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t3.0 INVESTIGATION METHODOLOGY All methods and associated standards employed by ESE during site soil and ground water investigations were consistent with appropriate guidelines established by the County and Regional Board ' All appropriate permitting for the subsurface investigations were secured by ESE through San Joaquin County All underground utilities were identified through the notification of ' Underground Service Alert (USA) and through review of all available site plans and discussions with AT&T ' 3.1 Soil Boring and Soil Sample Collection Two phases of site soil and ground water investigations were completed at this site For the fust 1 phase, ESE supervised the drilling of five soil borings in October 1990 All drilling during this phase was done by Beilik Drilling, a California Licensed Drilling Contractor Each boring was drilled with narrow-diameter augers so that soil samples could be collected with little difficulty ' Soil samples were collected at five foot intervals and at significant lithologic changes Three soil borings (MW-1, MW-2, and MW-3) were completed to a depth of 48 feet below ' ground surface (bgs) while the remaining two bormgs were terminated at obstructions of 8 and 15 feet bgs The two shallow borings were backfilled with a bentonite/neat cement grout The deeper borings were re-drilled with 8-inch diameter augers and completed as ground water ' monitoring wells Soil samples were collected by driving a California split spoon sampler lined with three six-mch ' brass sleeves, 18-inches into the undisturbed soil This was accomplished by dropping a 140- pound hammer thirty inches and recording the amount of blows required to advance the sampler ' six-inches These "blow counts" were recorded by an ESE geologist on a soil boring log included in this report as Appendix C - Soil Boring Logs Soil samples and soil cuttings were logged according to the Unified Soils Classification System (USCS) In addition to the USCS code, the ESE geologist described the soils color, relative density, relative moisture content, grain size, plasticity, and odors, if any Additionally, a portion of the soil sample was placed in a resealable ziploc bag and allowed sit for 15 minutes, at which time a photoionization detector(PID) was used to detect the presence of volatile organic vapors eminating from the soil The PID readmgs were also recorded on the boring logs During the second phase of subsurface investigation, ESE supervised the drilling of two soil borings All drilling during the second phase was completed by Soils Exploration Services, Inc ' (SFS) of Vacaville, California One of the bormgs was drilled in the vicinity of boring B-2Y and the other boring was completed west and downgradient of the former tank excavation The boring located nearest the former tank excavation was completed as a ground water monitoring ' well Soil samples were collected in the same manner as the previous phase F 169351MCLOSURE RPT ( Environmental Science&Engutcenng Inc 1