The Rio Grande Valley National Water‐Quality Assessment study unit encompasses about 45,700 square miles in Colorado, New Mexico, and Texas upstream from the gaging station Rio Grande at El Paso, Texas, and includes surface‐water closed basins east of the Continental Divide in New Mexico, and the San Luis Closed Basin in Colorado. The mean annual precipitation ranges from less than 6 to more than 50 inches; potential evapo‐transpiration ranges from less than 35 to more than 80 inches per year. Land use is mainly rangeland, forest land, and cropland. Total irrigated acreage in 1990 was about 914,000 acres and water use was about 3,410,000 acre‐feet. Two structural settings are found in the study unit: alluvial basins and bedrock basins. The alluvial basins can have through‐flowing surface water or be closed basins. The discussion of streamflow and water quality for the surface‐water system is based on four river reaches for the 750 miles of the main stem. The quality of the ground water is affected by both natural process and human activities and by nonpoint and point sources. Nonpoint sources for surface water include agriculture, hydromodification, and mining operations; point sources are mainly discharge from wastewater treatment plants. Nonpoint sources for ground water include agriculture and septic tanks and cesspools; point sources include leaking underground storage tanks, unlined or manure‐lined holding ponds used for disposal of dairy wastes, landfills, and mining operations.

science for a changing world Coordination among agencies and organizations is an integral part of the NAWQA Program. We thank the following agencies and organizations who directly participated in the Rio Grande Valley program.

Hydrologic testing was conducted in 1980 and 1981 at wells at hydrologictest pads H-7, H-8, H-9, and H-10 near the proposed Waste Isolation Pilot Plant site in southeastern New Mexico. Tests were conducted in three zones above the horizon of the proposed underground storage facility. The zones are the Magenta Dolomite Member of the Rustler Formation, the Culebra Dolomite Member of the Rustler Formation, and the Rustler Formation-Salado Formation contact zone. Data presented are from bailing tests, density profiles, shutin tests, slug tests, flow tests, pressure-pulse tests, and pumping tests.

The U.S. Geological Survey is investigating the geohydrology in the vicinity of the Waste Isolation Pilot Plant in southeastern New Mexico. Data presented in this report were compiled in support of a regional groundwater flow model. The data include water-level measurements obtained from the U.S. Geological Survey's GroundWater Site-Inventory and OMNIANA data bases and stratigraphic information interpreted from commercial geophysical logs. REFERENCE Davies, P.B., in press, Variable-density groundwater flow and paleohydrology in the region surrounding the Waste Isolation Pilot Plant (WIPP), southeastern New Mexico: U.S. Geological Survey Open-File Report 88-490.

The three water-bearing zones tested were the Magenta Dolomite Member of the Rustler Formation, Culebra Dolomite Member of the Rustler Formation, and the Rustler Formation-Salado Formation contact zone. Inflatable packers were used in a variety of test configurations. Tests conducted include bailing, recovery after perforation, shut in, slug, flow, and pressure pulse. Water-pressure response in the tested zone was monitored by a pressure-transducer system. Hydrologic testing was facilitated by using specially modified inflatable packers. These packers were inflated by filling the tubing with water. They were configured in three basic ways: Open-Casing Tests Open-casing tests included recovery from bailing and recovery after perforation. When recovery from bailing indicated a formation transmissivity greater than 1 foot squared per day, the yield was confirmed by using an opencasing slug-injection or slug-displacement test. The test wells were bailed to help develop the well, to remove foreign water used in testing, and to stress the well for a subsequent test. After bailing, very large or very small formation transmissivity sometimes precluded collection of recovery data. Bailing tests that did not have any recovery data are included in this report because the amount of fluid removed from a well may be significant for some purposes. Detailed discussion of bailing procedures and data collection is presented by Easier (1983, p. 15).