Compilation of EPA Mixing Zone Documents


OMPILATION OF
 EPA MIXING ZONE DOCUMENTS

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United States Environmental Protection Agency
              Office of Water
          Washington, DC 20460
                 (4305T)

            EPA 823-R-06-003
                July 2006

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  Compilation of EPA
Mixing Zone Documents

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                                        Please Note

The discussions in the documents collected in this Compilation are intended solely as guidance. The
statutory provisions and EPA regulations described in this Compilation contain legally binding
requirements. This document (or the documents referenced herein) are not a regulations, nor do they
change or substitute for those statutory provisions and regulations. Thus, this document or the
documents collected here do not impose legally binding requirements on EPA, states, authorized
tribes, territories, or the regulated community.  This Compilation does not confer legal rights or
impose legal obligations upon any member of the public.

While EPA has made every effort to ensure the accuracy of the discussion in this Compilation, the
obligations of the  regulated community are determined by statutes, regulations, or other legally
binding requirements. In the event of a conflict between the discussion in this Compilation and any
statute or regulation, this Compilation would not be controlling.

The general description provided here may not apply to every circumstance. Interested parties are free
to raise questions  and objections about the substance of this guidance and the appropriateness of its
application to a particular situation.  EPA and other decision-makers retain the discretion to adopt
approaches on a case-by-case basis that differ from those described in this guidance where
appropriate.

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

This is a living document and may be revised periodically without public notice. EPA welcomes
public input on this document at any time.

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                                                   Compilation of EPA Mixing Zone Documents
                               Table of Contents

Purpose	1

Organization of Information	1

Mixing Zone Definition	1

Types of Mixing Zones Covered	1
   Allocated impact zone	1
   Legal mixing zone	2
   Toxic dilution zone	2
   Zone of initial dilution	2

Types of Pollutants Addressed	2
   Toxic pollutants	2
   Conventional pollutants	2
   Nonconventional pollutants	2

Types of Concentrations Discussed	2
   CMC (criterion maximum concentration)  	2
   CCC (criterion continuous concentration) 	2
   RAC (reference ambient concentration	3

Code of Federal Regulations (CFR) Language	3

Technical and Policy Guidance Documents	6
    Technical Support Document for Water Quality-based Toxics Control (1991)	6
    Water Quality Standards Handbook: Second Edition (1994)	6
    Memorandum: EPA Guidance on Application of State Mixing Zone Policies in
        EPA-Issued NPDES Permits (1996)	7
    Allocated Impact Zones for Areas of Non-Compliance (1995)	7
    Technical Guidance Manual for Performing Waste Load Allocations, Book III: Estuaries.
        Part 3: Use of Mixing Zone Models in Estuarine Waste Load Allocations (1992)	8
    U.S. EPA NPDES Permit Writer's Manual (1996)	9

Modeling Documents	9
    Dilution Models for Effluent Discharges, 4th Edition (Visual Plumes) (2003)	9
    Dilution Models for Effluent Discharges, 3rd Edition (1994)	10
    CORMIX2: An Expert System for Hydrodynamic Mixing Zone Analysis of
        Conventional and Toxic Multiport Diffuser Discharges (1991)	10
    User's Manual for CORMIX: A Hydrodynamic Mixing Zone Model and Decision
        Support System for Pollutant Discharges into Surface Waters (1997)	11
    Expert System for Hydrodynamic Mixing Zone Analysis of Conventional and
        Toxic Single Port Discharges (CORMIX1) (1990)	12
    Compendium of Tools for Watershed Assessment and TMDL Development (1997)	12
EPA 823-R-06-003                            1                                   July 2006

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                                                  Compilation of EPA Mixing Zone Documents
    Initial Mixing Characteristics of Municipal Ocean Discharges: Volume 1 - Procedures
        and Applications (1985)	13

Great Lakes Rule	13
    Final Rule to Amend the Final Water Quality Guidance for the Great Lakes System to
        Prohibit Mixing Zones for Bioaccumulative Chemicals of Concern (2000)	13

Tables
Comparison of Mixing Zone Documents from EPA Headquarters by Topic	4
Major Topics in EPA Headquarters Mixing Zone Documents	5

Appendices
Appendix A: EPA Regional Documents	A-l
Appendix B: State Documents	B-l
Appendix C: Other Documents to Consider When Establishing Mixing Zones	C-l

Other Resources
Resources	Resources-1
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                                                   Compilation of EPA Mixing Zone Documents
Purpose

The purpose of this Compilation is two-fold: (1) to provide a source of information for states,
authorized tribes, and territories to use when developing and refining their mixing zone policies
and (2) to assist NPDES permit writers when implementing mixing zones.

This Compilation presents a number of regulatory, guidance, and policy documents available
from EPA on mixing zones. It also provides information and links to state and EPA regional
information on this subject.
Organization of Information

The Compilation is organized as follows:

   •   Basic information
   •   Technical and policy guidance documents (6 documents)
   •   Modeling documents (7 documents)
   •   Great Lakes Rule (1 document)
   •   Appendices
          o  Appendix A: EPA regional documents (3 documents)
          o  Appendix B: Reference list of state documents (16 documents)
          o  Appendix C: Reference list of other EPA and Federal documents (6 documents)
   •   Resources

A brief overview is included with each document except those in Appendices B and C.

The Compilation is available electronically at
http://www.epa.gov/waterscience/standards/mixingzone.
Mixing Zone Definition

According to EPA's Technical Support Document for Water Quality-based Toxics Control
(TSD) (USEPA, 1991), "a mixing zone is an area where an effluent discharge undergoes initial
dilution and is extended to cover the secondary mixing in the ambient waterbody. A mixing zone
is an allocated impact zone where water quality criteria can be exceeded as long as acutely toxic
conditions are prevented." (Water quality criteria must be met at the edge of a mixing zone.)
Types of Mixing Zones Covered

Allocated impact zone (AIZ): According to Allocated Impact Zones for Areas ofNon-
Compliance (USEPA, 1995), an allocated impact zone is the same as a mixing zone. The term is
also used in Water Quality Standards Regulation; Proposed Rule (USEPA, 1998).
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Compilation of EPA Mixing Zone Documents
Legal mixing zone (LMZ): Refers to a mixing zone in a regulatory sense (e.g., the dimensions of
the zone as the state has defined them) as opposed to the mixing zone that naturally occurs in a
stream. This term is used in Technical Guidance Manual for Performing Waste Load
Allocations, Book III: Estuaries. Part 3: Use of Mixing Zone Models inEstuarine Waste Load
Allocations (USEPA, 1992) and CORMIX2: An Expert System for Hydrodynamic Mixing Zone
Analysis of Conventional and Toxic Multipart Diffuser Discharges (USEPA, 1991).

