Two subsurface samples representing highly weathered sediments of the Upper Coastal Plain (Aiken, SC) that differed in Fe-oxide content (7.3 vs 35.9 g Fe kg-1) were evaluated in terms of mobile colloid generation in response to changes in solution composition. In repacked columns, the two sediments were leached (∼0.72 m d-1 Darcy velocity) with either 0.001 N NaCl or CaCl2 solutions for 10 pore volumes followed by 10 pore volumes of deionized water. Bulk clay mineralogy from the two samples and suspen sions generated in the column studies was characterized by energy dispersive X-ray analysis (EDXA) using a field-emission scanning electron microscope (SEM). SEM results were confirmed by selected-area electron diffraction (SAED) and EDXA in a transmission electron microscope. In column experiments, the sample lower in Fe oxide displayed increased effluent turbidity that coincided with a decrease in effluent pH during injection of the CaCl2 solutions. In contrast, no effluent turbidity was observed during the leaching of NaCl solutions. The sample higher in iron oxide displayed greater effluent turbidity from the onset of leaching that decreased over the duration of injection for both the CaCl2 and NaCl solutions. Colloids generated from both materials displayed positive electrophoretic mobilities, confirming the importance of iron oxides in controlling dispersion and surface charge properties of the mobile colloids. Minor differences in the clay mineralogy (i.e., iron oxide/kaolinite content) between the samples were reflected in both their sensitivity to pore-solution composition and the relative degree of dispersion observed for each sample. Electron microscopy, EDXA, and thermal gravimetric analysis (TGA) confirmed that the mobile colloids consisted mainly of submicron sized Al-rich goethite, with lesser amounts of kaolinite, the predominate layer silicate of the bulk sediments, and varying amounts of crandallite.

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Cesium in the Sa'_,annahRiver Site Environment is published as a part of the Radiological Assessment Program (RAP). lt is the fourth in a series of eight documents on individual radioisotopes released to the environment as aresult of Savannah River Site (SRS) operations. The earlier documents describe the environmental cortsequences of tritium, iodine, and uranium. Documents on plutonium,strontium, carbon, and technetium will be published in the future. These are dynamic documents andcurrent plans call for revising and updating each one on a two-year schedule. Radiocesium exists in the environment as aresult of above-ground nuclear weapons tests, the Chemobyl accident, the destruction of satellite Cosmos 954, small releases from reactors and reprocessing plants, and the operationof industrial, medical, andeducational facilities. Radiocesium has been produced at SRS during the operation of five production reactors. Several hundred curies of _TCswas released into streams in the late 50s and 60s from leaking fuel elements. Smaller quantifies were released from the fuel reprocessing operations. About 1400Ciof lrPCswas released to seepagebasins where it was tightly boundby clay in the soil. A much smallerquantity, about four Ci, was released to the atmosphere. Radiocesium concentration andtransport mechanisms for atmospheric, surface water, and groundwater have _en extensively studied by Savannah River Technology Center (SRTC) and ecological mechanisms have been studied by Savannah River Ecology Laboratory (SP, EL). The overall ngliological impactof SRS releases on the offsite maximum individual can be characterizedby total dosesof 0.33 nuem (atmospheric)and 60 mrem (liquid), compared with a dose of 12,960 nare_ fromtmn-SRSsouree_ duringthe same period of time. Isotope _r_Cs releases haveresultedin a negligiblerisk to the environment and the population it supports.

Cesium in the Sa'_,annahRiver Site Environment is published as a part of the Radiological Assessment Program (RAP). lt is the fourth in a series of eight documents on individual radioisotopes released to the environment as aresult of Savannah River Site (SRS) operations. The earlier documents describe the environmental cortsequences of tritium, iodine, and uranium. Documents on plutonium,strontium, carbon, and technetium will be published in the future. These are dynamic documents andcurrent plans call for revising and updating each one on a two-year schedule. Radiocesium exists in the environment as aresult of above-ground nuclear weapons tests, the Chemobyl accident, the destruction of satellite Cosmos 954, small releases from reactors and reprocessing plants, and the operationof industrial, medical, andeducational facilities. Radiocesium has been produced at SRS during the operation of five production reactors. Several hundred curies of _TCswas released into streams in the late 50s and 60s from leaking fuel elements. Smaller quantifies were released from the fuel reprocessing operations. About 1400Ciof lrPCswas released to seepagebasins where it was tightly boundby clay in the soil. A much smallerquantity, about four Ci, was released to the atmosphere. Radiocesium concentration andtransport mechanisms for atmospheric, surface water, and groundwater have _en extensively studied by Savannah River Technology Center (SRTC) and ecological mechanisms have been studied by Savannah River Ecology Laboratory (SP, EL). The overall ngliological impactof SRS releases on the offsite maximum individual can be characterizedby total dosesof 0.33 nuem (atmospheric)and 60 mrem (liquid), compared with a dose of 12,960 nare_ fromtmn-SRSsouree_ duringthe same period of time. Isotope _r_Cs releases haveresultedin a negligiblerisk to the environment and the population it supports.

No abstract