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Cleanup in Vulnerable Communities'Initiative Discovery Project Reference:Favorite Cleaners and Enforcement Discovery Investigation Work Plan Project Number:60688620 4. Quality Assurance Project Plan This section describes the QAPP,which provides an appropriate level of QA/QC regarding the reliability and usability of the data generated during this Discovery Investigation.An integral part of the QAPP is proper field sampling and documentation procedures, which have already been described in Section 3 above and,thus,will not be repeated herein.This section sets forth the policies, procedures, and activities for the identification and documentation of the quality of the data generated during the performance of this Discovery Investigation. During this Discovery Investigation, a variety of data will be collected. Each sample collected may be analyzed for a number of different chemicals, depending on the rationale for sample collection. However, not all chemicals detected will necessarily be attributable to an on-site release, and not all of the data will necessarily be of acceptable quality. Data collected will be evaluated to determine which of the chemicals identified are likely to be Subject Property- related and to assess whether the reported concentrations for these chemicals are of acceptable quality for use in the human health screening evaluation. 4.1 Data Quality Objective Process The project DQOs developed specifically for the planned sampling and analysis program have been determined based on USEPA's seven-step DQO process(USEPA 2000).The AECOM QA Manager will evaluate the project DQOs to determine whether the quantitative and qualitative needs of the sampling and analysis program have been met. The project definition associated with each step of the DQO process can be summarized as follows: • State the problem:The purpose of the sampling program is to determine whether the Subject Property is acceptable for an intended use scenario: The Subject Property was developed in 1940 and operated as a dry cleaner from at least 1970 to 2010, according to city directories,the EDR reports, and during an interview with an owner. Documented PCE was used from 1986 to 2010. The historical dry cleaner operations may have resulted in the release of hazardous substances, including halogenated solvents,which constitute a REC.Additionally, several gas stations, automotive repair, and two historical dry cleaners are located within 500 feet of the Subject Property. The potential release of halogenated solvents may pose a risk to human health and the environment. Currently,the Subject Property is operating as a commercial space and has been occupied by a barber shop and a flower shop. Discovery sampling is necessary to determine if the former dry-cleaning facility released halogenated solvents to the environment. • Identify the Decision:The data obtained from the sampling and testing activities will be used to evaluate whether releases of hazardous substances from historical uses have occurred at the Subject Property.The data obtained will be further evaluated to determine to what extent any found contamination or naturally occurring constituent concentration will result in risk of exposure.The data results will be compiled and used to assess the relative threat associated with on-site constituent concentrations through screening risk evaluations performed in accordance with the procedures set forth in the Programmatic QAPP. Based on the screening risk calculations for the Subject Property,the suitability of the property for its intended development will be determined. • Identify Inputs to the Decision:The investigation report will contain general descriptions of inputs to the decision. Inputs to the decision will include results of analytical testing of soil vapor, sub-slab vapor, and/or groundwater samples from selected locations on the Subject Property. Each matrix will be tested for the specified analytes discussed in Section 3 of this Work Plan, and the results will be presented in the investigation report. Table and figure templates are included as Table 4 and 5 and Figures 6A and 6B in this Work Plan. • Define the Study Boundaries: The boundaries of the field sampling and analysis program will be the perimeter of the Subject Property as defined by the AECOM Phase I ESA report(AECOM 2022b)and per Subject Property access. The investigation depth will be limited to 16 feet bgs. Soil vapor sampling will not be conducted during inclement weather or for 5 days following a rain event with greater than a half-inch of precipitation during a 24-hour period. Sampling will occur on only Monday through Friday between 7am and 6pm. • Develop a Decision Rule: Decisions will be based upon laboratory results for the target constituents and presented in figures and tables similar to the templates in Table 4 and 5 and Figures 6A and 6B,for each Prepared for: California Department of Toxic Substances Control AECOM 26