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Hydrodynamic Separators As Stormwater Best Management Practices

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Hydrodynamic Separators As Stormwater Best Management Practices Report No. UT-04.15 HYDRODYNAMIC SEPARATORS AS STORMWATER BEST MANAGEMENT PRACTICES Final Report Prepared For: Utah Department of Transportation Research and Development Division Submitted By: Stantec Consulting Inc. Authored By: Karen Nichols, P.E. Kade Moncur Julie Howe April 2005 NOTICE This report is disseminated under the sponsorship of the Utah Department of Transportation. The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. UDOT RESEARCH & DEVELOPMENT REPORT ABSTRACT 1. Report No. UT-04.15 2. Government Accession No. 3. Recipient’s Catalog No. 4. Title and Subtitle 5. Report Date November 2004/Revised April 2005 Hydrodynamic Separators as Stormwater Best Management Practices 6. Performing Organization Code 7. Author(s) 9. Performing Organization Report No. Stantec Consulting Inc. Karen Nichols, P.E. Kade Moncur Julie Howe 9. Performing Organization Name and Address 10. Work Unit No. Stantec Consulting Inc. 3995 S. 700 E., Ste. 300 11. Contract No. 81FR0215 Salt Lake City, UT 84107 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Utah Department of Transportation 4501 South 2700 West 14. Sponsoring Agency Code Salt Lake City, UT 84114-8410 15. Supplementary Notes 16. Abstract The use of hydrodynamic separators in the treatment of stormwater runoff for UDOT basins was evaluated. This evaluation included: 1) identifying potential stormwater pollutants of concern in transportation corridors, 2) identifying documented stormwater pollutant load estimation methods, 3) prepare a listing of available proprietary treatment BMPs, 4) develop a selection methodology for water quality BMPs, 5) prepare technical specifications for hydrodynamic separators. This project reviewed published literature and existing UDOT resources. Stormwater discharges contain constituents that can be characterized by land use activities and are largely dependent on climate patterns. Typical potential pollutants of concern for transportation use drainage basins consist of: sediment, floatables, metals and petroleum hydrocarbons. Specific land use analysis and evaluation of potential pollutants of concern is required prior to the selection and design of treatment BMPs. Total suspended solids (TSS) may be a target constituent of treatment BMPs, based on Salt Lake County’s EMC measurements; the average concentration of TSS in urban stormwater in Salt Lake County is 116 mg/l whereas oil and grease concentrations are typically in the range of 5 – 10 mg/l. Hydrodynamic separators cannot treat oil and grease in stormwater runoff to lower levels. Methods to estimate or predict pollutant loads are documented and recognized by many federal and state agencies. USGS and EPA both recognize quantitative analysis methods to estimate pollutant loads to receiving waters conveyed by stormwater runoff. Prediction of pollutant loads may be conducted to assist with the selection, operation and maintenance of stormwater treatment BMP’s. These methods are highly sensitive to land use, percent impervious areas and precipitation events, and therefore produce a wide range of potential loading numbers. To remove sediment from stormwater discharges, hydrodynamic separators may be designed to treat small storm events or the first flush produced during larger storm events. A design water quality storm event of 0.5 inches of rainfall has been identified as design criteria to size the hydrodynamic separator. Other design criteria include sediment storage capacity of the device, head loss, sediment particle size and overall efficiency of the treatment measure. Flows exceeding the design event will need to be routed around, or bypass the treatment device. Specifications for hydrodynamic separators were developed for use by UDOT design engineers. In conclusion, oil water/hydrodynamic separators are not recommended for use in removing oil and grease in typical urban stormwater runoff. These systems may be considered for use in spill containment, removal of oil and grease from high-risk areas, or to assist with the removal of sediments in stormwater. 17. Key Words 18. Distribution Statement Storm Water Quality Available: UDOT Research Division Best Management Practice Box 148410 Hydrodynamic Separator Salt Lake City, UT 84114-8410 19. Security Classification (of 20. Security Classification (of 21. No. of Pages 22. Price this report) this page) N/A N/A 104 THIS PAGE LEFT BLANK INTENTIONALLY TABLE OF CONTENTS Page TABLE OF CONTENTS............................................................................................................. iv ACKNOWLEDGEMENTS ......................................................................................................... vii EXECUTIVE SUMMARY ..........................................................................................................viii 1. STORMWATER POLLUTANTS OF CONCERN AND SEASONAL VARIATION...................1 1.1 Purpose........................................................................................................................1 1.2 Storm Water Quality.....................................................................................................1 1.2.1 National and Local Data....................................................................................1 1.2.2 Stormwater Pollutants.......................................................................................2 1.2.3 Common Pollutants Based on Land Use...........................................................4 1.3 Stormwater Impacts......................................................................................................5 1.4 Salt Lake County Data Comparison..............................................................................6 1.5 Seasonal and Regional Variation .................................................................................7 1.6 BMP Selection Criteria .................................................................................................9 1.7 Summary....................................................................................................................10 2. STORMWATER POLLUTANT LOAD ESTIMATION METHODS.........................................11 2.1 Purpose......................................................................................................................11 2.2 TSS Load Estimation Methods...................................................................................12 2.2.1 USGS Storm-Runoff Loads Regression Analysis ............................................12 2.2.2 Adjusting Regional Regression Models Using Local Data ...............................13 2.2.3 FHWA Method for Pollutant Load Estimation...................................................14 2.2.4 Salt Lake County Stormwater Monitoring ........................................................14 2.2.5 USGS and EPA Nationwide Urban Runoff Program........................................18 2.2.6 California Department of Transportation Stormwater Runoff Characteristics Data................................................................................................................18 2.3 Conclusions................................................................................................................18 3. TREATMENT OF HYDROCARBON CONSTITUENTS IN MUNICIPAL STORMWATER DISCHARGES....................................................................................................................20 3.1 Introduction ................................................................................................................20 3.2 Typical Hydrocarbon Concentrations in Stormwater Runoff........................................20 3.2.1 Oil Droplet Size...............................................................................................21 3.3 Separator Design .......................................................................................................21 3.4 Technical Performance Standards..............................................................................22 3.5 Maintenance...............................................................................................................22 3.6 Summary of Findings..................................................................................................24 iv 3.7 Recommendations .....................................................................................................24 4. EVALUATION OF STORMWATER TREATMENT TECHNOLOGIES .................................26 4.1 Purpose......................................................................................................................26 4.2 Design Storm .............................................................................................................26 4.3 Required Treatment Technology Information..............................................................26 4.3.1 Applications.....................................................................................................26 4.3.2 Site Characteristics.........................................................................................27 4.3.3 Design Criteria................................................................................................27 4.3.4 Construction....................................................................................................28 4.3.5 Operation and Maintenance............................................................................28
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