# Reasonable Potential Analysis Process for Toxic Pollutants Version 3.1

This page left intentionally blank 

## Internal Management Directive

Last Updated: 02/13/2012 By: Spencer Bohaboy DEQ 11-WQ-020-IMD Water Quality Division NPDES Permit Development 811 SW 6th Avenue Portland, OR 97204 Phone: (503) 229-5696 (800) 452-4011 Fax: (503) 229-6762 Contact: Spencer Bohaboy www.oregon.gov/DEQ

DEQ is a leader in restoring, maintaining and enhancing the quality of Oregon’s air, land and

water.Oregon DEQ Page ii 

## Reasonable Potential Analysis IMD


# Disclaimer

This internal management directive (IMD) represents the Department of Environmental Quality’s (D EQ) current directions to staff on how to conduct a Reasonable Potential Analysis for poin t source water quality permitting. This IMD is not final agency action and does not create any rights, duties, obligations, or defenses, implied or otherwise, in any third parties. This directive should not be construed as rule, although some of it describes existi ng state and federal laws. The recommendations contained in this di rective should not be construed as a requirement of rule or statute. DEQ an ticipates revising this document from time to time as conditions warrant.



# Contact Information

Oregon Department of Environmental Quality Water Quality Division 811 SW 6 th Ave. Portland, OR 97204 For more information: Spencer Bohaboy, (503) 229-5415

Alternative formats (Braille, large type) of this document can be made available. Contact DEQ’s Office of Communications & Outreach, Portland, at (503) 229- 5696, or toll-free in Oregon at 1-800-452-4011, ext. 5696. 

# Document Development

Prepared by: Spencer Bohaboy, Polic y Development Specialist, Surface Water Management

Developed by: Spencer Bohaboy, Policy Development Specialist Lyle Christensen, Permit Writer Northwest Region Steve Schnurbusch, Permit Writer Western Region Heidi Williams, PE, Plan Review Engineer Eastern Region

Reviewed by: Dennis Ades, Manager Surface Water Management Greg Aldrich, Interim Administrator, Water Quality Division Sonja Biorn-Hansen, Senior Water Quality Permit Specialist, Water Quality Division Jane Hickman, JJD, Policy An alyst, Water Qu ality Division

Approved by: Greg Aldrich, Interi m Water Quality Administrator

________________________________________ _________Oregon DEQ Page iii 

## Reasonable Potential Analysis IMD



# Table of Contents

Section 1: Introduction 1 1.1 Purpose of Directive 1.2 Directive A pplicability 1.3 Overview of Permit Process 1.4 Key Definitions 1.5 Overview of the Reasonable Potential Analysis 1.6 Sources of Information 1.7 Questions and Contact Information



### Section 2: Tier 1 Monitoring 7 2.1 Tier 1 Monitoring Overview 2.2 Determination of Pollutants Requiring Evaluation 2.2.1 Discussion of State and Federal Authority to Require Monitoring 2.2.2 Domestic Facilities: Evalua tion and Monitoring Requirements 2.2.3 Domestic Facility Pollutant Tables 2.2.4 Industrial Facilities: Evalua tion and Monitoring Requirements 2.2.5 Industrial Facility Pollutant Tables 2.3 Pollutant Parameters With-out Numeric Water Quality Criteria 2.4 Reporting Procedures 2.5 Schedule B: Suggested Mon itoring Requirement Language



### Section 3: Identify Pollutants of Concern 27
3.1 Process Overview 3.2 Entering General Facility Information 3.3 Analysis of Identified Parameters 3.4 Interpretation of Results 3.5 Additional Information: Narrative Cr iteria and Whole Effluent Testing 3.6 Next Step



### Section 4: Tier 2 Monitoring 33 4.1. Tier 2 Monitoring Overview 4.2. Monitoring Action Letter 4.3. Sampling Plan 4.3.1. Characterization of Receiving Water Body 4.3.2. Additional Effluent Characterization 4.3.3. Source Investigation 4.4. Next Steps



### Section 5: Reasonable Potential Analysis 39 5.1 Reasonable Potential Analysis Overview 5.2 General Facility Information 5.2.1 Flow Rates 5.2.2 In-Stream DilutionOregon DEQ Page iv 

## Reasonable Potential Analysis IMD

5.2.3 Fresh/Marine Water Status 5.2.4 Hardness 5.2.5 Statistical Calculation Values 5.3 Revised Effluent Characterization Data 5.4 Data Interpretation 5.5 Ambient Concentration 5.5.1 Data Entry Instructions 5.6 Comparison of Maximum Concentrati on to Water Quality Concentration 5.7 Troubleshooting 5.8 Conclusions 5.9 Next Steps



### Section 6: Effluent Limit Calculation and Determination 53
6.1 Effluent Limit Determination Process Overview 6.2 WLA and WQBEL Calculation 6.3 Compare WQBELs with TBELs 6.4 Next Steps



### Section 7: Permit Applicant Consultation 59
7.1 Overview 7.2 Permittee Notification of Results and Compliance Evaluation 7.3 Alternatives 7.4 Selected Management Option 7.5 Next Step



### Section 8: Finalization of RPA a nd Effluent Limits and Documentation of Decision Rational 63
8.1 Overview 8.2 Final RPA and Effluent Limit Evaluation 8.3 Documentation 8.4 Outcome 1: Evaluation Report com ponents for “no monitoring req’d” 8.5 Outcome 2: Evaluation Report compone nts where “monitoring is required” but “reasonable potential” is not determined 8.6 Outcome 3: Evaluation Report compone nts where “monitoring is required” and “reasonable potential” is determin ed, and “effluent limits” are calculated

Appendix A: Revision History 67 Appendix B: General Overview of RPA and WQBEL Calculation 69 Appendix C: Analytic Methods, Limi ts, and Implementation Guidance 71 Appendix D: RPA Workbook Walk-though and Example 73 Appendix E: Whole Effluent Toxicity Guidance 83 Appendix F: Intake Credit Guidance 103Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 1 of 117 

# Section 1: Introduction

1.1 Purpose of Directive

The purposes of this Internal Management Directive (IMD) are to provide guidance for Department of Environmental Quality (DEQ) staff in determ ining whether an individual point source discharge (poi nt source) contains toxic pollutants of concern (POCs) that might cause an exceedance of the water quality standard in the receiving water body, and how to calculate effluent limits. The current wa ter quality criteria for aquatic toxicity are listed in OAR 340-41 pollutant tables 20

, 33A and 33B , and for human health water quality criteria in OAR 340-41 pollutant table 40 . The IMD provides step-by-step guidance for identifying POCs, conducting th e Reasonable Potential Analysis (RPA), calculating Water Quality Base d Effluent Limits (WQBEL s), and discusses various technical and policy issues.

All of the RPA steps and calculations have been consolidated into a series of spreadsheets ( RPA Workbook ). When conducting the RPA, the permit writer uses these spreadsheets to determine the discharger’s monitori ng requirements, identify POCs, calculate reasonable potential and if necessary, devel op effluent limits. This document follows along with the spreadsheets, and provides basic instruction for each step and, where necessary, offers detailed tec hnical and regulatory guidance.

It is recommended that readers should first familiarize themselves with the RPA Workbook and refer to it while reading through th is document. This includes reading through the Appendix D: RPA Workbook Walk-Through and Example

. 

## 1.2 Directive Applicability

State and Federal regulation re quire that a RPA must be co nducted for all proposed and existing industrial and domestic NPDES i ndividual point source dischargers. The number and type of pollutants for which the RPA must be conducted will vary with the size, type and potential hazard of the facilit y. This process is explained in detail in Section 2

. 

## 1.3 Overview of Permit Process

For most major domestic and industrial point sources, DEQ permit writers review permit applications, perform water quality-based modeling, review laboratory test results, develop effluent limits (where applicable) a nd incorporate their findings into permits to ensure that the discharge of pollutants (i.e. toxic, nutrients, pH, BOD, etc.) do not result in violations of water quality standards. Some minor facilities re quire an equivalent degree of analysis, but typically for a greatly reduced number of toxic pollutants. These processes are usually repeated every five years upon permit renewal. The RPA for toxic pollutants is often the most technically involved portion of the permit developmentReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 2 of 117

process.

The Department has developed the following gui dance documents that describe the parts of the permit development process that relate to the subjects covered in this document:

• Anti-Degradation Policy Implementation IMD

• Compliance Schedules in NPDES Permits IMD

• Regulatory Mixing Zone IMD: Part 1 Allocating Regulatory Mixing Zones

• Regulatory Mixing Zone IMD: Part 2 Reviewing Mixing Zone Studies 

## 1.4 Key Definitions

• Reasonable Potential Analysis (RPA) is the process for determining "whether a discharge causes, has reasonable potential (RP) to cause, or contributes to an excursion above" Oregon's water quality criteria for toxic pollutants (in the receiving water body).

• A Pollutant of Concern (POC) is a toxic pollutant that h as been statistically evaluated and identified as having a “reasonable potential” to exceed the state water quality criteria (at the end of pipe).

• Water Quality Based Effluent Limit (WQBEL) is an effluent limitation determined by selecting the most stringent of the effluent limits calculated using all applicable water quality criteria (i.e. human health or aquatic toxicity) for a specific point source to a specific receiving water.

• Permit Evaluation Report (PER) is a document that summarizes the principal facts and the significant factual, legal, methodological, and policy question considered in preparing the draft permit and documents the decisions. The PER is also referred to as a “Fact Sheet” and the various requirements are covered under 40 CFR 124.8 and 124.56.

• Tier 1 Monitoring is a series of at least four sampling events designed to characterize a facility’s effluent and identify POCs. Each sample collected is subjected to laboratory analysis for a broad spectrum of pollutant para meters as determined by the permit writer.

• Tier 2 Monitoring is a second round of sampling (for identified POCs only) necessary to characterize the receiving water and provide additional effluent characterization. Tier 2 monitoring will enable the permit writer to model the impacts of a discharge upon the receiving waters, and complete the RPA. Gene rally, if the results of Tier 1 monitoring indicate that there is no reasonable potentia l for the discharge to exceed water quality standards at the end of the pipe, then Tier 2 monitoring is not needed. 

## 1.5 Overview of the Reasonable Potential Analysis

To paraphrase EPA's Technical Support Document for Water Quality-based Toxics Control , a RPA is the process for determini ng "whether a discharge causes, has reasonable potential to cause, or contribut es to an excursion above" Oregon's water quality criteria for toxic pollutants. Before conducting a RPA, a permit writer should first review any applicable Total Maximum Daily Loads (TMDLs) to determine if there are already facility-specific wa ste load allocations (WLA) 1 . The permit writer would then

1 If indicated, the permit writer should confer with the TMDL development section or Basin Coordinator to ensure that the TMDL is sufficien tly protective and that the underlying assumptions have not changed.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 3 of 117

continue with the RPA process described in Figure 1-1 and 1-2 for any pollutants not specifically addressed in a TMDL.

Figure 1-1 Permit Development and RPA Process Overview

• Step 1 : As part of the preceding permit development, the permit writer develops a list of effluent monitoring requirements based upon the facility and receiving water classifications. Section 2 (RPA IMD)

• Step 2 : During the first 24 months of the new permit term, the permittee conducts the required pollutant scan (Tier 1 Monitoring). Section 2

• Step 3 : Using the Tier 1 data, the permit writer initially characterizes the effluent and identifies POCs using the Aquatic Toxicity RPA and Human Health RPA spreadsheets of the RPA Workbook to conduct an “end of pipe” reasonable potential (RP) determination. Section 3

• Step 4 : The permit writer will report the identified POCs, associated monitoring requirements and recommendations to the permittee via Monitoring Action Letter (MAL). By the end of the month 36, for each POC the permittee will characterize the receiving water body, and (optionally) collect additional effluent or source investigation data (Tier 2 monitoring). Section 4

• Step 5 : The permit writer will use the Tier 1 and 2 data, along with other information, to model the potential in-stream water quality impacts and complete the “in-stream” RP determination. This may include the use of an intake credit analysis as part of the determination. Section 5

• Step 6 : For each POC found to have RP (in-stream), information will be transferred from the RPA spreadsheets to the Aquatic Limits and Human Health Limits spreadsheets to calculate a Water Quality Based Effluent Limit (WQBEL). This may include the use of rule-based intake credits in the limit calculation. The permit writer would normally include this limit in the permit unless a more stringent Technology Based Effluent Limit (TBEL) is applicable. Section 6

• Step 7 : The permit writers will discuss the results of the RPA with the applicants. If the facility is not capable of initially meeting the effluent limit, the permittee may use the remainder of the permit term (~24 months) to collect additional information, attemp t source reduction, develop treatment options, or justify a variance request or standards adjustment. In some cases, a Compliance Schedule may be granted, allowing the permittee additional time to implement source reduction or treatment options to meet the final effluent limit. Section 7

• Step 8: After receiving the EPA permit application forms (month 54), the permit writer would use the remaining time (six months) to finalize the RPA and WQBEL calculations, and then document their findings, interim calculations and management decisions in the Permit Evaluation Report. The permit would then be ready for re-issuance. Section 8Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 4 of 117

For new permit applications or permits where adequate monitoring da ta are not available to conduct a quantitative RPA, permit writers should use their best professional judgment to determine the most appropriate ways to characterize the facili ty and model the instream impacts. This might include the use of representative data or the use of an alternative qualitative RPA methodo logy as described in EPA guidance 2 . Please refer to Sections 4.2.1 and 5.4 of this document for more information.

Once the RPA and calculation of WQBELs is complete, a summary of the analysis and results is documented in the PER. To complete the permit development process, the permit writer will conduct a Whole Efflue nt Toxicity (WET) review, and where necessary, increase the stringency of the effluent limits or permit conditions. A summary of the RPA process is included in Figure 1-2 below.
Figure 1-2 RPA Process w/Timeline and Implementation Options

2 Technical Support Document for Water Quality-based Toxics Control, Section 3.2, P. 50. Issue Permit Run RPA & Calculate WQBEL

• Optional: Intake

Credit / Background Criteria

• WET review

• “ Can permittee mee t

WQBEL? ” Y / N

Now What?

• Source Reduction

• Engineering Study

• Compliance

Schedule

• Variance

• Standards Change No Identify POCs

• “ End of pipe RPA ” to identify Pollutants of Concern (POCs)

• Monitoring

Action Letter (MAL) Tier 2 Monitoring

• Ambient

characterization for POCs

• Optional: More

effluent data

• Optional: Source

Investigation Tier 1 Monitoring

• Characterize:

o All Tables 1 &

2 parameters

o Select Table 3

parameters

• Min. 4 samplesYear 0Year 2Year 3Year 5 Select Option

• Work with

p ermittee to select most appropriate implementation option

*Implementation options and re lated actions are colored in RED Yes

Write Permit

• Select appropriate limits (lowest)

• Det. Monitoring Requirements

• Special Conditions (if necessary)

o Compliance Schedule

o Additional Monitoring

o Req’d BMPs or Benchmarks

• WET review

• Document decisions in PERReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 5 of 117


## 1.6 Sources of Information

The following is the typical information a pe rmit writer must review to characterize the facility, effluent and the receiving waters. Most of the following are typically submitted by the permit applicant. In some cases, the pe rmit writer will need to request or collect additional information.

Domestic Facilities:

• Permit application forms

o EPA Forms 1 and 2A (new permit)

o EPA Forms 2A and OR DEQ Form NPDES-R (permit renewal)

o Bio-solids Plan

• Characterization and monitoring data as requi red by application form, permit and/or permit writer request

• Discharge Monitoring Reports (DMRs), with a focus on the adequacy of detection limits for non-detectable values 3

• Pretreatment Industrial Surveys or required information per 40 CFR 122.21 (j)(6).

• Total Maximum Daily Load Reports : Many facilities that discharge to 303(d) listed stream segments will be described and r eceive waste load allocations in TMDL Reports

• 303(d) listings for receiving stream segment

• Oregon DEQ LASAR ambient data for the applicable waterbody segment

Industrial Facilities:

• Permit application forms 4

o EPA Form 1 & 2D (new permit)

o EPA Form 2C and OR DEQ Form NPDES-R (permit renewal)

• Characterization and monitoring data as re quired by application form, permit or permit writer request

• Discharge Monitoring Reports (DMRs), with a focus on the adequacy of detection limits for non-detectable values

• Total Maximum Daily Load Reports (TMDL): Many facilities that discharge to 303(d) listed stream segments will be describ ed and receive waste load allocations in TMDL Reports

• 303(d) listings for receiving stream segment

• Oregon DEQ LASAR ambient data for the applicable receiving stream segment

• Design and process flow data

• Hazardous material inventories (SARA T itle III, RCRA, State Fire Marshal records).

If the facility has a Regulatory Mixing Zone (R MZ), then a detailed mixing zone analysis should have been conducted. At minimum, th e study should contain the dilutions values for the receiving water body and mixing zones un der critical conditions. Please refer to

3 Daily and weekly data fo r major facilities, in el ectronic form, is availabl e to the permit writer through the Discharge Monitoring System (DMS). Often monthly, annual and sporadic data are also available.
4 Other EPA application forms includ e 2E (facilities which do not discharge process wastewater), 2B (CAFOs and Aquatic Animal Production wastew ater) and 2F (industrial stormwater only).Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 6 of 117

the Regulatory Mixing Zone Inte rnal Management Directive for more information. The “dilution values” should be used instead of the effluent and ambient stream flow information in the RPA calculation. The permit writer can also contac t the regional Plan Review Engineer for additional information regarding the appropriate flow value to use in the RPA that is consistent with critical conditions. . If no mi xing zone analysis is available, it will be necessa ry to use the facility’s Design Flow 5 , along with critical effluent and ambient flow rates to ca lculate the available dilution using the RPA Workbook

.
Additionally, the following documents provide in-depth discussions of the permitting process and methods used in modeling reas onable potential and cal culating effluent limits:

• Technical Support Document for Wa ter Quality-based Toxic Control , USEPA, March 1991 ( TSD )

• U.S. EPA NPDES Permit Writers’ Manual , USEPA, September 2010

Finally, the Department maintains a website that contains various guidance documents, analytical and modeling tool s, state rules, pertinent forms and other permit writer

resources at: http://deq05/wq/wqpermits /PermitWritersCorner.htm

.

1.7 Questions and Contact Information

For questions about this guidance, contact the Surface Water Management Section in the Water Quality Division. At the time of release, the point of contact for this guidance is Spencer Bohaboy at (503) 229-5415 or mailto:bohaboy.spencer@deq.state.or.us

.

5 The flow that the facility was built to handleReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 7 of 117 

# Section 2: Tier 1 Monitoring

2.1 Tier 1 Monitoring Overview

The RPA process begins when the permit writer evaluates a facility to determine the spectrum of pollutant parameters that mu st be included in the permit monitoring requirements ( Step 1 ). This pollutant scan is intended as a periodic check to determine if any of the pollutants historically associated w ith domestic or industr ial facilities or for which the receiving water has b een listed as water qualitylimited are present, and quantify the resulting concentrations 6 . Typically, this evalua tion would occur during the preceding permit term so that the effluent monitoring requirements can be included in the Schedule B permit conditions 7

.
For domestic facilities, the number and type of pollutants that require an RPA increases along with incremental (<0.1, 0.1 – 1.0, > 1.0 MGD) changes in the facility “design flow”. There might also be additional mon itoring requirements for facilities with special conditions such as the discharge of PCB’s, pe sticides or mercury. This is described in Section 2.2.1 of this document.

For industrial facilities, the number and type of pollutants that require evaluation are determined by the facilities’ design flow rates, industrial categories, hazardous production materials, receiving wa ter’s status and permitting history. This is described in Section 2.2.2 of this document.

Upon permit renewal, the facili ty would implement their Tier 1 monitoring requirements by collecting at least four effluent samples that reflect the seasonal discharge characteristics (i.e. wet and dry) and have th em analyzed for the specified pollutants. These actions must be completed by the 24 th month of the permit term ( Step 2 ).

Once collected and analyzed, the permit writer w ould then evaluate the resultant data and identify any POCs in the facility’s effluent ( Step 3 ) as described in Section 3

. 

## 2.2 Determination of Pollutants Requiring Evaluation

The process to evaluate a facility and iden tify monitoring requirements is complex and depends upon the type of facility. Figures 2-3

, 2-4, 2-5 and the accompanying Domestic Facility Pollutant Table and Industrial Facility Pollutants Table walk the permit writer through the process to ensure that all federally and state mandated pollutant parameters are identified.

6 This scan is in addition to any compliance-based effluent monitoring
7 As part of the application for a new facility or extraordinary circumstances, a facility might be required by Permit Action Letter to conduct Tier 1 monitoringReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 8 of 117

Regardless of other factors, the following pollu tant parameters must be analyzed in the RPA:

• Pollutant parameters with effluent limits in the preceding permit

• Pollutant parameters with monitoring requirements in the preceding permit 8

• Pollutant parameters for which the recei ving water body has been listed as “water quality limited” on the 303d list

• Pollutant parameters that are “known 9 ” to be present in significant concentrations in a facilities’ source/intake water

• Pollutant parameters that are “known” or ot herwise expected to be present in significant concentrations in a facilities effluent

• Pollutant parameters identified through the permit application process and described in the rest of this Section

The RPA Workbook includes all the pollutant parame ters that might need to be evaluated for a domestic or industrial facili ty, based upon state and federal guidelines. The permit writer will evaluate each parameter for inclusion in the analysis and record the result (“ Yes ” or “ No ”) in the “ Monitoring Required? ” column of the Monitoring Requirements spreadsheet (See Figure 2-1 ) 10 . The permit writer should also document the facility’s Averag e Dry Weather Design Flow (ADWDF) rate in the appropriate box of the same spreadsheet. Once the evaluation is complete, the permit writer can supply a copy of the worksheet to the permit applic ant and include a summary of the Tier 1 monitoring requirements in Schedule B of the permit.

For a new permit application, the permit writer will identify the pollutant parameters that require monitoring during a pre- application conference, and th e results will be submitted as part of the facili ty’s application.

For the first round of permit renewals after im plementation of this IMD, the permit writer will develop the permit based upon the availabl e data and include the new monitoring and evaluation procedures into the permit’s m onitoring requirements (Schedule B).

At various points of the permit cycle (m onth 24 and permit renewal), the permit writer will have the opportunity to add additional monitoring requirements to reflect newly authorized water quality criteria or recent waterbody listings (303d). This is discussed in Section 4.2

.
If WET testing is required, th e permit writer should coordina te the testing to coincide with the Tier 1 monitoring. In the event of “toxicity” finding dur ing the WET analysis, the simultaneous sampling will help with the re quired source investigation. Please refer

to Appendix E (Whole Effluent Toxicity Guidance) or contact the Department’s WET

8 In some instances, such as a change in water quality criteria, change in treatment method (e.g. Cl - to UV) or de-listing of a water body, a permit writ er might determine that it is appropriate to not renew a permit monitoring requirement.
9 For example intake water is from a 303(d) listed water body or contaminated groundwater.
10 For some pollutant parameters, total data may be collected in lieu of sp ecies specific data for Tier 1 monitoring. In the event that the pollutant is identified as a POC, species specific may be collected as part of the Tier 2 monitoring.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 9 of 117

coordinator for more information.
Figure 2-1 Example of Monitoring Requirem ents Determination WorksheetReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 10 of 117

Figure 2-2 Example of the RPA Workbook Figure 2-1 Explanation Determine Monitoring Requirements

1. The permit writer (PW) evaluates each facility to determine which pollutant parameters should be included in Tier One monitoring. 2. On the Monitoring Required spreadsheet, the PW records facility identification information and the ADWDF rate used for the evaluation. 3. The PW indicates with a “ Yes ” or “ No ” in the “ Monitoring Required ” column if monitoring is required as shown in Figure 2-1

. 4. The information entered on the “ Monitoring Required?” spreadsheet will automatically be forwarded to the Aquatic Toxicity and the Human Health Spreadsheets as shown in Figure 2-2

. 5. The PW checks to ensure that all pollutant parameters listed on the spreadsheets have been evaluated and have either a “ Yes ” or “ No ” in the column.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 11 of 117

2.2.1 Discussion of Stat e and Federal Authority to Require Monitoring

The purpose of the RPA IMD is to direct DEQ permit writers on how to implement statutory and regulatory requirements for NP DES permitting. This IMD does not create any new authority but only implements ex isting authority. Following is a detailed discussion of these authorities.

