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Former Countryside Market,Stockton,California May 20, 2013 Feasibility Study and Interim Remedial Action Plan Testing will be conducted at flow rates up to 20 scfm. SGI will monitor pressures/injection air temperatures to ensure no damage to the AS wellheads. SGI will also monitor potential increases in injection pressures that do not result in corresponding flow rate increases, aiid limit maximum operational flows to below this threshold level. Required injection pressures will likely decrease with time as the injected ai finds preferential flow paths through the saturated zone. Pressure in observation wells MW-1 through MW-5 and OBS-1 will be measured before, during, and after testing. Pressure influence data will aid in determining air distribution (flow paths) at the Site and the directionality of sparging influence (i.e. homogeneous or heterogeneous air distribution). After the cessation of testing, pressure dissipation rates will be measured to evaluate whether air is potentially being trapped in the formation. DO dissipation and water level recovery data will also be measured to help determine optimal injection intervals/cycling times during system operations. 5.1.7 Helium Tracer Study During AS testing, helium gas will be injected at a fixed concentration as a#acer gas, in conjunction with the ambient air, into AS wells AS-1 and AS-2. Because helium does not naturally occur in unconsolidated sediment, and is not physically, chemically, or biologica ly altered in the process of migration, helium detection at a monitoring point will be used to estimate th, sparging radius of influence (ROI) and potential subsurface airflow travel rates. The distribution of helium in vapor monitoring points also provides an idea of the location of preferential paths and/or channels and allows for a quantitative assessment of the air distribution pattern around the sparging well. Such data can be used to identify treatment dead zones and help in planning modifications to the number of sparging wells and/or injection flow rates. SGI will routinely monitor for helium gas at all of the observation wells during sparge testing. 5.1.8 Radius of Influence The sparge ROI for each test will be determined using the following data obtained from the observation wells during testing: 1) induced/increased air pressures; 2) increased gr( undwater levels (mounding); 3) increased DO/ORP concentrations; 4) changes in TPHg/BTEX concentrations in the groundwater samples collected pre- and post-testing; and 5) measured helium conce trations in observation wells. The ROIs will be calculated based on average injection rates during hour of air injection. Specifically, the ROI will be calculated at the final proposed injection rate that does not enerate a buildup of COCs in the vadose zone and will not require operation of an active soil vapor recovery and treatment system. 5.1.9 Monitoring and Sampling Methods As indicators of sparge influence, monitoring before, during, and after the t@st will include water level and DO/ORP readings in observation wells using down-hole data loggers (rte Iti probe Trolls from In Situ, Inc.), as well as pressure measurements and PID readings. Monitoring wills MW-1 through MW-3 may be fitted with dedicated data loggers or manually monitored, based ori Copperopolis Road access Feasibility SW y aM lFeasibiliy StWy&IW Te Final.dm 5-6 The Source Group,Inc.