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Ongoing investigations of the permafrost and ground water conditions in the north-central area of the Fort Wainwright, Alaska, cantonment, north of the Chena River, show the hydrogeology of the site to be extremely complex. Permafrost, being impermeable and discontinuous, controls the distribution and dimensions of ground water aquifers to a great degree. Aquifers are above, below, and adjacent to permafrost, and in some locations are within unfrozen zones surrounded by it. This complexity makes it difficult to predict the direction and velocity of ground water flow, as well as its seasonal and annual variability. Data have been obtained from ground-penetrating radar surveys, borehole logs, and ground water instruments. They have then been combined with interpretations of aerial photographs and ground observations to delineate the permafrost and aquifer distribution. They have also been used to develop conceptual hydrogeological models of the area. This information is necessary to remediate ground water contamination, while furthering the basic understanding of aquifer distribution and ground water flow in discontinuous permafrost terrain.

The Poleline Road Disposal Area, located on Fort Richardson, Alaska, was a U.S. Army dump in the early 1950s. In 1990 it was identified as an area potentially contaminated with volatile organic compounds. CRREL conducted extensive geophysical investigations that delineated anomalous responses in many areas of burial within glacial outwash deposits. Ground penetrating radar and electromagnetic induction surveys were used prior and subsequent to excavation. Geophysical data collected on a 5-m grid defined locations for several anomalous areas containing both dispersed and large, discrete targets. Radar defined anomalous areas by the concentration of strong diffractions. The induction survey differentiated metallic from nonmetallic contaminations. The interpreted maximum depth of debris was 4 m. Uncontaminated areas were generally defined by continuous, horizontal radar reflections, suggesting undisturbed or compacted soil horizons. The anomaly maps produced from these surveys guided an excavation that removed hazardous material. The removed material included munitions, mustard gas cylinders, medical waste, steel drums, and other trash. The radar and electromagnetic surveys were repeated using a more closely spaced grid to verify that the excavated areas were clean and to define more precisely anomalies in the areas not excavated. That survey shows many targets of potential or present contamination that should be removed.

The hydrogeology of Fort Wainwright, Alaska, is extremely complex because of the relatively impermeable discontinuity of permafrost, which controls the distribution and dimensions of the aquifer. Aquifers occur above, below and adjacent to permanently frozen materials, as well as within thaw zones surrounded by permafrost. This complexity makes it difficult to predict the direction and rate of ground water flow, as well as its seasonal and annual variability. Considerable problems exist in locating suspected contaminant plumes, identifying source areas, defining transport paths and evaluating contaminant fate. This report summarizes the results of ongoing investigations of the permafrost and ground water conditions within the northwestern part of the Fort Wainwright cantonment area, north of the Chena River. Data from ground-penetrating radar, drilling, ground water flow sensors, aerial photographs and ground observations were used to delineate aquifer distribution and develop a conceptual physical model of hydrogeological conditions. Ground water seepage velocity and direction, which were measured during early to mid-winter 1994-95, reflect the role of local water sources and permafrost distribution in determining ground water flow patterns. Other factors, including the vertical and lateral extent of permafrost, a bedrock aquifer, and the alluvial origins of unfrozen sediments and landforms, are apparently more important than the subregional aquifer in determining ground water conditions during winter. Contaminant migration will be strongly affected by these factors as well.