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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 Accuracy of laboratory analyses will be assessed by laboratory control samples, surrogate standards, matrix spikes, and initial and continuing calibrations of instruments. Laboratory accuracy is expressed as the percent recovery(%R). Accuracy limits are statistically generated by the laboratory, required by specified USEPA methods. If the percent recovery%R is determined to be outside of acceptance criteria, associated data will be qualified. The calculation of percent recovery%R is provided below: % R= 100 (Xs—X)/T, where Xs is the measured value of the spiked sample,X is the measured value of the unspiked sample, and T is the true value of the spike solution added. Field accuracy will be assessed through the analysis of field equipment blanks,where appropriate.Analysis of blanks will monitor errors associated with the sampling process including equipment decontamination procedures,field contamination,sample preservation, and sample handling. The DQO for field equipment blanks is that all values are less than the reporting limit for each target constituent. If contamination is reported in the field equipment blanks, data will be qualified. 4.2.3 Representativeness Representativeness is the degree to which data accurately and precisely represent a characteristic, an environmental condition, or a population. It relates both to the area of interest and to the method of taking the individual sample. Representativeness of data collection is addressed by careful preparation of sampling and analysis programs, including use of procedures to avoid false negatives and false positives (USEPA 2004).This Work Plan addresses representativeness by specifying sufficient and proper numbers and locations of samples; incorporating appropriate sampling methodologies; specifying and performing proper sample collection and preservation techniques; performing required decontamination procedures; selecting appropriate laboratory methods to prepare and analyze soil, soil gas, and groundwater samples; and establishing proper field and laboratory QA/QC procedures for the parameters of interest. 4.2.4 Completeness Completeness is the amount of valid data obtained compared to the amount expected under ideal conditions. The number of valid results divided by the number of possible results,expressed as a percentage, determines the completeness of the data set.The DQO for completeness is to obtain valid results for at least 90 percent of the planned analytical results.The formula for calculation of percent completeness is presented below: % Completeness= 100 x(number of valid results)/(number of expected results) 4.2.5 Comparability Comparability is an expression of confidence with one data set compared to another. This QA/QC plan addresses comparability by specifying laboratory methods that are consistent with the current standards of practice as approved by the USEPA and the DTSC,which will allow the data to be evaluated for trends or changes(in space or time)at the Site(USEPA 2004). In addition, comparability is also addressed by specifying that associated standard units of measurement will be used for data reports. 4.2.6 Method Detection Limits Method detection limits(MDLs)should be below the screening levels, or else there is no way to know whether non- detect results are above or below the action level. For this DI,the ultimate action levels will be health-based criteria calculated in accordance with the methodology set forth in Programmatic QAPP using available cancer potency slope factors and non-cancer reference doses established by the California Office of Environmental Health Hazard Assessment(OEHHA), USEPA, or other organizations. However, it is impracticable to calculate all of these action levels in advance for all of the analytes.Therefore,for the purposes of this QAPP plan,the planned MDLs for 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. Prepared for: Department of Toxic Substances Control AECOM 25