In cooperation with the U.S. Air Force, the U.S. Geological Survey has collected hydrologic data about the Southern High Plains aquifer at Cannon Air Force Base in east-central New Mexico since 1994. Under the guidance of the State of New Mexico, ground-water quality of the aquifer has been analyzed as part of annual monitoring at regulated sites at the base. This report provides a summary and interpretation of all available hydrologic data collected by the U.S. Geological Survey for Cannon Air Force Base environmental managers for the regulated sites of Landfill 5 and the Sewage Lagoons between 1994 and 2005.

Cannon Air Force Base is in the Southern High Plains physiographic region, and saturated deposits of the Ogallala Formation underlying the base are within the western boundary of the Southern High Plains aquifer. The general direction of ground-water flow in the Southern High Plains aquifer at Cannon Air Force Base is from northwest to southeast. In 1962, ground water predominantly flowed northwest to southeast with minimal change in direction. Ground-water altitudes declined from 1962 to 1997, and a pronounced water-level recession (area of receding water level) developed northwest of the base, altering flow direction in this area. The recession northwest of the base and the subsequent change in direction of ground-water flow are indicative of local ground-water withdrawals upgradient from Cannon Air Force Base.

Historical water levels in wells within a 3-mile radius of Cannon Air Force Base declined in 52 of 56 wells for various periods of record between 1962 and 2004. Forty-three of the wells indicated strong linear decreases with time, and the largest decline was 91.80 feet, an average annual decline of about 2.13 feet per year. Water levels in monitoring wells at Cannon Air Force Base reflected the regional decline; water levels declined for all wells with periods of record greater than 1 year, and the decreases were strongly linear. From 1994 to 2005, rates of declining water levels at the base ranged from 1.45 to 1.64 feet per year near the Sewage Lagoons and from 2.24 to 4.01 feet per year near Landfill 5. The largest variation in water levels at Cannon Air Force Base was observed in wells C, D, and S, which are located adjacent to Landfill 5 near the southern boundary of the base and near an irrigation well immediately south of the base boundary. Water levels in these wells indicated a pattern of summer water-level decline followed by partial winter water-level recovery, which was likely a result of drawdown and recovery during the irrigation and nonirrigation seasons.

Ground-water sampling by the U.S. Geological Survey from 1994 to 2004 at monitoring wells associated with Landfill 5 and the Sewage Lagoons indicated temporal and spatial differences in water quality. At least one anthropogenic compound was detected in each monitoring well, but all concentrations detected were small and less than U.S. Environmental Protection Agency drinking-water standards. Anthropogenic compounds detected were either pesticide or industrial compounds. Perchlorate was detected in at least one sample from every well for which perchlorate was analyzed, and the source of perchlorate is likely natural and a result of atmospheric deposition. Trace-element concentrations in raw (pretreatment) ground water at Cannon Air Force Base were generally less than drinking-water standards (applicable to posttreatment samples), but maximum concentrations of aluminum, iron, and manganese exceeded secondary drinking-water standards, and maximum chromium concentrations exceeded the primary drinking-water standard.

Spatial and temporal differences of nitrate, major ions, and specific conductance indicated anthropogenic and natural influences on the Southern High Plains aquifer at Cannon Air Force Base. Larger nitrate concentrations decreased in ground water near the Sewage Lagoons during and following decommissioning of the lagoons, and concentrations decreased to levels detected in ground water in wells not affected by the infiltrated wastewater. Similar cation/sulfate ratios were present for ground water from nearly all wells, except for samples from certain wells along the southern boundary of the base and the background well for the Sewage Lagoon monitoring. Temporal changes in specific conductance also indicated the declining influence of the Sewage Lagoons but additionally provided evidence of natural spatial differences in water quality at Cannon Air Force Base similar to major-ion results. Spatial differences in major ions and specific conductance indicated that ground water at Cannon Air Force Base is likely a mixture of multiple sources from different formations or recharge areas.