26 the filling of Cactus Crater, the concentration of 779 ***pu in the fresh water within the crater was 0.116 + 0.062 pCi/L; the crater sediments had a concentration of 82 + 2 pCi/g (dry weight) (Noshkin 1980, Table 4). These values are higher than the concentrations measured from within the containment structure (see section 4.3). 5.3 Transuranics in the Surrounding Environment . Radionuclides in the groundwater at Runit were measured in 1975, prior to the cleanup, by Noshkin and co-workers (1976). These measurements showed that plutonium had penetrated the groundwater to the deepest depths measured (73 m). Dissolved za9*etp. ranged in value from 0.01 to 0.66 pci/t and in many of the wells was found to increase with depth. Two of the wells measured in 1975 are between Cactus Crater and the lagoon and are very near the two wells discussed in section 4.3. Measured values of dissolved ?3**?* py are similar in the two cases (between 0.08 and 0.17 pci/£L) and both show a higher concentration in the well closer to the lagoon. The largest quantities of transuranics at Enewetak are in the lagoon sediments. The entire distribution of the transuranics in the benthic environment at Enewetak has recently been reviewed by Noshkin (1980, Table 1). He estimates that the top 16 om of the sediments has an inventory of 1185 Ci of 73°**** pu, 167 Ci of 22* Pu, 2190 of 2°! Pu, and 475 Ci of 7*°*Am. These are distributed nonuniformly with the highest surface concentrations near the location of test sites. The highest concentrations are in the northwest area of the lagoon where ( surface activities of 73°***pu are some four times higher than off . Runit were surface activities range from 2 to 170 pCi/g (dry weight). The vertical distribution of the transuranics within the sediment column is highly variable from place to place (sometimes increasing with depth) and cannot be generalized easily. Transuranics within the water column of the lagoon show a complex distribution, the spatial patterns being different for surface and bottom concentrations of 73° **°*py as well as for dissolved and sus- pended components. In 1974 the soluble ??**?" "pu ranged in concen- tration from 0.002 to 0.075 pci/i. The total inventory in the water column of the lagoon in 1974 was 1.5 Ci in solution and 0.7 Ci associated with particulate material. Thus, the average quantity of Plutonium in the water column is a small fraction of the sediment inventory. ° : The investigations of Noshkin and co-workers have shown that at both Enewetak and Bikini from 75 to 94 percent of the seluble zas+2e¢py in the lagoon water is in the oxidized state (+5 or +6) with the remainder being in the reduced state (+3 or +4). All the Plutonium associated with the particulate material is in the reduced state. Noshkin (1980) believes that most of the plutonium associated with the lagoon particulates is from resuspended sediments and is not transported out of the lagoon. On the other hand, the dissolved Plutonium passes readily through dialysis membranes and seems to move without interaction with the sediment (Noshkin 1980). The water in the lagoon is exchanged with the ocean approximately twice a year. Thus, about 3 Ci of dissolved *3*+?**py are removed from the atoll each year and an equivalent quantity remobilized from the sediments and other sources on the atoll. Noshkin has shown that 900856]