Eagan Lakes - Minnesota Pollution Control Agency

Eagan Lakes - Minnesota Pollution Control Agency

Wenck File #2538-02 June 2015 Eagan Neighborhood Lakes TMDL and Management Plans Report Prepared for: CITY OF EAGAN MINNESOTA POLLUTION CONTROL AGE...

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Wenck File #2538-02 June 2015

Eagan Neighborhood Lakes TMDL and Management Plans Report

Prepared for:

CITY OF EAGAN MINNESOTA POLLUTION CONTROL AGENCY

Prepared by:

WENCK ASSOCIATES, INC.

1800 Pioneer Creek Center P.O. Box 249 Maple Plain, Minnesota 55359-0249 (763) 479-4200

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ACKNOWLEDGMENT From April 29, 2012, to April 28, 2015, the Neighborhood Lakes Management Plans Clean Water Partnership project was provided grant support through Minnesota Grant Agreement #43429.

i

Table of Contents ACKNOWLEDGMENT ...............................................................................................................i EXECUTIVE SUMMARY ........................................................................................................ viii 1.0

INTRODUCTION ........................................................................................................1-1 1.1 1.2 1.3 1.4 1.5 1.6 1.7

2.0

WATERSHED AND LAKE CHARACTERIZATION ............................................................. 2-1 2.1 2.2

2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10

3.0

Purpose ............................................................................................................... 1-1 Water Quality Characterization Goals ................................................................ 1-2 Total Maximum Daily Loads ................................................................................ 1-2 Impairment Summary ......................................................................................... 1-2 Beneficial Use Classifications .............................................................................. 1-3 Water Quality Standards For Designated Uses................................................... 1-4 Determination of Impairment ............................................................................ 1-5

Overview ............................................................................................................. 2-1 History of the Lakes and their Watersheds ........................................................ 2-1 2.2.1 Fitz, Holz, LP-30, and Hay Lakes .......................................................... 2-1 2.2.2 Quigley and Carlson Lakes................................................................... 2-1 2.2.3 Cliff and Bald Lakes ............................................................................. 2-2 2.2.4 Bur Oaks and North Lakes ................................................................... 2-2 2.2.5 O’Leary and LeMay Lakes .................................................................... 2-7 Land Use............................................................................................................ 2-10 Soils and Geology .............................................................................................. 2-12 Groundwater..................................................................................................... 2-12 Climatological Summary ................................................................................... 2-13 Lake Morphometry ........................................................................................... 2-14 Water Quality.................................................................................................... 2-15 Shallow Lake Ecology ........................................................................................ 2-16 2.9.1 General Description .......................................................................... 2-16 Fisheries and Aquatic Vegetation ..................................................................... 2-17 2.10.1 Fisheries ............................................................................................ 2-17 2.10.2 Submerged Aquatic Vegetation ........................................................ 2-18

PHOSPHORUS SOURCE ASSESSMENT.........................................................................3-1 3.1 3.2

Nutrients in PROPOSED Impaired and Protection Lakes .................................... 3-1 Nutrient Sources and Lake Response ................................................................. 3-1 3.2.1 Watershed PONDNET Models ............................................................. 3-1 3.2.2 Upstream Lakes ................................................................................... 3-5 3.2.3 Atmospheric Deposition...................................................................... 3-5 3.2.4 Internal Loading .................................................................................. 3-5 3.2.5 BATHTUB Model (Lake Response)....................................................... 3-6 i

4.0

NUTRIENT BUDGETS AND TMDL ALLOCATIONS.......................................................... 4-1 4.1

4.2 4.3 5.0

IMPLEMENTATION PLAN...........................................................................................5-1 5.1 5.2 5.3 5.4

5.5 5.6 5.7

6.0

6.4

Introduction ........................................................................................................ 6-1 Regulatory Approaches....................................................................................... 6-1 Local Management ............................................................................................. 6-2 6.3.1 Local Comprehensive Water Management Plans ............................... 6-2 6.3.2 Watershed Districts ............................................................................. 6-3 Monitoring .......................................................................................................... 6-3

PUBLIC PARTICIPATION .............................................................................................7-1 7.1 7.2

8.0

Management Activity Selection .......................................................................... 5-1 Adaptive Management ....................................................................................... 5-1 Implementation Plan Summary .......................................................................... 5-2 5.3.1 Watershed Nutrient Management...................................................... 5-2 In-Lake Management ........................................................................................ 5-14 5.4.1 Internal Nutrient Load Control .......................................................... 5-14 5.4.2 Fisheries Management and Monitoring............................................ 5-16 5.4.3 Aquatic Vegetation Management and Monitoring ........................... 5-19 5.4.4 Assess and Manage Filamentous Algae ............................................ 5-19 Education and Outreach ................................................................................... 5-22 Water Quality Monitoring ................................................................................ 5-22 Watershed BMP Descriptions ........................................................................... 5-22 5.7.1 LeMay and O’Leary Lakes .................................................................. 5-22 5.7.2 Bald Lake ........................................................................................... 5-30 5.7.3 Bur Oaks and North Lakes ................................................................. 5-33 5.7.4 Carlson Lake and Quigley Lake .......................................................... 5-37 5.7.5 Cliff Lake Watershed Nutrient Management .................................... 5-44 5.7.6 Fitz Lake, Holz Lake, Hay Lake, and LP-30 Watershed Nutrient Management..................................................................................................... 5-47

REASONABLE ASSURANCE.........................................................................................6-1 6.1 6.2 6.3

7.0

TMDL Methodology ............................................................................................ 4-1 4.1.1 Load Allocation Methodology ............................................................. 4-1 4.1.2 Wasteload Allocation Methodology ................................................... 4-2 4.1.3 Margin of Safety .................................................................................. 4-4 4.1.4 Lake Response Variables ..................................................................... 4-5 4.1.5 Seasonal Variation............................................................................... 4-5 4.1.6 Impact of Growth on Allocations ........................................................ 4-5 TMDL Summary................................................................................................... 4-7 Protection Lakes.................................................................................................. 4-9 4.3.1 Nutrient Loading Summary ................................................................. 4-9

Public Participation Process ................................................................................ 7-1 PUBLIC Meetings ................................................................................................. 7-1

REFERENCES .............................................................................................................8-1 ii

9.0

GLOSSARY ................................................................................................................9-1

TABLES Table 1.1. Proposed lake impairments addressed in this TMDL. .................................................. 1-3 Table 1.2. Lakes assessed for protection in this study.................................................................. 1-3 Table 1.3. Numeric standards for lakes in the North Central Hardwood Forest Ecoregion. ........ 1-4 Table 1.4. Lake impairment status for the 12 lakes in this study. ................................................ 1-5 Table 2.1. Land use percentage by type of use........................................................................... 2-12 Table 2.2 Lake morphometry for all lakes in the study area. ..................................................... 2-15 Table 2.3. Shallow and deep lake growing season averages for water quality parameters....... 2-16 Table 2.4. Fish and vegetation data for Eagan Lake. .................................................................. 2-19 Table 3.1. Sediment release rates (aerobic and anaerobic), anoxic factors, and annual internal loads for each neighborhood lake. ..................................................................... 3-6 Table 4.1. Potential non-permitted sources of phosphorus. ........................................................ 4-2 Table 4.2. Potential permitted sources of phosphorus. ............................................................... 4-3 Table 4.3. Permitted MS4s in each TMDL lakeshed...................................................................... 4-3 Table 4.4. TMDL allocations for Carlson Lake (Lake ID: 19-0066-00). .......................................... 4-7 Table 4.5. TMDL allocations for Fitz Lake (Lake ID: 19-0077-00). ................................................. 4-8 Table 4.6. TMDL allocations for Holz Lake (Lake ID: 19-0064-00). ............................................... 4-8 Table 4.7. TMDL allocations for LeMay Lake (Lake ID: 19-0055-00)............................................. 4-9 Table 4.8. Nutrient budgets and recommended reductions for Bald Lake (Lake ID: 19-006100). ................................................................................................................................. 4-10 Table 4.9. Nutrient budgets and recommended reductions for Bur Oaks Lake (Lake ID: 190259-00). ........................................................................................................................ 4-10 Table 4.10. Nutrient budgets and recommended reductions for Cliff Lake (Lake ID: 19-006800). ................................................................................................................................. 4-11 Table 4.11. Nutrient budgets and recommended reductions for Hay Lake (Lake ID: 19-006200). ................................................................................................................................. 4-11 Table 4.12. Nutrient budgets and recommended reductions for LP-30 (Lake ID: 19-0053-00). 4-12 Table 4.13. Nutrient budgets and recommended reductions for North Lake (Lake ID: 190136-00). ........................................................................................................................ 4-12 Table 4.14. Nutrient budgets and recommended reductions for O’Leary Lake (Lake ID: 190056-00). ........................................................................................................................ 4-13 Table 4.15. Nutrient budgets and recommended reductions for Quigley Lake (Lake ID: 190155-00). ........................................................................................................................ 4-13 Table 5.1. Capital projects to reduce TP loading to the Neighborhood Lakes.............................. 5-4 Table 5.2. Cost estimates for alum treatments in Bald, Bur Oaks, Fitz, Bald, and LP-30............ 5-15 Table 5.3. Lakes with potential internal load reduction. ............................................................ 5-15 Table 5.4. Fisheries management activities for the Neighborhood Lakes. ................................. 5-17 Table 5.5. Submerged aquatic vegetation management activities for the neighborhood lakes. .............................................................................................................................. 5-21 Table 5.6. Bald Lake residential rain garden program. ............................................................... 5-30 Table 5.7. Watershed LP-42 residential rain garden program.................................................... 5-41 Table 5.8. Watershed LP-44 Residential Rain garden Program. ................................................. 5-42 Table 5.9. Watershed LP-43 residential rain garden program.................................................... 5-44 Table 5.10. Watershed LP-31 Residential Rain garden Program. ............................................... 5-52

