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ExxonMobil Global Services Page 5 <br />Colony Shale Oil Project <br />ESR Reclamation Studies <br />• Weighing Lysimeter Performance 1990-2003 <br />Project No. 353 <br />simple leaching to remove salts). There was some question as to whether the leaching could <br />be practicably achieved, and Colony and the MI,RB ultimately settled on a topsoil thickness <br />requirement of 18". That difference may seem small, but at that time it was not known <br />whether or not there was enough suitable "topsoil" within the footprint of the proposed pile to <br />provide an I8" cover. Colony performed studies during the initial stages of construction to <br />confirm there was sufficient material to meet this requirement (J. P. Walsh, 1981), but <br />concluded it would necessarily involve use of some fairly stony soils, and it would imply <br />considerable double-handling and stockpiling. of the salvaged topsoil. <br />In the first generation shale projects, namely those that received mining permits in the <br />late 19'70's and eazly 1980's, the vegetative cover was viewed mainly in context of its ability <br />to become a pennanent self-sustaining cover suitable for rangeland and wildlife habitat. <br />• Consideration of percolate infiltrating water into the pile, and means to prevent it from <br />contaminating groundwater or surface water, were treated separately, relying in some cases on <br />the relatively impervious nature of the spent shale, or requirements for underliners and/or <br />drainage systems. By the time Chevron was pemutting its lazge open pit Cleaz Creek Project <br />in the mid-1980's the concept of what is now referred to as an "ET cover " (evapo- <br />transpiration cover) was evolving for use in municipal waste landfills, at least in acid and <br />semi-arid climates where the concept might be workable. The basis of this approach was to <br />have a thick enough soil cover to support plant roots, overlying anopen-graded rock zone one <br />to three feet thick. This open graded rock zone was intended to serve as a capillary barrier, <br />which would prevent salts fivm being drawn up into the root zone. If properly sized, the soil <br />cover could theoretically retain all incipient precipitation for consumption by plants and <br />natural evaporafion, thereby solving the other environmental issue for the surface shale piles. <br />However, Chevron's proposed pIle cover consisted of 5 feet of topsoil overlying a 2 foot <br />crushed stone capillary barrier, and iJNOCAL's then pending pemut amendment for an <br />expansion of its Parachute Creek Project would use a 4 foot thick soil zone over the shale <br />. waste. It was estimated that the cost of these would be four tunas the cost of a simpler 18"- <br />LAC'IIEL FELICE & Associates <br />