Field application and results of an engineered bioventing process

A full-scale in situ bioremediation cleanup effort is being performed at a former natural gas production well site near Traverse City, Michigan. Mechanical and bioprocess engineering design methods have been employed to control subsurface soil gas flow and amendment feed systems using soil gas recirculation, liquid nutrient injection, and groundwater containment processes. A 15,000-ft3 soil mass contained approximately 7,000 lb of hydrocarbon (HC) defined by benzene, toluene, ethylbenzene, and xylenes (BTEX) and the alkane chain HCs (C1 to C10) prior to implementing source area bioremediation in September 1993. After ten months of analyzing various operating modes for the Gas Research Institute, approximately 923 lb of HC remained. In July 1994 the field research was completed and a mode of soil gas recirculation and continuous liquid-phase nutrient injection was implemented for Union Pacific Resources Company. The bioventing and biosparging systems were amended with sodium nitrate, triethyl phosphate, pure oxygen, and inoculate grown from on-site groundwater. Inoculate containing 650,000 colony-forming units (CFU)/mL of toluene degraders and 5,200,000 CFU/mL hexadecane degraders was injected into the subsurface aquifer