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RM it PROBLEM ASSESSPiENT REPORT Hoare Petro[eun, Inc, 5941 F Street, Banta, U AGA Project No. 10-90.481 Page 4 representative portion of each soil sample collected within the unsaturated zone was placed in an air-tight plastic bag. Headspace -- gas measurements were made on these samples using a detector tube sensitive to the presence of TPH. TPH concentrations for each sample are recorded on soil boring logs. All drilling and sampling equipment was cleaned prior to drilling each soil boring using a high-pressure, steam-cleaning apparatus. The split-spoon sampler was cleaned with phosphate-free soap and rinsed with water following the collection of each soil sample. Drill cuttings were placed on plastic and stockpiled on-site and allowed to aerate under the guidelines of Rule 409.4 of the Rules _ and Regulations of the San Joaquin Air Pollution Control District. 3.21Konitori!_nq Well Installation and Development Monitoring wells Mw-4, MW-5y' and' MW-6 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. In order to - seat the filter pack prior to the emplacement of a bentonite seal, each well was surged using a surge block attached to the sand line of the drilling rig. Surging was continued until the elevation of the filter pack stabilized. Following well surging, a 2-foot-thick bentonite seal was placed above the filter pack using bentonite pellets. The annular space above the bentonite was filled with a cement-bentonite grout which extended to ground surface. Each monitoring well was completed . inside a steel cristy box. Monitoring well construction details are presented on the soil boring logs shown in Appendix A. in order to remove natural aquifer fines and drill cuttings from the vicinity of the well screen; following the construction of all wells, each monitoring well was developed either by hand bailing or by use of a bailer attached to the sand line of the drill rig. Development water was stored on-site in 55-gallon drums. Table 2 presents well development information.