EPA/440/5-88/015
States
imental Protection
I
Office of Water
Regulations and Standards
Washington, DC 20460
EPA 440/5-88/015
September 1988
..ixing Zones
Water Quality Standards
Criteria Summaries:
A Compilation
of State/Federal Criteria
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DISCLAIMER
This publication was prepared by Battelle under contract to
the U.S. Environmental Protection Agency (Contract 68-03-3534).
Secondary information sources were used to compile data presented
in this document. Each State was given an opportunity to review
and provide comments on a draft of this information document. In
no event shall either the United States or Battelle have any
responsibility or liability for any use, misuse, or reliance upon
the information contained herein, nor does either warrant or
otherwise represent in any way the accuracy, adequacy, efficacy,
or applicability of the contents hereof.
The reader should consult the water quality standards of a
particular State for exact regulatory language applicable to that
State. Copies of State water quality standards may be obtained
from the State's Water Pollution Control Agency or its
equivalent.
Additional information may also be obtained from the:
Standards Branch
Criteria and Standards Division (WH-585)
Office of Water Regulations and Standards
U.S. Environmental Protection Agency
Washington, D.C. 20460
202-475-7315
This document may be obtained only from the National Technical
Information Service (NTIS) at the following address:
National Technical Information Service
5285 Front Royal Road
Springfield, Virginia 22161
703-487-4650
The NTIS order number is: PB89-141477
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INTRODUCTION
This digest is compiled to provide general information to the public as well
as to Federal, State, and local officials. It contains excerpts from the
individual Federal-State water quality standards establishing pollutant
specific criteria for interstate surface waters. The water quality standards
program is implemented by the U.S. Environmental Protection Agency where
responsibility for providing water quality recommendations, approving
State-adopted standards for interstate waters, evaluating adherence to the
standards, and overseeing enforcement of standards compliance has been
mandated by Congress.
Standards, a nationwide strategy for surface water quality management, contain
three major elements: the use (recreation, drinking water, fish and wildlife
propagation, industrial, or agricultural) to be made of the navigable water;
criteria to protect these uses; and an antidegradation statement to protect
existing high quality waters, from degradation by the addition of pollutants.
Guidance for the development of standards by individual States is contained in
two EPA documents entitled Water Quality Standards Handbook (1983) and Quality
Criteria for Water (1986).
Mixing zones in State water quality standards, which are the subject of this
digest, enable a State to achieve aquatic protection through a less stringent
stream management approach. The mixing zone is a designated area or location
of a receiving water where waste waters and receiving waters mix and the
ambient water quality criteria do not need to be met. Although this mechanism
permits a zone of somewhat less desirable water quality than required by the
State in ambient waters, it does provide a diluting function which aids in the
achievement of the standards. If no such zone is recognized by a State, then
the waters must meet the criteria at the point of discharge.
The primary purpose of designating mixing zones is to limit areas of
degradation and to not require excessive wastewater treatment. Furthermore,
the in zone quality should be at a level to support the most sensitive aquatic
life form indigenous to the receiving water body. The 1983 EPA Water Quality
Handbook recommends the following consideration to be included in State water
quality standards mixing zone policy:
A limited mixing zone, serving as a zone of initial Dilution in the immediate
area of a point source of pollution, may be allowed. Whether to establish a
mixing zone policy is a matter of State discretion. Such a policy, however,
must be consistent with the Act and is subject to the approval of the Regional
Administator.
Careful consideration must be given to the appropriateness of a mixing zone
where a substance discharged is bioaccumulative, persistent, carcinogenic,
mutagenic, or teratogenic. In such cases the State must consider such effects
as sediment deposition, bioaccumulation in aquatic biota, bioconcentration in
the food chain, and the known or predicted safe exposure levels for the
In the broadest sense, the zone surrounding, or downstream from, a discharge
location is an "allocated impact zone" where numeric water quality criteria
can be exceeded as long as acutely toxic conditions are prevented.
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substance. The effects of bioaccumulation vill depend on the predicted
duration/concentration exposure of the biota; thus the likelihood that the
mixing zone vill be inhabited by resident biota for a sufficiently long time
to cause adverse effects, should be considered. Factors such as size of the
zone, concentration gradient vithin the zone, physical habitat, attraction of
aquatic life, etc., are important in this evaluation. In some instances, the
ecological ?nd human health effects may be so adverse that a mixing zone is
not appropriate.
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REFERENCES
5 California Water Quality Standards, ca. 1975.
9 Florida Administrative Code, Chapter 17-4, 1987 and Florida Administrative
Code, Chapter 17-3, 1988.
12 Idaho Department of Health and Welfare Rules and Regulations, Title 1,
Chapter 2, "Water Quality Standards and Wastevater Treatment
Requirements", 1980.
35 Ohio Water Quality Standards, Chapter 3745-1 of the Administrative Code,
Ohio Environmental Protection Agency, 1985.
42 Tennessee's Water Quality Criteria and Stream Use Classifications for
Interstate and Intrastate Streams, Tennessee Water Quality Control Board:
Department of Health and Environment, 1987.
43 Texas Surface Water Quality Standards, Texas Water Commission, Rule
Change, 1988.
44 Utah Standards of Quality for Waters of the State, Wastewater Disposal
Regulations: Part II, State of Utah Department of Health: Division of
Environmental Health, 1988.
45 Vermont Water Quality Standards, State of Vermont Water Resource Board,
1987.
51 Water Quality Standards for American Samoa, 1984, p. 12-16.
53 Revised Guam Water Quality Standards, Guam Environmental Protection
Agency, 1984, p. 15-19.
54 Commonwealth of Northern Mariana Islands Marine and Fresh Water Quality
Standards, Commonwealth Register, Vol. 8 No. 5, 1986, p. 4470.
55 Puerto Rico Water Quality Standards Regulation, Environmental Quality
Board, 1983.
56 Marine and Fresh Water Quality Standard Regulations, Trust Territory,
1986, p. 11-14.
57 Virgin Islands Water Pollution Regulations, Department of Conservation and
Cultural Affairs, 1985, Title 12, p. 266-267.
ENVIRONMENT REPORTER, The Bureau of National Affairs, Inc., Washington, D.C.
20037
1 Page 701:1002, June 26, 1986
2 Pages 706:1012-1013, November 7, 1986
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3 Page 711:1006, February 7, 1986
4 Page 716:1004, August 30, 1985
6 Page 726:1005, March 22, 1985
7 Pages 731:1001-1002, May 14, 1982
8 Page 736:1002, March 28, 1986
12 Pages 756:1011-1012, September 20, 1985
13 Page 766:0504, March 28, 1986
14 Page 771:1002, August 10, 1984
15 Page 776:1004, February 13, 1987
16 Pages 781:1002-1003, March 27, 1987
17 Pages 786:1007-1008, November 29, 1985
18 Page 791:1009, January 18, 1985
20 Pages 801:1003-1004, April 19, 1985
21 Page 806:1002, June 21, 1985
22 Page 811:1007, February 13, 1987
23 Page 816:1011, June 25, 1982
24 Page 821:1002, October 25, 1985
25 Page 826:1007, June 21, 1985
26 Page 831:1011, October 4, 1985
27 Page 836:1002, March 27, 1987
29 Page 846:1006, October 5, 1984
30 Page 851:1004, April 11, 1986
31 Page 856:1002, June 11, 1982
32 Pages 861:1002, 1040-1041, November 29, 1985
33 Page 866:1006, September 6, 1985
34 Page 871:1004, June 7, 1985
36 Page 881:1014, September 26, 1986
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37 Page 886:1007, May 9, 1986
39 Page 901:1002, August 9, 1985
40 Pages 906:1004-1005, November 29, 1985
41 Page 911:1003, March 22, 1985
46 Page 936:1001, February 28, 1986
47 Page 941:1002, October 21, 1983
48 Pages 946:1002-1003, August 10, 1984
49 Page 951:1003, December 19, 1986
50 Page 956:1004, July 5, 1985
52 Page 741:1005, March 28, 1986
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State
Mixing Zone Narrative
Alabama
In making any tests or analytical determinations to
determine compliance or non-compliance with water
quality criteria, samples shall be collected in such
manner and at such locations approved by a duly
authorized representative of the Commission as being
representative of the receiving vater after reasonable
opportunity for dilution and mixture with the wastes
discharged thereto. Mixing zones, i.e., that portion
of the receiving waters where mixture of effluents and
natural waters take place, shall not preclude passage
of free-swimming and drifting aquatic organisms to the
extent that their populations are significantly
affected.
Alaska
(a) In applying the water quality criteria of 18 AAC
70.020, the department (Alaska Department of
Environmental Conservation) will, in its discretion,
prescribe its permits or certifications a volume of
dilution for an effluent or substance within a
receiving water. Water quality standards may be
exceeded within this mixing zone. However the
standards must be met at every point outside its
boundaries. The department will not allow mixing
zones if:
(1) There is significant potential for adverse
environmental or health effects due to
discharge of a substance that bioaccumulates
in food chains; concentrates in sediments,
or is persistent, carcinogenic, mutagenic or
teratogenic, or
(2) Other potential environmental or health
effects are so adverse that a mixing zone is
not appropriate. A mixing zone will be
granted only after the applicant has shown
to the department's satisfaction that wastes
or substances that may exceed the water
quality criteria limits will be treated
using the methods found by the department to
be most effective.
(b) The department will, in its discretion, establish
effluent limitation requirements in its wastewater
disposal permits in lieu of or in addition to a
defined mixing zone.
(c) No individual mixing zone or combination of
mixing zones will be permitted to form a barrier to
the migratory routes of aquatic species.
(d) In determining the size of the mixing zones,
department will consider the following:
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State Mixing Zone Narrative
(1) The physical, biological and chemical
characteristics of the receiving water;
(2) The effects of the discharge on the present
and anticipated protected water uses and
quality of the receiving water;
(3) The mixing characteristics of the receiving
water; and
(4) The characteristics of the effluent,
including flow rate and composition.
(e) Unless it is demonstrated to the satisfaction of
the department, in accordance with (f) of this
section, that the size limitations can be increased,
mixing zones will be as small as practicable and will
comply with the following size limitations:
(1) The cumulative linear width of the mixing
zone(s) intersected on any given cross
section of a river or stream will not exceed
one third of the total width of that cross
section;
(2) The total horizontal area allocated to all
mixing zones on a lake will not exceed 10
percent of the lake's surface area;
(3) The cumulative linear length of the mixing
zone(s) intersected on any given cross
section of an estuary, inlet, cove, channel,
or other marine water measured at mean lower
low water may not exceed 10 percent of the
total length of that cross section, nor may
the total horizontal area allocated to
mixing zones in these waters exceed 10
percent of the surface area measured at mean
lower low water.
(f) A person conducting an operation for which a
mixing zone is sought or required by the department
shall submit to the department all information
necessary for assignment of a mixing zone, including
(1) Type of operation being conducted;
(2) The characteristics of the effluent,
including flow rate and composition;
(3) The characteristics of the receiving water
at the location of the proposed discharge or
activity including but not limited to, where
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State Mixing Zone Narrative
appropriate, water quality, flov rate,
current patterns, depth and width, and
seasonal changes;
(4) A description of the extent to which the
operation may impact the physical,
biological and chemical characteristics of
the receiving water; and
(5) A proposed design for outfall and diffuser
structures.
Arizona (A) The following requirements establish the allowable
conditions for a mixing zone;
1. The shape of a mixing zone should be a simple
configuration;
2. Shore and bottom hugging plumes shall be avoided;
3. A zone of passage of not less than one-half of the
stream cross-sectional area shall be provided when the
receiving water is a flowing stream;
4. The length of a mixing zone shall not exceed 500
meters in a flowing stream;
5. The surface area of a mixing zone shall not exceed
10 percent of the surface area of a lake, reservoir or
other impoundment;
6. In no case shall water quality in a mixing zone:
(a) Interfere with protected uses in areas
beyond such zone;
(b) Interfere with the established community of
aquatic life in areas of the water body
beyond such zone;
(c) Impinge on biologically-important areas in
areas beyond such zone;
(d) Contain materials in concentrations that
exceed the 96-hour LC 50 for biota
significant to the indigenous aquatic
community.
B. The Council (Arizona Water Quality Control Council)
shall determine conformance with R9-21-211.A. when
requested. The determinations shall be made either:
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State Mixing Zone Narrative
1. As part of the review of plans and
specifications for proposed vastevater
treatment facilities requiring new
construction or modifications to existing
capacity or treatment. Determination of
such conformance shall commence vith plans
and specification submitted after the
effective date of this Regulation; or
2. When a request, accompanied by information
necessary to determine the fulfillment of
requirements given in R9-21-211.A., is
submitted to the Council.
C. When the Council determines that a proposed mixing
zone satisfies the requirements given in R9-21-211.A.,
the Council may specify that within the approved
mixing zone, one or more pollutants, but not fecal
coliform may be allowed to exceed the limits
established R9-21-203, D., R9-21-205, or R9-21-208.
Arkansas The effects of wastes on the receiving stream shall be
determined after the wastes have been thoroughly mixed
with the stream water, but consideration will also be
given to the quality of the waste effluent in
determining the adequacy of treatment. Outfall
structures should be designed to minimize the extent
of mixing zones and in the larger streams the zone of
mixing shall not exceed 1/4 of the cross sectional
area and/or volume of the stream flow. The remaining
3/4 of the stream shall be maintained as a zone of
passage for swimming and drifting organisms, and shall
remain of such quality that stream ecosystems are not
significantly affected.
In the smaller streams, because of varying local
physical and chemical conditions and biological
phenomena, a site-specific determination shall be made
on the percentage of river width necessary to allow
passage of critical free-swimming and drifting
organisms so that negligible or no effects are
produced on their populations. As a guideline no more
than 2/3 the width of smaller streams should be
devoted to mixing zones thus leaving at least 1/3 free
as a zone of passage. In lakes and reservoirs the
size of mixing zones shall be defined by the
Department of Pollution Control and Ecology on an
individual basis, and the area shall be kept at a
minimum.
Mixing zones shall not prevent free passage of fish or
significantly affect aquatic ecosystems.
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State
Mixing Zone Narrative
California"
Ocean Waters:
Initial dilution is the process which results in the
rapid and irreversible turbulent mixing of wastewater
vith ocean water around the point of discharge.
For a submerged buoyant discharge, characteristic of
most municipal and industrial wastes that are released
from the submarine outfalls, the momentum of the
discharge and its buoyancy act together to produce
turbulent mixing. Initial dilution in this case is
completed when the diluting wastewater ceases to rise
in the water column and first begins to spread
horizontally.
For shallow water submerged discharges, surface
discharges, and non-buoyant discharges, characteristic
of cooling water wastes and some individual
discharges, turbulent mixing results primarily from
the momentum of discharge. Initial dilution, in these
cases, is considered to be completed when the
momentum induced velocity of the discharge ceases to
produce significant mixing of the waste, or the
diluting plume reaches a fixed distance from the
discharge to be specified by the Regional Board,
whichever results in the lower estimate for initial
dilution.
For the purpose of this plan, minimum initial dilution
is the lowest average initial dilution within any
single month of the year. Dilution estimates shall be
based on observed waste flow characteristics, observed
receiving water density structure and the assumption
that no currents of sufficient strength to influence
the initial dilution process flow across the discharge
structure.
The Executive Director shall issue guidelines to be
used by the State and Regional Boards for determining
the initial dilution achieved by each ocean discharge.
Colorado
(a) The mixing zone is that area of a water body
designated on a case-by-case basis by the Division
which is contiguous to a point source and in which the
standards may not apply. The mixing zone is intended
to serve as a zone of initial dilution in the
immediate area of a discharge; however, the ecological
and human health effects of some pollutants may be so
adverse that a mixing zone for such pollutants will
not be allowed.
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State Mixing Zone Narrative
(b) The size and shape of the mixing zone will be
determined by the Division considering the following
factors:
(i) Vhere necessary to protect aquatic life,
there shall be a zone of passage around the
mixing zone which allows sufficient passage
of aquatic life so as not to have a
detrimental effect on their population.
(ii) Biological communities or populations of
imported species shall not be interfered
with to a degree which is damaging to the
ecosystem in adjacent waters; nor shall
there be detrimental effects to other
beneficial uses.
