United States
Environmental Protection Region 10 EPA 910-B-03-002
Agency Office of Water April 2003
&EPA EPA Region 10 Guidance
For Pacific Northwest State
and Tribal Temperature
Water Quality Standards
-------
-------
Acknowledgments
The EPA Region 10 Guidance for Pacific Northwest State and Tribal Temperature Water
Quality Standards is a product of a three year interagency effort involving the Idaho Department
of Environmental Quality, Oregon Department of Environmental Quality, Washington
Department of Ecology, National Marine Fisheries Service, U.S. Fish and Wildlife Service, Nez
Perce Tribe, Columbia River Inter-Tribal Fish Commission (representing its four governing
tribes: the Nez Perce Tribe, Confederated Tribes of the Umatilla Indian Reservation,
Confederated Tribes and Bands of the Yakima Nation, and the Confederated Tribes of the Warm
Springs Reservation of Oregon), and EPA Region 10.
John Palmer of EPA Region 10's Office of Water chaired an interagency policy workgroup and
was the principal author of the guidance with assistance from the following workgroup members:
Randy Smith and Dru Keenan of EPA Region 10's Office of Water; Dave Mabe and Don Essig
of the Idaho Department of Environmental Quality; Mark Charles and Debra Sturdevant of the
Oregon Department of Environmental Quality; Dave Peeler and Mark Hicks of the Washington
Department of Ecology; Russ Strach, Jeff Lockwood, and Robert Anderson of the National
Marine Fisheries Service; Stephen Zylstra, Elizabeth Materna, and Shelley Spalding of the U.S.
Fish and Wildlife Service; Barbara Inyan of the Nez Perce Tribe, and Patti Howard and Dale
McCullough of the Columbia River Inter-Tribal Fish Commission.
The scientific and technical foundation for the guidance, as reflected in six scientific papers, was
developed by an interagency technical workgroup led by Dru Keenan and Geoff Poole of the
EPA Region 10. Other members of the technical workgroup were: Chris Mebane and Don Essig
of the Idaho Department of Environmental Quality; Debra Sturdevant of the Oregon Department
of Environmental Quality; Mark Hicks of the Washington Department of Ecology; Jeff
Lockwood of the National Marine Fisheries Service; Elizabeth Materna and Shelley Spalding of
the U.S. Fish and Wildlife Services; Dale McCullough of the Columbia River Inter-Tribal Fish
Commission; John McMillan of the Hoh Tribe; Jason Dunham of the U.S. Forest Service, and
John Risley and Sally Sauter of the U. S. Geological Service. Marianne Deppman of EPA
Region 10 provided organizational and facilitation support for the technical workgroup.
Two independent scientific peer review panels were convened to provide comment on various
aspects of the guidance and the scientific issue papers. The peer review scientists are identified
in the peer review reports, which are referenced in Section X of the guidance.
EPA issued two public review drafts, the first in October, 2001 and the second in October, 2002,
and received valuable comments from the public that helped shape the guidance.
An EPA review team consisting of the following individuals also provided valuable input into
the development of the guidance: Carol Ann Siciliano of EPA's Office of General Counsel; Cara
Lalley, Lars Wilcut, and Jim Keating of EPA's Office of Water; Adrianne Allen, Keith Cohon,
and Rich McAllister of EPA Region 10's Office of Regional Counsel; Paula Vanhaagen, Marcia
Lagerloef, Kerianne Gardner, Robert Robichaud, Kristine Koch, Kathy Collins, Patty McGrath,
-------
Mike Lidgard, Christine Psyk, Jannine Jennings, Rick Parkin, and Jayne Carlin of EPA Region
10's Office of Water; Ben Cope and Peter Leinenbach of EPA Region 10's Office of
Environmental Assessment; and Derek Poon and Steve Ralph of EPA Region 10's Office of
Ecosystems and Communities.
EPA gratefully acknowledges the above individuals, members of the peer review panels, and the
public for their participation and valuable input into the development of the guidance. Although
members of the organizations listed above contributed to the development of the guidance, this
guidance ultimately reflects the views of EPA.
This report should be cited as:
U.S. Environmental Protection Agency. 2003. EPA Region 10 Guidance for Pacific Northwest
State and Tribal Temperature Water Quality Standards. EPA 910-B-03-002. Region 10 Office
of Water, Seattle, WA.
To obtain a copy of this guidance free of charge, contact:
EPA Region 10's Public Environmental Resource Center
Phone: 1-800-424-4372
This guidance, along with other supporting material, is available on the internet at:
www. epa. gov/r 1 Oearth/temperature .htm
-------
Forward
The goal of the Clean Water Act (CWA) is to restore and maintain the chemical, physical, and
biological integrity of the Nation's waters and, where attainable, to achieve water quality that
provides for the protection and propagation offish, shellfish, and wildlife and recreation in and
on the water. As a means of meeting this goal, section 303(c) of the CWA requires States and
authorized Tribes to adopt water quality standards (WQS) and requires the U.S. Environmental
Protection Agency (EPA) to approve or disapprove those standards.
At this time, many Pacific Northwest salmonid species are listed as threatened or endangered
under the Endangered Species Act (ESA). As a result, the ESA requires that EPA must insure
that its approval of a State or Tribal WQS is not likely to jeopardize the continued existence of
any endangered or threatened species or result in the destruction or adverse modification of their
critical habitat.
Water temperature is a critical aspect of the freshwater habitat of Pacific Northwest salmonids.
Those salmonids listed as threatened or endangered under the ESA and other coldwater
salmonids need cold water to survive. Human-caused increases in river water temperatures have
been identified as a factor in the decline of ESA-listed salmonids in the Pacific Northwest. State
and Tribal temperature WQS can play an important role in helping to maintain and restore water
temperatures to protect Pacific Northwest salmonids and aid in their recovery. For these reasons,
EPA in collaboration with others, developed this guidance to better describe appropriate water
temperatures to protect Pacific Northwest salmonids.
The EPA Region 10 Guidance for Pacific Northwest State and Tribal Temperature Water
Quality Standards is intended to assist States and Tribes to adopt temperature WQS that EPA
can approve consistent with its obligations under the Clean Water Act (CWA) and the
Endangered Species Act (ESA). This guidance document, however, does not substitute for
applicable legal requirements; nor is it a regulation itself. Thus, it does not impose legally
binding requirements on any party, including EPA, other federal agencies, the states, or the
regulated community. Comments and suggestions from readers are encouraged and will be used
to help improve the available guidance as EPA continues to build experience and understanding
of water temperature and salmonids.
L. John lani, Regional Administrator
U.S. EPA Region 10
Seattle, WA 98101
-------
-------
Table of Contents
Forward iii
I. Introduction 1
II. Regulatory Background 2
III. Relationship of Guidance to EPA's 304(a) Criteria for Water Temperature 4
IV. Water Temperature and Salmonids 5
IV. 1. Importance of Temperature for Salmonids 5
IV.2. Human Activities That Can Contribute to Excess Warming of
Rivers and Streams 6
IV.3. Human-Caused Elevated Water Temperatures As A Factor in
Salmonid Decline 7
IV.4. General Life Histories of Salmonids and When Human-Caused
Elevated Water Temperatures May Be A Problem 12
V. EPA Region 10 Recommendations for Pacific Northwest State and Tribal
Temperature WQS 15
V. 1. Coldwater Salmonid Uses and Numeric Criteria to Protect Those Use 15
V.2. Provision to Protect Water Temperatures that are Currently Colder than
the Numeric Criteria 32
V.3. Provisions to Protect Salmonids from Thermal Plume Impacts 33
VI. Approaches to Address Situations Where the Numeric Criteria are Unattainable or
Inappropriate 34
VI. 1. Alternative Criteria 34
VI.2. Use of a State's or Tribe's "Natural Background" Provisions 36
VI.3. Overview of Methods to Estimate Natural Background Temperatures 39
VII. Using EPA's Guidance to Change Salmonid Use Designations 42
VIII. Temperature Limits for NPDES Sources 42
IX. The Role of Temperature WQS in Protecting and Recovering ESA-Listed
Salmonids and Examples of Actions to Restore Suitable Water Temperatures 44
X. References 46
-------
-------
EPA Region 10 Guidance
for
Pacific Northwest State and Tribal Temperature Water Quality Standards
I. Introduction
This guidance describes an approach that EPA Region 10 encourages States and authorized
Tribes (Tribes) in the Pacific Northwest to use when adopting temperature water quality
standards (WQS) to protect coldwater salmonids. The recommendations in this guidance are
intended to assist States and Tribes to adopt temperature WQS that EPA can approve consistent
with its obligations under the Clean Water Act (CWA) and the Endangered Species Act (ESA).
This guidance specifically addresses the following coldwater salmonid species in the Pacific
Northwest: chinook, coho, sockeye, chum, and pink salmon; steelhead and coastal cutthroat
trout; and bull trout. The information provided in this guidance may also be useful for States and
Tribes to protect other coldwater salmonid species that have similar temperature tolerances but
are not explicitly addressed in this guidance.
This guidance provides recommendations to States and Tribes on how they can designate uses
and establish temperature numeric criteria for waterbodies that help meet the goal of "protection
and propagation offish, shellfish, and wildlife" in section 101(a)(2) of the CWA. States or
Tribes that choose to adopt new or revised temperature WQS must submit those standards to
EPA for review and approval or disapproval. CWA section 303(c)(2)(A). EPA expects to be
able to expedite its review of revised temperature standards that follow the recommendations in
this guidance. States and Tribes that choose to follow the recommendations in this guidance,
particularly those described in Section V, may wish to reference this guidance when submitting
new or revised salmonid use designations and supporting criteria to EPA for approval.
EPA action on State and Tribal WQS that are consistent with this guidance is expected to be
significantly expedited because the scientific rationale in support of the State and Tribal WQS
would in large part already be described and supported by EPA, and by the National Marine
Fisheries Service and the U.S. Fish and Wildlife Service (the Services). However, because this
is a guidance document and not a regulation, EPA cannot bind itself to approve a WQS
submission that follows the recommendation of this guidance. Furthermore, the Services cannot
bind themselves to future consultation determinations (i.e., a "no jeopardy" determination) under
the ESA. So even though EPA expects the review process to be significantly expedited if this
guidance is followed, EPA and the Services must still examine every WQS submission on a
case-by-case basis, taking into consideration any public comments received or other new
information.
It is also important to note that this guidance does not preclude States or Tribes from adopting
temperature WQS different from those described here. EPA would approve any temperature
-------
WQS that it determines are consistent with the applicable requirements of the CWA and its
obligations under the ESA. Because this guidance reflects EPA's current analysis of temperature
considerations for Pacific Northwest salmonid species, EPA intends to consider it when
reviewing Pacific Northwest State and Tribal temperature WQS or promulgating federal
temperature WQS in Idaho, Oregon, or Washington.
Temperature WQS are viewed by EPA and the Services as an important tool for the protection
and recovery of threatened and endangered salmonid species in the Pacific Northwest. Attaining
criteria and protecting existing cold temperatures for waters used by these salmonids will help
maintain and improve their habitat and aid in their recovery. Meeting temperature WQS,
however, should be viewed as part of the larger fish recovery efforts to restore habitat.
Wherever practicable, implementation actions to restore water temperatures should be integrated
with implementation actions to improve habitat in general, and should be targeted first toward
those reaches within a basin that will provide the biggest benefit to the fish. It should also be
noted that the actions needed to improve water temperatures are, in many cases, the same as
those needed to improve other fish habitat features. For example, restoring a stream's riparian
vegetation can reduce water temperature as well as reduce sediment erosion, provide over bank
micro-habitat, and add fallen wood to the river that over time creates pools and a more diverse
stream habitat preferred by salmonids.
This guidance was developed with the assistance of representatives of the Pacific Northwest
States, the Services, and the Columbia River Inter-Tribal Fish Commission (CRITFC) Tribes.
As part of developing this guidance, EPA, with the assistance of technical experts from Federal,
State, and Tribal organizations, developed five technical issue papers and a technical synthesis
report summarizing technical issues related to water temperature and salmonids. These reports
represent the technical foundation of this guidance and summarize the latest literature related to
temperature and salmonids. See Section X, References, at the end of this guidance for a list of
these technical papers.
II. Regulatory Background
The goal of the CWA is to restore and maintain the chemical, physical, and biological integrity
of the Nation's waters and, where attainable, to achieve water quality that provides for the
protection and propagation offish, shellfish, and wildlife and recreation in and on the water. See
CWA section 101(a)(2). As a means of meeting this goal, section 303(c) of the CWA requires
States and Tribes to adopt WQS that include designated uses and water quality criteria to protect
those designated uses. In addition, Federal WQS regulations require States and Tribes to adopt a
statewide antidegradation policy and identify methods to implement such policy. See 40 C.F.R.
§ 131.12. States and Tribes may also adopt into their standards policies generally affecting the
application and implementation of WQS, such as mixing zones and variances. See 40 C.F.R. §
131.13.
-------
EPA is required to approve or disapprove new or revised State and Tribal WQS under section
303(c) of the CWA to ensure they are consistent with the requirements of the CWA and EPA's
implementing regulations. See CWA section 303(c)(3). New or revised State and Tribal WQS
are not in effect for CWA purposes until they are approved by EPA. If EPA disapproves a new
or revised WQS submitted by a State or Tribe, or if the EPA Administrator determines that a
new or revised WQS is necessary to meet the requirements of the CWA, EPA must propose and
promulgate appropriate WQS itself, unless appropriate changes are made by the State or Tribe.
See CWA section 303(c)(4).
Where EPA determines that its approval of State or Tribal WQS may affect threatened or
endangered species or their critical habitat, the approval action is subject to the procedural and
substantive requirements of section 7(a)(2) of the ESA. Section 7(a)(2) of the ESA requires EPA
to ensure, in consultation with the Service(s), that any action it takes is not likely to jeopardize
the continued existence of any endangered or threatened species or result in the destruction or
adverse modification of critical habitat. Under the ESA regulations, such consultations can be
concluded informally where EPA determines that its action is not likely to adversely affect listed
species or critical habitat, and where the Service(s) concur with that finding in writing. See 50
C.F.R. § 402.13. Where EPA does not make such a determination, or where the Service(s) do
not concur in writing, the ESA regulations require EPA to engage in formal consultation, which
results in the issuance of a biological opinion by the Service(s). See 50 C.F.R. § 402.14. If the
Service(s) anticipate that "take" will occur as a result of the action, the opinion in most cases
will include required reasonable and prudent measures and associated terms and conditions to
minimize such take, along with an incidental take statement providing EPA legal protection from
ESA section 9 take liability for its approval action. See 50 C.F.R. § 402.14(1). Section 7(a)(l) of
the ESA requires EPA to use its authorities to carry out programs for the conservation of
endangered and threatened species. The ESA, however, does not expand EPA's authorities
under the CWA. EPA approval or disapproval decisions regarding State and Tribal WQS must
be authorized by the CWA and EPA's implementing regulations.
In addition, EPA has a federal trust relationship with federally recognized Pacific Northwest
tribes. In the Pacific Northwest, federal courts have affirmed that certain tribes reserved through
treaty the right to fish at all usual and accustomed fishing places and to take a fair share of the
fish destined to pass through such areas. See Puyallup Tribe v. Department of Game. 391 U.S.
392 (1968); Washington v. Passenger Fishing Vessel. 443 U.S. 658 (1979); United States v.
