Potentiometric surfaces, summer 2013 and winter 2015, and select hydrographs for the Southern High Plains aquifer, Cannon Air Force Base, Curry County, New Mexico

Abstract

Cannon Air Force Base (Cannon AFB) is located in the High Plains physiographic region of east-central New Mexico (Miller, 2000), about 5 miles west of Clovis, N. Mex. Cannon AFB was originally established as a U.S. Army base in 1942 and then reactivated as the current Air Force base in 1951 following the U.S. Army base closure in 1947. The area surrounding Cannon AFB is primarily used for agriculture, including irrigated cropland and dairies. The Southern High Plains aquifer is the principal source of water for Cannon AFB, for the nearby town of Clovis, and for local agriculture and dairies (EPCOR Water, 2014). The Southern High Plains aquifer in the vicinity of Cannon AFB consists of three subsurface geological formations: the Chinle Formation of Triassic age, the Ogallala Formation of Tertiary age, and the Blackwater Draw Formation of Quaternary age (Langman and others, 2006). The Chinle Formation, 0–400 feet (ft) thick and locally known as the “red beds,” consists mostly of clay with some interbedded sand and silt in this area and forms the bottom of the unconfined Southern High Plains aquifer (Langman and others, 2006). The Ogallala Formation, 30–600 ft thick (Gustavson, 1996), is the main wateryielding formation of the Southern High Plains aquifer and consists of eolian sand and silt and fluvial and lacustrine sand, silt, clay, and gravel (McLemore, 2001). The Blackwater Draw Formation, 0–80 ft thick, overlies the Ogallala Formation and consists mainly of eolian sand (McLemore, 2001; Langman and others, 2006). Groundwater-supplied, center-pivot irrigation (the circular features on figs. 1 and 2) dominates pumping from the Southern High Plains aquifer in the area surrounding Cannon AFB, where the irrigation season typically extends from early March through October (Marsalis, 2007; oral commun. with local farmers). The U.S. Geological Survey (USGS) has a long history of groundwater hydrology and water-quality work on and surrounding Cannon AFB, with the most recent publications, Langman and others (2004) and Langman and others (2006), covering a period of study from 1994 to 2005. In addition, the USGS has been monitoring groundwater levels in the vicinity of Cannon AFB since 1954. Langman and others (2006) reported that groundwater levels have declined in the Cannon AFB and surrounding area and noted that summer water-level declines were followed by partial recovery during the winter. Prior to this study, the most recent potentiometric-surface map in the study area was developed by Langman and others (2006) by using groundwater levels measured during the winter of 1997. The 1997 potentiometric-surface map was developed by using data from approximately 27 wells located on Cannon AFB and in the surrounding area within about 3 miles of the boundary of the base. The 1997 potentiometricsurface map indicated a general northwest to southeast groundwater-flow direction, consistent with potentiometric-surface maps for groundwater conditions observed in 1962, 1967, 1977, and 1987 (Langman and others, 2006). In addition to the general northwest to southeast groundwater-flow direction observed in all these periods, a groundwater trough running diagonally from the northwest to the southeast becomes successively more distinct throughout the 1962–97 series of potentiometric-surface maps as the regional groundwater level declines (see fig. 3 in Langman and others, 2006). The potentiometric-surface maps developed by Langman and others (2006) are useful in determining the regional direction of groundwater flow; however, the sparse number and distribution of wells used to create these potentiometricsurface maps (approximately one well every 3 square miles) resulted in maps that are too general for determining detailed groundwater-flow directions on a local scale. The USGS in cooperation with the Air Force Civil Engineering Center, San Antonio, Texas, investigated the possible effects of seasonal groundwater-use differences (summer and winter) on groundwater-flow directions in the vicinity of Cannon AFB. To determine more local groundwater-flow directions, data from a dense well network in this study area were needed. In addition, because only groundwater levels measured during winter periods were used in the development of the Langman and others (2006) potentiometric-surface maps, an increased understanding of the effect of summer groundwater levels on the groundwaterflow directions was also needed.