Hays PCE Plume

Useful data for validation (as defined by Mirham, 1972) of capture-zone and transport models at Hays is provided by the presence of a tetrachloroethylene (PCE) plume beneath Hays. The PCE is suspected to have originated from two former dry-cleaning establishments, and is now found at city well C-20 and south-southeast from there (Fig. 8). Pump tests associated with this study indicate a hydraulic conductivity for intervals screened in Qal of 2.2-8.6 $\frac{\rm m}{\rm d}$. To preserve the PCE data as a validation suite, the numerical models in this study were in no way altered to improve the fit the PCE observations. As a result, comparison of the observed plume to calculated capture zones for well C-20 provides a crucial illustration of the accuracy of the modeled results.

Figure 8: Map of PCE distribution and Qal thickness (color contours). 100ppb contour show as measured in 1995 (white) and 1997 (black). Effects of remediation efforts at well C-20 (center of plume) are evident. Note EPA maximum contaminant level (MCL) for PCE in drinking water is 5 ppb. City streets shown in brown, white circles show city wells, brown & white line is Big Creek, Qal aquifer thickness shown in color. PCE plume after [Black & Veatch Waste Science, 1995]. Select figure to view full-sized image.