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' ealo e 4 kat nchda 11M Pa G g g Groundwater Monrtonng Report Project No 662 2 February 15,2005 ' 2.0 FINDINGS AND DISCUSSION t The results of the groundwater sample analysis show the following • MW-1 contained the gasoline oxygenate MTBE at 1400 µg/1 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 ' • MW-3 contained the gasoline oxygenate MTBE at 90 µg11, which is lower than normal but similar to last winters concentration ' • 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 120 µg/1 This well has consistently contained low levels of MTBE since its installation There appears to be a trend of increasing concentration of MTBE ' • The extraction well, EW-1, also contains MTBE at 120 µg11 It is screened in the same horizon as MW-104 • 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 four 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 ' • 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 • 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 negative or tlow 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 ' GTI makes the following recommendations • 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