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contamination has been confirmed in both the 2nd and 3rd Riverbank aquifers, additional wells in <br /> both aquifers are appropriate and there is no need to await the results from the 2nd aquifer to <br /> determine whether to set additional wells in the 151 and 3rd aquifers <br /> Secondly, EHD has requested a calculation of the mass of hydrocarbons remaining in place in both <br /> soil and groundwater As explained in section 3 5, most of the diesel fuel originally lodged in the <br /> Modesto Formation, but the samples collected from this formation in GT-15 this quarter were far <br /> less contaminated than those collected previously Hence, a mass calculation in 2004 using data <br /> collected in the 1990's would greatly overestimate the current mass if EHD requires an accurate, <br /> mass calculation, then EHD should request that new "confirmation" borings be drilled into the <br /> Modesto Formation in the vicinity of the UST cavity to obtain up-to-date concentration data from <br /> this formation <br /> Further, an accurate calculation of the mass in place in the groundwater cannot be made until after <br /> the dissolved-phase plumes in all three Riverbank aquifers have been fully delineated We <br /> anticipate that this can be accomplished after GT-16 through, GT-21 have been drilled, and <br /> therefore recommend postponing these calculations until then At the same time, revised cross <br /> sections that include diesel isoconcentration contours could be constructed to better illustrate the <br /> vertical and lateral extent of contamination Also, a fate and transport model would benefit from the <br /> additional data and would lead to a more detailed and more rigorous Conceptual Model for the site <br /> 14 <br />