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First, the hydrologic gradient is generally towazd the Colorado River. For the period of mid to late-April through late October, the gradient is enhanced by the addition of water from the irrigation ditches that irrigate the terrace just north of US 6&50. Second, the ambient ground water level is approximately 3 to 8 feet below the ground surface (at the overburden/gravel interface). During imgation season, the terrace to be mined has been historically flood imgated and therefore the water level is virtually at the surface. In both cases, the water is migrating through the gravel layer to the river. At approximately 25 to 30 feet in depth, a shale unit underlies the entire property. This is the same shale unit exposed in Phase I of the Mamm Creek pit. This shale unit acts as an aquatazd to the groundwater and limits the depth to the depth of the gravels. Lafazge has two years of operating experience at Mamm Creek and operating in the same units, at the same approximate depths; with irrigation ditches up-gradient from the mining operation has not experienced any impacts. This is further born out by the fact that none of the Mamm Creek neighbors have experienced any interruptions to their water wells and/or imgated lands and ditches. Currently, the surface water is comprised of surface runoff after precipitation events, tail water collected in the ditch at the bottom of the upper terrace, and from return flows of imgation ditches to the Colorado River. The irrigation ditch return flows will still occur. Most of the surface runoff will be captured by the pit lakes and then flow to the river via the return structures. Tail water from the ditch at the bottom of the upper tettace will also still return to the Colorado River via ditches at either end of the property and/or through the pit lakes. Since the pit lakes aze to be unlined, once they aze full, all flows will return to the river at their same approximate location. 14. Groundwater is artificially charged by irrigation practices occurring north of the property between the months of mid to late April and late October. During this period, groundwater can be found as high as the property surface, as the past practices have been to flood irrigate the property for hay and alfalfa production. However, generally, the groundwater level is shallower on the west end of the property than on the east end due to the depth of overburden. Drill logs from Lafarge's exploration program showed the groundwater layer to be approximately 3 feet below the ground surface on the west side of the property, while on the east side it is 8 feet below the surface and located at the overburden/gravel interface. I5. The cone of depression extending out 200 to 300 feet was estimated based on Lafarge's experience at the neighboring Mamm Creek site. The vertical profiles for both properties aze very similar, occur in the same geologic units, and have similar geography and hydrologic settings. That is, both properties have terraces and irrigation ditches on the opposite side of highways. Both properties have a mining terrace and a lower terrace. Both properties aze underlain by a shale unit that limits the depth of the gravel and acts as an aquatazd. The single most important difference is that the North Bank site is outside of the 100-yeaz flood plain. The 31-foot depth to shale layer was verified by Lafazge's exploration drill holes. There aze no springs, which Lafazge is aware of, within the permit area. Revised Figure J1 shows all wetlands, groundwater wells, irrigation channels, sub-imgated meadows, and riparian areas. 5757 Central Avenne ~ Phone 303-443-2209 Boulder, Colorado 80301 GuSrnysolV nssoclnrrs Fax: 303-443-3156