(iii) There shall be no mixing zones for certain
harmful substances such as those identified
pursuant to 307(a) of the Federal Act.
(iv) Mixing zones shall not overlap so as to
cause harmful effects in adjacent waters or
to interfere with zones of passage.
(v) Concentrations of harmful substances in the
mixing zone shall not exceed the 96-hour
LC-50 concentrations for biota significant
to the aquatic community.
(vi) The conditions of the mixing zone shall be
controlled so as to comply with items l(a),
(b) and (f) of the Basic Standards, Section
3.1.11.
(vii) In establishing a mixing zone, potential
groundwater aquifer contamination shall be
considered.
(viii) The Division will also be guided by other
concerns such as the mixing zone discussion
in EPA, Guidelines for State and Areawide
Water Quality Management Program
Development, published November 1976, or
similar documents.
Connecticut The zone of influence of a discharge may be described
as the soil or water area needed to allow the
treatment of effluent by soils or the mixing of
effluent with ground or surface waters. The
establishment of zones of influence created by a
permitted discharge shall not affect the adopted water
usage class. The zone of influence is used by the
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State Mixing Zone Narrative
commissioner in permitting and regulating discharges
to the waters of the State, The Commissioner is
required to determine whether any proposed system to
treat a discharge will protect the waters of the State
from pollution.
A. Surface Waters
1. Wherever zones of influence are allowed, zones of
passage for free swimming and drifting aquatic
organisms shall be provided.
2. No minimum criteria can be given for zones of
passage because of varying hydraulic, physical/
chemical, and biological considerations.
3. As a guideline, zones of influence should be
limited to no more than 25% of the cross-sectional
area or volume of flow, leaving at least 75% free for
a zone of passage.
A. The cross-sectional area or volume of flow assigned
to zones of influence shall be limited to that which
will not adversely affect biological value to a degree
which is damaging to the ecosystem.
B. Groundwaters
1. Zones of influence may be allowed and the
determination of boundaries of a zone shall be
required when natural soil materials are used to treat
a discharge or to allow the dilution of substances by
groundwater to acceptable concentrations for discharge
to the surface waters in an effluent/groundwater mix
which will not violate the established water quality
classification for the surface water.
2. The zone of influence for subsurface sewage
disposal systems which are permitted under the
authority delegated to the Commissioner of Health
Services by Section 25-54i-1.0-5.2 shall be defined as
the area required by the separating distances
established as minimum requirements of the Public
Health Code.
3. The zone of influence for all other discharges to
the groundwater shall be the area in which the
groundwater could be in violation of any pertinent
Federal and State drinking water standards or
otherwise be polluted by the discharge.
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State Mixing Zone Narrative
a
Delaware The following requirements shall apply to mixing zones:
1. Location: Mixing zones shall not be located in
areas of special importance, such as nursery areas for
aquatic life or vaterfovl, approved shellfish areas,
or heavily utilized primary contact recreation areas.
Zones shall not be located ia such a manner as to
disrupt the passage of fishes or ether organisms.
2. Size: Size of the zone shall be minimized. No
interference vith established aquatic communities or
diminution of designated uses shall be allowed.
3. Shape: Allowable shapes shall be simple
configurations, and shall be determined on a
site-specific basis using appropriate scientific
methods. Shore-hugging plumes shall be prohibited in
all water bodies.
4. Outfall Design: Outfalls shall be designed to
provide maximum protection to humans, aquatic life and
wildlife.
5. In Zone Quality: All mixing zones shall be free of
the following:
(a) Materials in concentrations that will cause
acute toxicity to aquatic life, or present
unacceptable risk to human health,
(b) Materials in concentrations that settle to
form objectionable deposits,
(c) Floating debris, oil, scum, foam, and other
matter in concentrations that form nuisances,
(d) Substances in concentrations that produce
objectionable color, odor, taste or
turbidity, and
(e) Substances in concentrations which produce
undesirable aquatic or marine life, result
in a dominance of nuisance species, or
affect species diversity.
Note: The United States Environmental Protection
Agency publications, Water Quality Standards Handbook,
December, 1983, or Technical Support Document for
Water Quality-Based Toxics Control, September, 1985,
or other sources deemed acceptable by the Department,
may be used, in addition to the above general
requirements, as guidelines for determining the
specifics of mixing zones.
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State Mixing Zone Narrative
a
Florida 17-4.244 Mixing Zones: Surface Waters.
(1) Zones of mixing for non-thermal components of
discharges.
(a) The Department may allow the vater quality
adjacent to a point of discharge to be
degraded to the extent that only the minimum
conditions described in Section 17-3.051(1),
Florida Administrative Code, apply vithin a
limited, defined region known as the mixing
zone. Under the circumstances defined
elsevhere in this section, a mixing zone may
be allowed so as to provide an opportunity for
mixing and thus to reduce the costs of
treatment. However, no mixing zone or
combination of mixing zones shall be allowed
to significantly impair any of the designated
uses of the receiving body of water.
(b) A zone of mixing shall be determined based on
consideration of the following:
1. The condition of the receiving body of
water including present and future flow
conditions and present and future sources
of pollutants.
2. The nature, volume and frequency of the
proposed discharge of waste including any
possible synergistic effects with other
pollutants or substances which may be
present in the receiving body of water.
3. The cumulative effect of the proposed
mixing zone and other mixing zones in the
vicinity.
(c) Except for the thermal component of discharges
and nitrogen and phosphorus acting as
nutrients, to which this paragraph is
inapplicable, mixing zones which do not adhere
to all of provisions (l)(d) through (l)(i)
below shall be presumed to constitute a
significant impairment of the designated uses
of surface waters of Classes I, II and III.
However, an applicant for a specified mixing
zone who affirmatively demonstrates after
public notice in the Florida Administrative
Weekly and in a newspaper of general
circulation in the area where the mixing zone
is proposed, and after a public hearing, if
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State Mixing Zone Narrative
one is requested, that a proposed mixing zone
which does not comply with one or more of the
provisions of paragraphs (l)(d) through (l)(i)
vill not produce a significant adverse effect
on the established community of organisms in
the receiving body of water or otherwise
significantly impair any of the designated
uses of the receiving body of water, shall be
exempt from those requirements. The Secretary
shall authorize that mixing zone for which the
applicant makes an affirmative demonstration
by the preponderance of competent substantial
evidence that the applicable requirements of
this section have been met.
(d) A mixing zone shall not include an existing
drinking water supply intake nor include any
other existing water supply intake if such
mixing zone would significantly impair the
purposes for which the supply is utilized.
(e) A mixing zone shall not include a nursery area
of indigenous aquatic life nor include any
area approved by the Department of Natural
Resources for shellfish harvesting.
(f) In canals, rivers, streams, and other similar
water bodies, the maximum length of a zone of
mixing shall be 800 meters unless a shorter
length is necessary to prevent significant
impairment of a designated use. In no case,
shall a mixing zone be larger than is
necessary for the discharge to completely mix
with the receiving water to meet water quality
standards.
(g) In lakes, estuaries, bays, lagoons, bayouts,
sounds, and coastal waters, the area of mixing
zone shall be 125,600 square meters unless a
lesser area is necessary to prevent
significant impairment of a designated use.
In no case shall a mixing zone be larger than
is necessary to meet water quality standards.
(h) In open ocean waters, the area of a mixing
zone shall be 502,655 square meters unless a
lesser area is necessary to prevent
significant impairment of a designated use.
In no case shall a mixing zone be larger than
is necessary to meet water quality standards.
(i) The mixing zones in a given water body shall
not cumulatively exceed the limits described
below:
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State Mixing Zone Narrative
1. In rivers, canals, and other similar water
bodies: 10Z of the total length;
2. In lakes, estuaries, bays, lagoons, bayous
and sounds: 102 of the total area.
(j) Additional standards which apply within mixing
zones in Class I, II and Class III waters are
as follows:
1. The dissolved oxygen within a mixing zone
shall not average less than 4.0 milligrams
per liter in the mixing zone volume; and,
2. The turbidity within the mixing zone shall
not average greater than 41 Nephelometric
Turbidity Units in the mixing zone volume
above natural background.
(k) Mixing zones in Class IV and V waters are
subject only to the provisions of (d) above
and of Section 17-3.051, F.A.C., and shall not
significantly impair the designated uses of
the receiving body of water.
(2) Until such time as a permit is issued, modified,
or renewed, discharges in existence prior to the
effective date of this rule shall continue to meet
such mixing zone restrictions (for each component
or characteristic of a discharge):
(a) As are specified by permit; or,
(b) Which were applied to the discharge in the
Department's permitting process prior to the
effective date of this rule.
(3) Except for discharges covered by (2) above, after
the adoption of this rule there shall be no zone
of mixing for any component of any discharge
unless a Department permit containing a
description of its boundaries has been issued for
that component of the discharge.
(4) (a) Vaters within mixing zones shall not be
degraded below the applicable minimum
standards prescribed for all waters at all
times in Section 17-3.051, F.A.C. In
determining compliance with the provisions of
17-3.051(1), F.A.C., the average concentration
of the wastes in the mixing zone shall be
measured or computed using scientific
techniques approved by the Department;
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State Mixing Zone Narrative
provided that, the maximum concentration of
wastes in the mixing zone shall not exceed the
amount lethal to 50% of the test organisms in
96 hours (96 hr kC50) f°r a species
significant to the indigenous aquatic
community, except as provided in subsection
(b) or (c) below. The dissolved oxygen value
within any mixing zone shall not be less than
1.5 milligrams per liter at any time or place.
(b) The maximum concentration of wastes in the
mixing zone (except for open ocean discharges)
may exceed the 96 hr LCcn only when all of the
following conditions are satisfied.
1. Dilution ratio of the efflulent exceeds
100:1 under critical conditions. That is,
flow in the receiving waters exceeds 100
units for every unit of effluent flow under
critical conditions. Critical conditions
are defined as those under which least
dilution of the effluent is expected, e.g.,
maximum effluent flow and minimum receiving
stream flow.
2. High rate diffusers or other similar means
are used to induce rapid initial mixing of
the effluent with the receiving waters such
that exposure of organisms to lethal
concentrations is minimized.
3. Toxicity must be less than acute (as
defined in Rule 17-3.021(1), F.A.C.) no
more than a distance of 50 times the
discharge length scale in any spatial
direction. The discharge length scale is
defined as the square-root of the
cross-sectional area of any discharge
outlet. In the case of a multiport
diffuser, this requirement must be met for
each port using the appropriate discharge
length scale of that port. This
restriction will ensure a dilution factor
of at least 10 within the distance under
all possible circumstances, including
situations of severe bottom interaction,
surface interaction, or lateral merging.
4. The effluent when diluted to 302 of full
strength, shall not cause more than 50%
mortality in 96 hours (95 hr. LC50) in a
species significant to the inaigenous
aquatic community.
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State Mixing Zone Narrative
5. If the following pollutants are present in
the effluent, their concentrations (in the
efflulent) shall not exceed the values
listed:
Acrylonitrile 65 yg/1
Aldrin 7.5 ng/1
Dieldrin 7.5 ng/1
Benzene 4 mg/1
Benzidine 53 ng/1
Beryllium 6.4 ug/1
Cadmium 100 ug/1
Carbon Tetrachloride 694 ug/1
Chlordane 48 ng/1
Hexachlorobenzene 74 ng/1
Chlorinated ethanes:
1,2-dichloroethane 24.3 mg/1
1,1,2-trichloroethane 4.2 mg/1
1,1,2,2-tetrachloroethane 1 mg/1
Hexachloroethane 874 ug/1
Chloroalkyl Ethers:
bis(chloromethyl) ether 184 ng/1
bis(2-chloroethyl) ether 136 ug/1
Chloroform 1.57 mg/1
Chromium (hexavalent) 0.5 mg/1
DDT 2.4 ug/1
Dichlorobenzidine 2 ug/1
1,1-Dichloroethylene • 185 ug/1
Dinitrotoluene 11 ug/1
Diphenqlhydrazine 56 ug/1
Ethylbenzene 33 mg/1
Fluoranthene 540 ug/1
Halomethanes 1.6 mg/1
Heptachlor 29 ng/1
Hexachlorocyclohexane
a Hexachlorocyclohexane 310 ng/1
3 Hexachlorocyclohexane 547 ng/1
Y Hexachlorocyclohexane 625 ng/1
Lead 0.5 mg/1
Mercury 1.5 ug/1
Nickel 1 mg/1
Nitrosamines 124 ug/1
Polynuclear aromatic hydrocarbons 3 Ug/1
Polychlorinated biphenyls (PCBs) 8 ng/1
Selenium 100 ug/1
Tetrachloroethylene 885 ug/1
Thallium 480 ug/1
Toxaphene 73 ng/1
Trichloroethylene 8 mg/1
Vinyl Chloride 52 mg/1
(c) For open ocean discharges, the effluent when
diluted to 30X full strength, shall not cause
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State Mixing Zone Narrative
more than 50% mortality in 96 hours (96 hr.
L.CCQ) in a species significant to the indigenous
aquatic community. Rapid dilution shall be
ensured by the use of multiport diffusers. The
discharge shall othervise comply with federal
lav.
(5) Except for the minimum conditions of waters as
specified in Section 17-3.051, F.A.C., and the
provisions of Section 17-4.244, F.A.C., no other
water quality criteria apply within a mixing zone.
(6) Mixing zones for dredge and fill permits shall not
be subject to provisions (l)(c) through (l)(j), (2),
(3), (4), or (5) of this section, provided that
applicable water quality standards are met at the
boundary and outside the mixing zone.
(a) The dimensions of dredge and fill mixing zones
shall be proposed by the applicant and approved,
modified or denied by the Department.
(b) Criteria for departmental evaluation of a
proposed mixing zone shall include site-specific
biological and hydrographic considerations.
(c) In no case, however, shall the boundary of a
dredge and fill mixing zone be more than 150
meters downstream in flowing streams or 150
meters in radius in other bodies of water, where
these distances are measured from the
cutterhead, return flow discharge, or other
points of generation of turbidity or other
pollutants.
(7) Where a receiving body of water fails to meet a
water quality standard for pollutants set forth in
department rules, a steam electric generating plant
discharge of pollutants that is existing or licensed
on July 1, 1984, may be granted a mixing zone,
provided that:
(a) The standard would not be met in the water body
in the absence of the discharge; and
(b) The discharge is in compliance with all
applicable technology-based effluent
limitations; and
(c) The discharge does not cause a ireasurable
increase in the degree of noncompliance vith the
standard at the boundary of the mixing zone; and
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State Mixing Zone Narrative
(d) The discharge otherwise complies vith the mixing
zone provisions specified in this section.
(8) Additional relief from mixing zone restrictions
necessary to prevent significant impairment of a
designated use is through:
(a) Reclassification of the water body pursuant to
Section 17-3.081, Florida Administrative Code;
(b) Variance granted for any one of the following
reasons:
1. There is no practicable means known or
available for the adequate control of the
pollution involved.
2. Compliance with the particular requirement or
requirements from which a variance is sought
will necessitate the taking of measures,
which, because of their extent or cost, must
be spread over a considerable period of time.
A variance granted for this reason shall
prescribe a timetable for the taking of
measures required.
3. To relieve or prevent hardship of a kind
other than those provided for in paragraphs
1. or 2. Variances and renewals thereof
granted upon authority of this sub-paragraph
shall each be limited to a period of 24
months except that variances granted pursuant
to the Florida Electrical Power Plant Siting
Act may extend for the life of the permit or
certification.
(c) Modification of the requirements of this section
for specific criteria by the Secretary upon
compliance with the notice and hearing
requirements for mixing zones set forth in
(l)(c) above and upon affirmative demonstration
by an applicant by the preponderance of
competent substantial evidence that:
1. The applicant's discharge from a source
existing on the effective date of this rule
complies with best technology economically
achievable, best management practices, or
other requirements set forth in Chapter 17-6,
F.A.C., and there is no reasonable
relationship between the economic, social,
and environmental costs and the economic,
social and environmental benefits to be
obtained by imposing more stringent discharge
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State Mixing Zone Narrative
limitations necessary to comply with mixing
zone requirements of Subsection 17-4.244(1),
F.A.C., and the provisions relating to
dissolved oxygen in Subsection 17-4.244(4),
F.A.C.
