ARCHIVED REPORTS XR0009919 - Laserfiche WebLink

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r.. �"A■ruAM Working to Restore Nature +� SUPPLEMENTAL INVESTIGATION Field Work On November 4 and 5, 1993, a RESNA field geologist observed Woodward Drilling of Rio $4W Vista, California, drill two offsite soil borings (B-23 and B-24) to 73 and 76 feet below surface grade (bsg). The borings were converted to groundwater monitoring wells MW-8 and MW-9. Groundwater was encountered at approximately between 61.5 feet and 67 feet bsg. During construction of MW-9, the bentonite seal broke and neat cement was introduced into the well casing. Because well MW-9 was not constructed properly, the well was destroyed on November 13, 1993 and another soil boring was drilled (B-25) near well MW-9 and converted to a monitoring well (MW-10). The boring was drilled to 73 feet bsg, and groundwater was encountered at 61.5 feet bsg. Drilling activities were performed by Woodward Drilling under the observation of our field geologist. Our field methods are described in an attachment to this report. Well permit and well destruction permit are presented in Appendix A. The geologist collected soil samples from the borings at approximately 5-foot intervals for possible laboratory analyses and to characterize the geology beneath the site. Samples were logged using visual and manual methods and classified according to the Unified Soil Classification System (Plate 3). Samples were not collected for laboratory analyses from boring B-25. Sediments encountered are shown on the Logs of Borings (Plates 4 through 12). Drill cuttings were stockpiled onsite and covered with plastic sheeting. Well MW-8 was developed by our technician on November 8, 1993, and well MW-10 was developed on November 23, 1993. Water samples collected after well development did not �• contain floating product or product sheen. On November 24, 1993, at the request of ARCO, purge water was removed from the site by IWM of Pleasanton, California. Tom O. Morrow Inc. of West Sacramento California, a licensed land surveyor (California Land Surveyors 3275) surveyed the wells on November 19, 1993. On November 5, 1993, our geologist collected soil samples (one composite of four samples) from the stockpiled soil for analyses to evaluate disposal options. At ARCO's request, on November 26, 1993, drill cuttings were transported by Dillard Trucking of Byron, California, to the BFT land fill in Livermore, California, for disposal. Laboratory Methods and Results Select soil samples from borings B-23 and B-24 and the sample from the drill cuttings stockpile were analyzed for total purgeable hydrocarbons (equivalent to total petroleum hydrocarbons as gasoline [TPHg]) with benzene, toluene, ethylbenzene, and total xylene v 1213ccar/30(}03-9 2 4r