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� v 0 ASSOC IATES I N C . After presenting the results of the soils investigation to PHS/EHD in a report prepared by ' Helmick and Lerner Inc. titled Preliminary Site Assessment- Stagg High School dated September 23, 1997, PHS/EHD requested additional work at the site. ' Helmick and Lerner Inc. subsequently submitted a workplan titled Work Plan for Installation of Monitoring Well, Stagg High School- Stockton Unified School District dated February 6, 1998. The workplan purposed methods and procedures evaluate groundwater for the presence of tpetroleum hydrocarbons with the installation of a single monitoring well. This workplan was approved by PHS/EHD, in correspondence dated March 25, 1998. ' On February 25, 1999, ATC supervised the advancement of soil boring MW-1 to a total depth of 24.5 feet bgs. This soil boring was subsequently converted into a 2-inch diameter PVC ' monitoring well which was completed at a depth of 23 feet bgs. Soil samples collected from boring MW 1 at 10.5 feet bgs and 23.5 feet bgs contained concentrations of for total petroleum hydrocarbons as gasoline (TPHg) at 1,900 part per million (ppm) and 2.5 ppm, respectively. The initial groundwater collected from well MW1 contained concentrations of TPHg (3,900 part per ' billion (ppb)), toluene (86 ppb), ethylbenzene (100 ppb), total xylenes.(530 ppb), and methyl tertiary butyl ether (MTBE) (12.5 ppb). Subsequent quarterly sampling events have shown decreasing concentrations of dissolved petroleum hydrocarbon constituents over time. 2.0 METHODS AND PROCEDURES ' To evaluate the presence of petroleum hydrocarbons in soil and groundwater, four soil borings g were advanced in the vicinity of the former UST and completed as groundwater monitoring wells. All field activities were performed in accordance with ATC's Workplan Addendum for Supplemental Subsurface Investigation at Stagg High School, 1621 Brookside Road, Stockton California, dated December 7, 2000 and ATC's Site Safety Plan submitted to PHS/EHD on July ' 1, 1999. ' 2_1 Soil Borine Advancement and Sampling Drilling was conducted on February 19, 2001 by V & W Drilling (State C57 license no. 720904) ' utilizing a hollow stem auger drill rig. The soil samples from soil boring MW2, advanced to 36.5 feet bgs, and soil borings MW3, MW4, and MW5, advanced to 26.5 feet bgs, were collected at five-foot intervals using a 2-inch diameter split-spoon sampler containing three brass tubes. A ' field geologist logged drill cuttings and soil samples utilizing the Unified Soil Classification I System. ' The drill cuttings were characterized for soil type, moisture content, and visual evidence of petroleum hydrocarbons. A flame ionization detection meter (FID) was used as a field-screening device for the detection of petroleum hydrocarbon vapors in drill cuttings and cored samples. 1 Drill cuttings were temporarily stored on site in 55-gallon DOT approved steel drums. Descriptions of soil types encountered and sample collection intervals are included on the w:117292V ports\Sup_subsurf invest.dw 2