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' 6.2.2 In-situ Treatment Alternatives Two methods of in-situ remediation are discussed in this section. Groundwater bioremediation could accompany bioremediation of the vadose zone. Alternatively, air sparging could be performed in conjunction with vapor extraction from the vadose zone. ' 6.2.2.1 Bioremediation 6.2.2.1.1 Principles In-situ bioremediation of the saturated zone involves many of the same principles and soil ' requirements as in-situ bioremediation of the vadose zone. Bacterial growth and migration may be somewhat more rapid in the saturated zone, due to increased mobility in saturated pore space. To increase subsurface air flow and enhance bacterial growth, a soil blower is ' commonly manifolded to the inoculation wells. Although blowers can lead to soil dehydration in the vadose zone, this is less likely in the saturated zone. However, regulatory ' agencies have been reticent to permit groundwater treatment by in-situ bioremediation, partly because of concerns over the introduction of bacteria and chemicals into groundwater. These concerns may force submittal of Waste Discharge Permits, which require additional ' time and expense. 6.2.2.1.2 Inoculation Wells In-situ bioremediation of groundwater at this site can be accomplished by injecting the bacteria into monitoring wells MW-1, MW-3, MW-4, and MW-5, as well as vadose-zone well ' RW-1. These wells are all located within the plume of contaminated groundwater, and wells MW-4 and MW-5 are screened at least 10 feet into the saturated zone. Although MW-3 is not screened within the saturated zone, the lower portion of this well is within the capillary ' fringe, allowing bacteria to reach groundwater. Slug tests on MW-4 and MW-6 indicated that aquifer permeability is moderate; depending on bacterial migration rates, each well could have a radius of influence of 15 feet within 3 months if inoculated with 100 gallons of ' medium. Additional inoculation wells, or reinoculation events, could be added to speed remediation if periodic monitoring indicates that the process is proceeding slowly. ' 6.2.2.1.3 Monitoring Activities The methods of monitoring in-situ bioremediation of groundwater are the same as those for ' remediation of soil, except that groundwater analyses include bacterial populations and dissolved oxygen. Monitoring is also more frequent; groundwater depth measurements and samples should be collected monthly for the first six months to ensure that injection of ' bacteria or distilled water has not altered groundwater flow or. caused spread of the contaminant plume. 1 Clog I Aud«Se rvkc Inc. �� ARI PARn-29-Wa.47