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h T Ms. Lori Duncan S E C O RMay 27, 2005 Page 3 (AS-8 through AS-11, MW-1R through MW-3R, and MW-10) at the locations shown on Figure 2, in addition to the replacement monitoring wells previously proposed for the Chevron site. Data collected from borings AS-8, AS-9, and AS-10 will be used to evaulate the vertical extent of the southern and central portion of the plume (ARCO). Boring AS-11 will be used to evaluate the lateral extent of the ARCO portion of the plume. Data collected from the deeper borings for replacement monitoring wells MW-1R through MW-3R, the borings for replacement wells MW-5R, MW-7R, MW-9R, and new well MW-10, will be used to evaluate the lateral and vertical extent of the northern portion of the plume (Chevron). Details of the specific scope of work are discussed in the following sections. Well construction details and proposed boring details are presented in Table 1, • Site Health and Safety Plan (HASP). As required by the Occupational Health and Safety Administration (OSHA) Standard "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910.120), and by the California Occupational Health and Safety Administration (Cal-OSHA) "Hazardous Waste Operations and Emergency Response" guidelines (CCR Title 8, Section 5192), SECOR will update the current site-specific HASP prior to the commencement of fieldwork. The HASP will be reviewed by the field staff and contractors before beginning field operations at the site. • Permitting. Well construction permits will be obtained from the SJCEHD prior to the commencement of drilling activities. An encroachment permit for the advancement/construction of offsite borings/wells AS-11 and MW-10 will be obtained from the City of Stockton prior to the commencement of drilling activities. • Soil Borings. In addition to the replacement well borings already proposed (MW-5R, MW-7R, and MW-91R), SECOR will supervise the advancement of six soil borings (AS-8, AS-9, AS-10, and deeper borings for MW-1 R through MW-3R) to an approximate depth of 60 feet bgs at the locations shown on Figure 2. The other two borings, for AS-11 and MW-100, will be advanced to approximately 25 feet deep. The borings will be advanced using a sonic or air casing hammer drill rig to protect against vertical migration of contaminants while allowing logging of soil stratigraphy. • Hydropunch Groundwater Sampling. Based on the soil stratigraphy and groundwater conditions encountered during drilling, two grab groundwater sample depth intervals near 45 and 60 feet bgs in more highly permeable soil zones will be identified for each boring location. Each grab groundwater sample will be collected using a modified HydroPunch sampler. Prior to sampling, a water level meter will be used to confirm that the drive rods do not contain water. The sampler will be driven to approximately 3 feet below the desired sampling depth and retracted 3 feet to expose the disposable schedule 20 polyvinyl chloride (PVC) screen and allow groundwater to enter the HydroPunch® sampler. The water sample will be collected by lowering a3/4"-diameter stainless steel bailer through the drive rods to groundwater. The