CHAPTER 4
 DISCUSSION

4.1 Inferred Initial PCE Architecture

 The characterization of PCE distribution at the Sages site demonstrated the discontinuous

architecture of subsurface DNAPL spills. Soil coring performed in the previous studies

determined discrete layers of high PCE saturation in the source zone. However, extensive coring

would be required to elucidate the NAPL extent that can be determined by exploring the same

area with a partitioning tracer test. Employing a network of multilevel sampling wells in the

region interrogated by the tracers quickly yields the vertical and horizontal spatial distribution of

NAPL.

 From the results of the MLS pre-remedial PITT, the Surfer visualizations, and the

remedial flow field fluid velocities, the PCE architecture of Sages can be inferred. MLS detected

high saturations of PCE in the upper region of the source zone, nearest the drycleaning facility

floor drain, at MLS-1. Although upper depth of the source zone (8.08 m bgs) demonstrated the

highest fluid velocities in the remedial flow field, it was measured to have hydraulic conductivity

nearly an order of magnitude lower than the materials overlying it [Mravik et al., 2003]. As PCE

collected on this fine sand, it fanned outward and drained down to the next depth. It seemed to

contact finer sands at 8.69 m bgs, evidenced by the marked decrease in remedial fluid velocities

at this depth in all MLS wells and high saturations detected at MLS-1 and MLS-4. From this

layer, PCE drained to the next low permeable strata at 9.07 m bgs and spread westward to MLS-

2 and eastward to MLS-4. The two lowest depths indicated PCE pooling as the average PCE

saturations recorded in the swept zone from IW-3 to MLS-4 and MLS-6 were greater than 1.0%

[NRC, 2005]. The high aqueous PCE concentrations in the middle and lowest depths of MLS-7