_REVISION - M1977208 (3) - Laserfiche WebLink

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5.0 Geologic and Hydrogeologic Setting of the Disposal Area The Lyons quarries are located entirely within the Upper Cretaceous Niobrara Formation. This Formation has a total thickness of about 400-feet and consists of two members, the Smokey Hill Shale Member and the Fort Hays Limestone Member. The Smokey Hill Shale is a fissile, calcareous shale and the Fort Hays Limestone is athick-bedded limestone. In the quarry area the bedding planes dip to the east -southeast at about 10-15 degrees. C-Pit was excavated into the Fort Hays Limestone and the pit is underlain by the Carlile Shale, Greenhorn Limestone, Graneros Shale and Mowry Shale. These rock units consist of interlayered siltstone, claystones, limestones and shales. This sequence is about 500-feet thick and is underlain by the Lower Cretaceous Dakota Group The area surrounding C-Pit has been heavily disturbed by mining. Mining and subsequent backfilling with overburden has occurred west and east of C-Pit, pursuant to the reclamation plan approved in M-77-208. North and east of C-Pit are alluvial deposits of the St. Vrain Creek The sand and gravel deposits are 25-30 feet thick and come into contact with the sedimentary rocks surrounding C-pit approximately 1,000 feet away at the closest point. There is absolutely no contact between the disposed CKD and the alluvial deposit. The CKD disposal mass is entirely contained within the sedimentary rocks described above. Significant surface water bodies in the area, and the approximate distance from the CKD disposal area in C-Pit are as follows: St. Vrain Creek - Approximately 4700' at the closest point Foothills Reservoir - Approximately 4200' at the closest point A-Pit Reservoir - Approximately 2000' at the closest point (A-Pit Reservoir is an approved water storage facility on Southdown property and within the M-77-208 permit boundary. The water is used for the cement plant.) Swede Ditch - Approximately 300' at the closest point Boulder Feeder Canal - Approximately 500' at the closet point Runoff from the disposed CKD can not escape C-Pit and is entirely contained within the pit. Groundwater in the area occurs in both the sedimentary rocks and in the alluvial aquifer of the St. Vrain Creek. Groundwater levels in the sedimentary strata are believed to be well below the bottom of C-Pit. Ponded water currently in C-Pit is from surface runoff, collected precipitation, ditch seepage, and runoff from the sprinkler system. Southdown drilled two water wells immediately east of the permit area and had to advance the holes 800 feet or more to encounter a useable water supply. The exposed highwalls of C-Pit are dry except for 12