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HIGHLIGHTED EDITS MADE PURSUANT TO OMB COMMENT

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; 

Supplemental Notice of Data Availability and Request for Comment

AGENCY: Environmental Protection Agency (EPA).

ACTION: Supplemental Notice of Data Availability and Request for Comment.

SUMMARY: This action is a supplemental notice of data availability and a request for 

comment related to EPA’s January 26, 2010 notice of proposed rulemaking (NPRM), 

proposing numeric nutrient water quality criteria to protect aquatic life in lakes and 

flowing waters within the State of Florida. In the January 2010 NPRM, EPA proposed to 

classify Florida’s streams into four regions (referred to in the proposed rule as “Nutrient 

Watershed Regions”) for application of total nitrogen (TN) and total phosphorus (TP) 

criteria. Streams within each of these regions (Panhandle, Bone Valley, Peninsula and 

North Central) reflect similar geographical characteristics including phosphorus-rich 

soils, nutrient concentrations and nutrient ratios. In this notice, EPA is requesting 

comment on revised stream region boundaries based on additional information about 

watershed delineations and phosphorus-rich geological formations in Florida. Based on 

comments and additional information, this revised regionalization approach would result 

in five Nutrient Watershed Regions for Florida’s streams and a clarification of certain 

watershed boundaries for the Bone Valley and Peninsula regions. EPA is also requesting 
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comment on basing the TN and TP criteria for the nutrient watershed regions on a 

combination of the 75th and 90th percentile values (depending on regions) of the 

benchmark sites outlined in the alternate approach at proposal. EPA is continuing to 

consider the primary approach proposed in January 2010 to use the 75th percentile of sites 

with healthy biological condition as measured by the Stream Condition Index (SCI). The

January 2010 proposal also proposed application of the Vollenweider equation to ensure 

that nutrient criteria in streams are protective of downstream lakes and requested 

comment on alternative approaches such as the BATHTUB model and whether there 

should be an allowance for use of other models that are demonstrated to be protective and 

scientifically defensible. Today’s notice also requests comment on using the BATHTUB 

model in place of the Vollenweider equation for deriving both TP and TN criteria to 

protect downstream lakes, allowing the use of alternative models under certain 

circumstances, and providing for an alternative approach to protect downstream lakes 

when limited data are available that would use the lake criteria themselves as criteria for 

upstream waters flowing into the lake. EPA is seeking comment on alternative stream 

regionalization approaches, use of the benchmark dataset to derive criteria, and derivation 

of lake downstream protection values discussed in more detail below, and will consider 

the comments received before finalizing the proposed rule, “Water Quality Standards for 

the State of Florida’s Lakes and Flowing Waters.” This supplemental notice focuses 

solely on the delineation of stream nutrient regions, resulting criteria associated with two 

approaches (EPA’s SCI-based approach and the alternative benchmark distribution 

approach), and protection of downstream lakes in Florida. EPA is not soliciting comment 

on any other provisions of the January 2010 proposal.
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DATES: Comments must be received on or before [insert date], 30 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 
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protected through www.regulations.gov or e-mail. The www.regulations.gov Web site is 

an “anonymous access” system, which means EPA will not know your identity or contact 

information unless you provide it in the body of your comment. If you send an e-mail 

comment directly to EPA without going through www.regulations.gov your e-mail 

address will be automatically captured and included as part of the comment that is placed 

in the public docket and made available on the Internet. If you submit an electronic 

comment, EPA recommends that you include your name and other contact information in 

the body of your comment and with any disk or CD-ROM you submit. If EPA cannot 

read your comment due to technical difficulties and cannot contact you for clarification, 

EPA may not be able to consider your comment. Electronic files should avoid the use of 

special characters, any form of encryption, and be free of any defects or viruses. For 

additional information about EPA’s public docket visit the EPA Docket Center homepage 

at http://www.epa.gov/epahome/dockets.htm. 

Docket: All documents in the docket are listed in the www.regulations.gov index. 

Although listed in the index, some information is not publicly available, e.g., CBI or 

other information whose disclosure is restricted by statute. Certain other material, such as 

copyrighted material, will be publicly available only in hard copy. Publicly available 

docket materials are available either electronically in www.regulations.gov or in hard 

copy at a docket facility. The Office of Water (OW) Docket Center is open from 8:30 

until 4:30 p.m., Monday through Friday, excluding legal holidays. The OW Docket 

Center telephone number is (202) 566-2426, and the Docket address is OW Docket, EPA 

West, Room 3334, 1301 Constitution Avenue, NW, Washington, DC 20004. The Public 
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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. 

