target residual PCE for future corrective action. Site characterization determined that hydraulic

conductivity decreased with depth. Thus, ethanol flushing encountered the difficulty getting

high concentrations to the deep, low flow zones. Furthermore, once remedial fluids penetrated

the lower depths, they were difficult to recover in the pumping rate and time frame of this test.

 The remedial performance was evaluated through comparison of pre and post-remedial

groundwater samples and partitioning tracer tests. The ethanol flushing test was effective at

removing significant levels of subsurface PCE and favorably reduced the contaminant flux at

most MLS locations.

 One of the benefits of using ethanol as the remedial fluid was the fostering of microbial

reductive dechlorination of residual PCE. Ethanol served as an electron donor in biodegradation.

From long term transect monitoring, the mass discharge of the source zone and downgradient

control plane were determined. Once higher levels of unrecovered ethanol were carried away by

natural gradient flow, microbial activity spiked up until four years after the 1998 event. Then,

dechlorination declined rapidly as all the ethanol was exhausted by microbes or removed by

groundwater flow. While residual PCE dissolution was microbially enhanced, significant PCE

remained in the source zone at the end of this study. Therefore, another combined effort took

place at the conclusion of this study in 2004 with a second full scale ethanol flushing.

 The combination of enhanced solubililization and residual source biotreatment was

effective at removing significant PCE mass, reducing PCE flux, and fostering bioremediation in

the source zone and plume. This combined technology will serve to decrease source strength and

longevity for sites meeting the proper criteria. Clean up and site closure will occur much faster

than natural gradient dissolution and plume control via a pump-and-treat system.