Toxic dilution zone (TDZ): According to Technical Guidance Manual for Performing Waste
Load Allocations, Book III: Estuaries. Part 3: Use of Mixing Zone Models inEstuarine Waste
Load Allocations (USEPA, 1992), the toxic dilution zone, which is a short distance from the
outfall or in the pipe itself, is an additional subregion within the usual mixing zone. The TDZ is
usually more restrictive than the legal mixing zone for conventional and nonconventional
pollutants. This term is also used in CORMIX2: An Expert System for Hydrodynamic Mixing
Zone Analysis of Conventional and Toxic Multiport Diffuser Discharges (USEPA, 1991).

Zone of initial dilution (ZID): According to Technical Guidance Manual for Performing Waste
Load Allocations, Book III: Estuaries. Part 3: Use of Mixing Zone Models inEstuarine Waste
Load Allocations (USEPA, 1992), the zone of initial dilution is a regularly shaped area (e.g.,
circular or rectangular) surrounding the discharge structure (e.g., submerged pipe or diffuser
line) that encompasses the regions of high (exceeding standards) pollutant concentrations under
design conditions. This term is also used in Initial Mixing Characteristics of Municipal Ocean
Discharges: Volume 1—Procedures and Applications (\JSEPA, 1985).
Types of Pollutants Addressed

Toxic pollutants: sometimes referred to as "priority pollutants." EPA identified 126 pollutants
from the 65 families of pollutants specified in Section 307(a) of the Clean Water Act. These
pollutants are listed at 40 CFR Part 423, Appendix A.

Conventional pollutants: the five pollutants as defined by Section 304(a)(4) of the Clean Water
Act and listed at 40 CFR 401.16. Those are biochemical oxygen demand (BOD), total suspended
solids (nonfilterable) (TSS), pH, fecal coliform, and oil and grease.

Nonconventional pollutants: any pollutant not already defined as a toxic or conventional pollutant.
Types of Concentrations Discussed

CMC (criterion maximum concentration): the EPA national water quality criteria
recommendation for the highest instream concentration of a toxicant or an effluent to which
organisms can be exposed for a brief period of time without causing an acute effect (USEPA,
1991). The term applies to all pollutant types.

CCC (criterion continuous concentration): the EPA national water quality criteria
recommendation for the highest instream concentration of a toxicant or an effluent to which
EPA 823-R-06-003 2 July 2006

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                                                    Compilation of EPA Mixing Zone Documents
organisms can be exposed indefinitely without causing unacceptable effect (USEPA, 1991). The
term applies to all pollutant types.

RAC (reference ambient concentration): the concentration of a chemical in water which will not
cause adverse impacts to human health; RAC is expressed in units of mg/L (USEPA, 1991).

Code of Federal Regulations (CfR} Language

Section 131.13 general policies. States may, at their discretion, include in their state standards,
policies generally affecting their application and implementation, such as mixing zones, low
flows and variances. Such policies are subject to EPA review and approval.
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Corrmarison of Mixina Zone Documents from EPA Headc

uarters by Topic
Technical guidance
Policy guidance
Recommends states specify whether
mixing zones are allowed
Effluent characterization — WET
Effluent characterization — specific
pollutants
Effluent characterization —
bioconcentratable pollutants
Application of criteria in mixing zones
Size and/or area considerations
Lethality to passing organisms
Determining WLAs
Special situations: lake, marine, estuarine
Cautions about mixing zones in certain
situations (e.g., near fish harvesting)
Mixing zone analyses (e.g., models)
Technical and Policy Guidance Documents
Technical Support Document for Water Quality- based Toxics Control ( U S E PA, 1991)
Water Quality Standards Handbook: Second Edition (USEPA, 1994)
Memorandum: EPA Guidance on Application of State Mixing Zone Policies in EPA-lssued
NPDES Permits (USEPA, 1996)
Allocated Impact Zones for Areas of Non-Compliance (USEPA, 1995)
Technical Guidance Manual for Performing Waste Load Allocations, Book III: Estuaries.
Part 3: Use of Mixing Zone Models in Estuarine Waste Load Allocations (USEPA, 1 992)
U.S. EPA NPDES Permit Writer's Manual (USEPA, 1996)
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Modeling Documents
Dilution Models for Effluent Discharges, 4th ed. (Visual Plumes) (USEPA, 2003)
Dilution Models for Effluent Discharges, 3rd ed. (USEPA, 1994)
CORMIX2: An Expert System for Hydrodynamic Mixing Zone Analysis of Conventional and
Toxic Mu/tiport Diffuser Discharges (USEPA, 1 991 )
User's Manual for CORMIX: A Hydrodynamic Mixing Zone Model and Decision Support
System for Pollutant Discharges into Surface Meters (USEPA, 1997)
Expert System for Hydrodynamic Mixing Zone Analysis of Conventional and Toxic Single
Port Discharges (CORMIX1) (USEPA, 1990)
Compendium of Tools for Watershed Assessment and TMDL Development (USEPA, 1997)
Initial Mixing Characteristics of Municipal Ocean Discharges: Volume 7 — Procedures and
Applications (USEPA, 1985)
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Great Lakes Rule
Final Rule to Amend the Final Water Quality Guidance for the Great Lakes System to
Prohibit Mixing Zones for Bioaccumu/ative Chemicals of Concern (USEPA, 2000)

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Maior Topics in EPA Headciuarter!

Application of criteria in mixing zones
Cautions about mixing zones in certain situations
(e.g., near fish harvesting)
Determining WLAs
Effluent characterization — bioconcentratable
pollutants
Effluent characterization — specific pollutants
Effluent characterization — WET
Lethality to passing organisms
Mixing zone analyses (e.g., models)
Recommends states specify whether mixing
zones are allowed
Size and/or area considerations
Special situations: lake, marine, estuarine

Technical and Policy Guidance Documents

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Compilation of EPA Mixing Zone Documents
Technical and Policy Guidance Documents

i) USEPA. 1991. Technical Support Document for Water Quality-based Toxics Control.
EPA 505-290-001. U.S. Environmental Protection Agency, Office of Water, Washington,
DC. http://www.epa.gov/npdes/pubs/owmo264.pdf.

EPA's 1991 Technical Support Document for Water Quality-based Toxics Control (TSD)
provides guidance to states and EPA Regions for the water quality-based control of toxic
pollutants. It includes recommendations for controlling point source discharges of toxic
pollutants to waters of the United States.

States and EPA Regions can use this document's "standards to permits" approach to
guide water quality protection from development of water quality standards through
development of compliance monitoring. The standards to permits approach incorporates
both human health and aquatic toxicity issues and uses an integrated approach to water
quality-based toxics control. This includes whole effluent and chemical-specific
approaches and the use of biological assessment to control toxic pollutants. The concept
of mixing zones is introduced in Chapter 2 (Water Quality Criteria and Standards) of the
TSD. More detailed guidance is provided in Chapter 3 (Effluent Characterization) and
Chapter 4 (Exposure and Wasteload Allocation).

The TSD recommends that mixing zones be designed to avoid lethality to aquatic
organisms and to ensure that the designated use of the waterbody as a whole is protected.
The TSD also recommends that states have a definitive statement in their standards on
whether or not mixing zones are allowed and describe the procedures for defining mixing
zones consistent with CWA goals.