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 

I. General Information

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

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

II. Background

III. Supplemental Information on Numeric Nutrient Criteria for the State of 

Florida’s Lakes and Flowing Waters

A. Stream Regionalization and Alternative Approaches to Stream Criteria 

Derivation

B. Downstream Protection of Lakes

I. General Information
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A. What Should I Consider as I Prepare My Comments for EPA?

 1. Submitting CBI. Do not submit this information to EPA through 

http://www.regulations.gov or e-mail. Clearly mark the part or all of the information that 

you claim to be CBI. For CBI information in a disk or CD-ROM that you mail to EPA, 

mark the outside of the disk or CD-ROM as CBI and then identify electronically within 

the disk or CD-ROM the specific information that is claimed as CBI. In addition to one 

complete version of the comment that includes information claimed as CBI, a copy of the 

comment that does not contain the information claimed as CBI must be submitted for 

inclusion in the public docket. Information so marked will not be disclosed except in 

accordance with procedures set forth in 40 CFR part 2.

 2. Tips for Preparing Your Comments. When submitting comments, remember to:

1. Identify the rulemaking by docket number and other identifying information 

(subject heading, Federal Register date, and page number).

2. Follow directions--The agency may ask you to respond to specific questions or to 

address a particular issue. 

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. Provide specific examples to illustrate your concerns, and suggest alternatives.

6. Make sure to submit your comments by the comment period deadline identified.

B. How Can I Get Copies of This Document and Other Related Information?
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 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.B.1.
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II. Background

On January 26, 2010, EPA proposed “Water Quality Standards for the State of 

Florida’s Lakes and Flowing Waters” (75 FR 4173). EPA conducted 13 public hearing 

sessions in six cities in Florida and held a 90-day public comment period as part of the 

proposed rule generating over 22,000 public comments. EPA is reviewing and 

considering these comments in preparation of the final rule, which is scheduled to be 

signed by the EPA Administrator on October 15, 2010. 

Today’s notice reflects a review of comments and new information received by

the Agency as part of the public comment process, and requests further comment on 

possible revisions, additional options, and new information related to specific approaches 

and issues identified in the January 26, 2010 proposal. EPA is only seeking comment on 

the items presented in this supplemental notice. EPA is not soliciting comment on any

other provisions of the January 2010 proposed rule.

III. Supplemental Information on Numeric Nutrient Criteria for the State of 

Florida’s Lakes and Flowing Waters

A. Stream Regionalization and Alternative Approaches to Stream Criteria Derivation

EPA proposed classification of Florida’s streams north of Lake Okeechobee by

separating watersheds with substantially different stream molar ratios of TN to TP 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 
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downstream water quality. EPA requested public comment on the stream regionalization 

approach as well as factoring in geological influences from phosphorus-rich soils when 

classifying stream regions (75 FR 4195-96). EPA received public comments and 

information that suggested refining the proposed stream regions to account for natural 

variability in soil nitrogen and phosphorus as well as clarifying the boundaries of the 

proposed stream regions. 

Today, EPA is requesting comment on a revised approach to certain stream 

regions suggested by FDEP and other commenters. More specifically, EPA is considering 

additional information on the influence of phosphorus-rich soils and geology in Florida 

(associated with the Hawthorne Group) for areas in the northern Panhandle region. Based 

on comments and information received, the Agency is also considering further 

refinements to the regional boundaries separating the Peninsula region from the West 

Central region (referred to in the proposed rule as “Bone Valley”).

Based on geological information1, EPA is considering dividing the proposed 

Panhandle region into a Panhandle West (less phosphorus-rich) and Panhandle East 

(more phosphorus-rich) region. In drawing the boundary between the two regions, EPA is 

continuing to rely on the watershed approach described in the proposed rule and is 

considering using the eastern boundary of the Apalachicola River watershed as the 

dividing line between the two regions. EPA believes that dividing the Panhandle region 

in this manner may more accurately represent the natural influences on stream TP 

 

1

Scott, T.S., 1988, The lithostratigraphy of the Hawthorn Group (Miocene) of Florida: Florida

Geological Survey Bulletin No. 59; 148 p.; Scott, T.S., K.M. Campbell, F.R. Rupert, J.D. Arthur, T.M. 

