Sampling unsaturated-zone water for trichloroethene at Picatinny Arsenal, New Jersey

A new method of collecting samples of unsaturated-zone water for quantitative analysis for a volatile organic compound, trichloroethene (TCE), was compared to three other, previously described sampling methodologies in the laboratory and in the field. In the laboratory, prepared water samples containing TCE in a known concentration (20 μg/L) were sampled repeatedly by using each of the four methods to quantify method precision and accuracy. To compare the four methods in the field, unsaturated-zone water above a TCE- contaminated water-table aquifer was transferred from a depth of 2 m to land surface with 0.15-m-long suction lysimeters attached to 1.85-m lengths of stainless-steel tubing. Statistical analyses of the laboratory and field data indicate that the new method, which involves collecting the water samples in gas-tight glass syringes, is superior to the other three methods for the quantitative sampling and analysis of TCE on the basis of its high precision and accuracy and ease of use. This method was used to collect additional samples from the field site to quantify the spatial variability of TCE concentrations in the unsaturated-zone water. Results of analysis of variance of the data indicate that the spatial concentration variability is important, and that differences in TCE concentration are statistically significant for horizontal distances less than 3.6 m.