ARCHIVED REPORTS XR0009904 - Laserfiche WebLink

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Corrective Action Plan Page 35 16 (I a one half the MDL), with the previously estimated standard deviation of 0 64 mg/Kg yields c= (10 - 05)/064 = 078 Then interpolating in Table A6 on Page A-6 of Reference 21, for a confidence level of 99% (1 e a = 0 01) at a power of 0 90 (1 e a = 0 10) that the complete volume of treated soil contains less than detectable concentrations of contaminants, yields an estimate of 21 8 for the number of samples required Rounding the above estimate up to the nearest whole number of samples yields a projected total of 22 samples required from the spread and treated soil to demonstrate with 99% confidence that less than detectable concentrations of components of gasoline are present anywhere within its total volume Selection of Sampling Locations To implement the statistical sampling methodology, samples will be recovered from random locations within the area of the spread aerated soil To select random sampling locations the spread of aerated soil will be sub-divided into a large number of uniformly sized, rectangular sub-areas which will be delineated by surveyor's flags stuck into the surface of the soil Each sub-area will be assigned an identifying number The total number of sub-areas set out will be sigmficantly greater than the estimated number of soil samples required to perform a statistically meaningful analysis of the mean and standard deviation of the contaminant content of the treated soil at the desired level of confidence Based on the prehnunary estimate of 22 samples derived above, for planning purposes, a nummum of 60 sub-areas is recommended However, the actual number of sub-areas into which the spread soil is divided may be adjusted to comply with field conditions or any revised estimate or calculation of the number of sampling points required that is developed as the work progresses The specific sub-areas to be sampled during any round of sampling and analysis of the treated soil will be determined randomly using a random number generator to select from the range of identifygng numbers assigned to the sub-areas Witlun the selected sub-areas, discrete sampling points will be arbitrarily selected by the field technician with no consideration for the appearance, olfactory properties or any other characteristic of the soil therein The precise number of samples required to make the statistical determination at the specified degree of confidence will depend upon the data obtained from analysis of the samples that are obtained in the field To check that the estimated number of samples is sufficient, 22 samples will be taken during the first round of sampling from the spread of soil The results obtained from that round of sampling will be used in a manner similar to that employed above but using actual values of mean contaminant concentration and their standard deviation to check that 22 samples is sufficient to comply with the stated statistical requirements If it is not, a new estimate of the number of samples required will r be made and additional samples gathered (from randomly selected sub-areas of the soil