Missimer, J.M. Lloyd, J.W. Yon and J.G. Duncan, 2001, Geologic map of the state of Florida: Florida 

Geological Survey Map Series 146; Scott, T.S., 2001, Text to accompany the geologic map of Florida: 

Florida Geological Survey Open-File Report 80; 29 p.
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concentrations and provide finer spatial resolution with respect to TP criteria; however, 

we request comment on this conclusion.

EPA is considering these adjustments in the Panhandle region to account for 

natural geological influences on stream phosphorus concentrations. EPA considered 

different approaches to classifying Florida’s streams for application of TN criteria, such 

as the four Nutrient Watershed Regions discussed in the January 2010 proposal and two 

regions as originally suggested by FDEP. However, differences in the resulting TN 

criteria based on these stream classification schemes were minor and the approaches were 

comparable. Therefore, to assure consistency and clarity in applicability decisions and 

implementation, EPA is also considering using the same revised Panhandle delineation 

for stream TN criteria as well as the TP criteria. This consistency in regionalization for 

TN and TP provides clarity to the public on which stream criteria apply at any given 

location, which can help facilitate the State’s implementation of both stream TN and TP 

criteria.

EPA also reexamined the watershed delineations of the West Central and 

Peninsula regions based on comments and information from FDEP and others. As a result 

of this review, EPA has gained greater knowledge of the watershed boundaries and is 

considering refining the boundary delineations accordingly. The result for the West 

Central region would be a modified western boundary that shifts from Florida’s west 

coast shoreline inland to the east as explained in more detail below. EPA believes that 

these possible adjustments to the West Central and Peninsula stream region boundaries 

more accurately reflect the watershed boundaries; however, we request comment on this 

conclusion.
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As a result of the new information and possible adjustments to the proposed 

stream regionalization approach that are outlined above, EPA is considering five Nutrient 

Watershed Regions for deriving TP and TN criteria for streams. The five Nutrient 

Watershed Regions would include a Panhandle West region encompassing Perdido Bay

Watershed, Pensacola Bay Watershed, Choctawhatchee Bay Watershed, St. Andrew Bay

Watershed, and Apalachicola Bay Watershed. It would also include a Panhandle East 

region encompassing Apalachee Bay Watershed, and Econfina/Steinhatchee Coastal 

Drainage Area. The West Central (Bone Valley) and Peninsula regions would be revised 

slightly to more accurately reflect watershed boundaries (e.g., the Sarasota Bay and 

Charlotte Harbor Watersheds would move from the West Central (Bone Valley) to the 

Peninsula region). The proposed North Central region encompassing the Suwannee River 

Watershed would remain unchanged.

EPA is providing the following information in the docket to illustrate and 

delineate the revised Nutrient Watershed Regions under consideration: 1. Map of revised 

TN, TP regions, 2. Map of Hawthorne group overlaid on revised Panhandle regions, 3. 

GIS shapefile of revised TN, TP regions, 4. Florida geological information on the 

Hawthorne group (see footnote 1).

EPA is also providing additional information in this notice and in the docket on 

the TN and TP criteria that are based on the revised Nutrient Watershed Regions under 

consideration. Using EPA’s previously proposed approach (75th percentile) and the 

revised stream regions discussed in this notice, the TN and TP criteria would be:

Panhandle West – 0.84 mg/L and 0.03 mg/L, respectively; Panhandle East – 0.77 mg/L

and 0.10 mg/L, respectively; North Central – 1.48 mg/L and 0.36 mg/L, respectively;
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West Central – 1.80 mg/L and 0.73 mg/L, respectively; and Peninsula – 1.20 mg/L and 

0.10 mg/L, respectively. To illustrate the derivation of stream criteria based on the 

revised regions, EPA has re-organized the same nutrient dataset provided in the proposed 

rule and is making it available to the public in the docket for this notice. These data were 

organized on the basis of site averages to derive the proposed criteria outlined above. 

