2001-05-29_PERMIT FILE - M2001023

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Memo to Tom Schreiner 3 Mav 29 2001 • The gas pipeline is a critical structure, and the consequences of a failure of the pipeline could be catastrophic. As such,a high degree of conservatism is called for in determining appropriate measures to protect the pipeline. • The strain gauges are an accepted and easy-to-use pipeline-monitoring device that can be installed at a reasonable cost. The added degree of pipeline protection provided by strain gauges can be realized relatively inexpensively; requiring their installation is a prudent addition to the proposed mine plan. An article on the use of strain gauges is attached to this memorandum. If the applicant agrees to install the strain gauges and is able to gain the cooperation of the pipeline operator,then an installation plan(number and location of strain gauge emplacements), a monitoring and reporting plan, and a threshold criteria for mitigative action must be developed and submitted for Division review and approval. It is the Division's understanding that a single strain gauge emplacement is adequate to monitor approximately 200 linear feet of pipeline (Mike Bukovansky, personal communication). Threshold criteria for mitigation can be developed by considering that maximum allowable stresses in the pipeline should not exceed 50 percent of the pipeline steel specified minimum yield strength. A two page discussion of strain measurements and threshold criteria is enclosed with this memo. If the pipeline operator chooses not to cooperate in the installation and monitoring of strain gauges,then the applicant could put together a proposal to monitor the pipeline easement through the use of inclinometers, extensometers, or similar devices. Rule 6.4.19 of the Construction Materials Rules provides that a pit operator or applicant may mine in proximity to structures such as the gas line or power line upon acceptance by the Division of a notarized agreement between the applicant and the person(s)having an interest in the structure,that the applicant is to provide compensation for any damage to the structure. In fact, this is the preferred mechanism for compliance under the regulations. If the Applicant for the Camilletti Milner Pit No. 2 wants to avoid the permit requirement to set back from the easement lines as described in this memo, and to avoid the requirement to monitor for pipeline strains, then agreements with the electric utility and the gas pipeline utility must be provided. Of course, if and when the power line is relocated as discussed in the permit application, the pit operator may apply to the Division to mine through the easement, which is also discussed in the application. A demonstration that the easement has been vacated will be a necessary element for the Division's approval to mine through this area. As a final consideration related to the long term stability of the power line if it is not relocated,the Division is concerned with the potential for downcutting and erosion around the power poles during a large flood. I did not see the regulatory (100-year) flood plain identified on any of the application maps, nor is the potential for flood related damage discussed in the permit application text. If the pit is in the flood plain, the potential for damage due to downcutting exists for what is in effect a raised berm left between two pits as illustrated on alternate reclamation plan map 4a included with the application. If any part of the raised berm will be in the flood plain,the applicant must provide an analysis of the downcutting potential around power poles and appropriate designs to equalize hydrostatic head between the pits in the event of flooding. The Division's"In Stream Aggregate Extraction and Reclamation Guidance Document"includes examples for mitigation of lateral berms in the floodplain such as riprpap, soil cement, or biotechnical armoring for