United States
          Environmental Protection
          Agency
          Office of Wastewater
          Management 4203
EPA 833-R-04-002A
July 2004
&EPA
Local  Limits
Development Guidance

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Background

       The Office of Wastewater Management of the U.S. Environmental Protection Agency's (EPA's)
Office of Water prepared this guidance document to assist municipalities that own or operate publicly
owned treatment works (POTWs) in developing and implementing local pretreatment programs.

       Section 402(b) of the Clean Water Act (CWA) provides for EPA to authorize a State to
administer its own National Pollutant Discharge Elimination System (NPDES) permit program. In order
to be authorized, a State program must include adequate authority to issue permits that ensure compliance
with the CWA including section 307(b) pretreatment standards. The program must ensure that permits
issued to POTWs include a program to assure compliance with pretreatment standards by significant
sources introducing pollutants subject to such standards to the POTW. [Section 402(b)(8), 33 U.S.C. ง
1342(b)(8)]. This guidance will assist POTWs in their efforts to meet their requirement to develop
pretreatment programs.

Disclaimer

       The discussion in this document is intended solely as guidance.  This guidance is not a
regulation nor does not it substitute for any requirements under the CWA or EPA's regulations.
Thus, it does not impose legally binding requirements on EPA, States, municipalities or the regulated
community.  The general descriptions provided in this document may not apply to a particular situation
based upon the circumstances. This guidance does not confer legal rights or impose legal obligations
upon any member of the public.

       Among other things, the document describes existing requirements with respect to industrial
dischargers and POTWs under the CWA and its implementing regulations at 40 CFR 122, 123, 124, and
403 and chapter I, subchapter N.  While EPA has made every effort to ensure the accuracy of the
discussion in this guidance, a discharger's obligations are determined, in the case of directly discharging
POTWs, by the terms of their NPDES permit and EPA's regulations or, in the case of indirect
dischargers, by permits or equivalent control mechanisms issued to POTW industrial users or by
regulatory requirements.  Nothing in this guidance changes any statutory or regulatory requirement. In
the event of a conflict between the discussion in this guidance and any permit or regulation, the permit or
regulation would be controlling.  EPA and local decision makers retain the discretion to adopt
approaches on a case-by-case basis that differ from those described in this guidance where appropriate
and authorized by EPA regulations, State law, or local ordinances.

       Mention of trade names or commercial products does not constitute endorsement or
recommendation for their use.

       EPA may decide to revise this guidance without public notice to reflect changes in the Agency's
approach to implementing pretreatment standards or to clarify and update text.  To determine whether the
Agency has revised this guidance and/or to obtain copies, contact the Water Permits Division at
(202) 564-9545. You can also determine whether EPA has revised or supplemented the information in
this guidance by accessing the document at: http://www.epa.gov/NPDES/pretreatment.

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CONTENTS
Acronyms	xi

Glossary	  xv

Chapter 1 - Introduction	1-1
       1.1 Purpose of This Manual	1-1
       1.2 Local Limits Statutory Authority	1-1
       1.3 Local Limits Process 	1-1
       1.4 National Pretreatment Standards	1-2
           1.4.1 Prohibited Discharges	1-2
           1.4.2 Categorical Standards	1-3
           1.4.3 Local Limits	1-3
       1.5 The Relationship of Local Limits to Categorical Standards 	1-3
       1.6 Organization of the Guidance Manual	1-4

Chapter 2 - Overview of Local Limits Development  	2-1
       2.1 Local Limits Decision Tree	2-1
       2.2 MAHL Approach to Local Limits Development	2-3
           2.2.1 Step 1: Determine Pollutants of Concern  	2-4
           2.2.2 Step 2: Collect and Analyze Data	2-4
           2.2.3 Step 3: Calculate  MAHLs for Each POC	2-4
           2.2.4 Step 4: Designate and Implement Local Limits	2-4
           2.2.5  Step 5: Addressing Collection System Concerns	2-4

Chapter 3 - Determining Pollutants of Concern  	3-1
       3.1 National POCs	3-1
       3.2 Other Potential POCs	3-2
           3.2.1 NPDES Permit Conditions	3-2
           3.2.2 Water Quality Criteria 	3-3
           3.2.3 Sludge Quality Standards	3-4
           3.2.4 Air Quality Standards	3-4
           3.2.5 Resource Protection Criteria  	3-5
           3.2.6 Prohibitions on Treatment Plant Interference  	3-5
           3.2.7 Prohibitions to Protect the Treatment Works, Collection System, and Workers ... 3 - 5
           3.2.8 Scans of POTW Influent, Effluent, and Sludge to Identify Priority Pollutants	3-6
           3.2.9 Evaluations of Industrial and Commercial Discharges  	3-7
           3.2.10  Hauled Waste 	3-8
           3.2.11  Remediation Site Waste 	3-9
           3.2.12  Hazardous Wastes	3-11
       3.3 Approval Authority Screening Process to Select Pollutants for Local Limits Sampling
           Program and Limit Development	3-11
       3.4 Summary 	3-12

Chapter 4 - Data Needed to Develop Local Limits	4-1
       4.1 Sampling Locations	4-2

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          4.1.1  AtthePOTW	4-2
          4.1.2  In the Collection System  	4-3
          4.1.3  At Industrial Users	4-4
       4.2 Pollutants for Which POTWs Should Sample	4-4
       4.3 Sampling Frequencies  	4-5
          4.3.1  Sampling Frequencies for Initial Program Development	4-5
          4.3.2  Sampling Frequencies for Ongoing Evaluation	4-6
       4.4 Other Sampling Tips  	4-7
       4.5 Sampling Methods	4-8
       4.6 Analytical Methods  	4-10
       4.7 Information Collection and Maintenance  	4-13
       4.8 Review and Evaluation of Analytical Results	4-13
       4.9 Flow Data	4-14
          4.9.1  Total POTW Flow  	4-14
          4.9.2  Sludge Flow to the Digester	4-14
          4.9.3  Sludge Flow to Disposal  	4-14
          4.9.4  Flows from Controlled Sources 	4-15
          4.9.5  Flows from Uncontrolled Sources 	4-16
       4.10  Summary 	4-16

Chapter 5 - Calculation of Maximum Allowable Headworks Loadings	5-1
       5.1 Calculation of Removal Efficiencies	5-1
          5.1.1  Removal Efficiency Calculation Methodologies	5-3
          5.1.2  Guidance on Using Different Methodologies  	5-5
          5.1.3  Data Quality	5-6
          5.1.4  Applying Removal Efficiencies Reported by Others	5-7
       5.2 Calculation of Allowable Headworks Loadings 	5-8
          5.2.1  Determination of Suitable Environmental Criteria 	5-8
          5.2.2  Effluent-Quality Based AHLs   	5-11
          5.2.3  Sludge-Quality Based AHLs  	5-14
          5.2.4  Inhibition-Based AHLs  	5-19
          5.2.5  Air-Quality Based AHLs  	5-21
       5.3 AHLs for Conventional and Non-Conventional Pollutants	5-21
          5.3.1  BOD/TSS	5-22
          5.3.2  Ammonia 	5-23
          5.3.3  Oil and Grease  	5-23
       5.4 Determination of the Maximum Allowable Headworks Loading   	5-25
       5.5 Sample MAHL Calculation  	5-25
       5.6 Summary  	5-26

Chapter 6 - Designating and Implementing Local Limits  	6-1
       6.1 Determination of the Need for New Local Limits	6-1
          6.1.1  Actual Loadings vs. MAHL	6-2
          6.1.2  Noncompliance Due to Pass Through or Interference	6-2
          6.1.3  Establishing Local Limits for Conventional Pollutants	6-2
       6.2 Calculation of Maximum Allowable Industrial Loading 	6-4
          6.2.1  Uncontrolled Sources  	6-5
          6.2.2  Hauled Waste  	6-6
          6.2.3  Safety Factor  	6-6
          6.2.4  Expansion/Growth Allowance	6-7

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       6.3  Comparison of MAIL Allocation and Implementation Methods  	6-7
       6.4  Allocation of MAILs Among Controlled Sources	6-8
           6.4.1 Limit Duration 	6-8
           6.4.2 Allocation Approaches	6-10
       6.5  Common Sense Assessment	6-13
       6.6  Best Management Practices	6-14
       6.7  Approval Authority and Adoption Process 	6-15
       6.8  Public Participation 	6-17
       6.9  Control Mechanisms 	6-18
       6.10 Summary  	6-19

Chapter 7 - Local Limits Reviews and Detailed Re-Evaluations  	7-1
       7.1  Reviews  	7-1
           7.1.1 Comparison of Current Loadings with MAHLs	7-1
           7.1.2 Review of Compliance History 	7-3
           7.1.3 Next Steps	7-3
       7.2  Detailed Local Limits Re-Evaluation 	7-3
           7.2.1 Step 1: Assess Current Conditions	7-4
           7.2.2 Step 2: Collect and Analyze Data	7-5
           7.2.3 Step 3: Recalculate Existing, or Determine New, MAHLs 	7-6
           7.2.4 Step 4: Implement the Local Limits	7-6
       7.3  Summary  	7-7

Chapter 8 - Local Limits to Address Concerns About Collection Systems	8-1
       8.1  Fires and Explosions 	8-1
           8.1.1 Flashpoint Limit	8-1
           8.1.2 Lower Explosive Limit Monitoring	8-2
           8.1.3 Sample Headspace Monitoring 	8-2
           8.1.4 Flammability and Explosivity Discharge Screening Levels  	8-3
       8.2  Corrosion	8-4
           8.2.1 pH	8-4
           8.2.2 Corrosive Pollutants	8-4
       8.3  Flow Obstructions  	8-5
       8.4  Temperature	8-6
       8.5  Toxic Gases, Vapors, and Fumes	8-7
       8.6  Summary  	8-8

Chapter 9 - Questions and Answers  	9-1
       9.1  General	9-1
       9.2  Potential Pollutants of Concern	9-3
       9.3  Sampling and Analysis 	9-3
       9.4  Determining MAHLs	9-5
       9.5  Establishing Local Limits  	9-7
       9.6  Oversight and Public Participation 	9-12
       9.7  Implementation and Enforcement of Local Limits  	9-13
       9.8  POTW Operations	9-14
       9.9  Industrial Users   	9-14
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List of Tables
Table 1-1: Comparison of Categorical Pretreatment Standards and Local Limits 	1-4
Table 3-1: Selected Information Sources for Determining Potential POCs  	3-8
Table 4-1: Minimum Recommended Sampling Days for Initial Local Limits Development	4-6
Table 4-2: Minimum Recommended Sampling Frequencies for Ongoing Local Limits
         Analysis and Evaluation  	4-7
Table 4-3: How to Prepare a Flow-Proportioned Grab Composite Sample	4-10
Table 4-4: Example  of a Flow-Proportioned Average
         Based on Grab Sample Results and Flow Intervals	4-10
Table 4-5: MDLs (ng/L) for EPA Wastewater Analytical Methods 	4-12
Table 5-1: Options for Managing Sampling Results Below the ML in Removal
         Efficiency Calculations 	5-6
Table 5-2: Suggested Criteria or Standards to be Considered
         For Each POC in the Development of AHLs	5-9
Table 5-3: Land Application Requirements	5-15
Table 6-1: Data for Implementation of MAHLs 	6-4
Table 6-2: Options for Allocating and Implementing Local Limits 	6-9

List of Exhibits
Exhibit 2-1: Example MAHL Determination Based on AHLs  	2-3
Exhibit 2-2: Example MAIL Determination 	2-3
Exhibit 3-1: EPA's 15 POCs  	3-2
Exhibit 3-2: Pollutants Regulated Under 40 CFR Part 503	3-4
Exhibit 5-1: Be Conservative in Selecting Criteria	5-11
Exhibit 5-2: How to Convert Dissolved Metals Criteria to Total Metals Criteria	5-13
Exhibit 5-3: The Challenge in Determining Plant Inhibition Values	5-19
Exhibit 5-4: Inhibition Value Study by Chesterfield County (VA)  	5-19
Exhibit 5-5: Less BOD, More Ammonia and Phosphorous	5-22
Exhibit 5-6: City of Richland (WA) POTW Evaluates FOG Removal Efficiency 	5-24
Exhibit 5-7: City of Portland (OR) Uses Current Influent Loading to Develop
           Non-Polar FOG Local Limit  	5-25
Exhibit 6-1: Safety Factor Example	6-6
Exhibit 6-2: Background Allocation  	6-10
Exhibit 6-3: Local Limits Documentation	6-18
Exhibit 7-1: Why Local Limits Should Be Re-evaluated 	7-3
Exhibit 7-2: When to Recalculate or Develop  Local Limits	7-4
Exhibit 7-3: An Example of Changing the Method for Allocating Local Limits 	7-7

List of Equations
Equation 5.1: Removal Efficiency Calculated Using Average Daily Removal Efficiency	5-3
Equation 5.2: Removal Efficiency Calculated Using Mean Removal Efficiency	5-4
Equation 5.3: Plant Removal Efficiency Calculated Using ADRE and Sludge Data	5-5
Equation 5.4: Plant Removal Efficiency Calculated Using MRE and Sludge Data 	5-5
Equation 5.5: AHL Based on NPDES Permit Limit 	5-11
Equation 5.6: AHL Based on Water Quality Criteria  	5-12
Equation 5.7: Converting Table 2 Cumulative Loading Rates to Dry Sludge Concentrations	5-16
Equation 5.8: Converting Table 4 Annual Loading Rates to Dry Sludge  Concentrations  	5-16
Equation 5.9: AHLs Based on Sludge Land Application and Surface Disposal Criteria	5-17
Equation 5.10: AHLs Based On Secondary Treatment Inhibition	5-20
Equation 5.11: AHLs Based On Tertiary Treatment Inhibition	5-20

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Equation 5.12: AHLs Based On Sludge Digestion Inhibition (Conservative Pollutants)	5-21
Equation 5.13: AHLs Based On Sludge Digestion Inhibition (Non-conservative Pollutants) 	5-21
Equation 5.14: AHLs Based On Air Criteria and Volatization Rates  	5-21
Equation 5.15: AHLs Based On Air Criteria and Existing Emissions  	5-21
Equation 6.1: Actual Loading vs. MAHL Calculation  	6-2
Equation 6.2: MAIL Calculation	6-4
Equation 6.3: Uncontrolled Loading Calculation  	6-5
Equation 6.4: IU Contributory Flow Calculation  	6-11
Equation 6.5: Mass Proportion Method for a Mass-Based Local Limit 	6-11
Equation 6.6: Mass Proportion Method for a Concentration-Based Limit	6-11
Equation 6.7: Uniform Allocation of Background Loading  	6-11
Equation 6.8: Uniform Concentration Limit Calculation  	6-12

List of Figures
Figure 2-1: POTW Local Limits Decision Tree 	2-2
Figure 3-1: Determining Hauled Waste Characteristics  	3-10
Figure 5-1: Process Flow Diagram for Calculating MAHL for a Single POC  	5-2
Figure 5-2: Decile Results for Hypothetical POTW	5-4
Figure 5-3: POTW Flow Diagram and Environmental Criteria   	5-10

Appendices
Appendix A - List of Supplemental Documents 	 A-
Appendix B - Industrial Categories with Pretreatment Standards	 B-
Appendix C - Pollutants Regulated by Categorical Pretreatment Standards	 C-
Appendix D - Clean Water Act Priority Pollutants and the Federal Water Quality Criteria	 D-
Appendix E - Federal Sewage Sludge Standards	 E-
Appendix F - Toxicity Characteristic Leachate Procedure (TCLP) Limitations	F-
Appendix G - Literature Inhibition Values  	 G-
Appendix H - Closed-cup Flashpoints  for Select Organic Compounds  	 H-
Appendix I - Discharge Screening Levels and Henry's Law Constants for Organic Compounds  	I-
Appendix J - OSHA, ACGIH and NIOSH Exposure Levels	J-
Appendix K - Landfill Leachate Loadings  	 K-
Appendix L - Hauled Waste Loadings	 L-
Appendix M - Hazardous Waste Constituents - RCRA Appendix VIII  	M-
Appendix N - Statistical Approach to Determining Sampling Frequency	 N-
Appendix O - Minimizing Contamination	 O-
Appendix P - Methods for Calculating Removal Efficiency	P-
Appendix Q - Methods for Handling Data Below Detection Level  	 Q-
Appendix R - Priority  Pollutant Removal Efficiencies	 R-
Appendix S - Specific Gravity of Sludge  	S-
Appendix T - Sludge AHL Equations Using Flow (in metric units)	T-
Appendix U - POTW Configurations  	 U-
Appendix V - Domestic Pollutant Loadings 	 V-
Appendix W - Best Management Practices Mini-Case Studies	W-
Appendix X - Region  1,  Reassessment of Technically Based Industrial Discharge Limits Checklist  . X-
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ACRONYMS
ACGIH    American Conference of Governmental Industrial Hygienists




ADRE     Average Daily Removal Efficiency




AHL      Allowable Headworks Loading




AMSA    Association of Metropolitan Sewerage Agencies




BPJ       Best Professional Judgment




BMP      Best Management Practice




BOD      Biochemical Oxygen Demand




CAA      Clean Air Act




CERCLA  Comprehensive Environmental Response, Compensation, and Liability Act




CFR      Code of Federal Regulations




CIU       Categorical Industrial User




CWA      Clean Water Act




CWF      Combined Waste stream Formula




EPA       United States Environmental Protection Agency




FOG      Fats,  Oils, and Greases




HAP      Hazardous Air Pollutant




HEM      Hexane Extractable Materials




ICP       Inductively Coupled Plasma




IF        Interval Flow




IQR       Interquartile Range




IU        Industrial User




IWS       Industrial Waste Survey




I&I       Inflow and Infiltration






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LEL      Lower Explosive Limit




MAHL    Maximum Allowable Headworks Loading




MAIL     Maximum Allowable Industrial Loading




MCL     Maximum Contaminant Level




MDL     Method Detection Limit




MG       Million Gallons




MGD     Million Gallons per Day




ML       Minimum Level of Quantitation




MLE     Maximum Likelihood Estimation




MRE     Mean Removal Efficiency




MSDS     Material Safety Data Sheet




NAAQS   National Ambient Air Quality Standards




NESHAP  National Emission Standards for Hazardous Air Pollutants




NIOSH    National Institute for Occupational Safety and Health




NPDES    National Pollutant Discharge Elimination System




OSHA     Occupational Safety and Health Administration




PEL      Permissible Exposure Limit




POC      Pollutant of Concern




POTW    Publicly Owned Treatment Works




PS        Percent Solids




QA/QC    Quality Assurance/Quality Control




RCRA     Resource Conservation and Recovery Act




REL      Recommended Exposure Limit




ROS      Regression Order Statistic




SGT-HEM Silica Gel Treated Hexane Extractable Materials







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SIP        State Implementation Plan




SIU        Significant Industrial User




SUO       Sewer Use Ordinance




STEL      Short-Term Exposure Limit




TCLP      Toxicity Characteristic Leaching Procedure




TLV       Threshold Limit Value




TMDL     Total Maximum Daily Load




TPH       Total Petroleum Hydrocarbons




TRE       Toxicity Reduction Evaluation




TSD       Technical Support Document




TSS        Total Suspended Solids




TWA-TLV  Time Weighted Average Threshold Limit Value




UIC        Underground Injection Control




VOC       Volatile Organic Compound




WET       Whole Effluent Toxicity




WQC      Water Quality Criteria




WQS       Water Quality Standards




WWTP    Wastewater Treatment Plant
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GLOSSARY
1Q10.  The lowest average flow for a one-day period that is expected to occur once every ten years.
1Q10 flows are generally available in the background documentation for the POTW's NPDES permit and
also may be obtained from the local district office of the US Geological Survey
(http: //water.usgs .gov/local_office s .html).

7Q10.  The lowest average flow for a seven-day period that is expected to occur once every ten years.
7Q10 flows are generally available in the background documentation for the POTW's NPDES permit and
also may be obtained from the local district office of the US Geological Survey
(http ://water.usgs .gov/local_offices .html).

Biochemical Oxygen Demand (BOD).  A measurement of the amount of oxygen utilized by the
decomposition of organic material, over a specified time period (usually 5 days) in a wastewater sample.
It is used as a measurement of the readily decomposable organic content of wastewater. When five days
are prescribed the acronym BOD5 is used.

Allowable Headworks Loading (AHL). The estimated maximum loading of a pollutant that can be
received at a POTW's headworks that should not cause a POTW to violate a particular treatment plant or
environmental criterion. AHLs are developed to prevent interference or pass through.

American Conference of Governmental Industrial Hygienists (ACGIH).  The American Conference
of Governmental Industrial Hygienists is a member-based organization and community of professionals
that advances worker health and safety through education and the development and dissemination  of
scientific and technical knowledge.

Approval Authority. The Director in a NPDES State with an approved State pretreatment program or
the appropriate EPA Regional Administrator in a non-NPDES State or NPDES State without an approved
State pretreatment program (40 CFR 403.3).  The Approval Authority approves POTW pretreatment
programs, oversees POTW program implementation, and assumes the responsibility of the Control
Authority for those POTWs that do not have a pretreatment program.

Clean Water Act (CWA). The primary Federal law that protects our nation's waters, including lakes,
rivers, aquifers and coastal areas. It provides for the establishment of comprehensive programs that
include standards, technical tools, permitting, enforcement and financial assistance to address the many
causes of pollution and poor water quality, including municipal and industrial wastewater discharges,
polluted runoff from urban and rural areas, and habitat destruction.

Clean Air Act (CAA). The Federal Clean Air Act is the Federal law that forms the basis for the national
air pollution control effort. Basic elements of the act include National Ambient Air Quality Standards
for major air pollutants, Hazardous Air Pollutants Standards, State  attainment plans, motor vehicle
emissions standards, stationary source emissions standards and permits, acid rain control measures,
stratospheric ozone protection, and enforcement provisions.

Code of Federal Regulations (CFR). A codification of the general and permanent rules published in
the Federal Register by the executive departments  and agencies of the Federal Government. The CFR is
divided into 50 titles, which represent broad areas subject to Federal regulation. EPA's regulations are in
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Title 40.  Each title is divided into chapters, which usually bear the name of the issuing agency.  Each
chapter is further subdivided into parts covering specific regulatory areas.  Large parts may be subdivided
into subparts. All parts are organized in sections, and most citations to the CFR are provided at the
section level.

Combined Wastestream Formula (CWF). As defined in 40 CFR 403.6 (e), a procedure under EPA's
pretreatment regulations for calculating alternative discharge limits at industrial  facilities where a
regulated wastestream from a categorical industrial user is combined with other wastestreams prior to
treatment.

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). CERCLA,
commonly known as Superfund, was enacted by Congress in 1980. This law created a tax on the
chemical and petroleum industries and provided broad Federal authority to respond directly to releases or
threatened releases of hazardous substances that may endanger public health or the environment.

Control Authority. As defined in 40 CFR 403.12, the POTW if the  POTW's submission for its
pretreatment program (40 CFR 403.3(t)) has been approved in accordance with the requirements of 40
CFR 403.11. If the submission has not been approved, the Control Authority is the Approval Authority.
The Control Authority is responsible for implementing the pretreatment program, including
establishment of control mechanisms for compliance assessment and enforcement of national standards,
categorical standards, and local limits.

Conservative Pollutants.  Pollutants that are presumed not to be destroyed, biodegraded, chemically
transformed, or volatilized within the POTW.  Conservative pollutants introduced to a POTW ultimately
exit the POTW solely through the POTW's effluent and sludge.  Most metals are considered conservative
pollutants.

Flashpoint.  The lowest temperature at which vapor combustion will propagate away from its source of
ignition.

Headworks. The point at which wastewater enters a wastewater treatment plant. The headworks may
consist of bar screens, comminuters, a wet well or pumps.

Industrial User (III). Non-domestic source of pollutants into a POTW regulated under Section 307(b),
(c) or (d) of the Clean Water Act.

Industrial Waste Survey (IWS). The process of identifying and locating industrial users and
characterizing their industrial discharges.

Inflow and Infiltration (I&I). Infiltration is the seepage of groundwater into a sewer system, including
service connections. Seepage frequently occurs through defective or cracked pipes, pipe joints,
connections or manhole walls. Inflow is the water discharged into a sewer system and service
connections from sources other than regular connections. This includes flow from yard  drains,
foundation drains and around manhole covers.  Inflow differs from infiltration in that it is a direct
discharge into the  sewer rather than a leak or seepage into the sewer itself.

Inhibition. Inhibition occurs when pollutant levels  in a POTW's wastewater or sludge cause operational
problems for biological treatment processes involving secondary or tertiary wastewater treatment and
alter the POTW's ability to adequately remove BOD, TSS, and other pollutants.
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Interference. EPA uses the term "interference" in its regulations to describe a discharge that, alone or
with discharges from other sources, inhibits or disrupts a POTW, its treatment processes and operations,
or its sludge processes, use, or disposal and, therefore, causes a violation of the POTW's NPDES permit,
increases the magnitude or duration of such a violation, or prevents the proper use or disposal of sewage
sludge in compliance with the Clean Water Act, Solid Waste Disposal Act, Toxic Substance Control
Acts, or the Marine Protection, Research and Sanctuaries Act.

Lower Explosive Limit (LEL).  The minimum concentration in air at which a gas or vapor will explode
or burn in the presence of an ignition source.

Maximum Contaminant Level  (MCL).  The maximum permissible level of a contaminant in water
delivered to any user of a public water system. An MCL is an enforceable standard.

Maximum Allowable Industrial Loading (MAIL). The estimated maximum loading of a pollutant that
can be received at a POTW's headworks from all permitted industrial users and other controlled sources
without causing pass through or interference. The MAIL is usually calculated by applying a safety factor
to the MAHL and discounting for uncontrolled sources, hauled waste and growth allowance.

Maximum Allowable Headworks Loading (MAHL). The estimated maximum loading of a pollutant
that can be received  at a POTW's headworks without causing pass through or interference.  The most
protective (lowest) of the AHLs (see definition) estimated for a pollutant.

Method Detection Limit (MDL). The minimum concentration of an analyte that can be measured and
reported with 99 percent confidence that the analyte concentration is present as determined by a specific
laboratory method in 40 CFR Part 136, Appendix B.

Minimum Level of Quantitation (ML).  The lowest level at which the entire analytical system must
give a recognizable signal and acceptable  calibration point for the analyte. It is equivalent to the
concentration of the  lowest calibration standard, assuming that all method-specified sample weights,
volumes, and cleanup procedures have been employed. The ML is calculated by multiplying the MDL
by 3.18  and rounding the result to the number nearest (1, 2,  or 5) x 10" where n is an integer.

National Ambient Air  Quality Standards (NAAQS). Standards established by EPA that apply for
outside air throughout the country.

National Institutes for Occupational Safety and Health (NIOSH).  The National Institute for
Occupational Safety and Health is the Federal agency responsible for conducting research and making
recommendations for the prevention of work-related disease and injury. The Institute is part of the
Centers for Disease Control and Prevention.

National Pollutant Discharge Elimination System  (NPDES).  The permitting system established by
the Clean Water Act, which regulates the discharge of pollutants into the waters of the United States.
Such a discharge is prohibited unless a NPDES permit is issued by EPA or, where authorized, a State; or
a Native American tribal government.

Non-conservative Pollutants. Pollutants that are presumed to be destroyed, biodegraded, chemically
transformed, or volatilized within the POTW to some degree.
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Occupational Safety and Health Administration (OSHA).  The Occupational Health and Safety
Administration is part of the U.S. Department of Labor. It regulates worker conditions and was founded
in 1971 to save lives, prevent injuries and protect the health of America's workers.

Pass Through.  A discharge that enters the waters of the United States from a POTW in quantities or
concentrations that, alone or with discharges from other sources, either causes a violation of any
requirement of the POTW's NPDES permit,  or increases the magnitude or duration of a violation of the
POTW's NPDES permit.

Pollutant of Concern (POC). Any pollutant that might reasonably be expected to be discharged to the
POTW in sufficient amounts to pass through or interfere with the works, contaminate its sludge, cause
problems in its collection system, or jeopardize its workers.

Pretreatment. As defined in  40 CFR 403.3, "pretreatment" means the reduction of the amount of
pollutants, the elimination of pollutants, or the alteration of the nature of pollutant properties in
wastewater prior to or in lieu of discharging or otherwise introducing such pollutants into a POTW.

Priority Pollutant. Pollutants listed by the EPA Administrator under Clean Water Act Section 307 (a).
The list of the current 126 Priority Pollutants can be found in 40 CFR Part 423, Appendix A.

Publicly Owned Treatment Works (POTW). A treatment works, as defined by Section 212 of the
CWA, that is owned by the State or  municipality. This definition includes any devices and systems used
in the storage, treatment, recycling,  and reclamation of municipal sewage or industrial wastes of a liquid
nature. It also includes sewers, pipes and other conveyances only if they convey wastewater to a POTW
treatment plant [40 CFR 403.3]. Privately owned treatment works, Federally owned treatment works,
and other treatment plants not owned by municipalities are not considered POTWs.

Resource  Conservation and Recovery Act  (RCRA). Passed by Congress in 1976, RCRA gave EPA
the authority to control hazardous wastes from the "cradle to grave." This includes the generation,
transportation, treatment, storage, and disposal of hazardous waste. RCRA also set forth a framework for
the management of non-hazardous wastes. The 1986 amendments to RCRA enabled EPA to address
environmental problems that could result from underground tanks storing petroleum and other hazardous
substances. RCRA focuses only on active and future facilities and does not address abandoned or
historical sites (see CERCLA).  The Federal  Hazardous and Solid Waste Amendments are the 1984
amendments to RCRA that required phasing  out land disposal of hazardous waste. Some of the other
mandates of this strict law include increased  enforcement authority for EPA, more stringent hazardous
waste management standards,  and a comprehensive underground storage tank program.

Sewer Use Ordinance (SUO).  A legal mechanism implemented by a local government entity that sets
out, among others, requirements for the discharge of pollutants into a POTW.

Short-Term Exposure Level  (STEL). Concentrations to which a worker should not be exposed for
longer than 15 minutes and which should not be repeated more than four times per day, with at least one
hour between exposures (commonly accepted exposure limits identified by the ACGIH).

Significant Industrial User (SIU). As defined in 40 CFR 403.3, all users subject to Categorical
Pretreatment Standards under  40 CFR 403.6  and 40 CFR chapter I, subchapter N; and any other
industrial user that discharges an average of 25,000 gallons per day or more of process wastewater to a
POTW (excluding sanitary, non-contact cooling and boiler blowdown wastewater); contributes a process
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wastestream that makes up 5 percent or more of the average dry weather hydraulic or organic capacity of
the POTW treatment plant; or is designated as such by the Control Authority defined in 40 CFR
403.12(a) on the basis that the industrial user has a reasonable potential for adversely affecting the
POTW's operation or for violating any pretreatment standard or requirement [in accordance with 40 CFR
403.8(f)(6)].

State Implementation Plan (SIP).  An EPA-approved State plan required by the Clean Air Act for the
establishment, regulation, and enforcement of air pollution standards.

Time Weighted Average Threshold Limit Value (TWA-TLV).  The concentration to which a worker
can be exposed for 8 hours per day, 40 hours per week and not have any acute or chronic adverse health
effects (commonly accepted exposure limits identified by the ACGIH).

Total Maximum Daily Load (TMDL). Total Maximum Daily Load is a calculation of the maximum
amount of a pollutant from point and non-point sources that a waterbody can receive and still meet water
quality standards, and an allocation of that amount to the pollutant's sources. The Clean Water Act,
Section 303, establishes the water quality standards and TMDL programs.

Total Suspended Solids (TSS).  A measure of the suspended solids in wastewater, effluent, or water
bodies, determined by tests for "total suspended non-filterable solids."

Toxicity Characteristic Leaching Procedure (TCLP).  A laboratory procedure designed to predict
whether a particular waste is likely to leach chemicals into groundwater at dangerous levels. Details are
provided in 40 CFR Part 261.

Volatile Organic Compound (VOC). As defined in 40 CFR 50.100, "volatile organic compounds"
means any compound of carbon,  excluding carbon monoxide, carbon dioxide, carbonic acid, metallic
carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical
reactions.

Whole Effluent Toxicity (WET) Tests. Whole effluent toxicity is the aggregate toxic effect of an
effluent measured directly by an aquatic toxicity test. Aquatic toxicity methods designed specifically for
measuring WET have been codified  in 40 CFR 136. WET test methods employ a suite of standardized
freshwater, marine, and estuarine plants, invertebrates, and vertebrates to estimate acute and short-term
chronic toxicity of effluents and receiving waters.
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CHAPTER 1 -
INTRODUCTION
1.1 PURPOSE OF THIS MANUAL

This manual provides guidance to municipalities on the development and implementation of local
controls or limits on discharges to publicly owned treatment works (POTWs). This manual replaces the
Guidance Manual on the Development and Implementation of Local Discharge Limitations Under the
PretreatmentProgram issued by the U.S. Environmental Protection Agency (EPA) in December 1987.
The audience for this manual is the POTW personnel responsible for local pretreatment program
implementation. The manual provides practical technical assistance and reasoned guidance on the
following:

       •    Determining pollutants of concern (POCs)
       •    Collecting and analyzing data
       •    Calculating maximum allowable headworks loadings (MAHLs) for each POC
       •    Designating and implementing local limits
       •    Performing local limits reviews and re-evaluations
       •    Developing local limits to address concerns about collection systems

Appendix A contains a list of supplemental EPA documents to this manual. If a POTW is located in a
State with an approved pretreatment program, POTW personnel should also refer to guidance manuals
and spreadsheets available from State Approval Authorities.

1.2 LOCAL LIMITS STATUTORY AUTHORITY

A component of the National Pollutant Discharge Elimination System (NPDES) Program, the National
Pretreatment Program was developed by EPA to control the discharge of pollutants from POTWs. The
statutory authority for the National Pretreatment Program lies in the Federal Water Pollution Control Act
of 1972, which was amended by Congress in 1977 and renamed the Clean Water Act (CWA).  Under
Section 307(b), EPA must develop Pretreatment Standards that prevent the discharge of pollutants that
pass through, interfere with, or are otherwise incompatible with POTWs.  The 1977 amendments to the
CWA required POTWs to ensure compliance with the pretreatment standards by each significant local
source introducing pollutants subject to pretreatment standards into a POTW. To meet the requirements
of the 1977 amendments, EPA developed the General Pretreatment Regulations for Existing and New
Sources of Pollution [40 Code of Federal Regulations(CFR) Part 403].

1.3 LOCAL LIMITS PROCESS

To protect its operations and to ensure that its discharges comply with State and Federal requirements, a
POTW will design its local limits based on site-specific conditions. Among the factors a POTW should
consider in developing local limits are the following: the POTW's efficiency in treating wastes; its history
of compliance with its NPDES permit limits; the condition of the water body that receives its treated
effluent; any water quality standards that are applicable to the water body receiving its effluent; the
POTW's retention, use, and disposal of sewage sludge; and worker health and safety concerns.  The
General Pretreatment Regulations require the following:
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       •   POTWs that are developing pretreatment programs must develop and enforce specific limits
           on prohibited discharges, or demonstrate that the limits are not necessary [40 CFR
           403.8(f)(4)].

       •   POTWs that have approved pretreatment programs must continue to develop and revise local
           limits as necessary [40 CFR 403.5(c)(l)].

       •   POTWs that do not have approved pretreatment programs must develop specific local limits
           if pollutants from non-domestic sources result in interference or pass through and such
           occurrence is likely to recur [40 CFR 403.5(c)(2)].

EPA and the States have approved more than 1,400 POTW pretreatment programs. Each program must
develop, implement, and enforce technically based local limits. Because most of the POTWs that require
pretreatment programs now have them, only a few new programs are approved each year. Work on local
limits continues, however, because POTWs with approved programs must periodically review these local
limits. EPA regulations require that POTWs with approved programs must "provide a written technical
evaluation of the need to revise local limits under 40 CFR 403.5(c)(l), following permit issuance or
reissuance" [ 40 CFR 122.44(j)(2)(ii)].  Additionally, EPA recommends that Control Authorities review
the adequacy of local limits if current wastewater treatment plant performance fails or will fail to attain
applicable NPDES, State, or local permit requirements or other operational objectives, including water
quality objectives  of receiving waters; and if the performance shortcomings may be reasonably attributed
to pass through or interference caused by a POC. Finally, Control Authorities may find  it beneficial to re-
evaluate their local limits when a change in POTW operations results in a significant change in
operational objectives; when the POTW experiences a significantly different influent flow or pollutant
characteristics; or when a significant alteration of key environmental criteria occurs.

1.4 NATIONAL PRETREATMENT STANDARDS

The National Pretreatment Program consists of three types of national pretreatment standards established
by regulation that  apply to industrial  users (Ills). These include prohibited discharges, categorical
standards, and local limits. Prohibited discharges, comprised of general and specific prohibitions, apply
to all Ills regardless of the size or type of operation. Categorical standards apply to specific process
wastewater discharges from particular industrial categories.  Local limits are site-specific limits developed
by the POTW to enforce general and specific prohibitions on Ills.

1.4.1  PROHIBITED DISCHARGES

Prohibited discharges include both general and specific prohibitions, as described below:

       •   General prohibitions [40 CFR 403.5(a)] forbid the discharge to a POTW of any pollutant that
           causes pass through or interference.  Pass through means a discharge that causes a violation
           of any requirement of the POTW's NPDES permit. Interference refers to  a discharge that
           inhibits or disrupts the POTW, its treatment process or operations, or its sludge processes and
           that leads to a violation of the NPDES permits or any other applicable Federal,  State, or local
           regulation.

       •   Specific prohibitions [40 CFR 403.5(b)(l) to (8)] forbid the following eight categories of
           pollutant discharges to POTWs: 1) Pollutants that create fire or explosion hazards;
           2) Pollutants that will cause structural damage due to corrosion; 3) Pollutants that will cause
           obstructions in the flow of discharges to the POTW; 4) Pollutants released at excessive rates
           of flow or concentrations; 5) Excessive heat in amounts that inhibit biological activity;

                                              1 -2

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           6) Certain oils that cause pass through or interference; 7) Pollutants that result in the presence
           of toxic gases, vapors, or fumes; and 8) Trucked or hauled pollutants, except at discharge
           points designated by the POTW.