At proposal, EPA also requested comment on the benchmark distribution 

approach. In response to comments, the Agency is considering using a combination of the 

75

th and 90th percentile values (depending on regions) based on benchmark sites, with 

additional data quality screens applied, to establish criteria. EPA is considering the 90th

percentile for all regions except the West Central, where the Agency is considering the 

75th percentile due to less data available. Using the benchmark distribution approach and 

the revised stream regions discussed in this notice, the TN and TP criteria would be: 

Panhandle West – 0.62 mg/L and 0.04 mg/L, respectively; Panhandle East – 0.97 mg/L

and 0.11 mg/L, respectively; North Central – 1.90 mg/L and 0.35 mg/L, respectively;

West Central – 1.30 mg/L and 0.35 mg/L, respectively; and Peninsula – 1.67 mg/L and 

0.11 mg/L, respectively. Included in the docket for today’s notice is the benchmark 

dataset presented at proposal with the additional quality assurance screens applied, that 

was used to calculate these values. The stream criteria using this approach are calculated 

on the basis of Waterbody Identifiers (WBIDs) and the derivation is outlined in more 

detail in the docket for today’s notice. EPA requests comment on this approach.

EPA is soliciting comment on the refined regionalization approach and criteria 

described in this supplemental notice. The Agency is specifically requesting comment on 

revised stream criteria using EPA’s previously proposed approach (applied to the revised 
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regions) as outlined above as well as alternative stream criteria based on utilization of the 

benchmark distribution approach applied to the revised regions, also outlined above. EPA 

will evaluate all data and information submitted by the close of the public comment 

period for this supplemental notice with regard to regionalization and criteria derivation 

for Florida’s streams. 

B. Downstream Protection of Lakes

In its January 2010 FRN, EPA proposed a phosphorus loading model equation 

first developed by Vollenweider2to relate a lake TP concentration criterion to the 

concentration necessary in incoming streams to support the lake criterion. EPA proposed 

to apply the equation’s resulting stream concentration as the applicable criterion for all 

stream segments upstream of the lake if those concentrations were more stringent than 

the otherwise applicable instream criteria for the stream segments. EPA mathematically

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

values intended to serve as protective criteria necessary to assure attainment and 

maintenance of the lake numeric nutrient criteria also included in the proposal (75 FR 

4198). 

The proposed Vollenweider model equation requires input of two lake-specific 

characteristics: the fraction of inflow due to stream flow and the hydraulic retention time. 

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

alternative preset values for percent contribution from stream flow and hydraulic 

retention time that could be used in those instances. EPA’s January 2010 proposed rule 

discussed the flexibility for the State to use site-specific inputs to the Vollenweider 

 

2 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.
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equation for these two parameters, as long as the State determines that they are 

appropriate and documents the site-specific values. 

EPA requested comment on several technical aspects of this equation and its 

application. In addition, EPA requested comment on the potential to develop a corollary 

approach for nitrogen. Several commenters suggested the need for protective TN values 

to protect downstream lakes that are nitrogen-limited (such as many of the lakes in the 

phosphorus-rich areas of the State). EPA recognized that more specific information may

be readily available for individual lakes that could allow the use of alternative approaches 

such as the BATHTUB model3and requested comment in the January 2010 proposal on 

the availability and application of this model. EPA also requested 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 current and readily 

available data.

EPA received many comments on this proposed approach for protection of lakes 

downstream of rivers and streams. Some felt that that the Vollenweider equation was 

overly simplistic to represent all lakes in Florida and that it does not include the 

necessary factors to account for physical, hydrologic, chemical, and biological processes 

necessary to determine protective criteria. Comments included a recommendation to use 

models that can better represent site-specific conditions, such as BATHTUB. 

 

3 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 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. 
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BATHTUB is designed to apply empirical eutrophication models to 

morphometrically complex lakes and reservoirs. The program performs steady-state

water and nutrient balance calculations, uses spatially segmented hydraulic networks, and

accounts for advective and diffusive transport of nutrients. BATHTUB predicts nutrientrelated water quality conditions such as total phosphorus, total nitrogen and chlorophyll a

concentrations, transparency, and hypolimnetic oxygen depletion rates. The model can 

apply to a variety of lake sizes, shapes and transport characteristics. A high degree of 

flexibility is available for specifying model segments as well as multiple influent streams. 

