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• RESULTS OF DECEMBER 1996 DRILLING,STOCKTON FORMER MGP SITE <br /> low to no PNAs detected below 20 feet). SB96-4 had TPH-gasoline (ND to 48 ppm)and <br /> TPH-diesel(ND to 13,000 ppm) detections with the highest concentrations at the 6 foot <br /> depth and ND at 30 and 35 feet bgs. <br /> These results indicate that the extent of the Source Area 1 boundary has been confirmed as being that <br /> of the outside of the former gas holder in this location. Borings SB96-1 and SB96-13 confirmed the <br /> northern extent and boring SB96-2 confirmed the southern extent,as shown in Figure 2-4. The <br /> results from the additional borings will be used to create additional polygons in the VLEACH model <br /> and will be used to examine potential impacts from soil to groundwater. <br /> The results for SB96-3 indicate low concentrations of PNAs and TPH-diesel in the soil column and <br /> SB96-4 indicates PNAs and TPH-diesel in the shallow parts of the soil column. These borings show <br /> concentrations that are less than and similar to some of the soil concentrations within the currently <br /> defined source area. Therefore, VLEACH will be used to examine impacts from all of the soil in this <br /> area without any imposed source area boundary. <br /> 2. Determine leachability of COCs using the DI WET and TCLP tests <br /> Four soil samples were analyzed by the deionized waste extraction test (DI WET)and the <br /> TCLP test in addition to the regular suite of analyses discussed above.These samples were <br /> from SB96-3 at 15 feet,SB96-5 at 14 feet,and SB96-12 at 25 and 35 feet. The samples sent for <br /> BTEX and TPH-gasoline analysis were analyzed by the TCLP method and the PNAs and <br /> TPH-diesel were analyzed with the DI WET test. The purpose of performing these analyses <br /> was to compare the leaching of a soil sample within a source area to the leaching <br /> characteristics of affected soils outside of a source area. Results from these analyses are <br /> presented in Table 3. <br /> Soil boring SB96-5 was drilled inside source area 2 near known residues. Refusal was <br /> encountered at 15 feet,therefore a sample of residue-filled soil was collected at 14 feet. The <br /> sample from SB96-3 was collected from a sample outside source area 4 and the two samples <br /> collected from SB96-12 were analyzed with DI WET because this boring had the highest <br /> PNA concentrations near the water table. All four soil samples were analyzed for total <br /> concentration and DI WET and TCLP extraction concentrations for PNAs,BTEX,TPH- <br /> gasoline,and TPH-diesel. <br /> The DI WET and TCLP tests were performed on soil with low and high detections. The <br /> results indicate that less than 0.1% of total PNAs leach out of the soil and that none of the <br /> class B2 carcinogenic PNAs leach. The data tables indicate that the low molecular weight, <br /> more soluble PNAs may leach and the higher molecular weight,less soluble PNAs do not <br /> leach out at low or high total PNA concentrations even under conservative,laboratory <br /> conditions. For example,in SB96-12 at 25 feet and 35 feet,only naphthalene was detected in <br /> the DI WET whereas the soil samples had detections of most of the PNAs. <br /> These results indicate that the less mobile COCs (and the carcinogenic PNAs)do not leach out of the <br /> soil and more mobile COCs barely leach out under laboratory conditions. This test also shows that the <br /> samples near the water table do not contribute very much in leached constituents. The table below <br /> summarizes the soil results and the leach test results. <br /> SFO/96RESLTS.DOC 3 <br />