EVALUATION OF SAMPLING METHOD EFFECTS ON VOLATILE ORGANIC-COMPOUND MEASUREMENTS IN CONTAMINATED SOILS

An experiment was conducted to evaluate the effects of sample disturbance, container headspace volume and integrity, and sample preservation on volatile organic compound (VOC) measurements in contaminated soil. A sandy soil was contaminated under controlled conditions at 10 °C by an aqueous solution containing six target VOCs: methylene chloride (157.5 mg/L), 1,2-dichloroethane (130 mg/L), 1,1,1-trichloroethane (16 mg/L), trichloroethane (12.8 mg/L), toluene (4.5 mg/L), and chlorobenzene (2.85 mg/L). Replicate soil samples were then collected by different methods at an air temperature of 20 °C. For all VOCs, the highest concentrations were measured in undisturbed soil samples immediately immersed in methanol in Teflon-sealed glass bottles. With these measurements as a reference, the relative negative bias was highest for container integrity (up to 100%) and lack of methanol immersion (up to 81 %) and considerably lower for container headspace volume (up to 17%) and soil disturbance (up to 15%). The potential for negative bias appeared to be correlated with the VOC soil sorption affinity (i.e., low Kh and high Kow). For accurate measurements of the more volatile compounds, rigorous sampling procedures are necessary. © 1990, American Chemical Society. All rights reserved.