[Federal Register: January 26, 2010 (Volume 75, Number 16)]
[Proposed Rules]
[Page 4173-4226]
[DOCID:fr26ja10-18]

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Part III

Environmental Protection Agency

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40 CFR Part 131

Water Quality Standards for the State of Florida's Lakes and Flowing
Waters; Proposed Rule

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 131

[EPA-HQ-OW-2009-0596; FRL-9105-1]
RIN 2040-AF11

Water Quality Standards for the State of Florida's Lakes and
Flowing Waters

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing numeric
nutrient water quality criteria to protect aquatic life in lakes and
flowing waters, including canals, within the State of Florida and
proposing regulations to establish a framework for Florida to develop
``restoration standards'' for impaired waters. On January 14, 2009, EPA
made a determination under section 303(c)(4)(B) of the Clean Water Act
(``CWA'' or ``the Act'') that numeric nutrient water quality criteria
for lakes and flowing waters and for estuaries and coastal waters are
necessary for the State of Florida to meet the requirements of CWA
section 303(c). Section 303(c)(4) of the CWA requires the Administrator
to promptly prepare and publish proposed regulations setting forth new
or revised water quality standards (``WQS'' or ``standards'') when the
Administrator, or an authorized delegate of the Administrator,
determines that such new or revised WQS are necessary to meet
requirements of the Act. This proposed rule fulfills EPA's obligation
under section 303(c)(4) of the CWA to promptly propose criteria for
Florida's lakes and flowing waters.

DATES: Comments must be received on or before March 29, 2010.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OW-
2009-0596, by one of the following methods:
    1. www.regulations.gov: Follow the online instructions for
submitting comments.
    2. E-mail<EMAIL_ADDRESS>    3. Mail to: Water Docket, U.S. Environmental Protection Agency,
Mail Code: 2822T, 1200 Pennsylvania Avenue, NW., Washington, DC 20460,
Attention: Docket ID No. EPA-HQ-OW-2009-0596.
    4. Hand Delivery: EPA Docket Center, EPA West Room 3334, 1301
Constitution Avenue, NW., Washington, DC 20004, Attention: Docket ID
No. EPA-HQ-OW-2009-0596. Such deliveries are only accepted during the
Docket's normal hours of operation, and special arrangements should be
made for deliveries of boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OW-2009-
0596. EPA's policy is that all comments received will be included in
the public docket without change and may be made available online at
www.regulations.gov, including any personal information provided,
unless the comment includes information claimed to be Confidential
Business Information (CBI) or other information whose disclosure is
restricted by statute. Do not submit information that you consider to
be CBI or otherwise protected through www.regulations.gov or e-mail.
The www.regulations.gov Web site is an ``anonymous access'' system,
which means EPA will not know your identity or contact information
unless you provide it in the body of your comment. If you send an e-
mail comment directly to EPA without going through www.regulations.gov
your e-mail address will be automatically captured and included as part
of the comment that is placed in the public docket and made available
on the Internet. If you submit an electronic comment, EPA recommends
that you include your name and other contact information in the body of
your comment and with any disk or CD-ROM you submit. If EPA cannot read
your comment due to technical difficulties and cannot contact you for
clarification, EPA may not be able to consider your comment. Electronic
files should avoid the use of special characters, any form of
encryption, and be free of any defects or viruses. For additional
information about EPA's public docket visit the EPA Docket Center
homepage at http://www.epa.gov/epahome/dockets.htm.
    Docket: All documents in the docket are listed in the
www.regulations.gov index. Although listed in the index, some
information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, will be publicly available only in hard copy.
Publicly available docket materials are available either electronically
in www.regulations.gov or in hard copy at a docket facility. The Office
of Water (OW) Docket Center is open from 8:30 until 4:30 p.m., Monday
through Friday, excluding legal holidays. The OW Docket Center
telephone number is<PHONE_NUMBER>, and the Docket address is OW
Docket, EPA West, Room 3334, 1301 Constitution Avenue, NW., Washington,
DC 20004. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m.,
Monday through Friday, excluding legal holidays. The telephone number
for the Public Reading Room is<PHONE_NUMBER>.
    Public hearings will be held in the following cities in Florida:
Tallahassee, Orlando, and West Palm Beach. The public hearing in
Tallahassee is scheduled for Tuesday, February 16, 2010 and will be
held from 1 p.m. to 5 p.m. and 7 p.m. to 10 p.m. at the Holiday Inn
Capitol East, 1355 Apalachee Parkway, Tallahassee, FL 32301. The public
hearing in Orlando is scheduled for Wednesday, February 17, 2010 and
will be held from 1 p.m. to 5 p.m. and 7 p.m. to 10 p.m. at the Crowne
Plaza Orlando Universal, 7800 Universal Boulevard, Orlando, FL 32819.
The public hearing in West Palm Beach is scheduled for Thursday,
February 18, 2010 and will be held from 1 p.m. to 5 p.m. and 7 p.m. to
10 p.m. at the Holiday Inn Palm Beach Airport, 1301 Belvedere Road,
West Palm Beach, FL 33405. If you need a sign language interpreter at
any of these hearings, you should contact Sharon Frey at<PHONE_NUMBER>
or<EMAIL_ADDRESS>at least ten business days prior to the meetings
so that appropriate arrangements can be made. For further information,
including registration information, please refer to the following Web
site: http://www.epa.gov/waterscience/standards/rules/florida/.

FOR FURTHER INFORMATION CONTACT: Danielle Salvaterra, U.S. EPA
Headquarters, Office of Water, Mailcode: 4305T, 1200 Pennsylvania
Avenue, NW., Washington, DC 20460; telephone number:<PHONE_NUMBER>; fax
number:<PHONE_NUMBER>; e-mail address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: This supplementary information section is
organized as follows:

Table of Contents

I. General Information
    A. Executive Summary
    B. What Entities May Be Affected by This Rule?
    C. What Should I Consider as I Prepare My Comments for EPA?
    D. How Can I Get Copies of This Document and Other Related
Information?
II. Background
    A. Nutrient Pollution
    B. Statutory and Regulatory Background
    C. Water Quality Criteria
    D. Agency Determination Regarding Florida
III. Proposed Numeric Nutrient Criteria for the State of Florida's
Lakes and Flowing Waters
    A. General Information
    B. Proposed Numeric Nutrient Criteria for the State of Florida's
Lakes
    C. Proposed Numeric Nutrient Criteria for the State of Florida's
Rivers and Streams

    D. Proposed Numeric Nutrient Criteria for the State of Florida's
Springs and Clear Streams
    E. Proposed Numeric Nutrient Criteria for South Florida Canals
    F. Comparison Between EPA's and Florida DEP's Proposed Numeric
Nutrient Criteria for Florida's Lakes and Flowing Waters
    G. Applicability of Criteria When Final
IV. Under What Conditions Will Federal Standards Be Either Not
Finalized or Withdrawn?
V. Alternative Regulatory Approaches and Implementation Mechanisms
    A. Designating Uses
    B. Variances
    C. Site-Specific Criteria
    D. Compliance Schedules
VI. Proposed Restoration Water Quality Standards (WQS) Provision
VII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132 (Federalism)
    F. Executive Order 13175 (Consultation and Coordination With
Indian Tribal Governments)
    G. Executive Order 13045 (Protection of Children From
Environmental Health and Safety Risks)
    H. Executive Order 13211 (Actions That Significantly Affect
Energy Supply, Distribution, or Use)
    I. National Technology Transfer Advancement Act of 1995
    J. Executive Order 12898 (Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations)

I. General Information

A. Executive Summary

    Excess loadings of nitrogen and phosphorus, commonly referred to as
nutrient pollution, are one of the most prevalent causes of water
quality impairment in the United States. Anthropogenic nitrogen and
phosphorus over-enrichment in many of the Nation's waters is a
widespread, persistent, and growing problem. Nutrient pollution can
significantly impact aquatic life and long-term ecosystem health,
diversity, and balance. More specifically, high nitrogen and phosphorus
loadings, or nutrient pollution, result in harmful algal blooms (HABs),
reduced spawning grounds and nursery habitats, fish kills, and oxygen-
starved hypoxic or ``dead'' zones. Public health concerns related to
nutrient pollution include impaired drinking water sources, increased
exposure to toxic microbes such as cyanobacteria, and possible
formation of disinfection byproducts in drinking water, some of which
have been associated with serious human illnesses such as bladder
cancer. Nutrient problems can exhibit themselves locally or much
further downstream leading to degraded lakes, reservoirs, and
estuaries, and to hypoxic zones where fish and aquatic life can no
longer survive.
    In the State of Florida, nutrient pollution has contributed to
severe water quality degradation. Based upon waters assessed and
reported in the 2008 Integrated Water Quality Assessment for Florida,
approximately 1,000 miles of rivers and streams, 350,000 acres of
lakes, and 900 square miles of estuaries are known to be impaired for
nutrients by the State.\1\ The actual number of stream miles, lake
acres, and estuarine square miles of waters impaired for nutrients in
Florida may be higher, as many waters currently are classified as
``unassessed.''
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    \1\ Florida Department of Environmental Protection. 2008.
Integrated Water Quality Assessment for Florida: 2008 305(b) Report
and 303(d) List Update, p. 67.
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    The challenge of nutrient pollution has been a top priority for
Florida's Department of Environmental Protection (FDEP). Over the past
decade or more, FDEP has spent over 20 million dollars collecting and
analyzing data on the relationship between phosphorus, nitrogen, and
nitrite-nitrate concentrations and the biological health of aquatic
systems. Moreover, Florida is one of the few states that has in place a
comprehensive framework of accountability that applies to both point
and nonpoint sources and provides the enforceable authority to address
nutrient reductions in impaired waters based upon the establishment of
site-specific total maximum daily loads (TMDLs).
    Despite FDEP's intensive efforts to diagnose and control nutrient
pollution, substantial water quality degradation from nutrient over-
enrichment remains a significant problem. On January 14, 2009, EPA
determined under CWA section 303(c)(4)(B) that new or revised WQS in
the form of numeric nutrient water quality criteria are necessary to
meet the requirements of the CWA in the State of Florida. The Agency
considered (1) the State's documented unique and threatened ecosystems,
(2) the high number of impaired waters due to existing nutrient
pollution, and (3) the challenge associated with growing nutrient
pollution resulting from expanding urbanization, continued agricultural
development, and a significantly increasing population that is expected
to grow 75% between 2000 to 2030.\2\ EPA also reviewed the State's
regulatory nutrient accountability system, which represents an
impressive synthesis of technology-based standards, point source
control authority, and authority to establish enforceable controls for
nonpoint source activities. However, the significant challenge faced by
the water quality components of this system is its dependence upon an
approach involving resource-intensive and time-consuming site-specific
data collection and analysis to interpret non-numeric narrative
nutrient criteria. EPA determined that Florida's reliance on a case-by-
case interpretation of its narrative nutrient criterion in implementing
an otherwise comprehensive water quality framework of enforceable
accountability was insufficient to ensure protection of applicable
designated uses. As part of the Agency's determination, EPA indicated
that it expected to propose numeric nutrient criteria for lakes and
flowing waters within 12 months, and for estuarine and coastal waters
within 24 months, of the January 14, 2009 determination.
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    \2\ http://www.census.gov/population/projections/
SummaryTabA1.pdf.
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    On August 19, 2009, EPA entered into a phased Consent Decree with
Florida Wildlife Federation, Sierra Club, Conservancy of Southwest
Florida, Environmental Confederation of Southwest Florida, and St.
Johns Riverkeeper, committing to sign a proposed rule setting forth
numeric nutrient criteria for lakes and flowing waters in Florida by
January 14, 2010, and for Florida's estuarine and coastal waters by
January 14, 2011, unless Florida submits and EPA approves State numeric
nutrient criteria before EPA's proposal. The phased Consent Decree also
provides that EPA issue a final rule by October 15, 2010 for lakes and
flowing water, and by October 15, 2011 for estuarine and coastal
waters, unless Florida submits and EPA approves State numeric nutrient
criteria before a final EPA action.
    Accordingly, this proposal is part of a phased rulemaking process
in which EPA will propose and take final action in 2010 on numeric
nutrient criteria for lakes and flowing waters and for estuarine and
coastal waters in 2011. The two phases of this rulemaking are linked
because nutrient pollution in Florida's rivers and streams affects not
only instream aquatic conditions but also downstream estuarine and
coastal waters ecosystem conditions. The Agency could have waited to
propose estuarine and coastal downstream protection criteria values for
rivers and streams as part of the second phase of this rulemaking
process. However, the substantial data, peer-reviewed methodologies,
and extensive scientific

