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1 GeotogwTfAmdaI/M Page 5 Site Conceptual Model Report Marci Property Project No 7012 August 23,2004 ' The borehole logs are included in Appendix B Figures 3 and 5 provide a geologic interpretation of the units observed in the borehole drill logs Note The cross sections were ' developed using data gathered by different individuals utilizing different methodologies Therefore, they need to be looked at as one of several possible interpretations of actual site conditions) See Figure 2 for cross section Iocations t Hydrogeology There are no surface water bodies near the area of sufficient size or volume to act as a hydrogeologic boundary An irrigation ditch/canal is adjacent to the north of the parcel and it may act as a shallow aquifer recharge source Regionally, groundwater is utilized as a source ' for domestic, agricultural, and industrial supply water. The groundwater elevations observed in the water table wells ranged from approximately-31 ' to -41 feet mean sea level (MSL) since August 2000 This corresponds to a depth to groundwater of 56 - 66 feet below grade surface (bgs) The site's shallow aquifer displays highly variable shifts in groundwater direction (Figure 7) But the groundwater direction has ' been predominantly to the southeast since additional wells were installed in May 2002. The horizontal gradient measurements for the study area range from 0 0001 to 0 017 ft/ft during the 2000—2004 monitoring period The deep well groundwater elevations also ranged from approximately -31 to -41 feet mean sea level (MSL) since August 2000 This corresponds to a depth to groundwater of 56 - 66 feet below grade surface (bgs) The deeper aquifer flow has been consistently to the east except for the April 28 and May 23, 2003 events, during which time the gradient reversed 180° from an easterly direction to a westerly direction (Figure 8) This suggests that the regional well pumping causes significant fluctuations in groundwater direction The horizontal gradient measurements for the deeper aquifer level ranged from 0 001 to 0 007 ft/ft during the 2000—2004 monitoring period 1 Vertical gradients have been calculated for the MW-51105 & MW-6/106 well pairs during the investigation Similar to the historical lateral directions, the direction of groundwater in the ' vertical plane also fluctuates at the site Both positive and negative vertical gradients have been calculated for the site The magnitude of vertical groundwater flow direction ranged from—0 02 to 0 01 for the site investigation - ' Tables 5 & 6 in Appendix A contain the groundwater elevations and gradients recorded for the water table and deep wells, respectively Table 7 shows the calculated vertical gradients ' for shallow/deep well pairs Table 8 includes the well construction details - The historical water table gradients are illustrated in Figure 7 & 8 Groundwater Gradient ' Rose Diagrams for Water Table and Deep Wells,respectively r 1