Regulatory Closure of a Large Groundwater Plume and Redevelopment at a Legacy Aerospace Site – NASA Downey CA

Regulatory closure has now been achieved for the 4,000-foot-long chlorinated solvent plume underlying the former NASA Industrial Plant located in Downey, California. The site was treated with soil vapor extraction, then enhanced reductive dichlorination (biostimulation) was conducted between 2005-2012. Spot treatments using permanganate-based in-situ chemical oxidation in the lower vadose zone and bioaugmentation in the groundwater were also conducted. The site was in post-remediation monitoring between 2012-2016 and the LARWQCB issued a no-further-requirements-for-groundwater letter in March, 2017.

Cleanup of large plumes is often thought to be unachievable and, as a result, management strategies typically employ containment or deferral approaches that require long-term stewardship. The former NASA Industrial Plant is a counter-example to conventional expectations, at which a large plume cleanup was achieved concurrent with a $1B redevelopment effort that includes a hospital, medical office complexm and extensive retail space.

Several sources contributed to the groundwater cVOC plume, which was eventually mapped to be greater than 4,000-feet long, comprising tetrachloroethene (PCE) and trichloroethene (TCE), and their dechlorination products cis-DCE and vinyl chloride. Groundwater was encountered approximately 45-60 feet below surface in the interbedded, predominantly fined-grained sediments of the San Gabriel River alluvium.

Groundwater remediation efforts began in 2005 with the installation of 10 injection well transects (144 injection wells, total) perpendicular to groundwater flow, supporting an inject-and-drift carbohydrate amendment process. The transect strategy allowed concurrent remedial action and redevelopment, with only limited need for rerouting or replacement of remedial system infrastructure.

The site is now fully utilized in its redeveloped state. All redevelopment and site cleanup obligations have been fulfilled, notably including successful completion of the guaranteed, fixed-cost-to-closure contract for cleanup of the 4,000-foot-long chlorinated solvent groundwater plume.

The performance of the groundwater remedy at the former NASA Downey site challenges conventional thinking on the restoration of large, complex, groundwater plumes.