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<br />((c <br /> <br />(( <br /> <br />(l <br /> <br />C-) <br /> <br />~ <br />"d" <br />r:-- <br /> <br />20 <br /> <br />r~ <br />...._1 <br /> <br />What seems apparent from these results is that without any <br />seepage control, seepage rates will be significant since the <br />estimated seepage rate is equal to approximately 30% of the total <br />inflow to be evaporated that was estimated in the Phase I study. <br />Certainly, refining these analyses or obtaining additional data, <br />which shows that the shale becomes less permeable with depth may <br />reduce the estimated rate of seepage. However, it is apparent <br />that seepage control will be necessary unless the loss of large <br />amounts of saline water into the Mancos shale and underlying <br />Dakota sandstone is not a problem. <br /> <br />7.2.3 Seepage Control <br /> <br />Several seepage control measures are-available and all have been <br />used in similar structures in the past. Those considered herein <br />include: <br /> <br />o A compacted clay liner <br />o A synthetic membrane liner <br />o A slurry cutoff wall <br />o A compacted clay cutoff wall <br /> <br />7.2.3.1 Compacted Clay Liner <br /> <br />Compacted on-site soils were found in our laboratory tests <br />(Appendix B) to have a permeability (using distilled water as a <br />permeant) of about 1.0 x 10-8 cm/sec (2.4 x 10-7 in/hr). <br />This is very low and would suggest that this material would be <br />suitable for controlling seepage. However, at this stage, no <br />work has been performed to evaluate the effects of long term <br />exposure to saline water on the compacted clay. Until this is <br />done, the seepage estimates, based on a compacted clay liner, are <br />qualified. <br /> <br />Assuming an 18 inch thick compacted clay liner is used and <br />keeping in mind all of the assumptions presented previously <br />including the applicability of Darcy's Law, then the total <br />seepage estimates for the West, Middle, and East areas are 30, <br />20, and 40 gpm for a rate of .0002 ft3/ft2 day. <br /> <br />Increasing or decreasing the thickness of the liner or the depth <br />of water would obviously change the seepage estimates. Also the <br />unknown effects of long term exposure to saline water may alter <br />the seepage rate either up or down. Therefore, compacted clay <br />may be a good seepage control measure. The question of the <br />suitability of compacted clay liners depends on its compatibility <br />with saline water and what limits if any are placed on loss of <br />salt into the Mancos shale by regulatory agencies. <br />