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i Q CLEARWATER G R O U •P, I N C. These activities will be conducted in accordance with directives set forth by the San Joaquin County PHS (Ms. Margaret Lagorio) in letters dated January 12 and June 14, 1995 and January 25, 1996. The monitoring wells will be installed to investigate the extent of soil contamination and to initiate a groundwater investigation. Depth to groundwater will be used to estimate the groundwater gradient at the site. According to Ms. Lagorio, groundwater levels in 1986 were approximately 30 to 35 feet bgs. Because TPHg and BTBX were detected in the soil sample collected at 32 feet bgs in the excavation, groundwater beneath the former UST location may have been impacted. 2.2 Installation of Monitoring Wells Three 8-inch-diameter soil borings will be drilled and converted to 2-irich- diameter monitoring wells in the locations shown on Figure 2. Ms. Margaret Lagorio concurred with the proposed locations during an August 1995 site visit by Clearwater to create a site map.. Drilling Specifications Prior to installing the monitoring wells, permits must be obtained from the San Joaquin County PHS by a California C-57 licensed driller. Drilling will be conducted using a truck-mounted hollow-stem auger rig equipped with 8- inch-diameter augers. Down-hole drilling and sampling equipment will be steam-cleaned prior to arriving onsite and between drilling at each boring location. All drilling and sampling methods will be consistent with ASTM Method D-1452-80 and local, state, and federal regulations. Soil Sampling z—� The first boring drilled will be continuously cored for the purpose of obtaining a detailed description of the stratigraphy. In the other two borings, discrete soil samples will be collected at five-foot intervals or at stratigraphic changes. Discrete soil samples will be obtained by-advancing a California-modified split spoon sampler lined with three 6-inch-long brass sampling tubes. The sampler will be driven 18 inches past the lead auger by a dropping a 140- pound hammer from a height of approximately 30 inches. The number of blows necessary to drive the sampler and the amount of soil recovered will be D108 WP(revised)1/96 4