Aqueous Sampling without NAPL-Based Impacts

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Aqueous Sampling without NAPL-Based Impacts

Author:
Michael J. Gefell and Masa Kanematsu, Ph.D. (Anchor QEA, LLC)
David S. Lipson, Ph.D. (Hydro Science + Engineering)

 

Presenter:

Michael J. Gefell

Anchor QEA, LLC

Speaker Bio:

Michael Gefell, P.G., C.P.G., is a principal scientist at Anchor QEA. He holds a B.A. in geological sciences from Cornell University and an M.S. in geology from the University of California – Davis. Mr. Gefell has more than 27 years of experience in environmental site assessment and remediation. Primary areas of interest include quantitative hydrogeology, NAPL assessment, fractured bedrock, groundwater/surface-water interaction, innovative site characterization methods, modeling, and remedial design. He is an associate editor of Ground Water journal and received the 2013 Technology Award from the National Ground Water Association.

Abstract:

The presence of nonaqueous phase liquids (NAPLs) can complicate water sampling and lead to false positives or overestimates of dissolved-phase concentrations in water samples. Devices that collect whole-water samples can entrain NAPLs in water samples and thereby result in unrealistic constituent concentrations. Passive sampling devices that rely on sorption can become fouled with NAPLs. Partitioning calculations of aqueous concentrations based on multi-component NAPL composition, or for whole-sediment or soil samples containing NAPL, is also complicated because this method requires assumptions regarding unidentified NAPL components and subcooled liquid effects. The objective of this study was to test a porous, hydrophilic sampling device that acts as a capillary barrier to NAPL but allows representative water samples to be collected by diffusion or pumping through the porous barrier. This study tested the following four key performance factors for the sampling device: 1) wettability of NAPL on the barrier material in the presence of water; 2) non wetting phase entry pressure; 3) diffusion-based equilibration of dissolved organic compounds; and 4) ability to expedite aqueous sampling by advection (pumping). Wettability test results indicate that in the presence of water, a PAH-rich NAPL was the non-wetting phase in contact with the porous sampling device. Entry pressure test results confirmed that the sampler pore sizes exclude non-wetting NAPLs under expected field conditions. Chemical equilibration testing results indicate that water inside the porous sampling device equilibrates with surrounding water due to diffusion. The potential for faster equilibration by pumping through the porous sampling device has also been confirmed. These results indicate that porous sampling devices that act as capillary barriers to NAPL flow could have a wide range of aqueous sampling applications in the presence of NAPL, including sediment porewater, monitoring wells, direct-push devices, and in situ or ex situ filtration of pumped fluid samples.

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