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April 30, 2015 Air Sparging Pilot Test Related Activities Report and Remedial Action Work Plan Former Countryside Market, Stockton, California in OBS-1 fluctuated slightly between 110 and 118.5 mV. ORP levels in MW-5 were effectively unchanged as the readings only decreased slightly over the course of testing from -390 to -410 mV. ORP levels in AS-1 increased modestly during testing to approximately 139 mV. AS-2 sparge testing ORP results are presented in Graph 20. As was the case for the first test (i.e., AS-1 testing), the ORP readings did not exhibit a strong correlation with the DO level data. ORP readings (raw data) recorded by the data loggers deployed in wells OBS-1, MW-5, and AS-1 are provided in Appendix J. 4.5.7 Soil Vapor Monitoring (AS-2 Testing) Initial soil vapor concentrations measured with a PID in OBS-1 during testing was 13.4 ppm which increased to maximum values during the low, medium and high-flow testing of 33.3 ppm, 56.8 ppm, and 292 ppm, respectively. Initial soil vapor concentrations measured with a PID in VW-1 during testing was 13.4 ppm which increased to maximum values during the low, medium and high-flow testing of 35.1 ppm, 5.5 ppm, and 998.9 ppm, respectively. The PID monitoring results can be found in the field data sheets in Appendix I and in Graph 2E. Following AS-2 testing, soil vapor analytical samples were collected from OBS-1 and \NV-1 and submitted under COG to American Analytics of Chatsworth, CA. Table 6 provides a summary of the soil vapor analytical laboratory results and the laboratory reports and COG forms are provided as Appendix E. 4.5.8 Helium Tracer Monitoring (AS-2 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 ROI and potential subsurface air flow travel rates. The helium monitoring results can be found in the field data sheets in Appendix I and in Graph 2F. Helium was detected within the well casing in each observation well. Significant helium concentrations of 4,000 to 6,000 ppmv were only detected in observation well OBS-1. Lower helium concentrations of 75 to 100 ppmv were measured in vapor well VW-1. Surface and well box measurements with the helium detector showed no indication of helium "leakage" to the surface. 4.6 Transducer Results Pressure transducers were place into monitoring wells MW-3, MW-6, and MW-7 located approximately 80 feet cross gradient and 90 and 175 feet downgradient of the former UST area, respectively. Transducers recorded groundwater levels before, during, and after AS pilot test activities. Data indicate groundwater mounding was apparent during AS activities in AS-1 and 4-10 The Source Group, Inc.