Thompson Engineering has been providing environmental consulting services at a Prichard, AL gas station since 2007 when testing found free product and a consistent presence of high concentrations of gasoline contaminants in the groundwater at the site.
To date, Thompson has completed more than 30 projects at the facility. They have included: soil borings, installation of monitor wells, collection of soil and groundwater monitoring samples, free product removal, groundwater pilot testing, Alabama Risk-Based Corrective Action assessments (ARBCA), Correction Action Plans (CAPs), and, the installation and operation of a dual-phase extraction (DPE) system.
DPE is a technology that uses a high-vacuum system to remove both contaminated groundwater and soil vapor. At this site, the unit separates free product, coalesce suspended or colloidal hydrocarbons, and settled solids and has the capability to pump 20-gallons per minute. The remediation via DPE began in February 2017. The system generally operates 24 hours a day. Maintenance visits are performed twice a month and groundwater is sampled at the end of each quarter. Since installation and startup, groundwater contamination levels have greatly decreased and free product has not been detected at the site since April 2017. Currently, 5 out of 31 monitor wells still show benzene (a chemical found in gasoline) concentrations above their allowable limits, but their concentrations continue to decrease with each quarter.
Thompson’s work will eventually end when the groundwater concentrations test below site-specific levels and ADEM says no further action is needed.