Report Abstract

GEOHYDROLOGIC SITE CHARACTERIZATION OF THE MUNICIPAL SOLID WASTE LANDFILL FACILITY, U.S. ARMY AIR DEFENSE ARTILLERY CENTER AND FORT BLISS, EL PASO COUNTY, TEXAS

By Cynthia G. Abeyta

Geohydrologic conditions of the Municipal Solid Waste Landfill Facility (MSWLF) on the U.S. Army Air Defense Artillery Center and Fort Bliss, El Paso County, Texas, were evaluated by the U.S. Geological Survey in cooperation with the U.S. Army. The 106.03-acre MSWLF has been in operation since January 1974. The landfill contains household refuse, Post solid wastes, bulky items, grass and tree trimmings from family housing, refuse from litter cans, construction debris, classified waste (dry), dead animals, asbestos, and empty oil cans.

The MSWLF, located about 1,200 feet east of the nearest occupied structure, is estimated to receive an average of approximately 56 tons of municipal solid waste per day and, at a fill rate of 1-4 acres per year, is expected to reach its capacity by the year 2004. The MSWLF is located in the Hueco Bolson, 4 miles east of the Franklin Mountains. Elevations at the MSWLF range from 3,907 to 3,937 feet above sea level. The climate at the MSWLF and vicinity is arid continental, characterized by an abundance of sunny days, high summer temperatures, relatively cool winters typical of arid areas, scanty rainfall, and very low humidity throughout the year. Average annual temperature near the MSWLF and vicinity is 63.3 degrees Fahrenheit and annual precipitation is 7.8 inches. Potential evaporation in the El Paso area was estimated to be 65 inches per year. Soils at and adjacent to the MSWLF are nearly level to gently sloping, have a fine sandy loam subsoil, and are moderately deep over caliche.

The MSWLF is underlain by Hueco Bolson deposits of Tertiary age and typically are composed of unconsolidated to slightly consolidated interbedded sands, clay, silt, gravel, and caliche. Individual beds are not well defined and range in thickness from a fraction of an inch to about 100 feet. The primary source of ground water in the MSWLF area is in the deposits of the Hueco Bolson. A relatively thick vadose zone of approximately 300 feet overlies the aquifer of the Hueco Bolson deposits in the vicinity of the MSWLF. A deep water table prevails for all of the study area. Whether any perched water zones exist below the MSWLF is unknown. Under current conditions, extensive ground-water development by the City of El Paso encompasses the MSWLF. Hydraulic characteristics of the Hueco Bolson vary significantly as a result of the nonuniform nature of the individual beds. Wells in the vicinity of the MSWLF range in depth from about 600 feet to greater than 1,200 feet. Recharge resulting from direct infiltration of precipitation is minor due to the high evaporation and low precipitation rates. The hydraulic gradient in the vicinity of the MSWLF is generally to the south but may vary due to pumpage of a well located on the northeast corner of the perimeter boundary. Ground-water monitoring data for the MSWLF vicinity show a water-level decline of 55.65 feet from November 1958 to December 1987. Depth to water at the northeast corner of the MSWLF as of July 26, 1994, was 325.8 feet below land surface.

The city-operated Shearman Well Field, located north of the MSWLF, is a primary source of ground water for the City of El Paso. The test-pumping rate of well JL-49-05-914 (the well nearest to the MSWLF having test-pumping data) was 1,972 gallons per minute on July 20, 1992; the static water level prior to pumping was 317.54 feet below land surface. El Paso Water Utilities reports that the pumping level after 8 hours of pumping was 367.80 feet below land surface, resulting in a drawdown of 50.26 feet, transmissivity of 22,200 feet squared per day (166,000 gallons per day per foot), and specific capacity of 39.2 gallons per minute per foot of drawdown. After the well was shut off, the well recovered to a static water level of 317.46 feet below land surface on July 21, 1992.

Ground water in the El Paso area is chemically suitable for most uses. El Paso Water Utilities reports that concentrations of dissolved solids in the vicinity of the MSWLF generally range from 297 to 625 milligrams per liter (wells JL-49-05-904 and JL-49-05- 915, respectively).

Abstract from Water-Resources Investigations Report 95-4217



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