1.4.2  CATEGORICAL STANDARDS

Categorical standards are uniform, technology-based, and applicable nationwide.  Developed by EPA,
these  standards apply to specific categories of Ills and limit the discharge of specified toxic and non-
conventional pollutants to POTWs. Expressed as numerical limits and management standards, the
categorical standards are found at 40 CFR 405 through 471. They include specific limitations for 35
industrial sectors. Appendix B provides a list of the industries for which EPA has promulgated
categorical standards.  Appendix C contains a list of pollutants regulated by categorical pretreatment
standards.

1.4.3  LOCAL LIMITS

Local limits are developed by POTWs to enforce the specific and general prohibitions, as well as any
State and local regulations.  The prohibitions and categorical standards are designed to provide a
minimum acceptable level of control over IU discharges. They do not, however, take into account site-
specific factors at POTWs that may necessitate additional controls. For  example, a POTW that discharges
into a river designated a "scenic river" under the Wild and Scenic Rivers Act may have extremely
stringent discharge limits. To comply with its discharge permit, the POTW may need to exert greater
control over IU discharges.  This additional control can be obtained by establishing local limits.

1.5 THE RELATIONSHIP OF LOCAL LIMITS TO CATEGORICAL STANDARDS

Categorical standards and local limits are complementary types of pretreatment standards.1  The former
are developed to achieve uniform technology-based water pollution control nationwide for selected
pollutants and industries.  The latter are intended to prevent site-specific POTW and environmental
problems due to non-domestic discharges. As shown in Table 1-1, local limits can be broader in scope
and more diverse in form than categorical standards.  The development of local limits requires the
assessment of local conditions and the judgment of POTW personnel.

EPA's promulgation of categorical standards does not relieve a POTW from its obligation to evaluate the
need for and to develop local limits to meet the general and specific prohibitions in the General
Pretreatment Regulations. Because specific prohibitions and categorical standards provide only general
protection against pass through and interference, local limits based on POTW-specific conditions may be
necessary.  Developed in accordance with 40 CFR 403.5(c), local limits  are Pretreatment Standards for
the purposes of CWA Section 307(d) [see 40 CFR 403.5(d)]. Therefore, EPA can take enforcement
actions against an IU that violates a local limit.  Affected third parties also may sue lUs or POTWs with
approved pretreatment programs for violations of local limits under the CWA's citizen suit provisions.  A
POTW may impose local limits on an IU that are more stringent, or cover more pollutants, than an
applicable categorical standard.  This may be necessary for the POTW to meet its discharge permit or
sludge quality limits. If a local limit is less stringent than an applicable categorical  standard, however, the
industry to which the local limit applies still must meet the applicable categorical standard.  Guidance on
permitting, including the comparison of Categorical Standards and local limits, is available in two EPA
        :A direct comparison of categorical standards and local limits may not be possible because local limits may apply at
the point(s) where an IU connects to the POTW collection system, while categorical standards may apply at the end of the lU's
regulated process(es) or immediately after pretreatment prior to mixing with other unregulated wastewater flows.

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guidance manuals: Industrial User Permitting Guidance Manual (EPA 833-B-89-001, September 1989)
and Guidance Manual for the Use of Production-Based Pretreatment Standards and the Combined
Wastestream Formula (EPA 833-B-85-210, September 1985).
          Table 1-1: Comparison of Categorical Pretreatment Standards and Local Limits
Characteristic
Agency responsible for development
Potential sources regulated
Objective
Pollutants regulated
Basis
Point of application
Categorical Standards
EPA
Industries specified in Clean Water
Act, or as determined by EPA
Uniform national control of non-
domestic discharges
Primarily Priority Pollutants listed
under Clean Water Act Section 307
(toxic and non-conventional pollutants
only)
Technology based
At the end of the regulated
process(es) or in-plant
Local Limits
Control Authority (usually POTW)
All non-domestic dischargers
Protection of POTW and local
environment
Any pollutant that may cause pass
through or interference
Technically based on site-specific factors:
• Allowable headworks loadings
• Toxicity reduction evaluation
• Technology in use
• Management practice
Depends on development methodology
[usually at the point of discharge(s) into
the collection system]
1.6 ORGANIZATION OF THE GUIDANCE MANUAL

This guidance manual provides an organized approach to the development and re-evaluation of local
limits.  Chapter 2 outlines the general approach for determining when to develop and when to re-evaluate
local limits (providing a roadmap through the remainder of the manual). It also provides an overview of
the local limits development process using the maximum allowable headworks load approach. Chapters 3
through 6 cover limit development and implementation. Chapter 7 discusses reviews and re-evaluations
of local limits, and Chapter 8 describes approaches to local limits development based on collection system
concerns.  The final chapter, Chapter 9, provides additional information in a question-and-answer format
on numerous issues that have arisen in local limits development efforts.
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CHAPTER 2 -
OVERVIEW OF LOCAL LIMITS DEVELOPMENT
Local limits development is a continual process for Control Authorities (usually POTWs). Technically
based limits are typically developed when a Control Authority/POTW first creates its local pretreatment
program. As noted in Chapter 1, a POTW required to develop a pretreatment program also must develop
and enforce local limits, as necessary, to protect against pass through, interference, and conditions
detrimental to the collection system infrastructure or dangerous to workers.  In addition, a Control
Authority's legal authority to  impose local limits on industrial and commercial users actually derives
from State law. Therefore, State law must confer the minimum Federal legal authority on a Control
Authority. Section 6.7 of Chapter 6 provides a more complete discussion of the need for and application
of this authority.

Once local limits have been developed, POTWs may wish to review them periodically and revise them as
necessary. Chapter 2 provides an overview  of the local limits development process.

2.1  LOCAL LIMITS DECISION TREE

Figure 2-1 presents a decision tree that POTWs can use to determine the appropriate local limit
implementation procedures. POTWs can follow the approach to evaluate their need for new local limits,
and the adequacy of existing limits. Three months before their annual reports are due, POTWs with
approved pretreatment programs are encouraged to evaluate their local limits through a "review" or a
"detailed re-evaluation" process if the plant  went through significant changes the past year. Then the
results may be discussed in their annual reports. Although EPA recommends reviewing the entire
manual, following the steps presented in Figure 2-1  will lead readers to the chapters  of this manual that
are appropriate for their situations.

Whenever possible, EPA recommends development of local limits to address constituents that could pass
through or cause interference  before such problems occur. While developing a new local limit, or re-
evaluating an existing one, a POTW will need to consider all relevant plant and environmental
information—including trends that may indicate likely future conditions. Anticipating changes and
setting local limits accordingly may reduce the need for future revisions, saving POTW resources and
enhancing IU compliance. For example, a POTW that anticipates changing its sludge disposal practices
can develop local limits that will be protective of more restrictive sludge standards that may apply in the
near future. Similarly, if economic growth within the service area is likely, a POTW can factor in a
safety margin, or hold some allowable headworks loading capacity in reserve so that an allocation will be
available in the future. Otherwise, new industrial hook-ups may have to be prohibited, or local limits
may have to be revised.
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                                               Figure 2-1:  POTW Local Limits Decision Tree
  Has the State or
 EPA required your
 POTW to develop
  and implement a
   pretreatment
       gram?
                                                                         Has your POTW
                                                                           developed
                                                                        technically-based
                                                                           local limits?
                                                                           Were these
                                                                        problems the result
                                                                         of industrial user
                                                                           discharges?
   Has your POTW
  experienced pass
through or interference
   in the past year'
                                                                                                                                Has the
                                                                                                                               Approval
                                                                                                                               Authority
                                                                                                                             requested that
                                                                                                                              you develop
                                                                                                                              local limits?
Has a technically-based
 local limits evaluation
   been performed?
                            Approval Authority
Has your local limits
  evaluation been
approved by EPA or
    the State?
                                     Did your evaluation
                                      determine a need
                                       for local limits?
Are approved local limits
incorporated into local law
and being implemented'
Await direction from
   EPA or State
                                                                        Have there been a
                                                                      significant changes1 since
                                                                         your last local limits
                                                                            evaluation?
                                                                       Perform detailed re
                                                                           evaluation
                                                                                                                              1 Significant changes may include items such as
                                                                                                                              modification to the POTW treatment plant(s), addition of
                                                                                                                              a new treatment plant, changes to the NPDES permit
                                                                                                                              discharge limitations, new sludge disposal practices, new
                                                                                                                              water quality standards for the receiving stream, new or
                                                                                                                              increased discharges to the POTW, and NPDES
                                                                                                                              discharge or sludge disposal violations.
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2.2 MAHL APPROACH TO LOCAL LIMITS DEVELOPMENT
EPA recommends that POTWs base their local
limits on the maximum allowable headworks
loading (MAHL)1 calculated for each pollutant of
concern. A pollutant's MAHL is  determined by
first calculating its allowable headworks loading
(AHL)2 for each environmental criterion; the
most stringent AHL would be the MAHL (see
Exhibit 2-1).

The MAHL approach enables POTWs to
calculate local limits taking into account the
portion of the MAHL that is readily controllable
(i.e., from industrial users (IUs)) and the portion
that is not as easy to control (i.e.,  from domestic
sources and background concentrations). The
maximum allowable industrial loading (MAIL) is the
portion of the MAHL  available to IUs. It is based on
sampling data (see Exhibit 2-2). As discussed in
Chapter 6, local limits are based on the allocation of
MAILs as uniform concentrations that apply to all
IUs, as mass allocations provided individually to each
IU, or some combination of the two options.
                                                     Exhibit 2-1: Example MAHL Determination
                                                                   Based on AHLs

                                                    To determine the MAHL for cadmium, a POTW:
                                                     •  Determines that it will meet its NPDES permit limit if
                                                        the AHL at its headworks does not exceed 14 Ib/day.
                                                     •  Determines that it will meet its land application
                                                        requirements for sludge if the AHL at its headworks
                                                        does not exceed 30 Ib/day.
                                                     •  Reviews its records and determines that an AHL at the
                                                        headworks of 60 Ib/day would protect its operations
                                                        from toxic inhibition.
                                                    Assuming no other criteria apply to this plant, its MAHL for
                                                    cadmium would be 14 Ib/day (the most limiting criterion).
                                                       With a MAHL of 14 Ib/day for cadmium—and assuming
                                                       no other uncontrollable sources exist—the MAIL would
                                                       be 8 Ib/day (14 Ib/day allowable minus 6 Ib/day from
                                                       uncontrollable sources).

                                                        Exhibit 2-2: Example MAIL Determination

                                                       To determine the MAIL for cadmium, a POTW collects
                                                       sampling data and finds that 6 of the 10 Ib of cadmium
                                                       received at its treatment plant every day comes from
                                                       domestic/background/commercial (i.e., uncontrollable)
                                                       sources.
Calculating MAHLs is not the appropriate method to
evaluate all pollutants. Pollutants may create
collection system conditions that can be harmful to
workers such as fires,  explosions, corrosion, flow
obstructions, high temperature, and toxic fumes. To address these issues, EPA recommends that POTWs
consider the options presented in Chapter 8. Developing and implementing local limits with the MAHL
approach requires the  following five basic steps:
        1.
        2.
        3.
        4.
        5.
            Determine the pollutants of concern (POCs)3
            Collect and analyze data
            Calculate MAHLs for each POC
            Designate and implement the local limits
            Address collection system concerns
         A MAHL is the estimated maximum loading of a pollutant that can be received at a POTW's headworks without
causing pass through or interference. It is the most protective (lowest) of AHLs (see definition) estimated for an individual
pollutant.

         An AHL is the estimated maximum loading of a pollutant that can be received at a POTW's headworks that should not
cause a POTW to violate a particular treatment plant or environmental criterion. AHLs are developed to prevent interference or
pass through.

         A POC is any pollutant that might reasonably be expected to be discharged to the POTW in sufficient amounts to pass
through or interfere with the works, contaminate its sludge, cause problems in its collection system, or jeopardize its workers.
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2.2.1 STEP 1: DETERMINE POLLUTANTS OF CONCERN

The first step in the MAHL approach is to identify the pollutants that should be evaluated to determine
the need for local limits to control them. Among these are pollutants with known environmental criteria
(such as limits in the POTW's NPDES permit), other pollutants that are known to be discharged to the
POTW, and pollutants known to be discharged to POTWs in general. The POTW should collect a
limited amount of screening data to determine which of these potential pollutants of concern should be
subject to more extensive data collection through the local limits sampling program. Chapter 3 discusses
the procedures POTWs can use to determine POCs.

2.2.2 STEP 2: COLLECT AND ANALYZE DATA

After identifying the POCs that warrant a closer look, the POTW should undertake the collection of the
necessary data, including additional sampling  and analysis of selected wastewater streams and sludge to
gauge the potential impacts of these POCs.  The recommended procedures for collecting and analyzing
data used to calculate MAHLs are provided in Chapter 4.

2.2.3 STEP 3: CALCULATE MAHLs FOR EACH POC

After collecting and evaluating the necessary data, the POTW should calculate AHLs for each POC
based on its treatment efficiency and on environmental criteria for pass through and interference. As
previously noted, the most stringent AHL will determine the MAHL. Chapter 5 discusses the procedures
used by POTWs to calculate  MAHLs.

2.2.4 STEP 4: DESIGNATE AND IMPLEMENT LOCAL LIMITS

Having calculated the MAHLs, the POTW needs to  compare these allowable loadings with the actual and
potential loadings received at the treatment plant to determine whether local limits are needed for each
POC. Once the need has been established, the POTW develops appropriate local limits.  This process
will include determining the amount of each pollutant that can be allocated to Ills, submitting a
development package to the Approval Authority for its review and approval, incorporating the local
limits into  local law (which includes following public notice requirements), and applying the local limits
to the Ills. Chapter 6 discusses these implementation procedures.

2.2.5 ADDRESS COLLECTION SYSTEM CONCERNS

In addition to the MAHL approach to setting local limits, POTWs may need to develop local limits to
address collection system concerns - fires and explosions, corrosion, flow obstructions, high
temperature, and toxic gases, vapors or fumes  - to meet the requirements of 40 CFR 403.5(b) regarding
prohibited discharges. Chapter 8 discusses developing limits to address these concerns.
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CHAPTER 3 -
DETERMINING  POLLUTANTS OF  CONCERN
POTWs develop local limits to protect their collection systems, treatment plants, the health and safety of
their workers, and the environment.  Chapter 3 provides guidance on identifying which pollutants of
concern (POCs) need to be controlled to meet these goals and to meet Federal, State, and local
requirements.

A POC is any pollutant that might reasonably be expected to be discharged to the POTW in sufficient
amounts to cause pass through or interference, cause problems in its collection system, or jeopardize its
workers. Pollutants that are contributing to or known to cause operational problems are also considered
POCs even if the pollutants are not currently causing National Pollutant Discharge Elimination System
(NPDES) permit violations. Some Approval Authorities have guidelines that POTWs can use in
determining POCs, and POTWs should contact their Approval Authority for details. The methods used to
determine POCs should account for daily fluctuations in POTW pollutant loadings and for the fact that
decisions often are based on limited data.

3.1 NATIONAL POCs

EPA has identified 15 pollutants often found in POTW sludge and effluent that it considers potential
POCs. They are listed in Exhibit 3-1. Ten of the pollutants were first identified in the Guidance Manual
on the Development and Implementation of Local Discharge Limitations Under the Pretreatment
Program (EPA 833-B87-202, December 1987).: EPA added molybdenum and selenium because they are
part of the Federal biosolids regulations for the land application of sludge. EPA added the conventional
pollutants 5-day Biochemical  Oxygen Demand (BOD5) and total  suspended solids (TSS) because many
POTWs have ongoing problems with excessive loadings of these pollutants from industrial and
commercial sources. EPA also added ammonia as a "conditional" POC, for POTWs that accept non-
domestic sources of ammonia, because many POTWs experience toxicity in their effluent from ammonia.

EPA recommends that each POTW, at a minimum, screen for the presence of the 15 pollutants presented
in Exhibit 3-1 using data on industrial user (IU) discharges and collected from samples of POTW influent,
effluent, and sludge.
         Cadmium, chromium, copper, lead, nickel, and zinc are listed "because of their widespread occurrence in POTW
influents and effluents in concentrations that warrant concern. Also, since they are usually associated with the suspended solids
in the wastestream, their presence may prohibit the beneficial reuse of municipal sewage sludge and reduces the POTW options
for safe sludge disposal." Memorandum entitled "Local Limits Requirements for POTW Pretreatment Programs," from Rebecca
W. Hanmer, Director, Office of Water Enforcement and Permits, to Regional Water Management Division Directors and NPDES
State Directors, August 5, 1985. [Copy of memo located in Appendix B of Guidance Manual on the Development and
Implementation of Local Discharge Limitations Under the Pretreatment Program (EPA 833-B87-202), December 1987.]
Arsenic, cyanide and silver are "not as widespread in POTW influents as the six metals but they have particularly low biological
process inhibition values and/or aquatic toxicity values. In the case of cyanide, production of toxic sewer gases is also a
concern." Guidance Manual on the Development and Implementation of Local Discharge Limitations Under the Pretreatment
Program (EPA 833-B87-202, December 1987) p. 2-17.

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3.2 OTHER POTENTIAL POCs

To identify additional potential POCs, EPA recommends that a
POTW:

       •   Determine the environmental standards and other
           statutory and regulatory requirements that it must meet.

       •   Define measures necessary to protect the plant,
           collection system, and workers.

       •   Identify the pollutants in the POTW influent, effluent,
           and sludge.

       •   Identify pollutants for which a total maximum daily
           load (TMDL) has been or will be developed for the
           POTW's receiving water.
Exhibit 3-1: EPA's 15 POCs

       10 Original POCs
Arsenic          Lead
Cadmium        Mercury
Chromium        Nickel
Copper          Silver
Cyanide         Zinc

        5 New POCs
Molybdenum
Selenium
5-day Biochemical Oxygen Demand
Total Suspended Solids
Ammonia (for plants that accept
non-domestic sources of ammonia)
       •   Characterize IU and other non-domestic discharges
           including hauled wastewater to assess which discharges, and which pollutants in those
           discharges, pose potential problems.

       •   Consider pollutants that have contributed to operational or maintenance problems at the
           POTW.

At a minimum, a POTW's local limits must ensure that a POTW will meet the statutory and regulatory
requirements of the Clean Water Act, General Pretreatment Regulations, and any applicable State or local
requirements. Because NPDES permit conditions, sludge disposal practices, and State and local
requirements vary from one POTW to another, they need to be addressed through local limits.

3.2.1  NPDES PERMIT CONDITIONS

The term "NPDES permit" as used in this guidance means either an EPA- or a State-issued permit. The
NPDES permit issued to  a POTW typically contains the following:

       •   Specific effluent limitations.

       •   Water quality-based toxic pollutant limitations.

       •   Whole effluent toxicity (WET) requirements expressed either as a narrative limitation (e.g.,
           "no toxics in toxic amounts") or a numerical criterion.

       •   Criteria and other conditions for sludge use or disposal.

       •   Removal efficiency requirements (e.g., "85-percent removal of BOD").

       •   Requirements that the POTW be well operated and maintained.
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These permit conditions, and other applicable requirements, establish the objectives that the POTW must
meet to prevent pass through and interference. POTWs are required to prohibit discharges from Ills in
amounts that result in or cause a violation of any requirement of the POTW's NPDES permit [see
403.2(a)&(b), 403.3 (i) and 403.3 (n)].  If pass through or interference is the result of inadequately
pretreated industrial discharges, the POTW must develop local limits for the pollutants responsible for the
pass through or interference.

Examples of POCs stemming from NPDES permit conditions include the following:

        •   Pollutants with specific limits.

        •   Pollutants that have caused violations or operational problems at the POTW, including
            conventional pollutants.

        •   Pollutants reasonably expected to lead to pass through, interference, sludge contamination,
            collection system problems, or increased worker jeopardy.

        •   Pollutants designated as "monitor only" in the NPDES permit.2

        •   Pollutants responsible for toxicity found through WET testing.


3.2.2 WATER QUALITY CRITERIA

Water quality criteria have been developed by EPA for protection of surface water, including receiving
water for permitted discharges. States may adopt EPA's criteria,  or establish more stringent criteria of
their own.3  A POTW does not have to develop a local limit for every pollutant for which there is a water
quality  standard or criterion. However, EPA recommends that where a POTW permit includes a narrative
water quality-based condition (e.g., "no discharge of toxics in toxic amounts"), the POTW may wish to
evaluate the discharge of a particular toxic pollutant by considering its effect on water quality for that
pollutant relative to EPA or State criteria for the pollutant.  EPA recommends that any pollutant that has a
"reasonable potential" to be discharged in amounts that could exceed water quality standards or criteria
should be considered a POC and evaluated accordingly.4
         Only discrete pollutants should be considered when a "monitor only" requirement is present in an NPDES permit.
Where the POTW is required to conduct scans for priority pollutants, the entire set of pollutants would not need to be
considered.

         Federal water quality criteria are listed in Appendix D, but readers should contact their States to determine whether
stricter criteria must be met.

         Discharge of a pollutant that results in a violation of a water quality standard is actionable even if the discharger's
NPDES permit does not include a specific permit condition limiting the discharge of that particular pollutant. The Ninth Circuit
has held that a general permit condition prohibiting the discharge of wastewater that violates water quality standards, including a
State water quality standard expressed as a broad narrative criterion, subjects a POTW to citizen suit under Section 505 of the
Clean Water Act. See Northwest Environmental Advocates, etal. v. City of Portland, 56 F.3d 979 (9th Cir. 1995). In
appropriate conditions, therefore, Section 403.5(c) would require a POTW to develop local limits to ensure compliance with the
POTW's permit condition requiring it to comply with State water quality standards.  Such conditions consist of those where the
record demonstrates that a discharge from a POTW is causing or would cause violation of State water quality standards,
including qualitative or broad narrative criteria, and the permit includes a permit condition prohibiting a discharge that violates
State water quality standards.

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     Exhibit 3-2: Pollutants Regulated Under 40
                   CFR Part 503

    The pollutants that are regulated depend on the type of
    sludge disposal method used:

    •  Land application: arsenic, cadmium, copper, lead,
      mercury, molybdenum, nickel, selenium, zinc.

    •  Surface disposal: arsenic, chromium, nickel

    •  Incineration: beryllium and mercury (National Emission
      Standards for Hazardous Air Pollutants under 40 CFR
      Part 61), lead (National Ambient Air Quality Standard),
      plus arsenic,  cadmium, chromium, nickel (risk-specific
      concentrations).
3.2.3 SLUDGE QUALITY STANDARDS

POTWs must prohibit IU discharges in amounts
that cause a violation of applicable sludge
disposal or use regulations, or that restrict the
POTW's use of its chosen sludge disposal or use
option. The national sludge standards  are found
at 40 CFR Part 503 and are shown in Exhibit 3-2.
They are based on human health and
environmental risks and include numerical
pollutant limits, operational standards,
management practices, and requirements for
sampling, record keeping, and reporting. The
sludge use and disposal options are:

       •   Land application
       •   Surface disposal
       •   Incineration
       •   Deposition in a municipal  solid waste landfill

To dispose of its sludge by land application, surface disposal, or incineration, a POTW must ensure that
its sludge meets the pollutant limits that apply to the selected disposal option.  Therefore, any pollutant
limited by an applicable sludge disposal standard should be considered a POC and evaluated.  If sewage
sludge is disposed of in a municipal solid waste landfill, no specific pollutant limitations apply; however,
narrative requirements in 40 CFR 257, 258, and 261 do apply.

The sludge standards found at 40 CFR 503 are presented in Appendix E. States are free to establish their
own sludge use and disposal standards, as long as they are at least as stringent or are as protective as the
Federal requirements. POTWs should contact their Approval Authorities or other State agencies for a
copy of the relevant State standards and adhere to the more stringent standards. EPA recommends that
POTWs consider the attainment of EPA "clean sludge " standards. These are spelled out in Table 3 of 40
CFR 503.13, and provide the broadest  choice of beneficial use options for sludge disposal.  Further,
achievement of these standards is consistent with the objectives of the National Pretreatment Program,
which are listed at 40 CFR 403.2.

POTWs that normally dispose of their  sludge in landfills also may be adversely affected by IU discharges.
EPA recommends that these POTWs also develop local limits to ensure their sludge disposal options are
not restricted.  When slated for disposal in a landfill, sludge and residual ash from the incineration of
sludge should be tested using the Toxicity Characteristic Leaching Procedure (TCLP) discussed in
Appendix II of 40 CFR Part 261. Sludge is considered a hazardous waste if TCLP test results on sludge
exceed concentrations listed in the TCLP method.  Hazardous wastes must be disposed of in accordance
with the Resource Conservation and Recovery Act (RCRA), which will likely increase disposal costs.
The pollutant limits for the TCLP rule  are listed in Appendix F.

3.2.4 AIR QUALITY STANDARDS

Air quality standards are generally not the basis for POCs. However, there are circumstances where a
State adopts a State Implementation Plan (SIP), to comply with National Ambient Air Quality Standards
(NAAQS), that requires a POTW to control emission standards. In addition, POTWs should be aware
that on October 21, 2002, amendments to the National Emission Standards for Hazardous Air Pollutants
(NESHAP) for POTWs were finalized. All newly re-constructed or new treatment plants required to
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develop a pretreatment program (40 CFR 403.8) and defined as major sources of hazardous air pollutants
(HAP) must institute air pollution controls (covers on emission points) or demonstrate low HAP
emissions. In addition, the regulations define industrial POTWs as those that provide treatment and
control for a wastestream regulated by an industrial NESHAP. (The industrial discharger complies with
NESHAP by using the treatment and controls located at the POTW.) In effect, the industrial POTW acts
as an agent of the industrial facility by treating the facility's wastewater to meet NESHAP.  As of 1999,
EPA had identified only six POTWs that are major sources of HAP.  Several POTWs have been identified
as industrial POTWs, and these numbers may increase as more industrial NESHAP are promulgated (40
CFR Part 63, Subpart VVV, 63.1580-1595).

3.2.5 RESOURCE PROTECTION CRITERIA

POTWs should be aware that some States integrate resource protection (watershed and aquifer protection)
criteria into permits separate from NPDES permits (for example, aquifer protection permits in the arid
Southwest States.) EPA recommends that POTWs consider those pollutant limits in determining POCs.

3.2.6 PROHIBITIONS ON TREATMENT PLANT INTERFERENCE

The General Pretreatment Regulations include prohibitions, at 40 CFR403.5(a), against the discharge by
any user of a POTW of pollutants that cause interference.  Interference, as defined by EPA, means a
discharge that inhibits or disrupts a POTW and therefore causes a violation of the POTW's NPDES
permit or non-compliance with the POTW's sewage sludge requirements.  Consequently, EPA
recommends that a POTW consider pollutants that may interfere with the treatment work's operation to
be potential POCs. And if a POTW has experienced interference in the past, the pollutants that caused the
interference should be considered POCs. Where a POTW has identified the pollutant that caused an
interference event and eliminated the problem - for example a one-time event that is not expected to
reoccur - the pollutant need not be considered a POC.

Although some pollutant discharges may not cause NPDES permit or sludge disposal violations, they
might disrupt POTW operations or increase operation and maintenance costs. For example, IU discharges
that inhibit a POTW's biological treatment system could reduce treatment efficiency and, as a result,
increase operating costs. Inhibition may result in the production of sludge that requires special treatment
before disposal, or that requires disposal in a manner not generally used by the POTW. Therefore, EPA
recommends that POTWs also consider pollutants that are known to cause operational or maintenance
problems.

Some pollutants that can cause inhibition, and the estimated concentrations at which inhibitory effects
have been reported, are listed in Appendix G. The inhibition data presented in Appendix G should be
used with caution. Data collected at other POTWs must be examined carefully to assure that the
treatment process and unit operations  are similar to the POTW for which local limits are being developed.
POTWs are encouraged to develop site-specific inhibition data for their POTW, and rely on Appendix G
only to verify the values.

3.2.7 PROHIBITIONS TO PROTECT THE TREATMENT WORKS, COLLECTION SYSTEM, AND WORKERS

The prohibitions in this category apply to discharges of pollutants that can cause a fire or explosion,
corrosive structural damage at the treatment plant, obstruction of flow, inhibition of biological activity
due to heat, and discharges that cause the formation of toxic gases, vapors, or fumes. A local sewer use
ordinance that applies to a POTW typically contains definitions or local limits that implement the specific
prohibitions. Definitions may consist of descriptions from 40 CFR 403.5 (b), or more specific quantitative
                                            3 -5

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definitions (e.g., specific readings on an explosimeter to protect against fire or explosion). Specific
quantitative limits generally are more effective for avoiding ambiguity and for supporting IU compliance
and POTW enforcement of IU non-compliance.  Chapter 8 provides additional detail on procedures for
identifying POCs based on these concerns and for setting local limits to address these concerns.

Explosive and Flammable Substances
Explosive and flammable pollutants discharged to a POTW can threaten the integrity of the collection
system and the health and safety of POTW workers.  Under the right conditions, the accumulation of such
pollutants in treatment works can produce explosions or fires. Local limits can be used to regulate the
discharge of these explosive or flammable pollutants. Lower explosive limits (LELs) and closed cup
flashpoints for various organic compounds are provided in Appendices H and I.

Fume Toxicity
The fume toxicity level of a pollutant discharged to a POTW indicates the likelihood that a POTW worker
will suffer an adverse health effect when the level is approached or exceeded. This level can be measured
by the time weighted average threshold limit value (TWA-TLV), which is the concentration to which a
worker can be exposed for eight hours per day, 40 hours per week and not have any acute or chronic
adverse health effects. Similarly, short-term exposure limits (STELs) are concentrations to which a
worker should not be exposed for longer than 15 minutes or more than four times per day (with at least
one hour between each exposure).  Guidelines on TWA-TLVs and STELs for gases that pose the threat of
acute or chronic health effects in people can be found in Appendix J.

Volatile organic compound (VOC) vapors are a major concern because they can be toxic and
carcinogenic, and may produce acute and chronic health effects after various periods of exposure. Also of
concern are the  hazards associated with toxic gases produced when certain inorganic discharges mix in
the collection system.  For example, acidic discharges can combine with nonvolatile substances such as
sulfide and cyanide to  produce toxic gases and vapors (e.g., hydrogen sulfide and hydrogen cyanide,
respectively), which are hazardous to people. To respond to this threat, POTWs can establish local limits
based on the maximum recommended levels of these POCs in air.  A list of pollutants and the NIOSH,
OSHA, and ACGIH guidelines and exposure levels also can be found in Appendix J.

3.2.8 SCANS OF POTW INFLUENT, EFFLUENT, AND SLUDGE TO IDENTIFY PRIORITY POLLUTANTS

Historical results of priority pollutant scans of POTW influent, effluent, hauled wastewater,  and sludge,
especially those conducted during the previous 12 months, can help identify pollutants discharged to the
POTW; and to determine which are potential POCs.  Priority pollutants5 specified under the  CWA are
listed in Appendix D.  EPA recommends that a POTW also analyze the influent, effluent, and sludge for
other pollutants that might reasonably be expected to be present, based on information about IU
discharges gathered by the POTW from previous sampling and from its industrial waste survey.  The
analytical methods and sampling procedures are  reviewed in Chapter 4.

EPA recommends that the POTW should conduct additional screening for any pollutant found in the
priority pollutant scans of its influent, effluent, or sludge to determine whether the pollutant  should be
listed as a POC. Although a pollutant found in this way is a potential POC, the POTW may  determine,
based on the pollutant's concentration and on other data from lUs and commercial dischargers, that the
pollutant need not be selected as a POC for the full headworks analysis.
         POTWs should be familiar with the chemicals and chemical impurities that are added to treat drinking water and
wastewater or to maintain the collection system. These chemicals may affect the levels of priority pollutants introduced or
pollutant characteristics being measured at the plant.

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3.2.9 EVALUATIONS OF INDUSTRIAL AND COMMERCIAL DISCHARGES

A POTW cannot make informed decisions about potential problem discharges without a comprehensive
understanding of the IU discharges to its collection system.  Whenever possible, EPA encourages the use
of site-specific (actual) data on Ills and commercial discharges for the identification of POCs.  Site-
specific data are particularly important when an individual Ill's discharges make up a large portion of the
POTW's total industrial loading, or when POCs are known to be, or are suspected of being, discharged in
large quantities or concentrations. Monitoring at IU discharge points and at other points in the collection
system may detect discharges that could cause problems in the collection system or at the treatment
works. POTWs may decide that discharges from commercial facilities also should be assessed because
some of these facilities (such as hospitals, dentists' offices, and photo processors) can be significant
sources of pollutant loadings.

In lieu of sampling data, numerous sources of information about Ills, commercial users, and their
discharges are available to POTWs. Collecting and reviewing data from such sources is an important
initial step in identifying POCs. Some of the available sources include the following:

       •   Industrial waste surveys (IWSs)
       •   IU permit applications
       •   The results of IU self-monitoring and POTW compliance monitoring
       •   The results of POTW inspections of lUs
       •   Chambers of Commerce and local trade organizations
       •   General surveillance of the types of facilities in an area
       •   EPA Pretreatment Program guidance manuals (see Appendix A)
       •   Approval Authorities
       •   State pollutant and chemical databases
       •   The Internet and the World Wide Web

Table 3-1 on the following page presents details on some of these potential sources  of information.
                                             3 -7

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              Table 3-1: Selected Information Sources for Determining Potential POCs
Source
Industrial Waste Survey (IWS)
IU Permit Applications
IU Self-Monitoring, POTW
Compliance Monitoring, and
Inspections
EPA Pretreatment Program
Guidance Manuals
Approval Authorities
State Pollutant and Chemical
Databases
Information Provided
POTWs can request in the IWS information that may help identify and assess the pollutants
discharged, or potentially discharged, by each user surveyed. The information gained from
the IWS can help the POTW:
• Identify ILJs of which the POTW had been unaware, orthat have recently moved into the
POTWs service area.
• Identify pollutants likely to be discharged to the collection system that should be
considered potential POCs.
• Identify previously unknown characteristics of an I U and its discharges.
• Evaluate the potential for slug loadings and periods of increased loadings from variable
discharges (e.g., from facilities that experience seasonal fluctuation in their discharges
and from batch dischargers).
• Plan a sampling program to help ensure efficient use of POTW resources.
• Estimate raw waste loadings of pollutants for which analytical methods are unavailable.
• Identify opportunities for pollution prevention.
Most, if not all, POTWs that have approved pretreatment programs will have conducted initial
IWSs. POTWs also may find it helpful to review IWS data in conjunction with pollutant
occurrence data for various industries.
Details of the pollutants likely to be discharged by an IU and received at the POTW. Through
permits or local ordinances, POTWs can require ILJs to provide toxicity data for pollutants
detected in the ILJ's wastewater. IDs can sometimes get such data from the manufacturers of
their raw feedstock, solvents, surfactants, and other chemicals from material safety data
sheets (MSDSs).
Indications of the pollutants discharged, or potentially discharged, by ILJs. Also, confirmation
of information provided by the industrial waste survey and IU permit applications.
Lists of priority pollutants likely to be found in discharges from various industries, lists of
guidance and other manuals, and information on how to obtain copies of the manuals. A list of
pretreatment guidance manuals and information on how to obtain copies is provided in
Appendix A.
Data on pollutants detected in direct dischargers' effluents, which can be reviewed by POTWs
to identify pollutants that may be discharged by similar I Us in their service areas.
Sources of information about industrial effluent*
The North Carolina Department of Resources and Community Development has created databases using reports of POTW
effluent toxicity and the associated discharges of toxics from ILJs, as well as information provided by chemical manufacturers
about the chemical characteristics, such as measured toxicity, of biocidal compounds.
3.2.10 HAULED WASTE

When determining POCs, EPA recommends that POTWs consider the pollutants in, and resultant
pollutant loadings from, any hauled waste that they accept for treatment and disposal.6 Hauled waste has
the potential to cause pass through, interference, or problems in the collection system as well as to
endanger POTW personnel. Although it typically consists of domestic sewage or septage, hauled waste
tends to be more concentrated than typical domestic wastewater and can contain the following:
         The General Pretreatment Regulations cover "pollutants from non-domestic sources covered by Pretreatment
Standards that are indirectly discharged into or transported by truck or rail or otherwise introduced into POTWs" [40 CFR
403. l(b)]. This means that any hauled waste from industries subject to categorical pretreatment standards should comply with
the standards before being accepted for treatment at the POTW. A POTW that has implemented a federally required
pretreatment program should have adequate legal authority to regulate its receipt of all non-domestic waste, including non-
domestic hauled waste.
                                                 3 -8

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       •   Industrial and commercial waste
       •   Grease and sand trap waste
       •   Chemical toilet waste
       •   Hazardous waste
       •   Groundwater remediation site waste
       •   Landfill leachate (see Appendix K for landfill leachate loadings)

An EPA analysis of nine POTWs found that hauled septage may contain relatively high amounts of heavy
metals and organic solvents.7 Many POTWs receive hauled chemical toilet wastes as well as septage.
Chemical toilet waste may contain significant concentrations of paradichlorobenzene (up to 14,000 (ig/L)
as a deodorizing chemical. In March 1995, a truckload of contaminated solvent was discharged to the
Wareham, Massachusetts POTW and resulted in one plant employee suffering from upper respiratory
problems and major treatment plant disruption as half of the digester microorganisms were killed.

Many POTWs accept only domestic wastes from waste haulers and will specify this limitation in their
sewer use ordinances.  If accepting hauled industrial wastes, however, the POTW should ensure that any
potential POCs in these wastes are identified and considered in the local limits evaluation. Additional
information on the acceptance and characterization of hauled wastes at POTWs is available in the
Guidance Manual for the Control of Waste Hauled to Publicly Owned Treatment Works (EPA/833-B98-
003).

The guidance discusses collection of information on waste haulers, characterization of hauled waste
received, evaluation of potential impacts and the development and implementation of controls.  Figure 3-1
on the following page is a flow chart from this manual on characterizing hauled waste. The guidance also
includes case studies of successful waste hauler programs.  POTWs should periodically monitor hauled
wastes to confirm that only appropriate wastes are being brought by waste haulers and to identify any
potential POCs that should be addressed by local limits.

