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Point of Compliance Well Investigation <br /> <br /> <br /> <br />AECOM <br />1 <br /> <br />1. Introduction <br />1.1 Background <br />The Colowyo Mine (“Colowyo” or “Mine”) is located in western Colorado in Moffat and Rio <br />Blanco counties immediately west of State Highway 13 (Figure 1). The Mine operates under <br />Permit No. C-1981-019 issued by the Colorado Mined Land Reclamation Division, a precursor <br />to the current regulatory agency, the Colorado Division of Reclamation, Mining and Safety <br />(Division). Stipulation 7 of the Colowyo Mine Permit includes a provision to evaluate the need <br />for groundwater points of compliance: <br />“The Colowyo Coal Company shall submit a technical revision to the Division which <br />provides an analysis of groundwater points of compliance at the Colowyo Mine pursuant <br />to Rule 4.05.13(1). This analysis will be done in consultation with the Division and will <br />include a written determination of the need for groundwater points of compliance at the <br />mine. If deemed appropriate, based on this analysis, Colowyo shall establish one or <br />more points of compliance for the Colowyo Mine.” <br />In an initial review of conditions at the Colowyo Mine, the Division (2006) evaluated three <br />specific zones of groundwater that have the potential to be impacted by mining activities. These <br />include bedrock groundwater systems, backfill and excess spoil groundwater systems, and <br />alluvial groundwater systems. As part of their review, the Division determined that coal mining <br />and reclamation activities at Colowyo do not have the potential to negatively impact bedrock <br />groundwater, and therefore do not require bedrock monitoring point of compliance wells. This <br />conclusion was based on the location of the nearest bedrock aquifer, the Trout Creek <br />Sandstone, which is approximately 590 feet below the lowest coal seam to be mined in the <br />South Taylor Pit. Another consideration was the many layers of lower permeability strata <br />between the mined coal seams and the Trout Creek Sandstone, including shales, coals, and a <br />laterally extensive clay layer. Due to these factors, the Division concluded it is unlikely that <br />infiltration through the mined areas will impact bedrock groundwater. <br />The Division also determined that meteoric water accumulating within backfilled areas of the <br />Mine and excess spoil piles is known to be of degraded quality and does not constitute a pre- <br />existing aquifer. Groundwater may locally develop in these areas due to the greater <br />permeability of the backfill compared to the surrounding bedrock strata; however, any <br />accumulated groundwater is not intended to be used as an aquifer. For these reasons, points of <br />compliance are not required for backfill and excess spoils at Colowyo Mine. The Division also <br />indicated that backfill seepage and spoil water discharge may have an impact on surface water <br />or alluvial groundwater. <br />Finally, the Division stated that mining activities do have the potential to impact alluvial <br />groundwater in the Taylor Creek, Wilson Creek, and Good Spring Creek drainages <br />hydrologically downgradient from disturbed areas, discharges, seepage from within backfill and <br />excess spoil areas, and from surface and subsurface flows from coal stockpiles at the Gossard <br />Loadout. If needed, point-of-compliance locations for the Mine would therefore be established <br />in the alluvial groundwater systems within these drainages.