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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 tested. If no valid detectable concentrations of target compounds are reported for the given samples,then a decision will be made that the Site is adequately characterized with respect to the compounds tested and no further sampling will be required as part of this DI. If target constituents are detected in the samples tested, depending on the data it may be necessary to perform additional sampling until the Site is completely characterized. Once the site is adequately characterized,the data will be compiled for use in calculating screening risks to human health and the environment. Once the site is adequately characterized,the data will be compiled for use in calculating screening risks to human health. The results of the risk evaluation will be used to request a determination from DTSC. • Specify Limits on Decision Error: The results of the analytical testing will be subject to data evaluation following the procedures for data review specified in Section 4.3 below. Data will be determined to be valid if the specified limits on precision, accuracy, representativeness, comparability, completeness, and sensitivity are achieved.The results of any detected target constituents will be considered in evaluating the need for additional sampling of soil gas, soil, or groundwater, and assessing the necessity for reducing any risks posed by the potential contamination.AECOM will review the signed data package from the laboratory and will be responsible for the quality of the data. • Develop the Plan for Obtaining Data:The field-sampling program has been designed to provide the type and quantity of data needed to satisfy each of the aforementioned objectives. Due to the absence of previous site investigations(i.e. site characterization and sampling)to the Site there is a possibility of constituent hot spots being inaccessible for sampling at this time.Areas of high concentration onsite may not be identified without additional access and investigation of the Site. The DI Work Plan provides the specifications for the data collection activities, including the numbers of samples, respective locations, and sampling techniques.The quality of the data will be assessed through the procedures further described herein. 4.2 Specific Data Quality Objectives Specific DQOs for the data quality indicators (DQIs)of precision, accuracy, representativeness, completeness, comparability, and method detection limits have been selected. These DQIs and their corresponding DQOs are discussed in turn below. 4.2.1 Precision Precision measures the reproducibility of repetitive measurements. It is strictly defined as the degree of mutual agreement among independent measurements as the result of repeated application of the sample process under similar conditions. Analytical precision is a measurement of the variability associated with duplicate or replicate analyses of the same sample in the laboratory and is determined by analysis of laboratory quality control samples, such as duplicate control samples, matrix spike duplicates(MSD), or sample duplicates. If the recoveries of analytes in the specified control samples are comparable within established control limits, then precision is within limits. Total precision is a measurement of the variability associated with the entire sampling and analytical process. It is determined by analysis of duplicate or replicate field samples, and measures variability introduced by both the laboratory and field operations. Field duplicate samples are analyzed to assess field and analytical precision. Duplicate results are assessed using the relative percent difference(RPD)between duplicate measurements. If the RPD for laboratory quality control samples exceeds 30 percent, data will be qualified. If the RPD between primary and duplicate field samples exceeds 50 percent, data will be qualified. The RPD will be calculated as follows: %RPD =200(X2—X1)/(X2+Xt), where Xi is the larger of the two observed values and X2 is the smaller of the two observed values. 4.2.2 Accuracy Accuracy is a statistical measurement of correctness and includes components of random error(variability due to imprecision)and systematic error. It reflects the total error associated with a measurement.A measurement is accurate when the value reported does not differ from the true value or known concentration of the spike or standard. Prepared for: Department of Toxic Substances Control AECOM 24