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'v � NEtrl�(-�lENNEN Mr. Charles Leubner 6 February 1998 Page 2 occurred in the tank's piping. Borings B-2 and B-3 were drilled on both sides of the former excavation to a depth of 20 feet below ground surface. In the soil samples submitted for analysis from the three borings, Total Petroleum Hydrocarbons as Gasoline (TPH-G), benzene, toluene, ethyl benzene, and xylenes (BTEX) were only detected in the samples collected from B-1. The results of the analyses are presented in Table 1. After presenting the results of the soil investigation to PHS/EHD in the Helmick and Lerner Inc. report entitled Preliminary Site Assessment for Underground Storage Tank Stockton Unified School District- Franklin High School dated 10 October 1991, the County requested the collection of a groundwater sample to determine whether or not petroleum hydrocarbons have migrated through soil and into groundwater. SCOPE OF WORK Task 1—Install Monitoring Well A monitoring well (MW-1) is proposed at the location shown on Figure 2. It will be installed using the hollow stem auger flight drilling method. Drilling activities will be conducted according to San Joaquin County regulations and permitting requirements. Drilling and Sampling Drilling will be performed 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." Soil samples will be collected by placing the drill rig above the desired sampling depth 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 sampled depth will be sealed using Teflon sheeting secured by tight fitting plastic caps. Soil samples will be collected at 5-foot intervals starting at a depth of 5 feet below ground surface. A soil sample will be collected from just above the approximate groundwater depth.