Per 40 CFR 123.1, the Department has been dele gated (by the EPA) to administer the Clean Water Act (CWA) and implement the NPDES program in Oregon (except for tribal lands). The Environmental Quality Commission has adopted water quality standards/criteria to protect th e beneficial uses of the State’s water bodies, as authorized by ORS 468B.048. These water quality st andards/criteria become effective upon approval by the EPA.

OAR 340-045-0035(1) requires DEQ to develop permits “in accordance with provisions of all applicable statutes, rule s, regulations, and effluent gui delines of the State of Oregon and the U.S. EPA.” Per OAR 340-041-0033(2), the “ levels of toxic substances in waters of the state may not exceed the applicable criteria ...”. Note, there are both federal and state water quality standards that permittees must meet.

To ensure that water quality standards appli cable to the receiving water are met, the Department conducts a water quality based assessment 11 to determine if there is a reasonable potential for a discharge to cause or contribute to an exceedance, and where appropriate, define effluent lim itations. The permittee must “ comply with the Department’s requirements for ..., reporting, monitoring, ... and sampling” (OAR 340- 045-0015 (5)(d)).

Finally, per 40 CFR 123.25 ( Requirements for permitting ) and OAR 340-045-0065, the department must follow federal permit de velopment and implementation procedures, including those described in 40 CFR 122.21 ( Application for a permit ) and 122.41(3)(h) ( Duty to provide information ). 40 CFR 122.21 directs the permittee to monitor for pollutant parameters, many of which are not reflected in Oregon’s water quality criteria 12

. 40 CFR 122.41(3)(h) gives the Department the authority to request from the permittee any information to determine if “ cause exists for modifying, revoking and reissuing, or terminating this permit or to dete rmine compliance with this permit.” When requesting a water quality variance, per OAR 340-041- 0059(4)(c) the permittee must provide

“ sufficient water quality data and analyses to characterize ambient and discharge water pollutant concentrations ”.

To summarize, the department has been de legated to implement the NPDES program and develop state water quality standards. Th e department must ensure that permittees comply with these standards. In order to develop appropriate effluent limits in permits,

11 Based upon EPA’s TSD
12 Conversely, there are state water quality criteria w/no federal monitoring requirements. This is shown in the “ No Fed. Req’s ” column of the “ RPA Workbook

, Monitoring Required? ” page.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 12 of 117

the department requires permittees to samp le their effluent and, in some cases, the receiving water body. The department also inco rporates monitoring requirements into the permit to verify that the permittees are m eeting the applicable effluent limitations.

2.2.2 Domestic Facilities: Eval uation and Monitoring Requirements

Per 40 CFR 122.21(j)(4) and DEQ guidance 13 , domestic facilities are required to monitor for specific pollutant parameters with a mini mum frequency. The type of pollutants and the frequency varies based upon the facili ty’s Average Dry Weather Design Flow (ADWDF) 14 in the following manner:

• For all domestic facilities with an ADWDF of at least 1 MGD, the permit writer must conduct an RPA for all identified toxic pollutants.

• For all domestic facilities with ADWDFs from 0. 1 to less than 1 MGD, the permit writer must, at minimum, perform a RPA for chlorine and ammonia.

• A permit writer should conduct a RPA for all 303(d) listed toxic pollutants in the receiving stream for a domestic facility of less than 1 MGD, when the pollutants are “known” or are reasonably expected to present in the effluent 15

. The guidance in Figure 2-3 (and Domestic Facility Pollutant Tables ) walks the permit writer through the process of identifying the facility’s monitoring requirements to meet both the requirements included in EPA Application Form 2A, and any additional state or federal requirements. The Domestic Facility Pollutant Tables in Section 2.2.3 are taken from 40 CFR 122, App. J and EPA Application form 2A , and are augmented with any state water quality criteria 16 not reflected in these sources. The missing state water quality criteria have been inserted into the appropriate chemical group within Tables 1A

, 1 and 2 , and would only require monitoring when the chemical group is indicated. The remaining water quality criteria have been consolidated into Table 3 , where only those individual pollutants known to be present in the effluent or for-which the receiving water body has been listed (303d) as “water qual ity limited”, would require monitoring.

The pollutant scan must occur within the first two years of a permit term and each sample must be taken between four and eight months apart in order to be representative of seasonal variation (i.e. wet a nd dry). When possible, mon itoring should be coordinated with other requirements such as local-lim it evaluation, compliance monitoring or WET testing, to increase the overall relevance of the analytic results and maximize efficiency. For a new permit application it might be n ecessary for the permit writer to conduct a qualitative assessment process (Qualitative RPA) when facility specific effluent monitoring data is not available. In these circumstances the permit writer should refer to guidance in the USEPA NPDES Permit Writers Manual 17 and EPA’s TSD, p. 49.

13 Letters entitled “Toxic Monitoring Requirement s for Domestic Wastew ater Treatment Plants with NPDES Permits” dated 1/6/2006.
14 if necessary, the permit wr iter should consider the use of an alte rnative “critical” effluent flow for pollutants or discharge scenarios where there might be wet weather impacts.
15 I.e., source water from listed water body, pot ential industrial pollutant sources w/in the collection area or contaminated ground water vi a I&I. Previously collected data may be used.
16 State water quality criteria are from Federal recommended criteria (section 304 A of CWA).
17 September 2010 revision, Section 6.3.3, Page 6-30.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 13 of 117

Figure 2-3 Domestic Tier 1 Monitoring Requirements Determination Process

All facilities must sample for all Table 1A pollutants • Includes BOD/CBOD, TSS, Fecal Coliform, Flow, Temp & pH

• Min. of 4 analyses

• Additional parameters: Alkalinity

In addition, all facilities w/design flow > 0.1 MGD must sample for all Table 1 pollutants • Includes NH3, Cl - , DO, nitrate/nitrite, TKN, oil & grease, phosphorous and TDS

• Min. of 4 analyses 

### Start (40 CFR 122.21(j))

In addition, all facilities w/design flow > 1.0 MGD must sample for all Table 2 pollutants • Metals [total recoverable], cyanide and total phenols

o Min. of 4 analyses

• VOCs, acid-extractable compounds and base-neutral compounds

o Min. of 4 analyses

• Additional parameters: Hardness & Whole Effluent Toxicity



## Required Tier 1 Monitoring Parameters

TMDL required monitoring: For example > 1.0 MGD facilities in Willamette Basin must sample for
mercury • See TMDL requirements • Includes pesticides, PCBs or other pollutants parameters with state water quality criteria

• Min. of 4 analyses for applicable pollutant In addition, all facilities w/design flow

> 1.0 MGD must sample for any Table 3 parameters:

• described as part of Dept.- approved pretreatment program

• for which the receiving water has been listed (303(d)) All facilities must sample for any pollutant paramete r:

• with current effluent limits or permit monitoring requirements

• “known” or otherwise expected to be present in significant conc.s in a facility’s effluent

• “known” to be present in significant conc.s in a facility’s source water (i.e. 303 d listed) • Min. of 4 analysesReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 14 of 117

2.2.3 Domestic Facility Pollutant Tables

Tables 1A

, 1 and 2 below are taken from Appendix J of 40 CFR, Part 122-NPDES permit Testing Requirements for Pu blicly Owned Treatment Works (POTW). State water quality criteria not addresse d by these documents are added to the tables in the appropriate chemical group 18 , with the remaining criteria consolidated into Table 3

. Please refer to Figure 2-3 for assistance in determining applicable monitoring requirements.

Table 1A – Effluent Parameters for All POTWS Alkalinity as CaCO3 * pH Biochemical oxygen demand (BOD-5 or CBOD-5) Temperature

Bacteria: (Fecal Coliform, E. Coli &/or Enterococci) Total suspended solids
Design Flow Rate

Table 1-Effluent Parameters for All POTWS w/a Flow > 0.1 MGD Ammonia (as N) Kjeldahl nitrogen (TKN) Chlorine (total residual, TRC) Oil and grease Dissolved oxygen Phosphorus (Total) Nitrate/Nitrite Total dissolved solids (TDS)

Table 2--Effluent Parameters for Selected POTWS Hardness (as CaCO3) Metals (total recoverable), cyanide and total phenols Antimony Lead Arsenic Mercury Arsenic (Inorganic) * Nickel Arsenic (III) * Selenium Beryllium Silver Cadmium Thallium Chromium Zinc Chromium (III) * Cyanide (Free)* Chromium (VI) * Cyanide (Total) Copper Total phenolic compounds Iron (Total) *

18 Please note that all parameters listed with a “ * ” are state water quality criteria not listed in 40 CFR 122 or in the EPA application forms.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 15 of 117

Table 2--Effluent Parameters fo r Selected POTWS (Continued) Volatile organic compounds Acrolein 1,1-dichloroethylene Acrylonitrile 1,2-dichloropropane Benzene 1,3-dichloropropylene Bromoform Ethylbenzene Carbon tetrachloride Methyl bromide Chlorobenzene Methyl chloride Chlorodibromomethane Methylene chloride Chloroethane 1,1,2,2-tetrachloroethane 2-chloroethylvinyl ether Tetrachloroethylene Chloroform Toluene Dichlorobromomethane 1,1,1-trichloroethane 1,1-dichloroethane 1,1,2-trichloroethane 1,2-dichloroethane Trichloroethylene Trans-1,2-dichloroethylene Vinyl chloride Acid-extractable compounds P-chloro-m-cresol 2-nitrophenol 2-chlorophenol 4-nitrophenol 2,4-dichlorophenol Pentachlorophenol 2,4-dimethylphenol Phenol 4,6-dinitro-o-cresol 2,4,5-trichlorophenol * Dinitrophenols * 2,4,6-trichlorophenol 2,4-dinitrophenol Base-neutral compounds Acenaphthene 3,3-dichlorobenzidine Acenaphthylene Diethyl phthalate Anthracene Dimethyl phthalate Benzidine 2,4-dinitrotoluene Benzo(a)anthracene 2,6-dinitrotoluene Benzo(a)pyrene 1,2-diphenylhydrazine 3,4 benzofluoranthene Fluoranthene Benzo(ghi)perylene Fluorene Benzo(k)fluoranthene Hexachlorobenzene Bis (2-chloroethoxy) methane Hexachlorobutadiene Bis (2-chloroethyl) ether Hexachlorocyclo-pentadiene Bis (2-chloroisopropyl) ether Hexachloroethane Bis (2-ethylhexyl) phthalate Indeno(1,2,3-cd)pyrene Bis (Chloromethly) ether * Isophorone 4-bromophenyl phenyl ether Naphthalene Butyl benzyl phthalate Nitrobenzene 2-chloronaphthalene N-nitrosodi-n-propylamine 4-chlorophenyl phenyl ether N-nitrosodimethylamine Chrysene N-nitrosodiphenylamine Di-n-butyl phthalate Pentachlorobenzene * Di-n-octyl phthalate Phenanthrene Dibenzo(a,h)anthracene Pyrene 1,2-dichlorobenzene 1,2,4-trichlorobenzene 1,3-dichlorobenzene 1,2,4,5-Tetrachlorobenzene * 1,4-dichlorobenzeneReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 16 of 117

Table 3 – Pesticides, PCBs and Other Parameters w/Water Quality Criteria Organochlorine Pesticides* Aldrin Endosulfan I (Alpha) Technical-BHC (Hexachlorcyclo- hexane)* Endosulfan II (Beta) alpha-BHC Endosulfan * beta-BHC Endosulfan sulfate delta-BHC Endrin gamma-BHC (Lindane) Endrin aldehyde Chlordane (tech) Heptachlor Chloropyrifos Heptachlor epoxide Dementon Malathion 4,4 ́-DDD Methoxychlor 4,4 ́-DDE Mirex 4,4 ́-DDT Parathion Dieldrin Toxaphene PCBs*
Total PCBs **

** A Total PCBs analysis is determined by moni toring for PCB Aroclors 1016,1221,1232,1242, 1248, 1254 and 1260 in one sample event and totaling the values. Other Parameters with Sate Water Quality Criteria* Barium, Total Guthion Manganese, Total Nitrosamines Sulfide-Hydrogen Sulfide N-Nitrosodibutylamine 2,4,5-TP [2-(2,4,5-Trichlorophenoxy) propanoic acid] N-Nitrosodiethylamine
2,4-D (2,4-Dichlorophenoxy acet ic acid) N-Nitr osopyrrolidine Dioxin 2,3,7,8-TCDD Phosphorus, Elemental

2.2.4 Industrial Facilities: Eval uation and Monitoring Requirements

Per 40 CFR 122.21 and DEQ guidance 19 , industrial facilities ar e required to monitor for specific parameters with a minimum freque ncy. The monitoring requirements at a specific facility are determined based upon indus trial category, pre-existing permit status, hazardous material present, new source performance standards or permit writer discretion 20 . The guidance in Figures 2-4 and 2-5 (and Industrial Facility Pollutant Tables I

, II

, III and IV 21 ) walks the permit writer through the process of identifying the facility’s monitoring requirements to address both the requirements included in EPA Forms 2C 22

, 2D 23 and 2E 24 , and any additional state or federal requirements. Figure 2-4

19 Letters entitled “Toxic Monitoring Requirement s for Industrial Wastew ater Treatment Plants with NPDES Permits” dated January 6, 2006.
20 e.g., discretion might include known environm ental concerns in the receiving waters or industrial category that could impact, or be impacted by the facility’s activity.

21 Tables II, III, IV contains pollutant paramet ers that require monitoring and analysis if required or expected to be present. Table V contains pollutant parameters t hat would require identification only (no monitoring) if they are expected to be present.
22 Existing manufacturing, commercial, mining an d silvicultural dischargers, 40 CFR 122.21(g)
23 New Sources and New Dischargers per 40 CFR 122.21(k)
24 Facilities Which Do Not Discharge Proces s Wastewater per 40 CFR 122.21(h)(4)Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 17 of 117

addresses industries identified as “ Primary Industry 25 ”, and Figure 2-5 addresses “ NonPrimary Industry ”. The Industrial Facility Pollutants Tables in Section 2.2.5 are taken from 40 CFR 122, App. D and EPA Application form 2A , and are augmented with any state water quality criteria not reflected in these sources. The missi ng state water quality criteria have been inserted into the appropriate chemical group within the tables and would only require monitoring when the polluta nt parameters are know n to be present in the effluent.

Due to the complexity of determining the a ppropriate industrial monitoring requirements, the permit writer should work directly with the industrial facility to ensure that all reporting requirements are included in the facil ity evaluation. This might include review of hazardous material inventories (SARA Title III, RCRA or State Fire Marshal records) combined with assessment of facility processes to determine if those pollutants have the potential to enter the effluent . Another good source of informa tion for the permit writer is the Hazardous Substances Used, Stored, Produ ced of Transferred at a Facility that Indicate Probability of Toxicity Table located in 40 CFR 302.4

.
Typically, the pollutant scan monitoring will o ccur within the first two years of a permit term and each sample must be taken between four and eight months apart, as to be representative of seasonal va riation. For a new permit app lication it might be necessary for the permit writer to conduct a Qualitative RPA when facility specific effluent monitoring data is not available. In these circumstances the permit writer should refer to guidance in the USEPA NPDES Permit Writers Manual and TSD. The permit writer should be aware of the small business and in take exemptions indi cated in 40 CFR 122 (g)(8), but in almost all cases these are not applicable or do not re sult in a meaningful reduction of required monitoring parameters.

Federal application rules requi re a minimum of one analysis (grab sample or composite sample) for each pollutant parameter. To en sure a robust effluent characterization, the department requires facilities to collect a minimum of four compos ite samples (or grab samples for pH, temperature, cyanide, total phenols, residual chlori ne, oil and grease and fecal coliform) for pollutant parameters with water quality criteria. Where it can be demonstrated that a facility has no history of pollutant discharge, the permit writer may introduce a sunset provision or reduce the monitoring requirements (min. of one analysis) in the permit, documenting the actio n in the permit evaluation report.

25 Facilities with activities described in Table I of this IMD or Table 2c-2 of the EPA Form 2-C.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 18 of 117

Figure 2-4 Primary Industry Monitoring Requi rements Determination Process

All facilities must sample for all “General Pollutants”

Follow procedure (right) to identify which “Organic Toxic Pollutants” to monitor for 1. Select industrial category, Table I 2. Determine pollutant fractions, Table I 3. List corresponding pollutants for selected fractions, Table II 4. List all other “known” Table II pollutants

o If < 10 & 100 ppb = quantitative data or “reason for discharge”

• Min. of 4 analyses w/quantitative data

• Min. of 1 analysis w/out WQ crit.

• Part 122.21(g)(7)(v)(A)

All facilities must sample for all “Toxic Metals, Cyanide & Total Phenols” • Includes BOD, COD, TOC, TSS, NH3, Flow, Temp (w/s) and pH

• As listed in Part 122.21 (g)(7)(iii)

• A dditional p arameter: Alkalinit y

• As listed in Table III

• Min. of 4 analyses w/WQ crit., rec. 10

• Additional parameter: Hardness

• Part 122.21 (g)(7)(v)(B)

All facilities must identify known“Conventional and NonConventional Pollutants” and provide information as directed and in 40 CFR 122.21 • Identify known pollutants from Table IV

• All identified pollutants w/effluent limits

(i.e. ELG, WQBEL, TBEL)

o Provide quantitative data

• All other identified pollutants, provide

one of the following:

o Quantitative data

o Reason for discharge

• Part 122.21 (g)( 7 )( vi )( A ) All facilities must identify known Certain Hazardous Substances & Asbestos and provide

information as directed

• Identify known pollutants from Table V

• Report reason for discharge and source

• Report any available quantitative data

• Part 122.21 (g)( 7 )( vii ) Start ( 40 CFR 122.21 (g)) 

### Required Tier 1 Monitorin g Parameters

• See TMDL requirements TMDL required monitoring: For example > 1.0 MGD facilities in Willamette Basin must sample for mercury All facilities must sample for

any pollutant parameter:

• with current effluent limits

• “known” or otherwise expected to be present in significant concentrations in a facility’s effluent

• “known” to be present in significant concentrations in a facility’s source/intake water • Min. of 4 analyses for parameters w/WQ criteria

• Min. of 1 analysis w/out WQ crit.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 19 of 117

Figure 2-5 Non-Primary Industry Monitoring Re quirements Determination Process

All facilities must sample for all “General Pollutants”

Follow procedure (right) to identify which “Organic Toxic Pollutants” to monitor for • List all “known” Table II pollutants

o If < 10 & 100 ppb = quantitative data or “reason for discharge”

• Min. of 4 analyses w/quantitative data

• Min. of 1 analysis w/out WQ crit.

• Part 122.21 (g)( 7 )( v )( A )

All facilities must sample for all known “Toxic Metals, Cyanide & Total Phenols” • Includes BOD, COD, TOC, TSS, NH3, Flow, Temp (w/s) and pH

• As listed in Part 122.21 (g)(7)(iii)

• A dditional p arameter: Alkalinit y

• Identify all “known” Table III pollutants

• Min. of 4 analyses w/quantitative data,

rec. 10

o If < 10 & 100 ppb = quantitative data or “reason for discharge”

• Min. of 1 analysis w/out WQ crit.

• Additional parameter: Hardness, for

Cd, Cr III, Cu, Pb, Ni, Ag or Zn

• Part 122.21 (g)( 7 )( v )( B )

All facilities must identify known“Conventional and NonConventional Pollutants” and provide information as directed and in 40 CFR 122.21 • Identify all “known” Table IV pollutants

• All identified pollutants w/effluent limits

(i.e. ELG, WQBEL, TBEL)

o Provide quantitative data

• All other identified pollutants, provide

one of the following

o Quantitative data

o Reason for discharge

• Part 122.21 (g)(7)(vi)(A) All facilities must identify known

“ Certain Hazardous Substances & Asbestos” and provide

information as directed • Identify known pollutants from Table V

• Report reason for discharge and source

• Report any available quantitative data

• Part 122.21 (g)( 7 )( vii ) Start ( 40 CFR 122.21 (g)) 

### Required Tier 1 Monitorin g Re q uirements

• See TMDL requirements TMDL required monito ring: For example > 1.0 MGD facilities in Willamette Basin must sample for

mercur y All facilities must sample for

any pollutant parameter:

• with current effluent limits

• “known” or otherwise expected to be present in significant concentrations in a facility’s effluent

• “known” to be present in significant concentrations in a facility’s source/intake water • Min. of 4 analyses for parameters w/WQ criteria

• Min. of 1 anal y sis w/out W Q crit.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 20 of 117

2.2.5 Industrial Facility Pollutant Tables

The tables below are taken from Appendix D to 40 CFR, Part 122-NPDES Permit Application Testing Requirements.