3.2.11 REMEDIATION SITE WASTE

Waste from remediation sites, especially groundwater remediation sites, may be discharged to the
collection system or hauled to POTWs for treatment and disposal.  Site operators should provide the
receiving POTW with information on waste volume, pollutants present, and pollutant concentrations.
POTWs can use such information to identify potential POCs.   Remediation wastes from sites being
cleaned up under the Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA) may include:
           Landfill leachate
           Contaminated groundwater
           Aqueous waste stored in containers
           Wastes from tanks and surface impoundments
           Treatment sludges
           Runoff from contaminated soils
        The monitoring data provided to the nine POTWs by septage haulers are summarized in Appendix L.

                                             3 -9

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Wastes from CERCLA sites commonly contain trichloroethylene, lead, toluene, benzene, polychlorinated
biphenyls, chloroform, tetrachloroethylene, phenol, arsenic, and cadmium.  Although many CERCLA
wastes are quite dilute, some sites have reported high concentrations of metals and organics. EPA
recommends that POTWs considering whether to accept CERCLA clean-up wastes require detailed
analyses and treatability testing before making any decisions. Data from these activities can be used to
determine the presence of POCs. Additional guidance on CERCLA wastes is available from the CERCLA
Site Discharges to POTWs Guidance Manual (EPA 542/6-90-005). POCs identified from the analysis of
remediation waste may include pollutants that require analytical methods not currently listed in 40 CFR
Part 136.

3.2.12 HAZARDOUS WASTES

Wastes identified as hazardous under the Resource Conservation and Recovery Act (RCRA)8 can be
legally introduced to a POTW by being discharged into the collection system through an Ill's normal
sewer connection. RCRA hazardous wastes may be transported to the  POTW by truck, rail, or dedicated
pipeline if the POTW is complying with the RCRA permit-by-rule requirements for treatment, storage,
and disposal facilities found at 40 CFR 270.60. A POTW that accepts  hazardous wastes may need
considerable resources to comply with CWA and RCRA requirements. The responsibility and liability of
POTWs accepting hazardous wastes in this manner are explained in EPA's 1987 document Guidance
Manual for the Identification of Hazardous Wastes Delivered to POTWs by Truck, Rail, or Dedicated
Pipeline. POTWs should note that acceptance of hazardous waste by truck, rail, or dedicated pipe (even
unknowingly) will make them subject to the RCRA permit-by-rule requirements.

When mixed with domestic sewage in a POTWs collection system before reaching the boundary of the
treatment works' property, RCRA hazardous wastes are excluded from regulation under RCRA by the
Domestic Sewage Exclusion, 40 CFR 261.4(a)(l). (They are, however, subject to the CWA, must be
reported to the POTW, and should meet all applicable categorical and local discharge limits.) As part of
their implementation of the industrial pretreatment program, municipal officials should ensure that Ills
control and properly manage their hazardous waste. EPA recommends that the POTW determine which
pollutants are being discharged and should evaluate whether the pollutants ought to be considered POCs.
POCs identified from the analysis of remediation waste may include pollutants that require analytical
methods not currently listed in 40 CFR Part 136.

3.3 APPROVAL AUTHORITY SCREENING PROCESS TO SELECT POLLUTANTS FOR LOCAL LIMITS
SAMPLING PROGRAM AND LIMIT DEVELOPMENT

Before undertaking collection and analysis of sampling data for the development of local limits discussed
in the next chapter, EPA recommends that a POTW conduct a screening to determine which potential
POCs should be included in the full headworks analysis. Some Approval Authorities have guidelines that
POTWs can use in determining POCs. POTWs should contact their Approval Authority for details. With
input from the Approval Authority, a POTW may then complete  POC screening, plan and implement its
local limits sampling program (Chapter 4), and conduct a headworks analysis for each remaining POC on
its list (Chapter 5). Although the screening process can reduce the number of potential POCs subject to
the POTW's more extensive local limits sampling program, EPA recommends in general that local  limits
sampling and headworks analysis be conducted for the following:
         Hazardous wastes are wastes listed as hazardous at 40 CFR 261.31-33, or wastes that exceed specified levels of
ignitability, corrosivity, reactivity, or toxicity as defined at 40 CFR 261.21-24. RCRA also lists hazardous constituents,
chemicals of concerns in listed waste in 40 CFR 261, Appendix VIII.  These constituents are reproduced in Appendix M of this
manual.

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       •   EPA's 15 POCs (see Exhibit 3-1).

       •   Any pollutant for which the POTW has a pre-existing local limit, has an applicable NPDES
           limit, State limit, or sludge disposal limit, or has caused inhibition or other problems in the
           past.

3.4 SUMMARY

After reviewing Chapter 3, POTWs should be able to determine POCs. As explained above, pollutants
should be designated POCs if they:

       •   Are on EPA's list of 15 pollutants that a POTW should assume to be of concern.

       •   Have a pre-existing local limit.

       •   Are limited by a permit or applicable environmental criteria.

       •   Have caused operational problems  in the past.

       •   Have important implications for the protection of the treatment works, collection system, or
           the health and safety of POTW workers.
EPA recommends that a POTW check with their Approval Authority for methodologies to screen out
certain POCs, before expending resources on local limits sampling discussed in Chapter 4.
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CHAPTER 4 -
DATA NEEDED TO DEVELOP LOCAL LIMITS
Developing maximum allowable headworks loadings (MAHLs), maximum allowable industrial loadings
(MAILs), and local limits requires various types of data. Some of the data come from dischargers to the
POTW, some come from the operation of the POTW itself, and some come from characterizations of the
conditions in the POTW's receiving water. Data such as flows can be measured directly, but other data
are acquired by taking samples from the POTW's wastestream and analyzing them to determine which
pollutants are present. Accurate and defensible local limits cannot be developed without the collection of
site-specific data on pollutant loadings at the POTW and on the POTW's removal of those pollutants.
Collecting those data requires a systematic effort. Chapter 4 discusses the types of data that are required
and the methods to obtain them.  It is recommended that POTWs seek input from their Approval
Authority on their sampling plans.

POTWs already conduct some sampling because the majority of NPDES permits require that POTW
effluent be monitored for constituents such as biochemical oxygen demand (BOD), fecal coliform
bacteria, total suspended solids (TSS), residual chlorine, and pH. In addition, many POTW NPDES
permits place limits on nitrogen, phosphorus, and trace metals. Because this monitoring is unlikely to
provide all of the data needed for a meaningful local limits calculation,  EPA recommends that POTWs
that have approved pretreatment programs routinely sample at other sites within the treatment works, both
for local limits development and to remain up to date on their loadings of each pollutant.

The sampling and analysis that support the determination of MAHLs and MAILs are used to:

       •   Identify or confirm the presence of individual pollutants
       •   Determine pollutants of concern (POCs)
       •   Determine current POTW pollutant loadings
       •   Calculate pollutant-removal efficiencies
       •   Determine site-specific inhibition thresholds
       •   Estimate loadings from industrial users (IDs), domestic, and other sources

The sampling and flow data needed to calculate local limits are as follows:

       •   Pollutant concentration data from POTW (influent, effluent, primary effluent, sludge),
          collection system, receiving stream, and Ills.

       •   Flow data, such as total POTW flow, POTW sludge flow to the digester, POTW sludge flow
          to disposal, IU flows, receiving stream, hauled waste, domestic flows, and commercial flows.
If the POTW conducts influent, effluent, and sludge sampling as part of its pretreatment program, the data
may be used in subsequent local limits reviews and headworks analyses. EPA recommends that POTWs
collect sampling and flow data from the sources noted above to develop a mass balance of pollutant
loadings to and pollutant releases from the wastewater treatment plant.  If based on accurate monitoring
data, the mass loadings can be used to verify measured background loadings (see Section 6.2.1).
                                          4- 1

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4.1 SAMPLING LOCATIONS

In EPA's view, POTWs will want to establish sampling locations within both the treatment works and the
collection system. EPA provides guidance on suggested sampling locations, as detailed below.

4.1.1 ATTHEPOTW

Most samples in support of local limits development are taken inside the POTWto determine removal
rates and the amount of pollutants in sludge. Therefore, at a minimum, EPA recommends that a POTW
establish one point to sample influent, one point to sample effluent, and one point to sample sludge.

       •   POTW Influent. EPA recommends that samples be taken at the POTW's headworks to
           determine the average and maximum levels at which POCs enter the treatment plant. Influent
           sampling provides data to be used in calculating POTW-specific removal efficiencies and in
           establishing the level at which the plant is loaded relative to the MAHL. The sample should
           be drawn from  a location that permits the collection of raw wastewater before it is mixed with
           any wastestreams returned to the headworks from operations within the POTW.

       •   POTW Effluent. Sampling the treatment works' effluent is essential to determining the
           POTW's overall removal efficiency. Samples taken to demonstrate compliance with the
           POTW's NPDES permit can be used for this purpose. In addition, the sampling location used
           for NPDES compliance can also be used to  draw  samples for POCs that do not have NPDES
           permit limits or NPDES monitoring requirements.

       •   POTW Sludge. EPA's sludge disposal regulations require that sludge be sampled at the time
           of its disposal and after addition of conditioners to determine the percentage of solids it
           contains. For those POTWs that use land application for sludge disposal, EPA recommends
           that they also sample periodically for other  pollutants. The frequency of sampling depends
           on the amount of sludge generated annually. Sludge samples taken to support compliance
           with the sludge disposal regulations found at 40 CFR 503 can also be used to calculate local
           limits.

       •   Other Suggested Sites. EPA encourages POTWs to develop site-specific data for the
           development of local limits.  In particular, site-specific data on pollutant concentrations in
           various unit processes is valuable for developing  site-specific inhibition values. For example,
           a POTW that digests its sludge, either aerobically or anaerobically, should sample the
           digester contents to determine the levels of  pollutants, primarily metals,  that are known to
           cause digester upset. As discussed in the next chapter, one requirement of a local limit is to
           guard against plant upset, including digester inhibition. Little information on digester
           inhibition is available in the literature and site-specific inhibition is difficult to measure.
           Consequently, site-specific information on pollutant concentrations that did not cause
           digester inhibition are sometimes used to estimate allowable loadings of pollutants to the
           digester. Similar data on the level of pollutants that did not cause inhibition should be
           collected on influent to secondary and tertiary biological treatment processes.
                                             4-2

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4.1.2 IN THE COLLECTION SYSTEM

Knowing the relative contributions of uncontrolled sources (domestic users, inflow and infiltration (I&I),
treatment chemicals added to sewers, drinking water, storm water, and some or all of a POTW's
commercial dischargers) is important in determining the amount of loading to be allocated to Ills.
Uncontrolled sources can contribute significant loadings of pollutants and can therefore have a profound
effect on the amount of pollutants available for Ills. However, wastestreams from uncontrolled sources
are assumed to contain lower pollutant concentrations than wastestreams from Ills. The pretreatment
regulations do not regulate domestic sources. POTWs may choose not to monitor or control commercial
sources, either because of the lower concentrations or because too many sources make regulation
impractical.

In order to measure pollutant loadings from uncontrolled sources, EPA recommends that a POTW take
samples from a point within the collection system that isolates these sources. EPA recommends that
POTWs designate representative sampling locations within their collection systems based on the
following considerations:

        •   The size of the service area or collection system.

        •   The variability of pollutant concentrations and loadings from one sector of the collection
           system to another. (For example, newer areas of a collection system may have higher
           concentrations of copper, while older areas may have higher concentrations of zinc or lead.)

        •   Whether a sewer section is  separate or combined or subject to excessive I&I.

        •   Types of commercial establishments represented.

        •   Whether more than one drinking water system operates within the POTW's service area.
           (Different water systems may have different water sources, or may add different chemicals to
           treat the water or to control corrosion.)

Under most circumstances, a POTW with a small service area will need to establish at least two sampling
points within its collection system. More sampling locations may be needed in areas likely to have
different pollutant concentrations based on the factors cited above. POTWs should remember that lower
loadings from uncontrolled sources give greater flexibility in determining how much of a given pollutant
will be available for lUs through the MAIL.  Consequently, EPA recommends more extensive sampling
in areas of the collection system where uncontrolled loadings appear to consume all of the calculated
MAHLs. Other tips for sampling include the following:

        •   POTWs should take care not to sample during or after periods of heavy rainfall when I&I is
           also high. Flows at these times will be diluted, and will not be representative of typical
           residential and commercial flows. I&I sometimes contributes to pollutant loadings—for
           example, in areas where mining once occurred and heavy rains wash pollutants from slag
           piles into collection systems.  Such instances should be dealt with on a case-by-case and
           pollutant-by-pollutant basis through the POTW's Approval Authority.
                                             4-3

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       •   Although characterizing domestic and commercial loadings separately may appear to be
           useful, the loadings can be combined to determine the loadings from the aggregate of
           uncontrolled sources, particularly if cost is a consideration. Only if a POTW intends to
           regulate commercial sources separately would background levels need to be determined for
           both domestic and commercial sources.

       •   The results of POTW influent sampling can serve as a check on the sampling points selected
           by the POTW to determine uncontrolled loadings. If the POTW's headworks levels are
           consistently lower than the levels from the residential and commercial source sampling
           points, then the sampling points do not accurately represent the background levels, or an
           inordinate amount of I&I may be present.

4.1.3 AT INDUSTRIAL USERS

Sampling at Ills is helpful if a POTW wants to set local limits based on IU need through one of the
various allocation methods available to the treatment works (see Section 6.3). In order to use one of these
methods, the POTW should know the mass of each POC discharged by each IU so it can rank the users by
size and,  therefore, by need.  For these cases, flows should be measured at, and samples taken from, each
IU. These data are probably available from the POTW's routine compliance monitoring and the IUs'
self-sampling programs. Therefore, if the POTW has already collected such data, there probably is no
need to make a special effort during local limits development unless a new POC has been identified.

Concentration and mass loading data from each IU also can be used to assess the impact a MAIL will
have on the POTW's industrial base. This assessment will help the  POTW to determine how the local
limit should be allocated among IUs. Moreover, knowing each facility's level of discharge tells  the
POTW which facilities will have difficulty meeting any new limits.

4.2 POLLUTANTS FOR WHICH POTWs SHOULD SAMPLE

In general, a POTW should sample for all the pollutants to be included in the calculation of MAHLs and
the possible development of local limits, including the following:

       •   The 15 national POCs
           -  Arsenic
           -  Cadmium
           -  Chromium
           -  Copper
           -  Cyanide
           -  Lead
           -  Mercury
           -  Molybdenum
           -  Nickel
           -  Selenium
           -  Silver
           -  Zinc
           -  5-day Biochemical Oxygen Demand
           -  Total Suspended Solids
           -  Ammonia
                                            4-4

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        •   Any POTW-specific POCs

        •   Clean Water Act (CWA) organic priority pollutants

        •   TCLP pollutants (if the POTW disposes, or is likely to dispose, of its sludge in landfills)

4.3 SAMPLING FREQUENCIES

 Local limits usually are scrutinized during their initial development, reviews, NPDES permit renewals,
and when detailed re-evaluations are conducted.  Conducted over different time periods, these efforts
often have different data requirements and consequently, results.  The initial development of local limits,
for example, may require rapid data collection and analysis to meet the schedule for developing a
Pretreatment Program submission, of which local limits evaluation is a part. In contrast, reviews and
detailed re-evaluations should be based on data collected as part of a routine, long-term sampling effort.
Detailed below are suggested sampling frequencies for initial program development and ongoing
evaluation. The reader should note that these minimum sampling frequencies are recommendations.  The
POTW has flexibility to adjust their sampling frequencies based on local concerns and economics. In
addition, EPA has provided guidance on establishing a sampling frequency through statistical means1 in
Appendix N.

4.3.1 SAMPLING FREQUENCIES FOR INITIAL PROGRAM DEVELOPMENT

To support the initial development of local limits, samples should be collected to provide the data
necessary to identify POCs, determine MAHLs, calculate MAILs, and implement local limits. Although
such sampling frequently occurs during a short period, the sampling program should account for the day-
to-day variability at a POTW and for all the pollutants known or suspected to be present in the POTW's
influent. Table 4-1 presents the sampling frequencies for influent, effluent, and sludge, as well as
suggested sampling frequencies for domestic and commercial dischargers.  The limited number of
sampling events may not generate enough data to calculate the POTW's efficiency at removing every
pollutant in its influent. In such cases, some Approval Authorities may allow—or even require—the use
of literature values if they believe a POTW's sampling provides less accurate information.
         The use of statistical analyses can help establish an acceptable minimum number of samples needed to adequately
represent a population of pollutants in the influent and effluent at an acceptable confidence level. Appendix N provides guidance
on the number of samples needed to estimate the true sampling mean based on confidence level, relative error, and variation of
the data. Depending on the desired confidence level and relative error, the number of samples needed can be cost-prohibitive.
For example, to be 90 percent confident that your sampling mean lies within +/- 10 percent of the true mean, the number of
samples needed is 68 (when the sample set has a coefficient of variation of 0.5). A program of continual sampling could ensure
that sufficient data are available and distribute the costs of sampling over time.

                                               4-5

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      Table 4-1: Minimum Recommended Sampling Days* for Initial Local Limits Development
Parameter
Organic Priority Pollutants (1)
National POCs (2)
POTW-specific POCs (2)
Percent solids, sludge (3)
TCLP pollutants (4)
POTW
Influent
(days to
sample)
1 -2
7-14
7-14


Effluent
(days to sample
1 -2
7-14
7- 14


Sludge
(days to
sample)
1
2
2
2
1
Residential/
Commercial
Collection
System
(days to sample)
1 -2
7
7


'Sampling days are defined as the number of days that samples are collected for a parameter. Sampling days should be
consecutive days for National POCs and POTW-specific POCs. Samples should be 24-hour composite samples unless sampling
methods only allow for grab samples (see Section 4.5).
(1) Conducted once or twice to determine potential POCs.
(2) The range of values for sampling days (7-1 4) for influent and effluent sampling of POCs is a minimum recommended range for
the number of days to sample. POTWs that are small [up to 5 million gallons per day (MGD)] should have at least 7 consecutive
sampling days for POCs while larger POTWs (5-1 0 MGD) should have at least 1 4 consecutive sampling days. POTWs larger
than 10 MGD should consider more sampling according to local concerns and economics. POTWs should seek input from the
Approval Authority for their sampling plan.
(3) The sludge regulations at 40 CFR Part 503 already require the percentage of solids to be determined every day that sludge is
applied to land.
(4) Sample for TCLP pollutants if sludge is disposed, or is likely to be disposed, in a landfill.
4.3.2 SAMPLING FREQUENCIES FOR ONGOING EVALUATION

The sampling frequencies presented in Table 4-2, based on POTW flow, should be used for ongoing
evaluations.  The importance of sampling POTW influent should not be overlooked. Not only is this
sampling essential for calculating POTW removal efficiency, it also enables the POTW to calculate the
headworks loading of each pollutant and compare it to the MAHL, thus indicating the degree to which the
treatment works is loaded. The data from headworks sampling also are used to determine when a local
limit must be adopted. If cost becomes a constraint, EPA recommends that sampling to calculate removal
rates focus on removal throughout the treatment works and that literature values be used for intermediate
process removal rates.
                                           4-6

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             Table 4-2: Minimum Recommended Sampling Frequencies for Ongoing
                              Local Limits Analysis and Evaluation
Parameter
Pollutants for which local limits were
adopted
Pollutants for which MAHLs were
calculated, but for which no local limits
were adopted
Organic Priority Pollutants
TCLP Pollutants (1), sludge
Sludge percent solids and specific
gravity (2)
Location
Influent,
Effluent,
Sludge
Influent,
Effluent,
Sludge
Influent
Sludge
Sludge
Less than
5MGD
Once every 3
months
Once every
12 months
Once per
year
Once per
year
Once every 6
months
5-10
MGD
Once every 3
months
Once every 6
months
Once per
year
Once per
year
Once every 4
months
10-50
MGD
Once every 3
months
Once every 6
months
Once per
year
Once per
year
Once every 3
months
Greater
than 50
MGD
Once every 2
months
Once every 3
months
Once every 6
months
Once per
year
Once every 2
months
(1) Conducted if sludge is (or is likely to be) disposed of in a landfill.
(2) The sludge regulations at 40 CFR Part 503 already require the percentage of solids to be determined every
day that sludge is applied to land.
4.4 OTHER SAMPLING TIPS

Local limits sampling should attempt to depict the POTW under typical operating conditions.  Therefore,
the sampling program should not bias the results by using sampling procedures that ignore the day-to-day
and seasonal variability that the POTW expects to encounter. To ensure that sampling data are
representative of the variety of conditions, EPA recommends that the POTW consider the following
points when setting its sampling schedule:

       •   Sampling should be conducted randomly and should be representative of the different days,
           months, and conditions throughout the year. If a POTW establishes a rigid sampling
           schedule (for example, the first Wednesday of each month), it may bias the local limits
           development process.

       •   If infrequent, yet routine, activities are conducted within the POTW, its collection system, or
           at its Ills, the sampling schedule established by the POTW should collect data representative
           of these events. Such activities should be represented in the sampling at  approximately the
           frequency at which they occur. Sampling documentation should note if any activity of this
           type occurred during the sampling period. Examples of infrequent, yet routine, activities
           include receipt of hauled waste, tank cleaning, or other maintenance activities that might
           affect wastewater characteristics.
                                             4-7

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       •   Ideally, POTW sampling should account for hydraulic retention times between the influent
           and effluent sampling points.  If unlagged historical data show wastestream loadings do not
           vary by more than 10 percent and POTW removal efficiencies remain relatively constant,
           delayed sampling based on hydraulic retention time may not be critical. However, because
           the retention time for sludge will likely be greater than the period when local limits
           monitoring occurs and because of the nature of the sludge sampling procedure itself, neither
           more frequent sludge sampling nor lagging  samples for sludge retention times is warranted.

       •   The sampling schedule should ensure the collection of samples that are representative of the
           weather conditions that affect POTW operations (i.e., wet weather; hot or cold ambient
           temperatures).

4.5 SAMPLING METHODS

The purpose of any sampling is to accurately quantify the contents of the wastestream being sampled.
Samples of wastewater typically are one of three types:  flow-proportioned composites, time composites,
or grab samples.  Each type has its use in the local limits development process, but the 24-hour, flow-
proportioned composite samples are the most accurate for this purpose.  This sampling technique should
be used whenever feasible for all pollutants except those that require grab  samples.

A flow-proportioned sample, sometimes called a flow-weighted sample,  is one in which a set aliquot of
the wastestream is taken after the passage of a set amount of wastewater. Samples are commonly taken
by an automatic sampler connected to a device that measures flow. For example, a 500 milliliter (mL)
sample may be taken from the wastestream every time 1,000 gallons has been discharged. The sample
volumes and flow intervals are usually determined by the capacity of the sampler and the expected total
flow of the source.

Time-composite samples consist of equal-volume aliquots taken at regular intervals throughout the
sampling period. Because the volume of discharge can vary between the times aliquots are drawn, time-
composite samples are not considered to be as accurate as flow-proportioned samples.  However, the
accuracy of the time-composite samples approaches that of the flow-proportioned samples as the
wastestream's flow rate becomes increasingly uniform.  Time-composite samples can be used to
accurately profile pollutants for local limits development, but the statistical variability of their data will be
greater than that of flow-proportioned samples.  Consequently, more time-composite samples will be
required to support a given confidence interval. EPA generally recommends using flow-proportioned
samples instead of time-composite samples.
                                             4-8

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Grab samples are individual aliquots collected at intervals of at least 15 minutes without regard to flow
rate. They normally are drawn manually, rather than by automatic equipment.  During the local limits
development process, grab samples should be avoided for most pollutants, except for the following:

       •   pH
       •   Cyanide
       •   VOCs
       •   Total phenols
       •   Oil and grease
       •   Total petroleum hydrocarbons
       •   Sulfide
       •   Flashpoint
       •   Temperature

When grab samples are required, at least four should be collected, although more than 12 grab samples
are desirable.  If enough grab samples are taken over the sampling period, they may be combined to create
a grab composite sample.  The aliquots must be collected in separate containers, preserved appropriately,
and either composited manually at the laboratory to create a single sample for analysis, or analyzed
separately and the results averaged into a single value. If the interval wastestream flow between each
grab sample is known, a flow-proportioned grab composite sample may be prepared (see Table 4-3). As
an alternative, the grab samples may be analyzed separately and the results averaged according to flow
weight (see Table 4-4).  Samples to be analyzed for pH should not be manually composited, however, and
the results for pH should not be averaged.

Sludge samples require that a composite sample be taken of the sludge mass.  To do that, a POTW
should use the sampling technique specified for demonstrating compliance with the sludge regulations
found at 40 CFR 503. Specifically, several aliquots are taken from randomly selected locations within the
sludge mass and the aliquots are composited to form a single sample for analysis. As with other types of
composite sampling, the more aliquots taken, the more accurate the determination of pollutant levels.
Additional discussion of this sampling method can be found in Environmental Regulations and
Technology: Control of Pathogens and Vector Attraction in Sewage Sludge, 1999 Edition (EPA/625-R-
92-013), POTW Sludge Sampling and Analysis Guidance Document (EPA/833-B-89-100), and A Plain
English Guide to the EPA Part 503 Biosolids Rule (EPA/832-R-93-003).
                                             4-9

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             Table 4-3: How to Prepare a Flow-Proportioned Grab Composite Sample
Sample

1
2
3
4
5
Sample Collection/Meter
Read Date and Time
08/16/99ฎ 01:1 2
08/16/99ฎ 06:00
08/16/99ฎ 10:48
08/16/99ฎ 15:36
08/1 6/99ฎ 20:34
08/1 7/99ฎ 01:1 2
Meter Reading
in million
gallons(MG)
6,306.5
6,307.5
6,309.2
6,312.0
6,313.5
6,314.3
Total Flow (TF)
Interval Flow
(IF) Volume
(MG)
-
1.0
1.7
2.8
1.5
0.8
7.8
Flow-Proportioned
Composite
(IF/TFMOOOmL)

128 ml
21 8 ml
359 ml
192 ml
103 ml

Note: This example assumes that a 1 -liter (1 ,000-mL) composite sample is prepared. If a different composite volume is used,
calculate the flow proportioned composite (the individual grab sample volume to be included in the grab composite) using that
volume.
                       Table 4-4: Example of a Flow-Proportioned Average
                       Based on Grab Sample Results and Flow Intervals
Sample
1
2
3
4
5
Sample Collection
Date and Time
08/1 6/99ฎ 06:00
08/16/99ฎ 10:48
08/1 6/99ฎ 15:36
08/1 6/99ฎ 20:34
08/1 7/99ฎ 01:1 2

Total Cyanide
(TC) (ug/L)
49
120
110
97
20
Average: 79
Interval Flow
(IF) Volume
(MG)
1.0
1.7
2.8
1.5
0.8
Total Flow (TF):
7.8
Flow-Proportioned
Average
(IF/TF * TC)
6 ug/L
26 ug/L
39 ug/L
19 ug/L
2 ug/L
Flow-weighted Average: 92 ug/L
4.6 ANALYTICAL METHODS

NPDES and pretreatment regulations require that all wastewater samples be analyzed for the presence of
pollutants using the approved methods found at 40 CFR Part 136. EPA recommends that these analytical
methods also be used in the development of local limits. When sampling sludge for metals and total
solids, however, the requirements in the sludge regulations in 40 CFR Part 503 still apply.2
        The analysis of sludge for the presence of metals should be performed according to EPA test method SW-846 and for
total solids according to Part 2540 G of the Standard Methods for the Examination of Water and Wastewater, 18th Edition.
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A principal reason for using the Part 136 methods is to allow the comparison of local limits and
categorical limits to determine which are more stringent, as required by the General Pretreatment
Regulations. However, a POTW may encounter a POC that is not regulated by the categorical standards
or for which no sampling and analytical techniques are listed in Part 136. In such cases, when the POTW
adopts the local limit, it would also specify the sampling and analytical technique used for measurement.
Prior approval, however, must be obtained from the Approval Authority through the provisions of the
General Pretreatment Regulations at 40 CFR 403.12(g)(4).

To ensure that samples are analyzed properly, EPA recommends that a POTW consider the following
factors:

        •   Anticipated pollutant concentration.

        •   Potential interferences.

        •   Total vs. a fraction thereof (e.g., total vs. dissolved metals, or total vs. amenable cyanide3).

        •   The minimum detection level  (MDL) of the analytical method to detect the presence of
           pollutants in trace amounts and the corresponding minimum level (ML)  of quantitation
           (generally 3.18 times the MDL) to determine removal efficiencies.

When selecting methods, POTWs likely will balance these considerations with the cost of the analyses.
However, costs should not influence the selection of methods to the extent that necessary detectable levels
are not achieved.  A data set that has a significant number of non-detectable results will provide limited
information for use in local limits development and may compromise the validity of the local limits.  If
that were to occur, the reduced costs would actually be a waste of money. POTWs should use approved
methods with the lowest detection levels to ensure the local limits calculation is robust and defensible. If
some of the analytical results are reported  as below the MDL, it may be due to the POTW's sampling
techniques or the analytical methods that were selected.  Given the need to accurately detect trace levels
of pollutants, POTWs should thoroughly examine potential sources of gross and trace contamination, then
select analytical methods that can detect very low levels  of pollutants. (See Appendix O on Minimizing
Contamination in Samples.)

Table 4-5 presents MDLs for different EPA wastewater analytical methods for metals. The table includes
some methods - inductively coupled plasma (ICP), flame atomic  absorption, and graphite furnace atomic
absorption - listed in 40  CFR Part 136. The table also includes the  1600 series with detection limits  in
the nanogram per liter range for metals. Of the 1600  series, only  Method 1631 for mercury is listed in 40
CFR Part 136. Although these methods were developed for ambient water quality monitoring,4 they  can
improve the reliability of the data collected.  EPA recommends POTWs check with their Approval
Authority before adopting the 1600 series  methods for wastewater analysis per 40 CFR 403.12(g)(4).

Also listed in 40 CFR Part 136, Method 1664 has been developed for oil and grease  and is actually two
methods. One is the n-hexane extractable  materials (HEM) method and the other is the silica gel treated
HEM(SGT-HEM). HEM measures all oils and greases while SGT-HEM is specific to mineral oils (non-
       Amenable cyanide refers to those metallic, cyanide-bearing compounds that are "amenable" to alkaline chlorination or
electrochemical chlorination treatment processes that will reduce the cyanide complexes to non-toxic chlorides, carbonates and
hydroxides.

       4 See EPA Methods and Guidance for Analysis of Water, Version 2, EPA 821 -C-99-004, June 1999.

                                             4- 11

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                  Table 4-5: MDLs (H9/L) for EPA Wastewater Analytical Methods

Metal
(Total)
Arsenic
Cadmium
Chromium
Copper
Cyanide
Lead
Mercury
Molybdenum
Nickel
Selenium
Silver
Zinc
Method Listed in 40 CFR Part 136
Flame/
Other
2*
(206.3)
5
(213.1)
50
(218.1)
20
(220.1)
5**
(335.3)
100
(239.1)
0.2t
(245.1)
100
(246.1)
40
(249.1)
2*
(270.3)
10
(272.1)
5
(289.1)
Furnace
1
(206.2)
0.1
(213.2)
1
(218.2)
1
(220.2)

1
(239.2)

1
(246.2)
1
(249.2)
2
(270.2)
0.2
(272.2)
0.05
(289.2)
ICP
(200.7)
8
1
4
3

10

4
5
20
2
2
(1631)






0.0002





Method Not Listed in 40 CFR Part 136
(1632)
0.003











(1637)

0.0075



0.036






(1638)

0.013

0.087

0.015


0.33
0.45
0.029
0.14
(1639)

0.023






0.65
0.83

0.14
(1640)

0.0024

0.024

0.0081


0.029



* Gaseous Hydride Method
t Cold vapor technique
"Manual Distillation
ICP - Inductively Coupled Plasma
Flame/Other = Flame Atomic Absorption unless otherwise indicated
Furnace - Graphite Furnace Atomic Absorption
(numbers in parentheses) = EPA-approved analytical methods
Sources: 40 CFR 136. 3 Table 1B and Method 1669, "Sampling Ambient Water for Determination of Metals at EPA
Water Quality Criteria Levels," EPA, July 1996 (which included information about MDLs for 1600 series).
polar) and is considered a substitute for the total petroleum hydrocarbon (TPH) analysis. It should be
noted that compounds other than TPH are extracted by n-hexane and this can lead to test results higher
than actual TPH values.  Laundry detergents and surfactants contribute to the interference.  This is a
potential source of interference when samples are collected. For additional information on sample
collection, preservation, documentation and analysis, see Industrial User Inspection and Sampling
Manual for POTWs, EPA Office of Water, EPA 831-B-94-001.
                                             4- 12

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4.7 INFORMATION COLLECTION AND MAINTENANCE

To document that sampling was conducted properly, EPA recommends POTWs use field measurement
records and chain-of-custody records. The latter are used to identify the person(s) who collected a sample
and the persons who may have handled the sample before it was received by the laboratory. They also
may be used for inter-laboratory transfers of samples.  Chain-of-custody records often contain such
information as the type of sample collected, the date(s) and time(s) of the collection, any chemical
preservatives added, type of sample container used (i.e., glass, amber glass, or polyethylene), and sample
temperature. These records also may include the weather conditions and ambient temperature when the
sample was taken, the color and odor of the sample, or other pertinent sampling information.

Laboratory reports not only give POTWs data to use in developing local limits, they also provide data to
verify that the holding times were met and the appropriate analytical methods were used. In addition to
the analytical results, reports should contain the unique sample ID assigned by the laboratory, the date
and time of the sample preparation  and analysis, the preparation and analytical methods used, the identity
of the analysts, and quality control  data if problems were encountered (including an explanation of the
problems and how they were addressed).  The POTW will want to maintain these records for as long as
the data they contain are  used to support the local limits developed by the treatment works.

4.8 REVIEW AND EVALUATION OF ANALYTICAL RESULTS

To develop sound, technically based local limits, the POTW should, out of necessity, review and evaluate
the data collected to ensure they are accurate, reliable, and representative.  Only data that meet the
POTW's quality  assurance/quality  control (QA/QC) requirements should be used to support the
development of local limits.  The EPA guidance document, Procuring Analytical Services:  Guidance for
Industrial Pretreatment Programs,  October, 1998 (EPA 833/B-98-004) provides pretreatment authorities
and Ills with guidance for procuring analytical services necessary to support CWA programs. (The
document is available at the  "publications" link at http://www.epa.gov/npdes.)

Sampling data evaluations may reveal improperly collected data, elevated detection limits, and new
POCs. Improperly collected data may mean a sample was taken from the wrong location, was collected
as a grab sample  instead  of a composite,  or was improperly handled (i.e., the wrong container was used or
the required chemical preservative  was not added). In response to improperly collected data, the POTWs
will want to educate the responsible person on data collection requirements and ask for additional samples
to replace the rejected data.

Measurements below the MDL are  fairly common in sampling for local limits development (such as
during a scan of organic priority pollutants).  However, if an elevated number of non-detects is reported,
EPA recommends that the POTW:

        •   Verify that the method detection limit of the analytical method can address compliance with
           applicable criteria.  If necessary, sampling and analysis should be performed at a lower MDL.

        •   Evaluate possible matrix interferences, other analytical methods, or sampling problems if an
           elevated number of non-detects are reported unexpectedly.
                                            4- 13

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New POCs may be identified by a POTW's sampling of influent, sludge, controlled or uncontrolled
sources. Additionally, a Toxicity Reduction Evaluation (TRE), or a change in applicable standards could
identify new POCs. A vigilant POTW may be able to identify changes in loadings quickly and add the
new POCs to its ongoing regimen of evaluation sampling. New POCs identified as a result of a TRE or a
change in standards may require multiple samples collected over a short period of time, in addition to
being added to the POTW's ongoing sampling program.

4.9 FLOW DATA

To calculate  MAHLs and MAILs,  data about the flow of various wastestreams will need to be collected
so that mass quantities can be computed. The flows for which data are needed are described in the
following sections.

4.9.1  TOTAL POTW FLOW

POTWs routinely measure the total flow into the treatment works.  The measurement of total flow
encompasses all sources, including industrial, domestic, commercial, and I&I. Any hauled wastes treated
by the POTW also may be measured at the headworks, depending on where the hauled wastes are
introduced to the treatment system. Total  POTW flow is needed for the calculation of effluent-quality
based allowable headworks loadings (AHLs) (see Section 5.2.2) and inhibition-based AHLs (see Section
5.2.4).

In EPA's view, the POTW will not want to use design flow to calculate local limits because the purpose
of a local limit is to protect the treatment works and the environment under existing conditions. If the
design flow were used and the actual influent flow is significantly less, a mass limit would exaggerate the
domestic and background loadings of pollutants to the POTW and possibly restrict unnecessarily the
pollutant load given to Ills.

4.9.2  SLUDGE FLOW TO THE DIGESTER

Primary and  secondary sludge sent to an aerobic or anaerobic digester will contain sorbed pollutants
whose mass a POTW will want to  determine. The flow and concentration values of sludge will be used to
calculate an AHL to prevent digester inhibition (see Section 5.2.4). Consequently, the average daily flow
rate of all sludge flows to digestion will need to be known.

4.9.3  SLUDGE FLOW TO DISPOSAL

Because one of the most significant environmental impacts an IU discharge can have is on POTW sludge
quality and its reuse as a resource, the mass of pollutants in sludge applied to the surface of the land or
disposed of in landfills will need to be known.  Most POTWs do not dispose of sludge every day because
weather conditions, among other factors, interfere with scheduling. To simplify the calculations, EPA
recommends that the flow of sludge to disposal be reported as an average over the entire year. This value
is calculated by dividing the total volume of sludge disposed in million of gallons by 365 to yield the
average volume of sludge disposed in millions of gallons per day.  The sludge flow along with the
pollutant concentration in sludge are used  to calculate an AHL to prevent sludge concentrations from
exceeding the sludge disposal pollutant concentration criteria (see Sections 5.2.3).
                                            4- 14

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4.9.4  FLOWS FROM CONTROLLED SOURCES

Converting MAHLs to MAILs requires knowing the flows from all controlled sources (IDs, hauled waste,
or specific commercial users) that the POTW intends to regulate with numerical local limits. Some
commercial sites (such as photo finishers) may discharge pollutants in quantities that can be controlled by
local limits. Discharges from waste haulers may be regulated by POTWs and thus considered controlled
sources. Flow rates are commonly determined by compiling flow data from water use records, IU
inspections, and periodic reporting from controlled sources.  Controlled source flow rates are used to
allocate MAILs among controlled sources.

