[Federal Register Volume 75, Number 148 (Tuesday, August 3, 2010)]
[Proposed Rules]
[Pages 45579-45583]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2010-19140]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 131

[EPA-HQ-OW-2009-0596; FRL-9185-2]
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.

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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 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.

DATES: Comments must be received on or before September 2, 2010.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OW-
2009-0596, by one of the following methods:
    1. http://www.regulations.gov: Follow the on-line instructions for 
submitting comments.
    2. E-mail: [email protected].

[[Page 45580]]

    3. Mail to: Water Docket, U.S. Environmental Protection Agency, 
Mail code: 2822T, 1200 Pennsylvania Avenue, NW., Washington, DC 20460, 
Attention: Docket ID No. EPA-HQ-OW-2009-0596.
    4. Hand Delivery: EPA Docket Center, EPA West Room 3334, 1301 
Constitution Avenue, NW., Washington, DC 20004, Attention Docket ID No. 
EPA-HQ-OW-2009-0596. Such deliveries are only accepted during the 
Docket's normal hours of operation, and special arrangements should be 
made for deliveries of boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OW-2009-
0596. EPA's policy is that all comments received will be included in 
the public docket without change and may be made available online at 
http://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 http://www.regulations.gov or e-mail. The http://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 http://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 http://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 http://www.regulations.gov or in hard copy at a docket facility. 
The Office of Water (OW) Docket Center is open from 8:30 a.m. 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.

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; e-mail address: [email protected].

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

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?

    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.

[[Page 45581]]

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 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 information,\1\ 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 concentrations and provide finer 
spatial resolution with respect to TP criteria; however, we request 
comment on this conclusion.
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    \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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    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.
    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; 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

[[Page 45582]]

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 75th 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 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 Vollenweider \2\ to 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).
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    \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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    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 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 model 
\3\ and 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.
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    \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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    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.
    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 nutrient-related 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\
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    \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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    For the provision of EPA's proposed rule for deriving criteria for 
protection of downstream lakes (Sec.  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

[[Page 45583]]

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 
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. 
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 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.
[FR Doc. 2010-19140 Filed 7-30-10; 4:15 pm]
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