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Environmental Protection Agency

40 CFR Part 131

[EPA-HQ-OW-2009-0596; FRL-XXXX-X]

[RIN 2040-AF11]

Water Quality Standards for the 

State of Florida’s Lakes and Flowing Waters

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed Rule.

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.
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DATES: Comments must be received on or before [insert date], 60 days after 

publication in the Federal Register. 

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OW2009-0596, by one of the following methods:

1. www.regulations.gov: Follow the on-line instructions for submitting comments.

2. Email: ow-docket@epa.gov

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-OW2009-0596. 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 
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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 (202) 566-2426, 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 (202) 566-1744. 
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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 1:00 p.m. to 5:00 p.m. and 7:00 p.m. 

to 10:00 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 1:00 p.m. to 5:00 p.m. and 7:00 p.m. to 10:00 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 1:00 p.m. to 5:00 p.m. and 7:00 p.m. to 10:00 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 202-566-1480 or 

frey.sharon@epa.gov 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: 202-564-1649; fax number: 202-566-9981; 

email address: salvaterra.danielle@epa.gov.

SUPPLEMENTARY INFORMATION: This supplementary information section is 

organized as follows: 

Table of Contents 
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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
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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)
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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 

 

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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square miles of waters impaired for nutrients in Florida may be higher, as many waters 

currently are classified as “unassessed.”

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 

 

2

http://www.census.gov/population/projections/SummaryTabA1.pdf
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source activities. However, the significant challenge faced by the water quality

components of this system is its dependence upon an approach involving resourceintensive and time-consuming site-specific data collection and analysis to interpret nonnumeric narrative nutrient criteria. EPA determined that Florida’s reliance on a case-bycase 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 estuaries and coastal waters within 24 months, of the 

January 14, 2009 determination.

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 estuaries and coastal waters in 2011. The two phases of this 
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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 estuaries 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 
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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 estuaries 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 
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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 stressorresponse 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 
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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.
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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 technicallybased 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.
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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 
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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 
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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:

Category Examples of potentially affected entities

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.

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?
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 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.
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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 202-

566-1744. 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).
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II. Background

A. Nutrient Pollution

1. What is Nutrient Pollution?

Excess anthropogenic concentrations of nitrogen (typically in oxidized, inorganic 

forms, such as nitrate)3and 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. 

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, 

 

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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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 

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 

 

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, D.C.; 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.
22

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

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

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 

 

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.

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.

14 WHOI. 2008. Marine Mammals. Woods Hole Oceanographic Institution. 

<http://www.whoi.edu/redtide/page.do?pid=14215>. Accessed December 2009.
23

dinoflagellate (a type of algae), were measured in all of the stranded dolphins examined, 

as well as in their fish prey.

15

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

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 

 

15 WHOI. 2008. Marine Mammals. Woods Hole Oceanographic Institution. 

<http://www.whoi.edu/redtide/page.do?pid=14215>. Accessed December 2009.

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.

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.
24

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

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 

 

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 D.C. PA-822-R-00-

012.

22 Ecological Society of America. 2009. Hypoxia. Ecological Society of America, Washington, D.C. <

http://www.esa.org/education/edupdfs/hypoxia.pdf> Accessed December 2009.

23 USEPA. 2007. Nitrates and Nitrites. U.S. Environmental Protection Agency. 

<http://www.epa.gov/teach/chem_summ/Nitrates_summary.pdf>. Accessed December 2009.
25

(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 

 

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-targetthemes/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.
26

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.

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 

 

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.
27

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.

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

 

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.

34 U.S. Census Bureau. 2009. 2008 Population Estimates Ranked by State. http://factfinder.census.gov
28

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

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.

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 

 

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.

37 Florida Department of Environmental Protection. 2008. Integrated Water Quality Assessment for Florida: 

2008 305(b) Report and 303(d) List Update.
29

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 as 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
30

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 peerreviewed, 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 

 

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).
31

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.

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, resourceintensive, 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
32

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 technologybased 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-bysite outreach and stakeholder engagement in the context of specific CWA-related actions, 

specifically NPDES permits, TMDLs required for both permitting and BMAP activities, 
33

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 
34

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 
35

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/fldetermination.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 nutrientimpaired waters. In a separate rulemaking, EPA intends to develop and propose numeric 
36

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 

estuaries 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 
37

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 
38

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
39

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. 
40

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 
41

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 Report41 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. 

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.

 

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.
42

(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.): 

A B C D E F

Long Term 

Average Lake 

Color and 

Alkalinity

Chlorophyll 

a

f

(g/L) a

Baseline Criteria b Modified Criteria

(within these bounds)

c

TP (mg/L) aTN (mg/L) aTP (mg/L) aTN (mg/L) a

Colored Lakes

> 40 PCU

20 0.050 1.23 0.050-0.157 1.23-2.25

Clear Lakes, 

Alkaline

≤ 40 PCU dand 

> 50 mg/L 

CaCO3 

e

20 0.030 1.00 0.030-0.087 1.00-1.81

Clear Lakes, 

Acidic

≤ 40 PCU dand 

≤ 50 mg/L 

CaCO3 

e

6 0.010 0.500 0.010-0.030 0.500-0.900

a

Concentration values are based on annual geometric mean not to be surpassed more than once in a threeyear 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 ambientbased, 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. 
43

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 

 

43 U.S. EPA. 1998. National Strategy for the Development of Regional Nutrient Criteria. Office of Water, 

Washington, D.C. 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 
44

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. 

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.

 

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.
45

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. 

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 

 

45 Shannon, E.E. and P.L. Brezonik. 1972. Limnological characteristics of north and central Florida lakes. 

Limnol. Oceanogr. 17(1): 97-110.
46

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 represents 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 (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 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.
47

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 

 

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).
48

conditions with respect to nutrients and algal productivity.

47

 EPA’s review of TSI

studies48,49 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 (μg/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 μg/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 μg/L). EPA requests comment on 

these conclusions regarding oligotrophic and mesotrophic status expectations for these 

categories of Florida lakes.

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 

 

47 Carlson, R.E. 1977. A trophic state index for lakes. Limnol. Oceanogr.. 22:361-369.

48Carlson, 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.
49

(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 studies50 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). 

In addition to this evidence, EPA used information from the application of a 

Morphoedaphic Index (MEI) model51 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 

 

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.

51 Vighi and Chiaudani. 1985. A simple method to estimate lake phosphorus concentrations resulting from 

natural background loadings. Wat. Res.19:987-991.
50

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:

(i) Colored Lakes: EPA proposes a chlorophyll a criterion of 20 μg/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 μg/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 μg/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 μg/L and the MEI model predicted reference chlorophyll a concentrations 

of 1-25 μg/L for a set of colored lakes in Florida. The model also predicted that 

concentrations of chlorophyll a ranging from 15-36 μg/L in individual lakes would result 

in a 10% loss of transparency (all but two lakes were above 20 μg/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) 
51

of lakes had predicted natural or referenced conditions below 20 μg/L chlorophyll a and 

the clear majority (nine of eleven) of lakes had predicted 10% transparency loss above 20 

μg/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

μg/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 

μg/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 μg/L. Similar to the results for 

colored lakes, half of the clear, alkaline lakes had predicted natural or referenced 

conditions at or below 20 μg/L chlorophyll a and all but one clear, alkaline lake had 

predicted 10% transparency loss above 20 μg/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 μg/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 
52

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 oligotrophic52 with chlorophyll a

levels of less than 2 μg/L. As discussed above, warm water TSI studies suggest a 

chlorophyll a level of approximately 7 μg/L at the oligotrophic-mesotrophic boundary.

In July 2009, FDEP proposed a chlorophyll a criterion for clear, acidic lakes of 9 

μg/L.

53

 In comments sent to EPA via email in October 2009,54 FDEP reported that the 

Nutrient TAC suggested in June 2009 that maintaining chlorophyll a below 10 μg/L in 

clear, acidic lakes would be protective of the designated use, because a value of <10 μg/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 μg/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 μg/L as supporting evidence for a chlorophyll a criterion of 

9 ug/L in clear acidic lakes. However, within this small range of chlorophyll a, it is not 

 

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).

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.
53

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 μg/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 μg/L (with seven of the eight values below 5 

μg/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 μg/L (with five of the eight 

values below 7 μg/L). All but one of the clear, acid lakes had predicted natural or 

reference conditions below 6 μg/L chlorophyll a and the majority (six of eight) of clear, 

alkaline lakes had predicted 10% transparency loss above 6 μg/L chlorophyll a. Given 

available information on reference condition and predicted effect levels, EPA adjusted 

the approximate oligotrophic-mesotrophic boundary value of 7 μg/L slightly downward 

to 6 μg/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 μg/L. 

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. 
54

(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 

μg/L for colored lakes and clear alkaline lakes and 6 μg/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 
55

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 
56

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, 
57

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 
58

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-

 

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.
59

magnitude and criterion-duration, in combination. A criterion-frequency specifies the 

maximum rate at which “excursions” may occur. 

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-thanonce-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 
60

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.

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 

 

56 Kenney (1998) as reported in Salas and Martino (1991).
61

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 
62

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. 

Another technical concern is that there may be a time lag between the presence of 

high nutrients and the biological response. In a study of numerous lakes, researchers 

found that there was often a lag period of a few years in chlorophyll a response to 

changes in nutrient loading, but that there was correlation between chlorophyll a and 
63

nutrient concentrations on an annual basis.57 The difference between nutrient loading and 

nutrient concentration as a function of time is related to the hydraulic retention time of a 

lake. EPA proposed TN and TP criteria as concentration values with an annual averaging 

period, so any time lag in response would not be expected to confound the derivation of 

modified criteria. Furthermore, EPA is proposing to require three years worth of data, 

which would reflect any short time lag in response.

A third technical concern is the presence of temporary or long-term site-specific 

factors that may suppress biological response, such as the presence of grazing 

zooplankton, excess sedimentation that blocks light penetration, extensive canopy cover, 

or seasonal herbicide use that impedes proliferation of algae. If any of these suppressing 

factors are removed, then nutrient levels may result in a spike in algal production above 

protective levels.

EPA is proposing to require that the ambient calculation for modified TP and TN 

criteria be based on at least a three-year record of observation, and be based on 

representative sampling (i.e., four samples per year with at least one between May and 

September and one between October and April) during each year. These requirements 

will minimize the influence of long-term site-specific factors and ensure longer-term 

stable conditions. EPA selected three years as a reasonable minimum length of time to 

appropriately account for anomalous conditions in any given year that could lead to 

erroneous conclusions regarding the true relationship between nutrient levels in a lake 

and chlorophyll a levels. EPA anticipates that the State would use all recent consecutive 

years of data on record (i.e., it would not be appropriate to select three random years 

 

57 Jeppeson et al. 2005. Lake responses to reduced nutrient loading – an analysis

of contemporary long-term data from 35 case studies. Freshwater Biology 50: 1747–1771.
64

within a complete record over the past seven years). EPA is requiring four measurements 

within a year to provide seasonal representation (i.e., May-September and OctoberApril). Providing seasonal representation is important because nutrient levels can vary

by season. In addition, this minimum sample size is conducive to the derivation of 

central tendency measurements, such as a geometric mean, with an acceptable degree of 

confidence. EPA is proposing that the chlorophyll a criterion must be met in each of the 

three or more years of ambient monitoring that define the record of observation for the 

lake to be eligible for the ambient calculation modified provision for TN and TP. EPA 

requests comment on whether three years of data is sufficient to establish for a particular 

lake that there is a fundamentally different relationship between chlorophyll a levels and

TN and TP levels. EPA also requests comment on whether less data or a different 

specification would be sufficient to establish this different relationship in a particular 

lake, e.g. whether revised TN and TP ambient criteria should be allowed when the 

chlorophyll a criterion concentration has been exceeded once in three years.

Application of the ambient calculation provision has implications for assessment 

and permitting because the outcome of applying this provision is to establish alternate 

numeric TN and TP values as the applicable numeric nutrient criteria for TN and TP. For 

accountability and tracking purposes, the State would need to document in a publicly

available and accessible manner, such as on an official State Web site, the result of the 

ambient calculation for any given lake. The State may wish to issue a public notification, 

with an opportunity to submit additional data and check calculations, to ensure an 

appropriate value is determined. The State may wish to publicly certify the outcome via 

a Secretarial order or some other official statement of intent and applicability. EPA’s 
65

preference is that once modified criteria are developed, they remain the applicable criteria 

for the long-term. The State has the flexibility to revise the criteria, but the expectation is 

that they will not be a continuously moving target for implementation purposes. As an 

example of how the lakes criteria might work in practice, consider a colored lake which 

meets the chlorophyll a criterion. If FDEP established a modified TP criterion of 0.110 

mg/L and subsequent monitoring showed levels at 0.136 mg/L, that lake would not be 

considered attaining the applicable criteria for CWA purposes (unless the State goes 

through the process of establishing a revised modified criterion).

The permitting authority would use publicly certified modified TN or TP criteria 

to develop water quality-based effluent limits (WQBELs) that derive from and comply

with applicable WQS. In this application, the permit writer would use the modified

ambient criterion, computed as described above, as the basis for any reasonable potential 

analysis or permit limit derivation. In this case, as in any other case, EPA expects the 

details to be fully documented in the permit fact sheet.

This type of ambient calculation provision based on meeting response criteria 

applicable to the assessed water may not be appropriate when the established TN and TP 

criteria are serving to maintain and protect waters downstream. To address this concern, 

EPA proposes that calculated TP and TN values in a lake that discharges to a stream may

not exceed criteria applicable to the stream to which a lake discharges. EPA requests 

comment on this provision.

(3) Request for Comment and Data on Proposed Approach

EPA is soliciting comment on the approaches described in this proposal, the data 

underlying those approaches, and the proposed criteria. EPA will evaluate all data and 
66

information submitted by the close of the public comment period for this rulemaking with 

regard to nutrient criteria for Florida’s lakes. For the application of the modified ambient 

calculation provision, EPA is seeking comment on allowing the calculation to occur one 

time only, based on an adequate period of record, and then holding that value as the 

protective TP or TN criteria for future assessment and implementation purposes. EPA is 

also seeking comment on whether to require an ambient chlorophyll a level demonstrated 

to be below the chlorophyll a threshold criterion for at least three years become the 

protective chlorophyll a criterion for a lake subject to the modified ambient calculation 

provision (i.e., whether to require a more stringent chlorophyll a criterion if three years of 

data show that the more stringent level reflects current conditions in the lake). EPA also 

requests comment on whether an additional condition for being able to apply a modified 

criterion include continued ambient monitoring and verification that chlorophyll a levels 

remain below the protective criterion. EPA could specify that modified criteria remain in 

effect as long as FDEP subsequently conducts monthly (or some other periodic)

monitoring of the lake to ensure that chlorophyll a levels continue to meet the protective 

criterion. If this monitoring is not conducted and documented, EPA could specify that 

the baseline criterion would become the applicable criterion. Among others, this 

provision may address concerns about whether the modified criterion adequately

represents long-term hydrologic variability. Finally, EPA requests comment on the 

appropriate procedure for documenting and tracking the results of modified criteria that 

allows transparency, public access, and accountability. 

(4) Alternatives Considered by EPA

During EPA’s review of the available data and information for development of 
67

numeric nutrient criteria for Florida’s lakes, EPA considered and is soliciting comment 

on an alternative approach to deriving lakes criteria from the statistical correlation plots 

and regression analysis. The alternative approach would use either the central tendency

values or the lower values associated with the 50th percentile prediction interval for TN 

and TP criteria and would not include the framework to calculate modified TP and TN 

criteria when the chlorophyll a criterion is met. EPA is also seeking comments on the 

following two supplementary modifications that EPA considered but did not include in 

this proposal: 1) the use of a modified categorization of lakes in Florida; and 2) the 

addition of upper percentile criteria with a different exceedance frequency.

(a) Single Value Approach to Derive Lakes Criteria - Derive TN and TP Criteria 

Using Correlations Associated with the Regression Line or Lower Value of the 50th

Percentile Prediction Interval 

One alternative means of selecting TN and TP criteria is to use the regression line 

(central tendency) to calculate TP and TN concentrations that correlate to the proposed 

chlorophyll a criteria for each lake class. A second alternative is to use the lower value

of the 50th percentile prediction interval to calculate TP and TN concentrations. 

Establishing TP and TN criteria using the central tendency of the regression line 

represents the best estimate of TN and TP associated with a protective chlorophyll a

criterion across all lakes, but carries some risk of being overprotective for some 

individual lakes and under-protective for others because of the demonstrated variability

of the data. On the other hand, establishing TP and TN criteria using the lower value of

the 50th percentile prediction interval will likely be protective in most cases, but could be 

overprotective for a greater number of lakes because the data demonstrate that many
68

lakes achieve the protective chlorophyll a criterion with higher levels of TN and TP. 

Neither approach accounts for lake-specific natural variability, apart from that accounted 

for by color and alkalinity classification. However, the correlated TP and TN 

concentrations within each lake class at these alternative statistical boundaries would 

result in single criteria values for TN and TP, which is an approach that water quality

program managers will have more familiarity. EPA’s rationale for proposing a 

framework that uses both the upper and lower values of the 50th percentile prediction 

interval to allow the derivation of modified TN and TP lake-specific criteria rather than 

either of these single values was to account for the natural variability in the relationship 

between chlorophyll a and TN and TP that may exist in lakes. EPA solicits comment, 

however, on this alternative approach of using single values for TN and TP criteria in 

Florida’s lakes.

(b) Modification to Proposed Lakes Classification 

As discussed in Section III.B(2)(a), EPA used available data to determine a 

classification scheme for Florida’s lakes, based on a color threshold of 40 PCU and a 

threshold of 50 mg/L alkalinity as CaCO3. In its July 2009 numeric nutrient criteria 

proposal, Florida considered a similar classification approach based on color and 

alkalinity but proposed a chlorophyll a criterion of 9 μg/L to protect aquatic life in clear, 

acidic lakes. As discussed above, EPA believes that the scientific evidence more strongly

supports a chlorophyll a criterion of 6 μg/L to protect Florida’s clear, acidic lakes that 

include the very oligotrophic lakes found in Florida’s sandhills, principally in three areas: 

the Newhope Ridge/Greenhead slope north of Panama City (locally called the Sandhill 

Lakes region); the Norfleet/Springhill Ridge just west of Tallahassee, and Trail Ridge 
69

northeast of Gainesville.58 However, some stakeholders have suggested that many lakes 

in the clear, acidic class (as currently defined) might be sufficiently protected with a 

chlorophyll a criterion of 9 μg/L. EPA believes the scientific basis for a 9 ug/L 

chlorophyll a value may be more applicable to clear acidic lakes other than those in 

Florida’s sandhills (i.e., other than those in the Sandhill Lakes region, the 

Norfleet/Springhill Ridge just west of Tallahassee and Trail Ridge northeast of 

Gainesville). To address this, EPA could separate clear, acidic lakes into two categories: 

one category for clear, acidic lakes in sandhill regions of Florida, and a second category

for clear, acidic lakes in other areas of the State. EPA could assign the first category

(clear, acidic sandhill lakes) a chlorophyll a criterion of 6 μg/L and the second category

(clear, acidic non-sandhill lakes) a chlorophyll a criterion of 9 μg/L. 

Alternatively, EPA could lower the defining alkalinity threshold to 20 mg/L

CaCO3 so that the clear, acidic lakes category would only include lakes with very acidic 

values and correspondingly low chlorophyll a, TN, and TP values. EPA’s analysis of a 

distribution of alkalinity data from Florida’s clear lakes found that lakes with alkalinity

values ≥ 20 mg/L CaCO3 had higher levels of nutrients and nutrient response parameters 

than lakes with alkalinity values < 20 mg/L CaCO3. By adjusting the alkalinity threshold 

to 20 mg/L CaCO3, EPA would be creating a smaller group of clear, acidic lakes that may

be more representative of naturally more acidic, oligotrophic conditions than the 

proposed alkalinity threshold of 50 mg/L CaCO3. EPA opted to propose a threshold of 

50 mg/L CaCO3 because it represents a more comprehensive group of lakes that may be 

naturally oligotrophic (i.e., ensures protection where there may be some uncertainty).

 

58 Griffith, G. E., D. E. Canfield, Jr., C. A. Horsburgh, J. M. Omernik, and S. H. Azevedo. 1997.

Florida lake regions. U. S. EPA, Corvallis, OR. http://www.epa.gov/wed/pages/ecoregions/fl_eco.htm
70

EPA solicits comment on these alternative approaches to classifying Florida’s lakes. 

EPA also notes, as discussed previously, that FDEP recommended a criterion of 9 μg/L 

as being protective of all clear acidic lakes, including sandhill lakes and that the Nutrient 

Criteria TAC supported “less than 10 μg/L” as protective. EPA also requests comment 

on 9 μg/L chlorophyll a as being protective of all clear acidic lakes, including sandhill 

lakes. 

(c) Modification to Include Upper Percentile Criteria 

EPA is considering promulgating upper percentile criteria for chlorophyll a, TN, 

and TP in colored, clear alkaline, and clear acidic lakes to provide additional aquatic life 

protection. Accordingly, EPA could add that the instantaneous concentration in the lake 

not surpass these criterion-magnitude concentrations more than 10% of the time 

(criterion-duration: instant; criterion-frequency: 10% of the time). EPA derived example 

upper percentile criteria using the observed standard deviation from the mean of lake 

samples meeting the respective criteria (lower values of the TN and TP ranges) within 

each lake class. Using this example, the calculated criteria-magnitude concentrations for 

chlorophyll a, TN, and TP respectively by lake class are: 63 μg/L, 1.5 mg/L and 0.09 

mg/L for colored lakes; 48 μg/L, 1.8 mg/L and 0.05 mg/L for clear, alkaline lakes; and 15 

μg/L, 0.6 mg/L and 0.02 mg/L for clear, acidic lakes. 

These criteria would provide the means to protect lakes from episodic events that 

increase loadings for significant periods of time during the year, but are balanced out by

lower levels in other parts of the year such that the annual geometric mean value is met. 

EPA chose not to propose such criteria because of the significant variability of 

chlorophyll a, TN, and TP, the variety of other factors that may influence levels of these 
71

parameters in the short-term, and that significant environmental damage from 

eutrophication is more likely when levels are elevated for longer periods of time. 

However, EPA solicits comment on this additional approach of promulgating upper 

percentile criteria for chlorophyll a, TN, and TP.

(5) Request for Comment and Data on Alternative Approaches

EPA is soliciting comment on the Agency’s proposed approach, as well as the 

alternative approach to deriving numeric nutrient criteria for Florida’s lakes and the 

supplemental modifications as described in Section III.B(4). EPA will evaluate all data 

and information submitted by the close of the public comment period for this rulemaking 

with regard to nutrient criteria for Florida’s lakes.

C. Proposed Numeric Nutrient Criteria for the State of Florida’s Rivers and Streams

(1) Proposed Numeric Nutrient Criteria for Rivers and Streams

EPA is proposing numeric nutrient criteria for TN and TP in four geographically

distinct watershed regions of Florida’s rivers and streams (hereafter, streams) classified 

as Class I or III waters under Florida law (Rule 62-302.400, F.A.C.). 

Nutrient Watershed Region Instream Protection Value Criteria

TN (mg/L) aTP (mg/L) a

Panhandle b0.824 0.043

Bone Valley c1.798 0.739

Peninsula d1.205 0.107

North Central e1.479 0.359

a

Concentration values are based on annual geometric mean not to be surpassed more than once in a threeyear 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).
72

b

Panhandle region includes the following watersheds: Perdido Bay Watershed, Pensacola Bay Watershed, 

Choctawhatchee Bay Watershed, St. Andrew Bay Watershed, Apalachicola Bay Watershed, Apalachee Bay 

Watershed, and Econfina/Steinhatchee Coastal Drainage Area.

c

Bone Valley region includes the following watersheds: Tampa Bay Watershed, Sarasota Bay Watershed, 

and Charlotte Harbor Watershed.

d

Peninsula region includes the following watersheds: Waccasassa Coastal Drainage Area, Withlacoochee 

Coastal Drainage Area, Crystal/Pithlachascotee Coastal Drainage Area, Indian River Watershed, 

Caloosahatchee River Watershed, St. Lucie Watershed, Kissimmee River Watershed, St. John’s River 

Watershed, Daytona/St. Augustine Coastal Drainage Area, Nassau Coastal Drainage Area, and St. Mary’s 

River Watershed.

e North Central region includes the Suwannee River Watershed.

The following section describes the methodology used to derive the proposed 

numeric nutrient criteria for streams. EPA is soliciting comments and scientific data and 

information regarding these proposed criteria and their derivation. 

(2) Methodology for Deriving EPA’s Proposed Criteria for Streams

Like other aquatic ecosystems, excess nutrients in streams increases vegetative 

growth (plants and algae), and changes the assemblage of plant and algal species present 

in the system. These changes can affect the organisms that are consumers of algae and 

plants in many ways. For example, these changes can alter the available food resources 

by providing more dead plant material versus live plant material, or providing algae with 

a different cell size for filter feeders. These changes can also alter the habitat structure by 

covering the stream or river bed with periphyton (attached algae) rather than submerged 

aquatic plants, or clogging the water column with phytoplankton (floating algae). In 

addition, these changes can lead to the production of algal toxins that can be toxic to fish, 

invertebrates, and humans. Chemical characteristics of the water, such as pH and 

concentrations of dissolved oxygen, can also be affected by excess nutrients. Each of 

these changes can, in turn, lead to other changes in the stream community and, ultimately, 

to the stream ecology that supports the overall function of the linked aquatic ecosystem.

Although the general types of adverse effects can be described, not all of these 
73

effects will occur in every stream at all times. For example, some streams are well 

shaded, which would tend to reduce the near-field effect of excess nutrients on primary

production because light, which is essential for plant or algae growth, does not reach the 

water surface. Some streams are fast moving and pulses of nutrients are swiftly carried 

away before any effect can be observed. However, if the same stream widens and slows 

downstream or the canopy that provided shading opens up, then the nutrients present may

accelerate plant and algal biomass production. As another example, the material on the 

bottom of some streams, referred to as substrate, is frequently scoured from intense rain 

storms. These streams may lack a natural grazing community to consume excess plant 

growth and may be susceptible to phytoplankton algae blooms during periods when water

velocity is slower and water residence time is longer. The effects of excess nutrients may

be subtle or dramatic, easily captured by measures of plant and algal response (such as 

chlorophyll a) or not, and may occur in some locations along a stream but not others.

