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Adequacy Issue#4: Potential for Seepage from the Toe of Existing and Proposed Overburden Storage <br /> Areas <br /> DRMS Adequacy Comment <br /> If the potential exists for the preferential flow path to be circumvented in ECOSA, it stands to reason the <br /> same low probability could exist in the other existing and proposed overburden storage areas that will be <br /> expanded under the proposed amendment. If it is CC&V's assertion that the same condition will not exist <br /> in other overburden storage areas as previously accepted by the Division, CC&V must explain the reasons <br /> in detail. If not, CC&V must also place a minimum of three feet of low infiltration cover in all current and <br /> proposed overburden storage areas as part of the final reclamation plan. Please provide a detailed <br /> response explaining how CC&V will address this concern. <br /> CC&V Response <br /> It is CC&V's determination and commitment that there will be no groundwater pathway from the other <br /> existing and proposed overburden storage areas ("OSAs") other than the pathway that passes through <br /> the diatreme and flows with the natural groundwater through the diatreme to the Carlton Tunnel. <br /> All OSAs are located over or within the drained Cripple Creek Diatreme, and as a result all infiltration <br /> that takes place at these locations will pass through the diatreme and exit via the Carlton Tunnel. This <br /> can be proven as follows: <br /> 1. Infiltration.Net infiltration through the natural ground surface above the diatreme averages 5.9 <br /> ± 1.0 inches per year, based on the infiltration observed prior to 2002(Plate 110). Infiltration is a <br /> function of precipitation and snowmelt, and in the natural state is quite variable over the short <br /> term, which is reflected in the variability of the Carlton Tunnel outflow prior to 2002 (Plate 1). <br /> This rate of shallow infiltration will re-establish after reclamation of the surface of the OSAs with <br /> local growth medium. <br /> 2. Discharge out of the base of the soil to the overburden. Water in the soil that escapes the root <br /> zone passes from the soil to the overburden beneath.This transfer takes place between the fine <br /> grained soil material with relatively high capillary tension, and a coarse-grained overburden <br /> material with very low capillary tension.This contrast limits the flow of water from the soil to <br /> the overburden, until the soil approaches or reaches saturation, at which point the flow is <br /> limited by the surface infiltration minus the evapotranspiration. This process keeps water in the <br /> soil, available for uptake and evapotranspiration by plants.The process depends primarily on <br /> the size of the capillaries in the soil, broadly the porosity of the soil, and is independent of the <br /> depth and permeability of the soil and the overburden. <br /> 3. Passage through the OSA.The water that exfiltrates from the soil base seeps through the <br /> overburden stored in the OSA. This seepage occurs as vertical unsaturated flow, because the <br /> hydraulic conductivity of the overburden (in the order of 100 cm/sec as shown on Plate 2), much <br /> greater than the hydraulic conductivity required for saturated flow of the 6" of net infiltration <br /> (5x10-7 cm/sec). The unsaturated flow in the substantial thicknesses of overburden results in <br /> attenuation of the pulses of infiltrating water released from the soil, as the moisture content, <br /> to Plate 1 is a reproduction of Hydrogeochemistry Report,Volume IV, Plate 7. <br /> Adrian Brown Consultants, Inc. Page 5 of 8 <br />