Table I—Testing Requirements for Organic Toxic Pollutants by Industry Category

Industry category GC/MS fraction 1
Volatile Acid Neutral Pesticide Adhesives and sealants X X X Aluminum forming X X X Auto and other (coin operated) laundries X X X X Battery manufacturing X X Coal mining Coil coating X X X Copper forming X X X Electric and electronic components X X X X Electroplating X X X Explosives manufacturing X X Foundries X X X Gum and wood (all subparts except D and F) X X Subpart D—tall oil rosin X X X Subpart F—rosin-based derivatives X X X Inorganic chemicals manufacturing X X X Iron and steel manufacturing X X X Leather tanning and finishing X X X Mechanical products manufacturing X X X Nonferrous metals manufacturing X X X X Ore mining (applies to the base and precious metals/Subpart B) X

Organic chemicals manufacturing X X X X Paint and ink formulation X X X Pesticides X X X X Petroleum refining X Pharmaceutical preparations X X X Photographic equipment and supplies X X X Plastic and synthetic materials manufacturing X X X X Plastic processing X Porcelain enameling Printing and publishing X X X X Pulp and paperboard mills See Pulp and Paperboard Mills Table Rubber processing X X X Soap and detergent manufacturing X X X Steam electric power plants X X Textile mills (Subpart C—Greige Mills are exempt from this table) X X X

Timber products processing X X X X
X = Testing required 1 The pollutants in each fraction are listed in Table II,Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 21 of 117

Pulp and Paperboard Mills Table 40 CFR 430, Subpart * GS/MS fractions VOA Acid Base/neutral Pesticides A 2 1 2 1 B 2 1 2 2 C 2 1 2 2 D 2 1 2 2 E 1 1 2 1 F 1 1 2 2 G 1 1 2 2 H 1 1 2 2 I 1 1 2 2 J 1 1 1 2 K 1 1 2 2 L 1 1 2 2
1 = Must test 2 = Do not test unless “reason to believe” it is discharged *Subparts are defined in 40 CFR Part 430

Table II—Organic Toxic Pollutants in Each of Four Fractions in Analysis by Gas Chromatography/Mass Spectroscopy (GS/MS)
Volatiles 1V acrolein 2V acrylonitrile 3V benzene 5V bromoform 6V carbon tetrachloride 7V chlorobenzene 8V chlorodibromomethane 9V chloroethane 10V 2-chloroethylvinyl ether 11V chloroform 12V dichlorobromomethane 14V 1,1-dichloroethane 15V 1,2-dichloroethane 16V 1,1-dichloroethylene 17V 1,2-dichloropropane 18V 1,3-dichloropropylene 19V ethylbenzene 20V methyl bromide 21V methyl chloride 22V methylene chloride 23V 1,1,2,2-tetrachloroethane 24V tetrachloroethylene 25V toluene 26V 1,2-trans-dichloroethylene 27V 1,1,1-trichloroethane 28V 1,1,2-trichloroethane 29V trichloroethylene 31V vinyl chloride Acid Compounds 1A 2-chlorophenol 2A 2,4-dichlorophenol 3A 2,4-dimethylphenol 4A 4,6-dinitro-o-cresol 5A 2,4-dinitrophenol 6A 2-nitrophenol 7A 4-nitrophenol 8A p-chloro-m-cresol 9A pentachlorophenol 10A phenol 11A 2,4,6-trichlorophenolReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 22 of 117

Table II—Organic Toxic Pollutants (continued)
Base/Neutral 1B acenaphthene 2B acenaphthylene 3B anthracene 4B benzidine 5B benzo(a)anthracene 6B benzo(a)pyrene 7B 3,4-benzofluoranthene 8B benzo(ghi)perylene 9B benzo(k)fluoranthene 10B bis(2-chloroethoxy)methane 11B bis(2-chloroethyl)ether 12B bis(2-chloroisopropyl)ether 13B bis (2-ethylhexyl)phthalate 14B 4-bromophenyl phenyl ether 15B butylbenzyl phthalate 16B 2-chloronaphthalene 17B 4-chlorophenyl phenyl ether 18B chrysene 19B dibenzo(a,h)anthracene 20B 1,2-dichlorobenzene 21B 1,3-dichlorobenzene 22B 1,4-dichlorobenzene 23B 3,3 ′ -dichlorobenzidine 24B diethyl phthalate 25B dimethyl phthalate 26B di-n-butyl phthalate 27B 2,4-dinitrotoluene 28B 2,6-dinitrotoluene 29B di-n-octyl phthalate 30B 1,2-diphenylhydrazine (azobenzene) 31B fluroranthene 32B fluorene 33B hexachlorobenzene 34B hexachlorobutadiene 35B hexachlorocyclopentadiene 36B hexachloroethane 37B indeno(1,2,3-cd)pyrene 38B isophorone 39B napthalene 40B nitrobenzene 41B N-nitrosodimethylamine 42B N-nitrosodi-n-propylamine 43B N-nitrosodiphenylamine 44B phenanthrene 45B pyrene 46B 1,2,4-trichlorobenzene Pesticides 1P aldrin 2P alpha-BHC 3P beta-BHC 4P gamma-BHC 5P delta-BHC 6P chlordane 7P 4,4 ′ -DDT 8P 4,4 ′ -DDE 9P 4,4 ′ -DDD 10P dieldrin 11P endosulfan I (alpha) 12P endosulfan II (beta) 13P endosulfan sulfate 14P endrin 15P endrin aldehyde 16P heptachlor 17P heptachlor epoxide 18P PCB- Aroclor 1242 19P PCB- Aroclor 1254 20P PCB- Aroclor 1221 21P PCB- Aroclor 1232 22P PCB- Aroclor 1248 23P PCB- Aroclor 1260 24P PCB- Aroclor 1016 25P toxaphene

Table III – Other Toxic Pollutants (Meta ls and Cyanide) and Total Phenols Antimony Nickel Arsenic Selenium Beryllium Silver Cadmium Thallium Chromium Zinc Copper Cyanide (Free & Total) Lead Phenols Mercury Hardness (required to det. WQ criteria)Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 23 of 117

Table IV – Conventional and Nonc onventional Pollutants Required To Be Tested by Existing Dischargers if Exp ected to be Present (in the effluent) Aluminum, Total Malathion * Arsenic (III) * Manganese, Total Arsenic, Inorganic * Methoxychlor * Barium, Total Mirex * BHC – Technical * Molybdenum, Total Boron, Total Nitrate-Nitrite Bromide Nitrogen, Total Organic Chloride Nitrosamines Chlorine, Total Residual N-Nitrosodibutylamine Chloromethly Ether, Bis * N-Nitrosodiethylamine Cobalt, Total N-Nitrosopyrrolidine Color Oil and Grease Chlorophenoxy Herbicide (2,4,5-TP) * Parathion * Chloropyrifos * PCBs, Total * Chromium (III) * Pentachlorobenzene * Chromium (VI) * Phosphorus, Elemental * &Total Dementon * Radioactivity 2,4-D (2,4-Dichlorophenoxy acetic acid) * Sulfate Dioxin 2,3,7,8-TCDD * Sulfide Dinitrophenols * Sulfide-Hydrogen Sulfide Endosulfan * Sulfite Fecal Coliform Surfactants Fluoride Tetrachlorobenzene,1,2,4,5 * Guthion * Tin, Total Iron, Total * Trichlorophenol, 2,4,5 * Magnesium, Total Titanium, Total Please note that all param eters with a “*” are state water quality criteria not listed in 40 CFR 122 or in the EPA application forms (i.e. 2A, 2C)

Table V - Toxic Pollutants and Hazardous Substances Required To Be Identified by Existing Discharge rs if Expected To Be Present Toxic Pollutants Asbestos Hazardous Substances Acetaldehyde Crotonaldehyde Allyl alcohol 2,4-D (2,4-Dichlorophenoxy acetic acid) Allyl chloride Diazinon Amyl acetate Dicamba Aniline Dichlobenil Benzonitrile Dichlone Benzyl chloride 2,2-Dichloropropionic acid Butyl acetate Dichlorvos Butylamine Diethyl amine Captan Dimethyl amine Carbaryl Dintrobenzene Carbofuran Diquat Carbon disulfide DisulfotonReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 24 of 117

Table V – Continued: Hazardous Substances Chlorpyrifos Diuron Coumaphos Epichlorohydrin Cresol Ethion Ethylene diamine Phenolsulfanate Ethylene dibromide Phosgene Formaldehyde Propargite Furfural Propylene oxide Guthion Pyrethrins Isoprene Quinoline Isopropanolamine Dodecylbenzenesulfonate Resorcinol Kelthane Strontium Kepone Strychnine Malathion Styrene Mercaptodimethur 2,4,5-T (2,4,5-Trichlorophenoxy acetic acid) Methoxychlor TDE (Tetrachlorodiphenylethane) Methyl mercaptan Trichlorofan Methyl methacrylate Triethanolamine dodecylbenzenesulfonate Methyl parathion Triethylamine Mevinphos Trimethylamine Mexacarbate Uranium Monoethyl amine Vanadium Monomethyl amine Vinyl acetate Naled Xylene Napthenic acid Xylenol Nitrotoluene Zirconium Parathion



## 2.3 Pollutant Parameters Without Numeric Water Quality Criteria

Following the preceding procedures will typically result in the selection of a number of pollutant parameters that do not have corresponding numeric water quality criteria 26

. These pollutants will be required to be in cluded in the permit monitoring conditions.

The RPA Workbook includes these pollutant pa rameters so that the permit writer may use the individual spreadsheet to identify all applicable monitoring requirements. Where visible on the Monitoring Required spreadsheet, these parameters are typically hidden on the remaining spreadsheets. To unhide these pollutant parameters the permit writer should highlight the rows above and below the hidden row, right click the mouse and select “ Unhide ”.

26 For example, Beryllium, Kjeldahl nitrogen, total chrome, etc.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 25 of 117 

## 2.4 Reporting Procedures

The permit must require the permittee to submit a Summary Report (both electronic and paper versions) and copies of th e laboratory analytic reports for all Tier 1 and subsequent Tier 2 effluent monitoring with a certification statement pursuant to 40 CFR 122.22(d). The Department will provide an electronic template to the permittee for developing the Summary Report, and the analy tic report can be generated by either the analytical laboratory or the permittee as long as it meets the requirements described in this section. Typically, effluent data collected for Tier 1 or 2 monitoring will be submitted to the Department’s Inspector at the regional o ffice for compliance purposes, and a duplicate data set sent to DEQ’s WQD OIS group to be entered into the Department’s reporting database, Discharge Monitoring System (DMS). The Summary Report must be submitted to the Department by the permittee within 30 cal endar days after receip t of the analytical report for the final round of sampling.

The permittee may use a letter with the certif ication statement to cover the submittal of the Summary Report and laboratory analyt ical reports. The letter should include:

• Facility Identification (facility legal name, DEQ File and Permit Numbers).

• Outfall identification.

• Reference to the specific analytic report.

• Signature from a responsible corporate officer (industrial), principal executive officer (domestic) or proprietor.

• The following statement:
I certify under penalty of law that this document and all attachments were prepared under my direction or supe rvision in accordance with a system designed to assure that qualified pers onnel properly gather and evaluate the information submitted. Based on my inqui ry of the person or persons who manage the system, or those persons di rectly responsible for gathering the information, the information submitted is, to the best of my knowledge and belief, true, accurate, and complete. I am aware that th ere are significant penalties for submitting false informati on, including the possibility of fine and imprisonment for knowing violations.
At a minimum, the analy tic report should include:

• Facility identification information and date of analysis.

• Each pollutant parameters stated with ex actly the same spelling as in the permit.

• Corresponding Chemical Abstract Service number for each pollutant parameter.

• The analytic method used fo r each pollutant parameter.

• The Method Detection and Quantitation Limit for each pollutant parameter.

• For all toxics, the reported analytic va lues in the units of micrograms per liter (ug/l).

• If a sample result is at or below the det ection level, report the result as less than the specified detection level. For exampl e, if the detection level is 1.0 ug/L and the result is non-detect, report “ <1.0 ug/L ” on the analytic report. To calculate the mass load from this result, use the detection level. Report the mass load asReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 26 of 117

less than the calculated mass load. For example, if flow is 2 MGD and the reported sample result is <1.0 ug/L, report “ <0.017 lb/day ” for mass load on the analytic report (1.0 ug/L x 2 MGD x conversion factor = 0.017 lb/day).

• If a sample result is above the detection level but below the quantitation level, report the result as the detection level pr eceded by the Department’s data code

“ e ”. This code identifies the result as being between the detection level and quantitation level. For example, if the detection level is 1 ug/l and the quantitation level is 5 ug/L and the sample result is 4 ug/L, report “ e1 ug/l ” on the analytic report. To calculate the mass load from this result, use the detection level. Report the mass load as less than the calculated mass load preceded by

“ e ”. For example, if flow is 2 MGD and the reported sample result is e1.0 ug/L, report “e0.017 lb/day” for mass load on th e analytic report (1.0 ug/L x 2 MGD x conversion factor = 0.017 lb/day).

• Quality Assurance/Quality Control information.

The permittee is already required to maintain the sampling and analysis records including chain of custody a nd quality assurance/quality control information and make monitoring records avai lable for inspection.


## 2.5 Schedule B: Suggested Monitoring Requirement Language

The department has developed suggested Schedule B permit language that includes recommended monitoring frequencies for most po llutant parameters. Various versions of this language applicable to different types of industrial and domestic facilities are located on the Permit Writers’ Corner of QNET under the “ Permit Template ” heading.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 27 of 117 

# Section 3: Identify Pollutants of Concern

3.1 Process Overview

The next step of the RPA process ( Step 3 ) is use the Tier 1 monitoring data to identify POCs in the effluent. The POCs are iden tified by statistically evaluating the data collected in the Tier 1 monitoring scan. The permit writer uses the Aquatic and Human Health RPA spreadsheets to project 27 a maximum potential effluent concentration value (at the “end of pipe”). The calculated maximum concentration is then compared to the State Water Quality Criterion 28 . Any pollutant exceeding the water quality criterion is identified as a POC and will require additional analysis in the Steps 4 and 5 , where the receiving water body is characte rized and (optionally) additi onal effluent or collection system data is collected to determine in-stream reasonable potential. No further action is required for the remaining pollutant paramete rs, although they would be included in the monitoring requirements for the next permit cycle. Please refer to Figure 3-1 for an example of this step. 

## 3.2 Entering General Facility Information

To begin using the RPA Workbook , enter the facility’s efflue nt flow and hardness data into the General Facility Information box at the top of the Aquatic RPA spreadsheet. Based upon the answer to Question 1 in the box, the spreadsheet is designed to either use a “dilution value” taken from a mixing zone analysis (in Question 4 ), or calculate a dilution value using general effluent and stream flow information (in Question 3). Please refer to the areas indicated by arrows on Figure 3-1

.
When calculating a dilution value in Question 3 , refer to the guidance 29 in the RMZ IMD Part 2 when determining the appropriate e ffluent values to enter into the “ Eff. Flow Rate ” portion of the information box. Although not ne cessary for this step, it is recommended that the balance of the ambient stream flow and dilution inform ation (if available) also be entered at this time.

27 The spreadsheets project a normal distribution curve about the available data points and the maximum projected value reflect a 95 th or 99 th percentile.
28 OAR 340-041-0033(2) Levels of toxic substances in waters of the state may not exceed the applicable (Aquatic Toxicity) criteria listed in Tables 20, 33A, and 33B. Additionally, concentrations may not exceed the currently e ffective Human Health Water Quality Criteria.
29 Section 4.4, Discharge Characteristics , p. 30.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 28 of 117

Figure 3-1 Example of the RPA Workbook

Figure 3-1 Explanation Identify Pollutants of Concern

6 The PW enters the effluent flow rate and hardness values into the “ General Facility Information ” portion of the spreadsheet. 7 The PW enters the “ # of samples ” collected, “ Highest Effluent Conc. ” (or

“ Effluent Conc.” ) and “ Coefficient of Variation ” into the spreadsheet. 8 The spreadsheet will calculate and report a “ Calculated Max. Eff. Conc. ” and compare it to the water quality criterion. 9 If the calculated concentration exceeds the water quality criterion, then a “Yes” is reported in the “ RP WQ at End of Pipe? ” column. 10 If the calculated concentration does not exceed the water quality criterion, then a

“ No ” is reported in the “ RP at End of Pipe? ” column. 11 The PW should check to ensure that there is a reported value for every pollutant parameter that is indicated as requiring evaluation or where monitoring data (“ # of Samples ” or “ Highest Conc. ”) has been entered. ?1

?3 ?4Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 29 of 117 

## 3.3 Analysis of Identified Parameters

For each pollutant parameter with a “Yes” in the “ Evaluation Required? ” column, the permit writer will perform a preliminary analysis and fill in effluent monitoring data for the applicable parameter located under the heading “ Identify Pollutants of Concern ” in the workbook. The permit writer enters the number of samples taken during the monitoring period into the “# of Samples ” column 30 . For the aquatic toxicity and noncarcinogen human health evaluations, the permit writer then enters the value (in ug/l) of the highest reported concentration du ring the monitoring period into the “ Effluent Conc. ” column. For the carcinogenic human health evaluations, the permit writer then enters the value of the geometric mean 31 of the data into the “ Effluent Conc. ” column. In cases where all analytic results are “ non-detect”, the permit writer should enter an

“ nd ” into the “ Effluent Conc .” column. Values should be entered into th e spreadsheets according to the department’s significant figures guidance ( Significant Figures IMD ).

Finally, the permit writer enters a Coefficient of Variance (CV) into the Column entitled

“ Coefficient of Variance ”. If the number of samples of th e data set is less than “10,” the permit writer should enter a defaul t of “0.6”. If the number of samples is greater than or equal to “10,” the permit writer should calcu late the CV using the following method.

30 In addition to copies of the analytic reports, the permittee will submit a Summary Report of the analytic results using an electronic template. This will help to simplify the data entry process.

31 In the case of geomeans, values of “0” cannot be used. It is recommended that the permit writer use their professional judgment and either use a geometric mean wher e “ND = 1⁄2 of DL”, or take the mean of the values and multiply by a sa fety factor of 0.9. (ref. Nehls & Akland, 1973) Example: How to calculate a CV from a data set

Given: I have the following values from the analytical reports
1.0, 1.0, 1.0, 2.0, 1. 0, 3.0, 2.0, 1.0, 3. 0, 4.0, 5.0, 1.0 ug/l

Answer: There are 12 data points, with a mean (or average) value of 2.1
(1.0+1.0+1.0+2.0+1.0+3.0+2.0+1 .0+3.0+4.0+5.0+1.0) / 12 = 2.1 To calculate the standard deviation, we compute the difference of each data point from the mean, and square the result:
(1.0-2.1) 2 = 1.2 (1.0-2.1) 2 = 1.2 (3.0-2.1) 2 = 0.8 (1.0-2.1) 2 = 1.2 (3.0-2.1) 2 = 0.8 (4.0-2.1) 2 = 3.6 (1.0-2.1) 2 = 1.2 (2.0-2.1) 2 = 0.0 (5.0-2.1) 2 = 8.4 (2.0-2.1) 2 = 0.0 (1.0-2.1) 2 = 1.2 (1.0-2.1) 2 = 1.2 Next we divide the sum of these values by the “degrees of freedom” (n-1), and take the square root, which gives the standard deviation: [(1.2+1.2+1.2+0.0+1.2+0.8+0.0+1. 2+0.8+3.6+8.4+1.2) / (12-1)] 1/2 = 1.4 Therefore, the standard deviation is 1.4 . Finally we divide the standard deviation by the mean, and round to arrive at a coefficient of variation of 0.7

. CV = 1.3 / 2.1 = 0.6666... rounds to 0.7

Note: When using a spreadsheet, there might be co mputational differences in the results when compared to rounding each calculation step.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 30 of 117 

## 3.4 Interpretation of Results

The workbook will auto-calculate a statisti cal maximum effluent concentration and compare the result to each water quality criterion 32 . This is reported in the column entitled “ Estimated Max. Eff. Conc. ” If the estimated effluent concentration is equal to or exceeds the criteria, then a “ Yes ” will be entered into the column entitled “ RP at end of Pipe? ”. Pollutant parameters that exceed the criteria at the end of pipe will require ambient water characterization and further analysis in Step 3 of the RPA. This is illustrated in Figure 3-2

.
Pollutant parameters with a “ No ” entered into the “ Exceed WQ” column do not exceed the water quality criteria at the end of pipe and do not require additional reasonable potential analysis. In instances where Tier 1 analytic results are “non-detect”, additional analyses are not typically re quired although the permit writer should review the analytic limits and consider additionally monitoring during the Tier 2 m onitoring. The permit writer should document the evaluation of both the affirmative and negative results by placing a copy of the applicab le workbook pages into the PER with a brief discussion.



## 3.5 Additional Information: Narrative Criteria and Whole Effluent Testing

It should be noted that a permittee will ty pically be required by 40 CFR 136 and EPA application forms to monitor for more pollu tants than there are State Water Quality Criteria. Based on this data, a permit write r might use their discretion to require WET analysis (if it is not already required). The da ta might also be used as part of a Toxic Identification Reduction Evaluation (TIRE) th at is mandated when an “affirmative” WET finding is made. Finally, the data might be us ed in the investigati on of a beneficial use impairment not addressed through the RPA nor WET analysis.

When required 33 , the WET analysis is conducted after the RPA and identifies instances of aquatic toxicity (not identified in the RPA) or synergistic effects. Whereas the RPA is designed to protect water qua lity using the State Water Quality Criteria, the WET analysis is the primary mechanism to protect water quality using the state’s Narrative Toxic Criteria 34 . In instances where there is evidence of beneficial use impairment, the

32 In the instance of a RPA for Aquatic Toxici ty, the maximum effluent concentration will be compared to water criterion for both the criterion continuous concentration (CCC) (chronic) and the criterion maximum concentration (CMC)(acute) and indicate a “Y es” if either are exceeded. In the instance of a RPA for Hu man Health, the maximum effluent concentration will be compared to the water criterion for both the Water + Fish Consumption and Fish Consumption criterion.
33 For example, facilities with a design flow greater than 1 MGD are re quired to conduct WET testing. When possible, WET sampling should oc cur in conjunction with priority pollutant sampling.

34 OAR 340-041-0033(1) Toxic substances may not be introduced above natural background levels in waters of the state in amounts, concen trations, or combinations that may be harmful, may chemically change to harmful forms in the en vironment, or may accumulate in sediments orReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 31 of 117

permit writer may use best professional j udgment and the guidance values listed in Table 33C to apply the Narrative Toxic Criteria. For additional information regarding WET, please contact the WET coordinator (locat ed at the DEQ Lab) or Surface Water Management Technical Staff.
Figure 3-2 Example of Result Interpretation



## 3.6 Next Step

After the permit writer has completed the identification of the POCs, the permit writer will report the results, (Tier 2) monitori ng requirements and recommendations to the permittee ( Step 4 ). The permittee must then devel op and implement a sampling plan to collect the necessary data during the following year. This is presented in Section 4 of the IMD.

bioaccumulate in aquatic life or wildlife to levels that adversely affect public health, safety, or welfare or aquatic life, wildlife, or other designated beneficial uses

.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 32 of 117



### This Page Intentionally BlankReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 33 of 117 

# Section 4: Tier 2 Monitoring

4.1. Tier 2 Monitoring Overview

By the end of the second year (month 24) of the permit term, the permit writer should have identified the pollutant parameters subj ect to evaluation and then performed an endof-pipe reasonable potential scr eening to identify the POCs ( Step 3 ). In Step 4 , the permittee conducts Tier 2 monitoring to collect /submit the ambient wa ter quality data and any additional effluent data for each identifi ed POC that will enab le the permit writer to model the impacts upon the receiving waters and complete the RPA in Step 5

.
Depending upon the potential source 35 of the pollutant, a Source Investigation (SI) should be considered to support a later request for compliance alternatives such as an intake credit 36 , site specific background criterion and/or a compliance schedule or variance. The nature and scope of the SI s hould be a reflection of environm ental issues and the type of compliance alternative being considered. (T he role of the source investigation as it relates to these compliance tools is outlined in Section 4.3.3 and relevant IMDs.)

Additionally, Tier 2 monitoring will be used to address cases where new water quality criteria have been recently promulgated or the receiving water body has recently been listed as “water quality limited.” This a ffords two opportunities (Tier 1 and 2) during a permit term to introduce new criterion or addr ess recently listed water bodies into the permit development process.

Finally, Tier 2 monitoring may be used to require the collection of “dissolved” or “fraction” pollutant concentration informa tion for those cases wh ere Tier 1 screening indicated significant concentr ations of the “total” counter parts of the same pollutant parameters 37 . This is intended to allow use of lo w cost screening methods to identify the need for higher cost methods fo r select pollutant parameters.

After evaluation of the Tier 1 data and identi fication of the POCs, the permit writer will issue a Monitoring Action Letter (MAL) reporti ng the POCs and requiring the permittee to develop a Sampling Plan and collect the data necessary to complete the RPA or support a compliance alternative (see Section 4.2 ). In cases where this data is already available or is not necessary 38 , the permit writer may decide to continue with the analysis without additional monitoring requirements. The permittee must submit the completed Sampling Plan to the permit writer for revi ew, and upon approval, begin implementation in a timely manner. The permit writer should ensure that Sampling Plan meets the permit

35 For example: Intake water, I&I, ground water etc.
36 Please refer to Appendix F for additional information on the use of Intake Credits

37 For example, cyanide, ar senic, chrome III and VI.
38 For example: Discharges to 303d listed waters where mixing zones are not permitted. Where data will be collected as part of a collaborative effo rt with other permittees . Where existing data is already available and is adequate for characterization.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 34 of 117

requirements and adequately characterizes the facility’s effluent and the receiving water body.