Notwithstanding natural environmental variability, there are well understood and 

documented analyses and principles about the underlying biological effects of TN and TP 

on an aquatic ecosystem. There is a substantial and compelling scientific basis for the 

conclusion that excess TN and TP will have adverse effects; however, it is often unclear 

where precisely the impacts will occur. The value of regional numeric nutrient criteria

for streams is that the substantial expenditure of time and scarce public resources to 

document and interpret inevitable and expected stream variability on a site-by-site, 

segment-by-segment basis (i.e., as in the course of interpreting a narrative WQS for 

WQBELs and TMDL estimations) is no longer necessary. Rather, regional numeric 

nutrient criteria for streams allows an expedited and expanded level of aquatic protection 
74

across watersheds and greatly strengthens local and regional capacity to support and 

maintain State designated uses throughout aquatic ecosystems. In terms of environmental 

outcomes, the result is a framework of expectations and standards that is able to extend

the protection needed to restore and maintain valuable aquatic resources to entire 

watersheds and associated aquatic ecosystems. At the same time, the ability to 

promulgate SSAC, as well as other flexibilities discussed in this proposal, allows the 

State to continue to address water bodies where substantial data and analyses show that 

the regional criteria may be either more stringent than necessary or not stringent enough 

to protect designated uses.

As mentioned earlier, to effectively apply this well understood and documented 

science, 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) for water 

bodies.

59

 EPA recommends causal variables, in part, to have the means to develop source 

control targets and, in part, to have the means to assess stream condition 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 stream condition 

that synthesizes the effect of causal variables over time, recognizing the daily, seasonal, 

and annual variability in measured nutrient levels.60 

 

59 U.S. EPA. 1998. National Strategy for the Development of Regional Nutrient Criteria. Office of Water, 

Washington, D.C. 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).

60 U.S. EPA. 2000. Nutrient Criteria Technical Guidance Manual: Rivers and Streams. Office of Water, 

Washington, DC. EPA-822-B-00-002.
75

The ability to establish protective criteria for both causal and response variables 

depends on available data and scientific approaches to evaluate these data. Whereas,

there are data available for water column chlorophyll a (phytoplankton) and algal 

thickness on various substrates (periphyton) for certain types of streams in Florida, there 

are currently no available approaches to interpret these data to infer scientifically

supported thresholds for these nutrient-specific response variables in Florida streams. 

Additionally, in previously published guidance,61 EPA has recommended water clarity as 

a response variable for numeric nutrient criteria because algal density in a water column 

results in turbidity, and thus a related decrease in water clarity can serve as an indicator 

of excess algal growth. 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 (32-302.530(67) and (69), F.A.C.). Therefore, EPA is 

not proposing criteria for any response variable in Florida’s streams at this time,

however, EPA will consider additional data that becomes available during the comment 

period. One approach for deriving criteria for water quality variables such as a measure 

for water clarity or chlorophyll a, could be to apply a statistical distribution approach to a 

population of streams for each of the proposed NWRs. This approach is further

described in previous EPA guidance.

62

For Florida streams, EPA has determined that there are sufficient available data 

on TN and TP concentrations with corresponding information on biological condition for 

 

61 U.S. EPA. 2000. Nutrient Criteria Technical Guidance Manual: Lakes and Reservoirs. Office of Water, 

Washington, DC. EPA-822-B-00-001; U.S.EPA. 2000. Nutrient Criteria Technical Guidance Manual: 

Rivers and Streams. Office of Water, Washington, DC. EPA-822-B-00-002; U.S. EPA.2001. Nutrient 

Criteria Technical Manual: Estuarine and Coastal Marine Waters. Office of Water, Washington, DC. EPA822-B-01-003.

62 U.S. EPA. 2000. Nutrient Criteria Technical Guidance Manual: Rivers and Streams. Office of Water. 

4304. EPA-822-B-00-002.
76

a wide variety of stream types that can be used to derive numeric nutrient criteria for 

those causal variables. EPA used multiple measures of stream condition (or metrics) that 

describe the biological condition of the benthic invertebrate community. EPA then 

coupled the stream condition metrics with associated measurements of TN and TP 

concentrations to provide the basis for deriving causal variable numeric nutrient criteria.

EPA’s proposed instream numeric nutrient criteria for Florida’s streams are based 

upon EPA’s evaluation of data on TN and TP levels in rivers and streams that have been 

carefully evaluated by FDEP, and subsequently by EPA, on a site-specific basis and 

identified as biologically healthy. EPA’s approach results in numeric criteria that are 

protective of the streams themselves. EPA has determined, however, that these instream 

values may not always be protective of the designated uses in downstream lakes and 

estuaries. Therefore, EPA has also developed an approach for deriving TN and TP values

for rivers and streams to ensure the protection of downstream lakes and estuaries. This 

approach is discussed in Section III.C(6).

(a) Methodology for Stream Classification: EPA’s Nutrient Watershed Regions 

(NWRs)

EPA classified Florida’s streams north of Lake Okeechobee by separating 

watersheds with a substantially different ratio of TN and TP export into Nutrient 

Watershed Regions (NWR). The resulting regions reflect the inherent differences in the 

natural factors that contribute to nutrient concentrations in streams (e.g., geology, soil 

composition, and/or hydrology). Reliance on a watershed-based classification approach 

reflects the understanding that upstream water quality affects downstream water quality. 
77

This watershed classification also facilitates the ability to address the effects of TN and 

TP from streams to downstream lakes or estuaries in the same watershed. 

EPA’s classification approach results in four watershed regions: the Panhandle, 

the Bone Valley, the Peninsula, and the North Central (for a map of these regions, refer to 

the EPA TSD for Florida’s Inland Waters or the list of watersheds in the table above). 

These four regions do not include the south Florida region (corresponding to FDEP’s 

Everglades Bioregion) that is addressed separately in Section III.E which sets out EPA’s 

proposed numeric nutrient criteria for canals in south Florida. All flowing waters in this 

region are either a canal or a wetland.

When classifying Florida’s streams, EPA identified geographic areas of the State 

as having phosphorus-rich soils and geology, such as the Bone Valley and the northern 

Suwannee River watershed . As indicated above, the Bone Valley region and the 

Suwannee River watersheds are classified in this proposal as separate NWRs because it is 

well established that the naturally phosphorus-rich soils in these areas significantly

influence stream phosphorus concentrations in these watersheds. EPA would expect from 

a general ecological standpoint that the associated aquatic life uses, under these naturallyoccurring, nutrient-rich conditions, would be supported. The Agency requests comment 

on this particular classification decision (regions based on phosphorus-rich soils), as well 

as an alternate classification approach that would not separate out the phosphorus-rich 

watersheds described in this notice. The latter approach is similar to the approach 

proposed by EPA, but would not result in separate NWRs for the Bone Valley and/or 

North Central. Rather these NWRs would be integrated within the other NWRs.
78

(b) The Use of the Stream Condition Index as an Indicator of Biologically

Healthy Conditions

For EPA’s proposed approach, the Agency utilized a multi-metric index of 

benthic macroinvertebrate community composition and taxonomic data known as the 

Stream Condition Index (SCI) developed by FDEP to assess the biological health of 

Florida’s streams.63 Of the metrics that comprise the SCI, some decrease in response to 

human disturbance-based stressors, such as excess nutrients; for example, 1) total taxa 

richness, 2) richness of Ephemeroptera (mayflies), 3) richness of Plecoptera (stoneflies), 

4) percentage of sensitive taxa, and 5) percentage of filterers and suspension feeders. 

Other metrics increase in response to human disturbance-based stressors; for example,

percent of very tolerant taxa (e.g., Genera Prostoma, Lumbriculus) and percent of the 

dominant taxa (i.e., numerical abundance of the most dominant taxon divided by the total 

abundance of all taxa).

The SCI was developed by FDEP in 2004, with subsequent revisions in 2007 to 

reduce the variability of results. In order to ensure that data are produced with the 

highest quality, field biologists and lab technicians must follow detailed Standard 

Operating Procedures (SOPs) and additional guidance for sampling and data use provided 

through a FDEP document entitled “Sampling and Use of the Stream Condition Index 

(SCI) for Assessing Flowing Waters: A Primer (DEP-SAS-001/09).” Field biologists

must pass a rigorous audit with FDEP, and laboratory taxonomists are regularly tested 

and must maintain greater than 95% identification accuracy. 

 

63 The SCI method was developed and calibrated by FDEP. See “Fore et al. 2007. Development and testing 

biomonitoring tools for macroinvertebrates in Florida streams (Stream Condition Index and BioRecon). 

Final report to Florida Department of Environmental Protection” and the EPA TSD for Florida’s Inland 

Waters for more information on the SCI.
79

EPA considered two lines of evidence in determining the SCI range of scores that 

would indicate biologically healthy systems. The first line of evidence was an evaluation 

of SCI scores in streams considered by FDEP to be least-disturbed streams in Florida. A 

statistical analysis balanced the probability of a stream being included in this reference 

set with the probability of a stream not being included in this reference set, and indicated 

that an SCI score of 40 was an appropriate threshold. SCI scores range from 1 to 100 

with higher scores indicating healthier biology. 

A second line of evidence was the result of an expert workshop convened by 

FDEP in October 2006. The workshop included scientists with specific knowledge and 

expertise in stream macroinvertebrates. These experts were asked to individually and 

collectively evaluate a range of SCI data (i.e., macroinvertebrate composition and 

taxonomic data) and then assign those data into one of the six Biological Condition 

Gradient (BCG)64 categories, ranging from highly disturbed (Category 6) to pristine 

(Category 1). EPA analyzed the results of these categorical assignments using a

proportional odds regression model65 that predicts the probability of an SCI score 

occurring within one of the BCG categories by overlapping the ranges of SCI scores 

associated with each category from the individual expert assignment. The results of the 

analysis provided support for identifying a range of SCI scores that minimized the 

probability of incorrectly assigning a low quality site to a high quality category, and 

incorrectly assigning a high quality site to a low quality category, using the collective 

judgment of expert opinion. The results indicated a range of SCI scores of 40-44 to 

 

64 Appendix H in “Fore et al. 2007. Development and testing biomonitoring tools for macroinvertebrates in 

Florida streams (Stream Condition Index and BioRecon). Final report to Florida Department of 

Environmental Protection”

65 See the EPA TSD for Florida’s Inland Waters for more information on the proportional odds regression 

model.
80

represent an appropriate threshold of healthy biological condition. Please refer to the 

EPA TSD for Florida’s Inland Waters for more information on such topics as EPA’s 

estimates of the Type I and Type II error associated with various threshold values. Thus, 

two very different approaches yielded comparable results. A subsequent EPA statistical 

analysis indicated that nutrient conditions in Florida streams within different regions 

remain essentially constant within an SCI score range of 40-50 providing further support 

for a selection of 40 as a threshold that is sufficiently protective for this application. The 

resulting TN and TP concentrations associated with a SCI score of 40 versus 50 did not 

represent a statistical difference and 40 was more in line with other lines of evidence for a 

SCI score threshold.

(c) Methodology for Calculating Instream Protection Values: The Nutrient 

Watershed Region Distribution Approach 

EPA evaluated several methodologies, including reference conditions and 

stressor-response relationships, to develop values that protect designated uses of Florida 

streams instream. EPA analyzed stressor-response relationships in Florida streams based 

on available data, but, as mentioned above, did not find sufficient scientific support for 

their use in the derivation of numeric nutrient criteria for Florida streams. More 

specifically, EPA was not able to demonstrate a sufficiently strong correlation between 

the biological response indicators (e.g., chlorophyll a, periphyton biomass, or SCI) 

and TN or TP concentrations. Thus, the Agency could not confidently predict a specific 

biological response (such as an SCI score) for an individual stream solely from the 

associated stream measurements of TN or TP concentrations. 
81

There may be several reasons why empirical relationships between field-derived 

data of nutrient stressor and biological response variables show a relatively weak 

correlation. First, the relationship between nutrient concentrations and a biological 

response, such as algal growth, can be confounded by the presence of other stressors. For 

example, other stressors, such as excessive scour could cause low benthic invertebrate 

diversity, as measured by the SCI, even where nutrients are low. Excessive scour could 

also suppress a biological response (such as chlorophyll a or periphyton biomass) when 

nutrients are high. Another reason for stressor-response relationships with low 

correlations is that algal biomass accumulation is difficult to characterize because 

dynamic conditions in an individual stream can allow algae to accumulate and be 

removed rapidly, which is difficult to capture with periodic monitoring programs. 

As an alternative to the stressor-response approach, EPA analyzed the TN and TP 

concentrations associated with a healthy biological condition in streams, and examined 

the statistical distributions of these data in order to identify an appropriate threshold for 

providing protection of aquatic life designated uses. To derive the instream protection 

values under this approach, EPA first assembled the available nutrient concentrations and 

biological response data for streams in Florida. EPA used FDEP’s data from the IWR 

and STORET66 databases and identified sites where SCI scores were 40 and higher. EPA 

further screened these sites by cross-referencing them with Florida’s CWA section 303(d) 

list for Florida and excluded sites with identified nutrient impairments or dissolved 

oxygen impairments associated with elevated nutrients. EPA grouped the remaining sites 

(hereafter, biologically healthy sites) according to its nutrient watershed regions

(Panhandle, Bone Valley, Peninsula, and North Central). For each nutrient watershed 

 

66 FL IWR and STORET can be found at: http://www.dep.state.fl.us/WATER/STORET/INDEX.HTM
82

region, EPA compiled nutrient data (TN and TP concentrations) associated with the 

biologically healthy sites, and calculated distributional statistics for annual average TN 

and TP concentrations.

The second step in deriving instream protection values was to further characterize 

the distribution of TN and TP among biologically healthy sites. Specifically, EPA 

calculated the number of biologically healthy sites within integer log-scale ranges of TN 

and TP concentrations, as well as the cumulative distribution. These nutrient 

distributions from biologically healthy sites in each nutrient watershed region are 

represented on a log-scale because concentration data are typically log-normally

distributed. A log-normal distribution is skewed, with a mode near the geometric mean 

rather than the arithmetic mean. 

The third step in deriving instream protection values was to determine appropriate

thresholds from these distributions for providing protection of aquatic life designated

uses. Selection of a central tendency of the distribution (i.e., the median or geometric 

mean of a log-normal distribution) would imply that half of the biologically healthy sites 

are not attaining their uses. In contrast, an extreme upper end of the distribution (e.g., the 

90th or 95th percentile) may be the most likely to be heavily influenced by extreme event 

factors that are not representative of typically biologically healthy sites. This might be 

the case because the upper tail of the distribution might reflect a high loading year 

(landscape and/or atmospheric), and/or lack of nutrient uptake by algae (in turn due to a 

myriad of physical and biological factors like scour, grazing, light limitation, other 

pollutants). Thus, this tail of the distribution may just represent the most nutrient

“tolerant” among the sites. Another possibility is that these streams may experience
83

adverse effects from nutrient enrichment that are not yet reflected in the SCI score. A

reasonable choice for a threshold is one which lies just above the vast majority of the 

population of healthy streams. This choice is reasonable because it reflects a point where 

most biologically healthy sites will still be identified as attaining uses, but avoids

extrapolations into areas of the distribution characterized by only a few data points (as 

would be the case for the 90th or 95th percentile). When a threshold is established as a 

water quality criterion, sites well below that threshold might be allowed to experience an 

increase in nutrient levels up to the threshold level. There is little assurance that 

biologically healthy sites with nutrient concentrations well below the 90th or 95th

percentile would remain biologically healthy if nutrient concentrations increased to those 

levels because relatively few sites with nutrient concentrations as high as those at the 90th

or 95th percentile are demonstrated to be biologically healthy. 

The range between the 25th and 75th percentiles, or inter-quartile range, is a 

common descriptive statistic used to characterize a distribution of values. For example, 

statistical software packages typically include the capability to display distributions as 

“box and whisker” plots, which very prominently identify the inter-quartile range. The 

inter-quartile range of a log normal distribution spans a smaller range of values than the 

inter-quartile range of a distribution of the data evenly spread across the entire range of 

values. This means that the further a value goes past the 75th percentile of a log normal 

distribution, the less representative it is of the majority of data (in this case, less 

representative of biologically healthy sites. Within the inter-quartile range of a log 

normal distribution, the slope of the cumulative frequency distribution will be the 

greatest. The 75th percentile represents a reasonable upper bound of where there is the 
84

greatest confidence that biologically healthy sites will be represented. Beyond the interquartile range (i.e., below the 25th percentile and above the 75

th percentile), there is a 

greater chance that measurements may represent anomalies that would not correspond to 

long-term healthy conditions in the majority of streams. Based on this analysis, EPA 

concluded that the 75th percentile represents an appropriate and well-founded protective 

threshold derived from a distribution of nutrient concentrations from biologically healthy

sites. EPA solicits comment on its analysis of what constitutes a protective threshold.

(d) Proposed Criteria: Duration and Frequency 

Aquatic life water quality criteria contain three components: magnitude, duration, 

and frequency. For the TN and TP numeric criteria for streams, the derivation of the 

criterion-magnitude values is described above and these values are provided in the table 

in Section III.C(1). The criterion-duration of this magnitude is specified in footnote a of 

the streams criteria table as an annual geometric mean. 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 to exceed the criterion-magnitude concentration. EPA anticipates 

that Florida will use their standard assessment periods as specified in Rule 62-303, 

F.A.C. (Impaired Waters Rule) to implement this second provision. These proposed 

duration and frequency components of the criteria are consistent with the data set used to 

derive these criteria, which applied distributional statistics to measures of annual 

geometric mean values from multiple years of record. EPA has determined that this 

frequency of excursions will not result in unacceptable effects on aquatic life as it will 
85

allow the stream ecosystem enough time to recover from an occasionally elevated year of 

nutrient loadings. The Agency requests comment on these proposed duration and 

frequency components of the stream numeric nutrient criteria.

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, and would still 

be protective. EPA requests comment on 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.

(3) Request for Comment and Data on Proposed Approach

EPA is soliciting comments on the approaches taken by the Agency to derive 

these proposed criteria, the data underlying those approaches, and the proposed criteria

specifically. EPA is requesting that the public submit any other scientific data and 

information that may be available related to nutrient concentrations and associated 
86

biological responses in Florida’s streams. EPA is soliciting comment specifically on the 

selection of criteria parameters for TN and TP; the proposed classification of streams into 

four regions based on aggregated watersheds; and the conclusion that the proposed 

criteria for streams are protective of designated uses and adequately account for the 

spatial and temporal variability of nutrients. In addition, EPA requests comment on

folding the Suwannee River watershed in north central Florida into the larger Peninsula 

NWR (i.e., not having a separate North Central region) or, alternatively, making a smaller 

North Central region within Hamilton County alone where the highest phosphorus-rich 

soils are located, with the remainder of the North Central becoming part of the Peninsula 

Region.

(4) Alternative Approaches Considered by EPA

During EPA’s review of the available data and information for derivation of 

numeric nutrient criteria for Florida’s streams, EPA also considered an alternative 

approach for criteria derivation. EPA is specifically requesting comment on a modified 

reference condition approach called the benchmark distribution approach, as described 

below.

(a) Benchmark Distribution Approach 

EPA’s previously published guidance has recommended a variety of methods to 

derive numeric nutrient criteria.

67 One method, the reference condition approach, relies 

on the identification of reference waters that exhibit minimal impacts from anthropogenic 

disturbance and are known to support designated uses. The thresholds of nutrient 

concentrations where designated uses are in attainment are calculated from a distribution 

 

67 U.S. EPA. 2000. Nutrient Criteria Technical Guidance Manual: Rivers and Streams. Office of Water. 

4304. EPA-822-B-00-002;
87

of the available associated measurements of ambient nutrient concentrations at these

reference condition sites.

EPA is seeking comment on a modified reference condition approach, which was 

developed by FDEP and is referred to as the benchmark distribution approach. The 

benchmark approach relies on least-disturbed sites rather than true reference, or 

minimally-impacted, sites. The benchmark distribution is a step-wise procedure used to 

calculate distributional statistics of TN and TP from identified least-disturbed streams.

(i) Identification of Least-Disturbed Streams

FDEP identified benchmark stream sites in the following step-wise manner 1) 

compiled a list of sites with low landscape development intensity using FDEP’s

Landscape Development Intensity Index,

68 2) eliminated any sites on Florida’s CWA 

section 303(d) list of impaired waters due to nutrients, as well as certain sites impaired 

for dissolved oxygen, where the State determined the dissolved oxygen impairment was 

caused by nutrients, 3) eliminated any sites with nitrate concentrations greater than 

FDEP’s 0.35 mg/L proposed nitrate-nitrite criterion in order to reduce the possibility of 

including sites with far-field human disturbance from groundwater impacts, 4) eliminated

sites known by FDEP district scientists to be disturbed, 5) eliminated potentially

erroneous data through outlier analysis, 6) verified sites using high resolution aerial 

photographs, and 7) verified a random sample of the sites in the field.

(ii) Calculation of Benchmark Distribution Approach and Selection of 

Percentiles from the Benchmark Distribution

 

68 A quantitative, integrated measure of the degree of human landscape disturbance within 100 meters on 

either side of a specified stream reach and extending to 10 kilometers upstream of the same stream reach.
88

FDEP selected either the 75th or 90th percentile of the benchmark distribution 

approach from FDEP’s proposed nutrient regions (75th percentile - Bone Valley; 90th

percentile - Panhandle, North Central, Northeast, and Peninsula). FDEP’s rationale for 

selecting either the 75th or 90th percentiles was based on the degree of certainty regarding 

the benchmark sites reflecting least-disturbed conditions and a probability (10% for the 

90th percentile) of falsely identifying a least-disturbed site as being impaired for nutrients. 

With this approach, the distribution of available annual geometric means of 

nutrient concentrations for the benchmark sites within the regional classes of streams is 

calculated. To compute the numeric criteria for the causal variables, TN, and TP, EPA is 

seeking comment on whether the 75th or 90th percentile of the benchmark distribution for 

each nutrient stream region should be selected. As mentioned above, the rationale for 

selecting either the 75th or 90th percentiles is based on the degree of certainty regarding 

the benchmark sites reflecting least-disturbed conditions and a probability of falsely 

identifying a least-disturbed site as being impaired for nutrients or vice-versa. In cases 

where data are more limited for a given nutrient region (i.e., in the Bone Valley there 

were only four sites), the 75th percentile may be more appropriate because the 90th

percentile may not be sufficiently robust (ie, may be highly sensitive to a few data 

points). In other cases, the 90th percentile may be more appropriate when there is a more 

extensive data set. For further information, please refer to EPA’s TSD for Florida’s 

Inland Waters, Chapter 2: Methodology for Deriving U.S. EPA’s Proposed Criteria for

Streams.

In evaluating whether to propose this approach, EPA determined that a 

considerable amount of uncertainty remained whether this approach would result in a list 
89

of benchmark sites that represented truly least-disturbed conditions. Specifically, EPA is 

concerned that nutrient concentrations at these sites may reflect anthropogenic sources 

(e.g., sources more than 100 meters away from and/or 10 kms upstream of the segment),

even if the sites appear least-disturbed on a local basis. EPA is particularly concerned 

that several benchmark sites in the FDEP dataset appear to have a high potential to be 

affected by fertilizations associated with forestry activities. FDEP provided an analysis 

in which FDEP concluded that this is not likely.

69

 EPA solicits comment on this issue 

and more generally on whether the benchmark sites identified by FDEP in its July 2009 

proposal are an appropriate set of least-disturbed sites on which to base the criteria 

calculations.

(5) Request for Comment and Data on Alternative Approach

EPA is soliciting comment on the alternative to deriving numeric nutrient criteria 

for Florida’s streams as described in Section III.C(4). 

(6) Protection of Downstream Lakes and Estuaries

Two key objectives of WQS are: first, to protect the immediate water body to 

which a criterion initially applies and, second, to ensure that criteria provide for 

protection of downstream WQS affected by flow of pollutants from the upstream water 

body. See 40 CFR 131.11 and 131.10(b). EPA WQS regulations reflect the importance 

of protecting downstream waters by requiring that upstream WQS “provide for the 

attainment and maintenance of the water quality standards of downstream waters.” 40 

CFR 131.10(b). Thus, in developing numeric nutrient criteria for Florida, EPA 

considered both instream aquatic conditions and downstream aquatic ecosystem needs. 

 

69 FDEP document titled, “Responses to Earthjustice’s Comments on the Department’s Reference Sites.” 

Draft October 2, 2009. Located in the docket ID EPA-HQ-OW-2009-0596.
90

In addressing the issue of how, if at all, instream criteria values need to be adjusted to 

assure attainment of downstream standards, EPA necessarily examined the WQS for 

downstream lakes and estuaries. For lakes, this analysis starts with the numeric nutrient 

criteria proposed in this notice. For estuaries, this notice proposes an analytical approach 

to determine the loadings that a particular estuary can receive and still assure attainment 

and maintenance of the State's WQS for the estuary (i.e., a protective load). An approach 

is then proposed for translating those downstream loading values into criteria levels in the 

contributing watershed stream reaches in a manner that ensures that the protective 

downstream loadings are not exceeded.

In connection with both lakes and estuaries, EPA fully recognizes that there are a 

range of important technical questions and related significant issues raised by this

proposed approach for developing instream water quality criteria that are protective of 

downstream designated uses. With regard, in particular, to the protection of estuaries, the 

Agency is working closely with FDEP to derive estuarine numeric nutrient criteria for 

proposal and publication in 2011. Even though estuarine numeric nutrient criteria will be 

developed in 2011, there is already a substantial body of information, science, and 

analysis that presently exists that should be considered in determining flowing water 

criteria that are protective of downstream water quality. 

The substantial data, peer-reviewed methodologies, and extensive scientific 

analyses available to and conducted by the Agency to date indicate that numeric nutrient 

criteria for estuaries, 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, 
91

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 TN as proposed criteria for 

rivers and streams to protect the State's estuaries in this notice. 

As described in more detail below and in EPA’s TSD for Florida’s Inland Waters 

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 for 

particular estuaries to help inform what water quality criteria are necessary to protect 

these waters. EPA also recognizes that substantial site-specific work (including some 

very sophisticated analyses in the context of certain TMDLs) 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 may 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. 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 estuaries scheduled for proposal in January of 2011. At this 

time, EPA plans to finalize any necessary downstream protection values for nitrogen in 

flowing waters as part of the second phase of this rulemaking process in coordination 

with the proposal and finalization of numeric criteria for estuarine and coastal waters in 
92

2011. However, if comments, data and analyses submitted as a result of this proposal 

support finalizing such 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 need for and the technical and scientific basis of these proposed 

downstream protection values as part of the broader comment and evaluation process that 

this proposal initiates.

EPA believes that a detailed consideration and related proposed approach to 

address protection of downstream water quality in this proposal is necessary for several 

reasons, including 1) water quality standards are required to protect downstream uses 

under Federal regulations at 40 CFR 131.10(b), meaning also for prevention of 

impairment; 2) it may be a relevant consideration in the development of any TMDLs, 

NPDES permits, and Florida BMAPs that the State completes in the interim period 

between the final rule for Florida lakes and flowing waters in October 2010 and a final 

rule for Florida estuarine and coastal waters in October of 2011; and 3) perhaps most 

importantly, it is essential for informing and supporting a transparent and engaged public 

consideration, evaluation, and discussion on the question of what existing information, 

tools, and analyses suggest regarding the need to ensure protection of downstream waters. 

