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Differences in horizontal and vertical permeability that were present in the compacted and . <br />stratified undisturbed material will decrease as a result of the less sorted, more <br />homogeneous texture present within the replaced spoil material, Vertical permeability <br />within the spoil will depend on the degree of interconnected porosity rather than <br />fractures present in the compacted layers of the overburden. The poorer sorting of <br />particle sizes in the spoil should not impede the vertical flow of water any more than <br />impedence produced by compacted layers and variable degrees of vertical fracturing within <br />undisturbed material. <br />Analysis of premining soils at Seneca II-W indicates that the soils generally display slow <br />to moderate rates of infiltration (see iab 9, Soils). Replaced topsoil is projected to <br />display a more even mixture of moderate infiltration rates. Sometimes infiltration rates <br />in topsoiled spoils are less than infiltration rates in undisturbed soils (Tab 7 section <br />on Infiltration and Permeability of the Unsaturated Zone). Three years of monitoring seem <br />to suggest that infiltration rates in replaced spoil at the Seneca II Mine are unchanged <br />or slightly increased since recharge has occurred at a greater rate than normal for the <br />area. Even though the topsoil is compacted somewhat during placement, deep ripping and <br />disking operations will enhance infiltration rates and prepare the soil for seeding, • <br />Regrowth of vegetation will induce retention of soil moisture and enhance infiltration <br />while preventing surface runoff. <br />In conclusion, the mining and reclamation activities planned for Seneca II-W will not <br />diminish the horizontal and vertical pe rmea bi lities of the aquifer materials, and in some <br />cases, the operation may enhance them. No significant impacts to ground water flow are <br />expected. The infiltration rate should remain the same or increase slightly in response <br />to the rise in the hydraulic conductivity anticipated to occur in the spoil material. <br />Precipitation will infiltrate the topsoiled spoil material at the Seneca II-W Mine and <br />flow downward to the saturated zone where it will recharge the regional ground water flow <br />system. <br />Containment of Pit Inflow Pumpage and Impacts on Water Quality. All runoff and pit <br />pumpage from disturbed areas are routed through sedimentation ponds. The ponds will be <br />designed and constructed to impound runoff and pit pumpage from areas disturbed by mining <br />and provide sufficient residence time to ensure that the pond discharge water chemistry <br />meets the effluent requirements specified in NPDES Permit No. CO-0000221 (see Tab 7, • <br />Appendix 7-6). In all, three NPDES ponds will contain runoff and pit pumpage from Che <br />mined areas: Ponds 005, 006, and 009. All ponds will be constructed in accordance with <br />accepted engineering practices. <br />16 <br />