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 Falls City PO Box 160 Falls City, OR 97344 File Number: 28830

SOURCE LOCATION: Four miles east of Hwy 223 behind High School, Falls City, Oregon

SOURCE CONTACT: Don Poe Telephone Number: 503-787-3631 PERMIT WRITER: Robert A. Dicksa Telephone Number: 503-378-5039

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

SOURCE CATEGORY: Minor Domestic

TREATMENT SYSTEM CLASS: Level I

COLLECTION SYSTEM CLASS: Level I

PERMIT APPLICATION DATE: January 28, 2005

PERMIT APPLICATION NUMBER: 982344

BACKGROUND Introduction

The City of Falls City operates a wastewater treatment facility located in Falls City, Oregon (See Figure 1). Wastewater is treated and discharged to Little Luckiamute River in accordance with National Pollutant Discharge Elimination System (NPDES) Permit number 101808. The Permit for the facility was issued on May 19, 2000 and expired on January 31, 2005.

The Department received a renewal application on January 28, 2005. The permit shall not be deemed to expire until final action has been taken on the renewal applications as per Oregon Administrative Rules (OAR) 340-045-0040. A renewal permit is necessary to discharge to state City of Falls City Evaluation Report Page 2 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 major treatment process used is the Recirculating Gravel Filter. The treatment facility consists of a main pump station, a 49,000 gallon recirculation tank, a 87 square foot recirculating Gravel Filter (RGF), an ultraviolet (UV) light disinfection unit, and a soil adsorption drainfield (approximately 12,000 lineal feet). The collection system is a Septic Tank Effluent Gravity (STEG) system. It consists of both commercial septic tanks and residential septic tanks. The facility was originally constructed in 1986.

The current permit allows all flows up to and equaling 0.0532 MGD to be discharged from the RGF to the soil adsorption drainfield. During the winter months, all flows in excess of 0.053 MGD are supposed to flow through the UV light disinfection system and discharged to the Little Luckiamute River at River Mile 12.0. The maximum daily flow to the receiving stream shall not exceed 26,250 gallons per day. However, the treated effluent flow rates vary on a day to day basis during the winter discharge period and therefore the UV disinfection system receives intermittent flows. Because the UV disinfection system does not receive effluent flow on a continual basis, the system cycles on and off and does not function properly, resulting in inadequate disinfection.

In the proposed permit, the Department is proposing to allow the City to direct the flow through the UV disinfection system starting on November 1st and running through April 30th. This would allow the UV system to operate continuously and provide better disinfection. Some of the flow would always go to the drainfield, but the majority of it would go to the Little Luckiamute River. When the plant flow nears the capacity of the UV system, the flow would then be diverted to the adsorption drainfield. The permitted mass loads will remain the same.

Biosolids Management and Utilization

The permittee's biosolids management plan was approved through a modification on May 5, 1998. The permittee currently contracts with a private DEQ licensed septage pumping and hauling management company. The permit requires that all septic tanks connected to the City's wastewater collection system are to be inspected and tested for depth of sludge and scum every two years. Each residential tank shall be pumped when 25% of the capacity of the tank is taken up with solids or every five years and each commercial septic tank shall be pumped when 25% of the capacity of the tank is taken up with solids or every four years. All septic tanks with screens shall be inspected every year. In addition, the Recirculating Gravel Filter (RGF) septage City of Falls City Evaluation Report Page 3 that accumulates in the dosing tanks, pump station, and recirculation tank shall be evaluated on annual basis and pumped at a minimum of once every five years.

The septage tank pumping and hauling company pumps the tank into the truck and adds lime for stabilization. Mixing takes place within the tank truck when the truck is driven over rough dirt roads to the application site. The pH is maintained at 12 for the first 30 minutes and then 11.5 or above for an additional 90 minutes prior to application. The septage may then be land applied on DEQ approved beneficial use sites. The solids from the RGF components may be land applied on pasture land and the septic tank solids may be land applied on land used for hay crop.

There are three septage storage tanks located at a 17 acre site owned by the City. The tanks are used only for emergencies (i.e. plugged lines or when the septic tank has to be completely pumped out). The contents of these tanks are mixed with lime by using pumps to pump the sludge back and forth from the hauling truck. The sludge is then land applied to the approved beneficial use sites.

