REP33845 - Laserfiche WebLink

Home Browse Search

5.0 Geotogic 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 bill 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 I about 500-feet thick and is underlain by the Lower Cretaceous Dakota Group. C- Pit is about 20 acres in size and 70-ft deep. i - Ttie 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 writh 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 1 rocks described above, Significant surface water bodies in the area, and the approximate distance from osal area in C Pit are as follows: the CKD dis p - 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 25' at the closest point Boulder Feeder Canal - Approximately 360' at the closet point The Swede Ditch which runs along the west rim of C-Pit was all enclosed in a 4- foot diameter corrugated steel pipe in 1998 in preparation for conversion of C-Pit from active quarry to CKD storage. All the pipe joints were sealed. The Boulder Feeder Canal is approximately 360-feet west and 9.5-feet higher (elevation difference from the bottom of the canal compared to the rim of C-Pit) than the rim of C-Pit. This eliminates the possibility of gravity flow from C-Pit to the canal. Runoff from the disposed CKD can not escape C-Pit and is entirely contained within the pit. C-Pit CKD storage has been designed and situated to eliminate the potential for leachate seepage into agricultural water canals now and in the future. 12