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Response to DRMS Adequacy Review (2) -Cotter SR -11 Mine Reclamation Plan Amendment <br />3) Page ESWMP -S, section 7.3. The second paragraph states the surface soils at the site are <br />considered Hydrologic Soils Group (HSG) B. The soil group on Figure U3 indicates the <br />natural soil in the area defined by the Onsite 30 analyzed is "75'; Pinon - Bowdish- Progresso <br />loams. The Soil Survey of San Miguel Area, Colorado Parts of Dolores, Montrose, and San <br />Miguel Counties lists the Pinon- Bowdish - Progresso series HSG C and D. Furthermore, <br />nearly all of Onsite 30 is essentially bare soil and there are no "Pinon1duniper" stands in this <br />area. Please revise the selected curve numbers (CN) to reflect HSG CID, bare soil or poor <br />herbaceous (CN = 8 7-94 for "Disturbed, mine yard, and stockpile areas), or provide <br />documentation to substantiate the claim of HSG B and a CN = 75 and "PinonlJuniper" <br />cover. <br />The primary vegetative cover for the area in general is Pinyon- Juniper. This can be <br />seen clearly from the Google Earth site images. Although little remnants of Pinyon - <br />Juniper exist within the general boundaries of the site itself, it was obviously the <br />original ground cover and the underlying soil would have the same characteristics <br />where there is shallow disturbance or placement of fill. Significant portions of Onsite <br />Basin 30 are covered by previously placed waste rock, some of which has been pocked <br />and partially reclaimed to aid in erosion protection and retention of stormwater. This <br />material makes up a significant portion of the onsite area. It consists of sandy material <br />partially fractured and crushed during the mining process. The area around the portal <br />is generally covered with a deep stockpile of this material. The area below the stockpile <br />is a sandy terrace, sloping generally to the south, with a thinner covering of waste rock <br />spread over most of the area. Thick stands of pinyon - juniper exist all around the site. <br />By site observation, the site soils consisted of well drained, gravelly, sandy material with <br />relatively high permeability. It is typically alluvium derived from the parent sandstone <br />outcrops found above the site. This is the base soil generally encompassed within <br />Onsite Basin 30. Assigning this area a CN value of 75, as we did, is conservatively high, <br />in our professional opinion. This mine site was evaluated based on multiple visits by <br />experienced personnel. During these visits, part of the observations included evaluation <br />of the vegetative cover and the general soils types found there for the future <br />quantification of runoff. These observations were not only performed for the specific <br />mine site, but also for the probable offsite watersheds thought to affect the area. <br />Broad -based soil evaluations intended for regional mapping tend to cover very large <br />areas within a state. As discussed previously, our selection of CN and Manning's "N" <br />coefficients involved looking at a range of possible values found in several reliable and <br />respected resources and making a subjective choice based on experience for the <br />accurate selection of the proper values. Copies of some of these resources are provided <br />in Attachment #2. We believe that the original designations of CN values for the onsite <br />and offsite areas were reasonable and applicable. <br />4 <br />