is necessaiy. Outfall 002 is located adjacent to the 

treatment plant and enters Dixon Creek, a small tributary to the Willamette River. Outfall 002 is only used as an 

emergency outfall when the river stage elevation of the Willamette River rises above 206 ft above mean sea 

level (msl). When the City does have to use Outfall 002, the duration of use is a graduated based on the elevation 

of the river level. The use of Outfall 002 has significantly decreased since the City implemented the new CSO 

treatment facilities and the last time the City had to utilize Outfall 002 was during the winter season in 2006. 

Outfalls 003, 005, and 007, are CSO overflow points, Discharges from these outfalls will be infrequent due to 

the recent construction of the new CSO treatment facilities. As a result of the completion of these facilities, the 

CSO Outfalls 004 and 006 have been eliminated. 

Outfalls 008, 009, and 011, were previously listed as emergency overflows points at pump stations. However the 

Department's Bacteria rule in OAR 340- 041-0009, prohibits discharges of raw sewage. Therefore, these 

emergency overflow points have been removed from the proposed NPDES permit. Outfall 010, the Beca Street 

pump station has also been eliminated. 

Outfall 012 is the discharge from the combined sewage treatment system and is a diffuser located in the 

Willamette River downstream from outfall 001. 

The major treatment process used is activated sludge. The engineer who designed the facility determined the 

average design dty weather flow. It is the estimated maximum flow during May 1 to October 31 (expressed as a 

daily average flow), at which the design engineer expects the treatment facility can still consistently meet all 

effluent limits. 

The diy weather flows do not include the high levels of infiltration and inflow that are associated with the winter 

in Oregon. Therefore, the design diy weather flows are used mostly to estimate how much treatment capacity 

there is for organic loads. For this facility, the average design dty weather flow is 9.7 million gallons/day 

(MGD). The current actual diy weather flow for May 1 to October 31, for the past two years, is 7.41 mgd. 

Based on the current flows, this facility is at 76% of hydraulic treatment capacity. Since the last permit issuance 

in 1999, the City of Corvallis has continually dealt with hydraulic capacity and treatment issues through ongoing 

maintenance and system improvements. Collection system improvements during the permit period have 

increased firm capacity and reduced inflow and infiltration. Five miles of sewer line were rehabilitated or 

replaced; two separate lift stations were replaced; one new, additional sewer lift station; and 726 manholes sealed. 

Conveyance system improvement expense totaled $21.2M. Treatment facility improvements since 1999 enhanced 

capacity, reliability and performance. Improvements included: two gravity sludge thickeners, additional anaerobic 

digester, disinfection facilities, electrical gear replacement and seismic upgrades. All treatment facility 

improvements totaled $14.2M. 

The current actual average wet weather flow (November 1 through April 30), for the past two years, is 12.0 

MGD. The peak day fknv over the past two years is up to 20.1 MGD. See the section on Inflow and Infiltration 

for a further discussion of winter flows and hydraulic capacity issues. 

Biosolids Management and Utilization 

The permittee's current biosolids management plan was approved August 6, 1999, and updated and approved by 

DEQ in January 2007. The updated plan will be available for review and comment as part of the permit 

documents for Public Notice. All biosolids must be managed in accordance with the Department approved 

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Biosolids Management Plan to ensure compliance with the biosolids regulations (OAR 340-050). After 

treatment necessaiy to comply with vector attraction and pathogen reduction requirements, the Class B biosolids 

are beneficially land applied on sites in Benton County and Linn County. Any future land application sites must 

conform to the site selection criteria in the Biosolids Management Plan and must be in Linn or Benton Counties. 

The permittee generates sludge from the primary sedimentation tanks and the secondaiy clarifiers. The sludge is 

thickened in gravity thickeners then pumped to one of the anaerobic digesters. The stabilized biosolids are 

stored in two facultative lagoons prior to spreading on agricultural land during the months of June through 

October. 

This permit requires reporting four times per year of the methods used to comply with vector attraction and 

pathogen reduction requirements. It also requires the submittal of an annual summary report 

The permittee produces approximately 850 dry metric tons of biosolids per year. The City conducts regular 

chemical testing of biosolids (see Table 1). Testing includes analyses for nutrients and 10 metals. Based on the 

analyses, there are no known potential impacts from the current land application program. 

Table 1 - Biosolids Metals Results Based on 2009 Annual Report 

Parameter 

Arsenic 

Cadmium 

Chromium 

Copper 

Lead 

Mg/dryKg 

6.10 

4.17 

76 

655 

94 

§503.13 

Table 3 Limit 

41 mg/kg 

39 mg/kg 

No limit 

1500 mg/kg 

300 mg/kg 

Parameter 

Mercury 

Molybdenum 

Nickel 

Selenium 

Zinc 

Mg/dry 

-'"..•Kg: 

3.13 

5.54 

25 

5.96 

852 

§503.13 

Table 3 Limit 

17 mg/kg 

No limit 

420 mg/kg 

100 mg/kg 

2800 mg/kg 

Inflow and Infiltration (I/I) 

The City of Corvallis sanitary sewage collection system is a combined system. Part of the collection system 

receives stormwater and sewage, and during significant rainfall events CSOs occur. Another source of non-sewage 

flow is Inflow/Infiltration (I&I). I&I is a concern due to the fact that it can negatively affect treatment plant 

performance and overwhelm the collection and treatment system capacity. Inflow is stormwater that enters the 

collection system through surface leaks at access points, such as manholes or pump stations. Infiltration is the entry 

of groundwater at cracked or broken pipes. While inflow can typically be controlled for the most part, infiltration is 

an on-going battle for the city as the collection system ages. It is economically and practicably unrealistic to expect 

that all infiltration could be removed. Rather, the City must continually evaluate the infiltration sources and correct 

those that offer the greatest cost-effective reduction. The proposed renewal permit requires that the city maintain an 

on-going I&I Reduction Program. Annual reports which summarize the status of the I&I removal efforts must be 

submitted to the Department. 

Industrial Pretreatment 

The City of Corvallis implements an industrial pretreatment program approved by the Department on June 2,1983. 

Federal and state pretreatment requirements were included in the NPDES permit for this facility when the existing 

permit was issued. The City of Corvallis won first place in EPA's National Pretreatment Award for excellence for 

2006 for small pretreatment programs. 

The City of Corvallis currently permits three significant industrial user (SIUs) of which two are federally 

designated categorical industrial users. A fourth permitted user is a categorical industrial user (CIU) but not a SIU. 

Annual pretreatment program reports are submitted yearly. A Pretreatment Compliance Audit of the industrial 

pretreatment program was conducted by the Department in September 2005. The primary focus of the audit was to 

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review and assess the core pretreatment program functions, source files, enforcement actions, pollution prevention 

efforts and compliance status. 

As a result of this audit, the Department determined the pretreatment program is functioning in compliance with the 

federal pretreatment requirements and the NPDES pretreatment-related permit conditions. The Department 

identified, required and recommended actions intended to further improve the industrial pretreatment program. 

Overall, the City's pretreatment program is an exceptionally well managed program in all aspects. 

Groundwater Issues 

The treatment plant is constructed entirely of impervious structures. It is not anticipated that the treatment 

process and discharge to surface waters will cause groundwater impacts. Schedule A of the proposed permit 

prohibits adverse impacts to groundwater. In addition, the City of Corvallis is evaluating WWRP effluent 

discharge alternatives to comply with the Willamette River Total Maximum Daily Load (TMDL) for 

temperature. Those alternatives include evaluations of subsurface hyporheic discharges to the Willamette River. 

Should any alternative be selected that includes a subsurface discharge, the permittee will need to comply with 

nitrate limits associated with the Department designated Southern Willamette Valley Groundwater Management 

Area (GWMA). 

Stormwater Issues 

General NPDES permits for stormwater are required for wastewater treatment facilities with a design flow of 

greater than 1 MGD if stormwater is collected and discharged from the plant site. However, all rain water at this 

facility flows through the treatment processes and is not discharged as stormwater. 

Outfalls 

The current NPDES Permit allows the treatment facility to discharge treated effluent into the Willamette River 

adjacent to the plant at River Mile 130.8 (Outfall 001), and into Dixon Creek at River Mile 0.1 (Outfall 002). 

Outfall 001 (Willamette River outfall) is located at approximately Latitude 44° 34' 29" North, Longitude 123° 15' 

2" West. Treated, disinfected and dechlorinated effluent is discharged through Outfall 001 to the Willamette River. 

When the river elevation causes gravity flow through Outfall OOlto be impeded, the use of outfall 002 to Dixon 

Creek is necessaiy. 

The existing permit identifies five combined sewer overflow points to the Willamette River at River Miles 131.3, 

131.4,131.6, 131.7, and 132.2. Two of these overflow points have been eliminated since the issuance of the 

current permit. The Department proposes to retain the other three combined sewer overflow points. 

The existing permit also identifies Outfall 013, which is used for the discharge of groundwater from drains below 

the CSO storage lagoon. This natural underdrain groundwater is necessaiy to protect the CSO storage lagoon liner. 

The water is not contaminated and therefore does not have any effluent limitations however, the City continues to 

monitor the water for flow and conductivity twice a year to ensure that the liner is not leaking. On the basis that 

this is natural groundwater that is not contaminated or co-mingled with the treatment process, the Department is 

proposing to remove this outfall from the permit. 

The City of Corvallis WWRP is also looking at various treatment alternatives to comply with the Total Maximum 

Daily Load (TMDL) Waste Load Allocation (WLA) for temperature. Part of the treatment alternatives may include 

utilizing recycled water for irrigation through land application. While the City has not made a final decision as to 

which Class of recycled wastewater, depending on the chosen alternative, the City is proposing to treat the 

wastewater to either Class A, Class B, Class C, or Class D standards in accordance with OAR 340-055 and conform 

to a Recycled Water Use Plan approved by the Department. 

