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JE MDU® San Joaquin County Public Health Services May 26, 1995 9347-1246 -- —J�- Y ( ) contrast, the March 1995 soil vapor hydrocarbon concentration of 45 ppmv indicates nearly 100% of the fuel currently consumed by the oxidizer is natural gas supplied by PG&E Figure 7 is a graph supplied by the manufacturer illustrating the relationship of natural gas consumption to hydrocarbon concentrations in soil vapor Proposed Remediation of Residual Hydrocarbons Fugro proposes to replace the SVE system with a low flow air diffuser system in five of the monitoring wells to increase the dissolved oxygen content of ground water beneath the site to enhance the attenuation of the remaining dissolved and adsorbed petroleum hydrocarbons The proposed scope of work includes • Obtaining the approval of the San Joaquin County Public Health Services for the installation and operation of the air diffuser system • Installing air diffusers in monitoring wells MW-2, MW-4, MW-7, MW-8, and MW-9, using the existing underground piping I • Installing a compressed air source for the infection of air into the five wells at low pressures and flow rates • Performing startup, operation, maintenance and monitoring of the diffuser system The compressor pump sustains air diffusion at very low flow rates The air flow and operating pressures may be subject to changes in site conditions, including ground water levels The diffuser system, by design, is intended to operate at sufficiently low flows to allow the diffused air to dissolve, thereby increasing concentrations of dissolved oxygen without generating vapors (off-gases) or ground water mounding The sandy-silt composition of the saturated zone appears suitable for the propagation of dissolved oxygen in ground water across the site The proposed air diffuser system is not air sparging Sparging is the injection of compressed air at comparatively high volumes and pressures into the saturated zone to accelerate the volatilization of dissolved hydrocarbons, as well as providing an oxygen source Air sparging is typically used in conjunction with vapor extraction Quarterly monitoring and sampling will assess the attenuation of dissolved hydrocarbons and remediation progress To monitor the performance of the diffuser system, dissolved oxygen measurements will be collected from the monitoring wells monthly for the first three months, and during quarterly monitoring thereafter 934712461 1-1 4-