iii

FIGURES Figure 2.1. City of Eagan and Dakota County boundaries. ........................................................... 2-3 Figure 2.2. Southeast lakesheds and general flow direction. ....................................................... 2-4 Figure 2.3. Carlson and Quigley subwatersheds and general flow direction. .............................. 2-5 Figure 2.4. Cliff subwatersheds and general flow direction. ........................................................ 2-6 Figure 2.5. Cliff Lake outlet structure. .......................................................................................... 2-7 Figure 2.6. Bur Oaks and North lakes subwatersheds and general flow direction. ...................... 2-8 Figure 2.7. LeMay and O’Leary subwatersheds and general flow direction................................. 2-9 Figure 2.8. Land use within study watersheds............................................................................ 2-11 Figure 2.9. Annual and average precipitation recorded at the Minneapolis/St. Paul International Airport. ..................................................................................................... 2-14 Figure 3.1. Average annual water yield subdivided by subwatersheds in each lake watershed. ....................................................................................................................... 3-2 Figure 3.2. Annual watershed loads from watershed, internal, atmospheric, and upstream lake sources. .................................................................................................................... 3-3 Figure 3.3. Annual watershed loads from watershed, internal, atmospheric, and upstream lake sources. .................................................................................................................... 3-4 Figure 5.1. Adaptive management................................................................................................ 5-1 Figure 5.2. Potential LeMay Lake and O’Leary Lake projects. ...................................................... 5-8 Figure 5.3. Potential Bald Lake projects........................................................................................ 5-9 Figure 5.4. Potential Bur Oaks Lake and North Lake projects..................................................... 5-10 Figure 5.5. Potential Carlson Lake and Quigley Lake projects. ................................................... 5-11 Figure 5.6. Potential Cliff Lake projects. ..................................................................................... 5-12 Figure 5.7. Potential Fitz Lake, Holz Lake, Hay Lake, and LP-30 projects. .................................. 5-13 Figure 5.8. Basin improvement projects for DP-3....................................................................... 5-23 Figure 5.9. Basin improvement project for Basins DP-4A, DP-4B, DP-26. .................................. 5-24 Figure 5.10. Basin improvement project for Basin DP-4.2.......................................................... 5-25 Figure 5.11. Basin improvement project for Basin DP-2.3.......................................................... 5-26 Figure 5.12. Stormwater Reroute with Basin Project Alternative for Watershed DP-4A_2. ...... 5-27 Figure 5.13. Underground storage and filtration system with pervious pavement project alternative for Watershed DP-4A_2. ............................................................................. 5-27 Figure 5.14. Stormwater reroute with iron enhanced filtration basin project alternative for Watershed DP-2. ............................................................................................................ 5-29 Figure 5.15. Stormwater reroute with treatment by clarifier project alternative for Watershed DP-2. ............................................................................................................ 5-29 Figure 5.16. Neighborhood rain garden program and street sweeping programs for the Bald Lake neighborhoods....................................................................................................... 5-31 Figure 5.17. Stormwater irrigation reuse project for Watersheds JP-20.1 and JP-20.2. ............ 5-32 Figure 5.18. Basin improvement project for Basin JP-20.5. ........................................................ 5-33 Figure 5.19. Basin improvement projects for Basin GP-1.2. ....................................................... 5-34 Figure 5.20. Basin improvement project for Basin EP-2.4_2. ..................................................... 5-35 Figure 5.21. Basin improvement project for Basin EP-2.91. ....................................................... 5-36 Figure 5.22. Basin improvement project for Basin EP-2.92. ....................................................... 5-37 Figure 5.23. Stormwater reroute with an underground filtration system. ................................ 5-38 Figure 5.24. Stormwater reroute with underground and basin iron enhanced filtration system project alternatives for Watershed LP-53. ........................................................ 5-39 Figure 5.25. Basin improvement project for LP-70. .................................................................... 5-40

iv

Figure 5.26. Residential rain garden and street sweeping programs for the LP-42 neighborhoods. .............................................................................................................. 5-41 Figure 5.27. Neighborhood rain garden and street sweeping programs for the LP-44 neighborhoods. .............................................................................................................. 5-43 Figure 5.28. Neighborhood rain garden and street sweeping program for the LP-43 Watershed. .................................................................................................................... 5-44 Figure 5.29. Basin improvement projects for AP-42. .................................................................. 5-45 Figure 5.30. Basin improvement projects for AP-44. .................................................................. 5-46 Figure 5.31. Commercial area BMP projects for Watershed AP-42............................................ 5-47 Figure 5.32. Stormwater Reroute and Basin improvement projects for LP-26.3. ...................... 5-48 Figure 5.33. Basin improvement project for LP-26.4. ................................................................. 5-49 Figure 5.34. Basin improvement project for LP-26.4. ................................................................. 5-50 Figure 5.35. Residential BMPs and street sweeping program for the LP-28 Watershed. .......... 5-51 Figure 5.36. Neighborhood rain garden and street sweeping programs for the LP-31 Watershed. .................................................................................................................... 5-52

APPENDICES Appendix A: Appendix B: Appendix C: Appendix D: Appendix E: Appendix F: Appendix G: Appendix H: Appendix I:

Historical Aerial Photos Lake Bathymetry Lake Water Quality Data Aquatic Vegetation Data Fisheries Data PondNET Model Sediment Chemistry and Release Rates Lake Response Model Cost Analysis

v

EPA/MPCA Required Elements

Summary

TMDL Page Number

Location

City of Eagan in Minnesota

Section 2.1, p. 2-1

303(d) Listing Information

Four lake nutrient impairments See Table 1.1, p. 1-3.

Section 1.4, p. 1-3

Applicable Water Quality Standards/ Numeric Targets

See Section 1.6 Total phosphorus: Table 1.3 Chlorophyll-a: Table 1.3 Turbidity/Secchi depth: Table 1.3

Section 1.6, p. 1-4

See Section 4.2, Tables 4.4 – 4.7

Section 4.2, p. 4-7

Loading Capacity (expressed as daily load)

Wasteload Allocation

Load Allocation

Margin of Safety

Seasonal Variation

See Section 4.2, Tables 4.4 – 4.7 Wasteload allocations are presented for each of four lakes. See Section 4.2, Tables 4.4 – 4.7 Load allocations are presented for each of four lakes.

An explicit margin of safety (MOS) of 5% of the load has been set aside to account for any uncertainty in the lake response models. The 5% MOS was considered reasonable for all of the modeled lakes due to the quantity of watershed and in-lake monitoring data available.

Seasonal variation is accounted for through the use of annual loads and developing targets for the summer period, where the frequency and severity of nuisance algal growth will be the greatest.

Section 4.2, p. 4-7

Section 4.2, p. 4-7

Section 4.1.3, p. 4-4

Section 4.1.5, p. 4-4

vi

EPA/MPCA Required Elements

Summary

TMDL Page Number

The goals of the TMDL study are consistent with the objectives of the City of Eagan’s Water Quality and Wetland Management Plan, and the stakeholder process has generated commitment and support from affected local government units. Several sources of technical assistance and funding are available to execute the Implementation Plan.

Section 6.1, p. 6-1

Monitoring

This plan discusses two types of monitoring needed to assess progress in meeting water quality standards.

Section 6.4, p. 6-2

Implementation

This plan identifies water quality goals and projects needed to reach those goals. Implementation will be conducted using Adaptive Management, a cyclical feedback process that is repeated until the established goals are met.

Section 5.2, p. 5-1

Public Participation

The public was invited to participate during three public meetings.

Chapter 7.0, p. 7-1

Reasonable Assurance

vii

Executive Summary In 2014, the Minnesota Pollution Control Agency listed Carlson (MNDNR ID# 19-0066-00), Fitz (MNDNR ID# 19-0077-00), Holz (MNDNR ID# 19-0064-00), and LeMay (MNDNR ID# 19-0055-00) Lakes as impaired for aquatic recreation under Section 303(d) of the Clean Water Act. In addition to the impaired lakes, the City of Eagan requested that this report include management strategies for lakes that are not currently listed as impaired for aquatic recreation to ensure that lakes with high water resource value are protected. These unimpaired lakes include Bald (MNDNR ID# 19-0061-00), Bur Oaks (MNDNR ID# 190259-00), Cliff (MNDNR ID# 19-0068-00), Hay (MNDNR ID# 19-0062-00), LP-30 (MNDNR ID# 19-005300), North (MNDNR ID# 19-0136-00), O’Leary (MNDNR ID# 19-0056-00) and Quigley (MNDNR ID# 190155-00). The watersheds of these lakes fall primarily within the city’s boundaries, however, some watersheds do fall within the boundaries of Inver Grove Heights (LP-30 and Hay Lake) and Apple Valley (Cliff Lake). The land use within the impaired and protection lake watersheds primarily includes residential, industrial and commercial land use. The purpose of this report is to develop total maximum daily load allocations for lakes that were classified as impaired for aquatic recreation due to excessive nutrient loading. In addition to providing allocations for impaired lakes, watershed nutrient reduction strategies have been developed for protection lakes (lakes not currently listed as impaired). This study analyzed each subwatershed by developing refined water and phosphorus budgets, including internal loading, for lakes within the City of Eagan boundaries to identify implementation actions to improve and protect water quality. The water and phosphorus budgets include the development of lake response models for the impaired and protection lakes to refine our understanding of internal versus external loading and target reductions to meet water quality goals. The watershed management and TMDL study also investigates fish and plant communities in the lakes to develop an understanding of the health of the biological communities and how these conditions may affect water quality. This detailed modeling process ultimately led to the calculation of watershed and internal phosphorus load reduction goals. Overall load reductions for impaired lakes range from 22 to 54 percent reduction from current loading. Phosphorus reduction goals developed for each lake were supplemented with detailed phosphorus reduction strategies and implementation plans. This allows the City of Eagan to integrate water projects with land use planning and development objectives to accomplish water quality goals through efficient use of public funding. The plan includes watershed and internal phosphorus reduction projects with detailed cost estimates and phosphorus load reduction estimates to assist the city’s lake nutrient management process. These projects include stormwater basin improvements, tree boxes, rain gardens, iron enhanced sand filters, street sweeping, underground filtration systems, aquatic fish and plant control, and aluminum sulfate additions. The projects listed in the implementation plan, in addition to others developed by the city, were selected to maximize the likelihood of each impaired and protection lake meeting water quality standards in the future.