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The proposed permit will include Outfall 014 to allow the permittee to beneficially land apply treated recycled 

wastewater in accordance with OAR 340-055 during the summer season (May 1-October 31). The proposed permit 

will contain limits and monitoring requirements for Class A, Class B, Class C, and Class D recycled water to allow 

the permittee to comply with either Class of recycled water depending on which alternative is selected. The 

permittee will be required to state the selected alternative and Class of recycled water in the Recycled Water Use 

Plan. The Recycled Water Use Plan must be approved by the Department prior to the permittee land applying the 

treated recycled wastewater through Outfall 014. Following Department approval, the land application of 

wastewater shall conform to the Department approved plan. All recycled water shall be distributed on land for 

dissipation by evapotranspiration and controlled seepage by following sound irrigation practices so as to prevent: 

1. Prolonged ponding of treated wastewater on the ground surface; 

2. Surface runoff or subsurface drainage through drainage tile; 

3. The creation of odors, fly and mosquito breeding or otherwise nuisance conditions; 

4. The overloading of land with nutrients, organics, or other pollutant parameters; and, 

5. Impairment of existing or potential beneficial uses of groundwater. 

RECEIVING STREAM 

Hvdroiogic Characteristics 

The outfall location is about 30 miles downstream of the nearest USGS gage on the Willamette River (Gage No. 

14166000) at Harrisburg. Several small streams enter the Willamette between the Harrisburg gage and the 

discharge point and add small amounts of water to the river. Two of these streams also have gages (USGS gage 

14170000 Long Tom River at Monroe and USGS gage 14171000 Maiys River near Philomath). The drainage 

area of the combined areas is 3970 square miles. 

Low river flow was determined using data from the above gages from 1970 through the present. The critical 

case low flows for the "summer" season (May tlyough October), the "winter" season (November through April), 

the salmonid rearing and migration season (May 16 through October 14) and the spawning season (October 15 

through May 15) were calculated. The harmonic mean flow is 7624 cfs. 

Season 

Summer (May ~ Oct) 

Winter (Nov - Apr) 

Rearing (5/16-10/14) 

Spawning (10/15-5/15) 

1Q10 

3590 

3432 

3600 

3253 

7Q10 

3686 

3622 

3686 

3468 

30Q5 

4109 

5357 

4129 

5019 

The proposed permit will allow the permittee to derive the receiving stream flow rate from combining the flow rates 

from USGS gauging station Number 14166000 (at Harrisburg), USGS gauging station Number 14170000 (Long 

Tom River at Monroe), and USGS gauging station Number 14171000 (Marys River near Philomath) or from USGS 

gauging station number 14171600 (Willamette River at Corvallis). 

Receiving Stream Water Oiialitv 

The City's discharge is to the Willamette River at River Mile 130.8. The discharge is within the Upper 

Willamette sub-basin. The designated beneficial uses of the receiving stream are: public and private domestic 

water supply, industrial water supply, irrigation, livestock watering, fish and aquatic life (including salmonid 

rearing, migration and spawning), wildlife and hunting, fishing, boating, water contact recreation, and aesthetic 

quality. The water quality standards for the Willamette Basin (OAR 340-041) were developed to protect the 

beneficial uses of the basin. 

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Treated wastewater is discharged to the Willamette River at river mile 130.8. At this location, the Willamette Rivetis water quality limited for the following parameters: 

Parameter 

Temperature 

Fecal Coliform 

Dissolved Oxygen 

Mercury 

Season 

Summer 

Winter/Spring/Fall 

Winter/Spring/Fall 

Year round 

Temperature Issues 

Water temperature affects the biological cycles of aquatic species and is a critical factor in maintaining and 

restoring healthy salmonid populations throughout the state. It is the policy of the Environmental Quality 

Commission (EQC) to protect aquatic ecosystems from adverse temperature changes caused by anthropogenic 

activities. The purpose of the temperature criteria listed in OAR 340-041-0028 is to protect designated 

beneficial uses that are temperature sensitive, including salmonids in waters of the State. 

The Department utilizes Fish Use Designation maps and Salmon and Steelhead Spawning Use Designations 

maps to identify applicable temperature criteria for each basin. The Willamette Basin maps are contained in 

OAR 340-041, Figures 340A and 340B, respectively. According to the approved use designation maps, salmon 

and steelhead spawning is a designated use of the Willamette River from October 15 through May 15. During 

this period, the applicable temperature criterion is 13 °C. For the remainder of the year, salmon and trout 

rearing and migration is the designated use with an applicable temperature criterion of 18 °C. 

The Department's List of Water Quality Limited Water Bodies (also called the 303(d) List) for 2004/2006 

indicates the Willamette River is water quality limited for temperature. The Willamette Total Maximum Daily 

Load (TMDL) was issued by the Department on September 21,2006 and approved by EPA on September 29, 

2006. The TMDL deals with temperature issues in most of the Willamette Basin including this segment of the 

Willamette River. The TMDL determined the temperature standard is violated from April 1 through October 31, 

The TMDL includes Waste Load Allocations (WLA) for the discharge from the City of Corvallis Wastewater 

Treatment Plant from April 1 through October 31. This permit includes limitations that are in accordance with 

the WLA. 

In addition, the Department evaluated the discharge to ensure compliance with the temperature standard during 

the rest of the year (November 1 through March 31). The evaluation (see Attachment #1) determined there was 

no reasonable potential for the discharge to violate the cold water protection rule (OAR 340-041-0028(1 l)(b). 

The Department also evaluated the thermal plume in accordance with OAR 340-041-0053 (2)(d). No permit 

limits for temperature are needed between November 1 and March 31 or for the thermal plume. 

Bacteria 

The Department's 303(d) List indicates the Willamette River is water quality limited for bacteria during fall, 

winter and spring. The 2006 Willamette TMDL deals with bacteria issues. The TMDL states there is currently 

an "excess bacterial load" to the Willamette River and wastewater treatment plants are allocated permitted 

effluent limits at the bacteria standard. When operating properly, these discharges will not cause or contribute 

to water quality violations and are a relatively small proportion of the total loading to the Willamette River. The 

City of Corvallis is in full compliance with the Willamette TMDL in regards to bacteria. 

Dissolved Oxygen 

The mainstem Willamette River is water quality limited for dissolved oxygen during the spawning season 

(October 15 through May 15) from river mile 149 through river mile 50. No TMDL has been written to address 

the Willamette River dissolved oxygen listing and therefore no WLA for oxygen demanding pollutants have 

been assigned to the City of Corvallis. The permit will include a clause allowing the Department to reopen the 

permit and include a dissolved oxygen WLA when a TMDL has been written and approved. 

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Mercury 

The Department's 303(d) List indicates the Willamette River is water quality limited for mercury because of 

excess concentrations found in fish tissues. The Department is proposing to perform the TMDL in a two-phased 

approach. The first phase has been completed and has received EPA approval. The first phase of the TMDL 

lays out an implementation strategy to gain a better understanding of the fate and transport of mercury in the 

Willamette Basin. The implementation strategy requires certain point sources (including Corvallis) to conduct 

monitoring for mercury and methylmercury and to submit a Mercury Minimization Plan if a source is found to 

be a significant contributor of mercury. This permit requires the facility to monitor for total and dissolved 

mercury and methylmercury twice per year using EPA Method 1631 E. Total and dissolved mercury must 

achieve a detection limit of 0.073 ng/L and total and dissolved methylmercury must achieve a detection limit of 

0.00599 ng/L unless otherwise approved in writing by the Department. The permittee may request the mercury 

monitoring be eliminated after two years of monitoring if the Department is satisfied with the results of the data. 

If there is wide variability within the results, the Department may require additional monitoring. 

The City of Corvallis has implemented a mercury reduction plan that includes working with dentists to minimize 

mercury waste through the use of amalgam separators, mercury permit limits for significant industrial users, and 

mercury collection programs domestically and through the schools. To date, mercury head works loading has 

been reduced by approximately 97% through the mercury reduction plan effort. 

Mixing Zone Analysis 

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

When using mixing zones acute toxicity to drifting organisms must be prevented and the integrity of the 

waterbody as a whole may not be impaired. Mixing zones allow the initial mixing of treated wastewater and 

receiving water, but are not designed to allow for treatment. EPA does not have specific regulations pertaining 

to mixing zones. Each state must 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. 

The Department has adopted the two-number aquatic life criteria and developed mixing zone regulations with 

respect to that. The regulations are primarily narrative and essentially require the permit writer to use best 

professional judgment in establishing the size of the mixing zone. 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". The acute mixing zone is designed to prevent 

lethality to organisms passing through the ZID. The chronic mixing zone is 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 

to the same water body, 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 Department's mixing zone regulations state the mixing zone must be less than the total stream width as 

necessaiy to allow passage offish and other aquatic organisms. Early recommendations regarding the size of the 

zone of passage originated from the Department of Interior (1968). They recommended a zone of passage of 75 

percent of the cross-sectional area and/or volume of flow of the receiving stream. Based on this 

recommendation, the Department's standard practice is to allow no more than 25 percent of the stream flow for 

mixing zones. 

The current permit provides for a mixing zone for Outfall 001 that consists of that portion of the Willamette 

River contained within a band extending out from the west bank thirty (30) feet beyond the eastern edge of the 

diffuser and extending from a point ten (10) feet upstream and three hundred (300) feet downstream from the 

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diffuser. The Zone of Immediate Dilution (ZID) is defined as that portion of the allowable mixing zone that is 

within thirty (30) feet of the point of discharge. The Department proposes to retain the existing mixing zone. 

The existing permit includes Outfall 002 in the section with the above mixing zone but the Dixon Creek 

discharge does not occur within the defined area. The Department is not proposing to define a mixing zone for 

Outfall 002 at this time. Given the intermittent nature of the discharge at Outfall 002 and the fact that it is only 

used during very high river flow periods, it is not expected that the discharge will cause or contribute to water 

quality standard violations. 

Finally, the Department evaluated the thermal plume in accordance with OAR 340-041-0053 (2)(d) to ensure the 

discharge does not cause adverse effects to salmonids as described below: 

Impairment of an active salmonid spawning area where spawning redds are located or likely to be located is 

prevented or minimized by limiting potential fish exposure to temperatures of 13°C or more for salmon and 

steelhead, and 9°C for bull trout. According to the Oregon Department of Fish and Wildlife (ODF&W) district 

biologist, this requirement is met because bull trout are not a designated beneficial use of the main stem 

Willamette River and there are no known active salmon spawning redds for Fall or Spring Chinook within this 

area of the river. 

Acute impairment or instantaneous lethality is prevented or minimized by limiting potential fish exposure to 

temperatures of 32°C or more to less than 2 seconds. This requirement is met because the maximum discharge 

temperature is less than 32°C. 

