Multiple technologies have been developed and applied over the past few decades for remediation of chlorinated solvents in the subsurface. The remediation of solvents in the form of dense non-aqueous phase liquids (DNAPLs) 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. To date, despite a multitude of reviews on several individual technologies, no comprehensive studies have been completed that illustrate which technologies generally work best under specific site conditions and desired remedial outcomes or goals.
The objective of this project was to develop a user-friendly screening tool that could be used by decision makers during the remedial technology selection or evaluation process to:
The DNAPL Technology Evaluation Screening Tool (DNAPL TEST) was developed using data from published literature cases and modeling simulations that were used to supplement existing data. Hence, the basis of the screening tool 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 impacting technology performance.
DNAPL TEST can assist environmental remediation practitioners in evaluating and selecting appropriate remedial technologies given particular site conditions and performance goals. With the U.S. Department of Defense moving rapidly towards achieving Response Complete at 95% of Installation Restoration Program sites by 2021, the information and screening tool developed as part of this project also can be used to evaluate existing remedial systems. For those sites where remedies are not meeting established remedial action objectives (RAOs), the screening tool can assist in determining whether there is a realistic expectation of meeting the RAOs for a given site and technology. It also can provide an assessment of alternative technologies to consider that may offer a higher likelihood of success.
Observations on technology performance can be made based on the modeling results and field case study data collection completed to date. Some of these are summarized below.
DNAPL TEST has been designed to be updated in the future to reflect new data. As new field, laboratory, or modeling case studies become available, they can be added to the database. When sufficient new case studies have been added, the statistical analysis can be conducted again to refine statistical relationships. The costs to operate DNAPL TEST are very low. The time required to run an analysis is approximately 10-20 minutes.
This 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. It cannot replace appropriate site-specific evaluations based on engineering judgment. DNAPL TEST cannot “predict” technology performance for a particular site but will provide the user with an anticipated range of performance and the ability to compare performance observed for multiple technologies. This information can be used as the basis for developing realistic remedial end goals, as well as developing a short list of potential technologies for a site.
For users interested in obtaining potential technology performance information for a specific site, a Site Specific Analysis will better focus the screening evaluation to include sites that are anticipated to have similar performance. Multiple Site Specific Analyses may be completed for the same site to focus on different areas with different site characteristics. It should be noted that the Site Specific Analysis does require a minimum level of knowledge of conditions at the user’s site, which may limit its usefulness for some sites. Guidance for estimating these parameters is provided within the tool.
For more general analyses of overall performance trends between parameters and for sites at which key site parameters are unquantified, the General Analysis will be a better option. Modifications to search parameters can easily be changed at any time during the screening process, allowing users to refine their analyses to better meet their needs.
Specific examples illustrating a General and a Site Specific Analysis are provided in the User’s Manual, accessible via the Database (DNAPL TEST Tool) link.