Winans. 198 U.S. 371 (1905). EPA's approval of a State or Tribal WQS, or promulgation of its
own WQS, may impact the habitat that supports the treaty fish. EPA has a responsibility to
ensure that its WQS actions do not violate treaty fishing rights.
Water Quality Standards set the water quality goals for specific waterbodies and serve as a
regulatory basis for other programs, such as National Pollutant Discharge Elimination System
(NPDES) permits, listings of impaired water bodies under CWA section 303(d), and total
maximum daily loads (TMDLs). In general, NPDES permits contain effluent limitations to meet
WQS; section 303(d) lists identify those water bodies where the WQS are not being met; and
TMDLs are mathematical calculations indicating the pollutant reductions needed to meet WQS.
-------
III. Relationship of Guidance to EPA's 304(a) Criteria for Water
Temperature
Under CWA section 304(a), EPA issues national criteria recommendations to guide States and
Tribes in developing their WQS. When EPA reviews a State or Tribal WQS submission for
approval under section 303(c) of the CWA, it must determine whether the adopted designated
uses and criteria are consistent with the CWA and EPA's regulations. See CWA section
303(c)(3). Specifically, 40 C.F.R § 131.11 requires States and Tribes to adopt water quality
criteria that are based on sound scientific rationale and contain sufficient parameters or
constituents to protect the designated uses. For waters with multiple use designations, the
criteria must support the most sensitive use. See 40 C.F.R. §131.1 l(a). When establishing
criteria, States should: (1) establish numerical values based on 304(a) guidance, or 304(a)
guidance modified to reflect site-specific conditions, or other scientifically defensible methods;
or (2) establish narrative criteria or criteria based upon biomonitoring methods where numerical
criteria cannot be established or to supplement numerical criteria. See 40 C.F.R. §131.1 l(b).
EPA develops its section 304(a) criteria recommendations based on a uniform methodology that
takes into account a range of species' sensitivities to pollutant loadings using certain general
assumptions; therefore, the national recommendations are generally protective of aquatic life.
However, these criteria recommendations may not be protective of all aquatic life designated
uses in all situations. It may be appropriate for States and Tribes to develop different water
quality criteria using current data concerning the species present, and taking into account site-
specific or regional conditions. EPA approval or disapproval would not depend on whether a
criterion adopted by a State or Tribe is consistent with a particular guidance document, such as
this guidance or the national 304(a) criteria recommendations, but rather on whether the State or
Tribe demonstrates that the criterion protects the most sensitive designated use, as required by
section 303(c) of the CWA and EPA's WQS regulations.
EPA's current 304(a) criteria recommendations for temperature can be found in Quality Criteria
for Water 1986, commonly known as the "gold book." The freshwater aquatic life criteria
described in this 1986 document were first established in 1977, and were not changed in the
1986 document. In general, EPA's national temperature recommendations for salmonids and
other fish consist of formulas to calculate the protective temperatures for short-term exposure
and a maximum weekly average exposure. Protective short term temperature exposure is based
on subtracting 2°C from the upper incipient lethal temperature (the temperature at which fifty
percent of the sample dies). Protective weekly average temperature exposure is based on the
optimal growth temperature plus 1/3 the difference between the optimal growth temperature and
the upper incipient lethal temperature. Using these formulas and EPA data for coho and sockeye
salmon, the 1986 document calculates suggested temperature criteria for short-term exposure as
22°C (sockeye) and 24°C (coho) and a maximum weekly average exposure of 18°C for both
species.
-------
Based on extensive review of the most recent scientific studies, EPA Region 10 and the Services
believe that there are a variety of chronic and sub-lethal effects that are likely to occur to Pacific
Northwest salmonid species exposed to the maximum weekly average temperatures calculated
using the current 304(a) recommended formulas. These chronic and sub-lethal effects include
reduced juvenile growth, increased incidence of disease, reduced viability of gametes in adults
prior to spawning, increased susceptibility to predation and competition, and suppressed or
reversed smoltification. It may be possible for healthy fish populations to endure some of these
chronic impacts with little appreciable loss in population size. However, for vulnerable fish
populations, such as the endangered or threatened salmonids of the Pacific Northwest, EPA and
the Services are concerned that these chronic and sub-lethal effects can reduce the overall health
and size of the population.
For these reasons, the national assumptions made when developing the section 304(a) criteria
recommendations for temperature may not necessarily protect the vulnerable coldwater
salmonids in the Pacific Northwest. EPA Region 10, therefore, has developed this guidance to
assist Pacific Northwest States and Tribes in developing temperature criteria that protect the
coldwater salmonids in the Pacific Northwest identified above.
IV. Water Temperature and Salmonids
IV. 1. Importance of Temperature for Salmonids
Water temperatures significantly affect the distribution, health, and survival of native salmonids
in the Pacific Northwest. Since salmonids are ectothermic (cold-blooded), their survival is
dependent on external water temperatures and they will experience adverse health effects when
exposed to temperatures outside their optimal range. Salmonids have evolved and thrived under
the water temperature patterns that historically existed (i.e., prior to significant anthropogenic
impacts that altered temperature patterns) in Pacific Northwest streams and rivers. Although
evidence suggests that historical water temperatures exceeded optimal conditions for salmonids
at times during the summer months on some rivers, the temperature diversity in these unaltered
rivers provided enough cold water during the summer to allow salmonid populations as a whole
to thrive.
Pacific salmon populations have historically fluctuated dramatically due to climatic conditions,
ocean conditions, and other disturbances. High water temperatures during drought conditions
likely affected the historical abundance of salmon. In general, the increased exposure to stressful
water temperatures and the reduction of suitable habitat caused by drought conditions reduce the
abundance of salmon. Human-caused elevated water temperatures significantly increase the
magnitude, duration, and extent of thermal conditions unsuitable for salmonids.
The freshwater life histories of salmonids are closely tied to water temperatures. Cooling rivers
in the autumn serve as a signal for upstream migrations. Fall spawning is initiated when water
temperatures decrease to suitable temperatures. Eggs generally incubate over the winter or early
-------
spring when temperatures are coolest. Rising springtime water temperatures may serve as a cue
for downstream migration.
Because of the overall importance of water temperature for salmonids in the Pacific Northwest,
human-caused changes to natural temperature patterns have the potential to significantly reduce
the size of salmonid populations. Of particular concern are human activities that have led to the
excess warming of rivers and the loss of temperature diversity.
IV.2. Human Activities That Can Contribute to Excess Warming of Rivers and Streams
Rivers and streams in the Pacific Northwest naturally warm in the summer due to increased solar
radiation and warm air temperature. Human changes to the landscape have magnified the degree
of river warming, which adversely affects salmonids and reduces the number of river segments
that are thermally suitable for salmonids. Human activities can increase water temperatures by
increasing the heat load into the river, by reducing the river's capacity to absorb heat, and by
eliminating or reducing the amount of groundwater flow which moderates temperatures and
provides cold water refugia. Specific ways in which human development has caused excess
warming of rivers are presented in Issue Paper 3 and are summarized below:
1) Removal of streamside vegetation reduces the amount of shade that blocks solar
radiation and increases solar heating of streams. Examples of human activities that
reduce shade include forest harvesting, agricultural land clearing, livestock grazing, and
urban development.
2) Removal of streamside vegetation also reduces bank stability, thereby causing bank
erosion and increased sediment loading into the stream. Bank erosion and increased
sedimentation results in wider and shallower streams, which increases the stream's heat
load by increasing the surface area subject to solar radiation and heat exchange with the
air.
3) Water withdrawals from rivers for purposes such as agricultural irrigation and
urban/municipal and industrial use result in less river volume and generally remove cold
water. The temperatures of rivers with smaller volumes equilibrates faster to surrounding
air temperature, which leads to higher maximum water temperatures in the summer.
4) Water discharges from industrial facilities, wastewater treatment facilities and
irrigation return flows can add heat to rivers.
5) Channeling, straightening, or diking rivers for flood control and urban and agricultural
land development reduces or eliminates cool groundwater flow into a river that
moderates summertime river temperatures. These human actions can reduce two forms
of groundwater flow. One form is groundwater that is created during over-bank flooding
and is slowly returned to the main river channel to cool the water in the summer. A
-------
second form is water that is exchanged between the river and the riverbed (i.e. hyporheic
flow). Hyporheic flow is plentiful in fully functioning alluvial rivers systems.
6) Removal of upland vegetation and the creation of impervious surfaces associated with
urban development increases storm runoff and reduces the amount of groundwater that is
stored in the watershed and slowly filters back to the stream in the summer to cool water
temperatures.
7) Dams and their reservoirs can affect thermal patterns in a number of ways. They can
increase maximum temperatures by holding waters in reservoirs to warm, especially in
shallow areas near shore. Reservoirs, due to their increased volume of water, are more
resistant to temperature change which results in reduced diurnal temperature variation
and prolonged periods of warm water. For example, dams can delay the natural cooling
that takes place in the late summer-early fall, thereby harming late summer-fall migration
runs. Reservoirs also inundate alluvial river segments, thereby diminishing the
groundwater exchange between the river and the riverbed (i.e., hyporheic flow) that cools
the river and provides cold water refugia during the summer. Further, dams can
significantly reduce the river flow rate, thereby causing juvenile migrants to be exposed
to high temperatures for a much longer time than they would under a natural flow regime.
It should also be noted that some human development can create water temperatures colder than
an unaltered river. The most significant example of this occurs when cold water is released from
the bottom of a thermally stratified reservoir behind a dam.
IV.3. Human-Caused Elevated Water Temperature as a Factor in Salmonid Decline
Many reports issued in the past decade have described the degradation of freshwater salmonid
habitat, including human-caused elevated temperatures, as a major factor in salmonid decline.
The following provides a brief summary of some of these reports:
National Marine Fisheries Service's Listing and Status Reviews for Pacific Northwest Salmonids
The National Marine Fisheries Service (NMFS) identified habitat concerns (including alteration
of ambient stream water temperatures) as one of the factors for decline of listed west coast
steelhead (NMFS 1996), west coast chinook (NMFS 1998), and Snake River spring/summer
chinook salmon (Mathews and Waples 1991). Specific effects attributed to increased
temperatures by NMFS include increased juvenile mortality, increased susceptibility and
exposure to diseases, impaired ability to avoid predators, altered migration timing, and changes
in fish community structure that favor competitors of salmonids. NMFS included high water
temperatures among risk factors related to the listings under the ESA of the following
evolutionarily significant units (ESUs) of chinook salmon: Puget Sound, Lower Columbia
River, Snake River spring/summer, and Upper Willamette (Myers et al. 1998). NMFS also
noted high water temperatures in its analyses of risk factors related to the ESA listings of Upper
Willamette River steelhead and Ozette Lake sockeye.
7
-------
U.S. Fish and Wildife Service Listing and Status Reviews for Bull Trout
When listing bull trout in the Columbia River and Coastal-Puget Sound population segments,
USFWS identified activities such as forestry, agriculture, and hydropower that have degraded
bull trout habitat and specifically have resulted in increased stream temperatures. Bull trout are
found primarily in colder streams, although individual fish are found in larger river systems.
Water temperature above 15°C is believed to limit bull trout distribution and this may partially
explain their patchy distribution within a watershed. The strict cold water temperature needs of
bull trout make them particularly vulnerable to human activities identified by USFWS that warm
spawning and rearing waters.
Return to the River Reports by the Independent Science Group
The Independent Scientific Group is a group of scientists chartered by the Northwest Power
Planning Council to provide independent scientific advice to the Columbia River Basin Fish and
Wildlife Program. In their 1996 Return the River report (updated in 2000), they include a
section discussing the effects of elevated temperature on salmonids as part of their overall
discussion of freshwater habitats. The report states:
"Temperature is a critical habitat variable that is very much influenced by regulation of
flow and impoundments. The mainstem reservoirs are relatively shallow and heat up in
late summer causing concern for salmon survival. The lower reaches of some key
tributaries also are very warm in late summer because they are dewatered by irrigation
withdrawals. Due to the extreme importance of temperature regimes to the ecology of
salmonids in the basin, temperature information merits special attention as a key habitat
descriptor (Coutant 1999)."
"Water temperatures in the Columbia River basin have been altered by development and
are, at times, suboptimal or clearly detrimental for salmonids. High temperatures alone
can be directly lethal to both juvenile and adult salmonids in the Snake River in summer
under recent conditions based on generally accepted thermal criteria and measured
temperatures."
Oregon Coastal Salmon Restoration Initiative
The Oregon Coastal Salmon Restoration Initiative (1997) included water temperature as a factor
for decline in populations of Oregon coastal coho salmon, noting that:
"Water temperatures are too warm for salmonids in many coastal streams. Altered water
temperatures can adversely affect spawning, fry emergence, smoltification, maturation
-------
period, migratory behavior, competition with other aquatic species, growth and disease
resistance."
Summer Chum Salmon Conservation Initiative
The Summer Chum Salmon Conservation Initiative (2000) for the Hood Canal and Strait of Juan
de Fuca region listed elevated water temperature in its limiting factor analysis, noting that:
"Elevated temperatures impede adult passage, cause direct mortality, and accelerate
development during incubation leading to diminished survival in subsequent life stages."
Interior Columbia Basin Ecosystem Management Project
The aquatic habitat assessment for the Interior Columbia Basin Ecosystem Management Project
(Lee et al. 1997) indicates that:
1. Changes in riparian canopy and shading, or other factors influencing stream
temperatures, are likely to affect some, if not most, bull trout populations.
2. In desert climates, the loss of riparian canopy has been associated with elevated
water temperature and reduced redband trout abundance.
3. Loss of vegetation has resulted in stream temperatures that have far exceeded
those considered optimal for Lahontan Cutthroat Trout.
4. Water temperatures in reaches of the John Day, upper Grande Ronde, and other
basins in eastern Oregon commonly exceed the preferred ranges and often exceed
lethal temperatures for chinook salmon.
Northwest Indian Fisheries Commission - Critical Habitat Issues by Basin for Natural Chinook
Stocks in the Coastal andPuget Sound Areas of Washington State
In this report, the Northwest Indian Fisheries Commission reviewed the habitat issues for the
basins in the coastal and Puget Sound areas of Washington State, and identified elevated
temperature as a critical habitat issue in 12 out of 15 basins reviewed.
Other Basin and Watershed Studies
Numerous scientific studies of habitat and elevated water temperature impacts on salmon,
steelhead and resident native fish have been completed in the Pacific Northwest over the past
two decades. The Northwest Power Planning Council is in the process of developing habitat
assessments and restoration strategies for all the sub-basins of the Columbia River Basin. In
many of these sub-basin summaries (e.g., Okanogan, Methow, Wenatchee, Yakima, Tucannon,
Grande Ronde, Umatilla, and John Day draft summaries - see www.cbfwa.org) elevated
-------
temperatures are cited as a major factor contributing to salmonid decline. These and other
studies elsewhere in the Pacific Northwest provide a consistent view of the importance of
restoring temperatures suitable for coldwater salmonds to aid in their recovery.
One specific study worth noting is by Theurer et al. (1985) in the Tucannon River in
southeastern Washington. This study shows how human-caused changes in riparian shade and
channel morphology contributed to increased water temperatures, reduced available spawning
and rearing space, and diminished production of steelhead and chinook salmon. Using a
physically-based water temperature model, the authors concluded that approximately 24 miles of
spawning and rearing habitat had been made unusable in the lower river due to temperature
changes. If the temperatures were restored, they estimated chinook adult returns would increase
from 884 that currently exist to 2240 (near historic levels) and that chinook rearing capacity
would increase from 170,000 to 430,000. The authors state that the change in temperature
regime caused by the loss of riparian vegetation alone is sufficient to explain the reduction in
salmonid population in the Tucannon River, while noting that increased sediment input also has
played a subsidiary role.
