Sources of Zinc in Highway Runoff

Focus Area

Water Quality/Wetlands


Natural Resources






Over 3 years

Research Idea Scope

General Scope of Work: Task 1: Literature Review. Complete a literature review to determine the sources of zinc in highway runoff. The literature review should also attempt to determine if there is the potential to reduce zinc oxide in tire tread. The review should include assessments of shredded tire backfill and crumb rubber in pavement. The literature review should examine research completed internationally as well as in the US. The findings of the literature review will serve as the basis for the subsequent tasks in the research to assign relative contributions to each of the identified sources. Task 2: Identify three catchments in urban areas across the US to perform the field investigations. The selected catchments should reflect the potential sources of zinc identified in Task 1 including aerial deposition and contributions from site soils and pavements, should be geographically diverse, and should have multiple zinc TMDLs. Task 3: Laboratory and Field Study Plan. Develop a laboratory and field study plan for bench scale testing and the selected catchments and based on the findings of the literature review to quantitatively assess the relative contributions of zinc from the identified sources in the highway right-of-way. This includes relative contributions in highway runoff and overall estimated contributions to the watershed. Laboratory work should be completed to preliminarily assess the potential relative contributions from tire wear, appurtenances such as guard rail, fences and sign posts/bridges and zinc coated storm drain pipe. Task 4: Perform the field study over a two-year period to gather data that will enable a characterization of the relative contribution of identified sources of zinc in highway runoff. Sources will often be site-specific. This task will include the following goals: 1. Identify the sources and relative contribution from vehicles: tires, motor oil, other vehicle parts, etc. This will include edge-of-pavement runoff monitoring 2. Identify the sources and relative contribution from other sources in the right-of-way: galvanized drainage pipes, fencing, signage, structures such as overpasses, and the soil reservoir (from previous deposition from particles carried to the roadside by vehicle-induced and natural air movement). 3. Assess localized zinc loading to runoff contributed by segments of the roadway constructed with rubberized asphalt concrete (laboratory only). 4. Assess aggregate contributions from highways compared with other sources in the watershed. Task 5: Draft Report. Prepare a draft report summarizing the findings from Tasks 1 – 4. Task 6: Final Report. Prepare a final report that includes recommendations for source control measures that can be implemented by DOTs or with the assistance of other entities to reduce the concentration and load of zinc in highway runoff. The recommendations should focus on technical feasibility. Task 7: Publish the final report and provide a list of recommended future studies or recommended research needed to further advance DOTs towards meeting water quality standards for zinc in highway runoff.

Urgency and Payoff

Departments of Transportation are required to comply with the requirements of the Clean Water Act (CWA) as well as state environmental regulations. Nationally, the EPA lists 323 waterbodies as impaired by zinc. This represents about 13% of all waterbodies nationally identified as impaired by metals, and is the 5th ranked metal causing impairment behind arsenic, selenium, copper, iron and lead. Zinc is a common constituent of concern in highway runoff. Zinc, plus copper and lead are the metals that most frequently exceed water quality standards at the point of discharge. Copper and lead loadings are expected to decrease significantly as legislative and other controls reduce their use in the transportation environment. Unfortunately, no similar efforts are underway for zinc. DOTs are being required to reduce the concentration of zinc in their runoff not only to comply with TMDLs but also to prevent exceedances of water quality standards. This research will provide DOTs with the information needed to determine the highest priority sources of zinc within their right-of-way, and the most economical approach to reducing each identified source. DOTs must find ways to utilize stormwater program resources in a cost efficient manner. The benefit of this research statement will be to allow DOTs to focus their resources in the most cost effective manner. DOTs have a variety of best management practice (BMPs) available for use that differ in cost and effectiveness. This project will allow DOTs to reduce zinc pollution at the source for the most significant sources in the right-of-way.

Suggested By

Scott Taylor AFB 65 Stormwater 760 603 6242

[email protected]