The proposed permit will require in Schedule B that the permittee keep a record of locations where the septage is applied including the date, quantity and location on a site location map.

Inflow and Infiltration (I/I)

The City entered into a MAO with the Department in 2004 to address excessive inflow/infiltration into the collection system which was hydraulically overloading the treatment plant. The MAO allowed the City two years to evaluate the system and correct deficiencies; that work has been completed. However, based on high winter flows; it appears that the approach was not successful. Minimal amounts of I/I were eliminated. In accordance with paragraph 18 of the MAO, the MAO is to terminate 60 days after completion of the schedule contained in paragraph 7.a. of the MAO. The Department recently terminated the MAO on May 21, 2007, and the City is now required to meet all of the limitations of the current and proposed NPDES permit. The Department recommends a long- term program that will completely replace the collections system based on life expectancy (usually 60 to 80 years). The replacement program should be directed at the oldest sub-basins or those in the worst condition. Therefore, Schedule C of the proposed permit will contain a compliance condition requiring the permittee to submit within one year of permit issuance, an approvable plan and schedule for an on-going collection system replacement program. In addition, Schedule B of the proposed permit will require that the permittee submit an annual report on inflow and infiltration reduction activities.

Pretreatment

The permittee does not have a formal pretreatment program, nor is one required for this source.

Outfalls City of Falls City Evaluation Report Page 4

Outfall 001 The proposed permit allows the treatment facility to discharge treated effluent through Outfall 001 to the Little Luckiamute River at River Mile (RM) 12.0 during the winter months (November 1-April 30). All wastewater up to and equaling 0.02625 MGD will be discharged to Outfall 001. All flow in excess of 0.02625 MGD will be discharged to Outfall 002, the soil adsorption drainfield. No discharge to state waters is allowed from May 1-Ocotber 31 without written authorization from the Department.

Receiving Streams/Impact

The City of Falls City discharge is within the Willamette Basin and Middle 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, passage, and spawning), wildlife and hunting, fishing, boating, water contact recreation, aesthetic quality and hydro power. The water quality standards for the Willamette Basin (OAR 340- 041-0340) were developed to protect the beneficial uses of the basin.

Section 303(d) of the Clean Water Act requires the establishment of a Total Maximum Daily Load (TMDL) in water bodies in which the technology based effluent limitations are not stringent enough to implement the water quality standards. The Willamette TMDL was issued on September 21, 2006, and approved by the EPA on September 26, 2006. OAR 340-041-0345 states no wastes shall be discharged and no activities shall be conducted which cause violations of the water quality standards in the Willamette Basin. The Little Luckiamute River is not included on the Department's List of Water Quality Limited Water Bodies (also called the 303(d) List) as water quality limited for any parameters at any time of the year. The TMDL does not address the Little Luckiamute River specifically because it was not listed for any parameters, however; the TMDL addresses temperature in the portion that includes Willamette Basin tributaries. This is discussed further below.

Antidegradation Review

OAR 340-041-0004 describes the Environmental Quality Commission's (EQC) Antidegradation Policy for Surface Waters. In summary, the policy is intended to guide the decisions that affect water quality such that unnecessary degradation from point and non-point sources of pollution is prevented. The Department must make certain findings and consider certain issues before renewing the permit. The Department performed an Antidegradation review and has determined that the Little Luckiamute River is a High Quality Water during the period of allowed discharge (See Attachment 1).

Temperature

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 the designated beneficial uses that are temperature sensitive, including salmonids in waters of the state. City of Falls City Evaluation Report Page 5

The Department utilizes Fish Use Designation and Salmon and Steelhead Spawning Use Designation maps to identify applicable temperature criteria for each basin. The Willamette Basin maps are contained in OAR 340-041, Figures 340A and 360B, respectively. According to the approved use designation maps, salmon and steelhead spawning is a designated use of the Little Luckiamute River from January 1 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 303(d) List for 2002 does not list the Little Luckiamute as water quality limited for temperature. In addition, the permittee only discharges to the Little Luckiamute River during the winter season when water temperatures tend to be cooler. However, in accordance with the Willamette Sub-basin TMDL, the Department has assessed the discharge from the City of Falls City for temperature impacts to the Little Luckiamute River.

