ConocoPhilips Facility No. 2634387
Manalapan, New Jersey

SKA was contracted to design a remediation system to treat contaminated subsurface soils and groundwater beneath an active Mobil gasoline station (former ConocoPhillips No. 2634837) site located in Manalapan, New Jersey.  A phase separated hydrocarbon (PSH) release from the underground storage tank (UST) system of the gasoline station into subsurface soils and groundwater was first detected in 1983.  Multiple environmental site investigations performed over the years determined that the PSH plume had spread from beneath the site to soils and groundwater beneath a commercial building on an adjacent property.  These investigations also identified gasoline-related volatile organic compounds (VOCs) including methyl tertiary butyl ether (MTBE) present in the soil and groundwater beneath the site and adjacent property.

Depth to groundwater at this site is 5 to 8 feet, and requirements for groundwater treatment include removal of dissolved phase VOCs including MTBE and PSH. The remediation system designed and installed by another firm had failed to effectively treat the groundwater because the effluent discharge failed to meet the bioassay discharge requirements of the New Jersey Department of Environmental Protection (NJDEP).  Naturally occurring iron and arsenic were consuming the dissolved oxygen in the groundwater; therefore, the insufficient dissolved oxygen concentration caused the bioassay failure.  The bioassay failure caused the system to be shut down which resulted in the PSH becoming trapped beneath the water table.

SKA used the results from a 3-D hydrogeologic model, a 2-D groundwater recovery flow model, and iron and arsenic removal treatability studies to design a new groundwater recovery and treatment system consisting of 15 multi-phase extraction (MPE) wells, one soil vapor extraction (SVE) well, a 300 scfm soil vapor extraction system, a 40 gpm water treatment system, and a 1,000 scfm vapor treatment system.  The recovery wells can operate as pumping wells, SVE wells, or in combination as MPE wells.  SKA designed this system to recover PSH beneath the gasoline station as well as the adjacent property.  The system is proposed to operate for a 2-year period or until it can be demonstrated that PSH and gasoline-related VOCs including MTBE have been remediated per the requirements of the NJDEP.