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Site Characterization- Second Event Page 13 <br /> Former Karlson Trucking Facility <br /> Project No. 191.2 <br /> April 27, 2000 <br /> Contarrinant Comentm ioNDepth <br /> 32 <br /> - - - Approxirrete intersection of detection lirrit for 1EPH(0.05nV/L) <br /> 28 ♦ w ith depth(30 feet tags). <br /> 26 <br /> 24 <br /> t 22 <br /> 5L 20 <br /> m <br /> D 18 . <br /> 16 <br /> 14 • <br /> 0.01 0.1 1 10 100 1000 <br /> TEPH Concentration(mg/1) <br /> The log-normal graph clearly shows the logarithmic attenuation in <br /> hydrocarbon concentration with depth. A vertical line representing the <br /> method detection limits show that the hydrocarbon concentration will fall <br /> below detection limits at about 30 feet below grade, about two feet deeper <br /> than the Geo-Probe was able to penetrate. <br /> 5. Based on the totality of the available analytic data and historical <br /> information, we now believe the most likely source of the groundwater <br /> contamination at this site is from a former battery of above ground diesel <br /> fuel tanks. Historical evidence indicates that a row of several large diesel <br /> tanks formerly existed between the pole barn and the shop buildings. The <br /> site of MW-4 is the near the approximate north end of the row of tanks, <br /> and this is also the point of the highest TEPH groundwater monitoring <br /> well concentrations obtained to date. (See the site map for graphical <br /> depiction of the AST location.) When the tank location is superimposed on <br /> the map generated from the soil gas survey (reported previously) the <br /> north end of the tank battery also seems to lie very near the point of <br /> highest soil vapor hydrocarbon concentration. There is a lower level <br /> plume from near the south end of the tank battery. This data could <br /> suggest that chronic small spills of diesel from the AST battery impacted <br /> the soil and groundwater, and the some of the diesel has since degraded to <br /> the point where it is now partially characterized as dielectric oil. <br /> 2937 Veneman Avenue,Suite B240 Geo-Phase Environmental Inc. Phone: (209) 569-0293 <br /> Modesto, Ca 95356 Fax: (209)569-0295 <br />