Environmental geochemistry for surface and subsurface waters in the Parijito Plateau and outlying areas, New Mexico

Blake, Wayne; Goff, Fraser; Adams, Andrew; Counce, Dale

This report contains a data base of major element, trace element, and isotope analyses of 130 water samples from 94 different springs, wells, and water bodies located in and around Los Alamos National Laboratory, New Mexico. Most waters in the study are calcium-bicarbonate waters. Well waters in the region generally have higher concentrations of conservative constituents than local surface waters because of their greater temperatures and ages at depth. Anthropogenic contamination, mixing with deep water, or significant water movement among aquifers can cause some cooler surface waters to actually become the most enriched in conservative constituents. The sites most impacted by man are located within Pueblo, Los Alamos, and DP Canyons, where the most likely contaminant sources are the older Laboratory facilities on the town mesa. Other impacted areas include the San Ildefonso reservation, where fertilizer and stock seem the most likely contaminant sources, and the southwestern part of the Laboratory, which at places shows slightly elevated lead. Only two samples in nitrate and three samples in lead exceed the EPA drinking water limits for any of the most common contaminants. Locations with tritium concentrations above 300 T.U. caused by Laboratory activities Include DP Spring at TA•21 (SS45 T.U.), the sewage outfall water at TA-21 (2800 T.U.), the drains at TA-33 (>1500 T.U.), and water residing in Test Well 2A (700 T.U. 3H in 1992 and 1993). The stable isotope analyses of waters in this study place the SD/o1SO ratio of most samples on or near the World Meteoric Water Line of Craig (1961) and the parallel Jemez Mountains line of Vuataz and Goff (1986). The stable isotopes indicate that most waters discharging in White Rock Canyon and located under the Pajarito Plateau and San Ildefonso reservation have been precipitated locally, or, possibly, have migrated from the north. These waters are isotopically different from those precipitated in the Valles Caldera and higher elevations in the Jemez Mountains. Waters in the confined aquifer described by Purtymun and Johansen (1974) have probably migrated from the Sangre de Cristo Mountains via western dipping strata in the Espanola Basin.