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' trough, known as the Great Valley Province The structural trough has been filled with thick sequences of sediments ranging in age from Jurassic to Recent Rocks which compose the basement floor of the province have not been completely defined but are believed to be derived from metamorphic and igneous origins. ' The site lies within the limas of San Joaquin Valley Water Basin (Basin No 5-22) of the San Joaquin Basin Hydrologic Study Area, which is drained primarily by the San Joaquin River Two aquifers are recognized to exist at the site, a deep and a shallow aquifer The deeper aquifer contains connate water occurring in the semi-consolidated to consolidated Merhten and Valley Spring Formations The fresh water bearing formation, consisting of alluvial sediments occurs in a shallower depth These two aquifers are hydraulically ' separated from each other. ' 3.0 PROCEDURES ' 3.1 Drilling and Sampling Eight soil borings (MW1 through MW3 and B4 through B8) were drilled on April 27-28, ' 1994 Borings MWI, MW2, and MW3 were advanced to a total depth of 34 5 feet, 34 feet, and 35 5 feet, respectively and completed as groundwater monitoring wells Bonngs 134, B5 and B6 were advanced to total depths of 23 5 feet, 10 feet and 15 feet, respectively. Borings B7 and B8 were advanced to a total depth of 20 feet Borings B4 through 138 were backfilled with Portland cement to the surface Auger returns were stockpiled on plastic sheeting and stored near the fence along the northern perimeter of the site All borings were ' drilled using a truck-mounted CME75 high torque drill ng The drill ng and two-man crew were supplied by Machell Drilling Environmental Corporation (MDE) of Rancho Cordova, California The bonngs were advanced using eight-inch diameter continuous flight hollow ' stem augers During drilling, auger returns were monitored for the presence of organic vapors using a photo-ionization detector (PID Thermo Environmental 580A, 10 0 eV, calibrated to isobutylene) ' Discrete soil samples were collected ahead of the drill bit using a split-tube sampler loaded with three pre-cleaned 2-mch by 6-inch brass sleeves The samples were collected at five- foot intervals, using a 140-1b hammer to advance the sampler 18 inches The number of blows required to advance the sampler in 6-inch increments was recorded on the boring logs (See Appendix A) To avoid cross contamination, the sampling equipment was washed in ' a tri-sodium phosphate (TSP) solution and nosed twice with water prior to each sampling run. The augers and drill bit were steam cleaned utilizing a portable decontamination unit, prior to drilling each boring ' For each sample, both ends of the lead brass tube were covered with aluminum sheets, capped and sealed with tape The samples were then stored on ice and transported under ' chain-of-custody to Pan-Agncultural Laboratories, Inc, in Madera, California 0-6#iW w.an Swn I— R"Rm S.'�QRX_%9B3 1