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 (t1/2 ≤ 2 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 slower 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 (no treatment), O2-only (intermittent O2 gas injection), and O2 + bioaugmented (MC-100) zones. Initial MTBE and dissolved oxygen (DO) concentrations in the plots prior to treatment varied from 2 to 9 mg/L and ≤1 mg/L, respectively. DO levels increased in the O2-only and O2 + MC-100 plots from 5 to >20 mg/L within a few weeks of O2 gas injection. MTBE levels decreased in the O2-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 O2 + 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.