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<br />(, <br /> <br />( <br /> <br /><... <br /> <br />o <br />C,J <br />r- <br /> <br />iv <br /> <br />.~ .:. <br /> <br />Coo"":> . <br /> <br />(; <br /> <br />~) <br /> <br />ABSTRACT--Continued <br /> <br />In-place, both the Quaternary deposits and the Mancos shale are <br />relatively permeable up to the depths explored (on the average 50 <br />feet). The range in permeability of all the materials tested was <br />between I x 10-3 and 1.4 x 10-7 cm/sec (1.4 in/hr to 2 x <br />10-4 in/hr), with the least permeable material being Mancos <br />shale located in the middle area of the site. The average <br />permeability of the Mancos was 1.4 x 10-4 cm/sec (0.2 in/hr) <br />and generally decreased in areas where the RQD of the rock was <br />higher and consistent with depth. In general, the rock quality <br />(RQD) of the Mancos shale was poor across the entire site to the <br />depths explored. <br /> <br />Construction of evaporation ponds have been recommended in three <br />separate areas comprising approximately 3,340 acres. These areas <br />were selected based on topographic considerations that result in <br />minimizing earthwork and placing the ponds outside of the major <br />north-south drainages that dissect the site. Preliminary <br />estimates of seepage in these areas, assuming they are constantly <br />full, ranged from several hundred to over 1,000 gallons per <br />minute (gpm) for individual areas and 2,860 gpm or 3.8 x 10-3 <br />ft3/ft2 day for the three areas combined. The middle <br />area located in relatively good quality Mancos shale had the <br />lowest estimated seepage at 470 gpm. When an 18 inch compacted <br />clay liner was considered, the seepage estimates were reduced <br />considerably ranging from 20 to 40 gpmfor an overall rate of 90 <br />gpm or 1.2 x 10-4 ft3/ft2 day for the entire 3,340 <br />acre area considered. <br /> <br />( <br /> <br />Consideration was given to the use of synthetic liners and cutoff <br />walls. Synthetic liners were considered inappropriate due to the <br />presence of good liner material on-site. However, if stringent <br />seepage control requirements are imposed, then synthetic liners <br />may be the only alternative left. The use of a cutoff wall would <br />be effective at cutting off horizontal seepage if a liner was not <br />used, however, there would still be a significant portion of <br />seepage downward. <br /> <br />Depending upon the regulatory requirements with respect to <br />seepage, additional geotechnical investigations will be required <br />prior to final design. These may include: <br /> <br />o Evaluation of the permeability of the upper 5 to 10 feet <br />of Mancos shale. <br /> <br />o Evaluation of the permeability of the Mancos shale at <br />depths greater than 60 feet. <br /> <br />c <br /> <br />o Evaluation of the effects of saline water on the long <br />term seepage rates for in situ Mancos shale and the liner <br />materials. <br />