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404hg&al re"la Inc Page 4 Groundwater Monitoring Report Project No 662 2 November 15, 2004 ' • MW-2, which is upgradient of the former USTs, has not contained contaminant concentrations above the laboratory detection limits for all quarterly events completed ' thus far in the investigation • MW-3 contained the gasoline oxygenate MTBE at 1500 µg/l • The detections of ETBE and TAME in wells MW-1 and MW-3 are intermittent and ' appear to be dependent on elevated MTBE concentrations and associated elevated reporting limits • Deep screened well MW-104 contained MTBE at 130 µg/1 This is the highest level ' recorded in the investigation • Figure 4 MTBE vs Groundwater Elevation in MW-3 illustrates a fairly direct relationship between the concentration of MTBE in groundwater and the elevation of groundwater in well MW-3 A reverse trend was present for the last several quarters A linear trend line has been added to the figure to show a general decline in both groundwater elevation and MTBE concentrations over time • TPH-G and BTEX were not present in any of the groundwater samples above the laboratory reporting limits 1 • In accordance with San Joaquin County directives, the groundwater samples were also analyzed for diesel, methanol, ethanol, 1,2-DCA, EDB and lead, which were all non- detect except for lead Wells MW-1, MW-3 and MW-104 contained 24, 28 and 37 1Ag/1 lead,respectively • Table 3 includes Dissolved Oxygen (DO) and Oxidation-Reduction Potential (ORP) measurements for the site's wells All four of the wells show low DO and low positive ORP values suggesting that the plume may be stable GTI makes the following conclusions • The latest monitoring event reflects the historical trends in groundwater direction and contaminant distribution L GTI makes the following reco endation • Discontinue-analysis for diesel, methanol, ethanol, ETBE, DIPE, TAME;TBA , 1,2-DCA, /EDB and lead\ These analyses do not contribute clarity to the site conceptual model nor augment site remedial alternatives ' Project Status Review • GTI's February 20, 2004 "Additional Site Characterization, Soil and Groundwater Investigation" report documents the advancement of several Cone Penetrometer Testing ' (CPT)borings in December 2003 Groundwater and soil data from these borings clarified the site conceptual model suggesting that residual contamination is localized beneath the former UST excavation, with the possibility that a submerged MTBE groundwater plume ' may be migrating off site I e In our April 19, 2004 work plan GTI proposed additional groundwater plume definition and an aquifer pumping test The SJC/EHD approved the work plan in their May 21,