2001-05-29_PERMIT FILE - M2001023

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Memo to Tom Schreiner 2 May 29, 2001 The setback proposed in the application for mining in the vicinity of the power line is once again 20 feet with a maximum pit slope angle of 1.25:1. However, in the case of the power line the Applicant's proposed setback is established from the base of the individual power poles rather than from the easement boundary. Similar to the discussion related to the gas line easement above,the Division will require a 70-foot horizontal setback as measured from the excavated toe of the slope. This setback must be established to the power line easement boundary rather than to the power pole structures themselves. This is because the actual land within the easement is due protection from damages that may be caused by pit slope failure, so the easement land may not be used as part of the potentially damaged buffer area between the mining excavation and the power poles. The regulatory basis for establishing the setback from the easement boundary rather than from the structure itself is not in the structure protection regulation at 6.4.19 of the Construction Materials Rules and Regulations of the Mined Land Reclamation Board, but at section 34-32.5-116(4)(i), C.R.S. requiring areas outside of the affected land to be protected from slides and damage occurring during the mining operation and reclamation. A complicating factor with establishment of the mining setback from the power line easement boundary specific to this site is that there is some confusion as to the width of the easement. The permit application states that the property deed references a 40 foot wide easement, but the electric utility claims that the easement is 100 feet wide. No documentary evidence for either of the claims is provided in the permit application; as a result, for permitting purposes, the Division must assume a 100 foot wide easement unless it can be demonstrated to the satisfaction of the Division, in consultation with the Attorney General's Office, that 40 feet is the correct easement width. In order to assure that the setbacks described above are maintained, the Division will require that the easement boundaries be delineated and marked prior to mining. The applicant must provide a clearly written commitment to have the rights-of-way surveyed by a licensed surveyor,and to erect a fence or other durable and clearly visible marker along the boundaries. It must be emphasized to the pit operator that the 70-foot setback is to the toe of the excavated pit slope. Excavation to a pit slope toe that is closer than 70- feet to the easement boundaries, then backfilling to restore the required setback, is not acceptable. The permit application states that the mining setback from the gas line easement is adequate to assure that the pipeline will not be damaged,and that strain gauges affixed to the pipeline are not necessary. However, the stability analysis provided applies only to relatively large-scale earth movements, such as deep-seated circular failure. The Division is concerned that smaller scale strains,such as may be caused by relief of pre- existing stresses in the bank when the gravel is excavated,may be sufficient to adversely affect the pipeline. The installation of three or more strain gauge emplacements on the pipeline would be a reasonable and prudent measure to detect any small movements in the pipeline that may occur. Early detection of small movements in the pipeline would allow for timely stress relieving measures that would prevent damage. In summary, the Division's position on the installation of strain gauges is that: