NOREAS scientists have been working on the investigation and remediation of groundwater at OU-20 at Naval Air Station (NAS), North Island in San Diego, California. Groundwater at the site is impacted with hexavalent chromium [Cr(VI)] and CVOCs (mostly TCE). The plume covers over 5 acres, in a very busy part of the NAS. NOREAS designed a site-specific bench-scale test to evaluate the feasibility of a number of in situ biological and abiotic approaches to simultaneously treat Cr(VI) and CVOCs via reduction. Microcosms were set up to test various electron donors including: zerovalent iron (ZVI), lactate, emulsified vegetable oil (EVO), and EHC-M. Ultimately, data from the bench test were used to perform a pilot test on site, where the selected donor was injected into “test cells.” The pilot test evaluated the EVO/abiotic reductant donor plus bioaugmentation using two different injection techniques – conventional direct push injection (DPI) and liquid atomized injection (LAI).
NOREAS has continued work on the full-scale remediation of groundwater at OU-20 at NAS, North Island. The primary focus of the full-scale system is to remove Cr(VI) from groundwater via in situ reduction and stabilization as trivalent chromium [Cr(III)]. However, because the Cr(VI) plume lies within the larger OU-20 CVOC groundwater plume, reduction of CVOCs within the footprint of the Cr(VI) plume, as well as two adjacent areas with high TCE concentrations, are also being addressed. Cleanup goals are in place for Cr(VI), TCE, and vinyl chloride, a daughter product of TCE degradation. NOREAS utilized the results of its bench and pilot testing to develop a full-scale design that involves engineered plume collapse, and injection of over 30,000 gallons of amendments, EVO, abiotic reductant [to enhance the rate of Cr(VI) reduction], and bioaugmentation culture using almost 500 injection locations.
To maximize cost-effectiveness, EVO containing the abiotic reductant is only being applied in areas where Cr(VI) treatment is needed. Areas where CVOCs are exclusively present are receiving only EVO. Bioaugmentation culture are applied in all target removal areas to aid reductive dechlorination of CVOCs, given that TCE is present throughout. In addition, PRZ is planned for upgradient plume control (CVOCs only). A performance monitoring program is planned to evaluate the critical aspects of the treatment action.