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.
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Table 1. Constituents and Sources in Highway Runoff
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| 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. |
Storm water Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring, USFHWA (http://www.fhwa.dot.gov/environment/ultraurb/uubmp1.htm)
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
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Storm water Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring, USFHWA (http://www.fhwa.dot.gov/environment/ultraurb/uubmp1.htm)
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