analyses available to and conducted by the Agency to date indicate that
numeric nutrient water quality criteria for estuarine and coastal
waters, when proposed and finalized in 2011, may result in the need for
more stringent rivers and streams criteria to ensure protection of
downstream water quality, particularly for the nitrogen component of
nutrient pollution. Therefore, considering the numerous requests for
the Agency to share its analysis and scientific and technical
conclusions at the earliest possible opportunity to allow for full
review and comment, EPA is including downstream protection values for
total nitrogen (TN) as proposed criteria for rivers and streams to
protect the State's estuaries and coastal waters in this notice.
    As described in more detail below and in the technical support
document accompanying this notice, these proposed nitrogen downstream
protection values are based on substantial data, thorough scientific
analysis, and extensive technical evaluation. However, EPA recognizes
that additional data and analysis may be available, including data for
particular estuaries, to help inform what numeric nutrient criteria are
necessary to protect Florida's waters, including downstream lakes and
estuaries. EPA also recognizes that substantial site-specific work has
been completed for a number of these estuaries. This notice and the
proposed downstream protection values are not intended to address or be
interpreted as calling into question the utility and protectiveness of
these site-specific analyses. Rather, the proposed values represent the
output of a systematic and scientific approach that was developed to be
generally applicable to all flowing waters in Florida that terminate in
estuaries for the purpose of ensuring the protection of downstream
estuaries. EPA is interested in obtaining feedback at this time on this
systematic and scientific approach. EPA is also interested in feedback
regarding site-specific analyses for particular estuaries that should
be used instead of this general approach for establishing final values.
The Agency further recognizes that the proposed values in this notice
will need to be considered in the context of the Agency's numeric
nutrient criteria for estuarine and coastal waters scheduled for
proposal in January of 2011.
    Regarding the criteria for flowing waters for protection of
downstream lakes and estuaries, at this time, EPA intends to take final
action on the criteria for protection of downstream lakes as part of
the first phase of this rulemaking (by October 15, 2010) and to
finalize downstream protection values in flowing waters as part of the
second phase of this rulemaking process (by October 15, 2011) in
coordination with the proposal and finalization of numeric nutrient
criteria for estuarine and coastal waters in 2011. However, if
comments, data and analyses submitted as a result of this proposal
support finalizing these values sooner, by October 2010, EPA may choose
to proceed in this manner. To facilitate this process, EPA requests
comments and welcomes thorough evaluation on the technical and
scientific basis of these proposed downstream protection values, as
well as information on estuaries where site-specific analyses should be
used, as part of the broader comment and evaluation process that this
proposal initiates.
    In accordance with the terms of EPA's January 14, 2009
determination and the Consent Decree, EPA is proposing numeric nutrient
criteria for Florida's lakes and flowing waters which include the
following four water body types: Lakes, streams, springs and clear
streams, and canals in south Florida. In developing this proposal, EPA
worked closely with FDEP staff to review and analyze the State's
extensive dataset of nutrient-related measurements as well as its
analysis of stressor-response relationships and benchmark or modified-
reference conditions. EPA also conducted further analyses and modeling,
in addition to requesting an independent external peer review of the
core methodologies and approaches that support this proposal.
    For lakes, EPA is proposing a classification scheme using color and
alkalinity based upon substantial data that show that lake color and
alkalinity play an important role in the degree to which TN and total
phosphorus (TP) concentrations result in a biological response such as
elevated chlorophyll a levels. EPA found that correlations between
nutrients and biological response parameters in the different types of
lakes in Florida were sufficiently robust, combined with additional
lines of evidence, to support stressor-response criteria development
for Florida's lakes. The Agency is also proposing an accompanying
supplementary analytical approach that the State can use to adjust TN
and TP criteria for a particular lake within a certain range where
sufficient data on long-term ambient TN and TP levels are available to
demonstrate that protective chlorophyll a criteria for a specific lake
will still be maintained and attainment of the designated use will be
assured. This information is presented in more detail in Section III.B
below.
    Regarding numeric nutrient criteria for streams and rivers, EPA
considered the extensive work of FDEP to analyze the relationship
between TN and TP levels and biological response in streams and rivers.
EPA found that relationships between nutrients and biological response
parameters in rivers and streams were affected by many factors that
made derivation of a quantitative relationship between chlorophyll a
levels and nutrients in streams and rivers difficult to establish in
the same manner as EPA did for lakes (i.e., stressor-response
relationship). EPA considered an alternative methodology that evaluated
a combination of biological information and data on the distribution of
nutrients in a substantial number of healthy stream systems. Based upon
a technical evaluation of the significant available data on Florida
streams and related scientific analysis, the Agency concluded that
reliance on a statistical distribution methodology was a stronger and a
more sound approach for deriving TN and TP criteria in streams and
rivers. This information is presented in more detail in Section III.C
below.
    In developing these proposed numeric nutrient criteria for rivers
and streams, EPA also evaluated their effectiveness for assuring the
protection of downstream lake and estuary designated uses pursuant to
the provisions of 40 CFR 130.10(b), which requires that WQS must
provide for the attainment and maintenance of the WQS of downstream
waters. For rivers and streams in Florida, EPA must ensure, to the
extent that available science allows, that its nutrient criteria take
into account the impact of near-field nutrient loads on aquatic life in
downstream lakes and estuaries. EPA currently has evaluated the
protectiveness of its rivers and streams TP criteria for lake
protection and also the protectiveness of its rivers and streams TN
criteria for 16 out of 26 of Florida's downstream estuaries using
scientifically sound approaches for both estimating protective loads
and deriving concentration-based upstream values. Of the ten downstream
estuaries not completely evaluated to date, seven are in south Florida
and receive TN loads from highly managed canals and waterways and three
are in low lying areas of central Florida.
    As noted above, EPA used best available science and data related to
downstream waters and found that there are cases where the nutrient
criteria EPA is proposing to protect instream aquatic life may not be
stringent enough to ensure protection of aquatic life in certain
downstream lakes and estuaries. Accordingly, EPA is also proposing an

equation that would be used to adjust stream and river TP criteria to
protect downstream lakes and a different methodology to adjust TN
criteria for streams and rivers to ensure protection of downstream
estuaries. These approaches as reflected in these proposed regulations
and the revised criteria that would result from adjusting TN criteria
for streams and rivers to ensure protection of downstream estuaries,
based on certain assumptions, are detailed in Section III.C(6)(b)
below. The Agency specifically requests comment on the available
information, analysis, and modeling used to support the approaches EPA
is proposing for addressing downstream impacts of TN and TP. EPA also
invites additional stakeholder comment, data, and analysis on
alternative technically-based approaches that would support the
development of numeric nutrient WQS, or some other scientifically
defensible approach, for protection of downstream waters. To the degree
that substantial data and analyses are submitted that support a
significant revision to downstream protection values for TN outlined in
Section III.C(6)(b) below, EPA would intend to issue a supplemental
Federal Register Notice of Data Availability (NODA) to present the
additional data and supplemental analyses and solicit further comment
and input. EPA anticipates obtaining the necessary data and information
to compute downstream protection values for TP loads for many estuarine
water bodies in Florida in 2010 and will also make this additional
information available by issuing a supplemental Federal Register NODA.
    Regarding numeric nutrient criteria for springs and clear streams,
EPA is proposing a nitrate-nitrite criterion for springs and clear
streams based on experimental laboratory data and field evaluations
that document the response of nuisance algae and periphyton to nitrate-
nitrite concentrations. This criterion is explained in more detail in
Section III.D below.
    For canals in south Florida, EPA is proposing a statistical
distribution approach similar to its approach for rivers and streams,
and based on sites meeting designated uses with respect to nutrients
identified in four canal regions to best represent the necessary
criteria to protect these highly managed water bodies. This approach is
presented in more detail in Section III.E below. The Agency has also
considered several alternative approaches to developing numeric
nutrient criteria for canals and these are described, as well, for
public comment and response.
    Stakeholders have expressed concerns that numeric nutrient criteria
must be scientifically sound. Under the Clean Water Act and EPA's
implementing regulations, numeric nutrient standards must protect the
designated use of a water (as well as ensure protection of downstream
uses) and must be based on sound scientific rationale. In the case of
Florida, EPA and FDEP scientists completed a substantial body of
scientific work; EPA believes that these proposed criteria clearly meet
the regulatory standards of protection and that they are clearly based
on a sound scientific rationale.
    Separate from and in addition to proposing numeric nutrient
criteria, EPA is also proposing a new WQS regulatory tool for Florida,
referred to as ``restoration WQS'' for impaired waters. This tool will
enable Florida to set incremental water quality targets (uses and
criteria) for specific pollutant parameters while at the same time
retaining protective criteria for all other parameters to meet the full
aquatic life use. The goal is to provide a challenging but realistic
incremental framework in which to establish appropriate control
measures. This provision will allow Florida to retain full aquatic life
protection (uses and criteria) for its water bodies while establishing
a transparent phased WQS process that would result in planned
implementation of enforceable measures and requirements to improve
water quality over a specified time period to ultimately meet the long-
term designated aquatic life use. The phased numeric standards would be
included in Florida's water quality regulations during the restoration
period. This proposed regulatory tool is discussed in more detail in
Section VI below.
    Finally, EPA is including in this notice a proposed approach for
deriving Federal site-specific alternative criteria (SSAC) based upon
State submissions of scientifically defensible recalculations that meet
the requirements of CWA section 303(c). TMDL targets submitted to EPA
by the State for consideration as new or revised WQS could be reviewed
under this SSAC process. This proposed approach is discussed in more
detail in Section V.C below.
    Overall, EPA is soliciting comments and data regarding EPA's
proposed criteria for lakes and flowing waters, the derivation of these
criteria, the protectiveness of the streams and rivers criteria for
downstream waters, and all associated alternative options and
methodologies discussed in this proposed rulemaking.

B. What Entities May Be Affected by This Rule?

    Citizens concerned with water quality in Florida may be interested
in this rulemaking. Entities discharging nitrogen or phosphorus to
lakes and flowing waters of Florida could be indirectly affected by
this rulemaking because WQS are used in determining National Pollutant
Discharge Elimination System (``NPDES'') permit limits. Stakeholders in
Florida facing obstacles in immediately achieving full aquatic life
protection in impaired waters may be interested in the restoration
standards concept outlined in this rulemaking. Categories and entities
that may ultimately be affected include:

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                                             Examples of potentially
                Category                        affected entities
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Industry...............................  Industries discharging
                                          pollutants to lakes and
                                          flowing waters in the State of
                                          Florida.
Municipalities.........................  Publicly-owned treatment works
                                          discharging pollutants to
                                          lakes and flowing waters in
                                          the State of Florida.
Stormwater Management Districts........  Entities responsible for
                                          managing stormwater runoff in
                                          Florida.
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    This table is not intended to be exhaustive, but rather provides a
guide for entities that may be directly or indirectly affected by this
action. This table lists the types of entities of which EPA is now
aware that potentially could be affected by this action. Other types of
entities not listed in the table could also be affected, such as
nonpoint source contributors to nutrient pollution in Florida's waters.
Any parties or entities conducting activities within watersheds of the
Florida waters covered by this rule, or who rely on, depend upon,
influence, or contribute to the water quality of the lakes and flowing
waters of Florida, might be affected by this rule. To determine whether
your facility or activities may be affected by this action, you should
examine this proposed rule. If you have questions regarding the
applicability of this action to a particular entity, consult the person
listed in the preceding FOR FURTHER INFORMATION CONTACT section.

C. What Should I Consider as I Prepare My Comments for EPA?

    1. Submitting CBI. Do not submit this information to EPA through
http://www.regulations.gov or e-mail. Clearly mark the part or all of
the information that you claim to be CBI. For CBI information in a disk
or CD-ROM that

you mail to EPA, mark the outside of the disk or CD-ROM as CBI and then
identify electronically within the disk or CD-ROM the specific
information that is claimed as CBI. In addition to one complete version
of the comment that includes information claimed as CBI, a copy of the
comment that does not contain the information claimed as CBI must be
submitted for inclusion in the public docket. Information so marked
will not be disclosed except in accordance with procedures set forth in
40 CFR part 2.
    2. Tips for Preparing Your Comments. When submitting comments,
remember to:
    1. Identify the rulemaking by docket number and other identifying
information (subject heading, Federal Register date, and page number).
    2. Follow directions--The agency may ask you to respond to specific
questions or organize comments by referencing a Code of Federal
Regulations (CFR) part or section number.
    3. Explain why you agree or disagree; suggest alternatives and
substitute language for your requested changes.
    4. Describe any assumptions and provide any technical information
and/or data that you used.
    5. If you estimate potential costs or burdens, explain how you
arrived at your estimate in sufficient detail to allow for it to be
reproduced.
    6. Provide specific examples to illustrate your concerns, and
suggest alternatives.
    7. Make sure to submit your comments by the comment period deadline
identified.

D. How Can I Get Copies of This Document and Other Related Information?

    1. Docket. EPA has established an official public docket for this
action under Docket Id. No. EPA-HQ-OW-2009-0596. The official public
docket consists of the document specifically referenced in this action,
any public comments received, and other information related to this
action. Although a part of the official docket, the public docket does
not include CBI or other information whose disclosure is restricted by
statute. The official public docket is the collection of materials that
is available for public viewing at the OW Docket, EPA West, Room 3334,
1301 Constitution Ave., NW., Washington, DC 20004. This Docket Facility
is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding
legal holidays. The Docket telephone number is<PHONE_NUMBER>. A
reasonable fee will be charged for copies.
    2. Electronic Access. You may access this Federal Register document
electronically through the EPA Internet under the ``Federal Register''
listings at http://www.epa.gov/fedrgstr/.
    An electronic version of the public docket is available through
EPA's electronic public docket and comment system, EPA Dockets. You may
use EPA Dockets at http://www.regulations.gov to view public comments,
access the index listing of the contents of the official public docket,
and to access those documents in the public docket that are available
electronically. For additional information about EPA's public docket,
visit the EPA Docket Center homepage at http://www.epa.gov/epahome/
dockets.htm. Although not all docket materials may be available
electronically, you may still access any of the publicly available
docket materials through the Docket Facility identified in Section
I.D(1).