Thermal shock is prevented or minimized by limiting potential fish exposure to temperatures of 25°C or more to 

less than five percent of the cross section of the water body. This requirement is met because the maximum 

discharge temperature is less than 25°C. 

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

more to less than 25 percent of the cross section of the water body. According to the temperature data at USGS 

Gage No. 14166500 since 2001, the 99th percentile of the running 7-day average maximum instream 

temperature is 20.8°C. Using worst case conditions (25% of 3670 cfs 7Q10 stream flow at 20.8°C and the 

discharge flow of 9.7 MGD or 15.0 cfs at 22.9°C), the mixed temperature can be calculated. 

The mixed temperature is calculated using dilution based on effluent flow and receiving stream flow, and using 

effluent temperature and background temperature, as follows: 

Dilution = (Effluent flow + 25% of River flow) = H5.0 cfs + (3670 cfs x 0.25V) = 62.2 

Effluent flow 15.0 cfs 

Mixed Temp. = (Effluent temp. - River temp.t + River temp. = (22.9oC-20.8°C1 + 20.8°C = 20.83°C 

Dilution 62.2 

The mixed temperature is 20.83°C and the final thermal plume requirement is satisfied. 

PERMIT HISTORY 

Previous Permit Action 

The Department issued NPDES Permit #101714 on August 9,1999. The permit expired on June 30,2004. The 

Department received renewal application #983793 on December 31,2003. The permit shall not be deemed to 

expire until final action has been taken on the renewal application. 

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Two treated effluent outfalls, five combined sewer overflow points, four emergency sanitary sewer overflow points, 

a treated combined sewer effluent outfall and a groundwater lagoon outfall point are identified in the 1999 permit. 

Current Permit Limits 

Schedule A contains the effluent limits for the treatment facility. Some limits are dependent upon the season 

(summer and winter) while others are year-round. The current permit limits are as follows: 

Outfalls 001 and 002- Wastewater Treatment Plant 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 

810 

810 

Weekly 

Average 

lb/day 

1200 

1200 

Daily 

Maximum 

lbs 

1600 

1600 

(2) November!-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 

3500 

4300 

Weekly 

Average 

lb/day 

5700 

6400 

Daily 

Maximum 

lbs 

7000 

8600 

(3) Other Parameters: 

Other parameters (year-round) 

E. coli Bacteria 

pH 

CBOD5 and TSS Removal Efficiency 

Total Chlorine Residual 

Limitations 

Shall not exceed 126 organisms per 100 ml monthly 

geometric mean. No single sample shall exceed 406 

organisms per 100 ml. (See Note 1) 

Shall not be outside the range of 6.0 - 9.0 for more than a 

total of 7 hours and 26 minutes in any calendar month, and 

no individual excursion from this range shall exceed 60 

minutes 

Shall not be less than 85% monthly average, except when 

flows exceed 12 MGD monthly average, the percent 

removal efficiency shall not be less than 75% monthly 

average 

Shall not exceed a daily average concentration of 0.5 mg/L 

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NOTES: 

1. If a single sample exceeds 406 organisms per 100 ml, then five consecutive re-samples may be taken at 

four hour intervals beginning within 28 hours after the original sample was taken. If the log mean of the 

five re-samples is less than or equal to 126 organisms per 100 ml, a violation shall not be triggered. 

Operational and maintenance requirements, discharge prohibitions and other conditions are included for the 

other outfalls. 

Compliance History 

The facility was last inspected on June 21,2010 and was found to be operating in compliance with the permit. 

The following Notices of Noncompliance (NON) have been issued for violations documented at this facility in 

the last five years: 

Date of Violation 

April 29, 2008 

Type of Enforcement Action 

Warning Letter 

Description of Violation ,. 

Incomplete Discharge Monitoring 

Report 

TYPES OF 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 have been established by EPA rules. 

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 (discussed above). These may be 

technology-based limits, water quality-based limits, or limits based on best professional judgment. When 

renewing a permit, the most stringent of technology-based, water quality-based, and existing effluent limits must 

be applied. 

Technology-Based Effluent Limits 

EPA has established secondaiy treatment standards for domestic wastewater treatment facilities. The standards 

are found in 40 CFR Part 133. This facility must achieve a biochemical oxygen demand (BOD5) monthly 

average of 30 mg/L and a weekly average of 45 mg/L or a carbonaceous biochemical oxygen demand (CBOD5) 

monthly average of 25 mg/L and a weekly average of 40 mg/L. The facility must also achieve a suspended 

solids (TSS) monthly average of 30 mg/L and a weekly average of 45 mg/L. The pH must be between 6.0 and 

9.0. 

In addition, a minimum level of percent removal for BODS and TSS for municipal dischargers is required by the 

Code of Federal Regulations (CFR) secondaiy treatment standards (40 CFR, Part 133). An 85 percent removal 

efficiency limit is generally included in permits in order to comply with federal requirements. 

However, federal regulations include special considerations for facilities with combined sewers. 40 CFR 

133.103 (a) states that "For such treatment works, the decision must be made on a case-by-case basis as to 

whether any attainable percentage removal level can be defined, and if so, what the level should be." 

Previously, the Department determined the facility should be capable of achieving a 75% removal efficiency 

when monthly average flows exceed 12 MGD. The facility has been able to comply with this limit and the 

Department proposes to retain the limit. 

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Oregon Administrative Rules also establish minimum design criteria for domestic treatment facilities. In the 

Willamette Basin, the CBOD5 and TSS minimum design criteria is 10 mg/L as a monthly average in the summer 

period and secondaiy treatment in the winter period. In addition, there are requirements for disinfection and 

reduction of oxygen demanding pollutants. 

Water Quality-Based Effluent Limits 

Pollutant parameters should be limited if there is a reasonable potential for the discharge to cause or contribute 

to an excursion above any state water quality criteria or standard. In addition, TMDLs may assign WLAs to 

sources to address in-stream violations of water quality criteria. 

The Department is required to determine whether the discharge has the reasonable potential to cause or 

contribute to an exceedence of a water quality criterion. EPA has developed a method to make this 

determination for toxic pollutants called a reasonable potential analysis (RPA). An RPA relies on statistical 

probability to determine the likelihood that a discharge will violate an instream criterion based on the effluent 

data, its variability, available dilution, and the receiving water background concentration. The Department has 

developed RPA spreadsheets that employ EPA's methodology. 

A reasonable potential analysis (RPA) for ammonia, chlorine, cyanide and metals and toxic organics was 

performed by evaluating effluent data in the DEQ spreadsheets. 

The RPA for ammonia (see Attachment #2) indicated that there is no reasonable potential to cause or contribute 

to an excursion of the state water quality criteria during the summer (low-flow), or winter (high-flow) season 

which includes the salmonid rearing (Oct 15-Mayl5) and migration seasons (May 16-Oct 14). The analysis for 

ammonia considered representative pH, temperature, and alkalinity conditions in both the treated effluent and 

receiving water upstream from the outfall to determine appropriate ammonia criteria according the state's rules. 

Effluent ammonia data from the past three years, as well as background ammonia from 1987 to 2004 from just 

upstream of the outfall, were also used in the analysis. No ammonia limits will be proposed. 

The RPA for metals indicated that there is no reasonable potential to exceed both the corresponding state aquatic 

(see Attachment #3),and human health (see Attachment #4) water quality standards for these pollutants. 

Effluent data derived using acceptable reporting limits from 2003-2009 was used in the analysis. Background 

metals data collected from 2002-2003 one-half mile upstream from the outfall was also used. 

Critical low Willamette River flows for all toxic analyses were derived from a DFLOW model. The raw 

receiving water data set included combined flows from the Willamette River measured at Harrisburg, and the 

Long Tom River before the confluence with the Willamette and the Maiys River. Data from 1969 through 2004 

was used. 

Whole Effluent Toxicity 

Whole Effluent Toxicity (WET) is a term used to describe the aggregate toxic effect of an aqueous sample (e.g., 

whole effluent wastewater discharge) as measured by an organism's response upon exposure to the sample (e.g., 

lethality, impaired growth or reproduction). WET tests replicate, to the greatest extent possible, the total effect 

and actual environmental exposure of aquatic life to toxic pollutants in an effluent without requiring the 

identification of the specific pollutants. WET testing is a vital component of the water quality standards 

implementation through the NPDES permitting process. 

EPA's WET test methods include an acute test (96 hours or less, endpoint: mortality), and a chronic test (7 day 

life-cycle test, endpoints: growth, reproduction, and mortality). EPA has developed WET test protocols using 

both freshwater and marine and estuarine test species. EPA recommends running tests using an invertebrate, 

vertebrate and a plant to identify the most sensitive species for developing NPDES WET permit limits or testing 

requirements. The organisms used in freshwater WET tests are Ceriodaphma dubia (freshwater flea), 

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Pimephales promelas (fathead minnow) and Raphidocelis subcapitata (green alga formerly known as 

Selanastrum capricornutum). These organisms 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 designed to predict the impact and toxicity of effluents discharged from point sources into waters 

of the United States. WET monitoring requirements are included in NPDES permits to generate data for use in 

assessing whether the effluent as a whole demonstrates toxicity. The 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. An acute WET test is considered to show toxicity if lethality is 

found at concentrations less than those occurring at the edge of the zone of immediate dilution (ZID). A chronic 

WET test is considered to show toxicity if any adverse affect occurs at concentrations less than that which is 

known to occur at the edge of the mixing zone. 

The City was required to conduct acute and chronic WET tests quarterly for one year with no further testing if 

tests resulted in no toxicity at the determined dilutions. The Department has reviewed the reports and found that 

all results of the tests passed all acute and chronic toxicity requirements. The proposed permit will require that 

acute and chronic WET tests be performed quarterly for one year or annually for four years during the permit 

cycle. 

PERMIT DRAFT DISCUSSION 

An Antidegradation Review was completed (see Attachment #5) with a recommendation to proceed with this 

permit action. The proposed permit limits and conditions are described below. Refer to the proposed permit and 

the discussion above when reviewing this section. 

