Research about San Mateo Creek Basin

USGS2019

Differentiating anthropogenic and natural sources of uranium by geochemical fingerprinting of groundwater at the Homestake Uranium Mill, Milan, New Mexico, USA

A multiparameter geochemical-isotopic fingerprinting approach was used to differentiate natural and anthropogenic signatures of uranium contamination near the Homestake uranium mill site (Site), near Milan, New Mexico, USA. The Site consists of two tailings piles from milling operations and groundwater contamination from these tailings have been noted. The Site lies within the lower San Mateo Creek Basin with multiple regional sources of U contamination from mining and mill operations and is underlain by a heterogeneous alluvial aquifer, which is underlain by basement rock of the Chinle Group and the lowermost San Andres-Glorieta aquifer. To help decipher signatures, several statistical approaches were used including PCA, NMDS, and cluster analysis. Trilinear piper diagrams indicate two end member water types at the Site, sulfate-Na-K and sulfate-Ca. Natural alluvial aquifer groundwater in this area, relatively unaffected by mining or milling, appears to be more dominated by bicarbonate than sulfate and the deeper San Andres-Glorieta aquifer that has a mixture of sulfate and bicarbonate. Uranium concentrations from the Site fall into three broad categories, less than the drinking water standard of 30 µg/L (n=3), from 30 to 100 µg/L (n=9) and greater than 100 µg/L (n=8). Component loadings in a principal component analysis are highest for uranium isotopes, 228Ra, gross alpha-beta, molybdenum, chloride, uranium, and sodium, which affect the similarities or differences among wells sampled. Results suggest that several alluvial wells upgradient from the Site have anthropogenic fingerprints from regional sources related to upgradient mining. Wells with higher uranium concentrations have uranium activity ratios close to 1, which is indicative of mining or milling signatures. These same wells have elevated radon activities. This information can be used to inform Site managers on the source of water related to uranium at the Site and provide an approach for geochemical fingerprinting.

New Mexico↗

USGS2012

Geologic framework, regional aquifer properties (1940s-2009), and spring, creek, and seep properties (2009-10) of the upper San Mateo Creek Basin near Mount Taylor, New Mexico

The U.S. Geological Survey, in cooperation with the U.S. Forest Service, examined the geologic framework, regional aquifer properties, and spring, creek, and seep properties of the upper San Mateo Creek Basin near Mount Taylor, which contains areas proposed for exploratory drilling and possible uranium mining on U.S. Forest Service land. The geologic structure of the region was formed from uplift of the Zuni Mountains during the Laramide Orogeny and the Neogene volcanism associated with the Mount Taylor Volcanic Field. Within this structural context, numerous aquifers are present in various Paleozoic and Mesozoic sedimentary formations and the Quaternary alluvium. The distribution of the aquifers is spatially variable because of the dip of the formations and erosion that produced the current landscape configuration where older formations have been exhumed closer to the Zuni Mountains. Many of the alluvial deposits and formations that contain groundwater likely are hydraulically connected because of the solid-matrix properties, such as substantive porosity, but shale layers such as those found in the Mancos Formation and Chinle Group likely restrict vertical flow. Existing water-level data indicate topologically downgradient flow in the Quaternary alluvium and indiscernible general flow patterns in the lower aquifers. According to previously published material and the geologic structure of the aquifers, the flow direction in the lower aquifers likely is in the opposite direction compared to the alluvium aquifer. Groundwater within the Chinle Group is known to be confined, which may allow upward migration of water into the Morrison Formation; however, confining layers within the Chinle Group likely retard upward leakage. Groundwater was sodium-bicarbonate/sulfate dominant or mixed cation-mixed anion with some calcium/bicarbonate water in the study area. The presence of the reduction/oxidation-sensitive elements iron and manganese in groundwater indicates reducing conditions at some time or in some location(s) in most aquifers. Frequent detections of zinc in the alluvium aquifer may represent anthropogenic influences such as mining. Along the mesas in the upper San Mateo Creek Basin, springs that form various creeks, including El Rito and San Mateo Creeks, discharge from the basalt-cap layer and the upper Cretaceous sedimentary layers. Streamflow in El Rito and San Mateo Creeks flows down steep gradients near the mesas sustained by groundwater discharges, and this streamflow transitions to shallow groundwater contained within the valley alluvium through infiltration where the subsequent groundwater is restricted from downward migration by the shaly Menefee Formation. This shallow groundwater reemerges at seeps where the land surface has been eroded below the groundwater level. Spring- and creek-water samples contained small amounts of dissolved solutes, and seep water contained substantially larger amounts of dissolved solutes. The pH of water within the creeks was neutral to alkaline, and all locations exhibited well-oxygenated conditions, although typically at substantially less than saturated levels. Changes in the stable-isotope ratios of water between spring and summer samples indicate differences in source-water inputs that likely pertain to seasonal recharge sources. Results of the water-isotope analysis and geochemical modeling indicate little evaporation and chemical weathering at the spring and creek sites but stronger evaporation and chemical weathering by the time the water reaches the seep locations in the center of the upper San Mateo Creek Basin.

New Mexico↗