During May and June 2003, the U.S. Geological Survey (USGS) installed monitoring wells and collected data to characterize the effectiveness of natural attenuation processes for remediating petroleum-contaminated ground water at Operable Unit A of the former Naval complex on Adak Island, Alaska. Evidence for petroleum biodegradation in ground water was evaluated at 10 sites, plans for future natural attenuation monitoring were suggested for those sites, and the natural attenuation monitoring strategy for all petroleum sites in the Downtown area of Adak Island was reviewed and refinements were suggested.
USGS personnel measured water levels and collected ground-water samples from about 100 temporary boreholes and 50 monitoring wells. Most samples were analyzed on-site for concentrations of selected petroleum compounds and natural attenuation parameters (NAPs) such as dissolved oxygen, ferrous iron, and carbon dioxide. The USGS evaluated the data onsite, selected new monitoring well locations, and installed, developed, and sampled 10 monitoring wells. This data collection approach facilitated accurate and rapid delineation of the downgradient margin of contaminant plumes, and the new wells generally were installed at downgradient locations where petroleum compounds were detected at concentrations less than the specified cleanup standards.
