Laserfiche WebLink
Windsor East Mine, Exhibit D – Mining Plan September 2022 <br /> Page 1 | 4 <br /> <br />EXHIBIT D – MINING PLAN <br />1.0 GENERAL <br />The Windsor East Mine property is located within the Town of Windsor in Weld County, Colorado. The Windsor <br />East Mine site is on land owned by GWIP, LLC (GWIP). Martin Marietta Materials (Martin Marietta) has a lease to <br />mine the GWIP property. The leased area is located within Parcel 08073600021, in Section 35 and 36, Township <br />6 North, Range 67 West of the 6th Prime Meridian. The geographic coordinates for the main entrance area are <br />40.450040° N, -104.851359° W. The property contains a significant commercial deposit of sand and gravel that is <br />associated with the Cache la Poudre River. While the property is owned by GWIP, LLC, the mineral rights in the <br />affected area are owned by the Colorado State Board of Land Commissioners. <br />The Windsor East Mine is 150.3 acres. The permit boundary and affected area are the same for this application. <br />Within the site, 90.1 acres of the land will be mined, and the remaining unmined acres will be used for overburden <br />and topsoil stockpiles, offsets from existing structures and property lines. <br />The permit boundary for the site was established to avoid impacting the riparian area along the Cache la Poudre <br />River. In addition, all mining excavations will be set back a minimum of 200’ from the riverbank and then <br />backfilled to be no closer than 400’ from the riverbank. Riverbank locations were located using GPS in June 2022 <br />and the locations may vary over time. Offset distances are in accordance with the Technical Review Guidelines <br />for Gravel Mining and Water Storage Activities, published by the Mile High Flood District in January 2013. <br />A wetland area was identified on the site and mapped. The US Army Corps of Engineers has determined that this <br />is non-jurisdictional. Please see Exhibit J-1 for the documentation. The proposed mining plan shows that Martin <br />Marietta will mine through this area. <br />There were oil and gas wells and flowlines through the middle of the property that were owned by Noble and DCP <br />Midstream that are no longer used. Most of the wells have been plugged and abandoned per COGCC <br />requirements. There is only one well left (State 8-36) for DCP to complete abandonment and the 150’ radius will <br />be maintained until the abandonment is complete. Martin Marietta has contacted DCP Midstream and found out <br />that all the flowlines were properly abandoned in place and Martin Marietta can remove them as they mine. <br />Martin Marietta will contact DCP Midstream as they encounter and remove these lines so that DCP can <br />appropriately document their removal. There is also an oil and gas flowline running north and south along the <br />east edge of the property. Martin Marietta is working with DCP Midstream to determine what needs to be done to <br />cross this line with conveyor and equipment. <br />It is estimated that the overburden will amount to approximately 676,000 cubic yards. Overburden exists to an <br />average depth of approximately 5 feet over the entire site. All overburden and clay needed for the construction of <br />the final reclamation will come from this site. The average depth of sand and gravel is 10 feet across the site and <br />mining at the site is intended to progress down to bedrock. <br />Deere & Ault Consultants, Inc. drilled 8 borings in 2017 for the property owner and Martin Marietta drilled 16 <br />borings across the site in December 2019 with similar results. The results of these borings were used to <br />understand the subsurface conditions across the Windsor East Mine area. Drilling logs indicate the general <br />subsurface profile consists of approximately 3 to 9 feet of silty to clayey sand overburden, overlying approximately <br />6 to 17 feet of well graded gravel with varying amounts of sand and silt, overlying claystone bedrock. <br />Groundwater was encountered at depths ranging from 4 to 7 feet in the most recent 2019 Martin Marietta <br />borings. There is evidence that dewatering from the Parsons Mine to the east has increased the depth of the <br />water table to 11-12 feet below the surface. <br />The site will be mined in four phases, called out on the Exhibit C Mining Plan map as Cells A, B, C and D. These <br />phases are neither representative of the maximum area of disturbance nor do they limit disturbance to a particular <br />phase.