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' CTeofo tcal7ecknlcsfisc Page 10 8 Site Conceptual Model Report Project No 724 2 May 2,2006 vertical gradient direction The magnitude of vertical groundwater flow direction ranged from-0 012 to 0 077 for the site investigation ' Tables 4, 5 & 6 in Appendix B contain the groundwater elevations and gradients recorded for the water table, intermediate 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 6A, 6B and 6C Groundwater Gradient Rose Diagrams for Water Table, Intermediate and Deep Wells, respectively Figure ' 7 includes well screened intervals 2.5 Contaminant Distribution t2.5.1 Vadose Zone ESE (1992) constructed cross section diagrams for their TH-1 through TH-7 boreholes and these are included in Appendix E As outlined in Section 10 above, Jim Thorpe Oil Co ' excavated gasoline impacted soils around former dispenser island and USTs to a depth of 20 - 28 feet under the supervision of Wm J Hunter & Associates (Hunter) in March & April 1993 Approximately 800 cubic yards of soil transported off site to Forward Landfill for ' disposal The soil excavations removed the majority of the documented soil contamination for the site The highest levels of TPH-G in soil were found in samples TK-2S (2250 mg/kg) and West-1 (1075 mg/kg) at depths of 12 -20 feet bgs [see Table 1 in Appendix B] Below a depth of 20 feet, all of the ESE 1992 borings had low to trace BTEX constituents ranging 0 005 - 1 3 ' mg/kg and some limited TPH-G "hits" ranging 0 54 - 5 85 mg/kg The highest detection of 5 85 mg/kg TPH-G was at 30 feet bgs in TH-4 This boring is adjacent to the Grant Street east sidewalk and it also had low BTEX in soil samples from 20', 40' and 45' bgs This ' suggests that some minor soil contamination remained undefined to the west under Grant Street However, in a September 3, 2002 letter correspondence (included Appendix A), the SJC PHS/EHD stated that "further assessment of the TH-4 area may not be necessary unless ' significant impacted groundwater is encountered at depths in new wells installed in the down gradient direction in the TH-4 area " No further investigation in this area was performed ' The ESE cross sections suggested that low levels of BTEX and TPH-G soil contamination was present in the areas beneath the former USTs and dispenser island But some of these ' detection points for gasoline constituents are now under the current water table level of approximately 36 feet bgs in February 2006 All of the borings advanced after the 1993 excavations, including the 2006 CPT borings, did not contain soil contaminant concentrations ' above the laboratory reporting limits One exception was the 1999 well MW-4 sample at 51 feet bgs (groundwater - 32 feet bgs in 1999) with trace benzene at 39 ug/kg Because of the increase in the water table during the investigation GTI has noted that trapped residual ' hydrocarbons below groundwater are acting as a continuing source of groundwater contamination But although the residual soil mass is sourcing a minor groundwater plume the quantity of that mass cannot be quantified Figures 8 & 9 illustrate the soil sample analytical data superimposed on cross sections A - A' and B - B' As can be seen in the