New Mexico Geological Society Annual Spring Meeting — Abstracts

Traditional methods for detennining health threats due to lead (Pb) contamination do not fully characterize Pb availability. Standard U.S. Environmental Protection Agency (EPA) procedures reveal total Pb concentration in ppm using a portable X-ray fluorescence unit (XRF), but this procedure may not be truly indicative of a particular site's health hazards. The abandoned Cuba Smelter site is such a site. At the Cuba Smelter site, elevated Pb levels in soils range from 900-9600 ppm. Whereas background-levels are near 50 ppm. Based on the EPA's "action level" of 500-1000 ppm Pb the site poses a possible health hazard for nearby residents. Several factors beyond metal concentration, such as mineralogy, must be considered.

Sampling was conducted in January of 1993. Thirty-three soil samples of the upper three inches of loose surficial material were collected for particle size, chemical, and X-ray diffraction (XRD) analyses. The soil's Pb concentration, pH, acid-neutralizing potential (ANP) and net-acid-producing potential (NAPP) were detennined. Five samples were impregnated with epoxy to preserve soil textures arid relationships. After impregnation the samples were cut and mounted as thin sections for petrographic and microprobe analyses.

XRD has shown the dominant soil minerals are quartz, feldspar, calcite, and clay minerals. Chemical analyses including pH, ANP and NAPP indicate an alkaline environment. Examination with the microprobe shows galena as the main Pb bearing phase. Each galena grain examined has an aluminosilicate coating.

Mineralogical and textural examination of the Pb contaminated soils from the Cuba Smelter site indicate airborne and onsite/direct contact pathways are the most significant threat. If ingested, Pb may be soluble in the digestive tract due to lack of anglesite annoring. However, an aluminosilicate coating encases the Pb grains and may act to retard dissolution in the digestive tract. Pb is immobile in the alkaline soils of the Cuba Smelter site and consequently is not a threat to the local ground water.