Application of natural attenuation for the remediation of dissolved BTEX

Gasoline released from leaking underground storage tanks adversely impacted soil and groundwater. The underground storage tanks were removed and a soil vapor extraction system was installed in the area of the tank excavation. Natural attenuation was chosen as the preferred strategy for groundwater treatment and a thorough evaluation of natural attenuation processes was undertaken. Previous site data and recently collected groundwater results were used to assess the effect of natural attenuation on the dissolved phase BTEX plume during the past three years. A median benzene biodegradation rate of 0.0056 per day was calculated using a first order decay equation. The biodegradative capacity of the aquifer was calculated to be at least 144,000 grams of hydrocarbon which exceeds the BTEX mass present in the aquifer. BIOPLUME II modeling of the aquifer indicated that natural attenuation, occurring at rates measured on the site, will effectively reduce the concentration of dissolved BTEX to target levels within 7 years. Plume migration is expected to be minimal.