The Agency continues to emphasize its interest in and request for additional information, 

further analysis, and any alternative technically-based approaches that may be available

to address protection of downstream water quality. EPA also reiterates its commitment to 

a full evaluation of all comments received and notes the ability to issue a NODA to allow 

a full public review should significant new additional information and analysis become 

available as part of the comment period.
93

In deriving criteria to protect designated uses, as noted above, Federal WQS 

regulations established to implement the CWA provide WQS must provide for the 

protection of designated uses in downstream waters. In the case of deriving numeric 

nutrient criteria for streams in Florida, EPA’s analyses reflected in this notice indicate 

that the proposed criteria values for instream protection of streams may not fully protect 

downstream lakes and downstream estuaries. EPA’s proposed criteria for lakes are, in 

some cases, more stringent than the proposed criteria for streams that flow into the lakes. 

For estuaries, EPA’s analyses of protective loads delivered to a specific estuary, and the 

corresponding expected concentration values for streams that flow into that estuary, 

indicate the proposed criteria for instream protection may not always be sufficient to 

provide for the attainment and maintenance of the estuarine WQS. For more detailed 

information, please consult EPA’s TSD for Florida’s Inland Waters, Chapter 2: 

Methodology for Deriving U.S. EPA’s Proposed Criteria for Streams. 

To address each of these issues, EPA is proposing first, for lakes, an equation that 

allows for input of lake characteristics to determine the concentration in flowing streams 

that is needed to attain and maintain the receiving lake’s designated use and protective 

criteria. Second, for estuaries, EPA is proposing an approach for identifying the total 

nutrient loads a particular estuary can receive and still attain and maintain the State’s 

designated use for the water body. Third, also for estuaries, the Agency is proposing a

methodology to derive protective concentration values for the instream criteria where 

necessary to assure that downstream estuarine loads are not exceeded. The following 

sections provide a more detailed explanation of the proposed downstream protective 

approach for lakes and then for estuaries.
94

(a) Downstream Protection of Lakes 

EPA is proposing an equation to relate a lake TP concentration criterion to the 

concentration needed to be met in incoming streams to support the lake criterion. EPA 

proposes to apply the resulting stream concentration as the applicable criterion for all 

stream segments upstream of the lake. EPA used a mathematical modeling approach to 

derive this equation, with allowable input of lake-specific characteristics, to calculate

protective criteria necessary to assure attainment and maintenance of the numeric lake 

nutrient criteria in this proposal. More specifically, EPA started with a phosphorus 

loading model equation first developed by Vollenweider.70 EPA assumed that rainfall 

exceeds evaporation in Florida lakes and that all external phosphorus loading comes from 

streams. EPA considers the first assumption reasonable given the rainfall frequency and 

volume in Florida. The second assumption is reasonable to the extent that surface runoff 

contributions are far greater than groundwater or atmospheric sources of TP in Florida 

lakes. EPA requests comment on both these assumptions. After expressing these 

assumptions in terms of the mathematical relationships among loading rates, stream flow, 

and lake and stream concentrations, EPA derived the following equation to relate a 

protective lake criterion to a corresponding protective stream concentration:

  L w

f

S

[TP] 1

c

1

[TP]   

where

[TP]S is the total phosphorus (TP) downstream lake protection value, mg/L

[TP]L is applicable TP lake criterion, mg/L

 

70 Vollenweider, R.A. 1975. Input-output models with special reference to the phosphorus loading concept 

in limnology. Schweizerische Zeitschrift fur Hydrologie. 37: 53-84; Vollenweider, R.A. 1976. Advances in 

differing critical loading levels for phosphorus in lake eutrophication. Mem. Ist. Ital. Idrobid. 33:53:83.
95

cf is the fraction of inflow due to all stream flow, 0  cf  1

w is lake’s hydraulic retention time (water volume divided by annual flow rate)

The term   1 w   expresses the net phosphorus loss from the water column (e.g. 

via settling of sediment-sorbed phosphorus) as a function of the lake’s retention 

time

This model equation requires input of two lake-specific characteristics: the 

fraction of inflow due to stream flow and the hydraulic retention time. Water in a lake 

can come from a combination of groundwater sources, rainfall, and streams that flow into 

it. Using the model equation above, the calculated stream TP criterion to protect a

downstream lake will be more stringent for lakes where the portion of its volume coming 

from streams flowing into it is the greatest. In addition, the calculated stream TP 

criterion to protect a downstream lake will be more stringent for lakes with short

hydraulic retention times (how long water stays in a lake) because the longer the water 

stays in the lake, the more phosphorus will settle out in the underlying lake sediment. 

Because lake-specific input values may not always be readily available, EPA is

providing preset values for percent contribution from stream flow and hydraulic retention 

time. In Florida lakes, rainfall and groundwater sources tend to contribute a large portion 

of the total volume of lake water. In fact, only about 20% of the more than 7,000 Florida 

lakes have a stream flowing into them,

71 with the rest entirely comprised of groundwater 

and rainwater sources. EPA evaluated representative values for percent contribution 

from stream flow72 and hydraulic retention time,73 and selected 50% stream flow 

 

71 Fernald, E.A. and E.D. Purdum. 1998. Water Resources Atlas of Florida. Tallahassee: Institute of 

Science and Public Affairs, Florida State University.

72 Gao, X. 2006. Nutrient and Unionized Ammonia TMDLs for Lake Jesup, WBIDs 2981 and 2981A. 

Prepared by Florida Department of Environmental Protection, Division of Water Resource Management, 

Bureau of Watershed Management, Tallahassee, FL.
96

contribution and 0.2 years (about two and a half months) retention time as realistic and 

representative preset values to provide a protective outcome for Florida lakes, in the 

absence of site-specific data. Using these preset values, streams that flow into colored 

lakes would have a TP criterion of 0.12 mg/L, and streams that flow into clear, alkaline

lakes would have a TP criterion of 0.073 mg/L, with respect to downstream lake 

protection. In the Peninsula NWR, this compares to a 0.107 mg/L TP stream criterion 

protective of instream designated uses. EPA’s proposed rule does offer the flexibility to 

use site-specific inputs to the Vollenweider equation for fraction of inflow from 

streamflow and hydraulic retention time, as long as data supporting such inputs are 

sufficiently robust and well-documented.

EPA carefully evaluated use of a settling/loss term for phosphorus in the model 

equation. Florida lakes tend to be shallow, and internal loadings to the lake water (e.g. 

from re-suspension of settled phosphorus after storms that stir up lake sediment) may be 

substantial. A more detailed model might be able to simulate this phenomenon 

mechanistically, but would likely require substantial site-specific data for calibration. 

For this reason, EPA chose to use the model formulation above. EPA considered a 

simpler alternative to exclude the settling/loss term from the above equation, or even to 

reverse the sign on the settling/loss term so that it becomes a net source term, perhaps 

with the inclusion of a default multiplier. However, EPA did not have sufficient 

information to conclude that such a conservative approach was necessary as a general 

application to all Florida lakes. EPA remains open and receptive to comment on these 

 

73 Steward, J.S. and E.F. Lowe. In Press. General empirical models for estimating nutrient load limits for 

Florida’s estuaries and inland waters. Limnol. Oceanogr. 55: (in press).
97

alternatives or other technically sound and protective approaches. EPA’s supporting 

analyses and detailed information on this downstream lake protection methodology are 

provided in the accompanying TSD for Florida’s Inland Waters, Chapter 2: 

Methodology for Deriving U.S. EPA’s Proposed Criteria for Streams.

The same processes that occur in lakes and affect lake water phosphorus 

concentration may also occur in streams that feed lakes and affect stream water 

phosphorus concentrations. These processes include sorption to stream bed sediments, 

uptake into biota, and release into the water column from decaying vegetation. EPA took 

into consideration these processes when deciding whether it would be appropriate to add 

a term to the model equation to account for phosphorus loss or uptake within the streams 

in deriving stream criteria for downstream lake protection. However, the net result of 

these processes is nutrient spiraling, whereby nutrients released upstream gradually

propagate downstream at a rate slower than that of the moving water, and cycle into and 

out of the food chain in the process. Over the short term, the result may be water 

concentrations that decrease in the downstream direction. However, unlike for nitrogen,

there are no long-term phosphorus net removal processes at work in streams. Phosphorus 

adsorbed to sediment particles is eventually carried downstream with the sediment, and 

phosphorus taken up by plants is eventually returned to the flowing water. Over the long 

term, upstream phosphorus inputs are in equilibrium with downstream phosphorus

outputs. Recognizing this feature of stream systems and the conservative nature of 

phosphorus in aquatic environments, EPA concluded that it was not appropriate to 

include a phosphorus loss term that would apply to streams as they progress toward a 

downstream lake. For further information, please refer to EPA’s TSD for Florida’s 
98

Inland Waters, Chapter 2: Methodology for Deriving U.S. EPA’s Proposed Criteria for 

Streams.

EPA requests comment on the need for additional instream criteria to protect uses 

in downstream lakes. EPA further requests comment on the model equation approach 

presented here to protect downstream lakes, and also requests comment on use of an 

alternative model such as one with a negative or zero settling term (i.e., set   1 w   in 

the equation above either equal to zero or with the plus sign switched to a minus sign). 

EPA also requests comment on whether and how to address direct surface runoff into the 

lake. Where this input is substantial and land use around the lake indicates that 

phosphorus input is likely, EPA believes it may be appropriate to include this water 

volume contribution as part of the fraction of inflow considered to be streamflow to be 

protective and consistent with the assumption of no loading from sources other than 

streamflow. EPA specifically requests comment on use of the Land Development Index 

(LDI) as an indicator of how to treat this inflow, examination of regional groundwater 

phosphorus levels to see if a zero TP input from this source is appropriate, and potential 

development of regionally-specific preset values as inputs to the equation. In addition, 

EPA requests comment on the potential to develop a corollary approach for nitrogen. 

EPA is open to alternative technically-supported approaches based on best 

available data that offer the ability to address lake-specific circumstances. The Agency

recognizes that more specific information may be readily available for individual lakes 

which could allow the use of alternative approaches such as the BATHTUB model.74 

 

74 Kennedy, R. H., 1995. Application of the BATHTUB Model to Selected Southeastern Reservoirs. 

Technical Report EL-95-14, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS. 

Walker, W. W., 1985. Empirical Methods for Predicting Eutrophication in Impoundments; Report 3, Phase 
99

The Agency welcomes comment and technical analysis on the availability and 

application of these models. In this regard, EPA requests comment on whether there 

should be a specific allowance for use of alternative lake-specific models where 

demonstrated to be protective and scientifically defensible based upon readily and 

currently available data, and whether use of such alternatives should best be facilitated 

through use of the SSAC procedure described in Section V.C.

(b) Downstream Protection of Estuaries

(i) Overview

EPA is proposing a methodology for calculation of applicable criteria for streams 

that flow into estuaries and provide for their protection. The proposed methodology

would allow the State to utilize either 1) EPA's downstream protection values (DPVs), or 

2) the EPA DPV methodology utilizing EPA's estimates of protective loading to estuaries 

but with the load re-distributed among the tributaries to each estuary, or 3) an alternative 

quantitative methodology, based on scientifically defensible approaches, to derive and 

quantify the protective load to each estuary and the associated protective stream 

concentrations. The DPV methodology with a re-distributed load may be used if the 

State provides public notice and opportunity for comment. To use an alternative 

technical approach, based on scientifically defensible methods to derive and quantify the 

protective load to each estuary and the associated protective stream concentrations, the 

State must go through the process for a Federal SSAC as described in Section V.C. In

 

II: Model Refinements. Technical Report E-81-9, U.S. Army Engineer Waterways Experiment Station, 

Vicksburg, MS. 

Walker, W. W., 1987. Empirical Methods for Predicting Eutrophication in Impoundments; Report 4, Phase 

III: Applications Manual. Technical Report E-81-9, U.S. Army Engineer Waterways Experiment Station, 

Vicksburg, MS. 
100

some cases, the substantial and sophisticated analyses and scientific effort already 

completed in the context of the TMDL process may provide sufficient support for a 

SSAC. In such circumstances, EPA encourages FDEP to submit these through the SSAC 

process and EPA looks forward to working with FDEP in this process. 

EPA's approach to developing nutrient criteria for streams to protect downstream 

estuaries in Florida involves two separate steps. The first step is determining the average 

annual nutrient load that can be delivered to an estuary without impairing designated 

uses. This is the protective load. The second step is determining nutrient concentrations 

throughout the network of streams and rivers that discharge into an estuary that, if 

achieved, are expected to result in nutrient loading to estuaries that do not exceed the 

protective load. These concentrations, called "downstream protection values" or DPVs, 

depend on the protective load for the receiving estuary and account for nutrient losses 

within streams from natural biological processes. In this way, higher DPVs may be 

appropriate in stream reaches where a significant fraction of either TN or TP is 

permanently removed within the reach before delivery to downstream receiving waters. 

EPA's approach utilizes results obtained from a watershed modeling approach called 

SPAtially Referenced Regressions on Watershed attributes, or SPARROW.75 The 

specific model that was used is the South Atlantic, Gulf and Tennessee (SAGT) regional 

SPARROW model.

76

 EPA selected this model because it provided the information that 

was needed at the appropriate temporal and spatial scales and it applies to all waters that 

 

75 http://water.usgs.gov/nawqa/sparrow

76 Hoos, A. B., and G. McMahon. 2009. Spatial analysis of instream nitrogen loads and factors controlling 

nitrogen delivery to stream in the southeastern United Sates using spatially referenced regression on 

watershed attributes (SPARROW) and regional classification frameworks. Hydrological Processes. DOI: 

10.1002/hyp.7323.
101

flow to Florida’s estuaries.77 SPARROW was developed by the United States Geological 

Survey (USGS) and has been reviewed, published, updated and widely applied over the 

last two decades. It has been used to address a variety of scientific applications, 

including management and regulatory applications.78 In order to fully understand EPA's 

methodology for developing DPVs, it is useful to understand how the approach utilizes 

results from SPARROW, as well some aspects of how SPARROW works.

The remaining discussion focuses on TN, for which EPA has already computed 

DPVs. The approach for computing DPVs for TP from estimates of the protective TP

load is expected to be essentially the same as for TN. However, there is some question as 

to whether the same approach used to determine the protective TN load will also apply to 

TP. EPA requests comment on this issue.

(ii) EPA Approach to Estimating Protective Nitrogen Loads for Estuaries

The first step in EPA’s approach is to narrow the range of possible values. The 

protective TN load is expected to vary widely among Florida estuaries because they 

differ significantly in their size and physical and biological attributes. For example, well 

flushed estuaries are able to receive higher TN loading without adverse effect compared 

 

77 Hoos, A.B., S. Terziotti,, G. McMahon, K. Savvas, K. C. Tighe, and R. Alkons-Wolinsky. 2008. Data 

to support statistical modeling of instream nutrient load based on watershed attributes, southeastern United 

States, 2002: U.S. Geological Survey Open-File Report 2008–1163, 50 p.

78 USGS SPARROW publications Web site: http://water.usgs.gov/nawqa/sparrow/intro/pubs.html

Estimate 

Protective

Load

DPV for 

Terminal 

Reaches

DPV 

for all Other

Reaches

Divide by 

Average 

Streamflow

Divide by 

Fraction 

Delivered
102

to poorly flushed estuaries. EPA recognized that it may be possible to narrow this 

initially very broad range of possible protective loads using one consistent approach, and 

then consider whether additional information might enable a further reduction in 

uncertainty. EPA is soliciting credible scientific evidence that may improve these 

estimates and further reduce uncertainty surrounding the proposed protective loads. The 

most useful evidence would provide a scientific rationale, an alternative estimate of the 

protective load, and an associated confidence interval for the estimate. For further 

information, please refer to EPA’s TSD for Florida’s Inland Waters, Chapter 2: 

Methodology for Deriving U.S. EPA’s Proposed Criteria for Streams.

EPA first narrowed the range of possible protective loads by establishing an 

estimate of current loading as an upper bound. Most of Florida's estuaries are listed as 

impaired to some extent by nutrients or nutrient-related causes. Florida's 1998 CWA 

section 303(d) verified list of impaired waters under the Impaired Waters Rule (FAC 62-

303) identify many estuaries or estuary segments that are impaired by nutrients, 

chlorophyll a, or low dissolved oxygen. Many or most estuaries have reduced water 

clarity and substantial loss of seagrass habitats. The National Estuarine Eutrophication 

Assessment79 reports that current conditions are poor for many estuaries in Florida. This

information implies that current levels of TN loading are at least an upper limit for the 

protective load and likely exceed the protective load in many estuaries. 

EPA used the SAGT-SPARROW regional watershed model to estimate current 

loading to each estuary in Florida. While nitrogen loads have been estimated from 

monitored gauge stations in many stream and rivers, a large fraction of Florida streams 

 

79 Bricker, S., B. Longstaff, W. Dennison, A. Jones, K. Boicourt, C. Wicks and J. Woerner, 2007. Effects of 

nutrient enrichment in the Nation’s estuaries: A decade of change. NOAA Coastal Ocean Program Decision 

Analysis Series No. 26. National Centers for Coastal Ocean Science, Silver Spring, MD 322 
103

and watersheds are not gauged and thus load estimates were not previously available. An 

approach was needed to spatially extrapolate the available measurements of loading to 

obtain estimates of loading for all streams including those in unmonitored watersheds or 

portions of watersheds. The SAGT SPARROW model provided these estimates for all 

Florida estuarine watersheds. The SPARROW modeling approach utilizes a multiple 

regression equation to describe the relationship between watershed attributes (i.e., the 

predictors) and measured instream nutrient loads (i.e., the responses). The statistical 

methods incorporated into SPARROW help explain instream nutrient water quality data 

(i.e., the mass flux of nitrogen) as a function of upstream sources and watershed 

attributes. The SAGT-SPARROW model utilized period of record monitored streamflow 

and nutrient water quality data from Florida and across the SAGT region for load 

estimation. SAGT-SPARROW also used extensive geospatial data sets describing 

topography, land-use, climate, and soil characteristics, nitrogen loading for point sources 

in Florida obtained from EPA's permit compliance system, and estimates of nitrogen in 

fertilizer and manure from county-level fertilizer sales, census of agriculture, and 

population estimates. TN load estimates explain 96% of the variation in observed loads 

from monitoring sites across the region with no spatial bias at Florida sites.80 A more 

thorough description of the SAGT-SPARROW model, the data sources, and analyses are

found in the EPA TSD for Florida’s Inland Waters and in USGS publications.

81

 

80 Hoos, A. B., and G. McMahon. 2009. Spatial analysis of instream nitrogen loads and factors controlling 

nitrogen delivery to stream in the southeastern United Sates using spatially referenced regression on 

watershed attributes (SPARROW) and regional classification frameworks. Hydrological Processes. DOI: 

10.1002/hyp.7323.

81 Hoos, A.B., S. Terziotti,, G. McMahon, K. Savvas, K. C. Tighe, and R. Alkons-Wolinsky. 2008. Data 

to support statistical modeling of instream nutrient load based on watershed attributes, southeastern United 

States, 2002: U.S. Geological Survey Open-File Report 2008–1163, 50 p.
104

EPA further narrowed the range of possible protective loads by establishing the 

background load as a lower bound. EPA recognizes that a measure of natural 

background TN loading is the true lower limit, yet EPA recognizes also that some level 

of anthropogenic nutrient loading is acceptable, difficult to avoid, and unlikely to cause 

adverse biological responses. The current TN load minus the fraction of TN loading 

estimated to result from anthropogenic sources is used as an estimate of the background 

TN load. EPA used the SAGT-SPARROW regional watershed model to estimate 

background loading. SAGT-SPARROW empirically associates 100% of the measured 

nutrient loading into one of five classes (fertilizer, manure, urban, point sources, and 

atmospheric). EPA recognizes that some watershed models define more types of sources, 

according to their modeling objectives; however, it is important to recognize that these 

are source classes, not sources, and that 100% of the measured loading is accounted for 

explicitly or implicitly by SPARROW in terms of these source classes. 

The class termed "atmospheric" reflects all loading that cannot be empirically

attributed to causal variables associated with the other classes. EPA used the estimate for 

this class of loading as the background TN load. EPA recognizes that the SPARROWestimated “atmospheric” load includes anthropogenic contributions associated with 

regional-scale nitrogen emissions and does not represent pre-industrial or true “natural” 

background loading. The “atmospheric” source term from SPARROW is also not equal 

to atmospheric nitrogen deposition as measured by the National Atmospheric Deposition 

Program (NADP). To properly interpret the TN load attributed to the “atmospheric” 

source term in SPARROW, it is useful to recognize that SPARROW is a nonlinear 

regression model that seeks to explain measured TN loads in streams and rivers in terms 
105

of a series of explanatory variables. The atmospheric term is in all cases less, and often 

much less, than the measured deposition because not all the nitrogen deposited to the 

landscape is transported to streams, and not all of the nitrogen transported in streams 

reaches estuaries. The atmospheric source term from SPARROW excludes all the 

loading associated with both local anthropogenic nitrogen sources and factors 

contributing to increased transport of nitrogen from all sources (e.g., impervious 

surfaces). Therefore, EPA expects that reasonable values for the protective TN load are 

not likely to be less than these values.

The protective TN load should be less than the current load and greater than the 

background load. Although this recognition may appear to be trivial, it is important. 

EPA estimates that TN loads to estuaries across Florida vary approximately 25-fold (~2 

to 50 grams of nitrogen per square meter of estuary area). However, the ratio of the 

current load to the background load varies only between 1.7 and 5; for most estuaries, the 

range is between 2 and 4. Alternatively stated, current TN loads, which include local 

anthropogenic nitrogen sources, are two to four-fold higher than the background loads 

which do not include those sources. Thus, for any specific estuary, there is a relatively 

narrow range between the upper and lower bounds of potential protective loads. 

EPA acknowledges that not all the TN entering estuaries comes directly from the 

streams within its watershed. In some estuaries, direct atmospheric nitrogen deposition to 

the estuary surface may be an important source of TN loading to the estuary. Similarly, 

point sources such as industrial or wastewater treatment plant discharges directly to the 

estuary can be significant. In general, these sources are most significant when the ratio of 

watershed area to estuary area is relatively small compared to other estuaries (e.g., St. 
106

Andrew Bay, Sarasota Bay). In a few cases in Florida, point source loads directly to the 

estuary account for a large fraction of the aggregate load from all sources. 

As a second step, EPA sought to further reduce the range of possible protective 

loading values by considering additional evidence. One line of evidence EPA considered 

is previous estimates of protective loads. These have been developed as part of TMDLs 

for Florida estuaries or as part of Florida's Pollutant Load Reduction Goal or PLRG 

program. The scientific approaches utilized for TMDLs and PLRGs vary from simple to 

sophisticated and have recommended TN loading reductions between 3% and 63%, with 

a median of 38%. Higher reductions are typically associated with portions of estuaries 

currently receiving higher anthropogenic loading. Unfortunately, these analyses have not 

been completed for all of Florida's estuaries. Steward and Lowe (2009)82 showed that the 

TN loading limits suggested by TMDLs and PLRGs for a variety of aquatic ecosystems 

in Florida, including estuaries, could be statistically related to water residence time for 

the receiving water. EPA evaluated these relationships as an additional line of evidence 

for estimating protective TN loads for estuaries. EPA found these relationships to 

confirm in most cases, but not all, that the loading limits were likely between the bounds 

EPA previously established using SPARROW. However, the limits of uncertainty

associated with the relationship were nearly as large as those already established. 

Nonetheless, the models provide additional support for EPA’s estimates of protective 

estuary loads, but no further refinement of the estimates.

Another approach to considering existing TMDLs and PLRGs is to consider 

directly the loading rate reductions recommended from those efforts, the median of which 

 

82 Steward, J.S. and E.F. Lowe. 2010. General empirical models for estimating nutrient load limits for 

Florida’s estuaries and inland waters. Limnology and Oceanography 55(1):433-445.
107

is 38% in Florida. This percent TN reduction is similar to the scientific consensus for 

several well-studied coastal systems elsewhere (e.g., Chesapeake Bay, northern Gulf of 

Mexico) which have been subjected to increased TN loads from known anthropogenic 

sources. EPA recognizes that the magnitude of anthropogenic TN loads varies across 

Florida estuaries and that applying a uniform percent reduction across all estuaries does 

not account for the variable extent of anthropogenic loads and could lead to estimates 

below background load. An alternative approach is to assume that the appropriate

loading reduction is proportional to the magnitude of anthropogenic enrichment. Thus, 

EPA suggests that protective TN loading may be estimated by assuming that the 

anthropogenic component of TN loading should be reduced by a constant fraction.

As a result, EPA computed the protective TN load by reducing the current TN 

load by one half of the anthropogenic contribution to that load. EPA's protective load 

estimates are on average 25% less than current TN loading (range=5 to 40%), consistent 

with most TMDLs and PLRGs for Florida estuaries.

EPA developed protective TN loads for 16 estuarine water bodies in Florida for 

the purpose of computing DPVs for streams that are protective of uses in the estuarine 

receiving waters. EPA did not develop loading targets for the seven estuarine water 

bodies in south Florida (Caloosahatchee, St. Lucie, Biscayne Bay, Florida Bay, North and 

South Ten Thousand Islands, and Rookery Bay), because requisite information related to 

TN loading from the highly managed canals and waterways cannot be derived from 

SAGT-SPARROW and were not available otherwise, and three in central Florida (coastal 

drainage areas of the Withlacoochee River, Crystal-Pithlachascotee River and Daytona-
108

St. Augustine) because EPA is still evaluating appropriate protective loads and the flows 

necessary to derive DPVs. 

EPA notes that some stakeholders, including FDEP staff,

83 have raised concerns 

about the suitability of the SAGT SPARROW to address downstream protection of 

estuaries and have suggested alternative models and approaches that have been applied 

for several of Florida's larger estuaries and their watersheds. These concerns include 

known limitations of the SPARROW model, particularly related to inadequate resolution 

of complex hydrology in several parts of the State. EPA also recognizes this limitation 

and as a result, has not used SAGT SPARROW to propose protective loads and 

associated downstream protection values for ten estuaries and their watersheds in Florida. 

EPA acknowledges that other approaches and models may also provide defensible 

estimates of protective loads. 

Among the technical concerns that stakeholders including FDEP staff have raised 

are that: 1) SPARROW is useful for general pattern, but the large scale calibration lead to 

large errors for specific areas, 2) SPARROW only utilizes four source inputs, and 3) 

SPARROW was calibrated to only one year’s worth of data. As presented in the above 

sections, but to briefly reiterate here: 1) SPARROW is calibrated across a larger area, but 

it utilizes a large amount of Florida site-specific data and it explains 96% of the variation 

in observed loads from monitoring sites, 2) SPARROW accounts for all sources, but 

groups them into four general categories, and 3) SPARROW uses available data from the 

 

83For further information on concerns raised by FDEP regarding the use of SPARROW, refer to "Florida 

Department of Environmental Protection Review of SPARROW: How useful is it for the purposes of 

supporting water quality standards development?," “Assessment of FDEP Panhandle Stream proposed 

benchmark numeric nutrient criteria for downstream protection of Apalachicola Bay,” and “Analysis of 

Proposed Freshwater Stream Criteria’s Relationship to Protective Levels in the Lower St. Johns River 

Based on the Lower St. Johns River Nutrient TMDL.” 

located in EPA’s docket ID No. EPA-HQ-OW-2009-0596.
109

1975-2004 period at monitored sites. This last concern may be confused with the 

technical procedure of presenting loading estimates as “detrended to 2002”. This 

procedure accounts for long-term, inter-annual variability to ensure that long-term 

conditions and trends are represented. The year 2002 was selected as a baseline because 

it has the best available land use/land cover information available, but the loading 

estimates, in fact, represent a long-term condition representative of many years of record. 

