2004-11-04_REVISION - M1977208 - Laserfiche WebLink

Home Browse Search

Erica Crosby Division of Minerals and Geology Page 2 of 3 November 1, 2004 (including measured strikes and dips by the USGS) along with borehole logs of nearby bedrock water wells from the Division of Water Resources, State Engineers Office. The attached base map and cross section A-A' indicate that A-pit water may be a suitable monitoring/compliance point but this finding in not conclusive. The water surface elevation in A-pit is 14 feet lower than the water surface elevation in C-pit as of October 18, 2004. A-pit water is topographically downgradient of C-pit water. C-pit was mined to recover the Fort Hays Limestone while A-pit was mined to recover the Smokey Hill Shale (both are members of the Niobrara Formation). The Smokey Hill Shale overlies the Fort Hays Limestone. If C-pit water was entering the Fort Hays Limestone it would be difficult to imagine water moving up the stratigraphic column given the minimal hydraulic head. Some Smokey Hill Shale is exposed in C-pit (removed as overburden to get to the limestone) and these beds of Smokey Hill Shale may connect to the bottom of A-pit however this is not known (the bedding in the vicinity of C-pit and A-pit dips approximately 6°-8° east-southeast). Due to the uncertainty about the degree of hydraulic connection between C-pit and A-pit, Cemex is proposing to install two new ground water monitoring wells located as shown on the base map. The wells will be screened in the Fort Hays Limestone and are proposed to be used as monitoring and compliance points. The off-site well completed in the Dakota Formation (which is not owned or controlled by Cemex) will continue to be monitored by Cemex but will not be designated as either a monitoring or compliance point. Neither Cemex nor the Division want a permit condition that cannot be assessed without the permission of a third party not bound by the DMG's regulations. The following summarizes proposed monitoring and compliance points: C-pit water -Source (C-pit is neither a monitoring nor a compliance point) A-pit water -Surface water monitoring point New monitoring well -Downgradient monitoring point New compliance well -Downgradient compliance point Off-site Dakota Formation well -Regional groundwater quality indicator In previous discussions with the Division, Cemex proposed monitoring St. Vrain Creek and the Boulder Feeder Canal water to establish some baseline water quality data. This is no longer deemed necessary because of the plans proposed herein. Cemex will submit a ground water mitigation plan to the Division if an exceedance of any of the five water quality parameters are observed in three consecutive monitoring events. The plan will be submitted to the Division within 30 days of the trigger event. The plan will identify the source(s) of the exceedance and the proposed remedy to comply with the applicable standards.