The Permian-age Capitan reef is a confined aquifer that is recognized by the New Mexico Office of the State Engineer and U.S. Geological Survey as a significant brackish water resource with a history of industrial use.
The Capitan aquifer is the most viable water supply option for the Ochoa project because (1) no water rights are needed to develop deep brackish water in New Mexico, (2) the New Mexico Office of the State Engineer and Bureau of Land Management are both supportive of the use of deep brackish groundwater for industrial purposes, (3) there is a track record of previous deep brackish groundwater development from the Capitan Reef, and (4) the hydrogeology of the system is favorable in that there would be no expected impacts on other water-right holders.
The Capitan aquifer is composed of the Capitan Formation, parts of the Goat Sheep Formation, and the Artesia Group (all referred to as the Capitan Reef complex). The Capitan Reef complex is a horseshoe-shaped limestone deposit surrounding the Delaware Basin, and is present in southeastern New Mexico and western Texas. The complex extends over a distance of approximately 200 miles. Within Lea County, the aquifer ranges from 800 to 2,200 feet thick and is approximately 12 miles wide near the Eddy County and Lea County boundary and 6 miles wide near Jal, New Mexico.
Brackish groundwater from the Capitan Reef has been used historically for secondary oil recovery, thus establishing a precedent for using this resource for industrial purposes. Historical sources discuss a number of brackish groundwater development projects in the Capitan Reef, including the Jal Water System near Jal, New Mexico, and El Capitan Well Field near Kermit, Texas.
The El Capitan system was developed in the mid-1960s by Shell Oil as a water source for secondary oil recovery. These wells were completed in the Capitan Reef with plans to pump up to 28,000 acre-feet per year. The New Mexico Office of the State Engineer documented water use from this well field in the range of 8,000 acre-feet per year in 1964, expected to be in the range of 13,000 acre-feet per year in 1965. In 1965, the estimated total fluid withdrawals from the Capitan Reef in Texas were in the range of 30,000 to 40,000 acre-feet per year from 1945 to 1965.
Thus there is clear evidence of significant historical usage of brackish water from the Capitan Reef, indicating a high probability of success for its use as a supply source for the Ochoa project.
The total water demand for the project is expected to be approximately 2,000 gallons per minute. Of the total supply required for the project, approximately 73% of the total supply (or 1,460 gpm) will be used for ore processing and 27% of the total supply (or 540 gallons per minute) will be treated to drinking water standards and provided to the plant facilities building.
ICP intends to use a desalination system to treat the brackish water obtained from the Capitan Reef. A preliminary design for the desalination system has been developed. The reverse osmosis (RO) water treatment system was designed assuming the Capitan Reef well water contains Total Dissolved Solids of 10,000 parts per million and is close to calcium sulfate saturation. The preliminary system includes a design feed rate of 4,000 gallons per minute (a high, conservative estimate) and will operate at a recovery rate estimated to be greater than 90% to provide at least 3,600 gallons per minute of purified water containing less than 250 parts per million of Total Dissolved Solids. The primary system consists of three skids, each providing 1,000 gallons per minute of low- Total Dissolved Solids source water. The secondary system includes an interstage precipitation reactor and will treat the concentrate stream from the primary system to recover an additional 750 gallons per minute of low- Total Dissolved Solids water, resulting in a final concentrated stream of only 250 gallon per minute. The membrane skids, interstage precipitation reactor, and associated pumps, tanks, motor control center (MCC) room, and cleaning skid will require a building approximately 125 feet long and 70 feet wide. The total power requirement for the entire system is approximately 2,000 kilowatts.