2. No discharger may be issued more than one
permit or permit modification or renewal
which allows a modification pursuant to this
subsection unless the applicant affirmatively
demonstrates that it has undertaken a
continuing program, approved by the
Department, designed to consider water
quality conditions and review or develop any
reasonable means of achieving compliance with
the water quality criteria from which relief
has been granted pursuant to this subsection.
3. With respect to paragraphs 17-4.244(l)(c),
F.A.C., and 17-4.244(7)(c), F.A.C., the
applicant must affirmatively demonstrate the
minimum area of the water body necessary to
achieve compliance with either subsection.
Vithin a minimum area determined by the
Secretary to be necessary to achieve
compliance, the discharger shall be exempt
from the criterion for which a demonstration
has been made.
(d) Vhenever site specific alternative criteria are
established pursuant to Section 17-3.031, or
Subsection 17-3.061(3)(g), Florida
Administrative Code, a mixing zone may be issued
for dissolved oxygen if all provisions of
Section 17-4.244, Florida Administrative Code
are met with the exception of Subparagraph
17-4.244(l)(j)l., or Subsection 17-4.244(4)
Florida Administrative Code.
Specific Authority: 403.061, 403.062, 403.087,
403.504, 403.704, 403.804, 403.805, F.S.
Law Implemented: 403.021, 403.061, 403.087,
403.088, 403.101, 403.121, 403.141, 403.161,
403.182, 403.201, 403.502, 403.702, 403.708,
F.S.
History: Formerly part of 17-3.05, Revised and
Renumbered 3-1-79, Amended 10-2-80, 1-1-83,
2-1-83, 12-19-84, 4-26-87.
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State
Georgia
10
Mixing Zone Narrative
Effluent released to streams or impounded waters shall
be fully and homogeneously dispersed and mixed insofar
as practical vith the main flow or water body by
appropriate methods at the discharge point. Use of a
reasonable and limited mixing zone may be permitted on
receipt of satisfactory evidence that such a zone is
necessary and that it will not create an objectionable
or damaging pollution i.ondition.
Hawaii
11
Zones of mixing for the assimilation of municipal,
agricultural, and industrial discharges which have
received the best degree of treatment or control are
recognized as being necessary. It is the objective of
this limited zone to provide for a current realistic
means of control over such discharges so as to achieve
the highest attainable level of water quality or
otherwise to achieve the minimum environmental impact
considering initial dilution, dispersion, and
reactions from substances which may be considered to
be pollutants.
Establishment, Renewal, and Temination:
1. Application for establishment of the zone of mixing
shall be made concurrently with any discharge permits
whenever applicable and the conditions of the zone of
mixing may be incorporated as conditions of such
discharge permits. Every application for a zone of
mixing shall be made on forms furnished by the
Director of Health and shall be accompanied by a
complete and detailed description of present
conditions, how present conditions do not conform to
standards, and such other information as the Director
of Health may prescribe.
2. Each application for a zone of mixing shall be
reviewed in light of the descriptions, statements,
plans, histories, and other supporting information as
may be submitted upon the request of the Director of
Health, and in light of the effect or probable effect
upon the water quality standards established pursuant
to this Chapter.
3. Whenever an application is approved, the Director
of Health shall establish the zone of mixing taking
into account protected uses of the body of water,
existing natural conditions of the receiving water,
character of the effluent, and the adequacy of the
design of the outfall and diffuser system to achieve
maximum dispersion and assimilation of the treated or
controlled waste with a minimum of undesirable or
noticeable effects on the receiving water.
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State Mixing Zone Narrative
4. Approval of a zone of mixing shall be made only
after a public hearing is held by the Director of
Health in the county where the source is situated in
accordance vith the Hawaii Administrative Procedure
Act and the Rules of Practice and Procedure of the
Department of Health or after the public notification
and comment process duly established for a discharge
permit in the case when the zone of mixing is baing
considered concurrently with the discharge permit.
5. No zone of mixing shall be granted by the Director
of Health unless the application and the supporting
information clearly show that:
(a) The continuation of the function or
operation involved in the discharge by the
granting of the zone of mixing is in the
public interest; and
(b) The discharge occurring or proposed to occur
does not substantially endanger human health
or safety; and
(c) Compliance with the existing water quality
standards from which a zone of mixing is
sought would produce serious hardships
without equal or greater benefits to the
public; and
(d) The discharge occurring or proposed to occur
will not unreasonably interfere with any
actual or probable use of the water areas
for which it is classified, and has received
(or in the case of a proposed discharge,
will receive) the best degree of treatment
or control.
6. Any zone of mixing or renewal thereof shall be
granted within the requirements of this section and
for time periods under conditions consistent with the
reasons therefore and within the following limitations:
(a) If the zone of mixing is granted on the
ground that there is no practicable means
known or available for the adequate
prevention, control, or abatement of the
discharge involved, it shall be only until
the necessary means for prevention, control,
or abatement become practicable and subject
to the taking of any substitute or alternate
measures that the Director of Health may
prescribe. No renewal of a zone of mixing
granted under this subsection shall be
allowed without a thorough review of known
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State Mixing Zone Narrative
and available means of preventing,
controlling, or abating the discharge
involved.
(b) The Director of Health may issue a zone of
mixing for a period not exceeding five years.
(c) Every zone of mixing granted under this
section shall include, but not be limited
to, conditions requiring the grantee to
perform effluent and receiving water
sampling and report the results of each
sampling to the Director of Health, and a
program of research to develop practicable
alternatives to the methods of treatment or
control in use by the grantee may be
required if such research is deemed prudent
by the Director of Health.
7. Any zone of mixing granted pursuant to this section
may be renewed from time to time on terms and
conditions and for periods not exceeding five years
which would be appropriate on initial granting of a
zone . of mixing; provided that the applicant for
renewal had met all of the conditions specified in the
immediately preceding zone of mixing, and provided
further, that the renewal, and the zone of mixing
established in pursuance thereof, shall provide for
discharge not greater in quantity of mass emissions
than that attained pursuant to the terms of the
immediately preceding zone of mixing at its
expiration. No renewal shall be granted except on
application. Therefore, any such application shall be
made at least sixty days prior to the expiration of
the zone of mixing.
8. No zone of mixing granted pursuant to this part
shall be construed to prevent or limit the application
of any emergency provisions and procedures provided by
law.
9. The establishment of any zone of mixing shall be
subject to the concurrence of the U.S. Environmental
Protection Agency.
10. The Director of Health, on his own motion, or upon
the application of any person, shall terminate a zone
of mixing, if after a hearing, he determines that the
water area does not meet the basic criteria applicable
to all water areas, or that the zone of mixing granted
will unreasonably interfere with any actual or
probable use of the water area that the discharge does
not receive (or in the case of a new discharge will
not receive) the best degree of treatment or control.
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State Mixing Zone Narrative
Such termination shall be made only after a hearing
held by the Director of Health on the Island where the
area is situated in accordance vith chapter 91, HRS
and the rules of Practice and Procedure of the
Department of Health. Upon such termination, the
standards of vater quality applicable thereto shall be
those established for the vater as otherwise
classified.
11. Upon expiration of the period stated in the
designation, the zone of mixing shall automatically
terminate and no rights shall become vested in the
designee.
12
Idaho After a biological, chemical, and physical appraisal
of the receiving water and the proposed discharge and
after consultation with the person(s) responsible for
the wastewater discharge, the Department will
determine the applicability of a mixing zone and, if
applicable, its size, configuration, and location. In
defining a mixing zone, the Department will consider
the following principles:
(a) The mixing zone may receive wastewater through a
submerged pipe, conduit or diffuser.
(b) The mixing zone is to be located so it does not
cause unreasonable interference with or ' danger to
existing beneficial uses.
(c) When two (2) or more individual mixing zones are
needed for a single activity, the sum of the areas and
volumes of the several mixing zones is not to exceed
the area and volume which would be allowed for a
single zone.
(d) Multiple mixing zones can be established for a
single discharge, each being specific for one (1) or
more pollutants contained within the discharged
wastewater.
(e) Mixing zones in flowing receiving waters are to
be limited to the following:
i. The cumulative width of adjacent mixing zones when
measured across the receiving water is not to exceed
fifty percent (50%) of the total width of the
receiving water at that point.
ii. The width of a mixing zone is not to exceed
twenty-five percent (25%) of the stream width of three
hundred (300) meters plus the horizontal length of the
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State Mixing Zone Narrative
diffuser as measured perpendicularly to the stream
flow, vhichever is less.
iii. The mixing zone is to be no closer to the ten
(10) year, seven (7) day low-flow shoreline than
fifteen percent (15X) of the stream width.
iv. The mixing zone is not to include more than
twenty-five percent (25Z) of the volume of the stream
flow.
(f) Mixing zones in reservoirs and lakes are to be
limited to the following:
i. The total horizontal area allocated to mixing zones
is not to exceed ten percent (10X) of the surface area
of the lake.
ii. Adjacent mixing zones are to be no closer than the
greatest horizontal dimension of any of the individual
zones.
(g) The water quality within a mixing zone is subject
to General Water Quality Standards contained in Idaho
Department of Health and Welfare Rules and Regulations
Sections 1.2200,3., "Radioactive Materials",
1.2200,04., "Floating and Submerged Matter", and
1.2200,05. "Excess Nutrients", and can be exempt from
the standards contained in Sections 1.2200,01.
"Hazardous Materials" and 1.2200,02. "Deleterious
Material", as well as from Section 1.2250, as
determined appropriate, provided that the receiving
water's existing quality is not in violation of that
standard or provision.
(h) Concentrations of hazardous materials within the
mixing zone must not exceed the ninety-six (96) hour
LC50 for biota significant to the receiving water's
aquatic community.
Illinois (a) In the application of this Chapter, whenever a
water quality standard is more restrictive than its
corresponding effluent standard then an opportunity
shall be allowed for the mixture of an effluent with
its receiving waters. Water quality standards must be
met at every point outside of the mixing zone. The
size of the mixing zone cannot be uniformly
prescribed. The governing principle is that the
proportion of any body of water or segment thereof
within mixing zones must be quite small if the water
quality standards are to have any meaning. This
principle shall be applied on a case-by-case basis to
ensure that neither any individual source nor the
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State Mixing Zone Narrative
aggregate of sources shall cause excessive zones to
exceed the standards. The vater quality standards must
be met in the bulk of the body of vater, and no body
of water may be used totally as a mixing zone for a
single outfall or combination of outfalls. Moreover,
except as othervise provided in this Chapter, no
single mixing zone shall exceed the area of a circle
with a radius of 183 meters (600 feet). Single sources
of effluents which have more than one outfall shall be
limited to a total mixing area no larger than that
allowable if a single outfall were used.
b) In determining the size of the mixing zone for any
discharge, the following must be considered:
1. The character of the body of water;
2. The present and anticipated future use of
the body of water;
3. The present and anticipated water quality of
the body of water;
A. The effect of the discharge on the present
and anticipated future water quality;
5. The dilution ratio; and
6. The nature of the contaminant.
(c) In addition to the above, the mixing zone shall
be so designed as to assure a reasonable zone of
passage for aquatic life in which the water quality
standards are met. The mixing zone shall not
intersect any area of any such waters in such a manner
that the maintenance of aquatic life in the body of
water as a whole would be adversely affected, nor
shall any mixing zone contain more than 25% of the
cross-sectional area or volume of flow of a stream
except for those streams where the dilution ratio is
less than 3:1.
Temperature standards contain additional requirements
for heated discharges.
Indiana • (a) All vater quality standards in this Regulation,
except those provided in subsection 6(a) belov, are to
be applied at a point outside of the mixing zone to
allow for a reasonable admixture of waste effluents
vith the receiving waters.
(b) Due to varying physical, chemical, and biological
conditions, no universal mixing zone may be
prescribed. The Board shall determine the mixing zone
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State Mixing Zone Narrative
upon application by the discharger. The applicability
of the guideline set forth in Section 4(c) vill be on
a case-by-case basis and any application to the Board
should contain the following information.
(1) The dilution ration;
(2) The physical, chemical, and biological
characteristics of the receiving body of
water;
(3) The physical, chemical, and biological
characteristics of the waste effluent;
(4) The present and anticipated uses of the
receiving body of water;
(5) The measured or anticipated effect of the
discharge on the quality of the receiving
body of water;
(6) The existence of an impact upon any spawning
or nursery areas of any indigenous aquatic
species;
(7) Any obstruction of migratory routes of any
indigenous aquatic species; and
(8) The synergistic effects of overlapping
mixing zones of the aggregate effects of
adjacent mixing zones.
(c) Where possible, the general guideline is to be
that the mixing zone should be limited to no more than
1/4 (25 percent) of the cross-sectional area and/or
volume of flow of the stream, leaving at least 3/4 (75
percent) free as a zone of passage for aquatic biota,
nor should it extend over 1/2 (50 percent) of the
width of the stream.
lova Mixing zone in the receiving water. The area of
diffusion of an effluent in the receiving water is a
mixing zone and the water quality standards shall be
applied beyond the mixing zone.
The mixing zone shall be a specified linear distance,
volume, or area which is determined on a case-by-case
basis using the following criteria:
(a) The mixing zone shall be as small as practicable
and shall not be of such size or shape as to cause or
contribute to the impairment of water uses.
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State Mixing Zone Narrative
(b) The mixing zone shall contain not more than 25
percent of the cross sectional area or volume of flow
in the receiving body of water;
(c) The mixing zone shall be designed to allow an
adequate passageway at all times for the movement or
drift of aquatic life;
(d) Where there are two or more mixing zones in close
proximity, they shall be so defined that a continuous
passageway for aquatic life is available.
(e) The mixing zone shall not intersect any area of
any waters in such a manner that the maintenance of
aquatic life in the body of water as a whole would be
adversely affected.
In determining the size and location of the mixing
zone for any discharge on a case-by-case basis, the
following shall be considered:
(f) The size of the receiving water, the volume of
discharge, the stream bank configuration, the mixing
velocities, and other hydrologic or physiographic
characteristics;
(g) The present and anticipated future use of the body
of water;
(h) The present and anticipated future water quality
of the body of water;
(i) The ratio of the volume of waste being discharged
to the seven-day, ten-year flow of the receiving
stream; and
(j) The mixing zone shall be free from unsightly
floating materials and wastewater constituents in
concentrations which are toxic or harmful to human,
animal or plant life, which will settle to form sludge
deposits, or which will produce aesthetically
objectionable color or odor.
Kansas 1. The water quality criteria listed herein shall
apply beyond the mixing zone for each individual
discharge, except that concentrations within the
mixing zone area shall be maintained below acute
toxicity levels for any parameter or combination of
parameters. The total area and/or volume of a
receiving stream assigned to mixing zones shall be
limited to that which will:
a) Not interfere with biological communities or
populations of important species to a degree
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State Mixing Zone Narrative
vhich is damaging to the ecosystem; and
b) Not disproportionately diminish other
beneficial uses.
2. Zones of passage shall be provided vherever mixing
zones are allowed. Such zones shall be continuous
vater routes of the volume, area, and quality
necessary to allow passage of free swimming and
drifting organisms with no harmful effects on their
populations.
3. In streams where the ratio of stream flow to
discharge is greater than 3:1 (flowrdischarge), mixing
zones shall be limited to no more than 1/4 of the
cross-sectional area, or volume of the stream, or
both, leaving at least 3/4 free as a zone of passage.
4. In streams in which the ratio of stream flow to
discharge is equal to or less than 3:1 (flow:
discharge), mixing zones shall be established on a
case-by-case basis. More stringent treatment
technology may be required, when necessary, to protect
the designated uses of the surface water segment and
to otherwise meet the requirements of these
regulations.
Kentucky Mixing zone means a domain of a water body continguous
to a treated or untreated wastewater discharge of
quality characteristics different from those of the
receiving water. The discharge is in transit and
progressively diluted from the source to the receiving
system. The mixing zone is the domain where wastewater
and receiving water mix.
The following guidelines are applicable in determining
all mixing zones:
(1) The cabinet shall, on a case-by-case basis,
specify definable geometric limits for mixing zones.
Applicable limits shall include but may not be limited
to the linear distances from the point of discharge,
surface area involvement, volume of receiving water,
and taking into account other nearby mixing zones.
