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LL }} ' 4mlo8 rcal Techtdes lxc, �� Page 9 - Site Conceptual Model Report 5 Project No 724 2 May 2,2006 --� ' MW-1 through MW-5, however, these boreholes were sampled at 5 foot intervals by different geologists The sand units at 25 and below 65 feet on-site do not appear to extend to the off- site location of CPT-4 Figure 5 Cross Section B — B' illustrates the geology trending from southwest to the northeast off site The geology is similar to that present in Figure 4 with more shallow sand layers near MW-108 and the CPT-2 location Hydrogeology ' There are no surface water bodies near the subject area to act as a hydrogeologic boundary Regionally, groundwater is utilized as a source for domestic, agricultural, and industrial supply water The average groundwater elevations observed in the water table wells ranged from approximately -16 to -39 feet mean sea level (MSL) since October 1992 This corresponds to ' a depth to groundwater of 31 - 54 feet below grade surface bgs The rose diagram included in Figure 6A shows that the water table groundwater gradients at this site are consistently towards the east In Figure 6A, arrows labeled 22 and above were measurements made after ' November 2000 Since additional wells were installed in November 2000, the groundwater direction has had a more southerly component suggesting that the earlier measurements were biased due to the spatial orientation of fewer wells The water table horizontal gradient measurements for the study area range from 0 0009 to 0 018 ft/ft during the 1992 — 2005 monitoring period ' The intermediate well groundwater elevations ranged from approximately -17 to -24 feet MSL since January 2001 This corresponds to a depth to groundwater of 32 - 39 feet below grade surface bgs The rose diagram included in Figure 6B shows that the intermediate ' aquifer gradients at this site have had a consistent easterly (northeast to southeast) direction The horizontal gradient measurements for the intermediate aquifer level ranged from 0 0014 to 0 0051 ft/ft during the 2001 —2005 monitoring period The deep well groundwater elevations also ranged from approximately -17 to -24 feet MSL since January 2001 This corresponds to a depth to groundwater of 32 - 39 feet bgs The rose ' diagram included in Figure 6C shows that the deep aquifer gradient has been to the east to southeast for the sounding events following the installation of four additional deep wells in December 2003 The horizontal gradient measurements for the deeper aquifer level ranged ' from 0 001 to 0 0042 ft/ft during the 2004 —2005 monitoring period ' Vertical gradients have been calculated for the MW-4/104, MW-6/106 & MW-7/107 well pairs during the investigation The site has a varying trend of negative and positive gradients in these wells The MW-4/104 well is generally negative, the MW-6/106 well pair is ' typically positive and the MW-7/107 well pair has a history of mostly positive gradients It is noted that the vertical distance to the deep well screen in the MW-4/MW-104 well pair is double that observed in the other two well pairs, which may have an influence over the