Civil Engineering ETDs

Publication Date

Spring 4-3-2017


Chemical and isotopic signatures were used to discriminate between anthropogenic ground water and naturally occurring constituents. The U-234/U-238 activity ratio (AR) was determined in 34 samples from several aquifers underlying two former uranium mills near Milan, NM. Disposal of uranium ore waste into unlined tailings resulted in ground water contamination in the Lower San Mateo Creek Basin area. Ground water contamination from uranium mills have impacted the local ground water for residents down-gradient from the mills.

Previous studies that used uranium isotopes identified activity ratios of mill-derived uranium were near the secular equilibrium of 1, and those from natural ground waters were greater than 1.3. Background water quality show uranium concentrations close to 10 μg/L and AR values above 1.5. Concentrations of uranium down-gradient from the two milling sites had elevated levels of uranium from 31.7 to 1290 μg/L and AR values near 1.

This research utilized several techniques for identifying the source of ground water contamination near two former uranium mills. Analysis of the major ion chemistry indicated similarities in ground water near both sites and were Na-Ca/SO4-HCO3 dominant. Oxygen and hydrogen isotopic analyses found the source of the water to be meteoric. There was little to no correlation between U and Mo in the ground water near both sites; however, samples from both sites had strong correlations between U and Se. Dissolved sulfate in Bluewater monitoring wells ground water were enriched with 34S, while wells near Homestake had ground water that were depleted in 34S. Chemical and isotopic analysis and water quality results indicate that the wells with elevated levels of contaminants were likely from anthropogenic sources and not naturally occurring ground water.


Contaminants, Ground Water, Isotopes, Uranium, Homestake Mill Site, Water Fractionation

Document Type




Degree Name

Civil Engineering

Level of Degree


Department Name

Civil Engineering

First Committee Member (Chair)

José M. Cerrato Corrales

Second Committee Member

Bruce M. Thomson

Third Committee Member

Patrick V. Brady