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SECTIQNTWO Summary of Field Sampling and Laboratory Analyses 2.4 DATA VALIDATION A quality assurance evaluation of the analytical data provided by Chromalab Analytical Laboratory from sod and groundwater samples collected at 1010 46th Street on August 2-3, 1999 was undertaken to confirm the accuracy and precision of the laboratory results for use in this report A total of 28 soil samples and one groundwater sample were collected Upon receipt of the final laboratory reports, the following steps were taken in accordance with the EPA guidance for data validation Sample custody documents were cross-checked with laboratory reports for sampling dates and required analyses Holding times were calculated using analysis date, preparation date, and/or test date in relation to sampling date The results were reviewed for QA/QC elements of precision, accuracy, reporting limits, and contamination The following QA/QC parameters were reviewed during data evaluation o Chain of Custody - Verify that requested analyses were performed and sampling dates are accurately noted in lab reports o Holding Times - Check for holding times in excess of EPA guidelines o Method Blanks - Review blank analyses for evidence of potential contamination o Matrix Spikes - Review spike and spike duplicate recoveries and relative percent differences (RPDs) as a check for analytical precision and accuracy o Laboratory Control Samples - Review control and control duplicate recoveries and relative percent differences (RPD-;) as a check for analytical accuracy and precision o Surrogates - Review surrogate recoveries as a check for sample specific accuracy 2 41 Chain of Custody All analyses were performed as requested and samples were adequately accounted for throughout ithe transfer from field to lab 2.4.2 Holding Times Holding time, (the time between sampling and sample preparation/analysis) was not exceeded in any case 2 4.3 Method Blanks Blank samples are analyzed in the same manner as field samples Laboratory method blanks consist of reagents specific to each individual analytical method that were prepared and analyzed by the laboratory to assess potential sample contamination within the laboratory Method blanks did not reveal any laboratory contamination 2.4 4 Matrix Spike . Matrix spike and matrix spike duplicate samples are prepared at the laboratory by dividing a control sample into two aliquots, then spiking each with identical concentrations of specific URS Greiner Woodward Clyde 1109967049\UST REPORT CHEROKEE DOC122 SEP 991\OAK 2-3