The timeline of the Tier 1 and 2 mon itoring is designed to identify potential environmental issues early in the permit deve lopment process so that treatment, reduction or compliance alternatives can be explore d, developed and approved by the end of the permit term. If the required or recommended Ti er 2 monitoring data is not collected, then the Department may not have sufficient data to approve the use of the compliance alternatives.

The permittee will report all effluent data using the procedures described in Section 2.4 of this document. For all other Tier 2 data (ambient, intake concentrations, etc.), the permittee will submit copies of the laborator y analytic reports w ith a certification statement to the Department’s Inspector at the regional office as described in Section 2.4

. 

## 4.2. Monitoring Action Letter

To initiate the Tier 2 monitoring, the perm it writer will issue a MAL to the permittee reporting the results of the “end of pipe analysis” and identified POCs, and the requirement for the permittee to develop a Sampling Plan that addresses the flowing requirements and recommendations:
Requirements

• ambient characterization of the receiv ing water body for each identified POC

o For aquatic toxicity pollutant eval uations, data containing a minimum of 4, 24-hour composite samples take n during the cri tical low flow period (i.e. dry period) must be provided.

o For human health pollutant evaluatio ns, data containing a minimum of 4, 24-hour composite samples taken to characterize the annual average condition must be provided. 39

• if necessary, effluent and ambient ch aracterization for pollutant fractions identified by screening an alysis for total pollutants 40

• if necessary, effluent and ambien t characterization for any recently 41 promulgated water quality criteria that are applicable to the permittee

• if necessary, effluent and ambient char acterization for any pollutant parameter for which the receiving water body has b een recently listed as “Category 5, Water Quality Limited” on the 303 d list

• all required monitoring and/or data subm ittal must be completed by the end of permit year three (month 36) 42

39 Two samples should be taken in the wet season (Feb.) and two in the dry season (Sept.).
40 i.e. Inorganic As and As III, for total As
41 Since the issuance of the permit.
42 This date may be extended up to month 48, as long as there is available time to investigate and pursue environmental compliance options prior to the permit expiration date.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 35 of 117

• the permittee must submit a data summary report and copies of all analytical laboratory reports to the permit writer by a specified date (~month 36-37).

Recommendations

• if necessary, additional effluent ch aracterization for identified POCs

• if necessary, a Source Inves tigation to identify pollutant sources and quantify mass loading in preparation for the use of an intake credit or site specific background pollutant criterion

The permit writer will typically develop the MAL in consultation with the permittee to identify characterization or investigation r ecommendations that address any site-specific considerations. Template language for the MAL and Schedule B permit language is posted on the Permit Writer’s Corner on the QNET. 

## 4.3. Sampling Plan

The main purpose of the Sampling Plan is to allow the permittee to efficiently consolidate the various monitoring requirements (see Section 4.3.1 and 4.3.2 ) into a site-specific monitoring plan. The secondary purpose is to integrate, when necessary, the elements of a source investigation (see Section 4.3.3 ) into the characterization process so as to make both efforts more robust and cost efficient. As described in the MAL, the permittee develops the plan in consulta tion with the permit writer.

The requirement to develop a Sampling Plan, and to provide ambient data for POCs and effluent and ambient data for pollutant fr actions is per a narrative statement in the Schedule B permit language and stems from th e authority under 40 CFR 122.41(3)(h) (“ duty to provide information ”); 40 CFR 122.21, (“ application requirements ”); and state monitoring requirements per OAR 340-045-0015(5)(c) and (d). The permit writer also has the legal authorities for changing the fre quency of the Tier 1 m onitoring or reporting requirements per minor modifica tion under 40 CFR 122.63 and OAR 340-045- 0055(2)(a)(B). Therefore, the permit writer s hould treat a permittee’s failure to submit a Sampling Plan or provide data per the approve d plan, as a permit violation. Additionally, the failure to provide the required monitori ng data may result in a more stringent RPA analysis and a limitation of available co mpliance options to address identified environmental issues. The permit writer w ill review the plan and provide written comments or approve within a timely manner. The permit writer should include the approved Sampling Plan and Departme ntal approval letter in the file.

The sampling dates in the plan should ensu re the completion of the required monitoring described in the plan by the end of year three (month 36) 43 . Accordingly, the plan must be developed, approved and the monitoring comp leted within one year after the POCs are identified. In cases where additional data is not required or already available to complete the RPA, a Sampling Plan and additional mon itoring are not necessary. In these cases,

43 This date may be extended up to month 48, as long as there is available time to investigate and pursue environmental compliance options prior to the permit expiration date.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 36 of 117

the permit writer must document in the PER that all data necessary to complete the RPA has been collected and a Sampling Plan is unnecessary.

4.3.1. Characterization of Receiving Water Body

The permit writer should first determine if it is necessary to characterize the receiving water body for each POC. For waters that are li sted as “water quality limited” (Cat 5) on the 303(d) list, the use of mixing zones and di lution values are gene rally not permitted for the listed pollutant para meters. Please refer to Section 5.5 and the RMZ IMD for additional information. If the water body is li sted as having a completed TMDL (Cat 3), the TMDL will assign waste load allocati ons. Check the TMDL webpage for more information at http://www.deq.state.or.us/WQ/TMDLs/basinlist.htm . In these instances, the collection of ambient characterization data for the specific pollutant parameters is generally not required 44 . The permit writer should note any pollutant parameters for which ambient characterization is not necessary in the PER.

For receiving water bodies not on the 303(d) list, it is n ecessary to characterize the ambient conditions for each POC during the permitted discharge periods (i.e., year round, summer-only). This data is us ed in conjunction with the effl uent characterization data to conduct the RPA. The ideal is to use a robust historic dataset 45 (see below) to characterize the water body, but when existing data is unavailable additional monitoring will be required. Per the m onitoring requirements in the MAL, a minimum of 4 data points per flow period would be required. In cases where there are multiple POCs in different flow periods (i.e. a quatic toxicity and human hea lth), the monitoring could be consolidated to a total of 6 samples with 4 in the critical period and 2 in the non-critical period.

Upon permit writer approval, the permittee ma y submit alternative ambient monitoring data in lieu of conducting sampling, as long as the submitted data is geographically relevant and current, and posse sses appropriate analytical lim its. Alternative data might include ambient data from U.S. EPA’s STORET database, DEQ’s LASAR database, Washington Dept. of Ecology data base or any other source of numeric or narrative data for the POC for the receiving water in the vicin ity of the point of discharge. If there are several applicants dischargi ng to the same reach of a receiving water body, chemical monitoring data may be derived from other a pplicants’ studies, or may be generated in a group monitoring study performed by multiple applicants discharging in the same receiving water environment. Please refer to Table 4-1 for data sources and internet links. The permit writer should describe the basis of alternative methodologies in the PER.

44 The Permit Writer might consider requiring ambi ent monitoring data if they believe that the particular river segment is not exceeding water qualit y criteria. In these cases, the data could be submitted to the LASAR data base and included in the next triennial state water quality assessment. This might allow for further segment ation of the water body, and the potential that a mixing zone might be permitted in the future if assimilative capacity is available.
45 For example, if a TMDL has been issued or updated, or DEQ has conducted a watershed assessment since the last permit renewal, there may be more current data available.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 37 of 117

Table 4-1 Water Quality and Stream Flow Databases

Data Source Data Type Internet Link

OR. DEQ Misc. WQ Data http://deq12.deq.state.or.us/lasar2/

OR DEQ 303d List / TMDL List http://www.deq.state.or.us/ wq/assessment/assessment.htm

NOAA, NW River Forecast Center Stream Flow Data, Forecasting http://www.nwrfc.noaa.gov/index.shtml

USACE, Columbia Basin Temp., TDG and Flow data http://www.nwdwc.usace.army.mil/TMT/wqwebpage/mainpage.htm
USEPA, STORET Misc. WQ Data http://www.epa.gov/storet/index.html

USGS Misc. WQ Data http://waterdata.usgs.gov/nwis

WA. DOE Misc WQ Data http://www.ecy.wa.gov/databases/wq.html

For new permit applications, it might be necessary for the permit writer to use representative data to conduct the RPA. This can include projected ambient data using a representative sample location, data from ot her, similar water bodi es, partial monitoring data sets, etc. If the permit writer can’ t make a reasonable projection, it might be necessary to proceed with the permit using an expedited monitoring plan and re-opener clause, or a final effluent limit paired with a compliance schedule.

4.3.2. Additional Effluent Characterization

The permit writer should conduct the RPA base d upon a robust data set with a minimum of ten sample points ( 4 (Tier 1) + 6 (Tier 2) = 10 ). This will allow better characterization of the effluent and the ability to calculate a facility-specific coefficient of variation

, resulting in a more representative RPA. Since the Tier 1 monitoring only requires a minimum of four samples per pollutant, additional mon itoring will be required to provide a robust data set for the universe of RPAs identified by Tier 1 monitoring.

Depending upon the results from the Tier 1 monitoring, the permit writer may send a permit action letter (as described in Section 4.2 ) requiring the permittee to collect additional effluent monitoring data (a minimum of 6 data points) for each POC. The permit writer might also require additional e ffluent sampling for any pollutant if there were issues meeting the Quantitation Limits, concerns regarding “false positives,” or any other implementation issue encountered during the Tier 1 monitoring. If it is determinedReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 38 of 117

that the Tier 1 monitori ng was adequately robust 46 to conduct the RPA, the permit writer might allow additional effluent monitoring to be omitted from the sample plan.

4.3.3. Source Investigation

Depending upon knowledge of the permittee’s f acility and the identified POCs, the permit writer may recommend the permittee to conduct a source inves tigation of the POC to identify the pollutant’s source, quantif y the mass transported and determine the ultimate fate. This information would be used to support a request for compliance alternatives such as intake credits, variance, site specific water quality criteria, etc. Without this source investigation data bei ng collected in a timely manner, the permit writer will have limited options for calcula ting WQBELs into the next permit renewal that the permittee can comply with.

A Source Investigation should, at minimum, identify the source (or sources) and quantify the mass loading rates for the pollutant of c oncern. The scope of the source investigation should depend upon the type and magnitude of the potential environmental impact. The permittee and permit writer should review the requirements for the use of an intake credit described in Appendix F or for the calculation of a S ite Specific Background Pollutant Criterion (described in future IMD). The s ource investigation can be developed in an iterative manner that relies upon periodic findi ngs and milestones to determine the need for additional monitoring.

The permit writer should encourage permittees to identify and use any existing ambient or intake monitoring databases as part of the source investigation. Examples include municipal pretreatment program information and the Department of Health Services (DHS) drinking water monitoring databases. 

## 4.4. Next Steps

By the end of year three, the permit writer will use the results from the Tier 1 & 2 Monitoring in calculating the RPA in the Step 5 and, if applicable, determining effluent limits in Step 6 . At the end of year five, the RPA and WQBELs (if applicable) will be finalized for incorporation into the renewed permit

.

46 ie. More than one sample detected above the Detection LimitReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 39 of 117 

# Section 5: Reasonable Potential Analysis

5.1 Reasonable Potential Analysis Overview

Once the Sampling Plan (Tier 2 monitoring) has been implemented and the appropriate effluent and ambient characterization data for each identified POC have been collected in Step 4 , the permit writer should be ready to enter the information into the RPA Workbook and conduct the initial RPA in Step 5 . At the end of the permit term and as part of the permit renewal, the permit writer will conduct a final RPA using any additional characterization data.

To conduct the initial RPA, the permit wr iter will use the partially completed RPA Workbook that was last used to identify POCs in Step 3 . The permit writer would then use the Summary Report of analytic results or retrieve collected effluent and ambient characterization data from the Department’s DMS 47 or LASAR databases to complete the RPA Workbook. The permit writer will then enter any additional General Facility Information , revised effluent ch aracterization values 48 and calculated Coefficients of Variation (if applicable). Finally, they will then enter the Ambient Concentration values and the RPA workbook will process the calculati ons and report the RP status. This is illustrated in Figure 5-1

.
The permit writer should proof check all data entries and ensure that the RPA Workbook made all required calculations. The RPA spreadsheet pages are linked to the corresponding Aquatic Toxicity and Human Health Limit spreadsheet pages and data will automatically be transferred to th e limit calculation page of the workbook in Step 6

. A summary of the values used in the va rious RPA calculations is described in Table 5-1 and each is discussed through the rest of this section. In the event that a facility has a non-typical discharge 49 , the permit writer should consu lt the discharge characterization guidance described in Section 4.4 of the RMZ IMD Part 2

.
Where adequate data is available and the minimum conditions have been met, the permit writer may consider conducting an intake cred it analysis. This ma y change the outcome of the RPA or adjust any calcu lated WQBELs to reflect intake pollutant concentrations. Guidance is available in Appendix F and an analysis module is included on the Aquatic Toxicity and Human Health RPA spreadsheet pages of the RPA Workbook

.

47 DMS and tutorial information are available on the Qnet: http://deqapp1/dms/default.aspx

. 48 Ie. Number of samples, highest/mean concentration, and coefficient of variance.
49 i.e. Wet Season only discharge, marine/estuar ine discharges or facilit ies operating between 85% and 100% of capacity.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 40 of 117

Figure 5-1 Example of the RPA Workbook

Figure 5-1 Explanation

12 The PW enters any remaining values into the “ General Facility Information ” portion of the spreadsheet. 13 Where additional effluent characterization was required in the Sampling Plan, the PW enters the updated “ # of samples ” collected, “ Highest (sample) Conc. ” and calculated “ Coefficient of Variation ” into the spreadsheet. 14 The spreadsheet will re-calculate and report a “ Calculated Max. Eff. Conc. ” and compare it to the water quality criterion. 15 The PW should check each revised parameter to determine if there is still a potential to exceed WQ criteria (at end of pipe). 16 If there is no longer a potential to exceed the WQ criteria, the “Yes” reported in the “Exceed WQ at End of Pipe?” column would have changed to “No”, and no further action is re q uired for that p ollutant p arameter. 

### General Facility Information

Revised DataReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 41 of 117 

## 5.2 General Facility Information

The General Facility Information box ( Figure 5-2 ) contains the general facility and receiving water characterization information su ch as fresh/marine status, flow rates, available dilution, hardness and the statistical values used in the calculations. The permit writer needs to complete this information to conduct the RPA. Please note that the boxes for the Aquatic Toxicity and Human Health RPAs have slight differences in ambient flow rates used and the need for harness information. Figure 5-2 General Facility Information

5.2.1 Flow Rates

Depending upon the type of RP analysis being conducted (i.e. aquatic toxicity vs human health ), various ambient and facility low flow conditions are used in the analysis. The flow conditions used are:

• 1Q10: The minimum 1-day flow which occurs once in 10 years on average

• 7Q10: The minimum 7-day flow which occurs once in 10 years on average

• 30Q5: The minimum 30-day flow which o ccurs once in 5 years on average

• Harmonic Mean Flow: This is the number of daily flow measurements divided by the sum of the reciprocals of the flows (that is, the reciprocal of the mean of reciprocals).

• Geometric Mean : is a type of mean or average, which indicates the central tendency of a set of numbers where the numbers are multiplied and then the nth root of the resulting product is taken. The geometric mean of a data set is given by:

• Average Dry-Weather Design Flow: (ADWDF) This is considered a “base flow” condition for a sewer collection area that is exclusive of additions due to inflow and infiltration or storm water additions.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 42 of 117

In some cases, adequate data to calculate these flow conditions might not be readil y avail a ble. There are a variety of accepted hydrolo g ic and stati st i cal approaches that might be used to project, interpolate, correlate or repr esent a data set to calculate these conditions. When used, a description of the hydrologic/sta tistical approach used should be included in the PER and, if necessary, requirements to collect additional data in the permit condition.

Table 5-1 Summary of RPA Variables

RPA Type Effluent Conc. Ambient Conc. Effluent Flow Rate Ambient Flow Rate %Confidence / %Probability
Aquatic Life: Acute Max Conc. • 1-3 samples: Max. Conc.

• > 4 samples: 90 th percentile See RMZ IMD Part 2, Sec. 4.4 1Q10 99% / 95%

Aquatic Life: Chronic Max Conc. • 1-3 samples: Max. Conc.

• >4 samples: 90th percentile See RMZ IMD Part 2, Sec. 4.4 7Q10 99% / 95%

Human Health • Carcinogens

• Geometric

Mean NonCarcin. Max Conc. Geometric Mean • Carcinogens Average Annual Flow

• Non-Carcin. ADWDF • Carcinogens Harmonic Mean Flow

• Non-Carcin. 30Q5 50 NA

5.2.2 In-Stream Dilution

The RPA is essentially a simple in-stream wa ter quality model that estimates the impacts of an effluent upon a receiving water body. One of the key variables in this model is the available dilution. The RPA Workbook allows for two methods of incorporating the available dilution. The first is to use a factor derived from a Mixing Zone Analysis per departmental guidance ( Regulatory Mixing Zone IMD ). The second is to use a default factor calculated directly fr om the ratio of discharge and stream flow rates, with an allowance fraction 51 . The General Facility Box has a series of questions and answers that, depending on how the permit writer answ ers, can facilitate either method. The permit writer must place a “ y ” or “ n ” in the appropriate box (Question #1) to tell the spreadsheet which method to employ.

Most major, and many minor facilities, s hould have conducted a mixing zone study to determine the available dilutions at the edge of the zone of in itial dilution a nd the edge of the mixing zone. This analysis must be conducted in accordance to the Department’s guidance and will result in the calculation of a series of dilution factors specifically for

50 If the effects from certain non-carcinogens are manifested after a lifetime of exposure, then harmonic mean flow may be appropriate, (EPA TSD, p. 89)
51 In both cases a mixing zone is established, but t he difference lies in how the dilution factors are determined.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 43 of 117

use in Aquatic Toxicity and Human Health RPAs. Permit writer should enter mixing zone factors into the indicted spaces ( Question #4 ). These factors will typically be listed in the Mixing Zone Analysis Report

.

If no mixing zone analys is is available, the RPA Workbook has the ability to calculate available dilution using the Design Flow 52 of the facility and various stream flow conditions ( Question #3 ). A summary of the various flow rates and conditions used for the RPAs is included in Table 5-1 . The permit writer should refer to the department’s mixing zone guidance for an explanation of how to calculate the various flow values. The databases listed in Table 4-1 are sources of stream flow data that can the basis of flow value calculations. The permit writer mi ght also contact the regional Plan Review Engineer for additional information re garding facility flow performance.

52 The flow that the facility was built to handle Primer on Regulated Mixing Zones

A regulatory mixing zone (RMZ) is an area defined in an NPDES permit where: 1. A discharge undergoes initial dilution and mixing in the receiving stream; 2. Water quality standards can be suspended for a short distance downstream of a discharge provided several conditions are met (see RMZ IMD Part 1 ); and 3. Mixing zones are designed to be protective of human health, aquatic habitat and the water body as a whole.

A RMZ is comprised of a both a chronic and acute mixing zone. The chronic mixing zone is the area encompassed by the entire RMZ and the water quality criteria for both aquatic toxicity (chronic) and human health must be met at the boundary.

The acute mixing zone or “Zone of Immediate Dilution” (ZID) is the area immediately surrounding the outfall and within the RMZ. In this area, the acute and chronic aquatic life criteria may be exceeded as long as lethal impacts prevented.
Example of Regulatory Mixing Zone (RMZ) for a River

Zone of immediate dilution (ZID)

Discharge Plume RMZ length

RMZ widthReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 44 of 117

5.2.3 Fresh/Marine Water Status

The state toxic water quality criteria vary based upon the t ype of water body; marine or freshwater. The permit writer must place a “ y ” (for fresh water) or “ n ” (for marine water) in the appropriate box (Question #2) to tell the spreadsheet which set of water quality criteria to employ. The permit writer shoul d request technical assistance when the salinity of the receiving water can not readily be determined (ie. the receiving water is between 1 and 10 ppt). 53

5.2.4 Hardness

For most metals, the state aquatic toxicity water quality criteria are dependent upon the hardness of the receiving water. Therefore, it is necessary to enter effluent and ambient hardness information to calculate the water quality criteria and m odel the effluent’s impact upon the receiving waters. Effluent hardness data must be included with the applicants monitoring data. Ambient ha rdness data can usually be found on the Department’s LASAR or other governmental database (see Table 4-1 ). Data entered should be reflective of the average effluent and ambient flow conditions being modeled. For example, a permit writer should calculate the average ambient hardness from data taken during the dry season, low flow conditi on or other appropriate seasonal condition based on the mixing zone st udy critical time period.

53 It should be noted that EPA’s WET testing protocols are also sa linity based but used different salinity levels than state water quality critieria. Fresh and Marine Waters Determination Process

The following salinity values are used to determine the status of the receiving water. Geographic salinity data is available on the Department’s LASAR database and on the QNET: Permit Writers Corner

• All waters with a salinity less than 1 parts per thousand (PPT) of salinity are considered fresh waters and use the fresh water criteria.

• All waters with a salinity greater than 10 PPT of salinity are considered marine waters and use the marine water criteria

• All waters with salinity between 1 and 10 PPT of salinity must meet the more conservative of the fresh or marine water quality criteriaReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 45 of 117

5.2.5 Statistical Calculation Values

The RPA calculates a log-normal distribution curve from the effluent data and then projects an “ Estimated Maximum Effluent Concentration ” 54 at a specified Probability Basis and Confidence Level (i.e. Figure 5-2 ). The Probability Basis reflects the upper boundary of the effluent distribution curve and the Confidence Level indicates the reliability of the estimated maximum effluent concentration. The statistical values recommended by the Department are included, by default, in the RPA Workbook . A permit writer may use best professional judgmen t to determine altern ative values and the decision criteria should be included in the PER.

The values used in the Aquatic Toxicity and Human Health Analysis are summarized in Table 5-1 . For a more detailed discussion of the statistics used in the RPA, please refer

to Section 3.3 of the TSD

. Figure 5-2 Example of a Log-Normal Dist ribution of Effluent Data



## 5.3 Revised Effluent Characterization Data

Working from the partially completed RPA spreadsheets from Step 3 , the permit writer should revise the data entered for those po llutant parameters identified as a POC and where Tier 2 monitoring information was collect ed or located. Typical revisions include an update to the “# of Sa mples”, reevaluation of the Maximum Effluent Concentration (Aquatic Toxicity), re-calculation of the Effluent Concentration (Human Health) and the calculation of a Coefficient of Variation 55

.

54 “The estimated maximum concentration is the upper bound of the expected lognormal distribution of effluent concentrati ons at a high confidence level.
55 See Section 3.3 of this IMD for information in calculation of a CV Est. Max Conc.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 46 of 117

Once completed, the spreadsheets wi ll automatically re-calculate the Estimated Maximum Effluent Concentration . If the estimated effluent concen tration is equal to or exceeds the water quality criteria, then a “ Yes ” will be entered into the column entitled “ Exceed WQ at end of Pipe? ”. Pollutant parameters that exceed th e criteria at the end of pipe require ambient water characterization. Note: The Permit Writer should maintain electronic and paper copies of both th e partially completed RPA Workbook and revised version for the record. 

## 5.4 Data Interpretation

Since the RPA is a statistical analysis that requires multiple data points, it is subject to greater uncertainty when base d upon a single or relatively few data points. Due to the large number of water quality cr iteria that are below available analytic limits, this can be a relatively common occurrence. This is part of the reason that additional monitoring is typically required for identified POCs. Even af ter additional data is collected in the Tier 2 monitoring, there might only be one, two or th ree detects out of a samp le set of ten. In these instances, the permit writer might cons ider contacting Surface Water Management for technical assistance in using one of the following alternative RPA processes:

• Single data point: Since a distribution curve cannot be developed around a single data point, the permit writer should utili ze a “Qualitative RPA” according to the guidelines discussed in Section 6.3.3 of the USEPA’s NPDES Permit Writers Manual (Sept. 2010) and Section 3.2 of the TSD

.

