CHAPTER 5
 CONCLUSIONS

 The primary goals of this work was to: (1) elucidate the architecture of PCE in the source

zone at the Sages site, (2) gain additional spatial information about the ethanol flushing test, (3)

assess the benefits of this technology to deplete source mass and reduce source flux, and (4)

evaluate the mass discharge at the site over the period from 1998 to 2004. The final PCE

subsurface distribution was determined by the post-remedial PITT. This information would

assist site managers in preparing future corrective action and monitoring. The flushing test

displayed the inherent limitations of tracer tests and ethanol flushing. While all the RWs

received tracers and remedial fluids, deep zone finer media prevented the arrival of tracers at all

deep MLS. The remedial fluids cleaned out more permeable zones, but there was difficulty

penetrating the lower zones with high concentrations of ethanol. Furthermore, once remedial

fluids interrogated the low flow zones, they were not easily recovered.

 This work demonstrated the benefits of this DNAPL source removal technology. Both

mass reductions and flux reductions were observed, translating into decreased source strength

and longevity compared to natural gradient dissolution with pump-and-treat plume capture. The

location of well data in the mass reduction flux reduction relationship displayed moderately to

highly heterogeneous PCE morphology.

 Additionally, the stimulation of microbial biodegradation was observed. The mass

discharge showed the 1% ethanol concentration toxicity threshold of microbes in Sages site

materials. When the ethanol concentration was reduced by the return of natural gradient

groundwater flow, the microbial response was strong and mass discharge increased. In the ten

meters of aquifer between the source zone and the downgradient MLS transect, DCE was not

observed to be degraded quickly. Thus, during periods of highly stimulated dechlorination of