Polydimethylsiloxane dialysis passive sampler monitoring of chlorinated solvent contaminated sites - A field study

The complexity of the subsurface contaminated by chlorinated solvents such as trichloroethylene (TCE) makes it challenging to gain a complete understanding of contamination distribution and establish a conceptual site model (CSM). High-resolution vertical contaminant concentration profiling across both the unsaturated zone and the saturated aquifer is desirable for mapping the distribution of contamination. A Fick's law-based polydimethylsiloxane (PDMS) dialysis passive sampler was developed and evaluated on a field scale for its potential application. This study tests the passive sampler at two TCE contaminated sites, and the sampling results were compared with the results from different sampling methods based on the relative percent difference. The PDMS dialysis passive sampler obtained more representative soil gas concentrations in the unsaturated zone than a portable monitoring and sampling device, which caused soil gas flow disturbance by soil gas pumping during sample collection. In the saturated aquifer sampling, the results obtained by the PDMS dialysis passive sampler correlated well with those obtained by a commercial polyethylene passive diffusion bag, and exhibited higher sensitivity under low TCE concentration conditions. Furthermore, the PDMS dialysis passive samplers were densely deployed inside each monitoring well at multiple depths, at two sites, to achieve high-resolution monitoring across the unsaturated zone and saturated aquifer. Based on the PDMS dialysis sampler data, a more comprehensive three-dimensional CSM was systematically established.