2) USEPA. 1994. Water Quality Standards Handbook: Second Edition. EPA 823-6-94-
oosa. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
http://www.epa.gov/waterscience/standards/handbook.

The second edition of the Water Quality Standards Handbook (the Handbook) is a
compilation of EPA's guidance on the water quality standards program and provides
direction for states in reviewing, revising, and implementing water quality standards. This
edition incorporates subsequent guidance issued since the 1983 handbook. The Handbook
is subject to future revisions as the water quality standards program moves forward to
reflect the needs and experiences of EPA and the states.

The handbook's overview of the water quality standards program provides a brief
discussion of mixing zones, including:

o How states have the discretion to use mixing zones in their water quality
standards, subject to EPA approval.
o How state water quality standards describe methods for determining location,
size, shape, and other factors of mixing zones.
EPA 823-R-06-003 6 July 2006
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o How states should give careful consideration to the appropriateness of a mixing
zone depending on the pollutants in the discharge (e.g., bioaccumulative,
persistent).

The Handbook provides information on the general provisions of 40 CFR Part 131
Subpart A, designated uses, water quality criteria, antidegradation, procedures for review
and revision of water quality standards, and water quality-based approaches to pollution
control. According to the Handbook, both it and the Technical Support Document for
Water Quality-based Toxics Control (TSD) (USEPA, 1991) evolved from and supersede
the following resources: Water Quality Criteria 1968 (the "Green Book"), Water Quality
Criteria 1972 (the "Blue Book"), Quality Criteria for Water 1976 (the "Red Book"), and
the first edition of the Water Quality Standards Handbook (1983).

3) USEPA. 1996. Memorandum: EPA Guidance on Application of State Mixing Zone
Policies in EPA-Issued NPDES Permits. U.S. Environmental Protection Agency. Memo
from Robert Perciasepe to Water Program Directors, dated August 6,1996.
http://www.epa.gov/waterscience/library/wqstandards/mixingguide.pdf.

EPA's Guidance on Application of State Mixing Zone Policies in EPA-Issued NPDES
Permits (the Guidance) is designed for EPA permit writers when EPA administers the
National Discharge Elimination System (NPDES) for a state. It discusses the
circumstances under which the EPA permit writer may include mixing zones in NPDES
permits. Specifically, the Guidance presents policy guidelines for EPA permit writers for
including mixing zones in EPA-issued permits for a state. The Guidance includes a
summary of EPA's water quality standards (WQS) Regulations, which allow states to
adopt provisions authorizing mixing zones in their water quality standards.

State WQS regulations addressing mixing zones generally fall into one of two categories.
Some states have regulations that genetically authorize mixing zones without specifying
who may exercise that authority. Other states have regulations that specifically confer
discretionary authority to allow mixing zones only on the state agency. The guidance
details when it is appropriate to interpret the state law to authorize EPA to grant a mixing
zone.

4) USEPA. 1995. Allocated Impact Zones for Areas ofNon-Compliance. EPA 823-11-95-
003. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
http://www.epa.gov/waterscience/library/modeling/zones.pdf.

Allocated Impact Zones for Areas of Non-Compliance (the AIZ document) presents an
impact allocation procedure. This procedure is an attempt to assess cumulative impacts
and addresses the potential limitations of state water quality standards mixing zone
policies. It organizes and manages discharges by including all point source discharges
within the decision making process. Specifically, this procedure can supplement mixing
zone policies that might be limited to the cross-sectional or surface area of streams and
lakes or a uniform linear distance limitation in mixing zone size determinations. For
example, prior to 1995, some state guidance did not consider multiple source impacts,
sensitivity of aquatic resources, and socioeconomic factors. In contrast, the impact
EPA 823-R-06-003 / July 2006
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allocation procedure addresses many of the socioeconomic and ecological factors that can
be considered in waste management decisions.

The procedure described in the AIZ document can be used to determine the
environmentally acceptable size of mixing zones. It defines allocated impacted zones
(AIZs) and provides a detailed discussion of the AIZ procedure. When using this
procedure to perform analyses of mixing zones, the results are carefully evaluated for
reasonableness using prior experience. In addition, the data requirements and
socioeconomic decisions required to complete all levels of the AIZ procedure are
extensive, and in most cases, not practically achievable. However, several of the initial
steps provide a reasonable approach to help state water quality regulators meet designated
use goals for a waterbody. A detailed discussion of the historical development of mixing
zone guidance is presented in Appendix A of the document. It also includes several
example allocation procedures.

5) USEPA. 1992. Technical Guidance Manual for Performing Waste Load Allocations,
Book III: Estuaries. Part 3: Use of Mixing Zone Models in Estuarine Waste Load
Allocations. EPA 823-^92-004. U.S. Environmental Protection Agency, Office of
Water, Washington, DC.
http://www.epa.gov/waterscience/library/modeling/wlabook3part3.pdf.

Technical Guidance Manual for Performing Waste Load Allocations, Book 111: Estuaries.
Part 3: Use of Mixing Zone Models in Estuarine Waste Load Allocations (Part 3) is the
third of a series of manuals that provide information and guidance for preparing waste
load allocations. Book I of the series provides general guidance for performing waste
load allocations. Book II provides guidance specifically directed toward streams and
rivers, while Book III provides guidance for preparing waste load allocations in estuaries.

Book III is divided into four parts. Part 1 provides technical information and policy
guidance for preparing estuarine waste load allocations. Part 2 provides a guide to
monitoring and model calibration and testing, and a case study tutorial on simulation of
waste load allocation problems in simplified estuarine systems. Part 3, summarized here,
describes the initial mixing of wastewater in estuarine and coastal environments and
mixing zone requirements. Part 3 also details the important physical processes that
govern the hydrodynamic mixing of aqueous discharges as well as application of
available models to four case study situations. Part 4 summarizes several historical case
studies, with critical review by experts.

Chapter 7 of Part 3, the first chapter of this document, describes initial mixing of
wastewater in estuarine and coastal waters. It also describes mixing zone definitions and
mixing zone recommendations, including special ones for toxic substances. Chapter 8
provides an overview of the important physical processes that govern the hydrodynamic
mixing of aqueous discharges. The chapter also reviews the mathematical background
and formulations for different mixing zone models. Chapter 9 illustrates the application
of jet integral models and of the expert system CORMIX. Four case studies are also
presented to demonstrate the capabilities and limitations of individual models.
EPA 823-R-06-003 8 July 2006
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6) USEPA. 1996. U.S. EPA NPDES Permit Writer's Manual. EPA 833-6-96-003. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
http://www.epa.gov/npdes/pubs/owmo243.pdf.

U.S. EPA NPDES Permit Writer's Manual (the Manual) provides guidance for writing
and issuing legally defensible and enforceable National Pollutant Discharge Elimination
System (NPDES) permits to dischargers, including technical and legal issues that should
be considered in permitting decisions. The document outlines the minimum requirements
that all state and regional NPDES permit programs share. The manual offers a variety of
information, ranging from basic knowledge about what elements should be required in an
NPDES permit to technical considerations related to the establishment of permit limits.

