Ground-water hydrology and water quality of Irwin Basin at Fort Irwin National Training Center, California

Abstract

Geohydrologic data were collected from Irwin Basin at Fort Irwin National Training Center in the Mojave Desert of southern California by the U.S. Geological Survey during 1992-96 to determine the quantity and quality of ground water available in this basin. In addition to data collected from existing wells and test holes, 17 monitoring sites were constructed in Irwin Basin to provide data on subsurface geology, ground-water levels, and ground-water quality. Eleven of these sites were multiple-well monitoring sites that were constructed to provide depth-dependent geohydrologic data in the aquifer system. The aquifer system of Irwin Basin, defined on the basis of hydrologic data collected from wells in Irwin Basin, consists of an upper and a lower aquifer. A 1994 water-table contour map shows that a cone of depression beneath Irwin Basin well field has developed as a result of ground-water development. Water-quality samples collected from Irwin Basin wells to determine potential sources of ground-water degradation indicate that water in three areas in the basin contains high nitrate and dissolved-solids concentrations. The stable isotopes of oxygen and hydrogen indicate that present-day precipitation is not a major source of recharge in this basin. Tritium and carbon-14 data indicate that most of the basin was recharged before 1953 and that this water may be more than 14,000 years old. Purpose and ScopeThe objectives of this study were to describe the geohydrologic and geochemical framework of the ground-water basins that supply water to the base, to develop ground-water-flow models to help refine the understanding of the geohydrology of the basins, and to Previous StudiesPrevious studies by the U.S. Geological Survey include a hydrogeologic reconnaissance by Kunkel and Riley (1959) that identified unconsolidated waterbearing and consolidated nonwater-bearing deposits and established that Irwin, Bicycle, and Langford Basins were favorable for development of ground water. Yount and others (1994) did detailed geologic mapping in Irwin Basin and part of Langford Basin and determined the location of several faults on the base.Several consulting and engineering investigations have been completed for the base (C.F. Hostrup and Associates, 1955; James M. Montgomery and Associates, 1981; Wilson F. So and Associates, 1989) to determine the long-term availability of ground water for the Fort Irwin NTC. The Montgomery study in 1981 concluded that ground water was being mined from Irwin and Bicycle Basins. Wilson F. So and Associates (1989) determined that if projected Irwin Basin water demands were accurate, water levels would be "critically deep" at some time between the years 2011 and 2020.

Evaluation of land subsidence and ground failures at Bicycle Basin, Fort Irwin National Training Center, California, 1992–2017

“…Potential evapotranspiration was reported to be 3,760 mm (148 in.) annually in Death Valley, about 56 km (35 mi) northeast of the basin (Densmore and Londquist, 1997), and about 1,930 mm (76 in. ) at Newberry Springs, about 40 km (25 mi) to the south of the basin (David Inouye, California Department of Water Resources, written commun., 1996).…”

“…After a large crack formed in 2005-06 on Bicycle Lake playa, which is used as an aircraft runway to transport troops and supplies, a monitoring study was initiated by the U.S. Geological Survey (USGS) to help determine the cause. Groundwater has been pumped in the Bicycle Basin since the 1960s and the amount pumped has increased since the 1990s with the expansion of NTC activities and a reduction of pumping in the neighboring Irwin Basin in response to water-quality concerns related to wastewater disposal practices (Densmore and Londquist, 1997). Increased pumping in Bicycle Basin has resulted in more than 27 meters (m; 90 feet, ft) of water-level decline in wells north of the Bicycle Lake playa from 1990 to 2017.…”

Summary of hydrologic testing, wellbore-flow data, and expanded water-level and water-quality data, 2011–15, Fort Irwin National Training Center, San Bernardino County, California

“…Typical of desert regions, natural recharge is mainly limited to precipitation runoff and infiltration along ephemeral washes and near the base of the surrounding hills during winter rains and short summer thunderstorms (Densmore and Londquist, 1997). No perennial streams are present on the NTC (Mendez and Christensen, 1997).…”

“…Surface runoff drains to Langford Well Lake, but the low permeability of the playa sediments impedes groundwater recharge; thus, most runoff is lost to evaporation. Groundwater flows from Irwin Basin to Langford Basin beneath an unnamed wash paralleling the Garlic Spring fault (Densmore and Londquist, 1997;fig. 2).…”

“…Water levels have declined as a result of pumping in Bicycle and Langford Basins, however. Continued groundwater extraction and artificial recharge by infiltration have resulted in two unintended consequences: (1) land subsidence and earth fissuring in Bicycle Basin, presumably as a result of water-level declines, differential compaction, and tectonic forces, and (2) increased total dissolved solids (TDS) and nitrate concentrations in Irwin Basin as a result of infiltration of treated wastewater (Densmore and Londquist, 1997;Densmore, 2003). The U.S. Geological Survey (USGS) has been investigating groundwater-related concerns of the U.S. Army at Fort Irwin since the early 1990s.…”