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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 6.0 TREATABILITY STUDY CONCLUSIONS AND RECOMMENDATIONS 6.1.1. Soil Vapor Extraction Analyses of field and analytical data from the SVE test confirmed that SVE technology would be successful at recovering mass and treating the vadose zone. The following conclusions are presented for the SVE test conducted at well FMS-SVE1: • The analytical results of influent samples collected at the beginning and end of SVE testing (TPH-g concentration 1,100 ppmv to 750 ppmv over the course of testing) indicate that TPH-g mass is present in the vadose zone and is recoverable via soil vapor extraction. • The ROI for soil vapor extraction at well FMS-SVE1 was calculated to be approximately 60 feet. The relatively large SVE ROI indicates that significant quantities of soil vapor can be effectively extracted from the contaminated area of the vadose zone with relatively few wells. • The sand zones encountered throughout the site between approximately 20 and 28 feet bgs creates a wide, flat capture zone above the saturated zone and is amenable to soil vapor extraction. • Based on the average flow rates and sample analytical results, soil vapor extraction from well FMS-SVE1 removed petroleum hydrocarbons from the subsurface at a rate of approximately 18 lbs/day. However, this initial rate would be expected to decline during remediation as petroleum hydrocarbon mass removal rates become limited by the rate of soil diffusion and groundwater volatilization. • Given the large ROI and high mass recovery rate, soil vapor extraction is likely to be a cost effective means for removing petroleum hydrocarbon from the vadose zone relative to excavation or other in situ technologies. • SVE well spacing of 30 to 60 feet at 40 to 50 scfm per well is recommended and would ensure ROI overlap and effective capture. • 1,2 -DCA was detected in the soil vapor which may require considerations for air permit requirements for a full-scale SVE system. 6.1.2. Air Sparge Analyses of field and analytical data collected during air sparge testing at FMS-AS1A and FMS-AS1 B confirmed that AS is effective at treating the saturated zone. The following conclusions are presented for the air sparge testing conducted at wells FMS-AS1A and FMS - AS 1 B: • Air sparge significantly reduced groundwater concentrations after two days of testing at FMS-AS1A and FMS -AS -B: o TPH-g concentrations decreased from 48,000 pg/L to 6,700 pg/L (86% reduction) at FMS-DPE1, located 17 feet from the test well; o TPH-g concentrations decreased from 18,000 pg/L to 15,000 pg/L (17% reduction) at FMS-MW5, located 20 feet from the test well; and OTI E 36