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_ tom. a. rt �� ,f 1 -• PROBLEM ASSESSMENT REPORT Moore Petroleum, inc. 1399 F. Yosemite Avenue, Manteca, C, NGA Project No. 10-90-480 Page S In order to seat the filter pack prior to the emplacement of a bentonite seal, the well was surged using a surge block attached to the sand line of the drilling rig. During surging, the surge block was dislodged from the sand line and fell to the bottom of the well, puncturing the bottom, threaded, well cap and damaging the uppermost five-foot section of blank casing, near the ground surface. Following retrieval of the surge block from the base of the well, and after consultation and approval iron the on-site representative of the San Joaquin Public Health Service, a slip-on well cap was pushed to within 0.5 feet of the base of the well to serve as a bottom well cap. The damaged, uppermost five-foot section of well casing was unthreaded and replaced. The slip-on well cap has approximately the same outside-diameter as the inside--diameter of the well casing, and should serve as an adequate bottom cap. 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 log shown in Appendix A. in order to remove natural aquifer fines and drill cuttings from the vicinity of the well screen, MW-1A was developed further by hand bailing p;:ior to sampling. Development water has been stored f.. on-site n 55-gallon drums. 3.3 installation of Below-Ground Components of a soil Venting system ' On September 26, 1989, USTs used to store gasoline at the site, R were removed. On that date, a Delta geologist, with the concurrence of a representative of the San Joaquin Public Health Services, collected samples of native soils beneath each end of the USTs and at 20 foot intervals beneath fuel product lines. Visual observation of native soils beneath the removed USTs, and tank backfill material that had been excavated previously indicated that the results of the soil analyses would likely indicate appreciable levels of petroleum hydrocarbons remaining in site soils. In order to provide a future soil remediation alternative (if needed) , the below ground components of a soil venting system were installed within the former tank basin on October 20, 1989. Below- ground components of the soil venting system within the tank basin --cansis -o -two -30-foot--long sections of 4-inc;t-diameter PVC well screen (0.020 inch slot size) wrapped in filter fabric and placed ` horizontally at a depth of about 15 feet. These sections of PVC