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• RESULTS OF DECEMBER 1996 DRILLING,STOCKTON FORMER MGP SITE <br /> the HydropunchT sample. Additional borings were drilled during this <br /> investigation to determine if the source of the TPH-diesel found in Area II <br /> groundwater is on PG&E property or is offsite. <br /> -Determine if the former auto repair shop located in Area II has potentially <br /> impacted soils in this area. <br /> 4. Establish downgradient extent of COCl in Zone B groundwater <br /> -Results from the Phase IV investigation and the most recent quarterly <br /> sampling events indicate that PNAs are present in groundwater samples <br /> from Zone B wells in Area II. A Zone B well was installed during this <br /> investigation to define the extent of PNAs in Zone B groundwater. <br /> Figure 1 shows the locations of the borings and wells that were drilled during this event. <br /> Results and Conclusions <br /> 1. Confirm/Modify Dimensions of Source Areas 1 and 4 <br /> Four borings,SB96-1,SB96-2,SB96-12,and SB96-13,were drilled to further define the extent <br /> of Source Area 1 and two borings,SB96-3 and SB96-4,were drilled to further define the <br /> extent of Source Area 4. These borings were continuously sampled to 35 feet below ground <br /> surface (bgs)with the exception of SB96-1 which was sampled to 31 feet and SB96-2 which <br /> was sampled to 26 feet bgs. Boring SB96-1 was sampled to 31 feet because there was no <br /> recovery at 35 feet and SB96-2 was sampled to 26 feet because a saturated sand was <br /> encountered at 26 feet. Soil samples were analyzed for PNAs,BTEX,TPH-gasoline,and <br /> TPH-diesel at five foot intervals. Seven of these samples were also analyzed for soil <br /> moisture and bulk density for the purpose of having additional site specific data for <br /> VLEACH modeling.Table 1 presents the analytical results for these borings. Figures 2-1 <br /> through 2-5 include the soil analytical data for all borings drilled in Area 1. <br /> To better define Source Area 1,SB96-1 was drilled to the north and SB96-2 was drilled on <br /> the southern boundary of Source Area 1. Field observations indicated possible presence of <br /> residues in soil samples from these borings. After discussions with PG&E,DTSC,and <br /> RWQCB, two more borings were drilled approximately five feet offset from SB96-1 and <br /> SB96-2. These borings were SB96-13 and SB96-12. Sample results indicate extremely low <br /> levels of PNAs in SB96-1 (0.1 ppm to 1.1 ppm)and in SB96-2 (ND to 3.6 ppm). PNAs were <br /> not detected in SB96-13. SB96-1,SB96-2,and SB96-13 were non-detect for BTEX,TPH- <br /> gasoline,and TPH-diesel. The northern boundary of Source Area 1 is defined as the edge of <br /> SB96-1 and the southern boundary as the edge of SB96-2. <br /> SB96-12,the offset boring from SB96-2 was drilled in the former lampblack separator and <br /> samples contained PNA,BTEX,and TPH detections from 6 to 35 feet. PNAs were detected <br /> from 0.814 ppm to 286.7 ppm. SB96-12 ranged from non-detect for TPH-gasoline and TPH- <br /> diesel to 34 ppm,TPH-gasoline,and 1,600 ppm,TPH-diesel. Benzene and toluene were not <br /> detected in SB96-12,however minor amounts of ethylbenzene and xylenes were detected. <br /> To better define Source Area 4,SB96-3 and SB96-4 were drilled to the west of the source <br /> area. SB96-3 had low total PNA concentrations (0.241 ppm to 4.66 ppm),low TPH-gasoline <br /> (ND to 9 ppm) and TPH-diesel(ND to 1800 ppm)detections from 5 to 35 feet. SB96-4 had <br /> some PNAs in the upper soils (with the highest concentration of 422.8 ppm at 6 feet,and <br /> SFO/96RESLTS.DOC 2 <br />