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Geologtcal Technics/Ac Page 9 Groundwater Monitonng Report Project No 723 2 June 15,2004 ' 3.0 CONCLUSIONS & RECOMMENDATIONS ' Conclusions 1 Groundwater flow trends northeast to east The southerly flow direction recorded on ' December 4, 2000, appears to be anomalous 2 High levels of BTEX and TPH-G are present in the groundwater of all six on site shallow and intermediate monitoring wells (MW-1 through MW-6) 3 Trace levels of BTEX are present in shallow/intermediate wells MW-7/107 4 Down gradient wells MW-8 and MW-208 contain low levels of TPH-G and BTEX Intermediate well MW-108 contains high levels of BTEX and TPH-G 5 The groundwater contaminant plume is not defined laterally down gradient of MW-108 Mass balance calculations are not presented for this reason 6 Well set MW-9/1091209 defines the lateral extent of the plume in an up gradient direction 7 The lack of contaminants in wells MW-101 and MW-201 suggests that these wells define the vertical lima of the plume beneath the site ' 8 Wells MW-207 and MW-209 define the vertical extent of the plume 1n up and cross gradients directions 9 The highly negative ORP and low DO values suggests that the contaminant plume is stable and that natural attenuation processes are dormant, which corroborates well with the laboratory data Recommendations ' 1 Continue quarterly groundwater monitoring, with the next monitoring event scheduled for April 2004 2 On November 20 - 26, 2003, three multi-chamber wells were installed at the site Each ' well has a maximum of four intervals that can be sampled The deepest interval (MW- 308) in CMTTM well MW-8/10811081308 should be sampled to determine the vertical limit of the plume in the down gradient direction This action has been scheduled for ' the second quarter of 2004 (April) 3 The lateral extent of the groundwater plume is undefined down gradient of CMTTM well MW-8/108/108/308 A limited site investigation should take place to define the down ' gradient extent of the plume This should consist of direct push probes to collect discrete groundwater samples rather than installing additional monitoring wells 4 We recommend that interim remediation be considered before this plume migrates 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 SJC PHS/EHD in their November 15, 2003 The first phase of the work, installing three extraction wells, is scheduled for June 2004