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' Interim Emergency Remedial Action/Monitoring Well Installation Work Plan Page 4 Former Union Facility,-Cutter Lumber Project No 102 2 May 20, 1997 ' 2.1 Proposed Soil Excavation Using an excavator operated by a properly licensed contractor, excavate vadose zone soil ' to remove petroleum impacted soil from the beneath the vicinity of the UST tank pit Soil which is estimated to contain 3,000 ppm, or more of gasoline range hydrocarbons ' will be removed to the approximate depth of the surface of groundwater or about 30 to 35 feet below grade A preliminary estimate of the area to be excavated is outlined in Figure 3 Aerially, the outline of the excavation roughly corresponds to the 20' depth vadose ' zone contour identified in Figure 2 This area is selected because it encompasses all of the soil samples collected which were found to contain more than about 3,000 ppm of TPH-G The estimate of soil to be removed was made based upon approximating the 10' ' and 20' contours as ellipses with the 10' contour having major and minor axes of 24' and 10' and the 20' contour having mayor and minor axes of 30' and 16' (See Figure 3) The volume of the contaminated soil was then calculated as follows Equation for area of ellipse; (area=nab), where a & b, are the mayor and minor axes for the ellipse ' Equation for volume between two stacked ellipses: (volume=1/2h[(na1b1)h+(na2b2A, where al and b1 are the major and minor axes for first ellipse, in this case the one approximating the 10' contour and a2 and b2 are the major and minor axes for the second ellipse, in this case approximating the 20' contour h being the 1 height between ellipses The total volume of the contaminated soil as suggested with this model would then be ' volume=112(10)[(n24*10)+(n30*16)]+1/2(15)[(ri30*]6)+(rt30*16)], where the first expression represents the estimated contaminated soil volume from 10' to 20' feet below ' grade and the second represents the estimated contaminated soil volume from 20' to 35' feet below ground surface Summing both halves of the equation equates to about 1260 cubic yards of contaminated material To calculate the volume of overburden that will need to be removed, the volume of the excavation (volume=1/2(35)[(n30*16)+(n30*16)]) was calculated and the volume of ' contaminated soil (1260 cubic yards) was subtracted from this volume This equates to about 690 yards of overburden material ' This estimate above is a simplification which assumes that the excavation can be completed without sloping or shoring It is likely that some sloping of the excavation will be required and that a bench be made for the excavator to access deeper soils within the excavation 1 2937 Veneman Ave, #13240 Geo-Please Environmental Inc Phone(209) 569-0293 Modesto, CA 95356 Fax (209) 569-0295