STABLE-ISOTOPE STUDY OF SOIL-WATER, WIPP SITE NEW-MEXICO - ESTIMATIONOF RECHARGE TO RUSTLER AQUIFERS

Defining the hydrologic setting of the Waste Isolation Pilot Plant (WI PP) is an important step for site characterization and performance ass essment. From past research there is a controversy about the timing of recharge to the aquifers in the Rustler Formation which overlies the repository. The stable isotopic composition (delta D and delta(18)O) o f the water has been used in this argument but with ambiguous conclusi ons. Soil cores from WIPP have been sampled for delta D, delta(18)O, C l- and water content. The data indicate the there is a small amount of infiltration (.2 to 2 mm/yr) through the desert soil. The delta D and delta(18)O analyses suggest that meteoric water in the area can have a stable isotope composition similar to that in the Rustler Fm. Furthe r supporting evidence come from the isotopic composition of drip and p ool waters in nearby Carlsbad Caverns. This indicates that the water i n the Rustler Fm. need not have been recharged in the past (> 10,000 y rs.) under different climatic conditions.