viii

1.0 Introduction 1.1

PURPOSE

Since the early 1990s, the City of Eagan (city) has engaged in intense and sustained management of its lakes and their watersheds in a comprehensive approach to improve water quality by reducing in-lake total phosphorus (TP) concentrations. The City focused extensive efforts in the mid- to late-1990s on Fish and Schwanz lakes, which are Eagan’s two highest priority lakes, through diagnostic/feasibility studies (City of Eagan, 1994 and 1992, respectively) and Clean Water Partnership (CWP) projects supported by MN Pollution Control Agency (MPCA) grants (Macbeth and Storland, 2002 and 2001, respectively). Recently, it finalized a 2007-2010 TMDL study of both lakes, also supported by a MPCA grant (City of Eagan, 2010). In 2012, the City prepared state-of-the-art water quality management plans for Eagan’s next highest priority lakes, Blackhawk and Thomas (Wenck 2012). This resource investigation and protection project is supported by a MPCA CWP grant and is cosponsored by the Gun Club Lake Watershed Management Organization which has since disbanded and been replaced by the Eagan-Inver Grove Heights Watershed Management Organization. There are two parts to this study. The first part develops TMDLs for four impaired lakes in the City of Eagan. Similar to a TMDL effort, the second part evaluates in-lake water quality, assesses TP loads, and proposes implementation plans to address needs in water bodies not designated as impaired. Ultimately, the project provides direction for implementing priority system improvement projects and activities to protect and improve these lakes, consistent with Eagan’s Water Quality & Wetland Management Plan (WQWMP; City of Eagan, 2007). The purpose of the plan is to develop proactive lake management plans for 12 lakes in Eagan that fulfill the following expectations: 1.

Satisfies TMDL study and report requirements for impaired listed lakes, including the development of allocations to achieve loads that would allow the lakes to meet established water quality standards. 2. Identifies protection activities for non-impaired lakes to maintain water quality and improve the overall ecological health of the lake 3. Articulates implementation elements to achieve any recommended phosphorus reductions. 4. Provides coherent strategies to improve the recreational suitability of the lakes that may be in addition to the phosphorus reductions called out in the protection plans or TMDLs above. Note that because this project was funded through the CWP program, it is fulfilling the specific objectives of that grant and is not intended to align with the required components of a Watershed Restoration and Protection Strategies (WRAPS) report, as outlined in Minn. Stat. 114D.26. This report does, however, emphasize implementation planning and therefore contains detailed plans to restore and protect the subject lakes.

1-1

1.2

WATER QUALITY CHARACTERIZATION GOALS

The water quality characterization goals of this project were: 1) quantify the maximum TP loadings that would still allow water quality standards to be met and 2) identify TP reduction strategies for source areas to restore or protect waters. 1.3

TOTAL MAXIMUM DAILY LOADS

Section 303(d) of the Clean Water Act establishes a directive for developing Total Maximum Daily Loads (TMDLs) to achieve Minnesota water quality standards established for designated uses of State water bodies. Under this directive, the State of Minnesota is recommending in its draft 2014 303(d) List (as of the preparation of this report) that TMDLs be prepared to address excess nutrients in 4 of the 12 lakes of this project. The goal of a TMDL study is to quantify the pollutant reductions needed to meet State water quality standards. This report presents the results of the study. A TMDL is defined as the maximum quantity of a pollutant that a water body can receive and continue to meet water quality standards for designated beneficial uses. Thus, a TMDL is simply the sum of point sources and nonpoint sources in a watershed. A TMDL can be represented in a simple equation as follows: TMDL = Σ Wasteload Allocation (WLA; Point Sources) + Σ Load Allocation (LA; nonpoint sources) + Margin of Safety (MOS) The Wasteload Allocation (WLA) is the sum of the loads from all point sources and the Load Allocation (LA) is the sum of the load from all nonpoint sources. The Margin of Safety (MOS) represents an allocation to account for variability in environmental data sets and uncertainty in the assessment of the system. Other factors that must be addressed in a TMDL include seasonal variation, future growth, critical conditions, and stakeholder participation. This TMDL report provides WLAs, LAs and MOS needed to achieve the state standard for each parameter in each of the lakes in this study proposed to be on the impaired waters list. 1.4

IMPAIRMENT SUMMARY

This report addresses four draft 2014 lake impairments in the City of Eagan. The MPCA’s projected schedule for TMDL completions, as indicated on Minnesota’s 303(d) impaired waters list (as noted in Table 1.1), implicitly reflects Minnesota’s priority ranking of this TMDL. Ranking criteria for scheduling TMDL projects include, but are not limited to: impairment impacts on public health and aquatic life; public value of the impaired water resource; likelihood of completing the TMDL in an expedient manner, including a strong base of existing data and restorability of the water body; technical capability and willingness locally to assist with the TMDL; and appropriate sequencing of TMDLs within a watershed or basin.

1-2

Table 1.1. Proposed lake impairments addressed in this TMDL. Lake ID

1

Name

19-0066

Carlson

19-0077

2

Fitz

1

2

19-0064

Holz

19-0055

LeMay

Year Listed

Priority

2014

2016

2014

2016

2014

2016

2014

2016

The state incorrectly refers to this lake as Quigley; a name change to Carlson is underway.

2

The state refers to these lakes as Unknown

The report also addresses eight lakes that are not considered impaired. These lakes were evaluated for protection (Table 1.2). Table 1.2. Lakes assessed for protection in this study.

1

Lake ID

Name

19-0061

Bald

19-0259

Bur Oaks

19-0068

Cliff

19-0062

Hay

19-0053

LP-30

19-0136

North

19-0056

O’Leary

19-0155

Quigley

1

1, 2

Determined to be a wetland and not a shallow lake.

2

The state incorrectly refers to this lake as Carlson; a name change to Quigley is underway.

1.5

BENEFICIAL USE CLASSIFICATIONS

This TMDL report addresses exceedances of the state standards for nutrients in four lakes in the City of Eagan. A discussion of beneficial water use classes in Minnesota and the standards for those classes is provided in order to define the regulatory context and explain the rationale behind the environmental result of the TMDL. All waters of Minnesota are assigned classes based on their suitability for the following beneficial uses (Minn. Rules Ch. 7050.0140 and 7050.0220): 1. 2. 3. 4. 5. 6. 7.

Domestic consumption Aquatic life and recreation Industrial consumption Agriculture and wildlife Aesthetic enjoyment and navigation Other uses Limited resources value

After each water body is assigned a beneficial use, they are also assigned a subcategory if applicable. So, for the aquatic life beneficial use, the life category that is targeted for protection is one of the classes below. This is important since each of these categories has different requirements to support a healthy

1-3

biological community. For example, cold water species such as trout are more sensitive to dissolved oxygen concentrations and therefore require higher minimum dissolved oxygen concentrations. A. B. C. D.

Cold water sport fish (trout waters), also protected for drinking water Cool and warm water sport fish, also protected for drinking water Cool and warm water sport fish, indigenous aquatic life, and wetlands, and Limited resource value waters

“2B” water is intended to protect cool and warm water fisheries, while“2C” water is intended to protect indigenous fish and associated aquatic communities, and a “3C” classification protects water for industrial use and cooling. All Class 2 surface waters are also protected for industrial, agricultural, aesthetics, navigation, and other uses (Classes 3, 4, 5, and 6, respectively). Minn. Rules Ch. 7050 contains general provisions, definitions of water use classes, specific standards of quality and purity for classified waters of the state, and the general and specific standards for point source dischargers to waters of the state. The designated beneficial use for Class 2 waters (the most protective use class in the project area) is as follows (Minn. Rules Ch. 7050.0140): Class 2 waters, aquatic life and recreation. Aquatic life includes all waters of the state which do or may support fish, other aquatic life, bathing, boating, or other recreational purposes, and where quality control is or may be necessary to protect aquatic or terrestrial life or their habitats, or the public health, safety, or welfare. All of the lakes in this report are “2B” waters. 1.6

WATER QUALITY STANDARDS FOR DESIGNATED USES

The criteria used for determining stream and lake impairments are outlined in the MPCA document Guidance Manual for Assessing the Quality of Minnesota Surface Waters for Determination of Impairment – 305(b) Report and 303(d) List, April 2014. The applicable water body classifications and water quality standards are specified in Minnesota Rules Chapter 7050. Minnesota Rules Chapter 7050.0470 lists water body classifications and Chapter 7050.0222 (subp. 5) lists applicable water quality standards for Minnesota water bodies. Under Minnesota Rules 7050.0150 and 7050.0222, Subp. 4, the lakes addressed in this study are within the North Central Hardwood Forest ecoregion, with numeric targets dependent on depth as listed in Table 1.3. Therefore, this TMDL presents load and wasteload allocations and estimated load reductions, assuming an end point of ≤60 mg/L and ≤40 mg/L total phosphorus for shallow lakes and deep lakes, respectively. Table 1.3. Numeric standards for lakes in the North Central Hardwood Forest Ecoregion.