As a policy related to water quality-based effluent limits, mixing zones may be
considered during the permitting process. If a mixing zone is being considered, permit
writers consider site-specific characteristics of a given discharge in addition to the
condition of the receiving water to determine the dilution that will occur from the point
source and to determine the impact that a discharge will have on the receiving water.

This manual discusses a number of factors that should be considered to assess the fate
and transport of pollutants and to determine how the mixing zone will affect water
quality. It also discusses models for assessing mixing zones.

Modeling Documents

7) USEPA. 2003. Dilution Models for Effluent Discharges, 4th Edition (Visual Plumes).
EPA/6oo/R-O3/O25. U.S. Environmental Protection Agency, Ecosystems Research
Division, Athens, Georgia. http://www.epa.gov/ceampubl/swater/vplume/VP-
Manual.pdf.

Dilution Models for Effluent Discharges, 4th Edition (Visual Plumes) describes a mixing
zone modeling system. Visual Plumes (VP) is a Microsoft Windows-based suite of
models that supersedes the DOS PLUMES mixing zone modeling system. VP allows
users to simulate single and merging submerged plumes in arbitrarily stratified ambient
flow and buoyant surface discharges. Among its additional features are:

VP includes several models intended to encourage the continued improvement of plume
models. VP also allows modelers to access the superseded DOS PLUMES if the user
EPA 823-R-06-003 9 July 2006
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Compilation of EPA Mixing Zone Documents
requires consistency in modeling applications. A time-series file-linking capability
provides a way to simulate outfall performance over long periods of time. Most effluent
and ambient variables can be input from files that store data that vary over time. This is
the heart of the pollutant buildup capability, designed for one-dimensional tidal rivers or
estuaries to estimate pollution from the source in question. The time-series file linking
capability is served by summary graphics (i.e., graphics that focus on overall
performance indicators, like mixing zone dilutions or concentrations).

8) USEPA. 1994. Dilution Models for Effluent Discharges, 3rd Edition. EPA/6oo/R-
94/086. U.S. Environmental Protection Agency, Pacific Ecosystems Branch, ERL-N,
Newport, Oregon.
http://www.epa.gov/waterscience/standards/mixingzone/files/RSB UM PLUMES.pdf.

The document describes two initial dilution plume models (RSB and UM) and a model
interface and manager (PLUMES) for preparing common model input and running the
models. Two farfield algorithms are automatically initiated beyond the zone of initial
dilution. In addition, PLUMES incorporates the flow classification scheme of the Cornell
Mixing Zone Expert System (CORMIX), with recommendations for model usage,
thereby providing a linkage between two existing EPA systems. The PLUMES models
are intended for use with plumes discharged to marine and fresh water. Both buoyant and
dense plumes, as well as single source and multiple diffuser outfall configurations may be
modeled. The PLUMES software accompanies the document. The use of the model
interface is explained in detail, including a user's guide and a detailed tutorial. Other
examples of RSB and UM usage are also provided. This document contains information
that is not duplicated in the Visual Plumes version, notably plume modeling theory. Also,
the software can be used to calculate similarity parameters.

9) USEPA. 1991. CORMIX2: An Expert System for Hydrodynamic Mixing Zone
Analysis of Conventional and Toxic Multipart Diffuser Discharges. EPA 600-3-91-073.
U.S. Environmental Protection Agency, Office of Research and Development,
Washington, DC.
http://www.epa.gov/waterscience/standards/mixingzone/files/i99i CORMIX2.pdf.

CORMIX2: An Expert System for Hydrodynamic Mixing Zone Analysis of Conventional
and Toxic Multipart Diffuser Discharges describes the Cornell Mixing Zone Expert
System (CORMIX). CORMIX is a series of software systems that allows users to
analyze, predict, and design aqueous toxic or conventional pollutant discharges into
watercourses. It emphasizes the geometry and dilution characteristic of the initial mixing
zone. CORMIX2 emphasizes rapid initial mixing and assumes no physical, chemical, or
biological decay processes.

CORMIX2 models submerged multiport discharges into flowing water environments
such as rivers, lakes, estuaries, and coastal waters. It includes effects of ambient
stratification, dynamic attachment of the plume to the bottom of the receiving water, and
the limiting case of stagnant conditions. This report documents the development and
implementation of an engineering tool for analyzing submerged multiport diffuser
discharges into waterbodies with variable and complex conditions.
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CORMIX2 requires relevant data for the ambient and discharge situations, computes the
physical parameters, and classifies the given discharge into one of many possible
hydrodynamic configurations. CORMIX2 then (1) simulates the corresponding
hydrodynamic simulation for the flow, (2) interprets the results of the simulation relative
to applicable requirements of a mixing zone, including toxic discharge criteria, and
(3) suggests possible design alternatives and improvements concerning the mixing
characteristics.

The results of CORMIX's hydrodynamic simulations have been validated and generally
agree with available field and laboratory data. In particular, CORMIX2 correctly predicts
highly complex discharge situations involving boundary interactions, internal layer
formation, buoyant intrusions, and large-scale induced currents in shallow environments,
all features that are beyond the predictive capabilities of other currently available initial
mixing models for multiport diffusers.

10) USEPA. 1997. User's Manual for CORMIX: A Hydrodynamic Mixing Zone Model
and Decision Support System for Pollutant Discharges into Surface Waters. EPA
823/6-97-006. U.S. Environmental Protection Agency, Office of Science and
Technology, Washington, DC. (Originally printed in 1996.)
http://www.epa.gov/waterscience/models/cormix.html.

The user's manual gives a comprehensive description of the CORMIX system and
provides guidance for assembly and preparation of required input data for the three
subsystems (CORMIX1, CORMIX2, and CORMIX3). It also delineates ranges of
acceptability, provides guidance for interpretation and graphical display of system output,
and illustrates practical system application through several case studies.

The manual is designed for personnel in environmental management positions who want
an overview of CORMIX systems capabilities and technical staff needing assistance in
applications. Chapter II provides a summary of the physical processes of effluent mixing
and an overview of the regulatory background and practice on mixing zone applications.
Chapter III explains the general features of the CORMIX system, including summaries of
(a) predictive capabilities and limitations, (b) overall system structure and method of
processing information, (c) user interaction, and (d) individual computational elements.
Detailed guidance on preparing and entering input data, as required by the three
CORMIX subsystems, is provided in Chapter IV. Chapter V describes system output and
contains descriptive, quantitative, and graphical information on the predicted effluent
flow. Chapter VI describes the background and input and output features of both the
CORJET jet integral model and the far-field plume locator program FFLOCATR.
Finally, Chapter VII provides information on system availability and user support, as well
as possible future developments and enhancements.
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11) USEPA. 1990. Expert System for Hydrodynamic Mixing Zone Analysis of
Conventional and Toxic Single Port Discharges (CORMIXi). Technical Report
EPA/6oo/3-9O/oi2. U.S. EPA Environmental Research Laboratory, Athens, GA.
http://www.epa.gov/waterscience/standards/mixingzone/files/i99Q CORMIXi.pdf.

