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i Geofogicuf Eechnics Znc. Page 2 Soil Groundwater Investigation Report C&B Equipment Project No.: 336..2 December 22, 1997 4 f7• 2.0 SCOPE OF INVESTIGATION In accordance with the approved work plan and for the purpose of further investigation of the lateral and vertical extent of soil and groundwater impacted with petroleum hydrocarbons, Geological Technics Inc. installed four soil borings to ±20 feet below grade and one soil boring to 40 feet below grade. The borings were subsequently converted into 2 inch diameter monitor wells. 2.1 Soil Boring Installation In an effort to define the lateral extent of petroleum hydrocarbons, four (4) soil borings, MW- 4 through MW-7 were advanced. They were drilled to 20 feet below grade and converted into monitoring wells. The soil borings were drilled using a 8 inch outside diameter (o.d.), continuous flight, hollow stem auger owned and operated by V&W Drilling (C57# 720904). Based on hydrologic data from the three existing monitoring wells on site, well placement F' was based on a northerly groundwater flow direction. To define the vertical extent of petroleum hydrocarbons, one (1) soil boring, MW-101, was .::.� advanced to 40 feet. Due to the geology consisting of clays and silts from 30 to 40 feet bgs = j Ron Rowe of SJC PHSIEHD and Michael Niemi, geologist for GTI, decided to grout the hole from 40 up to 29 feet bgs. A 2 inch i.d. casing was then set in the borehole with screen from 28.5 to 26 feet bgs. 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 30 feet. Soil samples were collected at five foot intervals from the surface to 20 feet bgs and =i continuously below that. SimulProbe samples were also collected as described in Section 2.1.1 . 2. In stage two the 8 inch augers were then pulled from the hole and the borehole was drilled out with a 12 inch hollow stem auger to 30 feet. This auger then was temporally g g left in the ground to function as a conductor casing during the installation of the deep well. '1 3. In stage three the 8 inch augers, which had been decontaminated, were lowered down the inside of the 12 inch augers. The borehole was then advanced to 40 feet. Samples were collected continuously and one SimulProbe sample was collected. -' This method of drilling reduced the possibility of dragging contamination from the shallow contaminated zone into the deeper soil and groundwater. However because the borehole was not completed as originally planned the monitoring well was actually set inside of the 12" augers. - I 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 I'd placed alongside the shed until there disposal could be arranged. i