2008-04-25_PERMIT FILE - M2008010

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Letter: Response to adequacy review, Permit Application M-2008-010 4125/2008 page 8 considered to be impermeables there will be little or no groundwater flow through the Mancos shale, and no significant erosion of the shale by the water flow through the permeable formation. Since the shale is impermeable, there is little dissolving of its component salts by water flowing through it: When exposed, the surface of the shale is subject to erosion and freeze-thaw allowing for more release of salt. 9. Mancos Conservation District concerns about lining basins: These are addressed in the above item. The District apparently wishes to require that any basins and ponds on the site be lined with synthetics, although existing ponds immediately adjacent to the site and within the general area of the Mud Creek drainage do not have synthetic liners, and many appear to be incised directly into the Mancos shale. In fact, the Mancos shale is impermeable enough that it is generally allowed to serve as a component of lining systems for solid waste facilities under RCRA Subtitle D federal regulations. The need for a synthetic liner is not justified given the nature of the shale and the potential exposure of water to that shale. If the potential for leaching of salts from the Mancos shale in ponds and basins is such a significant problem and can be reduced economically by synthetic liners, the District could have included such measures in the current project to improve water quality in the Mancos River watershed, and recommend it of all existing~~and future ponds. To our knowledge, they have not done so. 10. Mancos Conservation District concerns about surface flow: Erosion is the major cause of release of salts from the shale.' The "barrier to surface flow" referenced in the District comments, discussed 6 US EPA, www.epa.QOV/region8/compliance/nepa/negadocs/moabdeis1 pdf, and www.epa.gov/ciconference/previous/2007/2007 presentations/wednesdav/830am/unc superfund sits e.pdf See William L. Jackson, Randall P. Julander (1982) RUNOFF AND WATER QUALITY FROM THREE SOIL LANDFORM UNITS ON MANGOS SHALE' Journal of the American Water Resources Association 18 (6) , 995-1001 doi:10.1111/j.1752-1688.1982.tb00107.x [Messrs. Jackson and Julander are hydrologists with the US BLM.] ABSTRACT: Relative yields of water, sediment, and salt (as indexed by electrical conductivity) were determined using simulated rainfall plots on three soil landform units on Mancos shale in the Price River Basin, Utah. Final infiltration rates on residual shale derived soils were between 0.13 and 0.50 cm/hr. No runoff was generated on cracked soils derived from aeolian deposits. Suspended sediment concentrations and elehcal conductivities were 180 and 68 times greater, respectively, for a steep dissected Mancos shale upland than for a low relief shale pediment and recent alluvial surface. Riling accounted for approximately 80 percent of the sediment produced on the steep, dissected shale surface. Channel scow and soil creep also produced measurable mounts of sediment. A survey of sediment basins in steep, dissected shale up lands indicated that an average of 1.25 Mg/ha/year of sediment is produced by that landform unit Carefully designed and located basin plugs can be used effectively to trap sediment, water; and salt from dissected shale uplands.