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. Permits discharge of treated effluent to the Willamette River and to beneficially land apply treated 

Class A, Class B, Class C, and Class D recycled wastewater within limits set by Schedule A and the following 

schedules. All other discharges are prohibited. 

hi accordance with OAR 340, Division 49 all permitted municipal wastewater collection and treatment facilities 

are to receive a classification based on the size and complexity of the systems. The Department has incorporated 

the classification of the collection and treatment systems into the NPDES discharge permit. The Department 

evaluated the classifications for the treatment and collection systems (see Attachment #6). The Department is 

not proposing any changes to the system classifications for the facilities. 

Schedule A - Waste Discharge limitations 

Schedule A contains the effluent limitations proposed for Outfalls 001 and 002. There are requirements and 

conditions for discharges from the combined sewage overflow treatment facility, Outfall 012, Finally, Schedule 

A prohibits adverse impacts on existing or potential beneficial uses of groundwater. 

Outfalls 001 and 002 - Treated Effluent 

The Department is generally proposing to retain the existing limits. New limits are proposed for thermal 

discharges while more stringent limits are proposed for total residual chlorine. 

CBOD5 and TSS concentration and mass limits 

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Based on the Willamette Basin minimum design criteria, wastewater treatment resulting in a monthly average 

effluent concentration of 10 mg/L for CBOD5 and TSS must be provided from May 1 through October 31. From 

November 1 through April 30, a minimum of secondary treatment is required. Secondaiy treatment in Oregon is 

defined as monthly average concentration limit of 30 mg/L for BOD5 or 25 mg/L for CBOD5 and 30 mg/L for 

TSS. 

The City has previously requested concentration and mass limits based on CBOD5. The Department is 

proposing to renew the existing concentration limits that are at least as stringent as the basin minimum design 

criteria. The proposed monthly average summer CBOD5 and TSS concentration limits are 10 mg/L with a 

weekly average limit of 15 mg/L. The proposed monthly average winter CBOD5 concentration limits are 25 

mg/L with a weekly average limit of 40 mg/L. 

The summer monthly average mass loads are based on the average dty weather design flow (9.7 MGD) and a 

concentration of 10 mg/L. The weekly average and daily maximum mass limits were 1.5 and 2.0 times the 

monthly average mass limits, respectively. The calculations for the proposed summer limits are: 

a) 9.7 MGD x 8.34 lbs/gal x 10 mg/L = 809 (810) lbs/day monthly avg. 

b) 809 lbs/day monthly avg x 1.5 = 1214 (1200) lbs/day weekly avg. 

c) 809 lbs/day monthly avg x 2 = 1618 (1600) lbs daily maximum 

The winter CBOD5 and TSS monthly average mass limits were based on the average wet weather design flow to 

the facility equaling 17.0 MGD and monthly average concentrations of 25 and 30 mg/1, respectively. The 

weekly average and daily maximum mass limits were 1.5 and 2.0 times the monthly average mass limits, 

respectively. The calculations for the proposed CBOD5 winter limits are: 

a) 17 MGD x 8.34 lbs/gal x 25 mg/L = 3545 (3500) lbs/day monthly avg. 

b) 3545 lbs/day monthly avg x 1.5 = 5318 (5300) lbs/day weekly avg. 

c) 3545 lbs/day monthly avg x 2 = 7090 (7100) lbs daily maximum 

The previous two permit actions included a weekly average CBOD5 limit of 5700 pounds per day. This limit 

was calculated based on the weekly concentration limit of 40 mg/L times 17 MGD times 8.34 lbs/gal and not 1.5 

times the monthly average in lbs/day as indicated in the calculation above. This limit was agreed upon during 

the original design of the existing facility, Therefore, the Department proposes to retain the previous permits 

weekly average limit of 5700 pounds per day hi addition; the daily maximum limit calculation indicates the 

limit should have been 7100 pounds per day. However, the previous permit limited the daily maximum to 7000 

pounds per day and the City has been able to comply with the old limit. The Department camiot raise the limit, 

therefore the existing limit of 7000 pounds per day will be retained. 

The calculations for the proposed TSS winter limits are: 

a) 17 MGD x 8.34 lbs/gal x 30 mg/L - 4253 (4300 rounded) lbs/day monthly avg. 

b) 4253 lbs/day monthly avg x 1.5 ^ 6380 (6400 rounded) lbs/day weekly avg. 

c) 4253 lbs/day monthly avg x 2 ~ 8506 (8600 rounded) lbs daily maximum 

CBOD and TSS Percent Removal Efficiency 

A minimum level of 85 percent removal efficiency for CBOD5 and TSS for municipal dischargers is normally 

required by the Code of Federal Regulations (CFR) secondaiy treatment standards (40 CFR, Part 133.102). 

However, federal regulations include special considerations for combined sewers. 40 CFR 133.103(a) states 

such treatment works may not be capable of meeting the percent removal requirements during wet weather. For 

such treatment works, the decision must be made on a case-by-case basis as to whether any attainable percentage 

removal level can be defined, and if so, what the level should be. 

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The prior permit required the facility to achieve 85 percent removal efficiency as a monthly average except 

when flows exceed 12 MGD as a monthly average. When flows exceed 12 MGD, the percent removal 

efficiency may not be less than 75 percent monthly average. The Department proposes to retain the existing 

limits. 

Arsenic 

Arsenic is found at naturally occurring elevated concentrations in many of the streams in Oregon, including the 

Willamette River. Much of the City of Corvallis's drinking water is taken from the Willamette River where the 

total arsenic concentrations have been measured at approximately 0.466 ug/L, The total arsenic concentration in 

the wastewater facility's effluent was measured at 1.3 ug/L. 

The Department is currently in the process of revising its human health arsenic criterion and will be proposing a 

criterion to better reflect the more toxic speciation's of arsenic (inorganic arsenic) using a regionally appropriate 

health-risk calculation method. This will result in a shift of the standard from "total" to the "inorganic" fraction, 

and re-evaluation to better reflect regional health risks. Given these imminent changes, the facility is being 

directed to ensure that current treatment facilities are being operated at the highest and best extent practicable 

and that they implement an interim monitoring and source control strategy to collect the necessaiy data to 

implement the new standard during the next permit cycle. The minimum safeguards are discussed below: 

The facility has conducted a preliminary source investigation of all industrial users to ensure that no permitted 

significant industrial users discharge process wastewaters that contain arsenic as a process byproduct. There are 

no federally mandated technology-based effluent limits for arsenic for any of the industrial users in the system. 

There are no aquatic toxicity criterion for total arsenic and discharges are well below the aquatic toxicity criteria 

for Arsenic IH (190/360 ug/L). The activated sludge treatment process effectively removes some sedimentbased arsenic and incorporates a small percentage of dissolved arsenic in the sludge. The Department has 

established a quarterly average of 2.5 ug/L total arsenic as a non-regulatory benchmark to use in assessing 

whether the applicable treatment technology is providing the highest and best practicable treatment for arsenic in 

the discharge. This quarterly average value is the Calculated Maximum Effluent Concentration and reflects a 

worst case scenario, using historical discharge and ambient data at the 95% confidence level. For the purposes 

of the Departments' arsenic interim implementation procedure and this permit, the current treatment facility will 

be considered the "Best Available Treatment" and the requirement for the facility to continue to operate and 

manage treatment at the "highest and best extent practicable" is in the proposed permit. As a performance 

measure, if the quarterly average concentrations of total arsenic exceed 2.5ug/L, the facility will be required to 

submit a report to the Department detailing the conditions that lead to the exceedence. The Department will use 

the report, monitoring information and operation records to determine if the facility failed to comply with the 

narrative operational requirements. 

The "monitoring strategy" will require that the facility perform the following steps: 

• The permit will include the requirements (in Schedule D) for the facility to develop and submit for 

approval, within 120 days of permit issuance, an additional Arsenic Quantification Plan. At a minimum, 

the plan will reference the Schedule B and Pretreatment monitoring requirements in the permit. The 

permittee must begin implementation of the Arsenic Quantification Plan within two weeks of 

notification of plan approval by the Department. If the Department determines that the plan is not 

approvable, the Department will notify the permittee of the missing plan elements. The permittee is 

required to implement the plan until written notification by the Department that further implementation 

is not warranted. 

• The permit will require that the facility begin implementation of the approved plan within two weeks of 

Departmental approval. 

• Upon approval of the revised inorganic arsenic criterion, the Department intends to confer with the 

facility with the purpose of evaluating the collected Schedule B and Pretreatment monitoring data to 

determine if there might be an affirmative or negative Reasonable Potential Analysis (RPA) finding for 

the inorganic arsenic criterion. 

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• Upon approval of the revised inorganic arsenic criterion, if the collected Schedule B and Pretreatment 

monitoring data indicates the potential for an affirmative RPA finding, the Department expects the 

facility to develop a management strategy to ensure compliance. The facility would have the remainder 

of the permit cycle to collect any additional data to support the management strategy and undertake any 

required administrative actions (i.e variance, site-specific criterion, compliance schedule, permits 

modification, etc.). 

• Upon approval of the revised inorganic arsenic criterion, if the collected Schedule B and Pretreatment 

monitoring data indicates a negative RPA finding, the facility may conclude any monitoring or 

compliance requirements to address the narrative arsenic effluent limits or benchmarks but shall 

continue to comply with all other Schedule B and Pretreatment monitoring requirements in the permit. 

The non-regulatory benchmark to use in assessing whether the applicable treatment technology is providing the 

highest and best practicable treatment for arsenic in the discharge is only applicable until the EPA takes action 

on the proposed inorganic arsenic criterion. 

pH 

The Willamette Basin Water Quality Standard for pH is found in OAR 340-041-0345. The allowed range is 6.5 

to 8.5. Generally pH permit limits for treatment plants range from 6.0 to 9.0. These limits are based on Federal 

secondaiy treatment standards for sewage treatment facilities, and are applied to the majority of 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's Reasonable Potential Analysis (RPA) calculates the pH of the discharge combined with the 

receiving stream at the edge of the mixing zone. Based on the assumed critical case conditions, the RPA (see 

Attachment 7) demonstrates that mixing with ambient water within the mixing zone ensures that the pH meets 

the standard. 

Monitoring for pH is continuous. When continuous monitoring is provided, the permit allows the discharge to 

be outside the allowed range for up to 1 percent (7 hours and 26 minutes) of any calendar month. No single 

excursion may last longer than one hour. The Department considers the proposed permit limits to be protective 

of the water quality standard. 