Another similar analysis was done by Oregon Department of Environmental Quality (ODEQ,
2000) for the upper Grande Ronde River as part of their TMDL for this river. ODEQ modeling
showed that restoration of riparian shade, channel width and depth, and water flow would
drastically reduce maximum temperatures. As shown in Figure 1 (Figures 11 and 12 in ODEQ
2000), over 90% of the river currently exceeds 68°F (20°C), but with full restoration that
percentage drops to less than 5%. Similarly, the percentage of the river that exceeds 64°F
(18°C) is reduced from over 90% to less than 50% with full restoration. This represents nearly
50 additional miles that are colder than 18°C, which is a very large increase in available rearing
habitat. Although actual estimates of increased fish production were not calculated in this study,
one might expect similar results as those calculated for the Tucannon River.
Although temperature is highlighted here as a factor in the decline of native salmonid
populations, it by no means is the only factor in their decline. Certainly, degradation of habitat
unrelated to temperature (e.g., impassable barriers to spawning and rearing areas and physical
destruction or inundation of spawning grounds), fishing harvest, and hatchery operations have all
played a role in their decline. However, as described above, elevated temperatures are an
important factor in the decline of salmonids and restoring suitable temperature regimes for
salmonids is a critical element in protecting salmonid populations.
10
-------
UPPER GRANDE RONDE SUB-BASIN TMDL
Figure 11. Grande Ronde River Temperatures at Current Conditions and Site Potential
- - - - Site Potential + Masmum Potential Flow
-"Site Potential
Current Conditions
95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175
Longitudinal Distance from Mouth (Miles)
Figure 12. Percent of River Temperatures Below Specified Temperature
4- ^:
•Proportion under 68*F
E Proportion under 64"F
0 Proportion under 60*F
11
= t;
2 §
ill!
OREGON DEPARTMENT OF ENVIRONMENTAL QUALITY
APRIL, 2000
PAGE 29
Figure 1. Grande Ronde River temperature modeling using ODEQ's Heat Source Model, showing site
potential.
11
-------
IV.4. General Life Histories of Salmonids and When Human-Caused Elevated Water
Temperatures May Be a Problem
Different salmonid species have evolved to take advantage of the Pacific Northwest's cold water
environment in different ways. Each species has a unique pattern of when and where they use
the rivers, and even for a specific species this pattern of use may change from year to year. This
diversity in freshwater life history is a critical evolutionary trait that has allowed salmonids to
persist in a freshwater environment that naturally fluctuates and has natural disturbances.
Below is a general summary of the freshwater life history strategies for some of the coldwater
salmonids. This summary is intended to provide a "big picture" understanding of how each of
these fish use Pacific Northwest rivers and to highlight when and where human elevated water
temperatures have impacted these fish. As noted above, because of their life history diversity,
the discussion below may be an over-generalization for some situations. Further, because this
general discussion on fish distribution is simplified for purposes of understanding, it is not
intended to be used as a basis for salmonid use designations.
Chinook Salmon
Adult spring chinook salmon generally leave the ocean and enter Pacific Northwest rivers in the
spring (April - June) and swim upstream to hold and spawn in the mid-to-upper reaches of river
basins. Spawning generally occurs in late summer and fall (August - October). Egg and alevin
incubation extends over the winter and fry generally emerge in the early spring (March - May).
Juveniles rear in their natal streams and lower in the basin for a year, then migrate out to the
ocean the following spring. Human-caused elevated temperatures can adversely affect spring
chinook when adults hold and begin to spawn in the late-summer/early fall and throughout the
summer when juveniles rear. Human-caused elevated temperatures in these mid-to-upper
reaches can "shrink" the available habitat for adult holding/spawning and juvenile rearing
limiting spring chinook to habitat higher in the watershed.
Adult fall chinook salmon generally enter Pacific Northwest rivers in the summer (July - August)
and swim upstream to hold and spawn in the lower reaches of mainstem rivers and large
tributaries. Spawning generally occurs in the fall (October - December). For example, Snake
River fall chinook migrate past Bonneville dam from August-October and spawn in the Snake
River below Hells Canyon Dam and the lower reaches of the Clearwater, Grand Ronde, Imnaha,
and Tucannon rivers. Fry emerge from March through April and begin their downstream
migration several weeks after emergence. Downstream migration occurs mainly in the spring
under existing conditions, but may extend throughout the summer in some areas (e.g., Columbia
River). Historically, juvenile fall chinook out-migrated throughout the summer months, but
today human-caused elevated temperatures have made this impossible in some rivers (e.g.,
Yakima river). Human-caused elevated temperatures can adversely affect fall chinook in lower
river reaches during the summer months when the adults are migrating upstream and holding to
spawn and when juveniles are migrating downstream. Human-caused elevated temperatures in
the early fall may also delay spawning.
12
-------
Coho Salmon
Adult coho salmon generally enter Pacific Northwest rivers in the fall (late September through
October) and spawn in low gradient 4th and 5th order streams in fall-winter. Fry emerge in the
spring. Juvenile coho rear for 1 to 2 years prior to migrating to sea during the spring. Juvenile
coho salmon may migrate considerable distances upstream to rear in lakes or other river reaches
suitable for rearing. Coho salmon are most predominant in the rivers of the coastal mountains of
Washington and Oregon and the west-slopes of the Washington Cascades. Wild coho
populations were extirpated years ago in the Umatilla (OR), Yakima (WA), and Clearwater (ID)
rivers but they are now being re-introduced in these rivers. Human-caused elevated temperatures
can adversely affect coho salmon in the summer months when juveniles are rearing and in early
fall when adults start migrating. Human-caused elevated temperatures may render waters
unsuitable for rearing, thereby "shrinking" the amount of available habitat.
Sockeye Salmon
Adult sockeye salmon generally enter freshwater from mid summer through early fall and
migrate up to lakes and nearby tributaries to spawn in the fall. Juveniles generally rear in lakes
from 1 to 3 years, then migrate to the ocean in the spring. Pacific Northwest lakes that support
sockeye include Redfish (Idaho), Okanogan, Wenatchee, Baker, Washington, Sammamish,
Quinault, and Osoyoos. Historically, there were many other lakes in the Pacific Northwest used
by sockeye. Human-caused elevated temperatures can adversely affect sockeye adult salmon as
they migrate upstream in the mid-to-late summer.
Chum Salmon
Adult chum salmon generally enter freshwater in late-summer and the fall and spawn (October -
December) in the low reaches and side channels of major rivers just upstream from tidewater
areas. Upon emergence, juveniles begin their short migration to saltwater which generally
occurs between March and June. Juveniles will rear in estuaries for a while prior to entering the
ocean. Human-caused elevated temperatures can adversely affect adult chum salmon as they
migrate upstream in the late summer.
Pink Salmon
Adult pink salmon generally enter freshwater in late summer and spawn in the lower reaches of
large rivers in late summer and early fall. Like chum, juveniles will migrate to saltwater soon
after emerging in the late winter. Human-caused elevated temperatures can adversely affect
adult pink salmon as they migrate upstream in the late summer.
13
-------
Steelhead Trout
Adult steelhead enter Pacific Northwest rivers throughout the year, but can generally be divided
into a summer run (May - October) and a winter run (November-June). Both runs typically
spawn in the spring. Summer steelhead enter freshwater sexually immature and generally travel
greater distances to spawn than winter steelhead, which enter freshwater sexually mature (i.e.
with well-developed gonads). All steelhead runs upstream of the Dalles Dam are summer
steelhead. Fry generally emerge from May through July and juvenile steelhead will rear in the
mid-upper reaches of river basins for 1-2 years (sometimes 3 or 4 years) before migrating to the
ocean in the spring. Human-caused elevated temperatures can adversely affect steelhead in the
summer months when the juveniles are rearing in the mid-upper reaches. Human-caused
elevated temperatures may render waters unsuitable for rearing, thereby "shrinking" the amount
of available habitat. Human-caused elevated temperatures also can adversely affect summer run
adults as they migrate upstream during the summer as well as eggs and fry that incubate into July
in some watersheds.
Bull Trout
Bull trout generally are freshwater fish (although the adults of a few populations enter saltwater
estuaries). Adult bull trout generally migrate upstream in the spring and summer from their
feeding grounds (lower reaches in a basin for migrating fluvial forms or a lake for adfluvial
forms) to their spawning grounds higher in the basin. Bull trout generally spawn in September-
October, but in some watersheds spawning can occur as early as July. Bull trout have a long
incubation time with fry emergence generally from March through May. Juveniles will rear in
their natal streams for 2-4 years, then the migratory forms will migrate downstream to more
productive feeding grounds (i.e., lower river reaches or lakes) in the spring, but some fall
downstream migration has also been noted. Human-caused elevated temperatures can adversely
affect summer juvenile rearing in the upper reaches where elevated temperatures have rendered
water unsuitable for rearing, thereby "shrinking" the amount of available habitat. Adults
migrating upstream to spawn in the summer can also experience adverse effects from human-
elevated temperatures. Additionally, migratory adults can be adversely affected by the loss of
cold water refugia due to human activities.
14
-------
V. EPA Region 10 Recommendations for Pacific Northwest State and Tribal
Temperature WQS
EPA Region 10 offers the following recommendations to assist States and Tribes in adopting
temperature WQS that fully support coldwater salmonids in the Pacific Northwest. The
recommendations are intended to assist States and Tribes to adopt temperature WQS that EPA
can approve consistent with its obligations under the CWA and the ESA. As noted in Section I,
Pacific Northwest States and Tribes that adopt temperature WQS consistent with these
recommendations can expect an expedited review by EPA and the Services, subject to new data
and information that might be available to during that review.
EPA Region 10 recommends that States and Tribes adopt new or revised temperature WQS that
incorporate each of the following elements for the protection of salmonid designated uses. Each
of these elements is discussed in more detail below:
1) Coldwater Salmonid Uses and Numeric Criteria to Protect Those Uses;
2) Provisions to Protect Water Temperatures That Are Currently Colder Than the
Numeric Criteria; and
3) Provisions to Protect Salmonids from Thermal Plume Impacts.
If a State or Tribe decides to adopt new or revised temperature WQS, it is free, of course, to
adopt WQS that are different than these recommendations. EPA would evaluate these
submissions on a case-by-case basis to determine if it can approve the WQS consistent with its
obligations under the CWA and the ESA.
V.I. Coldwater Salmonid Uses and Numeric Criteria to Protect Those Uses
Tables 1 and 2 provide a summary of the important water temperature considerations for each
life stage for salmon and trout, and bull trout: spawning, egg incubation, and fry emergence;
juvenile rearing; and adult migration. Each temperature consideration and associated
temperature values noted in Tables 1 and 2 includes a reference to the relevant technical issue
papers prepared in support of this guidance (or other studies) that provide a more detailed
discussion of the supporting scientific literature. The temperatures noted in Tables 1 and 2 form
the scientific basis for EPA's recommended numeric criteria to protect coldwater salmonids in
the Pacific Northwest, which are presented in Tables 3 and 4.
V. 1 .A. Overall Context for Recommended Uses and Criteria
In addition to Tables 1 and 2, there are a number of other general factors that EPA considered in
recommending coldwater salmonid uses and numeric criteria to protect those uses. These factors
15
-------
Table 1 - Summary of Temperature Considerations For Salmon and Trout Life Stages
Life
Stage
Temperature
Consideration
Temperature
&Unit
Reference
Spawning and
Egg
Incubation
Temp. Range at which
Spawning is Most Frequently
Observed in the Field
* Egg Incubation Studies
- Results in Good Survival
-Optimal Range
*Reduced Viability of Gametes
in Holding Adults
4 - 14°C (daily avg)
4 - 12°C (constant)
6 - 10°C (constant)
> 13°C (constant)
Issue Paper 1; pp 17-18
Issue Paper 5; p 81
Issue Paper 5; p 16
Issue Paper 5; pp 16 and 75
Juvenile
Rearing
*Lethal Temp. (1 Week
Exposure)
*Optimal Growth
- unlimited food
- limited food
*Rearing Preference Temp, in
Lab and Field Studies
* Impairment to Smoltification
* Impairment to Steelhead
Smoltification
*Disease Risk (lab studies)
-High
- Elevated
- Minimized
23 - 26°C (constant)
13 - 20°C (constant)
10 - 16°C (constant)
10 - 17°C (constant)
< 18°C (7DADM)
12 - 15°C (constant)
> 12°C (constant)
> 18 - 20°C (constant)
14 - 17°C (constant)
12 - 13°C (constant)
Issue Paper 5; pp 12, 14
(Table 4), 17, and 83-84
Issue Paper 5; pp 3-6 (Table
1), and 38-56
Issue Paper 1; p 4 (Table 2).
Welsh etal. 2001.
Issue Paper 5; pp 7 and 57-65
Issue Paper 5; pp 7 and 57-65
Issue Paper 4, pp 12 - 23
Adult
Migration
*Lethal Temp. (1 Week
Exposure)
*Migration Blockage and
Migration Delay
*Disease Risk (lab studies)
-High
- Elevated
- Minimized
* Adult Swimming Performance
- Reduced
- Optimal
* Overall Reduction in
Migration Fitness due to
Cumulative Stresses
21-22°C (constant)
21-22°C (average)
> 18 - 20°C (constant)
14 - 17°C (constant)
12- 13°C (constant)
> 20°C (constant)
15 - 19°C (constant)
> 17-18°C (prolonged
exposures)
Issue Paper 5; pp 17, 83 - 87
Issue Paper 5; pp 9, 10, 72-74.
Issue Paper 1; pp 15 - 16
Issue Paper 4; pp 12 - 23
Issue Paper 5; pp 8, 9, 13, 65
-71
Issue Paper 5; p 74
16
-------
Table 2 - Summary of Temperature Considerations For Bull Trout Life Stages
Life Temperature Temperature
Stage Consideration & Unit Reference
Spawning and
Egg
Incubation
Juvenile
Rearing
* Spawning Initiation
Temp, at which Peak
Spawning Occurs
*Optimal Temp, for Egg
Incubation
* Substantially Reduced Egg
Survival and Size
*Lethal Temp. (1 week
exposure)
*Optimal Growth
- unlimited food
- limited food
*Highest Probability to occur in
the field
* Competition Disadvantage
< 9°C (constant)
< 7°C (constant)
2 - 6°C (constant)
6 - 8°C (constant)
22 - 23 °C (constant)
12 - 16 °C (constant)
8 - 12°C (constant)
12 - 13 °C (daily
maximum)
>12°C (constant)
Issue Paper 5 ;pp 88-91
Issue Paper 5 ;pp 88-91
Issue Paper 5 ;pp 18, 88-91
Issue Paper 5 ;pp 18, 88-91
Issue Paper 5; p 18
Issue Paper 5; p 90. Selong
etal2001. Bull trout peer
review, 2002.
Issue Paper 5; p 90. Issue
Paper 1; p 4 (Table 2).
Dunham etal., 2001. Bull
trout peer review, 2002.
Issue Paper 1; pp 21- 23. Bull
trout peer review, 2002.
and EPA's recommended approach for considering these factors (described below) provide the
overall context for EPA's salmonid use and criteria recommendations.
