Subsurface Soil and Groundwater Investigations and Remediation

We initially installed a series of groundwater monitoring wells, or MWs, at the site to obtain soil and groundwater samples for lab analysis. During the investigation, we encountered roughly three feet of free-phase hydrocarbons in the groundwater; in the end, we installed 32 monitoring wells on portions of four city blocks to fully map the extent of the dissolved and free-phase hydrocarbon plumes.

A remediation plan to remove the plumes included the installation of an additional 128 monitoring wells; chemical surfactant injection into the MWs to enhance release of free-phase hydrocarbons; removal of surfactant and free-phase hydrocarbons by vacuum extraction; and injection of a chemical oxidant into the MWs to degrade the dissolved-phase hydrocarbons.

The first round resulted in about 952,376 gallons of free-phase hydrocarbons being removed, and two additional rounds of chemical oxidation have reduced the concentration of analytes below the Corporation Commission’s Site-Specific Target Levels, or SSTLs. The extent of the dissolved phase plume above the SSTLs has been reduced from roughly 208,635 square feet to about 54,375 square feet.

Based on a review of several remediation efforts, we have been tasked with conducting additional groundwater and sampling events, additional vacuum extraction events, and/or plugging and closing out monitoring wells that are below the SSTL. We continue to monitor the site by collecting samples and gauging monitoring wells, and we’re conducting air quality monitoring as well. After each event, Guernsey prepares a report detailing our field activities and summarizing the lab analysis. Conclusions and recommendations with this report will include future activities to prepare the site for closure.