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• from the soil If so, desorption ceased during the `second quarter, because the concentrations of all analytes remained unchanged in three of the wells and declined by 20-50% in VM-4 (Table 2) It has been several years since concentrations remained so stable at this site, the last time this occurred was in late 1996-early 1997 Total Petroleum Hydrocarbon and total BTEX concentrations are graphed against time for VM-2 and VM-1 in Figures 4 and 5 Figure 4 illustrates that there has been a trend of increasing concentrations in VM-2 since monitoring began in 1996, and that concentrations have generally peaked during the third quarter 6f the year The annual low concentration has usually been recorded late in the first quarter If this pattern holds true in 2002, concentrations are likely to peak again within the next three months In contrast to VM-2, concentrations in VM-1 appear to be on a downward trend Further, neither the annual peak concentration nor the annual low concentration has been as consistent as in VM- 2 This is also true of VM-3 and VM-4, neither of which has shown a consistent long-term trend The samples were also analyzed for gasoline oxygenates, using EPA method 8260, because MTBE has been reported in four previous samples from VM-4 (Table 3) None of oxygenates were detected in this or any,of the other wells this quarter, and they have been detected only rarely Hence, it is clear that they are not a significant component of the contaminant plume 4.3 Extent of Groundwater Contamination Although the full lateral extent of groundwater contamination has not been determined and additional drilling is planned to complete this task, we have constructed a preliminary isocontour map of dissolved-phase gasoline (TPH-g) using the most recent laboratory data (Figure 6) In areas where older samples from the hydropunch borings or remediation wells are the only sample points, we have considered these in constructing the map Our tentative interpretation is that the plume is elongate in a northwest-southeast direction and extends beneath the sidewalk north of the site Groundwater beneath most of the site is contaminated, although it may not be contaminated beneath the garage building or the office building The total area underlain by the plume appears to be roughly one-quarter acre, and its center lies near the east end of the former dispenser island, between VM-2 and SW-I In this area, concentrations exceed 50,000 ppb and may approach 70,000 ppb The benzene concentration is between 5,000 and 10,000 ppb in the center 4