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<br />Brian Munson <br />-2- <br />March 3, 1981 <br />referred to by this section also fail to contain appropriate engineers signa- <br />ture. <br />2. Overburden swell factors have not been determined. <br />3. No geotechnical analysis is included within the application. The state- <br />ment contained in the application: "all fill design perameters based on current <br />industry practice.", is not adequate to satisfy the requirements of Rule 2.05.3 <br />(6)(c). <br />4. The application states that spoil will be placed in lifts not to exceed <br />50 feet in thickness. Lift thicknesses of this magnitude are not acceptable. <br />Lift thickness should be determined by the results of the design stability <br />analysis. Lift thickness included within the design should reflect that lift <br />thickness which will obtain the required densities necessary to achieve a <br />static safety factor of 1.5. <br />5. The application states that a slope safety factor of 1.5 will be met or ex- <br />ceeded. This statement is not adequate to satisfy the design requirements or <br />Rule 4.09. Such a statement must be supported by an appropriately performed <br />thorough geotechnical analysis. <br />2.05.3(6) <br />(c) Geotechnical Analysis: <br />1. As presented in the application, section 2.05.3(6)(c) is incorrect. Subsection <br />(ii) is actually subsection (iii). Subsection (ii), which is omitted in the <br />regulation rendition contained in the permit, should read: "(ii) a survey identi- <br />fying all springs, seepage and ground water flow observed or anticipated during <br />wet periods in the area of the disposal site;." <br />2. A geotechnical analysis including those items described in permanent regulation <br />section 2.05.3(6)(c) will have to be performed and submitted in order for review <br />of the application to be completed. <br />General Comments: <br />The excess spoil fill at the Hayden Gulch Coal Mine has been the subject of scrutiny <br />and concern on the part of our Division during the past several years, as witnessed <br />by the attached memo. The applicant has been informed of these problems and has <br />responded by regrading and re tops oiling the northern face of the pile. The <br />operator's engineering staff was informed that a thorough stability analysis of <br />the excess spoil pile would be required under the permanent program. This infor- <br />mation was conveyed by myself, in the company of Rick Mills, at the mine site on <br />May 14, 1980, as well as in several subsequent telephone communications. <br />The required geotechnical stability analysis of the proposed excess spoil pile <br />should include thorough auger or bori~ngi investigations of the foundational area <br />designed to determine bedrock, soil and hydrogeological conditions. The report <br />should include geologic profiles, material testing results and descriptions of <br />the materials encountered, and a mathematical analysis of slope static safety <br />factors. That analysis should include a thorough discussion and justification <br />of any geotechnical perimeter assumptions made, regarding factors such as shear <br />strength, spoil density, hydrogeology perameters, etc. Particular concern should <br />be focused on the mechanical properties of the existing end-dumped, thick-lifted <br />portions of the excess spoil pile. The mathematical analysis should reflect any <br />material differences between the existing portion of the pile and future portions <br />of the pile which will be built in conformance with both the design and performance <br />standards of the permanent regulatory program. <br />