The Willamette TMDL included Waste Load Allocations (WLA) for discharges to tributaries in Willamette River Sub-basins. Therefore, in accordance with the Willamette Sub-basin TMDL Waste Load Allocations, sources that discharge effluent warmer than ambient temperatures and applicable biologically-based criteria must be evaluated for potential to contribute to exceedances of numeric criteria. Facilities found to have no reasonable potential to warm the receiving water do not require a waste load allocation and are allowed to discharge within their current permit.

The City of Falls City's effluent temperature impacts were assessed for the discharge period during April 1 through April 30. The assessment was conducted in accordance with the Sub-basin TMDL Waste Load Allocations by using a flow chart process contained in the TMDL as follows:

Does the point source discharge warm the river less than 0.3° C above numeric criterion given 25% of 7Q10 flow? If yes, then the source is assigned an Allocation based on 0.3° C and 25% of 7Q10 low flow or the Department makes a determination of no reasonable potential for temperature increase and therefore, the source may discharge at current level.

The Department calculated the in-stream temperature increase using the maximum winter daily discharge flow allowed of 0.02625 MGD, an assumed maximum effluent discharge temperature of 15 °C (the permittee has not measured temperature of the effluent in the past, so the Department has to estimate using a typical number for effluent temperature from a similar type process plant), the applicable numeric criterion of 13 °C, and 25%) of the 7Q5 flow of the Little Luckiamute River (the 7Q5 flow was used because there was only five years of historical flow data available for the gauging station located on the Little Luckiamute River). This information was input into a thermal calculator spreadsheet (See Attachment 2) to determine if there is a reasonable potential to warm the river less than 0.3 °C above the numeric criterion. According the thermal calculator spreadsheet, the discharge warms the river less than 0.3 °C above the criterion. Therefore, the Department has determined that there is no reasonable potential for a temperature increase above the criteria and the City of Falls City may discharge at the current flow rate. City of Falls City Evaluation Report Page 6

Finally, based on the above assessment the Department has also determined that the effluent discharge is in accordance with OAR 340-041-0053 (2)(d) Temperature Thermal Plume Limitations as follows: Temperature mixing zones and effluent limits authorized under OAR 340-04l-0028(12)(b) will be established to prevent or minimize the following adverse effects to salmonids inside the mixing zone:

(A) Impairment of an active salmonid spawning area where spawning redds are located or likely to be located. This adverse effect is prevented or minimized by limiting potential fish exposure to temperatures of 13 °C or less for salmon and steelhead, and 9 °C for bull trout; (B) Acute impairment or instantaneous lethality is prevented or minimized by limiting potential fish exposure to temperatures of 32.0 °C or more to less than two seconds; (C) Thermal shock caused by a sudden increase in water temperature is prevented or minimized by limiting potential fish exposure to temperatures of 25.0 °C or more to less than five percent of the cross section of 100 percent of the 7Q10 flow of the water body; the Department may develop additional exposure timing restrictions to prevent thermal shock; and (D) Unless the ambient temperature is 21.0 °C or greater, migration blockage is prevented or minimized by limiting potential fish exposure to temperatures of 21.0 °C or more to less than 25 percent of the cross section of 100 percent of the 7Q10 low flow of the water body.

According to the Oregon Department of Fish and Wildlife (ODF&W) District Biologist, there are no active salmonid spawning redds in the vicinity of the City of Falls City effluent discharge to the Little Luckiamute River. In addition, the estimated maximum effluent temperature of the discharge during this period is 15.0 °C, which is in accordance with the Thermal Plume Limitations listed above. To support the Thermal Plume Limitations for C, above, the Department calculated the in-stream temperature increase using the maximum winter daily discharge flow allowed of 0.02625 MGD, the estimated maximum effluent temperature of the discharge of 15.0 °C, the applicable numeric criterion of 13 °C, and 5%> of the cross section of 100 percent of the 7Q5 flow of the Little Luckiamute River. This information was input into the thermal calculator spreadsheet to determine if there is a reasonable potential to warm the river above the criterion (See Attachment 2A). To support the Thermal Plume Limitations for D, above, the Department used the thermal calculator spreadsheet to determine the in-stream temperature increase using the same input data above, but using less than 25%> of the cross section of 100 percent of 7Q5 flow of the Little Luckiamute River (See Attachment 2B). Both spreadsheets indicated that there is no reasonable potential for the discharge to violate the criterion and that the discharge is in accordance with the Thermal Plume Limitations. The Department is not aware of any other water quality violations that may be attributable to this source.

