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GERAGHTY & MILLER, INC 6 hydrocarbons occurs when DO concentrations are greater than 2 milligrams per liter (mg/L) During aerobic biodegradation,DO levels are reduced as aerobic respiration occurs ' DO concentrations collected prior to the startup of the biosparging system in Monitoring Wells MW-1, MW-2, MW-3, MW-5, MW-6,MW-7, and MW-9 ranged from 1.03 milligrams per liter (mg/L) to 156 mg/L This indicates that aerobic biodegradation of petroleum hydrocarbons in the vicinity of these wells has resulted in the reduced DO concentrations The ' use of biosparging will enhance bioremediation by increasing DO levels in the groundwater. REMEDIATION SYSTEM INSTALLATION The installed system consists of nine remediation wells (GM-1 through GM-9) and one ' previously installed vadose-zone well (VW-1) All wells,except VW-1, are double-completion wells, with an SVE well screened from 10 feet to 17 feet bgs and a biosparging well completed ' with 2 to 3 feet of screened section between 27 feet and 30 feet bgs The locations of the remediation wells are shown in Figure 4 Construction details for the double-completion wells are shown in Figure 5. Geraghty & Miller installed all remediation wells, except for GM-5 and GM-9, in November 1996. Wells GM-5 and GM[-9 were installed in January 1997. A description of well-installation procedures, and the boring logs for the wells, are presented in Attachment 2. ' Analytical results from soil sampling conducted during the remediation system installation are shown in Attachment 4 Trenching, piping, and the SVE and biospargmg system installations ' were completed in February 1997, as shown in Figure 4 Due to the excessively wet season encountered during the winter of 1996/97, the groundwater level rose from approximately 17 ' feet bgs during the well installation to approximately 10 feet bgs, submerging the SVE well screens and disabling the ability to conduct mass removal by SVE until groundwater recedes. ' The biosparging system consists of a rotary-vane compressor set up to infect air cyclically into two manifolds, increasing the oxygenation of groundwater by enhancing mixing The biospargmg system was started in early April 1997 The first manifold injects air into Wells GM-1 through GM-5, the second manifold infects air into the remaining wells, ' GM-6 through GM-9. ' Project No RC0309.010