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Whetstone <br />Associates <br />Technical Memorandum <br />kriging algorithm with default options (linear interpolation) and then blanked with the estimated <br />horizontal extent boundaries described above. <br />2.7 Calculating Soil Volumes <br />The grid surfaces were imported to AutoCAD Map3D and the volumes between surfaces were <br />calculated. A base estimate of soil volume above the 7 pCir'g radium -226 threshold value was <br />calculated as the volune between TopRa7pCi/g and BotRa7pCi'g surfaces. A contingency soil <br />volume was calculated as the base soil volume estimate plus the volume between BotRa7pCig and <br />NatAlluvium surfaces in contingency zones. <br />3. ASSUMPTIONS <br />Assumptions made in the calculation of the base soil volume and contingency soil vohune estimates <br />include: <br />• The estimated x.y.z coordinates of soil sample locations and soil observation locations are <br />accurate to within 5 feet laterally and 1 foot vertically: this resolution is assumed to be <br />sufficiently accurate to derive gross soil volume estimates: <br />• Estimates of bottom elevation of threshold value material based on field observations in soil <br />sample locations where elevated analytical results extend to the bottom of excavation are <br />conservatively low: <br />• The bottom elevation of threshold value material in soil observation locations (TR -OBS <br />series) based on a qualitative comparison of gamma scan values to soil sample locations with <br />known radium -226 analytical results is conservatively low <br />• The estimated elevation of the natural alluvium surface is conservatively low based on using <br />a 2 -foot bank height above the calculated historical 1937 Ralston Creek channel depth to <br />represent the historical floodplain elevation: <br />• The estimated horizontal extent of above - threshold material is reasonable considering the <br />analytical radium -226 results. analysis of gamma scan results. and field observations: <br />• For the contingency volume estimate. the above-threshold material is assumed to extend to <br />the depth of natural alluviums in contingency zones where analytical radian -226 results. <br />analysis of ganuna scan results. and field observations indicate that elevated radian -226 <br />values extend to the bottom of the soil sample/observation excavation. <br />4. RESULTS <br />The total base material volume estimate is 32.560 cubic yards (cyds) with 27.680 cyds occuring in <br />the north zone and 4.880 cyds occurring in the south zone. The total contingency material volume <br />estimate is 53.900 cyds with 48.460 cyds occurring in the north zone and 5.440 cyds occurring in the <br />south zone. The results are presented in Table 2. Figure 2 shows the distribution of the total base <br />material volume. Figure 3 and Figure 4 show the distribution of base material volumes ill the north <br />and south zones. respectively. Figure 5 shows the distribution of the total contingency material <br />volume. Figure 6 and Figure 7 show the distribution of contingency material volumes in the north <br />and south zones. respectively. <br />4109C.110427 4 <br />37 <br />