• Site Characterization
  • Carbon Compound injection

Douglas County, MO

Site Description

Historical releases at a former gasoline service station resulted in two water bearing zones impacted. The resulting impact in both soil and groundwater was over 800 feet long approximately 150 feet wide within two separate water bearing zones. Numerous off-site properties and a state highway overlaid the subsurface soil and groundwater contamination. A small explosion had occurred at one of the off-site properties during excavation along the state highway right of way to install utilities.

Site Characterization Summary

A total of 78 soil borings, 22 permanent unconsolidated wells, and 6 bedrock wells were installed by Sunbelt crews in efforts to delineate the soil and groundwater contamination. Three deep groundwater wells were sampled to determine hydrogeological and chemical characteristics of the deeper potable groundwater zone. LNAPL was present at several monitoring well locations. occasions depended upon water levels. approximately 60 feet below grade.

Carbon Based Compound Injection Summary

Due to the risk of explosive vapors on and off-site, various remedial approaches were evaluated. Excavation and various in-Situ approaches were considered. Based on carbon’s ability to be used at sites with LNAPL and in sites with very low permeability (e.g. clay) a carbon based compound (BOS 200) injection was selected. A preliminary injection grid was designed for injection of approximately 46,000 pounds of BOS 200 and 55,000 pounds of supplemental gypsum. Prior to initiating injection and as part of the BOS 200 approach, a series of soil borings were installed and soil samples collected at high density in an attempt to confirm the extent and concentration of petroleum hydrocarbon mass in the subsurface. The collection of an additional 154 soil samples indicated that the proposed grid design needed to be modified to address LNAPL and petroleum hydrocarbon mass in  areas where LNAPL and impacted soil had not been encountered. The newly collected data also indicated how less BOS 200 was needed in other areas of the preliminary injection grid. The goal of the injection program was to eliminate the risk of fire and explosion at the site, eliminate LNAPL and reduce overall concentrations of petroleum hydrocarbons. A total of 343 injection points were installed with a total of 2009 separate injections of a mixture of BOS 200, gypsum and microbial concentrate within 5 separate injection grids.
Data collected subsequent to the injection indicates the elimination of LNAPL and explosive vapors as well as the reduction of dissolved COCs within the groundwater.