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Pric~l~ Permit <br />February 25, X108 <br />Page 2 <br />on the groundwater drain the City uses as part of their raw water supply. The <br />Pit is located upgradient of a horizontal groundwater drain and the dewatering <br />operation for the mining will remove the water prior to it entering the <br />groundwater drain. <br />• The permit application on Page 9 states the Pit will be backfilled with "inert <br />material;" however, "inert material" may contain asphalt or other contaminants, <br />which over time could leach hydrocarbons or other chemicals into the soil and <br />eventually into the groundwater drain that flows into the reservoir. <br />- - ----- - -- - -- -• =-C-urrently,--groundwater-flows-east-to-west through-the-areas-of-the_proposed-P~t_ _ <br />and into the City's groundwater drain. If the Pit is excavated to bedrock and <br />backfilled with "inert material," it could be assumed the hydraulic conductivity of <br />the "inert material" is several orders of magnitude less permeable than the <br />existing sand and gravel. This could greatly diminish the flow into the <br />groundwater drain and reduce the City's water supply from the groundwater <br />drain. <br />• A second affect of the "inert material" being several orders of magnitude less <br />permeable than the existing sand and gravel is that it could cause groundwater <br />to mound below properties to the east of the Pit. This mounding could cause <br />water to rise to the ground surface and impact drainage facilities along I-76 and <br />the I-76 frontage road and, in an extreme case, I-76 and the I-76 frontage road. <br />• The City does not intend to remove the monitoring wells referenced on page 18 <br />of the application. The City uses these to monitor performance of the <br />groundwater drain and soil-bentonite wall. <br />As discussed above, the proposed pit has significant impacts on an existing municipal <br />water supply system. <br />Thank you for your time and consideration of the City's concerns. Should you have <br />any additional questions or concerns, please contact me at 720-977-6504. <br />Sincerely, <br />~~.~--- <br />_ , <br />~.--~~ ~ ` <br />`__ - - <br />Emily Hunt <br />City of Thornton <br />Water Resources Manager <br />EM/pcj <br />cc: Mark Koleber, Water Supply Director <br />Eduardo Moreno, Project Manager <br />Project File <br />S:11D\Engineedng\Engineers\moreno\projects\Priola Pit1022208 Pdola mining reGamation permit - CO7 comments.doc <br />