Hauled wastes that are a significant source of pollutant loadings should be controlled through local limits.
Therefore, EPA recommends that the average daily volumes of hauled wastes accepted by the POTW be
included in the measurement of total industrial flows.  While hauled wastes commonly contain high
concentrations of pollutants, the wastes generally are low in mass.  Thus, for a POTW to determine the
additional loading contributed by hauled wastes, the POTW will need extensive sampling of the wastes.
Mass  loadings can then be calculated and factored into the  local limits calculations.

POTWs usually use the sum of all Ills' total plant wastewater flow to develop local limits. Thus, the local
limits apply "at the curb," where  the flow leaves an Ill's property.  However, this may pose some
problems for categorical industrial users (CIUs) because categorical standards always apply at the end of
the regulated process. Each POTW will need to carefully examine flow data from its Ills to assure that all
wastewater to be regulated by the local  limits is being properly quantified. Analysis results and flow data
used to evaluate compliance with categorical pretreatment  standards may not include all wastewater from
the industry. Ideally, categorical standards are applied at the end of the regulated processes after
pretreatment. Other wastestreams not subject to categorical standards, but subject to local limits, may be
discharged  downstream of the categorically regulated process wastewater flow.

Therefore, there may be more than one  sampling location established within a CIU to evaluate
compliance with  local limits and categorical pretreatment standards.  Non-categorically regulated
wastestreams often are discharged before treatment at an IU and upstream of the sampling point. The
combined wastestream formula (CWF)  is used to adjust the CIU standards. Flow and pollutant
concentration data that represent total plant wastewater from an IU should be used to develop local limits.
This may require that the developer of local limits become  more familiar with all sampling points, sewer
outfalls, and the wastewater characteristics at each IU, especially CIUs.  Detailed discussions on how to
establish effluent limits for categorical industries that do not segregate regulated wastestreams from
non-regulated or dilute wastestreams are provided in the Guidance Manual for the Use of
Production-Based Pretreatment Standards and the Combined Wastestream Formula (EPA 833-B-85-201,
September  1985) and in the Industrial User Permitting Guidance Manual (EPA 833-B-89-001,
September  1989).
                                             4- 15

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4.9.5  FLOWS FROM UNCONTROLLED SOURCES

Converting MAHLs to MAILs also requires knowing the flows of sources that the POTW does not
control, such as domestic sources, some commercial sites,5 infiltration and inflow, storm water, waste
haulers not regulated by local limits, and others. As discussed in Section 4.1.2 and 6.2.1, sampling points
to determine uncontrolled source flows must be within sections of the collection system that receive
wastewater only from these sources.

4.10 SUMMARY

After reviewing Chapter 4, POTWs should be able to support the determination of MAHLs through the
collection of various types of data. The applicability and accuracy of the collected data requires an
understanding of how pollutant types, sampling locations and frequencies, analytical methods, quality
assurance and quality control (QA/QC) requirements, and information collection and maintenance
procedures will affect the overall evaluation process. Chapter 5 describes how to use this information to
develop MAHLs.
         These refer to commercial sources with low pollutant discharges or with too many sites to make regulation practical.

                                             4- 16

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CHAPTER 5 -
CALCULATION OF MAXIMUM ALLOWABLE
HEADWORKS LOADINGS
Following the approach suggested by EPA, the POTW will have determined pollutants of concern
(Chapter 3) and analyzed and collected sufficient data to develop local limits (Chapter 4). This chapter
presents the methodology for calculating maximum allowable headworks loadings (MAHLs)—the third
step in the four-step recommended MAHL approach to determining local limits.  Later, this guidance will
show the POTW how to evaluate the need for local limits, calculate and allocate the maximum allowable
industrial loadings (MAILs), and develop final local limits (Chapter 6).

A MAHL is an estimate of the upper limit of pollutant loading to a POTW intended to prevent pass
through or interference. MAHLs are the basis for local limits. As shown in Figure 5-1, a MAHL for a
single pollutant of concern (POC) is calculated in three steps:

       •   Calculate POTW removal efficiency for the POC
       •   Calculate allowable headworks loadings (AHLs) for each environmental criterion
       •   Designate as  the MAHL the most stringent AHL for the POC

States have an integral role in the development of MAHLs. In addition to State environmental criteria
being the basis of many AHL calculations, some Approval Authorities require that the MAHL calculation
be performed on specific  spreadsheet models. The spreadsheet models ensure consistency in the
collection and analysis of data and simplify the AHL calculation by providing the pertinent State
standards. POTWs should check with their Approval Authorities to determine if a spreadsheet model is
recommended. For example, EPA Region 5, EPA Region 7, and EPA Region 8 have spreadsheet models.
5.1 CALCULATION OF REMOVAL EFFICIENCIES

Removal efficiency is the fraction or percentage of the influent pollutant loading that is removed from the
wastestream across an entire wastewater treatment works or specific wastewater treatment unit within the
works. Removal efficiency values for each POC are fundamental inputs to MAHL calculations. Removal
efficiency methodologies vary by degree of data quality and calculation method. This section will:

      •   Explain three different types of removal efficiency calculations methodologies: average daily
          removal efficiency, mean removal efficiency, and the decile method.

      •   Suggest when to use certain methodologies.

      •   Offer guidance on data quality.

      •   Discuss applying removal efficiencies reported by other POTWs or industry surveys.
                                        5- 1

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5.1.1  REMOVAL EFFICIENCY CALCULATION METHODOLOGIES

This section explains the three removal efficiency calculation methodologies commonly used by POTWs.
They are the average daily removal efficiency, the mean removal efficiency, and the decile method.

Average Daily Removal Efficiency
The average daily removal efficiency (ADRE) calculation requires that an influent sample be paired
with a lagged effluent sample to reflect removal efficiency accurately.  Samples are lagged by the
hydraulic residence time of wastewater within the
treatment plant. As shown in Equation 5.1, a series
of daily removal efficiencies based on paired
headworks influent (7J and POTW effluent data
(Epotw, n) is calculated first.  This series of removal
efficiencies is then summed (symbolized in the
equation by the Greek letter ฃ) and divided by the
total number of paired observations (N) to yield the
removal efficiency (RpotJ across the entire
wastewater treatment plant (from headworks to plant
effluent). To calculate the removal efficiency from
headworks to primary treatment effluent (Rprim), use
paired headworks influent (7J and primary treatment
effluent data (Eprim J. To calculate the removal
efficiency from headworks to secondary treatment
effluent (RseJ, use paired headworks influent (7J and
secondary treatment effluent data (EseC: J.
                                                    R „,. -
Mean Removal Efficiency
More flexible than the ADRE method, the mean
removal efficiency (MRE) can be used with paired
data lagged for retention time suitable for the ADRE
method and data that have not been lagged or paired.
As shown in Equation 5.2, instead of averaging
observed paired removal efficiencies, the MRE
calculation first averages (symbolized in the
equation by the overbars) all plant influent values
(Ir) and all plant effluent values (Epotw>t) separately
and then calculates removal efficiency across the
entire wastewater treatment plant from headworks to
plant effluent (RpotJ.  The MRE calculation averages all headworks influent data (I) and all primary
treatment effluent data (Eprim J to calculate the removal efficiency from headworks to primary treatment
effluent (Rprim). The MRE calculation averages all headworks influent data (I) and all secondary
treatment effluent data (EseCiy) to calculate the removal efficiency from headworks to secondary treatment
effluent (RSJ.
                                                        Equation 5.1: Removal Efficiency
                                                     Calculated Using Average Daily Removal
                                                                   Efficiency
                                                                         N
                                                                         N
                                                                        N
                                                    Where:
Rpofw =   Plant removal efficiency from headworks to
       plant effluent, as decimal
Rprjm =   Removal efficiency from headworks to
       primary treatment effluent, as decimal
       Removal efficiency from headworks to
       secondary treatment effluent, as decimal
       POTW influent pollutant concentration at
       headworks , mg/L
       POTW effluent pollutant concentration
       Primary treatment effluent pollutant
       concentration, mg/L
       Secondary treatment effluent pollutant
       concentration, mg/L
       Paired observations, numbered 1 to N
                                              5-3

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                                                          Equation 5.2: Removal Efficiency
                                                          Calculated Using Mean Removal
                                                                      Efficiency
                                                                             ^potw,t
                                                         a  - '  eec,y
                                                         "sec	=	

                                                                                     1,-E.
                                                   'pnm,x
                                                      Where:
                                                      D   —
                                                      ^ofw
Unpaired historical data from the same time period
(such as alternating months during the same year)
should not introduce bias.  However, unpaired
historical data from different time periods, if used in
the MRE calculation, can introduce bias when
significant changes in the POTW's industrial base
(such as the opening or closing of an industry or the
installation of significantly more efficient
pretreatment equipment units or source  control)
occurred between data collection times. Current
levels of POTW influent should be compared to
historical levels to determine if they are of the same
general magnitude. In addition, unpaired sampling
data representing some unusual one-time event should
not be included in the MRE calculation.

Decile Method
Mean removal efficiency does not indicate how often
the derived removal efficiency was achieved.  The
decile method requires at  least nine daily removal
efficiency values based on paired sets of influent and
effluent data.  However, instead of averaging the daily
removal efficiency values, the decile method sorts
daily removal  efficiency data from highest to lowest
and calculates the percentage of the daily  removal
efficiency above or below  a specified removal
efficiency. The methodology is similar to a data set
median.  A median divides an ordered data set into
two equal parts: with half the data set above the
median and the other half below. The decile method
is similar except it divides the ordered data set into 10   ^^^^^^^^^^^^^^^^^^^^^^™
equal parts. Therefore, 10 percent of the data set is
below the first decile; 20 percent of the  data set is below the second decile, etc.  The fifth decile is
equivalent to the data set median.
The results of an applied decile
                                                      t =
                                                      r =
                                                      x =

                                                      y =
                        Plant removal efficiency from headworks to
                        plant effluent, as decimal
                        Removal efficiency from headworks to
                        primary treatment effluent, as decimal
                        Removal efficiency from headworks to
                        secondary treatment effluent, as decimal
                        POTW influent pollutant concentration at
                        headworks, mg/L
                        POTW effluent pollutant concentration, mg/L
                        Primary treatment effluent pollutant
                        concentration, mg/L
                        Secondary treatment effluent pollutant
                        concentration, mg/L
                        Plant effluent samples, numbered 1 to T
                        Plant influent samples, numbered 1 to R
                        Primary treatment effluent samples,
                        numbered 1  to X
                        Secondary treatment effluent samples,
                        numbered 1  to Y
method approach are shown in
Figure 5-2.

Figure 5-2 shows the decile values
(labeled "Deciles - Percent of Data
Set Less than Stated Efficiency") on
the Y-axis and the corresponding
removal efficiencies on the X-axis.
From this figure, a POTW can gain
an understanding of the likelihood of
certain removal efficiencies. As
illustrated at the fifth decile or
median, this hypothetical POTW has
an overall plant removal efficiency
(RpotJ of 64.5 percent less than half
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         Figure 5-2: Decile Results for Hypothetical
                           POTW
                                             100% -,
                                              90% -
                                              80% -
                                              70% -
                                              60% -
                                              50% -
                                              40% -
                                              30% -
                                              20% -
                                              10% -
                                               0% -
            0%     20%    40%     60%     80%

                          Removal Efficiency
                                                                                          100%
                                               5-4

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of the time.  As illustrated in the third decile, the POTW achieves a removal efficiency of below 36
percent less than 30 percent of the time. If concerned about recurring effluent limitation violations due to
plant operation variation, the POTW may decide, based on historical knowledge, to use the more
conservative third decile, instead of the median fifth decile, as the removal efficiency. However, POTWs
should be aware that a lower removal efficiency for those pollutants that accumulate in sludge would lead
to lower, more protective, effluent-based local limits but higher, less protective, sludge-based local limits.
Appendix P includes sample calculations of removal efficiencies using ADRE, MRE, and decile methods.
Conservative Pollutant Removal Efficiency Derived
For conservative pollutants, such as metals, the
portion removed during POTW processes ends up in
the sludge. Therefore, for conservative pollutants,
POTWs can also use sludge data to estimate removal
efficiency across the entire plant (RpotJ.  Sludge data
should be used in place of effluent data when a
POTW has influent data above detection but does not
have adequate effluent data above detection and,
therefore, believes sludge data provide more
representative removal efficiencies.  (In general,
accurate representative sampling results are more
difficult to attain in the sludge than in the POTW
effluent sampling.)  As shown in Equations 5.3 and
5.4, ADRE and MRE can be used to calculate
removal efficiency across the entire plant (RpotJ by
comparing the sludge and headworks pollutant
loading.  Sludge loading is calculated by multiplying
the sludge concentration (S) by the sludge flow rate
(Qsidg), specific gravity (Gsldg), and percentage solids
(PS).  Influent pollutant loading is calculated by
multiplying the  influent concentration (I) by the
average POTW flow rate (QpotJ. The influent
pollutant concentration (I) should be a monthly
average in order to be compared with sludge pollutant
concentration, which accounts for pollutants that have
accumulated for 20 to 30 days. The  MRE method is
often more suitable technique than the ADRE in this
situation because:
from Sludge Data
    Equation 5.3: Plant Removal Efficiency
   Calculated Using ADRE and Sludge Data

       P    E(Sn* PS/100* Q^* Gsfda)/(/n* QpoJ
        pot*               N
     Equation 5.4: Plant Removal Efficiency
    Calculated Using MRE and Sludge Data
              (S,*8.34* PS/100*
   Where:
   P   —
   "pofw ~
   PS =
   8.34 =
   Sn, SB =
   n =
   u =
   r =
                    (/r*8.34*Qpo(w)
Plant removal efficiency from headworks to
plant effluent, as decimal
POTW influent pollutant concentration at
headworks, mg/L
Percentage solids of sludge to disposal,
Total sludge flow rate to disposal, MGD
POTW average flow rate, MGD
Specific gravity of sludge, kg/L
Unit conversion factor
Sludge pollutant concentration, mg/kg
Paired observations, numbered 1 to N
Sludge samples, numbered 1 to U
Influent samples numbered 1 to R
        1.  Most POTWs will not have monthly average influent pollutant concentrations readily
           available.

        2.  Sludge settling times are difficult to estimate when developing paired observations.

5.1.2  GUIDANCE ON USING DIFFERENT METHODOLOGIES

EPA offers the following guidance on implementing the three different methodologies:

        •   EPA recommends the MRE over the ADRE method if less than ten data pairs are available,
           because it is generally less sensitive to variation in daily removal efficiencies.
                                              5-5

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       •   Although requiring more data, the decile approach allows for a more comprehensive view of
           removal rates than the ADRE and MRE methods because it provides a frequency distribution
           and allows for explicit incorporation of daily removal efficiency.

       •   Although an overall depiction of the POTW removal efficiency frequency is gained in the
           decile method, an individual decile estimate, depending on how conservative the POTW
           wants to be in establishing removal efficiencies, can be less precise than the MRE and ADRE
           estimates.

Appendix P of this manual provides additional guidance in the form of an example and an examination of
the different methodologies applied to one data set.

5.1.3 DATA QUALITY

This section reviews some issues related to data quality, quantity, and analytical method limits that often
cause problems during local limits calculations.

Outliers
The following two simple tests can be conducted to see if outliers exist in a given data set:

        1.  If the data are known to closely follow a "bell-shaped" normal distribution, then any data
           point that lies more than two standard deviations from the mean is considered an outlier.

       2.  If the data values do not approximate a normal distribution, outliers can be determined based
           on the interquartile range (IQR) of the data set. The IQR equals the values between the 1st
           and 3rd quartile. Any data point that lies  more than 1.5  times this IQR below Ql, or 1.5 times
           this IQR above Q3 is  considered an outlier.

Both of these methods are demonstrated in Appendix P with a sample data set.

Concentrations Below the Minimum Level of Quantitation  (ML)
A POTW's sampling program will probably yield some sampling results that indicate a pollutant was
below the ML in the analyzed sample. The manner in which the POTW uses these data in the local limits
development process can significantly affect the MAHL calculation. Table 5-1 details the different
options available to POTW users.

     Table 5-1: Options for Managing Sampling Results Below the ML in Removal Efficiency
                                          Calculations
If only a few data values are below the ML:
Option 1 : Use surrogate value of % ML.
Option 2: Discard the few samples below the ML. (Influent
and effluent data should be discarded in pairs.)
If most data values are below the ML:
Option 1 : Re-evaluate the need for a local limit for the
pollutant. (However, if the pollutant is one of the 15 EPA
POCs an AHL should be developed.)
Option 2: Use removal rate data from other plants. (See
Section 5.1.4.)
In general, the surrogate value results in a greater bias when calculating the mean or standard deviation
and accuracy decreases as the proportion of non-detects increases.
                                             5-6

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Other statistical methods—Regression order statistics (ROS), probability plotting, and maximum
likelihood estimations (MLE)—are detailed in Appendix Q.  The probability plotting method provides
slightly more accurate results when non-detects represent 30 percent or more of the data set. The MLE
method works well when the data distribution is exactly normal or lognormal1 and when non-detects are
less than 30 percent of the data set. Other references for using statistics to analyze data sets containing
values below limits include:

        •   Appendix E in the Technical Support Document for Water Quality-based Toxics Control,
           EPA/505/2-90-001, March 1991.

        •   Use of Statistical Methods in Industrial Water Pollution Control Regulations in the United
           States, Journal of Environmental Monitoring and Assessment, Volume 12:129-148, 1989.

Although these methods can be applied by those without a background in statistics, EPA strongly
recommends that a statistician perform the necessary calculations.

Negative Removal Efficiency
Negative removal efficiencies, which reflect valuable operational data, should not be summarily
dismissed as outliers.  Unless technical justification (such as poor sampling or analytical technique) to
remove them is discovered, negative removal rates should be retained in the data set. Described below
are methods to manage negative removal efficiencies. Appendix P provides sample calculations to
address negative removal efficiencies.

Use the MREMethod or Decile Approach. Negative removal efficiencies are attributable to the fact that
POTWs do not operate in a steady state. Deviations from steady state  occur because of variability in
POTW influent, recycle streams and performance, accumulation of pollutants in POTW sludge, and
incidental generation of pollutants by POTW operations. This variability often leads to the ADRE
method of calculating removal efficiency, dependant on retention time lagged data, to yield negative
removal efficiencies. In these cases, the MRE method, less sensitive to data variability, should eliminate
negative removals efficiencies unless an underlying problem exists in the sampling, data analysis or plant
operations. The decile approach, which ranks instead of averages daily removal efficiencies, can be
applied to data sets with a few negative daily removal efficiencies because it determines efficiency based
on probability of occurrence and not averaging.

Manage data below the ML.  In addition, negative removal rates often result from the influent and
effluent concentrations below the ML.  Readings below the ML that can lead to negative removal
efficiencies should be examined as detailed above.

5.1.4  APPLYING REMOVAL EFFICIENCIES REPORTED BY OTHERS

Removal efficiencies are based largely on site-specific conditions such as climate, POTW design,
operation and maintenance, plant conditions, and sewage characteristics. Therefore, EPA strongly
suggests that site-specific data be used to calculate removal efficiencies. However, some POTWs still do
not have adequate data to calculate removals after conducting site-specific sampling and using analytical
         Log-normal distributions are probability distributions that are closely related to normal distributions: if X is a
normally distributed random variable, then exp(X) has a log-normal distribution. In other words, the natural logarithm of a
log-normally distributed variable is normally distributed.
                                              5-7

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methods that achieve the lowest detection levels possible. In these instances, POTWs may selectively use
removal efficiencies reported by other POTWs or by studies that have been published in professional
journals or by EPA. EPA urges POTWs to use performance data from plants employing the same
treatment technology and similar contributing sources.  Appendix R provides a listing of removal
efficiency data for priority pollutants gathered from other POTWs. (These data are the  same as those
presented in the 1987 Local Limit Guidance Manual.)

5.2 CALCULATION OF ALLOWABLE HEADWORKS LOADINGS

An AHL is the estimated maximum loading of a pollutant that can be received at a POTWs headworks
that should not cause a POTW to violate a particular treatment plant limit or environmental criterion. An
AHL is developed to prevent interference or pass through.  An AHL is calculated for each applicable
criterion: pass through, sludge contamination, air quality standards, and the various forms of interference
(biological treatment inhibition, sludge digestion inhibition).  The AHLs for each POC  are calculated
based on the various suitable  environmental criteria, plant flow rates, and plant removal efficiency.  After
calculating a series of AHLs for each POC, the lowest AHL is chosen as the MAHL.

Local limits  development uses a mass-balance approach to  determine the AHLs for a POTW based on the
environmental and  treatment plant criteria. With the mass-balance approach, the POTW calculates the
amount of loading received at the  POTW headworks that will still meet the environmental or treatment
plant criteria that apply to each pollutant. Steady-state equations are used for conservative pollutants
because the amount of pollutant loading is "conserved" throughout the treatment plant.  Conservative
pollutants can be removed from wastewater via chemical or physical separation or biological treatment
but always accumulate in the sludge or remain in wastewater. On the other hand, non-conservative
pollutants may be lost through degradation or volatilization in addition to accumulating in the sludge.
Because losses through degradation and volatilization do not contribute to pollutant loadings in sludge, it
is not valid to assume that all non-conservative pollutants removed during plant treatment are transferred
to sludge.  Therefore, for non-conservative pollutants, different equations are used to calculate AHLs
based on sludge criteria.

Fate and transport software can estimate the effects of biodegradation, sorption onto solids, and
volatilization on substances entering a treatment plant.  The most widely used model is  EPA's Water9
model for wastewater collection and treatment systems available at:
        http://www.epa.gov/ttn/chief/software/water/index.html.

5.2.1 DETERMINATION OF SUITABLE ENVIRONMENTAL CRITERIA

A properly functioning POTW will be in compliance simultaneously with air, effluent,  and sludge
environmental criteria (see Figure 5-3). For each POC identified, the POTW should examine the
appropriate environmental criteria to guard against interference or pass through. From these
environmental criteria, along with flow rates and removal efficiencies, AHLs are calculated. These
environmental criteria should have all been evaluated as part  of the POC development in Chapter 3.
Table 5-2 shows suggested criteria that should be evaluated for each POC. The next section provides
details regarding how to use these criteria in the AHL calculation.
                                             5-

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Table 5-2: Suggested Criteria or Standards to be Considered
        For Each POC in the Development of AHLs
Effluent Based

NPDES permit:
effluent limitations,
water quality-based
toxic pollutant limits,
Whole Effluent Toxicity
(WET)
[Source: POTWsown
NPDES permit]


State Water Quality
Criteria and Standards:
adoption of Federal
criteria or stricter
[Source: State
regulations]



National Recommended
Water Quality Criteria
for Priority Pollutants:
freshwater/saltwater
chronic and acute
criteria, human health
for consumption criteria
[Source: Appendix D or
National Recommended
Water Quality Criteria-
Correction. April 1999,
EPA822-Z-99-001]
Sludge-Based

State Sludge Quality
Criteria: adoption of
Federal criteria or
stricter
[Source: State
regulations]




Federal Sludge
Standards: land
application, surface
disposal, or
incineration
[Source: Appendix E
or Federal
regulations 40 CFR
Part 503]
Hazardous Waste
Criteria: Toxic
Characteristic
Leaching Procedure
(TCLP)
[Source: Appendix F
or Federal
regulations 40 CFR
Part 261 .24]



Inhibition-Based

POTW's own in-house
guidelines or criteria
for process inhibition
[Source: POTW
reports detailing
circumstances
surrounding last
inhibition]


Literature Inhibition
Values for activated
sludge, trickling filter,
and nitrification
processes
[Source: Appendix G]















Air Quality Based

Local regulatory
requirements to meet
National Ambient Air
Quality Standards
(NAAQS)
[Source: State
Implementation Plan
or local regulatory
requirements to meet
NAAQS ]





















Resource Protection
Based
State and local
groundwater, aquifer,
and watershed
protection permits
[Source: State
regulations and local
codes]
























                        5-9

-------
ra

(5

c
LU

TJ
C
ra



2
o
re
o
O
0.

CO

in
o
                                                 5- 10

-------
                                                      Where:
                                                      AHL
                                                      C,
  • npdes~
'npdes ~
                                                          R_
                                                       nntw
5.2.2 EFFLUENT-QUALITY BASED AHLs

National Pollutant Discharge Elimination System (NPDES) Permit
One of the most effective means of restricting the
discharge of toxic substances into waters of the
United States is through a NPDES permit limit. As
illustrated in Equation 5.5, the AHL based on NPDES
permit limit (AHLnpdes) is the pollutant loading at the
NPDES permit limit (Cnpdes * QpoJ divided by the
fraction of the pollutant not removed by the plant (1-
RpotJ. The NPDES permit limit can appear in many
forms—specific technology-based effluent
limitations, water quality-based pollutant limits,
whole effluent toxicity—and is commonly expressed
as milligrams per liter and usually specified as a daily
maximum2 and/or a monthly average3 discharge limit.
POTWs should use actual average POTW flow rate
data for Qpotw and not use design flows (see Exhibit 5-
1).
Water Quality Standards or Criteria
In general, POTWs will not have NPDES permit limits
for all of the POCs established during the local limits
analysis. In such cases, EPA recommends a POTW
base its effluent-quality-based AHL on State Water
Quality Standards (WQS) or Federal Water Quality
Criteria (WQC).4 State environmental agencies have
developed WQS that set maximum allowable pollutant
levels for their water bodies, specific to the receiving
stream reach's designated uses. Designated uses are
identified  by taking into consideration the use and
value of the water body for public water supply, for
protection offish, shellfish, and wildlife, and for
recreational, agricultural, industrial, and navigational
                                                         Equation 5.5: AHL Based on NPDES
                                                                     Permit Limit
                                                                AHL,
                                                                       _ (8.34)(Cnpdes)(QpoJ
                                                                   'npdes
AHL based on NPDES permit limit, Ib/day
NPDES permit limit, mg/L
POTW average flow rate, MGD
Plant removal efficiency from headworks to
plant effluent, as decimal
Conversion factor
                                                            Exhibit 5-1: Be Conservative in
                                                                  Selecting Criteria

                                                       A recurring theme in this guidance manual is to be
                                                       conservative in making your choices. For example,
                                                       a POTWs NPDES permit limit for a single pollutant
                                                       can sometimes be expressed in two forms - daily
                                                       maximum and monthly average. EPA recommends
                                                       that only the more conservative monthly average
                                                       should be used in calculating  NPDES-based AHLs.
                                                       Specific policies regarding this issue should be
                                                       explored with your Approval Authorities. See Section
                                                       6.4.1 fora more detailed discussion of the duration
                                                       of local limits.
purposes. Even though the POTW's NPDES permit
may not contain a numeric effluent limit for a POC, the permit will probably contain narrative provisions
requiring compliance with State WQS and prohibiting the discharge of any toxic pollutants in toxic
amounts. A local limit based on a State WQS helps ensure that the POTW can comply with the narrative
permit requirement specifying "no discharge of toxics in toxic amounts."  In the absence of State WQS,
local limits may be based on the EPA ambient WQC found in Appendix D.  These criteria are EPA's
recommended maximum pollutant levels for protecting aquatic life.  They offer a sound basis for
developing local limits for pollutants with the potential for causing toxicity problems in the receiving
         Daily maximum is the maximum allowable discharge of a pollutant during a 24-hour period.

        3 Monthly average is the arithmetic average value of all samples taken in a calendar month for an individual pollutant
parameter.

        4POTWs should, if possible, use their State's methodology to convert a WQS to NPDES permit limits and then use
these calculated NPDES limits to develop the MAHL. Also see Section 3.2.2.
                                              5- 11

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stream. A local limit based on WQC generally would fulfill the narrative permit requirement specifying
"no discharge of toxics in toxic amounts."
                                                           Equation 5.6: AHL Based on Water
                                                                    Quality Criteria
                                                             AHL  _
                                                                                Vfw
                                                       Where:
                                                       "pofw

                                                       8.34 =
: AHL based on water quality criteria, Ib/day
 Receiving stream background concentration,
 mg/L
 State WQS or EPA WQC, mg/L
 Receiving stream (upstream) flow rate, MGD
 POTW average flow rate, MGD
 Plant removal efficiency from headworks to
 plant effluent (as decimal)
 Conversion factor
As illustrated in Equation 5.6, the AHL based on
water quality criteria (AHLvq) is calculated as the
hypothetical pollutant loading to the water body at the
water quality limit [Cvq(Qstr+QpotJ] adjusted for the
background loading of the water body (Cst*Qstr) and
divided by the fraction of the pollutant not removed
by the plant (1- RpotJ.  The receiving stream
background concentration (Cstr) can be an average
background stream concentration. The receiving
stream (upstream) flow rate (QstrJ should be either
the 7Q10 or 1Q105 flow based on the particular
criteria used. The average POTW flow rate (Qpotw)
should be based on actual plant data and not on
design flows.6 Under most water quality based
analyses, Equation 5.6 is sufficient and, consequently,
is the only one presented here. Another method is the
five-step process based on the one described in EPA's
Technical Support Document For Water Quality-
based Toxics Control (EPA, 199la).

In general, WQS and WQC are classified into three
groups: freshwater aquatic life protection, saltwater
aquatic life protection, and human health protection.
Freshwater and saltwater aquatic life criteria include chronic and acute toxicity criteria. Chronic toxicity
criteria are designed to protect aquatic organisms from long-term effects over the organisms' lifetime and
across generations of organisms, while acute toxicity criteria generally are designed to protect organisms
against short-term lethality. EPA offers the following guidance on the use of WQS and WQC:

        •   Hardness, pH, and Temperature Dependence. WQS and WQC for some metals depend on
            the hardness of the receiving water. If the State has not factored this in, then the POTW
            should obtain from the State the appropriate hardness value for its receiving stream and use
            this value to determine the applicable WQS or WQC. Formulas for the common pollutants
            that are affected by hardness can be found in footnote E to Appendix D. In addition, WQS or
            WQC for some inorganic pollutants (e.g., ammonia) are pH- and/or temperature-dependent
            and should be treated similarly. If the State has not established site-specific values, the
            POTW should contact the State permitting authority to obtain appropriate temperature and
            pH values for its receiving stream. These values should then be used to calculate WQS or
            WQC for AHL determinations.
         1Q10 refers to the lowest average flow for a one-day period that is expected to occur once every ten years. 7Q10
refers to the lowest average flow for a seven-day period that is expected to occur once every ten years. Both values are available
in the background documentation for the POTW's NPDES permit issuance and also can be obtained from the local district office
of the US Geological Survey (http://water.usgs.gov/local_offices.html).

         Some States develop WQS to take into account dilution from the receiving stream and therefore the AHL calculation
in Equation 5.6 would not need to be adjusted for the background loading of the water body, Cstr*Qstr. POTWs should consult
with their State water quality control agencies.
                                               5- 12

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                                                        Exhibit 5-2:  How to Convert
                                                      Dissolved Metals Criteria to Total
                                                               Metals Criteria

                                                     NPDES permit writers often use metals
                                                     translators to convert dissolved water quality
                                                     standards or criteria to total recoverable
                                                     equivalents. Translators are specific to each
                                                     metal and may be 1) the theoretical
                                                     partitioning coefficients; 2) experimentally
                                                     determined through site-specific translator
                                                     studies; or 3) the EPA conversion factors
                                                     used to convert dissolved metals criteria to
                                                     total metals criteria. For establishing an
                                                     AHL, EPA recommends the theoretical
                                                     partitioning coefficient to calculate metal
                                                     translators detailed in The Metals Translator:
                                                     Guidance For Calculating A Total
                                                     Recoverable Permit Limit From A Dissolved
                                                     Criterion (EPA/823-B-96-007).
        •   Converting Dissolved Metals to Total Metals.
           WQS and WQC for some metals may be
           expressed in the dissolved form. Most metals
           measurements, however, are reported in the total
           or total recoverable form. Total and total
           recoverable metals concentrations are always at
           least as high as dissolved metals concentrations
           because a fraction of the metal has sorbed to
           particulate matter in the water. If dissolved
           metals WQS or WQC are used to develop local
           limits that are expressed as total metals, local
           limits will be more stringent than if total metals
           concentrations are used for the WQS. Therefore,
           POTWs should convert dissolved metals WQS or
           WQC into the total metals form before using
           them to calculate water quality-based AHLs (see
           Exhibit 5-2).

        •   Chronic and Acute Criteria Guidance. Chronic
           and acute criteria should be used in the
           calculation of AHLs to protect receiving water
           quality. POTWs should not develop a monthly
           average limit based solely on chronic criteria or a daily maximum limit based exclusively on
           acute criteria. AHLs should be calculated based on chronic and acute criteria and the more
           stringent criterion used for comparison with other AHLs.

        •   Stream Flow Guidance.  To calculate limits based on chronic WQS, the receiving stream
           flow rate should be consistent with State recommendations for chronic criteria, such as 7Q10
           flows. To calculate limits based on acute criteria, the POTW should also use the State-
           recommended receiving stream flow (e.g.,  1Q10).  POTWs should consult with their State
           water quality agencies to confirm the correct flow values.

Resource Protection
Many State water quality protection laws that are the basis for POTW permits protect all waters of the
State including groundwater. Some POTWs have discharges that have the potential to impact
groundwater resources such as water reclamation projects to recharge groundwater, saline intrusion
barriers (to minimize the intrusion of saline groundwater into fresh groundwater) or disposal of treated
effluent via underground injection control (UIC) wells. Potential groundwater impacts can also be of
concern in effluent dominated streams in arid regions of the country. Therefore, groundwater protection
may need to be considered during local limits development.  Some examples of groundwater protection
requirements that might need to be considered in local limits development include the following:

        •   Aquifer Protection Permits and Water Reuse Permits. Arizona issues aquifer protection
           permits and water reuse permits to POTWs that discharge to effluent-dominated streams or
           reuse the water for irrigation or other uses. The effluent limits in these permits are designed
           to protect diminishing groundwater resources and to assure adequate effluent quality for the
           reuse activity.7
Communication with John E. Watson, City of Phoenix Water Services Division, February 12, 2003.

                                      5-  13

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        •   State NPDESPermits. New York State law specifies groundwater effluent discharge
           limitations to protect groundwater quality.  When an effluent may have an impact on
           groundwater, State Pollutant Discharge Elimination System permits include effluent limits to
           protect groundwater.8

        •   Under ground Injection Control (UlC)Program Permits. The Miami-Bade County POTW
           system disposes effluent into underground injection wells. The POTW is required to comply
           with UIC permits as well as its NPDES permits.  The most stringent standards are being used
           in local limits calculations.9

UIC, groundwater, or aquifer protection criteria can be used in place of NPDES permit limit (Cnpdes) in
Equation 5.5 to calculate AHLs based on resource protection.

5.2.3  SLUDGE-QUALITY BASED AHLs

In February 1993, EPA issued the Part 503 Biosolids regulations governing the use or disposal of sewage
sludge.  Pollutant levels were  established for three disposal alternatives: land application to condition the
soil or fertilize crops  grown in the soil, surface disposal for final disposal, and incineration. The pollutant
levels, however, are different for each alternative. In addition to the Federal standards, States may have
sludge standards that are more stringent or that regulate more pollutants. Therefore, POTWs should
check with their State environmental agencies to confirm the applicable standards.  Regardless of how a
POTW disposes of sludge, POTWs may wish to consider using land application "clean sludge" values
from 40 CFR 503.13  in their calculation of AHLs.  Use of these criteria can improve a POTW's beneficial
use options for disposal of sludge. The further achievement of these standards is consistent with the
objectives of the National Pretreatment Program, which are listed at 40 CFR 403.2. Moreover, the land
application standards have a more extensive list of pollutants than either surface disposal or incineration
and they help control discharges of toxic pollutants that the other disposal alternatives do not address.

The Part 503 Biosolids Regulations also indicate that biosolids placed in a municipal solid waste landfill,
a fairly common practice, must meet only the Federal provisions of Part 258 RCRA Subtitle D landfill
regulations or delegated States' regulations. These provisions generally include a hazardous waste
evaluation, which is detailed in the last part of this section discussing municipal solid waste landfills.

Land Application
Federal  sludge use or disposal regulations, found at 40 CFR Part 503, establish limitations for nine
common metals (arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc) that
are primarily controlled by the Pretreatment Program.  As shown in Appendix E, four types of land
application limitations were established and are known by the table number in which they appear:

        •   Table 1:  Ceiling Concentrations [milligrams per kilogram (mg/kg)] establish the maximum
           concentration that can be in sludge when it is land applied.

        •   Table 2:  Cumulative Pollutant Loading Rates [pounds per acre (lb/acre)] establish the limits
           that cannot be exceeded over the lifetime of the disposal site.
         See Title 6 of the Official Compilation of Codes, Rules and Regulations of the State of New York (6 NYCRR)
Chapter 10, Part 703.6.

       9 Memo from M. Mallard Greene, US EPA Region IV dated January 14, 2003 with a copy of the UIC Permit and
NPDES permit.

                                             5- 14

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       •   Table 3: Pollutant Concentrations (mg/kg) set levels considered "clean" sludge and are
           subject to less restrictive reporting requirements.

       •   Table 4: Annual Pollutant Loading Rates (Ib/acre/year) establishes maximum loadings that
           can be applied in any given year.