1

Parameters Total Phosphorus (mg/L) Chlorophyll-a (mg/L) Secchi disk transparency (meters)

1

Shallow Lake Standard ≤60 ≤20 ≥1.0

Deep Lake Standard ≤40 ≤14 ≥1.4

Shallow lakes are defined as having a maximum depth of 15 feet or less, or with 80% or more of the lake area shallow enough to support emergent and submerged rooted aquatic plants (littoral zone).

1-4

In addition to meeting a respective phosphorus limit of 60 µg/L and 40 µg/L for shallow and deep lakes, chlorophyll-a and Secchi depth standards must also be met. In developing the lake nutrient standards for Minnesota lakes (Minn. Rule 7050), the MPCA evaluated data from a large cross-section of lakes within each of the state’s ecoregions (Heiskary and Wilson, 2005). Clear relationships were established between total phosphorus as the causal factor and chlorophyll-a and Secchi disk as the response variables. Based on these relationships it is expected that by meeting the phosphorus targets of 60 µg/L and 40 mg/ for shallow and deep lakes, the chlorophyll-a and Secchi standards will likewise be met. According to the WQWMP, the city’s goals for lakes are consistent with the NCHF standards. Thus, an Eagan lake does not meet its intended condition if the TP and either the chlorophyll-a or the Secchi depth standard is exceeded. 1.7

DETERMINATION OF IMPAIRMENT

The criteria used for determining impairments are outlined in the MPCA document Guidance Manual for Assessing the Quality of Minnesota Surface Waters for Determination of Impairment – 305(b) Report and 303(d) List, April 2014. The applicable water body classifications and water quality standards are specified in MR Chapter 7050. 0407 and MR 7050.2222 (5), respectively. As shown in Table 1.4, both Bald and Cliff lakes were categorized as having insufficient information to determine their impairment status at the time of their assessment. This was done because the lakes do not meet the total phosphorus portion of the standard, but do meet the chlorophyll-a and Secchi disk portions. The City opted to be proactive and reduce loading to meet the total phosphorus targets as a voluntary protection measure to better assure the lakes do not become impaired. A nutrient budget and targets to meet the State water quality standards for both of these lakes are included in this report. The targets are nonbinding until the point these lakes are assessed as impaired and a TMDL is required. Table 1.4. Lake impairment status for the 12 lakes in this study. 1

Lake

Lake ID

Type

Status

Bald

19-0061-00

Shallow

IF

Bur Oaks

19-0259-00

Shallow

FS

Carlson

19-0066-00

Deep

NS

Cliff

19-0068-00

Shallow

IF

Fitz

19-0077-00

Shallow

NS

Hay

19-0062-00

Shallow

FS

Holz

19-0064-00

Shallow

NS

LP-30

19-0053-00

Shallow

FS

LeMay

19-0055-00

Shallow

NS

North

19-0136-00

Shallow

FS

O’Leary

19-0056-00

Wetland

Determined to be a wetland.

Quigley

19-0155-00

Wetland

Determined to be a wetland.

1

NS-Not supporting; FS-Fully supporting; IF-Insufficient information

1-5

2.0 Watershed and Lake Characterization 2.1

OVERVIEW

All lakes in this study are completely or partially contained within the municipal boundaries of Eagan, MN (Figure 2.1). Fitz, LP-30, and Bur Oaks Lake have drainage areas that extend into neighboring Inver Grover Heights. Study lakes are considered relatively small (area <15 acres) when compared to lakes typically used for recreation in the State of Minnesota. Historical aerial photos of the lakes are included in Appendix A. 2.2

HISTORY OF THE LAKES AND THEIR WATERSHEDS

2.2.1

Fitz, Holz, LP-30, and Hay Lakes

Four lakes in the southeast area of the City of Eagan include Fitz, Holz, LP-30, and Hay (Figure 2.2). LP-30 receives some drainage from the City of Inver Grove Heights and ultimately drains to Hay Lake (total drainage area of 327 acres). The outlet of LP-30 drains through a 12-inch diameter pipe to a wetland before flowing into Hay Lake. The southern portion of the Hay Lake watershed includes two upstream lake watersheds (Fitz and Holz) that have a combined size of 318 acres. The Fitz Lake outlet is connected to a 12-inch storm sewer that drains directly to Holz Lake. Holz Lake drains to a small wetland through a 12-in storm sewer, which then drains directly to Hay Lake. This group of lakes drains stormwater runoff from approximately 808 acres to Thomas Lake which ultimately drains to the Minnesota River through Blackhawk Lake. Lake management plans were previously developed for Thomas and Blackhawk Lakes (Wenck 2012). 2.2.2

Quigley and Carlson Lakes

For purposes of applying water quality standards and making 303(d) assessments, in 2014 the MPCA determined Quigley to be a wetland rather than a shallow lake. Quigley and Carlson lakes also drain to Blackhawk Lake although Quigley Lake drains first to Carlson Lake. Carlson Lake is the only deep lake in this study and receives drainage from 664 acres. The names of these lakes may be confused because historically they have been locally called “Quigley Lake” for the shallow northeastern basin and “Carlson Lake” for the deep southwest basin. The State of Minnesota officially refers to these lakes oppositely: Carlson as the shallow basin and Quigley as the deep basin. This report follows the local naming convention for the lakes. An effort to officially change the names is underway. This watershed was divided into four subwatersheds to help characterize general flow patterns. The four sub-watersheds, Carlson-North, Carlson-South, Carlson-Direct, and Quigley-Direct, generally flow from east to west. The Quigley Lake watershed consists of only one direct subwatershed that drains by gravity directly to Carlson Lake. The Carlson-North subwatershed outlet flows directly to Carlson Lake, while the Carlson-South subwatershed outlet to Carlson Lake is controlled by the Oak Park Chase lift station (Figure 2.3). The outlet of Carlson Lake is controlled by the Carlson lift station (Figure 2.3). 2-1

2.2.3

Cliff and Bald Lakes

Cliff Lake is in the southwest part of the city and receives drainage from 619 acres. The lake is just west of Highway 35E while its drainage area is mostly east of Highway 35E. The general flow direction in the Cliff Lake watershed is from south to north with the Cliff-East and Cliff-South watersheds contributing 70% of the total discharge that reaches Cliff Lake. Prior to discharging, the Cliff-South, Cliff-West, and Cliff-East watersheds are routed to a MnDOT stormwater pond directly upstream of the lake (Figure 2.4). Cliff Lake has a unique outlet structure that acts as a skimmer with a higher overflow outlet above the normal outlet (Figure 2.5). The structure has clogged in the past, raising the overall water level of the lake. Additionally, corrugated metal piling was placed in front of the skimmer to prevent trash and debris from getting into the structure, raising the water level from one-half foot to a foot. This obstruction was removed in 2013, and water levels are expected to be fairly stable in the future. However, clogging by trash and debris may continue to cause some fluctuations in water elevations. Bald Lake has a relatively small watershed that covers 103 acres with no upstream lakes. For this study, the watershed has been split into three sub-watersheds, including Bald-Southeast, Bald-Northwest, and Bald-Direct areas. The general flow direction is from west to east with the largest water yield coming from Bald-Northwest (44%). 2.2.4

Bur Oaks and North Lakes

Bur Oaks and North lakes are in the northeastern part of the city that is characterized by commercial and industrial development. Bur Oaks Lake, consisting of two distinct shallow lobes separated by a small channel, drains into North Lake and eventually to the Minnesota River. The Bur Oaks Lake watershed covers approximately 944 acres and has three primary watersheds. The Bur Oaks-North watershed drains to the Highway 55 lift station that pumps stormwater directly to Bur Oaks Lake. The Bur OaksSouth watershed drains north through a heavily industrial area via gravity drainage directly to Bur Oaks Lake. The Bur Oaks Park lift station is located at the lake’s outlet and pumps stormwater to North Lake via a 12-inch sewer main (Figure 2.6). The North Lake watershed covers approximately 1,396 acres that includes the drainage area of the Bur Oaks Lake watershed. Of the annual water yield to North Lake, 55% is from the Bur Oaks watershed. The North Lake watershed has a relatively large direct-drainage area and two smaller upstream watersheds that have a relatively small water yield to North Lake.

2-2

Figure 2.1. City of Eagan and Dakota County boundaries.

2-3

Figure 2.2. Southeast lakesheds and general flow direction.

2-4

Figure 2.3. Carlson and Quigley subwatersheds and general flow direction.

2-5

Figure 2.4. Cliff subwatersheds and general flow direction.

