Tetra Tech NUS has indicated that the ground water modeling was not really performed to assess capture zones from the on-site wells, but rather was developed to assess the impact of off-site recovery wells at Mikes Fancy Service Station on the Cryochem system. Nevertheless, GeoTrans suggests that the use of a properly calibrated numerical ground water model in conjunction with particle tracking is a potentially valuable line of evidence regarding the capture zone of the on-site wells. Use of ground water modeling as a line of evidence for capture is particularly important given the difficulty in developing potentiometric surface maps for evaluation of capture at this site. These difficulties in developing potentiometric surface maps are due to the fact that there are relatively few water level measurements other than the extraction wells, and water levels in the extraction wells are not representative of aquifer water levels.