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URS Mr. Robert McClellon October 22, 2004 Page 3 • On December 1, 1988,the CIWMB conducted an investigation to evaluate the presence of methane. The CIWMB summarized their findings in a letter written to the Associacion Campesina Lazaro Gardenas,dated December 12, 1988. In that letter the CIWMB stated, "There is gas at and above potentially explosive concentrations at some locations on the site. The high readings seemed to be randomly scattered with little or no gas in between." • During an annual inspection of the site on July 17, 2003, SJCEHD measured methane gas concentrations at nine temporary boreholes located along the perimeter of the site. Methane was found within each borehole ranging in concentration from 10 parts per million(ppm)to 30,000 ppm(3%by volume). • On April 7, 2004, URS installed four landfill gas (LFG)migration monitoring probes (VW-1 through VW4) at the site. On July 9, 2004,URS measured methane gas concentrations from each of the four probes. Methane was found only within probe VW4, at 18.9 percent. Probe locations are shown on Figure 1. • To further evaluate the extent of the methane plume at the site,URS installed four sets of dual completion(shallow [S] and deep [D])LFG migration probes(VW-5 through VW-8),on October 12, 2004. These four new dual completion probes and the single completion probes (VW-1 through VW-4)were measured for methane on October 18 and 19,2004. Methane was only found within probes VW-4 at 15.0%,VW-5S at 8.5%,VW-5D at 10.3%,VW-6S at 17.9% and VW-6D at 18.7%. NATURE AND EXTENT OF THE PROBLEM Anaerobic bacteria are known to generate methane and carbon dioxide gases in relative equal proportions,among small quantities of other byproducts, as they metabolize the organic portion of the disposed wastes. Methane gas is odorless,colorless,and poses a potential flammable and explosive concern when allowed to accumulate within the nearby buildings or structures. The eastern extent of the methane plume along the northern boundary of the site terminates between probe VW4 and probe VW-7. The western extent of the methane plume along the northern boundary of the site extends west of probe VW-5. No methane was measured within the other probes located along the western, southern, and eastern boundaries of the site(VW-1, VW-2, VW-3,VW-7S,VW-7D, VW-8S,and VW-8D). REGULATORY REQUIREMENTS In its letter to Tandy Corporation dated July 13, 2004,SJCEHD is applying the following codes sections from Title 27 California Code of Regulations (27 CCR)Section 20919.5(a)and(c)that states the following: K:\Wprocess\25532\WorldEnterprise\Remediadon Plan\Izttendoc