Because water quality conditions are calculated using empirically-derived relationships, 

BATHTUB inherently accounts for internal loading of phosphorus from bottom 

sediments. Additional technical references are available that describe the model and its 

applications.4

For the provision of EPA’s proposed rule for deriving criteria for protection of 

downstream lakes (§ 131.43(c)(2)(ii)), EPA is considering requiring the use of 

BATHTUB rather than a loading model equation based on Vollenweider. The rule would 

therefore require that the criteria for protection of downstream lakes would be the more

stringent of the instream TP and TN criteria value or the concentration of TP and TN 

derived from application of BATHTUB. The resulting criteria using BATHTUB could 

be either more or less stringent than the criteria derived using Vollenweider, depending 

on site-specific lake factors. EPA believes BATHTUB may be more appropriate for 

 

4 Walker, W.W., 1981. Empirical Methods for Predicting Eutrophication in Impoundments; Report 1, 

Phase I: Data Base Development. Technical Report E–81–9, U.S. Army Engineer Waterways Experiment 

Station, Vicksburg, MS.; Walker, W.W., 1982. Empirical Methods for Predicting Eutrophication in 

Impoundments; Report 2, Phase II: Model Testing. Technical Report E–81–9, U.S. Army Engineer 

Waterways Experiment Station, Vicksburg, MS.; Walker, W.W., 1999. Simplified Procedures for 

Eutrophication Assessment and Prediction: User Manual; Instruction Report W-96-2, U.S. Army Corps of 

Engineers Waterways Experiment Station, Vicksburg, M.S.
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downstream protection value calculations than Vollenweider because BATHTUB has the 

capability to represent a greater number of site-specific variables, which may influence 

nutrient responses. In addition, BATHTUB can estimate TN concentrations. As noted 

above, a number of commenters observed that a limitation in EPA’s original proposal 

was that it only addressed TP.

EPA is also considering additional rule language that would specifically authorize 

FDEP or EPA to use a model other than BATHTUB when either determines that it would 

be appropriate to use another scientifically defensible technical model or approach that 

demonstrates protection of downstream lakes. While BATHTUB is a peer reviewed and 

versatile model, there are other models that, when appropriately calibrated and applied,

can offer additional capability to address more complex situations and address an even 

greater degree of site-specificity. 

One example of an alternative model that FDEP or EPA might consider using for 

particularly complex site-specific conditions is the Water Quality Analysis Simulation 

Program (WASP) model. This model allows users to conduct detailed simulations of

water quality responses to natural and manmade pollutant inputs. WASP is a dynamic 

compartment-modeling program for aquatic systems, including both the water column 

and the underlying benthos. WASP allows the user to simulate systems in 1, 2, or 3 

dimensions, and a variety of pollutant types. The model can represent time varying 

processes of advection, dispersion, point and diffuse mass loading, and boundary

exchange. WASP also can be linked with hydrodynamic and sediment transport models 

that can provide flows, depths, velocities, temperature, salinity and sediment fluxes. 
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Additional technical information may be found at 

http://www.epa.gov/athens/wwqtsc/html/wasp.html.

EPA is considering recommending BATHTUB as the method for calculating the 

TN and TP downstream protective values in streams that flow into lakes because of its 

ability to incorporate site-specific factors in estimates, its use of data that may be readily

available, and its ease of use and rapid processing time. BATHTUB has been used to 

model nutrients in lakes and reservoirs throughout the United States. BATHTUB allows 

for greater site-specificity than the Vollenweider approach, and input of more local 

information to calculate concentrations of both nitrogen and phosphorus in streams that 

assure downstream protection of lakes. In certain circumstances, a more complex model 

such as WASP may be appropriate, and EPA is considering and requesting comment on 

adding specific provisions to allow either the Agency or FDEP to use an alternative 

model such as WASP where greater spatial or temporal detail in model output is called 

for, or where water quality considerations that fall outside the scope of BATHTUB are to 

be explicitly considered. 

EPA is also requesting comment on including a provision in this section of the 

rule that would provide that if data are not readily available to derive a TN or TP 

downstream protection value using BATHTUB or another scientifically defensible 

model, the lake criteria values for TN and TP would be used as the downstream 

protection values where they are more stringent than the instream values. EPA believes 

that this approach is protective because the allowable concentration of nutrients entering 

the lake would be equal to criteria that are protective of the lake water itself; however, 

this approach may result in the application of more stringent criteria in the streams 
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entering the lake than would be calculated using BATHTUB or another scientifically

defensible model if site-specific data were available. 

EPA is soliciting comment on the approaches to protect downstream lakes

described in this supplemental notice. EPA will evaluate all data and information 

submitted by the close of the public comment period for this supplemental notice with 

regard to nutrient criteria to protect downstream lakes in Florida. 

Dated: July 29, 2010.

Peter S. Silva,

Assistant Administrator for Water.