• Two to three data points: Based upon permit writer discretion, an alternative statistical analysis technique may be considered. For example, the TSD (p. E-10) recommends the use of a Delta-Lognormal Di stribution analysis in cases when the data contain a mixture of non-detect values and values above th e detection limit. Other methods include Maximum Likeli hood Estimation (MLE) or Regression on Order Statistics (ROS)

The permit writer should also c onsider the potentia l of “false positives” due to sampling error or upset facility condition when evaluating characterization data.

• False positive: If there is conclusive information that a data point was a false positive due to laboratory error, the permit writer may remove the data point from the analysis and document the decision in the PER.

• Upset condition: If there is conclusive information that a data point was a false positive due to an upset condition, the permit writer should work with the permittee to develop and implement mitiga tion or operational practices to ensure that the upset condition does not re-occur. The terms of this should be included in the PER. The data point may then be removed from the analysis. Later, if another monitoring event detects a si milar upset condition, even after the implementation of the mitigation or operation practices, it should be considered representative of the effluent a nd used in subsequent analysis.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 47 of 117



## 5.5 Ambient Concentration

The goal of the ambient monitoring is to dete rmine the condition of the receiving water body and identify the ava ilable assimilative capacity for each POC. Assimilative Capacity is the capacity of a natural body of wa ter to receive wastewaters or toxic materials without exceeding wate r quality criteria. In cases where there is assimilative capacity, Departmental regulations may allow for the designation of a Regulatory Mixing Zone (RMZ). The RMZ is a small area around the outfall where suspension of water quality criteria are allowed as long as lethalit y is prevented and the integrity of the water body as a whole is protected. When a RMZ is permitted, the RPA is calculated at the regulatory boundary of the RMZ.

In cases where the ambient pollutant con centrations exceed the corresponding water quality criteria, no assimilative capacity is available and a RMZ is not permitted for that particular pollutant. In cases where the am bient pollutant concentrations are below the corresponding water quality crite rion, assimilative capacity is available and a RMZ might be allowed per the Department’s mixing zone guidance ( Regulatory Mixing Zone IMD ).

In cases where the stream segment of the receiving water body has been listed on the 303(d) list as “ Water Quality Limited ” (Cat 5), even if data indicates that assimilative capacity is available, RMZs may not be permitted 56 . The implications of this is that any POC discharged to a water body listed as water quality limited for the same pollutant will have reasonable potential and require an effluent limit calculated to meet the water quality criterion at the end of pipe.

Once the background concentrations are put into the RPA spreadsheet under the “ ambient concentrations ” column, the spreadsheet automatica lly calculates whether assimilative capacity is available and, if allowed, factors in dilution data to determine the M aximum Effluent Concentration at the acute (ZID) and chroni c (RMZ) mixing zone boundaries. This maximum concentration is essentially the total concentration value when the ambient pollutant concentration and effluent concentrations are combined and allowed to mix within the ZID and mixing zone.

56 In these instances where assimilative capacity is available, the permit writer should consider supplying ambient monitoring data to the DEQ Lab fo r inclusion into the LASAR database. This data would subsequently be evaluat ed as part of the Sate-wide Water Quality Assessment and might lead to a segmentation of the listed water body. This might result in the “Water Quality Limited” status being limited to only the segment s where the criteria are actually being exceeded.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 48 of 117

5.5.1 Data Entry Instructions

The permit writer would enter the data collected in the Tier 2 Monitoring into the RPA Workbook column entitled “ Ambient Conc .” using the following guidelines:

In cases where the receiving water body is listed on the 303d list as “Water Quality Limited” for a POC, the permit writer should set the “ Ambient Conc. ” to equal either the highest water quality criteria value or, an ev en higher recorded ambient concentration. This will effectively remove all dilution fr om the calculation. The permit writer should make a note of the actual ambient value in the “ RPA Run Notes: ” 57 . This is demonstrated in Figure 5-3

.

57 To set the ambient concentration equal to the water quality criteria, the permit writer should enter a “=” followed by the cell number of the highest criterion in the “ Ambient Conc. ” cell. Ambient Data guidelines for use in RPA Calculation

• Aquatic Toxicity Analysis 3⁄4 For 4 or more data points, the permit writer would enter the 90th percentile of the data range 3⁄4 For less than 4 data points, the permit writer would enter the most conservative value

• Human Health Analysis 3⁄4 The permit writer should calculate and enter the geometric meanReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 49 of 117

Figure 5-3 Example of 303(d) Procedure

Figure 5-3 Explanation

17 For each remaining POC, the PW enters the appropriate value for ambient pollutant concentration into the “ Ambient Conc. ” Column. 18 If the receiving stream segment is 303(d) listed for an POC then no mixing zone is permitted. The ambient value must be set to a value equal to or greater than the highest water quality criteria. See example. 19 The PW should describe any changes due to listing status in the RPA Run Notes of the spreadsheet and PER. 20 The spreadsheet will then calculated the pollutant concentrations at the various mixing zone boundaries (if allowed) and RP status.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 50 of 117 

## 5.6 Comparison of Maximum Concentration to Water Quality Concentration

In the case of the human health toxicity calculation, a maximum in-stream concentration will be calculated. If there is available assimilative capacity and a mixing zone is allowed, the calculated maximum concentration will reflect dilution and be calculated to reflect conditions at the boundary of the mi xing zone (RMZ). The aquatic toxicity spreadsheet will employ a similar calculati on, with the addition of a calculation to determine the concentration at the boundary of the acute mixing zone (ZID). The spreadsheet will then compare each calculated maximum concentration to the applicable water quality criteria and indicate the results in the “ Is there Reasonable Potential to Exceed ” column. A report of “ yes ” indicates that there is reasonable potential and a report of “ no ” indicates that there is not reasonable potential. An example of an aquatic toxicity calculation is illustrated in Figure 5-4 , below.

Figure 5-4 Example of RPA analysisReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 51 of 117 

## 5.7 Troubleshooting

Since all the calculation variables have already been entered, there is little to do in this step other than trouble-shoot th e process and evaluate the results. When receiving water body information is entered into the General Facility Information section, the applicable water quality criteria will be ca lculated and reported in the “ WQ Criteria ” columns. If the word “ data ” appears in the columns, either dilu tion or hardness data is missing. If a “0” appears in the column, a value less than ze ro was calculated and th e field is not set to report to the appropriate decima l point. If there is not an acute or chronic water quality criterion for a particular pollutant parameter, a “ na ” will be reported in the applicable field.



## 5.8 Conclusions

Before completing the RPA and calculating effluent limits, the permit writer should evaluate the results to ensu re accuracy. Probably the mo st relevant question is “ do the results make sense ?” Line 1 in Figure 5-5 below is a good example. Here the maximum concentration at the boundary of the mixing zone (RMZ) was reported as 0.00 ug/l as compared to the reported concentr ation of 0.0 ug/l, resulting in “ yes ” for reasonable potential to exceed the chronic criteria. In this case it would be prudent to check the calculated water quality criteria value by expanding the number of decimal points reported in both fields. This would resu lt in a maximum concentration of 0.0013 ug/l vs. the water quality criteria of 0.0010 ug/l 58

. Figure 5-5 Example of RPA Evaluation

58 Although the calculated maximum concentration (0.0013 ug/l) was greater than the calculated water quality criteria (0.0010 ug/l), these result s might be within the range of analytic variability and the permit writer should consult the department ’s policy on rounding and significant digits when ultimately determining whether there is reasonable potential.

Line 1Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 52 of 117

In some cases where RP is indicates, the pe rmit writer may consider conducting an intake credit analysis. As long as a number of stat utory conditions are met, the analysis allows the permit writer to consider pollutant concen trations originating from the municipalities or industries source water as a credit when determining RP or determining compliance with a WQBEL. Please refer to Appendix F for guidance on the use and calculation of an intake credit. The data required for th is analysis is similar in scope to the requirements for calculating a Site Specifi c Background Pollutant Criterion. At this point, the permit writer should keep this optio n in mind, but the actua l application of the criterion approach should not be undertaken until after a WQBEL has been calculated in Step 6 . The criterion approach would then de termine an alternative criterion, upon which a new RPA and WQBEL calcula tion would be conducted. 

## 5.9 Next Steps

Once the permit writer has evaluated and confirmed the results of the RPA, they should determine the applicable effluent limit as described in the next Section. The RPA Workbook has been designed to link the RPA spreadsheet with the effluent limit calculation spreadsheet. The general facili ty information and ambient/effluent water quality data will be automatically transferred to the effluent limit calculation spreadsheet.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 53 of 117 

# Section 6: Effluent Limit Calculation and Determination

6.1 Effluent Limit Determination Process Overview

Once the permit writer has conducted the RPA and determines that a facility has reasonable potential to exceed the in-stream water quality criteria, Step 6 is to calculate the Waste Load Allocations 59 (WLA) and derive Water Quality Effluent Limits (WQBELs). Much of this process occurs auto matically as relevant data is transferred from the RP spreadsheets to the Effluent Limits spreadsheets of the RPA Workbook 60

.
Because of the statistical variability of th e effluent concentration and the lack of a probability basis, it is necessary to translat e the WLAs into WQBELs to ensure proper implementation and enforcement. In 303-d listed stream segments where a formal TMDL has been completed and WLA’s assigned, the permit writer must translate the TMDL’s WLAs into WQBELs. In some cases , it might be possible to use an intake credit in determining compliance with the calculated WQBEL.

Once calculated, the permit writer would comp are the derived limits (WQBEL or TMDL based) with any applicable Technology Based Effluent Lim its (TBEL), and select the value that is most protective of the receiving water body. Th e elements of this process are presented in Figures 6-1

. 

## 6.2 WLA and WQBEL Calculation

The Department has developed methodol ogy from EPA’s 1991 Technical Support Document (TSD) to calculate WLAs and WQBE Ls to be protective of applicable water quality criteria in the receiving water. This methodology accounts for the allowable dilution, background concentration, effluent variability, and sampling frequency to calculate a WQBEL. Table 5-1 summarizes the critical conditions (effluent concentration, background concentration, effluent flow, etc.) that are used in effluent limit calculation to be protective of aquatic life and human health.

As previously mentioned, data and results are automatically transferred from the RPA spreadsheet to the WQBEL Calculation spreadsh eet. Of particular interest will be the RPA results that trigger the calculation of effluent limits. The only additional information the spreadsheet will require to be entered by the permit writer is the

59 WLAs are the portion of the receiving water’s TMDL that is allocated on one of its existing or future point sources of pollution so that surface water quality is protected at all flow conditions.

60 The detailed guidance for calculating a permit effl uent limit used in the workbook is described in depth in Section 5 (Permit Requirements) of EPA’s TSD

.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 54 of 117

monitoring requirement frequency (#/mo) that will be re quired in the permit (as shown in Figure 6-1 , boxed areas). These applicable area s are highlighted in orange on the spreadsheet 61

.
Once the applicable data has been entered into the WQBEL spreadsheets, the WLAs and WQBELs for the applicable pollutant paramete rs are calculated. A summary and list of formulas used in the calculations is include d in the boxes below. When available, an intake credit may be used in determining compliance with the WQBEL. Please refer to Appendix F for guidance in the use of intake credits and permit language. Figure 6-1 Example of WQBEL Calculation

61 When calculating the Average Monthly Limit (AML) as part of the Aquatic Toxicity WQBEL, it is necessary to use a value of greater than one samp le per month to prevent the calculation of a value could allow an exceedance of a water qualit y criterion. The applicable Aquatic Toxicity WQBEL calculation spreadsheet has been set up to automatically enter a value of “ 2 samples/month ” where the entered value is less than “ 2 ”. This is not applicable to Human Health WQBEL calculations since the AML is equal to the WLA and does not factor in monitoring frequency. Please refer to the TSD p. 107 & 110 for additional guidance.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 55 of 117

Summary of the Aquatic Toxicit y WQBEL Calculation Process Step 1: The first step is to calculat e Waste Load Allocations (WLA) based on the acute and chronic aquatic criteria. The WLAs are calculated based on available dilution and the background concentration.
The permit writer will calculate WLAs for both chronic and acute aquatic life impacts from respective water quality criteria (WQC’s). The formulas for calculating WLAs (chronic & acute) are:

eff ater receivingw eff background background chr MZ c 

### Q Q Q ion whereDilut C C WQC x Dilution WLA

/ ) ( ) (

+ = +

− =

eff ater receivingw eff background background acute ZID a 

### Q Q Q ion whereDilut C C WQC x Dilution WLA

/ ) ( ) (

+ = +

− =

Step 2 : A corresponding Long-Term Average (LTA) is then calculated from each of the WLAs by multiplying the LT A by a statistical factor derived from the Coefficient of Variation (CV) of the monitoring data. 

### [ ]
σ σ z a a e WLA LTA
− × = 2 5

. 0 

### [ ] 2 4 2 4 5

. 0 σ

σ z

c c e WLA LTA − × = Step 3: The permit writer then selects the most limiting (or lower) of the acute aquatic life and chronic aquatic life LTA’s to be protective of the most sensitive beneficial use.
LTA = min (LTA chr , LTA acute ) Step 4 : The most limiting LTA is then ex pressed as the Maximum Daily Limit (MDL) and/or Average Monthly Limits (AML ) in the permit by multiplying the LTA by a statistical factor derived from CV, Confidence Interval and monitoring frequency

. 

### [ ] 2 5

. 0 σ σ

− × = z e LTA MDL 

### [ ] 2 5

. 0
n n z 

### e LTA AML σ σ

− 

### × = Figure 6-1 Explanation

27 For each remaining pollutant parameter where a reasonable potential determination was made, the results will be transferred from the RPA page to the effluent limit calculation page. 28 For each pollutant parameter where reasonable potential is indicated, the spreadsheet will automatically calculate the Waste Load Allocations using data from the RPA pages. 29 The permit writer will need to enter the number of monthly compliance monitoring events to calculate the effluent limits.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 56 of 117



## 6.3 Compare WQBELs with TBELs

Once the permit writer has calculated the Aqua tic Toxicity and Human Health WQBELs, (both AMLs and MDLs) the next step is to compare the results to any applicable TBELs for toxic pollutants. The permit writer identifies the TBELs based upon the permitted facility’s Standard I ndustrial Classification (SIC) code or EPA’s industrial classification scheme. For each category and sub-category of process identified, the EPA has published a series of Effluent limit Guidelines (ELGs) and performance standards. These guidelines appear in 40 CFR Parts 405-499. A list of the existing ELGs with hyperlinks is provided in Table 6-2

.
The WQBEL or TBEL with the lowest valu e for each criteria (Human Health and Aquatic Toxicity) and each loading type (AML and MDL) should be included in the final permit. In most cases, it will be the WQB EL that is more environmentally protective than the corresponding TBEL. Summary of the Human Health WQBEL Calculation Process Setting limits based on human health criteria is slightly different from the procedure for aquatic toxicity because the exposure periods the criter ia are based on are generally longer than a month and may extend up to 70 years. EPAs TSD recommends a slightly different methodology to account for this exposure period.

Step 1 : First the WLA is calculated for both the Water + Fish Consumption and Fish Consumption water quality criteria (WQC). Depending on the carcinogen status of the pollutant param eter the dilution used for ca lculation varies from the 30Q5 to Harmonic Mean . If the back ground concentration of the receiving water body exceeds the WQC, then the WLA = WQC.



### ` / ) ( ) (

eff ater receivingw eff background background 

### Q Q Q ion whereDilut C C WQC Dilutionx WLA

+ = +

− =

Step 2 : The Average Monthly Limit (AML) is set equal to the minimum WLA calculated for Water + Fish Consumption and Fish Consumption

. AML = min (WLA Water + Fish , WLA Fish ) Step 3 : The Maximum Daily Limit (MDL) is then calculated based on the relationship between the AML and a multiplica tion factor statistically derived from the relationship between the confidence level

, coefficient of variation and proposed monitoring frequency

. MDL = AML x M factor
M

factor = 

### [ ] 2 5

. 0 σ σ

− z e / 

### [ ] 2 5

. 0
n n z 

### e σ σ

−

*a table of the M factors is included on pa g e 106 of the TSDReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 57 of 117

Table 6-2 Existing Effluent Limit Guidelines

Industry Category 40 CFR Part First Promulgated
Aluminum Forming 467 1983
Asbestos Manufacturing 427 1974 Battery Manufacturing 461 1984
Canned and Preserved Fruits and Vegetable Processing 407 1974
Canned and Preserved Seafood (Seafood Processing) 408 1974
Carbon Black Manufacturing 458 1978

Cement Manufacturing 411 1974
Centralized Waste Treatment 437 2000
Coal Mining 434 1985
Coil Coating 465 1983
Concentrated Animal Feeding Operations (CAFO) 412 1974
Concentrated Aquatic Animal Production (Aquaculture) 451 2004 Copper Forming 468 1983 Dairy Products Processing 405 1974
Electrical and Electronic Components 469 1983 Electroplating 413 1981 Explosives Manufacturing 457 1976 Ferroalloy Manufacturing 424 1974
Fertilizer Manufacturing 418 1974
Glass Manufacturing 426 1974
Grain Mills Manufacturing 406 1974

Gum and Wood Chemicals 454 1976 Hospitals 460 1976
Ink Formulating 447 1975 Inorganic Chemicals 415 1982

Iron and Steel Manufacturing 420 1982
Landfills 445 2000
Leather Tanning and Finishing 425 1982

Meat and Poultry Products 432 1974
Metal Finishing 433 1983

Metal Molding and Casting (Foundries) 464 1985
Metal Products and Machinery 438 2003 Mineral Mining and Processing 436 1975
Nonferrous Metals Forming and Metal Powders 471 1985
Nonferrous Metals Manufacturing 421 1984
Oil and Gas Extraction 435 1979
Ore Mining and Dressing (Hard Rock Mining) 440 1982 Organic Chemicals, Plastics and Synthetic Fibers (OCPSF) 414 1987
Paint Formulating 446 1975 Paving and Roofing Materials (Tars and Asphalt) 443 1975
Pesticide Chemicals Manufacturing, Formulating and Packaging 455 1978
Petroleum Refining 419 1982Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 58 of 117

Table 6-2 Continued Existing Effluent Limit Guidelines,

Industry Category 40 CFR Part First Promulgated
Pharmaceutical Manufacturing 439 1983 Phosphate Manufacturing 422 1974 Photographic 459 1976
Plastic Molding and Forming 463 1984
Porcelain Enameling 466 1982 Pulp, Paper and Paperboard 430 1998
Rubber Manufacturing 428 1974 Soaps and Detergents Manufacturing 417 1974

Steam Electric Power Generating 423 1982 Sugar Processing 409 1974
Textile Mills 410 1982
Timber Products Processing 429 1981 Transportation Equipment Cleaning 442 2000

Waste Combustors 444 2000 

## 6.4 Next Steps

After calculating and confirming the effluent limits, permit writers should ensure that all raw data, spreadsheets, mixing zone models a nd notes detailing any decision rationale are preserved in the permit file. This will he lp the permit writer to communicate the findings to the permit applicant and the publ ic at the end of year three, and ensure that all required information to write the PER at the end of year five is available.

In addition to the requirements to determin e if individual pollutants will have reasonable potential to exceed water quality criteria, there is also th e narrative requirement (OAR 340-041-0033(1)) to “prevent the discharge of toxic substances into Oregon’s waters above natural background levels in amounts that are toxic to aquatic life”. The Department employs WET analysis to determ ine if the effluent in its entirety causes toxicity in aquatic organisms. The permit wr iter should refer to any current Departmental guidance or the Department’s WET Te sting Coordinator located at the DEQ Laboratory

.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 59 of 117 

# Section 7: Permit Applicant Consultation

7.1 Overview

By the end of the third year of the permit term, the permit writer has used Tier 1 and 2 monitoring results to character ize the facility’s effluent and receiving water body, and conduct a RPA. Where pollutant paramete rs are found to possess RP, they then calculated a WQBEL and identified any applicable TBELS, se lecting the most conservative for the final permit. At this point in the permit development process ( Step 7 ), the permit writer is ready to inform the permit applicant of the results and work with them to develop a management strategy fo r achieving regulatory compliance during the remaining two years of the permit term.



## 7.2 Permittee Notification of Results and Compliance Evaluation

Once the RPA and effluent limit determinati on process has been completed, the permit writer should notify the permitt ee of the results via memorandum along with a copy of the applicable spreadsheets from the RP A Workbook. Shortly thereafter, the permit writer should meet with the perm it applicant to discu ss the results and wh ether the facility is currently able to meet the proposed effluent limits.

The permit applicant should perform a techni cal evaluation of their current or proposed treatment facility to determine if the proposed effluent limits can be met. Given the fact that the RPA was based upon facility performa nce data, in most cases the applicant will need to implement a source control effort , operational change or infra-structure improvement in order to meet the proposed effluent limit. The permit writer should discuss plans with the permit applicant to iden tify and select the best option to ensure a pathway to compliance.



## 7.3 Alternatives

In some cases, a readily available manageme nt option might not exist that will ensure compliance upon renewal of the permit. The permit writer should discuss with the permit applicants the various options that are available.

In cases where a management option is feasible, the permittee may not be able to comply with a newly applicable WQBEL immedi ately upon permit issuance, a Compliance Schedule allowing for the use of interim ef fluent limits may be allowed. A permit developed incorporating a compliance schedule w ill typically have a series of milestones and corresponding interim effluent limits, with the final effluent limit being implementedReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 60 of 117

as soon as practicable. Please refe r to the Department’s guidance, Compliance Schedules in NPDES Permits for more information.

In cases where a management option is not feasible in the remainder of the permit term, other Standards -based approaches are available. These options typically require a minimum of quantitative data to demonstrate th e origin and mobility of the pollutant in both the effluent and/or receiving waters. Typi cally, the permit writer will have required an initial look at collecting th is data as part of the Tier 2 monitoring. The management options include:

• Development of site specific water quality criteria: The Department may apply site specific water quality criteria in the Basin Descriptions in OAR Division 340-41- 033(b)(6) to reflect naturally occurring conditions. Please refer to the Site Specific Background Pollutant Criterion IMD (future) for guidance in the calculation and use of a criterion or contact the Surface Water Management Section for technical assistance.

• Variance from water quality criter i a: A variance is a short-term exemption from meeting water quality standards which would otherwise be applicable to an individual discharger. It is granted for a specific pollutant(s) and does not otherwise modify the standards. It does not exempt the discharger from compliance with applicable technology-based limits (TBELs) or water quality-based limits for ot her pollutants. Underlying water quality standards remain in effect for all other purposes (e.g., impaired water listings, TMDL development, etc.). It is granted for a sp ecific period of time (length of time varies by state). The discharger must either meet the standard upon the expiration of this time period or must make a renewed demonstration of "un-attainability.” Often, a variance is used as a bridging mechanism to a TMDL, providing the permittee and permitting authority the time to better characterize the watershed, identify po llutant sources, and ultimately develop achievable waste load allocations.

• Use Attainability Analysis : The Department may remove a designated beneficial use if it can demonstrate that attaining the use is not feasible due to one of several conditions. The process by which a use is removed is a Use Attainability Analysis (UAA). This option would most typically be used where there is a naturally occurring pollutant or a legacy pollutant present in the intake and receiving waters preventing the attainment of use. Please refer to the following link for additional information.

