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' 2 BACKGROUND <br /> The following background information presents EMCON Associates <br /> understanding of the site history based upon information supplied to <br />' EMCON Associates by Teichert. <br /> 2.1 Removal of Tanks C-14 South, C-14 North, and WO-4 <br /> Three underground petroleum storage tanks designated C-14 South, C-14 <br /> North, and WO-4 were removed from the Teichert equipment site in <br /> October 1986. These tanks were not replaced. The former tank locations, <br /> capacities, and contents are presented on Drawing 1. The work plan <br />' attached as Appendix A presents details of site characterizations conducted <br /> in regard to these tanks. However,the following summarizes those activities <br /> that led up to the recently completed characterization. <br />' Following the removal of the tanks, soil borings were drilled and <br /> ground-water monitoring wells were installed to characterize the lateral and <br /> vertical extent of soil and ground-water impact. Borings B-1 through B-16 <br /> were drilled and sampled in December 1986 and January 1987. Borings <br /> B-10, B-12, and B-13 were converted to monitoring wells MW-1 through <br /> MW-3, respectively. <br />' In September 1987, overexcavation of the impacted soil near the former <br /> tank complex was completed. Well MW-1 was damaged and well MW-2 <br />' was destroyed during removal of this soil. Based on safety and sidewall <br /> stability considerations, the overexcavation was terminated at a depth of <br /> approximately 38 feet. As a result, residual concentrations of petroleum <br />' hydrocarbons remained in soil at the .north-central side of the excavation <br /> where the pump island was located, at the bottom (38 feet) center of the <br />' tank excavation, and near the northwest corner of the excavation. <br /> Also, in September 1987, wells MW-4 and MW-5 were installed to assess <br /> impact to ground water, if any, resulting from the release. Section 2.3 <br />' presents additional information on completed ground-water characterization <br /> activities. <br />' 2.2 Removal of Tank C-12 <br /> Tank C-12, a 10,000-gallon-capacity regular gasoline storage tank, was <br /> removed in August 1988 (see Drawing 1). Two soil samples were collected <br /> from the tank excavation for chemical analysis. One of the samples <br />' pjOV9010900020.1 ag 2 - 1 Rev. 0 December 15, 1992 <br />