E. coli 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 resamples. If the log mean of the five re-samples is less than or equal to 126, a violation is not triggered. The resampling 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)), establishes a prohibition 

against discharging raw sewage, 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 Sanitaiy 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 

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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 sanitaiy 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 in the January 20, 1994 CH2M Hill paper on 

"Rainfall Analysis and SFO Design Storms" prepared specifically for Corvallis, Oregon. In the event that a 

permit holder reports an overflow event associated with a storm event and DEQ does not have information from 

the permit holder 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. go vAidsc/pfds/other/orpfds. html, however the file is veiy 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 source as 

necessaiy. 

In addition, the City of Corvallis in support of an effort to develop SSO compliance requirements has performed 

a flow frequency analysis to establish relationships between rainfall and wet weather flow in the City's 

separated sanitaiy sewer system. This information was developed to help the City of Corvallis define the storm 

duration, the beginning of a rainfall event, and the antecedent rainfall with a single 5-year frequency flow rate at 

specific locations in the sanitaiy sewer collection system. The City's statistical analysis of the flow rates in the 

collection system identified the flow rate associated with a 5-year storm recurrence interval with the intent that 

SSOs would not be allowed for measured flows up to and including this defined rate. The Department has 

informed the City of Corvallis that DEQ cannot predict whether a SSO is beyond the permittees control or if it 

will result in a violation based solely on the City's flow frequency analysis. However, the Department has 

agreed to review the City's determination for any single overflow event in conjunction with other storm related 

information in order to support the Departments decision as to whether a violation has occurred. 

Chlorine 

Chlorine is added to the discharge to disinfect the plant effluent and comply with the waste discharge limitations 

for bacteria. The minimum design criteria (OAR 340-041-0007) for sewage wastes requires the City to provide 

disinfection facilities capable of achieving 1.0 mg/L total chlorine residual. This concentration could be 

considered a technology based minimum concentration. 

Chlorine is a known toxic substance and as such is subject to limitation under Oregon Administrative Rules. 

The rule (OAR 340-041) states in part that toxic substances shall not be discharged to waters of the state at 

levels that adversely affect public health, aquatic life or other designated beneficial uses. In addition, levels of 

toxic substances shall not exceed the criteria listed in Table 20, which were based on criteria established by the 

EPA and published in Quality Criteria for Water (1986), unless otherwise noted. 

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However, OAR 340-041 -0053 states that the Department may allow a designated portion of a receiving water to 

serve as a zone of dilution for wastewaters and receiving waters to mix thoroughly and this zone will be defined 

as a mixing zone. The Department may suspend all or part of the water quality standards, or set less restrictive 

standards, in the defined mixing zone, provided the water within the mixing zone is free of materials in 

concentrations that will cause acute toxicity to aquatic life as measured by the acute Whole Effluent Toxicity 

method and outside the boundary of the mixing zone is free of materials in concentrations that will cause chronic 

toxicity. 

Furthermore, 40 CFR § 122.44(d) states that permit limitations must control all pollutants or pollutant parameters 

which are or may be discharged at a level which will cause, have the reasonable potential to cause, or contribute 

to an excursion above any state water quality standard, including state narrative criteria for water quality. The 

fresh water criteria for chlorine were used to calculate permit limitations. According to OAR 340-041, Table 20, 

chlorine concentrations of 11 ug/L can result in chronic toxicity in fresh waters while 19 ug/L can result in acute 

chlorine toxicity in fresh waters. 

Compliance with acute toxicity criteria is required at the edge of the Zone of Initial Dilution (ZED) and 

compliance with chronic toxicity criteria is required at the edge of the mixing zone. For the facility, outfall, and 

mixing zone as presently configured, the dilution factor is 33 at the edge of the ZID and 90 at the edge of the 

mixing zone during critical low (summer) stream flow conditions. Permit limits based on these dilutions, a 

coefficient of variance of 0.228 and the acute and chronic criteria were calculated (see Attachment 8). The 

calculated permit limits are: 

Shall not exceed a monthly average concentration of 0.41 mg/L and a daily maximum concentration of 

0.63 mg/L 

The current permit limits total residual chlorine to a daily average concentration of 0.5 mg/1. The proposed 

water quality based permit limits must be as restrictive as the existing permit limits. Therefore, the proposed 

chlorine permit limits are: 

Shall not exceed a monthly average concentration of 0.41 mg/L and a daily maximum concentration of 

0.50 mg/L 

Excess Thermal Load 

As discussed above, waters in the Willamette Basin are water quality limited for temperature from April 1 

through October 31. This facility received a temperature Waste Load Allocations (WLA) for that period in the 

2006 Willamette Total Maximum Daily Load (TMDL). There are WLA for the rearing and migration season 

(May 16 through October 14) and spawning season (April 1 through May 15 and October 15 through October 

31). The WLA are directly convertible to Excess Thermal Load (ETL) limits. There are three options for 

determining the ETL limit based on the amount of receiving stream monitoring the permittee is willing to 

perform and report. The options and limits are as follows: 

Option A - no stream monitoring needed 

During the rearing and migration season (May 16 through October 14), the WLA states the permittee may not 

discharge more than 108 million Kcals/day as a rolling seven-day average. However, the Department is 

allowing existing sources to temporarily use the reserve capacity in the TMDL. This is done by applying a 

multiplier to the WLA. During the rearing period, the multiplier allowed to Corvallis is 1.187. Therefore, the 

proposed permit limit will be 128 million Kcals/day as a rolling seven-day average. 

During the spawning season (April 1 through May 15 and October 15 through October 31), the permittee may 

not discharge more than 129 million Kcals/day as a rolling seven-day average. The Department has not 

proposed a temporary reserve capacity multiplier for the city of Corvallis during the spawning period. 

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Option B - stream monitoring for flow 

The ETL Limit for rearing and migration period may be calculated on a daily basis when river flows are 

reported. The ETL may be calculated using the formula: 

ETL = (((0.00007816 x QR) + 0.6532) - 0.1389) x 11.29 x 2.447 x (22.9 - 18) x 1.187 

The ETL Limit may also be calculated on a daily basis for the spawning period when river flows are reported. 

The ETL may be calculated using the formula: 

ETL = (((0.00009786 x QR) + 0.4072) - 0.3077) x 11.29 x 2.447 x (22.9 - 13) 

Where: QR - the rolling 7-day average ambient river flow (cfs) recorded at USGS Gage 14166000 plus 

USGS Gage 14170000 plus USGS Gage 14171000 added together, or alternatively, use Corvallis USGS 

Gage 14171600. 

Option C - stream monitoring for flow and temperature 

The ETL Limit for rearing and migration period may be calculated on a daily basis when both river flows and 

river temperatures (both daily average and daily maximum) are reported. The ETL may be calculated using the 

formula: 

ETL - (((0.00007816 x QR) + 0.6532) - a) x 11.29 x 2.447 x (22.9 - 18) x 1.187 

The ETL Limit for the spawning period may be calculated on a daily basis when both river flows and river 

temperatures are reported. The ETL may be calculated as follows: 

ETL - (((0.00009786 x QR) + 0.4072) -a)x 11.29 x 2.447 x (22.9 - 13) 

Where: QR = the rolling 7-day average ambient river flow (cfs) recorded at USGS Gage 14166000 plus 

USGS Gage 14170000 plus USGS Gage 14171000 added together, or alternatively, use Corvallis USGS 

Gage 14171600. 

The value for a is determined based on the relationship between the rolling seven-day average 

maximum natural thermal potential river temperature in °C (TRM N ), the rolling seven-day average 

natural thermal potential river temperature in °C (TRAN) and the applicable criteria in °C as follows: 

Daily Max NTP River Temp = (1.0804 x the daily maximum ambient river temperature in °C) - 2.25 

Daily Avg. NTP River Temp = (1.0543 x the daily average ambient river temperature in °C) - 2.07 

TRM„N= the rolling seven-day average daily maximum natural thermal potential river temperature (°C); 

and 

TRAN

 = the rolling seven-day average daily average natural thermal potential river temperature (°C) 

During rearing and migration: 

If TRM N is less than or equal to 18 °C, then a - 0 

If TRMN is greater than 18 °C and TRA N is greater than or equal to 18 °C, then a ~ 0 

If TRM_N is greater than 18 °C and TRA_N is less than 18 °C, then a - 1 - (TRA N -M 8 °C) 

During spawning: 

If TRM N is less than or equal to 13 °C, then a = 0 

If TRM H is greater than 13 °C and TRA N is greater than or equal to 13 °C, then a = 0 

If TRM N is greater than 13 °C and TRA N is less than 13 °C, then a ~ 1 - (TRA N

 + 13 °C) 

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The limits are based on a rolling seven-day average. Therefore, limits are to be calculated and compliance will 

be evaluated starting on the seventh day of each season (April 7th and October 21s1 for spawning and May 22nd 

for rearing). Whenever either Option B or C is used, there must be at least seven days (six preceding days and 

the day of use) of river data available. In addition, whenever either Option B or C is used, the Discharge 

Monitoring Report must state which option was used and include the result of the ETL limit calculation and 

include all data necessaiy to calculate the ETL limit. 

Shared Watershed Allocation of Thermal Load 

The permittee may participate in a Department approved Excess Thermal Load Sharing Agreement (Sharing 

Agreement) with other NPDES permittees (Sharing Partners) that were assigned thermal waste load allocations 

from the 2006 Willamette TMDL. All thermal load sharing must be managed in accordance with the 

requirements of the Sharing Agreement. The Agreement and amendments to the agreement must be submitted to 

the Department at least 30 days prior to implementation and approved by the Department in writing. Approvals 

and amendments to the Sharing Agreement are not considered permit modifications. The permittee may 

discharge the permitted Excess Thermal Load using the options listed in the permit, as allocated by the TMDL, 

plus temporary reserve capacity allocation, plus any borrowed unused portions of permitted ETL from Sharing 

Partners in accordance with the Department approved Sharing Agreement. The permittee may also share any 

unused portion of its permitted ETL including temporary reserved capacity allocation with Sharing Partners in 

accordance with the Department approved Sharing Agreement. The permittee must record the date, time, and 

the amount of ETL that was borrowed from the another permittee under the Sharing Agreement on the monthly 

Discharge Monitoring Report (DMR) and notify the other permittees and the Department's appropriate office 

within 24 hours of the date and time of the amount of borrowed ETL that was used under the Sharing 

Agreement. If the permittee exceeds its permitted ETL limit, it will not be deemed in violation of the limit if the 

amount of unused ETL from the Sharing Partners participating in the Sharing Agreement on the date of the 

exceedence is equal to or greater than the amount of the exceedence and as long as no Sharing Partners 

participating in the Sharing Agreement has utilized the amount of unused ETL on the same date. 