(2) Concentrations of toxic substances which exceed
the ninety-six (96) hour LC50 or other appropriate
LC50 tests for representative indigenous aquatic
organisms are not allowed at any point within the
mixing zone. A zone of initial dilution may be
assigned on a case-by-case basis at the discretion of
the cabinet. Concentrations of toxic substances which
exceed one-third (1/3) the ninety-six (96) hour LC50
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State Mixing Zone Narrative
or other appropriate LC50 tests for representative
indigenous aquatic organisms are to be met at the edge
of the zone of initial dilution. Chronic criteria for
the protection of aquatic life are to be met at the
edge of the allowable mixing zone.
(3) The location of a mixing zone shall not interfere
with spawning areas, nursery areas, fish migration
routes, public water supply intakes, bathing areas,
nor preclude the free passage of fish or other aquatic
life.
(4) Whenever possible the mixing zone shall not exceed
one-third (1/3) of the width or cross-sectional area
of the receiving stream and in no case shall exceed
one-half (1/2) of this volume.
(5) In lakes and other surface impoundments, the
volume of a mixing zone shall not affect in excess of
ten (10) percent of the volume of that portion of the
receiving waters available for mixing.
(6) In all cases, a mixing zone must be limited to an
area or volume which will not adversely alter the
legitimate uses of the receiving water; nor shall a
mixing zone be so large as to adversely affect an
established community of aquatic organisms.
(7) In the case of thermal discharges, a successful
demonstration conducted under Section 316(a) of the
Clean Water Act shall constitute compliance with all
provisions of this section.
(8) Criteria listed in Section 4 of 401 KAR 5:031 do
not apply in the mixing zone.
18
Louisiana Mixing Zones - Mixing zones are those portions of
waterbodies where effluent waters are dispersed into
receiving waters. They are exempted from criteria for
those substances that are rendered non-toxic by
dilution, dissipation or transformation. Mixing zones
must, however, be defined and have identifiable
limits, and the waters outside of mixing zones must
meet the Standards for that particular body of water.
Mixing must be accomplished as quickly as possible to
insure that the waste is mixed with the allocated
dilution water in the smallest practicable area.
A mixing zone shall not significantly affect a nursery
area for aquatic life or habitat for waterfowl nor any
area approved by the state for shellfish harvesting.
A mixing zone shall not include an existing public
water supply intake nor include any other existing
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State Mixing Zone Narrative
water supply intake if such mixing zone would
significantly impair the purposes for which the supply
is utilized.
Mixing zones must be free of the following:
1. Floating debris, oil, scum, and other material in
concentrations that constitute a. nuisance
2. Substances in concentrations which produce
undesirable or nuisance aquatic life
3. Materials in concentrations that will cause acute
toxicity to aquatic life. Acute toxicity refers to an
aquatic life lethality, such as fish kills, caused by
the passage through a mixing zone of migrating fish
moving up or downstream, or by less mobile forms
drifting through a mixing zone.
The state shall on a case-by-case basis specify
definable geometric limits for mixing zones.
Applicable limits shall include but may not be limited
to the linear distances from point source discharges,
surface area involvement, volume of receiving water
and taking into account other nearby mixing zones.
As a guideline, the mixing zone in canals, rivers,
streams, and other flowing waterbodies shall be no
more than one-third the width of the receiving stream
at the point of discharge. A mixing zone shall not
overlap another mixing zone in such a manner, or be so
large, as to impair any designated water use in the
receiving stream when considered as a whole.
In lakes, estuaries, bays, lagoons, and sounds, the
area of mixing shall not be so large as to cause
impairment of a designated use and will be defined by
the Office on a case-by-case basis.
Zones of Passage - In rivers, streams, reservoirs,
lakes, estuaries and coastal waters, zones of passage
are continuous water routes of the volume, area and
quality necessary to allow passage of free-swimming
and drifting organisms with no significant effects
produced on their populations. These zones must be
provided wherever mixing zones are allowed.
Because of varying local physical and chemical
conditions and biological phenomena, no single value
can be given on the percentage of stream vidth
necessary to allow passage of critical free-swimming
and drifting organisms so that negligible or no
effects are produced on their populations. However,
except when otherwise specified in a valid wastewater
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State Mixing Zone Narrative
discharge permit, the mixing zone will be limited to
no more than one-third of the width of the receiving
stream leaving at least tvo-thirds free as a zone of
passage.
Exceptions - The Standards shall not apply to:
1. Effluents
2. A valid state vastevater discharge permit and/or a
National Pollution Discharge Elimination System Permit.
19
Maine Not specified
20
Maryland Mixing Zone Policy:
1. Effluents may be mixed vith surface waters in the
mixing zone.
2. Effluents may not be treated in the mixing zone.
3. Surface waters outside the mixing zones shall meet
the water quality standards for that particular body
of water.
A. The Department may designate mixing zones subject
to the following requirements:
(a) There shall be no interference with
biological communities or populations of
indigenous species to a degree which is
damaging to the aquatic life or ecosystem;
(b) There shall be no diminishing of other
legitimate beneficial uses;
(c) Mixing zones may not form barriers to the
migratory routes of aquatic life;
(d) Mixing zones shall be designated and located
to protect surface waters and shallow water
shoreline areas.
(e) The general water quality criteria set out
in §C (General Water Quality Criteria) of
this regulation apply within the mixing
zones.
5. A mixing zone is not permitted for toxic materials
identified in §D(2) (Specific Water Quality Criteria)
of this regulation.
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State
Mixing Zone Narrative
6. Except for thermal mixing
regulation .13, mixing zones
following maximum limits.
zones established by
may not exceed the
(a) In freshwater streams and rivers, a mixing
zone width may not exceed one-third of the
width of the surface water body.
(b) In lakes, the combined area of all mixing
zones may not exceed 10 percent of the lake
surface area.
(c) In estuarine areas, the maximum
cross-sectional area of the mixing zone may
not exceed 10 percent of the cross-sectional
area of the surface water body.
Massachusetts
21
Mixing Zones - In applying these standards, the
Division may recognize, where appropriate, a limited
mixing zone or zone of initial dilution on a
case-by-case basis. The location, size and shape
of these zones shall provide for the maximum
protection of aquatic resources. At a minimum, mixing
zones must
(a) Meet the criteria for aesthetics;
(b) Be limited to an area or volume that will minimize
interference with the designated uses or established
community of aquatic life in the segment;
(c) Allow an appropriate zone of passage for migrating
fish and other organisms; and
(d) Not result in substances accumulating in
sediments, aquatic life or food chains to exceed known
or predicted safe exposure levels for the health of
humans or aquatic life.
Michigan
22
R 323.1082. Mixing Zones Rule 82.
1. A mixing zone to achieve a mixture of a point
source discharge with the receiving waters shall be
considered a region in which the response of organisms
to water quality characteristics is time dependent.
Exposure in mixing zones shall not cause an
irreversible response which results in deleterious
effects to populations of important aquatic life and
wildlife. As a minimum restriction, the final acute
value for aquatic life shall not be exceeded in the
mixing zone at any point inhabitable by these
organisms, unless it can be demonstrated to the
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State Mixing Zone Narrative
commission that a higher concentration is acceptable.
The mixing zone shall not prevent the passage of fish
or fish food organisms in a manner which would result
in adverse impacts on their immediate or future
populations. Watercourses or portions thereof which,
without 1 or more point source discharge, would have
flow except during periods of surface runoff may be
considered as a mixing zone for a point source
discharge. The area of mixing zones should be
minimized. To this end, devices for rapid mixing,
dilution, and dispersion are encouraged where
practicable.
2. For toxic substances, not more than 252 of the
receiving water design flow, as stated in R 323.1090,
shall be utilized when determining effluent
limitations for surface water discharges, unless it
can be demonstrated to the commission that the use of
a larger volume is acceptable. The commission shall
not base a decision to grant more than 252 of the
receiving water design flow for purposes of developing
effluent limitations for discharges of toxic
substances solely on the use of rapid mixing,
dilution, or dispersion devices. However, where such
a device is or may be employed, the commission may
authorize the use of a design flow greater than 25% if
the effluent limitations which correspond to such a
design flow are shown, based upon a site specific
demonstration, to be consistent with Act No. 245 of
the Public Acts of 1929, as amended, being §323.1 et
seq. of the Michigan Compiled Laws, and other
applicable law.
3. For substances not included in subrule (1) of this
rule, the design flow, as stated in R323.1090, shall
be utilized when determining effluent limitations for
surface water discharges if the provisions in subrule
(1) of this rule are met, unless the commission
determines that a more restrictive volume is necessary.
4. For all substances, defined mixing zone boundaries
may be established and shall be determined on a
case-by-case basis.
5. Mixing zones in the Great Lakes, their connecting
waters, and inland lakes shall be determined on a
case-by-case basis.
23
Minnesota Means for expediting mixing and dispersion of sewage,
industrial waste, or other waste effluents in the
receiving, interstate waters are to be provided so far
as practicable when deemed necessary by the Agency to
maintain the quality of the receiving interstate
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State Mixing Zone Narrative
waters in accordance with applicable standards. Mixing
zones can be established by the Agency on an
individual basis, vith primary consideration being
given to the following guidelines:
(a) Mixing zones in rivers shall permit an
acceptable passageway for the movement of
fish;
(b) The total mixing zone or zones at any
transect of the stream should contain no
more than 252 of the cross-sectional area
and/or volume of flow of the stream, and
should not extend over more than 50% of the
width;
(c) Mixing zone characteristics shall not be
lethal to aquatic organisms;
(d) For contaminants other than heat, the 96
hour median tolerance limit for indigenous
fish and fish food organisms should not be
exceeded at any point in the mixing zone;
(e) Mixing zones should be as small as possible,
and not intersect spawning or nursery area,
migratory routes, water intakes, nor mouths
of rivers; and
(f) Overlapping of mixing zones should be
minimized and measures taken to prevent
adverse synergistic effects. This provision
shall also apply in cases where a Class 7
water is tributary to a Class 2 water.
94
Mississippi It is recognized that limited areas of mixing are
sometimes unavoidable; however, mixing zones shall not
be used for, or considered as a substitute for waste
treatment. Mixing zones constitute an area whereby
physical mixing of a wastewater effluent with a
receiving water body occurs. Applications of mixing
zones shall be made on a case-by-case basis and shall
only occur in cases involving large surface water
bodies in which a long distance or large area is
required for the wastewater to completely mix with the
receiving water body.
The location of a mixing zone shall not significantly
alter the designated uses of the receiving water
outside its established boundary. Adequate zones of
passage for the migration and free movement of fish
and other aquatic biota shall be maintained. No
conditions shall be allowed to exist within the mixing
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State
Mixing Zone Narrative
zone that would result in an endangerment to public
health, nuisances, or fish mortality.
Missouri
25
1. The mixing zones shall be exempted from the
for those substances that are
by dilution, dissipation, or rapid
Acutely toxic concentrations of
allowed in the mixing zone. The
not overlap another mixing zone in
the maintenance of aquatic life in
as a whole would be adversely
specific criteria
rendered non-toxic
transformation.
substances are not
mixing zone shall
such a manner that
the body of water
affected.
2. In determining the size and location of the mixing
zone for any discharge, the following characteristics
must be considered:
i. The size of the river, the volume of
discharge, the stream bank configuration,
the mixing velocities, and other hydrologic
or physiographic characteristics;
ii. The present and anticipated future uses of
the water, including type of aquatic life
supported; and
iii. The dilution ratio, that is, the ratio of
the seven (7)-day once-in-ten (lO)-year low
flow of the receiving stream to the average
dry weather flow of the discharge.
C. Zones of passage must be provided wherever mixing
zones are allowed. As a guideline, at least three
quarters of the cross-sectional area or volume of flow
of a stream should be left free as a zone of passage.
Montana
26
Discharges to surface waters may be entitled a mixing
zone which will have a minimum impact on surface water
quality, as determined by the department.
Nebraska
27
The Water Quality Standards shall apply at and beyond
the mixing zone boundaries. The mixing zone exception
does not apply to fecal coliform criteria in waters
designated a primary contact recreational use. The
boundary limits of the mixing zone shall be a
specified linear distance, volume, or area, and should
meet the conditions listed belov unless the physical
characteristics of the receiving waters require
special considerations. In the latter case the
Department will establish mixing zones applicable to
the physical characteristic of the receiving waters in
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State
Mixing Zone Narrative
such a manner that will not affect the assigned
beneficial uses.
(a) The mixing zone should be kept as small as
possible and shall not be of a size or shape that
would impair or contribute to the impairment of water
use.
(b) The mixing zone shall allow for a continuous zone
of passage for aquatic life.
(c) The mixing zone shall not overlap other mixing
zones if beneficial uses are adversely affected.
Nevada
28
Not specified
Nev Hampshire
29
The commission (New Hampshire Water Supply and
Pollution Control Commission) may consider mixing
zones, except as otherwise provided in these rules or
by statute; and where mixing zones are allowed, they
shall conform to the latest requirements of the
Environmental Protection Agency or to the requirements
of the Commission which shall be no less rigorous than
existing federal requirements.
Nev Jersey
30
Water quality within a mixing zone may be allowed to
fall below applicable water quality criteria provided
the existing and designated uses outside the mixing
zone are not adversely impacted.
Mixing zone requirements will be determined by the
Department (New Jersey Department of Environmental
Protection) on a case-by-case basis taking into
special consideration the extent and nature of the
receiving waters so as to meet the intent and purpose
of the criteria and standards.
The total area and volume of a watervay or waterbody
assigned to mixing zones shall be limited to that
which will not interfere with biological communities
or populations of important species to a degree which
is damaging to the ecosystem or which diminishes other
beneficial uses disproportionately. Furthermore,
significant acute mortality of aquatic biota shall not
occur within the mixing zone.
Zones of passage shall be provided for the passage of
free-swimming and drifting organisms wherever mixing
zones are allowed.
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State Mixing Zone Narrative
Temperature changes in designated heat dissipation
areas shall not cause mortality of the aquatic biota
nor create conditions which allow the introduction or
maintenance of populations of undesirable organisms at
nuisance levels.
Adjacent heat dissipation areas: Vhere waste
discharges would result in heat dissipation areas in
such close proximity to each other as to impair
protected uses, additional limitations shall be
prescribed to avoid such impairment.
No heat dissipation areas shall be permitted in waters
classified as FV2-TP or within 1500 feet of the
shoreline in SC waters.
31
New Mexico Mixing Zones and Zones of Passage - In any waters
receiving a waste discharge, a continuous zone must be
maintained in the stream or reservoir where the water
is of adequate quality to allow the migration of all
desirable aquatic life presently common in New Mexico
waters with no significant effect on their
populations. Wastewater mixing zones, in which the
standards may be exceeded, shall generally be less
than 1/4 of the cross-sectional area of the stream or
reservoir, allowing at least 3/4 of the stream or
reservoir as a zone of passage.
32
Nev York Collection of Samples - In making any tests of
analytical determinations to determine compliance or
non-compliance of sewage, industrial wastes or other
waste discharges with established standards, samples
shall be collected in such manner and at such
locations as are approved by the commissioner. In
approving such locations, the commissioner shall be
guided by the fact that:
(a) There must be prompt mixing of the discharge with
the receiving waters;
(b) That the mixing will not interfere with
biological communities to a degree which is damaging
to the ecosystems; and
(c) That the mixing will not diminish other
beneficial uses disproportionately.
Mixing Zone Criteria - The following criteria shall
apply to all waters of the State receiving thermal
discharges, except as provided in section 704.6
(Applicability of Criteria) of this Part.
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State
Mixing Zone Narrative
(a) The department shall specify definable, numerical
limits for all mixing zones (e.g. linear distances
from the point of discharge, surface area involvement,
or volume of receiving water entrained in the thermal
plume).
(b) Conditions in the mixing zone shall not be lethal
in contravention of water quality standards to aquatic
biota which may enter the zone.
(c) The location of mixing zones for thermal
discharges shall not interfere with spawning areas,
nursery areas and fish migration routes.
Criteria Governing Thermal Discharges: General Criteria
(a) The following criteria shall apply to all waters
of the State receiving thermal discharges, except as
provided in section 704.6 (Applicability of Criteria):
1. The natural seasonal cycle shall be retained.
2. Annual spring and fall temperature changes
shall be gradual.
3. Large day-to-day temperature fluctuations
due to heat of artificial origin shall be
avoided.
4. Development or growth of nuisance organisms
shall not occur in contravention of water
quality standards.
5. Discharges which would lower receiving water
temperature shall not cause a violation of
water quality standards and section 704.3
(Mixing Zone Criteria).
6. For the protection of the aquatic biota from
severe temperature changes, routine shutdown
of an entire thermal discharge at any site
shall not be scheduled during the period
from December through March.
North Carolina
33
A mixing zone may be established- in the area of a
discharge in order to provide reasonable opportunity
for the mixture of the wastewater with the receiving
waters. The limits of such mixing zones will be
defined by the division on a case-by-case basis after
consideration of the magnitude and character of the
waste discharge and the size and character of the
receiving waters. Such zones shall not:
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State Mixing Zone Narrative
(1) Prevent free passage of fish around or cause
fish mortality vithin the mixing zone,
(2) Result in offensive conditions,
(3) Produce undesirable aquatic life or result
in a dominance of nuisance species outside
of the assigned mixing zone.
(4) 'Endanger the public health or welfare.
In addition, a mixing zone shall not be assigned for
fecal coliform organisms in waters classified "A-II",
"B", "SB", or "SA." For the discharge of heated
wastewater, compliance with federal rules and
regulations pursuant to Section 316(a) of the Federal
Water Pollution Control Act, as amended, shall
constitute compliance with this Subsection (b).
34
North Dakota The size and configurations of a mixing zone cannot be
uniformly prescribed for all streams due to the
particular characteristics of each stream. However
the following considerations are taken into account
when mixing zones are determined:
(a) The Water Quality Standards must be met at every
point outside the mixing zone. The department (North
Dakota State Department of Health) may require a means
of expediting mixing and dispersion of wastes, if
found necessary.
(b) The total mixing zone (or zones) at any
cross-sectional area of the stream should not be
larger than 25 percent of the cross-sectional area or
volume of flow and shall not extend more than 50
percent of the width. Mixing zones shall provide an
acceptable passageway for movement of fish and other
aquatic organisms.
(c) The 96-hour LC-50 for indigenous and/or resident
fish and fish food organisms shall not be exceeded at
any point in the mixing zone.
(d) Mixing zones shall be as small as possible and
shall not intersect spawning or nursery areas,
migratory routes, or municipal water intakes.
Overlapping of mixing zones should be avoided or
minimized to prevent adverse synergistic effects.
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Mixing Zone Narrative
(A) Non-Thermal
1. Vhere necessary to attain or maintain the use
designated for surface water by these water quality
standards, the director may establish, as a term of a
discharge permit or a permit to install issued
pursuant to Chapter 3745-31 of the Administrative
Code, a mixing zone applicable to the non-thermal
constituents of the point source discharge authorized
by such permit. No mixing zone established by the
director will:
(a) Interdict the migratory routes or interfere
with natural movements, survival,
reproduction, growth, or increase the
vulnerability to predation of any
representative aquatic species;
(b) Include spawning or nursery areas of any
representative aquatic species;
(c) Include a public water supply intake;
(d) Include any bathing area where bath houses
and/or lifeguards are provided;
(e) Constitute more than one-half of the width
of the receiving watercourse nor constitute
more than one-third of the area of any
cross-section of the receiving watercourse;
(f) Constitute more than one-fifth of the area
of any cross-section of the mouth of a
receiving watercourse (the mouth
constituting that area of the stream from
the confluence upstream for a distance five
times the width of the stream at the
confluence);
(g) Extend downstream at any time a distance
more than five times the width of the
receiving watercourse at the point discharge;
2. The Director may waive the requirements of Sections
(A)(l)(e), (A)(l)(f) and (A)(l)(g) of this rule
whenever a discharger provides:
(a) Information defining the actual boundaries
(where the Water Quality Standards are met)
of the mixing zone in question; and
(b) Information and data proving no violation of
Sections (A)(l)(a), (A)(l)(b), (A)(l)(c),
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State Mixing Zone Narrative
and (A)(l)(d) of this rule by the mixing
zone in question.
3. Vhen establishing a mixing zone, the director shall
require that the zone which is physically inhabitable
by aquatic life not exceed at any time the forty-eight
to ninety-six hour median tolerance limit (TLm) or
LCcn for any representative aquatic species, as
determined from applicable scientific literature or as
determined by static bioassays for persistent
toxicants and dynamic bioassays for non-persistent
toxicants in accordance vith methods described in
"Standard Methods for the Examination of Water and
Wastewater," fifteenth edition, 1981, published by the
American Public Health Association, American Water
Works Association, and the Water Pollution Control
Federation or "Manual of Ohio EPA Surveillance Methods
and Quality Assurance Practices," June, 1983,
available from the Ohio Environmental Protection
Agency offices in Columbus, Bowling Green, Logan,
Dayton, and Twinsburg.
4. For lakes and reservoirs, except Lake Erie defined
as state resource waters by rule 3745-1-05 of the
(Ohio) Administrative Code, no mixing zone shall be
permitted.
(B) Thermal
1. The director may establish as a terra of a discharge
permit or a permit to install issued pursuant to
Chapter 3745-31 of the Administrative Code, a mixing
zone applicable to the thermal component of the point
source discharge authorized by such permit. A thermal
mixing zone to permit dilution and cooling of a waste
heat discharge shall be considered a region in which
organism response to temperature is time-dependent.
Exposure to temperatures in a thermal mixing zone
shall not cause an irreversible response which results
in deleterious effects to the wildlife and aquatic
life representative of the receiving waters. The
daily average temperature in a thermal mixing zone at
a point nearest to the discharge that is accessible to
the resident aquatic organisms shall not exceed the
temperature in Table 1 at the corresponding ambient
temperature. At ambient temperatures of fifty-nine
degrees Fahrenheit (fifteen degrees Celsius) and
above, the daily average temperature in a thermal
mixing zone will be determined on a case-by-case basis.
2. Thermal mixing zone size limitations shall be
established by the director pursuant to paragraph
(B)(l) of this rule on a case-by-case basis for all
point source discharges subject to permit. The
analytical methods for determining mixing zones are
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State
Mixing Zone Narrative
those set forth in paragraph (C) of rule 3745-1-03 of
the Administrative Code.
3. Except as paragraphs (B)(l) and (B)(2) of this rule
establish different limitations, no thermal mixing
zone shall:
(a) Interdict the migratory routes or interfere
with natural movements, survival,
reproduction, growth, or increase the
vulnerability to predation of any
representative aquatic species;
(b) Interfere with or prevent the recovery of an
aquatic community or species population that
could reasonably be expected as previously
limiting water quality conditions improve,
(c) Include a public water supply intake, or;
(d) Include any bathing area where bathhouses
and/or lifeguards are provided.
4. For all watercourses classified as coldwater
habitat and exceptional warmwater habitat in rules
3745-1-08 to 3745-1-32 of the Administrative Code,
thermal mixing zones will not be permitted.
5. For lakes and reservoirs, (except Lake Erie),
classified as state resource waters in rule 3745-1-05
of the Administrative Code, no thermal mixing zone
shall be permitted.
6. Discharges of closed-cycle cooling blowdown with a
flow of less than five percent of the seven-day
once-in-ten-year low-flow of the receiving water body
will be exempt from paragraphs (B)(l) to (B)(3) of
this rule.
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State
Mixing Zone Narrative
Table 1: Daily average temperatures of thermal
mixing zones at corresponding ambient temperatures
as required in paragraph (B)(l) of this rule. Shown
as degrees Fahrenheit and (Celsius).
Ambient Daily Average Ambient
°F(°C) Temp. °F(°C) °F(°C)
32(0)
33(0.6)
34(1.1)
35(1.7)
36(2.2)
37(2.8)
38(3.3)
39(3.9)
40(4.4)
41(5.0)
42(5.6)
43(6.1)
44(6.7)
45(7.2)
46(7.8)
47(8.3)
Daily Average
Temp. QF(0C)
50(10.0)
50(10.0)
50(10.
51(10.
52(11,
54(12,
55(12.
57(13.
58(14.
60(15.
62(16.
63(17,
65(18.
66(18.
68(20.0)
70(21.1)
.0)
.6)
.1)
.2)
•8)
.9)
.4)
,6)
.7)
.2)
.3)
.9)
48(8.9)
49(9.4)
50(10.0)
51(10.6)
52(11.1)
53(11.7)
54(12.2)
55(12.8)
56(13.3)
57(13.9)
58(14.4)
59(15)
71(21.7)
73(22.8)
75(23.9)
76(24.4)
78(25.6)
79(26.1)
81(27.2)
83(28.3)
85(29.4)
86(30.0)
88(31.1)
and above
- daily
average limit vill be
determined on a case-by
case basis pursuant to
Rule 3745-l-06(B)(l) and
(2).
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State
Mixing Zone Narrative
Table 12d. Daily average temperatures of thermal
mixing zones at corresponding ambient temperatures.
Shown as degrees Fahrenheit and (Celsius).
Ambient
Daily Average
Temp. °F(°C)
Ambient
Ohio River
Daily Average
Temp. QF(°C)
32 (0)
33 (0.6)
3* (1.1)
35 (1.7)
36 (2.2)
37 (2.8)
38 (3.3)
39 (3.9)
40 (4.4)
41 (5.0)
42 (5.6)
43 (6.1)
44 (6.7)
45 (72.)
52
52.5
53.5
54.4
55
56
57
58
59
59.5
60
61
62
63
(11.1)
(11.4)
(11.9)
(12.4)
(12.8)
(13.3)
(13.9)
(14.4)
(15)
(15.3)
(15.6)
(16.1)
(16.7)
(17.2)
46 (7.8)
47 (8.3)
48 (8.9)
49 (9.4)
50 (10.0)
51 (10.6)
52 (11.1)
53 (11.7)
54 (12.2)
55 (12.8)
56 (13.3)
57 (13.9)
(14.4)
(15)
58
59
average
determined
65 (18.3)
66 (18.9)
68 (20.0)
70 (21.1)
71 (21.7)
73 (22.8)
75 (23.9)
77 (25.0)
78 (25.6)
80 (26.7)
82 (27.8)
84 (28.9)
86 (30.0)
and above-daily
limit, will be
on a
case-by-case basis.
(D) Mixing zone designation:
(1) A "mixing zone" shall be deemed to exist for
each discharge. When required, the specific
numerical limits for any mixing zone shall be
determined on a case-by-case basis, and shall
include considerations for existing uses, linear
distance (i.e., length and vidth) from the point of
discharge, surface area involved, and volume of
receiving vater within the defined zone.
(2) Conditions within the mixing zone shall not be
injurious to human health, in the event of a
temporary exposure.
(3) Conditions within the mixing zone shall not be
injurious to human health, in the event of a
temporary exposure.
(4) The mixing zone shall be free from substances
attributable to sewage, industrial wastes, toxic
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State Mixing Zone Narrative
wastes, other wastes, cooling water, or residues
from potable water treatment plants in quantities
which:
(a) Settle to form sludge deposits;
(b) Float as debris, scum, or oil;
(c) Contaminate natural sediments so as to cause or
contribute to a violation of:
(i) Appropriate stream criteria and parameter
levels outside the mixing zone; or
(ii) Any condition of the designated uses of the
water.
(d) Impart a disagreeable flavor or odor to flesh
of fish or other aquatic life, wildlife or livestock
which are consumed by man and which acquire such a
flavor because of passage through or ingestion of
the waters from the mixing zone.
(5) The mixing zone shall be located so as not to
interfere significantly with migratory movements and
passage of fish, other aquatic life and wildlife.
No waste discharge related to the mixing zone shall,
outside the limits of the mixing zone, interfere
with potable water supply intakes, bathing areas,
reproduction of fish, other aquatic life and
wildlife; or adversely affect fish or aquatic life
normally inhabiting waters prior to addition of
waste discharged; or result in any other violations
of appropriate stream criteria and parameter levels
relating to the designated use at or above critical
river flow as shown below.
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State
Mixing Zone Narrative
Critical Plow Values
River Reach
Critical Flow
Fro«
cfs*
Pittsburgh
Montgomery
Willow Island
Gallipolis
Greenup
Meldahl
Hcalpine
Uniontown
Smithland
To
Montgomery dam (mp 32.4)
Willow Island dam (mp 161.8)
Gallipolis dam (mp 279.2)
Greenup dam (mp 341.0)
Meldahl dam (mp 436.2)
Mcalpine dam (mp 605.8)
Uniontown dam (mp 846.0)
Smithland dam (mp 918.5)
Cairo point (mp 981.0)
in
4,800
5,800
6,800
8,500
9,800
11,000
13,000
18,800
46,300
*Minimum seven day, ten year low flow based on
calculations by the U.S. Corps of Engineers.
Oklahoma
36
When a liquid of different quality than the receiving
water is discharged into an aquatic system, a mixing
zone is formed. The concept of a mixing zone is
recognized as a necessary element in Oklahoma's Water
Quality Standards.
In streams, the mixing zone extends downstream a
distance equivalent to thirteen (13) times the width
of the water at the point of effluent discharge. The
concentration of toxic substances in a mixing zone
shall not exceed the 96-hour LC50 for sensitive
indigenous species. Mixing zones in lakes shall be
designated on a case-by-case basis.
It is recognized that the water quality in a portion
of the mixing zone may be unsuitable for certain
beneficial uses. Where overlapping mixing zones occur
because of multiple outfalls, the total length of the
mixing zone will extend thirteen (13) stream widths
downstream from the downstream discharge.
Zones of Passage
to insure that a
within the stream
mixing zone that
percent (75%) of
volume, whichever
free-swimming and
- All discharges shall be regulated
zone of passage shall be maintained
at the outfall and throughout the
shall be no less than seventy-five
the cross-sectional area or flow
is more beneficial to the
drifting organisms. Water quality
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State
Mixing Zone Narrative
standards shall be maintained throughout the zone of
passage. Zones of passage in lakes shall be
designated on a case-by-case basis.
Oregon
37
The Department may suspend the applicability of all or
part of the water quality standards set forth in this
rule, except those standards relating to aesthetic
conditions, vithin a defined immediate mixing zone of
specified and appropriately limited size adjacent to
or surrounding the point of waste water discharge.
The sole method of establishing such mixing zone shall
be by the Department defining same in a waste
discharge permit.
In establishing a mixing zone in a waste discharge
permit, the Department:
(a) May define the limits of the mixing zone in terms
of distance from the point of the waste water
discharge or the area or volume of the receiving water
or any combination thereof;
(b) May set other less restrictive water quality
standards to be applicable in the mixing zone in lieu
of the suspended standards; and
(c) Shall limit the mixing zone to that in all
probability, will:
i.
Not interfere
or population
degree which
and
with any biological community
of any important species to a
is damaging to the ecosystem;
ii.
Not adversely affect any
use disproportionately.
other beneficial
Pennsylvania
38
Not specified
Rhode Island
39
Thermal Mixing Zones - In the case of thermal
discharges into tidal rivers or estuaries, or fresh
water streams or estuaries, where thermal mixing zones
are allowed by the director, the mixing zone will be
limited to no more then 1/4 of the cross sectional
area and/or volume of flow river, stream or estuary,
leaving at least 3/4 free as a zone of passage. In
wide estuaries and oceans, the limits of mixing zones
will be established by the director.
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State Mixing Zone Narrative
Non-thermal Mixing Zones - In applying these standards
the director may recognize, where appropriate, a
limited mixing zone or zone of initial dilution on a
case-by-case basis. The locations, size, and shape of
these zones shall provide for the maximum protection
of aquatic resources. At a minimum, mixing zones must:
(a) Meet the criteria for aesthetics;
(b) Be limited to an area or volume that will minimize
interference with the designated uses in the segment;
(c) Allow an appropriate zone of passage for migrating
fish and other organisms; and
(d) Not result in substances accumulating in
sediments, aquatic life or food chains to exceed known
or predicted safe exposure levels for the health of
humans or aquatic life.
South Carolina A region or zone (called the mixing zone) in which one
or more specified water quality standards and
classified uses are not applicable may be allowed by
the Department (South Carolina Department of Health
and Environmental Control). The size of the mixing
zone shall be kept to a minimum and may be determined
on an individual project basis considering biological,
chemical, engineering, hydrological, and physical
factors.