As illustrated in Table 5-3, sludge standards are applied based on biosolid end use. For all land
application of biosolids, POTWs must comply with Table 1 ceiling concentrations. If its biosolids are
applied to agricultural land, a forest, a public-contact site, or a reclamation site, a POTW must comply
with either the cumulative loading rates in Table 2 or the monthly average pollutant concentrations in
Table 3.  If its biosolids are applied to a lawn or home garden, the sludge pollutant concentration may not
exceed the monthly average pollutant concentrations in Table 3. If its biosolids are sold or given away in
a bag or other container for land application, the  POTW must comply with monthly average pollutant
concentrations in Table 3 or the annual pollutant loading rates in Table 4.
                            Table 5-3: Land Application Requirements
Biosolids End Use

Applied to agricultural land, forest,
public contact site, reclamation
site
Applied to lawn or garden
Sold or given away in bag or
container
Table 1
Ceiling
limits
(mg/kg)
X
X
X


and


Table 2
Cumulative
limits
(Ib/acre)
X




or
and
and
Table 3
"Clean
Sludge"
Pol. Cone.
(mg/kg)
X
X
X




or
Table 4
Annual limits
(Ib/acre/
year)


X
To calculate AHLs based on sludge land application criteria, a POTW should:

       •   Determine which land application criteria apply to its biosolids by using Table 5-3.

           Determine the applicable Table 1, 2, 3, or 4 criteria in Appendix E for each POC.

           Convert the applicable Table 2 cumulative loading rates (CCUJ and applicable Table 4 annual
           pollutant loading rates (Cann) to equivalent sludge standards (Cslgstd) using Equation 5.7 and
           Equation 5.8, respectively.  The values for site life (SL) and site area (SA) are determined by a
           POTW's sludge management plan.  The POTW determines how long the sites will be used
           and how much land or acreage is needed for disposal of the total annual volume of sludge
           generated. Generally, the amount of land needed is determined by dividing the total annual
           sludge production by the agronomic application rate for nitrogen based on the crop grown.

       •   Determine the lowest sludge concentration standard (Cslgstd) derived from Equation 5.7,
           Equation 5.8, Table 1 Ceiling Concentrations, Table 3 Monthly Average  Pollutant
           Concentrations, and suitable State sludge standards.
                                             5- 15

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        •    Use Equation 5.9 with the lowest sludge
            concentration standard (Cslgstd) to
            determine the sludge land-application-
            based AHL for conservative pollutants.
            As shown in Equation 5.9, the AHL for
            land application  (AHLsldg) is the pollutant
            loading of sludge at the sludge standard
            [(CslgJ  * (PS/100)  * (Qslds)  * (GsMg)J,
            divided by the overall plant removal
            efficiency (RpoJ.

EPA offers the following guidance in performing the
calculations in Equations 5.7 through 5.9:

        •    Values greater than the Table 1 ceiling
            concentrations can not be used for Cslgstd,
            because the regulations governing use or
            disposal of sewage sludge (40 CFR Part
            503) expressly prohibit any form of land
            application if the sludge exceeds these
            concentration levels for any  regulated
            component.  In addition, EPA
            recommends that the POTW consider
            using the more conservative pollutant
            concentration levels for "clean sludge"
            specified in Table 3 because these levels
            are more protective of the environment,
            promote greater flexibility in the
            beneficial use of sludge, and are subject
            to less restrictive reporting and
            management requirements. This grade of
            sludge would meet the criteria for
            "exceptional quality"or "low pollutant
            concentration" sludge.10
     Equation 5.7: Converting Table 2
 Cumulative Loading Rates to Dry Sludge
             Concentrations
                    (Ccum)(S/\)
             3046(SL)(QWa)(PS/100)(GsB9)
Equation 5.8 : Converting Table 4 Annual
       Loading Rates to Dry Sludge
             Concentrations

                    (cann)(s/o
               3046(Q,a
Where:
PS =
Q,a =

SA =
SL =
3046 =
Equivalent sludge standard, mg/kg dry
sludge
Federal or State land application cumulative
pollutant loading rate, Ib/acre over the site
life
Federal or State land application annual
pollutant loading rate, Ib/acre/yr
Specific gravity of sludge, kg/L
Percent solids of sludge to disposal
Sludge flow rate to bulk land application
(agricultural, forest, public contact, or
reclamation site), MGD
Sludge flow rate to non-bulk land application,
MGD
Site area, acres
Site life, years
Unit conversion factor
            Generally, POTWs can assume the specific gravity of sludge (Gsldg) equals that of water (1
            kg/L).  For atypical wet sludge containing about 5 percent solids (PS) the specific gravity of
            the sludge does not differ significantly from that of water. However, drier sludges such as
            dewatered sludges with 30 percent solids may have a specific gravity of 1.1 kg/L or greater.
            In these circumstances, if the specific gravity is not considered, AHLs will be understated and
            any local limits based on these AHLs may be unnecessarily conservative. Therefore, the
            POTW can measure the specific gravity of its sludge to correct for the error introduced as the
            percent solids rises. If the POTW does not have data on the specific gravity of its sludge, it
            should assume conservatively that the specific gravity is 1 kg/L. Guidelines for determining
            the specific gravity of sludge are provided in Appendix S.
        10,
         'See Chapter 2 in A Plain English Guide to the EPA Part 503 Biosolids Rule, EPA/832/R-93/003, September 1994

                                               5- 16

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           If the POTW's data for sludge flow rate to disposal are expressed in dry metric tons per day
           (or can be converted to dry metric tons per day), a specific gravity factor is not needed. An
           equation for calculating an AHL using dry metric tons per day is provided in Appendix T.

           Table  1 sludge ceiling concentrations are instantaneous maximum concentrations, while the
           "clean sludge" criteria in Table 3 are monthly average concentrations. See Section 6.4.1 for a
           discussion of how the types of criteria - monthly average, instantaneous maximum - affect
           the type of local limit developed.
Surface Disposal
Sludge surface disposal occurs at dedicated disposal
sites, surface impoundments, waste piles, monofills,
or dedicated beneficial use sites. The difference
between surface disposal and land application is that
land application is performed at rates that do not
exceed the agronomic rates of the fertilizer value of
the sludge. For a more extensive discussion of
surface  disposal, see the sludge regulations at 40 CFR
503.20.  Surface disposal regulates only three metals
(arsenic, chromium, and nickel) at levels near the
"clean sludge" levels for land application. The
standards  apply to  sludge disposed at facilities
without a  liner or a leachate collection system.  AHLs
based on sludge surface disposal quality should be
calculated in the following manner:
           Table 1 (40 CFR 503.23) sludge surface
           disposal criteria should be used directly
           as the sludge standard (Cslgstd) in Equation
           5.9 for conservative pollutants.
  Equation 5.9: AHLs Based on Sludge
          Land Application and
        Surface Disposal Criteria
       (for conservative pollutants)
    AHL.
          _ (8.34)(Cs)gsM)(PS/1 OOKQ^KG^)
                      r\__|...
Cslgstd
PS =
Where:
AHLsldg =  AHL based on sludge, Ib/day
        Sludge standard, mg/kg dry sludge
        Percent solids of sludge to disposal,
Qsldg =    Total sludge flow rate to disposal, MGD
Rpotw =    Plant removal efficiency from headworks to
        plant effluent, as decimal
GsBg =    Specific gravity of sludge, kg/L
8.34 =    Unit conversion factor
        •   If the sewage sludge unit is less than 150 meters from the property line, Table 2 (40 CFR
           503.23) sludge disposal criteria, based upon distance from the property line, should be used
           directly as the sludge standard (Cslgstd) in Equation 5.9 for conservative pollutants.  See
           Appendix E for a list of Table 1 and Table 2 surface disposal options.

In addition, POTWs should be aware that surface disposal regulations allow for site-specific limits.  Site
owners or operators may have requested surface disposal criteria from the permitting authority  in place of
the Table  1 or Table 2 sludge surface disposal criteria. Therefore, the POTW should check with the
disposal site owner/operator to determine standards that apply. If the State has developed more stringent
sludge disposal standards for surface disposal, the POTW needs to use those  standards in its calculation of
AHLs when using Equation 5.9.

Incineration
Incineration, the third method  of sludge disposal, typically regulates arsenic,  cadmium, beryllium,
chromium, lead, mercury, and nickel. Limits are site-specific and based on feed rate, stack height
(dispersion factor), incinerator type, and control efficiency. EPA offers the following guidance on
incineration-based AHLs:
                                               5- 17

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       •   POTWs that dispose of their sludge through incineration should determine AHLs based on
           the calculated sludge standards that apply to the sludge feed to the incinerator. These
           standards may have been calculated by the owner/operator of the incinerator (and listed in a
           sludge disposal agreement), the State, or EPA from the equations provided in 40 CFR Part
           503, and should be expressed in mg/kg dry sludge. These standards should be used directly
           as the sludge standard (CslgsJ in Equation 5.9 to determine the AHL.

       •   If no sludge standards have been calculated for the sludge feed to the incinerator, POTWs
           should use the 40 CFR Part 503 equations (provided in Appendix T) to determine the
           maximum pollutant concentrations for the incinerator feed.  These standards should be used
           directly  as the sludge standard (Cslgstd) in Equation 5.9 to determine the AHL. As a general
           rule, an AHL for incineration will be an order of magnitude or greater than an AHL based on
           land application.

Municipal Solid Waste Landfill's Hazardous Waste Requirements
According to 40 CFR 503.4, "any person who prepares sewage sludge that is disposed in a municipal
solid waste landfill unit shall ensure that the sewage sludge meets the requirements of 40 CFR Part
258. . . ."  Part 258 does not allow municipal solid waste landfill units to accept hazardous waste.
Whether a POTW's  sewage  sludge is hazardous waste may be determined by using EPA's TCLP test. If
determined to be hazardous waste, sludge must be disposed of according to RCRA requirements. POTWs
cannot dispose of sludge determined to be hazardous waste in solid waste landfills designated for non-
hazardous waste. In general, POTWs will not generate sludge that exceeds TCLP limits.

However, because the costs and liabilities associated with the management and disposal of hazardous
sludge are high, POTWs may find it advantageous to periodically run the TCLP test on their sludge to
identify any trends of increasing pollutant concentrations that may lead the sludge to be considered
hazardous waste. The POTW should compare the quality of its sludge with the limits in the TCLP and, as
necessary, set local limits to help ensure that the pollutant levels in its sludge do not exceed TCLP levels.
If TCLP test results are close to or exceed the TCLP limit, the POTW needs to develop AHLs based on
TCLP criteria. To develop TCLP-based AHLs, the POTW should:

       •   Determine the dry weight metals and toxic organics concentrations (in mg/kg dry sludge) that
           would be protective against sludge being classified as hazardous based on the TCLP test from
           sampling data. The POTW can collect site-specific data for both total pollutant
           concentrations in the sludge and TCLP concentrations (10-12 data pairs) and use these data to
           correlate TCLP concentrations with total concentrations in the sludge.

       •   Use these dry-weight, correlation-based concentrations directly as the sludge standard (Cslgstd)
           in Equation 5.9 to  determine the AHL.
                                             5- 18

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                  Exhibit 5-3: The Challenge in
                          Determining
                     Plant Inhibition Values

               Determining site-specific inhibition values is
               difficult because the exact point at which
               pollutant concentration inhibition takes place
               is difficult to identify.  For instance, an
               activated sludge system's mixed liquor may
               run at about 1 mg/L zinc. An industrial
               discharge causes the plant to violate its
               NPDES permit by upsetting the plant and
               raising the mixed liquor concentration to 100
               mg/L zinc. How can one determine at which
               concentration the inhibition took place? The
               concentration lies somewhere between 1 and
               100 mg/L. An inhibition value set at 100
               mg/L would be incorrect because a lower
               value could have caused the inhibition.
               Some POTWs have attempted to estimate
               site-specific inhibition values by simply using
               the highest observed pollutant concentration
               in the biological process that did not cause
               interference.
5.2.4 INHIBITION-BASED AHLs

Secondary and Tertiary Treatment Unit Inhibition
Pollutant levels in a POTW's wastewater or sludge may
cause operational problems for biological treatment
processes involving secondary and tertiary treatment.
Disruption of a POTW's biological processes is referred to as
inhibition and can interfere with a POTW's ability to remove
biochemical oxygen demand (BOD) and other pollutants.  A
POTW should assess any past or present operational
problems related to inhibition and follow the protocol
outlined below.

        •   No Past Inhibition Problems at POTW.
            POTWs may not need to calculate AHLs to
            protect against inhibition because current
            loadings are acceptable to the treatment work's
            biological processes.  However, a POTW may
            still choose to calculate AHLs based on
            biological process inhibition criteria to prevent
            future loadings that may cause inhibition and
            should follow the steps outlined below for
            POTWs with past inhibition problems.

        •   Past Inhibition Problems at POTW. POTWs
            should calculate AHLs based on inhibition
            criteria. If site-specific data are needed (see
            Exhibits 5-3 and 5-4), the POTW may choose to
            substitute pollutant concentrations that either
            have occurred in the applicable biological
            process or are currently in its influent and have
            not caused inhibition, in place of process
            inhibition values that have been reported in
            studies published by EPA or in professional
            journals. Inhibition criteria for select secondary
            treatment units (such as activated sludge  and
            trickling filters) and one tertiary treatment unit
            (nitrification) are presented in Appendix  G.

Site-specific inhibition data are preferred to literature data
because they more accurately measure pollutant
concentrations that cause inhibition in actual biological
treatment environments. Inhibition of biological treatment
processes could be a function of toxic compounds (not a
single toxic compound), synergism, antagonism, pH,  temperature, hardness, stressed conditions,
microorganism acclimation, and the number and variety of microorganisms present. Sometimes based on
laboratory studies using pure cultures, literature values  can indicate inhibition at much lower
concentrations than in actual biological treatment environments for the following four main reasons: 1)
organic chemicals combine with the metals and reduce metal availability to the microbes; 2) activated
sludge environments generally have a variety of organisms present that may not be as sensitive to metal
                Exhibit 5-4: Inhibition Value Study
                   by Chesterfield County (VA)

               Chesterfield County's Pretreatment Program
               conducted a site-specific evaluation of
               inhibition values for several heavy metals as
               part of its recent recalculation of local limits. A
               pilot system was fed with primary effluent from
               the full-scale facility and was loaded with
               varying levels of several heavy metals to
               determine the loading rate that caused
               measurable deterioration in process
               performance. The measured inhibition values
               for this plant were typically found to be much
               higher than those given in Appendix G.  In this
               case, the controlling factor became the
               inhibition potential of the anaerobic digesters,
               and it was possible to substantially increase
               the local limits as a result of the data
               generated from pilot testing. [Contact Abha
               Sharma of Chesterfield County (VA)
               Pretreatment program.]
5- 19

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concentrations; 3) metals can chelate toxic organics, reducing their toxicity to nitrifiers; 4) acclimated
biological treatment populations can accept higher concentrations of metal and organic toxins than
laboratory cultures. In addition to the technical drawbacks, literature values, if eventually the limiting
basis of a local limit, will most likely engender more regulatory scrutiny.
Equation 5.10 is used to calculate inhibition-based
AHLs for secondary treatment processes such as
aerated lagoons, stabilization ponds, activated
sludge, rotating biological contactors, and trickling
filters. Equation 5.11 is used to calculate inhibition-
based AHLs for tertiary treatment for various
processes to remove nitrogen, phosphorus,
suspended solids, organics, metals, and dissolved
solids (see Figure 5-3).  As shown in Equation 5.10,
the AHL based on secondary treatment unit
inhibition (AHLsec) is calculated by dividing the
pollutant loading to the secondary treatment unit at
the inhibition criterion (Cinhib2 * QpotJ by the fraction
of the pollutant not removed after primary treatment
(1 - RpriJ. As shown in Equation 5.11, the AHL
based on tertiary treatment unit inhibition (AHLter) is
calculated by dividing the pollutant loading to the
tertiary treatment unit at the inhibition  criterion
(Cmhibs * Qpo J by the fraction of the pollutant not
removed after secondary treatment (1 - Rsec).  The
POTW flow rate (Qpotw) should be calculated using
actual average flow data and not design flow.
Appendix U shows where to sample in various plants
to calculate  inhibition-based loading. (Note that in
many POTWs nutrient removal is often more like an
advanced secondary process that occurs in the same
basin as an activated sludge process. In these cases,
the same primary removal efficiency (Rprim), would
be used in both Equations 5.10 and  5.11.)
     Equation 5.10: AHLs Based On
     Secondary Treatment Inhibition
         ,,,,    8.34(Cfn/,j62)(QpoJ
 Equation 5.11: AHLs Based On Tertiary
           Treatment Inhibition
Where:
AHLter =
Rprim =
8.34 =
          AHL
AHL based on secondary treatment
inhibition, Ib/day
AHL based on tertiary treatment inhibition,
Ib/day
Inhibition criterion for secondary treatment,
mg/L
Inhibition criterion for tertiary treatment, mg/L
POTW average flow rate, MGD
Removal efficiency from headworks to
primary treatment effluent, as decimal
Removal efficiency from headworks to
secondary treatment effluent, as decimal
Unit conversion factor
Sludge Digester Inhibition
Sludge digestion is also a biological process that can
be upset if pollutants are allowed to accumulate to toxic levels. Plant-specific sludge digestion inhibition
thresholds, like inhibition of secondary treatment, are difficult to know. Literature data on sludge digester
inhibition criteria are listed in Appendix G.  The preponderance of sludge digestion inhibition data are for
anaerobic digesters. There is no publicly available data about the effect of metals on aerobic digestion of
sludge.
                                               5-20

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  Equation 5.12: AHLs Based On Sludge
    Digestion Inhibition (Conservative
               Pollutants)
  AHL,
  Equation 5.13: AHLs Based On Sludge
  Digestion Inhibition (Non-conservative
               Pollutants)
                 •'dgsinhlb

                 Cdgstr
Where:
AHLdgstr= AHL based on sludge digestion inhibition,
       Ib/day
LM =    POTW influent loading, Ib/day
       Sludge digester inhibition criterion, mg/L
       Existing pollutant level in sludge, mg/L
Qdgsfr =  Sludge flow rate to digester, MGD
Rpotw =  Plant removal efficiency from headworks to
       plant effluent, as decimal
8.34 =  Unit conversion factor
modeling to predict existing air emissions (Cair)
wastewater collection and treatment systems, is available at:
http://www.epa.gov/ttn/chief/software/water/index.html.

POTWs can determine pollutant removal efficiency by
volatilization (Rvol) by examining sampling data of
influent,  effluent, sludge, and air and determining the
portions of the total removal efficiency associated with
adsorption to the sludge, biodegradation, and
volatilization. In addition, POTWs can model the
removal process to predict pollutant removal efficiency
by volatilization.

5.3 AHLs FOR CONVENTIONAL AND NON-
CONVENTIONAL POLLUTANTS

This section provides guidance on the development of
AHLs for three conventional pollutants [BOD, Total
Suspended Solids (TSS), oil and grease] and one  non-
conventional pollutant (ammonia), whose unique
circumstances allow for special mechanisms for their
AHL development.
  Using the steady-state mass balance approach across
  the influent to the digester, Equation 5.12 calculates
  the AHL based on sludge digestion inhibition
  (AHLdgstr) for conservative pollutants such as metals.
  AHLdgstr is calculated by dividing the pollutant loading
  at the inhibition criterion to the digester (Cdgstinhib *
  Qdgstr) by the removal efficiency across the entire
  POTW (RpotJ.  As shown in Equation 5.13, for non-
  conservative pollutants (AHLdgstr) is found by
  multiplying the POTW influent loading (Linfl) by the
  ratio of the sludge digester inhibition criterion
  (Cdgstinhib) and the level of the POC in the sludge
  (Cdgstr) •

  5.2.5 AIR-QUALITY BASED AHLs

  In rare circumstances, POTWs that have been
  regulated as air pollution sources and have air
  emissions standards for specific toxics may need to
  consider calculating AHLs for those toxics (see
  Section 3.2.4).  AHLs based on air emissions
  standards can be calculated using either Equation
  5.14, which uses the  air standard and removal
  efficiency by volatization, or Equation 5.15, which
  uses air standards and existing air emissions. The
  POTW can conduct air emissions sampling or conduct
The most widely used model, EPA's Water9 model for
                                                          Equation 5.14: AHLs Based On Air
                                                            Criteria and Volatization Rates

                                                                       _ 0.0022(Ca/reftld)
                                                          Equation 5.15: AHLs Based On Air
                                                           Criteria and Existing Emissions
                                                                                C_,
                                                       Where:
                                                       AHLa!r =  AHL based air emission standards, Ib/day
                                                       Lin,i=     POTW influent loading, Ib/day
                                                       Caป5h7
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5.3.1  BOD/TSS

One of the most commonly documented industry-related causes of POTW effluent violations is the
discharge of excessive conventional pollutants, particularly BOD and TSS (see Exhibit 5-5). As stated
earlier in the chapter on POC development, POTWs should develop MAHLs for all NPDES-permitted
conventional pollutants and understand the degree to which the plant is loaded.  In fact, some EPA
regions require any wastewater treatment plant that operates at 80 percent of any NPDES permitted
conventional pollutant MAHL for three months of the calendar
year to calculate a MAIL and establish local limits for those
pollutants. To establish MAHLs for BOD and TSS, EPA
recommends the following:
           The POTW's rated average design capacity, along
           with any improvements subsequent to construction
           that have increased plant capacity, should be used
           as a "monthly average"- based MAHL. The
           treatment works is designed to have the capacity to
           consistently treat a specified amount of
           conventional pollutants to acceptable levels for
           discharge.  A copy of the approved design capacity
           may be available from  the State as part of the         .       . _    .„„,. „,„„„„„ „
            ,  •:           .          , „       ~^              increased from 100:5:1 to 100:11:2.
           design or operating manual for the POTW.
   Exhibit 5-5: Less BOD, More
   Ammonia and Phosphorous
In the late 1980s, the City of Trenton
Wastewater Treatment Plant (WWTP)
violated NPDES permits due to excessive
BOD5 loading.  Today, BOD5 loading has
been cut in half after two industries that
accounted for half of the BOD5 loading
upgraded their  existing treatment facilities by
including nutrient addition and longer
retention times. However, the industries'
nutrient addition led to problems with high
amounts of Ammonia-N and Phosphorous
discharged to the WWTP. The ratio of BOD
to Ammonia-N to Phosphorous has
           The POTW's peak loading capacity should be
           used as the "daily maximum"- based MAHL. Based on a peaking factor, peak loading
           capacity reflects the plant's ability to handle diurnal, wet weather, or seasonal peaks.

EPA recognizes that sometimes average design capacity and the corresponding peak loading factor may
be too conservative when considering the industrial allocation of conventional pollutants. Therefore, the
POTW can provide a technically defensible argument for establishing a MAHL for the plant.  These
arguments could include the following:

        •   Performing mass balance calculations on the entire plant for the current condition, and scale
           up the plant loading until loading rates for individual processes exceed design guidelines,
           including solids handling facilities.

        •   Verifying capacity of hydraulic structures.

        •   Performing detailed modeling of biological process capacity under current loading conditions
           using software (e.g.,  BioWin by Envirosim).  Calibrate the model to current conditions and
           then increase loading rates to estimate failure.

        •   Determining maximum biological process loading compared to typical design guidelines -
           including aeration equipment capacity, basin sizing, mixing energy, secondary clarifier
           sizing, return activated sludge/waste activated sludge capacity, nutrient removal capacity,
           winter and peak operation.

           Evaluating current operating conditions. For example, a plant with three activated sludge
           trains is operating reliably at 2/3 of its design loading with only one train in service.
                                              5-22

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        •   Stress testing of individual processes. Increase loading through a single process train until
           failure is recognized.

           Benchmarking against similar plants and processes.

           Pilot or bench-scale testing of unit operations that have been determined to possibly be a
           bottleneck for plant capacity.

Smaller plants should incorporate a safety factor in developing the BOD/TSS MAHL for the plant using
these methods.

5.3.2 AMMONIA

Typical concentrations of ammonia in untreated domestic wastewater range from 10 to 50 mg/L.
Therefore, significant non-domestic industrial sources of ammonia will be unusual and the result of
industry-specific activities.  If the POTW was designed to remove ammonia through specific processes
such as nitrification and denitrification, breakpoint chlorination, or ammonia stripping, the engineering
specifications that establish design loading rates should be used as the MAHL. However, for most
conventional activated sludge and trickling filter plants, ammonia removal is incidental, and a study of the
plant will have to be conducted to determine its removal efficiency. The AHL for ammonia can then be
determined using Equation 5.5.  When the AHL is determined using site-specific removal efficiencies and
Equation 5.5, a safety factor of at least 20 percent should be applied.  NPDES ammonia limits are often
seasonal, with more stringent limits in place during warmer weather.  This needs to be taken into
consideration in the development of local limits.  A seasonal limit for ammonia might be developed for
Ills as  well.

5.3.3 OIL AND GREASE

The term fats, oil, and grease (FOG) includes materials of vegetable,  animal, and mineral origin. Mineral
oils include petroleum, hydrocarbon, and or non-polar fats, oils, and grease.  Petroleum-based oil and
grease  (non-polar concentrations) occur at businesses using oil and grease; and can usually be identified
and regulated by municipalities through local limits and associated pretreatment permit conditions.
Animal-based and vegetable-based oil and grease (polar concentrations) are more difficult to regulate
when the major source is a large number of restaurants and fast-food  outlets in the collection system.
Collection system issues related to animal-based and vegetable-based oil and grease are addressed in
Section 8.3 dealing with flow obstructions.

The pretreatment regulations 40 CFR403.5(b)(6) prohibit the  discharge of "petroleum oil, non-
biodegradable cutting oil, or products of mineral oil origin in amounts that will cause interference or pass
through." Most POTWs have adopted 100 mg/L as their local limit for petroleum-based oil and grease
because of its history of being protective of the treatment plant and receiving stream. Additionally, the
                                             5-23

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limit of 100 mg/L is achievable with the application
of best management practices (BMPs) or generally
available pretreatment. The basis of the 100 mg/L
limit is an April 1975 EPA document titled
Treatability of Oil and Grease Discharged to
Publicly Owned Treatment Works. This study
found a dilution of at least two occurs in collection
systems and that influent to biological treatment
systems should contain less than 75 mg/L and
preferably less than 50 mg/L oil and grease of
mineral or petroleum origin to prevent interference.
The 100 mg/L was recommended as the value that
prevents interference based on the dilution.
However, the basis for the 100 mg/L FOG limit is
not site specific.  The limit should be justified with
additional information in order to be considered a
technically based limit.  See Exhibit 5-6 for a
description of how the City of Richland,
Washington addressed this limit.

Developing a technically based local limit for FOG
requires an understanding of the unique manner in
which oil and grease can cause interference or pass
through. EPA recommends two different methods:

        •  With FOG limits often included in
           NPDES permits, POTWs  could
            determine FOG removal efficiency
           using Equation 5.5 to develop an AHL
           based on the plant's numeric NPDES
           permit limits.
            Although animal- and vegetable-based FOG at reasonable concentrations are easily broken
            down, petroleum-based, non-polar FOG can interfere with both aerobic and anaerobic
            treatment. Petroleum-based oils can coat the organisms responsible for biological treatment
            and result in less effective oxygen transfer rates.  In anaerobic processes, excessive
            concentrations of solid grease in digesters can reduce the  effectiveness of the process, lead to
            structural damage to pipes and supports as a result of the weight of scum and grease, and
            present accumulation problems when supernatant is recycled. When digesters are well mixed
            and heated to minimize scum loads, reasonable FOG concentrations can be anaerobically
            digested. If these types of process inhibition are occurring,  POTWs could calculate FOG
            primary and secondary removal efficiencies, determine FOG inhibition criteria, and use
            Equations 5.10 and 5.11 to determine AHLs based on inhibition. See  Exhibit 5-7 for a
            description of how the City of Portland established an inhibition-based local limit for non-
            polar FOG.
 Exhibit 5-6: City of Richland, Washington,
 POTW Evaluates FOG Removal Efficiency

The Richland POTW and the Washington Department of
Ecology ("WDOE") sought to address a laundry's inability
to meet its local limits permit limit of 100 mg/L FOG.
During 1995, the laundry discharged to the POTW at an
average of 200 mg/L FOG.

Monitoring of the POTW indicated average influent levels
for FOG of 25 mg/L and effluent levels averaging less
than 1  mg/L — a FOG removal efficiency of 96 percent.
Respirometer tests on samples of the laundry's
wastewater indicated that the wastestream was a
biodegradable food source and easily metabolized by the
POTWs microorganisms.

Despite the relatively high concentration of FOG (200
mg/L) in the laundry's effluent, based on the results of this
evaluation, the city eliminated the laundry's FOG effluent
limit but continued a sampling schedule. Furthermore,
the results support previous EPA findings that petroleum
based  oil and grease compounds "can be degraded to
various degrees especially if the microorganisms are
acclimated to use the compounds as a substrate", and
that "[i]f oil and grease are biodegradable and in a
physical state [i.e., emulsified] that does not cause
clogging or undue maintenance problems in the
wastewater facilities, the discharge of these substances
can be accepted in a wastewater treatment system."
(EPA,  Treatability of Oil and Grease Discharged to
Publicly Owned Treatment Works (April 1975), p.  11)

City of Richland POTW, Richland Laundry & Dry
Cleaning, Inc.  Wastewater Discharge Permit CR-IU003
                                                5-24

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                                         Exhibit 5-7: City of Portland, Oregon Uses
                                         Current Influent Loading to Develop Non-
                                         Polar FOG Local Limit

                                         The City of Portland wanted to develop a local limit for
                                         non-polar FOG to avoid any potential for inhibition at its
                                         POTW. However, as often is the case in developing
                                         inhibition- based local limits, the MAHL was difficult to
                                         define (see Exhibit 5-3) because the plant had never
                                         experienced inhibition.  The City determined that "the
                                         POTW had not experienced process inhibition from non-
                                         polar-FOG under these conditions.  Therefore the
                                         development of a local limit based upon current loading
                                         will be protective against process inhibition." The current
                                         loading of 8.6 mg/L of non-polar FOG was used as the
                                         inhibition-based MAHL.

                                         Although using current loading to establish an inhibition
                                         based MAHL is conservative, the methodology provides a
                                         scientific basis for the development of local  oil and
                                         grease limits.  Based on this MAHL, the City established
                                         a non-polar FOG local limit of 110 mg/L.

                                         See Industrial Source Control Division, Bureau of
                                         Environmental Affairs, City of Portland, Final Report -
                                         Update of Local Discharge Standards (April 1996).
5.4 DETERMINATION OF THE MAXIMUM
ALLOWABLE HEADWORKS LOADING

After calculating AHLs for each POC for a variety
of environmental criteria, MAHL determination is
simple. The lowest (i.e., most stringent) of the AHLs
for each POC is selected as the MAHL for that
pollutant.  Influent loadings below the MAHL will
lead to compliance with the AHLs based on all
environmental and treatment plant criteria. The
MAHL will be used for all further steps of local
limits  development and evaluation.

5.5 SAMPLE MAHL CALCULATION

A POTW is attempting to determine the MAHL for
copper. From its local limits sampling plan, the
POTW has determined the following plant data:

        •    Plant removal efficiency from
            headworks to plant effluent, Rpotw = 0.85
        •    Removal efficiency from headworks to
            primary treatment effluent, Rprim= 0.65
        •    Average plant flow rate,  Qpotv = 10 MOD
        •    Percent solids in the sludge, PS = 5 percent
        •    Specific gravity of sludge, Gsludge = 1 kg/L
        •    Average sludge flow rate, Qsiudge = 0.05 MOD

For copper, the POTW determines that the suitable environmental criteria are the following:

        •    The POTW has a specific copper limit in its NPDES permit, Cnpdes = 1 mg/L copper.

        •    With biosolids being used ultimately for lawn application, Federal Sludge Land Application
            Table 3 "Clean Sludge" Limits, Cslgstd= 1,500 mg/kg copper, are applicable.

        •    Although inhibition has never taken place at the plant's activated sludge secondary treatment
            unit, the POTW wants to develop an AHL based on activated sludge inhibition. Based upon
            the highest observed copper concentration in the secondary treatment unit that did not cause
            inhibition, the POTW sets the inhibition criterion for secondary treatment, Cinhib2 = 1 mg/L
            copper.

The following  equations for AHLs based on NPDES limits (Equation 5.5), sludge standards (Equation
5.9), and secondary treatment inhibition (Equation 5.10) are used.
            AHL
               npdes
                                                  (8.34)(lmg/L)(10MGD) = 556
                                                       (1 - 0.85)
AHL,
      _ (8.34)(Cs)gsM)(PS/100)(Q^>)(Grtfc)  (8.34)(1,500mg/frg)(5/100)(0.05M3D)(1 kg/L)) _
                  R,
                   potw
                                                               0.85
                                                                                    37/ft/day
                                  5-25

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                         AHL _  .jnM,2po   8.34(1mg/L)(10MGD)_238
                                   -
From these three AHLs, the most stringent (lowest) AHL based on the sludge standard (AHLsldg) was
chosen as the MAHL for copper at 37 Ib/day.

5.6 SUMMARY

After reviewing Chapter 5, POTWs should be able to:

       •   Calculate POTW removal efficiencies for each POC
       •   Calculate AHLs for each environmental criteria
       •   Determine MAHL as the most stringent AHL for each POC

Chapter 6 describes how to assess the need for local limits, allocate the maximum allowable industrial
loadings, and develop and implement final local limits and BMPs.
                                           5-26

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CHAPTER 6 -

DESIGNATING AND IMPLEMENTING LOCAL LIMITS


Chapter 6 provides guidance on how to:

      •      Determine the need for new local limits after establishing Maximum Allowable
             Headworks Loadings (MAHLs).

      •      Calculate Maximum Allowable Industrial Loadings (MAILs).

      •      Compare MAIL allocation and implementation methods.

      •      Allocate MAILs to controlled dischargers.

      •      Perform a common sense assessment of local limits.

      •      Use best management practices.

      •      Provide public participation.

      •      Gain Approval Authority approval.

      •      Conduct public outreach.

      •      Select the appropriate control mechanism to apply local limits.


6.1 DETERMINATION OF THE NEED FOR NEW LOCAL LIMITS

Once a POTW has calculated MAHLs for all of its pollutants of concern (POCs), it can determine for
which pollutants it will require local limits.  In making this pollutant-by-pollutant evaluation, the POTW
will also want to consider historical issues and the degree to which current influent loadings approach
calculated MAHLs. For example, the concentration of some pollutants in the POTW influent may be far
below the calculated MAHLs. These pollutants are unlikely to cause problems for the POTW, so the
treatment works may conclude that local limits for them are unnecessary. EPA recommends that the
POTW document such decisions and discuss them with its Approval Authority, as needed.

Some Approval Authorities require that local limits be established for a specific set of pollutants
regardless of the outcome of the headworks loading analysis. For example, some Approval Authorities
specify that local limits be developed for arsenic, cadmium, chromium, copper, cyanide, lead, mercury,
molybdenum, nickel, selenium, silver, and zinc regardless of whether they are in the POTW's influent. If
such specific guidance is not available, EPA recommends that the POTW conduct evaluations for each
POC.
                                        6-1

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No single approach applies for all pollutants at all POTWs. The approaches presented below are
intended to determine which POCs deserve to be covered by new local limits.  In EPA's view, a POTW
should not use the approaches below in deciding whether to continue to control a particular
pollutant by a local limit because the enforcement of the local limit may be the reason that the
pollutant loading has been reduced or is no longer causing problems. If the local limit were
removed, industrial users (IDs) may discontinue their use of wastewater pretreatment and POTW
loadings may increase above the threshold in the criteria. Re-evaluation  of existing local limits is
discussed in Chapter 7.

6.1.1 ACTUAL LOADINGS vs. MAHL

Equation 6.1 compares actual POTW loadings to the calculated MAHLs  for individual POCs.  A POTW
would use this equation to calculate the percentage of MAHL being received at the POTW.  The average
and highest daily influent loading should be calculated. EPA recommends that local limits are needed
when:
       Average influent loading of a toxic pollutant
       exceeds 60 percent of the MAHL.

       Maximum daily influent loading of a toxic
       pollutant exceeds 80 percent of the MAHL any
       time in the  12-month period preceding the
       analysis.

       Monthly average influent loading reaches 80
       percent of average design capacity for BOD,
       TSS, and ammonia during any one month in the
       12-month period preceding the analysis.
   Equation 6.1: Actual Loading vs.
          MAHL Calculation
 "-INFL
MAHL
                  x100
       Percentage of the MAHL
       Current influent loading (average or
       highest daily), Ib/day
MAHL = Calculated MAHL Ib/day
EPA recognizes that these percentages to trigger local
limits development are default assumptions that can vary from plant to plant. The approach used for
toxic pollutants is more conservative because most POTWs are not designed to treat toxic pollutants.

6.1.2  NONCOMPLIANCE DUE TO PASS THROUGH OR INTERFERENCE

The basic purpose of the pretreatment program is to prevent pass through and interference, and the
General Pretreatment Regulations require that local limits be established to prevent them. EPA
recommends that in the absence of strong evidence that the cause of pass through or interference has
been eliminated, a POTW retain local limits for the pollutants causing historic violations. By reviewing
past NPDES permit violations, sludge disposal restrictions, or inhibition incidents, the POTW can
identify the pollutants for which it should set or maintain local limits.

6.1.3  ESTABLISHING LOCAL LIMITS FOR CONVENTIONAL POLLUTANTS

Conventional pollutants such as BOD,  TSS and ammonia require additional evaluation before decisions
are made to set a MAIL and put in place a local limit. Controlling conventional pollutants from Ills must
be evaluated in a broader context, because the POTW was designed to treat conventional pollutants. A
                                             6-2

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comprehensive evaluation of the POTW may be needed (see Section 5.3) and many alternatives in lieu of
or in addition to local limits may be considered.

A POTW that is approaching its design capacity for BOD/TSS should begin planning to avoid future
violations.  NPDES permits sometimes include a reporting requirement when the POTW begins to
operate at 80-90 percent of its original design capacity for 90-180 consecutive days. EPA recommends
using a similar threshold as a basis for investigating alternatives for reducing or responding to future
conventional loadings.  If the rate of increase in influent conventional pollutants loadings suggests that
the full capacity of the plant will be utilized within five to seven years, then planning may need to begin
immediately. The planning need not automatically assume that local limits would be set for conventional
pollutants.  Several alternatives should be investigated in  addition to local limits. These include:

       •      Minimizing growth of the community by  controlling sewer connections.

       •      Initiating POTW modifications to optimize performance (through chemical additions,
              filtration, membrane filtration, and other methods).

       •      Modifying operation or flow configurations.

       •      Expanding POTW capacity via facilities planning.

