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' Geological Technics lnc Page 4 <br /> Groundwater Monitoring Report <br /> Project No 662 2 <br /> April 12,2004 <br /> ' • MW-3 contained the gasoline oxygenate MTBE at 55 ggll This is the lowest level <br /> recorded in the investigation <br /> • The detections of ETBE and TAME in wells MW-1 and MW-3 are intermittent and <br /> ' appear to be dependent on elevated MTBE concentrations and associated elevated <br /> reporting limits <br /> ' • Deep screened well MW-104 contained 15 ug/l MTBE This is the seventh consecutive <br /> event in which this well has tested positive for MTBE <br /> • New extraction well EW-1 contained 120 ug/1 MTBE <br /> ' • Figure 4 MTBE vs Groundwater Elevation in MW-3 illustrates a fairly direct <br /> relationship between the concentration of MTBE in groundwater and the elevation of <br /> groundwater in well MW-3 A reverse trend was present for the subject quarter A <br /> linear trend line has been added to the figure to show a general decline in both <br /> groundwater elevation and MTBE concentrations over time <br /> ' • Neither BTEX nor TPH-G was present in any of the groundwater samples above the <br /> laboratory reporting limits <br /> • In accordance with San Joaquin County directives, the groundwater samples were also <br /> ' analyzed for diesel, methanol, ethanol, 1,2-DCA, EBD and lead The samples did not <br /> contain any of these constituents above the laboratory reporting limits <br /> • Table 3 includes Dissolved Oxygen (DO) and Oxidation-Reduction Potential (ORP) <br /> measurements for the site's wells All four of the wells show low DO and low positive <br /> ORF values suggesting that the plume may be stable <br /> ' GTI makes the following conclusions <br /> • The latest monitoring event reflects the historical trends in groundwater direction and <br /> contaminant distribution <br /> 1 GTI makes the following recommendations <br /> ' • Discontinue analysis for diesel, methanol, ethanol, ETBE, DIPS, TAME, TBA, 1,2- <br /> DCA, EBD and lead These analyses do not contribute clarity to the site conceptual <br /> model nor augment site remedial alternatives <br /> Project Status Review <br /> • GTI's February 20, 2004 "Additional Site Characterization, Soil and Groundwater <br /> Investigation" report documents the advancement of several Cone Penetrometer Testing <br /> (CPT) borings in December 2003 Groundwater and soil data from these borings <br /> ' clarified the site conceptual model suggesting that residual contamination is localized <br /> beneath the former UST excavation, with the possibility that a submerged MTBE <br /> ' groundwater plume may be migrating off site <br />