Remediation of Petroleum-UST-Impacted Groundwater

Client Challenge

The Arizona Department of Environmental Quality (ADEQ) entered a vacant property, known as former Medina’s Garage, into its orphan site program. Characterization activities determined that a historical plume of volatile organic compounds (VOCs) originating at the service station had migrated off site, beneath a four-lane roadway and adjacent vacant properties.

GES Solution

GES was engaged to steward the site to closure, including additional site investigation activities, preparation of a remedial action plan (RAP), and implementation of the solutions specified in the RAP. GES utilized various statistical analyses of the groundwater data to develop a better understanding of the dissolved plume’s extent, concentration gradient, and natural attenuation. While continuing to monitor groundwater quality on site and in the surrounding area, GES installed a targeted air sparge and soil vapor extraction (AS/SVE) system, with thermal catalytic treatment of the SVE off-gas, to address source-area impacts. The system was operated for about a year, until decreasing concentrations made continued operation of the system economically impractical.

As a second phase of the remedial program, GES implemented an in-situ chemical oxidation (ISCO) program using injections of activated persulfate to mitigate the remaining groundwater impacts. This involved injection of a total of 5,200 pounds of the activated persulfate into on- and off-site injection wells in seven events over the course of 12 months.

Client Value

As monitoring of the site has continued, GES has noted a 90% decrease in groundwater VOC concentrations. Results appear favorable to support case closure. Due to the work performed by GES, a formerly undevelopable contaminated site will be returned to beneficial use within the city of Tucson.