Qal Connectivity

While well yield correlates directly with thickness of sand facies (Qal), detailed contaminant migration paths are likely to be highly influenced by connectivity of high transmissivity zones (sand bodies) in the area of interest. The complex nature of the connectivity between portions of the sand facies becomes apparent when viewing a thresholded map of sand thickness (i.e. zones greater than 1 m thick, Fig. 11). Sand thickness is poorly-correlated in space, except along the curved paths of truncated stream channels. Some suggestion of arcuate structures is evident (see also 8). Note that sparse data in most areas outside of the city limits renders thickness estimates there less reliable.

The sand facies distribution map indicates that transmissivity is incompletely correlated with depth to the Kc shale. The assumption of such a relationship was a major feature of the 1993 RSKERC AEM model and WHPA estimates [Kraemer and Burden, 1994]. The southeastern part of Hays was modeled as a high-transmissivity zone along a N-NW trending channel in the shale. The sand facies is quite thick in this area (Figs. 8 and 11), but this stringer appears to be separated from the bulk of the area underlying Hays by a low-transmissivity zone (see gray ``sand-absent'' areas, Fig. 11). Considering this limited connectivity, the capture zones modeled in 1993 as extending NW-SE through the center of Hays might be more likely to extend around the city limits to the SW and NE, with minor connection between the southern city water supply wells and the northwestern supply wells.

Figure 11: Distribution of sand-gravel facies (Qal) with thickness exceeding 1 m. Gray areas have Qal $\leq$ 1m, city water supply wells shown as magenta circles.