CONTAMINANT CONCENTRATIONS IN WATER AND BRYOPHYTES FOUND IN FOUR SPRINGS LOCATED ALONG THE UPPER RIO GRANDE, NEW MEXICO

In 2004, the New Mexico Environment Department (NMED), Department of Energy Oversight Bureau analyzed samples of water and bryophytes (aquatic mosses) from Springs 4A and 4C near Los Alamos National Laboratory (LANL), and two other springs located 70 km and 125 km upstream on the Rio Grande. Springs 4A and 4C discharge from the upper portion of the regional aquifer or from deep perched intermediate units beneath the Pajarito Plateau. The upstream springs discharge from Rio Grande basin sediments and are tritium-free indicating very old water (>100 years), and are used to represent background conditions. In 2003, an independent investigator reported detections of ¹³⁷Cs in both water and bryophytes at levels below standard reporting limits from Spring 4A and attributed those detections to past LANL disposal practices.

Spring samples were analyzed for ¹³⁷Cs, ³H, ⁹⁰Sr, ²³⁸Pu, ^239/240Pu, perchlorate, major anions, dissolved and total metals. Bryophytes were oven-dried for low-level perchlorate analysis, and reduced to ash for analysis for ¹³⁷Cs and other gamma-emitting radionuclides, ⁹⁰Sr, ²³⁸Pu, ^239/240Pu, and total metals. One hundred liters of water from each spring were purged through a series of filters to determine if colloidal or dissolved ¹³⁷Cs was detectable in the spring waters. The final filter was a 3M Cesium Rad Disk™ which was used to extract ¹³⁷Cs present in the dissolved and/or colloidal fraction. These methods reduced ¹³⁷Cs detection limits by two orders of magnitude for water and bryophytes.

Springs 4A and 4C show anthropogenic impact/influence such as elevated levels of tritium, chloride, nitrate, and perchlorate. While this indicates that some fraction of recharge to the springs is of a young age (<50 years) and possibly from past LANL discharges, we could not confirm previous detections of ¹³⁷Cs in water or bryophytes at Springs 4A or 4C.

Concentrations of total radionuclides, metals, and perchlorate found in aquatic bryophytes are provided. Concentrations of total radionuclides (including tritium), anions, cations, perchlorate, dissolved and total metals found in water are provided. Bioconcentration factors are provided when concentrations of metals or radionuclides in both water and bryophyte tissue were greater than detection limits.