Results of a reconnaissance water-quality sampling program of the Ogallala aquifer in Colorado, Kansas, Nebraska, Oklahoma, South Dakota, and Texas

Results of a reconnaissance water-quality sampling program of the Ogallala aquifer indicates the water generally is suitable for most uses. Fluoride and selenium were the only chemical constituents found to exceed the National Interim Primary Drinking Water Regulations in water from some of the wells.

Unusually large silica concentrations in many of the water samples probably were due to the presence of amorphous silica in relatively young volcanic-ash deposits present in the aquifer. Because the greatest silica concentrations (as much as 65 milligrams per liter) occurred in the Northern part of the aquifer, the volcanic source was probably from the northwest.