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COLORADO DEPARTMENT OF PUBLIC HEALTH & ENVIRONMENT -Water Quality Comrol pivision <br />Ratiowle -Page 13 Permit No. COR-040000 <br />~ VII. CHANGES AFTER PUBLIC NOTICE (cont.) <br />• modified to specify that waste products include any acid generating material exposed by the mining activity, <br />and the vegetative cover criteria addresses sediment production. The Division believes that this will address <br />the concerns of both the Division and the permittees. <br />Reeardine isolation or removal of mine waste: The regulations clearly require that stormwater discharges <br />from mirse and mill sites that are contaminated by the contact fist of materials, must be authorized by a <br />permit. Permittees must decide whether isolation or removal of the material is practical, feasible or <br />economically possible. Continued permit coverage is available if permittees decide not to attempt to isolate or <br />remove the material. <br />5. The Division's burden of proof reeardine water ouality impacts. <br />Many commenters objected to the latitude that is reserved to the Division regarding such things as requiring <br />subsequent monitoring, requiring an individual permit, and deciding whether or not to terminate a <br />certification. In general, commenters expressed the feeling that the Division should have a greater burden of <br />proof than "has reason to believe" that there is a water quality problem. Commenters assert that several of <br />the Division's decisions are too subjective and the vague language does not provide permittees with the kind of <br />cenainty that thry need for derision making. <br />Response The Division is aware that several of the decisions can be subjective. Once greater experience is <br />gained by the Division and permittees, the subjectivity can probably be reduced. At this time, however, the <br />Division believes the permittees wi(l benefit since we have the Latitude to consider site-specific factors. Had <br />the Division elected to eliminate the subjectivity to a greater extent, the necessarily conservative nature of the <br />criteria would have greatly reduced the fiexibiliry for the permittee and the Division, and imposed <br />requirements on al! permittees that may not be appropriate in al! cases. <br />• 6. Disposal of water stored within mine waste <br />A jew commeruors had quesrions or comments regarding the restrictions on discharge of water stored within <br />the mine waste. "Disposal of water stored within the mine waste' is a phrase that is used in Part I.C.S.e. <br />This is a section that described the additional SWMP items for sites seeking permit termination. General <br />clarification is necessary. <br />Response: This genera[ permit only authorizes stormwater discharges; stormwater is precipitation-induced <br />runoff. Water stored in tailings impoundments or other areas of mine waste is not runoff. The characteristics <br />of these stored waters can vary dramatically on a site-by-sire basis and can have deleterious impacts if <br />discharged imo receiving waters. Because of the nature of these waters (not runoffi and the potential water <br />quality impacts, discharge is not authorized under this permit. An individual permit is required which allows <br />for site-specific assessment of the quality, quantity and impacts of the stored water. <br />7. Veeetative termination criteria <br />Several commeuors questioned the vegetative cover criteria in Pan I.F.I.b. Some commenters thought that, <br />as written, the criteria are too onerous, may take too long, and require importing a soil matrix suitable for <br />plant growth. One commenter suggested that it be changed from a numeric criteria to a sanative criteria and <br />require "adequate" cover. One commeruor suggested that the term "vegetative cover" be defined. <br />Response: The vegetative criteria states that "a minimum of 40 percent vegetative cover, or 70 percent of the <br />vegetative cover of a similar undisturbed site, whichever is higher" is required. That means that 40 percent <br />cover is the lowest level. This number was determined through assessment of the relationship between cover <br />and soil erosion for a variety of conditions using the Universal Soil Loss Equation. Below 40 percent, a small <br />• increase in vegetative cover mdces a dramatic decrease in sail erosion; above 40 percem, a small increase <br />does not have so large an impact. Long-term stabilization is the goal and self-sustaining vegetative cover is <br />