Groundwater

The facility is designed to handle flows up to approximately 79,450 gallons per day (gpd). Discharges of flow up to or equaling 26,250 gallons per day are allowed through Outfall 001 to the Little Luckiamute River during the period from November 1 through April 30 each year. City of Falls City Evaluation Report Page 7

When the flow exceeds 26,250 gpd, the discharge shall be through Outfall 002 to the soil adsorption drainfield up to or equaling 53,200 gpd. During the summer season from May 1 through October 31, the discharges equal to or less than 53,200 gpd shall be strictly to soil adsorption drainfield through Outfall 002.

The soil adsorption drainfield is located behind the high school near the banks of the Little Luckiamute River. Soils are well drained to groundwater that is less than 100 feet deep year around. The direction of groundwater flow is to the southwest towards the Little Luckiamute River. Based on the Department's current information, this facility has a low potential for adversely impacting groundwater quality (See Attachment 3 Groundwater Prioritization Worksheet). Therefore, Schedule D of the proposed permit states that no groundwater evaluations will be required during this permit cycle. The permit also includes a condition in Schedule A that prohibits any adverse impact on groundwater quality.

Stormwater

General NPDES permits for storm water are required for facilities with a design flow of greater than 1 MGD if storm water is collected and discharge from the plant site. This facility's design flow is less than 1 MGD therefore no storm water permit is necessary.

Compliance History

This facility was last inspected on December 27, 2006. At the time of the inspection, the City was in compliance with the permit for Schedule B, Schedule C, Schedule D, the General Conditions, and the requirements of the MAO. However, the permittee was not in compliance with Schedule A - Permit Waste Discharge Limitations. The City of Falls City was cited for a Class II violation and sent a Warning Letter.

The monitoring reports for this facility were reviewed for the period since the current permit was issued, including any actions taken relating to effluent violations. Based on this review, the following violations have been documented at this facility during the term of the current permit:

Violation Date NON Date Violation NON Class November 2003 January 12, 2004 Exceeding TSS concentration and Class II loading limits

October 2003 December 17, 2003 Exceeding BOD5 and TSS concentration Class II and loading limits

July 2003 September 16, 2003 Exceeding BOD5 concentration limits Class II August 2002 December 9, 2002 Exceeding TSS concentration limits Class II

The City entered into a MAO with DEQ in 2004 to address excessive inflow/infiltration into the collection system which was hydraulically overloading the treatment plant. The MAO allowed the City two years to evaluate the system and correct the deficiencies. That work has been completed. As set forth in paragraph 18 of the MAO, the MAO is to terminate 60 days after completion of the schedule contained in paragraph 7.a. Therefore, the MAO was terminated on City of Falls City Evaluation Report Page 8

May 21, 2007. The interim effluent limits contained in the MAO no longer apply and the City is now required to meet all of the limitations of the NPDES permit.

PERMIT DISCUSSION 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 Little Luckiamute River and to a soil adsorption field within limits set by Schedule A and the following schedules. All other discharges are prohibited.

In accordance with OAR 340, Division 49 all permitted municipal wastewater and 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 collection and treatment systems are both currently considered Class I systems. Both systems were reevaluated to determine the appropriateness of the current classification for operator certification requirements (See Attachment 4). The Department is not proposing to make any changes to the classification of the collection or treatment systems in the proposed permit.

Schedule A - Waste Discharge limitations BODj and TSS concentration and mass limits

Based on the Willamette Basin minimum design criteria, wastewater treatment resulting in a monthly average effluent concentration of 10 mg/L for BOD5 and TSS must be provided from May 1 - October 31. From November 1 - April 30, a minimum of secondary treatment or equivalent control is required. Secondary treatment for this facility 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 Department is proposing concentration limits at least as stringent as the basin minimum design criteria. The proposed monthly average BOD5 concentration limit is 20 mg/L with a weekly average limit of 30 mg/L. The proposed monthly average TSS concentration limit is 20 mg/L with a weekly average limit of 30 mg/L.

The winter mass load limits for the facility are based on the wet weather flow of 0.02625 MGD and the monthly average BOD5 and TSS concentration limits of 20 mg/L . The limits are in accordance with OAR 340-041 -006 l(10)(a). All mass load limitations are rounded to two significant figures.

By basing the winter mass limits on AWWF, the permittee is required to remove all inflow sources from the collection system. The proposed permit includes a Schedule C condition requiring submittal of a program and time schedule for identifying and removing inflow.

BOD5 and TSS City of Falls City Evaluation Report Page 9

The limits are:

(1) May 1-October 31:

No discharge to state waters is permitted.

(2) November 1 - April 30: Average Effluent Monthly Weekly Daily Concentrations Average Average Maximum Parameter Monthly Weekly lb/day lb/day Lbs BOD5 20 mg/L 30 mg/L 4.4 6.6 8.8 TSS 20 mg/L 30 mg/L 4.4 6.6 8.8

Calculations:

(1) BOD5

(a) 0.02625 MGD x 8.34 #/gal x 20 mg/L monthly avg. = 4.4 lbs/day (b) 4.4 lbs/day monthly avg. x 1.5 = 6.6 lbs/day weekly avg. (c) 4.4 lbs/day monthly avg. x 2.0 = 8.8 lbs/day daily max.

(2) TSS

(a) 0.02625 MGD x 8.34 #/gal x 20 mg/L monthly avg. = 4.4 lbs/day (b) 4.4 lbs/day monthly avg. x 1.5 = 6.6 lbs/day weekly avg. (c) 4.4 lbs/day monthly avg. x 2.0 = 8.8 lbs/day daily max.

A review of recent monitoring data indicates the City should generally be able to comply with the permit limits.

BOD5 and TSS Percent Removal Efficiency

A minimum level of percent removal for BOD5 and TSS for municipal dischargers is required by the Code of Federal Regulations (CFR) secondary treatment standards (40 CFR, Part 133). An 85 percent removal efficiency limit is included in the proposed permit to comply with federal requirements. The permit allows assumed values for the influent BOD5 and TSS concentrations of 200 mg/L and actual sampled effluent concentrations to be used in the calculation of the monthly percent removal efficiency. The Department allows the assumed value of 200 mg/L for the influent BOD5 and TSS because the influent receives partial treatment in the individual septic tanks.

EH

The Willamette Basin Water Quality Standard for pH is found in OAR 340-041-0445(2)(d). The allowed range is 6.5 to 8.5. The proposed permit limits pH to the range 6.0 to 9.0. This limit is based on Federal wastewater treatment guidelines for sewage treatment facilities, and is applied to City of Falls City Evaluation Report Page 10 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. It is the Department's belief that mixing with ambient water within the mixing zone will ensure that the pH at the edge of the mixing zone meets the standard based on a Department approved pH evaluation spreadsheet that derives mixing zone boundary values for pH (See Attachment 5). Therefore, the Department considers the proposed permit limits to be protective of the water quality standard.

Bacteria

The proposed permit limits are based on an E. coli standard approved in January 1996. 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. The bacteria standard allows that if a single sample exceeds 406 E. coli per 100 mL, then the permittee may take five consecutive re-samples. If the log mean of the five re-samples is less than or equal to 126, a violation is not triggered. The rule states that the re-samples should be taken at four hour intervals beginning as soon as practicable (preferably within 28 hours) after the original sample was taken. The rule also allows for changing the re-sampling timeframe if it would pose an undue hardship on the treatment facility. After discussions with the permittee, the Department is proposing that the five re-samples be taken beginning no later than 48 hours after the original sample was taken.

Total Chlorine Residual

The treatment facility uses ultra-violet light to disinfect the treated wastewater. No chlorine or chlorine compounds may be used for disinfection purposes and no chlorine residual will be allowed in the effluent due to chlorine used for maintenance purposes.

Ammonia

The state of Oregon has adopted the EPA 1999 ammonia criteria but the new criteria have not been formally approved by EPA. Until that time, the existing toxicity standards currently contained in OAR Chapter 340, Table 20 from the EPA 1986 Gold Book Criteria are used to evaluate ammonia toxicity to determine if limits are necessary in a permit.

