A horizontal well recovery system to capture LNAPL and affected ground water

The use of a horizontal well recovery system and the existing subsurface hydraulic regime can be a very effective remedial alternative for capturing LNAPL and ground water affected by a release. The discovery of a leak in the floor of a 1-million-gallon aboveground tank prompted an investigation of the shallow soils in the immediate vicinity of the tank. Elevated levels of volatile organic compounds detected in soils around and underneath the tank led to the demolition of the tank and the removal of approximately 3,500 CYS of the most affected soil. The horizontal recovery system consists of 140 feet of well screen that is wrapped in geofilter fabric and placed in a bed of filter sand covering the bottom of the excavation to enhance fluid migration. The screen was laid in two fluid draining runs extending from a vertical standpipe. To enhance future vertical fluid migration to the filter sand, a geofilter fabric was laid along the sides of the excavation. A one-piece polyethylene liner was placed on top of the filter fabric and the filter sand in the base of the excavation and filled with clay. A pneumatic, low flow submersible pump installed in the standpipe is used to extract up to 720 gallons of LNAPL and affected ground water per day. Concentrations of the volatile organic compounds initially detected in the liquid collected from the standpipe were reduced from 4.23 percent to 0.1 percent over a 16-month time period