II. Background

A. Nutrient Pollution

1. What Is Nutrient Pollution?
    Excess anthropogenic concentrations of nitrogen (typically in
oxidized, inorganic forms, such as nitrate) \3\ and phosphorus
(typically as phosphate), commonly referred to as nutrient pollution,
in surface waters can result in excessive algal and aquatic plant
growth, referred to as eutrophication.\4\ One impact associated with
eutrophication is low dissolved oxygen, due to decomposition of the
aquatic plants and algae when these plants and algae die. As noted
above, high nitrogen and phosphorus loadings also result in HABs,
reduced spawning grounds and nursery habitats for aquatic life, and
fish kills. Public health concerns related to eutrophication include
impaired drinking water sources, increased exposure to toxic microbes
such as cyanobacteria, and possible formation of disinfection
byproducts in drinking water, some of which have been associated with
serious human illnesses such as bladder cancer.5 6 Nutrient
problems can manifest locally or much further downstream in lakes,
reservoirs, and estuaries.
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    \3\ To be used by living organisms, nitrogen gas must be fixed
into its reactive forms; for plants, either nitrate or ammonia.
    \4\ Eutrophication is defined as an increase in organic carbon
to an aquatic ecosystem caused by primary productivity stimulated by
excess nutrients--typically compounds containing nitrogen or
phosphorus. Eutrophication can adversely affect aquatic life,
recreation, and human health uses of waters.
    \5\ Villanueva, C.M. et al., 2006. Bladder Cancer and Exposure
to Water Disinfection By-Products through Ingestion, Bathing,
Showering, and Swimming in Pools. American Journal of Epidemiology,
165(2):148-156.
    \6\ U.S. EPA. 2009. What Is in Our Drinking Water. United States
Environmental Protection Agency, Office of Research and Development.
http://www.epa.gov/extrmurl/research/process/drinkingwater.html.
Accessed December 2009.
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    Excess nutrients in water bodies come from many sources, which can
be grouped into five major categories: (1) Sources associated with
urban land use and development, (2) municipal and industrial waste
water discharge, (3) row crop agriculture, (4) animal husbandry, and
(5) atmospheric deposition that may be increased by production of
nitrogen oxides in electric power generation and internal combustion
engines. These sources contribute significant loadings of nitrogen and
phosphorus to surface waters causing major impacts to aquatic
ecosystems and significant imbalances in the natural populations of
flora and fauna.\7\
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    \7\ National Research Council, 2000. Clean Coastal Waters:
Understanding and Reducing the Effects of Nutrient Pollution. Report
prepared by the Ocean Study Board and Water Science and Technology
Board, Commission on Geosciences, Environment and Resources,
National Resource Council. National Academy Press, Washington, DC;
Howarth, R.W., A. Sharpley, and D. Walker. 2002. Sources of nutrient
pollution to coastal waters in the United States: Implications for
achieving coastal water quality goals. Estuaries. 25(4b):656-676;
Smith, V.H. 2003. Eutrophication of freshwater and coastal marine
ecosystems. Environ. Sci. and Poll. Res. 10(2):126-139; Dodds, W.K.,
W.W. Bouska, J.L. Eitzmann, T.J. Pilger, K.L. Pitts, A.J. Riley,
J.T. Schloesser, and D.J. Thornbrugh. 2009. Eutrophication of U.S.
freshwaters: Analysis of potential economic damages. Environ. Sci.
Tech.. 43(1):12-19.
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2. Adverse Impacts of Nutrient Pollution on Aquatic Life, Human Health,
and the Economy
    To protect aquatic life, EPA regulates pollutants that have adverse
effects on aquatic life. For most pollutants, these effects are
typically negative impacts on growth, reproduction, and survival. As
previously noted, excess nutrients can lead to increases in algal and
other aquatic plant growth, including toxic algae that can result in
HABs. Increases in algal and aquatic plant growth provide excess
organic matter in a water body and can contribute to subsequent
degradation of aquatic communities, human health impacts, and
ultimately economic impacts.
    Fish, shellfish, and wildlife require clean water for survival.
Changes in the environment resulting from elevated nutrient levels
(such as algal blooms, toxins from HABs, and hypoxia/anoxia) can cause
a variety of effects. When excessive nutrient loads change a water
body's algae and plant species, the change in habitat and available
food resources can induce changes affecting an entire food chain. Algal
blooms block

sunlight that submerged grasses need to grow, leading to a decline of
seagrass beds and decreased habitat for juvenile organisms. Algal
blooms can also increase turbidity and impair the ability of fish and
other aquatic life to find food.\8\ Algae can also damage or clog the
gills of fish and invertebrates.\9\
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    \8\ Hauxwell, J. C. Jacoby, T. Frazer, and J. Stevely. 2001.
Nutrients and Florida's Coastal Waters. Florida Sea Grant.
    \9\ NOAA. 2009. Harmful Algal Blooms: Current Programs Overview.
National Oceanic and Atmospheric Administration. http://
www.cop.noaa.gov/stressors/extremeevents/hab/welcome.html. Accessed
December 2009.
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    HABs can form toxins that cause illness or death for some animals.
Some of the more commonly affected animals include sea lions, turtles,
seabirds, dolphins, and manatees.\10\ More than 50% of unusual marine
mortality events may be associated with HABs.\11\ Lower level
consumers, such as small fish or shellfish, may not be harmed by algal
toxins, but they bioaccumulate toxins, causing higher exposures for
higher level consumers (such as larger predator fish), resulting in
health impairments and possibly death.12 13
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    \10\ NOAA. 2009. Harmful Algal Blooms: Current Programs
Overview. National Oceanic and Atmospheric Administration. http://
www.cop.noaa.gov/stressors/extremeevents/hab/welcome.html. Accessed
December 2009.
    \11\ WHOI. 2008. HAB Impacts on Wildlife. Woods Hole
Oceanographic Institution. http://www.whoi.edu/redtide/
page.do?pid=9682. Accessed December 2009.
    \12\ WHOI. 2008. Marine Mammals. Woods Hole Oceanographic
Institution. http://www.whoi.edu/redtide/page.do?pid=14215. Accessed
December 2009.
    \13\ WHOI. 2008. HAB Impacts on Wildlife. Woods Hole
Oceanographic Institution. http://www.whoi.edu/redtide/
page.do?pid=9682. Accessed December 2009.
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    There are many examples of HAB toxins significantly affecting
marine animals. For example, between March and April 2003, 107
bottlenose dolphins (Tursiops truncatus) died, along with hundreds of
fish and marine invertebrates, along the Florida Panhandle.\14\ High
levels of brevetoxin (a neurotoxin), produced by a harmful species of
dinoflagellate (a type of algae), were measured in all of the stranded
dolphins examined, as well as in their fish prey.\15\
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    \14\ WHOI. 2008. Marine Mammals. Woods Hole Oceanographic
Institution. http://www.whoi.edu/redtide/page.do?pid=14215. Accessed
December 2009.
    \15\ WHOI. 2008. Marine Mammals. Woods Hole Oceanographic
Institution. http://www.whoi.edu/redtide/page.do?pid=14215. Accessed
December 2009.
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    In freshwater, cyanobacteria can produce toxins that have been
implicated as the cause of a large number of fish and bird mortalities.
These toxins have also been tied to the death of pets and livestock
that may be exposed through drinking contaminated water or grooming
themselves after bodily exposure.\16\ A recent study showed that at
least one type of cyanobacteria has been linked to cancer and tumor
growth in animals.\17\
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    \16\ WHOI. 2008. HAB Impacts on Wildlife. Woods Hole
Oceanographic Institution. http://www.whoi.edu/redtide/
page.do?pid=9682. Accessed December 2009.
    \17\ Falconer, I.R., A.R. Humpage. 2005. Health Risk Assessment
of Cyanobacterial (Blue-green Algal) Toxins in Drinking Water. Int.
J. Environ. Res. Public Health. 2(1): 43-50.
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    Excessive algal growth contributes to increased oxygen consumption
associated with decomposition, potentially reducing oxygen to levels
below that needed for aquatic life to survive and
flourish.18 19 Low oxygen, or hypoxia, often occurs in
episodic ``events,'' which sometimes develop overnight. Mobile species,
such as adult fish, can sometimes survive by moving to areas with more
oxygen. However, migration to avoid hypoxia depends on species
mobility, availability of suitable habitat, and adequate environmental
cues for migration. Less mobile or immobile species, such as oysters
and mussels, cannot move to avoid low oxygen and are often killed
during hypoxic events.\20\ While certain mature aquatic animals can
tolerate a range of dissolved oxygen levels that occur in the water,
younger life stages of species like fish and shellfish often require
higher levels of oxygen to survive.\21\ Sustained low levels of
dissolved oxygen cause a severe decrease in the amount of aquatic life
in hypoxic zones and affect the ability of aquatic organisms to find
necessary food and habitat. In extreme cases, anoxic conditions occur
when there is a complete lack of oxygen. Very few organisms can live
without oxygen (for example some microbes), hence these areas are
sometimes referred to as dead zones.\22\
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    \18\ NOAA. 2009. Harmful Algal Blooms: Current Programs
Overview. National Oceanic and Atmospheric Administration. http://
www.cop.noaa.gov/stressors/extremeevents/hab/welcome.html. Accessed
December 2009.
    \19\ USGS. 2009. Hypoxia. U.S. Geological Survey. http://
toxics.usgs.gov/definitions/hypoxia.html. Accessed December 2009.
    \20\ ESA. 2009. Hypoxia. Ecological Society of America. http://
www.esa.org/education_diversity/pdfDocs/hypoxia.pdf. Accessed
December 2009.
    \21\ USEPA. 2000. Ambient Aquatic Life Water Quality Criteria
for Dissolved Oxygen (Saltwater): Cape Cod to Cape Hattaras.
Environmental Protection Agency, Office of Water, Washington DC PA-
822-R-00-012.
    \22\ Ecological Society of America. 2009. Hypoxia. Ecological
Society of America, Washington, DC. http://www.esa.org/education/
edupdfs/hypoxia.pdf. Accessed December 2009.
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    Primary impacts to humans result directly from elevated nutrient
pollution levels and indirectly from the subsequent water body changes
that occur from increased nutrients (such as algal blooms and toxins).
Direct impacts include effects on human health through drinking water
or consuming toxic shellfish. Indirect impacts include restrictions on
recreation (such as boating, swimming, and kayaking). Algal blooms can
prevent opportunities to swim and engage in other types of recreation.
In areas where recreation is determined to be unsafe because of algal
blooms, warning signs are often posted to discourage human use of the
waters.
    Highly elevated nitrogen levels, in the form of nitrate, in
drinking water supplies and private wells can cause methemoglobinemia
(blue baby syndrome, which refers to high levels of nitrate in a baby's
blood that reduce the blood's ability to deliver oxygen to the skin and
organs resulting in a bluish tinge to the skin; in severe cases
methemoglobinemia can lead to coma and death).\23\ Monitoring of
Florida Public Water Supplies from 2004-2007 indicates that violations
of nitrate maximum contaminant levels (MCL) ranged from 34-40
violations annually.\24\ In addition, in the predominantly agricultural
regions of Florida, of 3,949 drinking water wells analyzed for nitrate
by the Florida Department of Agriculture and Consumer Services, (FDACS)
and the FDEP, 2,483 (63%) contained detectable nitrate and 584 wells
(15%) contained nitrate above the U.S. EPA MCL. Of the 584 wells
statewide that exceeded the MCL, 519 were located in the Central
Florida Ridge citrus growing region, encompassed primarily by Lake,
Polk and Highland Counties.\25\ Human health can also be impacted by
disinfection byproducts formed when disinfectants (such as chlorine)
used to treat drinking water react with organic carbon (from the algae
in source waters). Some disinfection byproducts have been linked to
rectal, bladder, and colon cancers; reproductive health risks; and
liver, kidney, and central nervous