A reasonable potential analysis was conducted using the worst case conditions for the winter discharge season (November 1-April 30). To perform the RPA for the winter discharge period, the Department used an effluent to stream ratio using the allowable winter discharge flow rate of 0.02625 gpd, 25%o of the 7Q5 stream flow, and the highest detected effluent ammonia value for the last three years (See Attachment 6). The spreadsheet analysis indicated that there is no reasonable potential to violate the ammonia toxicity standard at the edge of the mixing zone or at the edge of the ZID. Therefore, no effluent limitation for ammonia will be included in the proposed permit for the winter discharge season. However, monitoring for ammonia-N will remain in the permit at the frequency of one per month.

Dissolved Oxygen City of Falls City Evaluation Report Page 11

Ammonia is an oxygen demanding pollutant. Dissolved oxygen is consumed as ammonia is converted to nitrate. A Streeter-Phelps dissolved oxygen spreadsheet model was used to determine if the discharge had the potential to violate the dissolved oxygen standard. A dissolved oxygen depression less than 0.1 mg/L is considered immeasurable.

The model was used to simulate the same combination of effluent and stream flow conditions as in the ammonia toxicity analysis. Model simulations assumed maximum ammonia and BOD5 concentrations. This is a very conservative consumption considering a BOD5 test includes the oxygen demand associated with ammonia decay. CBOD5 tests exclude the oxygen demand due to ammonia decay. Because effluent CBOD5 values were not available, BOD5 values were used. Decay rates for BOD5 and ammonia were assumed based on literature values. Results of the dissolved oxygen analysis are shown in the tables in Attachment 7. Model results demonstrate that the dissolved oxygen depression is below 0.1 mg/L. Under these scenarios, the Department finds that there is no reasonable potential to violate the dissolved oxygen standard.

Temperature

As discussed previously, there is no reasonable potential for the discharge to warm the river more than 0.3 °C above the criterion. Therefore, the proposed permit will not contain an Excess Thermal Load Limit. However on the basis that the reasonable potential analysis was conducted using an estimated temperature effluent value, the proposed permit will contain temperature monitoring of the effluent when discharging to the Little Luckiamute River.

Mixing Zone and Zone of Immediate Dilution

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 water body as a whole may not be impaired. Mixing zones allow the initial mixing of waste 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. City of Falls City Evaluation Report Page 12

The Department's mixing zone regulations state the mixing zone must be less than the total stream width as necessary to allow passage of fish 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 that consists of that portion of the Little Luckiamute River 20 feet upstream and 200 feet downstream from the point of discharge.

The Department proposes to revise the mixing zone definition to include that portion of the Little Luckiamute River where the effluent mixes with 25 percent of the stream flow. The proposed mixing zone definition is:

The allowable regulatory mixing zone is that portion of the Little Luckiamute River where the effluent mixes with 25 percent of the stream flow but in no case shall it extend farther than fifteen feet out from the outfall pipe and from a point ten feet upstream of the outfall to a point 200 feet downstream from the outfall. The Zone of Initial Dilution (ZID) shall be defined as that portion of the allowable mixing zone that is within three feet of the point of discharge.

The Department believes that the beneficial uses of the receiving stream will not be affected by the discharge and that the defined mixing zone meets the criteria in the rule.

Groundwater

Based on the Department's current information, this facility has a low potential for adversely impacting groundwater quality. Therefore, the permit includes a condition in Schedule A that prohibits any adverse impact on groundwater quality. In addition, Schedule D of the proposed permit states that no groundwater evaluations will be required during this permit cycle. No other groundwater impacts are expected from this source when reclaimed water is used in accordance with OAR 340-055.

Schedule B - Minimum Monitoring and Reporting Requirements

Schedule B describes the minimum monitoring and reporting necessary 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 potential for a water quality concern.

In 1988, the Department developed a monitoring matrix for commonly monitored parameters. The matrix was updated in 2004. 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 City of Falls City Evaluation Report Page 13 frequencies for all parameters correspond to those of facilities of similar size and complexity in the state.

