Upward-leaking brine, from a confined aquifer at the base of the Rustler Formation, mixes with fresher water in a shallow aquifer, resulting in discharge to the Pecos River in southern Eddy County, New Mexico, of about 0.5 cubic feet per second of saturated brine. Pumping brine from the aquifer at a rate greater than 0.5 cubic feet per second lowered the potentiometric head in the confined aquifer.
From July 22, 1963 through December 1968, approximately 3,Et73 acre-feet of brine had been pumped. Total brine storage in July 1963 was 540 acre-feet, including about 200 acre-feet of salt precipitate. From 1963 to 1968, water downgradient of the storage depression increased in chloride concentration by amounts ranging from 1,500 to 99,400 milligrams per liter, and water levels near the depression increased over 3 feet.
For water years 1952-63, the Pecos River gained about 240 tons per day of chloride in the reach from Malaga gaging station to Pierce Canyon Crossing. In the same reach, the average chloride gain to the Pecos River from July 1963 to August 1966 was 167 tons per day; in 1967-68 the gain increased to 256 tons per day following a major flood in August 1966.
Seepage investigations made prior to pumping of the brine aquifer show that the main area contributing brine to the river was located between the Malaga gage and well USGS 11. In 1968 most of the brine inflow apparently entered the river downstream of the Malaga-USGS 11 reach. The head in the brine aquifer was lowered and discharge to the river was decreased above the Malaga gage. Leakage from the depression contributed salts to the river below the Malaga gage during brine pumpage.
