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Ms. Erica Crosby March 3Q, 2007 Page 6 Monitoring wells CEM-002 and CEM-003 will be completed in the Smokey Hill Shale unit to the east of C-Pit, at depths above the top of the Foxt Hays Limestone and below the bottom of C-Pit. These wells axe intended to help evaluate the occurrence of water, if any, in the shale in this area, and whether ox not it may be coming from C-Pit. Monitoring well CEM-004 is proposed fox north of C-Pit and will be completed in the St. Vxain alluvium north of the Highland Ditch as it rums Exom its north-south leg towazds the southeast (see Figures 1 and 2). This location is intended to help evaluate whether C-Pit water is migrating northward to the St Vrain Creek alluvial system. Review of the USGS geologic map for this area (Hygiene Quadrangle) confirms that the area to the north of the Highland Ditch is composed of stream alluvium. The boundary of the stream alluvium and the bedrock system where C-Pit is located generally runs between the plant site (which is sited on the alluvium) and C-Pit. The area has been heavily disturbed by mining, plant and road construction, and irrigation ditches. Earlier CEMEX hydrogeological investigations in this alluvial system indicate that the depth to water is shallow (less than 10 Eeet), and groundwater flows generally eastward toward St. Vrain Creek. Earlier investigators have emphasized and reported to the Division that C-Pit is located within the sedimentary units outside (south) of the St. Vxain alluvium, and that both the CKD and the water level in C-Pit axe well below the alluvial groundwater system (Report on Storage of Cement Kiln Dust, Southdown, Inc. Lyons Plant. Banks & Gesso LLC, Grant Environmental Inc. June 21, 1999). Brown and Caldwell proposes an alluvial well to determine the depth to water in relation to C-Pit and the surrounding area. Until the existing topographical mapping is expanded to include the area to the north of the Highland Ditch near C-Pit, and additional field information is collected to determine depth to groundwater in the alluvium relative to the depth to water in C-Pit, it is premature to site multiple wells in this unit. At the Febmary 22, 2007 site inspection, Erica Crosby of DRMS discussed the need for a compliance monitoring well completed in the Foxt Hays limestone unit near the eastern extent of the CEMEX property, down dip from C-Pit. Compliance well CEM-005 will be located approximately 2,600 Eeet down dip (southeast) of well CEM-001 and completed in the Foxt Hays Limestone, near the boundary of the CEMEX property with the adjacent Bashor Farm on Hygiene Road to the south. (See Figure 1.) Drilling logs of nearby water wells at the farm (completed in the much deeper Dakota Sandstone aquifer) indicate that the Fort Hays Limestone is approximately 30-feet thick and over 400 feet below ground surface at this location. The hole will be electrically logged prior to the placement of the casing to ensure that the completion is within the Foxt Hays unit. Monitoring Approximate Targeted Well/ Diameter, Depth, feet Lithologic Comments Piezometer inches b s Unit Intended to monitor potential leakage out -'itned area of Feeder Canal P-001 1 15 Backfill into the previously [Wined area to the east. -0594686.doc