This document is a technical report for CORMIXI. It describes the development and
implementation of an engineering tool (CORMIXI) for analysis of submerged single port
discharges into a stratified or uniform density ambient environment with or without cross
flow. Chapters of the document provide detailed information about hydrodynamic
elements of mixing processes, hydrodynamic flow classification, an outline of the
computer programs in CORMIXI, flow protocols and simulation modules for
CORMIXI, system evaluation and verification, design case studies showing applications
of CORMIXI, and conclusions and recommendations. Appendices provide further
information such as online user advice for data input, flow classifications, and a case
study.

12) USEPA. 1997. Compendium of Tools for Watershed Assessment and TMDL
Development. EPA 841-6-97-006. U.S. Environmental Protection Agency, Office of
Water, Washington, DC.
http://www.epa.gov/waterscience/standards/mixingzone/files/i997 Tool
Compendium.pdf.

Compendium of Tools for Watershed Assessment and TMDL Development (the
Compendium of Tools) represents an update to and expansion of a previous EPA
publication, Compendium of Watershed-scale Model for TMDL Development (EPA 841-
R-92-002). The revised Compendium of Tools broadens the review of models and
techniques to include receiving water models and ecological assessment techniques and
models in addition to watershed loading models.

The Compendium of Tools summarizes available techniques and models that assess and
predict physical, chemical, and biological conditions in waterbodies, including mixing
zones for point source discharges. The compendium provides watershed managers and
other users with helpful information for selecting models that are appropriate to their
needs and resources. Specifically, this document includes information regarding:

• A wide range of watershed-scale loading models
• Field-scale pollutant loading models
• Receiving water models, including eutrophication/water quality models, toxics
models, and hydrodynamic models
• Integrated modeling systems that can be used to link watershed-scale loading with
receiving water processes
• Ecological techniques and models that can be used to assess or predict the status
of habitat, single species, or biological community
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The Compendium of Tools contains short descriptions of near-field models developed for coastal
areas, rivers, and streams, including CORMIX, PLUME, PC-VirGIS, GISPLS, WSTT, LWWM,
and BASINS.

13) USEPA. 1985. Initial Mixing Characteristics of Municipal Ocean Discharges:
Volume i—Procedures and Applications. EPA 6003850733. U.S. Environmental
Protection Agency, Washington, DC.
http://www.epa.gov/waterscience/standards/mixingzone/files/iQ85 Municipal Ocean
Discharges.pdf.

Initial Mixing Characteristics of Municipal Ocean Discharges: Volume 1—Procedures
and Application (the Ocean Discharges document) describes the behavior of plumes
generated when municipal wastewater is discharged into the open ocean). Volume I
contains analytical solutions and descriptions of five mathematical models that address a
variety of discharge, diffuser, and receiving water characteristics. Model output includes
rise height and initial dilution. The Ocean Discharges document provides guidance for
the range of values within which analytical solutions provide acceptable estimates. The
format of model input data is the same for all five computer programs.

Great Lakes Rule

14) USEPA. 2000. Final Rule to Amend the Final Water Quality Guidance for the Great
Lakes System to Prohibit Mixing Zones for Bioaccumulative Chemicals of Concern. U.S.
Environmental Protection Agency. 40 CFR Part 132 Federal Register, November 13,
2000, 65:67638. http://www.epa.gov/fedrgstr/EPA-WATER/2OOO/November/
Day-i3/w287QQ.htm.

Final Rule to Amend the Final Water Quality Guidance for the Great Lakes System to
Prohibit Mixing Zones for Bioaccumulative Chemicals of Concern (the Final Rule) was
written to revise EPA's 1995 Final Water Quality Guidance for the Great Lakes System.
The original 1995 rule was challenged in court and, although the court upheld most of the
provisions contained in the 1995 rule, it remanded the provisions that would have
eliminated mixing zones for bioaccumulative chemicals of concern (BCCs). The court
held that EPA failed to address whether the measure was cost-justified and remanded the
issue to EPA.

In response, EPA reexamined the factual record and cost analyses and published a
proposal to amend the 1995 rule to reinstate the provision to prohibit mixing zones for
BCCs. This provision (Procedure 3C) is described in more detail in Appendix F of the
rule. After reviewing and analyzing information in the rule-making record and public
comments on the Proposal to Amend the Final Water Quality Guidance for the Great
Lakes System to Prohibit Mixing Zones for Bioaccumulative Chemicals of Concern
(published in the Federal Register on October 4, 1999), EPA finalized the rule in 2000.
EPA 823-R-06-003 13 July 2006
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Appendix A: EPA Regional Documents

Note: No guidance has been developed specifically by Regions 1, 2, 3, 5, 6, 7, 9, and 10.

USEPA. 1995. EPA Region VIIIMixing Zones and Dilution Policy. U.S. Environmental
Protection Agency, Region 8, Water Management Division, Denver, CO.
http://www.epa.gov/waterscience/standards/mixingzone/files/i99Fi Reg 8 MZ and
Dilution Policy.pdf.

The objective of Region VIIIMixing Zones and Dilution Policy is to help states and
Indian tribes upgrade methods for deriving water quality-based permit limits, improve the
technical defensibility of National Pollutant Discharge Elimination System (NPDES)
permits, and reduce risks associated with mixing zone and dilution practices. The basis
for the policy was the desire of the region to clarify the approaches for using mixing
zones in NPDES permits. Prior to the policy, some applications of mixing zones
presumptively provided the entire stream flow for dilution, which often resulted in
effluent plumes (with elevated pollutant concentrations) extending far downstream of the
discharge. The clarifications sought to prevent applications of mixing zones that did not
adequately control effluent plume size or quality, possibly posing considerable risk to
sensitive downstream uses.

USEPA. 1993. EPA Region VIII Interim Guidance: Water Quality Standards for Indian
Tribes. U.S. Environmental Protection Agency, Region 8, Water Management Division,
Denver, CO. http://epa.gov/region8/water/wqs/GUIDANCE.pdf.

EPA Region VIII Interim Guidance: Water Quality Standards for Indian Tribes is
intended to assist the Indian tribes in EPA Region 8 to qualify to administer water quality
standards programs and to develop water quality standards pursuant to Clean Water Act
(CWA) sections 518 and 303(c). The guidance includes recommendations on mixing
zone policy development.

USEPA. 1980. EPA Region IVGuidance on Mixing Zones. U.S. Environmental
Protection Agency, Region 4, Atlanta, GA.
http://www.epa.gov/waterscience/standards/mixingzone/files/i98o Reg 4 MZ
Guidance.pdf.

