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Cia6gual TedWd lice Page 16 <br /> Site Conceptual Model Report <br /> Project No 724 2 <br /> May 2,2006 <br /> COC February 2006 WQO <br /> [max. cone. (uo)] (RWQCB, April 1, 2004) <br /> ' Gasoline(off site) 1 80 5 /l <br /> Gasoline(on site) 73.2 5 /l <br /> Benzene <0 5 0 15 <br /> Toluene <0 5 42 g/l <br /> Ethyl benzene I <0 5 29 <br /> Xylenes I <1 17 /l <br /> ' MTBE 1 17.3 5 u /I Ed <br /> The gasoline and MTBE concentrations exceed the RWQCB-CVR water quality objectives <br /> ' But as noted above in Section 2 7 there are no wells in the immediate area (2000' radius) to <br /> act as a human exposure pathway from the groundwater plume The above table separates <br /> the TPH-G data into on or off site based on the source of the containination in the co-mingled <br /> plume as described below <br /> It is notable that the BTEX concentrations have fallen to non-detectable levels with only the <br /> ' MTBE and TPH-G remaining in the wells This situation is characteristic of a "weathered <br /> plume" <br /> 5.0 DISCUSSION AND CONCLUSIONS <br /> ' 5.1 Discussion <br /> ' Co-mingled Plumes <br /> The evidence suggests that there is a co-mingled TPH-G plume present at the site In Figure <br /> 15 discussed above, GTI used the CAD software to "close" the contours extending northward <br /> from intermediate well MW408 If the well MW-11's TPH-G data point (96 ug/1) from the <br /> ' GASCO site were "added" to the Morita Brothers plume one can envision the contours <br /> stretching across Charter Way for a unified plume front <br /> A limitation of Figure 15 is that it includes data from various depths from both sites across <br /> different aquifer depths as GTI has not determined the screened intervals of the GASCO <br /> site's wells But an additional revelation is noted when the GASCO site data is plotted with <br /> ' the Morita Brothers deep aquifer TPH-G concentrations as shown in Figure 16 In this plot a <br /> core of elevated TPH-G (1580 ug/1) is present to the east of the Morita Brothers site in well <br /> MW-208 The remainder of the Morita Brothers site's deep wells MW-202, MW-209 and <br /> ' MW-210, were non-detect for the February 2006 monitoring event GTI believes that this <br /> contanunation (Figure 16) is not sourced from the Morita site but rather the GASCO site <br /> ' The evidence for this conclusion is as follows <br /> • In an effort to further define the extent of the Morita groundwater plume additional <br /> monitoring wells/well sets were installed in December 2003 This resulted in the ability <br />