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from this knickpoint or anywhere else on the mine site. Vegetative cover appears to adequately <br />protect the site from erosion. Based on these field observations, and the calculated soil loss rates, the <br />Division finds that the La Plata site is not contributing more suspended solids to offsite streamflow <br />or runoff than premining conditions. <br />Evaluation of Hydroloaic Imnacts Required bV Section 3.03.2(21 <br />Rule 3.03.2(2) requires the Division to evaluate hydrologic impacts prior to releasing reclamation <br />liability. This evaluation must consider whether pollution of surface or subsurface water is <br />occurring, and the probability of future occurrence of such pollution. The Division's evaluation is <br />summarized below. <br />Ground Water Impacts - As shown in Figure 1, the underground workings of the La Plata Mine <br />are above the current ground water saturated zone. The elevation of the top of the saturated zone <br />is considered to be stabilized at its approximate current position. Only a significant long-term <br />change in regional climate or significant well pumping would significantly raise or lower this <br />elevation. Over time, meteoric water probably infiltrates from the land surface down into the <br />abandoned underground workings of the La Plata Mine. As this water slowly accumulates in the <br />workings, it would seep into the bedrock walls of the workings, and migrate downgradient to the <br />saturated zone. The expected migration direction would be generally southward from the <br />workings. Any minerals this migrating water picks up in the mine workings would be tamed to <br />the saturated zone. If the mineral content of this migrating water is high, then it could pollute the <br />ground water in the saturated zone. The infiltration and migration process would take many <br />decades owing to the slow infiltration rate and the low hydraulic conductivity of the Cliff House <br />Sandstone and Menefee Formation. It is improbable that any water from the La Plata workings <br />has reached the saturated zone, yet. Also, it is improbable that the La Plata workings have <br />discharged water to the land surface in the portal area because it would take many decades to fill <br />the workings enough to exert signiftcant pressure in the portal area. No seepage or dischazge <br />from the portal area has been found during the Division's regular inspections. The improbability <br />of current degradation to the saturated zone, and the absence of dischazges from the portal, <br />indicate the La Plata Mine is not causing ground water pollution, and the operation is in <br />compliance with the Basic Standards for Ground Water (Colorado Water Quality Control <br />Regulation 41.S.C.6). <br />Surface Water Impacts -The only surface water feature that would receive surface runoff from the <br />La Plata surface disturbance is Hay Gulch. The Gulch does not have a stream channel. An irrigation <br />ditch flows through the bottom of the Gulch. The King Coal Mine monitors the quality of Hay Gulch <br />alluvial water in the Wiltze well, approximately one mile downstream from the La Plata Mine. This <br />monitoring indicates no adverse impacts to the alluvial water from the La Plata Mine. The only <br />surface water from the La Plata surface disturbance that would reach Hay Gulch is surface runoff <br />from rain or snowmelt. (As previously discussed, a discharge from the portal azea has not occurred.) <br />Surface runoff from the disturbed area can be expected to be alkaline and free of contaminants as <br />there are no leachate-forming materials on the land surface. The quality of this runoff should be <br />closely similaz to runoff from surrounding undisturbed lands, and therefore, does not have the <br />potential to degrade surface waters or alluvial water in Hay Gulch. <br />2 <br />