News Release, Kansas Geological Survey, Oct. 28, 1996
Survey geohydrologist Don Whittemore will present the results of his study of the movement of poor-quality water in the Arkansas at the annual meeting of the Geological Society of America in Denver on Oct. 28.
Whittemore analyzed water from the river for the past three years, and has compiled earlier studies of water from the Arkansas. His findings show that the quality of river water is particularly bad during dry times, but remains a problem even when the river carries larger amounts of water.
Since the late 1970s, the Arkansas has generally been dry through much of western Kansas. Small amounts of water flow in the Arkansas where it enters western Kansas, mostly water that has been released from John Martin Reservoir in eastern Colorado and return flow from irrigation--water that has moved over fields and is directed back into the river. That small stream of water in the Ark, however, usually dries up before it reaches Garden City.
Whittemore's work shows that the river is saline and contains high levels of sulfate during these times of low flow, with sulfate concentrations as high as 2400 parts per million (or milligrams per liter). The maximum level for sulfate in drinking water has been proposed at 400 parts per million by the Environmental Protection Agency.
According to Whittemore, the elevated sulfate and salinity levels are caused by minerals that are naturally present in the water, but their levels are greatly increased by evaporation, particularly during irrigation. Water evaporates when it is stored in eastern Colorado reservoirs and when it moves across the land during irrigation. Evaporation concentrates minerals in the water, much the way they are concentrated in a pan of water that is heated on a stove. Water is also returned to the atmosphere by irrigated crops, which concentrates minerals in the water left behind.
When flows in the Arkansas are heavier, dilution improves the quality of river water, though it is still high in minerals. In 1995, the river flowed across western Kansas during much of July and August because of heavy snow melt in the Colorado Rockies and rains in eastern Colorado. Whittemore's analyses showed that the freshest water was still slightly saline, and that its sulfate levels were as high as 700 parts per million.
Mineralized water in the Arkansas is a particular problem because much of the river's flow currently soaks into the alluvial aquifer--the water-bearing sands and gravels that surround the river bed--then moves into the underlying Ogallala aquifer. The High Plains aquifer in southwestern Kansas includes both the Ogallala and alluvial aquifers.
"This mineralized water is contaminating the Ark River Valley," said Whittemore. "Based on current conditions, in about 40 years river water seepage has the potential to contaminate all of the High Plains aquifer underlying a 500-square mile corridor of the valley."
That contamination could be slowed by underground layers of clay or silt that retard movement of the water. Additional flows of fresh water in the Arkansas River would also lessen the contamination.
"Some of the groundwater that could be contaminated is the sole source of water for towns in the area," said Whittemore. "It's important that we manage and protect that fresh groundwater for municipal, agricultural, and industrial uses."
Whittemore's study is funded by the Kansas Water Plan, with assistance from several state and local water agencies. For more information, contact Don Whittemore (785-864-3965)