Field-Scale Evaluation of in Situ Bioaugmentation for Remediation of Chlorinated Solvents in Groundwater

Groundwater contaminated with 1000−2500 μg/L chlorinated ethenes (trichloroethene [TCE], dichloroethene [DCE], vinyl chloride [VC]) was treated by in situ bioaugmentation with a specialized microorganism, Burkholderia cepacia ENV435. The strain was selected for its limited adhesion to aquifer solids and its ability to degrade chlorinated ethenes in the absence of inducing cosubstrates. Ap proximately 550 L of the toluene ortho-monooxygenase-producing ENV435 culture (∼100 g/L) was injected along with oxygen (20 mg/L) into a semi-confined silty-sand aquifer (test plot). An equal volume of basal salts medium was simultaneously injected into an adjacent control plot. The plots each measured 4.6 m wide by 12 m long, were spaced 9.2 m apart, and contained 18 multilevel monitoring wells. Groundwater ENV435 concentrations exceeded 1 × 108 cfu/mL 7 days after injection, and the strain traveled the 12 m from injection to recovery well with an average linear velocity of 0.37 to 0.54 m/day. By comparison, a bromide tracer passed through the same formation at a rate of 0.53 to 0.68 m/day. In one trial, the total mass of TCE, DCE, and VC in the treated area was reduced by as much as 78% within 2 days after injecting the organisms.