The polluted Kesterson National Wildlife Refuge - which got national attention in 1983 when ducks, geese, nestlings, and other waterfowl mysteriously perished - continues to be a danger to animals as well as an enigma to scientists trying to determine how best to clean it up. During the past month federal agencies working on the cleanup have issued conflicting studies, in tone if not in hard data, about the scope of the pollution problem in and around Kesterson. The wildlife refuge and surrounding wetlands, located southeast of San Francisco in California's Central Valley, are important habitats for birds migrating along the Pacific Flyway.
Kesterson became contaminated by toxic levels of selenium in agricultural drainage water transported there to fill the refuge's ponds, scientists say. But a United States Fish and Wildlife Service study issued earlier this month says the selenium problem is probably much more widespread, extending into some of the ponds in the nearby 51,000-acre Grasslands Water District.
Agency biologists report some birds in the Grasslands district had higher selenium levels in their livers than birds found at Kesterson in 1983 - a factor that could be contributing to the decline in the numbers of birds in the Pacific Flyway. The report suggests birds may be carrying selenium back to their Canadian nesting grounds in the spring. These preliminary findings are based on birds collected in 1985, when area landowners were still flooding their land with the selenium-laced farm drainage water.
A second report, issued Nov. 24, indicates selenium levels in the water at Kesterson itself have dropped dramatically over the past year. The data ``clearly demonstrate'' that a controversial cleanup proposal championed by the US Bureau of Reclamation will work, according to scientists at the Lawrence Berkeley Laboratory, who are under contract with the bureau.
Under the bureau's experiment, some Kesterson ponds have been flooded with selenium-free fresh water in an effort to immobilize selenium in the sediment. As a result, researchers say, selenium levels have fallen from 400 parts per billion to 4 or 5 p.p.b. Selenium in the water is likely to fall to 3 p.p.b - the federal target level - during the next few years, says bureau spokesman Jason Peltier. Critics, however, note that selenium levels found in Kesterson animals are still unacceptably high.
The bureau report gets to the heart of the most controversial issue of all - how to clean up Kesterson, as well as other sites in the West with potential selenium-related problems.
Selenium deposits are found in the soils in many arid parts of the West. While the element is considered important to human and animal health, biologists say it can be harmful in high doses. Leached from the soil during irrigation, selenium in drain water often flows through rivers or canals to lakes, bays, or refuges like Kesterson, where waterfowl congregate.
Selenium is suspected to be a problem in Utah, Nevada, and possibly several other Western states.
The California Water Resources Control Board this spring rejected the Reclamation Bureau's cleanup proposal in favor of a more traditional - and more expensive - disposal method. It ordered the bureau to remove water from Kesterson's ponds, scrape up selenium-laden sediments and vegetation, and deposit the waste in an on-site landfill, which will be capped to prevent leakage.
Mr. Peltier says the bureau intends to proceed with the cleanup as ordered by the state board, despite the new findings about the feasibility of its preferred method. But if the bureau is to adhere to a timetable to complete the project by next fall, Congress must appropriate at least $15 million in the next few weeks.
Experts agree the method used at Kesterson could set a precedent for similar environmental problems expected to arise in the future.
Stephen Hall, executive director of the Land Preservation Association, which represents local water districts on the west side of the valley, says: ``There is a need to better understand how this element behaves in the environment, and then to use its natural properties to aid in alleviating the problem.''
``Promising'' research by two scientists from the University of California at Riverside, for example, would transform Kesterson's selenium in the soil into a gas that dissipates into the atmosphere, he says. William T. Frankenberger Jr., one of the scientists, says he expects to release preliminary findings from Kesterson field tests this month.