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t R <br /> C LEARWATER <br /> c R o t. II [ N c <br /> E—zroumevril St rz ices <br /> 4.3 Dissolved Oxygen in Groundwater <br /> i <br /> The dissolved oxygen (DO) content of purge water from each well was measured in <br /> the field DO content ranged from 13 milligrams per liter (mg/1) m groundwater <br /> from MW-2 to 2 3 mg/l in groundwater from MW-6 (Figure 4) <br /> In general, DO concentrations above 2 mg/1 indicate aerobic conditions, although <br /> some aerobic bioremediation may occur at DO concentrations down to 1 mg/l The <br /> DO concentration in groundwater from well MW-2 (1 3 mg/1) appears to be depleted <br /> relative to DO concentrations in wells MW-1, MW-3, MW-4 and MW-6 MW-2 is <br /> proximal to the source area, and the groundwater contains elevated contaminant <br /> concentrations <br /> i <br /> The depleted DO concentration in groundwater from MW-2 suggests that some <br /> natural bioremediation of petroleum hydrocarbons may be occurring in the center <br /> of the dissolved hydrocarbon plume However, historical analytical data indicate <br /> that, while petroleum hydrocarbon concentrations in groundwater from MW-2 <br /> have been variable, there is no apparent trend suggesting that the concentrations are <br /> decreasing over time The concentrations of dissolved hydrocarbons in MW-5, <br /> however, do appear to be decreasing over time, suggesting that the outer portion of <br /> the plume may be undergoing aerobic bioremediation <br /> D-101 1Q97 4 Apnl 15, 1997 <br />