Mixing Zone 

The regulatory mixing zone is that portion of the Willamette River contained within a band extending out from the 

west bank thirty (30) feet beyond the eastern edge of the diffuser and extending ten (10) feet upstream and three 

hundred (300) feet downstream from the diffuser. The Zone of Immediate Dilution (ZID) is defined as that portion 

of the regulatory mixing zone that is within thirty (30) feet of the point of discharge. The Department proposes to 

retain the existing mixing zone. 

Outfalls 003. 005. and 007. Combined Sewer Overflows 

The following requirements are in fulfillment of the Nine Minimum Controls for the operation and maintenance of 

the combine sewer systems, as set forth in EPA's Combined Sewer Overflow Policy, as applicable to the permittee: 

(1) The permittee shall implement proper operation and maintenance programs for the sewer system 

and all CSO outfalls to reduce the magnitude, frequency, and duration of CSOs. The program shall 

consider regular sewer inspections; sewer, catch basin, and regular cleaning: equipment and sewer 

collection system repair or replacement, where necessaiy; and disconnection of illegal connections. 

(2) The permittee shall implement procedures that will maximize use of the collection system for 

wastewater storage that can be accommodated by the storage capacity of the collection system in 

order to reduce the magnitude, frequency, and duration of CSOs. 

(3) The permittee shall review and modify, as appropriate, its existing pretreatment program to 

minimize CSO impacts from the discharges from nondomestic users. 

OpCertClassWorksheet (Rev. 12/03/2008) 
City of Corvallis Evaluation Report 

Page 21 

(4) The permittee shall operate the POTW treatment plant at maximum treatable flow during all wet 

weather flow conditions to reduce the magnitude, frequency, and duration of CSOs. The permittee 

shall deliver all flows to the treatment plant within the constraints of the treatment capacity of the 

POTW. 

(5) Dry weather overflows from CSO outfalls are prohibited. Each dty weather overflow must be 

reported to the DEQ as soon as the permittee becomes aware of the overflow. When the permittee 

detects a dry weather overflow, the permittee shall begin corrective action immediately. The 

permittee shall inspect the dty weather overflow each subsequent day until the overflow has been 

eliminated. 

(6) The permittee shall implement measures to control solid and floatable materials in CSOs. 

(7) The permittee shall implement a pollution prevention program focused on reducing the impact of 

CSOs on receiving waters. 

(8) The permittee shall implement a public notification process to inform citizens of when and where 

CSOs occur. The process must include (a) a mechanism to alert persons of the occurrence of 

CSOs and (b) a system to determine the nature and duration of conditions that are potentially 

harmful for users of receiving waters due to CSOs. 

(9) The permittee shall monitor CSO outfalls to characterize CSO impacts and the efficacy of CSO 

controls. This shall include collection of data that will be used to document the existing baseline 

conditions, evaluate the efficacy of the technology based controls, and determine the baseline 

conditions upon which the long-term control plan will be based. These data shall include: 

(a) Characteristics of the combined sewer system including the population served by the 

combined portion of the system and locations of all CSO outfalls in the CSS. 

(b) Total number of CSO events and the frequency and duration of CSOs for a representative 

number of events. 

(c) Locations and designated uses of receiving water bodies. 

(d) Water quality data for receiving water bodies. 

(e) Water quality impacts directly related to CSOs (e.g., public access closing, floatables 

wash-up episodes, fish kills). 

Outfall 012, Combined Sewage Treatment System Discharge 

The Permittee shall operate the combined sewer relief interceptor and CSO wet weather treatment facilities to 

minimize the frequency of CSOs through Outfalls 003,005, and 007, and maximize the volume of wastewater 

treated at the POTW and the wet weather treatment facility. 

Captured combined sewage shall receive a minimum of secondaiy treatment to the maximum extent practicable. 

For those storm events that exceed the capacity of the POTW and prompt the diversion of combined sewage to the 

wet weather treatment facility, the combined sewage shall receive equivalent of primary treatment and disinfection. 

Outfall 014 - Recycled Water 

Prior to irrigation of the recycled water, the discharge must comply with total coliform limits based on protection of 

human health due to human pathogens. Depending on the selected alternative of land application and the type of 

use for the recycled water, the permittee may generate Class D, Class C, Class B or Class A recycled water. For 

Class B recycled water, the recycled water must be oxidized and disinfected so as not to exceed a median of 2.2 

total coliform bacteria organisms per 100 mL, based on results of the last seven days that analyses have been 

OpCertClassWorksheet (Rev. 12/03/2008) 
City of Corvallis Evaluation Report 

Page 22 

completed, and 23 total coliform organisms per 100 mL in any single sample. For Class A recycled water, before 

disinfection, the wastewater must be treated with a filtration process and the turbidity must not exceed an average 

of 2 nephelometric turbidity units (NTU) within a 24-hour period, 5 NTU more than five percent of the time within 

a 24-hour period, and 10 NTU at any time. After disinfection, the wastewater must not exceed a median of 2.2 total 

coliform bacteria organisms per 100 mL, based on results of the last seven days that analyses have been completed, 

and 23 total coliform bacteria organisms per 100 mL in any single sample. 

A Recycled Water Use Plan must be approved by the Department prior to the permittee land applying the treated 

recycled wastewater through Outfall 014. Following Department approval, the land application of wastewater shall 

conform to the Department approved plan. 

Specific crops, application rates and buffers will be approved by the Department within the Recycled Water Use 

Plan. The bacterial effluent limitations are achievable through proper operation and maintenance. 

Schedule B - Minimum Monitoring and Reporting Requirements 

Schedule B describes the minimum monitoring and reporting necessaiy to demonstrate compliance with the 

conditions of this permit. The authority to require periodic reporting by permittees is included in ORS 

468.065(5). Self-monitoring requirements are the primary means of ensuring that permit limitations are being 

met. However, other parameters need to be monitored to collect information when insufficient information 

exists to establish a limit, but where there is a potential for a water quality concern. 

The Department has developed a monitoring matrix for commonly monitored parameters. Proposed monitoring 

frequencies for all parameters are based on this matrix and, in some cases, may have changed from the current 

permit. The proposed monitoring frequencies for all parameters correspond to those of facilities of similar size 

and complexity in the state. 

The permittee is required to have a laboratory Quality Assurance/Quality Control program. The Department 

recognizes that some tests do not accurately reflect the performance of a treatment facility due to quality 

assurance/quality control problems. These tests should not be considered when evaluating the compliance of the 

facility with the permit limitations. Thus, the Department is also proposing to include in the opening paragraph 

of Schedule B a statement recognizing that some test results may be inaccurate, invalid, do not adequately 

represent the facility's performance and should not be used in calculations required by the permit. 

Below is a discussion of some of the minimum monitoring requirements contained in the proposed permit: 

Influent and Outfall 00 L 002, and 012 (Treated Effluent) 

Daily monitoring of effluent flow and calibration of the flow meter eveiy six months is retained in this permit. 

Monitoring of the influent flow is not required. However, the City may use the influent flow meter (when 

properly calibrated) in place of the effluent flow meter when the effluent flow meter cannot be used (such as 

when the chlorine contact chamber is taken out of service for maintenance). 

Continuous monitoring of the influent and effluent for pH has been retained. Monitoring of the influent and 

effluent for CBOD5 and TSS is retained at three times per week. Pounds of CBOD5 and TSS in the discharge 

must be calculated at the same frequency. The City has previously requested that effluent limits (concentration, 

mass and percent removal) be based on CBOD5 rather than BOD5. 

Federal secondaiy treatment standards require municipal sources to achieve a specific CBOD5 and TSS removal 

efficiency as a monthly average. Reporting of the removal efficiencies is required in the current permit and no 

changes are proposed. 

The proposed permit requires monitoring of the effluent for total chlorine residual on a daily basis to confirm 

consistent performance of the disinfection system. The amount of chlorine used each day must also be 

OpCertClassWorksheet (Rev. 12/03/2008) 
City of Corvallis Evaluation Report 

Page 23 

monitored. Bacteria monitoring of the effluent for E. coli has been retained at three times per week. Monitoring 

for E. coli must be performed in accordance with one of the methods approved by EPA. 

Ammonia monitoring is required because CBOD5 replaces BOD5. Monitoring must be performed on the same 

samples as CBOD5 so the Department proposes to continue monitoring at three times per week monitoring. 

Continuous temperature monitoring of the effluent is required year round. The daily maximum temperature 

must be reported on the monthly Discharge Monitoring Report. The permittee will also be required to calculate 

the rolling 7-day average of the daily maximum effluent temperatures and the rolling 7-day average of the 

thermal load discharged from April 1 through October 31. These are new requirements. 

In order to fully characterize the facility's contribution of nutrients to the receiving stream, the Department is 

proposing to require monitoring of the treated effluent for nutrients. During the period from May through 

October, weekly monitoring of the effluent for nutrients (Total Kjeldahl Nitrogen (TKN), nitrate plus nitrite and 

total phosphorus) shall be required during the first year of the permit. After one year, monitoring of the effluent 

for nutrients may be eliminated unless notified in writing by the Department. 

The proposed permit requires continued monitoring of the influent and effluent for metals and cyanide semiannually using 3 consecutive days between Monday and Friday, inclusive. Results are to be submitted with the 

Pretreatment Program Annual Report. Submittal of metals monitoring results with the monthly Discharge 

Monitoring Report is not required. 

The proposed permit requires annual whole effluent toxicity (WET) tests for four years using three species, or 

quarterly for one calendar year. If the results of the first four annual tests show that the effluent is not toxic, no 

further Whole Effluent Toxicity testing will be required during this permit. Whole Effluent Toxicity tests are to 

be conducted in accordance with EPA test methods and procedural requirements as defined in Schedule D. 