2-6

Figure 2.5. Cliff Lake outlet structure. 2.2.5

O’Leary and LeMay Lakes

O’Leary and LeMay lakes are in the northwest part of the city, with Interstate 35E bisecting the LeMay Lake watershed. The LeMay Lake watershed is the largest watershed of this study, with an approximate area of 1,279 acres. It drains the relatively small O’Leary watershed that is upstream, and which supplies only 3% of its total annual water yield. The LeMay watershed is also the most complex of this study. The O’Leary watershed gravity drains to the LeMay-Southeast watershed, which flows north to the Yankee lift station (Figure 2.7). The Yankee lift station then pumps water to a series of MnDOT ponds located near the intersection of Yankee Doodle Road and Interstate 35E. The final MnDOT stormwater pond in the series flows directly to LeMay Lake through a 36-inch stormwater pipe. The Knox lift station located in the northern region of the LeMay-Northeast watershed pumps stormwater south into a large pond, which drains to the Lexington lift station. The Lexington lift station subsequently pumps water from the LeMay-Northeast subwatershed to a MnDOT pond, which then drains directly to LeMay Lake. O’Leary Lake drains approximately 51 acres to LeMay Lake, which is only a small portion of the LeMay Lake watershed (4%). LeMay Lake also receives stormwater from a large commercial and industrial area, including the Eagan Promenade Mall and a large industrial area to the north. For purposes of applying water quality standards and making 303(d) assessments, the MPCA has determined O’Leary to be a wetland rather than a shallow lake.

2-7

Figure 2.6. Bur Oaks and North lakes subwatersheds and general flow direction.

2-8

Figure 2.7. LeMay and O’Leary subwatersheds and general flow direction.

2-9

2.3

LAND USE

The City of Eagan provided land use information from its GIS parcel dataset, which was supplemented with Minnesota Department of Transportation (MnDOT) right-of-way (ROW) land use files. Watershed areas outside of the city were characterized using the 2010 Metropolitan Council land use coverage. Generally, land uses in the northern watersheds (LeMay, O’Leary, North, and Bur Oaks) and in the southern watersheds (Bald, Cliff, Carlson, Quigley, Hay, Holz, Fitz, and LP-30) are similar and shown in Figure 2.8. The land use in the southern lakes area is predominantly residential (>45%) with the remaining area comprised of open area (parks) and rights-of-way (Table 2.1). The Cliff Lake watershed has large areas of impervious surfaces with a section of Interstate 35E and a commercial area on the northwest side of the lake. The remaining lakes’ watersheds are mostly residential neighborhoods with a few parks. Land use in the northern watersheds is predominantly retail and industrial (25% to 49%) areas with the remaining area comprised of residential parcels. Other than Bald Lake, these watersheds are characterized by large areas of impervious surfaces including commercial parking areas, warehouses, and malls. Both Bur Oaks and North Lake receive drainage from highly impervious industrial areas of the city. LeMay Lake receives drainage from dense commercial areas in the eastern watershed and highly impervious industrial areas to the north. Bald Lake has the most lightly used land use, with a large area of its watershed in park lands.

2-10

Figure 2.8. Land use within study watersheds.

2-11

Table 2.1. Land use percentage by type of use.

1

Lake

Area (Acres)

Right of Way

Residential

Water

Open Area

Retail/ Industrial

Agricultural

Bald

103

13%

46%

11%

30%

0%

0%

Bur Oaks

944

15%

52%

3%

4%

25%

2%

Carlson

664

20%

64%

8%

8%

1%

0%

Cliff

619

25%

43%

5%

19%

7%

0%

Fitz

210

17%

60%

11%

10%

2%

0%

Hay

809

15%

51%

18%

16%

0%

0%

Holz

318

24%

52%

12%

12%

0%

0%

LeMay

1,279

21%

27%

8%

2%

42%

0%

LP-30

325

0%

85%

10%

4%

0%

0%

North

1,396

13%

42%

4%

6%

33%

1%

O'Leary

88

7%

57%

21%

13%

2%

0

Quigley

105

10%

58%

15%

18%

0%

0%

Watershed area includes upstream lakes.

2.4

SOILS AND GEOLOGY

Topography in the watersheds is dominated by steep and rolling hills with depressions that are filled with lakes and wetlands. These features are composed of glacial till and outwash from the advance and retreat of glacial lobes during the most recent ice age. Water tables throughout the watershed may be at or near the surface in depressional areas, and 10 ft. or deeper in the hills and higher elevations. The Kingsley and Mahtomedi series are the most common soils types in the watersheds. Both are characterized by very deep, well drained, moderate to rapidly permeable soil layers. These soils were formed in loamy glacial till and sandy outwash on glacial moraines. 2.5

GROUNDWATER

The Dakota County Geologic Atlas describes the quaternary geology (the most recent geological period) of northern Dakota County as primarily sand and gravel with laterally discontinuous till, clay and silt layers that is typical of areas exhibiting glacial outwash. First encountered bedrock is observed at a depth between 350 to 800 feet below the surface in the study area. Groundwater in the City of Eagan generally flows to the west towards the Minnesota River. However, groundwater in the eastern portion of the City of Eagan tends to flow east towards the Mississippi River. The break in groundwater flow direction generally follows surficial topography. There are isolated instances of thin discontinuous aquatard lenses that impede the vertical movement of recharge to regional groundwater. In the study area, these lenses were generally less than 40-ft below the surface and consist of clay till and silty-clay layers above bedrock. Surface water bodies can interact with groundwater in a variety of ways dependent on the hydrogeologic connections, the relative elevations of the groundwater compared to the Ordinary High Water 2-12

Level (OHW) elevation, and the average depth and the maximum depth of each individual lake in the study area. The groundwater elevation data for the study area were collected from the County Well Index (CWI). This information was used to infer the relationship between surface water features and groundwater. However, the static groundwater elevations reported on the CWI logs were observed at the time of drilling and may reflect seasonal highs, lows, or other temporal changes in groundwater elevations. Therefore, all inferences are interpreted to be a general condition. The interpretations may not describe the complete groundwater and surface water interaction, or how they may change during dry or wet periods. Driller logs collected from the CWI indicate that material below the lake bottoms of the study area is moderately to highly conductive. Lake OHW elevations compared to groundwater elevations measured in nearby wells show that the lakes in the study area are generally losing and contribute to groundwater. OHW elevations are generally 50 to 100 feet higher than static groundwater elevations, with the exception of North, Bur Oaks, and Cliff lakes. North and Bur Oaks Lakes Groundwater elevations in more recently drilled wells near North and Bur Oaks lakes are approximately equal to their respective OHW elevations. This could reflect a seasonal high groundwater period where groundwater could influence North and Bur Oaks lakes (as a flow through lake or connected to groundwater lake). Well Driller logs also indicate that a 10- to 15-foot thick layer of clay is present a few feet below the lake bottoms. The clay layer may contribute to mounding effects, which explains higher groundwater levels in the area as compared to other nearby areas. As you move away from North and Bur Oaks lakes, the clay layer is not present, and groundwater elevations are approximately 30 to 50 feet below OHW elevations. Cliff Lake Cliff Lake is located in one of the aforementioned isolated instances of a thin discontinuous lens that impedes the vertical movement of recharge to regional groundwater. Cliff Lake has little connectivity to groundwater based on well driller logs that indicate soils to the east are clay and soils to the west are silty sands, which limit both vertical and horizontal movement of surficial recharge. Even though groundwater elevations near Cliff Lake are recorded as approximately equal to the OHW elevation, those elevations are not reflective of regional groundwater elevations. Surface hydrology plays a dominant role in Cliff Lake’s water balance. 2.6

CLIMATOLOGICAL SUMMARY

Annual precipitation averaged 30.3 inches between 1990 and 2012 (Figure 2.9). Average annual snowfall is approximately 50 inches, with the most severe melt runoff conditions usually occurring in March and early April. Lakes in the Minneapolis-St. Paul metropolitan area average approximately 132 days of ice cover per year, with average freeze and thaw dates occurring the last week of November and the first week of April, respectively. The average date of the last below-freezing temperature in the spring is April 27, and the average date of the first below-freezing temperature in the fall is October 2, yielding an average growing season of 157 days.

2-13

Figure 2.9. Annual and average precipitation recorded at the Minneapolis/St. Paul International Airport. 2.7

LAKE MORPHOMETRY

The majority (11 of 12 lakes) of the lakes in this study are small (9 to 32 acres) and shallow (maximum depth less than 15 feet; Table 2.2; Appendix B). The MPCA defines shallow lakes as enclosed basins with maximum depths less than 15 feet or where 80% or more of the surface area may support emerged or submerged aquatic vegetation (littoral zone). Carlson Lake is the only one that meets the criteria for deep lakes set by the MPCA (Table 2.2). However, Carlson Lake’s maximum depth is only 19 feet and the littoral area is 74% of the lake. So, Carlson likely acts more like a shallow lake where the vegetation and fish play a large role in water quality. All of the lakes should support submerged aquatic vegetation over the majority of the lake area. Residence time can be an important indicator of how sensitive a lake will be to changes in runoff water quality. Generally, lakes with small watersheds such as Bald, Quigley, or LP-30 have residence times greater than a year and lakes with large watersheds (>200 acres) have residence times less than a year. Lakes with the shorter residence times are more sensitive to changes in runoff water quality. Six of the lakes have residence times less than 0.5 years, suggesting they will be quite sensitive to stormwater water quality.

2-14

Table 2.2 Lake morphometry for all lakes in the study area. Lake Name Units Bald Bur Oaks Carlson Cliff Fitz Hay Holz LeMay LP-30 North O’Leary 1

Quigley

Surface Area

Average Depth

Maximum Depth

Lake Volume

acre

feet

feet

ac-ft

10 10.8 12 11.8 12.3 22 10 32 9 16 9.3 15

6 2.4 8.4 2.8 5.5 3.9 5.9 5.3 10.3 4.8 2.9 3.1

9 9 19 7 11 9 10 16 14 11 10 6

60 26 100 33 68 82 59 168 94 77 27 48

Littoral Area

Depth Class

Total Drainage 1 Area

years

%

--

acre

2.5 0.1 0.5 0.2 1.3 0.5 0.7 0.3 1.6 0.1 1.5 1.8

100% 100% 74% 100% 100% 100% 100% 99% 98% 100% 100% 100%

Shallow Shallow Deep Shallow Shallow Shallow Shallow Shallow Shallow Shallow Wetland2 Wetland2

103 944 664 619 210 809 318 1,279 325 1,396 88 105

Residence Time

Areas include upstream drainage area 2 Considered by MPCA a wetland not a lake for purposes of State of Minnesota water quality assessments and 303(d) list determinations.

