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Ms. Barbara Coria <br />November 9, 2015 <br />Page 7 <br />or mined opening is rare.12 At Natural Soda, the depth of mining is typically over 1,900 feet so <br />this type of subsidence is highly unlikely. <br />All abandoned cavities will be kept full of saturated brine that will inhibit further <br />dissolution of the cavities and add structural support to the overlying formation. <br />There has been no damage to, or adverse effect on, the stability of any structures located <br />within two hundred (200) feet of the operation or affected land. In my opinion, the continued <br />operations as Natural Soda LLC will not affect the stability of any structures located within two <br />hundred (200) feet of the operation or affected land. <br />Sincerely, <br />Michael P. Hardy, Ph.D., P.E. <br />President <br />mhardy@agapito.com <br />MPH:hlw <br />Transmitted as a PDF via e-mail <br />Attachment: Resume, M. Hardy <br />Letter from WPX <br />cc: Jerry Daub, Daub and Associates, Inc. <br />Tim Buchanan, Enirgi Group Corporation <br />Travis Marshall, Colorado Division of Reclamation, Mining and Safety <br />Matheson, G. M. and A. E. Clift (1986), "Characteristics of Chimney Subsidence Sinkhole Development from <br />Abandoned Underground Coal Mines along the Colorado Front Range," Proceedings, 2"d workshop on Surface <br />Subsidence due to Underground Mining, Morgantown, WV, S. Peng (ed.), pp. 204-214. <br />2 Peng, S. S. (1992), Surface Subsidence Engineering, Society for Mining, Metallurgy, and Exploration, Inc., Ann <br />Arbor, MI, 161 pp. <br />Agapito Associates, Inc. <br />