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' 6.1.2.1.2 Nutrient Requirements and Toxicity ty The bacteria require certain essential nutrients, which are usually available in native soil. If supplements are needed, the amounts are generally very low, comparable to light agricultural use. ' There is considerable venation in the types of bacteria used by different remediation ' consultants for bioremediation. GeoAudit utilizes soil bacteria that are indigenous to highly contaminated oil field sites in the southern San Joaquin Valley. The bacteria are cultured and selected for their ability to degrade petroleum hydrocarbons. They are microaerophilic ' and facultatively anaerobic, and therefore abundant oxygen is neither necessary nor tolerable for the process to occur. No exotic forms of oxygen (such as hydrogen peroxide or liquid oxygen) are needed. Excess oxygen is toxic to the bacteria, which produce enzymes to destroy it. A small blower delivering atmospheric air to the subsurface at a rate of 2 to 5 psi per well can be used to enhance air flow during the process. This may result in unwanted dehydration of the soil, but dehydration can be prevented by monthly injection of distilled water to each well. The bacteria are also tolerant to a wide range of soil conditions. For instance, pH can range ' from 4 to 9.5 and electrical conductivity has little or no effect unless sodium levels reach greater than 5% on a weight basis. 6.1.2.1.3 Inoculation Well(s) Due to the limited lateral extent of soil contamination at the site and the high permeability ' of the unsaturated zone, the radius of influence of remedial well RW-1 should be adequate to remediate all of the soil contamination. It should not be necessary to install additional inoculation wells, but it may be necessary to inoculate MW-1 or to re-inoculate RW-1 if ' subsequent confirmatory sampling indicates that remediation is proceeding slowly or bacterial counts are low. RW-1 is screened to within 10 feet of the present water table; it is therefore probable that the bacteria will reach the groundwater. Inoculation of RW-1 will ' therefore result in partial remediation of the saturated zone. 6.1.2.1.4 Monitoring Activities After inoculation the inoculation u anon well (RW-1) and groundwater monitoring well MW-1 should be monitored by monthly field measurements of organic vapors, carbon dioxide, and oxygen. Groundwater monitoring wells MW-3 and MW-4 should be included in the monitoring program after the first three months; prior to that, the radius of influence of the inoculation well will not have reached these weIls. Quarterly monitoring activities should include collection of air samples from each ' monitoring and inoculation well for quantitative analysis of carbon dioxide, which is a by- product of hydrocarbon destruction. At least one boring should also be drilled to collect soil C-1.51.0 Audn Sc rvi�e..1- A 2 l ARA PAM-U-94n 47