system problems.26 27 Humans can also be impacted by
accidentally ingesting toxins, resulting from toxic algal blooms in
water, while recreating or by consuming drinking water that still
contains toxins despite treatment. For example, cyanobacteria toxins
can sometimes pass through the normal water treatment process.\28\
After consuming seafood tainted by toxic HABs, humans can develop
gastrointestinal distress, memory loss, disorientation, confusion, and
even coma and death in extreme cases. Some toxins only require a small
dose to cause illness or death.\29\ EPA expects that by addressing
protection of aquatic life uses through the application of the proposed
numeric nutrient criteria in this rulemaking, risks to human health
will also be alleviated, as nutrient levels that represent a balance of
natural populations of flora and fauna will not produce HABs nor result
in highly elevated nitrate levels.
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    \23\ USEPA. 2007. Nitrates and Nitrites. U.S. Environmental
Protection Agency. http://www.epa.gov/teach/chem_summ/Nitrates_
summary.pdf. Accessed December 2009.
    \24\ FDEP 2009. Chemical Data for 2004, 2005, 2006, 2007 and
2008. Florida Department of Environmental Protection. http://
www.dep.state.fl.us/water/drinkingwater/chemdata.htm. Accessed
January 2010.
    \25\ Southern Regional Water Program. 2010. Drinking Water and
Human Health in Florida. Southern Regional Water Program, http://
srwqis.tamu.edu/florida/program-information/florida-target-themes/
drinking-water-and-human-health.aspx. Accessed January 2010.
    \26\ USEPA. 2009. Drinking Water Contaminants. U.S.
Environmental Protection Agency. Accessed http://www.epa.gov/
safewater/hfacts.html. December 2009.
    \27\ CFR. 2006. 40 CFR parts 9, 141, and 142: National Primary
Drinking Water Regulations: Stage 2 Disinfectants and Disinfection
Byproducts Rule. Code of Federal Regulations, Washington, DC. http:/
/www.epa.gov/fedrgstr/EPA-WATER/2006/January/Day-04/w03.htm.
Accessed December 2009.
    \28\ Carmichael, W.W. 2000. Assessment of Blue-Green Algal
Toxins in Raw and Finished Drinking Water. AWWA Research Foundation,
Denver, CO.
    \29\ NOAA. 2009. Marine Biotoxins. National Oceanic and
Atmospheric Administration. http://www.nwfsc.noaa.gov/hab/habs_
toxins/marine_biotoxins/index.html. Accessed December 2009.
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    Nutrient pollution and eutrophication can also impact the economy
through additional reactive costs, such as medical treatment for humans
who ingest HAB toxins, treating drinking water supplies to remove algae
and organic matter, and monitoring water for shellfish and other
affected resources.
    Economic losses from algal blooms and HABs can include reduced
property values for lakefront areas, commercial fishery losses, and
lost revenue from recreational fishing and boating trips, as well as
other tourism-related businesses. Commercial fishery losses occur
because of a decline in the amount of fish available for harvest due to
habitat and oxygen declines. Some HAB toxins can make seafood unsafe
for human consumption, and can reduce the amount of fish bought because
people might question if eating fish is safe after learning of the
presence of the algal bloom.\30\ To put the issue into perspective,
consider the following estimates: For freshwater lakes, losses in
fishing and boating trip-related revenues nationwide due to
eutrophication are estimated to range from $370 million to almost $1.2
billion dollars and loss of lake property values from excessive algal
growth are estimated to range from $300 million to $2.8 billion
annually on a national level.\31\
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    \30\ WHOI. 2008. Hearing on 'Harmful Algal Blooms: The
Challenges on the Nation's Coastlines.' Woods Hole Oceanographic
Institution. http://www.whoi.edu/page.do?pid=8916&tid=282
&cid=46007. Accessed December 2009.
    \31\ Dodds, W.K., W.W. Bouska, J.L. Eitzmann, T.J. Pilger, K.L.
Pitts, A.J. Riley, J.T. Schloesser, and D.J. Thornbrugh. 2009.
Eutrophication of U.S. freshwaters: analysis of potential economic
damages. Environ.l Sci. Tech.y. 43(1):12-19.
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3. Nutrient Pollution in Florida
    Water quality degradation resulting from excess nitrogen and
phosphorus loadings is a documented and significant environmental issue
in Florida. According to Florida's 2008 Integrated Report,\32\
approximately 1,000 miles of rivers and streams, 350,000 acres of
lakes, and 900 square miles of estuaries are impaired for nutrients in
the State. To put this in context, these values represent approximately
5% of the assessed river and stream miles, 23% of the assessed lake
acres, and 24% of the assessed square miles of estuaries that Florida
has listed as impaired in the 2008 Integrated Report.\33\ Nutrients are
ranked as the fourth major source of impairment for rivers and streams
in the State (after dissolved oxygen, mercury in fish, and fecal
coliforms). For lakes and estuaries, nutrients are ranked first and
second, respectively. As discussed above, impairments due to nutrient
pollution result in significant impacts to aquatic life and ecosystem
health. Nutrient pollution also represents, as mentioned above, an
increased human health risk in terms of contaminated drinking water
supplies and private wells.
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    \32\ Florida Department of Environmental Protection. 2008.
Integrated Water Quality Assessment for Florida: 2008 305(b) Report
and 303(d) List Update.
    \33\ Florida Department of Environmental Protection. 2008.
Integrated Water Quality Assessment for Florida: 2008 305(b) Report
and 303(d) List Update.
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    Florida is particularly vulnerable to nutrient pollution.
Historically, the State has experienced a rapidly expanding population,
which is a strong predictor of nutrient loading and associated effects,
and which combined with climate and other natural factors, make Florida
waters sensitive to nutrient effects. Florida is currently the fourth
most populous state in the nation, with an estimated 18 million
people.\34\ Population is expected to continue to grow, resulting in an
expected increase in urban development, home landscapes, and
wastewater. Florida's flat topography causes water to move slowly over
the landscape, allowing ample opportunity for eutrophication responses
to develop. Similarly, small tides in many of Florida's estuaries
(especially on the Gulf coast) also allow for well-developed
eutrophication responses in tidal waters. Florida's warm and wet, yet
sunny, climate further contributes to increased run-off and subsequent
eutrophication responses.\35\ Exchanges of surface water and ground
water contribute to complex relationships between nutrient sources and
the location and timing of eventual impacts.\36\
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    \34\ U.S. Census Bureau. 2009. 2008 Population Estimates Ranked
by State. http://factfinder.census.gov.
    \35\ Perry, W.B. 2008. Everglades restoration and water quality
challenges in south Florida. Ecotoxicology 17:569-578.
    \36\ USGS. 2009. Florida Waters: A Water Resources Manual.
http://sofia.usgs.gov/publications/reports/floridawaters/. Accessed
June 9, 2009.
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    In addition, extensive agricultural development and associated
hydrologic modifications (e.g., canals and ditches) amplify the State's
susceptibility to nutrient pollution. Many of Florida's inland areas
have extensive tracts of agricultural lands. Much of the intensive
agriculture and associated fertilizer usage takes place in locations
dominated by poorly drained sandy soils and with high annual rainfall
amounts, two conditions favoring nutrient-rich runoff. These factors,
along with population increase, have contributed to a significant
upward trend in nutrient inputs to Florida's waters.\37\ High
historical water quality and the human and aquatic life uses of many
waterways in Florida often means that very low nutrients, low
productivity, and high water clarity are needed and expected to
maintain uses.
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    \37\ Florida Department of Environmental Protection. 2008.
Integrated Water Quality Assessment for Florida: 2008 305(b) Report
and 303(d) List Update.
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B. Statutory and Regulatory Background

    Section 303(c) (33 U.S.C. 1313(c)) of the CWA directs states to
adopt WQS for their navigable waters. Section 303(c)(2)(A) and EPA's
implementing regulations at 40 CFR part 131 require, among other
provisions, that state WQS include the designated use or uses to be
made of the waters and criteria that protect those uses. EPA
regulations at 40 CFR 131.11(a)(1) provide that states shall ``adopt
those water quality criteria

that protect the designated use'' and that such criteria ``must be
based on sound scientific rationale and must contain sufficient
parameters or constituents to protect the designated use.'' As noted
above, 40 CFR 130.10(b) provides that ``In designating uses of a water
body and the appropriate criteria for those uses, the state shall take
into consideration the water quality standards of downstream waters and
ensure that its water quality standards provide for the attainment and
maintenance of the water quality standards of downstream waters.''
    States are also required to review their WQS at least once every
three years and, if appropriate, revise or adopt new standards (CWA
section 303(c)(1)). States are required to submit these new or revised
WQS for EPA review and approval or disapproval (CWA section
303(c)(2)(A)). Finally, CWA section 303(c)(4)(B) authorizes the
Administrator to determine, even in the absence of a state submission,
that a new or revised standard is needed to meet CWA requirements. The
criteria proposed in this rulemaking apply to lakes and flowing waters
of the State of Florida. EPA's proposal defines ``lakes and flowing
waters'' to mean inland surface waters that have been classified by
Florida as Class I (Potable Water Supplies Use) or Class III
(Recreation, Propagation and Maintenance of a Healthy, Well-Balanced
Population of Fish and Wildlife Use) water bodies pursuant to Florida
Administrative Code (F.A.C.) Rule 62-302.400, excluding wetlands, and
which are predominantly fresh waters.

C. Water Quality Criteria

    EPA has issued guidance for use by states when developing criteria.
Under CWA section 304(a), EPA periodically publishes criteria
recommendations (guidance) for use by states in setting water quality
criteria for particular parameters to protect recreational and aquatic
life uses of waters. When EPA has published recommended criteria,
states have the option of adopting water quality criteria based on
EPA's CWA section 304(a) criteria guidance, section 304(a) criteria
guidance modified to reflect site-specific conditions, or other
scientifically defensible methods. 40 CFR 131.11(b)(1).
    For nutrients, EPA has published under CWA section 304(a) a series
of peer-reviewed, national technical approaches and methods regarding
the development of numeric nutrient criteria for lakes and
reservoirs,\38\ rivers and streams,\39\ and estuaries and coastal
marine waters.\40\ Basic analytical approaches for nutrient criteria
derivation include, but are not limited to: (1) Stressor-response
analysis, (2) the reference condition approach, and (3) mechanistic
modeling. The stressor-response, or effects-based, approach relates a
water body's response to nutrients and identifies adverse effect
levels. This is done by selecting a protective value based on the
relationships of nitrogen and phosphorus field measures with indicators
of biological response. This approach is empirical, and directly
relates to the designated uses. The reference condition approach
derives candidate criteria from distributions of nutrient
concentrations and biological responses in a group of waters.
Measurements are made of causal and response variables and a protective
value is selected from the distribution. The mechanistic modeling
approach predicts a cause-effect relationship using site-specific input
to equations that represent ecological processes. Mechanistic models
require calibration and validation. Each approach has peer review
support by the broader scientific community, and would provide adequate
means for any state to develop scientifically defensible numeric
nutrient criteria.
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    \38\ U.S. EPA. 2000a. Nutrient Criteria Technical Guidance
Manual: Lakes and Reservoirs. Office of Water, Washington, DC. EPA-
822-B-00-001.
    \39\ U.S. EPA. 2000b. Nutrient Criteria Technical Guidance
Manual: Rivers and Streams. Office of Water, Washington, DC. EPA-
822-B-00-002.
    \40\ U.S. EPA. 2001. Nutrient Criteria Technical Manual:
Estuarine and Coastal Marine Waters. Office of Water, Washington,
DC. EPA-822-B-01-003, and wetlands (U.S. EPA, 2007).
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    In cases where scientifically defensible numeric criteria cannot be
derived, EPA regulations provide that narrative criteria should be
adopted. 40 CFR 131.11(b)(2). Narrative criteria are descriptions of
conditions necessary for the water body to attain its designated use.
Often expressed as requirements that waters remain ``free from''
certain characteristics, narrative criteria can be the basis for
controlling nuisance conditions such as floating debris or
objectionable deposits. States often establish narrative criteria, such
as ``no toxics in toxic amounts,'' in order to limit toxic pollutants
in waters where the state has yet to adopt an EPA-recommended numeric
criterion and or where EPA has yet to derive a recommended numeric
criterion. For nutrients, in the absence of numeric nutrient criteria,
states have often established narrative criteria such as ``no nuisance
algae.'' Reliance on a narrative criterion to derive NPDES permit
limits, assess water bodies for listing purposes, and establish TMDL
targets can often be a difficult, resource-intensive, and time-
consuming process that entails conducting case-by-case analyses to
determine the appropriate numeric target value based on a site-specific
translation of the narrative criterion. Narrative criteria are most
effective when they are supported by procedures to translate them into
quantitative expressions of the conditions necessary to protect the
designated use.

