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_ _ p i k PR03LEMi ASSESSMENT REPORT Moore Petroleum, Inc. 14800 W. frontage Road, Manteca, CA NGA Project No. 10-90.479 Page 4 These recommendations were implemented by Delta in November and December, 1989. The results of the most recent investigative activities completed at the site by Delta have not been reported elsewhere. The results of the November and December, 1989, work by Delta as well as more recent activities at the site completed �. by NGA will be ]reported in the following sections. 3.0 RESULTS OF RECENT INVESTIGATION ACTIVITIES. 3.1 Drilling and Soil Sam lin ct A on November 29, 1989, a Delta geologist supervised the drilling of four soil borings at the site. Soil borings were advanced using 1 ` an Acker drilling rig utilizing 6.75-inch-diameter hollow stem augers. Soil borings were advanced to a depths ranging from 36 to 40 feet beneath griund surface. Samples of subsurface soils were obtained from each soil boring at fIvO footintervals using a California modified split-spoon sampler. All soil samples were examined in the field by a geologist and described for color, grain size, moisture content, mineral content, and odor. Soil samples were classified in accordance with the Unified .,oil Classification System. A representative portion of each i3oil sample collected within the unsaturated zone was placed ;n an air-tight glass jar. Headspace gas measurements of total organic vapors were made on these samples € using a photoionization detector (PID) . Information presented on soil #`. boring been used logs prepared by Delta (including PID readings) has prepare the soil boring logs presented in Appendix A. All drilling and sampling equipment was cleaned prior illing each soil boring using a high-pressure, steam-cleanin topdaratus. The split-spoon sampler was cleaned with phosphate-;tree soap and �,•a rinsed.with water following the collection of each soil sample. Drill cuttings were placed on plastic and stockpiled on-site. 3.2 Nonitorina Well Installation and Development Monitoring wells Mw--S, Mw-6, MW-7., and MW-8 were installed in the soil borings discussed in the previous section. Each monitoring well was constructed using flush-threaded, two-inch-diameter, Schedule 40 PVC blank casing and two-inch-diameter, Schedule 40 PVC well screen with 0.010 inch well slots. Following the placement of well casing and screen, a sand filter pack, extending from the bottom of the well screen to approximately two feet above the top of the well screen, was placed in the annular space between...the-.well_screen and borehole- --A- 2-foot-thick .