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i i Ge0bgfcal72c"Cs I La Page 9 Site Conceptual Model Report(2006 Revision) Valentine(Castle Motors) Project No 723 2 1 June 16,2006 Hydrogeology ' There are no surface water bodies near the area of sufficient size or volume to act as a hydrogeologic boundary Regionally, groundwater is utilized as a source for domestic supply ' water The wells have been grouped according to the aquifer interval that the screened section ' intercepted(see Figure 5 for well screen intervals) Shallow Wells (screened 35 —55 feet bgs) MW-4, 5, 6, 7, 8 & 9 i Intermediate Wells (screened 43 —70 feet bgs) MW-1, 2, 3, 107, 108 & 109 Deep Wells (screened 76—80 feet bgs) MW-207, 208 & 209 Deepest Wells (screened 94—97 feet bgs) MW-101, 307, 308 & 309 iThe groundwater elevations observed in the shallow wells ranged from approximately -15 to -29 feet mean sea level (MSL) since July 1996 This corresponds to a depth to groundwater i of 26 - 40 feet below grade surface (bgs) The site's shallow aquifer flow direction has ranged east to northeast during the investigation and this is illustrated in Figure 6 Groundwater Gradient Rose Diagram The December 2000 event recorded a southerly M direction that appears to be an anomaly The horizontal gradient measurements for the study area range from 0 002 to 0 02 ft/ft during the 1998— 2006 monitoring period i The intermediate and deep aquifer flow directions have flowed northeast since January 2005 [with the sounding of the new continuous multi-chambered tubing (CMTTM) wells] These gradients ranged from 0 003 to 0 008 ft/ft during the 2005 — 2006 monitoring period The i deepest aquifer flow direction monitored by wells MW-101, 307, 308 & 309 has been variable during the same period with three southwest events recorded in January, April and November 2005 This is the reverse of the historical shallow aquifer direction The deeper ' aquifer gradients ranged from 0 002 to 0 006 ft/ft during the 2005 —2006 monitoring period Vertical gradients have been calculated for the MW-3/201, MW-8/108 & MW-1081208 well i 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 11 to 0 06 for the site investigation Tables 6, 7, 8 & 9 in Appendix B contain the groundwater elevations and gradients ' recorded for the water table, iritermediate, deep and deepest wells, respectively Table 10 shows the calculated vertical gradients for shallow/deep well pairs Table 11 includes the well construction details i i