Extreme short-range variability in VOC-contaminated soils

To accurately characterize Volatile organic compound (VOC) distribution in contaminated soils for the purpose of ascertaining the need for site remedi ation, horizontal and vertical concentration fluctuations must be taken int o account when designing the sampling program. Soils at two Supelfund sites were collected to examine VOC concentration and soil property variability over extremely short distances (less than or equal to 15 cm). Differences i n VOC concentrations between the upper and lower core sections (15 cm apart ) were generally on the same order (1 to 4 times different) as the differen ces found for the TOC, sand, and clay contents; however, several notably la rger variations in VOC concentrations were found. Relative percent differen ces (RPDs) up to 161, 96, 117, and 191% were found for TOC, sand content, c lay content, and VOC concentrations between upper and lower core sections, respectively, These elevated RPDs correspond to maximum concentration diffe rences between upper and lower core sections of 25.5 and 72.5%, 5.8 and 22. 0%, 0.29 and 2.71%, and 78 and 3371 ng/g for TOC, sand content, clay conten t, and VOC concentrations, respectively. The large differences in soil prop erties and VOC concentrations that can occur over extremely short distances must be taken into account during site characterization. Without knowing t he magnitude of the extreme short-range variability, erroneous interpretati ons of contaminant concentrations and distributions can lead to costly reme diation when it is not necessary (i.e., false positives) or the leaving beh ind of a significant threat to human health and the environment when not de tected (i.e., false negatives).