• (Future Implementation Tools go here) 

## 7.4 Selected Management Option

Once the permit applicant and the permit write r have agreed upon either a pathway to compliance by the end of the (current) perm it term, compliance sche dule or standardsbased management option, the details shoul d then be documented (immediately) in correspondence to the permit app licant with copies to the f ile, and ultimately in the permit terms and conditions of the renewed pe rmit. The permit applicant will have the remainder of the permit term (and perhaps longer depending upon the option selected) to begin implementation the terms of the selected option and ensure that they are able to meet the requirements of the new permit without delay.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 61 of 117 

## 7.5 Next Step

A management option should have been sel ected and implementation begun within six months of the notifica tion of results. To complete the permit renewal, the permit writer would only need to evaluate any additional characterization data mandated by the selected management option and make any ne cessary adjustments to the final effluent limits before issuing the final permit

.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 62 of 117



### This Page Intentionally BlankReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 63 of 117 

# Section 8: Finalization of RPA and Effluent Limits and Documentation of Decision Rational

8.1 Overview

Near the end of the permit term ( Step 8 ), the permit writer will finalize the RPA using any additional characterization data collect ed since the initial RPA, and adjust the effluent limits accordingly. They will then document the decision making processes, calculations and any approved management op tions employed. The results of the RPA and effluent limit calculation process are then included in the permit (either new or renewed).



## 8.2 Final RPA and Effluent Limit Evaluation

The permit writer will use the completed RPA Workbook from Steps 5 & 6 at the end of year 3 and update the information entered to reflect any additional characterization data 62

. This might result in a change to the previously calculated effl uent limits. In this case, the permit writer should revaluate the calculated WQB ELs relative to TBELs (if applicable). If there is an effluent limit in the existing permit, then Anti-Backsliding requirements normally prevent any changes that would result in a less-conservative limit. Pursuant to the conditions in 40 CFR 122.44 (k)(2)(i) , a less stringent limit ma y be allowed. Please contact the Surface Water Management Section for technical assistance on this topic.



## 8.3 Documentation

The RPA Workbook has been designed to record all the decisions and calculations made in the course of the analysis from identifying monitoring requirements though effluent limit calculation. The permit wr iter should include the final RPA Workbook pages in the PER. Additionally, the permit writer should include additional supportive documentation based upon one of the three possible outcome s of RPA in the WQBEL section of the evaluation report: Finally, the RPA Wor kbook pages from the identification of POC ( Step 3 ), the initial RPA ( Step 5 ) and initial effluent calculation ( Step 6 ) should be included in the administrative record. The three outcomes are:

• Outcome 1 : Monitoring is not required for toxic pollutants

62 For example, there might be more detailed inform ation regarding season variation in ambient pollutant concentration that might affect the out come. At least, an increase number of sample events will reduce the amount of uncertainty in t he calculation and result in a less conservative CV and Multiplier

.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 64 of 117

• Outcome 2 : Monitoring is required for some or all toxic pollutants, and there is

not a reasonable potential to exceed wate r quality criteria for the monitored pollutants

• Outcome 3 : Monitoring is required for some or all toxic pollutants, and there is a reasonable potential to exceed water quali ty criteria. Accordingly, effluent limitations are calculated to prevent th e exceedance of water quality criteria.
Each of these outcomes and required docum entation are discussed in detail in Sections 8.4 through 8.6 . Additionally, the department has developed a Fact Sheet Evaluation Matrix located on the QNET to assist the permit writer in the documentation of the permit development process and provide re ady-made permit evaluation report language. 

## 8.4 Outcome 1: Evaluation Report Components for “no monitoring required”

The following applicants will not have to an alyze their effluent for toxic pollutant parameters (excluding NH3 and Cl - ) as described in Section 2 of this document, and thus will have neither, effluent limits nor monitoring requirements in their permit:

• Domestic plants with an average dry w eather design flow (A DWDF) of less than 1 MGD , and do not meet any of the following criteria:

o those with a significant i ndustrial user that discharges into the treatment plant that may be a potential source of pollutants

o any other conditions that the individu al permit writer feels would warrant such level of effort

o those discharging to water body listed as Category 5 on the 303 d list

o those “known” to contain Table 2 or 3 pollutants in source water or effluent

• Non-Primary Industrial f acilities that have no “k nown” pollutants from Table II

, III

, IV and V, and with no identifiable concern for such pollutants.

The components outlined below need to be a ddressed in the PER to provide the basis of why monitoring for toxic po llutants was not required:

• Attached RPA spreadsheet with the “M onitoring Required” Column completed

• Verification of ADWDF less than 1 MGD for domestics

• Verification of the finding of “no effluent limit monitoring required” as described in process set forth in Section 2

• Identification of any State Water Quality Criteria pollutants that are water quality limited for the receiving water body and if a TMDL has been completed for the pollutant

• Description of any potential source of St ate Water Quality Criteria pollutants in the influent load to the facility, including the results from an industrial waste survey if the facility has performed one

• Verification of the type of treatment technology, and whether the permit writer would expect a greater pass through of toxic pollutantsReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 65 of 117

• Any miscellaneous factors that may warrant a detailed evaluati on of potential risk of source to receiving wa ter for toxic pollutants. 

## 8.5 Outcome 2: Evaluation Report Components Where “reasonable potential” is Not Determined

The components outlined below need to be addressed in the evaluation report: 1. The completed RPA spreadsheet with all columns completed 2. Identification of any State Water Quality Criteria pollutants that are water quality limited for the receiving water body and if a TMDL has been completed for the pollutant 3. In addition to the summary statistics pr esented in the spreadsheets, the permit writer might opt to discuss standard devi ation and presence of “non-detects” in effluent and ambient sampli ng in the narrative summary 4. Rationale or source of informati on for dilution ratios and background concentrations 5. Rationale or source of information used in an intake credit analysis or in calculating a site-specific b ackground pollutant analysis 

## 8.6 Outcome 3: Evaluation Report Components Where “reasonable potential” is Determined, and “effluent limits” are Calculated

The components outlined below need to be addressed in the evaluation report: 1. The completed RPA and Effluent Limit Ca lculation spreadsheets with all columns completed 2. Items 2, 3, 4 and 5 from Outcome 2 ( Section 7.3 ), above 3. Rationale for the “probability basis” and the “confidence level” used in the effluent limit calculation. 4. Comparison of the calculated water quali ty-based effluent to the TMDL/WLAdriven limit, Best Available Technol ogy limit, and existing permit limit, if applicable for specific scenario 5. If applicable, discussion of the use of an intake credit in determining compliance with a WQBELReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 66 of 117



### This Page Intentionally BlankReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 67 of 117 

# Appendix A: Revision History

Revision Date Changes Editor

1.0 09/2005 Initial Publication MF 2.0 12/2006 Updated revision MF & JN

3.0 8/2011 Extensive revisions to reflect changes in environmental regulation, new Departmental policies regarding timing of the permit process, inclusion of new

RPA and WQBEL spreadsheets and revision of Quantitation Limit values. SRB

3.1 2/13/2012 Addition of Intake Credit guidance in App. F, removal of App. C Quantitation Limits to a stand-alone IMD, discussion of recently adopted water

quality criteria and implementation options, and numerous minor corrections and clarifications SRBReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 68 of 117



### This Page Left Intentionally BlankReasonable Potential Analysis IMD Oregon Department of Environmental QualityDEQ 11-WQ-020-IMD1/13/2012Version 3.1Page 69 of 120Reasonable Potential Analysis IMD Oregon Department of Environmental QualityDEQ 11-WQ-020-IMD1/13/2012Version 3.1Page 70 of 120This Page Intentionally BlankReasonable Potential Analysis IMD Oregon Department of Environmental QualityDEQ 11-WQ-020-IMD1/13/2012Version 3.1Page 71 of 120Note: Human Health Criterialisted here are incorrect. Pleaserefer to most current guidanceAppendix C: Analytic Methods, Limits, and ImplementationGuidanceGuidance has been moved to own IMD entitled AnalyticalMethods and Limits for NPDES Permit Development IMDReasonable Potential Analysis IMD Oregon Department of Environmental QualityDEQ 11-WQ-020-IMD1/13/2012Version 3.1Page 72 of 120Note: Human Health Criterialisted here are incorrect. Pleaserefer to most current guidanceThis Page Intentionally BlankReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 73 of 117

# Appendix D: RPA Workbook Walkthough and Example

The following is a walkthrough on how to conduct a Reasonable Potential Analysis (RPA) for toxics using the Department’s RPA workbook. Please note that the Steps de scribed here-in are slightly different than the steps discussed in the body of the IMD. Each workbook (Domestic and Industrial) is comprised of the following spreadsheets:

• Monitoring Required : Contains all pollutant parameters that the facility might potentially be subject to and is used to record the facility’s monitoring requirements for the RPA

process

• Aquatic Toxicity RPA : Used to identify Pollutants of Concern, model in-stream impacts and determine Reasonable Potential

• Aquatic Toxicity Limits : Takes information from Aquatic Toxicity RPA spreadsheet along with ambient characterization data to calculate a WQBEL

• Human Health RPA : Used to identify Pollutants of Concern, model in-stream impacts and determine Reasonable Potential

• Human Health Limits : Takes information from Human Health RPA spreadsheet along with ambient characterization data to calculate a WQBEL

• Misc. Pollutant Parameters : Spreadsheets used for the RPA and limit calculations for pH, Ammonia, and Chlorine, that are not coved in the RPA IMD.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 74 of 117

The spreadsheets are linked in order to forwar d information and calculation results between them. The case study is of a hypothetical Domes tic waste water treatment plant (WWTP) that discharges to a freshwater body within the Willa mette River Basin listed as water quality limited for 4’4’ DDT, Aldrin and Dieldrin. The primar y municipal water supply is the same water body approximately 3 miles upstream from the outfall. The average dry weather discharge flow rate is 10.1 MGD. Additionally, PCBs and copper have been identified in the receiving water body, and are presumed to be drawn into the munici pal water supply. Of the two, only PCB’s have been recorded at concentrations near or greater than water qualit y criteria. The WWTP currently has an effluent limit for Inorganic Arsenic. A mixing zone analysis has been completed by the facility and the results are included with the permit application.

Step 1: Determining which pollutant para meters require monitoring and analysis
As part of the preceding permit renewal or new permit application process, the permit writer would begin by using the guidance in Section 2 and the flowchart ( Figure 2-3 ) illustrating the domestic monitoring requirements determination proce ss to identify the facili ty’s Tier 1 effluent monitoring requirements. The following pollutant groups or specifically indicated pollutant parameters should be included:

• Inorganic Arsenic due to current effluent limits. Comp liance monitoring data may be submitted in-lieu of characterization data.

• PCB’s due to knowledge that the pollutant is presen t in the significant concentrations in the primary municipal water supply (ie. intake from Willamette River). Since they are in the source water, they are most likely also present in the e ffluent. The permit writer would need to evaluate the potential for the concentration of the intake pollutants (ie. copper) to determine if it might reach a threshold of significance (near or greater than the water quality criteria).

• 4’4’ DDT, Aldrin and Dieldrin due to the knowledge that the pollutant is present in the significant concentrations in the primary municipal water supply. Even if facility had a separate water supply, these pollutant parameters would still be flagged for monitoring due to the design flow (>1.0 MGD) and the listing stat us of the receiving waterbody.

• Table 1 Effluent parameters for all POTWs w/flow > 0.1 MGD

• Table 2 Effluent Parameters for Selected POTWs including metals

, volatile organic compounds

, acid-extractable compounds and base-neutral compounds pollutant groups. This would include copper

.

• Table 3 Departmental Pesticides and PCB Monitoring Requirements: Under this provision, only Aldrin, 4’4’ DDT and Dieldrin would require monitoring because of the listing status of the receiving water body.

• Methyl Mercury due to Willamette Basin Requirements.

The permit writer would record all iden tified monitoring requirements on the Monitoring Required spreadsheet by toggling a “ yes ” or “ no ” in the “ Monitoring Required? ” column. The number of samples required s hould be recorded in the “ # of Samples ” column. Portions of the completed spreadsheet may be cut and pasted into the Schedule B of the permit language (monitoring requirements). A screenshot of th e completed Monitoring Required Spreadsheet is presented below:Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 75 of 117

Upon issuance, an electronic vers ion of the spreadsheet that includes an Analytic Summary Report template will be provided to the permittee. The permittee will use the template to report the results of their Tier 1 monitoring in both elect ronic and physical copies . This will allow the permit writer to efficiently review and import an alytic data into the RPA Workbook. A screen shot of the monitoring spreadsheet and report template is presented below: # of Samples Column

Monitoring Required?

ColumnReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 76 of 117

Step 2: General Facility Information
The next step is to fill in the RPA Run and General Facility Information sections of the Aquatic Toxicity RPA spreadsheets. This includes facility id entification, effluent characterization, dilution rates (from RMZ analysis), whether th e water body is fresh and the hardness of the effluent and receiving water body. If a mixing zone analysis wher e not available, there is a provision to enter facility and stream flow information instea d. The spreadsheet will cross reference the “Monitoring Requi red?” information from the Monitoring Required spreadsheet. The section also has default confidence and probab ility basis for the calcul ations. Many of these elements are presented in the illustration below: Analytic Summary Report: Tier 1 ResultsReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 77 of 117

The permit writer would conclude the step by repea ting the process for the human health criteria using the Human Health spreadsheet. It should be noted that the Aquatic Toxicity and Human Health spreadsheets will only have the pollutant parameters listed for which there are state water quality criteria, and can look very different. Additionally, the spreadsh eets might potentially have differing mixing z one dilution numbers. Information forwarded from the Monitoring Required spreadsheet Alternative dilution calculation

RP at End of Pipe?Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 78 of 117

Step 3: Identifying the Pollutants of Concern in the Effluent

By the second year (Month 24) of a permit term, the Tier 1 Monitoring data should have been collected and is ready for analysis. For all po llutant parameters that require monitoring and analysis as denoted by a “ Yes ” in the “ Evaluation Required ” column, the permit writer will enter the number of samples and the coefficient of vari ation into the appropriate columns. For the Aquatic Toxicity Spreadsheet , the highest concentration (of efflue nt) will be entered, but for the human health spreadsheet the geometric mean or maximum concentration will be entered depending upon the carcinogen status i ndicated in the “Carcinogen” Column.
Once entered, the spreadsheet calculates the maximu m effluent concentration at the end of pipe and then compares it to the water quality criteria. Pollutants that exceed the water quality criteria are Pollutants of Concern (POC) and are subject to further characterization and RPA analysis. For each POC, a “ Yes ” will be indicated in the “ RP at end of pipe? ” column. In the example below, cadmium, lead and silver have been identified as a POCs. It should be noted that if there are errors in the calcua tion process (as with mercury ) neither a “yes” or “No” will appear in the column. In this case, a CV value was not ente red resulting in the calculation not occuring. Please refer to the screen shot below wh ere the applicable area is magnified.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 79 of 117

Step 4: Sampling Plan

The permit writer would use their knowledge of the facility, receiving water body, potential for the use of an intake credit or site specific bac kground pollutant criteri on, and the type of environmental issues suggested by the Tier 1 monitoring to develop the Tier 2 monitoring requirements (ambient data, additional effleunt data, source investigation, etc.). The permit writer would then send the permit applicant a Monitoring Action Lett er describing the identified POCs and Tier 2 monitoring requirements, with the direction to develop a Sampling Plan. Typically, the permit writer would advise th e permit applicant during the Sampling Plan development to ensure that the necessary data is gathered in the most time and cost efficent manner. The permit applicant would then submit the completed plan to the permit writer for review and approval. Once approved, the plan would be implemented over the course of the following year (Month 24 – 36).
The importance of a developing a robust data set th at more accuractly characterizes the pollutant concentration of the effluent is explified in the sc reen shot below. Here the permit writer has reevaluated the previosly identified POCs using a more robust data set. The most notable result of this can be seen with lead where previously an exceedance at th e end of pipe was indidcates, but using 10 data points as opposed to 4, no exceedance was projected.

RP at End of Pipe?Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 80 of 117

Step 5: Determining In-stream Concen tration After Mixing / Determining RP

Further analysis will be requi red for only those POCs identifie d as exceeding water quality criteria at the end of pipe. Accordingly the Sampling Plan a nd Tier 2 monitoring was designed to collected ambient data for the POCs, and wher e necessary develop a mo re robust data set. Once the TIER 2 monitoring data has been re ceived, the permit writer should update the

“ Identify Pollutants of Concern ” section of the spreadsheet with the more robust data sets. As seen in the previous example, this resulted in a pollutant parameter ( lead) as being determined that there was not potential to exceed water qualit y criteria at the point of discharge, and no further analysis is required.

For the Aquatic Toxicity Spreadsheet , the permit writer will enter the maximum or 90 th percentile ambient concentration (depending on the number of data points) in to the column entitled “ Ambient Concentration ”. For the Human Health spreadsheet the geometric mean of the ambient data will be entered. The spreadsheet will then calculate the in-stream concentrations at the boundaries of the various mixing zones.
The spreadsheet then compares the projected in-stream concentrations to the water quality criteria. If the criteria are exceeded, then a “ Yes ” will appear in the appropriate portion of the “ Is there Reasonable Potential to Exceed? ” column. Please note how reasonable potential is determined for both acute and chronic conditions.
If the necessary data is available, the permit wr iter may conduct an intake credit analysis and determine if RP is still present.

Step 6: Calculation of Effluent Limits

For all pollutant parameters where reasonable potential is determined, the information will automatically be transferred to the Aquatic Toxicity or Human Health effluent limit calculation spreadsheets. The permit writer need only inse rt the anticipated amount of monthly monitoring for the pollutant parameter. This number is important since it affects the how conservative the final calculated effluent will be. Both the Monthly Average and Maximum Daily effluent limits will be calculated in the final, “ Effluent Limit” columns of the spreadsheets. RP at End of Pipe?Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 81 of 117

In some instances, the permit writer might consider varying the Confidence Intervals to affect the effluent limit calculation outcome. For any changes from the default settings in the spreadsheet, the permit writer should document the basis be hind the changes in the Permit Evaluation Report (PER).

The analysis indicated that there was reasonable potential for cadmium and silver resulting in water quality based effluent limits (WQBELs). Once the permit writer has completed the human health portion of the analysis, any resulting limits would be compar ed and the most conservative (for each pollutant parameter) selected. The se lected WQBELS would then be compared to any applicable TBELS, and the most conservative placed into the permit. Since this case study is of a domestic WWTP there would be no TBELS. If allowed, the permit writer might opt to use the intake concentration of the source water when determining compliance with the selected WQBEL. Copies of the RPA and limit calculation spreadsheets should be included in the PER.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 82 of 117

Step 7: Quantitation Li mits and Compliance Levels

An additional feature of the RPA Workbook is a field that compares cal culated effluent limits to the Department’s Quantitation Limits. In cases where an effluent limit is below the analytic range of available methods the Quantitation Limit becomes the default compliance level. In this example, for silver a compliance level of 1.00 ug/l would be used in-lieu of the calculated WQBEL of 0.10 ug/l.

This field can be seen on the electronic spreadsheet, although it is hidden on printed report. An example is presented in the screen shot below:Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 83 of 117 

# Appendix E: Whole Effluent Toxicity Guidance

The Department’s Whole Effluent Toxicity (WET) guidance was not updated as part of this RPA IMD revision. Permit writer should refer to the guidance and example permit language presented on the WET Section of the Permit Writer’s Corner located on the QNET.

For additional information or technical assistance, please contact the WET Coordinator located at the DEQ Laboratory (Lor i Pillsbury (503) 693-5735).

The following language has been taken (unchang ed) from the September, 2005 revision of the RPA IMD. Permit Writers may refer to this gui dance, although they sh ould their discretion and defer to the updated guidance from the Permit Wr iter’s Corner or from the WET Coordinator when appropriate.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 84 of 117



## 7.1 Background

What is “Whole Effluent Toxicity” testing? “Whole Effluent Toxicity” (WET) testing measures whether an effluent in its entirety (with its mixture of various ch emicals) causes toxicity in aquatic organisms. WET testing is usuall y conducted in controlled laboratory experiments in which aquatic organisms ar e exposed to samples of effluent at different dilutions.

Why is it required? WET testing addresses the OAR 340-041- 0033(1) requirement to prevent the discharge of toxic substa nces into Oregon’s waters above natural background levels in amounts that are toxic to aquatic life. Although DEQ has adopted numeric water quality criteria in Tables 20, 33A, and 33B for the protection of aquatic life for a number of chemicals that might be found in wastewater discharges, other chemicals do not ha ve criteria because information on toxicity is limited and the data require ments for deriving criteria are rigorous. In addition, the numeric water quality cr iteria are derived for individual chemicals, whereas some wastewater disc harges contain mixtures of chemicals that might have synergistic toxic e ffects even though the amount of any individual chemical in the mixture is below toxicity levels. WET testing results are used to address these inform ation gaps and ensure that discharges are not toxic.

Acute toxicity What is it? OAR 340-041-0053(2)(a)(A) define s acute toxicity as le thality to aquatic life as measured by a significant difference in lethal concentration between the control and 100 percent effluent in an acute bioassay test

What is the performance standard (rule requirement)? OAR 340-041-0053(2)(a)(A) prohibits ac utely toxic discharges; however, lethality in 100% effluent may be allowed if there is a mixing zone with immediate dilution of the effluent (“zone of immediate diluti on” or “ZID”).

How is compliance with the standard determined? In permits where a mixing zone is allowed (e.g. discharge to a river with a large flow) and a ZID exists, acute to xicity would be indicated when a statistically significant difference in surv ival between the tested dilutions and the control occurs at dilutions greater than that found at the edge of the ZID. If there is no ZID, acute toxicity would be indicated when a statistically significant difference in survival oc curs between 100% effluent and the control.

To comply with the rule definition of acu te toxicity, “hypothes is testing” must be conducted to evaluate acute toxicit y. This means that there should be no statistical difference between the WET te st results from the effluent sample and control groups at a significance level of α =0.05. Often, the laboratory conducting the bioassays will test a series of dilutions of effluent (e.g. 100%,Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 85 of 117

50%, 25%, 12% and 6% effluent) to de termine the No-Observable-EffectConcentration (NOEC) of the effluent in order to meet the requirement for no statistical difference between effluent (at some dilution) groups and control groups. For more information on evalua tion WET test results, see the EPA methods documents cited in the Test Methods section below.

Chronic toxicity What is it? OAR 340-041-0053(2)(b)(A) characterizes me asurement of chronic toxicity as the concentration that cause s long-term sublethal effects, such as significantly impaired growth or reproduction in aqua tic organisms, during a testing period based on the test species life cycle.

What is the performance standard (rule requirement)? OAR 340-041-0053(2)(b)(A) does not allow chronic toxicity outside of a mixing zone.

How is compliance with the standard determined? In permits with a mixing zone, chronic toxicity is assessed by examining the effect of effluent at various doses on organisms in bioassays, making sure that the doses of effluent tested bracket the concentration at the edge of the mixing zone. If no mixing zone exists, chronic to xicity would still be assessed using a series of effluent doses (including 100%); however , the point of compliance would be at end of pipe.

To determine statistical significance in chronic toxicity tes ting, the Department uses EPA’s Technical Support Document for Water Quality-based Toxics Control, March 1991 (TSD), which recommends that the concentration of effluent that results in 25% inhibition of the parameter used to determine a chronic effect (e.g. growth) be the be nchmark for determining whether the results of chronic tests indi cate toxicity. (This 25% i nhibition concentration is also referred to as the IC 25 .) For example, when testi ng a series of dilutions of effluent on the growth of fathead min nows, a dilution yielding 12% inhibition of growth will not be considered as a significant chronic effect, but 25% inhibition of growth w ould be significant.

