CONTAINMENT AND REMOVAL OF FUEL OIL FROM GROUNDWATER BENEATH A DENSELY POPULATED HOUSING DEVELOPMENT

Abstract

ABSTRACT A leak from a buried pipeline resulted in the loss of approximately 30,000 gallons of No. 2 fuel oil beneath a housing development in suburban New Castle County, Delaware. After seeping to the water table, the resultant hydrocarbon plume threatened the homes as well as a downgradient stream and an irrigation pond. Site geology consisted of a highly-weathered metamorphic rock overlain by varying thicknesses of fill material. A steep water table gradient existed; the depth to the water table ranged between 6 and 17 feet below grade. Two-inch monitoring wells were installed in public easements and the back yards of private residences. The extent of the oil plume was determined by measuring product thicknesses, which ranged from a few inches to over 5 feet, in monitoring wells. To establish hydrodynamic control and prevent further migration of the plume, two eight-inch recovery wells were drilled and configured with water-table depression pumps. For product recovery, Auto-Skimmers were selected because of the variable water levels and need to leave no measurable product thickness in the wells. The potential for product recovery in other parts of the site was determined by performing unattended one-week recovery tests in the two-inch monitoring wells under non-pumping conditions using an Auto-Skimmer. Based on these results, three additional six-inch recovery wells were drilled. The recovery operation successfully halted the advancement of the contaminant plume and protected the downgradient stream and irrigation pond. In addition, more than 3,000 gallons of fuel oil were recovered from the subsurface. After 18 months, the recovery equipment was removed and only periodic monitoring of the monitoring wells was required.