STORMWATER BMPS FOR HIGHWAYS CHALLENGES Stormwater Mgt Vs
STORMWATER BMPS FOR HIGHWAYS
CHALLENGES • • Stormwater Mgt. Vs Highway Safety Limited Right-of-way Highly Impervious Drainage Areas Extensive Cuts and Fills Spill Potential Use of Deicing & Anti-skid Materials Higher Concentrations of Pollutants Thermal Impacts in Summer & Winter
TYPICAL POLLUTANTS IN HIGHWAY RUNOFF Pollutant Source Particulates Pavement wear, vehicles, atmosphere, anti-skid, maintenance activities Nitrogen, Phosphorus Atmosphere, fertilizers Leaded gasoline, tire wear Zinc Tire wear, motor oil and grease Iron Auto body rust, steel highway structures, engine parts Copper Metal plating, bearing & bushing wear, brake linings, fungicides & insecticides Cadmium Tire wear, insecticides Chromium Metal plating, engine parts, brake lining Nickel Diesel fuel, gasoline, lubricating oil, metal plating, brake lining, asphalt paving Manganese Engine parts Cyanide Anti-caking compounds in deicing salts Sodium Chloride & Calcium Chloride Deicing salts Sulphates Roadway beds, fuel, deicing salts
TYPICAL POLLUTANTS IN HIGHWAY RUNOFF Pollutant Concentration (mg/l) Total Suspended Solids (TSS) 45 - 798 Volatile Suspended Solids (VSS) 4. 3 – 79 Total Organic Carbon (TOC) 24 – 77 Chemical Oxygen Demand (COD) 14. 7 – 272 Biochemical Oxygen Demand (BOD) 12. 7 – 37 Nitrate + Nitrite (NO 3 + NO 2 ) 0. 15 – 1. 636 Total Kjeldahl Nitrogen (TKN) 0. 335 – 55. 0 Total Phosphorus (P) 0. 113 – 0. 998 Copper (Cu) 0. 022 – 7. 033 Lead (Pb) 0. 073 – 1. 78 Zinc (Zn) 0. 056 – 0. 929 Fecal coliform (organisms/100 ml) 50 - 590
BMP CONSIDERATIONS • Higher levels of Suspended Solids – Vegetated Systems • Grassed Swales • Filter Strips • Bioretention – Structural Elements • Catch Basin Inserts • Filters • Manufactured Treatment Units – Maintenance Measures • Street Sweeping • Vacuuming
BMP CONSIDERATIONS • Vegetated BMPs effective in removing pollutant loads if properly designed • Spill Containment – Subsurface, infiltration, or vegetative systems may have to be replaced • Deicing & Antiskid application may adversely affect BMPs
BMP CONSIDERATIONS • Temperature Impacts on aquatic life in receiving waters – Vegetated Systems replace Concrete – Discharge from Extended Detention through Vegetated Swales or Buffers – Extended Detention Design • • Minimize Permanent Pool Preserve existing Shade Trees Align Pond in North-South Direction if possible Avoid excessive Riprap & Concrete
HIGHWAY/ROAD STRATEGIES • Utilize sod-forming grasses adjacent to Roadway Shoulders & for Vegetated Swales to serve as Filters for Suspended Solids and Metals
HIGHWAY/ROAD STRATEGIES • Utilize non-invasive native species vegetation in lawn areas, on slopes and within wetland reconstruction/ banking areas to enhance Water Uptake and the storage of certain pollutants in plant tissue.
HIGHWAY/ROAD STRATEGIES • Limit use of curb-gutter sections as much as practical for Filtering and Temperature considerations
HIGHWAY/ROAD STRATEGIES • Limit use of storm sewers as much as practical for Filtering and Temperature considerations.
HIGHWAY/ROAD STRATEGIES • Consider Bioretention capability in the design of new detention basins (Dry Extended Detention Basin design)
HIGHWAY/ROAD STRATEGIES • Monitor the effectiveness of existing Constructed Wetlands, updating the current design practices as necessary
HIGHWAY/ROAD STRATEGIES • Consider alternative methods of energy dissipation (in lieu of rock aprons) at culvert and storm sewer outfalls for Temperature considerations Perforated Pipe in an Aggregate Trench Spreader with Filter Strip Trench
HIGHWAY/ROAD STRATEGIES • Where practical, discharge storm sewers into wetland areas or vegetated swales for Filtering & Temperature considerations
HIGHWAY/ROAD STRATEGIES • Consider vegetated islands in lieu of concrete islands for Filtering and Temperature considerations
HIGHWAY/ROAD STRATEGIES • Consider use of Infiltration Berms and Retentive Grading in areas downslope of the roadway Infiltration Berm Cross-section Series of Woodland Infiltration Berms
HIGHWAY/ROAD STRATEGIES • Continue to monitor & minimize volume of winter maintenance materials to Minimize Pollutant Loadings
HIGHWAY/ROAD STRATEGIES • Continue to protect all salt storage & loading areas from weather influences to Minimize Pollutant Loadings
HIGHWAY/ROAD STRATEGIES • Consider practices to dilute flows where high concentrations of salts are anticipated to Minimize Pollutant Loadings
HIGHWAY/ROAD STRATEGIES • Consider Porous Pavement on Parkand-Ride sites and for Department building site parking lots
HIGHWAY/ROAD STRATEGIES • Consider Dry Wells and other Subsurface Infiltration for Department building roof drains
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