(a) Surface Waters: Mixing zones which are used for
waste treatment effluents shall allow safe passage of
aquatic organisms, and shall allow the protection and
propagation of a balanced indigenous population of
aquatic organisms in and on the water body. The
mixing zone size shall be based upon critical flow
conditions. The mixing zone shall not be an area of
waste treatment nor shall it interfere with or impair
existing recreational uses, existing drinking water
supply uses, existing industrial or agricultural uses,
or existing or potential shellfish harvesting uses.
[see Antidegradation (l)(a)].
(b) Ground Waters: The numeric standards for Class GB
ground water, Section E. (11) (Class Descriptions and
Specific Standards), are applicable unless a mixing
zone solely within the bounds of the applicant's
property, setting forth certain conditions is granted
by the Department. Such a mixing zone shall be
granted upon satisfactory demonstration to the
Department that:
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State Mixing Zone Narrative
(1) Reasonable measures have been taken or
binding commitments are made to minimize the
addition of contaminants to ground water
and/or control the migration of contaminants
in ground water; and
(2) The ground water in question is confined to
the uppermost aquifer which has little or no
potential of being an Underground Source of
Drinking Water, and discharges or will
discharge to surface waters without
contravening the surface water standards set
forth in this regulation; and
(3) The contaminant(s) in question occurs on the
property of the applicant, and there is
minimum possibility for ground-water
withdrawals (present or future) to create
drawdown such that contaminants would flow
offsite; and
(A) The contaminants or combination of
contaminants in questions are not
dangerously toxic, mobile, or persistent.
South Dakota Each discharge to a flowing water is entitled to a
mixing zone at the edge of 'which the criterion
established for the beneficial uses of the receiving
water shall be met. Mixing zones in streams must
permit an acceptable passageway for movement of
aquatic organisms. The total mixing zone or zones, at
any transect of a stream may not contain more than 75
percent of the cross-sectional area of the stream and
may not extend over more than 75 percent of the width
of the stream or 100 yards, whichever is least. The
dimensions of the total mixing zone parallel to the
stream flow may not exceed one-half mile. Mixing zone
characteristics must not be lethal to aquatic
organisms. The 96-hour median lethal concentration
for indigenous fish or fish food organisms, whichever
is more stringent, may not be exceeded at any point in
the mixing zone. Mixing zones may not intersect
spawning or nursery areas, migratory routes, water
intakes, or mouths of rivers. Mixing zones should not
overlap, but where they do, measures shall be taken to
prevent adverse synergistic effects.
Lakes not allowed a mixing zone. Discharges to lakes
are not entitled to a mixing zone. These effluents
shall meet the vater quality standards at the point of
discharge. No discharge of pollutants is allowed
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State Mixing Zone Narrative
vhich reaches a lake classified for the beneficial use
of fish life propagation and causes impairment of an
assigned beneficial use.
42
Tennessee Mixing zone refers to that section of a flowing stream
or impounded vaters in the immediate vicinity of an
outfall where an effluent becomes dispersed and mixed.
Such zones shall be restricted in area and length and
shall not (i) prevent the free passage of fish or
cause aquatic life mortality in the receiving water;
(ii) contain materials in concentrations that exceed
recognized acute toxicity levels for biota
significant to the aquatic community in receiving
water; (iii) result in offensive conditions; (iv)
produce undesirable aquatic life or result in
dominance of a nuisance species; (v) endanger the
public health or welfare; or (vi) adversely affect the
reasonable and necessary uses of the area; (vii)
create a condition of chronic toxicity beyond the edge
of the mixing zone; and (viii) adversely affect
nursery and spawning areas.
Texas (b)Hixing zones. A reasonable mixing zone will be
allowed at the discharge point of permitted discharges
into surface water in the state, in accordance with
the following provisions.
(1) The following portions of the standards do not
apply within mixing zones:
(A) site-specific criteria, as defined in §307.7 of
this title (relating to Site-specific Criteria and
Uses) and listed for each classified segment in
Appendix A of §307.10 of this title (relating to
Appendices A through C);
(B) numerical chronic criteria for toxic materials as
established in §307.6 of this title (relating to Toxic
Materials);
(C) total chronic toxicity restrictions as established
in §307.6 of this title (relating to Toxic Materials);
and
(D) maximum temperature differentials as established
in §307.4(f) of this title (relating to General
Criteria).
(E) dissolved oxygen criteria for unclassified vaters,
as established in §307.4(h) of this title (relating to
General Criteria).
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State Mixing Zone Narrative
(F) dissolved oxygen criteria for intermittent streams
and barge canals, as established in §307.4(j) of this
title (relating to General Criteria).
(G) fecal coliform criteria for unclassified waters,
as established in §307.4(k) of this title (relating to
General Criteria).
(2) Numerical acute criteria for toxic materials and
preclusion of total acute toxicity as established in
§307.6 of this title (relating to Toxic Materials) are
applicable even in mixing zones. Numerical acute
criteria may be exceeded in small zones of initial
dilution at discharge sites. Zones of initial
dilution are restricted to the immediate point of
discharge and must be substantially smaller than
designated mixing zones.
(3) Provisions of the general criteria in §307.4 of
this title (relating to General Criteria) remain in
effect in mixing zones unless specifically exempted in
this section.
(4) Water quality standards do not apply to treated
effluents at the immediate point of discharge prior to
any contact with either ambient waters or a dry
streambed.
(5) Where a mixing zone is defined in a valid
commission or National Pollutant Discharge Elimination
System (NPDES) permit, the mixing zone defined in the
permit will apply.
(6) Mixing zones shall not preclude passage of
free-swimming or drifting aquatic organisms to the
extent that aquatic life use is significantly affected.
(7) Mixing zones will not overlap unless it can be
demonstrated that no applicable standards will be
violated in the area of overlap. Existing and
designated uses will not be impaired by the combined
impact of a series of contiguous mixing zones.
(8) Mixing zones will not encompass an intake for a
domestic drinking water supply. Thermal mixing zones
are excepted from this provision unless elevated
temperatures adversely affect drinking water treatment.
(9) Mixing zones will be individually specified for
all permitted domestic discharges with a permitted
monthly average flow equal to or exceeding one million
gallons per day and for all permitted industrial
discharges to water in the state (excepting discharges
which consist entirely of stormwater runoff). For
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State
Mixing Zone Narrative
domestic discharges vith permitted monthly average
flows less than one million gallons per day, a small
mixing zone will be assumed; and the commission may
require specified mixing zones as appropriate. For
existing permits and pending permit applications as of
the date of adoption of this chapter, mixing zones
will be defined upon permit renewal or amendment.
Utah
Vernont
45
A mixing zone is a limited portion of a body of water,
contiguous to a discharge, where dilution is in
progress but has not yet resulted in concentrations
which will meet certain standards for all pollutants.
At no time, however, shall concentrations within the
mixing zone be allowed which are acutely lethal as
determined by bioassay or other approved procedure.
Mixing zones may be delineated for the purpose of
guiding sample collection procedures. The zone shall
be small in extent and must not form a barrier to
migrating aquatic life. Domestic wastewater effluents
discharged to mixing zones shall meet effluent
requirements specified in R448-1-3.
A. Designation - Mixing zones shall not be created in
any Class A water. In all other waters, the Secretary
may, in conjunction with the issuance of a permit,
designate a specific portion of the receiving waters
not exceeding 200 feet from the point of discharge as
a mixing zone for any waste which has been properly
treated to comply with all applicable state and
federal treatment requirements and effluent
limitations. Vithin any mixing zone the Secretary
may, in accordance with the terms of a. permit, waive
the provisions of sections 1-03, 3-01, 3-03(B), and
3-04(B) provided that the quality of the waters
downstream of the mixing zone complies with all
applicable provisions of these rules.
B. Mixing Zone Criteria - The Secretary shall insure
that conditions within any mixing zone shall:
1. Not create a public health hazard, and
2. Not constitute a barrier to the passage or
migration of fish or result in an undue adverse effect
on fish, aquatic biota or wildlife, and
3. Not interfere with any existing use of the waters.
Virginia46
Zones for mixing wastes with receiving waters shall be
determined on a case-by-case basis; shall be kept as
small as practical; shall not be used for, or
considered as, a substitute for minimum treatment
technology required by the Federal Water Pollution
Control Act and other applicable State and Federal
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State
Mixing Zone Narrative
lavs; and shall be implemented, to the greatest extent
practicable, in accordance with the provisions of
subsections 1.01A and 1.01B of the Virginia Water
Quality Standards, and shall not contain toxic
substances in acutely toxic concentrations. An area
of initial dilution may be allowed. This area of
initial dilution will be determined on a case-by-case
basis and shall not at any time exceed the lethal
concentration for appropriate representative species
for time periods of exposures likely to be encountered
by that species and likely to cause acute effects.
Mixing within these zones shall be as quick as
practical and may require the installation and use of
devices which insure that waste is mixed with the
allocated receiving waters in the smallest practical
area. The need for such devices shall be determined
on a case-by-case basis. The boundaries of these
zones of admixture shall be such as to provide a
suitable passageway for fish and other aquatic
organisms. In an area where more than one discharge
occurs and several mixing zones are close together,
these mixing zones shall be so situated that this
passageway is continuous.
Washington
The total area and/or volume of a receiving water
assigned to a dilution zone shall be as described in a
valid discharge permit as needed and be limited to
that which will:
(a) Not cause acute mortalities of sport, food, or
commercial fish and shellfish species of established
biological communities within populations or important
species to a degree which damages the ecosystem.
(b) Not diminish aesthetic values or other beneficial
uses disproportionately.
West Virginia
In the permit review and planning process or upon the
request of a permit applicant or permittee the Chief
may establish on a case-by-case basis an appropriate
mixing zone.
(A) The following criteria shall
establishment of mixing zones:
(1) Mixing zones shall:
be applied to the
i. Be kept as small as practical in area
and length;
ii. Not be used for, or considered as, a
substitute for waste treatment;
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State Mixing Zone Narrative
iii. Provide for as rapid a mixing as
practicable;
iv. Not prevent the free passage of aquatic
species or include spawning or nursery
areas;
v. Not overlap a public water supply
intake;
vi. Not cause or contribute to any of :.-,e
conditions prohibited in Section 3; and
vii. Not interfere with any designated use
category.
(2) The boundaries of the mixing zone shall
reflect
(a) Receiving water body characteristics
such as:
i. Vater quality
ii. Local meteorology
iii. Flow regime (including low-flow
records),
iv. Magnitude of water exchange at point of
discharge,
v. Stratification phenomena,
vi. Vaste capacity of the receiving system
including retention time,
vii. Turbulence and speed of flow,
viii. Morphology of the receiving system as
related to plume behavior, and
biological phenomena,
ix. Designated water use categories; and
(b) Discharge characteristics such as :
i. Flow regime,
ii. Volume,
iii. Design,
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State Mixing Zone Narrative
iv. Location
v. Rate of mixing and dilution, and
vi. Plume behavior and mass-emission rates
of constituents including knowledge of
their persistence, toxicity, and
chemical or physical behavior with time.
(B) Where the 7-day, 10-year return frequency is 5 cfs
or less, no mixing zone may be established.
(C) In order to facilitate a determination or
assessment of a mixing zone pursuant to this section,
the Chief may require a permit applicant or permittee
to submit such information as deemed necessary.
49
Wisconsin Water quality standards must be met at every point
outside of a mixing zone. The size shall be based on
such factors as effluent quality and quantity,
available dilution, temperature, current, type of
outfall, channel configuration and restrictions to
fish movement. As a guide to the delineation of a
mixing zone, the following shall be taken into
consideration:
(a) Limiting mixing zones to as small an area as
practicable, and conforming to the time exposure
responses of aquatic life.
(b) Providing passageways in rivers for fish and other
mobile aquatic organisms.
(c) Where possible, mixing zones being no larger than
25 percent of the cross-sectional area or volume of
flow of the stream and not extending more than 50
percent of the width.
(d) For contaminants other than heat, the 96-hour TLm
to indigenous fish and fish food organisms not being
exceeded at any point in the mixing zone.
(e) Mixing zones not exceeding 10 percent of a lake's
total surface area.
(f) Mixing zones not interfering with spawning or
nursery areas, migratory routes, nor mouths of
tributary streams.
(g) Mixing zones not overlapping, but vhere they do,
taking measures to prevent adverse synergistic effects.
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State
Mixing Zone Narrative
(h) Restricting the pH to values greater than 4.0 s.u.
and to values less than 11.0 s.u. at any point in the
mixing zone for the protection of indigenous fish and
food organisms.
Exemptions. The thermal mixing zone provisions of
this chapter are not applicable to municipal waste and
water treatment plants, to vessels, or to discharges
to enclosed harbors.
Resource Management Exemptions. Application of
chemicals for vater resource management purposes in
accordance with statutory provisions is not subject to
the requirements of the standards except in case of
water used for public water supply.
Wyoming
50
Except for Sections 15 (Settleable Solids), 16
(Floating Solids), 17 (Taste, Odor and Color) and 28
(Undesirable Aquatic Life) of these regulations,
compliance with Vater Quality Standards shall be
determined after allowing reasonable time for mixing.
Size of the mixing zone shall be determined after
consideration of the effect of the discharge on the
biological community, water uses and aesthetic
conditions, as well as consideration of the flow
conditions and physical nature of the receiving water.
The portion of a surface water body designated as a
mixing zone shall be limited to that which will not
interfere with biological communities or populations
of important species to a degree which is damaging to
the ecosystem and which will not cause substantial
damage to other beneficial uses. In addition, there
shall be a zone of passage through the mixing zone
sufficient to allow passage of free-swimming and
drifting organisms in a manner producing no
significant effects on their populations, except
during periods when stream flows are less than the
average of the minimum 7 consecutive day flow which
has the probability of occurring once in 10 years.
American Samoa
51
the waters of
the policy of
all waters in
for a variety
The activities of man will result in the production of
a variety of effluents that must be discharged into
the territory for disposal. Although
the EQC is to maximize the quality of
American Samoa, the EQC realizes that
of reasons it will not always be
feasible to generate effluents whose quality equals or
exceeds that required of. the receiving water.
Therefore, effluents discharged into waters of certain
water quality categories will be allowed an area of
initial dilution called a zone of mixing. In the zone
or mixing some water quality parameters will be
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State Mixing Zone Narrative
assigned maximum concentrations that are less
stringent than permitted in the waters surrounding the
zone of mixing. Areas where zones of mixing will not
be allowed and the water quality parameters that can
be changed in a zone of mixing are listed in the
following criteria and procedures. The criteria and
procedures must be complied with to establish a zone
of mixing.
A. Criteria:
A zone of mixing can only be granted by the
Environmental Quality Commission if the application
and the supporting information clearly shows that all
or the following conditions have been met:
1. The beginning or continuation of the function or
operation involved in a discharge by the granting
of the zone of mixing is in the public interest;
and
2. The proposed discharge does not substantially
endanger human health or safety; and
3. Compliance with the existing water quality
standards at the point of discharge would produce
serious economic hardships without equal or
greater benefit to the public; and
4. Alterations generated by a proposed discharge do
not disrupt the marine ecology of the receiving
waters outside the zone of mixing; and
5. A zone of mixing shall not be granted for fresh
surface waters, Pala Lagoon, Fagatele Bay, that
portion of Pago Pago Harbor described in section
IV.B.3.C. , or in those waters in Manu'a
described in section Iv.C.5 . Those water
quality parameters which are subject to zones of
mixing are chlorophyll a, light penetration
depth, nutrients, pH, temperature, turbidity, and
fecal coliform. Furthermore, those water quality
parameters which are subject to zones of mixing
must conform to alternative within-zone limits
determined by the EQC. The zone of mixing is
defined in section V.B.4.g . Determination of
effluent limits for toxic substances must comply
with section VI.A.8,9 ; and
6. The proposed discharges shall be substantially
free from visible floating materials, grease,
oil, scum, foam and other floating matter
attributable to sewage, industrial wastes, or
other activities; and
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State Mixing Zone Narrative
7. The proposed discharge vill not result in a
lowering of vater quality outside the zone of
mixing so as to violate the standards of Section
VI as they may be applicable.
