Field scale demonstration of enhanced MTBE bioremediation through aquifer bioaugmentation and oxygenation

In situ bioaugmentation and biostimulation experiments were conducted at the USN Hydrocarbon National Environmental Test Site at Port Hueneme, CA (PH), where the dissolved MTBE groundwater plume is over 1500 m long. Laboratory microcosm experiments prepared with PH groundwater showed that MTBE was rapidly metabolized (t(1/2) less than or equal to weeks) after inoculation with a high-activity MTBE-degrading bacterial consortium (MC-100). Microcosm studies also showed that natural ether degraders were present at PH; however, the rates were 3-5 times stower than with the bioaugmented treatment. The field pilot test was conducted to assess the efficacy of creating an MTBE biobarrier by inoculating with MC-100 and maintaining well-oxygenated conditions. Three test plots located in the MTBE-only portion of the plume included control tno treatment), O-2-only (intermittent O-2 gas injection), and O-2 + bioaugmented (MC-100) zones. Initial MTBE and dissolved oxygen (DO) concentrations in the plots prior to treatment varied from 2 to 9 mg/L end less than or equal to 1 mg/L, respectively. DO levels increased in the O-2-only and O-2 + MC-100 plots from 5 to >20 mg/L within a few weeks of O-2 gas injection. MTBE levels decreased in the O-2-only plot to 0.01-0.1 mg/L after a lag period of 186-261 days, indicating the apparent stimulation of naturally occurring ether degraders. In contrast, in the O-2 + MC-100 plot, MTBE concentrations decreased after 30 days and throughout the 261-day experiment eventually to < 0.001-0.01 mg/L. tert-Butyl alcohol(TBA) concentrations also declined in the bioaugmented plot to <0.01 mg/L.