Groundwater Treatment System Design

Farallon incorporated groundwater circulation wells in the design of an innovative system to treat petroleum hydrocarbon-contaminated groundwater at a retail gasoline station. The system included airlift air sparge wells to treat groundwater in shallow and deep water-bearing zones that were separated in some areas by a silt aquiclude. Conventional air sparging techniques could not be used because of the potential for petroleum vapors to become trapped beneath the silt layer and migrate off the site. Farallon therefore used airlift air sparge wells to aerate groundwater from the deeper zone, stripping the dissolved-phase petroleum hydrocarbons and lifting the aerated water above the silt layer. Petroleum vapors are removed from the vadose zone using soil vapor extraction technology, with the aerated water being recirculated into the subsurface, enhancing natural biological degradation to reduce residual petroleum-hydrocarbon compound concentrations in groundwater above the silt layer. The wells' control system allows each well in the network to be adjusted individually to optimize performance and balance. A conventional soil vapor extraction system with similar controls was incorporated into the design to maintain optimum system performance and balance. Air emissions from the system are treated using granular activated carbon.