Gilkeson notes that the aquifer has two layers: a slow-moving sandy layer at the water table, and the actual drinking water source beneath. To accurately track wastes, both layers must be sampled. Only one monitoring well reaches the drinking water layer, but its screens cross both layers, mixing the waters.
Some of the stainless steel well screens are also corroded and clogged. Sandia engineers say that corrosion is responsible for the chromium and nickel that have been found in water samples at higher levels than drinking-water standards allow. Gilkeson suspects that these levels are too high to be accounted for by corroded screens alone. Bentonite clay from the drilling process clogs many screens, "hiding the contaminants (the wells) are intended to detect, especially radionuclides," he says. The same drilling process was used in Los Alamos, and those wells failed to detect groundwater contamination. Now, plutonium is showing up in Santa Fe's drinking water.
THE FINAL MONITORING plan now being reviewed by New Mexico's environmental department corrects some of these problems, but not all. Three new wells will be dug through the landfill cover, with plastic screens instead of stainless steel. They'll be located on the west side of the dump, closer to the potential contaminants. But there are still no wells on the landfill's south side, and none directly over the "hot spots" where tritium was dumped and where tetracholoroethane (PCE), a probable carcinogen, has been found.
"The landfill is being monitored by very competent staff at present," says Jerry Peace, a Sandia geophysical engineer, "and will continue to be monitored in the future." Sandia officials say the soils appear to slow the transport of wastes, and given the short half-life (12.5 years) of tritium, it may not reach groundwater until it has become relatively harmless.
For the city's half-million residents, though, the implications are unsettling. Sandia and the Department of Energy appear to be taking a calculated risk, banking on the probability that contaminants will not reach groundwater. But in water-sparse New Mexico, Albuquerque's aquifer may well be priceless, and any risk too great.
The author is a freelance writer who researches nuclear issues in Albuquerque.