SITE INFORMATION AND CORRESPONDENCE 1995-2004

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• RESULTS OF DEC19 1996 DRILLING,STOCKTON FORMER MGP SITE 4.Establish downgradient extent of COCs in Zone B groundwater One additional monitoring well,MW-26R was installed on the eastern side of El Dorado street for the purpose of defining the extent of PNAs in Zone B groundwater. A boring was originally drilled in the MW-26 location on the western side of El Dorado as shown on Figure 1. Grab groundwater samples were collected with the Hydropunchm in Zones A and B,at 45 feet bgs and 100 feet bgs,respectively. These samples were analyzed for PNAs, BTEX,TPH-gasoline,and TPH-diesel. Tert-Butyl methyl ether (MTBE)was detected in the A Zone sample for MW-26 at 2.4 ppb. Total PNAs were detected at 33 ppb and TPH-diesel was detected at 0.98 ppb in the B Zone sample for MW-26. Due to the PNA detection,a second B Zone boring,MW-26R was drilled in the alternate location across El Dorado Street and downgradient from MW-26. An A Zone HydropunchT'sample from MW-26R did not have any detections for PNAs,BTEX,TPH-gasoline, or TPH-diesel. A well was installed according to the workplan in the MW-26R boring location,developed, and sampled. Sampling results indicate PNAs were present at concentrations of 15 ppb with acenaphthene being the only PNA being detected. This is the lowest Zone B PNA detection in Area II,suggesting that this well is at or near the downgradient extent of PNAs.This well will be sampled along with the rest of the wells during the first quarter 1997 sampling event. BTEX and TPH were not detected in MW-26R The results of the well installation and recent quarterly monitoring indicate that PNAs exist in Zone B groundwater in Area II and the downgradient extent appears to be at or near El Dorado Street. PG&E will assume for the purpose of conducting the Feasibility Study that the nondetect line for Zone B groundwater runs along El Dorado Street. Further sampling of Zone B wells needs to occur to justify this assumption. SFO/96RESLTS.DOC 5