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5 <br /> CAPILLARY FRINGE/GROUNDWATER <br /> Groundwater can be remediated through the use of air spargeng to enhance bioactivity <br /> or contained through the use of groundwater extraction An air-sparging system was installed <br /> in February 1997 as an interim remedial measure to enhance bioactivity to remediate <br /> hydrocarbons Groundwater extraction is ineffective for hydrocarbon mass removal for the <br /> dissolved petroleum hydrocarbons in groundwater and has poor cost-effe;anro <br /> to the <br /> cost of long-term operation and maintenance <br /> The use of a combination soil-vapor extraction/air-sparging seously <br /> address source removal and enhance biological activity in the vadose zodwater <br /> help enhance the cost-effectiveness of this remedial alternate Geraghrecom- <br /> mends the adoption of the installed soil-vapor extraction/ r-s g system as the primary <br /> remedial technology for the site <br /> PROPOSED CLEAN-ITP LE LS <br /> ACTIVE REMEDIATION GOALS <br /> In accordance with the SJCPHS equ in a ultimate project goal is to reduce <br /> concentrations of petroleum hydrocarbons be w the MCLs established for drinking water <br /> Geraghty & Miller proposes that the sys m operated until significant enhancement of <br /> bioactivity is shown ough decreased ncentrations of petroleum hydrocarbons in <br /> groundwater Opera no e S E system well continue until the system is no longer effective <br /> on a mass-remov base Effectiv ess well be evaluated on the bases of SVE influent <br /> concentrations attamm asym o evels <br /> pera n of the beosparging system well continue to add oxygen to the subsurface until <br /> ave ge entra ons of petroleum hydrocarbons have been reduced by approximately 95% <br /> is re cteo go corresponds to approximately 1 milligram per liter (mg/L) of TPH as <br /> gas ne an 0 g/L of benzene in groundwater At that point, the biospargeng system will <br /> be turn of , allowing natural attenuation to achieve acceptable levels of petroleum hydro- <br /> carbons in groundwater It would not be cost-effective to operate the system until drinking- <br /> water objectives are achieved <br /> Project No RC0309 010 <br /> GERAGHTY&MILLER, INCA <br />