D. Agency Determination Regarding Florida

    On January 14, 2009, EPA determined under CWA section 303(c)(4)(B)
that new or revised WQS in the form of numeric nutrient water quality
criteria are necessary to meet the requirements of the CWA in the State
of Florida. Florida's currently applicable narrative nutrient criterion
provides, in part, that ``in no case shall nutrient concentrations of a
body of water be altered so as to cause an imbalance in natural
populations of aquatic flora or fauna.'' Florida Administrative Code
(F.A.C.) 62-302-530(47)(b). EPA determined that Florida's narrative
nutrient criterion alone was insufficient to ensure protection of
applicable designated uses. The determination recognized that Florida
has a proactive and innovative program to address nutrient pollution
through a strategy of comprehensive National Pollutant Discharge
Elimination System (NPDES) permit regulations, Basin Management Action
Plans (BMAPs) for implementation of TMDLs which include controls on
nonpoint sources, municipal wastewater treatment technology-based
requirements under the 1990 Grizzle-Figg Act, and rules to limit
nutrient pollution in geographically specific areas like the Indian
River Lagoon System, the Everglades Protection Area, and Wekiva
Springs. However, the determination noted that despite Florida's
intensive efforts to diagnose and control nutrient pollution,
substantial water quality degradation from nutrient over-enrichment
remains a significant challenge in the State and one that is likely to
worsen with continued population growth and land-use changes.
    Florida's implementation of its narrative water quality criterion
for nutrients is based on site-specific detailed biological assessments
and analyses, together with site-by-site outreach and stakeholder
engagement in the context of specific CWA-related

actions, specifically NPDES permits, TMDLs required for both permitting
and BMAP activities, and assessment and listing decisions. When
deriving NPDES water quality-based permit limits, Florida initially
conducts a site-specific analysis to determine whether a proposed
discharge has the reasonable potential to cause or contribute to an
exceedance of its narrative nutrient water quality criterion. The State
then determines what levels of nutrients would ``cause an imbalance in
natural populations of aquatic flora or fauna'' and translates those
levels into numeric ``targets'' for the receiving water and any other
affected waters. Determining on a water-by-water basis for thousands of
State waters the levels of nutrients that would ``cause an imbalance in
natural populations of aquatic flora or fauna'' is a difficult,
lengthy, and data-intensive undertaking. This work involves performing
detailed site-specific analyses of the receiving water and any other
affected waters. If the State has not already completed this analysis
for a particular water, it can be very difficult to accurately
determine in the context and timeframe of the NPDES permitting process.
For example, in some cases, adequate data may take several years to
collect and therefore, may not be available for a particular water at
the time of permitting issuance or re-issuance.
    When developing TMDLs, as it does when determining reasonable
potential and deriving limits in the permitting context, Florida
translates the narrative nutrient criterion into a numeric target that
the State determines is necessary to meet its narrative criterion and
protect applicable designated uses. This process also involves a site-
specific analysis to determine the nutrient levels that would ``cause
an imbalance in natural populations of aquatic flora or fauna'' in a
particular water. Each time a site-specific analysis is conducted to
determine what the narrative criterion means for a particular water
body in developing a TMDL, the State takes site-specific considerations
into account and devises a method that works with the available data
and information.
    In adopting the Impaired Waters Rule (IWR), Florida took important
steps toward improving implementation of its narrative nutrient
criterion by establishing and publishing an assessment methodology to
identify waters impaired for nutrients. This methodology includes
numeric nutrient impairment ``thresholds'' above which waters are
automatically deemed impaired. Even when a listing is made, however,
development of a TMDL is then generally required to support issuance of
a permit or development of a BMAP.
    Based on the considerations outlined above, EPA concluded that
numeric criteria for nutrients will enable the State to take necessary
actions to protect the designated uses, in a timelier manner. The
resource intensive efforts to interpret the State's narrative criterion
contribute to delays in implementing the criterion and therefore,
affect the State's ability to provide the needed protections for
applicable designated uses. EPA, therefore, determined that numeric
nutrient criteria are necessary for the State of Florida to meet the
CWA requirement to have criteria that protect applicable designated
uses.
    The combined impacts of urban and agricultural activities, along
with Florida's physical features and important and unique aquatic
ecosystems, made it clear that the current use of the narrative
nutrient criterion alone and the resulting delays that it entails do
not ensure protection of applicable designated uses for the many State
waters that are either unimpaired and need protection or have been
listed as impaired and require loadings reductions. EPA determined that
numeric nutrient water quality criteria would strengthen the foundation
for identifying impaired waters, establishing TMDLs, and deriving water
quality-based effluent limits in NPDES permits, thus providing the
necessary protection for the State's designated uses in its waters. In
addition, numeric nutrient criteria will support the State's ability to
effectively partner with point and nonpoint sources to control
nutrients, thus further providing the necessary protection for the
designated uses of the State's water bodies. EPA's determination is
available at the following Web site: http://www.epa.gov/waterscience/
standards/rules/fl-determination.htm.
    The January 14, 2009 determination stated EPA's intent to propose
numeric nutrient criteria for lakes and flowing waters in Florida
within twelve months of the January 14, 2009 determination, and for
estuarine and coastal waters within 24 months of the determination. EPA
has also entered into a Consent Decree with Florida Wildlife
Federation, Sierra Club, Conservancy of Southwest Florida,
Environmental Confederation of Southwest Florida, and St. Johns
Riverkeeper, committing to the schedule stated in EPA's January 14,
2009 determination to propose numeric nutrient criteria for lakes and
flowing waters in Florida by January 14, 2010, and for Florida's
estuarine and coastal waters by January 14, 2011. The Consent Decree
also requires that final rules be issued by October 15, 2010 for lakes
and flowing waters, and by October 15, 2011 for estuarine and coastal
waters.
    In accordance with the determination and EPA's Consent Decree, EPA
is proposing numeric nutrient criteria for Florida's lakes and flowing
waters with this proposed rule. As envisioned in EPA's determination,
this time frame has allowed EPA to utilize the large data set collected
by Florida as part of a detailed analysis of nutrient-impaired waters.
In a separate rulemaking, EPA intends to develop and propose numeric
nutrient criteria for Florida's estuarine and coastal waters by January
14, 2011. EPA's determination did not apply to Florida's wetlands, and
as a result, Florida's wetlands will not be addressed in this
rulemaking or in EPA's forthcoming rulemaking involving estuarine and
coastal waters.

III. Proposed Numeric Nutrient Criteria for the State of Florida's
Lakes and Flowing Waters

A. General Information

(1) Which Water Bodies Are Affected by This Proposed Rule?
    The criteria proposed in this rulemaking apply to lakes and flowing
waters of the State of Florida. EPA's proposal defines ``lakes and
flowing waters'' to mean inland surface waters that have been
classified as Class I (Potable Water Supplies) or Class III
(Recreation, Propagation and Maintenance of a Healthy, Well-Balanced
Population of Fish and Wildlife) water bodies pursuant to Rule 62-
302.400, F.A.C., excluding wetlands, and which are predominantly fresh
waters. Pursuant to Rule 62-302.200, F.A.C., EPA's proposal defines
``predominantly fresh waters'' to mean surface waters in which the
chloride concentration at the surface is less than 1,500 milligrams per
liter (mg/L) and ``surface water'' means water upon the surface of the
Earth, whether contained in bounds created naturally, artificially, or
diffused. Waters from natural springs shall be classified as surface
water when it exits from the spring onto the Earth's surface.
    In this rulemaking, EPA is proposing numeric nutrient criteria for
the following four water body types: Lakes, streams, springs and clear
streams, and canals in south Florida. EPA's proposal also includes
definitions for each of these waters. ``Lake'' means a freshwater water
body that is not a stream or other watercourse with some open
contiguous water free from emergent vegetation. ``Stream'' means a
free-flowing, predominantly fresh surface water in a

defined channel, and includes rivers, creeks, branches, canals (outside
south Florida), freshwater sloughs, and other similar water bodies.
``Spring'' means the point where underground water emerges onto the
Earth's surface, including its spring run. ``Spring run'' means a free-
flowing water that originates from a spring or spring group whose
primary (>50%) source of water is from a spring or spring group.
Downstream waters from a spring that receive 50% or more of their flow
from surface water tributaries are not considered spring runs. ``Clear
stream'' means a free-flowing water whose color is less than 40
platinum cobalt units (PCU, which is assessed as true color free from
turbidity). Classification of a stream as clear or colored is based on
the instantaneous color of the sample. Consistent with Rule 62-312.020,
F.A.C., ``canal'' means a trench, the bottom of which is normally
covered by water with the upper edges of its two sides normally above
water. Consistent with Rule 62-302.200, F.A.C., all secondary and
tertiary canals wholly within Florida's agricultural areas are
classified as Class IV waters, not Class III, and therefore, are not
subject to this proposed rulemaking. The classes of waters, as
specified in this paragraph and as subject to this proposed rulemaking,
are hereinafter referred to as ``lakes and flowing waters'' in this
proposed rule.
    The CWA requires adoption of WQS for ``navigable waters.'' CWA
section 303(c)(2)(A). The CWA defines ``navigable waters'' to mean
``the waters of the United States, including the territorial seas.''
CWA section 502(7). Whether a particular water body is a water of the
United States is a water body-specific determination. Every water body
that is a water of the United States requires protection under the CWA.
EPA is not aware of any waters of the United States in Florida that are
currently exempted from the State's WQS. For any privately owned water
in Florida that is a water of the United States, the applicable numeric
nutrient criteria for those types of waters would apply. This rule does
not apply to waters for which the Miccosukee Tribe of Indians or
Seminole Tribe of Indians has obtained Treatment as a State for Section
303 of the CWA, pursuant to Section 518 of the CWA.
(2) Background on EPA's Derivation of Proposed Numeric Nutrient
Criteria for the State of Florida's Lakes and Flowing Waters
    In proposing numeric nutrient criteria for Florida's lakes and
flowing waters, EPA developed numeric nutrient criteria to support a
balanced natural population of flora and fauna in Florida lakes and
flowing waters, and to ensure, to the extent that the best available
science allows, the attainment and maintenance of the WQS of downstream
waters. Where numeric nutrient criteria do not yet exist, in proposed
or final form, for a water body type that is downstream from a lake or
flowing water (e.g., estuaries) in Florida, EPA has interpreted the
currently applicable State narrative criterion, ``in no case shall
nutrient concentrations of a body of water be altered so as to cause an
imbalance in natural populations of aquatic flora or fauna,'' to ensure
that the numeric criteria EPA is proposing would not result in nutrient
concentrations that would ``cause an imbalance in natural populations
of aquatic flora or fauna'' in such downstream water bodies. EPA's
actions are consistent with and support existing Florida WQS
regulations. EPA used the best available science to estimate protective
loads to downstream estuaries, and then used these estimates (and
assumptions about the distribution of the load throughout the
watershed), along with mathematical models, to calculate concentrations
in upstream flowing waters that would have to be met to ensure the
attainment and maintenance of the State's narrative criterion
applicable to downstream estuaries.
    EPA relied on an extensive amount of Florida-specific data,
collected and analyzed, in large part, by FDEP and then reviewed by
EPA. EPA worked extensively with FDEP on data interpretation and
technical analyses for developing scientifically sound numeric nutrient
criteria for this proposed rulemaking. Because EPA is committed to
ensuring the use of the best available science, the Agency submitted
its criteria derivation methodologies, developed by EPA in close
collaboration with FDEP experts and scientists, to an independent,
external, scientific peer review in July 2009.
    To support derivation of EPA's proposed lakes criteria, EPA
searched extensively for relevant and useable lake data. In this case
the effort resulted in 33,622 samples from 4,417 sites distributed
among 1,599 lakes statewide.
    Regarding the derivation of EPA's proposed streams criteria, EPA
evaluated water chemistry data from 11,761 samples from 6,342 sites
statewide in the ``all streams'' dataset. EPA also used data collected
for linking nutrients to specific biological responses that consisted
of 2,023 sample records from more than 1,100 streams.
    For EPA's proposed springs and clear streams criteria, EPA
evaluated data gathered and synthesized by FDEP using approximately 50
studies including historical accounts, laboratory nutrient amendment
bioassays, field surveys, and TMDL reports that document increasing
patterns of nitrate-nitrite levels and corresponding ecosystem level
responses observed within the last 50 years. At least a dozen of these
studies were used to develop and support the proposed nitrate-nitrite
criterion for spring ecosystems.
    For EPA's proposed criteria for canals for south Florida, EPA
started with more than 1,900,000 observations from more than 3,400
canal sites. These were filtered for data relevant to nutrient criteria
development and resulted in observations at more than 500 sites for
variables (nutrient parameter data and chlorophyll a data). Reliance on
these extensive sets of data has enabled EPA to use the best available
information and science to derive robust, scientifically sound criteria
applicable to Florida's lakes and flowing waters.
    Section III describes EPA's proposed numeric nutrient criteria for
Florida's lakes, streams, springs and clear streams, and canals and the
associated methodologies EPA employed to derive them. These criteria
are based on sound scientific rationale and will protect applicable
designated uses in Florida's lakes and flowing waters. EPA solicits
public comment on these criteria and their derivation. This preamble
also includes discussions of alternative approaches that EPA considered
but did not select as the preferred option to derive the proposed
criteria. EPA invites public comment on the alternative approaches as
well. In addition, EPA requests public comment on whether the proposed
numeric nutrient criteria are consistent with Florida's narrative
criterion with respect to nutrients at Rule 62-302.530(47)(a), F.A.C.,
specifying that the discharge of nutrients shall be limited as needed
to prevent violations of other standards. EPA seeks scientific data and
information on whether, for example, nutrient criteria should be more
stringent to prevent exceedances of dissolved oxygen criteria.
    EPA has created a technical support document that provides detailed
information regarding all methodologies discussed herein and the
derivation of the proposed criteria. This document is entitled
``Technical Support Document for EPA's Proposed Rule For Numeric
Nutrient Criteria for Florida's Inland Surface Fresh Waters''
(hereafter, EPA TSD for Florida's Inland Waters) and is

located at www.regulations.gov, Docket ID No. EPA-HQ-OW-2009-0596.

