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that have been qualified as estimated (J) and a quantification of these uncertainties (e.g., bias high by a maximum of 80%) wherever possible. A1.3.3 Data Qualifiers During validation and assessment procedures, data results will be flagged with U.S. EPA CLP data qualifiers based upon QC criteria and best professional judgment. A1.4 Quality Control Review During data validation and assessment, results for QC sample analyses, including blanks, spikes, and duplicates will be evaluated as described below, using the Precision, Accuracy, Reproducibility, Comparability, and Completeness (PARCC; U.S. EPA 1987) QC criteria defined below, to determine the validity and usability of the data. A1.4.1 Accuracy The determination of accuracy of a measurement requires knowledge of the true or accepted value for the signal being measured. It is a statistical measurement of correctness, and includes components of random error (variability due to imprecision) and systematic error (bias). It therefore reflects the total error associated with a measurement. Errors as they pertain to accuracy may result from several sources including the sampling processes, field contamination, improper preservation, handling of samples, sample matrix biases, and analytical procedures. A measurement is accurate when the reported value does not differ from the true value or the known concentration of the spike or standard. Accuracy will be calculated in terms of percent recovery of a known amount of a spiked compound according to the following formula: %R = [(Cs-Cn)/Csa] x 100 Where: %R: percent recovery Cs: measured concentration in spiked aliquot Cn: measured concentration in unspiked aliquot Csa: actual concentration of spike added Accuracy will be evaluated based upon percent recoveries of the internal standards, MSs, MSDs, system monitoring compounds, and surrogates for VOC analyses. The following are specific guidelines for the usability assessment of QC results that give an indication of the accuracy of the sample data. Reference or Check Standard Evaluation. Standard reference materials analyzed by the laboratory following U.S. EPA method protocols (e.g., laboratory control sample [LCS], continuing calibration [CC]) are compared with true values and acceptable ranges as indicators of accuracy. Values outside the acceptable ranges require corrective action Sampling Plan for Small Waste Disposal Areas(final).doc A-4