This study reviewed the literature on the occurrence of lead in soils and its relationship to waste oil tank leaks. Many studies have been conducted on the natural occurrence of lead in rocks, soils and water. Very low levels (0.001 mg/l to 0.01 mg/l) are found in surface and groundwater, variable levels are found in soils (from less that 10 ppm to as high as 700 ppm but more normally a high of 70 ppm), and the lead levels found in rocks range from 7 to 80 mg/kg.
Risk assessment calculations have been made by several individuals, also with variable results. One value was computed at 20 mg/kg lead in soil and another was calculated as high as 200 mg/kg. A standard of 25 mg/kg is proposed for Kentucky based on the natural background level found in soils studied in the state. For sample values taken in tank pits that do not meet this standard a background value must be determined by taking 5 soil samples at one-meter depth upgradient from the tank pit and averaging them.
Even though recommended cleanup level is not based on risk analysis methods, when referring to various risk documents, the value selected here is slightly lower than mean value (36 mg/kg) derived from an analysis of background samples at various remediation sites across the state. Standards in place in other states range from less than 0.1 mg/kg to as high as 2000 mg/kg. Texas uses 20 times the MCL, and Pennsylvania uses 200 ppm for the non-indiustrial sites and 600 ppm for industrial sites.
Struttmann, T. W.; Sendlein, Lyle V. A.; and Fletcher, Dave, "Lead in Kentucky Soils" (1995). KWRRI Research Reports. 222.