C-. LAKE COUNTY, FLORIDA
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LAKE COUNTY STORMWATER MANAGEMENT NEEDS ASSESSMENT FINAL Prepared by Camp Dresser & McKee Inc. MAY 1991 environmental engineers, scientists, M.. planners, & rnonogernent cmsultonts c-. LAKE COUNTY, FLORIDA STORMWATER MANAGEMENT NEEDS ASSESSMENT FINAL REPORT CAMP DRESSER & McKEE INC. MAY 1991 CONTENTS Section Page 1.0 INTRODUCTION 1-1 1.1 Background 1.2 Report Purposes and Contents 2.0 DATA SOURCES 2-1 Lake County Neighboring Counties Participating Cities and Towns Non-Participating Cities Lake County Water Authority (LCtJA) United States Geological Survey (USGS) United States Army Corps of Engineers (USACOE) United States Department of Agriculture Soil Conservation Service (USDA-SCS) Federal Emergency Management Agency (Fm) National Climatic Data Center (NCDC) St. Johns River Water Management District (SJRWMD) Southwest Florida Water Management District (SWFWMD) Florida Department of Environmental Regulation (FDER) Florida Department of Transportation (FDOT) Florida Department of Community Affairs (DCA) 3.0 HYDR0UX;IC AND HYDRAULIC BACKGROUND 3-1 Major Basins 3.1.1 Oklawaha River 3.1.2 Withlacoochee River 3.1.3 Wekiva River 3.1.4 Kissimmee River 3.1.5 St. Johns River Hydrologic Boundaries Topography Aerial Photography Soils Rainfall Stage and Discharge Floodplains and Floodways Land Use and Growth Trends Regional Aquifer Characteristics Inventory of Major Stomter Conveyance Structures 4.0 STORMWATER MANAGEMENT REGULATIONS 4-1 4.1 Lake County 4.2 Cities and Towns 4.3 Federal and State CONTENTS (contents) Section Page 5.0 WATER QUALITY 5-1 5.1 General 5.2 Best Management Practices (BMPs) 5.2.1 Structural BMP Alternatives 5.2.2 Comparison of Structural BMPs 5.2.3 Design Criteria for Preferred Structural BMPS 5.2.4 Pollutant Removal Efficiencies 5.3 Regional vs. Onsite Deployment of Structural BMPs 5.4 Water Quality Evaluations 5.4.1 Existing Lake County Monitoring 5.4.2 Trophic State Index 5.4.3 Stormwater Pollutant Loadings 5.4.4 Failing Septic Tank Impacts 5.4.5 Average Annual Non-Point Pollution Loads 5.5 Summary 6.0 PROBLEM AREAS 6.1 General 6.1.1 Water Quantity (Flooding) 6.1.2 Water Quality 6.2 Problem Area Identification and Evaluations 6.2.1 Water Quantity Problem Areas 6.2.2 Water Quality Problem Areas 6.2.3 Non-Problem Facilities 7.0 COMPUTER MODEL COMPARISONS 7.1 Water Quantity Models 7.1.1 Water Quantity Model Comparison Items 7.1.2 Available Water Quantity Models 7.1.3 Water Quantity Model Recommendations 7.2 Water Quality Models 8.0 LEVELS OF SEKVICE 8.1 Water Quantity 8.2 Water Quality 8.3 Summary 8.4 Prioritization CONTENTS (continued) Section Xe 9.1 on-Structural Improvements 9.1.1 Goals, Objectives, and Policies 9.1.2 Stormwater Management Regulations and Ordinances 9.1.3 Maintenance Practices 9.2 Structural Improvements 9.2.1 Problem Area Improvements 9.2.2 Unknown Problem Area Improvements 9.2.3 Additional Stormwater Management Program Needs 9.3 Prioritization 9.4 Additional Program Needs APPENDICES APPENDIX A - LAKE COUNTY'S STORMKATER SUB-ELEMENT, CHAPTER V1-C, OF THE COUNTY'S COMPREHENSIVE PLAN APPENDIX B - DATA o Hydrologic Boundary Map o Stormwater Facility Inventory by SubBasin o Soils by Sub-Basin o Land Use by Sub-Basin APPENDIX C - DRAFT STORMNRTER MANAG- ORDINANCE (Provided to Lake County under separate cover) iii LIST OF TABLES Table Page Design Storms Recommendations for the Major Basins Rainfall Summary for Lake County Area, Florida Estimated Water Quality Based on Historic Storms USGS Lake Gages in the Study Area USGS Stream Gages in the Study Area USGS Well Gages in the Study Area Imperviousness by Land Use Category CDM vs. County Land Use Categories Monitored Wet Detention Basin Efficiencies Total-P and Dissolved P Summary Summary of Lake Water Quality Monitoring Data Sumrnary of Lake County Trophic State Index Analysis Summary of Lake County Land Use and Hydrological Soils Group Comparison of Average Annual Total-P Loading Factors for Urban Land Uses: Occoquan Watershed Monitoring Study vs. NURP National Statistics Summary of Non-Point Pollution Loading Factors by Hydrologic Soils Group Event Mean Concentrations for the Orlando Metro Areawide Water Quality Study (ECFRPC, 1978) Event Mean Concentrations and Impervious Percentages for the Tampa Bay Study (CDM, 1984) Event Mean Concentrations and Impervious Percentages for the Manatee County Southeast Area Study (CDM, 1985) Water Quantity Problem Areas by Sub-Basin Water Quality Problem Areas by Sub-Basin Water Quantity Model Sceening Matrix Recommended Maintenance Frequencies by Facility Type Annual Maintenance Costs Problem Area Summary Conceptual Probable Costs for Retrofit Treatment Facilities Lake County Stomwater Master Plan Basin Studies Cost Estimate Priorities for Stormwater Master