The transport problem of greatest importance at Hays is prediction of the movement and remediation of the PCE plume (Fig. 8), which has forced shut-down of one major water supply well and is threatening others. For simplicity, detailed results are presented only for the shut-down well, C-20 (Fig. 6). To further simplify consideration of this plume, a steady-state non-reactive transport setting was assumed. To remain consistent with typical hydrologic applications at the local level, particle tracking was used to evaluate potential transport (i.e. transport paths modeled, concentrations not modeled).
Transport model results demonstrate strong influence by the connectivity between zones of thick sand facies (Qal). The distribution of surficial zones of rapid transport to water supply wells is primarily controlled by this connectivity, and the presence of unconfined conditions in the Qal (Fig. 21). Note that C-20 was shut off in 1996 when PCE was produced from the well; therefore the models described here represent pre-1997 conditions, and the extension of the plume south of C-20 is not modeled (compare 1995 and 1997 100 ppb plumes, Fig. 8).