Vulnerability of ground water in the Tokio and Warwick aquifers to surface contamination, Fort Totten Indian Reservation, North Dakota

The vulnerability of ground water in the Tokio and Warwick aquifers to surface contamination was evaluated using existing hydrologic, climatic, geologic, topographic, and land-use/land-cover data and geographic information system procedures. The aquifers underlie parts of the Fort Totten Indian Reservation in northeastern North Dakota. The vulnerability was evaluated using vertical hydraulic leakance, depth to water, hydraulic conductivity, land use/land cover, land-surface slope, hydrologic sinks, and drainage basin areas. Data were discretized using a land-surface altitude grid divided into 50-foot-square cells. Vertical hydraulic leakance was determined by combining data from ring-permeameter and slug tests, land-use/land-cover data were obtained from data sets, and land-surface slope and hydrologic sinks were calculated from land-surface altitude data.

The vulnerability of ground water in the Tokio and Warwick aquifers to surface contamination is high in terms of land use/land cover and land-surface slope. The land surface of the Warwick aquifer also has numerous hydrologic sinks that result in areas of increased vulnerability of ground water to surface contamination.