ANALYSIS OF GEO-SPATIAL DISTRIBUTION OF HEAVY METALS IN HIGHWAY SURFICIAL SOILS LOADED BY URBAN STORM WATER

In the highway environment, traffic generates heavy metals and particulate matter through various vehicular and tire-pavement abrasive mechanisms. These materials are deposited, accumulate and then are transported by storm water. Soils subject to years of such loading can serve as a sink and a potential source for heavy metals depending on loading and drainage conditions. This paper reports on results of geotechnical analyses, heavy metal distributions, drainage influences and correlations to geotechnical indices for surficial (0–15 cm) glacial till samples recovered from two transects located along a heavily traveled urban inter state highway. Results are compared to a control site subject only to urban atmospheric deposition. Results of this investigation indicate, for this site, that heavy metal accretion in the surficial soils is a function of depth, surface drainage patterns, distance from the pavement edge and soil indices. Particulate-bound heavy metals deposition and accretion or export were a function of surface flow conditions such as velocity, flow depth and surface cover. Results indicate that heavy metal accretion rapidly decreases as a function of distance from the traveled roadway. Multiple linear regression method was also used to correlate geotechnical indices to heavy metal concentrations in soils. It was found that plasticity and organic matter content are two important parameters determining heavy metal concentrations in soils. While there is little control of traffic levels and past accretion, the use of geotechnical indices such as soil organic content and plasticity index as well as pavement runoff surface drainage patterns can provide information as to whether soils might act as a sink or source of heavy metals and, consequently, if pavement runoff best management practices (BMPs) may be justified.