EVALUATION OF VARIATION IN BACKGROUND CONCENTRATIONS OF SELECTED METALS IN SOIL BASED ON PARENT GEOLOGIC MATERIAL

A total of 107 soil samples were collected from 36 soil core locations across Onondaga County, New York (USA) to evaluate naturally occurring (background) concentrations of the metals silver (Ag), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn). Soils in the area of study developed on one of six geologic materials: 1) glacial till; 2) glaciolacustrine or glaciofluvial sand; 3) glaciolacustrine silt and clay; 4) glacial outwash deposits; 5) modern alluvium; or 6) organic-rich deposits. Sample locations were selected primarily based on the type of geologic parent material from which the soil was derived rather than a standardized, random sampling grid employed in some background studies. All samples were analyzed by flame atomic absorption spectroscopy using United States Environmental Protection Agency-approved methods. Appropriate quality control samples were analyzed to allow evaluation of precision, accuracy, and reproducibility.

Background concentrations of Ag and Cd were typically less than method detection limits. Calculated geometric means for the complete data set for Cr, Cu, Ni, Pb, and Zn were 27, 19, 28, 19, and 45 micrograms per gram, respectively. Variation between soil samples collected from different parent geologic materials were evaluated using statistical techniques when appropriate. Statistically significant differences in background concentrations of Cu and Zn were documented in soils derived from several parent geologic materials. Statistically significant differences for Cu and Zn were also documented in mean background concentrations for Onondaga County soils relative to previously published background means for the eastern United States (values often utilized by regulatory agencies in the development of soil cleanup criteria). The results of this investigation reinforce the importance of considering regional and site-specific geologic variations with regards to sampling design, interpretation of analytical data, and evaluation of appropriate and enforceable soil remediation goals.