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:1 <br /> k <br /> Genstar/Western Stone Products,Inc. <br /> 8181 West Eleventh St.,Tracy,CA <br /> Project No.OW0195.00 <br /> Page 2 <br /> This average or <br /> operative concentration", <br /> was then used to calculate the residual contamination. <br /> The mass of residual contamination was computed for the three concentration zones shown on <br /> Figure 3. The mass of residual TPHD equals: <br /> (Area FTZ)x(4FT thickness) x(TPHD conc. at 8FT mg/kg)x(2 . 875)x(1.00 lbs/FT3) <br /> 106 mg/kg <br /> The three results were then added to obtain the total mass. <br /> It should be remembered that this is but one of a number of ways to simplify the calculation of <br /> the total volume of residual soil contamination. An identical but more time consuming result <br /> would be obtained by calculating the residual contaminant mass in each depth interval separately <br /> and summing the results. <br /> Attached are the chromatograms for the samples collected from the recent soil borings along <br /> with a brief letter of explanation from Sequoia Analytical Labs. <br /> It would appear that the residual soil contamination is comprised of a mixture of fuel types. <br /> Weathered diesel alone is present in the 7.5' sample from boring B1W while the samples <br /> collected at 8' and 9.25' contain a mixture of diesel and gasoline or kerosene. The variation that <br /> occurs over a depth interval of only 6" is curious. The laboratory data sheets from past <br /> analyses, primarily those associated with the over-excavation of the tank pit area and the <br /> stockpiled soil from the excavation also indicate this variability. <br /> If you have any questions or 'comments please call me at your convenience. <br /> Respectfully, <br /> RESNA Industries, Inc. <br /> Gregory P. Stahl, <br /> CA Registered Geologist No.'�5023 <br /> GPS/ggk <br /> Attachments <br /> PC: Mr. Bill Keller, Western Stone Products, Inc. <br /> Ms. Elizabeth Thayer;' CRWQCB <br /> L-082593.FNL <br />