CHAPTER 3
 LONG TERM MONITORING

3.1 MLS Monitoring

 The multilevel wells were sampled semi-annually for the six-year period following the

1998 ethanol flood pilot test. This included the downgradient MLS installed after the remedial

effort, as well as the previously installed source zone MLS. The MLS orthogonal to the mean

groundwater flow in the source zone will be referred to as the source zone transect. The MLS

perpendicular to groundwater flow ten meters downgradient from the source zone will be

designated the downgradient transect. MLS monitoring ceased at the initiation of Phase II

flushing in 2004.

 Normal groundwater flow was assumed to initiate following the cessation of the pilot

test, but not to fully dominate the region until at least four months post-flood, December 1998.

All the data in this chapter will be termed natural gradient flow, contrasted to Chapter 2, where

all sampling was in the remedial flow field induced by the injection and extraction of the source

zone well system.

 The long term MLS monitoring was performed to assess the changes in concentration

throughout the site over the stated time period. Spatial patterns of the dissolved plume

emanating from the source zone will be discussed as well as mass discharge estimates across the

transects. The concentrations will be reported as the molar sum concentration due to the

initiation of microbial reductive degradation of residual PCE evidenced by increases in PCE

biodegradation daughter products. The biological dehalogenation or dehalorespiration of PCE

follows the following pathway.

 PCE -> TCE -> DCE -> VC -> ethene (3-1)