       •      Reducing industrial sources of conventional pollutants through incentives and
              disincentives.

Each POTW has a unique, historical background of successful operation with respect to conventional
pollutants, and whether each POTW can operate successfully at a given  (elevated) loading will vary from
plant to plant.  Some of these concepts are reviewed in Section 5.3.

POTW expansions can take up to 5 years. Therefore, it is vitally important to monitor loadings to the
plant against the POTW design capacity.  Failure to plan in a timely manner can result in NPDES
violations.  With respect to nitrogen management, it is useful to note that nitrogen removal at the POTW
typically requires four times the biological treatment volume needs of BOD, hence the need to quantify
significant industrial sources of nitrogen to optimize control and treatment.
                                              6-3

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6.2 CALCULATION OF MAXIMUM ALLOWABLE INDUSTRIAL LOADING

MAHLs estimate the maximum combined loadings that can be received at the POTW's headworks from
all sources.  MAILs developed by the POTW represent the amount of pollutant loadings the POTW can
receive from controlled sources (i.e.,
industrial users, some commercial
sources1, and some hauled waste) that
the POTW chooses to control through
local limits.  As shown in Equation 6.2,
the MAIL is calculated by subtracting
estimates of:
               Loadings from
               uncontrolled sources
               \Lunc)
               Hauled waste not
               regulated through local
               limits (HW)
               Growth allowance (GA)
            Equation 6.2: MAIL Calculation
               MAIL= MAHL(\ - SF)- (LUNC+ HW+ GA)
Where:
MAIL =
MAHL =
SF =
HW =
GA =
Maximum allowable industrial loading, Ib/day
Maximum allowable headworks loading, Ib/day
Safety factor, if desired
Loadings from uncontrolled sources (uncontrolled sources=
domestic + some commercial + l&l)
Loadings from hauled waste, if not regulated through the local
limits
Growth allowance.
from a MAHL adjusted with a safety factor (SF).  These four elements of the MAIL calculation-
loadings from uncontrolled sources, hauled waste, growth allowance, and safety factor - are further
explained in the next four subsections.  Table 6-1 provides a summary on the information needed to
calculate the MAIL.
                          Table 6-1: Data for Implementation of MAHLs
Parameter
IU and significant
industrial user (SIU)
flow
Uncontrolled Source
Pollutant
Concentrations
Uncontrolled Source
Flow
Hauled Waste Loadings
Safety Factor
Growth Allowance
Comments
Total flow from all SlUs and lUs, plus any commercial dischargers
that the POTW intends to control
Levels of POCs in domestic and commercial discharges that the
POTW does not intend to control with local limits
Flow from all uncontrolled sources, either in total or divided by
type of facility (domestic, commercial, l&l, storm water)
Based on volume and pollutant concentration data
Varies depending on quality and amount of data
Varies based on the projected growth for the area
Source of Data
POTW local use sampling
program, periodic reports from
SI Us
POTW local use sampling
program
POTW local use sampling
program
POTW sampling of waste
hauler loads
POTW choice based on data
analysis
POTW choice based on data
analysis
         For example, a POTW may choose to regulate or limit the discharges from some or all of its commercial dischargers
(e.g., dental offices, hospitals, and restaurants), in which case they would be considered controllable sources.
                                               6-4

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6.2.1 UNCONTROLLED SOURCES
As noted above, some sources of pollutant loadings to the POTW are considered uncontrolled.  They
include domestic users, inflow and infiltration (I&I), treatment chemicals added to sewers, storm water,
and some or all of a POTW's commercial dischargers.  Because the POTW does not control the loadings
that these users discharge [except through the general and specific prohibitions in the POTW's sewer use
ordinance (SUO)], the POTW needs to subtract these loadings from its MAHLs before it can determine
the MAIL (see Equation 6.2).  EPA recommends the following approach for calculating the contribution
to the MAHL from these uncontrolled loadings: First, the POTW conducts site-specific  monitoring of
the uncontrolled discharges at sewer trunk lines that receive wastewater from only these  sources (see
Section 4.1.2). This activity will enable the POTW to develop data on average pollutant concentration
levels. The POTW then multiplies the concentration loadings for each pollutant obtained from these
locations (Cmc) by the POTW's total uncontrolled flow rate (Qmc) to determine total loadings to the
POTW for that specific pollutant from all uncontrolled sources (see Equation 6.3).

EPA strongly encourages POTWs to use site-specific data for uncontrolled loadings whenever possible.
Appendix V includes data on pollutant concentrations found in typical domestic wastewater discharges,
which can be used if site-specific data are not available. Because domestic wastewater values may not be
representative of the uncontrolled discharges in their systems, POTWs should use care with these data.

A POTW may find that the total uncontrolled loadings of a particular pollutant approach or exceed the
MAHL.  In these cases, little or no pollutant loading is available for Ills. This situation may arise in part
because some of the facilities considered uncontrolled are commercial facilities such as gas stations,
radiator repair shops, car washes, or hospitals, which may discharge high levels of pollutants.  These
facilities may be grouped initially with uncontrolled sources because they are small  or have low
discharge flows.  The POTW may need to  carefully evaluate the sources it considers uncontrolled to see
if some of them would be better classified  as controlled sources with reducible pollutant loadings.  Refer
to the Supplemental Manual on the Development and Implementation of Local Discharge Limitations
under the Pretreatment Program (EPA-W21-4002,
May 1991) for typical pollutant loadings for selected
commercial industries.  This is recommended for
POTWs whose allocations to uncontrolled sources
consume most or all of its MAHLs for some
pollutants. In addition, see Section 9.5 for additional
guidance addressing this issue.
Equation 6.3: Uncontrolled Loading
            Calculation
                                                    Where:
                                                    '-u/vc =
                                                    8.34 =
     Uncontrolled loading, Ib/day
     Uncontrolled pollutant concentration, mg/L
     Uncontrolled flow rate, MGD
     Unit conversion factor.
If a POTW has considerable loadings from I&I and
storm water (from combined sewer systems), it
should try to estimate their loadings and include them
in the uncontrolled loadings estimate.  The POTW
may be able to select sampling locations that include
these flows, or it may be able to estimate them by
analyzing the variations in flow between periods of
wet and dry weather. In some cases, the POTW may be able to decrease the flows and loads from I&I
and storm water through sewer system rehabilitation and pollution prevention programs so that loads
from these sources do not consume a substantial portion of the POTW's MAHLs.
                                              6-5

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The POTW may be able to estimate loadings from uncontrolled sources by subtracting loadings of
controlled sources from total influent loadings.  This method may be useful when most or all of a
POTW's data for uncontrolled sources are below detection levels for a pollutant. When the data are
mostly below detection levels, the POTW should carefully evaluate how to handle these data because
these decisions can greatly affect the loadings available for Ills.  Additional guidance on setting local
limits when uncontrolled source loading exceeds the MAHL has been  developed by EPA Region 5 and
can be found at: http://epa.gov/r5water/npdestek/npdprtg3.htm.

6.2.2 HAULED WASTE
As previously noted, POTWs that do not regulate
waste haulers through local limits will want to
determine the loads they receive from hauled waste
and subtract these loads from their MAHLs before
determining their MAILs.  EPA recommends that
POTWs base the allocations for hauled waste on
actual data - pollutant concentrations and flows from
waste haulers collected by sampling hauled waste
brought to the treatment works. EPA further
recommends that POTWs regularly sample these
loads to ensure that they are not hazardous waste, do
not contain  toxic pollutants in amounts greater than
expected or greater than local limits, and will not
pose risks to the treatment plant or its workers.  In
addition, EPA reminds POTWs that hauled waste
subject to categorical limitations must meet those
limits when accepted at the POTW and that
pretreatment standards apply to wastes hauled from
Ills. Additional information on the acceptance and
characterization of hauled wastes at POTWs is
available in Guidance Manual for the Control of
Waste Hauled to Publicly Owned Treatment Works
(EPA/833-B98-003). The guidance discusses
collection of information on waste haulers,
characterization of hauled waste received,  evaluation
implementation of controls.

6.2.3 SAFETY FACTOR
        Exhibit 6-1: Safety Factor Example

    If a POTW's data for cadmium were all below detection
    and the POTW used literature data for cadmium
    removal efficiencies, the treatment works should
    consider using a safety factor for cadmium.  At the
    same time, if the POTW's zinc data were mostly above
    detection and the daily removal efficiencies were all
    between 60 and 80 percent, the POTW may not need
    to use a safety factor for zinc. The decision to use a
    safety factor for zinc removal on pass through would
    depend on the quality of the data used to calculate the
    removal efficiency. In this example, assume that the
    removal efficiency is based on 12 months of paired
    influent and effluent samples that range from 60 and
    80 percent and collected as hydraulically lagged pairs.
    Because this data set is of high quality, the POTW
    might not use a safety factor. If an ADRE is
    calculated, it will lie in the 60 to 80 percent range. If
    the ADRE is 72 percent, the POTW will want to
    consider the degree of safety that would exist should
    the actual removal efficiency be lower. This, along with
    the potential to violate water quality standards or
    NPDES effluent limits, also needs to be considered.

    Note that the ADRE for pass through is the same value
    used for sludge quality protection calculations. The
    POTW should also examine the data set to determine
    the potential for removals to be higher than the ADRE
    leading to violations of sludge disposal quality criteria.
of potential impacts and development and
Determining safety factors is an imprecise process, which has the potential to affect significantly the final
local limits.  A safety factor is site specific and depends on local conditions. The main purpose of a
safety factor is to address data "uncertainties" that can affect the ability of the POTW to calculate
accurate local limits. Some Approval Authorities may have mandatory safety factors. At a minimum,
EPA generally recommends a 10 percent safety factor.  The determination of whether a safety factor is
needed and, if it is, how large the safety factor should be depends on the following elements:

               The variability of the POTW's data.
                                                6-6

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       •      The amount of data the POTW used to develop its MAHLs.

              The quality of the POTW's data.

       •      The amount of literature data the POTW used.

       •      The history of compliance with the parameter.

       •      The potential for IU slug loadings (e.g., as a result of chemical spills).

       •      The number and size of each IU with respect to the POTW's total flow rate.

The POTW may use different safety factors for different pollutants.  The above elements may vary from
pollutant to pollutant, making it appropriate for a POTW to use different safety factors (see Exhibit 6-1).

6.2.4 EXPANSION/GROWTH ALLOWANCE

A POTW that anticipates a significant amount of growth in the future can consider holding in reserve a
portion of its MAHLs for this growth.  This expansion/growth allowance is separate from the safety
factor.  Anticipated growth should be projected for known, planned expansions such as Ills moving into
the POTW's service area or existing Ills expanding their operations, the development of a shopping mall
or the opening of other commercial businesses in a new office park, or the construction of a new housing
development. The expansion and growth allowance is most commonly justified for BOD, TSS, and other
pollutants the POTW was designed to remove.  By holding in reserve some of the MAHL, the POTW has
a portion to allocate to the new discharges and may not need to revise its existing IU permits or SUO.

6.3  COMPARISON OF MAIL ALLOCATION AND IMPLEMENTATION METHODS

Uniform-concentration local discharge limitations have become synonymous in the Pretreatment Program
with the term "local limits." However, local limits can take many forms based on how MAILs are
allocated to lUs.  The designation and implementation of these MAILs, including the allocation of
loadings to lUs, are left to each POTW, as long as the implementation procedures do not allow the
calculated MAHL to be exceeded and provide a reasonable method for making allocations to the lUs.
This section describes some of the implementation decisions facing POTWs. The selection of an
appropriate implementation approach is an integral aspect of a POTW's local limits process.

A POTW may select any allocation and implementation method that results in enforceable local limits to
prevent pass through and interference and to comply with the prohibitions in the Federal regulations.
The POTW should choose the allocation approach that best fits its own situation. It may choose one
approach for some pollutants and another approach for other pollutants, depending on the amount  of
loading available to lUs and the number of lUs discharging a given pollutant. For example, if only three
of a POTW's ten lUs discharge silver, the POTW may prefer to allocate its allowable industrial silver
loading among the three lUs that discharge silver so that these lUs receive more achievable limits. At the
same time, if all of the users discharge  copper, the POTW may choose to allocate the MAIL for copper to
all of the users on a uniform basis. All regulated lUs should receive at least a background allocation for
copper and all other POCs.
                                             6-7

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Table 6-2 on the next page lists issues that POTWs will want to consider when determining how to
allocate and implement its local limits.  Ultimately, the POTW will want to allocate pollutant loadings in
a fair and sensible way that does not favor any one industry or group of industries, considers the
economic impacts, maintains compliance with the NPDES permit, and otherwise achieves the
environmental goals of the program.  The allocation method selected may be subject to State and local
public participation requirements in order for the resulting local limits to become legally enforceable.

6.4 ALLOCATION OF MAILs AMONG CONTROLLED SOURCES

A POTW can apply to its controllable sources concentration-based limits (typically in mg/L), or mass-
based limits (typically in Ib/day), or both. The type of limit depends in part on the method chosen by the
POTW to allocate its MAILs among the controlled dischargers. For example, a POTW that uses the
uniform concentration method based  on total IU flow typically implements a pollutant limit as a single
concentration (generally in its  SUO) applicable to all controlled users. If the POTW allocates its MAILs
on a case-by-case basis depending on an Ill's need for a certain loading allocation, the POTW may find it
easier to apply mass-based limits (in individual permits) that allow for the needed loading at the IU. The
POTW needs to consider the ability to determine and enforce  compliance. EPA recommends that the
POTW consider the lU's sampling capabilities when determining the type of limits to apply to an IU. An
IU may not have flow meters or sampling points necessary to determine mass-based limits. In these
cases, the POTW may instead put concentration-based limits in the IU permits or, potentially, both types
of limits in the permit. Thus, the POTW may first allocate its MAILs based on loadings, but then apply
the allocations to lUs as concentration-based limits based on flow. EPA recommends that POTWs use
mass-based limits only for users that have the capability (or are required to develop the capability) to
accurately measure their flows at the  designated sampling points.  Mass-based limits have the added
benefit of allowing lUs to reduce their water consumption through conservation or recycling without
affecting their ability to meet local limits.

6.4.1 LIMIT DURATION

When applying its local limits, a POTW needs to determine the appropriate limit duration.  The POTW
may establish limits that are daily maximums, monthly averages, or instantaneous maximums. In
general, a POTW should base the limit duration on the type of criteria - long-term or short-term - used to
develop the local limit. However, most local limits will be implemented as daily maximums based upon
two main factors:  1) the short-term nature of the event that the local limit is protecting against; and
2) the infrequency of IU  sampling. Scenarios illustrating this  are presented below.
                                             6-8

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                   Table 6-2:  Options for Allocating and Implementing Local Limits
          Method
              Pros
                 Cons
 Allocate MAILs uniformly
 among all Ills and place
 uniform concentration limits in
 the local SUO
-Limits are clear to I Us
-Requires little time to calculate limits
-Easy to determine compliance
-Need to update SUO when limits change
-Inflexible
-Limits may be overly stringent because some
I Us may get an allocation but do not discharge a
pollutant
 Place general language about
 complying with local limits in
 the local SUO and announce
 the actual uniform limits outside
 the SUO
-Do not have to revise the SUO every
time local limits change
-Easy to monitor for compliance
-Relatively easy to calculate limits
-lUs may not be clear on the limits with which
they must comply
-Action may be overlooked by the general public
and interested parties
 Place general language about
 complying with local limits in
 the local SUO and place
 individual limits in IU permits
-Do not have to revise the SUO every
time local limits change
-Provides flexibility
-Requires issuing a permit to all lUs to which the
POTW wants limits to apply
-Action may be overlooked by the general public
and interested parties
 Put MAILs in SUO, allocate
 loadings on an IU contributory
 flow or mass proportion basis,
 and place limits in IU permits
-Only I Us that discharge a pollutant are
given a full allocation so limits are more
efficiently allocated
-Helps avoid setting excessively
stringent or unattainable limits
-Requires knowing more about IU discharges
(need to know their pollutant content)
-Requires updating the SUO when MAILs change
-Requires issuing permits to all lUs with specific
limits
-May penalize I Us that are currently pretreating if
others are not
 Put MAILs in SUO, allocate
 loadings on a case-by-case
 basis to those I Us that need an
 allocation for a specific
 pollutant, and place limits in IU
 permits
-Only I Us that discharge a pollutant are
given a full allocation so limits are more
efficiently allocated
-Helps avoid setting excessively
stringent or unattainable limits
-Provides flexibility
-Requires knowing more about IU discharges
(need to know their pollutant content) and
applicable pretreatment systems
-More time-consuming to determine allocation
-Can lead to an inequitable allocation among I Us
-Requires updating SUO when MAILs change
-Requires issuing permits to all lUs with individual
limits
EPA recommends use of a daily maximum in the following circumstances:

        •       A local limit based upon short-term criteria should be a daily maximum.  For
                example, local limits based upon NPDES permit limits expressed as daily maximums
                should be considered daily maximums.

        •       A local limit based upon long-term criteria, BUT protecting against a short-term
                event, should be a daily maximum. For example, a local limit based on chronic water
                quality criteria would appear to warrant assigning a long-term limit duration such as
                monthly average. However, the local limit should be considered a daily maximum
                because the MAHL calculation using water quality criteria is based on either the
                receiving stream's  1Q10 or 7Q10 flows, both of which are short-term phenomena (see
                Equation 5.6).  Another short-term condition that leads to a daily maximum limit is
                biological inhibition for both secondary and tertiary treatment, both of which have short
                residence times.
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               A local limit based upon long-term criteria and protecting against a long-term
               event, BUT the sampling cannot generate a true monthly average, should be a daily
               maximum.  For example, monthly average "clean sludge" criteria, can be the basis of a
               local limit. Residence times in sludge digesters and storage facilities are commonly 20
               to 30 days or more. Consequently, to change the concentration to any appreciable
               degree, any excessive loading would have to be maintained for three to four weeks - a
               long-term event. These two factors favor a monthly average type local limit. However,
               an IU will rarely sample for the metals that end up in the POTW sludge more than once a
               month. Therefore, local limits for sludge disposal, although based upon a long-term
               criteria and protecting against a long-term event, should be considered a daily maximum
               limit.
This means of assigning local limit duration is protective in that it leads to enforcing local limits based on
monthly average criteria as daily maximums.

In terms of other duration types, EPA recommends that local limits should be monthly averages when
the environmental criteria that they are based upon is long term, the protected event is long term, and
frequent IU sampling can generate a true monthly average. EPA recommends that instantaneous limits
be developed for pollutants that cannot be composited. A limit derived from a MAHL based on one-hour
acute toxicity water quality criteria may not be protective if it is implemented as a daily maximum
instead of as  an instantaneous limit. However, if the instantaneous limit is converted to a daily maximum
limit using a  statistical procedure that
accounts for the variation in
concentrations over a 24-hour period, the
daily maximum limit should be adequately
protective. The EPA Technical Support
Document (TSD) approach, described in
the Technical Support Document for Water
Quality Based Toxics Control (EPA,
199 la), accounts for these variations.
Instantaneous limits may also be
appropriate where Approval Authorities
require lUs to accumulate all wastewater
flows in batch tanks.  Grab samples can
then be collected to evaluate an
instantaneous limit.
6.4.2 ALLOCATION APPROACHES

A POTW can use several basic approaches
to assign limits to its controlled
dischargers.  As noted above, the POTW
can select different allocation methods for
different pollutants. Several common
approaches for allocating MAILs for
conservative pollutants are described in
this section.  A POTW may choose to use
         Exhibit 6-2: Background Allocation

When using the IU Contributory Flow Method or Mass Proportion
method, any user that discharges at or below the background level is
given a background allocation (unless a different allocation can be
justified based on actual sample data). Please note that:

• Background loading can be calculated for each pollutant using the
  uncontrolled concentration for that pollutant and the flow of that
  pollutant from the "non-contributing" industries.  (Background flow
  from non-contributing industries may be different for each
  pollutant.)

• These background "limits" are then applied to non-contributing
  industries.
  Similar to how estimated uncontrolled source loading can actually
  exceed the MAHL (see Section 6.2.1), estimated loadings from
  non-contributing I Us discharging the pollutant at background
  levels can result in an over-allocation of the MAIL. In other words,
  the estimated loading from lUs discharging at pollutant
  background levels plus the loading from I Us discharging the
  pollutant at local limit levels is greater than the MAIL.  Generally,
  this occurs because background levels are set too high. POTWs
  should make sure that their determination  of background levels is
  sound and check their allocation method.  For instance, a uniform
  concentration specified in a Sewer Use Ordinance for a
  background concentration can lead to an over-allocation error
  (see Equation 6.7 on the next page).
                                               6-10

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another method, such as a statistical method, as long as it results in local limits that are enforceable and
adequately protective.
Limits Based on IU Contributions of a
Pollutant
Two allocation methods divide the MAILs
among only the controlled dischargers that
discharge a particular pollutant. These
methods develop Ill-specific discharge
limits. Any user that discharges at or below
the background level is given a background
allocation unless a different allocation can
be justified based on actual sample data (see
Exhibit 6-2 on the previous page).

The IU Contributory Flow method is similar
to the uniform method described below,
except that the portion of MAILs above
background (MAIL - LBACK) is divided by the
flow rate from controlled sources (Qcomo)
discharging the pollutant above background.
The concentration-based limits (CLIM) apply
only to those users (see Equation 6.4).

The Mass Proportion method allocates
MAILs to each controlled discharger in
proportion to the discharger's loading of
that pollutant. To calculate the allowable
loading for a user (LALLx) the portion of the
MAIL above background (MAIL - LBACK) is
multiplied by the ratio of the current loading
from user x (LCURRJ to the current total
loading of a pollutant from controlled
sources (LCURRt).  The mass-based loading
calculated using the mass proportion
method can be converted to a concentration-
based limit (see Equations 6.5 and  6.6).

Uniform Limits For All Controlled
Dischargers
As illustrated in Equation 6.8 (on the
following page), the uniform limits method
of allocating MAILs for conservative
pollutants yields one limit per pollutant
(CUM) that applies to every controlled
discharger. It requires that the MAIL for
each pollutant be divided by the total flow
rate from all controlled dischargers (QcoNr),
  Equation 6.4: ID Contributory Flow Calculation
   Equation 6.5: Mass Proportion Method fora
             Mass-Based Local Limit
                  LCURR,
   Equation 6.6: Mass Proportion Method fora
            Concentration-Based Limit
                       <-ALLx
                     (Qx)(8.34)
       Equation 6.7: Uniform Allocation of
               Background Loading
Where:
Q/M =

r*    —
^BACK ~

MAIL =




Qco/vro =
1-CURRx ''

•—C.IIRRt ~
                      (CWX8-34)
Concentration-based limit for all users discharging a
pollutant, mg/L
Concentration-based limit for all users discharging
pollutant at or below background, mg/L
Maximum allowable industrial loading, Ib/day
Total background loading allocation for all users for
which no contributory flow limit is being established for
that pollutant, Ib/day
Flow rate from all industrial and other controlled
sources discharging the pollutant, MGD
Flow rate from all industrial and other controlled
sources not discharging the pollutant at or below
background, MGD
Allowable loading allocated to userx, Ib/day
Current loading from userx, Ib/day
Total current loading to POTWfrom controlled sources,
Ib/day
Discharge limit for user x, mg/L

                                                6-11

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even those that do not discharge the pollutant. This method can be overly stringent because some Ills
that do not discharge the pollutant will be given an allocation of the MAIL that they may not need.  Other
Ills that do discharge that same pollutant may have to pretreat to comply with the local limit.

Basis of IU Needs for Discharge Loading/Case-by-Case Basis
A POTWmay set lU-specific limits case by case.  This type of allocation relies on the POTW's judgment
to determine the amount of the MAIL to allocate to each controlled discharger.  The limits can be based
on the discharger's current loading, its need for a continued loading allocation, its ability to apply
pretreatment to achieve certain discharge pollutant levels (i.e., treatability), or any other factor that the
POTW determines is relevant.  The POTW needs to ensure that the sum of the allocated loadings does
not exceed the MAIL and that it provides for at least a background allocation for each pollutant for each
user, unless a lower allocation can be justified by sampling data. To ensure that it does not allocate more
than the MAIL, the POTW should develop a mechanism to track the loading allocated to each IU and
compare the allocated total to the MAIL.
Creative Allocation Methods
In general, once the MAIL is calculated, the
POTW has substantial flexibility in
allocating the pollutant load among its Ills
as long as a margin of safety is maintained,
the POTW has carefully accounted for all
allocations, and public notice of the
allocation is properly issued and allocation
is adopted. For example, the Hampton
Roads Sanitation District (HRSD) has
developed flow-based local limits.
Industries are placed in one of the following
flow categories:
    Equation 6.8: Uniform Concentration Limit
                   Calculation

                          MAIL
Where:
CUM =
MAIL =
Qco/vr =

8.34 =
Uniform concentration limit, mg/L
Maximum allowable industrial loading, Ib/day
Total flow rate from industrial and other controlled
sources, MGD
Unit conversion factor
        •       0 to 9,999 gallons per day (gpd)
               10,000 to  19,999 gpd
               20,000 to 29,999 gpd
               30,000 to 39,999 gpd
               40,000 to  199,999 gpd
               200,000 to 399,999 gpd
               Greater than 400,000 gpd

Uniform limits are applied to each industry within the same flow category. The local limits become
progressively more stringent as the industry's discharge flow increases.  lUs that discharge above 400,000
gpd are assigned specifically calculated local limits based on domestic loadings and the industrial
processes from the specific facility. As an illustration, lUs with a flow rate of 0 to 10,000 gpd would
have a nickel limit of 10.0 mg/L, while those with a rate of 200,000 to 400,000 gpd would have daily
maximum nickel limit of 1.0 mg/L. HRSD uses this scheme for its local limits for the following
parameters: arsenic, cadmium, chromium, copper, cyanide, lead, mercury, nickel, phenolic compounds,
silver, zinc, and non-saponifiable oil and grease.

Another creative form of MAIL allocation that POTWs may consider is pretreatment trading or effluent
trading. These programs allow one source to meet its regulatory obligations by using pollutant
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reductions created by another source that has lower pollution control costs.  Trading capitalizes on
economies of scale and the control cost differentials among and between sources. Trading policy is
applicable to local limits, only. The policy does not apply to categorical standards.  EPA supports a
municipality or regional  sewerage authority developing and implementing trading programs among
industrial users that are consistent with the pretreatment regulatory requirements at 40 CFR Part 403 and
the municipality's or authority's NPDES permit. See Final Water Quality Trading Policy, EPA, Office of
Water, Water Quality Trading Policy, January  13, 2003.  Available at:
       http://www.epa.gov/owow/watershed/trading/finalpolicy2003.html.

6.5 COMMON SENSE ASSESSMENT

After developing and allocating local limits, POTWs should determine whether their local limits pass a
"common sense test."  An effective public participation process can help with this assessment. Some of
the questions a POTW should ask to determine if its limits pass the "common sense" test are:

       •       Are the  limits technologically achievable? Are Ills  and other controlled dischargers
               likely to meet these limits with currently available forms of pretreatment and pollution
               prevention (e.g., process modifications)? Local limits are meant to protect the POTW
               and the environment and therefore are not specifically based on technological
               achievability.

       •       Can the POTW  and dischargers determine compliance with the local limits? Are
               the limits above sampling method detection  levels?  If the limits are below the detection
               level of the most  sensitive analytical method, neither the POTW nor the Ills will be able
               to definitively determine compliance.

       •       Are the  limits sensible in light of actual conditions at the treatment plant and past
               compliance experience?  For  example, if the POTW is currently violating its NPDES
               limit for copper but the local limits analysis  indicates that the POTW can accept its
               current influent loading and maintain compliance with that limit, the calculations and the
               past experience are in conflict. In this situation, the POTW should determine the
               reason(s) for the inconsistency.

If a POTW's calculated limits do  not pass the "common sense test," the POTW may need to reassess its
limits development process or investigate other options for reducing pollutant loads (e.g., source
reduction measures).  Besides the environmental criteria used in the calculations, the two pieces of data
that can have the greatest impact on the local limits calculations are the removal rates and the
uncontrolled pollutant concentrations. A reassessment of the limits development process may show that
several of the limits are affected by a lack of data and the use of literature values.  By conducting
additional sampling (possibly using lower detection limits), a POTW may obtain better data and, thus, be
able to calculate more appropriate limits.

Despite the POTW's efforts to obtain the best data available for the calculations, the local limit
calculated for a specific pollutant may at times be  unreasonable and warrant other actions to establish
valid limits. Other options for reducing pollutant loads to the POTW include the following:

       •       Adding other commercial facilities to the set of controlled sources and requiring those
               facilities to reduce the pollutant load in their discharges.  For example, a POTW's

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               MAHL for silver could be less than the uncontrolled loading resulting in a negative local
               limit.  By adding other silver dischargers (e.g., photoprocessors) to the group of
               controlled Ills, the uncontrolled loading may be reduced significantly enough to
               calculate a reasonable limit.

       •       Instituting a public education program to reduce problem discharges from domestic and
               other non-industrial (e.g., dental offices) sources.  Some POTWs have worked with area
               dental associations to help educate dentists about proper disposal practices for mercury
               amalgam. Other POTWs have held hazardous waste disposal days to reduce the amount
               of household hazardous wastes discharged into sewers. See more on working with
               industry on Best Management Practices (BMPs) in Section 6.6.

       •       Limiting acceptance of hauled waste to fewer loads, smaller loads, or lower pollutant
               levels.  If hauled wastes contribute significantly to uncontrolled loadings, the POTW
               may need to stop accepting some hauled waste.

       •       Conducting an I&I reduction program. Although I&I will generally contain lower
               concentrations of most pollutants than typical domestic sewage, it may contribute
               loadings that can increase problems with limits calculations.

       •       Encouraging the replacement of piping that contributes significant loads of copper and
               lead.

       •       Examining impurities, such as  mercury, in chemicals used by industry, POTWs and
               water suppliers.  Additionally, POTWs should be aware that the chemicals used in
               potable water treatment, such as fluoride (hydrofluorosilicic acid additive to prevent
               tooth decay) and zinc (zinc orthophosphate for corrosion control), can contribute to
               POTW pollutant loads.

A POTW that cannot develop reasonable local  limits may need to consider changing sludge disposal
methods (if sludge is the limiting factor) or, in the long term, expanding the capacity of its treatment
plant (especially for pollutants such as BOD, TSS, or ammonia).  In any event, a POTW that is
experiencing difficulty developing reasonable limits should contact its Approval Authority to discuss
possible solutions.

6.6 BEST MANAGEMENT PRACTICES

The General Pretreatment Regulations do not specifically address the use of BMPs. The regulations at
40 CFR 403.5(c) require the POTW only to develop "specific limits" for prohibited discharges.  The
current regulatory language is ambiguous as to whether BMPs may serve in lieu of numeric limits.
However, the proposed Pretreatment Streamlining Rule (40 CFR Part 403, Streamlining the General
Pretreatment Regulations for Existing and New Sources of Pollution, July 22, 1999) states that BMPs
may be enforceable as local limits as an alternative to  numerical limits or may supplement local limits.
BMPs would need to be included in the technical evaluation of local limits. BMPs are defined in the
NPDES regulations (40 CFR 122.2) as scheduled activities, prohibitions of practices, maintenance
procedures and other management practices to  prevent or reduce pollution. Some recently developed
Effluent Limitation Guidelines, such as those for Pulp, Paper and Paperboard (40 CFR 430),
Transportation Equipment Cleaning (40 CFR 442) and Pesticide Formulating, Packaging and

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Repackaging (40 CFR 455), allow for use of BMPs in meeting prescribed limits. BMPs also include
treatment requirements, operating procedures, sludge or waste disposal, or drainage from raw material
storage, and practices to control plant site runoff, spillage or leaks.

Some commercial establishments may discharge pollutants in quantities that can be controlled either by
local limits or by BMPs. A photofmisher that discharges to a POTW that is critically loaded with silver
is one example. The POTW might elect to require silver BMPs in lieu of a permit and account for this
allocation and anticipated reduction in silver in coordination with more traditional permits issued to Ills
with mass-based or concentration-based local limits. However, to the extent that BMPs are used as an
alternative or supplement to technically based local limits, the technical evaluation will need to assign an
allocation to the pollutants and users covered by the BMP. A series of BMP mini-case studies is
presented in Appendix W.

EPA suggests the following resources in POTW development of BMPs:

        •       Pollution Prevention Information Clearinghouse Resource List: This comprehensive Web
               site has sector-specific guidelines on pollution prevention.
               http://www.epa.gov/opptintr/library/ppicdist.htm

        •       Guides to Pollution Prevention: Municipal Pretreatment Program, (EPA 625/R-93/006
               October 1993)

        •       Guidance Manual for Developing Best Management Practices, (EPA 833/B-93/004
               October 1993)

        •       Pollution Prevention (P2) Guidance Manual for the Pesticide Formulating, Packaging,
               and Repackaging Industry: Implementing the P2 Alternative, (EPA 821-B-98-017 June
               1998)

        •       The Massachusetts Water Resources Authority (MWRA) currently prohibits the
               discharge of mercury by industrial facilities to its sewer system. Additionally,  MWRA
               imposes an effective discharge limitation for mercury of 1.0 part per billion (ppb) from
               its regulated sources, including hospitals and institutions. To address this  complex issue,
               the MWRA established  a Mercury Products Work Group to examine the problem and
               develop strategies to reduce the amount of mercury being discharged.  Read about this
               effort at: http://www.masco.org/mercury/index.htm.

6.7 APPROVAL AUTHORITY AND ADOPTION PROCESS

A Control Authority's legal authority to  impose local limits on industrial and commercial users derives
from State law. Therefore, State law must confer the minimum Federal legal authority on a Control
Authority. Where deficient, State law must be modified to grant the minimum requirements. In order to
apply regulatory authority provided by State law, the Control Authority generally must establish local
regulations to legally implement and enforce pretreatment requirements.  If the Control Authority is a
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municipality, legal authority is detailed in a Sewer Use Ordinance (SUO),2 which is usually part of a city
or county code. Regional Control Authorities frequently adopt similar provisions in the form of "rules
and regulations." Likewise, State agencies implementing a State-wide program under 40 CFR 403.10(e)
set out pretreatment requirements as State regulations, rather than as a SUO.  However, local regulations
cannot give the Control Authority greater authority than that provided by State law.

Establishing or revising local limits is considered to be a modification of the POTW's pretreatment
program. Therefore, the new or changed local limits must be submitted to the Approval Authority for its
review and approval. The POTW must submit a notice to the Approval Authority that states the basis for
the modification and must provide a modified program description and other documentation requested by
the Approval Authority.  After a modification is approved by the Approval Authority, it will be
incorporated into the POTW's NPDES permit [40 CFR 403.18(e) and 40 CFR122.62].

In most instances, the initial adoption of a MAIL or BMP will be a substantial modification where it
replaces a different form of local limits.  Unless the mass-based limit or BMP is specifically tied to an
existing concentration limit, the  switch to mass-based limits or to BMPs will likely result in less stringent
local limits for at least some group of industrial users. As specified at 40 CFR 403.18(b)(2), making a
local limit less stringent is considered a substantial modification of a POTW's pretreatment program.
Not only is the relaxation of a uniform concentration limit considered a substantial modification, but if a
POTW calculates  a less stringent concentration limit, the MAHL or MAIL also becomes less stringent.
If this is the case, the Approval Authority may be required to process any new local limits as a substantial
modification as well. For substantial modifications, the Approval Authority must issue a public notice of
the request for approval and must provide an opportunity for interested parties to comment or request a
public hearing. After deciding whether to approve the modification, the Approval Authority must issue a
public notice  of approval or disapproval, unless certain conditions are met [40 CFR 403.18(c)(3)].

Non-substantial modifications may be implemented after 45 days, unless the Approval Authority notifies
the POTW that a modification is disapproved or determines that the modification is substantial (e.g.,
would result in an increase in pollutant loadings at the POTW) [40 CFR 403.18(d)]. To be approved by
the Approval Authority, local limits must first be made legally enforceable by the POTW. This is
generally done by incorporating  them in the local SUO by following local public noticing procedures.
The SUO need not contain local limits already allocated to industries. However, at a minimum, the SUO
should authorize the POTW to establish individual limits through the permits based on the MAIL.

The activities described above are regulatory requirements that must be met by all Approval Authorities
and POTWs.  Approval Authorities may have different procedures for implementing these requirements,
and POTWs should check with their Approval Authority for details.  In general, however, the approval
and adoption process includes the following steps:
         Consult Model Pretreatment Ordinance, (EPA 833-B-92-003, June 1992) for recommended formats for a Sewer Use
Ordinance.

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        (1)     The POTW develops or recalculates draft local limits.

        (2)     The POTW submits the draft new or revised local limits and supporting documentation
               to the Approval Authority for review,3 makes the proposed new or revised limits
               available to the public for comment, and provides individual notice to the affected
               parties.

        (3)     The Approval Authority notifies the POTW of the adequacy of its submission.  The
               submission may be:

           •   Not accepted. The Approval Authority provides comments to the POTW, the POTW
               addresses the issues raised in the  comments and repeats Step 2.

           •   Accepted.  The Approval Authority notifies the POTW that its proposed limits have
               been accepted.

        (4)     Once accepted by the Approval Authority, the POTW adopts the new or revised limits,
               which also  are adopted by all the contributing jurisdictions (i.e., all municipalities in the
               service area). Note that the public must be given the opportunity to review and comment
               according State and local law (see Section 6.8 for a discussion on public participation).

        (5)     Once approved and adopted by the control authority (and thereby enforceable), the
               proposed changes to local limits become a formal pretreatment program modification and
               need to be publicly noticed and approved (as noted in the above discussion of regulatory
               requirements) by the Approval Authority. (The specific procedures for review and final
               approval may vary among Approval Authorities. POTWs should check with their
               Approval Authority.)

6.8 PUBLIC PARTICIPATION

Section 101(e) of the CWA establishes public participation as one of the goals in the development,
revision, and enforcement of any regulation, standard, effluent limitation, plan, or program established by
EPA or any State.  The General Pretreatment Regulations encourage public participation by requiring
public notices or hearings for program approval, removal credits, program modifications, local limits
development and modifications, and Ills in significant non-compliance.

