414 RADIOLOGICAL CLEANUP OF ENEWETAK ATOLL e technical guidance to the troops on containmentoperations and especially on mixingthe slurry and placing it by the tremie. 28.29 To develop formulas for the slurry and soil-cement mixtures, POD engaged the U.S. Army Corps of Engineers Waterways Experiment Station (WES). Using samples of Enewetak sand, Type I Portland cement, salt water, and bentonite-attapulgite, WES prepared several different mixtures and evaluated them for mixability, pumpability, placeability, ang strength. Bentonite is a fresh-water clay which is used as a colloidal suspending agent, or lubricant, in drilling wells and pumping concrete, while attapulgite is a salt-water clay used for the same purposes. The Enewetak sand contained a high percentageofcalcium, little silica, and was very angular and sharp.It lacked the fine particles which normally promote pumpability in sanded grouts; consequently, higher proportions of bentonite and water were required in the mixture so that it could be pumped through the tremie pipes.39 The samples of Enewetak sand which had been furnished for the experiments was not sufficient for full-scale field tests. WES prepared a substitute using crushed limestone and an expanded clay combined 50/50 by weight so as to matchas nearly as possible the physical characteristics of Enewetak sand. This material was mixed with cement, bentonite, andsalt water in various proportions and pumped througha tremiepipeintoa test pit filled with salt water.3! Field tests also were made on various soil- cement mixturesto be used in stabilizing contaminated soil once the crater itself was full. Based on these experiments, formulas were developed for use at Enewetak. The report by WES concluded by emphasizing the need for quality control in the makeup of the slurry and soil-cement mixtures. In adopting the mixtures recommended by WES, Field Commandchose to use TypeII cement which provided greater strength whenusedwithsalt water and was no more expensive than the Type I used in the experiment. After considerable discussion, attapulgite was chosen as the colloidal agent. The mixture adopted by Field Commandfor tremie slurry was three bags of cement and one-half bag (50 pounds) of attapulgite per cubic yard of mix. For the soil-cement mixture, two bags of cement were to be used for each cubic yard ofsoil.32 To protect the containment structure from the initial shock of wave action during construction, POD designed a mole, or revetment, to be located on the ocean side of the keywall (Figure 8-9). It was to be constructed of armor stone (pieces of blast rock, concrete, or other rocks weighing over 1,500 pounds) and choked with smaller rock and aggregate.33 Design of the crater containment worksite was complicated by the apparent presence of concentrations of highly contaminated material found on the rim of Cactus Crater by earlier radiological surveys ————