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1Cecfaguaf IecFinus 2r • ! Page 2 Sail Groondwater.Investigation Report George's Service P%lett No 425 2 November 30 1998 • 2.1 Soil Boring :rnstallatioBn Intermediate Depth Borings In an effort to define the lateral extent of petroleum hydrocarbons, two borehole/monitoring wells, MW-105 and MW-107, were installed They were drilled to 37 5 and 52 feet below grade and converted into monitoring wells The soil borings were drilled using an 8-inch outside diameter (o d ), continuous flight, hollow stem auger owned and operated by V&W Drilling (C57# 720904) Based on hydrologic data collected for the site, well placement was based on a northerly groundwater flow direction and the screen interval was planned for the gravel layer encountered in MW-102 at 45 feet bgs During the first attempt at MW-105 the gravel layer was not located and the boring was terminated at 50 feet bgs and renamed SB- 101 This borehole was grouted up with a neat cement grout and the ng was moved over six feet to drill again It was decided to install the screen of MW-105 in the sandy gravel layer located at 30 to 35 feet bgs Deep Soil Boring To define the vertical extent of petroleum hydrocarbons beneath the former tank location, one borehole/monitoring well, MW-202, was drilled to a depth of 84 feet and then converted to a monitoring well screened from 79 to 81 5 feet below ground surface The boring was drilled in three stages as described below 1 The first stage was drilled with an 8-inch hollow stem auger down to 50 feet, the previous known vertical extent of contamination This stage was free drilled because it was drilled next to MW-102 2 In stage two the 8-inch augers were then pulled from the hole and the borehole was drilled out with a 15-inch hollow stem auger to 50 feet A permanent conductor casing � . was then installed inside the 15-inch augers and grouted in place The 15-inch augers were then pulled from the hole 3 In stage three the 8 inch augers, which had been decontaminated, were lowered down the inside of the conductor casing The borehole was then advanced to 84 feet Samples were collected at five-foot intervals This method of drilling reduced the possibility of dragging contamination from the shallow contaminated zone into the deeper soil and groundwater A monitoring well permit was secured from San Joaquin County and the agency was notified 48 hours prior to commencing work The subsurface was cleared of underground utilities by notifying Underground Service Alert and by consulting with the property owner Soil cuttings and drilling decontamination water were placed in DOT-17 55 gallon drums and placed alongside the building until their disposal could be arranged 2.1.1 Soil Sampling Procedure Soil samples were collected for geological and analytical evaluation at five-foot intervals, unless otherwise noted A boring log providing sediment description using the USCS and field observations was maintained by a professional geologist working under the supervision of a registered geologist Soil samples were collected in 6 0-inch brass liners using a 2 0 inch modified California split spoon sampler All soil samples were sealed with Teflon sheets, capped with plastic end caps, labeled, and placed in a cooler at 4° Celsius for transport to the laboratory following Chain of Custody protocol