Coldwater Salmonid Uses
Coldwater salmonids are considered a sensitive aquatic life species with regard to water
temperatures and are a general indicator species of good aquatic health. EPA, therefore, believes
it is appropriate for States and Tribes in the Pacific Northwest to focus on coldwater salmonids
when establishing temperature criteria to support aquatic life.
Under EPA's WQS regulations, States and Tribes must adopt appropriate uses and set
criteria to protect those uses. See 40 C.F.R § 131.10(a). Because Pacific Northwest salmonids
have multiple freshwater life stages with differing temperature tolerances, it is generally
appropriate to designate uses based on life stages. In addition, EPA's WQS regulations allow
States and Tribes to adopt seasonal uses where a particular use applies for only a portion of the
17
-------
year. See 40 C.F.R § 131.10(f). EPA's recommended approach is for States and Tribes to
utilize both of these use designation options in order to more precisely describe where and when
the different coldwater salmonid uses occur.
In this guidance, EPA recommends seven coldwater salmonid uses (see Tables 3 and 4). Four
uses apply to the summer maximum temperature condition and three apply to specific locations
and times for other times of the year (except for some instances when these uses may apply
during the period of summer maximum temperatures).
Focus on Summer Maximum Conditions
In general, increased summertime temperatures due to human activities are the greatest water
temperature concern for salmonids in the Pacific Northwest, although temperatures in the late
spring and early fall are also a concern in some areas. EPA therefore believes it is appropriate
that temperature criteria focus on the summer maximum conditions to protect the coldwater
salmonid uses that occur then. Generally, improving river conditions to reduce summer
maximum temperatures will also reduce temperatures throughout the summer and in the late
spring and early fall (i.e., shift the seasonal temperature profile downward). Thus, the data
indicate that, because of the natural annual temperature regime, providing protective
temperatures during the summer maximum period will in many areas provide protective
temperatures for more temperature sensitive uses that occur other times of the year.
In some areas, however, more temperature-sensitive salmonid uses (e.g., spawning, egg
incubation, and steelhead smoltification) that occur in the spring-early summer or late summer-
fall may not be protected by meeting the summer maximum criterion. Thus, in addition to
summer maximum criteria, EPA also recommends criteria be adopted to protect these more
temperature-sensitive uses when and where they occur. Doing so provides an added degree of
protection for those situations where control of summer maximum temperatures is inadequate to
protect these more temperature-sensitive uses. An additional reason for having these seasonal
uses is to provide protection for rivers that are flow-regulated, which can alter the natural annual
temperature pattern.
In recommending protective summer maximum criteria, EPA took into consideration that
meeting a criterion during the warmest period of the summer (e.g., warmest week) will result in
cooler temperatures during other times in the summer. The duration of exposure to near summer
maximum conditions, however, can vary from one to two weeks in some areas to over a month
in other areas.
Optimal, Harmful, and Lethal Temperatures for Salmonids
Each salmonid life stage has an optimal temperature range. Physiological optimum temperatures
are those where physiological functions (e.g., growth, swimming, heart performance) are
optimized. These temperatures are generally determined in laboratory experiments. Ecological
optimum temperatures are those where fish do best in the natural environment considering food
18
-------
availability, competition, predation, and fluctuating temperatures. Both are important
considerations when establishing numeric criteria. Exposure to temperatures above the optimal
range results in increased severity of harmful effects, often referred to as sub-lethal or chronic
effects (e.g., decreased juvenile growth which results in smaller, more vulnerable fish; increased
susceptibility to disease which can lead to mortality; and decreased ability to compete and avoid
predation), as temperatures rise until at some point they become lethal (See Table 1 and 2).
Water temperatures below the optimal range also cause sub-lethal effects (e.g., decreased
growth); however, this is generally a natural condition (with the exception of cold water releases
from a storage dam) and is not the focus of this guidance.
When determining the optimal range for bull trout and salmon/trout juvenile rearing, EPA
looked at both laboratory and field data and considered both physiological and ecological
aspects. Optimal growth under limited food rations in laboratory experiments, preference
temperatures in laboratory experiments where fish select between a gradient of temperatures, and
field studies on where rearing predominately occurs are three independent lines of evidence
indicating the optimal temperature range for rearing in the natural environment. As highlighted
in Tables 1 and 2 (and shown in detail in the technical issue papers) these three lines of evidence
show very consistent results, with the optimal range between 8 - 12°C for bull trout juvenile
rearing and between 10 - 16°C for salmon and trout juvenile rearing.
Use of the 7 Day Average of the Daily Maximum (7DADM) Unit of Measurement
The recommended metric for all of the following criteria is the maximum 7 day average of the
daily maxima (7DADM). This metric is recommended because it describes the maximum
temperatures in a stream, but is not overly influenced by the maximum temperature of a single
day. Thus, it reflects an average of maximum temperatures that fish are exposed to over a week-
long period. Since this metric is oriented to daily maximum temperatures, it can be used to
protect against acute effects, such as lethality and migration blockage conditions.
This metric can also be used to protect against sub-lethal or chronic effects (e.g., temperature
effects on growth, disease, smoltification, and competition), but the resultant cumulative thermal
exposure fish experience over the course of a week or more needs to be considered when
selecting a 7DADM value to protect against these effects. EPA's general conclusion from
studies on fluctuating temperature regimes (which is what fish generally experience in rivers) is
that fluctuating temperatures increase juvenile growth rates when mean temperatures are colder
than the optimal growth temperature derived from constant temperature studies, but will reduce
growth when the mean temperature exceeds the optimal growth temperature (see Issue Paper 5,
pages 51-56). When the mean temperature is above the optimal growth temperature, the "mid-
point" temperature between the mean and the maximum is the "equivalent" constant
temperature. This "equivalent" constant temperature then can be directly compared to laboratory
studies done at constant temperatures. For example, a river with a 7DADM value of 18°C and a
15°C weekly mean temperature (i.e., diurnal variation of ± 3°C) will be roughly equivalent to a
constant laboratory study temperature of 16.5°C (mid-point between 15°C and 18°C). Thus,
19
-------
both maximum and mean temperatures are important when determining a 7DADM value that is
protective against sub-lethal/chronic temperature effects.
For many rivers and streams in the Pacific Northwest, the 7DADM temperature is about 3°C
higher than the weekly mean (Dunham, et al. 2001; Chapman, 2002). Thus, when considering
what 7DADM temperature value protects against chronic effects, EPA started with the constant
temperatures that scientific studies indicate would be protective against chronic effects and
added 1-2°C degrees (see Table 1 for summary of studies done under constant temperatures).
For bull trout waters, EPA started with the constant temperatures that scientific studies indicate
would be protective for chronic effects and added about 0.5°C because bull trout waters typically
have less diurnal variation. Following this general procedure takes into account the maximum
and mean temperature (i.e., reflects a "mid-point") when protecting for growth and other sub-
lethal effects.
It is important to note that there are also studies that analyzed sub-lethal effects based on
maximum or 7DADM temperature values which need not be translated for purposes of
determining protective 7DADM temperatures. For example, there are field studies that assess
probability of occurrence or density of a specific species based on maximum temperatures (Issue
Paper 1, Haas (2001), Welsh et al. (2001)). These field studies represent an independent line of
evidence for defining upper optimal temperature thresholds, which complements laboratory
studies.
It is also important to note that there are confounding variables that are difficult to account for
but are important to recognize. For instance, the amount of diurnal variation in rivers and
streams in the Pacific Northwest varies considerably; therefore, the difference between the
7DADM and the weekly mean will vary. The difference between the 7DADM temperature and
the weekly mean may be less than 1°C for rivers with little diurnal variation and as high as 9°C
for streams with high diurnal variation (Dunham et al., 2001). Another variable is food
availability. The temperature for which there is optimal juvenile growth depends on the food
supply. Optimal growth temperatures under limited food supply are lower than those under
unlimited/satiated food supply. Generally, EPA believes that laboratory studies under limited
food availability are most reflective of environmental conditions fish typically experience.
However, there are likely situations where food is abundant, with the result that optimal growth
temperatures would be higher. Thus, a particular 7DADM numeric criteria will be more
protective in situations where there is high diurnal variation and/or abundant food and will be
less protective in situations where there is low diurnal variation and limited food.
Unusually Warm Conditions
In order to have criteria that protect designated uses under the CWA, EPA expects that the
criteria would need to apply nearly all the time. However, EPA believes it is reasonable for a
State or Tribe to decide not to apply the numeric temperature criteria during unusually warm
conditions for purposes of determining if a waterbody is attaining criteria. One possible way for
a State or Tribe to do this would be to explain in its WQS that it will determine attainment with
20
-------
the numeric temperature criterion based on the 90th percentile of the yearly maximum 7DADM
values calculated from a yearly set of values of 10 years or more. Thus, generally speaking, the
numeric criteria would apply 9 out 10 years, or all but the hottest year. Another way may be to
exclude water temperature data when the air temperature during the warmest week of the year
exceeds the 90th percentile for the warmest week of the year based on a historical record (10
years or more) at the nearest weather reporting station.
A State or Tribe wishing to consider adopting a provision to account for unusually warm
conditions might be able to justify that decision by pointing out that extreme annual peaks in
water temperature typically caused by drought conditions are a natural component of the
environment and then concluding, as a matter of policy, that these infrequent conditions should
not drive attainment determinations. Salmonids may experience some adverse effects during
these periods, but by definition, they would be infrequent. It is important to note that not taking
into account unusually warm conditions should only be for CWA 303(d) listing purposes when
determining if a waterbody is in attainment with temperature WQS. NPDES permitted facilities
should not be exempt from applicable temperature effluent limits during these periods.
Even assuming that a State or Tribe decides to account for unusually warm conditions in its
temperature WQS, attainment determinations should be based on all climatic conditions except
for the extreme condition in order to protect the salmonid designated uses. Thus, given that river
temperatures exhibit year-to-year variation in their maximum 7DADM values, the average
maximum 7DADM value from a yearly series, as a statistical matter, would need to be lower
than the numeric criteria in order to meet the criteria 9 out of 10 years. Therefore, in most years,
the maximum 7DADM temperature would also probably need to be lower than the numeric
criteria in order to meet the criteria in the warm years. EPA took this into consideration when it
formulated its numeric criteria recommendations.
A De Minimis Temperature Increase Allowance
A State or Tribe may, if it has not already done so, wish to consider adopting a provision in its
WQS that allows for a de minimis temperature increase above the numeric criteria or the natural
background temperature. A State or Tribe might choose to include a de minimis increase
allowance as a way of accounting for monitoring measurement error and tolerating negligible
human impacts. The data and information currently available to EPA appear to indicate that an
increase on the order of 0.25°C for all sources cumulatively (at the point of maximum impact)
above fully protective numeric criteria or natural background temperatures would not impair the
designated uses, and therefore might be regarded as de minimis.
21
-------
Numeric Criteria Should Apply Upstream of the Furthest Downstream Extent of Use
Water quality criteria must protect the relevant designated uses. See 40 C.F.R. §131. 1 l(a).
Therefore, a criterion should apply to all the river miles for which a particular use is designated,
including the lowest point downstream at which the use is designated. Because streams
generally warm progressively in the downstream direction, waters upstream of that point will
generally need to be cooler in order to ensure that the criterion is met downstream. Thus, a
waterbody that meets a criterion at the furthest downstream extent of use will in many cases
provide water cooler than the criterion at the upstream extent of the use. EPA took this into
consideration when it formulated its numeric criteria recommendations.
EPA also believes that the numeric criteria should apply upstream of the areas of actual use
because temperatures in upstream waters significantly affect the water temperatures where the
actual use occurs and upstream waters are usually colder. Of course, if a more sensitive use is
designated upstream, the more protective criterion would apply upstream. See 40 C.F.R. §
Selection of Protective Criteria for the Recommended Salmon Uses
As described above, numeric criteria that apply to uses that occur during the summer maximum
period are intended to apply to the warmest times of the summer, the warmest years (except for
extreme conditions), and the lowest downstream extent of use. Because of the conservative
nature of this application, EPA believes that it is appropriate to recommend numeric criteria near
the warmer end of the optimal range for uses intended to protect high quality bull trout and
salmon/trout rearing (see Section V.l.C for use descriptions). EPA expects that adopting a
numeric criterion near the warmer end of the optimal range that is applied to the above
conditions is likely to result in temperatures near the middle of the optimal range for most of the
spring through fall period in the segments where most of the rearing use occurs. EPA has
identified two reasons for this. First, if the criterion is met at the summer maximum, then
temperatures will be lower than the criterion during most of the year. Second, because the
criterion would apply at the furthest point downstream where the use is designated, temperatures
will generally be colder across the full range of the designated use.
EPA also recognizes that salmonids will use waters that are warmer than their optimal thermal
range and further recognizes that some portions of rivers and streams in the Pacific Northwest
naturally (i.e., absent human impacts) were warmer than the salmonid optimal range during the
period of summer maximum temperatures. To account for these realities, EPA is also
recommending two salmonid uses (see Section V. 1 .C) during the period of summer maximum
temperatures where the recommended numeric criteria exceed the optimal range, but provide
protection from lethal conditions and sub-lethal effects that would significantly adversely affect
these uses.
If applied collectively, EPA believes its recommended salmonid uses and associated numeric
criteria, if attained, will support healthy sustainable salmonid populations. However, EPA notes
22
-------
that it must still consider any new or revised temperature WQS submitted by a State or Tribe on
a case-by-case basis and must take into account any new information made available to EPA at
that time.
Determining the Spatial Extent of the Recommended Salmonid Uses
It is well recognized that the current distribution of salmonids in the Pacific Northwest has
significantly shrunk and is more fragmented than their historical distribution due to human
development. It is also unlikely that the current distribution of salmonids will provide for
sustainable salmonid populations. EPA believes that, in order to meet the national goal of
providing for the protection and propagation offish wherever attainable, salmonid use
designations should be of sufficient geographic and temporal scope to support sustainable levels
of use. This is because, unless the designated use specifically provides otherwise, a salmonid
use reasonably implies a healthy and sustainable population. Because of the importance of
restoring healthy salmonid populations in the Pacific Northwest, EPA Region 10 advises States
and Tribes not to limit salmonid use designations to where and when salmonid uses occur today
when assigning uses in areas with thermally degraded habitat.
For areas with degraded habitat, EPA recommends that coldwater salmonid uses be designated in
waters where the defined use currently occurs or is suspected to currently occur, and where there
is reasonable potential for that use to occur (e.g., if temperatures or other habitat features,
including fish passage improvements, were to be restored in areas of degraded habitat). In most
areas of degraded habitat, temperatures have risen, thereby forcing salmonids upstream to find
suitable water temperatures for rearing and spawning. As a result, the downstream extent of
current use is likely farther upstream than it was prior to habitat degradation. For areas with
minimal habitat degradation, where human impacts have not likely altered fish distribution, EPA
recommends use designations based on where the use currently occurs or is suspected to
currently occur.
EPA's recommendations for designating the spatial extent of the various salmonid uses are
described below in Sections V.l.C and V.l.D. The goal of these recommendations is to include
the potential use areas for each salmonid use where the habitat has been degraded due to human
impacts. For example, for the bull trout rearing use and the salmon/trout core rearing use, which
are intended to protect waters of moderate to high density rearing use, EPA recommends that for
areas of degraded habitat, these uses cover the downstream extent of low density rearing that
currently occurs during the period of maximum summer temperatures (typically July and
August). The concept here is that waters where rearing currently occurs in low density during
the summer is a reasonable approximation of waters that could support moderate to high density
use if the temperature were reduced.
