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These XMT Images were taken at the designated depths within the core and show the changes in fracture pore structure moving through the core. |
The hydraulic conductivity results below show the relative influence of the fracture.
UFA COLLOID EXPERIMENTS
To investigate the behavior of actual smectite colloids in YMP materials colloid runs were performed on whole rock and backfill materials using three successive solutions: 1) 5000 mg/L Br as KBr; 2) 3 mg/L solution of a 280-nm carboxyl modified latex particle purchased from IPC, Inc., Portland, OR, having a negative charge, and 3) solutions of SW(y-1) smectite colloid in 5 mM of NaCl at 10 mg/L and at 100 mg/L. Samples were collected every 5 minutes to obtain well defined curves and determine mass-balance. The SWy-1 Montmorillonite Wyoming clay has a surface area of 31.8 m2/g, a CEC of 76.4 meq/100 g with principle exchange cations of Na and Ca and a mean particle size of about 1 micron. The results for the whole rock are shown below.
The total water content in the whole rock core of Prow Pass Tuff (UE-25b) was 16%, but the fracture volume was only 0.75 ml. Such a small volume makes the curve less detailed because of the limits of detection of the analytical techniques, especially turbidity. A bromine ion-specific electrode was used for measuring Br in the effluents. Fluorescence spectroscopy was used to measure the latex colloids. A turbidimeter was used to measure the smectite colloids. Since turbidity results from all colloids, turbidity cannot separate smectite from colloids that might be produced during the experiment. However, the blank runs with DI water and with 5 mM NaCl did not show production of significant colloids in the absence of the introduced smectite colloids. The breakthrough and leach curves are shown in the following figures. These first runs were primarily to assess our experimental protocols in running colloids.
The Br behaved conservatively in the rock with a retardation factor of 1, in both the sorption and desorption phases, but the 280 nm latex colloid was slightly retarded, between 1.5 and 2. The 10 ppm smectite run was very noisy and the mass balance was poor. A run with 100 ppm smectite was better behaved but the resolution was poor. Using turbidity as the measurement method is not adequate as the volume of the fracture is so small relative to what is needed for a measurement. Even so, retardation appears to be low, <= 3. Another measurement technique for smectite colloids needs to be developed for the small sample sizes of the fracture flow runs, and for the small samples of the unsaturated runs. We will investigate microscopy methods or gravimetric methods.
