New Mexico Geological Society Annual Spring Meeting — Abstracts

A preliminary study of recharge at the Navajo Mine, based on a chloride mass-balance approach, indicated are charge rate of 0.51 mm/yr for both undisturbed upland flats (Fruitland) and depressions constructed during reclamation (spoil). As a check of these results, these settings were resampled for analysis of stable-isotope (oxygen 18 and deuterium) and natural tritium content of soil water.

Typical of arid settings, o¹⁸/D data from the upland flat plot along an evaporation line lying to the right of and diagonal to the meteoric water line. The evaporation line has a slope of 2.3 and a regression correlation coefficient of 0.95. Using R = (k/D)1/2 (where, R is recharge, k is a constant, and D is the displacement of deuterium from the meteoric line), a recharge value of 0.69 mm/yr is obtained. This compares well with the 0.51 mm/yr value obtained by the chloride method.

A tritium vs depth plot for the upland flat shows 1960 bomb peaks at a depth of 0.3-1.2 m, suggesting an unreasonable recharge rate of 61 mm/yr. These anomalous results apparently arise from movement of soil water in the vapor phase, as might be expected under these arid conditions.

Although chloride data seemed to suggest otherwise, isotope results for the reclaimed depression are incongruous, indicating that the soil-water chemistry there has not fully regained equilibrium in the 6 yrs since reclamation.

Tritium data were problematical, but stable-isotope results generally confirmed those of the chloride mass-balance method.