Installation Restoration Optimization

Challenge & Solution

Two groundwater treatment plants were installed at federal government sites to treat contamination including volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs).  The removal efficiency of the groundwater treatment plants became asymptotic, but the levels of the chemical constituents were still above the federal and state criteria. Because of our closure experience, Rhea was retained to review the plume delineations and develop an optimization plan for the continued use of the groundwater treatment plants, which actively treat the 590 acre site.

Rhea also performed an investigation to locate additional VOC sources of groundwater contamination at the site.  Highly variable contamination levels of PCA and PCE in some of the site recovery wells indicated a potential source area in the vadose zone that becomes saturated during periods of high groundwater.  The goal of the investigation was to improve the subsurface contamination capture, thereby reducing operational time to closure.

Project Description & Highlights

At one site, Rhea determined the groundwater and geology had not been fully characterized for optimal groundwater treatment.  Further, six of the 15 recovery wells had not been properly maintained. At several of the wells, a substantial silt build up was encounteredrather than removing the silt, the pumps had been raised to a higher elevation. Thus, the pump screen had been raised out of the impacted groundwater zone.

Rhea prepared a Work Plan (WP), to better define the vertical and lateral extent of the plume and to optimize the contaminated groundwater recovery.  This project is currently underway, and preliminary sampling has shown that the contaminant plume has migrated beyond the existing remedial system capture zone in some locations.

At the second site, once an Explosive Safety Submission Report was prepared by Rhea, a geophysical survey was performed at the site to assess the possible presence of buried metallic objects. The results indicated several concentrated areas of buried metal.  After preparing a UXO WP and an overall WP, including a Quality Control Plan (QCP), the investigation was performed to delineate the contamination.

After completing the field work, a summary report was prepared with recommendations to accelerate the time for groundwater remediation and cost estimates for each recommendation. The cost savings was estimated to approach $30 million. 


North Carolina