2.8

WATER QUALITY

Water quality in Minnesota lakes is often evaluated using three associated parameters: total phosphorus, chlorophyll-a, and Secchi depth. Total phosphorus is typically the limiting nutrient in Minnesota’s lakes, meaning that algal growth will increase with increases in phosphorus. However, there are cases where phosphorus is widely abundant and the lake becomes limited by nitrogen or light availability. Chlorophyll-a is the primary pigment in aquatic algae and has been shown to have a direct correlation with algal biomass. Since chlorophyll-a is a simple measurement, it is often used to evaluate algal abundance rather than expensive cell counts. Secchi depth is a physical measurement of water clarity, measured by lowering a black and white disk until it can no longer be seen from the surface. Increasing Secchi depths indicate less light refracting particulates in the water column and increasing water quality. Conversely, rising total phosphorus and chlorophyll-a concentrations point to decreasing water quality and thus lowering water clarity. Measurements of these three parameters are interrelated and can be combined into an index that describes water quality. Lake water quality samples were routinely collected by the City of Eagan at each of the 12 lakes throughout the growing season since 1991. Lake water quality varies depending on factors such as annual precipitation, annual temperature, biotic population dynamics, and other factors. However, annual summer averages from 2000 to 2012 (depending on annual data availability) were averaged to assess the general water quality of each lake (Table 2.3). Of the 12 lakes in this study Hay, LP-30, Bur Oaks, and North lakes typically have the best water quality while Fitz, Holz, and LeMay typically have the worst water quality. Water quality data for each year are presented in Appendix C.

2-15

Table 2.3. Shallow and deep lake growing season averages for water quality parameters.

Lake Name

Proposed Impairment (2014)

"Average" Condition Calculation Years

Water Quality Standard for Shallow Lakes

60.0

20.0

1.0

Bald

No

2001-2010; 2012

75.0

26.9

1.2

Bur Oaks

No

2003-2010; 2012

41.9

6.9

0.7

Cliff

No

2002; 2005-2010; 2012

112.7

46.1

1.0

Fitz

Yes

105.0

57.2

0.6

Hay

No

31.3

8.5

1.7

Holz

Yes

72.5

24.8

1.5

LeMay

Yes

2004-2009; 2012 2000-2004; 2005-2010; 2012 2001; 2003; 2005; 2007; 2009; 2012 2000-2010; 2012

76.2

25.2

1.5

LP-30

No

34.3

11.7

1.6

North

No

2005; 2009; 2012 2003; 2005-2006; 2009; 2012 2005-2006; 2008; 2010; 2012

47.0

17.6

2.0

76.0

25.8

1.0

74.8

45.8

0.9

40.0 49.6

14.0 32.7

1.4 1.4

O’Leary Quigley

1

In-Lake "Average" Condition (Calculated June September) TP Chl-a Secchi Concentration Concentration Depth (m) (µg/L) (µg/L)

Wetland

1

Wetland

1

2002; 2005-2007; 2010

Water Quality Standard for Deep Lakes Yes Carlson 2000-2010; 2012

Considered by MPCA a wetland not a lake for purposes of State of Minnesota water quality assessments and 303(d) list determinations. Because wetlands do not have TP, Chl-a or Secchi standards, the standards for shallow lakes (which O’Leary and Quigley are close to morphometrically) were applied in this project as a voluntary target for improving water quality.

2.9

SHALLOW LAKE ECOLOGY

2.9.1

General Description

Shallow lakes are ecologically different from deep lakes. Compared to deep lakes, shallow lakes have a greater proportion of sediment area to lake volume, allowing potentially larger sediment contributions to nutrient loads and higher potential sediment resuspension that can decrease water clarity. Biological organisms also play a greater role in maintaining water quality. Rough fish, especially carp, can uproot submerged aquatic vegetation and stir up sediment. Submerged aquatic vegetation stabilizes the sediment, reducing the amount that can be resuspended and cloud water clarity. Submerged aquatic vegetation also provides refugia for zooplankton, a group of small crustaceans that consumes algae. All of these interactions in shallow lakes occur within a theoretical paradigm of two alternative stable states: a clear water state and a turbid water state (Scheffer 2004). The clear water state is characterized by a robust and diverse submerged aquatic vegetation community, balanced fish community and large daphnia (zooplankton that are very effective at consuming algae). Alternatively, the turbid water state typically lacks submerged aquatic vegetation, is dominated by rough fish, and is characterized by both sediment resuspension and algal productivity. The state in which the lake persists 2-16

depends on the biological community as well as the nutrient conditions in the lake. Therefore, lake management must focus on the biological community as well as the water quality of the lake. The following five-step process for restoring shallow lakes that (Moss et al. 1996) was developed in Europe is also applicable here in the United States: ·

Forward “switch” detection and removal

·

External and internal nutrient control

·

Biomanipulation (reverse “switch”)

·

Plant establishment

·

Stabilizing and managing restored system

The first step refers to identifying and eliminating those factors, also known as “switches,” that are driving the lake into a turbid water state. These can include high nutrient loads, invasive species such as carp and Curly-leaf pondweed, altered hydrology, and direct physical impacts such as plant removal. Once the switches have been eliminated, an acceptable nutrient load must be established. After the first two steps, the lake is likely to remain in the turbid water state even though conditions have improved, and it must be forced back into the clear lake state by manipulating its biology (also known as biomanipulation). Biomanipulation typically includes whole lake drawdown and fish removal. Once the submerged aquatic vegetation has been established, management will focus on stabilizing the lake in the clear lake state (steps 4 and 5). 2.10

FISHERIES AND AQUATIC VEGETATION

The biological conditions (fish, plants, zooplankton, and invertebrates) in shallow lakes play a critical role in maintaining water quality. The balance between top predators and their prey (panfish, minnows) can have a large effect on the size of the cladoceran population, an effective algae grazer. Likewise, the amount and type of vegetation can affect the fish and zooplankton balance, ultimately affecting the cladocerans population. Because all the lakes are highly dependent on biological conditions, fish and vegetation data were compiled for each of the assessment lakes (Table 2.4). Blue Water Science conducted vegetation surveys on each of the lakes in the summer of 2014 (Appendix D). The City of Eagan conducts periodic fish surveys on the lakes, however not all of the lakes were surveyed when this report was completed. All Minnesota DNR files were reviewed for this study. Compiled fish data are provided in Appendix E. Fish and vegetation conditions in the lakes are summarized in Table 2.4. 2.10.1 Fisheries Fisheries play a direct role in controlling water clarity by affecting large zooplankton grazer abundance which can have a large influence on water clarity. An overabundance of zooplankton predators such as stunted panfish or fathead minnows can lead to increased algal blooms and a potential collapse of the submerged aquatic vegetation population. Common Carp and Rough Fish Rough fish (bullheads) and common carp can have negative effects on water quality in shallow lakes. Common carp are an invasive species that can be especially destructive in shallow lakes. Carp uproot 2-17

aquatic macrophytes during feeding and spawning and re-suspend bottom sediments and nutrients. These activities can lead to increased nutrients in the water column, ultimately resulting in increased nuisance algal blooms. None of the lakes have observed or surveyed carp populations at this time. However, sizeable roughfish populations exist in several of the lakes, including Bur Oaks, Hay and LeMay lakes. Fathead Minnows Fathead minnows are particularly effective at grazing large zooplankton grazers, which can lead to increased algal populations. Bald, O’Leary and Quigley lakes have observed large fathead minnow populations. 2.10.2 Submerged Aquatic Vegetation Aquatic plants are beneficial to lake ecosystems, providing spawning and cover for fish, habitat for macroinvertebrates, refuge for prey, and stabilization of sediments. However, in high abundance and density, they limit recreation activities, such as boating and swimming, and may reduce aesthetic values. Excess nutrients in lakes can lead to non-native, invasive aquatic plants taking over a lake. Some exotics can lead to special problems in lakes. For example, under the right conditions, Eurasian watermilfoil can reduce plant biodiversity in a lake when it grows in great densities and out-competes all the other plants. Ultimately, this can lead to a shift in the fish community because these high densities favor panfish over large game fish. Species such as Curly-leaf pondweed can cause very specific problems by changing the dynamics of internal phosphorus loading. Ultimately, there is a delicate balance within the aquatic plant community in any lake ecosystem. All of the study lakes have submerged aquatic vegetation throughout, with coverage ranging from 40 to 100% of the lake area. As is typical of urban, nutrient-enriched shallow lakes, coontail is the dominant species in all. Coontail is a native species that is tolerant of poor water quality and grows very aggressively. It is not a rooted species and sometimes grows dense enough to mat at the surface. Curly-leaf Pondweed Curly-leaf pondweed is an invasive, like Eurasian watermilfoil, that can easily take over a lake’s aquatic macrophyte community. It presents a unique problem because it is believed to affect significantly the inlake availability of phosphorus, contributing to the eutrophication problem. Curly-leaf pondweed begins growing in late fall, continues growing under the ice, and dies back relatively early in summer, releasing nutrients into the water column as it decomposes, possibly contributing to algal blooms. Curly-leaf pondweed can also out-compete desirable native plant species. All of the lakes except LP-30, O’Leary, and Quigley have Curly-leaf pondweed present. Although some of the lakes have Curly-leaf over much of the lake area, none of the lakes have dense growth at any of the locations at this time. Coverage ranges from 4% to 78% of the lake area and in most of the surveys only light growth was observed. Holz Lake is dominated by Curly-leaf pondweed in the early season.

