3.5 Source Zone Transect Mass Discharge

 The post-remedial mass discharge results from MLS monitoring of the source zone

transect is presented in Table 3-4. As aqueous PCE discharge decreased in 1999 and 2000, DCE

mass flux rate increased as a result of biological dehalorespiration. This trend continued until

2003. In the last two years of the study period, 2003 and 2004, all discharges decreased except

VC. Vinyl chloride analysis recorded non-detect values until 2003 and 2004.

Table 3-4. Sages post-flood source zone transect mass discharge in mmol/day.
 Oct-98 Dec-98 Jan-99 May-99 May-00 Mar-01 Feb-02 Oct-02 Oct-03 Jun-04
 (mmol/d) (mmol/d) (mmol/d) (mmol/d) (mmol/d) (mmol/d) (mmol/d) (mmol/d) (mmol/d) (mmol/d)

 PCE 12.317 20.818 23.284 20.462 15.671 18.221 10.441 8.397 3.695 0.508
 TCE 0.000 2.461 5.324 3.227 19.780 4.056 5.079 4.871 2.141 0.435
 DCE 0.000 0.000 0.082 2.709 2.187 12.225 31.715 45.316 20.867 11.134
 VC 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.150 0.511

 Sum 12.317 23.280 28.690 26.398 37.638 34.502 47.234 58.584 26.852 12.588


 Maximum and minimum mass discharge values determined in the source zone transect

ranged from 0.51 to 23.3 mmol/day for PCE, 0 to 19.8 mmol/day for TCE, 0 to 45.3 mmol/day

for DCE, and 0 to 0.5 mmol/day for VC. Source zone source PCE strength rebound was detected

in the first six months after the pilot flushing test. This can be attributed to the higher residual

ethanol concentrations enhancing PCE solubility until natural gradient flow removed the

majority of the ethanol. However, by the end of the first year PCE discharge began to decrease

and continued to decrease until the end of the study period with the exception of 2001 when

there was a slight PCE discharge spike. Figure 3-4 shows the source zone transect mass

discharge over the six-year period after the 1998 ethanol flood.

 After the initial post remedial rebound, up to 24 mmol/day, aqueous PCE discharge

decreased below 20 mmol/day, eighteen months after the flood event. Simultaneously, DCE

discharge increases to 20 mmol/day. The increase in the sum chlorinated ethene mass discharge