The permittee is required to have or use a laboratory with a 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

Item or Parameter Minimum Frequency Type of Sample Total Flow (MGD) Daily Measurement Flow Meter Calibration Annually (November) Verification

BOD5 1 per 2 Weeks Grab TSS 1 per 2 Weeks Grab pH 2/Week Grab

Treated Effluent Outfall 001 (Discharge to the Little Luckiamute River not to exceed 0.02625 MGD)

Item or Parameter Minimum Frequency Type of Sample Total Flow (MGD) Daily Measurement Flow Meter Calibration Annually (November) Verification

BOD5 1 per 2 Weeks Grab TSS 1 per 2 Weeks Grab pH 2/Week Grab Effluent Temperature 2/Week Record E. coli 1 per 2 Weeks Grab UV Radiation Intensity Daily Reading (See Note)

Pounds Discharged (BOD5 and TSS) 1 per 2 Weeks Calculation Average Percent Removed (BOD5 and TSS) Monthly Calculation TKN,NH3-N, NO3-N+NO2-N Monthly Grab Note: The UV disinfection process must be monitored on a daily basis for turbidity and UV intensity. Treated Effluent Outfall 002 (Discharge to the Soil Adsorption Field not to exceed 0.0532 MGD)

Item or Parameter Minimum Frequency Type of Sample Total Flow (MGD) Daily Measurement Flow Meter Calibration Annually (November) Verification

BOD5 1 per 2 Weeks Grab City of Falls City Evaluation Report Page 14

TSS 1 per 2 Weeks Grab pH 2/Week Grab

TKN,NH3-N, NO3-N+NO2-N Monthly Grab

Biosolids Management

Item or Parameter Minimum Frequency Type of Sample Record of locations where septage is applied on Each Occurrence Date, quantity and each DEQ authorized site. (Site location maps locations where to be maintained at the treatment facility for septage was applied review upon request by DEQ. and recorded on site location map.

Other Parameters

Item or Parameter Minimum Frequency Type of Sample Test pumps and alarms at Recirculation Tank Quarterly Visual/Audible Test alarms at Dosing Tank Quarterly Visual/Audible Inspect pump screens at Recirculation and Annually (August) Visual Dosing Tanks Inspect, clean, and maintain gravel filter laterals Annually (August) Flush Depth of effluent in soil adsorption trenches March 1 and Sept. 1 Measurement

Maintenance Activities

The permittee shall implement preventative maintenance practices or corrections in accordance with the following time schedule:

• All septic tanks connected to the City's wastewater collection system are to be inspected and tested for depth of sludge and scum every two years. • Pump residential septic tanks either when sludge and scum volume exceeds 25% of the liquid capacity of the tanks or every five years, whichever is less; commercial septic tanks either when sludge and scum volume exceeds 25% of the liquid capacity of the tanks or every four years, whichever is less. • Clean pump screens when 25%> of the screen surface area becomes clogged. • Pump solids from each recirculation tank a minimum of once every five years.

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. City of Falls City Evaluation Report Page 15

Schedule B of the permit includes the requirement for the submittal of annual report on inflow and infiltration reduction activities.

Schedule C - Compliance Conditions

The proposed permit includes three compliance conditions with compliance deadlines. The requirements include:

• By no later than one year after permit issuance, the permittee shall submit an approvable plan and schedule for an on-going collection system replacement program to reduce the amount of I/I.

• Schedule C of the Permit includes a compliance condition requiring submittal a report identifying known raw sewage overflow points and providing a schedule to eliminate the overflows.

• The final condition requires the permittee to meet the compliance dates established in this schedule or notify the Department within fourteen days following any lapsed compliance date.

Schedule D - Special Conditions

The proposed permit includes four special conditions. The requirements include:

• The permittee must have the facilities supervised by personnel certified by the Department in the operation of treatment and/or collection systems.

• The permittee shall not be required to perform a hydrogeologic characterization or groundwater monitoring during the term of this permit.

• All reclaimed 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. All landscape irrigation must be confined to the treatment plant site. No spray or drift will be allowed off the treatment plant site. Landscape irrigation must be conducted following sound irrigation practices.

• The permittee shall notify the Department's Western Region - Salem Office of any malfunctions so that corrective action can be coordinated between the permittee and the Department in accordance with the General Conditions of this permit.