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<br /> <br />-32- <br />As discussed above, the mining plan for the east area of the Martinez Strip <br />Mine includes the excavation and deposition of approximately 7 million cubic <br />yards of swollen backfilled spoil. Because of the close proximity of this <br />fill to Stollsteimer Creek and the Intermountain gas pipeline, the company <br />was reouired to complete an analysis of the fill's slope stability during <br />the interim permit period. This analysis, completed in August of 1979, <br />recommended modification of the original design configuration for the fill. <br />Zn addition, this analysis, prepared by CTL/Thompson, Inc., recommended <br />*_he installation of a subsurface teodrain paralleling the western edge of <br />the spoil fill. The consultant observed: "Subsurface drainage is <br />necessary only at the western edge of the proposed pit. ... Subsurface <br />drainage should consist of coarse sandstone gravel, cobble and boulder- <br />sized material placed in a 4-foot thickness and a minimum of ZS feet in <br />width. ...If ground water is encountered in the southwest portion of <br />area 9, the sandstone drain thickness should be increased to extend at <br />least 9 feet above the maximum anticipated ground water levels. Outlets <br />for the subdrain should be provided at least 2 points at or close to the <br />location shown on Figure I1. The outlets should consist of a sandstone <br />drain or two 8-inch diameter metal pipes. The pipes should be provided <br />at daylight points." (pg. 12, "Spoil Pile Slope Stability Analysis, <br />Mining Areas No. Z through 4, Chimney Rock Coal Company, Near Pagosa <br />Springs, Colorado", CTL/Thompson, Inc., August 31, 1979) <br />During the spring of 1980, Chimney Rock Coal was cited by the Division for <br />failing to construct the toedrain within Area No. Z at the northern end <br />of the spoil fill. In response, Chimney Rock Coal had CTL/Thompson, Inc., <br />complete a reanalysis of that portion of the completed spoil fill, <br />in July of 1980. That analysis determined that the northernmost position <br />of the spoil fill could achieve a static slope safety factor of Z.5 if <br />the originally approved slope gradients were reduced from 2:1 (horizontal <br />to vertical slope) to 2.25:1. <br />Chimney Rock Coal amended the permit application on page 2.05-45 to state <br />that it does not believe that the subdrain is necessaru to assure stability <br />of the spoil fill at the Martinez Strip. In support of this opinion, the <br />company refers the Division to the hydrologic baseline data and analysis <br />contained within Section 2.09.7 of the amended permit application. That <br />hydrology baseline information concerns the configuration of the piezometric <br />surface within the undisturbed, pre-mining bedrock stratigraphy within the <br />pit area of the Martinez Strip Pfine. The information is insufficient to analyze <br />or project probable post-mining water table elevations which might develop <br />within the backfilled spoil of the eastern pit area. For this reason, the <br />Division imposes the following stipulation upon approval of the permit: <br />Stipulation <br />22. THE DIVISION DIRECTS CHIMNEY ROCK COAL, TO CONTINUE CONSTRUCTING THE SPOIL <br />FILL TOEDP_97N AT TNE~fARTINEZ STRIP AS OR IG IIJALL I' DEPICTED AND DESCRIBED <br />IN TXE TEXT AND FIGGIE'S OF T17E REPORT ENTITLED "SPOIL PILE SLOPE STABILITY <br />ANALYSIS, hli fllNG AR E45 NO. 1 THROUGH NO. 4, CHIMNEY ROCK COAL COMPANY, <br />NEAR PAGOSA SPRINGS, CO_IORALY~", PREPARED BY CTL/_TN.OA?PSON, INC., DATED <br />AUGUST 31, 1979 AND SUBMITTED BY CHIMNEY ROCK COAL, AS A IdODIFICATIOI! TO <br />ITS OR IGIfJAL PERMIT NUAIBER 78-252 FOR THE MARTINEZ STRIP. <br />