Refining NAPL-related Risk and Remediation

September 12, 2019

It should go without saying that we all want to use resources wisely and avoid needless expenditures. When it comes to environmental remedies, overdesign can be costly in terms of time and money.

It’s important to accurately assess risk and support reliable, protective, and cost-effective remedial strategies. In sediments containing a nonaqueous phase (oily) liquid (NAPL), for example, it’s easy to overestimate environmental risk because NAPL can readily contaminate traditional porewater samplers like push-points and sorption-based passive samplers. NAPL entrained in porewater samples can cause reported aqueous concentrations to be overestimated by orders of magnitude, exaggerating actual risk and needlessly increasing remediation cost.

To minimize the risk of overestimating NAPL concentrations, Anchor QEA researched a variety of ceramic filters (Figure 1a) in the laboratory (Figure 1b) and field and pioneered their use for excluding NAPL from water samples, even in direct contact with NAPLs. Porous ceramic filter properties promote water entry but exclude NAPL; they can be used to sample for a wide range of chemicals by diffusion or pumping (Figure 2) (Gefell et al. 2018).

Figure 1

Figure 2

Porous ceramics have been used for decades to sample water in unsaturated soil and they are widely used to filter pathogens from drinking water. Ceramic filters are economical, readily available, versatile in shape and size, and relatively inert.

Anchor QEA has developed and used standardized ceramic sampling procedures at multiple sites for in situ porewater sampling in oily sediments, filtering porewater removed from sediment ex situ, and sampling groundwater at wells that contained light or dense NAPL (LNAPL or DNAPL) by diffusion or pumping.

The cost of an overdesigned NAPL site remedy can be well into the millions of dollars. But, at $30 to $100 per ceramic filter, this is an economical solution to avoid overestimating aqueous concentrations that drive perceived risk and actual remediation cost.

Gefell, M.J., D. Vlassopoulos, M. Kanematsu, D.S. Lipson, and B.R. Thompson, 2019. Advancing Mobility Testing and Aqueous-Phase Sampling in NAPL Zones. RemTEC Summit (Denver), February 26-28, 2019.

Gefell, M.J., M. Kanematsu, D. Vlassopoulos, and D. Lipson, 2018. “Aqueous-phase sampling with NAPL exclusion using ceramic porous cups.” Groundwater 56(6):847–851.

Gefell, M.J., D. Vlassopoulos, M. Kanematsu, and D. Lipson, 2018. Improving Dissolved Organic Chemical Concentration Measurements at Groundwater/Surface-Water Interfaces Containing NAPL. Eleventh International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Palm Springs, California); April 8-12, 2018.

Gefell, M.J., D. Vlassopoulos, M. Kanematsu, and D. Lipson, 2017. Aqueous Sampling without NAPL-Based Impacts. MGP 2017 (New Orleans); October 16-18, 2017.

Gefell, M.J., D. Vlassopoulos, M. Kanematsu, and M. Mahoney, 2017. Aqueous Sampling without NAPL Artifacts. RemTEC Summit (Denver), March 7-9, 2017