WORK PLANS - Laserfiche WebLink

Home Browse Search

Precision is usually stated in terms of standard deviation, but other estimates, such as the coefficient of variation (relative standard deviation), range (maximum value minus minimum values), and relative range are common, and may be used pending review of the data. Precision will be determined through the collection of field duplicates at a frequency of one field duplicate for every 20 samples, per matrix, and the analysis of MS/MSD and LCS/LCSD samples for the work performed at the Site. The overall precision of measurement data is a mixture of sampling and analytical factors. Sampling precision will be measured through the laboratory analysis of field duplicate samples. Laboratory precision will be measured through the analysis of MS/MSD and LCS/LCSD samples. Precision will be determined from replicate samples and will be expressed as the RPD between replicate/duplicate sample results, computed as follows: IX1 — X21 RPD = (X1 + X2) / 2 x 100 where XI and X2 are reported concentrations for each replicate sample and subtracted differences represent absolute values. For field duplicates, the precision goal for this project is 30% for groundwater and 50% for air samples. For MSD and LCSD, the RPD goals will be specified by the selected laboratories. 3.3.3 Accuracy and Bias Accuracy refers to the degree of difference between measured or calculated values and the true value. The closer the numerical value of the measurement comes to the true value, or actual concentration, the more accurate the measurement. The converse of accuracy is bias, in which a systematic mechanism tends to consistently introduce errors in one direction or the other. Laboratory accuracy will be measured through the analysis of MS/MSD and LCS/LCSD samples. Accuracy, when potentially affected by high or low recoveries, is presented as percent recoveries (%R), defined as: Measured Concentration % R = Expected Concentration x 100 Appendix C 9