EPA fully recognizes the difficulties in spatially designating the recommended salmonid uses.
First, information on fish distribution, particularly juvenile rearing distribution, is sparse in many
locations. For example, in some situations there may be fairly good information on spawning
areas, but minimal information on juvenile rearing distribution. In those situations, a State or
23
-------
Tribe could consider using the spawning distribution along with inferences drawn from what
information exists on juvenile rearing as the primary basis for designating the bull trout and the
core salmon and trout rearing uses. Second, there is a fair degree of both inter-annual and
seasonal variability in fish distribution. Third, there is no bright line that defines degraded
habitat; rather there is a spectrum from non-degraded to highly degraded.
States and Tribes, therefore, should use the best available scientific information (e.g., the types
of information described in Sections V.l.C and V.l.D) and make well-reasoned judgments when
designating the various salmonid uses. In some cases, that may mean extrapolating from limited
information and making generalizations based on stream order, size, and elevation. Thus, EPA
recognizes there is an inherent element of subjectivity to designating the recommended salmonid
uses. However, because the recommended salmonid uses are fairly broad scale (applying to
large areas of a river basin), EPA believes that the recommended use designations are reasonable
given the current level of information. If a State or Tribe decides to revise its salmonid use
designations and submit them to EPA for approval, it should include a description of the
information and judgments it made to determine the spatial extent of its salmonid uses.
Lastly, EPA also believes that better information on fish distribution is valuable for both CWA
and ESA purposes and that adopting the recommended salmonid use designations (or others
justified by the best available scientific information) will provide impetus to acquire more and
better information in the future.
V.l.B. EPA Region IP's Recommended Salmonid Uses and Numeric Criteria
EPA Region 10's recommended coldwater salmonid uses and criteria to protect those uses are
presented in Tables 3 and 4. Table 3 describes uses that occur during the summer maximum
temperature conditions. Designating the uses in Table 3 would result in apportioning a river
basin to up to 4 salmonid use categories with associated criteria (e.g., 12°C, 16°C, 18°C, and
20°C). The colder criteria would apply in the headwaters and the warmer criteria would apply in
the lower river reaches, which is consistent with the typical thermal and salmonid use patterns of
rivers in the Pacific Northwest during the summer. It should be noted, however, that there may
be situations where a warmer use and criteria would apply upstream of a colder use and criteria
(e.g., where a relatively large cold tributary enters a warmer river, which significantly cools the
river).
Table 4 describes coldwater salmonid uses that generally occur at times other than during the
summer maximum period, except for some circumstances. EPA recommends that these criteria
apply when and where these uses occur and may potentially occur.
24
-------
Table 3. Recommended Uses & Criteria That Apply To Summer Maximum Temperatures
Notes: 1) "7DADM" refers to the Maximum 7 Day Average of the Daily Maximums; 2) "Salmon" refers to
Chinook, Coho, Sockeye, Pink, and Chum salmon; 3) "Trout" refers to Steelhead and coastal cutthroat
trout
Salmonid Uses During the Summer Maximum Conditions
Criteria
Bull Trout Juvenile Rearing
12°C (55°F) 7DADM
Salmon/Trout "Core" Juvenile Rearing
(Salmon adult holding prior to spawning, and adult and sub-
adult bull trout foraging and migration may also be included in
this use category)
16°C (61°F) 7DADM
Salmon/Trout Migration plus Non-Core Juvenile Rearing
18°C(64°F)7DADM
Salmon/Trout Migration
20°C (68°C) 7DADM,
plus a provision to protect
and, where feasible,
restore the natural thermal
regime
Table 4. Other Recommended Uses & Criteria
Notes: 1) "7DADM" refers to the Maximum 7 Day Average of the Daily Maximums; 2) "Salmon" refers to
Chinook, Coho, Sockeye, Pink, and Chum salmon; 3) "Trout" refers to Steelhead and coastal cutthroat
trout;
Salmonid Uses
Criteria
Bull Trout Spawning
9°C (48°F) 7DADM
Salmon/Trout Spawning, Egg Incubation, and Fry Emergence
13°C (55°F) 7DADM
Steelhead Smoltification
14°C (57°F) 7DADM
25
-------
V. l.C. Discussion of Uses and Criteria Presented in Table 3
Bull Trout Juvenile Rearing - J2°C 7DADM
EPA recommends this use for the protection of moderate to high density summertime bull trout
juvenile rearing near their natal streams in their first years of life prior to making downstream
migrations. This use is generally found in a river basin's upper reaches.
EPA recommends a 12°C maximum 7DADM criterion for this use to: (1) safely protect juvenile
bull trout from lethal temperatures; (2) provide upper optimal conditions under limited food for
juvenile growth during the period of summer maximum temperature and optimal temperature for
other times of the growth season; (3) provide temperatures where juvenile bull trout are not at a
competitive disadvantage with other salmonids; and (4) provide temperatures that are consistent
with field studies showing where juvenile bull trout have the highest probability to occur (see
Table 2).
EPA recommends that the spatial extent of this use include: (1) waters with degraded habitat
where high and low density juvenile bull trout rearing currently occurs or is suspected to
currently occur during the period of maximum summer temperatures, except for isolated patches
of a few fish that are spatially disconnected from more continuous upstream low density use; (2)
waters with minimally-degraded habitat where moderate to high density bull trout rearing
currently occurs or is suspected to currently occur during the period of maximum summer
temperatures; (3) waters where bull trout spawning currently occurs; (4) waters where juvenile
rearing may occur and the current 7DADM temperature is 12°C or lower; and (5) waters where
other information indicates the potential for moderate to high density bull trout rearing use
during the period of maximum summer temperatures (e.g., recovery plans, bull trout spawning
and rearing critical habitat designations, historical distributions, current distribution in reference
streams, studies showing suitable rearing habitat that is currently blocked by barriers that can
reasonably be modified to allow passage, or temperature modeling).
Salmon and Trout "Core " Juvenile Rearing - 16°C 7DADM
EPA recommends this use for the protection of moderate to high density summertime salmon
and trout juvenile rearing. This use is generally found in a river basin's mid-to-upper reaches,
downstream from juvenile bull trout rearing areas. However, in colder climates, such as the
Olympic mountains and the west slopes of the Cascades, it may be appropriate to designate this
use all the way to the saltwater estuary.
Protection of these waters for salmon and trout juvenile rearing also provides protection for adult
spring chinook salmon that hold throughout the summer prior to spawning and for migrating and
foraging adult and sub-adult bull trout, which also frequently use these waters.
EPA recommends a 16°C maximum 7DADM criterion for this use to: (1) safely protect juvenile
salmon and trout from lethal temperatures; (2) provide upper optimal conditions for juvenile
26
-------
growth under limited food during the period of summer maximum temperatures and optimal
temperatures for other times of the growth season; (3) avoid temperatures where juvenile salmon
and trout are at a competitive disadvantage with other fish; (4) protect against temperature-
induced elevated disease rates; and (5) provide temperatures that studies show juvenile salmon
and trout prefer and are found in high densities (see Table 1).
EPA recommends that the spatial extent of this use include: (1) waters with degraded habitat
where high and low density salmon and trout juvenile rearing currently occurs or is suspected to
currently occur during the period of maximum summer temperatures, except for isolated patches
of a few fish that are spatially disconnected from more continuous upstream low density use; (2)
waters with minimally-degraded habitat where moderate to high density salmon and trout
juvenile rearing currently occurs or is suspected to currently occur during the period of
maximum summer temperatures; (3) waters where trout egg incubation and fry emergence and
salmon spawning currently occurs during the summer months (mid-June through mid-
September); (4) waters where juvenile rearing may occur and the current 7DADM temperature is
16°C or lower; (5) waters where adult and sub-adult bull trout foraging and migration occurs
during the period of summer maximum temperatures; and (6) waters where other information
indicates the potential for moderate to high density salmon and trout rearing use during the
period of maximum summer temperatures (e.g., recovery plans, critical habitat designations,
historical distributions, current distribution in reference streams, studies showing suitable rearing
habitat that is currently blocked by barriers that can reasonably be modified to allow passage, or
temperature modeling).
Please note that at this time EPA is recommending that adult and sub-adult bull trout foraging
and migration be included in this use category as opposed to establishing a separate use and
associated criterion. Our current knowledge of bull trout migration timing and their main
channel temperature preference is limited, but we do know that they prefer water temperatures
less than 15°C, that they take advantage of cold water refugia during the period of summer
maximum temperatures, and that spawning adults move toward spawning grounds during the
period of summer maximum temperatures. EPA, therefore, believes its recommended approach
would protect migrating and foraging bull trout because average river temperatures will likely be
below 15°C, a fair amount of cold water refugia is expected in rivers that attain a maximum
7DADM of 16°C, and maximum temperatures below 16°C are likely to occur upstream of the
downstream point of this use designation where most bull trout migration and foraging is likely
to occur during the period of summer maximum temperatures. As more is learned about adult
and sub-adult bull trout foraging and migration, EPA, in consultation with the U.S. Fish and
Wildlife Service, may reconsider this recommendation.
Salmon and Trout Migration Plus Non-Core Juvenile Rearing - 18°C 7DADM
EPA recommends this use for the protection of migrating adult and juvenile salmonids and
moderate to low density salmon and trout juvenile rearing during the period of summer
maximum temperatures. This use designation recognizes the fact that salmon and trout juveniles
will use waters that have a higher temperature than their optimal thermal range. For water
27
-------
bodies that are currently degraded, there is likely to be very limited current juvenile rearing
during the period of maximum summer temperatures in these waters. However, there is likely to
be more extensive current juvenile rearing use in these waters during other times of the year.
Thus, for degraded waters, this use designation could indicate a potential rearing use during the
period of summer maximum temperatures if maximum temperatures are reduced.
This use is generally found in the mid and lower part of a basin, downstream of the Salmon and
Trout Core Juvenile Rearing use. In many river basins in the Pacific Northwest, it may be
appropriate to designate this use all the way to a river basin's terminus (i.e., confluence with the
Columbia River or saltwater).
EPA recommends an 18°C maximum 7DADM criterion for this use to: (1) safely protect against
lethal conditions for both juveniles and adults; (2) prevent migration blockage conditions for
migrating adults; (3) provide optimal or near optimal juvenile growth conditions (under limited
food conditions) for much of the summer, except during the summer maximum conditions,
which would be warmer than optimal; and (4) prevent adults and juveniles from high disease risk
and minimize the exposure time to temperatures that can lead to elevated disease rates (See
Table 1).
The upstream extent of this use designation is largely driven by where the salmon and trout core
juvenile rearing use (16°C) is defined. It may be appropriate to designate this use downstream to
the basin's terminus, unless a salmon and trout migration use (20°C) is designated there.
Generally, for degraded water bodies, this use should include waters where juvenile rearing
currently occurs during the late spring-early summer and late summer-early fall, because those
current uses could indicate potential use during the period of summer maximum temperatures if
temperatures were to be reduced.
Salmon and Trout Migration - 20° C 7DADM plus a provision to protect and, where feasible,
restore the natural thermal regime
EPA recommends this use for waterbodies that are used almost exclusively for migrating salmon
and trout during the period of summer maximum temperatures. Some isolated salmon and trout
juvenile rearing may occur in these waters during the period of summer maximum temperatures,
but when it does, such rearing is usually found only in the confluence of colder tributaries or
other areas of colder waters. Further, in these waters, juvenile rearing was likely to have been
mainly in cold water refugia areas during the period of maximum temperatures prior to human
alteration of the landscape. It should also be noted that most fish migrating in these waters do so
in the spring-early summer or in the fall when temperatures are cooler than the summer
maximum temperatures, but some species (e.g., late migrating juvenile fall chinook; adult
summer chinook, fall chinook, summer steelhead, and sockeye) may migrate in these waters
during the period of summer maximum temperatures.
This use is probably best suited to the lower part of major rivers in the Pacific Northwest, where
based on best available scientific information, it appears that the natural background maximum
28
-------
temperatures likely reached 20°C. When designating the spatial extent of this use, EPA expects
the State or Tribe to provide information that suggests that natural background maximum
temperatures reached 20°C. However, EPA does not expect the State or Tribe to have conducted
a process-based temperature model (see Section VI.3 below for a discussion on methods to
demonstrate natural background temperatures). If a State or Tribe determines that the natural
background temperature is higher than 20°C for a particular location and wants to establish a
numeric criterion higher than 20°C, it should follow the procedures described in Section VI. 1 .B
for the establishment of site-specific numeric criteria based on natural background conditions.
To protect this use, EPA recommends a 20°C maximum 7DADM numeric criterion/?/^ a
narrative provision that would require the protection, and where feasible, the restoration of the
natural thermal regime. EPA believes that a 20°C criterion would protect migrating juveniles
and adults from lethal temperatures and would prevent migration blockage conditions. However,
EPA is concerned that rivers with significant hydrologic alterations (e.g., rivers with dams and
reservoirs, water withdrawals, and/or significant river channelization) may experience a loss of
temperature diversity in the river, such that maximum temperatures occur for an extended period
of time and there is little cold water refugia available for fish to escape maximum temperatures.
In this case, even if the river meets a 20°C criterion for maximum temperatures, the duration of
exposure to 20°C temperatures may cause adverse effects in the form of increased disease and
decreased swimming performance in adults, and increased disease, impaired smoltification,
reduced growth, and increased predation for late emigrating juveniles (e.g., fall chinook in the
Columbia and Snake Rivers). Therefore, in order to protect this use with a 20°C criterion, it may
be necessary for a State or Tribe to supplement the numeric criterion with a narrative provision
to protect and, where feasible, restore the natural thermal regime for rivers with significant
hydrologic alterations.
Critical aspects of the natural thermal regime that should be protected and restored include: the
spatial extent of cold water refugia (generally defined as waters that are 2°C colder than the
surrounding water), the diurnal temperature variation, the seasonal temperature variation (i.e.,
number of days at or near the maximum temperature), and shifts in the annual temperature
pattern. The narrative provision should call for the protection, and where feasible, the
restoration of these aspects of the natural temperature regime. EPA notes that the protection of
existing cold water refugia should already be provided by the State's or Tribe's antidegradation
provisions or by the cold water protection provisions discussed in Section V.2 below. Thus, the
new concept introduced by the narrative provision EPA recommends here is the restoration of
the natural thermal regime, where feasible.
Although some altered rivers, such as the Columbia and Snake, experience similar summer
maximum temperatures today as they did historically, there is a big difference between the
temperatures that fish experience today versus what they likely experienced historically.
Unaltered rivers generally had a high degree of spatial and temporal temperature diversity, with
portions of the river or time periods that were colder than the maximum river temperatures.
These cold portions or time periods in an otherwise warm river provided salmonids cold water
refugia to tolerate such situations. The loss of this temperature diversity may be as significant to
29
-------
salmon and trout in the Columbia and Snake Rivers and their major tributaries as maximum
temperatures. Therefore, protection and restoration of temperature diversity is likely critical in
order for salmonids to migrate through these waters with minimal thermal stress.
