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TETRA TECH RMC Mr. Larry Oehler Adequacy Response M-2004-044 November 22, 2004 Page 11 of 20 moves toward the river through the alluvium. It appears that the slurry wall may cut offground water flow to the natural area. Demonstrate that the slurry wall will not block the groundwater flow into the natural area to the extent that it will cause the trees and other vegetation reliant on the normal groundwater surface to die from lack of water. What is the expected shadowing effect on the ground water table? Will the shadowing effect be enough to cause cottonwood trees and other vegetation to die in the natural area? What will Aggregate Industries do to correct it if this problem begins to occur? Tetra Tech RMC performed a groundwater model analysis for the Tucson South site, Tucson South Resource Groundwater Modeling Study on the Hydraulic Effects of Mining (August 2004). The modeling report was submitted to the Division on August 3, 2004. Groundwater flows from south-southwest to north-northeast, and hence no "shadowing effect" in the Morgan Smith Natural Area. The proximity of the River also minimizes the impacts of groundwater levels in the Morgan Smith Natural Area. Scenario 4 (Figures 5 and 6), was modeled as dewatering the Tucson South Phase 2A area, dewatering the Challenger mine, and the slurry wall around the Tucson South Phase 2 east cell is not yet constmcted. The groundwater model predicts a 2-3 foot draw-down in the Morgan Smith Natural Area. However, the impact from the Phase 2A area has historically been occumng for the period mining and dewatering has been happening in this area, with no known measured impact. If the trees in this area are impacted, Aggregate can direct dewatering water to the ground surface in this area for imgation. This draw-down would be temporary until the slurry wall in installed around the Phase 2 east cell area. As indicated in Scenario 5 and shown graphically in Figure 7 and 8 of the modeling report, the simulated cumulative effect of the groundwater for the area after the slurry wall is installed around the Phase 2 east cell, has no impact on groundwater levels in the Morgan Smith Natural Area. 10. The Division of Wildlife recommends that the proposed operation avoid destroying the black-tailed prairie dog town on the west edge of the west area. The DOW did not provide a map showing where the town is located. From their description, it appears that the town may be in the West Fil[ Area where it may be buried when overburden, clay lens material and topsoil is placed there. The DOW lists the prairie dogs as a "species of special concern "and recommends that the prairie dogs be relocated or humanely killed prior to any earth moving. Please discuss how Aggregate Industries will contend with the prairie dogs. Refer to Rule 3 Section 1.8(1). H:U919_Ol9_OIVvfLRH\DMG Response\I st Adequacy Response to DMG I I-5-04.doc