j= Reduce the average concentration of the "defined Iwoinm 2. region’ te some lower number which shall be determined by cost-benefit (4} Condition D: i comsicerations, but will usually not be belowlocal background. An assay area whose average Pu concentration is exy 5 ca thickness of soil below the suriace layer wiici measured(at& the to exceed 400 pCi/g will be wt 67 vercent ccorfidence level) excavated Bete and measured iteratively until its averare Pu concentration » in the new 5 cm lever is found by measurement (at the 50 percent conficence level) to be reduced in the defined region to some lower number Which shall be cetertined by cost - benefit considerations, but wil] ust2ily not be below Jocal background. Footnotes: 1 L Assay Area. =: . The field of view of the in situ detector in its normal operating position; typically a 28 meter diameter circle of 53 - 5 cm in depth. Scattered measurement can be used to estimate average presven known as ‘'hrigzing. 5 at — Stetisticaliy, t¥o-thirds of the time the actual concentration will he below the guide rougher. TS fllDe One-third of the time the actual concentration may exceed the mother by some percentage.which must be empirically deter- mined fp to 20-59 percent, as an estimate). This is similar to using a lower. If a 90 percent confidence level were used with the numerical guide, the equivalent guide at a 50 percent confidence level would C-2-E-7 fro $9 percent conficence level with a numerical guide 20-30 percent (estimated) [Nh oo belew ‘2 rCi/g.