EPA encourages technical reviewers to consult with the technical references cited in this 

section for the complete explanations of technical procedures.

EPA requests comment on its use of the SPARROW model to derive protective 

loads for downstream estuaries, as well as data and analyses that would support alternate 

methods of deriving downstream loads, or alternate methods of ensuring protection of 

designated uses in estuaries. For estuaries where sophisticated scientific analyses have 

been completed, relying on ample site-specific data to derive protective loads in the 

context of TMDLs, EPA encourages FDEP to submit resulting alternative DPVs under 

the SSAC process.

(iii) Computing Downstream Protection Values (DPVs)

Once an estimate of protective TN loads is derived, EPA developed a

methodology for computing DPVs, for streams that, if achieved, are expected to result in 

an average TN loading rate that does not exceed the protective load. EPA’s 

methodology, which is used as the narrative translator, allows for the fraction of the 

protective TN loading contributed from each tributary within the watershed of an estuary

to be determined by the fraction of the total freshwater flow contributed by that tributary. 

The DPV is specified as an average TN concentration, which is computed by dividing the 
110

protective TN load by the aggregate average freshwater inflow from the watershed. This 

approach results in the same DPV for each stream or river reach that terminates into a 

given estuary.

EPA’s methodology accounts for instream losses of TN. EPA recognizes that not 

all the TN transported within a stream network will ultimately reach estuaries. Rather, 

some TN is permanently lost from streams. This is not the same as reversible 

transformations of TN, such as algal uptake. Losses of TN are primarily associated with 

bacterially-mediated processes in stream sediments that convert biologically available 

nitrogen into inert N2 gas, which enters the atmosphere (a process called denitrification). 

This occurs more rapidly in shallow streams and at almost negligible rates in deeper 

streams and rivers. EPA refers to the fraction of nitrogen transported in streams that 

ultimately reaches estuaries as the "fraction delivered.” Estimates of the fraction 

delivered in Florida are less than 50% in streams very distant from the coast, but is 

between 80 and 100% in approximately half the stream reaches in Florida's estuarine 

watersheds.

EPA’s approach relies on estimating the fraction of TN delivered to downstream

estuaries. Measuring instream loss rates at the appropriate time and space scale is 

exceedingly difficult, and it is not possible to do State-wide. EPA is not aware of other 

models or data suitable to estimating nitrogen losses in streams across the State of 

Florida. EPA obtained estimates from the SAGT-SPARROW model,84 which is possibly

the best generally applicable approach to obtaining these estimates. One reason is that 

 

84 Hoos, A. B., and G. McMahon. 2009. Spatial analysis of instream nitrogen loads and factors controlling 

nitrogen delivery to stream in the southeastern United Sates using spatially referenced regression on 

watershed attributes (SPARROW) and regional classification frameworks. Hydrological Processes. DOI: 

10.1002/hyp.7323.
111

SPARROW estimates watershed-scale instream losses at the annual time scales across 

the entire region. Estimates of instream losses are modeled in SPARROW using a firstorder decay rate as a function of time-of-travel in the reach. The inverse exponential 

relationship is consistent with scientific understanding that nitrogen losses decrease with 

increasing stream size and with results from experimental reach-scale studies using a 

variety of methods.85 EPA recognizes that stream attributes other than reach time-oftravel or size may influence instream loss rates and though the SPARROW model did not 

include these, the lack of spatial bias in model residuals suggests that inclusion of other 

potential subregional-scale or State-wide stream attributes may not improve modeled 

instream loss estimates. 

EPA developed and applied this methodology to compute DPVs for every stream 

reach in each of 16 estuarine watersheds starting with estuarine-specific estimates of the 

protective load. These estuarine watersheds align with the Nutrient Watershed Regions 

(NWR) used to derive instream protection values (IPVs). It is important to note that the 

scale at which protective loads and DPVs were derived is smaller than for IPVs (i.e., 16

estuarine watersheds vs. 4 nutrient watershed regions). EPA’s recognition that some 

fraction of nitrogen transported in streams is retained or assimilated before reaching 

estuarine waters help ensure that the DPVs are not overprotective of downstream use in 

any particular estuary. 

In determining TN DPVs, EPA considered the contribution of TN inputs from 

wastewater discharged in shoreline catchments directly to the estuary. EPA found these 

 

85 Bohlke, J.K., R.C. Antweiler, J.W. Harvey, A.E. Laursen, L.K. Smith, R. L. Smith, and M.A. Voytek. 

2009. Multi-scale measurements and modeling of Denitrification in streams with varying flow and nitrate 

concentration in the upper Mississippi River basin, USA. Biogeochemistry 93: 117-141. DOI 

10.1007/s10533-008-9282-8.
112

point source inputs to be significant (>5% of total loading) in three (St. Andrew’s Bay, 

St. Marys, St. John’s) of the 16 estuaries. However, for the purpose of computing stream 

reach DPVs for a given estuarine watershed, EPA considered only those TN loads 

delivered from the estuarine watershed stream network and did not include TN inputs 

from wastewater discharged in shoreline catchments directly to an estuary because these 

loads do not originate from upstream sources. However, point sources loads directly to 

the estuary would need to be considered in developing TMDLs based on estuary-specific 

criteria. 

EPA's computation of DPVs using estimates of protective loading for each 

estuary and the fraction-delivered to estuaries is shown by equation (1): 

W i

i est Q F

C kL 1 , (1)

where the terms are defined as follows for a specific or ( i

th ) stream reach:

Ci maximum flow-averaged nutrient concentration for a specific (the i

th ) 

stream reach consistent with downstream use protection (i.e., the DPV)

k fraction of all loading to the estuary that comes from the stream network

resolved by SPARROW

Lest protective loading rate for the estuary, from all sources

QWcombined average freshwater discharged into the estuary from the portion 

of the watershed resolved by the SPARROW stream network

Fifraction of the flux at the downstream node of the specific (i

th)reach that is 

transported through the stream network and ultimately delivered to 

estuarine receiving waters (i.e. Fraction Delivered).

Note that the quantity kLest is equal to the loading to the estuary from sources 

resolved by SPARROW. For the purposes of practical implementation, EPA classified 

each stream water body (i.e., Water Body Identification or “WBID” using the FDEP 
113

term) according to the estuarine receiving water and one of six categories based on the 

fraction of TN delivered (0 to 50%, 51-60%, 61-70%, 71-80%, 81-90%, and 91-100%). 

For each category, the upper end of the range was utilized to compute the applicable DPV 

for streams in the category, resulting in a value that will be protective. This approach 

reduces the number of unique DPVs from thousands to less than 100. Because the stream 

network utilized by the SAGT-SPARROW watershed model (ERF1) does not recognize 

all of the smaller streams in Florida (i.e., it is on a larger scale), EPA mapped WBIDs to 

the applicable watershed-scale unit, or “incremental watersheds,” of the ERF1 reaches, 

assigning to each WBID the fraction of TN delivered estimated for the ERF1 reach 

whose incremental watershed includes the WBID. Where the WBID includes portions of 

the incremental watersheds of more than one ERF1 reach, EPA computed a weightedaverage based on the proportion of WBID area in the watershed of each ERF1 reach. 

Given an even distribution of reaches within each 10% interval, EPA’s “binning” 

approach to the fraction-delivered estimates results in a 5% to 10% margin of safety for 

the average reach in each range (closer to 10% for the lower fraction-delivered ranges). 

Potentially larger margins are possible within the 0 to 50% range, where the fraction 

delivered might be 20%, but the DPV would be computed assuming a fraction delivered 

of 50%. However, only one watershed in Florida for which EPA is proposing DPVs, the 

St. Johns River, has a substantial number of reaches estimated to have less than 50% TN 

delivered to estuarine waters. The SAGT-SPARROW watershed model estimates that

17% of the stream reaches in the St. Johns watershed are in this category, with about half 

the reaches delivering nearly 50% of TN and a substantial number delivering only 20% of 

TN. Given EPA’s DPV for terminal reaches in the St. Johns watershed, however, the 
114

DPV for reaches with a fraction delivered less than 50% will be higher than the IPV, and 

therefore, will not apply. EPA requests comment on the binning approach for calculating 

DPVs, which allows for a relatively simple table of DPVs to be presented as compared to 

using the actual estimate of fraction TN delivered to calculate a DPV unique to each 

WBID using formula (1), above.

At this time, EPA has not calculated protective TP loads for Florida’s estuaries or 

DPVs for TP. However, advances in the application of regional watershed models, such 

as SPARROW, that address the sources and terrestrial and aquatic processes that 

influence the supply and transport of TP in the watershed and delivery to estuaries are

currently in advanced stages of development.86 EPA anticipates obtaining the necessary

data and information to compute TP loads for the estuarine water bodies in Florida in 

2010 and could make this additional information available by issuing a supplemental 

Federal Register Notice of Data Availability (NODA), which would also be posted in the 

public docket for this proposed rule. EPA intends to derive proposed protective loads 

and DPVs for TP using an analogous approach as used for TN DPVs. EPA expects the 

approach will recognize that TP, like TN, is essential for estuarine processes but in excess 

will adversely impact aquatic life uses. 

(iv) EPA Downstream Protection Values (DPVs)

The following criteria tables and corresponding DPVs for a given stream reach 

category have been geo-referenced to specific WBIDs which are managed by FDEP as 

the principal assessment unit for Florida’s surface waters. To see where the criteria are 

 

86 Hoos, A.B., S. Terziotti,, G. McMahon, K. Savvas, K. C. Tighe, and R. Alkons-Wolinsky. 2008. Data 

to support statistical modeling of instream nutrient load based on watershed attributes, southeastern United 

States, 2002: U.S. Geological Survey Open-File Report 2008–1163, 50 p.
115

geographically applicable, refer to EPA’s TSD for Florida’s Inland Waters, Appendix B18: In-Stream and Downstream Protection Value (IPV/DPV) Tables with DPV GeoReference Table to Florida WBIDs.

Perdido Bay WatershedPH (EDA Code1: G140x)

Protective TN Load for the Estuary2: 847,520 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.043 TBD

50.1 – 60.0% NR NR 0.043 TBD

60.1 – 70.0% NR NR 0.043 TBD

70.1 – 80.0% NR NR 0.043 TBD

80.1 – 90.0% 0.824 0.34 0.043 TBD

90.1 – 100% 0.824 0.30 0.043 TBD

Pensacola Bay WatershedPH (EDA Code1: G130x)

Protective TN Load for the Estuary2: 4,388,478 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.043 TBD

50.1 – 60.0% NR NR 0.043 TBD

60.1 – 70.0% NR NR 0.043 TBD

70.1 – 80.0% NR NR 0.043 TBD

80.1 – 90.0% 0.824 0.48 0.043 TBD

90.1 – 100% 0.824 0.43 0.043 TBD

Choctawhatchee Bay WatershedPH (EDA Code1: G120x)

Protective TN Load for the Estuary2: 2,875,861 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.043 TBD

50.1 – 60.0% NR NR 0.043 TBD

60.1 – 70.0% NR NR 0.043 TBD

70.1 – 80.0% 0.824 0.48 0.043 TBD

80.1 – 90.0% 0.824 0.43 0.043 TBD
116

90.1 – 100% 0.824 0.39 0.043 TBD

St. Andrew Bay WatershedPH (EDA Code1: G110x)

Protective TN Load for the Estuary2: 310,322 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV

5

TN DPV6TP IPV7TP DPV8

Less than 50% 0.824 0.48 0.043 TBD

50.1 – 60.0% NR NR 0.043 TBD

60.1 – 70.0% NR NR 0.043 TBD

70.1 – 80.0% 0.824 0.30 0.043 TBD

80.1 – 90.0% 0.824 0.27 0.043 TBD

90.1 – 100% 0.824 0.24 0.043 TBD

Apalachicola Bay WatershedPH (EDA Code1: G100x)

Protective TN Load for the Estuary2: 10,971,582 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% 0.824 0.91 0.043 TBD

50.1 – 60.0% NR NR 0.043 TBD

60.1 – 70.0% 0.824 0.65 0.043 TBD

70.1 – 80.0% 0.824 0.57 0.043 TBD

80.1 – 90.0% 0.824 0.51 0.043 TBD

90.1 – 100% 0.824 0.46 0.043 TBD

Apalachee Bay WatershedPH (EDA Code1: G090x)

Protective TN Load for the Estuary2: 2,539,883 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.043 TBD

50.1 – 60.0% NR NR 0.043 TBD

60.1 – 70.0% NR NR 0.043 TBD

70.1 – 80.0% 0.824 0.67 0.043 TBD

80.1 – 90.0% 0.824 0.59 0.043 TBD

90.1 – 100% 0.824 0.53 0.043 TBD

Econfina/Steinhatchee Coastal Drainage AreaPH (CDA Code1: G086x)

Protective TN Load for the Estuary2: 185,301 kg y-1
117

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Fraction Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.043 TBD

50.1 – 60.0% NR NR 0.043 TBD

60.1 – 70.0% NR NR 0.043 TBD

70.1 – 80.0% NR NR 0.043 TBD

80.1 – 90.0% 0.824 0.41 0.043 TBD

90.1 – 100% 0.824 0.37 0.043 TBD

Suwannee River WatershedNC (EDA Code1:G080x)

Protective TN Load for the Estuary2: 5,421,050 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.359 TBD

50.1 – 60.0% NR NR 0.359 TBD

60.1 – 70.0% 1.479 0.78 0.359 TBD

70.1 – 80.0% 1.479 0.69 0.359 TBD

80.1 – 90.0% 1.479 0.61 0.359 TBD

90.1 – 100% 1.479 0.55 0.359 TBD

Waccasassa Coastal Drainage AreaPN (CDA Code1: 078x)

Protective TN Load for the Estuary2: 433,756 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.107 TBD

50.1 – 60.0% NR NR 0.107 TBD

60.1 – 70.0% NR NR 0.107 TBD

70.1 – 80.0% NR NR 0.107 TBD

80.1 – 90.0% 1.205 0.45 0.107 TBD

90.1 – 100% 1.205 0.40 0.107 TBD

Withlacoochee Coastal Drainage AreaPN (CDA Code1: G076x)

Protective TN Load for the Estuary2: TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8
118

Less than 50% 1.205 TBD 0.107 TBD

50.1 – 60.0% 1.205 TBD 0.107 TBD

60.1 – 70.0% 1.205 TBD 0.107 TBD

70.1 – 80.0% 1.205 TBD 0.107 TBD

80.1 – 90.0% 1.205 TBD 0.107 TBD

90.1 – 100% 1.205 TBD 0.107 TBD

Crystal/Pithlachascotee Coastal Drainage AreaPN (CDA Code1: G074x)

Protective TN Load for the Estuary2: TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% 1.205 TBD 0.107 TBD

50.1 – 60.0% NR TBD 0.107 TBD

60.1 – 70.0% NR TBD 0.107 TBD

70.1 – 80.0% NR TBD 0.107 TBD

80.1 – 90.0% 1.205 TBD 0.107 TBD

90.1 – 100% 1.205 TBD 0.107 TBD

Tampa Bay WatershedBV (EDA Code1: G070x)

Protective TN Load for the Estuary2: 1,289,671 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% 1.798 1.11 0.739 TBD

50.1 – 60.0% 1.798 0.93 0.739 TBD

60.1 – 70.0% 1.798 0.80 0.739 TBD

70.1 – 80.0% 1.798 0.70 0.739 TBD

80.1 – 90.0% 1.798 0.62 0.739 TBD

90.1 – 100% 1.798 0.56 0.739 TBD

Sarasota Bay WatershedBV (EDA Code1: G060x)

Protective TN Load for the Estuary2: 155,576 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.739 TBD

50.1 – 60.0% NR NR 0.739 TBD

60.1 – 70.0% NR NR 0.739 TBD
119

70.1 – 80.0% NR NR 0.739 TBD

80.1 – 90.0% NR NR 0.739 TBD

90.1 – 100% 1.798 0.54 0.739 TBD

Charlotte Harbor WatershedBV (EDA Code1: G050w)

Protective TN Load for the Estuary2: 2,710,107 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.739 TBD

50.1 – 60.0% 1.798 1.58 0.739 TBD

60.1 – 70.0% 1.798 1.35 0.739 TBD

70.1 – 80.0% 1.798 1.18 0.739 TBD

80.1 – 90.0% 1.798 1.05 0.739 TBD

90.1 – 100% 1.798 0.95 0.739 TBD

Indian River Watershed PN (EDA Code1: S190x)

Protective TN Load for the Estuary2: 463,724 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR NR 0.107 TBD

50.1 – 60.0% NR NR 0.107 TBD

60.1 – 70.0% NR NR 0.107 TBD

70.1 – 80.0% 1.205 0.87 0.107 TBD

80.1 – 90.0% 1.205 0.77 0.107 TBD

90.1 – 100% 1.205 0.69 0.107 TBD

Caloosahatchee River WatershedPN, # (EDA Code1: G050a)

Protective TN Load for the Estuary2: TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% 1.205 TBD 0.107 TBD

50.1 – 60.0% 1.205 TBD 0.107 TBD

60.1 – 70.0% 1.205 TBD 0.107 TBD

70.1 – 80.0% 1.205 TBD 0.107 TBD

80.1 – 90.0% 1.205 TBD 0.107 TBD

90.1 – 100% 1.205 TBD 0.107 TBD
120

St. Lucie River WatershedPN, # (EDA Code1: S190x)

Protective TN Load for the Estuary2: TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% 1.205 TBD 0.107 TBD

50.1 – 60.0% 1.205 TBD 0.107 TBD

60.1 – 70.0% 1.205 TBD 0.107 TBD

70.1 – 80.0% 1.205 TBD 0.107 TBD

80.1 – 90.0% 1.205 TBD 0.107 TBD

90.1 – 100% 1.205 TBD 0.107 TBD

Kissimmee River Watershed PN, ^

Protective TN Load for the Estuary2: TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6, LOTP IPV7TP DPV8, LO

Less than 50% 1.205 TBD9

0.107 TBD9

50.1 – 60.0% 1.205 TBD9

0.107 TBD9

60.1 – 70.0% 1.205 TBD9

0.107 TBD9

70.1 – 80.0% 1.205 TBD9

0.107 TBD9

80.1 – 90.0% 1.205 TBD9

0.107 TBD9

90.1 – 100% 1.205 TBD9

0.107 TBD9

St. John’s River Watershed PN (EDA Code1: S180x)

Protective TN Load for the Estuary2: 4,954,662 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% 1.205 1.41 0.107 TBD

50.1 – 60.0% 1.205 1.17 0.107 TBD

60.1 – 70.0% 1.205 1.00 0.107 TBD

70.1 – 80.0% 1.205 0.88 0.107 TBD

80.1 – 90.0% 1.205 0.78 0.107 TBD

90.1 – 100% 1.205 0.70 0.107 TBD

Daytona/St. Augustine Coastal Drainage AreaPN (CDA Code1: S183x)

Protective TN Load for the Estuary2: TBD

Protective TP Load for the Estuary3: TBD
121

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% NR TBD 0.107 TBD

50.1 – 60.0% NR TBD 0.107 TBD

60.1 – 70.0% NR TBD 0.107 TBD

70.1 – 80.0% NR TBD 0.107 TBD

80.1 – 90.0% 1.205 TBD 0.107 TBD

90.1 – 100% 1.205 TBD 0.107 TBD

Nassau Coastal Drainage AreaPN (CDA Code1: S175x)

Protective TN Load for the Estuary2: 131,389 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV5TN DPV6TP IPV7TP DPV8

Less than 50% 1.205 0.59 0.107 TBD

50.1 – 60.0% NR NR 0.107 TBD

60.1 – 70.0% NR NR 0.107 TBD

70.1 – 80.0% NR NR 0.107 TBD

80.1 – 90.0% 1.205 0.33 0.107 TBD

90.1 – 100% 1.205 0.30 0.107 TBD

St. Mary’s River WatershedPN (EDA Code1: S170x)

Protective TN Load for the Estuary2: 562,644 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4

TN (mg L

-1

) TP (mg L-1)

TN IPV 5TN DPV6TP IPV 7TP DPV8

Less than 50% NR NR 0.107 TBD

50.1 – 60.0% NR NR 0.107 TBD

60.1 – 70.0% NR NR 0.107 TBD

70.1 – 80.0% 1.205 0.43 0.107 TBD

80.1 – 90.0% 1.205 0.38 0.107 TBD

90.1 – 100% 1.205 0.34 0.107 TBD

Footnotes associated with this table: 

1 Watershed delineated by NOAA’s Coastal Assessment Framework and associated Florida Department of 

Environmental Protection’s estuarine and coastal water body identifier (WBID).

2 Estimated TN load delivered to the estuary protective of aquatic life use. These estimates may be revised 

pursuant to the EPA final rule for numeric nutrient criteria for Florida’s estuaries and coastal waters 

(October 2011).
122

3 Estimated TP load delivered to the estuary protective of aquatic life use. These estimates are currently 

under development. Preliminary estimates may be revised pursuant to the EPA final rule for numeric 

nutrient criteria for Florida’s estuaries and coastal waters (October 2011).

4 River/Stream reach categories within each estuarine watershed are linked spatially to a specific FDEP 

water body identifier (WBID). See Appendix B-18 of the "Technical Support Document for EPA's 

Proposed Rule for Numeric Nutrient Criteria for Florida's Inland Surface Fresh Waters.”

5

Instream Protection Value (IPV) is the TN concentration protective of instream aquatic life use. 

6 Downstream protection values (DPVs) are estimated TN concentrations in the river/stream reach that 

meet the estimated TN load, protective of aquatic life use, delivered to the estuarine waters. These 

estimates may be revised pursuant to the EPA final rule for numeric nutrient criteria for Florida’s estuaries 

and coastal waters (October 2011).

7

Instream Protection Value (IPV) is the TP concentration protective of instream aquatic life use. 

8 Downstream protection values (DPVs) are estimated TP concentrations in the river/stream reach that meet 

the estimated TP load, protective of aquatic life use, delivered to the estuarine waters. These estimates are 

currently under development. Preliminary estimates may be revised pursuant to the EPA final rule for 

numeric nutrient criteria for Florida’s estuaries and coastal waters (October 2011).

9 EPA’s proposed TN and TP criteria for colored lakes (> 40 PCU) are 1.2 and 0.050 mg L-1

, respectively.

# Estimated TN and TP loads protective of aquatic life in the Caloosahatchee and St. Lucie River estuaries, 

and in turn estimated TN and TP concentrations that would meet those protective loads, could not be 

calculated using EPA’s downstream protection approach. An alternative downstream protection approach 

will be proposed in EPA’s proposed rule for FL estuaries (January 2011).

^ Kissimmee River watershed does not have an EDA or CDA code because it does not drain directly to an 

estuary or coastal area, but rather indirectly through Lake Okeechobee and the south Florida canal system. 

A protective TN and TP load for Lake Okeechobee has not been calculated, however, a TMDL is in effect 

for TP. EPA’s proposed colored lake criteria (> 40 PCU) could be used to develop DPVs for TN and TP 

for the Kissimmee watershed (see footnote 9).

LO DPVs to be based on protective TN and TP loads for Lake Okeechobee. EPA’s proposed colored lake 

criteria (> 40 PCU) could be used to develop DPVs for TN and TP for the Kissimmee watershed (see 

footnote 9).

NR There are no stream reaches present in this watershed that have a percent-delivered within this range and 

thus criteria are not applicable.. 

PH Panhandle Nutrient Watershed Region.

BV Bone Valley Nutrient Watershed Region.

PN Peninsula Nutrient Watershed Region.

NC North Central Nutrient Watershed Region

TBD To be determined.

(v) Application of DPVs for Downstream Estuary Protection

The following discussion further explains the conceptual relationship between 

IPVs and DPVs for stream criteria. EPA developed IPVs to protect the uses that occur 

within the stream itself at the point of application, such as protection of the benthic 

invertebrate community and maintenance of a healthy balance of phytoplankton species. 

In contrast, EPA developed DPVs for streams to protect WQS of downstream waters. 

EPA derived DPVs in Florida streams by distributing the protective load from the 

aggregate stream network identified for each downstream estuary (that is protective of 
123

estuarine conditions) across the watershed in proportion to the amount of flow 

contributed by each stream reach. EPA’s approach also accounts for attenuation of 

nutrients (or loss from the system) as water travels from locations upstream in the 

watershed to locations near the mouth of the estuary. 

When comparing an IPV and DPV that are each deemed to apply to a particular 

stream segment, the more stringent of the two values is the numeric nutrient criterion that 

would need to be met when implementing CWA programs. Water bodies can differ 

significantly in their sensitivity to nutrients in general and to TN specifically. Although 

not universally true, freshwaters are generally phosphorus-limited and thus more 

sensitive to phosphorus enrichment because nitrogen is present in excess. Enriching 

freshwaters with phosphorus does not usually drive these systems into nitrogen limitation 

but can simply encourage growth of nitrogen-fixing algal species which can convert 

atmospheric nitrogen into ammonia. Conversely, estuaries are more often nitrogen 

limited and thus more sensitive to adverse impacts from nitrogen enrichment. As a result, 

it is not at all surprising that DPVs for TN in Florida are often less than the corresponding 

IPVs.

Adjustments to DPVs are possible with a redistribution approach, which revises 

the original uniform assignment of protective downstream estuarine loadings across the 

estuarine drainage area using the DPV methodology, or by revising either the protective 

load delivered to the downstream estuary and/or the equivalent DPVs using a technical 

approach of comparable scientific rigor and the Federal SSAC procedure described in 

section V.C of this notice.
124

Re-distributing the allocation of protective loading within an estuarine drainage 

area, or subset of an estuarine drainage area, is appropriate and protective because the 

total load delivered to the mouth of the estuary would still meet the protective load. 

DPVs may be a series of values for each reach in the upstream drainage area such that the 

sum of reach-specific incremental loading delivered to the estuary equals the protective 

loading rate taking into account that downstream reaches must reflect loads established 

for upstream reaches. Adjustments to DPVs may also factor in additional nutrient 

attenuation provided by already existing landscape modifications or treatment systems, 

such as constructed wetlands or stormwater treatment areas, where the attenuation is 

sufficiently documented and not a temporary condition. Unlike re-allocation of an even 

distribution of loading, these types of adjustments, as well as other site-specific 

information on alternative fractions delivered, would require use of the SSAC procedure 

under this proposal. EPA requests comment on whether these adjustments should be 

allowed to occur in the implementation of the re-allocation process rather than as a 

SSAC. 

