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Air Sparging Pilot Test Related Activities Report and Remedial Action Work Plan Former Countryside Market, Stockton, California April 30, 2015 groundwater level in response to both initiation and changes in flow rate, the groundwater levels quickly returned to background levels for the duration of each phase of testing. Groundwater levels in the observation wells returned to background levels within approximately 20 to 30 minutes after air injection was ceased, and the measured displacements during testing were confirmed to not be the result of changes in barometric pressures. 4.4.5 Dissolved Oxygen Monitoring (AS-1 Testing) Approximate background (i.e. pre-injection) DO levels in milligrams per liter (mg/L) recorded were as follows: 2.4 (OBS-1); 0.9 (AS-1), and 0 (MW-5). DO concentrations increased rapidly to approximately 12 mg/L in well OBS-1 (located 15 feet from AS-1) and remained at the same level during the low-flow, medium-flow, and high-flow steps. An increase to approximately 8.5 mg/L indicates DO saturation, typical of an air flow path directly intersecting the well (i.e. bubbling in the water column). DO concentrations in well AS-2 (20 feet from AS-1) decreased slightly during the flow steps. DO levels in MW-5 remained generally constant during the course of the test. Observed DO during AS test in AS-1 are presented on Graph 1C. Continued DO measurements were recorded in the observation wells with the data loggers after injection was ceased. After injection was stopped, the DO concentration fell slightly in well OBS-1 for three hours from approximately 12 to 11 mg/L, followed by a more gradual decline over the next eight hours to approximately 10 mg/L. Note that a more significant decline in DO levels over this time frame likely occurred as such elevated readings are not generally feasible without a sustained source of air/oxygen. As a result, it is suspected that a DO sensor calibration problem occurred sometime near the end of the first test as these unusually high levels were maintained at the start of the second test, as described in Section 4.5. DO readings (raw data) recorded by the data loggers deployed in wells OBS-1, MW-5, and AS-2 are provided in Appendix J. 4.4.6 Oxidation-Reduction Potential Monitoring (AS-1 Testing) Pre-injection ORP levels in OBS-1 and AS-2 were approximately 64 millivolts (mV) and 127 mV, respectively. During the low-, medium-, and high-flow steps, ORP levels in OBS-1 increased to a maximum of approximately 110 mV and rose slightly following the test to approximately 115 mV (Graph 1D). ORP levels in AS-2 were effectively unchanged during the low-flow step as the readings only decreased slightly to approximately 115 mV. During the medium-flow step, ORP levels in AS-2 increased to approximately 125 mV and remained at approximately 125 mV during the high-flow step (Graph 1D). ORP levels in AS-2 quickly returned to pre-testing levels of approximately 110 mV following the test. Note that the ORP readings did not exhibit a strong correlation with the DO level data although a marked increase did occur in well OBS-1 after low- flow injection was initiated. Sparging did not have a nneasureable influence on ORP in MW-5. ORP readings (raw data) recorded by the data loggers deployed in wells OBS-1 AS-2 and MW-5 are provided Appendix J. 4-6 The Source Group, Inc.