decrease in 2003. By 2004 further decreases were observed at levels much lower than the initial

post flushing concentrations. A paired t-test of the data demonstrated that the molar sum of

concentrations in June 2004 were statistically different from the initial molar sum in September

1998. Several plausible explanations for the significant decrease in source zone concentration

include, source mass depletion, aging of the source zone, and decrease of microbial activity due

to loss of ethanol substrate.

Table 3-2. Sages source zone transect natural gradient concentration. Values are molar sum
 of all chlorinated species in mM. Transect is MLS-1, MLS-3, MLS-7.

 Well Depth 12/1998 01/1999 05/1999 05/2000 03/2001 02/2002 10/2002 10/2003 06/2004
 m bgs (mM) (mM) (mM) (mM) (mM) (mM) (mM) (mM) (mM)

 MLS-1 8.08 0.654 0.649 0.427 0.578 0.336 0.040 0.011 1.147 0.053
 8.69 0.509 0.592 0.393 1.053 0.789 1.037 1.777 1.245 0.594
 9.07 0.600 0.696 0.650 0.926 0.811 0.680 1.332 0.497 0.123
 9.45 0.555 0.596 0.422 0.672 0.246 0.516 0.712 1.165 0.347
 9.91 0.326 0.547 0.388 0.471 0.330 0.933 1.054 0.033 0.306
 Mean 0.529 0.616 0.456 0.740 0.502 0.641 0.977 0.817 0.285
 Std Dev 0.126 0.058 0.110 0.243 0.274 0.394 0.666 0.532 0.212
 MLS-3 8.08 0.340 0.359 0.200 0.556 0.316 0.000 0.005 0.749 0.159
 8.69 0.494 0.490 0.640 1.201 0.742 0.936 1.258 0.575 0.230
 9.07 0.562 0.756 0.802 1.030 0.777 0.743 1.235 0.570 0.403
 9.45 0.513 0.585 0.523 1.057 0.555 0.940 0.909 0.905 0.270
 9.91 0.580 0.685 0.518 1.028 0.648 0.361 1.593 0.053 0.073
 Mean 0.498 0.575 0.537 0.974 0.607 0.596 1.000 0.570 0.227
 Std Dev 0.095 0.157 0.220 0.245 0.185 0.408 0.607 0.321 0.124
 MLS-7 8.08 0.060 0.066 0.110 0.335 0.180 0.111 0.136 0.519 0.117
 8.69 0.710 0.839 0.760 1.222 0.540 1.048 0.833 0.182 0.224
 9.07 0.186 0.218 0.197 0.438 0.572 0.907 1.264 0.253 0.260
 9.45 0.402 0.338 0.200 0.301 0.393 0.683 1.005 0.262 0.142
 9.91 0.672 0.987 0.823 1.105 1.027 0.307 1.899 0.000 0.198
 Mean 0.406 0.490 0.418 0.680 0.542 0.611 1.028 0.243 0.188
 Std Dev 0.288 0.402 0.343 0.446 0.312 0.396 0.642 0.187 0.059


 SurferTM was used to create visualizations of the source zone transect molar sum of

chlorinated species. In Figure 3-2, the concentrations in the cross section listed in Table 3-1 are

presented. As before, standard kriging was applied to interpolate between measured data points.


The black plus (+) marks indicate the location of each MLS sampling point.