B. Proposed Numeric Nutrient Criteria for the State of Florida's Lakes

    Florida's 2008 Integrated Water Quality Assessment Report \41\
indicates that Florida lakes provide important habitats for plant and
animal species and are a valuable resource for human activities and
enjoyment. The State has more than 7,700 lakes, which occupy close to
6% of its surface area. The largest lake, Lake Okeechobee (covering
435,840 acres), is the ninth largest lake in surface area in the United
States and the second largest freshwater lake wholly within the
coterminous United States.\42\ Most of the State's lakes are shallow,
averaging seven to 20 feet deep, although many sinkhole lakes and parts
of other lakes are much deeper.
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    \41\ FDEP. 2008. Integrated Water Quality Assessment for
Florida: 2008 305(b) Report and 303(d) List Update. Florida
Department of Environmental Protection.
    \42\ Fernald, E.A. and E.D. Purdum. 1998. Water Resources Atlas
of Florida. Tallahassee: Institute of Science and Public Affairs,
Florida State University.
---------------------------------------------------------------------------

    Florida's lakes are physically, chemically, and biologically
diverse. Many lakes are spring-fed, others are seepage lakes fed by
ground water, and still others (about 20%) are depression lakes fed by
surface water sources. For purposes of developing numeric nutrient
criteria, EPA identified two classifications of lakes, colored lakes
and clear lakes, which respond differently to inputs of TN and TP, as
discussed in detail below. EPA further classified the clear lakes into
clear alkaline lakes (relatively high alkalinity) and clear acidic
lakes (relatively low alkalinity), which have different baseline
expectations for the level of nutrients present.
(1) Proposed Numeric Nutrient Criteria for Lakes
    EPA is proposing the following numeric nutrient criteria and
geochemical classifications for Florida's lakes classified as Class I
or III waters under Florida law (Rule 62-302.400, F.A.C.):

----------------------------------------------------------------------------------------------------------------
                                                       Baseline criteria \b\        Modified criteria  (within
Long-term average lake color and   Chlorophyll a --------------------------------        these bounds) \c\
           alkalinity              \f\ ([mu]g/L)                                 -------------------------------
                                        \a\        TP (mg/L) \a\   TN (mg/L) \a\   TP (mg/L) \a\   TN (mg/L) \a\
----------------------------------------------------------------------------------------------------------------
A                                              B               C               D               E               F
----------------------------------------------------------------------------------------------------------------
Colored Lakes > 40 PCU..........              20           0.050            1.23     0.050-0.157       1.23-2.25
Clear Lakes, Alkaline <= 40 PCU               20           0.030            1.00     0.030-0.087       1.00-1.81
 \d\ and > 50 mg/L CaCO3 \e\....
Clear Lakes, Acidic <= 40 PCU                  6           0.010           0.500     0.010-0.030     0.500-0.900
 \d\ and <= 50 mg/L CaCO3 \e\...
----------------------------------------------------------------------------------------------------------------
\a\ Concentration values are based on annual geometric mean not to be surpassed more than once in a three-year
  period. In addition, the long-term average of annual geometric mean values shall not surpass the listed
  concentration values. (Duration = annual; Frequency = not to be surpassed more than once in a three-year
  period or as a long-term average).
\b\ Baseline criteria apply unless data are readily available to calculate and apply lake-specific, modified
  criteria as described below in footnote c and the Florida Department of Environmental Protection issues a
  determination that a lake-specific modified criterion is the applicable criterion for an individual lake. Any
  such determination must be made consistent with the provisions in footnote c below. Such determination must
  also be documented in an easily accessible and publicly available location, such as an official State Web
  site.
\c\ If chlorophyll a is below the criterion in column B and there are representative data to calculate ambient-
  based, lake-specific, modified TP and TN criteria, then FDEP may calculate such criteria within these bounds
  from ambient measurements to determine lake-specific, modified criteria pursuant to CWA section 303(c).
  Modified TN and TP criteria must be based on at least three years of ambient monitoring data with (a) at least
  four measurements per year and (b) at least one measurement between May and September and one measurement
  between October and April each year. These same data requirements apply to chlorophyll a when determining
  whether the chlorophyll a criterion is met for purposes of developing modified TN and TP criteria. If the
  calculated TN and/or TP value is below the lower value, then the lower value is the lake-specific, modified
  criterion. If the calculated TN and TP value is above the upper value, then the upper value is the lake-
  specific, modified criterion. Modified TP and TN criteria may not exceed criteria applicable to streams to
  which a lake discharges. If chlorophyll a is below the criterion in column B and representative data to
  calculate modified TN and TP criteria are not available, then the baseline TN and TP criteria apply. Once
  established, modified criteria are in place as the applicable WQS for all CWA purposes.
\d\ Platinum Cobalt Units (PCU) assessed as true color free from turbidity. Long-term average color based on a
  rolling average of up to seven years using all available lake color data.
\e\ If alkalinity data are unavailable, a specific conductance of 250 micromhos/cm may be substituted.
\f\ Chlorophyll a is defined as corrected chlorophyll, or the concentration of chlorophyll a remaining after the
  chlorophyll degradation product, phaeophytin a, has been subtracted from the uncorrected chlorophyll a
  measurement.

    The following section describes the methodologies EPA used to
develop its proposed numeric nutrient criteria for lakes. EPA is
soliciting comments and scientific data regarding the proposed criteria
for lakes and their derivation. Section III.B(4) describes one
alternative approach and two supplementary modifications considered by
the Agency in developing this lakes proposal. EPA solicits comments and
data on that approach and those modifications.
(2) Methodologies for Deriving EPA's Proposed Criteria for Lakes
    The process used to develop proposed numeric nutrient criteria for
a range of diverse waters begins with grouping those waters into
categories that generally have a common response to elevated levels of
the stressor pollutants, in this case TN and TP. The following sections
provide a discussion of (1) the lake classification approach for this
proposal, (2) identification of an appropriate response variable and
the levels of that variable that indicate or represent healthy aquatic
conditions associated with each water body classification, and (3) the
concentrations of TN and TP that correspond to protective levels of the
response variable, in this case, chlorophyll a.
    EPA has recommended that nutrient criteria include both causal
(e.g., TN and TP) and response variables (e.g., chlorophyll a and some
measure of clarity) when establishing numeric nutrient criteria for
water bodies.\43\ EPA

recommends causal variables, in part, to have the means to develop
source control targets and, in part, to have the means to assess water
body conditions with knowledge that responses can be variable,
suppressed, delayed, or expressed at different locations. EPA
recommends response variables, in part, to have a means to assess water
body conditions that synthesize the effect of causal variables over
time, recognizing the daily, seasonal, and annual variability in
measured nutrient levels.\44\ The ability to establish protective
criteria for both causal and response variables depends on available
data and scientific approaches to evaluate these data. For its lake
criteria, EPA is proposing causal variables for TN and TP and a
response variable for chlorophyll a. For water clarity, Florida has
criteria for transparency and turbidity, applicable to all Class I and
III waters, expressed in terms of a measurable deviation from natural
background (Rules 32-302.530(67) and (69), F.A.C.). For further
information on this topic, refer to EPA's TSD for Florida's Inland
Waters.
---------------------------------------------------------------------------

    \43\ U.S. EPA. 1998. National Strategy for the Development of
Regional Nutrient Criteria. Office of Water, Washington, DC. EPA
822-R-98-002; Grubbs, G. 2001. U.S. EPA. (Memorandum to Directors of
State Water Programs, Directors of Great Water Body Programs,
Directors of Authorized Tribal Water Quality Standards Programs and
State and Interstate Water Pollution Control Administrators on
Development and Adoption of Nutrient Criteria into Water Quality
Standards. November 14, 2001); Grumbles, B.H. 2007. U.S. EPA.
(Memorandum to Directors of State Water Programs, Directors of Great
Water Body Programs, Directors of Authorized Tribal Water Quality
Standards Programs and State and Interstate Water Pollution Control
Administrators on Nutrient Pollution and Numeric Water Quality
Standards. May 25, 2007).
    \44\ U.S. EPA. 2000. Nutrient Criteria Technical Guidance
Manual: Rivers and Streams. Office of Water, Washington, DC. EPA-
822-B-00-002.
---------------------------------------------------------------------------

    Interested readers should consult EPA TSD for Florida's Inland
Waters, Chapter 1: Methodology for Deriving U.S. EPA's Proposed
Criteria for Lakes, for more detailed information, data, and graphs
supporting the development of the proposed lake criteria.
(a) Methodology for Proposed Lake Classification
    Based on analyses of geochemical influences in Florida's lakes, EPA
proposes the following classification scheme for Florida lakes: (1)
Colored Lakes > 40 Platinum Cobalt Units (PCU), (2) Clear Lakes <= 40
PCU with alkalinity > 50 mg/L calcium carbonate (CaCO3), and
(3) Clear Lakes <= 40 PCU with alkalinity <= 50 mg/L CaCO3.
    Following original work conducted by FDEP, EPA considered several
key characteristics to categorize Florida's lakes and tailor numeric
nutrient criteria, recognizing that different types of lakes in Florida
may respond differently to nutrients. Many of Florida's lakes contain
dissolved organic matter leached from surface vegetation that colors
the water. More color in a lake limits light penetration within the
water column, which in turn limits algal growth. Thus, in lakes with
colored water, higher levels of nutrients may occur without exceeding
desired algal levels. EPA evaluated the relationships between nutrients
and algal responses for these waters (as measured by chlorophyll a
concentration), which indicated that water color influences algal
responses to nutrients. Based on this analysis, EPA found color to be a
significant factor for categorizing lakes. More specifically, EPA found
the correlations between nutrients and chlorophyll a concentrations to
be stronger and less variable when lakes were categorized into two
distinct groups based on a threshold of 40 PCU. This threshold is
consistent with the distinction between clear and colored lakes long
observed in Florida.\45\ Different relationships between nutrients and
chlorophyll a emerged when lakes were characterized by color, with
clear lakes demonstrating greater sensitivity to nutrients as would be
predicted by the increased light penetration, which promotes algal
growth.
---------------------------------------------------------------------------

    \45\ Shannon, E.E. and P.L. Brezonik. 1972. Limnological
characteristics of north and central Florida lakes. Limnol.
Oceanogr. 17(1): 97-110.
---------------------------------------------------------------------------

    Within the clear lakes category, where color is not generally the
controlling factor in algal growth, EPA evaluated alkalinity as an
additional distinguishing characteristic. Calcium carbonate
(CaCO3), dissolved from limestone formations and calcareous
soils, affects the alkalinity and pH of groundwater that feeds into
lakes. Alkalinity and pH increase when water is in contact with
limestone or limestone-derived soil. Limestone is also a source of TP,
and lakes that are higher in alkalinity in Florida are often associated
with naturally elevated TP levels. These types of lakes are often in
areas of the State where the underlying geology includes limestone. The
alkalinity (measured as CaCO3) of Florida clear lakes ranges
from zero to well over 200 mg/L. FDEP's Nutrient Criteria Technical
Advisory Committee (TAC) evaluated available data from Florida lakes
and concluded that 50 mg/L alkalinity as CaCO3 is an
appropriate threshold above which associated nutrient levels would be
expected to be significantly elevated among clear lakes. EPA concluded
that FDEP's proposed approach of using 50 mg/L alkalinity as
CaCO3 is an appropriate distinguishing characteristic in
clear lakes in Florida because lakes with alkalinity <=50
CaCO3 represent a comprehensive group of lakes that may be
naturally oligotrophic. Thus, EPA proposes to classify Florida clear
lakes as either acidic (<=50 mg/L alkalinity as CaCO3) or
alkaline (>50 mg/L alkalinity as CaCO3).
    EPA recognizes that in certain cases FDEP may not have historic
alkalinity data on record to classify a particular clear lake as either
alkaline or acidic. When alkalinity data are unavailable, EPA proposes
a specific conductivity threshold of 250 microSiemens per centimeter
([mu]S/cm) as a substitute for the threshold of 50 mg/L alkalinity as
CaCO3. Specific conductivity is a measure of the ionic
activity in water and a data analysis performed by FDEP and re-examined
by EPA found that a specific conductivity threshold value of 250 [mu]S/
cm is sufficiently correlated with alkalinity to serve as a surrogate
measure. Of these two measures, alkalinity is the preferred parameter
to measure because it is less variable and therefore, a more reliable
indicator, and also because it is a more direct measure of the presence
of underlying geology associated with elevated nutrient levels.
    EPA solicits comment on the proposed categorization scheme and
associated thresholds used to classify Florida's lakes. Please see
Section III.B(4)(b) below in which EPA invites comment on alternative
lake categorization approaches that EPA considered, in particular,
those approaches with respect to alkalinity classification and lakes
occurring in sandhills of northwestern and central Florida.
(b) Methodology for Proposed Chlorophyll a Criteria
    Because excess algal growth is associated with degradation in
aquatic life and because chlorophyll a levels are a measure of algal
growth, EPA is using chlorophyll a levels as indicators of healthy
biological conditions, supportive of aquatic life in each of the
categories of Florida's lakes described above. EPA found multiple lines
of evidence supporting chlorophyll a criteria as an effective indicator
of ambient conditions that would be protective of Florida's aquatic
life use in lakes. These lines of evidence included trophic state of
lakes, historical reference conditions in Florida lakes, and model
results.
    As a primary line of evidence, EPA reviewed and evaluated the
Trophic State Index (TSI) information in deriving chlorophyll a
criteria that are protective of designated aquatic life uses in
Florida's lakes. The TSI quantifies the degree of eutrophication
(oligotrophic, mesotrophic, eutrophic) \46\ in a water body based on
observed measurements of nutrients and chlorophyll a. These types of
boundaries are commonly used in scientific literature and represent an

established, scientific classification system to describe current
status and natural expectations for lake conditions with respect to
nutrients and algal productivity.\47\ EPA's review of TSI studies
\48\ \49\ indicated that in warm-water lakes such as those
in Florida, TSI values of 50, 60, and 70 are associated with
chlorophyll a concentrations of 10, 20, and 40 micrograms per liter
([mu]g/L), respectively. Studies indicated that mesotrophic lakes in
Florida have TSI values ranging from 50 to 60 and eutrophic lakes have
TSI values ranging from 60 to 70. Thus a TSI value of 60 (chlorophyll a
concentration of 20 [mu]g/L) represents the boundary between mesotrophy
and eutrophy. EPA concluded that mesotrophic status is the appropriate
expectation for colored and clear alkaline lakes because they receive
significant natural nutrient input and support a healthy diversity of
aquatic life in warm, productive climates such as Florida, and
mesotrophy represents a lake maintaining a healthy balance between
benthic macrophytes (i.e., plants growing on the lake bottom) and algae
in such climates under such conditions. However, clear acidic lakes in
Florida do not receive comparable natural nutrient input to be
classified as mesotrophic, and for those lakes, EPA has developed
criteria that correspond to an oligotrophic status. Oligotrophic lakes
support less algal growth and have lower chlorophyll a levels. Studies
indicate that a TSI value of 45 reflects an approximate boundary
between oligotrophy and mesotrophy (corresponding to chlorophyll a at
about 7 [mu]g/L). EPA requests comment on these conclusions regarding
oligotrophic and mesotrophic status expectations for these categories
of Florida lakes.
---------------------------------------------------------------------------

