Traditional two-dimensional capture zones (i.e. projection of particle pathlines to the ground surface) for all of the Hays city wells are similarly effected by Qal distribution. In particular, pathlines for particles tracked backward from wells C-17, C-29, C-30 and C-32 show gaps where the Qal aquifer is thin (Fig. 19). Temporal changes in computed two-dimensional capture zones at Hays also reflect the influence of estimated Qal thickness (Fig. 20). For example, particles entering well C-17 within 5 years are separated by a zone of thin Qal, while at 10 years the capture zone completely surrounds the area of thin Qal aquifer.
Figure 19: Ten-year capture zones and particle paths, Hays city wells.
Capture zones calculated by backward tracking in modpath,
shown in magenta. Representative particle pathlines shown in white,
showing complete path of particle (i.e. extending beyond 10-year
travel time). Hays 1983 city limit, Big Creek, and PCE 100ppb
contour shown by black lines. Qal aquifer thickness shown by color fill.
Figure 20: Five-
(magenta) and Ten- (black) year capture zones, Hays city wells. shown
in magenta. Digital map of Hays city streets circa 1993 and location
of Big Creek shown in brown.