2005-01-31_REVISION - M1977208 - Laserfiche WebLink

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~~~mcx r~~~c~J~o~~~~~ Erica Crosby ,JAN ~ 2Gu5 January 27, 2005 Environmental Protection Specialist Division of Minerals and Geology pivi~ia~~ nt r8mure~a>u GeoloOtl 1313 Sherman Street, Room 215 C®~~® Denver, Colorado 80203 ~/ RE: Response to Adequacy3.etters (dated November 22 and December 17, 2004), '~CEMEX, Inc., Lyons uarry, Permit No. lyI-1977-208, TR-04,Znd TR-O5. Deaz Erica: This letter contains Cemex's response to the adequacy letters for the above referenced Technical Revisions. Cemex requests that TR-OS be withdrawn and combined into TR-04. There is obvious overlap and interrelationship between the two Technical Revisions and combining the two provides for a clearer response. All of the material submitted in TR-OS is hereby included in TR-04. This letter is outlined as follows: Discussion of Cemex's position on the hydrogeologic setting and computer model results Cemex's proposal for monitoring and control of C-pit water Point by point response to the Division's two adequacy letters (included as Attachment 2) Hydrog_eoloeic Setting and Modeling Results Duting a meeting with the Division on December 17, 2004, Cemex provided a summary of the hydrogeologic setting of C-Pit and the contaminant transport modeling results. The presentation was made using Attachment 1 which shows a hydrogeologic cross-section through C-Pit and the underlying formations, including the Dakota sandstone. Attachment 1 also shows [he regional groundwater flow direction and results of the transport model performed by URS Corporation on behalf of Cemex. Attachment 1 indicates that C-Pit is excavated in the low permeability Smoky Hill shale and Fort Hays limestone members of the Niobrara Formation. C-Pit is underlain by approximately 650 feet of a low permeability, heterogeneous sequence.of claystones, siltstones, shales, and limestones of the Cretaceous Cazlile shale, Greenhorn limestone, Graneros shale, and Mowry shale. All of these formations dip approximately 6° to 15°east-southeast. Groundwater flow within the units is primarily horizontal along the bedding and parting planes of the strata, although vertical flaw is possible, but less significant, along the fractures. The Dakota group, comprised of siltstones, sandstones, and shales underlies [he Mowry shale. Regional groundwater flow n the Dakota, as well as the overlying formations, is to the east- southeast. The first sandstone member of the Dakota group is an artesian aquifer that locally supplies groundwater. In 1999, the artesian conditions caused groundwater to flow freely at the surface from the well completed in the first sandstone member on the Hall property adjacent to the southeastern Cemex property boundary. These artesian pressures would likely limit Untied States Operatfena P0. Box 529, Lyons, Colorado 80540, USA, Phone: (303) 8232100, fax: (303) 8232199