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Treatability Study Report and Feasibility Evaluation for In Situ Petroleum Hydrocarbon Remediation Field Maintenance Shop #24, 8020 South Airport Way Stockton, California had increased to above 13.50 mg/L, where it remained throughout the remainder of air sparge testing. Dissolved oxygen in well FMS-DPE2 (approximately 34 feet from the injection wells) was similarly depleted with a baseline measurement of -0.04 mg/L. Approximately 2 hours after sparging at well FMS-AS1 B ceased, dissolved oxygen in well FMS-DPE2 increased sharply to above 5.0 mg/L. Dissolved oxygen concentrations in wells FMS-MW1 and FMS-MW5 were not observed to increase significantly during air sparge testing. The results of dissolved oxygen monitoring are summarized in the Pilot Test Summary Data sheets included in Appendix F. 4.3.6. Groundwater Concentrations Groundwater samples from monitoring wells FMS-DPE1, FMS-DPE2, and FMS-MW5 were collected prior to the SVE test on May 14, 2012 and after the air sparge test (and prior to the DPE test) on May 17, 2012 using the groundwater sampling methodology mentioned previously. Each groundwater sample was submitted to State -certified BC Labs in Bakersfield, California for analysis of petroleum hydrocarbons by U.S. EPA Method 8015 -modified and VOCs, including Naphthalene and Fuel Oxygenates, by U.S. EPA Method 8260. The TPH-g groundwater concentrations decreased in monitoring wells FMS-DPE1 (approximately 17 feet from the injection well) from 48,000 lag/L to 6,700 pg/L, in FMS-MW5 (approximately 20 feet from the injection well) from 18,000 lag/L to 15,000 tag/L, and in FMS-DPE2 (approximately 34.5 feet from the injection well) from 24,000 lag/L to 8,200 pg/L. Groundwater BTEX concentrations generally decreased in all three monitoring wells. Benzene decreased from 8,400 lag/L to 890 lag/L in FMS-DPE1, from 4,800 lag/L to 2,600 pg/L in FMS-DPE2, and from 7,400 lag/L to 5,200 lag/L in FMS-MW5. The groundwater analytical results are summarized in Table 3. Laboratory reports and Chain -of -Custody are provided in Appendix C. 4.3.7. Field Measurements of Vapor Concentrations VOC concentrations were measured in the headspace of the observation wells with a MiniRae 2000 PID and a GasTech GT -408 Multi -Gas meter, before, during, and after each test using the methodology described previously. The following notable changes in vapor concentrations were observed over the course of FMS-AS1A testing (measurements taken using GT -408 meter): • VOC concentrations measured in well FMS-MW5 (20.16 feet from the injection well) increased from 9,760 ppmv (19% LEL, as methane) to >10,000 ppmv (28% LEL, as methane) by the end of FMS-AS1A testing; • VOC concentrations measured in well FMS-DPE1 (16.66 feet from the injection well) increased from 5,360 ppmv (10% LEL, as methane) to >10,000 ppmv (44% LEL, as methane) by the end of FMS-AS1A testing; and • VOC concentrations measured in well FMS-DPE2 (34.59 feet from the injection well) increased from 600 ppmv (1% LEL, as methane) to 7,540 ppmv (15% LEL, as methane) by the end of FMS-AS1A testing. Air sparging at well FMS-AS1 B caused the following notable changes in VOC concentrations: OTI E 25