EPA Region IV Guidance on Mixing Zones provides a basis for Region 4 review and
approval of state use of mixing zones in the development of effluent limitations. The
guidance provides detailed descriptions of (1) appropriateness of assigning a mixing zone
to a discharger, (2) the level of water quality that should be maintained in a mixing zone
and surrounding waters, and (3) the factors governing the size and shape of a mixing
zone.
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Appendix B: State Documents

California Environmental Protection Agency. 2005. Policy for Implementation of Toxics
Standards for Inland Surf ace Waters, Enclosed Bays, and Estuaries of California.
California Environmental Protection Agency, State Water Resources Control Board.
http://www.waterboards.ca.gov/iswp/docs/final.pdf. Accessed July 2006.

Colorado Department of Public Health and Environment. 2002. Colorado Mixing Zone
Implementation Guidance. Colorado Department of Public Health and Environment,
Water Quality Control Division.
http://www.cdphe.state.co.us/op/wqcc/Guidance/comixzoneimplguid.pdf. Accessed
July 2006.

Massachusetts Department of Environmental Protection. 1993. Massachusetts Surface
Water Quality Standards Implementation Policy for Mixing Zones. Massachusetts
Department of Environmental Protection, Boston, MA.
http://www.epa.gov/ost/wqs/ma/ma i mswqs.pdf. Accessed July 2006.

New York State Department of Environmental Conservation. 1996. Total Maximum
Daily Loads and Water Quality Based Effluent Limits. Memo dated July 8,1996.
Reissued February 26,1998.
http://www.dec.state.ny.us/website/dow/togs/togsi3i.pdf. Accessed July 2006.

North Carolina Department of the Environment and Natural Resources. 1999. Mixing
Zones in North Carolina. North Carolina Department of the Environment and Natural
Resources, Division of Water Quality. Available online:
http://h2o.enr.state.nc.us/NPDES/documents/mixing.pdf. Accessed July 2006.

Oregon Department of Environmental Quality. 2000. A Mixing Zone Guidance
Document Prepared for the Oregon Department of Environmental Quality.
S. Schnurbusch. Portland State University.
http://www.esr.pdx.edu/ESR/docs/mem/schnurbusch.pdf. Accessed July 2006.

South Carolina Department of Health and Environmental Control. 1997. Groundwater
Mixing Zone Application Guidance. South Carolina Department of Health and
Environmental Control, Columbia, SC.
http://www.scdhec.gov/water/pubs/mixingzone.pdf. Accessed July 2006.

South Dakota Department of Environmental and Natural Resources. 1998. Mixing Zone
and Dilution Implementation Procedures. South Dakota Department of Environmental
and Natural Resources.
http://www.epa.gov/ost/standards/wqslibrary/sd/sd 8 zone dil.pdf. Accessed
July 2006.
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Utah Division of Water Quality. 2000. Mixing Zone Implementation Procedure. Utah
Division of Water Quality.
http://www.epa.gov/waterscience/standards/wqslibrary/ut/ut 8 wq.pdf. Accessed
July 2006.

Virginia Department of Environmental Quality. 2000. Guidance Memo No. 00-2011;
Guidance on Preparing VPDES Permit Limits. Memo from Larry G. Lawson to Regional
Directors, dated August 24, 2000. Virginia Department of Environmental Quality,
Richmond, VA. http://www.deq.state.va.us/waterguidance/pdf/oo2Oii.pdf.Accessed
July 2006.

Virginia Department of Environmental Quality. 2004. Guidance Memorandum
No. 04-2021; Guidance for Exceptional State Waters Designations in Antidegradation
Policy Section of Virginia Water Quality Standards Regulation (9 VAC 25-260-30^.3).
Memo from Ellen Gilinsky to Regional Directors, dated November 15, 2004. Virginia
Department of Environmental Quality, Richmond, VA.
http://www.townhall.state.va.us/Utils/DisplayContent.cfm ?fileName=E%3A%5Ctownh
all%.sCdocroot%.sCGuidanceDocs%.sC440%.sCGDoc%.sFDEO%.sF2.s.s.^%.sFvi%2Epdf.
Accessed July 2006.

Washington Department of Ecology. No date. Guidance for Conducting Mixing Zone
Analyses. Washington Department of Ecology, Olympia, WA.
http://www.ecy.wa.gov/programs/eap/mixzone/mixzone.doc. Accessed July 2006.

Washington Department of Ecology. 2005. Water Quality Program Permit Writer's
Manual. Washington Department of Ecology, Olympia, WA.
http://www.ecy.wa.gov/pubs/Q2iOQ.pdf. Accessed July 2006.

West Virginia Division of Environmental Protection. iQQy. Water Quality
Standards/Mixing Zones Implementation Guidance. West Virginia Division of
Environmental Protection Office of Water Resources.
http://www.epa.gov/ost/wqs/wv/wv 3 wqs.pdf. Accessed July 2006.

Wisconsin Department of Natural Resources. 1QQ2. Mixing Zone Guidance for Chronic
Toxicity and Zones of Initial Dilution. Wisconsin Department of Natural Resources,
Modeling and Analysis Unit, Bureau of Water Resources Management.
http://www.epa.gov/ost/wqs/wi/wi 5 mixin zone.pdf. Accessed July 2006.

Wyoming Department of Environmental Quality. 2001. Wyoming Surface Water
Quality Standards, Implementation Policies for Antidegradation, Mixing Zones,
Turbidity, and Use Attainability Analysis. Wyoming Department of Environmental
Quality.
http://deq.state.wy.us/wqd/watershed/surfacestandards/Downloads/Standards/
iiQ68-doc.pdf. Accessed July 2006.
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Appendix C: Other Documents to Consider When Establishing
Mixing Zones*

*Note: these documents are often referred to in mixing zone guidance, but they have been updated or
superseded by newer guidance documents and rules.
FWPCA. 1968. Water Quality Criteria (Green Book). Federal Water Pollution Control
Administration. Report of the National Technical Advisory Committee to the Secretary
of the Interior. U.S. Department of Interior, Washington DC. (Superseded by USEPA,
1994.)

NAS/NAE. 1973. Water Quality Criteria 1972 (Blue Book). A Report of the Committee
on Water Quality Criteria. National Academy of Science and National Academy of
Engineers, Washington, DC. NTIS-PB 236199. USGPO #5501-00520. (Superseded by
EPA, 1994.)

USEP A. 1976. Quality Criteria for Water (Red Book). U.S. Environmental Protection
Agency, Washington, DC.

USEPA. 1986. Quality Criteria for Water (Gold Book). EPA 440586001. U.S.
Environmental Protection Agency, Office of Regulations and Standards,
Washington, DC.

