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i Jff�ZMA . November 12, 1992 Working To Restore Nature ARCO Station No 6100, Tracy, California i Vapor-Extraction Well Construction The wells are constructed using clean 4-inch-inner-diameter, thread-,jointed, Schedule 40 polyvinyl chloride (PVC) casing. No chemicals, glues, or solvents are used in construction of the wells The screened portion of the vapor-extraction well consists of a 5- and 10-foot sections of factory-perforated casing with slots Unperforated casing is set from the top of the screen to several inches below surface grade. i The annular space of each well is packed with pea gravel from the bottom of the screen portion to approximately 1 foot above the top of the screen A plug of bentonite pellets (approximately 2 feet thick) was placed above the sand to prevent cement from entering the sand pack The remaining annulus is backfilled to the ground surface with a mixture of water, cement, and bentonite The construction details of the individual wells are shown on the Logs of Borings The wellheads are secured in cast-aluminum utility boxes with PVC aprons The boxes have watertight seals and are set in concrete approximately flush with the surrounding ground surface to reduce surface-water infiltration A special wrench is required to open the box . This design discourages vandalism and reduces the possibility of accidental disturbance to the well Each wellhead is also fitted with a locking well cage to further protect against unauthorized disturbance of the well. Sample Labeling and Handling Sample containers are labeled in the field with the job number, sample location and depth, and date and promptly placed in iced storage for transport to the laboratory A Chain of Custody Record is initiated by the geologist and updated throughout handling of the samples and accompanies the samples to a laboratory certified by the State of California for the analyses requested Samples are transported to the laboratory promptly to help ensure that recommended sample holding times will not be exceeded Samples in our custody will be properly disposed of after their useful life has expired 0623ccar 30041-3