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1;ECE/V~D <br />EXHIBIT S -Structural Stability of City Sewer Main JAN 2 ~ ZQQ3 <br />Division olfvgine~ :. _. <br />The attached drawing is a graphic representation of the proposed mining operations near the "` ~~~'cg„ <br />existing City of Loveland Sewer Main which runs roughly East and West along the Northern <br />boundary of the proposed mine area. <br />An analysis of the "Record Drawings" for the Namaqua Interceptor owned and operated by the <br />City of Loveland indicates that the 15-inch sanitary sewer has an average cover of 3.5 feet except <br />for the area immediately adjacent to the Electrical Switch Station. At this location, the sewer has <br />cover of approximately 16 feet at it's deepest. <br />The soil characteristic in the area has overburden ranging in depth from 1 to 5 feet with an <br />average depth of 3.3 feet. Underlying this overburden is an alluvial sandy gravel stratum that is <br />the material to be mined. This stratum has a depth ranging from 7 to 11 feet. Below the sandy <br />gravel is a silty shale bedrock. From existing grade to the shale is 11.5 to 13.5 feet. The mining <br />operation will not penetrate deeper than the shale. The sand and gravel aze a cohesionless soil. <br />For cohesionless soils, the angle of internal friction typically is the angle from the horizontal <br />naturally formed by a pile. For sands and gravels the internal angle of friction is typically 30 <br />degrees to 38 degrees. However, in our analysis we have used a conservative 45 degrees. <br />The site that remains to be mined, which is adjacent to the sewer main, is that azea East of <br />County Road 19 (Namaqua Ave.) The minimum distance that will be maintained from the <br />sewer main is 25 feet. If the soil should slough at the conservative 45 degree angle depicted, the <br />closest the mine excavation would be to the sewer main is 18.5 feet. With the average depth of <br />the sewer main being 3.5 feet, the 18.5 feet of horizontal cover is more than adequate to maintain <br />a sufficient bedding and stability of the sewer main. The maximum depth of the sewer main that <br />would be in the sands and gravels would be at the approximate 13.5 foot depth. This is the <br />location where the gravel strata makes contact with the shale strata. However, even at a depth of <br />13.5 feet, the sewer would still have adequate horizontal cover to maintain sufficient bedding and <br />stability of the sewer main. Sewer at a depth deeper than this will be bedded in the surrounding <br />shale. <br />It should be noted that the area West of Namaqua Ave., which is also adjacent to the City sewer <br />main, has already been mined in this fashion with no adverse effect on the sewer main. <br />Therefore, this analysis has determined that the mining operation, when performed no closer that <br />25 feet from the sewer main, will not adversely affect the sanitary sewer main, nor the electrical <br />switch station farther from the excavation. <br />