USEPA. 1987. Permit Writers Guide to Water Quality-based Permitting for Toxic
Pollutants. EPA 440487005. U.S. Environmental Protection Agency, Office of Water,
Washington, DC. (Rescinded)

USEPA. 1995. Final Water Quality Guidance for the Great Lakes System; Final Rule.
U.S. Environmental Protection Agency. Federal Register, March 23,1995, 60:15366.
(Superseded by the 2000 Final Rule)
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Resources
Models
Cornell Mixing Zone Expert System (CORMIX)
The Cornell Mixing Zone Expert System (CORMIX) is a mixing zone model and decision
support system for environmental impact assessment of regulatory mixing zones
resulting from continuous point source discharges. CORMIX emphasizes the role of
boundary interaction to predict steady state mixing behavior and plume geometry.

http://www.epa.gov/waterscience/models/cormix.html (EPA Office of Water)

http: //www. cormix.info (CORMIX Home Page)

Visual Plumes (VP)
Visual Plumes (VP) is a windows-based computer application that supersedes the DOS-
based version, called simply PLUMES. VP simulates single and merging submerged
aquatic plumes in arbitrarily stratified ambient flow and buoyant surface discharges.

http://www.cee.odu.edu/model/visual plume.php (VP Home Page)

Training

Water Quality Standards Academy
The "Water Quality Standards Academy" is best known for the "Basic Course," which is an
introductory course designed for those with fewer than six months experience with water
quality standards and criteria programs. However, others may benefit from the course,
including veterans of the water quality standards program who want a refresher course.

http://www.epa.gov/ost/standards/academy.html

NPDES Permit Writers' Training Course
The objective of the NPDES Permit Writers' Training Course is to provide the basic
regulatory framework and technical considerations that support the development of
wastewater discharge permits as required under the National Pollutant Discharge
Elimination System (NPDES) Permit Program. The course is designed for new permit
writers, highlighting the process of developing, issuing and complying with NPDES
permits. The format of the course is a combination of lecture, case examples, and
practical exercises that are geared to acquaint participants with the tools and resources
available to assist them in writing NPDES permits.

http://cfpub.epa.gov/npdes/courses.cfm7program id=0&outreach id=i&o tvpe=i
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Links to NPDES Permitting Information

Overview of the Water Quality Standards-to-Permits Process
http://cfpub.epa.gov/npdes/wqbasedpermitting/wqoverview.cfm

Water Quality and Technology-Based Permitting
http://cfpub.epa.gov/npdes/generalissues/watertechnology.cfm7program id=4Fi
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Comparison of All EPA Documents
Full document available at
http://www.epa.gov/waterscience/standards/mixingzone
Standards and Health Protection Division
Office of Water
U.S. Environmental Protection Agency
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Comparison of Mixing Zone Documents from EPA Headquarters by Topic

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"o
Q.
Recommends states specify whether
mixing zones are allowed
Effluent characterization — WET
Effluent characterization — specific
pollutants
Effluent characterization —
bioconcentratable pollutants
Application of criteria in mixing zones
Size and/or area considerations
Lethality to passing organisms
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Special situations: lake, marine,
estuarine
Cautions about mixing zones in certain
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Technical and Policy Guidance Documents
Technical Support Document for Water Quality-based Toxics Control (USEPA, 1 991 )
Water Quality Standards Handbook: Second Edition (USEPA, 1 994)
Memorandum: EPA Guidance on Application of State Mixing Zone Policies in EPA-
Issued NPDES Permits (USEPA, 1 996)
Allocated Impact Zones for Areas of Non-Compliance (USEPA, 1995)
Technical Guidance Manual for Performing Waste Load Allocations, Book III: Estuaries.
Part 3: Use of Mixing Zone Models in Estuarine Waste Load Allocations (USEPA, 1 992)
U.S. EPA NPDES Permit Writer's Manual (USEPA, 1 996)
•
•

•
•
•

•

•
•
•

•
•

•

•
•

0
•

•
•

•

•
•
Modeling Documents
Dilution Models for Effluent Discharges, 4th ed. (Visual Plumes) (USEPA, 2003)
Dilution Models for Effluent Discharges, 3rd ed. (USEPA, 1 994)
CORMIX2: An Expert System for Hydrodynamic Mixing Zone Analysis of Conventional
and Toxic Multiport Diffuser Discharges (USEPA, 1991)
User's Manual for CORMIX: A Hydrodynamic Mixing Zone Model and Decision Support
System for Pollutant Discharges into Surface Waters (USEPA, 1 997)
Expert System for Hydrodynamic Mixing Zone Analysis of Conventional and Toxic Single
Port Discharges (CORMIX1) (USEPA, 1990)
Compendium of Tools for Watershed Assessment and TMDL Development
(USEPA, 1997)
Initial Mixing Characteristics of Municipal Ocean Discharges: Volume 1 — Procedures
and Applications (USEPA, 1 985)
•
•
•
•
•
•
•

•

•
•
•
•
•
•
•
Great Lakes Rule
Final Rule to Amend the Final Water Quality Guidance for the Great Lakes System
to Prohibit Mixing Zones for Bioaccumulative Chemicals of Concern (USEPA, 2000)

•

1 The document describes in detail the associated topic; © The document provides very little detail concerning the associated topic
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Compilation of EPA Mixing Zone Documents
Subject Comparison Table
Full document available at
http://www.epa.gov/waterscience/standards/mixingzone
Standards and Health Protection Division
Office of Water
U.S. Environmental Protection Agency
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cxEPA
C United States EPA-823-R-06-003
^"•^^» Environmental Protection , , Onno
F!f^Agency July 2006
Compilation of EPA Mixing Zone Documents
Overviews Only
Full document available at
http://www.epa.gov/waterscience/standards/mixingzone
Standards and Health Protection Division
Office of Water
U.S. Environmental Protection Agency
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Compilation of EPA Mixing Zone Documents: Overviews Only
Overviews Only

Technical and Policy Guidance Documents

The handbook's overview of the water quality standards program provides a brief
discussion of mixing zones, including:

o How states have the discretion to use mixing zones in their water quality
standards, subject to EPA approval.
EPA 823-R-06-003 1 July 2006
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o How state water quality standards describe methods for determining location,
size, shape, and other factors of mixing zones.
o How states should give careful consideration to the appropriateness of a mixing
zone depending on the pollutants in the discharge (e.g., bioaccumulative,
persistent).

Allocated Impact Zones for Areas of'Non-Compliance (the AIZ document) presents an
impact allocation procedure. This procedure is an attempt to assess cumulative impacts
and addresses the potential limitations of state water quality standards mixing zone
policies. It organizes and manages discharges by including all point source discharges
within the decision making process. Specifically, this procedure can supplement mixing
zone policies that might be limited to the cross-sectional or surface area of streams and
lakes or a uniform linear distance limitation in mixing zone size determinations. For
EPA 823-R-06-003 2 July 2006
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Compilation of EPA Mixing Zone Documents: Overviews Only
example, prior to 1995, some state guidance did not consider multiple source impacts,
sensitivity of aquatic resources, and socioeconomic factors. In contrast, the impact
allocation procedure addresses many of the socioeconomic and ecological factors that can
be considered in waste management decisions.

Technical Guidance Manual for Performing Waste Load Allocations, Book III: Estuaries.
Part 3: Use of Mixing Zone Models in Estuarine Waste Load Allocations (Part 3) is the
third of a series of manuals that provide information and guidance for preparing waste
load allocations. Book I of the series provides general guidance for performing waste
load allocations. Book II provides guidance specifically directed toward streams and
rivers, while Book III provides guidance for preparing waste load allocations in estuaries.

