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i 1 Ciwfogi ul Te&oUa I= Page 4 Groundwater Morutonng Report Project No 662 2 August 30,2004 • 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 e MW-3 contained the gasoline oxygenate MTBE at 940 gg/1 This is the lowest level recorded in the investigation ' • 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 28 ug/l MTBE This is consistent with past results • 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 two 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 was not present in any of the groundwater samples above the laboratory reporting ' limits • Well MW-104 contained BTEX 0 4 toluene and 0 3 ug/l xylenes This is the first detection of these constituents in this well • In accordance with San Joaquin County directives, the groundwater samples were also analyzed for diesel, methanol, ethanol, 1,2-DCA, EBD and lead Wells MW-3 and MW- 104 contained 21 and 16 ug/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 ' GTI makes the following recommendations • Discontinue analysis for diesel, methanol, ethanol, ETBE, DIPE, TAME, TBA, 1,2-DCA, EBD and lead These analyses do not contribute clarity to the site conceptual model not ' 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