The non-radioactive chemical has not been detected in the regional aquifer, an underground reservoir that supplies the Los Alamos area with drinking water, and has not been detected in wells that provide drinking water to Los Alamos.
Perchlorate is the name given to a chemical compound that contains a chlorine atom bound to four oxygen atoms. Perchlorate is used in a variety of industrial processes. At Los Alamos, perchloric acid is used in nuclear chemistry research. Industrial perchlorate uses include leather tanning, as a solid fuel for rockets, high explosives and fireworks, as a component of air-bag inflators, in electroplating and rubber manufacturing.
During the late 1990s, the U.S. Environmental Protection Agency identified perchlorate as a contaminant of concern, although the chemical is not regulated under the federal Safe Drinking Water Act or New Mexico drinking-water regulations.
Perchlorate is mobile and can persist for decades in groundwater. EPA has not established a drinking water standard for perchlorate. The state of California, which has perchlorate contamination in drinking water supplies in some areas, has established a perchlorate water-supply action level for concentrations greater than 18 parts per billion. The state of New Mexico has not established an action level or regulatory standards for perchlorate.
After EPA named perchlorate as a contaminant of concern in 1998, Laboratory hydrologists began testing water supplies for the chemical as part of their program to monitor Los Alamos drinking water. To date, the chemical has not been found in Los Alamos water-supply wells.
Los Alamos hydrologists obtained Mortandad Canyon shallow groundwater perchlorate data from samples that were split with EPA during an EPA sampling visit to Los Alamos last December. Los Alamos' analysis of the samples indicated perchlorate concentrations ranging from 80 to 220 parts per billion. The EPA's preliminary sampling results also indicate the presence of perchlorate in shallow-groundwater-monitoring wells ranging from one to 40 feet below the surface. The top of the regional aquifer in that area is about 900 feet below the surface.
Laboratory hydrologists and geochemists tested other groundwater monitoring and surveillance wells for perchlorate early this year. They looked at recently installed characterization wells R-25, near the Laboratory's southwest boundary; R-31, in Ancho Canyon near the Laboratory's southern boundary; and R-15 in Mortandad Canyon. The hydrologists did not detect perchlorate in the regional aquifer at any of the three locations, but did detect perchlorate in concentrations of 12 parts per billion in a perched water zone 646 feet below the surface in the R-15 well in Mortandad Canyon.
Hydrologists with the Laboratory's Water Quality and Hydrology Group in February retested drinking-water-supply wells nearest to Mortandad Canyon for perchlorate. They did not detect the chemical in those nearby wells -- Pajarito Mesa-1, Pajarito Mesa-2 and Pajarito Mesa-5 -- which are located one- to one-and-a-half miles away from the Mortandad test wells. Other Los Alamos water-supply wells - Pajarito Mesa-3, Pajarito Mesa-4, Otowi-1 and Otowi-4 - will be checked for perchlorate as they become operational this spring.
"It is important for the Laboratory to continue its groundwater characterization and surveillance programs, its water-quality-assurance activities, and its groundwater modeling activities in order to detect and understand the movement of any contaminants of concern," said Charlie Nylander, leader of the Laboratory's Hydrogeologic Workplan and Monitoring Well Project. "The results of these activities will help us better understand contaminant movement and can help the Laboratory determine the best strategies to prevent contaminants from entering our drinking water."
Although potential health effects stemming from perchlorate contamination are not well understood, the chemicals do present a health concern because of the chemical's ability to affect the human thyroid gland. EPA and other organizations are conducting studies to better understand risks associated with perchlorate contamination.
Meantime, Laboratory personnel are working to reduce perchlorate discharges with an eventual goal of zero discharges of the chemical in coming years. The Laboratory is monitoring the influent and effluent of the TA-50 Radioactive Liquid Waste Treatment Facility, which discharges treated effluent to Mortandad Canyon, to determine what levels of perchlorate are being discharged from Laboratory operations and to establish treatment/removal efficiencies, said Beverly Ramsey, deputy director of the Laboratory's Facility and Waste Operations Division.
In addition, Laboratory officials are planning to modify treatment operations to further reduce perchlorate concentrations in water discharged from the RLWTF. The treatment plant currently reduces perchlorate in the waste stream by 80 to 90 percent. Treated water discharged from the TA-50 RLWTF contains perchlorate concentrations that recently were measured between 24 and 66 parts per billion. Laboratory officials hope to achieve an effluent concentration of less than 18 parts per billion through control of perchlorate entering the TA-50 treatment plant and through modification of treatment operations.
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