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i~ SECTION 3 1 GROUNDWATER SAMPLING LOCATIONS AND SCHEDULE ' The Dakota sandstone aquifer is a confined aquifer that lies approximately 500 feet below the GCC Rio Grande, Inc. Red Rock Plant and Limestone Mine and will supply potable water for the mine and plant operation. Groundwater in the St. Charles River alluvium is tributary to the St. Charles River and the Arkansas River. The Codell sandstone, which may not be water-bearing, is the upper member of Caxlile shale formation and lies directly beneath the Fort Hayes limestone, the target resource of the Red Rock Limestone Mine. 3.1 Sampling Locations Groundwater samples will be collected from five wells at the Red Rock Plant and Limestone Mine site (Site). Three monitoring wells to be installed within the St. Charles River alluvial aquifef, which will allow fox characterization of alluvial groundwater upstream and downstream of the mine stoxmwater outfall to the St. Charles River and as it leaves the Site. The potable water-supply well, designed by Leonard Rice and Associates and constructed by Layne Western (Permit No. 057033), will be a source of baseline water quality for the Dakota Aquifer underlying the Site. A monitoring hole was recently installed in the Codell sandstone (MW-OOl) by Contour Consulting Engineering, Inc. (Monitoring Hole No. 41499). Free water was not encountered during drilling of the Codell sandstone well. The location of the wells installed in the Dakota aquifer (DW-1) and the Codell sandstone (MW-001) are shown on Figure 1. As MW-001 will likely be disturbed during mining, a second well into the Codell sandstone will be installed (MW-OOIA) to allow fox monitoring of the existence of water in the Codell sandstone. MW-OOlA will be located north of MW-001, in an area were the Codell sandstone is likely to be intercepted (see Figure 1). Monitoring of MW-OOlA will indicate whether the Codell sandstone is a waterbearing unit and provide baseline water quality data for the aquifer if it exists. The proposed locations of the Sc. Charles River alluvial aquifer monitoring wells (MW-002, MW-003, and MW-004) are also presented on Figure 1. The final location of these wells is subject to change based on field conditions, access, and observations during drilling at the time of installation to ensure that all three wells are located within the alluvium. The locations of MW-002 and MW-003 will be surveyed to ensure that construction of the St Charles River bridge will not disturb the wells. Descriptions and purpose of sample locations are summarized in Table 3-1. Table 3-I. Aquifer Sampling Locations Sample Site Desi ation Sam le Site Location Pu ose- DW-1 1,000 feet east and 50 feet north of Recently installed water supply well. Site will the southwest comer of Section 18, be sampled to establish baseline groundwater Township 22 South, Range 64 West. conditions within the Dakota aquifer. Screened across the Dakota a uifer. D:\Dav\GEN\F-s-P-T\22021\Pemrimng\Snpulanon Response\Groundwarer Sampling plan\Gond~non 1 Groundwam Sampf~g Plan }_24_03 doc