nememeeenpwneene ea gas é inCz ani’fae Rainfall produces only smal} amounts of fresh groundwater on the large islands of Bikini and Eneu, and probably no potable groundwater on the smaller islands. Rainfall drains quickly through the soil and accumulates in a roughly “lens-shaped" body of fresh water floating on the more dense salt water. Most of the fresh groundwater is very rapidly mixed with the underlying salt water by wave and tidal activity, leaving only a very thin Fresh layer, generally in the central portion of the island (Figure g). Development of potable groundwater in Bikini Atoll is limited by two -factors: chemical quality and radiological quality. In terms of chemical quality, salinity is most important, with chloride content normally being the limiting constituent. In the United States the standard for chloride content in drinking water is set at 250 mg/1 (for Bikini groundwater this is approxi- mately equivalent to 0.45 ppt total salinity), but a higher standard has been set by TTPI of 400 mg/1 Cl for drinking water (for Bikini groundwater this is approximately equivalent to 0.75 ppt total -salinity). In terms of radiological quality the most important constituents in Bikini groundwater are 90s; and oa In the United States (oresumably the same standards wil] be applied © Bikini) the limiting concentrations of 90s, and 137c¢. are 10-and 200 pCi/l, respectively. When both nuclides are present the standard for each is reduced proportionally. Groundwater chemical and radiological quality data collected from wells on Bikini and Eneu Islands by Lawrence Livermore Laboratory since 1975 are summarized in Figure 9 and Table 2. As can be seen from these data, a very smal } body of marginally potable (from a salinity standpoint) groundwater. exists in the south-central part of Bikini Island in the vicinity of wells HFH2 and HFH7. All Cl and total salinity data collected from these two wells during the period 1975-79 meet United States drinking water standards. However, salinity measurements made by two of the Committee members (Peterson and Robison) on May 10-11, 1984, after nearly two years of very low rainfall show , Cl and total salinity levels of the freshest water sampled (well HFH7) to be approximately triple the limits set in the United States for potable water, and about double those of TTPI (see Table 2). Water salinity data collected by the United States Geological Survey in April and-May 1972 generally confirm these 1984 results. These data raise a serious question about the availability of potable groundwater on Bikini Island during times when it would be needed most, that is during periods of drought. This question may be moot, however, because as can be seen in Table 2, the concentration of both 90s, and 137¢.5 in Bikini groundwater exceed drinking water standards. From both a chemical and a radiological standpoint the groundwater picture on Eneu looks much more promising than on Bikini. As can be seen in Table 2 and Figure 9 a moderately-sized body of potable groundwater exists in the central part of the island near the runway. All samples collected from wells FWR 4, 5, 6, and 7.during the period 1975-84 yielded water that meets TTP] standards for potability. In fact, groundwater collected from FWR 4 on May 12, 1984 contained only 23.2 mg/1 C1, an extremely low value considering the long period of drought conditions preceding this sampling. Furthermore, an 8-hour pump test run on well FWR 4 on May 13, 1984, during which time about 82,000 liters (21,500 gallons) of water were pumped from the well, produced virtually no increase in water salinity, thus further substantiating the existence of a significant fresh groundwater lens. The very freshness of this groundwater undoubtedly is due to extensive runoff from the runway, and hence this general region would be a good place for groundwater development. I009bb A-5