Comparison of sampling techniques and evaluation of semipermeable membrane devices (SPMDs) for monitoring polynuclear aromatic hydrocarbons (PAHs) in groundwater

Groundwater was sampled at the site of a former manufactured-gas plant using three conventional methods (bailing, low-flow, and bailing with filtering) and longterm in-situ samplers (semipermeable membrane devices [SPMDs]). Samples from each technique were analyzed for polynuclear aromatic hydrocarbons (PAHs) and total suspended solids (conventional methods only) to determine the effect of sampling procedure on PAH concentrations. In general, among the conventional techniques, bailing indicated the highest PAH concentrations, and bailing/filtering the lowest, with low-flow sampling in between. High-molecular-weight PAHs were most prevalent in bailed samples and most impacted by filtering, suggesting these species are particle-associated. SPMD results corroborated this finding. SPMDs performed well in this study; SPMD-derived PAH concentrations in the groundwater were similar to values obtained by the conventional techniques. Furthermore, they allowed detection of some PAHs not detected by conventional approaches in wells with low levels of contamination. An alternative method to the traditional equations for estimating aqueous contaminant concentrations from SPMDs is proposed. This method may be more appropriate in groundwater where low flows prevail. Overall, this study suggests that SPMDs have high potential for use in groundwater monitoring, producing results consistent with conventional grab-sampling techniques, providing enhanced sensitivity integrated over extended time periods, and facilitating accurate determinations of truly dissolved PAH concentrations.