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Geological Techlacs Inc. Page 4 Groundwater Monitoring Report Project No. 662.2 January 27,2004 v 2.0 FINDINGS AND DISCUSSION The results of the groundwater sample analysis show the following: • MW-I contained the gasoline oxygenate MTBE at 720 �tgll. This is consistent with past results. • 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. Ln • MW-3 contained the gasoline oxygenate MTBE at 1300 pg/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 2.8 ug/l MTBE. This is the sixth consecutive event in which this well has tested positive for MTBE, however the concentrations are La the lowest observed to date. • Figure 4: MTBE vs. Groundwater Elevation -- MW-3 illustrates a fairly direct relationship between the concentration of MTBE in groundwater and the elevation of groundwater in well MW-3. A linear trend line has been added to the figure to show a - general decline in both groundwater elevation and MTBE concentrations over time. • Neither BTEX nor TPH-G was present in any of the groundwater samples above the laboratory reporting limits. • In accordance with San Joaquin County directives, the groundwater samples were also L. analyzed for diesel, methanol, ethanol, 1,2-DCA, EBD and lead. The samples did not contain any of these constituents above the laboratory reporting limits. • 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 values suggesting that the plume may be stable. `= GTI makes the following conclusions: • The lateral extent of the groundwater contamination plume is only defined upgradient to k„ the northwest by MW-2. • . The vertical extent has not been defined since well MW-104 continues to exhibit low concentrations of MTBE. However, given the low concentration of MTBE in the well, Le we believe it to be near the bottom of the contaminant plume. Project Status Review: L. • Perform plume definition and evaluate the mass of contaminants present by installing additional monitoring wells. GTI had submitted to the SJC PHS/EHD a "Soil & Groundwater Investigation Work Plan" dated October 8, 2001. The work plan was approved with conditions in the SJC PHS/EHD's October 26, 2001 correspondence.