PCE and TCE, DCE downgradient risk is increased and plume containment is necessary. By the

end of the study, ethanol was no longer observed due to advective and microbial losses. This

resulted in sharp decreases in site mass discharge. Although this decrease results in decreased

downgradient risk, it is estimated that 21 L of PCE still remain in the source zone at Sages.

 If reductive dehalogenating bacteria are present in a sandy aquifer PCE site, they will

probably rebound from high concentration ethanol flushing. Before the study the site assessment

found these microbes present, but the aquifer was substrate limited. Thus, little daughter

products were observed before the 1998 remediation. However, after the flood, microbial

dechlorination was greatly stimulated by residual ethanol including enhancing natural dissolution

of PCE.

 This technology demonstrated the ability to enhance PCE solubility for source removal

while concurrently adding a residual biotreatment polishing. If lower residual PCE volumes are

determined after an ethanol flood and mass discharge decreases sharply after a few years, the

periodic introduction of low concentration ethanol will re-stimulate the microbial biodegradation

process. This has several distinct advantages. First, the PCE source will continue to be depleted.

Second, microbial activity in the plume will enhance natural attenuation processes, leading to

less concentrated and shorter downgradient plumes. Finally, the polishing of residual PCE with

ethanol will speed site closure time scales by decreasing site longevity.