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Cleanup in Vulnerable Communities'Initiative Final Project Reference:Bobson Cleaners Discovery and Enforcement Discovery Project Number:60688620-5.1 Investigation Work Plan groundwater samples have been compared with the Preliminary Remediation Goals (PRGs)published by USEPA Region IX(including the Cal/EPA-modified PRGs)to verify that all MDLs are below their respective PRGs, with the exception of arsenic(typical background concentrations of arsenic in California soil are above the MDL,so the arsenic MDL is considered acceptable).The planned MDLs for soil gas samples comply with the Programmatic QAPP. 4.3 Data Collection and Evaluation The AECOM QA Manager or her/his designee will review the laboratory reports and prepare a data-review verification sheet that will be appended to the DI Report. The laboratory reports will be reviewed for the following: • Data Completeness, • Chain of Custody, • Holding Times, • Sample Preservation, • Blanks, • Laboratory Control Samples, • Matrix Spike/Matrix Spike Duplicates, • Surrogates/Internal Standards(as applicable), and • Field Quality Control Samples. Data that do not meet the DQOs set forth in Section 4.2 will be qualified and flagged. Data qualification flags will indicate whether results are considered anomalous, estimated, or rejected. Only rejected data are considered unusable for decision-making purposes; however, other qualified data may require further verification, such as reviewing the laboratory's raw data. Detection limits associated with the analytical data will be reviewed before eliminating chemicals from the human health screening evaluation because they were not detected. In some cases, the detection limit for a chemical may be greater than the corresponding standards,criteria, or concentrations derived from toxicity reference values; therefore, the chemical may be present at levels greater than these corresponding reference concentrations,which may result in undetected risk. In other cases, a particular detection limit may be significantly higher than positively detected values in other samples in a data set.After considering these cases and any other reasonable reasons why contaminants may not have been detected,chemicals that have not been detected in any medium will be eliminated if appropriate. If information exists to indicate that the chemicals are present,they will not be eliminated.The DI report will identify the possibility of undetected or non-sufficiently characterized contaminants and recommend additional sampling as part of further investigation, as appropriate. A laboratory may identify VOC and SVOC tentatively identified compounds (TICS)during sample analysis. Both the identity and reported concentration of a TIC are not definitive. Depending on the relative number of TICS compared to non-TICs, options exist to address TICS during the screening evaluation (Chapter 5, USEPA, 1989). If a significant number of TICS are identified during the investigation, the use of these data in the human health screening evaluation will be discussed with the DTSC. For analytical results,various qualifiers pertaining to the quality of the data may be assigned to certain analytical results by either the laboratory conducting the analysis or by persons conducting data review as discussed above. For example,some results may be marked as estimated if the concentration is below the verifiable or contract- required detection limit but may be detected at a lower value by the instrument.All qualified results will be reviewed prior to use of the chemical data set for the human health screening evaluation.Any data discrepancies will be reviewed and explained in the DI Report. If enough data are rejected as unusable for decision-making purposes, such that the DQO for completeness is not achieved,then corrective actions such as reanalysis or resampling will be performed,with DTSC concurrence[USEPA, 2004]. Prepared for: Department of Toxic Substances Control AECOM 26