U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings
of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993,
Water-Resources Investigations Report 94-4015
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Uraniferous Waters of Southeastern Colorado: A Function of Geology,
Climate and Land Use
by
Robert A. Zielinski (U.S Geological Survey, Denver, CO) and Sigrid
Asher-Bolinder (U.S Geological Survey, Denver, CO)
Abstract
The effect of local geology and land-use practices on dissolved uranium
in water is indicated by reconnaissance sampling of surface waters and some
springs along the Arkansas River valley of southeastern Colorado. The rate
of increase of uranium concentration with distance downriver increases markedly
as the river flows from predominantly undeveloped lands underlain by igneous
and metamorphic rocks to agriculturally developed lands underlain by marine
shale and limestone. An additional abrupt increase in dissolved uranium
is observed along the section of river where discharge is greatly reduced
because of extensive diversions for irrigation and where remaining flow
is largely composed of irrigation return water. Water collected along this
last section of river is anomalously enriched in dissolved uranium compared
to the average concentration reported in water from outside of the irrigated
areas. As is commonly observed, dissolved uranium shows particularly strong
positive correlation with specific conductance. Uranium also shows strong
positive correlations with sodium, magnesium, sulfate and chloride that
contribute heavily to total dissolved solids and specific conductance in
these waters. Lithium, boron, strontium and selenium are also positively
correlated with uranium. The combination of natural weathering of uranium-bearing
soils and sediments, extensive soil leaching by irrigation return waters,
and evaporative concentration in a semiarid climate produce concentrations
of dissolved uranium that may threaten local water supplies.
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