POTW pretreatment program approval requests require the Approval Authority (a State or EPA) to
publish a notice (including a notice for a public hearing) in a newspaper of general circulation within the
jurisdiction served by the POTW. All comments  regarding the request as well as any request for a public
hearing must be filed with the Approval Authority within the specified comment period, which generally
lasts 30 days. The Approval Authority is  required to account for all comments received when deciding to
        3 Although not required, POTWs are encouraged to submit draft local limits to their Approval Authority for review
prior to formal submission. This step can be helpful in identifying revisions necessary to make limits approvable and can save
the POTW (and any contributing jurisdictions) from having to re-adopt revised limits after addressing Approval Authority
comments.
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approve or deny the submission.  The decision is then provided to the POTW and other interested parties,
and published in the newspaper.  All comments received are made available to the public for inspection
and copying.

Once a local pretreatment program is approved, the Control Authority (usually the POTW) must
implement that program as approved. Before there is a significant change in the operation of a POTW
pretreatment program, a program modification must be initiated.  For a substantial program modification,
such as the development of new or less stringent local limits, the Control Authority is required to notify
the Approval Authority of the desire to modify its program and the basis for the change. Approval
Authorities (or POTWs) also are required to issue public notice of the request for a modification, but are
not required to issue public notice of the decision if no comments are received and the request is
approved without changes. These changes become effective upon approval by the Approval Authority.
Federal regulations also require POTWs to notify
affected persons and groups and give them an
opportunity to respond before final promulgation
of a local limit [40 CFR 403.5(c)(3)]. While the
regulations do not specify the exact public notice
process that a POTW should follow, EPA
recommends that the POTW conduct public
participation in the local limits process as openly
as possible. This process would include
notifying affected users and other parties that the
POTW knows are interested that the POTW is
beginning a detailed reevaluation of its local
limits. When new limits are drafted, EPA
recommends notifying the Ills and other
interested parties, individually, of the proposed
limits and announce a public comment period in
the  local newspaper.  This public comment
period can be open while the proposed limits are
submitted to the  Approval Authority for initial
review, or the  POTW can wait until it receives
comments from the Approval Authority. In EPA's view, POTWs should allow sufficient time in their
limits development process to provide for public participation. A POTW that plans to establish
individual limits through the permits issued to users also should provide for public comments in the
permit issuance process.  During the comment period, the public may present technical challenges to the
rationale for a particular local limit. To be adequately prepared to address such challenges, the POTW
needs to thoroughly document its local limits development process.  Similar issues need to be addressed
during the re-evaluation process as  well (see Exhibit 6-3).

6.9  CONTROL MECHANISMS

POTWs have discretion in selecting the control mechanism through which they will apply local limits to
Ills and thereby making them enforceable. Examples  of control mechanisms may include a SUO,
individual permits, and orders. A POTW's choice of control mechanism may depend on the type of user
(SIU or non-SIU) and on the method the POTW uses to allocate its MAHLs among its lUs. A POTW
should consider the following:
   Exhibit 6-3: Local Limits Documentation

Among the items a POTW should keep to document its
local limits development process are:

  •  All data used for determining pollutants of concern and
    performing calculations.

  •  Rationale for choosing pollutants of concern.

  •  Record of calculations (formulas used) and related
    assumptions.

  •  Printouts from any spreadsheets or computer
    programs used.

  •  Rationale for choosing local limits (comparison of
    maximum allowable headworks loadings for all
    applicable criteria, allocation methods and
    calculations).

  •  Reasons for not setting limits for particular pollutants or
    deleting any existing limits.
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       •      An SUO alone may not be adequate with any allocation method other than the uniform
              concentration method.

       •      The POTW does not need to allocate its local limits in an SUO. It may instead include
              MAILs in the SUO, then allocate the loadings in individual control mechanisms. Again,
              care must be  taken to ensure that the sum of each pollutant allocation does not exceed the
              MAIL.

       •      Limits based on the contributory flow method may result in over-allocation of the MAIL
              when uniform concentration values are specified in the SUO for "background
              concentrations" for SIUs that do not discharge the pollutant. POTWs should ensure that
              the implementation of the allocation scheme into a control mechanism does not result in
              an over-allocation of the MAIL.

       •      An individual control mechanism (such as a permit) is necessary for most POTW-IU
              relationships. Even if one uniform set of local limits were applicable for all lUs, an
              individual control mechanism may be desirable to specify monitoring locations and
              frequency, special conditions such as solvent management or spill prevention plans,
              applicable categorical standards, and reporting requirements, and to provide clear
              notification to lUs (as required by  40 CFR 403.8). Note that 40 CFR 403.8(f)(l)(iii)
              requires a POTW to control the contribution of SIUs through individual control
              mechanisms (e.g., permits). The development of IU permits is discussed in detail in
              EPA's Industrial User Permitting  Guidance Manual (EPA, 1989a).

6.10 SUMMARY

After reviewing Chapter 6, POTWs should understand how to:

       •      Determine the need for new local limits after establishing MAHLs.

       •      Calculate MAILs.

       •      Compare MAIL allocation and implementation methods.

       •      Allocate MAILs to controlled dischargers.

       •      Perform a common sense assessment of local limits.

       •      Use best management practices.

       •      Provide public participation.

       •      Gain Approval Authority approval.

       •      Select the appropriate control mechanism to apply local limits.
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CHAPTER 7-

LOCAL LIMITS REVIEWS AND DETAILED RE-

EVALUATIONS	


According to 40 CFR 122.44(j)(2)(ii), POTWs must "provide a written technical evaluation of the need
to revise local limits under 40 CFR 403.5(c)(l), following permit issuance or reissuance." EPA
recommends that a periodic evaluation of local limits be tied to the permit cycle and that more detailed
evaluations be conducted on an "as needed" basis.  Chapter 7 provides guidance on two means to meet
this requirement - local limits reviews and detailed re-evaluations -depending on the conditions at the
POTW.  Reviews compare current headworks loadings with the maximum allowable headworks loading
(MAHL) and examine any recent violations.  When plant conditions have changed, EPA suggests a
detailed re-evaluation be conducted that includes an in-depth look at all the data, criteria, and
assumptions on which local limits are based to determine whether any changes affecting the local limits
have occurred.

7.1  REVIEWS

For POTWs with past performance problems (pass through, interferences, or collection system issues),
EPA suggests performing reviews annually as part of its preparation of the Annual Pretreatment Report.
Reviews are intended as a quick check for any obvious signs that local limits may not be adequately
protective of its treatment works, its workers, and the environment. This review will help ensure that any
changes made during the previous year have not weakened the local limits' effectiveness in protecting the
POTW from pass through and interference. Presented below is a suggested methodology for performing
reviews.

7.1.1 COMPARISON OF CURRENT LOADINGS WITH MAHLs

During a local limits review, EPA recommends that a POTW identify its maximum daily and maximum
monthly average headworks loadings during the previous year for each pollutant of concern (POC) for
which it calculated a MAHL—regardless of whether a local limit for each POC was adopted.  Similar to
the calculations made to determine  the need for local limits in Section 6.1, comparisons of the MAHL to
the headworks loadings will determine if local limits need to be recalculated, or established for additional
POCs. The comparisons also may indicate if there  is a need for an investigation into the cause of
increased loadings, possibly due to  noncompliant industrial users (Ills).

As previously explained, dividing the headworks loading of all POCs by their respective MAHL will
yield a "percentage of MAHL" represented by the POC headworks loading (see Equation 6.1). If a POC
headworks loading is a high percentage of the MAHL, the POTW may choose to revise the local limit for
that pollutant or develop a local limit for it if none exists.  For example, a POTW may decide to develop
a local limit for any pollutant whose headworks loading is above a "threshold value" of 50 percent of the
MAHL.  EPA recommends maximum threshold values of 60 percent for metals and toxic organics and 80
percent for non-toxic organics, and conventional pollutants. However, in most circumstances, a POTW
will use threshold values that are consistent with the criteria it used to determine if a local limit was
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needed for a POC. EPA offers the following guidance on this comparison between MAHLs and POCs
for which local limits were not established:

       1.      If the current POC headworks loading exceeds the MAHL, EPA recommends that
              the POTW establish a local limit for the pollutant, investigate the cause of elevated
              loading, increase its IU monitoring, identify any noncomplying industries, and consider
              undertaking pollution prevention efforts.

       2.      If the current POC headworks loading exceeds the established threshold value for
              the first time (i.e., the loading was below the threshold value during the year
              before), EPA recommends the POTW increase monitoring for the POC, or establish a
              local limit for it.

       3.      If the current POC headworks loading exceeds the established threshold value for
              the second time, EPA recommends establishing a local limit and increasing POC
              monitoring.

       4.      If the current loading is below the established threshold, EPA recommends that the
              POTW review the pollutant's loading as part of its preparation of next year's annual
              report.

Similarly, EPA recommends that the POTW prepare to address situations involving POCs for which local
limits have already been established in the follow circumstances:

       •      If the current POC loading exceeds the MAHL, EPA recommends revising the local
              limit (unless an investigation reveals that the elevated loading is due to an unusual, one-
              time event), investigating the cause of the high loading, identifying any noncomplying
              industries, increasing monitoring of Ills, and considering adopting pollution prevention
              efforts.

       •      If the current POC loading has increased significantly from the previous year (e.g.,
              from 55 percent to 75 percent of the MAHL), EPA recommends that the POTW
              investigate the cause of the increased loading,  increase its monitoring for the POC, or
              revise the local limit.

       •      If the current POC loading is below the established threshold, EPA recommends that
              the POTW review the POC's loading when it prepares next year's report.

As part of its investigation into the cause of an elevated loading, the POTW will investigate whether the
loading is an aberration. If the high loading resulted from an unusual, or one-time, occurrence, the
POTW may not need to establish or recalculate the local  limit for the  POC. For example, if the POC
load increased as a result of an IU oil spill, the POTW may better address the situation by ensuring that
the IU properly implements a spill control plan, rather than by  setting or revising a local limit.  In
addition, the POTW should also look at whether any sampling  or analytical problems caused the
aberration.
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When the current loading of one or more POCs approaches the MAHL, the POTW can respond in several
ways. It can compare current IU loadings with the MAILs.  If the comparison shows that the increased
loadings come from domestic or commercial sources, the POTW can educate these sources about
pollution prevention, or it can impose local limits on the commercial sources rather than change the IU
local limits. If the IU loadings exceed the MAILs, one or more IU may be violating local limits.  Such
violations should be found during the POTW's regular review of IU monitoring data. Another response
is to review the data used to set the local limits in the first place. If changing conditions have affected the
removal efficiencies, flow rate, or other criteria on which the MAHLs were based, the POTW should
recalculate  the MAHLs.

7.1.2 REVIEW OF COMPLIANCE HISTORY

If a review  is performed, the POTW will also want to consider its compliance record over the previous
year to determine whether the local limits it has set provide sufficient protection from pass through and
interference. If the POTW has violated its NPDES permit or sludge disposal standards, has caused or
contributed to violations of water quality standards in its receiving waters, or has experienced
interference of its treatment processes, the POTW's local limits may not be adequately protective.
Unless it has identified as the cause of the violation a specific, unusual incident that is unlikely to recur,
the POTW  is required to investigate the violation's cause and take appropriate enforcement action
against any noncomplying lUs. Alternatively, the POTW may revise the local limit, or establish a local
limit if none exists for the pollutants that caused the violations.

7.1.3 NEXT STEPS

POTWs that find further action is necessary after conducting reviews outlined above can turn to the
earlier chapters of this document for guidance on ensuring that local limits remain protective. Chapter 4
has information about sampling issues; Chapter 5 covers the calculation or recalculation of MAHLs; and
Chapter 6 discusses the reallocation of existing MAHLs and other implementation issues, such as control
mechanisms and revisions to the POTW's sewer use ordinance.

7.2 DETAILED LOCAL LIMITS RE-EVALUATION
Periodically, POTWs need to re-evaluate their
local limits to ensure that they remain protective,
or to determine whether they should be revised,
reallocated, or developed for additional
pollutants (see Exhibit 7-1). As discussed above,
POTWs may wish to review their local limits
when preparing their annual Pretreatment
Program Reports. However, the annual review
may not have addressed conditions that can          pass  rou9
  Exhibit 7-1: Why Local Limits Should Be
                Re-evaluated

Conditions change overtime, and these changes may
make it necessary to revise some or all of a POTW's local
limits. Periodic re-evaluation of local limits will help the
POTW ensure that the limits are effective in protecting the
treatment works, its workers,  the local collection system,
and the environment from the effects of interference and
change over time and undermine the                ^^^^^^^^^^^^^^^^^^^^^^^^^^™
effectiveness of local limits.  When a POTW
needs to address changes in its operating conditions or environmental criteria, the data or assumptions
used to establish local limits in the first place may no longer be appropriate (see Exhibit 7-2).

As these and other changes occur, the POTW will need periodically to undertake a more  detailed re-
evaluation of its local limits.  In addition, if a POTW violates its NPDES permit or sludge requirements,

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but all of its regulated sources have been maintaining compliance, the POTW will need to evaluate the
adequacy of its local limits to protect the treatment works, its workers, and the environment.

POTWs can avoid having to re-evaluate local limits for some of the events described in Exhibit 7-2 if
adequate growth allowances (covered in Section 6.2.4) were used during local limits development. In
addition, if Ill's have stopped discharging a pollutant, or reduced their discharge of a pollutant, POTWs
should place the load formerly contributed by those Ills into a reserve account to accommodate future
growth. If local limits are developed with flexibility, POTWs can respond to changes in IU loadings
without a complete recalculation and approval of their local limits.
The detailed re-evaluation of local limits
is a four-step process:

        1.      Assess current conditions
               to determine whether
               existing MAHLs should
               be recalculated or
               reallocated, or additional
               local limits should be
               developed. Also
               determine which
               pollutants need to be
               further evaluated and for
               which criteria. (If only
               re-allocation of existing
               MAHLs is needed, skip to
               step 4.)

        2.      Based on the pollutants
               and criteria identified in
               step 1,  determine whether
               existing data are
               sufficient. If not, develop
               and implement a local
               limits sampling plan, then
               analyze the data
               collected.
   Exhibit 7-2: When to Recalculate or Develop
                   Local Limits

A POTW that answers "yes" to any of these questions should re-
evaluate its local limits:

  • Has the treatment plant been modified, or has a new
    treatment plant been brought on line?

  • Have the treatment plant processes or operation changed
    in a way that affected the removal efficiencies?

  • Has the flow to the treatment plant changed significantly?

  • Is the POTW subject to new or revised NPDES limits?

  • Have the State water quality standards changed for the
    receiving water?

  • Has the POTW changed, or intend to change, its sludge
    disposal method?  If yes, will this change affect the sludge
    quality standards that the POTW must meet?

  • Have loadings been affected  by new I Us discharging to the
    POTW?

  • Have loadings been affected  by I Us that have stopped
    discharging to the POTW?

  • Have loadings been affected  by changes in discharges
    from current I Us?

  • Are new data available about the POTW or the I Us that
    invalidate assumptions made during the last local limits
    development effort?
        3.      Recalculate the MAHLs
               of pollutants for which local limits have been developed, and determine MAHLs for new
               pollutants.

        4.      Implement the local limits. This step may include the reallocation of existing MAILs, if
               required.

The following sections describe these four steps in more detail.

7.2.1  STEP 1: ASSESS CURRENT CONDITIONS

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To determine whether MAHLs should be recalculated, MAILs reallocated, or additional local limits
developed, the POTW first will need to compare its current conditions and requirements with those that
existed when the local limits were last developed.  In this process, EPA suggests that the POTW also
evaluate whether a new MAHL is required for a POC, or if the previously determined MAHL remains
valid, but needs to be reallocated. To determine which response is appropriate, the POTW will want to
consider the change that led it to re-evaluate its local limits in detail.

Usually, a POTW will undertake a detailed re-evaluation of its local limits in response to one or more
significant changes at the treatment works or in the discharges it receives. Recalculating existing
MAHLs or determining MAHLs for new POCs is generally an appropriate response  to changes in:

       •       Removal efficiencies
               Total POTW or IU loading
       •       Limiting criteria (NPDES permits, water quality standards, sludge criteria)
       •       Sludge characteristics or method of disposal  (e.g., percent solids, disposal site  life)
       •       Background concentrations of pollutants in receiving water

Simply reallocating existing MAHLs may be appropriate when:

       •       Some Ills need a larger loading allocation and other Ills are not using all of their
               allocations.

       •       Total POTW flow is unchanged, but the amount of uncontrollable loading relative to the
               IU loading has changed.

       •       Total POTW flow has not changed but new lUs have come on line while existing lUs
               have  stopped discharging.

In these cases the current MAHLs are usually still appropriate, and the POTW can skip to step 4.

Some Approval Authorities have worksheets that POTWs can use to determine whether existing local
limits need to be recalculated. The worksheets help POTWs  compare existing local  limits and the data
on which they are based with current conditions and applicable environmental and treatment plant
criteria. They consider such parameters  as POTW and SIU flows; sludge disposal method and associated
disposal criteria; occurrence of violations, upsets, and interference;  current influent and effluent
loadings; water quality criteria; and NPDES permits. A copy of one of these worksheets and instructions
for its use can be found in Appendix X.

On occasion, a relaxation of local limits  may be appropriate.  However, in EPA's view, the POTW first
should demonstrate that the revised local limits will satisfy all of the minimum Federal and State
requirements and will adequately protect in-stream water quality and sludge quality. If its analysis shows
that local limits can be relaxed, the POTW would next determine whether their relaxation will  result in
new or increased IU discharges that will affect the volume or character of POTW influent or effluent.
Relaxation of local limits would likely result in a major modification that must be approved by the
Approval Authority in accordance with 40 CFR 403.18(b)(2).

7.2.2  STEP 2: COLLECT AND ANALYZE  DATA

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Properly re-evaluating local limits requires representative sampling data. If sufficient data are not
available, the POTW obviously will want to develop and implement a sampling plan to provide
additional data on relevant POCs. The availability of accurate site-specific data is critical to the
development of sound, technically based local limits. Local limits developed using data from the
literature are often conservative.

The data necessary to calculate a MAHL for a new POC may not be available if that pollutant was not
part of the POTW's local limits monitoring. Similarly, data collected to support development of a
current MAHL may not be valid for recalculating the MAHL if the data were collected before any
changes occurred. For example, upgrading a treatment unit may increase removal efficiencies beyond the
levels when the POTW conducted most of the sampling for local limits. Consequently, the POTW may
need to collect new samples to obtain sufficient data that represent current conditions in order to support
the MAHL's recalculation. Chapter 4 covers the data needed to develop local limits.

7.2.3  STEP 3: RECALCULATE EXISTING, OR DETERMINE NEW, MAHLs

If the results of the analyses conducted in Steps 1 and 2 warrant, the POTW will next recalculate existing
MAHLs or determine MAHLs for new POCs. Chapter 5 of this guidance covers MAHL calculations.
The POTW will want to ensure that current data are used for all the variables in the equations for
calculating MAHLs.

7.2.4  STEP 4: IMPLEMENT THE LOCAL LIMITS

The evaluation conducted in Step 1 may indicate that the MAHL for a POC need not be recalculated, but
rather should be reallocated among the sources of pollutant loadings (IDs, domestic and commercial
sources, hauled waste, and any reserve for future growth).  In such cases, the POTW will go directly from
step 1 to this step.

Implementing local limits may involve:

       •      Allocating or reallocating MAHLs (between the group of Ills and uncontrollable
              sources, as well as to individual non-domestic sources).

       •      Public participation.

       •      Approval of revised local limits considered either  a "non-substantial" or "substantial"
              modification as defined in 40 CFR 403.18(b).

       •      Adoption of local limits and revision of the SUO.

       •      Revisions of control mechanisms or IU permits.
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Implementing new and revised local limits is
covered in Chapter 6 of this guidance.
Although most of the information presented in
Chapter 6 applies to  both new and revised local
limits, the POTW may have to take additional
considerations into account when implementing
revised local limits.  For example, the POTW
may want to use the  same allocation method it
used previously but may have a different
number of Ills to consider. Or the POTW may
want to use a new allocation method (see
Exhibit 7-3). In addition, the POTW does not
have to use the same allocation method for
every POC, but it should document which
method is used for which pollutant and why.  If
a POTW wants to change its allocation method,
it should consider how the change may affect its
existing users.  If some Ills become subject to more
equipment to remain in compliance with local limits

7.3 SUMMARY
    Exhibit 7-3: An Example of Changing the
       Method for Allocating Local Limits

Using the uniform allocation method, a POTW gave all of its
Ills the same local limit for cadmium through its sewer use
ordinance. Since then, an IU changed its operating process
and now generates a significant amount of cadmium. If the
POTW reallocates cadmium using the same method, the IU
may be subject to a local limit that will be difficult for it to
meet.

The POTW can change its local limits implementation method
by including the MAILs for cadmium in its SUO and allocating
cadmium loadings to lUs through individual permits. The new
allocations would be based on how much loading each IU
discharger needs. In this way, the POTW can provide the IU
that changed its operating process with a cadmium allocation
sufficient for its needs. This would be considered a
"substantial" modification as defined in 40 CFR 403.18(b).
stringent limits, they may need to install pretreatment
Chapter 7 provides the tools for POTWs to evaluate the circumstances that would lead it to conduct a
review or re-evaluation of the local limits program.
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CHAPTER 8-
LOCAL LIMITS TO ADDRESS CONCERNS ABOUT
COLLECTION SYSTEMS
POTWs may need to develop local limits to address concerns about their collection systems and meet the
requirements found at 40 CFR 403.5(b), which include protecting the health and safety of workers at the
POTW. Chapter 8 describes methods to address the following collection system concerns:

             Fires and explosions [40 CFR 403.5(b)(l)]
             Corrosion [40 CFR403.5(b)(2)]
             Flow obstructions [40 CFR 403.5(b)(3)]
             Temperature [40 CFR403.5(b)(5)]
      •      Toxic gases, vapors, or fumes [40 CFR 403.5(b)(7)]

POTWs should address each of these potential problems through their local limits development and re-
evaluation processes.

8.1 FIRES AND EXPLOSIONS

The General Pretreatment Regulations prohibit the discharge of pollutants that will create a fire or
explosion hazard in the POTW. This prohibition includes wastestreams shown to have a closed cup
flashpoint of less than  140 degrees Fahrenheit (60 degrees Celsius) using the test methods specified at 40
CFR 261.21. This provision is intended to protect POTW workers and the POTW collection system. To
comply, a POTW can establish a local limit equal to the flashpoint provision, or opt to develop other
protection methods. The flashpoint provision and three common alternatives are described below.

8.1.1  FLASHPOINT LIMIT

The flashpoint is the lowest temperature at which vapor combustion will propagate away from its source
of ignition. At temperatures below the flashpoint, vapor combustion immediately above the liquid either
will not occur, or will occur only at the exact point of ignition. Temperatures above the flashpoint are
required for combustion to spread.  If a POTW prohibits discharges, typically volatile organic
compounds, that have a closed cup flashpoint of less than 140ฐF, it will protect against fires and
explosions. (A flashpoint limit applies to the entire wastestream, not to a specific pollutant.)

A flashpoint limit ensures that discharges to a POTW will not combust. It is important to note that a
flashpoint prohibition does not necessarily account for the flammability of mixtures from more than one
discharger. Dilution effects in sewer systems, however, generally prevent the creation of explosive
conditions.

The closed cup is used because this test simulates the confinement of vapors in a  sewer.  EPA requires a
flashpoint of less than  140ฐF [see 40 CFR 403.5(b)]for several reasons:
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       •      Ambient temperatures in a sewer are not expected to exceed 140ฐF.

       •      Typical industrial discharges of wastewater are cooler than 140ฐF.

       •      The specified flashpoint is consistent with hazardous waste regulations, which will help
              ensure that POTWs do not face increased hazardous waste liabilities.

Regulations require that the flashpoint be determined by a Pensky-Martens Closed-Cup Tester, using the
test method specified in ASTM Standard D-93-79 or D-93-80, or by a Setaflash Closed-Cup Tester, using
the test method specified in ASTM Standard D-3278-78, or as determined by an equivalent test method
approved by the EPA Administrator under specified procedures. Appendix H lists closed cup flashpoints
for select organic compounds.

8.1.2 LOWER EXPLOSIVE LIMIT MONITORING

Another way to protect POTW workers is to monitor the collection system for combustible gases.  A
combustible gas detector measures the concentration of these gases and vapors in the air as a percentage
of the lower explosive  limit (LEL). The LEL is the minimum concentration in air at which a gas or vapor
will explode or burn in the presence of an ignition source.

LEL monitoring measures pollutant concentrations in the headspace above the wastewater, rather than in
the wastewater itself. This method makes setting local limits difficult.  Consequently, POTWs often use
LEL monitoring to identify potentially problematic discharges, rather than as a numerical limitation to
implement and enforce against Ills. LEL monitoring is also an important way to protect POTW workers
who enter the collection system.

One approach to monitoring explosion potential is to measure LEL levels at key locations in the
collection system. Continuous monitoring at pump stations or key manholes can provide a constant
source of data on the potential for an explosion.  Many POTWs establish a percentage of the LEL,
often 10 to 30 percent, as the level of concern. This ensures that discharges are safely below an
explosive level.  The entire LEL should not be used to establish the level of concern.

8.1.3 SAMPLE HEADSPACE MONITORING

Sample headspace monitoring is a discharge screening technique to detect the presence of explosive
compounds and toxic gases and vapors. Initial screening using this method can identify discharges that
warrant detailed chemical-specific screening.

Sample headspace monitoring involves collecting a wastewater sample using proper volatile organic
sampling techniques (i.e., zero headspace), withdrawing a set percentage of the sample, injecting nitrogen
gas into the sample container (to maintain a total pressure of one atmosphere), and performing a gas
chromatography analysis of the sample headspace gas.

Volatile organic concentrations of the sample headspace gas are converted to an equivalent
concentration of hexane and compared to a set hexane limit (usually 300 parts per million of
hexane). Concentrations below the limit are usually deemed sufficient to protect the collection system
from fires and explosions and to provide minimal protection from toxic gases and vapors.  Details of this
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method are available in Guidance to Protect POTW Workers from Toxic and Reactive Gases and Vapors
(EPA/812-B-92-001).

8.1.4 FLAMMABILITY AND EXPLOSIVITY DISCHARGE SCREENING LEVELS

Discharge screening levels can be used to set local limits on the discharge of pollutants that can create
flammable or explosive conditions in sewers. This approach requires converting the LELs of individual
compounds into corresponding IU discharge screening levels.  These levels are then compared with
actual IU discharge concentrations. Appendix I contains a table of discharge screening levels based on
explosivity.  A variety of screening levels have been developed for limiting flammable and explosive
discharges, including the four-step approach summarized here:

       1.      Identify the LEL for each POC.

       2.      Use the following equation to  convert the compound's LEL concentration to a vapor
               phase concentration (CVAP) expressed as moles per cubic meter (mol/m3). (Ten percent
               of the LEL often is used in this equation, instead of the full LEL.)

                      CVAP = LEL x P/RT x  1000 = LEL x 40.87 (at 1 atm and 25ฐC)

                     Where:
                      P = total pressure, 1 atmosphere (assumed)
                      R = ideal gas constant, 0.08206 atm L/mol ฐK
                      T = absolute temperature, 298.15ฐK (equal to 25ฐC) (assumed)

       3.      Determine the Henry's Law Constant (H) for the POC. This constant converts LEL air
               phase values to corresponding water phase discharge levels.  Note that H is presented in
               a variety of units [e.g., (atm m3)/(mol), (mol/m3)/(mg/L), and (mg/m3)/(mg/L)] and may
               require converting H into the appropriate units of (mol/m3)/(mg/L).  Appendix I contains
               a listing of Henry's Law constants in various units and provides the appropriate
               conversions.

       4.      Calculate the IU discharge screening level (CLVL) using the Henry's Law expression:

                      CLVL = CVAP/H

                     Where CLVL is the discharge screening level in mg/L.

Screening levels derived by this method should be compared directly with the actual IU discharge
concentrations.  Some of the assumptions made using this method are:

       •       Although temperature dependent, H typically is reported at 25 ฐC  (77ฐF), which is a
               reasonable estimated temperature of discharges to POTWs. Warmer wastewaters will
               exhibit higher concentrations in the vapor phase, while cooler wastewaters will exhibit
               more of the pollutant in the liquid phase.
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       •       The pollutant instantly volatizes to the sewer atmosphere. Although this is a
               conservative assumption, the more turbulence in the sewer, the closer the assumption is
               to actual conditions.  In addition, air flow through the sewers prevents the reaching of
               equilibrium, thereby acting to reduce concentrations below threshold levels in the vapor
               phase.

       •       The equation does not take into account the solubility effects that result from organic
               contaminants in the wastewater, thereby limiting volatilization into the atmosphere.

For details of this method, see Guidance to Protect POTW Workers from Toxic and Reactive Gases and
Vapors (EPA 812-B-92-001).

8.2 CORROSION

The General Pretreatment Regulations prohibit discharges of pollutants that will cause corrosive
structural damage to a POTW.  The regulations also prohibit discharges with a pH lower than 5.0 unless
the POTW is specifically designed to accommodate such discharges.

8.2.1 PH

Besides the low-end pH limit specified in the General Pretreatment Regulations, EPA recommends
POTWs evaluate the need to set upper pH limits or more stringent low-end pH limits. A POTW should
set an upper pH limit if corrosion damage attributable to high-pH discharges is identified. An upper limit
pH of up to 12.5 may be  an appropriate upper limit in lieu of any identified high pH corrosion concerns.
However, because wastewater of pH 12.5 or higher is considered a hazardous waste (exhibiting the
characteristic of corrosivity) under 40 CFR 261.22(a)(l), additional reporting and liability results when
hazardous waste is discharged to a sanitary sewer. The POTW needs to set an upper pH limit that is
protective of the POTW, but also allows for some margin of safety to avoid characterization as hazardous
waste.

EPA acknowledges that there are advantages to accepting high pH industrial wastewater. These include:

       •       Reducing odor emissions from the collection system and plant processes due to a
               reduction in the amount of aqueous hydrogen sulfide.

       •       Aiding the nitrification process (which often requires an external source of alkalinity).

       •       Improving precipitation and removal of toxic heavy metals by primary clarification.

       •       Limiting IU use of acids to neutralize high pH effluent and thus minimizing chloride and
               sulfate ions  detrimental to POTW operation.

8.2.2 CORROSIVE POLLUTANTS

In addition to discharges whose pH is high or low, the following pollutants can contribute to the
corrosive properties of wastewater:
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        •       Sulfide and sulfate.  Much of the sulfide in collection systems is present as hydrogen
               sulfide due to the anaerobic degradation of sulfate. This degradation occurs where
               oxygen is absent and organic matter is present. Collection systems are particularly
               conducive to this reaction if wastewater is allowed to stagnate. The formation of
               hydrogen sulfide is primarily a function of the collection system's design, however, and
               not a function of the characteristics of industrial discharges. Hydrogen sulfide corrodes
               metals such as iron, copper, lead, and zinc. It is also a precursor to sulfuric acid, which
               corrodes concrete and metals. Sulfate causes corrosion by reacting with the calcium in
               concrete to form calcium sulfate, which can cause concrete to crack.  For more
               information, see Detection, Control, and Correction of Hydrogen Sulfide Corrosion in
               Existing Wastewater System,  (EPA-832-R92-001, September 1992).

        •       Chloride. This pollutant can adversely affect inorganic films and precipitates that form
               on sewer wall and provide a physical barrier that protects from chemical corrosion. Not
               only can chloride decay and penetrate these coatings, it can also prevent them from
               developing by forming more  soluble metal chloride instead.

        •       Chlorine. By reacting to form hydrochloric (HC1) and hypochlorous (HOC1) acids that
               decrease the pH of wastewater, chlorine can increase the rate at which iron and steel
               corrode.

        •       Nitrate and nitrite. They can contribute to iron and steel corrosion.

        •       Dissolved salts. The electrolytic action of dissolved salts on the base material can
               corrode concrete, asbestos-cement, and cement mortar.

        •       Suspended solids.  The abrasive and erosive contact of suspended solids with sewer
               pipes and pumps can cause corrosion, particularly at joints, elbows, bends, and other
               non-uniform areas.

        •       Organic compounds. If present in excessive concentrations, organic compounds such
               as solvents will  promote the dissolution of gaskets and rubber and plastic linings.

8.3 FLOW OBSTRUCTIONS

The discharge of solid or viscous pollutants in amounts that will obstruct flows to POTWs and result in
interference is prohibited by the General Pretreatment Regulations. The greatest threat of obstruction in
POTWs comes from polar fats, oils, and greases  (FOG) of animal and vegetable  origin.  Typical sources
include restaurants, residences, food processors,  and food-based industries. Certain polar FOGs, such as
non-ionic surfactants, do not contribute to flow obstruction. Additional discussions on the potential for
interference and pass through  due to FOG are provided in Section 5.3.3.

Although more  compatible with wastewater treatment operations than non-polar mineral oil or
petroleum-based oil and grease,  polar FOG can accumulate and congeal in collection systems, pumping
stations, and treatment plants. By obstructing influent flows, polar FOG reduces the capacity of pipes
and pumps, interferes with POTW instruments (such as flow meters and probes), reduces treatment
efficiency, and increases POTW operation and maintenance costs. Polar FOG can interfere with the
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POTW's collection system through blockages when the wastewater cools sufficiently to allow the
suspended fat, oil, or grease to congeal. This condition is a function primarily of interceptor size, length,
and slope; ambient temperature; wastewater temperature; and concentration of FOG. These factors vary
throughout the collection system.  To develop a technically based FOG limit for protecting the collection
system, empirical data (observations and measurements) are needed to document problems and
contributing factors. The empirical data along with generally available pretreatment and control
measures for FOG become the technical basis for the proposed local limit.

To collect data, the POTW first identifies collection system sections that have a critical low slope (i.e.,
relatively flat) profile and may be subject to low temperatures. Data are collected that identify FOG
levels corresponding to deposition rates of solidified oil and grease.  The level of oil and grease at which
deposition is negligible would be the basis for the collection system MAHL.

Local limits on FOG may require POTWs to investigate and monitor the  activities of non-SIUs that are
the sources of FOG. The use of controls other than numerical limitations may be a more appropriate way
to address the problem of FOG from non-SIUs. These controls can include:

        •      Requirements to install and maintain grease traps
        •      Pretreatment requirements
        •      Best management practices
        •      Prohibitions of specific materials, such as free-floating FOG
        •      Prohibitions of FOG that are in a solid or semisolid form
        •      Surcharge programs
        •      Cost recovery efforts to defray the expenses associated with cleaning sewers
        •      Pollution prevention measures

Many POTWs have oil and grease control programs. The Oregon Association of Clean Water Agencies
has authored Fats, Oil, and Grease Best Management Practices Manual: Information, Pollution
Prevention, and Compliance Information for Publicly Owned Treatment Plants.  The manual provides
municipal pretreatment staff, along with restaurant and fast food business managers and owners, with
information  about animal and vegetable-based oil and grease pollution prevention techniques focused on
their businesses.  The techniques are effective in both reducing maintenance costs for business owners,
and preventing oil and grease discharges to the sewer system. Go to:
        http://www.oracwa.org/Pages/intro.htm to review the manual.

8.4  TEMPERATURE

The General Pretreatment Regulations prohibit heat discharges that will inhibit biological activity in a
POTW and result in interference.  And in no case can discharges increase the temperature at the
POTW headworks above 40ฐC (104ฐF) unless the Approval Authority, upon request of the POTW,
approves alternative temperature limits.

The dilution of heated industrial wastewaters in the collection system typically ensures compliance with
this prohibition.  Temperature is generally more of a hazard to workers who must enter the sewer system
than it is to POTW treatment operations.  A POTW that encounters IU discharges hot enough to prevent
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or restrict sewer entry should require the IU to reduce the temperature of its discharge. The installation
of heat exchangers on high-temperature discharges may help the IU save on heating costs for its facility
or its process streams.

8.5 Toxic GASES, VAPORS, AND FUMES

The General Pretreatment Regulations prohibit the discharge of pollutants that lead to the accumulation
of toxic gases, vapors, or fumes in the POTW in sufficient quantity to cause acute worker health and
safety problems.

Discharge screening levels can be developed to identify IU discharges that have the potential to generate
toxic gases or vapors in the sewer. A common approach is to convert gas and vapor toxicity criteria for
individual compounds into corresponding IU discharge screening levels using Henry's Law Constants.
These constants relate the concentration of a constituent in the air to the corresponding equilibrium
concentration in the water. The screening levels should be compared to the actual pollutant
concentrations in the IU discharge. Calculating these wastewater screening levels is a three-step process:

        •       Identify the toxicity criteria, also known as the threshold concentration (CVAP, in mg/m3),
               for the POC. Typical threshold values are available from the National Institute for
               Occupational Safety and Health's (NIOSH's) Recommended Exposure Limits (RELs),
               the Occupational Safety and Health Administration's (OSHA's) Permissible Exposure
               Limits (PELs), and the American Conference of Governmental Industrial Hygienists'
               (ACGIH) Threshold Limit Values (TLVs).  Each organization can provide chronic and
               acute exposure thresholds that can be used to develop screening levels. See Appendix J
               for a listing of some of these threshold concentrations. Consistent with the specific
               prohibitions for toxic gases, vapors, and fumes, screening  levels may be based most
               appropriately on acute worker health and safety levels (i.e., short-term exposure levels or
               ceiling concentrations).

        •       Identify the Henry's Law Constant (H) for the POC and convert the constant to the
               appropriate units of (mg/m3)/(mg/L). Appendix I contains a listing of Henry's Law
               constants in various units and the appropriate conversions.

        •       Calculate the IU discharge screening level (CLVL) from the Henry's Law expression:

                       CLVL = CV
                      Where:
                      CLVL = IU discharge screening level (in mg/L)
                      CVAP = Threshold concentration (in mg/m3)

As with the flammability and explosivity screening level, this screening method assumes instantaneous
volatilization of the pollutants to the atmosphere and does not consider the dilution of IU wastewater in
the collection system. Therefore, these screening levels will  in many cases be more conservative than
necessary to protect POTW workers.

