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Orchard Valley Mine is located in the D seam and utilizes conventional <br />room-and-pillar methodology. The applicant has completed the required <br />inventory of structures and renewable resource lands, a projection of <br />probable subsidence, and developed a subsidence control plan and an <br />appropriate accompanying subsidence monitoring plan. <br />Inventory - <br />The operator has identified thirty-six (36) structures within the <br />permit and adjacent areas, depicted on Map 9-7. Twenty-nine (29> of <br />these structures were inventoried within the permit area, as well as <br />two water pipelines and an all-weather gravel road within Steven's <br />Gulch. No inventoried structures will be affected by mining <br />operations proposed during this permit term. The operator has also <br />identified several alluvial/colluvial surficial deposits which <br />constitute renewable resource lands within the revised permit area. <br />Surficial deposits have been identified within Steven's Gulch, East <br />Roatcap Creek, and in the area of the Morrell Cow Camp. The applicant <br />completed a subsidence survey of hydrologic features which is <br />described in Section 2.05.b(b)(e) Additional shallow alluvial <br />monitoring wells were installed within the alluvial/colluvial deposits <br />for the purposes of monitoring potential effects of subsidence upon <br />the hydrology of the surficial deposits. <br />Subsidence Protections - <br />The operator retained Geo-Hydro Consultants, Inc. to complete a <br />technical projection of subsidence expected within the revised permit <br />area. Atypical subsidence profile.is graphically depicted on Plate <br />11 of the subsidence study in Volume 3. Vertical subsidence is <br />projected to reach a maximum of approximately six feet. In <br />consultation with the Division, and through the employment of Dunrud's <br />(1976) research, the operator estimates the conservative angle-of-draw <br />to be 20.5 degrees from vertical. The technical projections included <br />in the subsidence study conform with the prudent state-of-the-art of ` <br />subsidence projection. <br />Subsidence monitoring has been conducted within the Orchard Valley <br />permit area, in compliance with the originally approved permit. The <br />data collected to date is well within the technical projections for <br />vertical subsidence and draw angle (See Table 8, Volume 3 and annual <br />subsidence reports). Current data consistently demonstrates a maximum <br />vertical subsidence magnitude of 3.5 to 4.0 feet and a maximum angle <br />of draw of approximately sixteen (16) degrees from vertical. <br />The operator has completed strain projections for the structures <br />inventoried on Map 9-7. Strain projections have also been completed <br />for the Pitkin Mesa and Orchard Valley Mine water supply water <br />pipelines which cross the potential subsidence zone of the <br />life-of-mine area. The Pitkin Mesa pipeline supplies potable water to <br />roughly 160 domestic taps. <br />-40- <br />