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Treatability Study Report and Feasibility Evaluation for <br />In Situ Petroleum Hydrocarbon Remediation <br />Field Maintenance Shop #24, 8020 South Airport Way <br />Stockton, California <br />4.2.1. Step Testing <br />Immediately after breakthrough was established at both FMS-AS1A and FMS-AS1B, injection <br />pressure versus flow rate step tests were performed. The injection flow rates were manually <br />increased from 10 to 16 scfm with associated injection pressures of during FMS-AS1A testing <br />and 7 to 22 scfm during FMS-AS1 B testing. <br />The resulting injection pressures and flows were recorded in the field logs. <br />4.2.2. Pressure Response Monitoring <br />Prior to, and periodically throughout air sparge testing, well head pressure was measured at <br />nearby monitoring wells using Dwyer® Magnehelic pressure gauges to aid in the determination <br />of the air sparge zone of influence (ZOI). Wells monitored during air sparge testing included <br />FMS-MW1, FMS-MW2, FMS-MW4, FMS-MW5, FMS-DPE1, FMS-DPE2, FMS-AS1A, FMS- <br />AS1B, and FMS-SVE1. In addition, pressure was monitored in well FMS-AS1A during sparging <br />of well FMS-AS1 B to verify the integrity of the bentonite seal between the two screened <br />intervals of the double -nested well. <br />4.2.3. Helium Injection and Monitoring <br />Following the step tests at wells FMS-AS1A and FMS-AS1 B, helium injection was initiated. <br />Helium was injected as a tracer gas and monitored in nearby wells to aid in the determination of <br />an air sparge ZOI. The helium flow rate was adjusted to so that the helium concentration in the <br />injected air stream remained between approximately 3% and 5% by volume. Helium was <br />injected continuously until testing ceased. <br />Helium concentrations were measured periodically in field samples collected into Tedlar° bags <br />from the head space of wells FMS-MW1, FMS-MW2, FMS-MW4, FMS-MW5, FMS-SVE1, <br />FMS-DPE1, and FMS-DPE2 and analyzed using a Radiodetection MGD -2002 helium detector. <br />Depth to Water Monitoring <br />To monitor for groundwater mounding in the air sparge test area, the Troll® 9500 transducers <br />installed in wells FMS-MW1, FMS-MW5, FMS-DPE1, and FMS-DPE2 were programmed to <br />record a water level reading every 30 seconds before, during and after testing. Depths to water <br />in wells not equipped with Troll° 9500 transducers was measured periodically using a 100 -foot <br />water level meter. <br />4.2.4. Dissolved Oxygen Monitoring <br />The Troll® 9500 transducers installed in wells FMS-MW1, FMS-MW5, FMS-DPE1, and <br />FMS-DPE2 were programmed to record dissolved oxygen reading every 30 seconds before, <br />during, and after testing. This data, in conjunction with other monitoring results, was used to <br />determine the air sparge ZOI. <br />4.2.5. Field Measurements of Vapor Concentrations <br />Before air sparge testing, and periodically throughout testing, field vapor samples were collected <br />from the surrounding monitoring wells. Samples were pumped from the sample ports into <br />dedicated Tedlar° bags using a Gast° oil -less vacuum pump. Measurements of VOCs, % LEL <br />(as methane), oxygen, and carbon dioxide were recorded on field logs. Increases in soil vapor <br />concentrations can be an indication that sparged air is transferring contamination from <br />groundwater to the vadose zone. These measurements, in conjuction with other monitoring <br />results, were used for the determination of the air sparge ZOI. <br />OTI E 21 <br />