A technical approach of comparable scientific rigor will include a systematic data 

driven evaluation and accompanying analysis of relevant factors to identify a protective 

load delivered to the estuary. An acceptable alternate numeric approach also includes a 

method to distribute and apply the load to streams and other waters within the estuarine 

drainage area in a manner that recognizes conservation of mass and makes use of a peerreviewed model (empirical or mechanistic) of comparable or greater rigor and scientific 

defensibility than the USGS SPARROW model. To use an alternative technical 
125

approach, the State must go through the process for a Federal SSAC procedure as 

described in Section V.C.

EPA requests comment on the DPV approach, the technical merit of the estimated 

protective loadings, and the technical merit of the method for calculating stream reach 

values. EPA also requests comment on other scientifically defensible approaches for 

ensuring protection of designated uses in estuaries. At this time, EPA plans to take final 

action with respect to downstream protection values for nitrogen as part of the second 

phase of this rulemaking process in coordination with the proposal and finalization of 

numeric standards 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 part of the broader 

comment and evaluation process that this proposal initiates.

D. Proposed Numeric Nutrient Criteria for the State of Florida’s Springs and Clear 

Streams

(1) Proposed Numeric Nutrient Criteria for Springs and Clear Streams

Springs and their associated spring runs in Florida are a unique class of aquatic 

ecosystem, highly treasured for their biological, economic, aesthetic, and recreational 

value. Globally, the largest number of springs (per unit of area), occur in Florida; Florida 

has over 700 springs and associated spring runs. Many of the larger spring ecosystems in 

Florida have likely been in existence since the end of the last major ice age
126

(approximately 15,000 to 30,000 years ago). The productivity of the diverse assemblage 

of aquatic flora and fauna in Florida springs is primarily determined by the naturally high 

amount of light availability of these waters (naturally high clarity).87 As recently as 50 

years ago, these waters were considered by naturalists and scientists to be some of the 

most unique and exceptional waters in the State of Florida and the Nation as a whole. 

In Florida, springs are also highly valued as a water resource for human use: 

people use springs for a variety of recreational purposes and are interested in the intrinsic 

aesthetics of clear, cool water emanating vigorously from beneath the ground. A good 

example of the value of springs in Florida is the use of the spring boil areas that have 

sometimes been modified to encourage human recreation (bathing or swimming).

88

Over the past two decades, scientists have identified two significant 

anthropogenic factors linked to adverse changes in spring ecosystems that have the 

potential to permanently alter Florida’s spring ecosystems. These are: 1) pollution of 

groundwater,

89 principally with nitrate-nitrite, resulting from human land use changes, 

cultural practices, and explosive population growth; and 2) simultaneous reductions in 

groundwater supply from human withdrawals.90 Pollution associated with human 

activities is one of the most critical issues affecting the health of Florida’s springs.91 

 

87 Brown M.T., K. Chinners Reiss, M.J. Cohen, J.M. Evans, P.W. Inglett, K. Sharma Inglett, K. Ramesh 

Reddy, T.K. Fraze, C.A. Jacoby, E.J. Phlips, R.L. Knight, S.K. Notestein, R.G. Hamann, and K.A. McKee.

2008. Summary and Synthesis of the Available Literature on the Effects of Nutrients on Spring Organisms 

and Systems. http://www.dep.state.fl.us/springs/reports/files/UF_SpringsNutrients_Report.pdf, University 

of Florida, Gainesville, Florida.

88 Scott, T.M., G.H. Means, R.P. Meegan, R.C. Means, S.B. Upchurch, R.E. Copeland, J. Jones, T. Roberts, 

and A. Willet. 2004. Springs of Florida. Bulletin No, 66. Florida Geological Survey. Tallahassee, FL. 677 

pp.

89 Katz, B.G., H.D. Hornsby, J.F. Bohlke and M.F. Mokray. 1999. Sources and chronology of nitrate 

contamination in spring water, Suwannee River Basin, Florida. U. S. Geological Survey Water-Resources 

Investigations Report 99-4252. Reston, VA.

90 Brown M.T., K. Chinners Reiss, M.J. Cohen, J.M. Evans, P.W. Inglett, K. Sharma Inglett, K. Ramesh 

Reddy, T.K. Fraze, C.A. Jacoby, E.J. Phlips, R.L. Knight, S.K. Notestein, R.G. Hamann, and K.A. McKee.

2008. Summary and Synthesis of the Available Literature on the Effects of Nutrients on Spring Organisms 
127

Excess nutrients, in particular excess nitrogen, seep into the soils and move to 

groundwater.92 When in excess, nutrients lead to eutrophication of groundwater-fed 

springs, allowing algae and invasive plant species to displace native plants, which in turn 

results in an ecological imbalance.93 Excessive growth of nuisance algae and noxious 

plant species in turn result in reduced habitat and food sources for native wildlife,94

excess organic carbon production, accelerated decomposition, and lowered quality of the 

floor or “bottom” of springs and spring runs, all of which adversely impact the overall 

health and aesthetics of Florida’s springs.

Adverse impacts on the overall health of Florida’s springs have been evident over 

the past several decades. Within the last 20-30 years, observations at several of Florida’s 

springs suggest that nuisance algae species have proliferated, and are now out-competing 

and replacing native submerged vegetation. Numerous biological studies have 

documented excessive algal growth at many major springs. In some of the more extreme 

examples, such as Silver Springs and Weeki Wachee Springs, algal mat accumulations 

have become over three feet thick.95, 96

 

and Systems. http://www.dep.state.fl.us/springs/reports/files/UF_SpringsNutrients_Report.pdf, University 

of Florida, Gainesville, Florida.

91 Ibid.

92 Katz, B.G., H.D. Hornsby, J.F. Bohlke and M.F. Mokray. 1999. Sources and chronology of nitrate 

contamination in spring water, Suwannee River Basin, Florida. U. S. Geological Survey Water-Resources 

Investigations Report 99-4252. Reston, VA.

93 Doyle, R.D. and R.M. Smart. 1998. Competitive reduction of noxious Lyngbya wollei mats by rooted 

aquatic plants. Aquatic Botany 61:17-32.

94 Stevenson, R.J., A. Pinowska, A. Albertin, and J.O. Sickman. 2007. Ecological condition of algae and 

nutrients in Florida springs: The Synthesis Report. Prepared for the Florida Department of Environmental 

Protection. Tallahassee, FL. 58 pp.

Bonn, M.A. and F.W. Bell. 2003. Economic Impact of Selected Florida Springs on Surrounding Local 

Areas. Report prepared for the Florida Department of Environmental Protection. Tallahassee, FL.

95 Pinowska, A., R.J. Stevenson, J.O. Sickman, A. Albertin, and M. Anderson. 2007. Integrated 

interpretation of survey for determining nutrient thresholds for macroalgae in Florida Springs: Macroalgal 

relationships to water, sediment and macroalgae nutrients, diatom indicators and land use. Florida 

Department of Environmental Protection, Tallahassee, FL.
128

As a result of human-induced land use changes, cultural practices, and explosive 

population growth, there has been an increase in the level of pollutants, especially nitrate, 

in groundwater over the past decades.97 Because there is no geologic source of nitrogen

in springs, all of the nitrogen emerging in spring vents originates from that which is 

deposited on the land. Historically, nitrate concentrations in Florida’s spring discharges 

were thought to have been around 0.05 mg/L or less, which is sufficiently low to restrict 

growth of algae and vegetation under “natural” conditions.98 

Regions where springs emanate in Florida have experienced unprecedented 

population growth and changes in land use over the past several decades.99 With these 

changes in population and growth came a transfer of nutrients, particularly nitrate, to 

groundwater. Of 125 spring vents sampled by the Florida Geological Survey in 2001-

2002, 42% had nitrate concentrations exceeding 0.50 mg/L and 24% had concentrations 

greater than 1.0 mg/L.

100

 Similarly, a recent evaluation of water quality in 13 springs 

shows that mean nitrate-nitrite levels have increased from 0.05 mg/L to 0.9 mg/L 

between 1970 and 2002. Overall, data suggest that nitrate-nitrite concentrations in many

 

96 Stevenson,R.J., A. Pinowska, and Y.K. Wang. 2004. Ecological condition of algae and nutrients in 

Florida springs. Florida Department of Environmental Protection, Tallahassee, FL. 

97 Scott, T.M., G.H. Means, R.P. Meegan, R.C. Means, S.B. Upchurch, R.E. Copeland, J. Jones, T. Roberts, 

and A. Willet. 2004. Springs of Florida. Bulletin No, 66. Florida Geological Survey. Tallahassee, FL. 677 

pp.

98 Maddox, G.L., J.M. Lloyd, T.M. Scott, S.B. Upchurch and R. Copeland. 1992. Florida’s Groundwater 

Quality Monitoring Program – Background Hydrochemistry. Florida Geological Survey Special 

Publication 34. Tallahassee, FL.

99 Katz, B.G., H.D. Hornsby, J.F. Bohlke and M.F. Mokray. 1999. Sources and chronology of nitrate 

contamination in spring water, Suwannee River Basin, Florida. U. S. Geological Survey Water-Resources 

Investigations Report 99-4252. Reston, VA.

Brown M.T., K. Chinners Reiss, M.J. Cohen, J.M. Evans, P.W. Inglett, K. Sharma Inglett, K. Ramesh 

Reddy, T.K. Fraze, C.A. Jacoby, E.J. Phlips, R.L. Knight, S.K. Notestein, R.G. Hamann, and K.A. McKee. 

2008. Summary and Synthesis of the Available Literature on the Effects of Nutrients on Spring Organisms 

and Systems. http://www.dep.state.fl.us/springs/reports/files/UF_SpringsNutrients_Report.pdf, University 

of Florida, Gainesville, Florida.

100 Scott, T.M., G.H. Means, R.P. Meegan, R.C. Means, S.B. Upchurch, R.E. Copeland, J. Jones, T. 

Roberts, and A. Willet. 2004. Springs of Florida. Bulletin No, 66. Florida Geological Survey. Tallahassee, 

FL. 677 pp.
129

spring discharges have increased from 10 to 350 fold over the past 50 years, with the 

level of increase closely correlated with anthropogenic activity and land use changes 

within the karst regions of Florida where springs predominate. 

As nitrate-nitrite concentrations have increased during the past 20 to 50 years, 

many Florida springs have undergone adverse environmental and biological changes. 

According to FDEP, there is a general consensus in the scientific community that nitrate 

is an important factor leading to the observed changes in spring ecosystems, and their 

associated biological communities. Nitrogen, particularly nitrate-nitrite, appears to be the 

most problematic nutrient problem in Florida’s karst region.101 

Because nitrate-nitrite has been linked to many of the observed detrimental 

impacts in spring ecosystems, there is an immediate need to reduce nitrate-nitrite 

concentrations in spring vents and groundwater. A critical step in achieving reductions in 

nitrate-nitrite is to develop a numeric nitrate-nitrite criterion for spring systems that will 

be protective of these unique and treasured resources.

102

 

To protect springs and clear streams and to provide assessment levels and 

restoration goals for those that have already been impaired by nutrients, EPA is proposing 

numeric nutrient criteria for the following parameter for Florida’s springs and clear 

streams (< 40 PCU) classified as Class I or III waters under Florida law (Rule 62-

302.400, F.A.C.): 

 

101 Brown M.T., K. Chinners Reiss, M.J. Cohen, J.M. Evans, P.W. Inglett, K. Sharma Inglett, K. Ramesh 

Reddy, T.K. Fraze, C.A. Jacoby, E.J. Phlips, R.L. Knight, S.K. Notestein, R.G. Hamann, and K.A. McKee.

2008. Summary and Synthesis of the Available Literature on the Effects of Nutrients on Spring Organisms 

and Systems. http://www.dep.state.fl.us/springs/reports/files/UF_SpringsNutrients_Report.pdf, University 

of Florida, Gainesville, Florida.

102 Brown M.T., K. Chinners Reiss, M.J. Cohen, J.M. Evans, P.W. Inglett, K. Sharma Inglett, K. Ramesh 

Reddy, T.K. Fraze, C.A. Jacoby, E.J. Phlips, R.L. Knight, S.K. Notestein, R.G. Hamann, and K.A. McKee.

2008. Summary and Synthesis of the Available Literature on the Effects of Nutrients on Spring Organisms 

and Systems. http://www.dep.state.fl.us/springs/reports/files/UF_SpringsNutrients_Report.pdf, University 

of Florida, Gainesville, Florida.
130

Nitrate (NO3

-

)+Nitrite (NO2

-

) shall not surpass a concentration of 0.35 mg/L as an 

annual geometric mean more than once in a three-year period, nor surpassed as a

long-term average of annual geometric mean values.

In addition to the nitrate-nitrite criterion, TN and TP criteria developed for streams on a 

watershed basis are also applicable to clear streams. See Section III.C(1) “Proposed 

Numeric Nutrient Criteria for the State of Florida’s Rivers and Streams” for the table of 

proposed TN and TP criteria that would apply to clear streams located within specific 

watersheds.

(2) Methodology for Deriving EPA’s Proposed Criteria for Springs and Clear 

Streams

EPA’s proposed nitrate-nitrite criterion for springs and clear streams are derived

from a combination of FDEP laboratory data, field surveys, and analyses which include 

analyses conducted to determine the stressor response-based thresholds that link nitratenitrite levels to biological risk in springs and clear streams. These data document the 

response of nuisance algae, Lyngbya wollei and Vaucheria sp., and periphyton to nitratenitrite concentrations. Please refer to EPA’s TSD for Florida’s Inland Waters, Chapter 3:

Methodology for Deriving U.S. EPA’s Proposed Criteria for Springs and Clear Streams.

As described in Section III.C(2), the ability to establish protective criteria for both 

causal and response variables depends on available data and scientific approaches to 

evaluate these data. EPA has not undertaken the development of TP criteria for springs 

because phosphorus has historically been present in Florida’s springs, given the State’s

naturally phosphorus-rich geology, and the lack of an increasing trend of phosphorus 

concentrations in most spring discharges. EPA is not proposing chlorophyll a and clarity 

criteria due to the lack of available data for these response variables in spring systems. 
131

Furthermore, scientific evidence examining the strong relationship between rapid 

periphyton survey data (measurements of the thickness of algal biomass attached to 

substrate rather than free-floating) and nutrients in clear streams (those with color <40 

PCU and canopy cover ≤ 40% which are comparable to most waters found in springs and 

spring runs) show that benthic algal thickness is highly dependent on nitrogen parameters 

(TN and total inorganic nitrogen), as opposed to phosphorus. In addition, EPA is

proposing to apply the nitrate-nitrite criteria derived for springs to clear streams as a 

measure to gauge anthropogenic contributions to TN. EPA is not currently proposing 

criteria for clarity and chlorophyll a for clear streams due to the lack of scientific 

evidence supporting the relationship between these response variables and nutrients. 

Clear streams show weak relationships between nutrients and chlorophyll a, as opposed 

to color streams where phytoplankton responses occur more readily than periphyton 

growth. Please refer to EPA’s TSD for Florida’s Inland Waters, Chapter 3: Methodology

for Deriving U.S. EPA’s Proposed Criteria for Springs and Clear Streams.

(a) Derivation of Proposed Nitrate-Nitrite Criteria

EPA’s goal in deriving nitrate-nitrite criteria for Florida springs and clear streams 

is to ensure that the criteria will preserve the ecosystem structure and function of 

Florida’s springs and clear streams. EPA reviewed Florida data, FDEP’s approach and 

analyses, and FDEP’s proposed nitrate-nitrite criterion for springs and clear streams and 

has concluded that the FDEP approach and the values FDEP derived represent a 

scientifically sound basis for the derivation of these criteria. FDEP evaluated results 

from laboratory scale dosing studies, data from in-situ algal monitoring, real-world 
132

surveys of biological communities and nutrient levels in Florida springs, and data on 

nitrate-nitrite concentrations found in minimally-impacted reference locations.

FDEP analyzed laboratory data103 that evaluated the growth response of nuisance 

algae to nitrate addition. FDEP’s analysis showed that Lyngbya wollei and Vaucheria sp.

reached 90% of their maximum growth at 0.230 mg/L and 0.261 mg/L nitrate-nitrite, 

respectively. FDEP also reviewed long-term field surveys that examined the response of 

nuisance algae, periphyton, and eutrophic indicator diatoms to nitrate-nitrite

concentration.104 The results showed a sharp increase in abundance and/or biomass of the 

nuisance algae, periphyton, and diatoms at 0.44 mg/L nitrate-nitrite.

FDED also reviewed the field surveys used to develop TMDLs for Wekiva River 

and Rock Spring Run to evaluate the relationship between the observed excessive algal 

growth and imbalance in aquatic flora with measurements of nutrients in these particular 

systems. FDEP found that taxa indicative of eutrophic conditions increased significantly 

with increasing nitrate-nitrite concentrations above approximately 0.35 mg/L. 

Based on its review of a combination of this laboratory and field data, FDEP 

concluded that significant alterations in community composition (eutrophic indicator 

diatoms), in combination with an increase in periphyton cell density and biomass, clearly 

demonstrate that a nitrate-nitrite level in the range between 0.23 mg/L (the laboratory

threshold) and 0.44 mg/L (the field study derived value associated with the upper bound 

nitrate-nitrite concentration where substantial observed biological changes were apparent) 

 

103 Stevenson, R.J., A. Pinowska, A. Albertin, and J.O. Sickman. 2007. Ecological condition of algae and 

nutrients in Florida springs: The Synthesis Report. Prepared for the Florida Department of Environmental 

Protection. Tallahassee, FL. 58 pp.

Cowell, B. C. and C. J. Dawes. 2004. Growth and nitrate-nitrogen uptake by the cyanobacterium Lyngbya

wollei. J. Aquatic Plant Management 42: 69-71.

104 Gao, X.. 2008. Nutrient TMDLs for the Wekiva River (WBIDs 2956, 2956A, and 2956C) and Rock 

Springs Run (WBID 2967). Florida Department of Environmental Protection, Tallahassee, Florida.
133

is the amount of nitrate-nitrite associated with an imbalance of aquatic flora in spring 

systems.105

FDEP conducted further statistical analyses of the available data from the 

multiple lines of evidence, applied an appropriate safety factor to ensure that waters 

would not reach the nitrate-nitrite levels associated with “substantial observed biological 

changes,” and averaged the results to arrive at a final protective threshold value for 

nitrate-nitrite in springs and clear streams of 0.35 mg/L. Based on the discussion above 

and corresponding analysis in the TSD for Florida’s Inland Waters, EPA has concluded 

that this value was derived in a scientifically sound manner, appropriately considering the 

available data, and appropriately interpreting the multiple lines of evidence. 

Accordingly, EPA is proposing 0.35 mg/L nitrate-nitrite as a protective criterion for 

aquatic life in Florida’s springs and clear streams. 

(b) Proposed Criteria: Duration and Frequency

EPA is proposing a duration and frequency expression of an annual geometric 

mean not to be surpassed more than once in a three-year period to be consistent with the 

expressions of duration and frequency for other water body types (e.g., lakes, streams, 

canals) for TN and TP and for the same reasons EPA selected a three-year period for 

those waters. 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. EPA has determined that 

this frequency of excursions should not result in unacceptable effects on aquatic life as it 

 

105 Mattson, R. A., E. F. Lowe, C. L. Lippincott, D. Jian, and L. Battoe. 2006. Wekiva River and Rock 

Springs Run Pollutant Load Reduction Goals. St. Johns River Water Management District, Palatka, Florida.
134

will allow the springs and clear streams aquatic systems enough time to recover from an

occasionally elevated year of nutrient loadings. The Agency requests comment on these 

proposed duration and frequency expressions of the springs and clear streams numeric 

nutrient criteria.

EPA also considered as an alternative, expressing the criterion as a monthly 

median not to be surpassed more than 10% of the time. Stated another way, the median 

value over any given calendar month shall not be higher than the criterion-magnitude 

value in more than one out of every ten months. It is appropriate to express a monthly

criterion as a median because the median is less susceptible to outliers than the geometric 

mean. This is particularly important when dealing with small sample sizes. This 

alternative is consistent with the expression that FDEP proposed in July 2009 for its State 

rule and the expression in the TSD for Florida’s Inland Waters that EPA sent out for 

external scientific peer review in July 2009. The rationale for this alternative is that field 

data indicate that the response in springs is correlated to monthly exposure at the 

criterion-magnitude concentration value and a 10% frequency of excursions is a 

reasonable and fully protective allowance given small sample sizes in any given month

(i.e., the anticipated amount of data that will be available for assessment purposes in the 

future). The clear streams nitrate-nitrite criterion was derived by FDEP based on 

multiple lines of evidence, with the primary lines of evidence being mesocosm dosing 

experiments and field studies. These two main studies were conducted by FDEP over 

very different time frames. One set of mesocosm studies was conducted by FDEP for 

periods just under one month (i.e., 21 to 28 days), while another, the algal biomass field 

survey, was conducted over an 18-year period and was analyzed using four to five year 
135

averaging periods.106 While lab studies indicate that algal communities can respond to 

excess nitrate-nitrite over a short period of time, the mesocosm and other dosing studies 

indicate that this response occurs on the order of a month, which might support a monthly

expression of the criterion.107 However, there is no evidence to suggest that the responses 

observed within a month under controlled lab settings equate to impairment of the 

designated use in conditions experienced in State waters. Please refer to EPA’s TSD for 

Florida’s Inland Waters, Chapter 3: Methodology for Deriving U.S. EPA’s Proposed 

Criteria for Springs and Clear Streams.

The 10% excursion frequency would recognize that in most cases the monthly

“median” would actually be based on a single sample, given that most springs are only 

sampled monthly at the most. A 10% excursion frequency may be considered a 

reasonable and fully protective allowance given small sample sizes in any given month, 

essentially requiring that the monthly median nitrate-nitrate concentrations thought to be 

fully supportive of relevant designated uses be met 90% of the time.

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 

expresssed as simply a long-term average of annual geometric means, consistent with 

data used in criteria derivation, would still be protective. EPA requests comment on 

 

106 Gao, X. 2008. Nutrient TMDLs for the Wekiva River (WBIDs 2956, 2956A, 2956C) and Rock Springs 

Run (WBID 2967). Florida Department of Environmental Protection, Tallahassee, Florida.

107 Stevenson, R.J., A. Pinowska, A. Albertin, and J.O. Sickman. 2007. Ecological condition of algae and 

nutrients in Florida springs: The Synthesis Report. Prepared for the Florida Department of Environmental 

Protection. Tallahassee, FL. 58 pp.
136

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 the 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.

(3) Request for Comment and Data on Proposed Approach

EPA believes the proposed nutrient criterion for springs and clear streams in this 

rule are protective of the designated aquatic life use of these waters in Florida. EPA is 

soliciting comment on the approach FDEP used and EPA adopted to derive nitrate-nitrite

criterion for springs and clear streams, including the data and analyses underlying the 

proposed criterion. EPA is seeking additional, readily-available, pertinent data and 

information related to nutrient concentrations or nutrient responses in springs and clear 

streams in Florida. EPA is also soliciting views on other potential, scientifically sound 

approaches to deriving protective nitrate-nitrite criterion for springs and clear streams in 

Florida.

(4) Alternative Approaches: Nitrate-Nitrite Criterion for All Waters as an 

Independent Criterion

EPA is soliciting comment on the environmental benefits associated with deriving 

a nitrate-nitrite criterion for all waters covered by this proposal (i.e., all streams, lakes, 
137

and canals), in addition to the other proposed nutrient criteria for those water bodies. 

Adoption of a nitrate-nitrite criterion for waters other than springs and clear streams

could be useful from an assessment and management perspective. Florida could use 

nitrate-nitrite data to identify increasing trends that may indicate the need for more 

specific controls of certain nitrogen enrichment sources. In cases where waters are 

impaired for either TN, nitrate-nitrite, or both TN and nitrate-nitrite, FDEP could use the 

nitrate-nitrite data to potentially target discharges of anthropogenic origin given their 

relative source contribution to nitrogen enrichment. 

This alternative approach, which would involve EPA deriving nitrate-nitrite

criteria for all waters or alternatively applying 0.35 mg/L nitrate-nitrite to all waters,

could provide additional protection for aquatic life designated uses. The alternative 

approach would also eliminate the need for FDEP to characterize streams as clear or not. 

Deriving and applying a nitrate-nitrite criterion to all waters would reduce the likelihood 

of excess loading of the specific anthropogenic components of TN to colored waters. 

However, these colored streams may be less likely to show an observed response to 

nitrate-nitrite due to the presence of tannins that block light penetration. Thus, the 

presence of color in streams may confound the relationship that produced the 0.35 mg/L 

nitrate-nitrite criterion. 

E. Proposed Numeric Nutrient Criteria for South Florida Canals 

(1) Proposed Numeric Nutrient Criteria for South Florida Canals

There are thousands of miles of canals in Florida, particularly in the southeastern 

part of the State. Canals are artificial waterways that are either the result of modifications 
138

to existing rivers or streams, or waters that have been created for various purposes, 

including drainage and flood control (stormwater management), irrigation, navigation, 

and recreation. These canals also allow for the creation of many waterfront home sites in 

Florida. Ecosystems that existed in rivers and streams prior to their modification into 

canals are altered. These changes can affect fish and wildlife and plant growth, as further 

explained in the following paragraphs. Newly created canals may have a tendency to fill 

with aquatic plants. Canals in south Florida vary greatly in size and depth. They can be 

anywhere from a few feet wide and a few feet deep to hundreds of feet wide and as deep 

as 30-35 feet.

South Florida canals vary in their hydrology and behavior due to their size, 

function, and seasonality. Shallow canals with slow water flow have poor turnover of 

water and little flushing. Large canals also may have low flow and turnover during the 

dry season. In contrast, during the wet season these same large canals are flowing 

systems that quickly move large volumes of water, as they were designed to accomplish. 

Excess nutrients in canals in combination with poor water circulation and decreased 

levels of dissolved oxygen, can lead to accelerated eutrophication and adverse impacts on 

other forms of aquatic life such as fish and other aquatic animals. In these canals, the 

accumulation of decaying organic matter on the canal bottom can also adversely impact 

healthy aquatic ecosystems. 

South Florida canals are highly managed waterways. Some canals are prone to an 

over-abundance of aquatic plants. Without regular and frequent management, dense 

vegetation can clog the waterways making navigation difficult and slowing the 

movement of water through the canal system. This can interfere with flood control,
139

boating, and fishing. Aquatic plants (like plants in the terrestrial environment) respond 

and grow when fertilized with nutrients such as phosphorus and nitrogen, and thus 

nutrient runoff into canals is likely a significant contributor to both nuisance algal blooms 

and clogging of canal systems by aquatic plants.

EPA is proposing numeric nutrient criteria for the following parameters and 

geographic classifications in south Florida, for canals classified as Class III waters under 

Florida law (Rule 62-302.400, F.A.C.). The proposed and alternative approaches 

described herein would not apply for TP in canals within the Everglades Protection Area

(EvPA) since there is an existing TP criterion of 0.010 mg/L that currently applies to the 

marshes and adjacent canals within the EvPA (Rule 62-302.540, F.A.C.). 

