Groundwater from Lower Cretaceous rocks in Kansas

Abstract

Sandstones in Lower Cretaceous rocks contain supplies, of water that may be adequate to meet increasing present and future demands for supplemental municipal and domestic use in central and western Kansas. An estimated 70 to 80 million acre-feet (86,000 to 99,000 cubic hectometers) of water containing less than 1,000 milligrams per liter dissolved solids may be acceptable for use at the present (1976). An additional 10 to 15 million acre-feet (12,000 to 18,000 cubic hectometers) containing 1,000 to 3,000 milligrams per liter dissolved solids is estimated to be available for use in the future with appropriate desalinization. Lower Cretaceous rocks crop out from Washington County on the north to Comanche County on-the south. The rocks dip from a structural high in the southwest part of the State to structural lows in the northwest and north-central part. Depth below land surface increases generally northwestward to about 2,600 feet (790 meters); thickness of the rocks increases westward, nearly zero to about 850 feet (260 meters). The rocks consist chiefly of marine to nonmarine shale and silt- stone interbedded with coastal to deltaic sandstone. The interbedded sandstone, which composes about one-third of the rocks, consists of one or more lenses that thicken westward to about 400 feet (120 meters) in the central part of western Kansas. The yield of water to individual wells is related to areal extent, thickness, and interconnection of the sand lenses and to grain size and cementation of the sand. Large amounts of water may be pumped by wells where loosely cemented sand lenses are interconnected. Wells commonly yield adequate supplies for domestic and stock use; reported yields from municipal and irrigation wells range from about 100 to 2,000 gallons per minute (6 to 125 liters per second). Recharge to the Lower Cretaceous-rocks occurs in the area of outcrop and from hydraulically connected saturated Cenozoic rocks, especially in the southern part of the State. Movement of water is principally northeastward from areas of recharge to areas of discharge where streams intersect the sandstone outcrops. Water in the sandstone aquifers commonly is confined between beds of relatively impermeable shale, causing water in wells to rise above the top of the aquifer. Water levels fluctuate in response to changes in atmospheric pressure, recharge, and discharge; greatest fluctuations result from discharge to wells for municipal and irrigation use. Progressive declines in water levels have occurred where irrigation withdrawals exceed recharge. Calcium bicarbonate water is dominant near recharge areas; mixed sodium and calcium bicarbonate water and sodium chloride water become successively dominant as the water moves downgradient from the recharge areas. The quality of water ranges from fresh to very saline (less than 1.000 to 35,000 milligrams per liter dissolved solids). In the areas of generally fresh water, localized areas of calcium sulfate water result from solution of gypsum in the Kiowa Formation, and areas of sodium chloride water result from contamination by oil-field brines.