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. Approximately 550 L of the toluene ortho-monooxygenaseproducing 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 × 10 8 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.

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Vapor extraction (soil venting) has been demonstrated to be a successful and cost‐effective remediation technology for removing VOCs from the vadose (unsaturated) zone. However, in many cases, seasonal water table fluctuations, drawdown associated with pump‐and‐treat remediation techniques, and spills involving dense, non‐aqueous phase liquids (DNAPLS) create contaminated soil below the water table. Vapor extraction alone is not considered to be an optimal remediation technology to address this type of contamination. An innovative approach to saturated zone remediation is the use of sparging (injection) wells to inject a hydrocarbon‐free gaseous medium (typically air) into the saturated zone below the areas of contamination. The contaminants dissolved in the ground water and sorbed onto soil particles partition into the advective air phase, effectively simulating an in situ air‐stripping system. The stripped contaminants are transported in the gas phase to the vadose zone, within the radius of influence of a vapor extraction and vapor treatment system. In situ air sparging is a complex multifluid phase process, which has been applied successfully in Europe since the mid‐1980s. To date, site‐specific pilot tests have been used to design air‐sparging systems. Research is currently underway to develop better engineering design methodologies for the process. Major design parameters to be considered include contaminant type, gas injection pressures and flow rates, site geology, bubble size, injection interval (areal and vertical) and the equipment specifications. Correct design and operation of this technology has been demonstrated to achieve ground water cleanup of VOC contamination to low part‐per‐billion levels.