The IC 25 is based on a point estimate tech nique, which assumes a continuous dose-response relationship (often repr esented by a sigmoid curve describing the relation between amount of inhibition or effect and the dose of compound or mixture).Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 86 of 117

Since the relationship is continuous, a choi ce must be made as to some level of effect that will be considered “safe” and statistically significant. According to EPA (TSD), “point estimation techniques are the preferred statistical methods in calculating endpoints for effl uent toxicity tests” for chronic toxicity. This is due to the inability to estimate test precision when using hypothesis testing for deriving a No Observed Effect Conc entration (NOEC), thus making the inherent variability of bioassay result s difficult to address statistically. EPA compared data from the point estimate and NOEC approaches and concluded that the “IC25 is approximately th e analogue of an NOEC derived using hypothesis testing.”

For more information on evaluation W ET test results, see the EPA methods documents cited in the Test Methods section below.

Test methods EPA has published methods for conducti ng and evaluating WET testing (the latest are listed below).

• “Methods for measuring the acute toxicity of effluents and receiving waters to freshwater and marine organisms” (Fifth Edition, October 2002) (EPA 821-R-02-012; http://www.epa.gov/OST/WET/ ).

• “Short-term methods for estimating th e chronic toxicity of effluents and receiving waters to freshwater organisms” (Fourth Edition, October 2002) (EPA 821-R-02-013).

• “Short-term methods for estimating th e chronic toxicity of effluents and receiving waters to marine and estuarine organisms” (Third Edition, October 2002) (EPA 821-R-02-014) and such methods should be used for meeting WET testing requirements.

• “Short-term methods for estimating th e chronic toxicity of effluents and receiving waters to west coas t marine and estuarine organisms” (August 1995) (EPA/600/R-95/136)

Use Table 6 below to determine whethe r to use a freshwater or saltwater method. Effluent ConcentrationPercent Inhibition

100% 100%

0% 0%Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 87 of 117

Table 6. Choosing Freshwater or Saltwater Method IF Receiving Stream is AND Intake or Influent is THEN Species for WET Test is

Freshwater 1 Freshwater Freshwater Saltwater Freshwater

Saltwater 2 Freshwater Freshwater for acute test Saltwater for chronic test Saltwater Saltwater
1 Freshwater is water in which the salinity is equal to or less than 1 part per

thousand 95% or more of the time.

2 Saltwater is water in which the salinity is equal to or gr eater than 10 parts

per thousand 95% or more of the time. Note: Water between 1 and 10 parts per thou sand salinity should be considered of mixed salinity and WET determined for both fresh and salt water.

Test species Acute toxicity testing re quires exposure of multipl e species (which at a minimum will include a fish and an inve rtebrate to effluent for 48 (for an invertebrate) or 96 hours (for a fish). Chronic toxicity testing also requires exposure of multiple species (which at a minimum will include a fish, an invertebrate, and a plant) to effluent for various durations depending on the experimental endpoint speci fied in the methods. Th e species appropriate for acute and chronic testing are listed in Table 7.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 88 of 117

Table 7. WET Test Species
FRESHWATER

IF appropriat e WET Test is AND Species Type required is THEN Species for WET test should include one of the following per Species Type

Acute invertebrate Ceriodaphnia dubia (daphnid) Daphnia pulex and D. magna (daphnids)

fish Pimephales promelas (fathead minnow) Oncorhynchus mykiss (rainbow trout)

Chronic invertebrate Ceriodaphnia dubia (daphnid) fish Pimephales promelas (fathead minnow)
plant Raphidocelis subcapitata (green alga also known as Selanastrum capricornutum )
ESTUARINE & MARINE

IF appropriat e WET Test is AND Species Type required is THEN Species for WET test should include one of the following per Species Type

Acute invertebrate Mysidopsis bahia (mysid shrimp) Holmesimysis costata (mysid shrimp), specific to Pacific Coast

waters

fish Cyprinodon varieganus (sheepshead minnow) Menida beryllina (inland silverside) M. menidia (Atlantic silverside) M peninsulae (tidewater silverside)

Chronic invertebrate Mysidopsis bahia (mysid shrimp) Arbacia punctulata (sea urchin) Haliotis rufescens (red abalone), specific to Pacific Coast waters Crassostrea gigas (Pacific oyster), specific to Pacific Coast waters Mytilus spp . (mussel), specific to Pacific Coast waters Holmesimysis costata (mysid shrimp), specific to Pacific Coast

waters Strongylocentrotus purpuratus (sea urchin), specific to Pacific Coast waters Dendraster excentricus (sand dollar), specific to Pacific Coast

waters

fish Cyprinodon variegatus (sheepshead minnow) Menidia beryllina (inland silverside) Atherinops affinis (topsmelt), specific to Pacific Coast waters
plant Champia parvula (red macroalga) Macrocystis pyrifera (giant kelp), specific to Pacific Coast waters

Species used Several of the species listed in the ab ove table can be used for both acute andReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 89 of 117

for both acute and chronic toxicity testing chronic toxicity testing using what is called a “dual endpoint” laboratory test. Dual endpoint test are those in which th e protocols for chronic toxicity testing are carried out with additional informa tion collected on surv ival at 48 and 96 hours to check for acute toxicity. These tests are desirable because analytical costs are lower and the permit write r may allow the submission of dual endpoint test results in lieu of individual acute and chronic test results.

For freshwater, these include:

• Ceriodaphnia dubia (water flea), and

• Pimephales promelas (fathead minnow). In this example, the acute test endpoi nts would be survival at 48 hours for water flea and at 96 hours for fath ead minnow and the chronic endpoints would be survival and reproduction after 8 days for water flea and body weight after 7 days for fathead minnow.

When both intake and receiving stream are saltwater, species with dual endpoints include:

• Cyprinodon variegatus (sheepshead minnow)

• Menida beryllina (inland silverside)

• Holmesimysis costata (mysid shrimp)

• Mysidopsis bahia (mysid shrimp)



## 7.2 WET Review in the Permitting Process

Where WET review fits in the permit
process Once an application for a discharge perm it has been subjected to reasonable potential analysis for th e pollutants listed in Tables 20, 33A, and 33B of OAR 340-041 (see previous chapters), then the analysis turns to determining whether there is reasonable potential for th e discharge to cause toxicity due to chemicals or combinations in the effluent that have not been addressed in the tables listed above.

What does the permit writer need to do? The permit writer must: 1. Conduct a WET review as part of the application review process. 2. If necessary, include appropriate WET requirements in Schedule D Special Conditions of the NPDES permit. 3. Document decision making process.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 90 of 117

Overview of WET review
process The WET review process cons ists of two major steps: 1. Determining if the discharge has a risk of causing aquatic toxicity. (Figure 5) 2. If there is a risk, determining if WE T testing is required in the permit. (Figure 6)

Figures 5 and 6 provide summaries of these processes in flow charts, expressing each process as a series of yes and no questions and findings. In some instances, information for answeri ng the questions can be taken directly from the application materials; in ot hers, answers result from analyzing information from other sources (e.g. federal regulations specifying which chemicals are considered toxic to aquatic life). A more complete explanation of the steps within each flowchart is given in Section 7.3 for Figure 5 and Section 7.4 for Figure 6.

Compliance with WET requirements If WET requirements are included in the permit in Schedule D, compliance with these requirements must be evalua ted. Section 7.6 and Figure 7 describe the necessary steps staff must take to pe rform this evaluation. At this time, the Department recommends this Special C onditions approach rather than numeric limits; however, if WET requirements ar e included in the permit as numeric limits, then the permit writer should consult the TSD for possible approaches.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 91 of 117



## 7.3 Step A: Determining if there is a risk of aquatic toxicity

Is there a risk of aquatic toxicity (Figure 5)? A risk of aquatic toxicity in the discharg e exists if the faci lity meets at least one of the following conditions (see Fi gure 5 for the decision flow chart): 1. The facility uses, stores, produces as a product or wast e, or transfers any hazardous substance listed in 40 CFR §302.4 with a statutory code of 1 or 2 [referring to Sections 311 (b)(4) or 307(a) of the Clean Water Act] unless permittee demonstrates to DEQ’s satisfaction that there is no possibility of these items being discharged. Appendix F contains a list of these substances based on the July 2005 electronic code of federal regulations ( http://ecfr.pgoaccess.gov , select “Title 40 – Protection of Environment” and then navigate to 40 CFR 302.4). (Figure 5, Step 1) 2. The facility’s discharge contains an y toxic pollutant li sted in Appendix D of 40 CFR Part 122 for which ther e are no water quality criteria for aquatic life protection listed in 40 CFR 131.36(b)(1). Appendix G contains a list of these substances. (Figure 5, Step 2) 3. The facility belongs to an industr y category identified in 40 CFR Part 122, Appendix A (NPDES Primary Indus try categories), listed in the Table 8. (Figure 5, Step 3) 4. The facility is a municipal sewage collection and treatment system with a flow equal to or greater than 1 million gallons per day (MGD). (Figure 5, Step 4) 5. The facility is a municipal sewage collection and treatment system that receives a discharge from any indus try category identified in 40 CFR Part 403, Appendix C (currently not specified). (Figure 5, Step 5) 6. The facility exceeded the acute or chronic whole effluent toxicity performance standard within the last five years (unless that facility already has whole effluent toxicity li mits or the Department has made a finding that such limits should be re moved because of attainment of WET performance standard). (Figure 5, Step 6) 7. The facility’s discharge is suspected to be toxic because of apparent damage to aquatic life in the recei ving water. (Figure 5, Step 7) 8. The Department determines that the facility has potential to discharge toxics (including those chemicals listed in Table 33C Water Quality Guidance Values in OAR 340-041) in toxic amounts. (Figure 5, Step 8)

What’s next? If the discharge from the facility does not meet any of the above conditions, then there is no risk of aquatic toxici ty and there are no WET requirements for the permit. If it does, the permit writ er must determine if WET requirements are needed in the permit (s ee Section 7.3 and Figure 6).Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 92 of 117

2. Discharge any toxic pollutant listed in 40 CFR Part 122 Appendix D that do not have aquatic life criteria?

Yes

N o N o

N o

N o N o

N o Yes

Yes

Yes

Yes

Yes

Yes N o N o 1. Use, store, produce as a product or waste, or transfer any hazardous substance listed in 40 CFR 302.4 with a statutory code of 1 or 2 (See App. F)? Does the facility...

3. Belong to an industry category listed in 40 CFR Part 122 Appendix A (See Table 8)?

5. Constitute a municipal sewage collection & treatment system which receives a discharg e from any industry listed in 40 CFR Part 403 Appendix C?

6. Have at least one instance of exceeding the acute or chronic WET test performance standard in the last 5 years?

8. Have the potential to discharge toxics in toxic amounts? 7. Have suspected toxicity because of apparent damage to aquatic biota?

9. Proceed to worksheet for determining WET compliance requirements (Figure 6) 4. Constitute a domestic sewage collection & treatment system with a flow ≥ 1 MGD? Yes

10. Off-Ramp: No WET testing requirement in permit Fi g ure 5. WET Testin g : Is there a Risk of A q uatic Toxicit y
.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 93 of 117

Table 8. NPDES Primary Industry Ca tegories from 40 CFR 122 Appendix A
Adhesives & sealants Inorgani c chemicals mfg. Photographic equipment/supplies Aluminum forming Iron & stee l mfg. Plastics processing

Auto & other laundries Leat her tanning & finishing Pl astic/synthetic materials mfg. Battery mfg. Mechanical produc ts mfg. Porcelain enameling Coal mining Nonferrous metals mfg. Printing & publishing Coil coating Ore mining Pulp & paper mills Copper forming Organic chemi cals mfg. Rubber processing

Electrical/electronic
components Paint & ink formulation Soap & detergent mfg.

Electroplating Pesticides St eam electric power plants Explosives mfg. Petroleum refining Textile mills Foundries Pharmaceutical preparati ons Timber products processing

Gum & wood chemicals



## 7.4 Step B: Determining WET requirements

Are WET requirements needed (Figure 6)? If a risk of aquatic toxicity exists, then the permit writer must determine whether the permit should include WET re quirements. This process involves evaluating WET testing data (if available) to assess the reasonable potential for the effluent to cause toxicity and, therefor e, exceed the narrative toxics criteria.

The following steps, corresponding to Fi gure 6, detail key decision steps for the permit writer:

Step 1. Does the applicant have existi ng, adequate WET test results?

• At least 10 test results from qua rterly tests conducted within the past permit cycle or, for smaller sources (at the discretion of the permit writer), results from 4 tests performed in the past 41⁄2 years. Permit writer has th e option of requiring WET testing on only the most sensitive species (as established in previous tests) once 4 tests us ing all 3 species have been adequately performed.

• Testing must have been done on the EPA-approved species for both acute and chronic toxicity using EPA-approved methods.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 94 of 117

• Depending on the degree of dilution at the edge of the zone of immediate dilution (ZID) and mixing zone, results should be from testing that focused on brack eting the relevant dilution to increase the likelihood of iden tifying the lowest observed effect level (LOEL) and no obs erved effect level (NOEL).

If yes, go to Step 2. If no, require testing as deta iled in the next section, WET Testing Requirements

.
Step 2. Do the test results indicate that the discharge meets the WET performance standard? See Section 7.5, Evaluating WET data

.
If yes, require yearly WET test in permit and monitor for changes. If source has less than 10 test results, then permit writer should require additional WET tests to al low for 10 test results to be submitted for the next renewal application. If no, specify WET requirements in permit as detailed in the next section, WET Testing Requirements . If source has less than 10 test results, then permit writer should require additional WET tests to allow for 10 test results to be submitted for the next renewal application.

WET testing requirements See Table 9 to determine th e WET testing requirements.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 95 of 117

Table 9. WET Testing Requirements IF there are AND the results Then

No data NA 1) require semiannual (yearly for smaller sources) WET testing for duration of permit; 2) may reopen permit if discharge fails WET test performance standard in first two years of permit; and 3) Go to Figure 7

Partial data Meets performance standard No WET requirements; monitor for changes in process; require yearly WET tests in permit. Fails performance standard 1) 1) require semiannual (yearly for smaller sources) WET testing for duration of permit; 2) Specify WET compliance requirements in permit and compliance monitoring; and 3) Go to Figure 7.

Sufficient data Meets performance standard No WET requirements; monitor for changes in process; require yearly WET tests in permit. Fails performance standard 1) Specify WET compliance requirements in permit and compliance monitoring; and 2) Go to Figure 7.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 96 of 117

Additionaltesting: bioassessment studies Although following the EPA WET tes ting methodology using a fish, an invertebrate, and a plant significantly increases th e likelihood of detecting aquatic toxicity from the whole effluent if it exists, there remains a chance that such tests will fail to predict toxicity to local biota. Therefore, the use of bioassessment methods could add importa nt information for evaluation of an application and should be considered wh en appropriate. Surveys to identify and enumerate macroinvertebrates (the Department has adopted a modified version of Water Quality Monitoring Guide as the appropriate methodology; contact the Watershed Assessment secti on of the DEQ Laboratory Division for details) above and below a discharge out fall can be used in conjunction with laboratory WET tests to more fully charac terize the chance that an effluent poses a risk of aquatic toxicity.

At this time, the Department will not require such bioassessment studies for fulfilling the WET requirements for the purposes of issuing a permit. However, permit writers should consid er including bioassessment monitoring when a permittee fails to meet a performance standard during routine monitoring. Such bioassessment monito ring should be conducted in parallel with traditional laboratory WET testing so that results can be compared to give a more complete assessment of poten tial effects of th e discharge on the receiving water. In the case of conf licting results between the laboratory WET test and the bioassessment monitoring, the laboratory WET test results should carry precedence (until such time that the Department’s experience with bioassessment monitoring indicates a need to change this approach).Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 97 of 117

1. Does applicant have 10 WET test results prior to application or results from 4 tests performed in the last 4.5 years for smaller sources?

2. Has the discharge met the WET test performance standard? See Section 7.X, p. X. Require: 1) semiannual (yearly for smaller sources) WET testing for duration of permit;
2) reopening permit if discharge
fails WET test performance
standard in first two years of

Require yearly WET tests in permit (or additional tests to reach 10 tests for renewal) and monitor for changes. N o

Yes N o Yes

Specify WET requirements in permit.

Go to Figure 7. See Section 7.1 Background , for proper WET testing method and species selection. Fi g ure 6. WET Testin g : Determinin g Limits.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 98 of 117



## 7.5 Evaluating WET data and determining next steps

Evaluating WET data The permit writer must evaluate WET test results to determine if the performance standard is being met. Figure 7 provides an overview of the decision process for evaluating WET data and determining what actions the permittee must take in response to this evaluation.

Step 1. If the discharge is in compliance, then WET monitoring is continued according to the frequency and conditions specified in the permit. If the discharge is not in compliance then further evaluation is

necessary.

• Acute toxicity: If there is no statistical difference between the WET test results from the effluent sample dilution as allowed by a ZID (100% effluent sample if no ZID) and control groups at a significance level of α =0.05

• Chronic toxicity: If there is less than 25% inhibition of growth or other chronic effect (e.g., reproduction), there is no indication of chronic toxicity and th e discharge complies.

Evaluating WET test results is not an easy task. EPA provides several guidance documents on this issue (see Test Methods in Section 7.1), but the permit writer is not expected to be an expert on the subject.

What to do when WET tests indicate toxicity If WET testing indicates a problem w ith ongoing toxicity, the permit writer must determine if further monitoring is required or a toxicity identification/reduction evaluation pl an should be prepared. Which determination to make depends on whether the permittee acknowledges the toxicity of the effluent or believes th e WET testing results are inaccurate.

Permittee does not acknowledge toxicity of effluent Step 2. If the permittee does not acknowledg e that the effluent is toxic (e.g. claims that WET monitoring tests are erroneous), then permit writer should require:

a. Submission of results from three (3) monthly acute/chronic tests that repeat the monitoring tests that returned indications of toxicity, and b. Possibly at least one (1) bio- assessment test to be done simultaneously with one of th e acute/chronic tests.

These increased monitoring requirements should resolve any uncertainty regarding the initial results and prevent delay of the steps necessary to come into compliance.

Step 3a. Further testing indicates no impact: If the result of the increasedReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 99 of 117

WET monitoring reveals no further occurrence of toxicity and the bio-assessment indicates no adverse impact, then the permit writer requests and reviews the permittee’s transient toxicity report that documents the possible causes a nd prevention of the transient toxicity. See Transient toxicity report later in this section for information on what needs to be in this report.

Note: If the bio-assessment indicat es an adverse impact, then further bio-assessment monitoring should be required in support of the subsequent permit application. Af ter filing the acceptable transient toxicity report, the permittee c onducts further monitoring according to the frequency and conditions specified in the permit. For more information, see When WET test and bio-assessments differ , p. 51.

Further testing indicates impact: If the results of increased WET test monitoring indicate further occurrence of toxicity, then the process of developing a toxicity identifica tion/reduction evaluation plan is initiated regardless of the bio- assessment monitoring results.

Step 4. Evaluate if the reduc tion effort is successful.

• If the reduction effort is unsuccessful, then the permittee must continue to carry out the TI/RE pl an until the cause of the toxicity is clearly identified through the TI/RE, or toxicity is eliminated.

• If the reduction effort is successful, then the permittee conducts further monitoring according to the frequency and conditions specified in the permit.

Permittee acknowledges toxicity of effluent Step 2. If the permittee acknowledges that the effluent is toxic, then the permit writer requests a toxicity identification/reduction evaluation plan from the permittee for Department review and approval within 60 days of receipt of the final test results. See Toxicity Identification/Reduction Evaluation Plan , for more information on this plan requirement.

Step 3b. Evaluate results of the TI/RE pl an to determine whet her the source of the toxicity is apparent. 1. If “no,” then the permittee continues to carry out the TI/RE plan until the source of the toxicity is identified or toxicity is eliminated through other actions. 2. If “yes,” then the permit writer should allow the permittee 2 to 6 months to confirm the identity of and eliminate the source of toxicity. The Department may allow up to six months before the permittee initiates the investigation outlined in the EPA manuals for facility personnel to attempt to control the most likely sources of toxicity through efforts such as changes in plant operation,Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 100 of 117

replacement of a toxic material used in the facility, or improvement of best management practices.

Step 4. Evaluate if the reduc tion effort is successful.

• If the reduction effort is unsuccessful, then the permittee must continue to carry out the TI/RE pl an until the cause of the toxicity is clearly identified through the TI/RE, or toxicity is eliminated.

• If the reduction effort is successful, then the permittee conducts further monitoring according to the frequency and conditions specified in the permit.

When WET results andbioassessments differ If the results from the laboratory WET tests conflict with those of the bioassessment study, then the results of th e laboratory WET tests should be used to decide whether to file a transient toxicity report or develop a toxicity identification/reduction evaluation plan. In the case where results from laboratory WET tests are uncl ear (i.e. some low level t oxicity is suggested but is not definitive), then th e bio-assessment results can be used to decide on which path to proceed.

Interpretation of the possible outcom es of laboratory WET tests and bioassessment monitoring is shown in the following table:

If WET test results indicate: and bio-assement results indicate: Then require:

Toxicity Adverse impact Toxicity Identification/Reduction Evaluation Plan
No impact Toxicity Identification/Reduction Evaluation Plan

No Toxicity Adverse impact Transient toxicity report & additional bio-assessment monitoring
No impact Transien t toxicity report

Transient toxicity report The transient toxicity report must include: 1. The results of the initial failed WET test, 2. The results of the follow up WET te sts/bio-assessment studies, and 3. An explanation for the initial failed WET test, e.g. WET test result is an outlier due to high rainfall or ammonia value.

Toxicity Identification/ Reduction Evaluation This plan should follow the steps descri bed in the latest versions of EPA manuals (and references therein), such as (but not limited to):

• “Toxicity reduction eval uation guidance for municipal wastewater treatment plants” (EPA 833/B-99-002;Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 101 of 117

Plan http://www.epa.gov/npdes/pubs/tre.pdf )

• “Generalized methodology for conduc ting industrial toxicity reduction evaluations” (EPA 600/2-88-070)

• “Toxicity Identification Evaluations: Characteriz ation of Chronically Toxic Effluents, Phase I” (EPA 600/6-91-005F)

Removing WET requirement A specific requirement in the permit to comply with the WET performance standard may be removed upon permit renewal if: 1. The permittee has demonstrated compliance with the WET performance standard associated with that limit for at least the last 3 consecutive test years following e ffluent characterization or for an entire subsequent permit term, and 2. There have been no changes made to operations or effluent quality within the last three years that would otherwise require additional effluent characterization.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 102 of 117

3a. Does Toxicity

occur again?

Implement TI/RE

p lan 1. Does monitoring indicate compliance with WET standard?

2. Does permittee acknowledge

effluent is

toxic? Require increased WET

testing to 3 monthly

chronic/acute and possibly 1 bio-assessment Request TI/RE plan

for DEQ approval

3b. Is source of toxicity

a

pp arent?

