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PES Environmental , Inc . 2 . 3 . 2 . 1 Sub - Slab Vapor Sampling and Analytical Methods The sub - slab vapor sample will be collected using a Vapor Pin® , which will be installed in accordance with manufacturer specifications using a roto -hammer drill and stainless - steel drill bits . The slab boring will be drilled 3 to 4 inches into subsurface materials below the slab . Prior to drilling , a private underground utility locating service will be contracted to conduct a subsurface electromagnetic survey to screen the proposed sampling location for the presence of sub - slab utilities . The sub - slab sample will be collected in accordance with the procedures outlined in the Advisory for Active Soil Gas Investigations (ASGI) published by the Department of Toxic Substances Control , the Regional Water Quality Control Board , Los Angeles Region and the California Regional Water Quality Control Board , San Francisco Bay Region dated July 20158 . The sub - slab vapor sampling location will be allowed to equilibrate for a minimum of 2 hours after installation prior to purging and soil vapor sampling . Prior to the collection of sub - slab vapor sample , shut-in leak testing , purging , and sample train leak testing will be performed . The shut- in test will consist of assembling above - ground sampling apparatus (e . g . , valves , lines , and fittings downstream from the top of the vapor pin) , and evacuating the lines to a measured vacuum of approximately 100 inches of water column (in-H20 ) , then shutting the vacuum in with closed valves on opposite ends of the sampling train . A vacuum gauge will be used to assess if there is any observable loss of vacuum (for at least one minute) prior to purging and the collection of the sub - slab vapor sample . If observable vacuum loss is noted , the sample train will be re - assembled , and the shut- in test will be repeated . This process will be repeated as necessary until a successful shut-in test has been performed . A default of three purge volumes will be extracted . The stagnant air will be purged with a six-liter SUMMA canister . The purge volume will be calculated using the volumes of: ( 1 ) the internal volume of the vapor pin/tubing ; and (2) the void space in the concrete below the vapor pin . In accordance with the ASGI , purging and collection of sub - slab vapor samples will be performed using a flow rate of 100 to 200 milliliters per minute (mL/min) and maintaining a low vacuum of less than 100 in-H20 to mitigate ambient air breakthrough . Following completion of the shut- in leak test and purging , sample train leak testing will be performed using a propellant tracer in combination with a shroud box . The shroud box will consist of a polycarbonate box equipped with an access port to allow charging of the box with a propellant tracer . The shroud box will be positioned over the sub - slab vapor pin and 14iter SUMMA canister connected to the sample train . The shroud box will then be charged by spraying the tracer propellant into the shroud box . The shroud box will be allowed to remain in place for the duration of sampling . For quality assurance / quality control ( QA/ QC ) 8 DTSC , 2015 . Advisory - Active Soil Gas Investigations . Jointly developed by the California Environmental Protection Agency Department of Toxic Substances Control (DTSC) , and the California Regional Water Quality Control Board - Los Angeles Region (LARWQCB) and RWQCB - San Francisco Region (SFRWQCB) . July . 148400101W006 . docx 4 D R A F T