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NfIMICR+IfANfR I I Mr.Charles Leubner 6.February 1998 Page 3 Former Underground Diesel and Gasoline Tanks Our experience with previous investigations at the Corporation Yard using the Geoprobe drilling method indicates that achieving depths deeper that 15 to 20 feet using the Geoprobe method of direct penetration technology(DPT)would be difficult. Based on this experience we are proposing that drilling be performed in these areas by hollow-stem auger drilling techniques using a truck- mounted drill rig equipped with 8-inch outside diameter hollow-stem augers. Augers and associated drilling and soil sampling equipment will be cleaned with a high pressure hot water washer before drilling each boring. The sampling equipment and brass tubes will be cleaned with an Alconox or trisodium phosphate wash and rinsed with distilled water prior to collecting each soil sample. Drilling and sampling will be performed according to ASTM Method D 1452-80, "Soil Investigation and Sampling by Auger Borings." For logging and analytical purposes, soil samples will be collected from each boring at five foot intervals beginning at ground surface. Additional samples may be collected at changes in lithology and intervals specified at the discretion of the j field geologist. Samples will be collected by advancing the auger to a location above the desired sampling depth a and then driving a modified California split-spoon sampler lined with three brass tubes into the undisturbed soil. The sampler will be driven by a 140-1b hammer with a 30-inch drop (or an automatic hammer system with an equivalent force) according to ASTM Methods D 1586-84 "Split Barrel Sampling of Soil." Blow counts will be recorded in six-inch intervals after every sampling event. The ends of the middle of the three brass tubes filled at each sample depth will be sealed using Teflon sheeting secured by tight fitting plastic caps. The brass tubes will be labeled with a unique sample number, date and time sampled, sampler's identification, and placed in a chilled ice chest for preservation. The contents of the remaining brass tubes will be used in describing soil characteristics and for qualitative field screening. Each soil sample will be described according to the Unified Soil Classification System as described in the ASTM Standard D 2488-84 "Description and Identification of Soils (Visual-Manual Procedure)". Selected samples will be delivered with chain-of-custody forms to a State-certified laboratory,for analysis. j Soil borings at the former underground diesel tank site will be drilled to a depth of 35 feet below ground surface to evaluate the vertical extent of diesel range hydrocarbons. The lateral borings will also be drilled to a depth of 35 feet below ground surface. A minimum of three samples from each boring will be submitted for laboratory analysis. The three samples will be the 20-foot depth, the 35-foot depth (or deepest sample), and one other sample that is the likeliest to contain i' high concentrations of hydrocarbons based on field observations such as staining, odors, or field screening for the presence of elevated organic vapors using a portable organic vapor analyzer.