Arsenic in groundwater in the Socorro Basin, New Mexico

Lynn Brandvold, New Mexico Bureau of Mines and Mineral Resources, Socorro, 87801


The presence of high concentrations of arsenic in the Socorro Basin groundwater is well known, but the distribution of arsenic in the basin has not been investigated. The object of this study was to investigate the levels and distribution of arsenic in groundwater in the Socorro Basin and the relationship, if any, of arsenic to other groundwater parameters. The data is presented as collected and with little interpretation. A total of 74 groundwater samples were collected and analyzed. The location of the wells extended from the Sevilleta Wildlife Refuge headquarters, just north of the Socorro Basin, to the Bosque del Apache Wildlife Refuge on the south. Arsenic distribution ranged from less than 2 ppb to 43 ppb. The wells north of the City of Socorro contained low arsenic (2-10 ppb) with only one exception. High arsenic levels (30 ppb or greater) occur in three separate areas: (1) the thermal springs located at the southwest corner of Socorro city limits, (2) three wells located 2-3 miles below San Antonio, and (3) the thermal well at the Bosque del Apache Wildlife Refuge. Eight wells have intermediate arsenic levels of 15-30 ppb. In a study of the Albuquerque basin, arsenic concentration correlated with many geochemical parameters; temperature, depth, fluoride, sodium, chloride, silica, and alkalinity. In this study there was only a negative correlation with hardness. The water varied in general composition within the basin, from the springs with low sodium, low hardness, and low TDS; to wells with high sodium, low hardness, and high TDS; to wells with low sodium and high hardness, and high TDS.