2-18

Table 2.4. Fish and vegetation data for Eagan Lake. Lake

Recent Fish Survey MonthYear

Carp Present?

Curly-leaf Pondweed Present?

(% Occurrence)

Native Plant Coverage

City operated aeration system?

Fisheries Notes

Plentiful FHMs. Stocked BLG in 2010 but no aeration until 2012-13; survival may be limited. Stocked LMB young of the year in Sept 2012. Fish survey planned in 2015. Frequent winter kills occurred during the 1990s; the city now aerates the lake. NOP present, LMB absent in 2010 survey; stocked LMB young of the year in spring 2013. Winterkill 2013-14; restocked with LMB and BLG in spring 2014. Modest stocking of walleye, bluegill, black crappie, and largemouth bass, and channel catfish.

Aquatic Vegetation Notes (no Eurasian watermilfoil was observed in any lake in the 2013 plant surveys)

Dominant plant species is coontail; Curlyleaf pondweed established

Bald

(2015)

--

Yes (56%)

Bur Oaks

Sep-2010

No

Yes (22%)

100%

Yes

Carlson

Jul-2012

No

Yes (16%)

42%

Yes

Cliff

Sep-2011 EF Sep-2013 TN

No

Yes (78%)

100%

Yes

BLG common, LMB present. Aerator operated when needed since 2008.

Dominant plant species is coontail; Curlyleaf pondweed established

Fitz

Sep-2013

No

Yes (32%)

80%

No

All BLB in 2013 survey, no other species caught.

Dominant plant species is coontail; Curlyleaf pondweed established

Hay

2014

No

Yes (16%)

97%

Yes

Serious winterkill 2013-14 when aeration system failed. Restocked in spring 2014 with BLG (by DNR).

Dominant plant species is coontail; Curlyleaf pondweed established; Heavy growth of native vegetation in summer

Holz

Sep-2011 EF Sep-2013 TN

No

Yes (53%)

40%

Yes

Frequent winter kills occurred during the 1990s. Now aerated, eliminating fish kills. Large LMB, crappies, and smaller BLG.

Dominant plant species is coontail; Curlyleaf pondweed established

LP-30

N/A

--

No

93%

No

--

Dominant plant species is coontail; No Curly-leaf pondweed established

94%

Yes

Dominant plant species coontail; Curly-leaf pondweed established; filamentous algae covers 48% of lake in August Dominant plant species coontail and Elodea; Curly-leaf pondweed established

2-19

Table 2.4 (continued). Fish and vegetation data for each assessed lake. Lake

Recent Fish Survey

Carp Present?

Curly-leaf Pondweed Present?

(% Occurrence)

Native Plant Coverage

City operated aeration system?

Fisheries Notes

Aquatic Vegetation Notes (no Eurasian watermilfoil was observed in any lake in the 2013 plant surveys)

Dominant plant species is coontail; Curlyleaf pondweed established

LeMay

2014

No

Yes (59%)

67%

Yes

Survey planned for summer 2014. At least a partial kill winter 2013-14 when aerator failed twice and was off about 1 week each time. Otherwise, LMB, smaller BLC, medium BLG and HSF. Restocked spring 2014 with LMB, BLG.

North

2012

No

Yes (4%)

58%

No

BLC and BLG common, HSF and LMB are present.

Dominant plant species is coontail; Curlyleaf pondweed established

O’Leary

N/A

--

No

100%

No

--

Dominant plant species is coontail; Curlyleaf pondweed established

Quigley

N/A

--

No

100%

No

--

Dominant plant species is coontail and white water lilies; Curly-leaf pondweed established

LMB= Large Mouth Bass, BLB=Black Bullhead BLC=Black Crappie BLG=Bluegill FHM=Fathead Minnows HSF=Hybrid Sunfish NOP=Northern Pike EF=Electrofishing TN=Trap Net

2-20

3.0 Phosphorus Source Assessment 3.1

NUTRIENTS IN PROPOSED IMPAIRED AND PROTECTION LAKES

A key component to developing a nutrient TMDL or lake management plan is to understand the sources contributing to the impairment. This section provides a brief description of the potential sources in the watershed contributing to excess nutrients in the lakes addressed in this TMDL. The latter sections of this report discuss the major pollutant sources that have been quantified using collected monitoring data and water quality modeling. The information presented here and in the upcoming sections together will provide information necessary to target pollutant load reductions. 3.2

NUTRIENT SOURCES AND LAKE RESPONSE

Following is a description of the nutrient sources and methods used to quantify each sources. 3.2.1

Watershed PONDNET Models

Watershed water and nutrient loading was estimated using a PONDNET (Walker, 1989) model developed for each lake watershed. PONDNET is a spreadsheet model based on routing of flow and TP through networks of wet detention ponds. Watershed runoff is estimated using a runoff coefficient while TP load is predicted using a land use specific runoff concentration (event mean concentration). TP removal is predicted using an empirical TP retention function. The City of Eagan originally developed a PONDNET model as a part of its nondegradation loading assessment to comply with MPCA’s Municipal Separate Storm Sewer System (MS4) General Permit. The portions of this model that drain to each lake were updated with most current land use and watershed data and used to predict water yields and TP loading to each lake. The model operates on an annual time-step and was used to predict watershed yields/loads for a 12-year period (2000-2012). The watershed model was validated using storm sewer flows through lift stations and pond water quality (Appendix F), where available. Model runoff coefficients were systematically reduced to provide the best fit possible for runoff volumes at seven lift stations. Average modeled discharge at the seven lift stations was within 11% of the recorded discharge (Appendix F). The watershed model included several upstream lakes as boundary conditions (i.e., model inputs). Flow from the model or lift station where monitoring data was available, was used along with lake water quality data to estimate loading from that part of the watershed. Lakes included in the model using monitoring data include Schwanz, Carlson, and Fish Lake. Watershed water and phosphorus balances were developed for each of the lakes including loads from identified subwatersheds (Figures 3.1 through 3.3). Each of the watershed budgets includes upstream lakes as direct load to the downstream lake. These water and nutrient loads are directly input into the BATHTUB Model for lake response analysis.

3-1

Figure 3.1. Average annual water yield subdivided by subwatersheds in each lake watershed.

3-2

Figure 3.2. Annual watershed loads from watershed, internal, atmospheric, and upstream lake sources.

3-3

Figure 3.3. Annual watershed loads from watershed, internal, atmospheric, and upstream lake sources.

3-4

3.2.2

Upstream Lakes

Some of the lakes addressed in the TMDL have upstream lakes which are also addressed in the TMDL. Meeting water quality standards in the downstream lakes is contingent on water quality improvements in the proposed impaired upstream lakes. For these situations, outflow loads from the upstream lake were routed directly into the downstream lake and were estimated using monitored water quality. 3.2.3

Atmospheric Deposition

A study conducted for the MPCA, “Detailed Assessment of Phosphorus Sources to Minnesota Watersheds” (Barr Engineering, 2004), estimated the atmospheric inputs of phosphorus from deposition for different regions of Minnesota. The rates vary based on the precipitation received in a given year. Precipitation received during 2005-2011 was within that study’s average range (25” to 38”). That study’s annual atmospheric deposition rate of 26.8 kg/km2 for average precipitation years was used to calculate annual atmospheric deposition load for these lakes. 3.2.4

Internal Loading

Internal phosphorus loading from lake sediments has been demonstrated to be an important part of the phosphorus budgets. Internal loading is typically the result of organic sediment releasing phosphorus to the water column. This often occurs when anoxic conditions are present, meaning that the water in and above the sediment is devoid of oxygen. However, studies have shown that internal loading can and does occur when the overlying water column is well oxygenated. For Carlson Lake, the only deep lake in this study, temperature and dissolved oxygen profiles were used to determine the volume of water under anoxic conditions throughout the summer growing season. This volume was then used to calculate an anoxic factor (Nürnberg 2004) normalized over the lake basin and reported as number of days. Shallow lakes can often demonstrate short periods of anoxia due to instability of stratification, which can last a few days or even a few hours, that are often missed by periodic field measurements. Thus, the following equation was used to estimate the anoxic factor for all shallow lakes in this TMDL study (Nürnberg 2005): AFshallow = -35.4 + 44.2 log (TP) + 0.95 z/A0.5 Where TP is the average summer phosphorus concentration of the lake, z is the mean depth (m) and A is the lake surface area (km2). To calculate total internal load for a lake, the anoxic factor (days) is multiplied by an estimated or measured phosphorus release rate (mg/m2/day). Release rates were obtained by collecting sediment cores in the field and incubating them in the lab under oxic and/or anoxic conditions to measure phosphorus release over time (Table 3.1; Appendix G).

3-5

Table 3.1. Sediment release rates (aerobic and anaerobic), anoxic factors, and annual internal loads for each neighborhood lake.