Planning by Basin Stomwater Management Program Probable Cost Summary LIST OF FIGURES Following Fiaure Page Major Basins Detailed Topographic Coverage Generalized SCS Soils Mean Annual, 24-Hour Maximum Rainfall for Northeast Florida, Inches 10-Year, 24-Hour Maximum Rainfall for Northeast Florida, Inches 25-Year, 24-Hour Maximum Rainfall for Northeast Florida, Inches 100-Year, 24-Hour Maximum Rainfall for Northeast Florida, Inches 25-Year, 96-Hour Maximum Rainfall for Northeast Florida, Inches Rainfall Gages Adapted from SJRWMD TP-88 USGS Lake Gages USGS Stream Gages High Growth Areas Groundwater Characteristics Wet Detention Basin Settling Curves Onsite vs. Regional BMPs Typical Multi-Purpose Facility Typical Swale Mean Concentration 1985-1990: Total-P Mean Concentration 1985-1990: Total-N Mean Concentration 1985-1990: Secchi Mean Concentration 1985-1990: CHL-A Average Annual Load: Total-P Average Annual Load: Total-N Average Annual Load: Lead Average Annual Load: Zinc Average Annual "Per Acre" Load: Total-P Average Annual "Per Acre" Load: Total-N Average Annual "Per Acre" Load: Lead Average Annual "Per Acre" Load: Zinc Water Quantity Problem Areas by Sub-Basin Water Quality Problem Areas by Sub-Basin Water Quantity Levels of Service Water Quality Levels of Service 1.0 INTRODUCTION 1.1 BACKGROUND In May 1990, Lake County initiated a phased Stormwater Management Program (SWMP) to manage surface and groundwater resources in the County. Camp Dresser & McKee Inc. was selected to perform services related to this program. The main purposes of the County's overall Stormwater Management Program are identified as the following: 1. Build a stormwater management system data-base and information management system which will inventory, locate and describe existing stormwater management systems, hydrologic basins, and other related hydrologic parameters in Lake County. 2. Evaluate existing stormwater management system ordinances, maintenance conditions, and practices. 3. Develop and apply a stormwater management computer model to simulate stormwater runoff of various frequencies under existing and future planned land use conditions. 4. Analyze the capability of the existing stormwater system to accommodate present and future stormwater flows. 5. Assess the magnitude of existing and anticipated future stormwater problems within the County and prioritize those problems relative to their need for attention. 6. Establish desired level of service criteria for the various components of the stormwater management system. 7. Evaluate alternative management plans to meet the desired service level based on existing and future anticipated deficiencies identified through data collection and modeling. 8. Develop cost estimates for needed improvements. 9. Develop a Stormwater Management System Capital Improvement Plan based on identified system improvement needs and a prioritized implementation schedule. 10. Identify and, if required, develop alternative funding methodologies, including a stormwater utility, necessary to fund stormwater management system capital improvements, operations and maintenance and administration. 11. Meet the planning requirements of the Stormwater Sub-Element of Chapter 95-5, Florida Administrative Code (FAC). 1.2 REPORT PURPOSES AND CONTENTS This report presents results from Tasks 1 and 2 of the SWMP: Data Collection and Preliminary Needs Assessment. Within these two tasks, the foundation for completing the 11 overall purposes of the SWMP has been formed. For this report, stormwater-related data were collected, evaluated for adequacy and quality, and utilized to establish levels of detail and priorities for subsequent SWMP tasks. In addition, conceptual Capital Improvement Program (CIP) probable cost estimates were made for facilities to mitigate known stormwater quantity problems, and to provide for the treatment of stormwater in areas where such facilities do not exist. This report also presents the recommended levels of service and detail to meet the requirements of Chapter 95-5, FAC, and the additional future tasks which will be required for Lake County to complete the overall Stormwater Management Program objectives. 2.0 DATA SOURCES Presented below is a summary of the numerous entities and agencies which retain the stomter data and previous reports pertinent to the Lake County stomter management system. These entities and agencies were contacted to obtain or reference existing data and previous reports. The pertinent data and reports are referenced by the respective entity which retains them. LAKE COUNTY Departments within the Lake County government infrastructure were contacted to evaluate and document the County's stormwater management resources and existing data and reports. The information provided by Lake County personnel is presented below: