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1 <br /> soil contamination at the site; (2) evidence that surface or groundwater <br /> have been, or may be, affected by the release of fuel; (3) evidence that <br /> free product occurs at the site; (4) evidence that polluted soils are, or may <br /> be, in contact with surface or groundwater; or (5) any other conditions <br /> which would cause the DEH to require a full soil and groundwater <br /> investigation. <br /> In addition, approximately 1600 cubic yards of contaminated soil is <br /> stockpiled on site and will need to be treated. <br /> B: Background <br /> Manteca Unified School District has been operating at the subject location <br /> since 1972. On May 26, 1993, Manteca Unified School District contracted <br /> with SEMCO, a licensed hazardous substances removal and remediation <br /> contractor, to remove their underground fuel tanks. On June 15, 1993, <br /> SEMCO removed one (1) 12,000 gallon gasoline tank (designated as Tank <br /> #2) and one (1) 12,000 gallon diesel fuel tank (designated as Tank #3). A <br /> 1,000 gallon tank (known as Tank #1) had been previously removed. Soil <br /> samples taken at the time of Tanks 2 and 3 removal showed the presence <br /> of contamination to a depth of 19 feet below surface. An Excavation Work <br /> Plan was submitted by SEMCO to the San Joaquin County Environmental <br /> Health Department on June 22, 1993, and amended by an Addendum <br /> Number One letter dated June 30, 1993. The Work Plan designated WHF <br /> Environmental Consultants, Inc., to oversee all activities and coordinate <br /> with San Joaquin County Public Health Services, Environmental Health <br /> Department. <br /> On July 7, 1993, SEMCO excavated the former underground tank facility at <br /> Manteca Unified School District. WHF screened soil samples with a <br /> portable PID and logged the lithology of the exposed walls (Appendix A), <br /> using the Unified Soil Classification System (USCS). Highly contaminated <br /> soils were encountered both above and below the water table of 16 feet in <br /> the original tank removal excavation. The amended Work Plan called for <br /> vertical excavation to approximately -23 feet. . <br /> Two trenches were excavated from the northwest corner of the pit and <br /> screened with the PID to delineate the lateral extent of contamination <br /> (Figure 3). These trenches were limited to 16 feet in depth because of <br /> sand caving and sloughing. The estimated excavation size at that time was <br /> beyond the school district's budget, and additional exploration trenching <br />