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Qwbgkal7'Whgics Inc Page 2 Groundwater Monitonng Report Project No 723 2 October 29,2004 tgradient recorded in the investigation but it is consistent with the site's historical directions that have been predominantly to the northeast Field evidence recorded during borehole installation indicates that contamination is present on the adjacent property across N El Dorado Street — an active Shell service station GTl recommends that the SJC PHS/EHD files be reviewed for the adjacent site to obtain well construction information and historical contaminant data The data suggest that a co-mingled plume situation may exist and the file review will help clarify the site conceptual model ' Because the lateral extent of the plume down gradient of the MW-8/108/208/308 has not been defined, the SJC PHS/EHD will probably require additional site definition ' We recommend that interim remednatnon be considered before this plume nugrates any further and the cost for cleanup continues to increase A feasibility study work plan for dual ' phase soil vapor and groundwater extraction was previously submitted to SJC PHS/EHD GTI's September 8, 2003 "Feasibility Study Work Plan - Dual Phase Soil Vapor and Groundwater Extraction Pilot Test" was approved by SIC PHS/EHD in their November 15, 2003 The pilot test was performed in late July 2004 and a report of its findings is being prepared 1.0 GROUNDWATER MONITORING ' On November 20 - 26, 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 5 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 El Dorado and W Adams streets, respectively ' Unfortunately, the CMTTM 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 Although depth to water ' measurements can not be performed in the individual tubing chamber, water samples are obtained by utilizing smaller diameter tubing with a Waters pumping system ' Due to this tubing twist constraint the water gradient was determined using wells MW-1 through MW-6 as has been done in the past. ' 1.1 Hydrogeology of Site A site-specific groundwater gradient and bearing were calculated from computer-generated contours for the August 6, 2004 event The groundwater was flowing N52°E at a gradient of