Formatted Title
Using Electrical Hydrogeology for Reduced Risk in Final Remedial Design
Background/Objectives
Environmental site characterization field efforts since the 1980s have demonstrated that conceptual site models (CSMs) typically require high subsurface data density to accurately predict contaminant distribution and groundwater transport. Electrical hydrogeology via specialty electrical resistivity imaging (ERI) has been applied to site characterization for multiple decades with great success and increasing use. This technology can be used to build a robust CSM of the site for better remedial design characterization.
Approach/Activities
Electrical hydrogeology principles were added to the workflow at a Brownfields site contaminated with PCE and PAHs in Washington State. Targeted drilling locations were selected from the resulting images, and the CSM was updated. This scan-first-then-drill approach located additional areas of concern and helped identify bioremediation and zero valent iron injection as a potential remedial technology to compliment electrical resistance heating (ERH).
Results/Lessons Learned
The use of electrical hydrogeology revealed three primary areas of concern on the site that were the focus of the subsequent targeted drilling. The drilling confirmed that two of the areas were previously unidentified sand channels that were influencing the lateral migration of dissolved phase contaminants. The third area was located near a potential source zone that was determined to not be a concern for remediation. The specialty ERI results also indicated the presence of high biological activity in the dissolved phase contaminant plume. These results were supported by monitoring well data with PCE degradation products downgradient from the primary source area. Stakeholders were able to incorporate these results into their remedial design plans, providing discrete target zones for more cost-effective remediation and reducing the risk of trailing liabilities. The electrical resistance heating has reduced PCE/TCE to (+/- 40 ppb or less) in groundwater and the bioremediation amendment/ISCR in the injection area has reduced VC to below 0.48 ppb.