One of the benefits of MLS PITT resolution is that residual contaminants can be depth

identified. There seems to be residual PCE hot spots in the tracer swept zones from IW-1 to

MLS-1 and MLS-3 and from IW-3 to MLS-4 for the area between 8.0 and 8.7 m bgs. The

greatest residual PCE was detected in the lower swept zones of IW-1 to MLS-7 and IW-3 to

MLS-4. This information would allow future corrective action to focus efforts on the areas of

highest source zone residual saturation.

2.9 Estimated Mean Arrival Times

 After the post-remedial PITT, a comparison of conservative tracer mean arrival times was

possible. Figure 2-11 shows the relationship of the pre-remedial non-partitioning tracer (MeOH)

to the post (HexOH).




 MLS
 3.5 RW

 U)


 I-
 S 2.5

 o 2


 S 1.5
 4-

 0.5 -




 0
 0 0.5 1 1.5 2 2.5 3 3.5 4


 Pre PITT MeOH MAT (days)

Figure 2-11. Comparison of pre and post remedial conservative tracer mean arrival times at
 Sages. The blue points are the MLS data and the pink are the RW results. The
 gray line is 'cpre = Tpost.