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Geosptec consultants One blind field duplicate sample per media type will be collected to assess the precision and overall quality of the sampling and analytical procedures, as well as the variability (sample heterogeneity) in obtaining samples that represent one sampling point. The duplicate sub slab and soil vapor samples will be collected simultaneously with the primary sample by using a "T" connector between two SummaTM canisters. The duplicate sample will be stored in the same manner as the primary sample and submitted to the appropriate laboratory for analysis of VOCs by EPA Method TO-15. One blind duplicate groundwater and indoor air sample will also be collected simultaneously with the primary samples. As an additional quality control measure,50%of the soil vapor samples will be analyzed for helium by the analytical laboratory by modified ASTM method D-1946. 3.5.1.1 Sample Handling and Custody Requirements Chain of custody forms will be completed during sampling and will include the sample identification, location,date and time of the sampling,number and type of container,and the requested analytical method. Sample documentation will be completed in the field, and the chain(s) of custody will accompany the samples through transportation and analysis. The chain of custody procedures will be strictly adhered to during sample collection,transportation, and laboratory handling to ensure the integrity of the samples. 3.5.2 Laboratory Quality Control Samples Laboratory QC samples,or reference standards,will be introduced into the measurement process to evaluate laboratory performance and sample measurement for the EPA TO-15, TO-15 SIM, 826013, and ASTM D- 1946 analytical methods. Control samples will be prepared from environmental samples or be generated from standard materials in the laboratory. Laboratory QC samples include method blanks, laboratory control samples (LCS) and laboratory control sample duplicates (LCSD), and continuing calibration verification(CCV) standards. 3.5.3 Data Verification and Validation Data verification and validation consist of evaluating data and accepting, qualifying, or rejecting data on the basis of sound criteria using established EPA guidelines. Laboratory data will be subjected to a data evaluation that will include the following: • A review of the full data package for completeness; • Review of chain of custody forms against laboratory reported information,including review of transfer of custody signatures, sample condition upon receipt by the laboratory, and sample preservation in comparison to method requirements; • Review of holding times and assessment of any holding time exceedances; • Review of QC information provided by the laboratory which will include: o assessment of LCS, LCSD, and laboratory duplicate sample percent recoveries and relative percent differences,as appropriate; and o assessment of CCV standards and surrogate recovery results in comparison to the laboratory's quality control requirements. 10 September 2025