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Gealagua!recluua lxc Page 2 Groundwater Monitoring Report Project No 723 2 April 24,2006 the northeast The intermediate and deep aquifer zones' gradients were calculated to be N52°E at 0 004 ft/ft and N50°E at 0 003 ft/ft, respectively The deepest aquifer zone gradient monitored by wells MW-101, MW-307, MW-308 and MW-309 had a variable gradient due to a localized high near MW-101 ' Field evidence recorded during borehole installation indicates that petroleum hydrocarbon contamination is present on the adjacent property across N El Dorado Street —an active Shell service station The Valentine (Castle Motors) site plume extends off site toward the Shell Station and evidence suggests that a co-mingled plume may be present The lateral extent of the groundwater plume is undefined down gradient of CMTrM well set MW-8/108/208/308 A limited site investigation consisting of three CPTrm borings was completed on February 21 — 23, 2006 The results of that effort will be used to update the Site Conceptual Model (SCM) We have recommended that interim remediation be considered before this plume migrates any further and the cost for cleanup continues to increase A work plan for intenm remedial ' action utilizing high vacuum dual phase extraction, air stripping and carbon filtration of extracted groundwater technologies has been sent to SJC/EHD for approval SJC/EHD approved the work plan and the permitting for the extraction and treatment system M procurement installation, and operation is underway We have received building and sewer discharge permits from the City of Stockton PG&E has identified high pressure gas service at the adjacent residential property and we are attempting to get permission from this property owner to extend a line to the Castle Motors site If we are successful in obtaining this permission, we will have to re-apply to the City of Stockton Building Department for an amended permit for the new gas service GTi will continue to follow up on this issue ' 1.0 GROUNDWATER MONITORING In November, 2003, three new continuous multi-chambered tubing (CMTrm) wells were ' installed to further define the vertical and lateral extent of the soil and groundwater plumes (see Figure 13 for well locations and Table 8 for well construction details) The boreholes for the new wells' were installed to the north, east, and southwest of the site across E Castle, N ' E1 Dorado Street and W Adams Street, respectively As previously reported by GTI, the CMTs wells were so tightly coiled for shipping that it ' was difficult to install the wells without the tubing corkscrewing in the borehole, even when the casing was stretched out on the ground in the sun to warm and relax the coils The result of this twist in the tubing is that depth to water measurements could not be made because the ' instrument probe becomes lodged in the small chambers of the tubing But Del-Tech Geotechnical Support procured a new micro-water level meter that can be used in the CMVm wells The first quarter of 2005 was the first time that the well chambers were sounded 1