1

Lake

Aerobic Release Rate 2 (mg/m /day)

Anaerobic Release Rate 2 (mg/m /day)

Average Oxic Factor (days)

Average Anoxic Factor (days)

Average Annual Internal Load (lbs/yr)

Bald Bur Oaks Carlson Cliff Fitz Hay Holz 2 LP-30 LeMay North O’Leary Quigley

0.4 0.34 0.56 0.2 0.13 0.15 0.17 0.21 0.27 0.12 0.13 0.36

3.2 5.7 4.7 4.6 3.7 1.2 2.3 2.6 3.4 6 2.4 0.4

61 -35 122 26.8 -61 48 61 -61 122

58.8 3.6 55.8 1 59.9 1 61.6 31.4 1 55.9 11 15.8 17 17.1 1 47.3

18.8 1.9 9.4 31.6 26.8 7.4 38.3 18.2 19.9 14.6 4.1 8.5

The shallow lake anoxic factor from Nurnberg 2005 were used for these lakes rather than field data because the field data likely underestimate the anoxic factor. 2 Internal load estimates are based on sediment chemistry since release rates were not measured.

3.2.5

BATHTUB Model (Lake Response)

Once the nutrient budget for a lake has been developed, the lake’s response to those nutrient loads must be established. Lake response to nutrient loading was modeled using BATHTUB and the extensive data set available for the proposed impaired lakes. BATHTUB is a series of empirical eutrophication models that predict the response to phosphorus inputs for morphologically complex lakes and reservoirs (Walker 1999). Several models (subroutines) are available for use within the BATHTUB model, and the Canfield-Bachmann model was used to predict the lake response to total phosphorus loads. The Canfield-Bachmann model (Canfield and Bachmann 1981) estimates the lake phosphorus sedimentation rate, which is needed to predict the relationship between in-lake phosphorus concentrations and phosphorus load inputs. The phosphorus sedimentation rate is an estimate of net phosphorus loss from the water column through sedimentation to the lake bottom and is used in concert with lake-specific characteristics, such as annual phosphorus loading, mean depth, and hydraulic flushing rate, to predict in-lake phosphorus concentrations. These model predictions are compared to measured data to evaluate how well the model describes the lake system. Once a model is well calibrated, the resulting relationship between phosphorus load and in-lake water quality is used to determine the assimilative capacity. Construction, calibration, and results of the BATHTUB model are presented in Appendix H.

3-6

4.0 Nutrient Budgets and TMDL Allocations 4.1

TMDL METHODOLOGY

The first step in developing an excess nutrient TMDL for lakes is to determine the total nutrient loading capacity or assimilative capacity. A key component for this determination is to estimate the current phosphorus loading by the sources for each lake. Following this estimation, BATHTUB is used to model responses of proposed impaired lakes to phosphorus loading and to determine loading capacities. The components of this process are described below. To set the TMDL for each proposed impaired lake in the study, the nutrient inputs partitioned between sources in the lake response model is systematically reduced until the model predicted when each lake meets the current total phosphorus standard of 60 mg/L as a growing season mean for shallow lakes and 40 mg/L for deep lakes. Lake response model results are included in Appendix H. To develop the appropriate loads under TMDL conditions, each load is evaluated sequentially to determine appropriate loads. Since atmospheric load is impossible to control, no reduction in this source is assumed for the TMDLs. Any upstream lakes are assumed to meet water quality standards, and the resultant reductions are applied to the lake being evaluated. If all of these reductions result in the lake meeting water quality standards, then the TMDL allocations are done. If more reductions are required, then the internal and external loads are evaluated simultaneously. The capacity for watershed load reductions is considered first by looking at watershed loading rates and runoff concentrations compared to literature values. For example, some watershed phosphorus export rates are already so low that large reductions would be infeasible. Therefore, an internal load reduction is required to achieve water quality goals. In other cases, the situation is reversed and the internal load is already so low that only watershed reductions are required. The general approach to internal load reductions is to evaluate the capacity for reducing the internal loading based on review of the existing sediment release rates and the lake morphometry. This is accomplished by reviewing the release rates versus literature values of healthy lakes. If the release rates are high, then they are reduced systematically until either a minimum of 1 mg/m2/day is reached or the lakes meet TMDL requirements. In some extreme cases, the release rate has to be reduced below 1 mg/m2/day to meet requirements. However, this is only done after all feasible watershed load reductions are included. 4.1.1

Load Allocation Methodology

The LA includes all non-permitted sources, including: atmospheric deposition, septic systems, discharge from upstream lakes, watershed loading from non-regulated areas, and internal loading. Some discharges from areas geographically located in a regulated MS4 that do not drain through a conveyance system (and therefore are not regulated sources) are also included in the LA (determined as described in the following section).

4-1

Table 4.1 summarizes the potential non-permitted nutrient sources in the Eagan Neighborhood Lakes watersheds. Table 4.1. Potential non-permitted sources of phosphorus. Non-Permitted Source Atmospheric Phosphorus Loading Watershed Phosphorus Export

Internal Phosphorus Release

Groundwater Contribution

4.1.2

Source Description Precipitation and dryfall (dust particles suspended by winds and later deposited). Variety in land use creating both rural and urban stormwater runoff that does not pass through a regulated MS4 conveyance system. There are no non-permitted runoff sources in these watersheds. Under anoxic conditions, weak iron-phosphorus bonds break, releasing phosphorus in a highly available form for algal uptake. Carp and other rough fish present in lakes can lead to increased nutrients in the water column as they uproot aquatic macrophytes during feeding and spawning and re-suspend bottom sediments. Over-abundance of aquatic plants can limit recreation activities and invasive aquatic species such as curlyleaf pondweed can change the dynamics of internal phosphorus loading. Historical impacts, such as WWTP effluent discharge, can also affect internal phosphorus loading. Groundwater can be a source or sink for water in a lake and contains varying levels of phosphorus.

Wasteload Allocation Methodology

The WLA includes all permitted sources, including MS4 regulated stormwater and permitted point sources discharges. Table 4.2 summarizes the potential permitted sources for the Eagan Lakes.

4-2

Table 4.2. Potential permitted sources of phosphorus. Permitted Source Phase II Municipal Stormwater NPDES/SDS General Permit

Source Description Municipal Separate Storm Sewer Systems (MS4s)

Construction Stormwater NPDES/SDS General Permit

Permits for any construction activities disturbing: 1) One acre or more of soil, 2) Less than one acre of soil if that activity is part of a “larger common plan of development or sale” that is greater than one acre or 3) Less than one acre of soil, but the MPCA determines that the activity poses a risk to water resources. Applies to facilities with Standard Industrial Classification Codes in ten categories of industrial activity with significant materials and activities exposed to stormwater.

Multi-sector Industrial Stormwater NPDES/SDS General Permit

Phosphorus Loading Potential Potential for runoff to transport grass clippings, leaves, car wash wastewater, and other phosphorus containing materials to surface water through a regulated MS4 conveyance system. The Environmental Protection Agency (EPA) estimates a soil loss of 20 to 150 tons per acre per year from stormwater runoff at construction sites. Such sites vary in the number of acres they disturb.

Significant materials include any material handled, used, processed, or generated that when exposed to stormwater may leak, leach, or decompose and be carried offsite.

4.1.2.1 MS4s There are four MS4s that are completely within or have a portion of their boundary in at least one of the proposed impaired lake watersheds (Table 4.3). Runoff from these MS4 entities that drains to proposed impaired lakes discussed in this report was assigned WLAs according to the following methodology. The current annual phosphorus load from the permitted sources was calculated by multiplying the percent area of each MS4 by the total annual watershed phosphorus load that reaches each lake. To calculate the WLAs, the required watershed reduction to meet water quality standards, as determined by the methodology described in Section 4.1, was applied to the calculated MS4 load. This approach assumes that an equal load reduction is required from all watershed areas. Table 4.3. Permitted MS4s in each TMDL lakeshed. MS4 Name

City of Eagan

City of Inver Grove Heights

MnDOT

Dakota County

MS4 ID Number

MS400014

MS400096

MS400170

MS400132

--

--

Yes

19-0066

Carlson

Yes

19-0077

Fitz

Yes

19-0064

Holz

Yes

19-0055

LeMay

Yes

1

Yes Yes --

1

--

1

--

1

Yes

Yes Yes Yes

MnDOT ROW areas used to calculate WLAs were 6 acres for Fitz, 7 acres for Holz, and 124 acres for LeMay.

To determine each MS4’s WLA, their current loading was determined by multiplying the percent area of each MS4 by the total annual watershed phosphorus load that reaches each lake. The Right-of Way area used to calculate MnDOT’s load was provided by MnDOT (Barbara Loida, pers. comm.). To determine MnDOT’s WLA, the required watershed reduction to meet state water quality standards was applied to

4-3

their load. If the load was less than 1 pound, no reduction was required for MnDOT. Rather, the City of Eagan claimed responsibility for that reduction. 4.1.2.2 Construction and Industrial Stormwater Construction and industrial stormwater WLAs were established based on estimated percentage of land in the watershed that is currently under construction or permitted for industrial use. A recent permit review across Dakota County watershed showed minimal construction (<1% of watershed area) and industrial activities (<0.5% of the watershed area). To account for future growth, allocations in the TMDL were rounded up to 1% for construction stormwater and 0.5% for industrial stormwater. The wasteload allocation for stormwater discharges from sites where there is construction activities reflects the number of construction sites > 1 acre expected to be active in the watershed at any one time, and the Best Management Practices (BMPs) and other stormwater control measures that should be implemented at the sites to limit the discharge of pollutants of concern. The BMPs and other stormwater control measures that should be implemented at construction sites are defined in the State's NPDES/SDS General Stormwater Permit for Construction Activity (MNR100001). If a construction site owner/operator obtains coverage under the NPDES/SDS General Stormwater Permit and properly selects, installs and maintains all BMPs required under the permit, including those related to impaired waters discharges and any