    \46\ Trophic state describes the nutrient and algal state of an
aquatic system: Oligotrophic (low nutrients and algal productivity),
mesotrophic (moderate nutrients and algal productivity), and
eutrophic (high nutrients and algal productivity).
    \47\ Carlson, R.E. 1977. A trophic state index for lakes.
Limnol. Oceanogr. 22:361-369.
    \48\ Carlson, R.E. 1977. A trophic state index for lakes.
Limnol. Oceanogr. 22:361-369.
    \49\ Salas and Martino. 1991. A simplified phosphorus trophic
state index for warm water tropical lakes. Wat. Res. 25:341-350.
---------------------------------------------------------------------------

    Another line of evidence that supports EPA's proposed chlorophyll a
criteria is historical reference conditions. Diatoms are a very common
type of free-floating algae (i.e., phytoplankton) that have shells or
``frustules'' made of silica that are preserved in the fossil record.
Diatoms preserved in lake sediments can be used to infer chlorophyll a
levels in lakes prior to any human disturbance. Paleolimnological
studies \50\ that examined preserved diatom frustules in Florida lake
sediments indicate that historical levels of chlorophyll a are
consistent with mesotrophic expectations derived from the TSI studies
described above, with chlorophyll a levels falling just below the
selected criterion for mesotrophic lakes. (These studies did not
evaluate lakes expected to be naturally oligotrophic so there is no
comparable information for those lakes).
---------------------------------------------------------------------------

    \50\ Whitmore and Brenner. 2002. Paleologic characterization of
pre-disturbance water quality conditions in EPA defined Florida lake
regions. Univ. Florida Dept. Fisheries and Aquatic Sciences. 30 pp.
---------------------------------------------------------------------------

    In addition to this evidence, EPA used information from the
application of a Morphoedaphic Index (MEI) model \51\ that predicts
nutrient and chlorophyll a concentrations for any lake given its depth,
alkalinity, and color to support the proposed chlorophyll a criteria.
Scientists from the St. John's Water Management District presented
modeling results for various Florida lakes in each colored and clear
category at the August 5, 2009 meeting of the Nutrient Criteria TAC in
Tallahassee. In addition to predicting natural or reference conditions,
these scientists used the model to predict chlorophyll a and TP
concentrations associated with a 10% reduction in water transparency
for a set of lakes with varying color levels and alkalinities. Because
submerged aquatic vegetation is dependent on light, maintaining a
lake's historic balance between algae and submerged aquatic plants
requires maintaining overall water transparency. The risk of disrupting
the balance between algae and submerged aquatic plants increases when
reductions in transparency exceed 10%. The MEI predictions corroborated
the results from lake TSI studies and investigations of
paleolimnological reference conditions because natural or reference
predictions (i.e., a ``no effect'' level) were generally below selected
criteria levels and 10% transparency loss predictions (i.e., a
``threshold effect'' level) were at or slightly above selected criteria
levels. EPA considered these lines of evidence to develop the proposed
chlorophyll a criteria, discussed below by lake class:
---------------------------------------------------------------------------

    \51\ Vighi and Chiaudani. 1985. A simple method to estimate lake
phosphorus concentrations resulting from natural background
loadings. Wat. Res.19:987-991.
---------------------------------------------------------------------------

    (i) Colored Lakes: EPA proposes a chlorophyll a criterion of 20
[mu]g/L in colored lakes to protect Florida's designated aquatic life
uses. As indicated by the warm-water TSI studies discussed above,
chlorophyll a concentrations of 20 [mu]g/L represent the boundary
between mesotrophy and eutrophy. Because mesotrophy maintains a healthy
balance of plant and algae populations in these types of lakes,
limiting chlorophyll a concentrations to 20 [mu]g/L would, therefore,
protect colored lakes in Florida from the adverse impacts of
eutrophication. Paleolimnological studies of six colored lakes in
Florida demonstrated natural (i.e., before human disturbance)
chlorophyll a levels in the range of 14-20 [mu]g/L and the MEI model
predicted reference chlorophyll a concentrations of 1-25 [mu]g/L for a
set of colored lakes in Florida. The model also predicted that
concentrations of chlorophyll a ranging from 15-36 [mu]g/L in
individual lakes would result in a 10% loss of transparency (all but
two lakes were above 20 [mu]g/L). Because of natural variability, it is
typical for ranges of natural or reference conditions to overlap with
ranges of where adverse effects may begin occurring (such as the 10%
transparency loss endpoint) for any sample population of lakes. In
addition, these modeling results, as with any line of evidence, have
uncertainty associated with any individual lake prediction. Given these
considerations, EPA found that because the clear majority (eight of
eleven) of lakes had predicted natural or referenced conditions below
20 [mu]g/L chlorophyll a and the clear majority (nine of eleven) of
lakes had predicted 10% transparency loss above 20 [mu]g/L chlorophyll
a, these results supported the TSI-based proposed chlorophyll a
criterion.
    (ii) Clear, Alkaline Lakes: EPA proposes a chlorophyll a
concentration of 20 [mu]g/L in clear, alkaline lakes to protect
Florida's designated aquatic life uses. As noted in Section
III.B(2)(a), alkalinity and TP are often co-occurring inputs to Florida
lakes because of the presence of TP in limestone, which is often a
feature of the geology in Florida. Clear, alkaline lakes, therefore,
are likely to be naturally mesotrophic. EPA's analysis determined that
aquatic life in clear, alkaline lakes is protected at similar
chlorophyll a levels as colored lakes (at the TSI boundary between
mesotrophy and eutrophy). The MEI model predicted reference chlorophyll
a concentrations of 12-24 [mu]g/L for a set of clear, alkaline lakes in
Florida, and predicted a 10% loss of transparency when chlorophyll a
concentrations ranged from 19-33 [mu]g/L. Similar to the results for
colored lakes, half of the clear, alkaline lakes had predicted natural
or referenced conditions at or below 20 [mu]g/L chlorophyll a and all
but one clear,

alkaline lake had predicted 10% transparency loss above 20 [mu]g/L
chlorophyll a. Thus, EPA found this evidence to be supportive of the
proposed chlorophyll a criterion. EPA solicits comment on this
chlorophyll a criterion and the evidence EPA used to support the
criterion.
    (iii) Clear, Acidic Lakes: EPA proposes a chlorophyll a
concentration of 6 [mu]g/L in clear, acidic lakes to ensure balanced
natural populations of flora and fauna (i.e., aquatic life) in these
lakes. In contrast to colored lakes and clear, alkaline lakes, this
category of lakes does not receive significant natural nutrient inputs
from groundwater or other surface water sources. EPA has thus based the
proposed criteria on an expectation that these lakes should be
oligotrophic in order to support balanced natural populations of flora
and fauna. Some of Florida's clear, acidic lakes, in the sandhills in
northwestern and central Florida, have been identified as extremely
oligotrophic \52\ with chlorophyll a levels of less than 2 [mu]g/L. As
discussed above, warm water TSI studies suggest a chlorophyll a level
of approximately 7 [mu]g/L at the oligotrophic-mesotrophic boundary.
---------------------------------------------------------------------------

    \52\ Canfield, D.E., Jr., M.J. Maceina, L.M. Hodgson, and K.A.
Langeland. 1983. Limnological features of some northwestern Florida
lakes. J. Freshw. Ecol. 2:67-79; Griffith, G.E., D.E. Canfield, Jr.,
C.A. Horsburgh, J.M. Omernik, and S.H. Azevedo. 1997. Lake regions
of Florida. Map prepared by U.S. EPA, Corvallis, OR; available at
http://www.epa.gov/wed/pages/ecoregions/fl_eco.htm (accessed 10/09/
2009).
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    In July 2009, FDEP proposed a chlorophyll a criterion for clear,
acidic lakes of 9 [mu]g/L.\53\ In comments sent to EPA via e-mail in
October 2009,\54\ FDEP reported that the Nutrient TAC suggested in June
2009 that maintaining chlorophyll a below 10 [mu]g/L in clear, acidic
lakes would be protective of the designated use, because a value of <
10 [mu]g/L would still be categorized as oligotrophic. However, EPA's
review of the TSI categorization based on the work of Salas and Martino
(1991) on warm water lakes indicates that a chlorophyll a of 10 [mu]g/L
(TSI of 50) would better represent the central tendency of the
mesotrophic category rather than the oligotrophic-mesotrophic boundary.
In the October 2009 comments, FDEP also presented an analysis of lake
data that showed lack of correlation between an index of benthic
macroinvertebrate health and chlorophyll a levels in the range of 5-10
[mu]g/L as supporting evidence for a chlorophyll a criterion of 9
[mu]g/L in clear acidic lakes. However, within this small range of
chlorophyll a, it is not surprising that a correlation with an
indicator responsive to numerous aspects of natural conditions and
stressors such as benthic macroinvertebrate health would not exhibit a
clear statistical relationship. Importantly, there was some evidence of
meaningful distinctions within the range of 5-10 [mu]g/L chlorophyll a
based on endpoints more directly responsive to nutrients. In this case,
the MEI model predicted reference chlorophyll a concentrations within
the range of 1.4-7.0 [mu]g/L (with seven of the eight values below 5
[mu]g/L) for a set of clear, acidic lakes in Florida, and predicted a
10% loss of transparency when chlorophyll a concentrations ranged from
5.6-11.8 [mu]g/L (with five of the eight values below 7 [mu]g/L). All
but one of the clear, acid lakes had predicted natural or reference
conditions below 6 [mu]g/L chlorophyll a and the majority (six of
eight) of clear, alkaline lakes had predicted 10% transparency loss
above 6 [mu]g/L chlorophyll a. Given available information on reference
condition and predicted effect levels, EPA adjusted the approximate
oligotrophic-mesotrophic boundary value of 7 [mu]g/L slightly downward
to 6 [mu]g/L as the proposed chlorophyll a criterion. For determining
the proposed chlorophyll a criterion in the three lake categories, only
in this case for clear, acid lakes did EPA use reference condition
information and predicted effect levels for more than just support of
the value coming from the TSI-based line of evidence, and in this case
EPA deviated from that value by only 1 [mu]g/L.
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    \53\ More information on this issue is available on FDEP's Web
site at http://www.dep.state.fl.us/water/wqssp/nutrients/docs/dep_
responses_100909.pdf and included in the ``External Peer Review of
EPA's `Proposed Methods and Approaches for Developing Numeric
Nutrient Criteria for Florida's Inland Waters' '' and EPA's TSD for
Florida's Inland Waters located in the docket ID No. EPA-HQ-OW-2009-
0596.
    \54\ FDEP document titled, ``DEP's Responses to EPA's 9/16
Comment Letter.'' October 9, 2009. Located in the docket ID EPA-HQ-
OW-2009-0596.
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    EPA specifically solicits comment on the chlorophyll a criterion of
6 ug/L and the evidence EPA used to support the criterion. EPA also
solicits comment on whether a higher criterion of 9 ug/L, as proposed
by Florida in its July 2009 proposed nutrient WQS, would be fully
protective of clear acidic lakes, and the scientific basis for such a
conclusion.
(c) Methodology for Proposed Total Phosphorus (TP) and Total Nitrogen
(TN) Criteria in Lakes
    EPA proposes TP and TN criteria for each of the classes of lakes
described in Section III.B(2)(a). The proposed TP and TN criteria are
based principally on independent statistical correlations between TN
and chlorophyll a, and TP and chlorophyll a for clear and colored lakes
in Florida. Each data point used in the statistical correlations
represents a geometric mean of samples taken over the course of a year
in a particular Florida lake. After establishing the protective levels
of chlorophyll a as 20 [mu]g/L for colored lakes and clear alkaline
lakes and 6 [mu]g/L for clear acidic lakes, EPA evaluated the data on
TN and TP concentrations associated with these chlorophyll a levels and
the statistical analyses performed by FDEP in support of the State's
efforts to develop numeric nutrient criteria.
    These analyses showed that the response dynamics of TN and TP with
chlorophyll a were different for colored versus clear lakes, as would
be expected because color blocks light penetration in the water column
and limits algal growth. These analyses also showed that the
correlation relationships for TN and TP compared with chlorophyll a in
acidic and alkaline clear lakes were comparable, as would be expected
because alkalinity does not affect light penetration. These analyses
are available in EPA's TSD for Florida's Inland Waters, Chapter 1:
Methodology for Deriving U.S. EPA's Proposed Criteria for Lakes.
    The difference between clear, acidic and clear, alkaline lakes is
that clear, alkaline lakes naturally receive more nutrients and,
therefore, have an expected trophic status of mesotrophic to maintain a
healthy overall production and balance of plants and algae. On the
other hand, clear, acidic lakes naturally receive much lower nutrients
and, therefore, have an expected trophic status of oligotrophic to
maintain a healthy, but lower than mesotrophic, level of plant and
algae aquatic life. Because of the different expectations for trophic
condition, different chlorophyll a criteria are appropriate (as
mentioned earlier, chlorophyll a is a measure of algal production).
Although clear, alkaline lakes and colored lakes have the same proposed
chlorophyll a criterion, they will have different TP and TN criteria
because of the effect of color on light penetration and algal growth.
    The TN and TP values EPA is proposing are based on the lower and
upper TN and TP values derived from the 50th percentile prediction
interval of the regression (i.e., best-fit line) through the
chlorophyll a and corresponding TN or TP values plotted on a
logarithmic scale. In other words, the prediction interval displays the
range of TN and TP values typically associated with a given chlorophyll
a concentration. At any given chlorophyll a concentration, there will
be a lower