Chlorophyll a

(μg/L) a

Total Phosphorus (TP)

(mg/L) a, b

Total Nitrogen (TN)

(mg/L) a

Canals 4.0 0.042 1.6 

a

Concentration values are based on annual geometric mean not to be surpassed more than once in a threeyear 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 Applies to all canals within the Florida Department of Environmental Protection’s South Florida 

bioregion, with the exception of canals within the Everglades Protection Area (EvPA) where the TP 

criterion of 0.010 mg/L currently applies.

The following sections detail the methodology EPA used to develop the proposed 

numeric nutrient criteria for canals in south Florida, and request comment on the

proposed criteria and their derivation. In addition, EPA is providing details of two

alternative options for deriving canal criteria values that EPA considered and is soliciting

comments on these alternatives.

(2) Methodology for Deriving EPA’s Proposed Criteria for South Florida Canals

Based on the available information for canals, EPA determined that the most 

scientifically sound way to derive protective numeric nutrient criteria for south Florida’s 
140

canals is to use a similar approach to what EPA used to derive numeric nutrient criteria 

for streams. That is, EPA chose a nutrient concentration distribution-based approach 

using data from only those canals that have been determined to support the applicable 

designated use. EPA used existing water quality assessments and identified canals that 

have been determined to be impaired for nutrients. Data for those canals were excluded 

from the larger data set in order to create a set of data representing canals attaining the 

designated use of aquatic life, according to FDEP’s assessment decisions. For further 

information, please refer to EPA’s TSD for Florida’s Inland Waters, Chapter 4:

Methodology for Deriving U.S. EPA’s Proposed Criteria for Canals.

(a) Derivation of Proposed Numeric Nutrient Criteria for South Florida Canals

EPA derived numeric nutrient criteria for south Florida canals for two causal 

variables, TN and TP, and one response variable, chlorophyll a. In contrast to EPA’s 

proposed criteria for Florida’s streams, EPA concluded that there was a sufficient 

scientific basis for a chlorophyll a criterion for south Florida canals. EPA considered 

chlorophyll a to be an appropriate indicator of nutrient impairment in canals on the basis 

of the observed seasonal flow regimes, particularly during the relatively drier winter 

months when flows are relatively lower and canal water residence time is relatively

higher (as compared to wetter, summer months). Furthermore, EPA found evidence that 

canals are susceptible to impairment due to excessive chlorophyll a based on the number 

of canals on Florida’s CWA section 303(d) list with chlorophyll a cited as the parameter 

of concern. EPA analyzed the range of chlorophyll a concentrations in canals and found 

that 12% of chlorophyll a concentration observations occurred at 10 g/L or higher and 

5% of chlorophyll a concentration observations occurred at 20 g/L or higher. As a point 
141

of reference, Florida has chlorophyll a thresholds of 20 as the numeric interpretations of 

its narrative nutrient criteria for streams and 11 g/L for estuaries/open coastal waters, 

respectively, in its Impaired Waters Rule (IWR) (Rules 62-303.351 and 62-303.353, 

F.A.C.). Thus, EPA included chlorophyll a as a nutrient criterion to protect canal aquatic 

life designated uses from an unacceptable biological response to excess nutrients.

EPA employed a statistical distribution approach for deriving numeric nutrient 

criteria for south Florida canals. Specifically, EPA computed statistical distributions and 

descriptive statistics (e.g., quartiles, mean, standard deviation) of TN, TP, and 

chlorophyll a concentrations from data derived at canal sites across south Florida that are 

not on the impaired waters list for Florida. EPA has determined that the criteria derived

from a distribution of canal data from canals with no evidence of nutrient impairment are 

appropriate and protective of designated uses. 

As described in detail in Section III.C(2)(c), EPA concluded that the 75th

percentiles of the respective TN, TP, and chlorophyll a distributions would yield values 

that would ensure that aquatic life designated uses would be protected in south Florida 

canals. A reasonable choice is one that lies just above the vast majority of the 

population. The 75th percentile represents such a point on the distribution of TN, TP, and 

chlorophyll a values.

(b) Other Data and Analyses Conducted and Considered by EPA in the 

Derivation of Proposed Numeric Nutrient Criteria for South Florida Canals

EPA undertook extensive analyses and considered a variety of data and methods 

for deriving numeric nutrient criteria for Florida’s canals. Although EPA derived the 

proposed values based on the approach outlined in the section above, EPA also factored 
142

into its decision-making process the results of these other analyses as additional lines of 

evidence. 

One line of additional evidence is based on an evaluation of the stressor-response 

relationship between chlorophyll a levels in canals and TN and TP levels using a variety 

of statistical tools. A second line of evidence is based on a consideration of the 

distribution of chlorophyll a measurements, TN measurements, and TP measurements 

from all canals, impaired and not impaired. Nutrient concentrations at the lower end of 

these distributions were compared to the concentration that the stressor-response analysis 

determined to be associated with canals with no evidence of nutrient impairment. The 

third line of evidence is based on a consideration of the distribution of chlorophyll a, TN,

and TP values from only those canals considered to be minimally impacted by nutrientrelated pollution. EPA considered each of these lines of evidence in deriving the numeric 

nutrient criteria for canals.

Because soil or substrate type at the bottom of a canal can influence the nutrient 

cycling and relationships between the observed biological response and the TP and TN 

levels in canals, EPA used data on soil types in south Florida along with knowledge of 

the Everglades Agricultural Area (EAA) and the Everglades Protection Area (EvPA) to 

subdivide the canal areas for criteria derivation. Thus the first step in these other 

analyses was to group canals and canal data by soil type. The four groupings consist of 

histosol and entisol soils of the EAA; histosol and entisol soils of the EvPA; spodosol and 

alfisol soils and areas west of the EvPA and EAA (hereafter, West Coast); and spodosol, 

entisol and alfisol soils and areas east of the EvPA and EAA (hereafter East Coast).
143

EPA then sorted canal data (provided by FDEP, Miami-Dade County, and the 

South Florida Water Management District) into the four canal groupings. EPA screened 

the data to ensure the exclusion of the following: 1) sites without relevant data (e.g., 

nitrogen, phosphorus, chlorophyll a), 2) sites influenced by marine waters, 3) sites within 

Class IV canals or Lake Okeechobee, 4) data not originating within a canal, 5) data with 

questionable units, and 6) outlier data. Data were organized by canal regions and year. 

Each site occurring near the border of a region and/or WBID was visually inspected using 

geographic information system (GIS) tools to ensure the correct placement of those sites. 

Local experts were also consulted by EPA. EPA analyzed the resulting regionalized data 

using statistical distribution and regression analyses. EPA undertook its additional 

analyses using these canal (and data) groupings.

EPA’s analysis of the distribution of chlorophyll a values in each of the four 

groupings of canals (using data from impaired and unimpaired sites) indicated that the 

lower percentile (i.e., 25th percentile) ranged from 1.9 to 2.2 μg/L for chlorophyll a in the 

EvPA, West Coast, and East Coast, and was 6.3 μg/L for the EAA. EPA’s analysis of the 

distribution of TN values in each of the four groupings of canals indicated that the lower 

percentile (i.e., 25th percentile) ranged from 0.8 to 1.4 mg/L for the EvPA, West Coast, 

and East Coast and was 2.1mg/L for the EAA. EPA’s analysis of the distribution of TP 

values in each of the four groupings of canals indicated that the lower percentile (i.e., 25th

percentile) ranged from 0.013 to 0.023 mg/L for the EvPA, West Coast, and East Coast 

and was 0.048 mg/L for the EAA canals. 

In an effort to consider chlorophyll a, TN, and TP values in canals minimally

impacted by nutrient pollution, EPA identified canal sites surrounded by the EvPA in the 
144

east and the Big Cypress National Preserve in the west and considered the distribution of 

chlorophyll a, TN and TP values for these sites. Although EPA acknowledges that these 

sites have not been thoroughly vetted for biological condition, EPA believes that because 

they are remote and surrounded by wetlands, that these canal sites represent sites with the 

lowest impact from human activities. The upper percentile values (i.e., the 75th

percentile) from the distributions of chlorophyll a, TN and TP values for these lower 

impact sites are 3.4 μg/L for chlorophyll a, 1.3 mg/L for TN and 0.018 mg/L for TP.

When considering the results of these additional analyses and comparing these 

results to the outcome of EPA’s analysis of TN, TP, and chlorophyll a concentrations

from data derived at canal sites across south Florida that are not on the impaired waters 

list for Florida, it is clear that EPA’s proposed criteria for canals are similar to those

derived from alternative approaches and therefore, represent a reasonable integration of 

these multiple lines of evidence. For further information, please refer to EPA’s TSD for 

Florida’s Inland Waters, Chapter 4: Methodology for Deriving U.S. EPA’s Proposed 

Criteria for Canals.

(c) Proposed Criteria: Duration and Frequency

Aquatic life water quality criteria contain three components: magnitude, duration, 

and frequency. For the TN and TP numeric criteria for canals, the derivation of the 

criterion-magnitude values is described above and these values are provided in the table 

in Section III.E(1). The criterion-duration for this magnitude (or averaging period) is 

specified in footnote a of the canals criteria table as an annual geometric mean. 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 
145

geometric mean criteria for canals. 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 their standard assessment periods as specified in 

Rule 62-303, F.A.C. (Impaired Waters Rule) to implement this second provision. These 

proposed duration and frequency components of the criteria are consistent with the data 

set used to derive the criteria that contained data from multiple years of record, all 

seasons, and a variety of hydrologic conditions. EPA has determined that this frequency

of excursions should not result in unacceptable effects on aquatic life as it will allow the 

canal aquatic system enough time to recover from an occasionally elevated year of 

nutrient loadings. The Agency requests comment on these proposed duration and 

frequency expressions of the canal numeric nutrient criteria.

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 requests comment on 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 of the years of a given 

assessment period, and 4) a criterion-frequency expressed as meeting the allowable 

magnitude and duration as a long-term average only. EPA further requests comment on 
146

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.

(3) Request for Comment and Data on Proposed Approach

EPA believes the proposed numeric nutrient criteria for south Florida canals in 

this rule are protective of the designated uses, consistent with CWA section 303(c)(2)(A) 

and 40 CFR 131.11(a)(1). EPA solicits comment on the approaches taken by the Agency

in this proposal, the data underlying those approaches, and the proposed criteria. EPA is 

seeking other pertinent scientific data and information that are readily available related to 

nutrient concentrations or nutrient responses in Class III canals in south Florida. 

EPA is soliciting comment specifically on the selection of criteria parameters for 

TN, TP, and chlorophyll a; development of criteria for Class III canals across south 

Florida; and the conclusion that the proposed criteria for Class III canals are protective of 

designated uses and adequately account for the spatial and temporal variability of 

nutrients. 

(4) Alternative Approaches for Comment

EPA is requesting comments and views on the advantages and disadvantages of 

alternative approaches to deriving protective criteria for south Florida canals. These 

approaches include: 1) a stressor-response approach (based on data from all canals or 

canals grouped by soil type), and 2) methodologies that have been employed to develop 

nutrient targets in an EPA-proposed TMDL for dissolved oxygen and nutrients.108 

 

108 Proposed Total Maximum Daily Load (TMDL) for Dissolved Oxygen and Nutrient in the Everglades. 

Prepared by U.S. EPA Region 4. September 2007.
147

As previously described in Section III.E(2)(b), EPA considered the underlying 

soil type of south Florida canals as a possible basis for geographic classification. 

Analysis of the underlying soil types, indicated by STATSGO,

109 led EPA to identify the 

following four canal regions: Everglades Agricultural Area (EAA) comprised of histosol 

and entisol soils, EvPA comprised of histosol and entisol soils, areas west of the EvPA 

and EAA, or West Coast, comprised of spodosol and alfisol soils, and areas east of the 

EvPA and EAA, or East Coast, comprised of spodosol, entisol, and alfisol soils. 

Subsequent to classification, the proposed statistical distribution-based approach 

or the alternatives to the proposed approach described in the following sections could be 

used to derive numeric nutrient criteria by canal region for any or all of the proposed 

criteria (i.e., TN, TP, and chlorophyll a) provided that sufficient data are available. 

(a) Stressor-Response Approach

EPA considered two statistical analyses for assessing the stressor-response 

relationship between nutrients and biological response. In contrast to the proposed 

option, which included only data from sites with no evidence of nutrient impairment, the 

stressor-response analyses included all data regardless of whether sites were associated 

with WBIDs that have been determined to be impaired. EPA conducted linear and 

quantile regression analyses between chlorophyll a, TP, and TN on a regional and 

aggregated regional basis. EPA used the linear regression model as a statistical tool to 

predict the chlorophyll a response based on matched chlorophyll a and TN and TP data. 

Similarly, quantile regression was used to analyze the matched nutrient and chlorophyll a 

 

109 State Soil Geographic (STATSGO) database provided by the U.S. Department of Agriculture, Natural 

Resources Conservation Service (NRCS).
148

data. In this application, quantile regression was used to predict the 90th percentile of the 

distribution of chlorophyll a concentration at a given concentration of TN or TP. 

To apply either statistical approach for developing numeric nutrient criteria for TP 

or TN, EPA would need to identify the concentration of chlorophyll a that would be 

protective of the designated use for these canal systems. One approach would be to use 

EPA’s proposed chlorophyll a criterion of 4.0 μg/L for canals to derive the TN and TP 

criteria from stressor-response relationships. 

(b) Calculation of TP Criteria for the Everglades Agricultural Area (EAA) Using 

a Downstream Protection Approach

EPA considered using the methodologies described in the EPA-proposed 

TMDL110 for dissolved oxygen and nutrients to develop numeric nutrient criteria, 

specifically TP, for portions of the EAA. These methodologies are described in the 

TMDL in Section 4.2.2.1 of the TMDL document, “Approach #1: Estimate STA inflow 

loads resulting in WQS in downstream waters”, and Section 4.2.2.2 of the TMDL

document, “Approach #2: Simple modeling approach.” The first approach takes into 

account the downstream criterion of the EvPA and the performance of the stormwater 

treatment areas (STAs). Based on these considerations, inflowing TP concentrations 

within the EAA to the STAs were derived to meet the downstream EvPA TP criterion of 

0.010 mg/L. The second approach used a model that extrapolated natural background TP 

concentrations, based on land use changes, for specific WBIDs within the EAA. These 

approaches could support the derivation of numeric nutrient criteria for TP within the 

 

110 Proposed Total Maximum Daily Load (TMDL) for Dissolved Oxygen and Nutrient in the Everglades. 

Prepared by U.S. EPA Region 4. September 2007.
149

EAA region. Approach #1 would result in a TP concentration of 0.10 mg/L, while 

Approach #2 would result in a TP concentration of 0.087 mg/L.

(5) Request for Comment and Data on Alternative Approaches

The alternatives for Class III south Florida canal criteria in this proposed rule 

represent alternative approaches given the availability of data in the State of Florida to 

date and are consistent with the requirements of both the CWA and EPA’s implementing 

regulations. EPA is soliciting comment on the alternative approaches considered by the 

Agency in this proposal, the data underlying those approaches, and the proposed 

alternatives themselves, including criteria expressed as an upper percentile maxima not to 

be exceeded more than 10% of the time in one year, similar to those discussed for lakes. 

For further information on the upper percentile criteria for canals, refer to EPA’s TSD on 

Florida’s Inland Waters, Chapter 4: Methodology for Deriving U.S. EPA’s Proposed 

Criteria for Canals. EPA is seeking other pertinent data and information related to 

nutrient concentrations or nutrient responses in Class III canals in south Florida. 

F. Comparison Between EPA’s and Florida DEP’s Proposed Numeric Nutrient Criteria 

for Florida’s Lakes and Flowing Waters

To date, Florida has invested significant resources in its statewide nutrient criteria 

effort, and has made substantial progress toward developing numeric nutrient criteria. 

For several years, FDEP has been actively working with EPA on the development of 

numeric nutrient criteria and EPA has worked extensively with FDEP on data 

interpretation and technical analyses for developing EPA’s recommended numeric 

nutrient criteria proposed in this rulemaking. 
150

On January 14, 2009, EPA formally determined that numeric nutrient criteria 

were necessary to protect Florida’s lakes and flowing waters and should be developed by

January 14, 2010. FDEP, independently from EPA, initiated its own State rulemaking 

process to adopt numeric nutrient water quality criteria protective of Florida’s lakes and 

flowing waters. According to FDEP, the State initiated its rulemaking process to 

facilitate the assessment of designated use attainment for Florida’s waters and to provide 

a better means to protect its waters from the adverse effects of nutrient over-enrichment. 

Florida established a technical advisory committee, which met over a number of years, to 

help develop its proposed numeric nutrient criteria. The State also held several public 

workshops to solicit comment on the draft WQS. While FDEP was progressing with its 

State rulemaking, EPA moved forward to develop Federal numeric nutrient criteria for 

Florida’s lakes and flowing waters, consistent with EPA’s January 14, 2009 

determination and based on the best available science.

Most recently, in July 2009, FDEP solicited public comment on its proposed 

numeric nutrient criteria for lakes and flowing waters. In October 2009, FDEP decided 

not to bring the draft criteria before the Florida Environmental Regulation Commission 

(ERC), as had been previously scheduled. FDEP did not make any final decisions as to

whether it might be appropriate to ask the ERC to adopt the criteria or some portions of 

the criteria at a later date. 

As described in Section III., EPA is proposing numeric nutrient criteria for the 

following four water body types: lakes, streams, springs and clear streams, and canals in 

south Florida. Given that FDEP has made its proposed numeric nutrient criteria available 

to the public via its Web site 
151

(http://www.dep.state.fl.us/water/wqssp/nutrients/index.htm), it is worth providing a 

comparative overview between the criteria and approaches that EPA is proposing in this 

rulemaking and the criteria and approaches FDEP had initially proposed. Both EPA and 

FDEP developed numeric criteria recognizing the hydrologic and spatial variability of 

nutrients in Florida’s lakes and flowing waters. As FDEP indicated on its Web site,

FDEP’s preferred approach is to develop cause and effect relationships between nutrients 

and valued ecological attributes, and to establish nutrient criteria based on those cause 

and effect relationships that ensure that the designated uses of Florida’s waters are 

protected and maintained. As described in EPA’s guidance, EPA also recommends this 

approach when scientifically defensible data are available. Where cause and effect 

relationships could not be demonstrated, however, both FDEP and EPA relied on a 

distribution-based approach to derive numeric nutrient criteria protective of applicable 

designated uses.

To set numeric nutrient criteria for lakes, EPA, like FDEP, 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 TP 

concentrations result in a biological response such as elevated chlorophyll a levels. EPA 

and FDEP both found that correlations between nutrients and response parameters were 

sufficiently robust to use for criteria development in Florida’s lakes. EPA is proposing 

the same chlorophyll a criteria for colored lakes and clear alkaline lakes as FDEP 

proposed, however, EPA is proposing a lower chlorophyll a criterion for clear acidic 

lakes. EPA, like FDEP, is also proposing an accompanying supplementary analytical 

approach that Florida can use to adjust general TN and TP lake criteria within a certain 
152

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. 

Lake Class

EPA Proposed Criteria Florida Proposed Criteria

Chl a, μg/L TN, mg/L TP, mg/L Chl a, μg/L TN,

mg/L

TP,

mg/L

Colored Lakes 

> 40 PCU 20 1.23-2.25 0.050-

0.157

20 1.23-2.25 0.05-0.157

Clear Lakes, 

Alkaline

≤ 40 PCU and 

> 50 mg/L CaCO3

20 1.00-1.81 0.030-

0.087

20 1.00-1.81 0.03-0.087

Clear Lakes, 

Acidic

≤ 40 PCU and 

≤ 50 mg/L CaCO3 

6 0.500-0.900 0.010-

0.030

9 0.85-1.14 0.015-0.043

To set numeric nutrient criteria for streams, FDEP recommended a statistical 

distribution approach based on “benchmark sites” identified in five nutrient regions (five

regions for TP and two regions for TN), given that FDEP determined cause and effect 

relationships to be insufficiently robust for establishing numeric thresholds. FDEP relied

on the use of a narrative criterion to protect downstream waters. EPA also concluded that 

a scientifically defensible cause and effect relationship could not be demonstrated with 

the available data and that a distribution-based approach was most appropriate. However, 

EPA considered an alternative approach that evaluated a combination of biological 

information and data on the distribution of nutrients in a substantial number of healthy 

stream systems to derive scientifically sound TN and TP criteria for streams.

The respective criteria for instream protection of Florida’s streams derived using 

EPA’s recommended approach and FDEP’s recommended approach are comparable.
153

EPA Nutrient 

Watershed 

Regions

EPA Proposed Instream 

Criteria

Florida Nutrient 

Watershed 

Regions

FL Proposed Instream 

Criteria

TN (mg/L) TP (mg/L) TN (mg/L) TP (mg/L)

Panhandle 0.824 0.043 Panhandle 0.820 0.069

Bone Valley 1.798 0.739 Bone Valley

1.730

0.415

Peninsula 1.205 0.107 Peninsula 0.116

North Central 1.479 0.359 North Central 0.322

Northeast 0.101

In terms of protecting downstream waters, EPA used best available science and 

data related to downstream waters and found that there are cases where the numeric

nutrient criteria EPA is proposing to protect instream aquatic life may not be stringent 

enough to ensure protection of WQS for aquatic life in certain downstream lakes and 

estuaries. Accordingly, EPA is proposing an equation to be used to adjust stream TP 

criteria to protect downstream lakes, and a different methodology to adjust TN criteria for 

streams to ensure protection of WQS for downstream estuaries. In cases where a stream 

first flows into a lake and then flows out from the lake into another lake or estuary, the 

portion of the stream that exits the lakes needs to comply with the downstream protection 

values for estuaries, assuming that is the terminal reach.

EPA is proposing the same nitrate-nitrite causal variable criterion for springs and 

clear streams as proposed by FDEP. For canals in south Florida, EPA is proposing a 

statistical distribution approach based on sites meeting designated uses with respect to 

nutrients (i.e., not identified as impaired by FDEP) identified in four canal regions. 

FDEP did not propose numeric nutrient criteria for canals in its rulemaking. 

Please refer to Section IV. Under What Conditions Will Florida Be Removed 

From a Final Rule for information on how State-adopted and EPA-approved WQS could 

become effective under the CWA 303(c). 
154

G. Applicability of Criteria When Final 

EPA’s proposed numeric nutrient criteria for Florida’s lakes and flowing waters 

will be effective for CWA purposes 60 days after publication of final criteria and will 

apply in addition to any other existing CWA-effective criteria for Class I or Class III 

waters already adopted by the State and submitted to EPA (and for those adopted after 

May 30, 2000, approved by EPA). EPA requests comment on this proposed effective 

date. FDEP establishes its designated uses through a system of classes and Florida 

waters are designated into one of several different classes. Class III waters provide for 

healthy aquatic life and safe recreational use. Class I waters include all the protection of 

designated uses provided for Class III waters, and also include protection for designated 

uses related to drinking water supply. Class I and III waters, together with Class II 

waters that are designated for shellfish propagation or harvesting, comprise the set of 

Florida waters that meet the goals articulated in section 101(a)(2) of the CWA and the 

waters for which EPA is proposing criteria. Pursuant to the schedule set out in EPA’s 

January 2009 determination, Class II waters will be addressed in rulemaking in January

2011. For water bodies designated as Class I and Class III predominately fresh waters, 

any final EPA numeric nutrient criteria will be applicable CWA water quality criteria for 

purposes of implementing CWA programs including permitting under the NPDES 

program, as well as monitoring and assessment based on applicable CWA WQS and 

establishment of TMDLs.

The proposed criteria in this rule, if and when finalized, would be subject to 

Florida’s general rules of applicability in the same way and to the same extent as are 

other State-adopted and/or federally-promulgated criteria for Florida waters. See
155

proposed 40 CFR 131.43(d)(2). For example, Florida regulations at Rule 62-4.244,

F.A.C. authorize mixing zones when deriving effluent limitations for discharges of 

pollutants to Florida waters. These regulations would apply to permit limitations 

implementing the criteria in this rule. This proposal includes some additional language 

on mixing zone requirements to help guide Florida in developing and applying mixing 

zone policies for nutrient criteria. Specifically, EPA provides that the criteria apply at the 

appropriate locations within or at the boundary of the mixing zones; otherwise the criteria 

apply throughout the water body including at the point of discharge into the water body. 

See proposed 40 CFR 131.43(d)(2)(i). Likewise, EPA includes proposed regulatory

language specifying that Florida use an appropriate design flow condition, one that 

matches the proposed criteria duration and frequency, for use in deriving permit limits 

and establishing wasteload and load allocations for a TMDL. See proposed 40 CFR 

131.43(d)(2)(ii). 

In addition, EPA recognizes that Florida regulations include provisions for 

assessing whether waters should be included on the list of impaired waters pursuant to 

section 303(d) of the CWA. See Rule 62-303, F.A.C. The Impaired Waters Rule, or 

IWR, sets out a methodology to identify waters that do not meet the State’s WQS and, 

therefore, are required to be included on CWA section 303(d) lists. The current IWR 

does not address how to assess waters based on EPA’s proposed numeric nutrient criteria. 

The numeric nutrient criteria in any final rule, nevertheless, will be applicable WQS that 

must be addressed when the State assesses waters pursuant to CWA section 303(d). 

EPA proposes language in this rulemaking that acknowledges the IWR 

procedures and their function, specifying that those procedures apply where they are 
156

consistent with the level of protection provided by the proposed criteria. See proposed 40 

CFR 131.43(d)(2)(iii). Some IWR provisions, which describe the sufficiency or 

reliability of information necessary for the State to make an attainment decision, do not 

change the level of protection afforded Florida waters. These are beyond the scope of 

WQS under CWA section 303(c). Other provisions of the IWR may provide some 

additional detail relevant to assessment, such as the number of years worth of data 

assessed for a particular listing cycle submittal, which should be consistent with the level 

of protection provided with the proposed criteria. Should any IWR provisions apply a 

different level of protection than the Federal criteria when making attainment decisions 

based on proposed criteria, EPA would expect to take appropriate action to ensure that 

the States’ CWA section 303(d) list of impaired waters includes all waters not attaining 

the Federal criteria.

IV. Under What Conditions Will Federal Standards Be Either Not Finalized or 

Withdrawn?

