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4.2 Groundwater Gradient Figure 3 illustrates the general direction of groundwater flow Presently, flow is to the ea3t The gradient is essentially unchanged since October It decreases from 0 004 ft/ft in the nortlt,.m part of the site to 0 0025 ft/ft in the %outhem part of the site The steeper gradient near VM-4 is probably due to the low-permeability clay that is present in the northern part of the site 7 his clay may confine groundwater to a slightly deeper depth by restricting flow from the west 4.3 Analytical Results In monitor wells VM-1 and VM-2, gasoline and BTEX concentrations generally increas:d over their concentrations in February and returned to the ranges that were seen in most previous sampling events (Table 2) Concentrations in VM-3 remain generally below detection it hits, but the gasoline concentration in VM-4 increased to its highest level since that well was drilled BTEX concentrations in VM-4 also increased, but to a lesser extent As in most of the previous monitoring events, this is the only well in which MTBE was detected (Table 3) None o -the other oxygenates were detected in any of the wells 4.4 Bacterial Analyses Cytoculture prepared glass plates for each sample and grew the bacterial colonies for se'Im days before conducting plate counts of bacterial populations Their report is included in Appt radix B Natural ly-occuring bacteria were present in the water samples from all four wells Meas fired in bacterial colony-forming units per milliter (CFU/ml), concentrations of non-specific heterotrophic bacteria ranged from 1 1 x 103 CFU/ml in VM-1 to 3 4 x 104 CFU/ml in N M-3 Concentrations of hydrocarbon-degrading bacteria ranged from below the reliable quant ti tation limit of 1 0 x 101 CFIJ/ml in VM-4 to 2 0 x 104 CFU/ml in VM-3 These results are interesting, and indicate that populations from VM-1 and VM-2 grew butter on gasoline food sources than on non-gasoline sources This implies that bacteria in these vi,,lls, both of which are contaminated. have adapted to the gasoline food source that is present n the water in the vicinity of these wells hi contrast, very limited bacterial populations are prv,,ent in the vicinity of VM-4 Neither hydrocarbon degraders nor other heterotrophs are abundain there Heterotrophs are most abundant in VM-3, but somewhat surprisingly, hydrocarbon degraders are also abundant in the sample from this well 'Little or no hydrocarbon contamination has -)sen detected in this well in any sampling event This suggests that there may be another type 2f hydrocarbon food source in the i,icinity of this well, such as decomposing organic matter from a sewer line A sewer odor has been noted occasionally in VM-2 during purging, but not in VM-3 Another possibility is that the bacteria have adapted to feeding on remnant organic matt:, in the soil, when this well was drilled in 1996, decomposed plant material was noted in soil saniples at depths of 15 and 30 feet • 4