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6.3 Proposed Vapor Intrusion Assessment A vapor intrusion assessment will consist of indoor and outdoor air samples and soil gas samples from sub-slab probes and a five-foot deep soil gas probe that will be collected during the same sampling event. 6.3.1 Proposed Indoor Air Sampling Methods Indoor air sampling is part of the step-wise approach of the assessment of intrusion of subsurface vapors into buildings as promulgated in the October 2011 DTSC technical document titled Final Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion in Indoor Air (Vapor Intrusion Guidance). The proposed indoor air sampling will be conducted at the Quality Cleaners, the Fred Loya Insurance office (3085 North Tracy Boulevard and the adjacent tenant west of Quality Cleaners)and the Comcast store(3115 North Tracy Boulevard and the adjacent tenant east of Quality Cleaners). At least two weeks prior to indoor air sampling, on-site managers of the three suites will be contacted in person to inspect the suites for potential sources of VOCs, schedule the testing and to explain the testing procedures. Also,written instructions will be provided. The instructions should state that use of certain consumer products is discouraged due to potential biasing of the sampling results. After performing the inspections, Partner will place two six-liter Summa canisters in each of the three suites in locations diagrammatically shown on Figure 5. It is the intent of this task to include the number of indoor air samples that will be appropriate for the internal configuration and use of each suite. Indoor air samples will be collected in primary work areas as well as possible vapor entry locations(e.g.,utility entrances in the stockroom or floor drains found in restrooms or boiler rooms). The canisters will be placed at a height of three to five feet above the floor. The actual locations of the indoor air samples will be based on the inspections that will occur at least two weeks in advance of the field sampling event and the proposed locations will be conveyed to DTSC staff for concurrence. A single canister will be located to the southwest exterior(anticipated upwind location)of the target suites to assess target compounds in outdoor air. The canisters will have flow regulators set to allow the air samples to be collected over a 24-hour period. In accordance with the Vapor Intrusion Guidance, soil gas should be sampled at a frequency that allows detection of seasonal variation and other temporal changes and to determine long-term stability of constituent concentrations. Therefore, a follow-up sampling for indoor air will be tentatively scheduled for approximately six months after the initial indoor sampling is Sampling and Analysis Workplan Tracy Corners Shopping Center 3225 North Tracy Boulevard Tracy,California 95376 Partner Project Number SM14-129814 Docket Number HAS-VCA 14/15-108 August 15,2016 Page 22