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0 <br /> r <br /> Fritz Carlson presented the mixing cell model used to estimate the potential concentrations of <br /> benzene, naphthalene, and chrysene in groundwater. The calculations were done for two <br /> different aquifer thicknesses: the A Zone(15 feet thick) and the A and B Zone (45 feet thick). <br /> A mixing cell was developed for each polygon. It was assumed the concentration of the <br /> underflow entering the mixing cell was zero. The mixing cell model did not account for <br /> degradation. Polygons which exceeded the Regional Water Quality Control Board Beneficial <br /> Use Criteria for benzene and naphthalene were identified. Chrysene did not exceed this <br /> criteria during the 1,000 year study period. <br /> Published degradation rates were included in the meeting handout package. Using the more <br /> conservative values in this package (high value), degradation of benzene and naphthalene is <br /> significant and, if incorporated into the model, will greatly reduce the estimates of <br /> concentrations over the 1,000 year study period. <br /> DTSC expressed concerns with the assumption that the underflow concentration entering each <br /> polygon was zero and whether additional polygons qualify as areas of concern if the <br /> underflow concentration is adjusted to include concentrations from the upgradient polygons. <br /> In addition, it was not clear how to apply the mixing cells to estimate downgradient <br /> concentrations at the property boundary. <br /> It was agreed that a series of strips, of unit width, will be drawn across the site and the <br /> additive concentration will be estimated at the property perimeter. This will help both in <br /> understanding the additive affect of adjacent polygons and estimating the concentration at <br /> the property boundary. The methodology for setting up the proposed "strips"for analysis <br /> will be presented to DTSC during a conference call. <br /> In addition Fritz Carlson will pull together recommendations on alternate ways to evaluate <br /> groundwater concentrations to the mixing cell approach and discuss these alternatives on a <br /> conference call. <br /> It was agreed that these alternate approaches should also account for degradation. It was <br /> agreed that CH2MHILL will look into the practicality of estimating site specific degradation <br /> rates. <br /> 4.0 VLEACH, Groundwater Model Application During FS <br /> The use of the VLEACH and mixing cell analysis during the FS was discussed. A flow chart <br /> was developed illustrating that, for each polygon where mass delivery to groundwater is <br /> considered significant, the polygon will be carried through to the remedial options analysis. <br /> The dimensions of the source areas may be modified when the VLEACH analysis is complete <br /> and incorporates the new soil data being collected. <br /> 5.0 Action Items from Previous Meeting <br /> Tricia Sullivan reviewed location of sanitary sewer and water supply underground utilities. <br /> These underground lines do not cross the site. <br /> 2 <br />