Laserfiche WebLink
ERC <br /> 2.0 DEPOSIT TO BE MINED <br /> As stated previously, the initial objective of the dredging operation was to remove materials from the <br /> basin to restore and expand the water storing capacity of the reservoir. The constraints of the excavation <br /> are based on maintaining gravity drainage from the outer edges of the reservoir to the invert of the outlet <br /> pipes that extend under the dam. Using the inlet elevation of the outlet works as a low point in the <br /> grading, contours representing the maximum excavated surface were generated by radiating outward at <br /> a slope of 0.5%. Across the reservoir floor there will be an approximate 5 foot elevation difference. <br /> Equipment on the dredge is used to monitor excavation elevations. The proposed ultimate excavated <br /> surface is shown on Drawing C-2. Dredging of the basin will occur in four quadrants by focusing on a <br /> single area before moving onto another area. Area 1, where current operations have been focused, is <br /> located in the northwest quadrant of the reservoir. Dredging will occur in a counterclockwise direction <br /> with Area 2 being the southwest quadrant, Area 3 the southeast, and Area 4 the northeast. An isopach <br /> showing the estimated excavation depths within the basin is shown on Drawing C-3. The average <br /> excavation depth ranges between 12 to 13 feet with maximum excavations reaching 20 feet. The deepest <br /> regions of the excavation are in the northwest quadrant where the Platte Valley Canal enters the reservoir. <br /> It makes sense that this area would have a deep sandy sediment deposit as this type of material would be <br /> first to settle out. <br /> A geotechnical investigation was completed in 2019 to evaluate the properties of the accumulated <br /> sediments, to the extent possible, and the underlying native materials along the west shoreline of the <br /> reservoir. The investigation was completed in November when the reservoir was low exposing more of <br /> the reservoir basin ground surface, however, due to the soft nature of the basin materials, drilling was <br /> limited to a maximum distance of 400 feet from the shoreline. From this investigation, it was possible to <br /> get an understanding of the sediment characteristics along with the localized existing ground conditions <br /> even though the sampling was limited to only a small fraction of the entire reservoir. At this point of the <br /> project the primary intent of the project was to increase the water storage space within the reservoir by <br /> removing materials and stockpile materials around the lake into permanent fill areas. The investigation <br /> was done to develop an understanding of the materials to see if dredging was the best option for the <br /> removal process,to make business decisions, and to see from a broad perspective if the materials could <br /> potentially have a use for other off-site third-party construction projects. Once dredging began and it <br /> became evident that the materials being dredged were primarily sand with a large portion of the sand <br /> being of the grains sizes used in the oil and gas industry for fracking,the concept of being able to use the <br /> sand as a fracking material along with using the oversize and undersize materials for construction borrow <br /> sources became a possibility. <br /> The results of the 2019 investigation revealed three distinct stratums within the explored areas. Each <br /> stratum is summarized as follows. <br /> 1. Stratum 1: This layer consists of sediments or materials transported with flows into the reservoir <br /> over the course of 100 plus years since the dam was built. These materials consisted primarily of <br /> sand and were found at depth ranging between 5 to 15 feet deep. <br /> 5 <br />