The areas where relatively cold tributaries join the mainstem river and where groundwater
exchanges with the river flow (hyporheic flow) are two critical areas that provide cold water
refugia for salmonids to escape maximum temperatures. As described in Issue Paper 3 and the
Return to the River report (2000), alluvial floodplains with a high level of groundwater exchange
historically provided high quality habitat that served as cold water refugia during the summer for
large rivers in the Columbia River basin (and other rivers of the Pacific Northwest). These
alluvial reaches are interspersed between bedrock canyons and are like beads on a string along
the river continuum. Today, most of the alluvial floodplains are either flooded by dams, altered
through diking and channelization, or lack sufficient water to function as refugia. Efforts to
restore these alluvial river functions and maintain or cool down tributary flows will probably be
critical to protect this use.
As noted above, EPA recommends that States and Tribes include a natural thermal regime
narrative provision to accompany the 20°C numeric criterion. If a State or Tribe chooses to do
so, TMDL allocations would reflect the protection, and where feasible, the restoration of the cold
water refugia and other aspects of the natural thermal regime described above. If it is
impracticable to quantify allocations to restore the natural thermal regime in the TMDL load
allocations, then the TMDL assessment document should qualitatively address the human
impacts that alter the thermal regime. Plans to implement the TMDL (e.g., watershed restoration
plans) should include measures to restore the potential areas of cold water refugia and the natural
daily and seasonal temperature patterns. See Section VI.2.B below for a similar discussion
regarding TMDLs designed to meet temperature targets exceeding 18°C.
V. 1 .D. Discussion of Uses and Criteria Presented in Table 4
As discussed in Section V.l.B above, EPA recommends additional uses and criteria that would
generally apply during times other than the period of summer maximum temperatures. These
additional uses and criteria are intended to provide an added degree of protection for those
situations where control of the summer maximum temperature is inadequate to protect these
sensitive uses. EPA's recommendations assume that when these uses do occur during the time
of summer maximum temperatures, these more sensitive uses and associated numeric criteria
would apply.
In many situations, if the summer maximum criteria are attained (e.g., 12°C, 16°C, 18°C, 20°C),
EPA expects that temperatures will be low enough due to typical spring warming and fall
cooling patterns to support the uses described below. However, in developing this guidance,
EPA did not assess data in sufficient detail to determine the extent to which these uses are
protected vis-a-vis the summer maximum criterion. With respect to spawning and egg
incubation, EPA is most concerned about protecting spawning and egg incubation that occurs
during, or soon before or after, the period of summer maximum temperatures (e.g., spring
30
-------
chinook, summer chum, and bull trout spawning that occurs in the mid-to-late summer, and
steelhead trout egg incubation that extends into the summer months).
In waters where there is a reasonable basis in concluding that control of the summer maximum
criterion sufficiently protects some or all of the uses described below, it may be reasonable not to
designate some of all of these specific salmonid uses (i.e., the use will be protected by the
summer maximum criterion).
Bull Trout Spawning - 9°C 7DADM
EPA recommends this use for the protection waterbodies used or potentially used by bull trout
for spawning, which generally occurs in the late summer-fall in the upper basins (the same
waters that bull trout juveniles use for summer rearing). EPA recommends a 9°C maximum
7DADM criterion for this use and recommends that the use apply from the average date that
spawning begins to the average date incubation ends (the first 7DADM is calculated 1 week after
the average date that spawning begins). Meeting this criterion at the onset of spawning will
likely provide protective temperatures for egg incubation (2 - 6°C) that occurs over the winter
assuming the typical annual thermal pattern.
Salmon and Trout Spawning, Egg Incubation, and Fry Emergence - 13°C 7DADM
EPA recommends this use for the protection of waterbodies used or potentially used for salmon
and trout spawning, egg incubation, and fry emergence. Generally, this use occurs: (a) in spring-
early summer for trout (mid-upper reaches); (b) in late summer-fall for spring chinook (mid-
upper reaches) and summer chum (lower reaches); and (c) in the fall for coho (mid-reaches),
pink, chum, and fall chinook (the latter three in lower reaches). EPA recommends a 13°C
maximum 7DADM criterion to protect these life stage uses for salmon and trout and
recommends that this use apply from the average date that spawning begins to the average date
incubation ends (the first 7DADM is calculated 1 week after the average date that spawning
begins). Meeting this criterion at the onset of spawning for salmon and at the end of incubation
for steelhead trout will likely provide protective temperatures for egg incubation (6 - 10°C) that
occurs over the winter (salmon) and spring (trout), assuming the typical annual thermal pattern.
Steelhead Trout Smoltification - 14°C 7DADM
EPA recommends this use for the protection of waters where and when the early stages of
steelhead trout smoltification occurs or may occur. Generally, this use occurs in April and May
as steelhead trout make their migration to the ocean. EPA recommends a 14°C maximum
7DADM steelhead smoltification criterion to protect this sensitive use. As described in Table 1,
steelhead smoltification can be impaired from exposure to greater than 12°C constant
temperatures. The greatest risk to steelhead is during the early stages of smoltification that
occurs in the spring (April and May). For the Columbia River tributaries, 90% of the steelhead
smolts are typically past Bonneville dam by the end of May (Issue Paper 5, pg 59), indicating
that applying this criterion at the mouths of major tributaries to the Columbia River in April and
31
-------
May will likely protect this use. Applying this criterion to the Columbia River itself is probably
unnecessary because the more temperature-sensitive early stages of smoltification occur in the
tributaries. If steelhead in the early smoltification process are exposed to higher temperatures
than the recommended criterion, they may cease migration or they may migrate to the ocean
undeveloped, thereby reducing their estuary and ocean survival.
V.2. Provisions to Protect Water Temperatures That Are Currently Colder Than The
Numeric Criteria
One of the important principles in protecting populations at risk for any species is to first protect
the existing high quality habitat and then to restore the degraded habitat that is adjacent to the
high quality habitat. Further, EPA's WQS regulations recognize the importance of protecting
waters that are of higher quality than the criteria (in this case, waters that are colder than numeric
temperature criteria). See 40 C.F.R. § 131.12. EPA, therefore, believes it is important to have
strong regulatory measures to protect waters with ESA-listed salmonids that are currently colder
than EPA's recommended criteria. These waters likely represent the last remaining strongholds
for these fish.
Because the temperatures of many waters in the Pacific Northwest are currently higher than the
summer maximum criteria recommended in this guidance, the high quality, thermally optimal
waters that do exist are likely vital for the survival of ESA-listed salmonids. Additional
warming of these waters will likely cause harm by further limiting the availability of thermally
optimal waters. Further, protection of these cold water segments in the upper part of a river
basin likely plays a critical role in maintaining temperatures downstream. Thus, in situations
where downstream temperatures currently exceed numeric criteria, upstream temperature
increases to waters currently colder than the criteria may further contribute to the non-attainment
downstream, especially where there are insufficient fully functioning river miles to allow the
river to return to equilibrium temperatures (Issue Paper 3). Lastly, natural summertime
temperatures in Pacific Northwest waters were spatially diverse, with areas of cold-optimal,
warm-optimal, and warmer than optimal water. The 18°C and 20°C criterion described in Table
3 and the natural background provisions and use attainability pathways described in Section VI
are included in this guidance as suggested ways to address those waters that are warmer than
optimal for salmonids. EPA believes it is important, however, for States and Tribes to balance
the effects of the warmer waters by adopting provisions to protect waters that are at the colder
end of their optimal thermal range.
EPA, therefore, recommends that States and Tribes adopt strong regulatory provisions to protect
waterbodies with ESA-listed salmonids that currently have summer maximum temperatures
colder than the State's or Tribe's numeric criteria. EPA believes there are several ways a State
or Tribe may do this. One approach could be to adopt a narrative temperature criterion (or
alternatively include language in its antidegradation rules) that explicitly prohibits more than a
de minimis increase to summer maximum temperatures in waters with ESA-listed salmonids that
are currently colder than the summer maximum numeric criteria. Another approach could be to
identify and designate waterbodies as ecologically significant for temperature and either
32
-------
establish site-specific numeric criteria equal to the current temperatures or prohibit temperature
increases above a de minimis level in these waters. States and Tribes following this latter
approach should conduct a broad survey to identify and designate such waters within the state
(or tribal lands). For non-summer periods it may be appropriate to set a maximum allowable
increase (e.g., 25% of the difference between the current temperature and the criterion) for
waters with ESA-listed salmonids where temperatures are currently lower than the criteria.
Provisions to protect waters currently colder than numeric criteria can also be important to
ensure numeric criteria protect salmonid uses. As discussed in Section V.I.A, the recommended
criteria in this guidance are based in part on the assumption that meeting the criteria at the lowest
downstream point at which the use is designated will likely result in cooler waters upstream.
Cold water protection provisions as described here provide more certainty that this will be true.
Further, if a State chooses to protect some or all of the sensitive uses in Table 4 (e.g., spawning)
by using only the summer maximum criteria, it may also be necessary to protect waters currently
colder than the summer maximum numeric criteria in order to assure that these sensitive uses are
protected. Further, as described in Section V.l.B, protecting existing cold water is likely
important in river reaches where a 20°C numeric criterion applies to protect salmon and trout
migration use.
V.3. Provisions to Protect Salmonids from Thermal Plume Impacts
EPA recommends that States and Tribes add specific provisions to either their temperature or
mixing zone sections in their WQS to protect salmonids from thermal plume impacts.
Specifically, language should be included that ensures that thermal plumes do not cause
instantaneous lethal temperatures; thermal shock; migration blockage; adverse impact on
spawning, egg incubation, and fry emergence areas; or the loss of localized cold water refugia.
The following are examples from the scientific literature of potential adverse impacts that may
result from thermal plumes, and EPA's recommendations to avoid or minimize those impacts.
Exposures of less thanlO seconds can cause instantaneous lethality at 32°C
(WDOE, 2002). Therefore, EPA suggest that the maximum temperature within
the plume after 2 seconds of plume travel from the point of discharge does not
exceed 32°C.
Thermal shock leading to increased predation can occur when salmon and trout
exposed to near optimal temperatures (e.g., 15°C) experience a sudden
temperature increase to 26 - 30°C for a short period of time (Coutant, 1973).
Therefore, EPA suggests that thermal plumes be conditioned to limit the cross-
sectional area of a river that exceeds 25°C to a small percent of the river (e.g., 5
percent or less).
• Adult migration blockage conditions can occur at 21°C (Table 1). Therefore,
EPA suggests that the cross-sectional area of a river at or above 21°C be limited
to less than 25% or, if upstream temperature exceeds 21°C, the thermal plume be
33
-------
limited such that 75% of the cross-sectional area of the river has less than a de
minimis (e.g., 0.25°C) temperature increase.
Adverse impacts on salmon and trout spawning, egg incubation, and fry
emergence can occur when the temperatures exceed 13°C (Table 1). Therefore,
EPA suggests that the thermal plume be limited so that temperatures exceeding
13°C do not occur in the vicinity of active spawning and egg incubation areas, or
that the plume does not cause more than a de minimis (e.g., 0.25°C) increase in
the river temperature in these areas.
VI. Approaches to Address Situations Where the Numeric Criteria are
Unachievable or Inappropriate
There are likely to be some streams and rivers in the Pacific Northwest where the criteria
recommended in this guidance cannot be attained or where the criteria recommendations would
otherwise be inappropriate. The following approaches are available under EPA's regulations to
address these circumstances. See 40 C.F.R. Part 131. EPA describes these approaches below
and recommends when it believes each approach may be appropriate.
It is important to note that most of these approaches are subject to EPA review and approval on a
case-by-case basis (either in the form of a WQS, TMDL, or a 303(d) list approval), and where
appropriate, are subject to consultation with the Services and affected Tribes.
VI. 1. Alternative Criteria
The following are three possible ways to establish alternative numeric criteria that would apply
to a specific location.
VILA. Site-Specific Numeric Criteria that Supports the Use
Under this approach, the State or Tribe would demonstrate that conditions at a particular location
justify an alternative numeric criterion to support the designated salmonid use. See 40 C.F.R. §
131.1 l(b)(l)(ii). One example may be the adoption of a 13°C 7DADM criterion (instead of
EPA's recommended 12°C criterion) to protect bull trout rearing use in areas where competition
with other fish is minimal and food sources are abundant. Another example may be where there
is exceptionally high natural diurnal temperature variation and where the maximum weekly
mean temperature is within the optimal temperature range but, because of the high diurnal
variation, summer maximum temperatures exceed the State or Tribe's numeric criteria. In this
situation, a State or Tribe may choose to develop a site-specific numeric criterion based on a
metric other that the 7DADM (e.g., a maximum weekly mean criterion plus a daily maximum
criterion). There may be other situations as well when an alternative site-specific criterion
would be appropriate. The State or Tribe would need to provide a clear description of the
34
-------
technical basis and methodology for deriving the alternative criterion and describe how it fully
supports the designated use when it submits the criterion to EPA for approval. See 40 C.F.R. §
VI.l.B. Numeric Criteria Based on Estimates of Natural Background Temperatures
Under this approach a State or Tribe could establish numeric criteria based on an estimate of the
natural background temperature conditions. This would be another form of site-specific criteria
under 40 C.F.R. §131. 1 l(b)(l)(ii). Natural background temperatures are those that would exist
in the absence of human-activities that alter stream temperatures. States or Tribes following this
approach may elect to adopt a single numeric criterion for a particular stream segment, such as a
lower mainstem river, or adopt a numeric profile (i.e., a range of numbers typically colder in the
headwaters and warmer downstream) for a whole watershed or sub-basin.
EPA views numeric criteria that reflect natural background conditions to be protective of
salmonid designated uses because river temperatures prior to human impacts clearly supported
healthy salmonid populations. Thus, when establishing site-specific numeric criteria in this
manner, EPA believes it is unnecessary to modify the use designations. For example, if a State
has designated a waterbody as salmon/trout core juvenile rearing use with an associated numeric
criterion of 16°C 7DADM and later estimates the natural background temperature is 18°C
7DADM, the 18°C 7DADM could be adopted as a site-specific criterion that fully supports the
salmon and trout core juvenile rearing use. A State or Tribe may also want to modify the spatial
extent of its various salmonid use designations within the basin if the estimates of natural
background provide new information that warrants such revisions. Additionally, at the time the
State revises a salmonid use for a waterbody (e.g., designating a salmon/trout migration use), it
could choose to establish a numeric criterion based on natural background conditions for that
particular waterbody (e.g., 22°C 7DADM), which may be different from the generally applicable
numeric criterion to support that use in the State's WQS (e.g., 20°C 7DADM).
States and Tribes following this approach will need to submit any such new or revised numeric
criteria to EPA for approval and must include the methodology for determining the natural
background condition. See 40 C.F.R. §§ 131.6& 131.11(a). An alternative to establishing
numeric criteria based on natural background conditions as described here is to adopt a narrative
natural background provision, which would then be used in CWA section 303(d) listings,
TMDLs, and NPDES permits as described in Section VI.2.
VI.l.C. Numeric Criteria In Conjunction with a Use Attainability Analysis
In situations where it appears that the numeric criterion or natural background provision (see
Section VI.2) cannot be attained and the appropriateness of the designated use is in question, a
State or Tribe could conduct a use attainability analysis (UAA) pursuant to 40 C.F.R. §§
131.3(g) & 131.10. If it can be demonstrated that the current designated use is not attainable due
35
-------
to one of the factors at 40 C.F.R § 131.10(g), the State or Tribe must then adopt a different use
appropriate to that water. See 40 C.F.R. § 131.10(a). In most cases, EPA expects that the
appropriate use would be the most protective salmonid use that is attainable. The State or Tribe
must then adopt a temperature criterion sufficient to protect that new use. See 40 C.F.R. §
131.11. EPA notes that, in all cases, uses attained since 1975, referred to as "existing uses,"
must be protected. See 40 C.F.R Part 131.10(h)(l). The new use could be described as a
"compromised" or "degraded" salmonid use. It should be noted that a "compromised" or
"degraded" level of use may be appropriate during part of the year (e.g., summer), but that an
unqualified, healthy salmonid use may be attainable other times of the year and therefore may be
the appropriate use then.
