A pilot scale field study was conducted at the Amoco Production Company Kalkaska Gas Processing Plant (KGPP) near Kalkaska, Michigan, to assess the efficacy of utilizing in situ air sparging to remediate subsurface BTEX contamination in the aquifer and vadose zone. In situ air sparging is an innovative soil and groundwater remediation technology where air is injected into the saturated zone below the water table to facilitate the volatilization of volatile organic compounds (VOCs). The goals of this study were to: (1) evaluate the potential for enhancing the removal of dissolved BTEX contaminants in the groundwater by sparging air into the aquifer; (2) determine if vadose zone soils at the site contained an indigenous microbial population capable of degrading BTEX contaminants; (3) evaluate the potential for air sparging to enhance microbial numbers and microbial activity in the vadose zone; (4) determine if sparging air into the aquifer enhanced partitioning of BTEX dissolved in groundwater into the advective gas phase with subsequent transport to the vadose zone; (5) evaluate the potential for BTEX in the advective gas phase to be volatilized to the atmosphere; and (6) determine if in situ air sparging causes significant downward or lateral dispersion of BTEX in the aquifer.

A significant decrease in dissolved BTEX contaminants in the groundwater was measured during the four-month study interval. Sparging air into the aquifer did enhance partitioning of BTEX dissolved in groundwater into the advective gas phase and transport to the vadose zone. Laboratory microcosm studies, utilizing soil cores from the study site, confirmed the presence of an indigenous soil microbial population in the vadose zone capable of degrading BTEX contaminants. Selective enrichment of benzene/toluene degraders was noted in the vadose zone as a result of air sparging. BTEX was not volatilized to the atmosphere during the study period and no significant downward or lateral dispersion of BTEX in the aquifer was measured. Results showed that soil vapor extraction (SVE) wells and surface treatment of VOCs may not be necessary during in situ air sparging. Consequently, remediation costs could be significantly reduced. This study supports the results obtained in earlier field trials by Amoco Production Company and provides additional evidence for the viability of in situ air sparging as a low-cost remediation technology.

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