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1 Geo[ogical recluucs w Page 4 Groundwater Momtonng Report Project No 723 2 all November 7,2001 3.0 CONCLUSIONS & RECOMMENDATIONS ' Conclusions 1 The groundwater contaminant plume is not defined vertically or laterally 2 Groundwater flow trends to the northeast to east The southerly flow direction recorded on December 4, 2000 appears to be anomalous 3 High levels of BTEX and TPH-G are present in the groundwater of all six water table ' monitoring wells It is noted that the groundwater elevation exceeded the level of the well screens Low concentrations of BTEX and TPH-G are present in the deep well 4 Oxidation-Reduction Potential measurement (Table 3) shows that all seven wells are ' screened in areas of the groundwater plume that are affected by the biodegradation reactions occurring within the plume Negative ORP values indicate that the wells are within the halo of reaction depleted water caused by biodegradation of the contaminants This corroborates well with the laboratory data Recommendations ' 1 Investigate the vertical and lateral extent of the groundwater plume GTI submitted a "Vertical Definition Work Plan" to SJC PHS/EHD by facsimile on August 24, 2000 SJC PHS/EHD approved the work plan on June 14, 2001 A deeper short screened well -� was installed in late October 2001 A report on the installation of this well and the test results will be submitted shortly 2 Additional groundwater monitoring wells are needed to define the lateral extent of the plume off site GTI proposes installing two well pairs (shallow and intermediate wells) MW-7/MW-107 & MW-8/MW-108 to the north and northeast of the site, respectively — ' see Figure 2 for proposed well locations A deep well is also needed in the location of well MW-4 GTI proposes to install well MW-104 adjacent to well MW-4 to further define the up gradient plume ' 3 Continue quarterly groundwater monitoring, with the next monitoring event scheduled in December 2001 4 Due to the infrequent detection of the oxygenated fuel compounds at this site, future ' quarterly monitoring events will not include analysis by EPA method 8260. However, testing for MTBE by 8020/602 is justified ' 4.0 LIMITATIONS ' This report was prepared in accordance with the accepted standards and practices of the field of environmental geology, groundwater hydrology and good business practices It should be recognized that definition and evaluation of environmental conditions is a difficult and inexact science Judgments leading to conclusions and recommendations are generally made with an incomplete knowledge of the site-specific conditions present 1