TN or TP value and an upper TN or TP value corresponding to this
prediction interval. EPA agrees with the FDEP approach that uses the
50th percentile prediction interval because it effectively separates
the data into three distinct groups. This analysis of the substantial
lake data collected by Florida indicates that the vast majority of
monitored lakes with nutrient levels below the lower TN or TP value
have associated chlorophyll a values below the protective chlorophyll a
threshold level. Similarly, the vast majority of monitored lakes with
measured nutrient levels above the upper TN or TP value have associated
measured chlorophyll a values above the protective chlorophyll a
threshold level. Between these TN and TP bounds, however, this analysis
indicates that monitored lakes are equally likely to be above or below
the protective chlorophyll a threshold level. Setting TN and TP
criteria based on the bounds of the 50th percentile prediction
interval, in conjunction with lake-specific knowledge of whether the
lake chlorophyll a threshold is met, accounts for the naturally
variable behavior of TN and TP while ensuring protection of aquatic
life.
    EPA's proposed criteria framework sets a protective chlorophyll a
threshold and TN and TP criteria at the lower values of the range
defined by the 50th percentile prediction interval for the three
different categories of lakes as ``baseline'' criteria. The criteria
framework also provides flexibility for FDEP to derive lake-specific,
modified TN and TP criteria within the bounds of the upper and lower
values based on at least three years of ambient measurements where a
chlorophyll a threshold is not exceeded. More specifically, if the
chlorophyll a criterion for an individual lake is met for a period of
record of at least three years, then the corresponding TN and TP
criteria may be derived from ambient measurements of TN and TP from
that lake within the bounds of the lower and upper values of the
prediction interval discussed above. Both the ambient chlorophyll a
levels as well as the corresponding ambient TN and TP concentrations in
the lake must be established with at least three years worth of data.
EPA's proposed rule provides that these modified criteria need to be
documented by FDEP. EPA's rule, however, does not require that FDEP go
through a formal SSAC process subject to EPA review and approval.
    In this proposed rule, EPA specifies that in no case, however, may
the modified TN and TP criteria be higher than the upper value
specified in the criteria bounds, nor lower than the lower value
specified in the criteria bounds. In addition to nutrients, chlorophyll
a in a lake may be limited by high water color, zooplankton grazing,
mineral turbidity, or other unknown factors. In the absence of
detailed, site-specific knowledge, the upper values represent
increasing risk that chlorophyll a will exceed its criterion value. To
maintain the risk at a manageable level, the upper values are not to be
exceeded. EPA requests comments on this approach. EPA also requests
comment on whether the rule should specify that the modified TN and TP
criteria be set at levels lower than the lower value of the criteria
bounds if that is what is reflected in the outcome of the ambient-based
calculation.
    EPA's proposed approach for TN and TP criteria in lakes reflects
the natural variability in the relationship between chlorophyll a
concentrations and corresponding TP and TN concentrations that may
exist in lakes. This variability remains even after some explanatory
factors such as color and alkalinity are addressed by placing lakes in
different categories based on color and alkalinity because other
natural factors play important roles. Natural variability in the
physical, chemical, and biological dynamics for any individual lake may
result from differences in geomorphology, concentrations of other
constituents in lake waters, hydrological conditions and mixing, and
other factors.
    This approach allows for consideration of readily available site-
specific data to be taken into account in the expression of TN and TP
criteria, while still ensuring protection of aquatic life by
maintaining the associated chlorophyll a level at or below the proposed
chlorophyll a criterion level. Because the chlorophyll a level in a
lake is the direct measure of algal production, it can be used to
evaluate levels that pose a risk to aquatic life. The scientific
premise for the lake-specific ambient calculation provision for
modified TN and TP criteria is that if ambient lake data show that a
lake's chlorophyll a levels are below the established criteria and its
TN and/or TP levels are within the lower and upper bounds, then those
ambient levels of TN and TP represent protective conditions. Basing the
ambient calculation upon at least three years worth of data is a
condition set to address and account for year-to-year hydrologic
variability in the derivation of modified criteria. EPA requests
comment on the requirement of three years worth of data for both
chlorophyll a and TN and TP in order to use this option. Specifically,
are there situations in which less than three years of data might be
adequate for an adjusted TN or TP criterion?
    EPA selected the proposed TP and TN criteria based on the
relationships with chlorophyll a described above. However, the MEI
modeling results described in Section III.B(2)(b) also provide
additional support for the TP criteria selection. The MEI predicted a
10% transparency loss when TP concentrations ranged from 0.053-0.098
mg/L in colored lakes (with one predicted value at 0.037 mg/L), from
0.038-0.068 mg/L in clear, alkaline lakes, and from 0.012-0.024 mg/L in
clear, acidic lakes. All but one of these predicted values are within
the lower and upper bounds of the proposed TP criteria. The MEI
modeling results did not address TN.
(d) Proposed Criteria: Duration and Frequency
    Numeric criteria include magnitude (i.e., how much), duration
(i.e., how long), and frequency (i.e., how often) components. Beginning
with EPA's 2004 Integrated Report Guidance,\55\ EPA has used the term
``exceeding criteria'' to refer to situations where all criteria
components are not met. The term ``digression'' refers to an ambient
level that goes beyond a level specified by the criterion-magnitude
(e.g., in a given grab sample). The term ``excursion'' refers to
conditions that do not meet the criterion-magnitude and criterion-
duration, in combination. A criterion-frequency specifies the maximum
rate at which ``excursions'' may occur.
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    \55\ USEPA. Guidance for 2004 Assessment, Listing and Reporting
Requirements Pursuant to Sections 303(d) and 305(b) of the Clean
Water Act. http://www.epa.gov/OWOW/tmdl/tmdl0103/Accessed December
2009.
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    For the chlorophyll a, TN, and TP criteria for lakes, the
criterion-magnitude values (expressed as a concentration) are provided
in the table and the criterion-duration (or averaging period) is
specified as annual. The criterion-frequency is no-more-than-once-in-a-
three-year period. In addition, the long-term arithmetic average of
annual geometric mean values shall not exceed the criterion-magnitude
values (concentration values).
    Appropriate duration and frequency components of criteria should be
based on how the data used to derive the criteria were analyzed, and
what the implications are for protection of designated uses given the
effects of exposure at the specified criterion concentration for
different periods of time and recurrence patterns. For lakes, the
stressor-response relationship was based on annual geometric means for

individual years at individual lakes. The appropriate duration period
is therefore annual. The key question is whether this annual geometric
mean needs to be met every year, or if some allowance for a particular
year to exceed the applicable criterion could still be considered
protective.
    Data that contribute to the analysis of TSI, as well as data
generated from supporting paleolimnological studies and MEI modeling,
typically represent periods of time greater than a single year.
Moreover, many of the models and analyses that form the basis of TSI
results are designed to represent the ``steady-state,'' or long-term
stable water quality conditions. However, researchers have suggested
caution in applying steady-state assumptions to lakes with long
residence times.\56\ In other words, the effects of spikes in annual
loading could linger and disrupt the steady-state in some lakes. As a
result, EPA is proposing two expressions of allowable frequency, both
of which are to be met. First, EPA proposes a no-more-than-one-in-
three-years excursion frequency for the annual geometric mean criteria
for lakes. Second, EPA proposes that the long-term arithmetic average
of annual geometric means not exceed the criterion-magnitude
concentration. EPA anticipates that Florida will use its standard
assessment periods as specified in Rule 62-303, F.A.C. (Impaired Waters
Rule) to implement this second provision. These selected frequency and
duration components recognize that hydrological variability will
produce variability in nutrient regimes, and individual measurements
may exceed the criteria magnitude concentrations. Furthermore, they
balance the representation of underlying data and analyses based on the
central tendency of many years of data (i.e., the long-term average
component) with the need to exercise some caution to ensure that lakes
have sufficient time to process individual years of elevated nutrient
levels and avoid the possibility of cumulative and chronic effects
(i.e., the no-more-than-one-in-three-year component). More information
on this specific topic is provided in EPA's TSD for Florida's Inland
Waters, Chapter 1: Methodology for Deriving U.S. EPA's Proposed
Criteria for Lakes.
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    \56\ Kenney (1998) as reported in Salas and Martino (1991).
---------------------------------------------------------------------------

    EPA requests comment on these proposed criteria duration and
frequency expressions, and the basis for their derivation. EPA notes
that some scientists and resource managers have suggested that nutrient
criteria duration and frequency expressions should be more restrictive
to avoid seasonal or annual ``spikes'' from which the aquatic system
cannot easily recover, whereas others have suggested that criteria
expressed as simply a long-term average of annual geometric means,
consistent with data used in criteria derivation, would still be
protective. EPA also requests comment on any alternative duration and
frequency expressions that might be considered protective, including
(1) a criterion-duration expressed as a monthly average or geometric
mean, (2) a criterion-frequency expressed as meeting allowable
magnitude and duration every year, (3) a criterion-frequency expressed
as meeting allowable magnitude and duration in more than half the years
of a given assessment period, and (4) a criterion-frequency expressed
as meeting allowable magnitude and duration as a long-term average
only. EPA further requests comment on whether an expression of the
criteria in terms of an arithmetic average of annual geometric mean
values based on rolling three-year periods of time would also be
protective of the designated use.
(e) Application of Lake-Specific, Ambient Condition-Based Modified TP
and TN Criteria
    As described in Section III.B(2)(c), EPA is proposing a framework
that uses both the upper and lower bounds of the 50th percentile
prediction interval to allow the derivation of modified TP and TN lake-
specific criteria to account for the natural variability in the
relationship between chlorophyll a and TP and TN that may exist in
certain lakes. The proposed rule would allow FDEP to calculate ambient
modified criteria for TN and TP based on at least three years of
ambient monitoring data with (a) at least four measurements per year
and (b) at least one measurement between May and September and one
measurement between October and April each year. If a calculated
modified TN and TP criterion is below the lower value, then the lower
value is the criteria. If a calculated modified TN and TP criterion is
above the upper value, then the upper bound is the criteria. Calculated
modified TP and TN values may not exceed criteria applicable to streams
to which a lake discharges.
    EPA's proposed rule provides that FDEP must document these modified
criteria and establish them in a manner that clearly recognizes their
status as the applicable criterion for a particular lake so that the
public and all regulatory authorities are aware of its existence.
However, EPA's proposed rule does not require that FDEP go through a
formal SSAC process subject to EPA review and approval. (For more
information on the SSAC process, please refer to Section V of this
proposal). EPA believes such modified criteria do not need to go
through the SSAC process because the conditions under which they are
applicable are clearly stated in the proposed rule and the methods of
calculation are clearly laid out so that the outcome is predictable and
transparent. By providing a specific process for deriving modified
criteria within the WQS rule itself, each individual outcome of this
process is an effective WQS for CWA purposes and does not need separate
approval by EPA.
    One technical concern is the extent to which the variability in the
data relating chlorophyll a levels to TN and TP levels truly reflects
differences between lakes, as opposed to temporal differences in the
conditions in the same lake. To address this issue, EPA verified that
the observed variability in the supporting analysis was indeed
predominantly ``across lake'' variability, not ``within lake''
variability.