Occurrence of ground water near Ana Springs, Summer Lake Basin, Lake County, Oregon

Abstract

Ana Springs are near the north end of Summer Lake Basin, a closed fault-block basin in Lake County Oregon. The water of the springs rises by artesian pressure from lava-rock aquifers through about 150 feet of overlying thinly bedded lake deposits to discharge at the bottom of an impounding reservoir, the spring orifices being beneath 30 to 36 feet of water. On the valley floor less than a mile south and southwest of the reservoir artesian wells appear to tap the same lava rock from which the waters of the springs arise. Observations of the piesometric surface of the artesian water during flow tests show that three artesian wells, 30/16-1R1, 30/17-7D1, and -7F1, are hydraulically connected with a fourth, 30/16-1R2, and that well 30/16-1R2 is hydraulically connected with Ana Springs. A fifth artesian well, 30/16-12A1, did not show hydraulic connection with the other four wells during the short-term tests made. Mathematical constant derived from the tests permit calculations which indicate that the four wells, 30/16-1R1, -1R2, 30/17-7D1, and -7F1, when flowing at a combined rate of 4,600 gpm for 100 days, may lower the pressure head on Ana Springs by an amount equal to 2.7 feet of water, This lowering in pressure may cause a decrease in the rate of discharge of Ana Springs by about 4.4 cubic feet per second, or about 5 percent of the present wintertime rate of discharge. This diversion (5 percent) would be within the limit of error of single measurement of the the spring discharge. Chemical and temperature characteristics of thew Ana Spring water indicate it is similar to the water of the five lava-rock wells.