Environmental geophysics and sequential aerial photo study at Sunfish and Marsden Lakes, Twin Cities Army Ammunition Plant

摘要

Geophysical studies at Site H of Twin Cities Army Ammunition Plant have delineated specific areas of dumping and waste disposal. Anomalous areas noted in the geophysical data sets have been correlated with features visible in a chronological sequence of aerial photos. The photos aid in dating the anthropogenic changes and in interpreting the geophysical anomalies observed at Site H and across Sunfish Lake. Specifically, two burn cages and what has been interpreted as their surrounding debris have been delineated. The areal extent of another waste site has been defined in the southwest corner of Area H-1. Depth estimates to the top of the Area H-1 anomalies show that the anomalies lie below lake level, indicative of dumping directly into Sunfish Lake. Except for these areas along the northwestern shore, there is no evidence of waste disposal along the shoreline or within the present-day lake margins. Magnetic, electromagnetic, and ground-penetrating-radar data have pinpointed the locations of mounds, observable in aerial photos, around the first burn cage. The second burn cage and its surrounding area have also been clearly defined from aerial photos, with support from further geophysical data. Additional analysis of the data has yielded volumetric estimates of the amount of material that would need removal in the event of excavation of the anomalous areas. Magnetic and electromagnetic profiles were also run across Marsden Lake. On the basis of these data, it has been concluded that no large-scale dumping has occurred in or around Marsden Lake.