Chapter 7 of Part 3, the first chapter of this document, describes initial mixing of
wastewater in estuarine and coastal waters. It also describes mixing zone definitions and
mixing zone recommendations, including special ones for toxic substances. Chapter 8
provides an overview of the important physical processes that govern the hydrodynamic
mixing of aqueous discharges. The chapter also reviews the mathematical background
and formulations for different mixing zone models. Chapter 9 illustrates the application
EPA 823-R-06-003 3 July 2006
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Compilation of EPA Mixing Zone Documents: Overviews Only
of jet integral models and of the expert system CORMIX. Four case studies are also
presented to demonstrate the capabilities and limitations of individual models.

6) USEPA. 1996. [7.5. EPA NPDES Permit Writer's Manual. EPA 833-6-96-003. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
http://www.epa.gov/npdes/pubs/owmo243.pdf.

Modeling Documents

• Graphics
• Time-series input files
• User specified units
• A conservative tidal background-pollutant buildup capability
• A sensitivity analysis capability
• A multistressor pathogen decay model that predicts coliform mortality using
temperature, salinity, solar insolation (the amount of radiation hitting a surface or
object), and water column light absorption
EPA 823-R-06-003 4 July 2006
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VP includes several models intended to encourage the continued improvement of plume
models. VP also allows modelers to access the superseded DOS PLUMES if the user
requires consistency in modeling applications. A time-series file-linking capability
provides a way to simulate outfall performance over long periods of time. Most effluent
and ambient variables can be input from files that store data that vary over time. This is
the heart of the pollutant buildup capability, designed for one-dimensional tidal rivers or
estuaries to estimate pollution from the source in question. The time-series file linking
capability is served by summary graphics (i.e., graphics that focus on overall
performance indicators, like mixing zone dilutions or concentrations).

CORMIX2 requires relevant data for the ambient and discharge situations, computes the
physical parameters, and classifies the given discharge into one of many possible
hydrodynamic configurations. CORMIX2 then (1) simulates the corresponding
hydrodynamic simulation for the flow, (2) interprets the results of the simulation relative
to applicable requirements of a mixing zone, including toxic discharge criteria, and
(3) suggests possible design alternatives and improvements concerning the mixing
characteristics.

The manual is designed for personnel in environmental management positions who want
an overview of CORMIX systems capabilities and technical staff needing assistance in
applications. Chapter II provides a summary of the physical processes of effluent mixing
and an overview of the regulatory background and practice on mixing zone applications.
Chapter III explains the general features of the CORMIX system, including summaries of
(a) predictive capabilities and limitations, (b) overall system structure and method of
processing information, (c) user interaction, and (d) individual computational elements.
Detailed guidance on preparing and entering input data, as required by the three
CORMIX subsystems, is provided in Chapter IV. Chapter V describes system output and
contains descriptive, quantitative, and graphical information on the predicted effluent
flow. Chapter VI describes the background and input and output features of both the
CORJET jet integral model and the far-field plume locator program FFLOCATR.
Finally, Chapter VII provides information on system availability and user support, as well
as possible future developments and enhancements.
EPA 823-R-06-003 6 July 2006
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11) USEPA. 1990. Expert System for Hydrodynamic Mixing Zone Analysis of
Conventional and Toxic Single Port Discharges (CORMIXi). Technical Report
EPA/6oo/3-9O/oi2. U.S. EPA Environmental Research Laboratory, Athens, GA.
http://www.epa.gov/waterscience/standards/mixingzone/files/i99Q CORMIXi.pdf.

• A wide range of watershed-scale loading models
• Field-scale pollutant loading models
• Receiving water models, including eutrophication/water quality models, toxics
models, and hydrodynamic models
• Integrated modeling systems that can be used to link watershed-scale loading with
receiving water processes
• Ecological techniques and models that can be used to assess or predict the status
of habitat, single species, or biological community
EPA 823-R-06-003 / July 2006
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Compilation of EPA Mixing Zone Documents: Overviews Only
The Compendium of Tools contains short descriptions of near-field models developed for
coastal areas, rivers, and streams, including CORMIX, PLUME, PC-VirGIS, GISPLS,
WSTT, LWWM, and BASINS.

Great Lakes Rule

In response, EPA reexamined the factual record and cost analyses and published a
proposal to amend the 1995 rule to reinstate the provision to prohibit mixing zones for
BCCs. This provision (Procedure 3C) is described in more detail in Appendix F of the
rule. After reviewing and analyzing information in the rule-making record and public
comments on the Proposal to Amend the Final Water Quality Guidance for the Great
Lakes System to Prohibit Mixing Zones for Bioaccumulative Chemicals of Concern
(published in the Federal Register on October 4, 1999), EPA finalized the rule in 2000.
EPA 823-R-06-003 8 July 2006
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Appendix A: EPA Regional Documents

Note: No guidance has been developed specifically by Regions 1, 2, 3, 5, 6, 7, 9, and 10.

USEPA. 1980. EPA Region IVGuidance on Mixing Zones. U.S. Environmental
Protection Agency, Region 4, Atlanta, GA.
http://www.epa.gov/waterscience/standards/mixingzone/files/i98o Reg 4 MZ
Guidance.pdf.

EPA Region IV Guidance on Mixing Zones provides a basis for Region 4 review and
approval of state use of mixing zones in the development of effluent limitations. The
guidance provides detailed descriptions of (1) appropriateness of assigning a mixing zone
to a discharger, (2) the level of water quality that should be maintained in a mixing zone
and surrounding waters, and (3) the factors governing the size and shape of a mixing
zone.
EPA 823-R-06-003 A-l July 2006
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Major Topics in EPA Headquarters Mixing Zone Documents

Application of criteria in mixing zones
Cautions about mixing zones in certain
situations (e.g., near fish harvesting)
Determining WLAs
Effluent characterization —
bioconcentratable pollutants
Effluent characterization — specific
pollutants
Effluent characterization — WET
Lethality to passing organisms
Mixing zone analyses (e.g., models)
Recommends states specify whether
mixing zones are allowed
Size and/or area considerations
Special situations: lake, marine, estuarine

Technical and Policy Guidance Documents

.y
Technical Support Document for Water Quality-based To,
Control (USEPA, 1991)
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Water Quality Standards Handbook: Second Edition
(USEPA, 1994)

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.e'en
Memorandum: EPA Guidance on Application of State Mix
Zone Policies in EPA-lssued NPDES Permits (USEPA, 1 <

Allocated Impact Zones for Areas of Non-Compliance
(USEPA, 1995)

CM
Technical Guidance Manual for Performing Waste Load
Allocations, Book III: Estuaries. Part 3: Use of Mixing Zon
Models in Estuarine Waste Load Allocations (USEPA, 1 9<
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a.S. EPA NPDES Permit Writer's Manual (USEPA, 1 996

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Modeling Documents

Dilution Models for Effluent Discharges, 4th ed. (Visual
Plumes) (USEPA, 2003)

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Dilution Models for Effluent Discharges, 3rd ed.
(USEPA, 1994)

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