Challenge

The Stringfellow Superfund Site is a former Class I industrial waste disposal facility that included as many as 20 surface impoundments to contain and evaporate liquid chemical wastes.  During its operating life from 1956 to 1972, about 36 million gallons of liquid industrial process wastes containing spent acids and caustics, solvents, pesticide by-products, metals, and other inorganic and organic constituents were discharged to the ponds.

Solutions

GLA was contracted to work on behalf of the Department of Toxic Substances Control in 2001. Since that time, we have provided routine groundwater monitoring at up to 450 annually of the site’s more than 500 on- and off-site monitoring and extraction wells. We have also providing drilling and well installation using a variety of drilling techniques. We have prepared monitoring reports since 2001 for this monitoring program that include analytical results, statistical analyses, trend analyses, and maps showing contaminant concentrations. Our groundwater monitoring program has also included non-routine sampling and analyses of privately-owned wells in communities downgradient of the site.

During non-routine sampling of community wells, GLA discovered perchlorate in the water. Our contract was extended to include assisting with remediation for this issue through an investigation to identify potential sources of perchlorate contamination. We used cone penetrometer testing and in situ groundwater sampling at 46 community locations to character the extent of the impact, as well as exploratory drilling, soil sampling, monitoring well installation, and groundwater monitoring to identify the vertical and lateral extent of the impact. We developed a three-dimensional, numerical groundwater flow and contaminant model of the area downgradient of the site, and the Department of Toxic Substances Control has subsequently used this model to evaluate perchlorate impacts. The project was completed over a period of 8 months, including collecting soil samples at 5-foot intervals, compositing the soil samples for each 20-foot interval above groundwater, and culminating in the installation of 41 groundwater monitoring wells.

GLA has also provided services to help remedy other issues presented to the community by the former facility. We have performed unexploded ordinance surveys to clear adjacent properties that were historically used for explosives manufacturing and/or testing, performed soil testing to characterize geologic and environmental conditions at adjacent properties, and provided general environmental support to remove debris and other relics from the former facility on surrounding properties. Our team also consists of bilingual staff to assist with coordination of gaining access to privately owned wells within the largely Hispanic community.

Results

Our work on the site over the last nearly 25 years providing routine and non-routine services has ensured that the Superfund site meets all regulatory requirements for groundwater monitoring. We have worked with all the affected property owners to minimize impacts, while maximizing benefit to the community by remediating the direct threat posed by both the perchlorate in the groundwater and the bigger, lingering environmental threat from the prior waste disposal facility.