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02/02/00 WED 15:08 FAd X004 <br />+' ~ • <br />that aze not appropriate for the hydrogeologic setting of this azea This determination was <br />perfomed using a distance of 2.8 miles. "This distance was acquired from an EPA report that <br />considered the shortest map distance from the facility boundary to the town's nearest water- <br />supply well. However, the hydrogeological assessment that was performed for the area and <br />presented in my letter of January 18, 2000 indicated that the southwest permit boundary area of <br />the facility is underlain by the Santa Fe Formation. This is a low germeabiliry unit and does not <br />possess the same hydraulic properties that were input into the analytical calculation performed. <br />In this area of the facility surface-water transport would be the greater pathway of concern. <br />Based on my evaluation of the area's hydrogeology, it is the potential grour:d-water <br />flowpath along the alluvium of the Rito Seco drainage that would be monitored by the <br />recommended well location in my letter of January 18, 2000. The distance from the western <br />mine permit boundary to the town's nearest drinking water-supply well along this pathway is <br />approximately 4.5 miles. Using the same conservative values for hydraulic properties of the <br />aquifer and the ultraconservative ground-water velocity calculation using Dazcian Principles, the <br />time of travel over this flowpath would be on the order of 24 years. This determination is <br />performed for the purpose of deten,,;n;ng whether this area of the facility would fall within the <br />WHPA/S WAA based on ground-water flow time of bevel determinations under the existing <br />State programs. As can be seen by this result, the estimated time of travel from the western <br />extreme of the mine property to the town exceeds the State policy value for drinking water <br />protection by a factor of about 4. <br />With this in mind consideration should be given as to whether a monitoring well is <br />needed in the area recommended in my previous letter. It is recommended that the CDPHE in <br />cooperation with the community complete the source water assessment for the SLWSD's <br />wellfield. A completed assessment would provide the community with more comprehensive <br />information upon which to base a decision concerning this facility and any other potential <br />sources of contaminants which may be identified. <br />If you should have any questions, please feel free to contact me at 303-312-5595. <br />O <br />