Under the CWA, Congress gave states primary responsibility for developing 

and adopting WQS for their navigable waters. See CWA section 303(a)-(c). Although 

EPA is proposing numeric nutrient criteria for Florida’s lakes and flowing waters, Florida 

continues to have the option to adopt and submit to EPA numeric nutrient criteria for the 

State’s lakes and flowing waters consistent with CWA section 303(c) and implementing 

regulations at 40 CFR part 131. Consistent with CWA section 303(c)(4), if Florida 

adopts and submits numeric nutrient criteria and EPA approves such criteria as fully 

satisfying the CWA before publication of the final rulemaking, EPA will not proceed 

with the final rulemaking for those waters for which EPA approves Florida’s criteria.
157

Pursuant to 40 CFR 131.21(c), if EPA does finalize this proposed rule, the EPA 

promulgated WQS would be applicable WQS for purposes of the CWA until EPA 

withdraws the federally-promulgated standard. Withdrawing the Federal standards for 

the State of Florida would require rulemaking by EPA pursuant to the requirements of the 

Administrative Procedure Act (5 U.S.C.551 et seq.). EPA would undertake such a 

rulemaking to withdraw the Federal criteria only if and when Florida adopts and EPA 

approves numeric nutrient criteria that fully meet the requirements of section 303(c) of 

the CWA and EPA’s implementing regulations at 40 CFR part 131. 

If EPA finalizes the proposed restoration standard provision (discussed in Section 

VI below), that provision would be adopted into regulation and would allow Florida to 

establish interim designated uses with associated water quality criteria, while maintaining 

the full CWA section 101(a)(2) aquatic life and/or recreational designated use of the 

water as the ultimate goal. EPA may proceed to promulgate numeric nutrient criteria for 

Florida together with or separate from EPA’s proposed restoration standards provision, 

depending on the comments received on that proposal.

V. Alternative Regulatory Approaches and Implementation Mechanisms

A. Designating Uses 

Under CWA section 303(c), states shall adopt designated uses after taking “into 

consideration the use and value of water for public water supplies, protection and 

propagation of fish, shellfish, and wildlife, recreation in and on the water, agricultural, 

industrial and other purposes including navigation.” Designated uses “shall be such as to 

protect the public health or welfare, enhance the quality of water and serve the purposes 

of [the CWA].” CWA section 303(c)(1). EPA’s regulation at 40 CFR 131.3(f) defines 
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“designated uses” as “those uses specified in water quality standards for each water body 

or segment whether or not they are being attained.” Under 40 CFR 131.10, EPA’s 

regulation addressing “Designation of uses”, a “use” is a particular function of, or activity 

in, waters of the United States that requires a specific level of water quality to support it. 

In other words, designated uses are a state’s concise statements of its management 

objectives and expectations for each of the individual surface waters under its 

jurisdiction. 

In the context of designating uses, states often work with stakeholders to identify

a collective goal for their waters that the state intends to strive for as it manages water 

quality. States may evaluate the attainability of these goals and expectations to ensure 

they have designated appropriate uses (see 40 CFR 131.10(g)). Consistent with CWA 

sections 101(a)(2) and 303(c)(2)(A), 40 CFR 131.2 provides that states “should, wherever 

attainable, provide water quality for the protection and propagation of fish, shellfish, and 

wildlife and for recreation in and on the water.” Where states do not designate those 

uses, or remove those uses, they must demonstrate that such uses are not attainable 

consistent with 40 CFR 131.10(g). States may determine, based on a UAA, that attaining 

a designated use is not feasible and propose to EPA to change the use and/or the 

associated pollutant criteria to something that is attainable. This action to change a 

designated use must be completed in accordance with EPA regulations (see 40 CFR 

131.10(g) and (h)). 

Within the framework described above, states have discretion in designating uses. 

EPA’s proposed numeric nutrient criteria for lakes and flowing waters would apply to 

those waters designated by FDEP as Class I (Potable Water Supplies) or Class III 
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(Recreation, Propagation and Maintenance of a Healthy, Well-Balanced Population of 

Fish and Wildlife). If Florida removes the Class I or Class III designated use for any

particular water body ultimately affected by this rule, and EPA finds that removal to be

consistent with CWA section 303(c) and the regulations at 40 CFR part 131, then the

federally-promulgated numeric nutrient criteria would not apply to that water body. 

Instead, the nutrient criteria associated with the newly designated use would apply to that 

water body. FDEP has recently restarted an effort to refine the State’s current designated 

use classifications. As this process continues, EPA expects that the State may find some 

instances where this particular discussion may be relevant and useful as the refinement of 

uses is investigated further. 

Where states can identify multiple waters with similar characteristics and 

constraints on attainability, EPA interprets the Federal WQS regulation to allow states to

conduct a “categorical” use attainability analysis (UAA) under 40 CFR 131.10(g) for 

such waters. This approach may reduce data collection needs, allowing a single analysis 

to represent many sites. To use such an approach, however, the State would need to have 

enough information about each particular site to reliably place each site into a broader

category and Florida would need to specifically identify each site covered by the analysis. 

Florida may wish to consider such an approach for certain waters, such as a network of 

canals with similar hydrologic and morphological characteristics, which can be 

characterized as a group and where the necessary level of protection may differ 

substantially from other lakes or flowing waters within the State.

B. Variances 
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A variance is a temporary modification to the designated use and associated water 

quality criteria that would otherwise apply to the receiving water. A variance is based on 

a UAA and identifies the highest attainable use and associated criteria during the variance 

period. Typically, variances are time-limited (e.g., three years), but renewable. 

Modifying the designated use for a particular water through a variance process allows a 

state to limit the applicability of a specific criterion to that water and to identify an 

alternative designated use and associated criteria to be met during the term of the 

variance. A variance should be used instead of removal of a use where the state believes 

the standard can be attained in a short period of time. By maintaining the standard rather 

than changing it, the state ensures that further progress will be made in improving water 

quality and attaining the standard. A variance may be written to address a specified 

geographical coverage, a specified pollutant or pollutants, and/or a specified pollutant 

source. All other applicable WQS not specifically modified by the variance would

remain applicable (e.g., any other criteria adopted to protect the designated use). State 

variance procedures, as part of state WQS, must be consistent with the substantive 

requirements of 40 CFR part 131. A variance allows, among other things, NPDES 

permits to be written such that reasonable progress is made toward attaining the 

underlying standards for affected waters without violating section 402(a)(l) of the Act, 

which requires that NPDES permits must meet the applicable WQS. See also CWA 

section 301(b)(1)(C). 

For purposes of this proposal, EPA is proposing criteria that apply to use 

designations that Florida has already established. EPA believes that the State has 

sufficient authority to use its adopted and EPA-approved variance procedures with 
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respect to modification of their Class I or Class III uses as it pertains to any federallypromulgated nutrient criteria. For this reason, EPA is not proposing a Federal variance 

procedure. 

C. Site-specific Criteria 

A site-specific criterion is an alternative value to a statewide, or otherwise 

applicable, water quality criterion that meets the regulatory test of protecting the 

designated use and having a basis in sound science, but is tailored to account for sitespecific conditions. Site-specific alternative criteria (SSAC) may be more or less 

stringent than the otherwise applicable criteria. In either case, because the SSAC must 

protect the same designated use and must be based on sound science (i.e., meet the 

requirement of 40 CFR 131.11(a)), there is no need to modify the designated use or 

conduct a UAA. SSAC may be appropriate when additional scientific consideration can 

bring added precision or accuracy to express the necessary level or concentration of a 

water quality parameter that is protective of the designated use.

Florida has adopted procedures for developing and adopting SSAC in its WQS 

regulations at Florida Administrative Code (Rule 62-302.800, F.A.C.). Florida’s Type I 

SSAC procedure is intended to address site-specific situations where a particular water 

body cannot meet the applicable water quality criterion because of natural conditions. 

See Rule 62-302.800(1). Florida’s Type II SSAC procedure is intended to address sitespecific situations other than natural conditions where it can be established that an 

alternative criterion from the broadly applicable criteria established by the State is

protective of a water’s designated uses. See Rule 62-302.800(1), F.A.C. Florida’s Type 

II procedure is primarily intended to address toxics but there is no limitation in its use for 
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other parameters, except for certain parameters identified by FDEP, including nutrients. 

See Rule 62-302.800(2). Florida’s regulations currently do not allow use of Type II 

procedures for nutrient criteria development because the State currently does not have 

broadly applicable numeric nutrient criteria for State waters. Rather, the current narrative 

criterion for nutrients is implemented by translating it into numeric loads or 

concentrations on a case-by-case basis. EPA’s proposed rule would not affect Florida’s 

Type I or Type II SSAC procedures.

EPA believes that there would be benefit in establishing a specific procedure in 

the Federal rule for EPA adoption of SSAC. In this rulemaking, EPA is proposing a 

procedure whereby the State could develop a SSAC and submit the SSAC to EPA with 

supporting documentation for EPA’s consideration. The State SSAC could be developed 

under either the State SSAC procedures or EPA technical processes as set out more fully

below. EPA elected to propose this approach because this procedure maintains the State

in a primary decision-making role regarding development of SSAC for State waters. The 

procedure that EPA is proposing would also allow the State to submit a proposed SSAC 

to EPA without having to first go through the State’s rulemaking process.

The proposed procedure would provide that EPA could determine that the SSAC 

should apply in lieu of the generally applicable criteria promulgated pursuant to this rule. 

The proposed procedures provide that EPA would solicit public comment on its 

determination. Because EPA’s rule would establish this procedure, implementation of 

this procedure would not require withdrawal of federally-promulgated criteria for 

affected water bodies in order for the SSAC to be effective for purposes of the CWA. 
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EPA has promulgated similar procedures for EPA granting of variances and SSACs in 

other federally-promulgated WQS.

EPA also considered technical processes necessary to develop protective numeric 

nutrient criteria on a site-specific basis. To complete a thorough and successful analysis 

to develop numeric nutrient SSAC, EPA expects the State to conduct, or direct applicants 

to the State to conduct, a variety of supporting analyses. For the instream protection 

value (IPV) for streams, this analysis would, for example, consist of examining both 

indicators of longer-term response to multiple stressors such as benthic macroinvertebrate 

health, as determined by Florida’s Stream Condition Index (SCI) and indicators of 

shorter-term response specific to nutrients, such as periphyton algal thickness or 

chlorophyll a levels. The former analysis will help address concerns that a potential 

nutrient effect is masked by other stressors (such as turbidity which can limit light 

penetration and primary production response to nutrient response), whereas the latter 

analysis will help address concerns that a potential nutrient effect is lagging in time and 

has not yet manifested itself. Indicators of shorter-term response generally would not be 

expected to exhibit a lag time.

It will also be important to examine a stream system on a watershed basis to 

ensure that a SSAC established for one segment does not result in adverse effects in 

nearby segments. For example, a shaded, relatively swift flowing segment may open up 

to a shallow, slow moving, open canopy segment that is more vulnerable to adverse 

nutrient impacts. Empirical data analysis of multiple factors affecting the expression of 

response to nutrients and mechanistic models of ecosystem processes can assist in this 

type of analysis. It will also be necessary to ensure that a larger load allowed from an 
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upstream segment as a result of a SSAC does not compromise protection on a 

downstream segment that has not been evaluated. 

The intent of this discussion is to illustrate a process that is rigorous and based on 

sound scientific rationale, without being inappropriately onerous to complete. Corollary

analyses for a lake, spring or clear stream, or canal situation would need to be pursued for 

a SSAC on those systems. 

In addition to the procedure that EPA is proposing, Florida always has the option 

of submitting State-adopted SSAC as new or revised WQS to EPA for review and 

approval under the CWA section 303(c). There is no bar to a state adopting new or 

revised WQS for waters covered by a federally-promulgated WQS. For any Stateadopted SSAC that EPA approves under section 303(c) of the Act, EPA would also have 

to complete federal rulemaking to withdraw the Federal WQS for the affected water body 

before the State SSAC would be the applicable WQS for the affected water body for 

purposes of the Act. As discussed above, Florida WQS regulations currently do not 

authorize the State to adopt nutrient SSAC except where natural conditions are outside 

the limits of broadly applicable criteria established by the State (Rule 62-302.800, 

F.A.C.)

This proposed SSAC process would also not limit EPA’s authority to promulgate 

SSAC in addition to those developed by the State under the process described in this rule. 

The proposed rule recognizes that EPA always has the authority to promulgate through 

rulemaking SSAC for water that are subject to federally-promulgated water quality

criteria.

D. Compliance Schedules
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A compliance schedule, or schedule of compliance, refers to “a schedule of 

remedial measures included in a ‘permit,’ including an enforceable sequence of interim 

requirements ... leading to compliance with the CWA and regulations.” 40 CFR 122.2. 

In an NPDES permit, WQBELs are effluent limits based on applicable WQS for a given 

pollutant in a specific receiving water (See NPDES Permit Writers Manual, EPA-833-B96-003, December, 1996). In addition, EPA regulations provide that schedules of 

compliance are to require compliance “as soon as possible.” 

Florida has adopted a regulation authorizing compliance schedules, and that 

regulation is not affected by this proposed rule (Rule 62-620.620(6), F.A.C.). The 

regulation provides, in part, for schedules providing for compliance “as soon as sound 

engineering practices allow, but not later than any applicable statutes or rule deadline”. 

The complete text of the Florida rules concerning compliance schedules is available at 

https://www.flrules.org/gateway/RuleNo.asp?ID=62-620.620. Florida is, therefore, 

authorized to grant compliance schedules under its rule for WQBELs based on federallypromulgated criteria.

VI. Proposed Restoration Water Quality Standards (WQS) Provision

As described above, many of Florida’s waters do not meet the water quality goals 

established by the State and envisioned by the CWA because of excess amounts of 

nutrients. In some cases, restoring these water could take many years to achieve, 

especially where there is a large difference between current water quality conditions and 

the nutrient criteria levels necessary to protect aquatic life. In such cases, Florida may
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conclude that restoration programs will not result in waters attaining their designated 

aquatic life use (and associated numeric nutrient criteria) for a long period of time.

EPA’s current regulations provide that a state may remove a designated use if it 

meets certain requirements outlined at 40 CFR 131.10. Under this provision, if the State 

demonstrates that a designated use is not attainable it may conduct a use attainability

analysis (UAA) to revise the designated use to reflect the highest attainable aquatic life 

use, even though that use may not meet the CWA section 101(a)(2) goal.111 Another 

option that states use to address situations for an individual discharger is a dischargerspecific variance112. Neither of these approaches may be optimal or appropriate solutions 

if a state determines that certain waters cannot attain aquatic life uses due to excess 

nutrient in the near-term. 

Based on numerous workshops, meetings, conversations and day-to-day

interactions with state environmental managers, EPA understands that states interested in 

restoring impaired water may desire the ability to express, in their WQS, successive time 

periods with incrementally more stringent designated uses and criteria that ultimately

result in a designated use and criteria that reflect a CWA section 101(a)(2) designated 

use. Such an approach would allow the state and stakeholders necessary time to take 

incremental steps to achieve interim WQS as they move forward to ultimately attain a 

CWA section 101(a)(2) designated use. Some states have used variances to provide such 

time in their WQS. However, variances are typically time limited (e.g.,three years) and 

 

111 Clean Water Act section 101(a)(2) states that it is a national goal for water quality, wherever attainable, 

to provide for the protection and propagation of fish, shellfish, and wildlife and provide for recreation in 

and on the water

112 A variance is a temporary modification to the designated use and associated water quality criteria that 

would otherwise apply. It is based on a use attainability demonstration and targets achievement of the 

highest attainable use and associated criteria during the variance period.
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discharger-specific and do not address the challenges of pursuing reductions from a 

variety of sources across a watershed. In addition, Federal regulations are not explicit in 

requiring that states pursue feasible (i.e. attainable) progress toward achieving the highest 

attainable use when implementing a variance. Variances also often lack specific 

milestones and a transparent set of expectations for the public, dischargers, and 

stakeholders. 

EPA seeks comment on this approach to providing Florida with an explicit 

regulatory mechanism for directing state efforts to achieve incremental progress in a stepwise fashion, applicable to all sources, as a part of its WQS. The proposed regulatory

mechanism described in this section applies only to WQS for nutrients in Florida waters 

subject to this proposed rule. 

A “restoration water quality standard” under EPA’s proposed rule would be a 

WQS that Florida could adopt for an impaired water. Under EPA’s proposal, the State 

would retain the current designated use as the ultimate designated use (e.g. providing for 

eventual attainment of a full CWA section 101(a)(2) designated use and the associated 

criteria). However, under the restoration standard approach proposed in this rule, the 

State would also adopt interim less stringent designated uses and criteria that would be 

the basis for enforceable permit requirements and other control strategies during the 

prescribed timeframes. These interim uses could be no less stringent than an existing use 

as defined in section 131.3, and would have to meet the requirements of 131.10(h)(2). 

The State would need to demonstrate that the interim uses and criteria, as well as the 

timeframe, are based on a UAA evaluation of what is attainable and by when. These 

interim designated uses and criteria and the applicable timeframes would all be 
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incorporated into the State WQS on a site-specific basis, as would be any other 

designated use change or adoption of site-specific criteria. 

For example, a restoration WQS for nutrients for an impaired Class I or Class III 

colored lake in Florida may take the form of the following for a lake whose current 

condition represents severely impaired aquatic life with chlorophyll a = 40 mg/L, TN = 

2.7 mg/L, and TP = 0.15 mg/L: 

Time Chl a TN TP Designated Use Description 

Year 0-5 35 2.4 0.10 Moderately Impaired Aquatic Life

Year 6-10 25 1.45 0.06 Slightly Impaired Aquatic Life

Year 11 20 1.2 0.05 Full Aquatic Life Use

Including such revised interim designated uses and criteria within the regulations 

could support efforts by Florida to formally establish enforceable long-term plans for 

different watersheds or stream reaches to attain the ultimate designated use and the 

associated criteria. At the same time, the State would be able to ensure that its WQS 

explicitly reflect the attainable designated uses and water quality criteria to be met at any 

given time, consistent with the CWA and implementing regulations. 

Restoration WQS would provide in the Federal regulations the framework for 

authorizing the State of Florida to adopt restoration WQS for nutrients, along with 

maintaining the availability of other tools (e.g., variances and compliance schedule 

provisions), which provide flexibility regarding permitting individual dischargers. 

Restoration WQS would require a full public participation process to assure transparency

as well as the opportunity for different parties to work together, exchange information 

and determine what is actually attainable within a particular time frame. Going through 
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this process would provide Florida with a transparent set of expectations to push its 

waters towards restoration in a realistic yet verifiable manner. 

In this notice, EPA proposes restoration WQS as a clear regulatory pathway for 

the State of Florida to adjust the Class I and Class III designated uses (and associated 

nutrient criteria) of waters impaired by nutrients that is intended to promote active 

restoration, maintain progressive improvement, and ensure accountability. This approach 

would provide the State of Florida with the flexibility to adopt revised designated uses 

and criteria under a set of specific regulatory requirements. 

Under this proposal, the interim designated uses and criteria would be the basis 

for NPDES permits during the applicable period reflecting the fact that the restoration 

WQS introduces the critical element of time as part of the complete WQS. This is 

intended to allow imposition of the maximum feasible point source controls and nonpoint 

source nutrient reduction strategies to be phased in within the overall context of 

restoration activities within the watershed. By reflecting how it expects the existing poor 

quality of its waters to incrementally improve to achieve longer-term WQS goals, Florida 

could create the flexibility to explore more innovative ways to reach the requirements of 

the next phase, thus possibly reducing costs or allowing new approaches to resolve 

complex technological issues, and maximizing transparency with the public during each 

phase. These waters, however, would still be considered impaired for CWA assessment 

and listing purposes because the ultimate designated use and criteria would be part of the 

restoration WQS and would not yet be met.

The restoration standards would be Florida WQS revisions that would go through 

the process of first being adopted under State law and then approved by EPA. This 
170

proposal would include eight requirements for the development of a restoration WQS for 

nutrients: 

1. It must be demonstrated that it is infeasible to attain the full CWA section 

101(a)(2)aquatic life designated use during the time periods established for the 

restoration phases with a UAA based on one of the factors at 40 CFR 131.10(g). 

2. The highest attainable designated use and numeric criteria that apply at the 

termination of the restoration WQS (i.e., the ultimate long-term designated use 

and numeric criteria to be achieved) must be specified and this use is to include, at 

a minimum, uses that are consistent with the CWA section 101(a)(2) uses. 

3. Interim restoration designated uses and numeric water quality criteria, with each 

based on achieving the maximum feasible progress during the applicable phase as 

determined in the UAA, must be established.

4. Specific time periods for each restoration phase must be established. The length 

of each phase must be based on the UAA demonstration of when interim uses can 

be attained on a case-specific basis. Interim restoration designated uses and 

numeric water quality criteria must reflect the highest attainable use during the 

time period of the restoration phase. The sum of these times periods may not 

exceed twenty years. 

5. The spatial extent to which the restoration WQS will apply (e.g., how far 

downstream the restoration WQS would apply) must be specified. EPA notes the 

importance of continuing to meet the requirements for protection of downstream 

WQS as expressed in section 40 CFR 131.10(b). Adopting restoration WQS 
171

upstream of another impaired water may mean the State should also consider 

restoration WQS for the downstream water.

6. The regulatory requirements for public participation and EPA review and 

approval whenever revising its WQS must continue to be met. Specifically, a 

restoration WQS may not include interim uses less stringent than a use that is an 

“existing use” as defined in 131.3 or that do not meet the requirements of 

131.10(h)(2). 

7. The State must include in its restoration WQS that if the water body does not 

attain the interim designated use and numeric water quality criteria at the end of 

any phase, the restoration WQS will no longer be in effect and the designated use 

and criteria that was to become effective at the end of the final restoration phase 

will become immediately effective unless Florida adopts and EPA approves a 

different revised designated use and criteria.

8. The State must provide that waters for which a restoration WQS is adopted will 

be recognized as impaired for the purposes of listing impaired waters under 

section 303(d) of the CWA until the final use is attained.

Under this proposal, EPA would require Florida to adopt the ultimate highest 

attainable designated use and criteria along with multiple phases reflecting the stepwise 

improvements in water quality between the initial effective date and when they expect to 

meet the ultimate highest attainable use as a single restoration WQS package. As with 

any revision to an aquatic life use, Florida would be required to demonstrate that the 

ultimate highest attainable designated use cannot be attained during the restoration 

period, based on one of the factors at CFR 131.10(g)(1)-(6) (i.e., through a UAA). EPA 
172

would review the WQS and all supporting documents before approving the restoration 

WQS. 

At the beginning of the first restoration phase, the State would identify current 

conditions and establish the principle that there can be no further degradation. WQS for 

the first restoration phase should reflect the outcomes of all controls that can be 

implemented within the first restoration phase. Additionally, EPA expects that the 

interim restoration designated use and numeric criteria that are attainable at the end of the 

restoration phase apply at the beginning of each phase as well as throughout the phase. 

For each phase, the State would adopt interim designated uses and numeric water quality 

criteria that reflect achieving the maximum feasible progress. At the end of the first 

phase, EPA would expect the water body to be meeting the first interim designated use 

and water quality criteria. 

At the beginning of the second phase, the next (more stringent) interim designated 

use and water quality criteria would go into effect as the applicable WQS that the State 

would use to direct the next set of control actions. At the conclusion of the second phase, 

the next (more stringent) interim designated use and water quality criteria would become 

the applicable WQS. This process would repeat with each subsequent phase. Permit 

limits written during the restoration phases would include effluent limits as stringent as 

necessary to meet the applicable interim designated uses and numeric water quality

criteria. In constructing each restoration phase (i.e. duration and interim designated use 

and numeric water quality criteria), EPA will require the maximum feasible progress. 

This means that necessary control actions that would improve water quality and can be 

implemented within the first phase must be reflected in the interim targets for the first 
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restoration phase. This would include all technology-based requirements for point 

sources, and cost-effective and reasonable BMPs for nonpoint sources. For treatment 

upgrades to point sources, EPA expects careful scrutiny of technology that has been 

successfully implemented in comparable situations and presumes that this is feasible 

EPA further expects careful scrutiny of all existing and new technology that will help 

achieve the ultimate highest attainable use.

EPA recognizes that circumstances may change as controls are implemented and 

that new information may indicate that the timeframes established in the restoration WQS 

are too lengthy or possibly unrealistically short. If this is the case, the state has the 

discretion under CFR 131.10 to conduct a new UAA and revise the interim targets in its 

restoration WQS after a full public process and EPA approval. However, there is a 

significant burden on the state to demonstrate what changed to alter the initial analysis 

and associated expectations for what was attainable for that phase. EPA would expect 

such a revision only if there was significant new information that demonstrated that a 

different schedule and/or set of interim standards represents the maximum feasible 

progress towards the final designated use and criteria. 

If at the end of a phase, the water body is not meeting interim targets, then the 

restoration WQS would no longer be applicable. In such a case, the applicable WQS 

would be the ultimate highest attainable use and associated criteria unless the State 

adopted and submitted for EPA approval a revised WQS. This would help ensure that 

there would be no delay in implementing control measures. Alternatively, EPA 

considered an option of allowing the subsequent restoration phases to become applicable 

on the schedule adopted in the restoration WQS and as supported by the original UAA 
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demonstration, even if the interim use and criteria are not fully achieved on schedule. 

This might have the advantage of encouraging the adoption of ambitious interim goals in 

the initial restoration standards, and would allow continued orderly progress towards 

achievement of the final use and criterion even where an interim step was not fully

attained. EPA solicits comment on this alternative approach. 

To develop restoration WQS for numeric nutrient criteria, EPA would expect that 

the State identify waters in need of restoration, produce an inventory of point and 

nonpoint sources within the watershed, and evaluate current ambient conditions and the

necessary reductions to achieve the numeric criteria. The next part of the process would 

involve determining the combinations of control strategies and management practices 

available, how likely they are to produce results, and the resources needed to implement 

them. At this point, the State would be in a good position to determine how much 

pollution reduction is likely to be attainable under what timeframes. The State could use 

this information to establish the time periods for each restoration phase consistent with 

the maximum feasible and attainable progress toward meeting the numeric criteria, 

establish interim restoration designated uses and water quality criteria, and make the 

necessary demonstration that it is infeasible to attain the long-term designated use during 

the time periods established and that the interim phases reflect the highest attainable uses 

and associated criteria.

For excess nutrient pollution, the contributors to nutrient pollution could include 

publicly-owned treatment works (POTWs), industrial dischargers, urban and agricultural 

runoff, atmospheric deposition, and septic systems. Restoration WQS might reflect in an 

early phase, for example, all feasible short-term POTW treatment upgrades and a 
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schedule to select, fund, and implement longer term nutrient reduction technologies, 

while aggressively pursuing reductions in nonpoint source runoff. This might include 

specific plans and a schedule to develop and implement innovative alternative 

approaches, such as trading programs, where appropriate. 

In Florida, many of the steps described above occur in the context of Basin 

Management Action Plans (BMAPs). FDEP describes BMAPs as:

...the “blueprint” for restoring impaired waters by reducing pollutant loadings to 

meet the allowable loadings established in a Total Maximum Daily Load (TMDL). 

It represents a comprehensive set of strategies--permit limits on wastewater 

facilities, urban and agricultural best management practices, conservation 

programs, financial assistance and revenue generating activities, etc.--designed 

to implement the pollutant reductions established by the TMDL. These broadbased plans are developed with local stakeholders--they rely on local input and 

local commitment--and they are adopted by Secretarial Order to be enforceable.

