Laserfiche WebLink
1 <br /> 5.0 Geologic and Hydrogeologic Setting of the Disposal Area <br /> The Lyons quarries are located entirely within the Upper Cretaceous Niobrara <br />' Formation. This Formation has a total thickness of about 400-feet and consists <br /> of two members, the Smokey Hill Shale Member and the Fort Hays Limestone <br /> Member. The Smokey Hill Shale is a fissile, calcareous shale and the Fort Hays <br />Limestone is athick-bedded limestone. In the quarry area the bedding planes <br /> dip to the east -southeast at about 10-15 degrees. C-Pit was excavated into the <br />' Fort Hays Limestone and the pit is underlain by the Carlile Shale, Greenhorn <br />Limes one, eros Shale and Mowry Shale. These rock units consist of <br /> interlayered siltstone, claystones, limestones and shales. This sequence is <br /> about 500-feet thick and is underlain by the Lower Cretaceous Dakota Group. C- <br />' Pit is about 20 acres in size and 70-ft deep. <br />' The area surrounding C-Pit has been heavily disturbed by mining. Mining and <br /> subsequent backfilling with overburden has occurred west and east of C-Pit, <br /> pursuant to the reclamation plan approved in M-77-208. <br />' <br /> North and east of C-Pit are alluvial deposits of the St. Vrain Creek The sand and <br /> gravel deposits are 25-30 feet thick and come into contact with the sedimentary <br />' rocks surrounding C-pit approximately 1,000 feet away at the closest point. <br /> There is absolutely no contact between the disposed CKD and the alluvial <br /> deposit. The CKD disposal mass is entirely contained within the sedimentary <br />' rocks described above. <br /> Significant surface water bodies in the area, and the approximate distance from <br />' the CKD disposal area in C-Pit are as follows: <br />St. Vrain Creek - Approximately 4700' at the closest point <br />Foothills Reservoir - Approximately 4200' at the closest point <br />A-Pit Reservoir - Approximately 2000' at the closest point <br />(A-Pit Reservoir is an approved water storage facility on Southdown <br />' property and within the M-77-208 permit boundary. The water is <br />used for the cement plant.) <br />' Swede Ditch - Approximately 25' at the closest point <br />Boulder Feeder Canal - Approximately 360' at the closet point <br /> The Swede Ditch which runs along the west rim of C-Pit was all enclosed in a 4- <br />' foot diameter corrugated steel pipe in 1998 in preparation for conversion of C-Pit <br /> from active quarry to CKD storage. All the pipe joints were sealed. The Boulder <br />' Feeder Canal is approximately 360-feet west and 9.5-feet higher (elevation <br />difference from the bottom of the canal compared to the rim of C-Pit) than the rim <br /> of C-Pit. This eliminates the possibility of gravity flow from C-Pit to the canal. <br /> Runoff from the disposed CKD can not escape C-Pit and is entirely contained <br />within the pit. C-Pit CKD storage has been designed and situated to eliminate <br /> the potential for leachate seepage into agricultural water canals now and in the <br />' future. <br /> 12 <br />