Comparison of sampling techniques and evaluation of semipermeable membranedevices (SPMDs) for monitoring polynuclear aromatic hydrocarbons (PAHs) ingroundwater

Groundwater was sampled at the site of a former manufactured-gas plant usin g three conventional methods (bailing, low-flow, and bailing with filtering ) and longterm in-situ samplers (semipermeable membrane devices [SPMDs]). S amples from each technique were analyzed for polynuclear aromatic hydrocarb ons (PAHs) and total suspended solids (conventional methods only) to determ ine the effect of sampling procedure on PAH concentrations. In general, amo ng the conventional techniques, bailing indicated the highest PAH concentra tions, 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. SP MD results corroborated this finding. SPMDs performed well in this study; S PMD-derived PAH concentrations in the groundwater were similar to values ob tained by the conventional techniques. Furthermore, they allowed detection of some PAHs not detected by conventional approaches in wells with low leve ls 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. Ove rall, this study suggests that SPMDs have high potential for use in groundw ater monitoring, producing results consistent with conventional grab-sampli ng techniques, providing enhanced sensitivity integrated over extended time periods, and facilitating accurate determinations of truly dissolved PAH c oncentrations.