WHEN PUMP AND TREAT WON'T DO: LINDANE REMOVAL FROM GROUNDWATER

摘要

A pump and treat system was recommended to address "hot spots" of pesticide contamination in groundwater at a Superfund site in the southeastern United States. However, pilot testing demonstrated it to be ineffective in removing lindane at an appreciable rate. Natural attenuation and an atypical phytoremediation application were evaluated and compared to the pump and treat system designed for the site. Defining natural attenuation at this site was a particular challenge due to the lack of precedents with respect to natural attenuation of lindane, extremely low contaminant concentrations (less than 100 μg/L) and even lower remediation goals (quantitation limits, <0.02 μg/L). The 28-acre site was primarily aerobic, with small anaerobic areas caused by a commingling xylene plume, allowing comparison of the relative rates of lindane biodegradation. Through the extensive sampling program, transient transformation products (including several chlorinated benzenes and chlorophenol isomers) associated with lindane biodegradation were detected. To further protect the downgradient receptpr, more than 2500 hybrid poplar trees were planted to transect the plume, effectively reducing contaminant mass available for downgradient transport. Transpiration rates were monitored and attenuation rates were estimated. Based on the extensive site database from more than 40 wells sampled over five years, it was concluded that the combined effect of natural attenuation and phytoremediation could meet or exceed the prescribed remedial objectives.