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i 4.1 Installation of Test Boring and Wells f� In order to perform an enhanced bioremediation pilot test, a liquid medium containing a culture of hydrocarbon-degrading bacteria must be introduced directly into the zone of contaminated soil At the Valley Motors site, this zone is the sand bed that spans the interval between 20 and 35 feet None of the existing monitor wells are screened within this interval, making them unsuitable for innoculation Therefore, a 10-inch-diameter soil boring(BT-1 in Figure 5) will be drilled to the base of the sand bed Depending on groundwater fluctuations, the water tal)le will probably be near the base of the sand bed and both the vadose and saturated zones will lie influenced by the innoculum Prior to innoculation, a regenerative blower will be connected to monitoring well VM-2 and air will be infected under pressure into the soil and groundwater in order to provide an oxygen source Boring BT-1 will then be innoculated with 100 gallons of innoculum (Figure 6) After the innoculum has infiltrated the soil, the boring will be backfilled with grout to the surface Soil vapor extraction requires an extraction well that is screened within the vadose zone (above the water table), so that air from the dry soil can enter the well and be withdrawn under a vacuum To perform this test, an extraction well will be drilled with 10-mch diameter augers to a df pth of 35 feet and screened with 4-inch diameter schedule 40 PVC casing from 15 to 35 feet below surface grade (bgs) The well location is shown in Figure 5, and the well design is shown in Figure 7 Soil . samples will be collected at 5-foot intervals beginning at 15 feet, and up to 5 samples will be analyzed for TPH-g and BTEX Air sparging can be used in combination with soil vapor extraction to remove contaminants from the groundwater Air is injected under pressure into the soil below the water table, and air bubbles help to transfer the contaminants from the dissolved phase to the vapor phase so that they can be withdrawn from the vapor extraction well To be most effective, the screened interval in a sparging well is normally less than 5 feet None of the existing monitor wells are suitable for this purpose because of their long screened intervals Therefore, a sparging well will be installed near the vapor extraction well and bioremediation test boring The proposed location of the sparging well is south of the dispenser island (Figure 5) Like the other test wells, the sparging well will be drilled to the base of the channel deposit and completed with 2 feet of screened casing To insure that the screen is located at the base of the channel, the well will be continuously sampled from 25 feet until the base is reached Details of the well construction are shown in Figure 8 4.2 In-situ Enhanced Bioremediation Bioaugmentation ("enhanced bioremediation") is a method in which specially prepared cultures of hydrocarbon-degrading bacteria are infected into the contaminated zone to treat the contaminants This technique has had varying degrees of success, depending on soil typ-;, bacterial populations, contaminant type, distribution, and concentration, application methods, and • other factors The technique has been tested at the laboratory (bench) scale as well as at the field