Request transient toxicity report or TI/RE report for review

Continue monitoring specified in permit Yes N o Yes

N o Yes

Allow 2 to 6 months to

confirm & eliminate

source Continue monitoring specified in

permit

N o

Yes Yes

N o 4. Is reduction

effort successful? N o Fi g ure 7. WET Testin g : Com p liance and Enforcement.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 103 of 117 

# Appendix F: Intake Credits

Introduction

On June 16 th Oregon Environmental Quality Co mmission adopted into rule ( OAR 340-045- 0105 ) the use of Intake Credits for determining reasonable potential (RP) and establishing water quality based effluent limits (WQBELs). The intake credit provision allows a permit writer to quantify the amount of a pollutant ( intake pollutant 63 ) in a facility’s source water and deduct a corresponding amount from the f acility’s estimated discharge when evaluating reasonable potential or demonstrating complian ce with an effluent limit. The im pact of this provision is that a facility is only held accountable for their direct impacts to the source water and water quality. Previously, a facility would have been responsible for any pollu tants contained in the source water plus their direct impacts.
A permit writer might initially consider the use of an intake credit after reviewing Tier 1 monitoring results. If there are indications that a significant portion of an identified Pollutant of Concern (POC) can be attributed to the source wa ter, the permit writer should require the facility to include appropriate source investigation steps in their Sampling Plan and Tier 2 monitoring.
In implementing an intake credit, the permit wr iter will need to assemble adequate data to quantify both the pollutant concentration and volume of the s ource water withdrawn, demonstrate that the a series of conditions has b een met, and use the resultant findings in the RP and WQBEL calculations. Finally, the permit write r might need to make special considerations (i.e. on-going monitoring requireme nts, or treatment performance m easures) attributed to intake credits when finalizing the permit.

Reasonable Potential Threshold Conditions

The Intake Credit rules have a seri es of threshold conditions that must be met in order for the use of an intake credit to determin e RP. There are also a similar se t of conditions that must be met for the use of an intake credit to establish WQ BELs. The permittee must satisfy all the following five conditions to qualify for the “ reasonable potential ” use of the procedure:

1. The facility withdraws 100 percent of the intake water containing the pollutant from the same body of water into which the discharge is made ; An intake pollutant is considered to be from t he “same body of water” as the discharge if the intake pollutant would have reached the vicinity of the outfall point in the receiving water within a reasonable period had it not been removed by the permittee. This finding may be deemed established if:

• There is a direct hydrological connection between the intake and discharge points;

• The background concentration of the pollut ant in the receiving water (excluding any amount of the pollutant in the facility's discharge) is similar to that in the intake water; and

• Water quality characteristics (e.g., temperatur e, pH, hardness) are similar in the intake and receiving waters.
An intake pollutant from groundwater may also be considered to be from the “same body of water” if the aforementioned conditions are met and the pollutants are not a result of human

63 An “intake pollutant” is the am ount of a pollutant that is present in public waters (including groundwater) at the time it is withdrawn from such waters by the discharger or other facility supplying the discharger with intake water.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 104 of 117

activity such as industrial, commercial, or mu nicipal operations, disposal actions, or treatment
processes. 2. The facility does not contribute any additional mass of the identified intake pollutant to its wastewater Mass Conditions
Any facilities (or municipalities) introducing a meas urable mass of the po llutant into an effluent stream would not be allowed an intake credit for that pollutant when determining RP. 3. The facility does not alter the identified intake pollutant chemically or physically in a manner that would cause adverse water quality impacts to occur that would not occur if the pollutants were left in-stream;
Of particular concern are shifts in pollutant specia tion that might result in increased toxicity (e.g. Chrome III to Chrome VI) 4. The facility does not increase the identified intake pollutant concentration at the edge of the mixing zone, or at the point of discharge if a mixing zone is not allowed, as compared to the pollutant concentration in the intake water, unless the increased concentration does not cause or contribute to an excursion above an applicable water quality standard; and
In most cases the receiving water body will exceed the water quality criterion, although in rare instances a small amount of assimilative capacity might be available and a intake credit in conjunction with an intake credit would be allowed.
5. The timing and location of the discharge would not cause adverse water quality impacts to occur that would not occur if the identified intake pollutant were left in-stream.

WQBEL Threshold Conditions The Intake Credit rules have a seri es of threshold conditions that must be met in order for the use of an intake credit to establish WQBELs. A su mmary and brief explanati on of the conditions is presented below: (please note th at these conditions are numbered 6 - 10 so they can be uniquely referred to later in the discussion)

6. The facility withdraws 100 percent of the intake water containing the pollutant from the same body of water into which the discharge is made;
Please refer to the guidance described in Condition #1 7. The observed maximum ambient background concentration and the intake water concentration of the pollutant exceeds the most stringent applicable water quality criterion for that pollutant;

The intent of the condition is to limit the use of intake credit based WQBELs to bodies of water that are determined, or have the potential to be determined as “water quality limited”. 8. The facility does not alter the identified intake pollutant chemically or physically in a manner that would cause adverse water quality impacts to occur that would not occur if the pollutants were left in-stream;
Please refer to the guidance described in Condition #3 9. The facility does not increase the identified intake pollutant concentration, as defined by the department, at the point of discharge as compared to the pollutant concentration in the intake water; and
10. The timing and location of the discharge would not cause adverse water quality impacts to occur that would not occur if the identified intake pollutant were left in-stream.Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 105 of 117

Intake Credit Procedure
The following is a discussion of the steps the pe rmit writer should pursue to evaluate each of the threshold conditions. The permit writer should document this process and include an intake credit analysis summary in the Permit Evaluation Report.

Reasonable Potential Threshold Evaluation
Step 1 : The permit writer should collect available data with the intension of evaluating the RP and WQBEL threshold conditions. Typically, the data required to perform all of these evaluations (especially Condition #’s 3, 4 & 5 ) will not be readily available, and can be resolved later in the facility’s Sampling Plan described in Step 2 . This data will also be sufficient to evaluate the WQBEL Condition #’s 8

, 9 & 10

. To evaluate Condition #1 , the permit writer should establish the location of the source water intake points, relative to the location of the outfall. The following are likely sources of information that can be used for performing these evaluations:

• DEQ’s drinking water program for well locations and logs: http://www.deq.state.or.us/wq/dwp/contacts.htm

• DEQ’s LASAR and USGS’s Water Data for Oregon databases for ambient surface and ground water quality data

• Oregon’s municipal Drinking Water Data Online database for municipal intake concentrations, source type and well locations

• Facility permit renewal application data summary (facility file) and Discharge Monitoring Reports

• Municipal drinking water and waste water treatment plant flow and pollutant concentration records

The permit writer should develop a location map s howing the outfall and various intake locations for inclusion in the Permit Evaluation Report (see Figure 1 ). The permit writer should also develop a process diagram showing the identified intake water sources, process use, treatment and discharge (see Figure 2 ).
Only those sources “upstream” of the outfall locat ion would be permitted for consideration of an intake credit. With ground water sources (well or I&I), the permit writer need to establish the direct hydrologic connection with the receiving water body and how the pollutant would have reached the vicinity of the outfall within a reas onable period. The Drinking Water Data Online database identifies those municipal wells that ar e under direct influence of surface water or are located close enough to nearby surface water to r eceive direct surface water recharge (under Source Type). For example, the wells id entified in Figure 1 are listed as “ GU - Under direct influence of surface water ” in the database.
The condition does not require that a 100% of a facility’s source water come from the same body of water. Rather, the condition requires that 100 % of the intake pollutant credited be from the same body of water. For faciliti es with multiple intakes from different bodies of water, the intake concentration should be fl ow weighted (see below) to refl ect only those sources that meet the rule’s condition (i.e. be from the same body of water).Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 106 of 117

If Condition #1 cannot be met, the facility may not dete rmine RP or establish WQBELs using an intake credit. Figure 1 Example of an Intake Credit Evaluation Map

To evaluate Condition #2 , the permit writer should investigate th e facility to determine if there is the potential for additional contributions of a pollutant resulting in a measurable increase in mass. For industrial facilities, a review of the production process description, hazardous material data bases and handling records 64 may identify likely sources of pollutant contributions. For domestic facilities, the municipali ties pretreatment program (if pres ent) is the most ready source

64 For example, Toxic Release Inventory

, Oregon Hazardous Substance Information Survey forms, Material Safety Data Sheets and Hazardous Waste (RCRA) Records. Intake Concentration Flow Weight ed Concentration Calculation

I

total = [(I 1 *Q 1 )+(I 2 *Q 2 )+(...)+(I n *Q n )]/Q total

I

total = Total allowable Intake concentration

I

i = pollutant concentrati on from intake source i
Q i = Flow rate from intake source i

Outfall Locatio n

Intake LocationsReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 107 of 117

of information, although it might be necessary to review likely source s with-in the collection area followed up by further investig ation. In any case (domestic or industrial) where pollutant contribution is suspected, the permit writer should request point source monitoring to confirm presence and quantify the discharge 65

. If Condition #2 cannot be met, the facility may not dete rmine RP using an intake credit, although there is still the potential of establishing WQBELs . Typically, the data necessary to evaluate Conditions #3, #4 and #5 is not readily available, and mu st be collected as part of the Sampling Plan

. Step 2 : To evaluate Condition #3 and #4, the permit writer will need further characterization of the identified intake waters and discharged effluent relative to each other during the same discharge period. Unless the facility already has the necessary data, a series of parallel monitoring events and appropriate laboratory analysis must be included in the facility’s Sampling Plan

. The Sampling Plan should quantify the mass and concentra tion of the subject pollutant in the intake waters and effluent thr ough a series of parallel monitori ng events. Ideally, flow rates should be recorded at all sample locations and, if required, the average hy drologic residence time (HRT) between intake and discharge should be es timated. A subset of the collected samples should be split and analyzed to determin e if there are any physical or chemical 66 changes that would result in additional adverse water qual ity impacts. Where an engineering study or variance request might later be necessary, the fa cility might consider monitoring the ambient source water (pre-filtration) or treatment facility influent as to better characterize the process and determine treatment efficiencies (see Figure 2 ).

65 Even if this action disqualifies the ability to conduct a RP , a WQBEL is still available and the data will assist the facility’s source reduction efforts.
66 i.e. change in speciation or pH that results in greater toxicityReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 108 of 117
Figure 2 Example of a Simple Process Diagram for a Domestic Facility w/Sample Locations

An example of the various elements described in the Sampling Plan is presented below:Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 109 of 117

Using the collected data, the permit writ er will evaluate the facility for Conditions #3 and #4

. When evaluating Condition #3 , the permit writer should be aw are of potential changes in pollutant speciation or water chemistry that might result in an increased pollutant toxicity, mobility or bio-availability. The permit writer should also consider potential changes in temperature, flow regime, dissolved oxygen, nutrient c ontent, etc. that might result in an adverse water quality impact. Please consult with staf f in the Department’s Laboratory Division or TMDL Sections when determining monitoring requirements or evaluating resultant data.

In order to evaluate Condition #4 , the permit writer e ssentially needs to conduct the RPA to determine if there is an “ increase the identified intake pollutant concentration at the edge of the mixing zone 67 , or at the point of discharge if a mixing zone is not allowed, as compared to the pollutant concentration in the intake water.” The RPA Workbook has been modified to perform an intake credit analysis and will indi cate if an intake credit is not allowed as described in Step 3 in the next Section.

To evaluate Condition #5 , the permit writer should consider the timing and location impacts of the discharge upon the receiving waterbody. Of part icular concern, would be those waterbodies that are effluent dominated, have a very low base flows or are subject to channelization. Where it can be demonstrated that the receiving water body would be adversely impacted, a intake credit would not be permitted in determining RP.

67 In rare cases where a receiving water body’s ambient concentration is just below the water quality criteria, a mixing zone might be permitted. Example of Sampling Plan Elemen ts for Inorganic Arsenic in a

POTW Required Elements

• 7 consecutive 24-hour composite samples for:

o Intake location (treated drinking water)

o Effluent (may stagger sampling ti me from Intake by 2 days to account for system residence time)

• Continuous flow monitoring for th e intake and effluent location during the monitoring period

• Analyze all samples for Inorganic Arsenic

• Split 2 of the aforementioned sa mpling events (both intake and effluent) and analyze for Total Arseni c, Inorganic Arsenic, Arsenic III, Arsenic V, pH, tem perature, DO and hardness.
Optional Elements

• 7 consecutive 24-hour composite samples for:

o Ambient location (Raw water intake)

o Influent (may stagger sampling time from Intake by 2 days to account for system residence time)

• Analyze all samples for Inorganic Arsenic

• Continuous flow monitoring for the influent location during the monitoring periodReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 110 of 117

If it can be demonstrated conclusively that c onditions #s 1, 3, 4, & 5, cannot be met, an intake credit (for both RP and WQB EL purposes) would not be allowe d and no further action should be taken. If condition #2 ( no addition of pollutant mass ) cannot be met, the facility is disqualified from using an intake credit in determining RP, but is still allowed to use an intake credit in establishing WQBELs. Conducting a Reasonable Potential Analysis using an Intake Credit
Step 3 : To apply an intake credit , it is necessary of conduct an intake credit analysis by calculating a series of adjusted effluent and ambient pollutant c oncentrations using an intake concentration (IC) value. This The RPA Workb ook has been modified (see below) to perform this analysis, although th e permit writer will stil l need to calculate an appropriate IC value depending upon the type of RPA (aquatic toxicity vs. human health) and the carcinogen status of the pollutant of concern.

For an Aquatic Toxicity RPA, the IC is ca lculated using the following instructions:

For a human health RPA, the IC is calcul ated using the following instructions: Intake Concentration calculation in structions for Aquatic Toxicity

RPA 1. Calculate the Ratio of average in take concentration (I) to average effluent concentration (E) Intake Ratio = [(I 1 +I 2 +...+I n )/n] / [(E 1 +E 2 +...+E n )/n] *where necessary, use flow wei ghted individual intake values 2. Multiply the maximum effluent c oncentration by intake ratio to determine intake concentration (IC) used in RPA
IC = E max x Intake Ratio Intake Credit Analysis

Enter appropriate Intake Concentration ResultsReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 111 of 117

Once the appropriate IC values have been calculated and entered, the RPA Workbook checks to ensure that the IC is greater than or equal to the effluent concentration. If th ere is an increase in concentration, an “X” will be reported and the calculation ends per Condition #4 in Step 2 . In this case, the determination of RP for the pollutant of concern stands and a WQBEL would be necessary.

If there is not an increase in effluent concentration over intake, then a check mark (“ √ ”) is reported and the intake credit calculations progresses and a final RP determination is reported in the “ Is there Reasonable Potential to Exceed? ” columns (see screen shot right) . If a “No” is reported, there is not RP and no WQBEL is necessary. If a “Yes” is reported, there is still RP and a WQBEL is necessary in Step 4

. Establishing Water Quality Efflue nt Limits Threshold Evaluation
Step 4 : If a permittee is found to have RP, th e permit writer should evaluate the WQBEL Threshold Conditions, and if met, calculate WQBELs in Step 5 . Since most of these threshold conditions ( #6, #8 and #10 ) are the same as the RP Threshold conditions ( #1, #3 and #5 ), they are already met. To evaluate Condition #7 the permit writer would review “t he observed maximum ambient background concentration and the intake water concentration of the pollutant” and where these values “ exceed(s) the most stringent applicable water quality criterion for that pollutant” , allow the development of a WQBEL for that parameter. This condition is to limit the establishm ent of WBELs using intake cred its to those water bodies with ambient concentrations at or a bove water quality criteria. It s hould be noted that there are no limitations on the addition of additional mass of a pollutant to the effluent as described in Condition #2 68

. Condition #9 will be met by the establishment of WQBELs that prevents the facility from increasing “the identified intake pollutant concentration, as defined by the

68 Any additional mass must be removed prior to discharge as determined by Condition #9

. Intake Concentration calculation inst ructions for Human Health RPA

• For Carcinogens, use the geometric mean of intake data

• For Non-Carcinogens, follow instructions for Aquatic Toxicity RPA
*where necessary, use flow weighted intake values

Intake ConfirmationReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 112 of 117

department, at the point of discharge as compared to the pollutant concentration in the intake water”

. Calculating Aquatic Toxicity Effl uent Limits using an Intake Credit
Step 5 : If the facility has me the applicable WQBEL Threshold Conditions, a WQBEL may be established using an intake cr edit. The following language may be used in the permit:
If the (compliance) effluent monitoring result s indicate that the effluent concentration of the pollutant is equal to or le ss than the intake c oncentration, then the calculated effluent limits are not applicable, and therefore, the disc harge is in compliance. Otherwise, the effluent must comply with th e calculated effluent limitations.
This will require that the facility monitor both the intake source and effluent in tandem, and make a rolling comparison to ensure the terms of the language is being met. The alternative effluent limit is calculated on the Effluent Li mit page of the RPA Workbook. Upon entering the number of monthly compliance samples, the Effl uent Limits page will automatically calculate the applicable effluent limits as seen below:

Various Intake Credit Scenarios
The following figures have been prepared to dem onstrate a very simplistic intake credit scenario. Scenario 1 is a simplified example where a Facil ity is using surface water that ambient concentration is above water quality criteria. Based upon current rule, the evaluation only reflects the concentration at the point of discharge to address th e application of current rules. Scenario 2 and 3 demonstrate the use of intake credit pr ocedure using the same variables as in Scenario 1 for the RPA and WQBEL calculation processes, respectively. Enter # of Monthl y Sam p les Calculated Effluent LimitsReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 113 of 117Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 114 of 117

Rule Language
The following is the app licable rule language fr om OAR, Division 45-0105.
(1) General Provisions. The following provisions apply to the consideration of intake pollutants in determining reasonable potential under section (2) of this rule and the consideration of intake pollutants in establishing water quality based effluent limits under section (3) of this rule. These provisions do not alter the permitting authority's obligation under 40 CFR 122.44(d)(vii)(B) to develop effluent limitations consistent with the assumptions and requirements of any available waste load allocations for the discharge, that is part of a TMDL prepared by the department and approved by EPA pursuant to 40 CFR 130.7, or prepared by EPA pursuant to 40 CFR 130.7(d). (a) An “intake pollutant” is the amount of a pollutant that is present in public waters (including groundwater as provided in subsection (d), below, at the time it is withdrawn from such waters by the discharger or other facility supplying the discharger with intake
water. (b) An intake pollutant is considered to be from the “same body of water” as the discharge if the department finds that the intake pollutant would have reached the vicinity of the outfall point in the receiving water within a reasonable period had it not been removed by the permittee. This finding may be deemed established if: (A) The background concentration of the pollutant in the receiving water (excluding any amount of the pollutant in the facility's discharge) is similar to that in the intake water; (B) There is a direct hydrological connection between the intake and discharge points; andReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 115 of 117

(C) Water quality characteristics (e.g., temperature, pH, hardness) are similar in the intake and receiving waters. (c) The department may also consider other site-specific factors relevant to the transport and fate of the pollutant to make the finding in a particular case that a pollutant would or would not have reached the vicinity of the outfall point in the receiving water within a reasonable period had it not been removed by the permittee. (d) An intake pollutant from groundwater may be considered to be from the “same body of water” if the department determines that the pollutant would have reached the vicinity of the outfall point in the receiving water within a reasonable period had it not been removed by the permittee, except that such a pollutant is not from the same body of water if the groundwater contains the pollutant partially or entirely due to human activity, such as industrial, commercial, or municipal operations, disposal actions, or treatment
processes. (e) The determinations made under Sections (2) and (3), below, will be made on a pollutant-by-pollutant and outfall-by-outfall basis. (2) Consideration of Intake Pollutants in Determining Reasonable Potential: (a) The department may determine that there is “no reasonable potential” for the discharge of an identified intake pollutant to cause or contribute to an excursion above a narrative or numeric water quality criterion contained in Oregon’s water quality standards where a discharger demonstrates to the satisfaction of the department (based upon information provided in the permit application or other information) that: (A) The facility withdraws 100 percent of the intake water containing the pollutant from the same body of water into which the discharge is made; (B) The facility does not contribute any additional mass of the identified intake pollutant to its wastewater; (C) The facility does not alter the identified intake pollutant chemically or physically in a manner that would cause adverse water quality impacts to occur that would not occur if the pollutants were left in-stream; (D) The facility does not increase the identified intake pollutant concentration at the edge of the mixing zone, or at the point of discharge if a mixing zone is not allowed, as compared to the pollutant concentration in the intake water, unless the increased concentration does not cause or contribute to an excursion above an applicable water quality standard; and (E) The timing and location of the discharge would not cause adverse water quality impacts to occur that would not occur if the identified intake pollutant were left in-stream. (b) Upon a finding under subsection (a) of this section that an intake pollutant in the discharge does not cause, have the reasonable potential to cause, or contribute to an excursion above an applicable water quality standard, the department is not required to include a water quality-based effluent limit for the identified intake pollutant in the facility's permit, provided: (A) The NPDES permit evaluation report incl udes a determination that there is no reasonable potential for the discharge of an identified intake pollutant to cause or contribute to an excursion above an applicable numeric water quality criterion and references appropriate supporting documentation included in the administrative record;Reasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 116 of 117

(B) The permit requires all influent, effluent, and ambient monitoring necessary to demonstrate that the conditions above in subsection (a) of this section are maintained during the permit term; and (C) The permit contains a re-opener clause authorizing modification or revocation and re-issuance of the permit if new information shows the discharger no longer meets the conditions in subsection (a) (A) through (E) of this section. (3) Consideration of Intake Pollutants in Establishing Water Quality Based Effluent Limits (WQBELs): (a) The department may consider pollutants in intake water as provided in section (3) when establishing water quality-based effluent limitations based on narrative or numeric criteria, provided that the discharger has demonstrated that the following conditions are
met: (A) The facility withdraws 100 percent of the intake water containing the pollutant from the same body of water into which the discharge is made; (B) The observed maximum ambient background concentration and the intake water concentration of the pollutant exceeds the most stringent applicable water quality criterion for that pollutant; (C) The facility does not alter the identified intake pollutant chemically or physically in a manner that would cause adverse water quality impacts to occur that would not occur if the pollutants were left in-stream; (D) The facility does not increase the identified intake pollutant concentration, as defined by the department, at the point of discharge as compared to the pollutant concentration in the intake water; and (E) The timing and location of the discharge would not cause adverse water quality impacts to occur that would not occur if the identified intake pollutant were left in-stream. (b) Where the conditions in subsection (a) of this section are met, the department may establish a water quality-based effluent limitation allowing the facility to discharge a mass and concentration of the intake pollutant that are no greater than the mass and concentration found in the facility’s intake water. A discharger may add mass of the pollutant to its waste stream if an equal or greater mass is removed prior to discharge, so there is no net addition of the pollutant in the discharge compared to the intake water. (c) Where proper operation and maintenance of a facility’s treatment system results in the removal of an intake water pollutant, the department may establish limitations that reflect the lower mass and concentration of the pollutant achieved by such treatment. (d) Where intake water for a facility is provided by a municipal water supply system and the supplier provides treatment of the raw water that removes an intake water pollutant, the concentration of the intake water pollutant will be determined at the point where the water enters the water supplier’s distribution system. (e) Where a facility discharges intake pollutants from multiple sources that originate from the receiving water body and from other water bodies, the department may derive an effluent limitation reflecting the flow-weighted amount of each source of the pollutant provided that adequate monitoring to determine compliance can be established and is included in the permit. (f) The permit will specify how compliance with mass and concentration-based limitations for the intake water pollutant will be assessed. This may be done by basing the effluent limitation on background concentration data. Alternatively, the department may determine compliance by monitoring the pollutant concentrations in the intake water andReasonable Potential Analysis IMD Oregon Department of Environmental Quality DEQ 11-WQ-020-IMD 2/13/2012 Version 3.1 Page 117 of 117

in the effluent. This monitoring may be supplemented by monitoring internal waste streams or by a department evaluation of the use of best management practices. (g) In addition to the above, effluent limitations must be established to comply with all other applicable State and Federal laws and regulations including technology-based requirements and anti-degradation policies.(h) When determining whether WQBELs are necessary, information from chemicalspecific, whole effluent toxicity and biological assessments will be considered independently. (i) Permits limits must be consistent with the assumptions and requirements of waste load allocations or other provisions in a TMDL that has been approved by the EPA.