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Mr.Nuel Henderson,Jr. • October 15,2002 ARCO Station 6100 Project No.U 6100 Work Plan Page 6 and to keep the hole from collapsing. This method of drilling has been selected primarily because of its capability of being able to drill deep (>100 feet) through difficult material, and to collect continuous cores for lithologic logging. Because the use of drilling mud typically causes the sidewalls of the borehole to become semi-impermeable and often impedes the flow of groundwater, these borings will not be converted to groundwater monitoring wells. histead, well borings will be drilled adjacent to the mud-rotary borings using an air-rotary casing-hammer rig ora drilling rig with similar capabilities. The mud rotary bortngs will b b cae'�kfilled to ground-' surface with neat cement. Continuous sampling will be conducted to the total depth explored. Select soil samples will be extracted from the continuous core using pre-cleaned brass tubes. The ends of the tube from each sample will be lined with Teflon TM sheets, capped, and sealed. Each sample will then be labeled, placed in a resealable plastic bag and stored in an ice-chilled cooler. The samples will remain chilled until relinquished to a state-certified analytical laboratory. Strict chain-of-custody procedures will be followed from the time the samples are collected until the time the samples are relinquished to the laboratory. Additional soil from the sample point will be placed in a resealable plastic bag and screened for volatile organic compounds using field instrumentation equipped with a photoionization detector (PID). Delta will record PID readings, soil types, and other pertinent geologic data on the borehole log. Soil samples used for logging will be classified using the Unified Soil Classification System. A minimum of five soil samples from each boring will be submitted for chemical analysis, including the sample exhibiting the highest PID response, the sample from just above groundwater (if encountered), and the sample collected from the bottom of the boring. Borings B-33 through B-38 were drilled during the previous phase of investigation. These borings were continuously cored and logged by a geologist during drilling, and down-hole geophysical logs (electrical conductivity, electrical resistivity, spontaneous potential, and natural gamma radiation) were made of each boring. The geophysical logs did not detect any lithologic units not observed by the geologist during logging activities. Therefore, geophysical logs of the borings will not be made during this investigation. The observations made by the geologist from the cores should be adequate to correlate hydraulically connected strata. Following removal of the drilling mud, the hole will be pressure grouted using neat cement slurry containing approximately 5%bentonite. Monitoring Well Installation A hollo - cm auger drill rig will advance four 10-inch diameter soil borings. The borings will be located approximately 6 to 10 feet from each of the mud-rotary borings. Given the proximity of the borings to the mud-rotary borings, soil samples will not be collected. The new borings will be converted to 4-inch diameter groundwater monitoring wells. The actual completion depth and screen interval of the monitoring wells will be based on the geologist's observations of the cores collected during drilling of the mud-rotary borings. The screen interval of each monitoring well will be targeted at the Sand 2 stratum, using 20 feet of 0.02-inch diameter machine-slotted PVC well casing set to a depth approximately 10 feet P:\Bp-Arco for URS\6100\Work Plans\6100 workplan-1.doc