SITE INFORMATION AND CORRESPONDENCE 1995-2004

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0 DRAFT activities. To determine if the TPH-gasoline and diesel in the groundwater is from soils on PG&E property and whether solvents are present, the following field activities will be implemented: • Three borings(SB96-6, -7,and-8)will be drilled on site within the footprint of the former auto repair facility and upgradient of MW-2311 to Zone A groundwater(approximately 35 feet) • A fourth boring(SB96-9)will be drilled offsite,upgradient from Area 11 (Figure 2). • Grab groundwater samples from Zone A will be collected from one on-site boring and the offsite, upgradient boring using HydropunchTM or equivalent groundwater sampling techniques • The soil and groundwater at this site will be analyzed for COCs It is anticipated that approximately 7 samples per boring will be collected for analysis. Sample collection will be every 5 feet to the bottom of the vadose zone. Additional samples may be collected if residues are observed in the field. If COCs are not detected in soil, the source of the TPH-diesel in groundwater will be assumed to be upgradient of the PG&E property. Establish Downgradient Extent of COCs in Zone B Groundwater One additional groundwater monitoring well(MW-26)is proposed along the eastern perimeter of Area II. The Phase IV investigation indicated the presence of PNAs in Zone B groundwater beneath Area II. In order to define the extent of PNAs in Zone B groundwater the following field work will be performed: • One boring will be drilled along the eastern perimeter of Area II • Grab groundwater samples will be collected from the boring in both Zone A and Zone B • If PNAs are detected in the Zone B sample, the monitoring well will be relocated to the alternate location across E 1 Dorado. • The boring will be converted to a perimeter monitoring well • The monitoring well will be developed • The monitoring well will be sampled The proposed well will be installed along the perimeter of the site. The proposed location and alternate location of this well are shown in Figure 2. Due to overhead and underground obstructions as well as limitations presented by the City of Stockton(the City),these locations also represent physical limits to future drilling. The City will not permit drilling in the streets or within 10 feet of the toe of the Mormon Slough levee and overhead obstructions and underground obstructions also preclude drilling at these locations. Field Methodology Soil borings will be drilled using direct push drilling techniques described in the Supplemental Soil Investigation Workplan (June 1995). Soil from the soil borings will be collected continuously to the water table. Samples will be selected every 5 feet for laboratory analysis. In addition,grab groundwater samples from the Area II borings will be collected from one on-site boring and the offsite,upgradient boring(SB-96-5) using Hydropunch1m or equivalent groundwater sampling techniques. Descriptions of the groundwater sampling technique are provided in Workplan Phase IV Groundwater Investigation(February 1996). SF0/GAAV1 I.DOC 3