Ground-water problems in the vicinity of Moscow, Latah County, Idaho

Abstract

The water supply in the Moscow area in southwestern Latah County, northern Idaho, presents a potentially critical problem because the present supply is barely adequate and the total supply available within the Moscow basin probably will become inadequate in the near future. The area includes about 60 square miles in the Moscow basin. An evaluation of the available geologic and hydrologic data, an estimate of the amount of usable ground water, and a description of the occurrence of ground water in the Moscow basin are presented in this report to assist city and State officials in appraising supplemental sources of water for municipal and other needs in Moscow and vicinity. Crystalline rocks of low permeability crop out in highlands north, east, and south of Moscow and are believed to underlie younger rocks throughout the basin. At places sand, gravel, silt, and clay resulting from weathering and erosion overlie the crystalline rocks, but at other places they interfinger with the Columbia River basalt and constitute the Latah formation. These sedimentary deposits form a permeable zone through which water moves from the surface and becomes confined in sand beds of the Latah formation and permeable zones in the Columbia River basalt. Quaternary eolian and fluviatile sediments compose the surface deposits which contain unconfined ground water, but the yield of water is small. Available data are insufficient to determine accurately the average annual recharge to the artesian aquifers. Natural and artificial discharge from the artesian aquifers in 1955 exceeded the recharge, and records of water levels in artesian wells have shown an annual decline for many years. The amount of water carried off by streams from the Moscow basin is estimated at 12,000 acre-feet yearly. The water in both the artesian and water-table aquifers is of the calcium bicarbonate type: It is moderately hard and contains relatively high concentrations of iron and silica. Reduction of the hardness and the iron content would make the water more suitable for municipal, domestic, and industrial use. The demand for water in Moscow in 1970 is expected to be double that of 3955, thereby increasing the rate of overdraft on the artesian aquifers. Surface water is suggested as a direct supplemental source and for possible artificial recharge of the artesian aquifers as a means of increasing the yield of the present source. 325 326 CONTRIBUTIONS TO HYDROLOGY