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Data on chemical composition of ground water collected from the "post-Middle Chadron" Oligocene strata are compared with those from water of the basal Chadron hydrological unit in an area near Crawford, Nebraska, where uranium mineralization is known to occur. Uncorrected Eh values, using a calomel reference electrode, indicated water from the "post-Middle Chadron" Oligocene unit was positive, whereas water from the basal Chadron was negative. The basal Chadron waters contained lower levels of calcium and uranium and higher concentrations of sodium, chloride, sulfate, and total dissolved solids, than did waters from the "post-Middle Chadron" Oligocene zone. Radon and radium concentrations in the water samples from the basal Chadron unit fluctuated widely. Radium levels in the oxidizing waters were consistently low (<2 pCi>/l), while radium in several water samples from the reduced unit exceeded the maximum recommended level of 5 pCi/l for drinking purposes. These samples, however, are not used domestically.
Radon and radon daughter products in air were also evaluated on a limited basis. Their concentrations appeared similar to reported background levels in other midwestern regions.