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i <br /> 7810 Thornton Road,Stockton,California <br /> 5.0 ANALYTICAL RESULTS AND DISCUSSION <br /> ' 5.1 Soil Samples <br /> Soil samples were collected from each of the exploratory soil borings;selected <br /> samples were analyzed for volatile aromatic hydrocarbons (BTEX), total <br /> C} petroleum hydrocarbons as gasoline(TPH-g),oil and grease(418.1)and lead. <br /> The laboratory results are summarized and presented in Table 1. Complete <br /> analytical reports are located in Appendix B. All samples obtained from the <br /> exploratory soil borings were classified and samples which defined a change <br /> in lithology or exhibited a characteristic petroleum odor were submitted for <br /> analysis. TPHg was detected only in soil samples collected from SB-3. The <br /> results ranged from 1.9 to 6.4 mg/kg and decreased with depth.Ethyl benzene <br /> and xylene were also detected in SB-3 in a similar decreasing pattern to a depth <br /> of 16 feet. The maximum concentration of ethyl benzene and xylene were at a <br /> depth of six feet and were 280 and 87 µg/kg respectively. <br /> Heavier petroleum hydrocarbons were also detected in the shallow soils at <br /> i <br /> concentrations less than 100µg/kg,with the exception of the sample collected <br /> from a depth of six feet in boring SB-L,Lead was not detected in the only sample <br /> analyzed from boring S13-3 at a depth of 15 feet. EPA Method 418.1 detects <br /> other organic compounds in addition to petroleum hydrocarbons. <br /> I <br /> 5.2 Discussion- <br /> The <br /> iscussionThe analytical results identified gasoline and heavier (oily) hydrocarbons are <br /> present in the near surface soils in the vicinity of the former tank excavation. <br /> Lateral spreading of the fuel away from the former underground tank was not <br /> evident since all samples collected from SB-1 were clean,lateral spreading of <br /> hydrocarbons has been restricted to less than 25 feet. The limited lateral and <br /> vertical movement has apparently been controlled by the clay nature of the soil <br /> at the site. TPHg appears to be confined to the permeable backfill material <br /> L• (from the former excavation)and is restricted to the upper 10 to 15 feet of the <br /> soil column. The silty and sandy soils below 16 feet are dense and low in <br /> permeability. <br /> Project Number: US=0192 Page 7 of 9 <br />