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) ≤ 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 pots 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.
ASJC Scopus subject areas
- Environmental Chemistry