Examples of factors at 40 C.F.R. § 131.10(g) that could preclude attainment of the use include:
human caused conditions or sources of pollution that cannot be remedied or would cause more
environmental damage to correct than to leave in place; dams, diversions or other types of
hydrologic modifications that cannot be operated in such a way as to result in the attainment of
the use; and controls more stringent than those required by sections 301(b) and 306 of the CWA
that would result in substantial and widespread economic and social impact.
Whenever a State or Tribe adopts new or revised designated uses, such as those described here, it
is changing its WQS. Therefore, the State or Tribe must make the proposed change available for
public notice and comment and must submit the new use and associated criteria, together with
the supporting UAA, to EPA for review and approval. See CWA section 303(c)(l) & (c)(2)(A);
40 C.F.R. §§ 131.5 & 131.6. EPA recommends that a UAA seeking to demonstrate human
impacts (including dams, diversions, or other hydrologic modifications) that prevent attainment
of the current use, should include a full assessment of all possible mitigation measures and their
associated costs when demonstrating which mitigation measures are not feasible. EPA's
decision to approve or disapprove a use and criteria change associated with a UAA will need to
be made on a case-by-case basis, taking into account the information available at the time, and
where appropriate, after consultation with the Services and affected Tribes.
VI.2. Use of a State's or Tribe's "Natural Background" Provisions
If it has not already done so, a State and Tribe may wish to consider adopting narrative natural
background provisions in its WQS that would automatically take precedence over the otherwise
applicable numeric criteria when natural background temperatures are higher than the numeric
criteria. See 40 C.F.R. §131.1 l(b)(2). If adopted by a State or Tribe and approved by EPA,
narrative natural background provisions would be the applicable water quality criteria for CWA
purposes when natural background temperatures are higher than the numeric criteria and would
be utilized in 303(d) listings of impaired waterbodies, TMDLs, and NPDES permits in such
situations. As discussed in Section V.l.B above, a State could also consider adopting a specific
numeric criterion that reflects natural background temperatures (rather than leave natural
background temperatures to case-by-case interpretation). The discussion here, however,
36
-------
assumes that a State or Tribe has not done so and instead has adopted a narrative natural
background provision and would interpret it when necessary for CWA purposes.
VI.2.A. 303((D Listings
If it can be demonstrated that a particular waterbody exceeds a temperature numeric criterion due
to natural conditions (or natural conditions plus a de mimimis human impact, if a State or Tribe
has this allowance in its WQS - see Section V.I.A), then the waterbody need not be listed on a
State's or Tribe's 303(d) list. Such waterbodies would not be considered impaired because they
would be meeting the narrative natural background provisions of the WQS. These waterbodies
should be identified as an attachment to a State's or Tribe's section 303(d) list submission to
EPA along with the demonstration that these waters do not exceed the natural background
provision.
For situations where waterbodies exceed the applicable numeric criteria due to a combination of
apparent natural background conditions and known or suspected human impacts (above a de
minimis impact level, if applicable), it would be appropriate to list those waters on the 303(d) list
because the waters would be exceeding the narrative natural background provision because of
the human impacts. The TMDL process, described below, will provide the opportunity to
distinguish the natural sources from the human caused sources.
VI.2.B. TMDLs
A State's or Tribe's narrative natural background provisions can be utilized in TMDLs to set
water quality targets and allocate loads when natural background conditions are higher than the
otherwise applicable numeric criteria. When doing so, estimated temperatures associated with
natural background conditions would serve as the water quality target for the TMDL and would
be used to set TMDL allocations. Thus, the TMDL would be written to meet the WQS natural
background provision, and the load reductions contemplated by the TMDL would be equivalent
to the removal of the human impacts (or all but de minimis human impacts, if applicable). It
should be noted that if a State or Tribe has a de minimis temperature increase allowance above
natural background temperatures (see Section V. 1 .A), the TMDL allocations should be based on
attaining the natural background temperature plus the de minimis temperature allowance (e.g.,
natural background temperature plus 0.25°C).
When estimating natural background conditions, States and Tribes should use the best available
scientific information and the techniques described in Section VI.3 below. For TMDLs, this
usually includes temperature models. Those human impacts that cannot be captured in a model
(e.g., loss of cooling due to loss of hyporheic flow, which is water that moves between the
stream and the underlying streambed gravels) should be identified in the TMDL assessment
document (i.e., supporting material to the TMDL itself) along with rough or qualitative estimates
of their contribution to elevated water temperatures. Estimates of natural conditions should also
be revisited periodically as our understanding of the natural system and temperature modeling
techniques advance.
37
-------
When using natural background maximum temperatures as TMDL targets and to set TMDL
allocations, the TMDL assessment document should assess other aspects of the natural thermal
regime including the spatial extent of cold water refugia (which, generally are defined as waters
that are >2°C colder than the surrounding water), the diurnal temperature variation, seasonal
temperature variation (i.e., number of days at or near the maximum temperature), and shifts in
the annual temperature pattern. Findings from this assessment should be integrated into the
TMDL and its allocations to the extent possible. For example, if possible, TMDL allocations
should incorporate restoration of the diurnal and seasonal temperature regime and cold water
refugia that reflect the natural condition. If it is impracticable to address these impacts
quantitatively through allocations, then the TMDL assessment document should qualitatively
discuss the human activities that modify these aspects of the natural thermal regime. Plans to
implement the TMDL should include measures to restore and protect these unique aspects of the
natural condition.
EPA believes it is particularly important for the TMDL itself or the TMDL assessment document
to address the above aspects of the natural thermal regime for waterbodies where the natural
background maximum 7DADM temperature exceeds 18°C and where the river has significant
hydrologic alterations (e.g., dams and reservoirs, water withdrawals, and/or significant river
channelization) that have resulted in the loss of temperature diversity in the river or shifted the
natural temperature pattern. For example, there may be situations where the natural background
maximum temperatures exceed 18°C, but historically the exposure time to maximum
temperatures was limited due to the comparatively few number of hours in a day that the water
reached these temperatures, the comparatively few number of days that reached these
temperatures, and plentiful cold water refugia from cold tributary flows and hyporheic flow in
alluvial floodplains where salmonids could avoid the maximum water temperatures.
If human impacts as identified at 40 C.F.R. 131.10(g) are determined to prevent attainment of the
natural background conditions, the State or Tribe should follow the UAA process described in
Section VI.l.C above and revise the use and adopt numeric criteria that would support a revised
use. This new numeric criteria, if approved by EPA, would then be the temperature target in the
TMDL and used to set load allocations.
Before determining that some of the human impacts preclude use attainment and pursuing a
UAA, EPA Region 10 encourages States to develop and begin implementing TMDLs that reflect
the applicable numeric criteria or natural background provisions and allow some time for
implementation to proceed. EPA Region 10 encourages this approach because it is often the
case that at the time a TMDL is developed there is little information on all the possible
implementation measures and their associated costs, which may be important to justify a UAA.
Further, after feasible implementation measures are completed, there will be better information
as to what is the actual attainable use and associated water temperatures. If information is
available at the time, however, it is possible for a State to conduct a UAA concurrently with the
TMDL development process and, if appropriate, to revise the designated use and adopt new
applicable numeric criteria for use when establishing the TMDL.
38
-------
VI.2.C. NPDES Permits
When a permitting authority is establishing a temperature water quality-based effluent limit for
an NPDES source, it must base the limit on the applicable water quality standards, which could
be the numeric criteria or, if applicable, the narrative natural background provision. See 40
C.F.R. § 122.44(d)(l). EPA expects that, in most cases, the natural background temperature will
be interpreted and expressed for the first time in a TMDL, but it is possible for the natural
background temperature to be determined outside the context of a TMDL, although this would
be unusual given the complexities involved in estimating natural background temperatures.
VI.3. Overview of Methods to Estimate Natural Background Temperatures
There are a number of different ways of estimating natural background temperature conditions
for the purposes of either adopting a site-specific criterion (see Section VI. 1 .B) or interpreting a
narrative natural background provision (see Section VI.2). These include: (1) demonstrating that
current temperatures reflect natural background conditions, (2) using a non-degraded reference
stream for comparison, (3) using historical temperature data, (4) using statistical or computer
simulation models, and (5) assessing the historical distribution of salmonids. There may be other
ways as well. Each approach has its strengths and weaknesses and therefore may or may not be
most appropriate for a given situation. Moreover, all of these approaches have uncertainty,
which should be quantitatively described where possible. EPA encourages the use of a
combination of approaches to estimate natural background temperatures, where feasible. Below
is an overview of the five approaches listed above.
Demonstrating That Current Temperatures Reflect Natural Background Conditions
Under this approach, the past and present human activities that could impact the river
temperatures are documented and a technical demonstration is made that the human activities do
not currently impact temperatures. This approach is most applicable to non-degraded watersheds
(e.g., state and national parks, wilderness areas, and protected state and national lands). These
watersheds can be used as "reference" streams for estimating the natural background
temperatures of degraded streams (see below). If there is a small human impact on temperatures,
it may also be possible to estimate the human impact and subtract it from current temperatures to
calculate the natural background temperatures.
Comparisons to a Reference Stream
It is often reasonable to assume that the natural background temperatures of a thermally
degraded stream are similar to that of a non-degraded stream, so long as the location, landscape
context, and physical structure of the stream are sufficiently similar. The challenge to this
approach is finding a reference stream that is of similar location, landscape context, and physical
39
-------
structure. Because large rivers are unique and most in the Pacific Northwest have been
significantly impacted by human activities, this approach is most applicable to smaller streams
where a reference stream with current temperatures at natural background conditions exist.
Historical Data
For some rivers, historical temperature data are available that reflect temperatures prior to human
influences on the river's temperature regime, and can be used as an estimate of natural
background temperatures. Factors that lend uncertainty to historic temperature data are the
uncertain nature of the quality of the data and whether or not humans affected temperature prior
to data collection. Further, historical temperature data often do not adequately capture the
spatial and/or temporal variability in stream temperature due to limited spatial or temporal
sampling. Historical data may be useful, however, for verifying estimates of modeled natural
background temperatures.
Temperature Models
Two major methods have been commonly used for water quality modeling in the United States
over the last 20 years: 1) statistical models, which are based on observed relationships between
variables and are often used in conjunction with measurements from a reference location, and 2)
process-based models, which attempt to quantify the natural processes acting on the waterbody.
Process-based models are often employed when no suitable reference locations can be identified.
Statistical models, also referred to as empirical models, estimate the thermal conditions of
streams by using statistics to find correlations between stream temperature and those landscape
characteristics that control temperature (e.g., elevation, latitude, aspect, riparian cover, etc.). The
equations in statistical models describe the observed relationships in the variables as they were
measured in a specific location. If the specific location is a non-degraded reference stream, then
the model can be used to estimate natural background conditions in degraded streams.
Statistical models have the advantage of being relatively simple, as they rely on general data and
statistics to develop correlations.
The comparability between the reference waterbody where the statistical correlations are
generated and the assessment waterbody strongly affects the applicability of statistical models.
Uncertainties in statistical model results increase with increasing dissimilarity between the
landscape characteristics of the reference and assessment water bodies. Uncertainties also
increase when models do not include landscape characteristics that control important processes
affecting the water temperature. For these reasons, statistical models are best suited for small
headwater streams or for generalized predictions across a large landscape.
Process models, also referred to as simulation models, are based on mathematical
characterizations of the current scientific understanding of the critical processes that affect water
temperature in rivers. The equations are constructed to represent the observed or expected
relationships and are generally based on physical or chemical principles that govern the fate and
40
-------
transport of heat in a river (e.g., net heat flux from long-wave radiation, direct short wave
radiation, convection, conduction, evaporation, streamside shading, streambed friction, and
water's back radiation) (Bartholow, 2000).
Estimating water temperature with a process model is generally a two-step process. As a first
step, the current river temperatures are estimated with the input parameters (e.g., amount of
shade provide by the canopy and river depth, width, and flow) reflecting current conditions and
the model error is calculated by comparisons of the model estimate to actual temperature
measurements. The second step involves changing the model input parameters to represent
natural conditions, which results in a model output that predicts the natural background
conditions. In recent years, increases in computer processing power have led to the development
of distributed process models, which incorporate a high degree of spatial resolution. These
models use Geographical Information Systems (GIS), remotely-sensed data, and site-specific
data to vary the model's input parameters at different locations in the waterbody or the
landscape.
Unlike statistical models, process models do not rely upon data from reference locations, so they
can be used for rivers that have no suitable natural reference comparisons available. Thus,
process models are well suited for estimating natural conditions for larger streams and rivers.
Although powerful, process models are by no means infallible. Errors can arise when there are
locally important factors that the model does not address, or when there is a great deal of
uncertainty in input parameters that strongly influence the model results.
In addition to estimating natural background conditions, process-based models are useful for
understanding the basic mechanisms influencing water temperature in a watershed,
understanding the relative contributions from different sources at different locations,
understanding cumulative downstream impacts from various thermal loads, performing "what if
scenarios for different mitigation options, and setting TMDL allocations.
Historical Fish Distributions
Maps of historic salmonid distributions and their time of use can provide rough estimates of
natural background temperatures. Where and when salmonids existed historically likely provided
temperatures suitable for salmonids and, as described in this guidance, we have a fairly good
understanding of suitable temperatures for various life stages of salmonids.
VII. Using EPA's Guidance to Change Salmonid Use Designations
The States of Idaho, Oregon, Washington and Pacific Northwest Tribes with WQS currently
have salmonid use designations that are less spatially and temporally specific than those
recommended in Section V.I of this guidance. For instance, several States and Tribes employ
broad salmonid use designations (e.g., migration, rearing, spawning) that apply generally to an
entire basin or watershed. EPA's recommendations in Section V.I are intended to assist States
41
-------
and Tribes with broad use designations to more precisely define when and where the different
salmonid uses currently occur or may potentially occur within a basin.
For example, at the present time, a State may have a spawning use designated for an entire basin
(or large waterbody), but not specify the waterbody segments or times of year to which that use
designation should apply. After considering information that indicates where and when
spawning currently occurs or may potentially occur, that State might decide that only certain
locations and times in the basin should be designated for spawning. This same situation may
also occur in the context of rearing and migration uses.
The intent of EPA's recommendations is to encourage States and Tribes, through these types of
use refinements, to adopt a suite of interdependent salmonid uses. This suite of uses, in essence,
would function as a single aquatic life use designation for the protection, at all life stages, of a
sustainable salmonid population. Consequently, EPA believes that, as a general matter, use
designations within a basin that reflect, at the appropriate times and places, the complete suite of
uses to protect healthy salmonid populations at all life stages would fully protect the CWA
section 101(a)(2) aquatic life uses. EPA, therefore, would not expect a UAA to accompany such
use refinements as long as the overall sustainable salmonid population use is still being
protected. See 40 C.F.R. § 131.10(k). It should be noted, however, that these types of use
refinements are changes to a State's of Tribe's WQS and therefore require public notice and
review and EPA approval.
