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Preliminary Endangerment Assessment Page 8 Former Haley's Flying Service GPE Project 474.2 4.0 DATA QUALITY EVALUATION Data evaluation is the process of analyzing site characteristics and data to identify Chemicals of Potential Concern (COPCs) to be evaluated in the human health risk assessment. This section identifies data of sufficient quality for use in the risk assessment, summarizes the chemical characterizations of soil and groundwater, and provides a summary of COPCs. 4.1 Data Quality The following criteria were considered to evaluate the quality of the laboratory data points: • Laboratory QC data sheets are reviewed to verify that the analytical laboratory analytical procedures were within acceptable limits as regards repeatability and contaminant recoverability. • Blank contamination is evaluated based on the results of field and laboratory blank data. Common laboratory contaminants are eliminated if detected concentrations are within 10 times the associated blank concentrations (Cal-EPA, 1994). All other chemicals are eliminated if detected concentrations are within 5 times blank concentrations. • Sample Quantitation Limits (SQLs) must be sufficiently low such that chemicals can be selected at levels of potential concern. Data are reviewed to determine if SQLs are sufficiently low. 4.2 Groundwater Sample Data The temperature blank from the ice chest in which the samples were transported to the laboratory was measured upon reaching the lab with an infrared digital thermometer. (See CoW form for details). The temperature blank indicated the temperature in the ice chest was less than 4 degrees C. The travel blank provided by the laboratory did not contain detectable concentrations of any chemical that was tested for. Laboratory data sheets describing QC analytical tests indicate that laboratory procedures were of an acceptable quality (see Appendix A). All matrix spike and matrix spike duplicate analytical results were within the acceptable range of recovery for the analytical methods, and all laboratory blanks were non- detect for the chemicals tested for. During soil boring installation, an equipment blank was created to verify the reusable sample equipment was being cleaned adequately between uses. The equipment blank was obtained by pouring uncontaminated water over the lead inner drill string tube and the bailer after they had been steam cleaned and before installing the final boring. The equipment blank did not contain detectable organo-chlorine pesticides. 4.3 Chemical Characterization This sub-section briefly summarizes the nature and extent of chemicals detected in the groundwater for purposes of providing context to the risk assessment. Based on the information from the laboratory analytical results (Summary Table 1), the following table was prepared to summarize the identity of detected chemicals, total number of samples 2937 Veneman Avenue,Suite B240 Geo-Phase Environmental Inc. Phone: (209)569-0293 Modesto,Ca 95356 Fax: (209)569-0295