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likTe ENVIRONMENTAL • GEOTECHNICAL BUILDING SCIENCES • MATERIALS TESTING _ . 7 Lone Palm Avenue, Suite 201B Modesto, CA 95351 Telephone 209-579-2221 Fax 209-579-2225 wvvw.atcgroupservices.com each portion of the sample apparatus, including the area where the Teflon tubing exits the ground. Testing for the leak check compound will not be performed in the field. If windy conditions are present at the time of sampling, a shroud will be employed instead of cloths. For Quality Assurance/Quality Control purposes, one duplicate sample will be collected from a selected vapor probe location using a separate dedicated sampling manifold. Soil Vapor Sample Analysis Soil vapor samples collected from the soil vapor probes will be immediately transferred under chain-of- custody procedures to an off-site State-certified laboratory, H & P Mobile Geochemistry, Inc. (H&P, Inc.; ELAP Cert: 2741). Each soil vapor sample will be analyzed for compounds of concern, including Total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and total xylenes (BTEX), fuel oxygenates including MTBE, and lead scavengers including 1,2-DCA, using EPA Method TO-15, an analytical method employed for air quality studies, as well as naphthalene by TO-16 and oxygen. Each soil vapor sample will also be analyzed for the leak check compound, with a method detection limit of less than 10 lag/1. Each sample will be screened at the laboratory to evaluate for elevated concentrations. If elevated concentrations are detected that would compromise the desired detection limits of the TO-15 Method, the screening method, typically EPA Method 8260M, will be reported instead. Risk Assessment and Report Preparation A tiered evaluation will be conducted using the laboratory analytical data. The soil vapor data will be compared to the values listed in Table 2 of the Tier 1 ESLs as published by the San Francisco Bay Regional Water Quality Control Board (SF RWQCB) in May 2015 and the California Human Health Screening Levels (CHHSLs) published by the California Environmental Protection Agency (CAL EPA) in January 2005. ATC will also compare the results to the SWRCB's Low Threat Closure Policy values. If any of the analytes of interest exceed the ESLs and/or CHHSLs, ATC will provide an interpretation of the vapor data using the current appropriate Low Threat Closure Policy (LTCP) thresholds. CHARACTERIZATION OF DIRECT CONTACT RISK AND METALS CONTENT Advancement of soil borings This task includes advancing five shallow soil borings via direct push to ten feet bgs to collect soil samples in two intervals. Soil samples will also be collected during the installation of the proposed soil vapor points, and during the clearance steps for hydropunch borings described in the following section. Proposed boring locations are shown on Figure 2. The five borings will be advanced using truck mounted Geoprobee narrow diameter, direct push technology. Drilling will be conducted by a State-licensed (C57) drilling company. A field geologist S: \ 62596 \ reports \ SVIS_WP_ADD-2016.doc 3 ATC