SITE INFORMATION AND CORRESPONDENCE FILE 2

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Rodger Liston Darpetro Inc. 749 E. Charter Way, Stockton, California Page 4 of 7 Charter Way site ranged from 2000 to 8500 micrograms per liter (µg/1) and were 350 µg/I on April 2003. EHD's review of the 701 site data shows that MTBE concentrations in the well, generally the well most impacted by MTBE on the 701 site , ranged from 220 to 850 µg/I , an order of magnitude less than CGG reported . The actual concentration of MTBE in MW-1 in April 2003 was 310 gg/1 . During the same time period , the MTBE concentrations on your site in BM-3 ranged from 27 to 2200 µg/1 , and were most commonly in excess of 480 µg/I. Although CGG does not explicitly state the implication of the soil data collected from the VW-7 and B-3 borings, EHD infers the implication to be that the vertical extent of impacted soil has been delineated , if so, EHD disagrees. The VW-7 and B-3 borings are approximately 45 feet from BM-1 in the former UST pit and the contaminant concentration profile of VW-7 does not even closely match that of BM-1 . Therefore EHD believes that the vertical extent of impacted soil has not been delineated as the area of highest impact has not been assessed vertically. CGG states that the dissolution of the oxygenates in the ground water on the site increases the ground water density such that it sinks at a rate of 1 foot per 20 feet of lateral flow under the gradient at the site. EHD isnot aware of this occurring due to dissolution of contaminants having a density less than water. By 03 May 2004; please have CGG provide EHD with references to this phenomenon occurring on other sites with ground water impacted by hydrocarbons and MTBE and the specific calculations CGG generated to derive the rate of sinking under the existing gradient on your site. Although EHD has no references for this , it seems that the negligible mass added to ground water by the dissolved MTBE would not create a great enough density difference between impacted and unimpacted ground water that would be sufficient for the impacted ground water to displace the underlying unimpacted ground water. Assuming nearly equal densities (MTBE and petroleum hydrocarbons have a density less than 1 ), the addition of, say 2000 µg/l MTBE would increase the weight of 1 pound of water to approximately 1 . 000002 pounds. It would take a fairly delicate scale to even detect such a small increase in weight; it seems incredible that such a small increase of mass could cause the plume to sink 1 foot per 20 feet of horizontal migration - except under a ground water gradient equal to or greater than 0.05. EHD and CVRWQCB is confused by the inclusion of the un-cited interpretational 'boring logs' as unnumbered figures in the report. These 'logs' appear to be individual cutouts from cross sections; they have no scale and do not indicate what the database is. This is especially curious as CGG has boring logs that could have been included . CGG interprets their MTBE and TBA concentration maps to indicate two plumes migrating onto the site, one from under the Sun's Garden Restaurant building and one from the south from Charter Way. EHD believes these maps show the opposite; most show a " bull's eye" on or near BM-3 or BM-5 ; which indicates a source at or near BM-3. The contouring on several maps are influenced ND (not detected) readings being accepted as zero concentrations, which is not necessarily so. Not detected indicates that the analyte is not present at or above a specific concentration high enough for quantification for the method utilized . For example, the tert-butanol concentration on the 10/97 map is plotted as less than 10 parts per billion (ppb) , but the detection limit is 100 ppb; it could be 8 ppb or 98 ppb and still be 'ND'; but if it is 98 ppb, the contour map