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~1emo to 1'rica Crosby' 2 Junc 1, 21>n6 <br />Gcutcchnical Adcc~uacy Rcvicw Permit ~Io. M-19137-028 <br />the State Engineer (OSE1, any water captured in the lower pit out of <br />priority must he rcleascd to the natural drainage or must lirlly soak into the <br />ground within 72-hours of the out of priority detention. <br />ii) If the capability of the well fractured carbonate ruck in the lower pit to <br />consume water is to he considered by the D~1G in the review of the water <br />detention capacity of the lower pit and to satisfy the OSE 72-hour <br />maximum detention requirement, a technical assessment of the rock's <br />permcahility must be provided. <br />iii) fhc peak Ilow of water, if any, that would spill liom the lower pit during a <br />IOU-ycar•?4-hour stomt must be detcrtttined, and it must he demonstrated <br />that the lower pit cunliguration thmughout the life of mint and the down <br />gradient Ilow path cnn safely pass this flow to Taylor Gulch, otherwise a <br />design for a spillway and conveyance rhanncl must he provided. <br />iv) ~4'hether water collected up gradient of the quarry is routed to the lower pit <br />or directly to 7~aylor Gulch, sufficient capacity must be maintained in the <br />lower pit to contain runoff from the I0-year, 24-hour event and to safely <br />spill the lU0-year, 24-hour event, and these capacities must he maintained <br />until vegetation has established in the areas to he seeded. i~he Operator <br />must further describe reclamation of the lower pit are in this regard. 1Vill <br />the lower pit he Icfl as a water collecting depression in the final reclaimed <br />setting? Or will it he hacklillcd to provide positive drainage'' If it will he <br />a depression, the Operator must demonstrate that routing of 100-year, 24- <br />harr nututl'thmugh the lower pit and to Taylor Gulch will he cllective in <br />the long terns without the need tier periodic maintenance. <br />b. Cunccyance of drainage Isom up gradient historic metal mines into the lower quarry pit <br />to provide passive drainage, as discussed in the application, may result in adverse legal <br />consequences to the Operator. l Indcr current federal law, the Operator runducting a <br />partial cleanup of historic mine drainage could subscyuently be held liable lix more <br />extensive cleanup or coulJ be obligated to obtain a discharge pemtit requiring <br />compliance with strict water quality stmtdards in streams that may already nc in <br />violation of-these standards. Liability may occur even though the Operator did nothing <br />to cause the pollution li•om the historic mines. The Operator should consult an attomev <br />and may wish to consult with the United States Em ironmental Agency prior to <br />embarking on a course ufactiun that may result in this type of liability. Also, the <br />OFtcrttor must provide sufficient infomuuion for the DViG to dctcmtinc that Ute state of <br />Colorado would not he liable if historic mine water is routed to the lower pit and the <br />Dh1G were to subscyucntly reclaim dte quarry in a nand fitrteilure situation. <br />3. Dunng field inspections ufihis operation conducted by DMG in 21104 and 2005, certain <br />unapproved waste rock disposal practices were observed. '1'hcsc practices included the <br />dumping of waste rock unto previously undisturbed surface soil and vegctatiun, including <br />