B. Procedures To Apply For Zone Of Mixing:
1. Every application for a zone of mixing shall be
accompanied by a complete and detailed
description of present conditions, how present
conditions compare to standards, and such other
information as the Commission may prescribe.
2. Application for a zone of mixing for an existing
discharge must be filed within six months of the
effective date of these standards. The EQC will
certify a proposed NPDES permit (initial issuance
or reissuance) only if conformance with the
standards is demonstrated or a zone of mixing
approved.
3. Each application for a zone of mixing shall be
reviewed in light of the descriptions,
statements, plans, histories, and other
supporting information as may be submitted upon
the request of the EQC and the effect or probable
effect on the water quality standards established
in Section VI of these standards.
4. A zone of mixing, or a renewal, shall be granted
within the requirements of this section for the
following time periods and conditions:
(a) If a zone of mixing is granted on the
grounds that there is no technically and/or
financially efficient means known, or
available, for the adequate prevention,
control, or abatement of the discharge
involved, it shall be only until the
necessary means of prevention, control, or
abatement becomes practicable and it shall
be subject to the taking of any substitute
or alternative measures that the EQC may
prescribe.
No renewal of a zone of mixing granted under
this section shall be allowed without a
thorough review of known and available means
of preventing, controlling or abating the
discharge involved.
(b) The Environmental Quality Commission may
permit a zone of mixing for a period not
exceeding five years. Any zone of mixing
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State Mixing Zone Narrative
approval is subject to EPA concurrence.
(c) Every zone of mixing granted under this
section shall include, but not be limited
to, grantee requirements to perform effluent
and receiving water sampling and testing and
to report the results of each test to the
Environmental Quality Commission. A program
of research to develop practicable
alternatives to the methods of treatment or
control in use by the grantee may be
required as a condition of the zone of
mixing.
(d) Any zone of mixing granted pursuant to this
section may be renewed periodically on terms
and conditions (for periods not exceeding
five years) which would be appropriate for
the initial granting of a zone of mixing,
provided that:
(1) The applicant for renewal has met all
of the conditions specified in the
previously prescribed zone of mixing;
and
(2) No renewal shall be granted except on
application therefore. Any such
application shall be made at least 120
days prior to the expiration of the
current zone of mixing permit.
e. The Environmental Quality Commission on its
own motion, or upon the application of any
person, shall terminate a zone of mixing if,
after a hearing, it is determined that:
(1) The water area outside the zone of
mixing does not meet the standards
applicable to that water as given in
section VI; or
(2) The zone of mixing granted will
unreasonably interfere with any actual
or probable use of the water area; or
(3) If any NPDES permit condition is not
being met and the discharger has failed
to take action to bring the effluent
into compliance-
Such termination shall be made only after a
hearing held by the Environmental Quality
Commission in accordance with the
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State Mixing Zone Narrative
Administrative Procedures Act of the
American Samoa Code. Upon such termination,
the standards of water quality applicable
thereto shall be those established for the
water as otherwise classified.
f. Upon expiration of the period stated in the
zone jf mixing, the zone of mixing shall
automatically terminate and no rights shall
be vested to the grantee. If a renewal of a
zone of mixing has been applied for as
specified in Section V.B.A.d the zone of
mixing shall continue until the renewal is
approved or denied by the EQC.
g. Whenever an application is approved, the
zone of mixing shall be defined as the
initial dilution volume and shall be
determined by PLUME or some other EQC
approved model. The initial dilution volume
is to be the only dispersion zone that will
be considered as a zone of mixing. Vater
quality standards will be strictly enforced
in the waters adjacent to the zone of
mixing. Requirements for discharge permits
shall be determined to assure compliance
with the zone of mixing at zero current and
worst case receiving water conditions and to
assure protection of adjacent waters under
other current conditions.
Further, the following will be considered by
the EQC in determining whether to grant or
deny a zone of mixing:
(1) Protected uses of the body of water;
(2) Existing natural conditions of the
receiving water;
(3) Character of the effluent;
(4) Adequacy of the design of the outfall
and diffuser system to achieve the
desired dispersion and assimilation in
the receiving water; and
(5) Other pertinent policies or plans of
Territorial agencies.
h. No part of a shoreline, reef or bottom
substrate shall be included in any zone of
mixing.
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State Mixing Zone Narrative
i. No zone of mixing granted pursuant to this
section shall be construed to prevent or
limit the application of any emergency
provisions or procedures provided by law.
VI. Standards or Water Quality
A. The following standards apply to all fresh surface
water, erabayments, open coastal water and oceanic
waters of the Territory, (2,4,7,8,9,10,11,12 and 13)
shall apply as a minimum within the zone of mixing).
1. They shall be substantially free from materials
attributable to sewage, industrial wastes, or
other activities of man that will produce color,
odor, or taste, either of itself or in
, combinations, or in the biota.
2. They shall be substantially free from visible
floating materials, grease, oil, scum, foam, and
other floating matter attributable to sewage,
industrial wastes, or other activities of man.
52
District of Columbia Mixing zones shall be established for point source
discharges of pollutants which immediately threaten
the present nearby aquatic community or present or
future water uses. The following factors shall be
used in establishing mixing zones:
(a) Permissible size of the zone shall be dependent on
an acceptable amount of impact and the size of the
receiving water body;
(b) Mixing zones shall be free from discharged
substances that will settle to form objectionable
deposits; float to form unsightly masses; or produce
objectionable color, odor, or turbidity;
(c) Mixing zones shall protect aquatic life in shallow
areas which serve as nursery areas;
(d) A mixing zone, or two (2) or more mixing zones,
shall not form a barrier to migratory aquatic life;
(e) As a guideline, the quality for life within a
mixing zone shall be such that the acute toxicity for
biota significant to the area's aquatic life community
is not exceeded;
(f) The positioning of mixing zones shall be rione in a
manner that provides the greatest protection to
aquatic life and for the various uses of the water;
and,
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State Mixing Zone Narrative
(g) Within the estuary, the maximal dimension of the
mixing area shall not exceed ten percent (102) of the
numerical value of the cross-sectional area of the
waterway and shall not occupy more than one third
(1/3) of the width of the waterway.
53
Guam Mixing Zones in Receiving Waters - Whenever a Water
Quality Standard is more restrictive than the
corresponding effluent standard then an opportunity
may be allowed by the Agency for the mixture of an
effluent with its receiving water provided that the
zone in which mixing occurs will not adversely affect
the designated uses of the receiving waters. If
mixing zones are used, Water Quality Standards for a
receiving water must be met at every point outside of
the boundaries of the designated mixing zone. The
following criteria apply to all mixing zones:
1. Whenever mixing zones are allowed, zones of
passage, i.e., continuous water routes of the
volume, area, and quality necessary to allow
passage of free-swimming and drifting organisms
with no significant effects produced on their
populations, shall be provided.
2. Where two or more mixing zones are in close
proximity, they shall be so defined that a
continuous zone of passage for aquatic life is
available.
3. Biologically important areas, including spawning
and nursery areas, shall be protected.
4. No criteria shall be set aside in the mixing zone
which shall cause conditions in the mixing zone
to be lethal to aquatic life and wildlife which
may enter the zone or injurious to human health
in the event of a temporary exposure.
5. The area or volume of an individual mixing zone
shall be limited to an area or volume that will
minimize impacts on users.
6. The discharge shall not violate the basic
standards applicable to all waters (Section II A
and Section III E) nor shall it unreasonably
interfere with any actual or probable use of the
water within the mixing zone.
7. For those water quality criteria eligible for a
mixing zone, alternate limits will be established
if the limits in II B are to be revised in the
zone of mixing.
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State Mixing Zone Narrative
C. Boundaries of Non-thermal Mixing Zones - Non-
thermal discharges shall be permitted by the National
Pollutant Discharge Elimination System (NPDES) permit
process or through the Guam Environmental Protection
Agency's local permit program only after careful
analysis of the nature of the effluent and a thorough
study to assess the consequences of the effluent upon
the environment. Mixing zones for non-thermal
discharges shall be based on the following models,
taking into consideration the criteria in Section III
B above.
1. Mixing Zones for Non-Thermal Discharges into
Surface Waters - For non-thermal discharges into
streams and rivers the mixing zone will be
limited to no more than 1/4 of the cross
sectional area and/or volume of flow of the
stream, leaving at least 3/4 free as a Zone of
Passage. The mixing zone shall not extend more
than 5 stream widths downstream from the point of
discharge. Mixing zones will not be allowed in
standing bodies of water.
2. Mixing Zones for Non-Thermal Discharges into
Coastal Waters - For non-thermal discharges to
coastal waters the mixing zone shall be equal in
depth to the depth of the water over the
diffuser, in width to twice the depth of the
water plus the width of the diffuser, and in
length to twice the depth of the water plus the
length of the diffuser, with the diffuser
geographically centered within the mixing zone.
All discharges to marine waters will comply with
the Ocean Discharge Criteria promulgated under
Section 403 (c) of the federal Clean Water Act.
D. Mixing Zones for Thermal Discharges - Thermal
discharges pertain to effluent water with a
temperature component either above or below ambient
conditions of the receiving body of water. All
thermal discharges, existing or proposed, into
receiving bodies of water shall be subject to criteria
established in Section 316 (a) of the Federal Water
Pollution Control Act (FWPCA), Public Law 95-217.
Thermal discharges shall be permitted by the National
Pollutant Discharge Elimination System (NPDES) permit
process or through the Guam Environmental Protection
Agency's local permit program only after careful
analysis of the nature of the effluent and a thorough
study to assess the consequences of the effluent upon
the environment.
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1. All Above-Ambient Discharges:
a) Shall conform to a zone of mixing defined
for that particular discharge on a
case-by-case basis. This zone of mixing
shall be defined by the following references
or other references depicting appropriate
thermal mixing zone models.
- Water Quality Criteria, March 1973. EPA.
- Quality Criteria for Water, July 1976.
EPA.
- Biological Methods for the Assessment of
Water Quality. American Society of
Testing and Materials, July 1976.
And take into consideration the following
criteria:
- Time of exposure
- Concentration of effluent
- Depth of discharge
- Type of environment
- Volume of discharge
- Mass emission rate of critical materials
- Aesthetics and the assessment of damage
to biota on the population basis
Although final authority in defining a zone
of mixing rests vith the GEPA, it is
intended that cooperation between the
discharger and the Agency will result in the
most appropriate zone.
b) Shall not increase the temperature of the
receiving body of water to cause substantial
damage or harm to the flora and fauna or
interfere with the beneficial uses assigned
therein.
c) Shall comply with all other water quality
criteria as defined in these standards,
unless specific criteria are established in
the discharge permit.
d) These zones of mixing shall be monitored by
the discharger on a regular schedule
established by the NPDES Permit and/or GEPA
Discharge Permit, to ensure compliance with
established criteria-
e) If the Agency, pursuant to notice and
opportunity for public hearings, finds
evidence that a discharge has caused
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substantial damage, it may require
conversion of such discharge to an approved
alternative method. In making such a
determination, the Agency may consider:
1. The nature and extent of damage to the
environment.
2. Projected lifetime of discharge.
3. Adverse economic and environmental
impacts, marine and terrestrial,
resulting from such conversion
4. All available data, reports, surveys
and projects related to the discharge.
5. Such other factors vhich may prove to
be appropriate.
2. Above-Ambient Discharges in Existence Prior to
Approval of These Standards.
a) Shall be given special attention when
defining a zone of mixing. All criteria
established for part D-l above, shall apply
vith special emphasis on specific criteria
listed in part D-la.
b) It is the intent of this section to
establish a reasonable zone of mixing for
discharges not in compliance with existing
laws, codes and practices.
c) Description of mixing zones for Tanguisson
and Piti/Cabras Power Plants.
1. Tanguisson Power Plant Zone of Mixing
The zone of mixing for the Tanguisson
Power Plant is defined as»a rectangle
of approximately 10,000 m with the
following reference points.
Northern Boundary - North side of
intake channel
South Boundary - 1969 ft (600 m) south
of intake channel
Eastern Boundary - Shoreline at mean
high tide
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Western Boundary - 591 ft (180 m)
off-shore or a depth of approximately
23 ft (7m)
2. Piti/Cabras Zone of Mixing
The zone of mixing for the Piti/Cabras
Power Plants combined is inclusive of
all water in the Commercial Port and
Piti Channel area bordered by a line
from the GORCO Tanker mooring and the
Navy Fuel Pier on Dry Dock Island.
Because of the topography of this area,
no zone of passage can be designated.
3. Below-Ambient Discharges.
All below-ambient discharges shall follow the same
guidelines set down for thermal discharges and be
evaluated on a case-by-case basis.
54
Marianas Islands The water quality criteria in these regulations shall
apply within a mixing zone unless specific alternate
criteria are approved by the Chief for specified
parameters. The mixing zone, in accordance with Part
4(j), shall be defined by specific linear distance,
volume or area, discharge location, maximum flow, and
maximum concentrations of important constituents which
are determined on a case-by-case basis using the
following criteria:
9.1 Mixing zones shall be as small as practicable and
shall not be of such size or shape as to cause or
contribute to the impairment of water uses. In
determining the size and location of the mixing
zone for any discharge, the following shall be
considered:
(a) Size of receiving water volume of discharge,
streambank or shoreline configuration, the
mixing velocities, and other hydrologic and
physiographic characteristics;
(b) Present and anticipated future use of the
body of water;
(c) Present and anticipated future quality of
the body of water; and
(d) The ratio of the maximum flow rate of waste
being discharged t" the lowest recorded flow
rate of the receiving waters.
9.2 An adequate zone of passage shall exist at all
times for the movement or drift of aquatic life.
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Mixing Zone Narrative
Puerto Rico
55
9.3 Where two or more mixing zones are in close
proximity, they shall be so defined that a
continuous zone of passage for aquatic life is
available.
9.4 Mixing zones shall not intersect any area of the
waters in such a manner that the maintenance of
aquatic life in the body of water as a whole
would be adversely affected.
9.5 The discharge shall not violate the basic
standards applicable to all water nor shall it
unreasonably interfere with any actual or
probable use of the waters within the mixing zone.
PUERTO RICO MIXING ZONES
5.1 Requirenents for the Authorization of Mixing
Zones - A discharge will be permitted for which a
mixing zone has not been defined and authorized by the
Board only when the petitioner demonstrates to the
satisfaction of the Board that the discharge,
undiluted, complies with all the water quality
standards (at the discharge sampling point).
5.2 Natural Background Concentration - If the
petitioner demonstrates to the satisfaction of the
Board, through extensive field monitoring and
investigations, that the natural background
concentration of the receiving waters exceed one or
more of the water quality standards set forth for the
corresponding classification, the Board may allow the
parameters in the discharge to be equal to or less
than the natural background values.
5.3 Mixing Zone Authorization Application - Each
application for a mixing zone shall include the
following:
1. Evidence that the project has complied with
Article 4-C, Law No. 9 of June 18, 1970,
Environmental Public Policy Act, as amended, if
the application is related to a new or modified
discharge; a new or modified submerged outfall;
or a new or modified discharge channel, by the
submittal of the corresponding environmental
document.
2. Physical, chemical and biological
characterization of the discharge and of the
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receiving waters at the site in which the
background concentration is measured, as
specified in the latest version of the "Mixing
Zone and Bioassay Guidelines" approved by the
Board. This characterization shall include the
results of bioassays using organisms approved by
the Board and following the methodology described
in said guidelines.
3. Existing discharge flow or proposed discharge
flow for new or modified discharges.
4. Concentration of each one of the substances or
parameters that do not comply with the applicable
water quality standards at the point of
discharge, after using best practicable
technology (BPT), as defined by EPA, for their
control.
5. Detailed hydraulic design calculations for the
proposed discharge system demonstrating that the
best engineering practices (BEP) have been used
for obtaining the required dilution in the least
possible tridimensional space.
6. Description of each mathematical model utilized
to determine the critical initial dilution for
open coastal waters and dilution for closed body
of waters, used to define the mixing zone and the
corresponding calculations, and/or the field
studies where the oceanographic data, measure-
ments of the physical/chemical parameters around
the existing discharges and the associated
ecological studies demonstrate the extension and
effects of the mixing zone.
7. Diagram showing the proposed mixing zone and
indicating the coordinates of the points that
define the boundaries of the mixing zone.
8. Proposed method to validate and calibrate (if
necessary) each mathematical model, including a
monitoring plan and a Quality Assurance Plan that
includes field sampling and laboratory analysis.
9. Proposed method for the maintenance of the
discharge system.
10. Discussion of agreements reached vith the Board
on how the applicable provisions of Article 5 of
this Regulation will be compiled.
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5.4 General Standards for Granting Interim
Authorizations for Mixing Zones - An interim
authorization for a mixing zone will be granted when
the petitioner has submitted an application in which
it is demonstrated, to the satisfaction of the Board,
the following:
1. Compliance with Article 4-C, Law No. 9 of June
18, 1970, Environmental Public Policy Act, as
amended, when the application is related to a new
or modified discharge, new or modified submerged
outfall, or a new or modified discharge channel.
2. The proposed discharge system constitutes the
best engineering practices (BEP) to minimize the
size of the tridimensional space of the mixing
zone, maintaining the required dilution.
3. Solids in the discharge will not settle on the
bottom of the receiving waters.
4. At the boundaries of the proposed mixing zone,
after critical initial dilution for open coastal
waters and after dilution for closed bodies of
waters each one of the following requirements are
met:
a. The concentration of pollutants or physical
parameters, as defined in Section 5.5, do not
exceed the applicable water quality standards.
b. The acute toxicity units do not exceed the
criteria maximum concentration (CMC).
c. The chronic toxicity units do not exceed
criteria continuous concentration units (CCC).
d. For fresh waters, and in coastal waters where
the effluent is not discharged through a high
rate diffuser, the CMC shall be reached in the
most restrictive of the following conditions:
1. Ten percent (10£) of the distance from the
boundary of the outfall to the mixing zone
boundary.
2. A distance of fifty (50) times the
discharge length scale in any spacial
direction. This requirement, in the case
of multiple ports diffusers, shall be met
for each port using the discharge length
scale of said port.
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State Mixing Zone Narrative
3. A distance of five (5) times the local
water depth in any horizontal direction
from any port discharge.
4. The discharge shall not cause the growth or
propagation of organisms that negatively
disturb the ecological equilibrium in areas
adjacent to the mixing zone.
5. The mixing zone shall be located as to
allow, at all times, passageways for the
movement or drift of the biota. Also, the
passageways shall comply with the following
in the specific cases mentioned:
a. If the receiving body of water is a
closed body of water, estuary, river or
creek, the mixing zone shall be located
close to the bank itself in such a
manner that the passageway permits the
adequate and safe flow of free floating,
swimming or drifting organisms, or
organisms that have self propulsion.
b. If the receiving body of water is an
estuary, the surface area and volume of
passageway shall be at least
seventy-five percent (75X) of the
corresponding surface area of the volume
of the receiving body of water across
each segment of the estuary.
c. If the receiving body of water is a
river or a creek, the surface area and
the cross-sectional area of the
passageway at the point of discharge and
downstream of this point shall be at
least sixty-seven percent (67%) of the
surface area and the cross-sectional
area of each segment of the river or
creek.
d. If the receiving body of water is a
closed body of water, the sum of all
mixing zone surface areas shall not
exceed twenty percent (20%) of the
surface area of the receiving body of
water.
6. The mixing zones requested will not overlap
with an adjacent mixing zone.
7. The control technology in accordance with
Article 6, Section 8, of this Regulation is
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being used or proposed.
8. The mixing zones shall be free of debris
scum, floating oils, and any substances
which produce objectionable odors.
9. Each mathematical model used by the
petitioner to define the mixing zones and
inputs of said mathematical model were
approved by the Board.
10. The mixing zones shall not be located in a
recognized fish spawning or aquatic
organism nursery area.
11. The mixing zones shall not affect in any
manner drinking vater supply intakes or
water intakes for livestock enterprises
located less than one hundred (100) meters
upstream, or five (5) kilometers downstream.
12. Except in the case of cooling waters,
mixing zone limits in coastal waters shall
not be located in such a manner that its
boundaries are at a distance less than one
(1) kilometer from areas designated as
public beaches, or classified as SA, and in
every body of water shall be restricted to
avoid interferences with the designated
uses of the receiving waters.
13. The proposed methodology to calibrate and
validate each mathematical model used is
acceptable to the Board.
14. The proposed method for maintaining in good
working conditions the discharge system is
acceptable to the Board.
15. The proposed method for defining the mixing
zone boundaries is acceptable to the Board.
16. Each proposed mixing zone complies with
applicable requirements set forth in
Article 5 of this Regulation.
5.5 Mixing Zone Boundaries - The mixing zone
boundaries shall be determined according to the
procedures described in "Mixing Zone and Eioassays
Guidelines" approved by the Board.
5.6 Additional Standards for Granting Interim
Authorization for Mixing Zones - Interim
authorizations for mixing zones shall be granted when
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the petitioner demonstrates to the satisfaction of the
Board compliance with the requirements set forth in
the "Mixing Zone and Bioassay Guidelines", approved by
the Board.
5.7 Period to Grant Interim Authorization for Mixing
Zones - Within sixty (60) days of the subraittal of an
approvable application, the Board shall make public
their intention to issue or modify the Water Quality
Certificate and to define a Mixing Zone Interim
Authorization. The effectiveness of said interim or
final mixing zone authorization vill be when EPA
incorporates it in the final NPDES permit of the
petitioner.
5.8 Period of Validity of Interim Mixing Zone
Authorization - The interim mixing zone authorization
shall be valid for a period not to exceed one and a
half (1 1/2) years; or until the NPDES permit expires;
or a date which the Board determines, based on the
data submitted by the petitioner pursuant to Section
5.9 or that the mixing zone(s) cannot be validated,
whichever occurs first.
5.9 Calibration and Validation of Mathematical Models
Used to Define a Mixing Zone - In the process of
obtaining a mixing zone authorization, the petitioner
shall submit to the Board information related to the
following:
1. Calibration
The petitioner shall calibrate those mathematical
models that require calibration as part of the
process of granting an interim authorization for
a mixing zone.
2. Monitoring Program for Validation
The petitioner shall implement a one (1) year
monitoring program to obtain the necessary data
required to validate each mathematical model
during two (2) seasons (winter and summer).
The monitoring program shall include as a minimum:
a. Continuous flow measurements.
b. Sampling of a frequency to be established
by the Board on a case-by-case basis, at
the following locations:
1) Effluent.
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State Mixing Zone Narrative
2) Station approved by the Board to determine
the background concentration for each one
of the substances for which a mixing zone
is requested.
3) Stations approved by the Board at the
boundaries of each mixing zone.
3. Analysis for all parameters that prompted the
mixing zone application and other parameters
needed to run each corresponding mathematical
model.
4. Current velocities at a frequency to be
established by the Board on a case-by-case basis,
if current velocities are an input to the
mathematical model used to define the mixing zone.
5. Shov that the model passes the validation test.
This shall be done by means of a comparative
analysis between the obtained values in the
sampling program, against the values indicated by
the model for corresponding points throughout the
periphery of the mixing zone. The model whose
calculated limits are equal to or less than the
ones obtained through the sampling program shall
be validated. Since the field data are affected
by variations in water currents, tides, etc.,
which vary as a function of time, the referred
comparison shall be done considering the data
obtained in real time or as close to it as
possible.
5.10 Standards for Granting Final Mixing Zones
Authorizations - A final mixing zone authorization
will be issued if the mathematical model is validated
as established in Section 5.9 of this Regulation.
5.11 Period of Validity of Final Authorization of
Mixing Zone - A final authorization of a mixing zone
shall be valid for a period not to exceed five (5)
years, but in no case will it exceed the expiration
date of the NPDES permit.
5.12 Renewal of Mixing Zone Authorizations - At least
one hundred and eighty (180) days prior to the
expiration date of a final mixing zone, the person to
whom the authorization was issued, shall submit a
complete application for the renewal of the mixing
zone authorization. The renewal application shall
contain the information that has changed with respect
to the information previously submitted in compliance
with the specifications of Section 5.3, and a
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certification indicating that the remainder of the
information has not changed.
5.13 Revocation of Interim and Final Authorizations
of Mixing Zones - The Board may revoke an interim or
final authorization of a mixing zone for the following
reasons:
1. The mathematical model used to define the mixing
zone was not validated. The Board, upon request
by the petitioner, can approve a Compliance Plan
in which corrective actions are committed to take
place within the shortest time possible to obtain
the necessary validation. The Board can maintain
in force the Interim Authorization while the
conditions incorporated in the mentioned plan are
executed.
2. The petitioner's failure to fully disclose all
relevant facts in the authorization application
or renewal, or the petitioner's misrepresentation
of any relevant facts during the mixing zone
evaluation or during the validation process.
3. Non-compliance with any applicable provision in
article 5 of this Regulation.
A. Changes in the conditions under which the mixing
zone was approved, including, but not limited to,
discharge flow, effluent characteristics, and the
discharge system, as originally approved by the
Board.
5. There is an imminent threat to human health or
the environment.
5.14 Procedures for Revoking Mixing Zone Authori-
zations - If there are reasons to revoke a mixing zone
authorization as specified in Section 5.11, the Board
shall notify the person to whom the authorization was
granted indicating the intention of revoking the
authorization by means of a Show Cause Order. The
procedures to follow are those specified in EQB's
Internal Regulations for Administrative Hearings.
Notwithstanding the foregoing, the Board may
immediately revoke a mixing zone authorization without
previous notice, nor the opportunity of hearings if
there is an imminent threat to human health or the
environment.
5.15 Ocean Outfall and Diffuser Requirements - The
ocean outfalls and the diffusers shall be designed,
constructed and operated in accordance to best
engineering practices. When the proposed discharge
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system incorporates said technology, the petitioner
shall include in the mixing zone application,
information regarding the following:
1. Length and diameter of the diffuser.
1. Number, diameter and the diffuser ports
distribution.
'3. Maximum and minimum exit velocities in the
diffuser ports.
4. Measures to avoid the intrusion of surrounding
waters within the diffuser.
5. The Froude number used for the design of the
ports.
6. Outfall diameter and average value of the
transversal area that will be full under normal
operating conditions.
7. Minimum and maximum design velocities for the
outfall flow.
8. Any other design detail that could contribute to
optimize the discharge's fast dilution.
5.16 Compliance Plans - As requested by the
petitioner, the Board may consider and approve
Compliance Plans for existing discharges that do not
comply with the requirements specified in this
Regulation. Such plans shall indicate the way in
which those discharges will be made to comply, using
the best engineering practices and within the shortest
period of time, which will not exceed the NPDES permit
expiration date, but under no circumstances should
exceed more than three (3) years.
Trust Territory (1) General - The water quality criteria in Part 6(B)
shall apply within a mixing zone unless specific
alternative criteria have been approved by the Board
and concurred upon by the U.S. Environmental
Protection Agency. Mixing zones will not be granted
in lieu of reasonable control measures to reduce point
source pollutant discharges but will be granted to
compliment the application of reasonable controls.
(2) New Discharges - All new point source discharges
beginning after the effective date of these
regulations shall apply to the Board for a zone of
mixing on forms supplied by the Board, unless it can
be demonstrated that the point of discharge will meet
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the applicable water quality standards at the point of
discharge. It shall be a violation of these standards
for any person to commence discharging from a new
point source without either obtaining a valid mixing
zone from the Board or demonstrating to the Board's
satisfaction that a mixing zone is not required.
Any application for a zone of mixing must contain the
following:
(a) Evidence that a NPDES permit has been applied for
and will be obtained.
(b) A description of the waste to be discharged
including flow rate and pollutant types and
quantities.
(c) The location of the discharge and a description
of the disposal methods (e.g., outfall size,
number and type of diffusers, etc.).
(d) Evidence that the concentration of toxic
substances present in the discharge will not
violate water quality standards for toxic
substances.
(e) Identification of those substances for which the
mixing zone is required.
(f) Either:
A certification for each substance
identified in (e) above, that after initial
mixing, the concentration of the substance
will not exceed the applicable water quality
standard. The following equation shall be
used to calculate concentration after
initial dilution:
Cf = Concentration after mixing
Ce = Effluent concentration (instantaneous
maximum)
Cb = Background concentration
DI = Dilution ratio
ii. A description of the shape, size, volume and
other physical characteristics of the mixing
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zone required for each pollutant in the
discharge so that the applicable water
quality standards will be achieved at the
boundary of the zone. The mixing zone shall
be defined under those conditions of tide,
wind, runoff, density stratification and
discharge that vould require the largest
zone of mixing.
iii. Method (i) above should be used over method
(ii) whenever possible.
(g) Evidence that the basic water quality standards
(Part 6(a)) will not be violated within the
mixing zone.
(h) A proposed schedule of effluent and receiving
water monitoring to determine compliance with the
proposed mixing zone.
(3) Existing Discharges - All existing point source
discharges must apply to the Board for a mixing zone
or demonstrate that one is not required within
eighteen (18) months of the effective date of these
standards. The application procedure is identical to
the one for new sources.
(4) It shall be in violation of these standards for
any person to knowingly present false or misleading
information to the Board in an application for a
mixing zone.
(5) Determination by the Board
(a) Review of Application
In reviewing a mixing zone application, the Board
will consider:
i. Present and anticipated uses of the water
body.
ii. Whether an adequate zone of passage will
exist for the movement of aquatic life.
iii. The proximity of other mixing zones.
iv. Whether the granting of a mixing zone is in
the public interest.
The Board may request additional information
from the applicant that is deemed relevant
to the Board's determination.
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(b) Issuance of Mixing Zone
The Board may either approve, conditionally
approve or disapprove a mixing zone application
after conducting a public hearing on the
application. The Board will notify the applicant
in writing of its determination after receiving
EPA concurrence. The notification will include,
but is not limited to:
i. The duration of the mixing zone.
ii. Any conditions placed upon the Board's
approval of the application. Conditions may
include:
(a) Effluent and receiving water monitoring
and reporting requirements.
(b) A timetable for the reduction
elimination of the discharge.
or
iii. The parameters for which the mixing zone is
being granted and the alternative criteria
that will apply within the mixing zone.
If the Board disapproves a mixing zone
application, it will notify the applicant of
the reasons for the disapproval.
Virgin Islands
57
The need, location, size and depth of the mixing zones
in surface waters and estuaries shall be established
according to the following mixing zone criteria and
boundaries.
(a) Mixing Zone Criteria:
1. Mixing zones shall be provided solely of mixing.
Mixing must be accomplished as quickly as
possible through the use of devices which insure
that the waste is mixed with the allocated
dilution water in the smallest practicable area.
2. For the protection of aquatic life resources, the
mixing zones, must not be used for or be
considered as, a substitute for waste treatment
facilities.
3. At the boundary of the mixing zone the water
should comply with all the water quality
standards set forth for its classification. If,
after complete mixing with the available dilution
water, these requirements are not met, the
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effluent must be adequately pretreated until
standards are met.
4. No conditions shall be permitted to exist within
the mixing zone, (A) that are rapidly lethal
(i.e. exceed the 96-hour median tolerance limit)
to locally important and desirable indigenous
aquatic life, (B) that prohibit planktonic
organisms from being carried through the mixing
zone. These organisms vill be exposed to its
conditions only for the period of time required
to drift through the mixing zone and will survive
without undue damage or stress while they are
passing through.
5. Maximum vertical dispersion of waste water
discharge flow shall be provided for in the
mixing zone.
6. Mixing zones shall not intersect spawning or
nursery areas, migratory routes, water intakes or
mouths of rivers.
7. Suspended solids in waste waters being discharged
shall not settle in measurable amounts in the
mixing zones.
(b) Mixing Zone Boundaries:
1. The mixing zone must be located in such manner as
to allow at all times, passageways for the
movement on drift of the biota (pelagic or
invertebrate organisms). The width of the mixing
zone and the volume of flow in it shall depend on
and will be determined by the nature of the water
current and/or the estuary. The area, depth, and
volume of the flow must be sufficient to provide
a usable and desirable passageway for fish and
other aquatic organisms.
2. The passageway must contain at least 75 percent
of the cross sectional area and/or volume of flow
of the estuary, and should extend to at least 50%
of the width.
3. A mixing zone shall not overlap with an adjacent
mixing zone.
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