On Bikini Island, however, the radionuclide concentrations for '37Cs and 90sr in ground water do exceed EPA recommended guidelines for drinking water. Although the radionuclide concentrations exceed the EPA quidelines for drinking water, the ground water does not provide a source of usable water in any case because it 13 too saline to be potable. We have taken groundwater samples at each of the next two largest islands, Nam and Enidrik, and, in both cases, the ground water is very saline and unpotable. In our study of Bikini Istand, werhave observed that since 1975 there has been a decrease in the 137c¢. concentrations in the ground water and an increase in the salinity, wae attribute this to the continued growth and development of the root system of the thousands of coconut trees planted on a 30'-grid across the island in 1970 and 1971. The isiand had been cleared before the start of the agriculture program and from 1971 through 1975 the trees were very small with rather small root systems. The trees grew to significant height from 1975 to 1987, with a corresponding increase in the root zone; now, the top 40 cm of soil has a high density of coconut roots. At the same time that the coconuts started reaching maturity, a dense undergrowth of native vegetation was reestablished under the coconut canopy, also with a corresponding increase in root mass. . As a result of the maturation of the coconut trees and native vegetation, more and more of the annua] rainfall is required for evapotranspiration by the plants, consequently, less and less of the annual rainfall percolates downward through the soil column to reach the ground water. In fact, we estimate the annual water requirement of the current stand of vegetation on the island to be 40 to 50 inches, or essentially equal to the average annual rainfall. The !37cs and 90s; reach the ground water by being dissolved in the soil water and carried into the lens when there is adequate rainfall to recharge the lens, 1.€., to provide a flow of water down the entire length of the soil column into the groundwater lens. As a result of the increased water requirement of the growing vegetation and the resulting reduction of water Flow to the’ lens, the amount of 137cs transported to the lens has been less and the '3/Cs concentration has been reduced. At the same time, the lack of, or reduced, flow of fresh water from the annual rainfall Inventory to the lens has created a situation, over the past several years, where the Salinity of the lens has increased. oa wool te 69 Only on Eneu