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Stormwater Runoff

Environmental Effects of Highway Runoff

Table 1 presents a summary of potential sources of chemical constituents generally found in highway runoff. Suspended sediment concentrations typically are the highest of any storm water runoff parameters associated with storm water runoff (Driscoll and Mangarella, 1990). Sediments with high organic or clay content typically act as a carrier of bacteria, trace metals, and toxicants. Heavy metal concentrations within storm water runoff are of concern because of their potentially toxic effects on aquatic habitat and drinking water sources.

Table 1. Constituents and Sources in Highway Runoff
Constituent Source
Particulate Pavement wear, vehicles, atmospheric deposition, maintenance activities
Nitrogen, Phosphorus Atmospheric deposition and fertilizer application
Lead Leaded gasoline from auto exhausts and tire wear
Zinc Tire wear, motor oil, and grease
Iron Auto body rust, steel highway structures such as bridges and guardrails, and moving engine parts
Copper Metal plating, bearing and brushing wear, moving engine parts, brake lining wear, fungicides and insecticides
Cadmium Tire wear and insecticide application
Chromium Metal plating, moving engine parts, and brake lining wear
Nickel Diesel fuel and gasoline, lubricating oil, metal plating, bushing wear, brake lining wear, and asphalt paving
Manganese Moving engine parts
Cyanide Anti-caking compounds used to keep deicing salts granular
Sodium, Calcium, Chloride Deicing salts
Sulphates Roadway beds, fuel, and deicing salts
Petroleum Spill, leaks, antifreeze and hydraulic fluids, and asphalt surface leachate
Source: Adapted from USEPA, 1993.

Table 2 summarizes the constituent removal processes employed by the various types of BMP categories. For additional discussion of BMP categories and specific design features, refer to Chapter 3. Review of the primary constituent removal mechanisms for the BMP to be monitored can guide selection of the constituents to be monitored in inflow and outflows (i.e., dissolved, adsorbed, transformation products), the type of supplementary monitoring (i.e., filter media, depositional materials), and the timing of the monitoring (i.e., settling, infiltration timing).

Table 2. Primary Constituent Removal Mechanism in Selected BMP Categories
Constituent Infiltration Bioretention Detention/Retention/Wetlands Sand Filters Vegetated Swales/Filter Strips Water Quality Inlets Porous Pavement Street-sweeping Other Nonstructural BMPs
Heavy Metals Adsorption Filtration Adsorption Settling Settling Filtration Settling Filtration Adsorption Settling Filtration Adsorption Physical Removal Source Control
Organics Adsorption Biodegradation Adsorption Settling Biodegradation Volatilization Settling Filtration Adsorption Settling Filtration Adsorption Physical Removal Source Control
Nutrients Adsorption Bioassimilation Bioassimilation Settling Bioassimilation Settling Filtration Adsorption None Source Control
Solids Adsorption Adsorption Settling Settling Filtration Settling Filtration Settling Filtration Adsorption Physical Removal Source Control
Oil & Grease Adsorption Adsorption Settling Filtration Adsorption Adsorption Settling Filtration Adsorption None Source Control
Source: Adapted from Maestri et al., 1988; Scholze et al., 1993

Storm water Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring, USFHWA

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