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2 2 Laboratory Procedures <br />' Groundwater samples were analyzed by Quanterra, Inc , located in West Sacramento, <br /> California The samples were analyzed for TPH-D using EPA Method 8015M with <br /> Northwest Cleanup Procedure, which was requested in order to remove non-petroleum <br /> hydrocarbons identified in the third quarter 1999 monitoring event As discussed in the <br /> Third Quarter 1999 Quarterly Monitoring Report, the Northwest Cleanup Method allows <br /> for the removal of unknown hydrocarbon which does not correspond to the weathered <br /> diesel or other recognizable petroleum products The non-petroleum hydrocarbons are <br /> 1 assumed to be derived from organic material naturally present in the groundwater The use <br /> of the Northwest Cleanup Method allows for a more accurate assessment of petroleum <br /> hydrocarbon concentrations at the Site <br /> 2.3 Data Validation <br /> The laboratory report provided by Quanterra was reviewed by Dames & Moore's data <br /> validation group in order to assess if the reported data results are usable for their intended <br /> purpose Results of the Dames & Moore's validation of the data are included in Appendix <br /> B All data were determined to be acceptable for use, with the following qualification <br /> • TPH-D was detected in the laboratory method blank, indicating that initial results were <br /> erroneous Therefore, all samples were re-extracted and re-analyzed Because the <br /> samples were re-extracted out of holding time, the reported results detection limits are <br /> 1 considered estimated, and the true results may be higher However, because TPH-D is <br /> not volatile, the reported results are assumed to be accurate <br /> 1 DAMES&MOORE 3 11DM_5ACIWOL_21JOB1AFPIREPORTIQ4-1999 DOC <br />