Investigation of artificial recharge of aquifers in Nebraska
Large withdrawals of ground water for irrigation are causing progressive declines of ground-water levels in some areas of Nebraska. An investigation was conducted to determine the technical feasibility of artificially recharging aquifers through wells and through surface spreading by means of impoundments, pits, and canals. Information gained from a literature search and from preliminary tests was used to design several artificial-recharge experiments. The experiments showed that large quantities of water can be recharged through wells and by surface spreading if conditions are favorable. In the well experiments, about 0.5 billion gallons of water from an aquifer recharged by the Platte River was transported 3 miles by pipeline and recharged through a well into a Pleistocene sand and gravel aquifer near Aurora where ground-water levels are declining. The recharge rate was about 730 gallons per minute during two tests of 6 and 8 months duration. The rise in ground-water levels due to recharge extended more than a mile from the recharge well in both tests. The pattern of ground-water-level buildup during the 8-month test was similar to that during the 6-month test. Two-thirds of the way through the test the rate of water-level buildup in the recharge well increased greatly because casing failure allowed a large amount of sediment to enter the well. Although the chemical quality of the recharge water was markedly different from that of the native aquifer water, no evidence of clogging due to chemical reaction was detected; also, there was no evidence of clogging due to air entrainment or bacterial growth. Evaluation of water-level changes in the recharge well and in observation wells during the 6-month test indicated some clogging of the aquifer in the immediate vicinity of the recharge well due to a small amount (0.04 milligram per liter) of fine sediment in the recharge water. Analysis of water-level buildup in the recharge well during the 6-month test indicated that recharge could have continued at a rate of about 700 gallons per minute for several years before rehabilitation of the recharge well would have been necessary. In surface-spreading experiments, the maximum sustained infiltration rates from a 24-foot-diameter ring infiltrometer set in loess at the well-recharge site near Aurora were about 0.5 foot per day during a 140day test. The recharge water caused water levels in a perched zone of saturation at depths between 36 and 38 feet to rise 15 feet, to within 21 feet of the surface, indicating that if the test had continued or if the impoundment area had been larger, the water level in the perched zone of saturation might have risen to the surface thereby reducing the infiltration rate. The maximum sustained infiltration rate from a similar experiment in the Sand Hills near Tryon was 11 feet per day. Perching layers also retarded downward infiltration and caused lateral movement of water in the subsurface at this site. Infiltration rates from re-use pits near the Aurora site ranged from 0.01 to 1.60 feet per day, indicating that the permeability of the subsurface material is extremely variable and that perching layers probably are absent in some areas. Flow measurements in an irrigation canal excavated in loess near Farwell indicate an infiltration rate of 0.36 foot per day from a 2.7mile reach.