(http://www.dep.state.fl.us/Water/watersheds/bmap.htm) 

Florida has adopted BMAPs for the Hillsborough River Basin, Lower St. John’s River, 

Log Branch, Orange Creek, and Upper Ocklawaha, and has plans for others to follow. 

To the extent necessary, FDEP could potentially use aspects of the BMAP process and 

plans such as these to help form the basis for restoration WQS. 

In summary, the WQS program is intended to protect and improve water quality

and WQS are meant to guide actions to address the effects of pollution on the Nation’s 

waters. The reality is that as more assessments are being done and TMDLs are being 

contemplated, and as new criteria are developed and considered, EPA and states face 
176

questions about what pollution control measures will meet the WQS, how long it might 

take, and whether it is feasible to attain the WQS established to meet the goals of the Act. 

These questions are often difficult to answer because of lack of data, lack of knowledge, 

and lack of experience in attempting restoration of waters. Stakeholders and coregulators alike have expressed a desire for ways to pursue progressive water quality

improvement and evaluate those improvements to gain the data, knowledge, and 

experience necessary to ultimately determine the highest attainable use. In response,

EPA has been investigating the best ways to use UAAs and related tools to make 

progress in identifying and achieving the most appropriate designated use.

EPA requests comments on the usefulness of the “restoration WQS” proposal for 

Florida. EPA requests comment on how restoration WQS will operate in conjunction 

with listing impaired waters, and establishing NPDES permit limitations, and nonpoint 

source control strategies, as well as how these requirements should be reflected in 

regulatory language. EPA also requests comment on the proposed 20 year limit on the 

schedule to attain the final use and criteria. EPA also requests comments on how a

restoration WQS process would be coordinated with the TMDL program and whether the 

transparency and review procedures for the two approaches, including the conditions 

under which a State or EPA would be required to develop a TMDL, are comparable. 

EPA also requests comment on any unintended adverse consequences for any of its water

quality programs. Finally, EPA requests comment on potential definitions of “maximum 

feasible progress.”

VII. Statutory and Executive Order Reviews 
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A. Executive Order 12866: Regulatory Planning and Review 

Under Executive Order (EO) 12866 (58 FR 51735, October 4, 1993), this action is 

a "significant regulatory action.” Accordingly, EPA submitted this action to the Office of 

Management and Budget (OMB) for review under EO 12866 and any changes made in 

response to OMB recommendations have been documented in the docket for this action.

This proposed rule does not establish any requirements directly applicable to 

regulated entities or other sources of nutrient pollution. Moreover, existing narrative 

water quality criteria in State law already require that nutrients not be present in waters in 

concentrations that cause an imbalance in natural populations of flora and fauna in lakes 

and flowing waters in Florida.

B. Paperwork Reduction Act

This action does not impose an information collection burden under the 

provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. Burden is defined at 

5 CFR 1320.3(b). It does not include any information collection, reporting, or recordkeeping requirements.

C. Regulatory Flexibility Act

The Regulatory Flexibility Act (RFA) generally requires an agency to prepare a 

regulatory flexibility analysis of any rule subject to notice and comment rulemaking 

requirements under the Administrative Procedure Act or any other statute unless the 

agency certifies that the rule will not have significant economic impact on a substantial 

number of small entities. Small entities include small businesses, small organizations, 

and small governmental jurisdictions.
178

For purposes of assessing the impacts of this action on small entities, small 

entity is defined as: (1) A small business as defined by the Small Business 

Administration's (SBA) regulations at 13 CFR 121.201; (2) a small governmental 

jurisdiction that is a government of a city, county, town, school district or special district 

with a population of less than 50,000; and (3) a small organization that is any not-forprofit enterprise that is independently owned and operated and is not dominant in its 

field.

Under the CWA WQS program, states must adopt WQS for their waters and 

must submit those WQS to EPA for approval; if the Agency disapproves a state standard 

and the state does not adopt appropriate revisions to address EPA’s disapproval, EPA 

must promulgate standards consistent with the statutory requirements. EPA also has the 

authority to promulgate WQS in any case where the Administrator determines that a new 

or revised standard is necessary to meet the requirements of the Act. These state 

standards (or EPA-promulgated standards) are implemented through various water 

quality control programs including the NPDES program, which limits discharges to 

navigable waters except in compliance with an NPDES permit. The CWA requires that 

all NPDES permits include any limits on discharges that are necessary to meet applicable 

WQS.

Thus, under the CWA, EPA’s promulgation of WQS establishes standards that 

the State implements through the NPDES permit process. The State has discretion in 

developing discharge limits, as needed to meet the standards. This proposed rule, as 

explained earlier, does not itself establish any requirements that are applicable to small 

entities. As a result of this action, the State of Florida will need to ensure that permits it 
179

issues include any limitations on discharges necessary to comply with the standards 

established in the final rule. In doing so, the State will have a number of choices 

associated with permit writing. While Florida’s implementation of the rule may

ultimately result in new or revised permit conditions for some dischargers, including 

small entities, EPA’s action, by itself, does not impose any of these requirements on 

small entities; that is, these requirements are not self-implementing. Thus, I certify that 

this rule will not have a significant economic impact on a substantial number of small 

entities. 

EPA has prepared an analysis of potential costs associated with meeting these 

standards.113 EPA’s analysis uses the criteria proposed by FDEP in July 2009 as a 

baseline against which to estimate the incremental costs of meeting the standards in this

proposal. The baseline costs of meeting Florida’s proposed standards are estimated to be 

$102 to $130 million per year. The incremental costs, over and above these baseline 

costs, of meeting the standards in this NPRM are estimated to be $4.7 to $10.1 million 

per year. This analysis assumes that most of these costs would fall on non-point sources 

and the categories of point sources that would be primarily affected are municipal 

wastewater treatment plants and industrial and general dischargers.114 EPA estimates the 

incremental costs for these two categories of dischargers, including small entities, at 

about $1 million per year. 

D. Unfunded Mandates Reform Act

 

113

 Refer to Docket ID EPA-HQ-OW-2009-0596.

114 EPA was not able to estimate costs for municipal stormwater systems because the need for incremental 

controls is uncertain.
180

Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public Law 

104-4, establishes requirements for Federal agencies to assess the effects of their 

regulatory actions on state, local, and tribal governments and the private sector. Under 

section 202 of the UMRA, EPA generally must prepare a written statement, including a 

cost-benefit analysis, for proposed and final rules with ``Federal mandates'' that may

result in expenditures to state, local, and Tribal governments, in the aggregate, or to the 

private sector, of $100 million or more in any one year. Before promulgating an EPA 

rule for which a written statement is needed, section 205 of the UMRA generally requires 

EPA to identify and consider a reasonable number of regulatory alternatives and adopt 

the least costly, most cost-effective or least burdensome alternative that achieves the 

objectives of the rule. The provisions of section 205 do not apply when they are 

inconsistent with applicable law. Moreover, section 205 allows EPA to adopt an 

alternative other than the least costly, most cost-effective or least burdensome alternative 

if the Administrator publishes with the final rule an explanation of why that alternative 

was not adopted. Before EPA establishes any regulatory requirements that may

significantly or uniquely affect small governments, including tribal governments, it must 

have developed under section 203 of the UMRA a small government agency plan. The 

plan must provide for notifying potentially affected small governments, enabling officials 

of affected small governments to have meaningful and timely input in the development of 

EPA regulatory proposals with significant Federal intergovernmental mandates, and 

informing, educating, and advising small governments on compliance with the regulatory

requirements.
181

This proposed rule contains no Federal mandates (under the regulatory

provisions of Title II of the UMRA) for state, local, or tribal governments or the private 

sector. The State may use these resulting water quality criteria in implementing its water 

quality control programs. This proposed rule does not regulate or affect any entity and, 

therefore, is not subject to the requirements of sections 202 and 205 of UMRA.

EPA determined that this proposed rule contains no regulatory requirements 

that might significantly or uniquely affect small governments. Moreover, WQS, 

including those proposed here, apply broadly to dischargers and are not uniquely 

applicable to small governments. Thus, this proposed rule is not subject to the 

requirements of section 203 of UMRA.

E. Executive Order 13132 (Federalism)

This action does not have federalism implications. It will not have substantial 

direct effects on the states, on the relationship between the national government and the 

states, or on the distribution of power and responsibilities among the various levels of 

government, as specified in Executive Order 13132. EPA’s authority and responsibility

to promulgate Federal WQS when state standards do not meet the requirements of the 

CWA is well established and has been used on various occasions in the past. The 

proposed rule would not substantially affect the relationship between EPA and the states 

and territories, or the distribution of power or responsibilities between EPA and the 

various levels of government. The proposed rule would not alter Florida’s considerable 

discretion in implementing these WQS. Further, this proposed rule would not preclude 

Florida from adopting WQS that meet the requirements of the CWA, either before or 
182

after promulgation of the final rule, thus eliminating the need for Federal standards. 

Thus, Executive Order 13132 does not apply to this proposed rule.

Although section 6 of Executive Order 13132 does not apply to this action, EPA 

had extensive communication with the State of Florida to discuss EPA’s concerns with 

the State’s nutrient water quality criteria and the Federal rulemaking process. In the spirit 

of Executive Order 13132, and consistent with EPA policy to promote communications 

between EPA and state and local governments, EPA specifically solicits comment on this 

proposed rule from State and local officials.

F. Executive Order 13175 (Consultation and Coordination with Indian Tribal 

Governments)

Subject to the Executive Order 13175 (65 FR 67249, November 9, 2000) EPA 

may not issue a regulation that has tribal implications, that imposes substantial direct 

compliance costs, and that is not required by statute, unless the Federal government 

provides the funds necessary to pay the direct compliance costs incurred by tribal 

governments, or EPA consults with tribal officials early in the process of developing the 

proposed regulation and develops a tribal summary impact statement. EPA has 

concluded that this action may have tribal implications. However, the rule will neither 

impose substantial direct compliance costs on tribal governments, nor preempt Tribal 

law. 

In the State of Florida, there are two Indian tribes, the Seminole Tribe of Florida 

and the Miccosukee Tribe of Indians of Florida, with lakes and flowing waters. Both 

tribes have been approved for treatment in the same manner as a state (TAS) status for 
183

CWA sections 303 and 401 and have federally-approved WQS in their respective 

jurisdictions. These tribes are not subject to this proposed rule. However, this rule may

impact the tribes because the numeric nutrient criteria for Florida will apply to waters 

adjacent to the tribal waters. 

EPA has contacted the tribes to inform them of the potential future impact this 

proposal could have on tribal waters. A meeting with tribal officials has been requested 

to discuss the draft proposed rule and potential impacts on the tribes. EPA specifically 

solicits additional comment on this proposed rule from tribal officials. 

G. Executive Order 13045 (Protection of Children From Environmental Health and 

Safety Risks)

This action is not subject to EO 13045 (62 FR 19885, April 23, 1997) because it is 

not economically significant as defined in EO 12866, and because the Agency does not 

believe the environmental health or safety risks addressed by this action present a 

disproportionate risk to children.

H. Executive Order 13211 (Actions That Significantly Affect Energy Supply, Distribution, 

or Use)

This rule is not a “significant energy action” as defined in Executive Order 13211, 

“Actions Concerning Regulations That Significantly Affect Energy Supply,

Distribution, or Use” (66 FR 28355 (May 22, 2001)), because it is not likely to have a 

significant adverse effect on the supply, distribution, or use of energy. 

I. National Technology Transfer Advancement Act of 1995
184

Section 12(d) of the National Technology Transfer and Advancement Act of 1995 

(“NTTAA”), Public Law 104–113, section 12(d) (15 U.S.C. 272 note) directs EPA to use 

voluntary consensus standards in its regulatory activities unless to do so would be 

inconsistent with applicable law or otherwise impractical. Voluntary consensus standards 

are technical standards (e.g., materials specifications, test methods, sampling procedures, 

and business practices) that are developed or adopted by voluntary consensus standards 

bodies. The NTTAA directs EPA to provide Congress, through OMB, explanations 

when the Agency decides not to use available and applicable voluntary consensus 

standards.

This proposed rulemaking does not involve technical standards. Therefore, EPA 

is not considering the use of any voluntary consensus standards.

J. Executive Order 12898 (Federal Actions To Address Environmental Justice in 

Minority Populations and Low-Income Populations)

Executive Order (EO) 12898 (59 FR 7629 (Feb. 16, 1994)) establishes Federal 

executive policy on environmental justice. Its main provision directs Federal agencies, to 

the greatest extent practicable and permitted by law, to make environmental justice part 

of their mission by identifying and addressing, as appropriate, disproportionately high 

and adverse human health or environmental effects of their programs, policies, and 

activities on minority populations and low-income populations in the United States.

EPA has determined that this proposed rule does not have disproportionately high 

and adverse human health or environmental effects on minority or low-income 

populations because it would afford a greater level of protection to both human health 
185

and the environment if these numeric nutrient criteria are promulgated for Class I and 

Class III waters in the State of Florida.

List of Subjects in 40 CFR Part 131

Environmental protection, water quality standards, nutrients, Florida.

Dated: 

Lisa P. Jackson,

Administrator

For the reasons set out in the preamble, EPA proposes to amend 40 CFR part 131 as 

follows:

PART 131 – WATER QUALITY STANDARDS 

1. The authority citation for part 131 continues to read as follows:

Authority: 33 U.S.C. 1251 et seq.

Subpart D-[Amended]

2. Section 131.43 is added as follows:

§ 131.43 Florida.

(a) Scope. This section promulgates numeric nutrient criteria for lakes, streams, 

springs, canals, estuaries, and coastal waters in the State of Florida. This section also 

contains provisions for site-specific criteria.

(b) Definitions. 
186

(1) Canal means a trench, the bottom of which is normally covered by water with 

the upper edges of its two sides normally above water, excluding all secondary and 

tertiary canals, classified as Class IV waters, wholly within Florida’s agricultural areas. 

(2) Clear stream means a free-flowing water whose color is less than 40 platinum 

cobalt units (PCU). 

(3) Lake means a freshwater water body that is not a stream or other watercourse 

with some open contiguous water free from emergent vegetation.

(4) Lakes and flowing waters means 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 are predominantly fresh 

waters. 

(5) Nutrient watershed region means an area of the State, corresponding to 

coastal/estuarine drainage basin and differing geographical conditions affecting nutrient 

levels, as delineated in the Technical Support Document for EPA’s Proposed Rule for 

Numeric Nutrient Criteria for Florida’s Inland Surface Fresh Waters.

(6) Predominantly fresh waters means surface waters in which the chloride 

concentration at the surface is less than 1,500 milligrams per liter. 

(7) Spring means the point where underground water emerges onto the Earth’s 

surface, including its spring run. 

(8) 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. 
187

(9) State shall mean the State of Florida, whose transactions with the U.S. EPA in 

matters related to this regulation are administered by the Secretary, or officials delegated 

such responsibility, of the Florida Department of Environmental Protection (FDEP), or 

successor agencies.

(10) 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. 

(11) Surface water means water upon the surface of the earth, whether contained 

in bounds created naturally or artificially or diffused. Water from natural springs shall be 

classified as surface water when it exits from the spring onto the Earth’s surface. 

(c) Criteria for Florida waters.

(1) Criteria for lakes. The applicable criterion for chlorophyll a, total nitrogen 

(TN), and total phosphorus (TP) for lakes within each respective lake class is shown on 

the following table:

A B C D E F

Long Term 

Average Lake 

Color and 

Alkalinity

Chlorophyll 

a

f

(g/L) a

Baseline Criteria b Modified Criteria

(within these bounds) c

TP (mg/L) aTN (mg/L) aTP (mg/L) aTN (mg/L) a

Colored Lakes

> 40 PCU

20 0.050 1.23 0.050-0.157 1.23-2.25

Clear Lakes, 

Alkaline

≤ 40 PCU dand 

> 50 mg/L 

CaCO3 

e

20 0.030 1.00 0.030-0.087 1.00-1.81

Clear Lakes, 

Acidic

≤ 40 PCU dand 

≤ 50 mg/L 

CaCO3 

e

6 0.010 0.500 0.010-0.030 0.500-0.900
188

a

Concentration values are based on annual geometric mean not to be surpassed more than once in a threeyear 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 ambientbased, 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.

(2) Criteria for streams. 

(i) The applicable instream protection value (IPV) criterion for total nitrogen 

(TN) and total phosphorus (TP) for streams within each respective nutrient watershed 

region is shown in the following table:

Nutrient Watershed Region Instream Protection Value Criteria

TN (mg/L) aTP (mg/L) a

Panhandle b0.824 0.043

Bone Valley c1.798 0.739

Peninsula d1.205 0.107

North Central e1.479 0.359

a

Concentration values are based on annual geometric mean not to be surpassed more than once in a threeyear period. In addition, the long-term average of annual geometric mean values shall not surpass the listed 
189

concentration values. (Duration = annual; Frequency = not to be exceeded more than once in a three-year 

period or as a long-term average).

b

Panhandle region includes the following watersheds: Perdido Bay Watershed, Pensacola Bay Watershed, 

Choctawhatchee Bay Watershed, St. Andrew Bay Watershed, Apalachicola Bay Watershed, Apalachee Bay 

Watershed, and Econfina/Steinhatchee Coastal Drainage Area.

c

Bone Valley region includes the following watersheds: Tampa Bay Watershed, Sarasota Bay Watershed, 

and Charlotte Harbor Watershed.

d

Peninsula region includes the following watersheds: Waccasassa Coastal Drainage Area, Withlacoochee 

Coastal Drainage Area, Crystal/Pithlachascotee Coastal Drainage Area, Indian River Watershed, 

Caloosahatchee River Watershed, St. Lucie Watershed, Kissimmee River Watershed, St. John’s River 

Watershed, Daytona/St. Augustine Coastal Drainage Area, Nassau Coastal Drainage Area, and St. Mary’s 

River Watershed.

e North Central region includes the Suwannee River Watershed.

(ii) Criteria for protection of downstream lakes. 

(A) The applicable total phosphorus criterion-magnitude for a stream that flows 

into downstream lakes is the more stringent of the value from the preceding table in 

(c)(2)(i) or a downstream lake protection value derived from the following equation to 

protect the downstream lake: 

  L w

f

S

[TP] 1

c

1

[TP]   

where

[TP]S is the total phosphorus (TP) downstream lake protection value, mg/L

[TP]L is applicable TP lake criterion, mg/L

cf is the fraction of inflow due to all streamflow, 0  cf  1

w is lake’s hydraulic retention time (water volume divided by annual flow rate)

The term   1 w   expresses the net phosphorus loss from the water column 

(e.g., via settling of sediment-sorbed phosphorus) as a function of the lake’s 

retention time.

(B) The preset values for cf and w, respectively, are 0.5 and 0.2. The State may

substitute site-specific values for these preset values where the State determines that they

are appropriate and documents the site-specific values in an easily accessible and publicly 

available location, such as an official State Web site. 
190

(iii) Criteria for protection of downstream estuarine waters.

(A) The applicable criteria for a stream that flows into downstream estuary is the 

more stringent of the values from the preceding table in (c)(2)(i) or downstream 

protection values derived from the following equation to protect the downstream estuary. 

EPA’s preset DPVs are listed in the Technical Support Document (TSD) for Florida’s 

Inland Waters located at www.regulations.gov, Docket ID No. EPA-HQ-OW-2009-0569, 

and calculated for each stream reach as the average reach-specific concentration (Ci) 

equal to the average reach-specific annual loading rate (Li) divided by the average reachspecific flow (Qi

) where:

W i

i est Q F

C kL 1 ,

and where the terms are defined as follows for a specific or ( i

th ) stream reach:

Ci maximum flow-averaged nutrient concentration for a specific (the i

th ) 

stream reach consistent with downstream use protection (i.e., the DPV)

k fraction of all loading to the estuary that comes from the stream network 

resolved by SPARROW 

Lest protective loading rate for the estuary, from all sources 

QWcombined average freshwater discharged into the estuary from the portion 

of the watershed resolved by the SPARROW stream network 

Fifraction of the flux at the downstream node of the specific ( i

th)

reach that 

is transported through the stream network and ultimately delivered to 

estuarine eceiving waters (i.e. Fraction Delivered). 

DPVs may not exceed other criteria established for designated use protection in this 

section, nor result in an exceedance of other criteria for other water quality

parameters established pursuant to Rule 62-302, F.A.C.

(B) The State may calculate alternative DPVs as above for Ciexcept that Li is 

determined as a series of values for each reach in the upstream drainage area such that the 

sum of reach-specific incremental loading rates equals the target loading rate to the 
191

downstream water protective of downstream uses, taking into account that downstream 

reaches must reflect loads established for upstream reaches. Alternative DPVs may

factor in additional nutrient attenuation provided by already existing landscape 

modifications or treatment systems, such as constructed wetlands or stormwater treatment 

areas. For alternative DPVs to become effective for Clean Water Act purposes, the State 

must provide public notice and opportunity for comment.

(C) To use an alternative technical approach of comparable scientific rigor to 

quantitatively determine the protective load to the estuary and associated protective 

stream concentrations, the State must go through the process for a Federal site-specific 

alternative criterion pursuant to paragraph (e) of this section.

(3) Criteria for springs, spring runs, and clear streams. The applicable nitratenitrite criterion is 0.35 mg/L as an annual geometric mean not to be surpassed more than 

once in a three year period, nor surpassed as a long-term average of annual geometric 

mean values. In addition to this nitrate-nitrite criterion, criteria identified in paragraph 

(c)(2) of this section are applicable to clear streams. 

(4) Criteria for south Florida canals. The applicable criterion for chlorophyll a, 

total nitrogen (TN), and total phosphorus (TP) for canals within each respective canal 

geographic classification area is shown on the following table:

Chlorophyll a

(μg/L) a

Total Phosphorus (TP)

(mg/L) a, b

Total Nitrogen (TN)

(mg/L) a

Canals 4.0 0.042 1.6 

a

Concentration values are based on annual geometric mean not to be surpassed more than once in a threeyear 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 Applies to all canals within the Florida Department of Environmental Protection’s South Florida 

bioregion, with the exception of canals within the Everglades Protection Area (EvPA) where the TP 

criterion of 0.010 mg/L currently applies.
192

(5) Criteria for estuaries. [Reserved]

(6) Criteria for coastal waters. [Reserved]

(d) Applicability.

(1) The criteria in paragraphs (c)(1) through (7) of this section apply to surface 

waters of the State of Florida designated 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 apply concurrently with other applicable water quality criteria, except 

when 

(i) State regulations contain criteria which are more stringent for a particular 

parameter and use,

(ii) The Regional Administrator determines that site-specific alternative criteria 

apply pursuant to the procedures in paragraph (e) of this section, 

(iii) The State adopts and EPA approves a water quality standards variance to the 

Class I or Class III designated use pursuant to § 131.13 that meets the applicable 

provisions of State law and the applicable Federal regulations at § 131.10, or 

(iv) The State adopts and EPA approves restoration standards pursuant to 

paragraph (g) of this rule.

(2) The criteria established in this section are subject to the State’s general rules 

of applicability in the same way and to the same extent as are the other federally-adopted

and State-adopted numeric criteria when applied to the same use classifications. 

(i) For all waters with mixing zone regulations or implementation procedures, the 

criteria apply at the appropriate locations within or at the boundary of the mixing zones;
193

otherwise the criteria apply throughout the water body including at the point of discharge 

into the water body. 

(ii) The State shall use an appropriate design flow condition, where necessary, for 

purposes of permit limit derivation or load and wasteload allocations that is consistent 

with the criteria duration and frequency established in this section (e.g., average annual 

flow for a criterion magnitude expressed as an average annual geometric mean value). 

(iii) The criteria established in this section apply for purposes of determining the 

list of impaired waters pursuant to section 303(d) of the Clean Water Act, subject to the 

procedures adopted pursuant to Rule 62-303, F.A.C., where such procedures are 

consistent with the level of protection provided by the criteria established in this section.

(e) Site-specific alternative criteria.

(1) Upon request from the State, the Regional Administrator may determine that 

site-specific alternative criteria shall apply to specific surface waters in lieu of the criteria 

established in paragraph (c). Any such determination shall be made consistent with

§131.11.

(2) To receive consideration from the Regional Administrator for a determination 

of site-specific alternative criteria, the State must submit a request that includes proposed 

alternative numeric criteria and supporting rationale suitable to meet the needs for a 

technical support document pursuant to paragraph (e)(3) of this section.

(3) For any determination made under paragraph (e)(1) of this section, the 

Regional Administrator shall, prior to making such a determination, provide for public 

notice and comment on a proposed determination. For any such proposed determination, 

the Regional Administrator shall prepare and make available to the public a technical 
194

support document addressing the specific surface waters affected and the justification for 

each proposed determination. This document shall be made available to the public no 

later than the date of public notice issuance.

(4) The Regional Administrator shall maintain and make available to the public an 

updated list of determinations made pursuant to paragraph (e)(1) of this section as well as 

the technical support documents for each determination.

(5) Nothing in this paragraph (e) shall limit the Administrator's authority to 

modify the criteria in paragraph (c) of this section through rulemaking.

(f) Effective date. All criteria will be in effect [date 60 days after publication of 

final rule].

(g) Restoration Water Quality Standards (WQS). The State may, at its 

discretion, adopt restoration WQS to allow attainment of a designated use over phased 

time periods where the designated use is not currently attainable as a result of nutrient 

pollution but is attainable in the future. In establishing restoration WQS, the State must:

(1) Demonstrate that the designated use is not attainable during the time periods 

established for the restoration phases based on one of the factors identified in

§131.10(g)(1) through (6);

(2) Specify the designated use to be attained at the termination of the restoration 

period, as well as the criteria necessary to protect such use, provided that the final 

designated use and corresponding criteria shall include, at a minimum, uses and criteria 

that are consistent with CWA section 101(a)(2) ;
195

(3) Establish interim restoration designated uses and water quality criteria, that 

apply during each phase that will result in maximum feasible progress toward the 

highest attainable designated use and the use identified in paragraph (g)(2) of this section. 

Such interim uses and criteria may not provide for further degradation of a water body

and may be revised prior to the end of each phase in accordance with §131.10 and 

131.20and submitted to EPA for approval;

(4) Establish the time periods for each restoration phase that will result in 

maximum feasible progress toward the highest attainable use and the designated use

identified in paragraph (g)(2) of this section, except that the sum of such time periods 

shall not exceed twenty years from the initial date of establishment of the restoration 

WQS under this section; (5) Specify the spatial extent of applicability for all affected 

waters; 

(6) Meet the requirements of §§131.10 and 131.20; and 

(7) Include, in its State water quality standards, a specific provision that if the 

interim restoration designated uses and criteria established under paragraph (g)(3) of this 

section are not met during any phased time period established under paragraph (4) of this 

section, the restoration WQS will no longer be applicable and the designated use and 

criteria identified in paragraph (g)(2) of this section will become applicable immediately.

(8) Provide that waters for which a restoration water quality standard is adopted 

will be recognized as impaired for the purposes of listing impaired waters under section 

303(d) of the CWA until the use designated identified in paragraph (2) of this section is 

attained.