2017-01-30_PERMIT FILE - C1981041 (8)

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Roadside Mine W "" #00489-0004 Huddleston-11crry 05/09/16 Initial reconnaissance was conducted in the summer of 2014 and HBET was shown the aforementioned ditch. At the north end of the ditch, HBET observed fairly large openings that Snowcap believes to be the beginning of a sinkhole conduit to the mine workings. Also during the initial reconnaissance, HBET observed a large pond that had been excavated west of the ditch for use as a stock pond. The pond was dry at the time. However, HBET observed that the surficial soils at the site consisted of boulders and cobbles in a sandy clay matrix. Subsequent reconnaissance was conducted in September 2015. At that time, HBET observed two large excavations which had been conducted by Mr. Fontanari. The eastern pit was excavated to a depth of approximately twenty-two feet. The ,western pit was excavated to a depth of approximately nineteen feet from the bottom of the aforementioned stock pond. In both pits, the soils consisted of boulders and cobbles in a sandy clay matrix. The soils were dry, dense, and competent. No evidence of fractures or other potential water pathways were observed. Also during the September 2015 reconnaissance, HBET observed a drilling contractor conducting borings a couple of hundred feet east of the ditch. During discussion with the contractor, he indicated that he had drilled three borings in the area to a depth of sixty feet and had not hit bedrock in any of the holes. He also indicated that the overburden soils were very dense. Working Hypothesis In general, sinkhole features develop from the bottom up where there is an opening at some depth in the subsurface. Water moves through the soil and either washes out fines or dissolves the rock (i.e. limestone, gypsum, etc.) such that the opening becomes larger. Eventually, sufficient soil/rock is washed away that the soils above cannot bridge across the void. The hole collapses and the `sinkhole' appears at the ground surface. Although it is likely that some void spaces exist in the old mine workings. The mine workings are at a depth of approximately 100 feet in the subject area. Based upon the soil profile observed in the deep test pits, our knowledge of the area geology, and information provided by the drilling contractor, HBET believed that it was unlikely that the water pathway to the mine workings was the result of natural sinkhole processes originating at the mine workings. HBET believed that it was far more likely that an existing feature such as an old air shaft, borehole, or other vertical feature associated with the mining was the `opening' from which the sinkhole originated. Soon after, HBET was provided information regarding an old air shaft that was located in close proximity to the ditch and HBET hypothesized that this could be the pathway. Geophysical Survey In order to evaluate our hypothesis, HBET contacted Fugro Consultants, Inc. to develop a non - intrusive geophysical survey plan. Based upon the site geology, depth of mine workings, and desired data resolution, Fugro recommended an Electromagnetic Resistivity Tomography (ERT) survey. X:\2008 ALL PROJECTS\00489 - JE Stover Associates Inc\00489-0004 Roadside Mine\200 - Geo\00489-0004 LR050916.doc 2 TR -69 A14-14-2 09/16