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2-27-1998 S:44PM FROM HORIZON/ELDORADO 916 939 2172 P. 3 Former Discuvury ChcvrolCt February 27, 1998 Tracy.California Soil Sainpline and Analysis Letter impacted soil may be present at this depth. Soil samples were also selected for analysis from the 15-foot depths for lateral and vertical definition below groundwater beneath the site. Results of the laboratory analyses of the 5-foot and 15-foot soil samples are summarized in Table I attached to this letter. It is noted that four of the five 5-foot soil samples Otat have indicated detectable concentrations of either TPHg (320 parts per million (ppm]), BTEX (between 0.0068 ppm and 28 ppm), MTBE (between 0.0073 ppm and 0.021 ppm), or the fuel oxygenates (0.0052 ppm and 0.063 ppm of tert-butanol), reported low but detectable OVM readings (between 8 ppm and 15 ppm) during field screening while drilling at the site. Thu only exception was the 5-foot soil sample collected in GP8 which reported a zero OVM reading, but recorded a trace concentration of 0.0073 ppm (or 7.3 parts per billion fppb]) of NTYB i. On February 26, Horizon verbally communicated the laboratory soil results to the SJCPHS- END. During the telephone discussion with the SJCPHS-EHD, it was the stated opinion of the SJCPHS-EIID that all soil and water samples collected at the site were to be submitted for laboratory analysis for TPHg, BTEX, MTBE and fuel oxygenates. It is Horizon's professional opinion that based on the soil sample results shown in Table 1,additional soil samples from the 10-foot depths are justified to he selected for analysis for lateral and vertical definition beneath the site. However, because of the nondeteetable laboratory results for TPHg, BTEX, MTRE and fuel oxygenates recorded in the 15-foot soil samples, lateral and vertical delineation below groundwater has been provided, and it is unnecessary to analyze the soil samples collected at depths of 20 feet and 25 feet. It is further noted that these additional soil samples all reported nondetectable OVM readings (zero ppm readings) during field screening while drilling at the site. All analytical data collected and analyzed to date in an effort to confirm whether the fuel oxygenates are present beneath the site have not detected fuel oxygenates at concentrations that warrant concern. Since no evidence of fuel oxygenates are present in the subsurface soils below 15 feet, and no history of the groundwater fluctuating below 11.6 feet below surface grade(bsg)have been recorded at the site, it is our professional opinion that vertical definition is complete and analysis of additional soil samples collected below a depth of 15 leer bsg is unnecessary. 0227jwon 2 HORIZON ENVIRONMENTAL INC.