The proposed permit requires the City to monitor the effluent for metals (except arsenic), cyanide, total phenolic 

compounds and hardness semi-annually over three consecutive days for five years. In addition, Arsenic is to be 

monitored quarterly for two and one half years. The permittee must perform "priority pollutant" scans for 

organic pollutants in order to complete Part D of EPA Form 2A for the next renewal application. Three scans 

are required during the two years after permit issuance. Two of the three scans must be performed no fewer than 

four months and no more than eight months apart. 

Test methods used must have quantitation limits less than or equal to those listed in the tables in Schedule B 

unless otherwise approved by the Department in writing. 

Biosolids 

OAR 340, Division 50, "Land Application of Domestic Wastewater Treatment Facility Biosolids, Biosolids 

Derived Products, and Domestic Septage" requires monitoring and reporting of specific sludge parameters under 

Section 35. These parameters are identified in Schedule B under "Biosolids Management" and include: Total 

solids, Volatile solids, Nitrogen, eleven metals (Ag, As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Se & Zn), Phosphorus, 

Potassium and pH. 

In order to demonstrate compliance with pathogen reduction requirements, the proposed permit requires 

monitoring of biosolids for fecal coliform. The Permittee may use any alternative method of demonstrating 

compliance with pathogen reduction requirements approved under 40 CFR Part 503.32 and as listed in the 

Department approved Biosolids Management Plan. In order to demonstrate compliance with vector attraction 

reduction requirements, the proposed permit requires monitoring of percent volatile solids reduction. The 

Permittee may use any alternative method of demonstrating compliance with vector attraction reduction 

requirements in accordance with OAR 340-050 and as listed in the Department approved Biosolids Management 

Plan. The permittee must also record land application information about the biosolids that are beneficially used. 

OpCertClassWorksheet (Rev. 12/03/2008) 
City of Corvallis Evaluation Report 

Page 24 

Reporting 

The reporting period is the calendar month. Discharge monitoring reports must be submitted to the Department 

monthly by the 15th day of the following month. The monitoring reports need to identify the principal operators 

designated by the Permittee to supervise the treatment and collection systems. The reports must also include 

records concerning application of biosolids and all applicable equipment breakdowns and bypassing. 

Schedule B of the permit includes the requirement for the submittal of four annual reports. The permittee must 

submit an annual report on inflow and infiltration reduction activities, a report on recycled water utilization, a 

report on biosolids handling and sludge disposal activities and a report on activities undertaken to implement the 

Nine Minimum Controls related to EPA's Combined Sewer Overflow Policy. 

Schedule D - Special Conditions 

The permit contains eleven special conditions. The requirements include: 

1. The first condition describes the seasonal delineation of the secondaiy treatment works and the CSO 

facility. 

2. Biosolids be managed in accordance with the approved biosolids management plan. 

3. The permit may be modified to incorporate changes in federal biosolids standards. 

4. The permittee must notify the Department of malfunctions. 

5. The permittee must have the facilities supervised by personnel certified by the Department in the 

operation of treatment and/or collection systems. 

6. The permittee is required to comply with the rules concerning the use of recycled water and the 

Recycled Water Use Plan approved by the Department. 

7. The permittee shall conduct Whole Effluent Toxicity Testing. 

8. Any recycled water used at the treatment plant site for landscape irrigation will be exempt from OAR 

340-055 provided the reclaimed water receives secondary treatment and disinfection. 

9. The permittee may develop a water quality trading program to help meet the thermal limits. 

10. The Permittee shall be required to submit updated Mixing Zone dilutions using a center line approach 

with the next permit renewal application. 

11. The permittee must submit an Arsenic Quantification Plan. 

Schedule E - Pretreatment Program 

The current permit contains twelve conditions that are standard for most cities in Oregon that have Industrial 

Pretreatment Programs. These twelve conditions were last updated in December 2008. This Schedule 

implements the requirements of a pretreatment program as required by Part 403.8 of the Code of Federal 

Regulations. The Department is proposing to include these updated conditions in the proposed permit. 

Schedule F - NPDES General Conditions 

All NPDES permits issued in the State of Oregon contain certain conditions that remain the same regardless of 

the type of discharge and the activity causing the discharge. These conditions are called General Conditions. 

OpCertClassWorksheet (Rev. 12/03/2008) 
City of Corvallis Evaluation Report 

Page 25 

These conditions can be changed or modified only on a statewide basis. The September 18, 2009 edition is 

included as Schedule F of the draft permit. 

Section A contains standard conditions which include compliance with the permit, assessment of penalties, 

mitigation of noncompliance, permit renewal application, enforcement actions, toxic discharges, property rights 

and referenced rules and statutes. Section B contains requirements for operation and maintenance of the 

pollution control facilities. This section includes conditions for proper operation and maintenance, duty to halt 

or reduce activity in order to maintain compliance, bypass of treatment facilities, upset conditions, treatment of 

single operational events, overflows from wastewater conveyance systems and associated pump stations, public 

notification of effluent violation or overflow, and disposal of removed substances. Section C contains 

requirements for monitoring and reporting. This section includes conditions for representative sampling, flow 

measurement, monitoring procedures, penalties of tampering, reporting of monitoring results, additional 

monitoring by the permittee, averaging of measurements, retention of records, contents of records, and 

inspection and entry. Section D contains reporting requirements and includes conditions for reporting planned 

changes, anticipated noncompliance, permit transfers, progress on compliance schedules, noncompliance which 

may endanger public health or the environment, other non-compliances, and other information. Section D also 

contains signatory requirements and the consequences of falsifying reports. Section E contains the definitions 

used throughout the permit. 

The General Conditions were revised in 2008/2009. A summary of the changes is as follows: 

• 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. 

OpCertClassWorksheet (Rev. 12/03/2008) 
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Attachment 5 

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: Municipal wastewater treatment 

Is this review for (rene^y_l OR new (circle one) permit application? 

Go to Step 2. 

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

Resource Water? 

No. Go to Step 3. 

3. Is this surface water a High Quality Water? 

No. Go to Step 4. 

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

Yes. Go to Step 14. 

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] 

No. Proceed with Permit Application. Applicant should provide basis for conclusion. Go to Step 21. 

This conclusion is explained and supported by data and evaluations included with the Permit Evaluation 

Report and attachments accompanying the proposed NPDES Permit Renewal. This is an existing 

discharge and there is no change in their operation. The discharge must meet the water quality criteria 

for all parameters at the edge of the mixing zone. There is no request for a mass load increase. 

Waste load allocations assigned by the Willamette Basin TMDL to this source have been incorporated 

into the permit by this permit renewal. 

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: 
Review Prepared By: Mark E. Hamlin 

Phone: (503) 378-53 l.J 

Date Prepared: March 19, 2007^ 

Please provide the following information and submit with the completed application form to: 

Department of Environmental Quality 

Water Quality Division—Surface Water Management 

811 SW Sixth Avenue 

Portland, Oregon 97204-1390 

Name: 

Address: 

Phone: 

City of Corvallis 

P.O. Box 1083 

Corvallis, OR 97339-1083 

541 754-1757 

OpCertClassWorksheet (Rev. 12/03/2008) 
Attachment 6 

Operator Certification Worksheet 

General Requirements (OAR 340-049-0015) - Each owner of a regulated wastewater system must have its system 

supervised by one or more operators who hold a valid certificate for the type of system, wastewater treatment or collection, 

at a grade equal to or greater than the wastewater system classification as defined in OAR-340-049-0020 and 0025. 

Because classification establishes the operator certificate type and grade required for compliance, it must be determined 

prior to start-up of a new or upgraded facility. 

Wastewater treatment system classifications are derived from the total points assigned based on criteria shown in OAR 340-

049-0025 (see Step 1 of the worksheet). Pursuant to OAR 340-049-0020(4), if the complexity of a treatment system is not 

reflected in -0025, DEQ may classify a system higher as long as the designation is consistent with the intent of the 

classification system (see Step 2 of the worksheet). 

Collection system classifications are based on a service area design population to be handled by the wastewater treatment 

facility (see footnote on page 1 of worksheet). Like treatment, if deemed appropriate, DEQ may classify the system higher 

than by population alone (OAR 340-049-0020(5)). For example, the design service area population for "X" Sanitary District is 

1350 (Class I), but there are 280 city-maintained STEP or STEG units and a chemical feed system for control of hydrogen 

sulfide. A Class II designation may be appropriate to meet the intent of the classification system to establish minimum 

operator requirements for experience and knowledge. 

Upon written notice to the wastewater system owner, DEQ may change the classification of a wastewater system and give 

the owner reasonable time to comply with requirements of the new classification (OAR 340-049-0020(6)). If you have any 

questions, please contact the Operator Certification Program office in The Dalles at (541) 298-7255 x35. 

Classification of Wastewater Systems (OAR 340-049-0020) All wastewater systems regulated under OAR 340-049 will be 

classified by DEQ as wastewater treatment systems and/or wastewater collection systems, as appropriate, in accordance 

with the following classification system: 

Wastewater Treatment Systems 

Class I - 30 total points or less 

Class II - 31-55 total points 

Class III - 56-75 total points 

Class IV - 76 or more points 

Wastewater Collection Systems 

Class I -1,500 or less design population 

Class II -1,501 to 15,000 design population 

Class III -15,001 to 50,000 design population 

Class IV - 50,001 or more design population 

Definitions used in these regulations unless otherwise required by context (see OAR 340-049-0010): 

"Average Dry Weather Flow" (ADWF) means the design average dry weather flow capacity of the wastewater treatment 

system in gallons per day or Million Gallons per Day (MGD), as approved by the Department. 

"Industrial Waste" means liquid wastes from an industrial or commercial process discharged into a wastewater system for 

conveyance and treatment. 

"NPDES Permit" means a waste discharge permit issued in accordance with requirements and procedures of the National 

Pollutant Discharge Elimination System authorized by Section 402 of the Federal Clean Water Act and OAR 340, Division 

45. 

"Population" means the design population of the wastewater system represented as the number of people or the population 

equivalent the system is designed to serve. Equivalent population ordinarily is determined based on 70 gallons per person 

per day average dry weather flow (ADWF) or 0.17 lbs. BOD5 per person per day, whichever is greater. 

"Wastewater" or "sewage" means the water-carried human or animal waste from residences, buildings, industrial 

establishments or other places, together with such groundwater infiltration and surface water as may be present. The 

admixture of domestic and industrial waste or other by-products, such as sludge, is also considered wastewater or sewage. 

