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Evaluating Technology Performance at DNAPL Sites

A new screening tool developed with support from ESTCP assists practitioners in selecting remediation technologies for dense non-aqueous phase liquid (DNAPL) source zones that best fit specific site conditions and performance goals. The tool will help users evaluate potential technology performance and reduce the uncertainty of estimating and predicting remedial outcomes and implementation costs.

Multiple technologies have been developed and applied over the past few decades to remediate chlorinated solvents in the subsurface, but remediation of DNAPL is particularly challenging. Factors such as geology, geochemistry, hydrogeology, the composition and distribution of the DNAPL, as well as the presence and absence of other contaminants, play a role in technology selection and performance. While individual technologies have been reviewed, a comprehensive assessment was needed to illustrate which technologies are most effective for specific site conditions and desired remedial goals.

The Naval Facilities Engineering Command - Engineering Service Center in collaboration with researchers from Geosyntec Consultants, Queen’s University, and the University of Edinburgh developed the DNAPL Technology Evaluation Screening Tool (DNAPL TEST), a user-friendly, Microsoft Access^TM-based screening tool. The foundation of DNAPL TEST is a database of information derived from case studies of field implementation of various remedial technologies, supported by numerical modeling of targeted technologies to address data gaps, and laboratory studies to provide information on fundamental processes that impact technology performance. Remedial technologies evaluated include in situ chemical oxidation; thermal technologies; surfactant enhanced aquifer remediation; hydraulic displacement; enhanced in situ bioremediation; and chemical reduction with zero-valent iron.

DNAPL TEST enables users to extract data from the database and perform simple statistical analyses to determine average behavior of data trends. Output reports provide comparative technology performance for a range of metrics—decrease in the DNAPL mass remaining in the subsurface, decrease in volatile organic compound (VOC) concentrations in groundwater, reduction of VOC concentrations in soil, achievement of maximum contaminant level (MCL) in groundwater, occurrence of rebound in groundwater concentrations, duration of treatment, achievement of remedial goals, and unit treatment cost—as well as indications of output data quality and references for source material. The user can perform multiple analyses to assess various scenarios, build complex sites, evaluate common trends, or complete a site-specific analysis of anticipated technology performance. This information can be used as the basis for developing realistic remedial end goals and for developing a short list of potential technologies for a site.

DNAPL TEST can help the Department of Defense move toward its goal of achieving Response Complete at 95 percent of Installation Restoration Program sites by 2021. The tool is most effectively used as a preliminary screening for technology selection or as a screening for possible performance limitations for a remedy in place. For those sites where remedies are not meeting established remedial action objectives (RAOs), DNAPL TEST can assist in determining whether there is a realistic expectation of meeting the RAOs for a given site and technology. The screening tool also can provide an assessment of alternative technologies to consider that may offer a higher likelihood of success.