These screening levels address only the toxicities of individual compounds, but mixtures of toxic
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compounds can be evaluated against an adjusted threshold value of the mixture of all the toxic
compounds. Appendix I contains a table of discharge screening levels based on fume toxicity.  Details
on the specifics of using the discharge screening level method, including evaluating mixtures of toxic
gases, vapors, or fumes, is available in EPA's Guidance to Protect POTW Workers from Toxic and
Reactive Gases and Vapors (EPA 812-B-92-001).

8.6 SUMMARY

After reviewing Chapter 8, POTWs should be able to address collection system concerns: fire and
explosions, corrosion, flow obstructions, temperature, and toxic gas, vapors and fumes.

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CHAPTER 9 -
QUESTIONS AND ANSWERS
This chapter presents EPA's responses to many commonly asked questions about local limits
development and implementation. The questions and answers are grouped by topic for ease of finding
subjects of interest.

9.1 GENERAL

Q:     Once I establish a local limit, will I ever be able to drop it?

A:     As emphasized throughout this guidance, development of local limits is a continuing, dynamic
       process. EPA recommends a re-evaluation of specific local limits whenever there are significant
       changes in the overall program as a step that every prudent Control Authority should do on a
       regular basis. If changes in IU discharge conditions or installed treatment technologies at the
       POTW dictate that some pollutants of concern (POCs) are no longer present or are present only
       in concentrations that will not cause pass through, interference, or degradation of sludge
       quality, then the local limits for those pollutants may be dropped after appropriate procedures
       are taken.  However, POTWs should be cautioned that dropping a particular local limit
       completely may motivate lUs to discontinue a treatment process designed to remove or recycle
       that particular pollutant.  POTWs should have a complete understanding of the makeup of
       untreated IU waste streams before dropping a local limit completely. The regulations at 40 CFR
       403.18(c) specify that eliminating or changing a local limit to make it less stringent requires
       notification of the Approval Authority and appropriate public notice because such actions are
       considered substantial program modifications.

Q:     How do multi-jurisdictional systems affect local limit requirements?

A:     For multi-jurisdictional systems in which one Control Authority accepts industrial wastes from
       one or more other,  independent municipalities, EPA strongly recommends that all contributing
       jurisdictions adopt a set of local limits that are at least as stringent as those of the Control
       Authority that maintains the collection system and operates the receiving POTW. If this policy is
       impractical, then the contributing jurisdictions should agree to a maximum total mass loading of
       pollutants that would be discharged to the primary collection system and POTW. As an
       alternative, the contributing jurisdiction may adopt two sets of local limits and apply to each IU
       the limit appropriate to the treatment works to which the user discharges.  Consult EPA 's
       Multijurisdictional Pretreatment Programs Guidance Manual (EPA 833-B-94-005, June 1994) for
       additional information.

Q:     Do a minimum number of parameters need to be evaluated?

A:     There is no minimum number of parameters required by regulation. EPA recommends that the
       need for local limits be evaluated for a list of specific pollutants.  EPA recommends that
       technical evaluations for POCs by every POTW should include a determination of the need for
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       limits for arsenic, cadmium, chromium, copper, lead, mercury, nickel, silver, zinc, and cyanide.
       This Guidance adds total suspended solids, 5-day biochemical oxygen demand, ammonia,
       molybdenum and selenium to the list of recommended minimum pollutants to be considered as
       POCs.

Q:     Do local limits have to be developed individually for multiple treatment works? Is it necessary
       that identical numeric local limits be established?

A:     There is no regulatory requirement that a Control Authority develop local limits that are specific
       to a single treatment works. However, EPA recommends that the Control Authority perform a
       separate evaluation for each works to determine if each plant is being protected and not subject
       to pass through or interference problems. After completing these independent evaluations, the
       Control Authority can determine whether individual local limits should be provided to the lUs
       that discharge into the parts of the system served by a particular treatment works. The only
       regulatory requirement is that there be local limits developed that prevent pass through and
       interference and are  enforceable on a technical basis. The preferred method is to establish
       MAILs individually for the treatment plants, but if that is politically infeasible, then set a single,
       conservative local limit (i.e., the lowest limit developed in the assessment for the individual
       treatment works) for a POC.  The limit should then apply to all lUs that discharge to the POTW,
       without regard as to  which works actually treats the wastewater discharged by a particular IU.

Q:     Can best management practices (BMPs) and best professional judgment (BPJ) limits be applied
       in lieu of the traditionally derived numeric local limits?

A:     The General Pretreatment Regulations do not specifically address the use of BMPs and BPJ as
       local limits.  The regulations at 40 CFR 403.5 (c) require the POTW only to develop "specific
       limits " for prohibited discharges. The current regulatory language is ambiguous as to whether
       BMPs could serve in lieu of numeric limits. BMPs may reduce the amount of the POC at the
       headworks thus leaving more pollutant loading to be distributed as numerical limits to facilities
       that cannot control their discharge through BMPs. If adopted, the proposed Pretreatment
       Streamlining Rule would specify  that BMPs could be considered as local limits and also fulfill
       the statutory requirements of Section 307 (d) of the Clean Water Act. As with BMPs, using BPJ
       to develop local limits is not specifically prohibited. If adopted following the process in 40 CFR
       403.5, BPJs are enforceable.

Q:     Can local limits evaluation and development be contracted out?

A:     In EPA 's view,  the optimum process is for the Control Authority to evaluate and develop the
       appropriate local limits because  it provides the Control Authority with a better understanding of
       limit development and the importance of compliance. However, recognizing the fact that some
       Control Authorities may be severely constrained by an overextended workforce, or require
       access to technical expertise that is not internally available, the Control Authority may secure
       the necessary manpower and expertise through an outside consultant or engineering firm.
       However, the Control Authority should be aware that any mistakes or improper determinations
       would be its legal responsibility if the Approval Authority, an IU,  or any outside party challenges
       the POTW on the assignment of the limits.
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9.2 POTENTIAL POLLUTANTS OF CONCERN

Q:     If a pollutant is below the detection level in influent, effluent, and sludge, may a POTW exclude
       it as a POC (and not develop a MAHL), even if it is one of EPA's 15 pollutants?

A:     Yes, it may.  If a POC is not detected in the influent, effluent, or sludge during the POTW 's
       assessment of the need for local limits, an accurate calculation of the MAHL for that particular
       pollutant is not possible. The goal of setting stringent local limits is to protect the POTW and
       avoid violations ofNPDES permit.  However, if no MAHL is established for a "potential" POC,
       there is always the possibility that a new industrial user (or users) of the system will discharge
       wastes that are in excess of the POTW's ability or capacity to treat such wastes. Therefore, EPA
       recommends that MAHLs be developed for all 15 EPA-designatedPOCs even if local limits are
       not adopted.  Of course, POTWs should assess a new  user's impact on local limits before
       granting authorization  to discharge.

 Q:    Should  local limits be developed as dissolved metals, total metals, or both? How does
       hexavalent chromium relate to total chromium, and which should be used for local limits
       development?

A:     While it may be desirable to develop local limits for both dissolved and total metals, in reality it
       may be  impractical because of cost. POTW data are developed almost exclusively in terms of
        "total" because of NPDES requirements and the fact that Categorical Pretreatment Standards
       are always expressed as total. Because the POTW should be able to apply the more stringent of
       either the local limit or the Categorical Standard,  it makes sense to develop the local limits as
        "total" values. Although the dissolved form of metals is usually more  toxic, POTWs need to
       control the total metal entering the  treatment works because paniculate metal or metal
       compounds may exert some  toxicity or may later be resolubilized. A large percentage of the
       toxic metals present in aeration  basins at some treatment works has come from recycled solids
       handling sidestreams. These contributions can continue to exert a toxic effect long  after the
       source has been controlled.  Although most heavy metals "passing through " a treatment works
       are discharged into receiving waters in the dissolved form, significant concentrations of heavy
       metals may accumulate as fine particulates in the sludge produced at the POTW. By
       implementing local limits to control total metal concentrations, a POTW will reduce the chances
       for pass through and ensure that the quality of the sludge is not degraded.  Local limits should
       be developed for total chromium. Hexavalent chromium is the more toxic of the two forms of the
       metal, but it can be converted to a total chromium value by using proper mathematical
       equations. If a POTW has contributions of hexavalent chromium, EPA recommends it develop
       local limits for both hexavalent chromium and total chromium.  The basis of the limits will likely
       be different because the allowable holding time for hexavalent chromium samples is less than 24
       hours.

9.3 SAMPLING AND ANALYSIS

Q:     What analytical requirements and quality assurance/quality control procedures apply to local
       limits evaluation sampling?

A:     There are no different or "special" quality assurance/quality control procedures that apply
       strictly  to local limits sampling.  EPA recommends that all wastewater sampling for POCs follow


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       prescribed protocols found in 40 CFR Part 136 (Guidelines for Establishing Test Procedures for
       the Analysis of Pollutants^ and information provided in EPA-issued technical guidance. When
       sampling sludge for metals and total solids, however, the requirements in the sludge regulations
       at 40 CFR Part 503 apply. Therefore, EPA recommends that the analysis of sludge for the
       presence of metals be performed according to EPA test method SW-846 and for total solids
       according to Part 2540 G of the Standard Methods for the Examination of Water and
       Wastewater, 18th Edition.

Q:     Are there minimum analytical detection levels that should be achieved when analyzing samples
       for local limits?

A:     As discussed in Chapter 3, a POTW's NPDES permit conditions, sludge disposal practices, and
       State and local requirements need to be addressed through local limits. Therefore, the analytical
       techniques for detecting POCs need to be able to identify and quantify concentration levels that
       are at least as stringent as the prescribed maximum concentrations for conventional and non-
       conventional pollutant effluent limitations, water quality-based toxic pollutant limitations, whole
       effluent toxicity (WET) requirements, and any numeric criteria for sludge use and disposal
       practices. In addition, POTWs will want to specify the lowest reasonable detection limit for a
       local limit monitoring to minimize the possibility of a POC being reported as "non-detectable. "

Q:     Is it necessary to account for hydraulic detention time through the treatment works when
       conducting sampling?

A:     Treatment works sampling should account for hydraulic detention times within the plant
       whenever possible.  Developing relevant removal efficiencies depends in part on accounting for
       hydraulic detention times. For some systems, such as lagoon systems, hydraulic detention times
       may be lengthy (e.g., 21 days). If it is not feasible to account for detention times,  local limits can
       still be developed, but the options for determining removal rates will be reduced.  Various
       methods for determining removal efficiencies are reviewed in Chapter 5.

Q:     Do I have to outline a sampling plan for the local limits evaluation?

A:     Outlining a sampling plan for local limits evaluation is not required by 403 regulations,
       although some Approval Authorities may require submission of such a plan. However, EPA
       highly recommends that a POTW develop a sampling program to  ensure that it has adequate
       data for developing local limits that have sound technical bases. A sampling program can also
       enable a POTW to use fewer resources for evaluating local limits by providing the data
       necessary to determine and justify that local limits are not necessary for some pollutants and by
       enabling the POTW to manage its data and ensure that unnecessary sampling is not performed.
       Information regarding local limits data  collection is reviewed in Chapter 4.

Q:     Is sampling and analysis of the receiving stream necessary?

A:     Receiving stream data (flow and ambient background concentrations of pollutants) provide key
       input parameters for allowable headworks loading (AHL) calculations when NPDES permit
       limits do not exist and the POTW needs  to evaluate for pass through based on water quality
       standards. These data may already be available from sources such as the U.S.  Geological
       Survey, State environmental agencies, and the POTW's NPDES permit. Therefore, a POTW may


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       not need to conduct sampling and analysis of the receiving stream to gather these values.
       However, if these data are not available, the POTWwill want to consider sampling the receiving
       water so that AHLs can be calculated based on applicable values. The Approval Authority may
       require this information on a case-by-case basis for individual lUs. Other dischargers to the
       same portion of the receiving stream may already have performed sampling and may be willing
       to share the data or the costs of new monitoring.
9.4 DETERMINING MAHLs

Q:     Water quality standards have been established for our treatment works' receiving waters, but no
       water quality-based effluent limitations are included in our permit. Is it necessary to include the
       analysis for an allowable headworks loading (AHL) based on water quality standards in this
       case?

A:     Yes, it is.  If a POC loading measured at the headworks exceeds a MAHL that was set by the
       AHL for a water quality standard, there may be pass  through of the pollutant, thereby causing a
       violation of the water quality standard and (consequently) of the Clean Water Act. In general,
       POTWs will not have NPDES permit limits for all of the POCs established during the local limits
       analysis.  In such cases, a POTWmay base its effluent-quality-based AHL on State Water
       Quality Standards (WQS) or Federal Water Quality Criteria (WQC).  State environmental
       agencies have developed WQS that set maximum allowable pollutant levels for their water
       bodies, specific to the receiving stream reach 's designated uses. Even though the POTWs
       NPDES permit may not contain a numeric effluent limit for a POC, the permit probably will
       contain narrative provisions requiring compliance with State WQS and prohibiting the discharge
       of any toxic pollutants in toxic amounts. A local limit based on a State WQS fulfills the narrative
       permit requirement specifying  "no discharge of toxics in toxic amounts. "  See Section 3.2.2 and
       the associated footnotes for additional information.

Q:     How much literature data are acceptable in deriving MAHLs?  How much site-specific data are
       sufficient? How recent must data be for deriving MAHLs?

A:     The answers  to these questions will vary significantly from facility to facility.  Depending on the
       POC and on  the type and accuracy of the data available, a considerable range of techniques are
       acceptable for deriving the MAHL.  EPA recommends that the Control Authority make a case-
       by-case determination about type and age of data that are sufficient to calculate accurate,
       technically defensible MAHLs.  For example, data collected prior to  major construction should
       not be used.  However,  the most accurate and technically defensible limits are the result of using
       site-specific data, rather than "generic " removal efficiency data derived from average, national-
       level treatment works "literature " data.

Q:     We do not have NPDES or sludge limits for all of the POCs required to be evaluated; further,
       there are no State WQS for these pollutants. What criteria are we supposed to use in our
       evaluation?

A:     Sludge, NPDES, or water quality criteria may not exist for all POCs.  In these instances, the
       POTWmay want to develop MAHLs based on system design criteria, air quality standards,
       inhibition criteria, or worker health and safety standards. In addition, the POTWwill want to


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       determine the original purpose for adding a POC (e.g., WET test failure) and establish criteria
       through researching other applicable standards and guidelines.

Q:     How does a POTW develop local limits based on a NPDES WET limit?

A:     Nothing in the pretreatment regulations prohibits using Whole Effluent Toxicity (WET) test data
       as the basis for developing a local limit.  WET tests are primarily designed to protect the
       receiving waters from the aggregate toxic effect of a mixture of pollutants in the effluent. The
       WET approach is most useful for complex effluents where it may be infeasible to identify and
       regulate all toxic pollutants in the discharge, or where chemical-specific pollutants are set, but
       synergistic effects are a problem. However, unless you can identify each compound in the
       effluent that produces measurable acute or chronic toxicity concentrations, WET testing cannot
       be used to set local limits for a particular POC. If the toxic pollutant or pollutant parameter
       cannot  be identified, then a POTW will want to evaluate all of the possible POCs present in the
       mixture. In this situation,  WET test data may not be a cost-effective methodology for identifying
       POCs for evaluation in the local limits development process.  The guidance Toxicity Reduction
       Evaluation Guidance for Municipal Wastewater Treatment Plants (EPA/833-B-99-002, August
       1999) provides further information on conducting a Toxicity Identification Evaluation.

Q:     Influent and effluent pollutant concentrations are below quantifiable levels yet the pollutant is
       detected in the sludge. What removal rate should I use?

A:     EPA recommends that a POTW first evaluate those levels below the minimum level of
       quantitation (ML) as outlinedin Section 5.1.3.  If the methodologies outlined in Section 5.1.3 do
       not allow the calculation of a removal rate, a POTW then may selectively  use removal
       efficiencies reported by other POTWs or by studies that have been published in professional
       journals or by EPA.  Appendix R provides a list of removal  efficiency data for priority pollutants
       gathered from other POTWs.

Q:     Why should POTWs use the Table 3 Land Application Part 503 sludge standards when the
       POTW's sludge is disposed in a landfill?

A:     POTWs are encouraged to use the Table 3 standards because the Pretreatment Regulations list
       recycling of sludge as one of the goals of the program.  Land application standards help meet
       this  goal and also allow for more sludge disposal options, because the Table 3 standards are the
       most stringent.  EPA recommends that POTWs consider the attainment of EPA "clean sludge "
       standards,  that are delineated in Table 3 of 40 CFR 503.13, and provide the broadest choice of
       beneficial use options for sludge disposal. Further achievement of these standards is consistent
       with the objectives of the National Pretreatment Program, which are listed at 40 CFR 403.2.
       Additionally, until a sludge landfill is properly closed and abandoned there is always a potential
       for the leachate to affect groundwater. See Appendix Kfor landfill leachate loadings. In some
       cases, collected leachate can be trucked (as hauled waste) to a POTW and treated to non-toxic
       concentration levels. For this option to be viable, the metals content of the sludge should be
       limited  to concentrations that will not cause potential pass through or interference problems for
       the POTW.  Table 3 sludge standards for land application cover all nine toxic metals,  while the
       surface disposal sludge standards specify limits only for arsenic, chromium and nickel.
       Imposing land application standards on sludge increases the probability that the leachate can be
       successfully treated in the future at a POTW. Nevertheless, if a POTW has a choice of disposal


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        options, EPA recommends that it use land application disposal techniques because they are
        generally more controllable and have less potential for serious environmental degradation of
        surface water and groundwater.

9.5 ESTABLISHING LOCAL LIMITS

Q:      All of my influent, effluent, and sludge concentration data for a specific pollutant are below the
        method detection limit.  Can the pollutant still be considered a POC and local limits established?

A:      Yes. The Control Authority (generally, the POTW) has the authority to consider any chemical
        compound or pollutant as a potential POC and establish a local limit for that pollutant. If your
        POTW serves a high-growth municipality or incorporated area where the number and type of
        non-domestic users change frequently, it may be prudent to establish aMAHL limit in your
        ordinances for any pollutant that could potentially cause interference, pass through, or degrade
        your sludge quality—even if the concentration of that pollutant is currently below detection
        levels. Several statistical approaches to evaluating "below detection level" or below
        quantitation level data are discussed in Section 5.1.3 and Appendix Q.

Q:      If a POTW's local limits evaluation indicates that its sludge disposal method (e.g., land
        application) is the most limiting factor, may the POTW pursue a less stringent sludge disposal
        method (e.g., landfill)?

A:      The determination of the manner in which the sewage sludge is used or disposed of is a local
        determination.  As long as a POTW adheres to all of the regulatory requirements specified in 40
        CFR Part 503, it may select the optimum method of sludge disposal. EPA recommends that
        POTWs consider the attainment of EPA "clean sludge " standards, that are delineated in Table 3
        of 40 CFR 503.13, and provide the broadest choice of beneficial use options for sludge disposal.
        Further, achievement of these standards is consistent with the objectives of the National
        Pretreatment Program, which are listed at 40 CFR 403.2.

Q:      What do I do when my total domestic/background loading of a pollutant is equal to or greater
        than my MAHL, so I have no allowable loading for Ills?

A:      The POTW may wish to consider a program that involves short-term, intermediate, and long-
        term measures.  Short-term measures include evaluating the data and calculations used to
        develop the local limits to assess the validity of results. Intermediate measures include
        establishing interim local limits, looking into other possible sources of pollutants (including
        expansion  of your list oflUs), and determining how to manage these sources. Long-term
        measures  involve evaluating controls for users not already covered by your pretreatment
        program.  If the short-term measures do not take care  of the problem and provide loadings to
        allocate to lUs, the POTW would proceed to intermediate measures, and then, if necessary,  to
        long-term measures.  Examples of activities for each of the steps are listed below:

        Short-term

        •      Ensure that all significant industrial and commercial dischargers of the pollutants have
              been identified.
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       Evaluate all sampling sites that have been used to estimate background concentration to
       ensure that commercial facilities were not missed and are not contributing pollutants of
       concern to the sampling location.

       Use actual sewer trunk line monitoring data in place of any literature data used in
       determining total domestic pollutant loadings to the POTW.

       Use removal efficiencies based on in-plant monitoring in place of any literature removal
       efficiencies used in determining MAHLs.

       Verify the applicability of criteria (e.g., sludge disposal standards, and water quality
       criteria) used as the basis for AHL calculations.

       Verify that appropriate sampling locations have been used, and that samples are
       representative (i.e., do not reflect peak loading periods only).

       Check the accuracy of all calculations made and the reliability of data used.

       Evaluate the method for handling non-detect monitoring results (e.g.,  equal to the
       detection level was used) and consider using other conventions (e.g., half the detection
       level).

       If the MAHL is based on inhibition criteria, current headworks loadings are greater than
       the inhibition criteria and the POTW has not experienced inhibition, the current
       loadings may be a more appropriate basis for inhibition values.
Intermediate

•       Verify the sampling frequency through statistical methods.

•       Collect additional sampling data to refine values used (e.g., for removal efficiencies) or
        replace literature values.

•       If hauled waste is being accepted, consider discontinuing this practice or instituting a
        program to determine individual wastewater components versus those contained in the
        septage.

•       If chemicals are added in the plant or sewer system (e.g., to control root growth),
        consider alternatives that do not introduce POCs.

•       Calculate a mass balance for the collection system (i.e., check if the sum of industrial
        plus domestic/commercial plus any hauled waste loadings are between 80 percent and
        120 percent of the total influent loading). If not, one or more sources may not be
        accounted for or data may be invalid.

•       Establish interim local limits such as a local limit equal to  the POTW's NPDESpermit
        limit, to the NPDES limit adjusted for the POTW removal efficiency for a particular
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               pollutant, or to the lowest achievable method detection level (so that IU compliance with
               the limit can be determined). If the POTWis not experiencing pass through or
               interference for a given pollutant (e.g., no NPDES limit or sludge disposal criterion
               violations, no collection system problems), consider substituting the current influent
               loading for the MAHL and recalculate the allowable industrial loading. The interim
               limits should be replaced as long-term measures take effect.
       Long-term

       •       Require industries to perform pollutant minimization/prevention evaluations.

       •       Consider implementing measures to address or regulate elevated loadings from non-
               industrial sources.  These non-industrial sources include nonpoint sources (e.g., runoff)
               discharging to combined sewers, elevated pollutant levels in water supplies, household
               disposal of chemicals into sanitary sewers, and toxic pollutant discharges from
               commercial sources (e.g., photo labs or dry cleaners).
       Pollution prevention/minimization programs can address each of these sources.  Nonpoint
       sources of pollutants may be addressed through combined sewer overflow control programs and
       urban and agricultural chemical management programs. The POTWmay be able to reduce
       elevated pollutant levels in water supplies by working with the local water department. For
       example, elevated levels of metals in water supplies often arise from corrosion in water
       distribution pipes. The local water department may be able to reduce corrosion by adjusting the
       pH of the water supply.  The POTWmay be able to assist the water company in developing a
       program to optimize the use of chemical additives in lieu of making simple adjustments to the pH
       by using acidic or caustic chemical agents.  The POTWcan make efforts to educate the public on
       proper disposal of household chemicals and to provide chemical and used-oil recovery facilities.
       Each of these efforts is not directly part of the local limits process.

       Reducing toxic pollutant discharges from commercial facilities is generally most effectively
       addressed through local limits.  Commercial sources of pollutants, such as radiator shops, car
       washes, hospitals, laundries and photo processors, are often not considered significant sources
       of toxics because they typically have relatively low flows or are assumed to have insignificant
       pollutant levels in their discharges. However, these commercial sources may discharge at
       surprisingly high pollutant loading levels and are potential lUs that should be considered for
       control during local limits development.  In some cases, the POTWmay best address these
       sources through pollution prevention/minimization efforts, such as providing guidance to small
       commercial dischargers (e.g., informing dentists about how they can reduce mercury discharges
       to sewers).

Q:     How useful are priority pollutant data in determining the need for and in setting local limits?

A:     The "best case scenario " is that a POTW knows everything about each of its lUs, including the
       manufacturing processes involved and the types and amounts of pollutants discharged into the
       collection system by a particular facility. However, despite the requirements to notify the POTW
       of any changed discharges, some facilities might install new process technology, change to the


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       production of new chemical compounds, or use new or substitute chemicals in their processes.
       In these cases, new POCs might be introduced into the POTW.  Use of priority pollutant scan
       data would provide added insurance that none of the 126 priority pollutants are being
       introduced (inadvertently or otherwise) into a POTW before problems with pass through,
       interference or sludge quality are detected by other analytical means.

Q:     Do local limits apply to all Ills? Do they have to be included in all permits issued by the
       POTW?

A:     The assignment of local limits depends on how the MAIL calculations were performed and how
       the sewer use ordinance requires the local limits to be implemented. There is no regulatory
       requirement that "all limits " be included in every permit.  However, the regulations at 40 CFR
       403.8(f)(l) require that the contribution to the POTW by each Industrial User be 'controlled'
       through permit, order,  or similar means, to ensure compliance with applicable Pretreatment
       Standards and Requirements. The regulations also specify that permits issued to Significant
       Industrial Users (SIUs) must contain certain minimum  conditions, which include: "Effluent
       limits based on applicable general pretreatment standards in part 403 of this chapter,
       categorical pretreatment standards, local limits, and State and local law. " [40 CFR
        The applicability issue is determined by the local limit allocation method (i.e., uniform
        concentration, mass proportion, industrial contributory) that the POTW chooses when
        developing the local limits and how the POTW expressly states the applicability of the local
        limits within its sewer use ordinance (SUO). The Control Authority may elect to codify local
        limits in the local SUO or place general enabling authority language about local limits in the
        SUO and announce the actual limits by another mechanism (e.g., as a technical directive, etc.).
        Including the limits in the SIU permit provides individual notice to a permittee of the pollutant
        limits that are applicable to that particular SIU.

Q:      My local limits re-evaluation indicates that a less stringent local limit than the one currently in
        the ordinance can be applied. Is this allowed in light of EPA' s anti -backsliding policy?

A:      First, you need to consider the full meaning of the "anti-backsliding" policy.  The "anti-
        backsliding " concept associated with NPDES permit limits does not apply to local limits.  Local
        limits apply to a particular IU and can be raised or lowered based on the periodic re-evaluation
        of the need for those limits. Second, a POTW may need to modify its SUO before it may impose a
        less stringent limit.  Otherwise, the permit may conflict with the POTW' s authority. Third, in the
        case of a Categorical Industrial User discharge  regulated by a categorical effluent standard, the
        more stringent limit (either the local limit or the categorical standard) must be
        applied — regardless of the local limit established for that pollutant.  Though rare, some
        categorical standards may be made less stringent as a result of removal credits (40 CFR 403. 7).
        Also, because any less stringent change in prescribed local limits would be a significant
        program modification, you  must notify and seek  the approval of the Approval Authority prior to
        making such a change.
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Q:     Is effluent trading of local limits allowed?

A:     Yes. A POTWmay decide to negotiate with its lUs in allocating its calculated allow able
       industrial loadings.  However, the POTWneeds to ensure that no more than the total MAHL is
       allocated among domestic/background sources,  lUs, commercial sources not considered lUs by
       the POTW, and other sources of loadings such as hauled waste. Effluent trading, which must be
       authorized in the POTW's sewer use ordinance,  may result in a program modification, as defined
       in 40 CFR  403.18 and results of the trades should be incorporated into any control mechanisms
       (see Section 6.4.2).

Q:     If a calculated local limit is excessive (i.e., a large number), should the POTW implement this
       limit?

A:     The POTW should consider the potential IU discharge for the particular pollutant and the
       possibility  that a high limit might encourage increased discharges to the system.  Of course, the
       POTW must receive Approval Authority concurrence on the local limit.

Q:     How do I develop local limits for other pollutants (e.g., BTEX compounds) that may be specific
       to certain users?

A:     For BTEX, some options to consider for determining if pass through or interference will occur
       include:

       •      Fume toxicity criteria.

       •      Aquatic life protection criteria.

       •       Worker safety and health criteria. Consult the Guidance to Protect POTW Workers
              from Toxic  and Reactive Gases and Vapors (EPA, 1992).
       Once the most stringent criteria are determined, POTWs may want to compare the proposed
       local limit with BTEX treatment technology. The Model NPDES Permit for Discharges Resulting
       from the Cleanup of Gasoline Released from Underground Storage Tanks (EPA,  1989) contains
       two sets of effluent limits: 1) BTEX of 100 /ug/L and benzene of 5 /ug/L (assumes approximately
       15 mg/L of dissolved product is treated to a removal efficiency of 99.5 percent, which can be
       achieved with a commercially available stripper unit), and 2) BTEX of 750 /ug/L and benzene of
       50 jUg/L (assumes approximately 15 mg/L of dissolved product is treated to a removal efficiency
       of 95 percent, using equipment that a small business is more likely to purchase).
Q:     How should lU-specific limits be developed for "atypicaP'dischargers (i.e., groundwater
       cleanups, hauled waste, landfill leachate, and underground storage tank cleanups) containing
       pollutants for which no local limits or MAHLs are established and which cannot be measured at
       the headworks?

A:     First, EPA recommends you ensure that your local ordinance gives you the authority to impose
       limits for pollutants that are not specifically listed in your ordinance limits or other document


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       pertaining to local limits adoption policy. Second, EPA suggests that you review the
       Supplemental Manual on the Development and Implementation of Local Discharge Limitations
       under the Pretreatment Program (EPA-W21-4002, May 1991) and relevant RCRA site
       remediation guidelines (for underground storage tanks and groundwater contamination) to
       determine what types and concentrations of pollutants are typically discharged by these
       wastewater sources.  The POTWnext may determine (on a site-specific basis) which of these
       sources are likely to be a problem and establish a sampling program for the sewer trunk lines
       into which the wastewater is discharged. If this sampling program identifies the potential for an
       adverse impact on the POTW,  then specific local limits can be developed and incorporated into
       the discharge permit of the IU(s) that are problematic.  The Guidance to Protect POTW Workers
       from Toxic and Reactive Gases and Vapors (EPA, 1992) provides additional data relating to
       health and safety concerns.

9.6 OVERSIGHT AND PUBLIC PARTICIPATION

Q:     What kind of public participation should I expect during the local limits development process?

A:     Although the public does not usually become actively involved in the development process, the
       CWA established public participation as an integral part of developing any regulatory program,
       including standards and effluent limitations associated with the pretreatmentprogram.
       Obviously, "public " participation includes all affected entities.  The lUs are critically important
       participants in the whole local limits development process. The General Pretreatment
       Regulations encourage public participation by requiring public notices or hearings on local
       limits development.  Federal regulations require POTWs to notify affected persons and groups
       and give them an opportunity to respond before final promulgation of a local limit [40 CFR
       403.5(c)(3)]. Any subsequent modifications that are deemed significant modifications (as
       defined in 40 CFR 403.18 (b) ) must be publicly noticed. Minor modifications, such as the
       adoption of a more stringent local limit for a POC, do not require public  notice. However, the
       POTW must ensure that it has  the authority to impose more stringent limits. Modifications to
       local limits for pH and reallocation of the MAIL are considered to be minor program
       modifications and do not require public notice (see Sections 6.7-6.9).

Q:     Do I need Approval Authority approval to implement and enforce local limits?

A:     No, you do not unless you are making changes to your legal authority or amending your local
       limits to make them less stringent than those currently incorporated in your approved
       pretreatment program. In accordance with 40 CFR 403.18, changes to legal authority or
       making local limits less stringent is considered a significant modification to the approved
       pretreatment program and must therefore be approved by the Approval Authority. However,
       modifications to local limits for pH and reallocation of the MAIL are considered to be minor
       program modifications and do not require Approval Authority approval or public noticing. As
       prescribed in 40 CFR Part 403, the authority to develop and enforce local limits needs to be
       incorporated into a POTWs pretreatment program at the time of program approval (see
       Sections 6.7-6.9).
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9.7 IMPLEMENTATION AND ENFORCEMENT OF LOCAL LIMITS

Q:     Are local limits enforceable if not contained in a sewer use ordinance (SUO)?

A:     Local limits are enforceable if included in a valid user permit or similar enforceable control
       mechanism. From a notification standpoint, local limits may be more difficult to enforce if the
       SUO does not specifically reference them so that lUs know what is expected of them. Even if the
       limits are not in the SUO, the Control Authority must ensure that it has the legal authority to
       enforce limits or procedures in documents other than the SUO and that all required public
       participation procedures are conducted. The Control Authority will need to evaluate the
       availability of resources and the respective burden of enforcing local limits before deciding
       whether to use general language about complying with local limits versus putting specific MAIL
       values in its SUO (see Sections 6.7 - 6.9).

Q:     Can my State or EPA take enforcement action against Ills in my jurisdiction for violations of
       local limits?

A:     All local limits developed in accordance with the provisions stated in 40 CFR 403.5(c) are
       deemed to be Pretreatment Standards for the purposes of Section 307 (d) of the Clean Water Act.
       Consequently, EPA or the State Approval Authority may take enforcement action against any
       industrial user for a violation of a local limit.  The CWA also provides that affected third parties
       may bring  "citizen suits " against users for violations of these local limits.

Q:     How can a POTW justify imposing stringent local limits on Ills when the  POTW is not subject
       to an NPDES permit limit or sludge standards  for the same pollutant?

A:     If a POTW believes that one or more POCs may cause or have the potential  to cause damage to
       the system infrastructure (i.e., corrosion, erosion, disruption of plant treatment efficiencies),
       affect worker safety and health, or negatively impact water quality, it must impose a local limit
       for these POCs.  The use of site-specific data (rather than less precise "literature " data) for local
       limits calculations will always produce better, more technically defensible limits.  In addition,
       POTWs have the ability to establish land application of its sludge as the goal ofitspretreatment
       program and to use sludge land application criteria (as opposed to sludge surface disposal
       criteria) in the development of the limits.

Q:     Can a POTW allocate local limits to non-categorical SIUs only and require CIUs to comply with
       the categorical standards only?

A:     This is an allocation method issue.  As long as the appropriate categorical standards are
       imposed on the  CIUs and the sum of the loadings allocated to alllUs does not exceed the  total
       MAIL, the POTW may assign MAILs as it sees fit (i.e., each IU'need not be given the identical
       limit for a particular POC). Note that if the POTW establishes a MAIL for a pollutant,  then EPA
       recommends that CIUs receive an allocation for that pollutant even if the  categorical standard
       does not regulate that pollutant. Also, note that local limits based on the general prohibitions
       (e.g., corrosion, flammability, etc.) would still need to be applied to categorical industries.
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9.8 POTW OPERATIONS

Q:     Our POTW consists of multiple treatment plants. Wastewater flow and sludges can be diverted
       between them. How does this affect local limits evaluation and development?

A:     To ensure that all treatment plants are protected from pass through, interference, and sludge
       degradation, each treatment plant should calculate allowable headworks loadings.  The MAHL
       can then be selected from the most stringent AHL. This practice will effectively impose a safety
       factor on all of the treatment plants in the POTW and avoid any disruption of the plant treatment
       process or violation of the POTW's NPDES discharge permit.

Q:     Is expansion of my POTW's service area cause for me to re-evaluate local limits?

A:     EPA recommends that a POTW evaluate the characteristics of its  "new " service area to
       determine how the POTW's current local limits requirements would be affected.  Although not an
       absolute requirement (due to presumed safety factors built into  a POTW's local limits
       determination), it is always prudent to re-evaluate the local limits calculations if the expansion
       will add a number ofSIUs to the POTW's collection system. The decision about what triggers
       the need for a re-evaluation is left to the POTW.  However, as has been previously noted, EPA
       recommends that local limits be re-evaluated periodically whenever there are significant
       changes in the mix oflUs or in the total daily flow through the system  (see Exhibit 7-2).

Q:     How do contract operations or privatization affect local limits evaluations and development?

A:     A POTW's type of management should have no impact on the evaluation and development of
       local limits. Local limits are designed to protect the POTW from pass through, interference, or
       degradation of sewage sludge.  As long as the public has some fiduciary interest in the POTW
       the need for local limits should be assessed on a routine basis.  If the POTW is sold to a private
       entity, then the 403 regulations regarding local limits would no longer apply upon reissuance of
       the permit. The new owner of the treatment plant is not required to develop or implement local
       limits unless it is made a management practice requirement in its new NPDES permit.

Q:     Is it possible to develop local limits for a wastewater treatment lagoon where sludge is dredged
       only every 20 years?

A:     The POTW can always develop local limits based on water quality. A  lagoon system would not
       be significantly different than any other type of system in that respect.  For sludge, the POTW
       should ensure that the sludge, when dredged, will meet the standards for its chosen sludge
       disposal option by establishing local limits protective of that option.

9.9 INDUSTRIAL USERS

Q:     If a new significant industrial user/categorical industrial user (SIU/CIU) commences its process
       discharge, or if an existing SIU/CIU ceases its process discharge, is a local limits re-evaluation
       necessary?

A:     It depends. If the SIU/CIU contributes a "significant percentage " (as determined by the POTW
       based on total design flow or number oflUs contributing a particular POC) of the total loading


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       for a particular pollutant or pollutants, then EPA recommends that the POTW recalculate the
        local limits. However, if the SlU/CIUin question does not have the capability of adversely
        affecting the entire POTW, then (depending upon the allocation method, SUO language, or
        applicable categorical standards) the local limits can be specified in the lU's discharge permit.

Q:      If I have CIUs with specific, numeric categorical pretreatment standards, is it necessary for me to
        apply local limits to these CIUs for these pollutants?

A:      No, it is not necessary unless the numeric categorical standards for a specific POC covered by
        local limits are less stringent than the values specified in the local limits.  In this case, the more
        stringent local limits must prevail (see Section 1.5).

Q:      Does promulgation of new categorical pretreatment standards affect local limits evaluation?

A:      The promulgation of a new categorical standard should have no effect on local limits
        requirements. All industrial users subject to the categorical standard(s) will have to meet that
        discharge standard. However, if the categorical standard for a particular POC is less stringent
        than the local limit set for that pollutant, the more stringent local limit must be met by the lUs
        subject to the categorical pretreatment standard. In addition, if the new categorical standard is
        more stringent than the local limit, the "freed up " loading could be reallocated to the other lUs.
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