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STATE OF COLORADO DIVI!iION OF MINERALS AND GEOLOGY Department of Natural Resources 1313 :iherman 5t., Room 215 DenvE~r, Colorado 80203 Phone: (303) 866-3567 FAX: (303) 832-8106 ~ July 8, 2004 COLORADO DIVISION O F MILVESRALS GEOLOGY 0.EC LA MATION•MI NING SAFETT•SCIENCE Bill Owens Governor Russell George Mr. GOrdOn M. GIOVe - Executive Director 38,7 Horse Thief Lane Ronald w. cottony Dlrrango, CO 81301 Division Director Natural Resource Trustee ,~ ,.f' ~' Re;: Sandco Pit, Permit M-1987-064, Amendment Application AM-Ol, Division Response to Citizen Concern. De:az Mr. Greve, Thank you for sending your June 11, 2004 letter of concern regazding the above-named gravel pit amendment. Your letter raised questions as to the geomorphologic effects on the stability of the site if the proposed plan is implemented. The amendment submitted by Sandco, Inc. proposes to cease gravel extraction in the Animas River channel and begin excavation east of the river, eventually resulting in a 44-acre pond. We discussed your concerns during a telephone conversation last week, and this letter is intended as a follow-up to that conversation. When we spoke, I mentioned that a written report describing the hydrologic effects on that reach of the Animas River was available for review. I have recently received and reviewed a copy of that report, and find that it appeazs to address your concerns. In this letter, I will briefly quote from that report, titled "Hydrologic Study of the Sandco Reach, Arlimas River Valley, La Plata County, Colorado, 2004," by Winfield G. Wright of Southwest Hydro- Logic. As you know, a commonly accepted benchmark flood level is the 100-yeaz flood elevation, below which aeeas and structures aze statistically more prone to flood damage, and above which areas and structures aze regazded as more protected. Though the 100-yeaz figure may be an azbitrary interval, it is widely accepted and recognized as serving the practical purpose of defining a line that allows for a satisfactory balance between lands appropriate for various types of activity and those that aze not. Tfds agency has jurisdiction in several aeeas of this question of stability of the river channel and the banks, which aze pertinent to the review of this gravel pit amendment application. In the context of this amendment, the 100-yeaz flood line is considered to be an important reference for assessing long-term site stability. It would not be appropriate for this office to require the operator's plans to meet a more stringent standard than the 100-yeaz flood. The report cited above states on page 9, "Water-surface elevations for the 100-yeaz flood...do not exceed the height of the east bank." The report further explains that there aze aeeas on the west bank in this reach, which are not involved in this amendment nor affected by this operation, which aze below the 100-yeaz flood elevation. A series of figures are included showing cross sections of the river along this reach. Based on this report, geomorphological stability issues that aze under the jurisdiction of this office are considered to be adequately addressed at this time. I have included a full copy of the report with [his letter to you, for your information. A copy of the report is also on file with the other permit amendment materials at the county clerk and recorder's office and at my office. Copies of all other materials associated with the amendment application aze also on file for public review at these two locations. Please feel free to contact me if you have questions about the application. Office of Office of Colorado