VIII. Temperature Limits for NPDES Sources
Section 301(b)(l)(C) of the CWA requires the achievement of NPDES effluent limitations as
necessary to meet applicable WQS. EPA Region 10's general practice is to require that numeric
criteria be met at end-of-pipe in impaired waterbodies (i.e., those that exceed water quality
criteria). However, EPA Region 10 believes that in some situations numeric criteria end-of-pipe
effluent limits for temperature may not be necessary to meet applicable WQS and protect
salmonids in impaired waters. This is because the temperature effects from point source
discharges generally diminish downstream quickly as heat is added and removed from a
waterbody through natural equilibrium processes. The effects of temperature are unlike the
effects of chemical pollutants, which may remain unaltered in the water column and/or
accumulate in sediments and aquatic organisms. Further, temperature impairments in Pacific
Northwest waters are largely caused by non-point sources. However, there may be situations
where numeric criteria (or near numeric criteria) end-of-pipe effluent limits would be warranted,
such as where a point source heat discharge is significant relative to the size of the river.
If a facility discharging heat into an impaired waterbody is seeking an effluent limit that is
different than end-of-pipe numeric criteria, it should undertake a comprehensive temperature
42
-------
study. EPA recommends that regulatory authorities develop guidance on the content of these
studies and on how alternative effluent limits may be developed that protect salmonids. EPA
recommends that a temperature study, at a minimum, should consist of the following:
A detailed engineering evaluation of sources of heat and possible measures to
eliminate/reduce the heat sources and/or mitigate the effect of the heat sources.
This could, for example, take the form of an engineering analysis of
manufacturing processes or an investigation of sources of heat into publically-
owned treatment plants. The engineering evaluation should include cost
estimates for the possible temperature reduction measures.
A modeling evaluation to determine a preliminary temperature effluent limit that
meets the numeric criterion for the waterbody (or natural background temperature
if applicable - see Section VI.2.C). For instance, it may be appropriate to use a
simple energy balance equation (U.S. EPA, 1996) to calculate an effluent
temperature that would ensure any downstream temperature increase above the
numeric criterion (or natural background temperature) is de minimis (e.g., less
than 0.25°C) after complete mixing. This approach assumes the State's or Tribe's
WQS includes a de minimis temperature allowance as described in Section V.I.A.
When using this approach, EPA recommends that the upstream water
temperatures be assumed to be at the numeric criterion (or natural background
temperature) and that a river flow be used that minimizes the percentage of the
flow utilized for mixing purposes (e.g., 25% of 7Q10). The preliminary
temperature effluent limit using this method should not exceed the current
effluent temperature. In some situations it may be appropriate to utilize more
complex modeling than described here (e.g., waters with multiple point source
impacts).
An evaluation of localized impacts of the thermal plume on salmonids based on
plume modeling. The physical characteristics of the thermal plume (e.g., a 3-
dimensional profile of temperatures) can be estimated using a near-field dilution
model and adequate input data to run the model (e.g., river and effluent
temperatures and flows). The preliminary effluent temperature derived from
above (i.e., the effluent temperature derived from the energy balance equation or
the current effluent temperature, whichever is lower) should be used in the model
along with the current river temperature and flow for the seasons of concern. The
preliminary effluent limit should be lowered, if necessary, to ensure that the
localized adverse impacts on salmonids described in Section V.3 are avoided or
minimized.
The results of these evaluations should be used to assist in the development of the final permit
effluent limit in waters where a temperature TMDL has yet to be completed. Modeling
evaluations, such as those described above, should be used in temperature TMDLs to help set
wasteload allocations that can be used as temperature limits in NPDES permits. It may not be
43
-------
practicable, however, to complete near-field plume modeling for some or all point sources in
large-scale temperature TMDLs. In these situations, the TMDL should indicate that the thermal
plume modeling be done during permit development, which may result in an effluent limit lower
than the TMDL wasteload allocation.
EPA Region 10 also believes that water quality trading may hold some promise to meet
temperature WQS in a cost-effective manner that is beneficial for salmonids. In particular, a
point source may be able to seek trades with non-point sources as a mechanism to meet its
NPDES obligations. For example, a point source may help secure non-point controls beyond
minimum state requirements, such as re-vegetation of a river's riparian zone, and use those
temperature reductions to help meet its temperature reduction obligations. EPA encourages the
use of this potentially valuable approach to help attain temperature WQS.
IX. The Role of Temperature WQS in Protecting and Recovering ESA-Listed
Salmonids and Examples of Actions to Restore Suitable Water Temperatures
EPA Region 10 and the Services believe that State and Tribal temperature WQS can be a
valuable tool to protect and aid in the recovery of threatened and endangered salmonid species in
the Pacific Northwest. The following are three important ways that temperature WQS, and
measures to meet WQS, can protect salmonid populations and thereby aid in the recovery of
these species. The first is to protect existing high quality waters (i.e., waters that currently are
colder than the numeric criteria) and prevent any further thermal degradation in these areas. The
second is to reduce maximum temperatures in thermally degraded stream and river reaches
immediately downstream of the existing high quality habitat (e.g., downstream of wilderness
areas and unimpaired forest lands), thereby expanding the habitat that is suitable for coldwater
salmonid rearing and spawning. The third is to lower maximum temperatures and protect and
restore the natural thermal regime in lower river reaches in order to improve thermal conditions
for migration.
The following are examples of specific on-the-ground actions that could be done to meet
temperature WQS, protect salmonid populations and also aid in the recovery of threatened and
endangered salmonid species. Logically, these example actions are oriented toward reversing
the human activities that can contribute to excess warming of river temperatures described in
Section IV.2. See Issue Paper 3, Coutant (1999), and Return to the River (2000) for more
detailed discussion. EPA encourages and hopes to help facilitate these types of actions and
recognizes that collaborative efforts with multiple stakeholders holds the most promise to
implement many of these measures.
• Replant native riparian vegetation
• Install fencing to keep livestock away from streams
• Establish protective buffer zones to protect and restore riparian vegetation
• Reconnect portions of the river channel with its floodplain
44
-------
• Re-contour streams to follow their natural meandering pattern
• Increase flow in the river derived from more efficient use of water withdrawals
• Discharge cold water from stratified reservoirs behind dams
• Lower reservoirs to reduce the amount of shallow water in "overbank" zones
• Restore more natural flow regimes to allow alluvial river reaches to function
Restore more natural flow regimes so that river temperatures exhibit a more
natural diurnal and seasonal temperature regime
EPA and the Services acknowledge that efforts are underway on the part of some landowners,
companies, non-profit organizations, tribes, local and state governments, and federal agencies in
the Pacific Northwest to take actions to protect and restore suitable temperatures for salmonids
and improve salmonid habitat generally. A few examples of broad-scale actions to improve
temperatures for salmonids are: the Aquatic Conservation Strategy of the Northwest Forest Plan
(federal lands); the State of Washington's forest protection regulations; and timber company
Habitat Conservation Plans (HCPs), particularly the Simpson HCP, which was done concurrent
with a temperature TMDL. Additionally, there are small-scale projects, which are too numerous
to list here (e.g., tree plantings, fencing, and re-establishing the natural meandering channel of
small streams), that have already contributed or will contribute to improved thermal conditions
for salmonids. These efforts represent a good direction and start in the process of restoring
stream temperatures in the Pacific Northwest.
EPA and the Services believe it is important to highlight these examples of on-the-ground
actions to recognize their contribution to improving water temperatures, to demonstrate their
feasibility, and to provide a model for others to take similar actions.
45
-------
X. References
Technical Papers Developed in Support of EPA Region IP's Temperature Guidance - see EPA's
website at www.epa.gov/rlOearth/tetnperature.httn for the below references
Issue Paper 1: Salmonid Behavior and Water Temperature, Prepared as Part of EPA Region 10
Temperature Water Quality Criteria Guidance Development Project. EPA-910-D-01-001, May
2001.
Issue Paper 2: Salmonid Distribution and Temperature, Prepared as Part of EPA Region 10
Temperature Water Quality Criteria Guidance Development Project. EPA-910-D-01-002, May
2001.
Issue Paper 3: Spatial and Temporal Patterns of Stream Temperature, Prepared as Part of EPA
Region 10 Temperature Water Quality Criteria Guidance Development Project. EPA-910-D-01-
003, May 2001.
Issue Paper 4: Temperature Interaction, Prepared as Part of EPA Region 10 Temperature Water
Quality Criteria Guidance Development Project. EPA-910-D-01-004, May 2001.
Issue Paper 5: Summary of Technical Literature examining the Physiological Effects of
Temperature on Salmonids, Prepared as Part of EPA Region 10 Temperature Water Quality
Criteria Guidance Development Project. EPA-910-D-01-005, May 2001.
Technical Synthesis: Scientific Issues Relating to Temperature Criteria for Salmon, Trout, and
Char Native to the Pacific Northwest, A summary report submitted to the policy workgroup of
the EPA Region 10 Water Temperature Criteria Guidance Project. EPA-910-D-01-007, May
2001.
Bull Trout Peer Review, 2002. The following papers were part of the bull trout peer review.
Myrick, Christopher A. et. al. 2002. Bull Trout Temperature Thresholds Peer Review
Summary
Bull Trout Peer Review Questions and EPA's "Straw" Proposal. 2002.
McCullough, D. and Spaulding, S. 2002. Multiple Lines of Evidence for Determining
Upper Optimal Temperature Thresholds
Idaho Department of Environmental Quality (IDEQ). 2002. Dissenting Opinion on
Biological Threshold Numbers proposed by Regional Temperature Criteria Development
Technical Workgroup.
46
-------
Washington Department of Ecology (WDOE). 2002. Evaluating Standards for
Protection Aquatic Life in Washington's Surface Water Quality Standards, Temperature
Criteria, Draft Discussion Paper and Literature Summary. Pages 17 - 30.
Johnson, L. Sherri, et. al. 2002. Summary of Scientific Peer Review Discussion Concerning US
EPA Region 10 Guidance For Stream Temperature Water Quality Standards
Other Reports or Studies Cited in Draft Guidance
Bartholow, J.M., 2000, Estimating cumulative effects of clearcutting on stream temperatures,
Rivers, 7(4), 284-297.
Chapman, D. W. 2002. Review of Proposed Regional Temperature Criteria. Report to Idaho
Department of Environmental Quality. Contract Number C165. BioAnalysts, Inc.
Coutant, C. Charles. 1973. Effect of thermal shock on vulnerability of juvenile salmonids to
predation. J. Fish. Res. Board Can. 30(7):965-973.
Coutant, C. Charles. 1999. Perspectives On Temperature In The Pacific Northwest's Fresh
Waters. Prepared for the Environmental Protection Agency, Region 10. Oak Ridge National
Laboratory. ORNL/TM-1999/44.
Dunham, J., B. Rieman, and G. Chandler. 2001. Development of Field-Based Models of
Suitable Thermal Regimes For Interior Columbia Basin Salmonids. Interagency Agreement
#00-IA-11222014-521. Final Report to EPA Region 10.
Haas, R. Gordon. 2001. The Mediated Associations and Preferences of Native Bull Trout and
Rainbow Trout With Respect to Maximum Water Temperature, its Measurement Standards, and
Habitat. Pages 53-55 in M.K. Brewin, AJ. Paul, and M. Monica, editors. Ecology and
Management of Northwest Salmonids: Bull Trout II Conference Proceedings. Trout Unlimited
Canada, Calgary, Alberta.
Independent Scientific Group. 1996. Return to the River: Restoration of salmonid fishes in the
Columbia River ecosystem.
Independent Scientific Group. 2000. Return to the River 2000: Restoration of salmonid fishes
in the Columbia River ecosystem. Document NWPPC 2000-12, Northwest Power Planning
Council, Portland, OR
Lee, D.C., JR. Sedell, B.E. Reiman, R.F. Thurow, J.E. Williams. 1997. Broadscale assessment
of aquatic species and habitats. P. 1058-1496. In: T.M. Quigley and S.J. Arbelbide, eds. An
Assessment of Ecosystem Components in the Interior Columbia Basin and portions of the
47
-------
Klamath and Great Basins. U.S. Forest Service General Technical Report PNW-GTR-405.
Portland, OR.
Mathews, G.M. and R.S. Waples. 1991. Status review for Snake River spring and summer
chinook salmon. U.S. Dept. Commer., NOAA Tech. Memo. NMFS F/NWC-200.
Myers, J.M., et al. 1998. Status review of chinook salmon from Washington, Idaho, Oregon, and
California. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-35.
National Marine Fisheries Service. 1996. Factors for Decline. A supplement to the Notice of
Determination for west coast steelhead under the Endangered Species Act. Protected Resources
Branch, Portland, Oregon.
National Marine Fisheries Service. 1998. Factors contributing to the decline of chinook salmon:
An addendum to the 1996 west coast steelhead factors for decline report. Protected Resources
Division, Portland, Oregon.
Northwest Indian Fisheries Commission. 1996. Critical Habitat Issues by Basin for Natural
Chinook Stocks in the Coastal and Puget Sound Areas of Washington State.
Oregon Coastal Salmon Restoration Initiative - Final Plan. 1997. The Oregon Plan for Salmon
and Watersheds.
Oregon Department of Environmental Quality (ODEQ). 2000. Upper Grande Ronde River sub-
basin. Total maximum daily load (TMDL).
Selong, J.H., T.E. McMahon, A.V. Zale, and F.T. Barrows. 2001. Effect of Temperature on
Growth and Survival of Bull Trout, with Application of an Improved Method for Determining
Thermal Tolerance in Fishes. Transactions of the American Fisheries Society 130:1026-1037.
Summer Chum Salmon Conservation Initiative. 2000. An Implementation Plan to Recover
Summer Chum in the Hood Canal and Strait of Juan de Fuca Region. Washington Department
of Fish and Wildlife & Point No Point Treaty Tribes.
Theurer, F.D., I. Lines and T. Nelson. 1985. Interaction Between Riparian Vegetation, Water
Temperature, and Salmonid Habitat in the Tucannon River. Water Resources Bulletin, 21 (1):
53-64.
U.S. EPA NPDES Permit Writers'Manual. 1996. EPA-833-B-96-003. Chapter 6.
Washington Department of Ecology (WDOE). December 2002. Evaluating Standards for
Protection Aquatic Life in Washington's Surface Water Quality Standards, Temperature Criteria,
Draft Discussion Paper and Literature Summary. Pages 105 -108.
48
-------
Welsh, H. Hartwell et al. 2001. Distribution of Juvenile Coho Salmon in Relation to Water
Temperatures in Tributaries of the Mattole River, California. North American Journal of
Fisheries Management 21:464-470, 2001.
Other Related Documents
Oregon Department of Environmental Quality (ODEQ). 1995. 1992-1994 Water quality
standards review. Temperature final issue paper.
McCullough, Dale A. 1999. A Review and Synthesis of Effects of Alterations to the Water
Temperature Regime on Freshwater Life Stages of Salmonids, with Special Reference to
Chinook Salmon. Prepared for the Environmental Protection Agency, Region 10. Columbia
River Inter-Tribal Fish Commission.
Sullivan, K., D.J. Martin, R.D. Cardwell, J.E. Toll, and S. Duke. 2000. An Analysis of the
Effects of Temperature on Salmonids of the Pacific Northwest with Implications for Selecting
Temperature Criteria. Sustainable Ecosystems Institute, Portland, OR.
Washington Department of Ecology (WDOE). December 2002. Evaluating Standards for
Protection Aquatic Life in Washington's Surface Water Quality Standards, Temperature Criteria,
Draft Discussion Paper and Literature Summary.
49
------- |