"Wastewater Treatment System" or "Sewage Treatment System" means any structure, equipment or process for treating and 

disposing of, or recycling or reusing wastewater and sludge (including industrial waste) that is discharged to the wastewater 

system. 

"Wastewater Collection System" or "Sewage Collection System" means the trunks, arterials, pumps, pump/lift stations, 

piping and other appurtenances necessary to collect and carry away wastewater or other liquid waste treatable in a 

community or private wastewater treatment facility. 

"Wastewater System" means "Sewage Treatment Works" defined in ORS 448.405 as any structure, equipment or process 

required to collect, carry away and treat domestic waste and dispose of sewage as defined in ORS 454.010. Typically, 

components of a wastewater system include a wastewater collection system and a wastewater treatment system. 

"WPCF Permit" means a Water Pollution Control Facilities permit to construct and operate a collection, treatment and/or 

disposal system with no discharge to navigable waters. 
Attachment 6 

Operator Certification Worksheet 

WW System Common Name; City of Corvallis Wastewater Reclamation Plant (WWRP) 

Facility ID: 20151 Location: 1304 NE Second St., Corvallis. Oregon 

Total Points (from page 3): UJ WWT Class (check): • I Ql l D IN 

l_3 iv 

Design Population1:138.000 WWC Class (check): • I • II • III 

EEIIV 

Design ADWF load (Influent MGD) 97 Design BOD load (Influent Ibs./day) 

Classified bv: Robert A. Dicksa Date: 08/18/2010 

Date this classification filed with the Operator Certification Office: 

System start-up date for this classification (new, upgrade or expansion): 

Is this a change from a prior classification? (check): • Yes __<_ No 

STEP 1 - Criteria for Classifying Wastewater Treatment Systems (OAR 340-049-0025) 

(1) Design Population or Population Equivalent Points (10 Points Maximum) 

• Less than 750 0.5 points 

D751 to 2000 1 point 

Q2001 to 5000 1.5 points 

D5001 to 10,000 2 points 

(X] Greater than 10,000 3 points+1 pt. for ea. add. 10k 

Part 1 Subtotal 17 points 

(2) Average Dry Weather Flow (Design Capacity) Points (10 points Maximum) 

• Less than 0.075 MGD 0.5 point 

• Greater than 0.075 to 0.1 MGD 1 point 

• Greater than 0.1 to 0.5 MGD 1.5 points 

• Greater than 0.5 to 1.0 MGD 2 points 

|X] Greater than 1.0 MGD 3 points+1 pt. for 

ea. add. MGD 

Part 2 Subtotal 13 points 

(3) Unit Process Points (Check ail that apply) 

Preliminary Treatment and Plant Hydraulics: See also STEP 2 

• Comminution (cutter, shredder, grinder, barminutor, etc.) 1 point 

1

 See "Population" definition. Use the design average daily equivalent load per person for 

Influent Flow or Influent BOD5, whichever is greater. This value is used to determine the 

Collection System Classification. 
• Grit Removal, gravity 1 point 

[X] Grit Removal, mechanical 2 points 

[X] Screen(s)( in-situ or mechanical (coarse solids only) 1 point 

[X] Pump/Lift Station(s) (pumping of main flow) 2 points 

• Flow Equalization (any type) 1 point 

Subtotal 5 points 

Primary Treatment: 

• Community Septic Tank(s) (STEP, STEG, etc) 2 points 

[X] Clarifier(s) 5 points 

• Flotation Clarifier(s) 7 points 

• Chemical Addition System 2 points 

• Imhoff Tanks, (large septic tank or similar sedimentation _ digestion) 3 points 

Subtotal 5 points 

Page 1 Subtotal 40 points 

Page 1 of 3 

Unit Process Points - Continued (Check all that apply), 

Secondary, Advanced, and Tertiary Treatment See also STEP 2: 

• Low Rate Trickling Filter(s) (no recirculation) 7 points 

G High Rate Trickling Filter(s) (recirculation) 10 points 

Hl_ Trickling Filter - Solids Contact System 12 points 

• Activated Sludge (includes SBR & basic MBR process) 15 points 

• Pure Oxygen Activated Sludge 20 points 

• Activated Bio Filter Tower less than 0.1 MGD 6 points 

• Activated Bio Filter Tower greater than 0.1 MGD 12 points 

• Rotating Biological Contactors 1 to 4 shafts 7 points 

• Rotating Biological Contactors, 5 or more shafts 12 points 

• Stabilization Lagoons, 1 to 3 ceils without aeration 5 points 

• Stabilization Lagoons, 1 or more cells with primary aeration 7 points 

• Stabilization Lagoons, 2 or more cells with full aeration 9 points 

• Recirculating Gravel Filter 7 points 

• Chemical Precipitation Unit(s) 3 points 

• Gravity Filtration Unit(s) 2 points 

• Pressure Filtration Unit(s) 4 points 

• Nitrogen Removal, Biological (BNR) or Chemical/Biological System 4 points 

• Nitrogen Removal, Designed Extended Aeration Only (Nitrification) 2 points 

• Phosphorus Removal Unit(s) 4 points 

• Effluent Microscreen(s) 2 points 

• Chemical Flocculation Unit(s) 3 points 

• Chemical Addition System @ 2 points (describe): points 

Subtotal 12 points 

Solids Handling (Excludes long-term storage in lagoons above) See also STEP 2: 

• Anaerobic Primary Sludge Digester(s) w/o Mixing and Heating 5 points 

• Anaerobic Primary Sludge Digester(s) with Mixing and Heating 7 points 

OpCertClassWorksheet (Rev. 12/03/2008) 
__ Anaerobic Primary and Secondary Sludge Digesters 10 points 

[X] Sludge Digester Gas reuse 3 points 

• Aerobic Sludge Digester(s) 8 points 

[X] Sludge Storage Lagoon(s) (List Basin(s) or Tank(s) under STEP 2) 2 points 

• Sludge Lagoon(s) with aeration 3 points 

• Sludge Drying Bed(s) 1 point 

[X] Sludge Air or Gravity Thickening 3 points 

• Sludge Composting, In Vessel 12 points 

• Sludge Belt(s) or Vacuum Press/Dewatering 5 points 

• Sludge Centrifuge(s) 5 

points 

• Sludge Incineration 12 points 

• Sludge Chemical Addition Unit(s) (alum, polymer, alkaline stab, etc.) 2 points 

• Non-Beneficial Sludge Disposal (landfill or burial) 1 point 

__<_ Beneficial Sludge Utilization (see also STEP 2) 3 points 

Subtotal 21 points 

Disinfection: 

[X] Liquid Chlorine Disinfection 2 points 

• Gas Chlorine Disinfection 5 points 

[El Dechlorination System 4 points 

• Other disinfection systems including ultraviolet and ozonation 5 points 

Subtotal 6 points 

Page 2 Subtotal 39 points 

Page 2 of 3 

(4) Effluent Permit Requirement Points (Check as applicable) See also STEP 2: 

• Minimum of secondary effluent limitations for BOD and/or TSS 2 points 

• Minimum of 20 mg/L BOD and/or Total Suspended Solids 3 

points 

[X] Minimum of 10 mg/L BOD and/or Total Suspended Solids 4 

points 

• Minimum of 5 mg/L BOD and/or Total Suspended Solids 5 points 

• Effluent limitations for effluent oxygen (For other limits see Step 2) 1 point 

Part 4 Subtotal 4 

points 

(5) Variation in Raw Waste Points. Points in this category will be awarded only 

when conditions are extreme to the extent that operation and handling 

procedure changes are needed to adequately treat waste due to variation of raw 

waste (strength or flow) 

H__ Recurring deviations or excessive variations 100% to 200% 2 points 

• Recurring deviations or excessive variations of more than 200%, or 

conveyance and treatment of industrial wastes by pretreatment program 4 points 

• Septage or truck-hauled waste 2 points 

Part 5 Subtotal 2 points 

OpCertClassWorksheet (Rev. 12/03/2008) 
(6) Sampling and Laboratory Testing Points (check as applicable) 

• Sample for BOD, Total Suspended Solids performed by outside lab or 2 points 

[X] BOD or Total Suspended Solids analysis performed at treatment plant 4 points 

• Bacteriological analysis performed by outside lab or 1 point 

__<_ Bacteriological analysis performed at WWT plant lab 2 points 

• Nutrient, Heavy Metals or Organics analysis performed by outside lab or 3 points 

(<1/mo. 1 pt) 

|Xl Nutrient, Heavy Metals or Organics analysis performed at WWT plant 5 points 

Part 6 Subtotal H points 

Parts 4-6 Total 17 points* 

OAR 340-049-0025 Accumulated Points. pg1 40, pg2 39 & pg3* 17_= 96 Go to Step 2T 

STEP 2 - Complexity Not Reflected Above (OAR 340-049 0020(4)) 

Note: This step may justify a higher classification. Points shown are given as guidance. 

• Fine Screen Preliminary Treatment (includes washing & compaction) 2 points 

[X] SCADA or similar instrumentation providing data w/ process op. (2-4 pts) points 

• Post aeration, includes mechanical and diffused aeration (not cascade) 1 point 

• Class A recycled water (storage, distribution & monitoring) 6 points 

• Class B, C, D and non-disinfected recycle (surface & subsurface) 3 

points 

• Sludge dewatering using bag or tube system 1 point 

D Composting, ASP or windrow 6 points 

n Land application of biosolids by system operator (add to BSU pts. Pg. 2) 5 points 

I I Odor or corrosion control (separate or combined) 2 points 

• Chemical/Physical advanced waste treatment (10-15 points) points 

• Reverse Osmosis or Electro-dialysis 15 points 

|X] Other Effluent Requirements @ 1 pt (describe): Ci2, NH3, temp. 3 point(s) 

[Xj Other (describe): Wet weather treatement 10 point(s) 

OAR 340-049-0020(4) points 15 points 

Accumulated Point Total - Steps 1 and 2 (enter here and on page 1) H I points 

A COPY OF THIS COMPLETED WORKSHEET TO BE FILED WITH THE OPERATOR 

CERTIFICATION PROGRAM OFFICE, WQ DIVISION, PRIOR TO SYSTEM START-UP 

OpCertClassWorksheet (Rev. 12/03/2008) 
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