2014-06-17_REVISION - M2000041 - Laserfiche WebLink

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SOLUTIONS May 27, 2014 Environmental Alternatives, Inc. Attn: Dr. Angela Bellantoni 11.07 Main Street Canon City CO, 81212 RE: Evans#2 Pit(M-2000-041)Hydrogeologic Evaluation Review Dear Dr. Bellantoni: The following discussion is in response to the Hydrogeologic Evaluation for the Fremont Paving Evans #2 Pit (December 2013) review comments prepared by RJH Consultants, Inc. (Englewood, Colorado) in a letter to Mr. John Sliman dated May 8, 2014. The hydrogeologic evaluation was prepared as part of the response to Division of Reclamation, Mining and Safety (DRMS) permit amendment application adequacy review comments. As stated in the evaluation report, objectives of the impact analysis included estimating the static groundwater elevations at the site prior to dewatering, the radius of influence of the current and future dewatering operation, project dewatering flow rates, and providing recommendations for a groundwater monitoring plan. The report objectives and analysis approach were further discussed at a December 12, 2013 meeting with DRMS staff. Relative to the other report objectives, more emphasis was placed on estimating the Evans #2 Pit current and future dewatering radius of influence for use in developing a groundwater monitoring plan. For estimating the dewatering radius of influence, the analysis approach using the Marinelli and Niccoli analytical solution was discussed in detail. It was understood that the analytical solution is a simplified groundwater modeling tool and relies on certain aquifer characteristic assumptions that are not always satisfied by Evans #2 Pit site and regional conditions. Following discussion, it was agreed that, at this time, the need for a more comprehensive finite-difference flow modeling effort was not necessary and the proposed Marinelli and Niccoli analysis approach was adequate. Additionally, discussions at the DRMS meeting confirmed that the analysis would rely on existing, readily available information and that assumptions regarding aquifer parameters would need to be made. It was also recognized that the analysis assumes that all aquifer parameters are steady-state and uniform within the dewatering radius of influence, while the actual alluvial aquifer parameters vary both spatially and seasonally/annually within the site area. These limitations in the analytical solution and potential variability in the estimated dewatering radius of influence emphasized the need to establish a groundwater monitoring plan that could be used to better quantify potential dewatering impacts. The Marinelli and Niccoli analytical solution assumes that there is a uniform aquifer of infinite extent that can supply groundwater to the radius of influence. As noted in the review comments, these assumptions are not valid within the study area since an alluvial aquifer boundary exists to the north of the site and the Arkansas River runs immediately south of the property. The Blue Earth Solutions,LLC ♦ P.O.Box 2427 ♦ Fort Collins,CO 80522 ♦ (970)227-2803