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Air Sparging Pilot Test Related Activities Report and Remedial Action Work Plan Former Countryside Market, Stockton, California April 30, 2015 4.4.7 Soil Vapor Monitoring (AS-1 Testing) In addition to the background analytical samples collected as discussed in Section 4.2, vapor samples were collected following testing of both AS-1 and AS-2. Soil vapor concentrations measured with a PID in well OBS-1 increased during testing from background level of 33 parts per million (ppm) to a maximum of 463 ppm recorded after two hours of testing. PID concentrations in OBS-1 generally decreased over the remainder of the test. PID readings from VW-1 collected during testing generally decreased from a high of approximately 31.7 ppm to less than 10 ppm at the end of testing. The PID monitoring results can be found in the field data sheets in Appendix I and in Graph 1E. Following AS-1 testing, soil vapor analytical samples were collected from OBS-1 and VW-1 and submitted under COG to American Analytics of Chatsworth, California. Table 6 provides a summary of the soil vapor analytical laboratory results and the laboratory reports and COG forms are provided as Appendix E. 4.4.8 Helium Tracer Monitoring (AS-1 Testing) During AS testing, helium gas was injected, along with the ambient air, as a tracer at an average of 3% to 10% of the air injection flow rate. Because helium does not naturally occur in unconsolidated sediment, and is not physically, chemically, or biologically altered in the process of migration, helium detection at a monitoring point can be used to estimate the sparging radius of influence (ROI) and potential subsurface air flow rate. The helium monitoring results can be found in the field data sheets in Appendix I and in Graph 1F. Helium was detected within the well casing of OBS-1. Helium concentrations in OBS-1 gradually increased over the course of AS-1 testing and appear to have increased stepwise with the low, medium, and high flow rates applied to a maximum concentration of 21,000 ppm at the end of high flow testing. No helium was detected in the well casing of VW-1 during AS-1 testing. Surface and well box measurements with the helium detector showed no indication of helium "leakage" to the surface. 4.5 AS-2 Testing Discussion and Results 4.5.1 Breakthrough Testing (AS-2 Testing) Initial breakthrough testing was started on January 28, 2015 at approximately 8:00 AM by initiating airflow into AS well AS-2. Injection air pressure was incrementally increased to determine the minimum pressure required to displace the groundwater above the top of the screened interval and induce measurable airflow into the sparge well (min). Estimated Breakthrough Pressure: Gmin (psi) = 0.4 (psi/foot) x Water Column above Top of Screen (feet) 4-7 The Source Group, Inc.