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Mr . Ted Knowles 202/799-5004 October 22 , 1987 Page 2 Selected soil samples were analyzed for total volatile hydrocarbons ( TVH) and benzene , toluene , ethylbenzene and xylene (BTEX ) using EPA Methods 5030/8015/8020 . BTEX concentrations , if any , were non-detectable . However , detectable concentrations of miscellaneous aromatic hydrocarbons were found within all 3 monitoring wells ( see Attachment II , Laboratory Analyses ) . Two - inch diameter monitoring wells were installed in the three borings . Monitoring wells 1 and 2 were installed to the total boring depth of 65 feet . Monitoring well 3 , however , was installed to a total depth of 56 feet as a result of flowing sands . The three monitoring wells were constructed by installing a 30-foot section of PVC well screen ( 0 . 020-inch machine slotted) in the bottom of each boring with blank PVC casing to the surface . A well pack consisting of washed #20 Monterey sand was placed in the annulus from the bottom of the borings to approximately one foot above the screened interval . A surface seal was then installed consisting of approximately 1 foot of bentonite overlain by a cement grout to ground surface . A slip cap and traffic rated street box were then installed to provide access to the monitoring wells ( see Attachment I for specific well construction details ) . The three monitoring wells were developed by hand bailing using a clean acrylic bailer until the water appeared clear and free of sediment . On October 1 , 1987 all three monitoring wells were purged and sampled . Prior to sampling, four well volumes were removed from each well using an acrylic bailer . Each well was subsequently sampled with a EPA approved Teflon sampler used to transfer groundwater into 40 milliliter ( ml ) Teflon capped vials . The sampler was cleaned with laboratory grade detergent and rinsed with distilled water before and after collection of each water sample . The samples were labeled , placed on ice and transported to GTEL in Concord , California , accompanied by a Chain-of-Custody manifest . Water samples from all three wells were submitted for Modified EPA Method 602 analysis ( includes xylene quantification) . A review of the laboratory analyses indicated benzene concentrations to be 60 parts per billion (ppb ) , 36 ppb and 85 ppb in monitoring wells 1 , 2 and 3 , respectively ( see Attachment II , Laboratory Analyses ) . The State of California , Department of Health Services , which regulates drinking water quality has set the action level for benzene at 0 . 7 ppb . In the Central Valley , all groundwater is considered to be potential drinking water and must be dealt with accordingly .