Evaluation of the Fennel Weyerhaeuser Mine within the Fennel Creek Delta; McMillian, WA
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This report is an evaluation of aggregate resources for the 60 acre Fennel Weyerhaeuser active sand and gravel mine located in McMillian, Washington. The Fennel Weyerhaeuser mine is one of two sand and gravel mines located within the 900 acre Fennel Creek delta complex and has been active since 2015. The Fennel Creek delta complex is a series of four nested Gilbert-type deltas. Gilbert-type deltas are coarse grained deltas that form when a high energy drainage intersects a low energy marine or lacustrine environment. Thirty-eight borings have been completed within the delta complex. The USCS soil classification scheme was used to describe the materials encountered in each boring. The regional stratigraphy was developed from open pit exposures and from the information obtained from each bore log. Groundwater data was collected for seventeen of the borings. The USCS and groundwater data were entered into Rockworks 16 software to create a three dimensional model of the Fennel Weyerhaeuser mine. Gradation data from samples taken from the borings was compiled for each of the three major stratigraphic units within the study area. The 3D model generated from Rockworks 16 utilized a 2H:1V final mine perimeter slope and a 5-foot vertical groundwater buffer. A maximum volume of 14.5 million cubic yards (about 26 million tons) of sand and gravel is available with a 2H:1V final mine slope. Including the groundwater buffer in the Rockworks model reduces the total possible extractable sand and gravel to 8.8 million cubic yards (15.8 million tons). The extraction plan for the mine will be guided by two equally important aspects, 1) the aggregate products that will be produced, and 2) the infrastructure to support aggregate production. The Fennel Weyerhaeuser mine primarily produces ìgravel borrow,î a multiuse, free draining, fill material consisting of sand and gravel typically mixed in the proportion of native occurrence, i.e without deliberate mechanical prescriptive blending. In order to produce gravel borrow, the topset and foreset beds will be combined at a ratio of 2:5 respectively. To accomplish the material mixing a 1H:1V mine face will be exposed extending from the upper surrounding land surface to the bottom of the mine. In addition, the mine face will be roughly perpendicular to the front slope of the delta. The foreset beds have alternating debris flow and turbidite facies which have different gradations. By mining perpendicular to the delta face the two facies are combined, resulting in a more consistent feed material. Mining and conveying infrastructure in place as of March 2017 will be expanded. The mining plan calls for five mining phases lasting a total of 15-20 years. The first mining phase will expose the 1H: 1V face toward the center of the mine and will include the installation of a 900ft conveyor. The second phase will extract the material in the northwest area comprising 10 acres and an additional 200ft of conveyor. Phase three calls for the extraction of 21 acres to the southwest and 900ft of conveyor. Material extraction of phases four and five will vary as mine conveyors will need to be removed from the site.