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4.0 DRILLING AND SOIL TESTING Drilling and sampling were performed to determine the presence of any contamination to the surrounding soil should the tank have leaked. Four borings were drilled at each corner around the tank periphery. The drilling was performed after visual inspection of the tank indicated no apparent leakage from or damage to the tank. The age of the tank is estimated to be ? I9"lam about six years old. Drilling permits were obtained from the San Joaquin County Health District. Copies are provided in Appendix V. As required by the permit, a copy of this report is provided to the client for forwarding to ` the local Health Authority. The borings were drilled on a 15° angle from vertical to intercept the backfill of the tank and obtain samples from the area directly beneath the ` tank. The sampling scheme is shown in Figure 4. The borings were backfilled with a concrete grout and finished to conform with the surface grade. Boring logs are presented in Appendix IV. ` The samples were sent to the IT Stoner Laboratory, Santa Clara, California for analysis. The results indicated high levels of contamination which were inconsistent with visual observation. The client was informed of this fact and that a laboratory mix-up was suspected. A decision was therefore made to ` redrill four more borings in order to obtain new samples. All samples were taken by using a 2" diameter standard penetrating sampler with brass liners, driven 18-inches. The samples were taken at depths of ` approximately 10, 15 and 20 feet as shown on the boring logs. The samples were packed in ice and shipped to the IT-Stoner laboratory, Santa Clara, California, under standard chain-of-custody procedures. The samples were analyzed for total petroleum hydrocarbons by solvent extraction and gas chromatography. The samples were analyzed for lead by McIntosh Laboratories and none was detected. The certified analytical results appear in Appendix VI and Table I. 4 ENG:0551/02246