2011-09-09_GENERAL DOCUMENTS - M2008070

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Technical Comments Regarding Site Conditions September 7, 2011 Western Gravel Disposal Facility CD Application Page 2 In accordance with solid waste statute C.R.S., 30 -20 -103 (2), a technical evaluation of the Application has been completed to determine compliance with the requirements set forth in the Regulations. Section 3.1 of the Regulations provides criteria for "location restrictions and site standards" and Section 3.2 provides the design requirements. In reviewing a proposed engineering design and operations plan (D &O) for a facility, the natural site conditions are a key component and greatly affect the design itself particularly for the liner system, leachate collection and environmental monitoring. The waste itself also plays a role in the site selection and the engineering design. The proposed facility would be situated near a very steep slope elevated approximately 45 feet above the White River (after removal of 15 to 20 feet of a younger sand/gravel deposit via mining). The geologic conditions at the proposed facility consist of over 1000 feet of Wasatch Formation bedrock dipping gently to the south - southwest. This formation is home to many solid waste facilities in the region including the Wray Gulch landfill, RN Industry's Piceance Creek produced water impoundments in Rio Blanco County, Rifle UMTRA disposal cell and the West Garfield County landfill in Garfield County. The sandstone members of the Wasatch are reportedly NOT laterally connected such that they generally are not considered key aquifers as a water resource. The interbeds of claystone, mudstone and shale provide intervals with low permeability that will restrict fluid movement. The water quality in the Wasatch is generally poor as well. The site characterization information provided in the application is good. Two of the 3 test holes were cored in the bedrock and the rock quality designation (RQD) for the bedrock between the facility and the elevation of the White River indicate fair to good rock quality. RQD values are used to delineate_ zones of poor quality - rock -- that could- adversely- affect- engineering structures. It appears -that the Wasatch bedrock is not greatly weathered, having been protected by the sand/gravel deposit, and will adequately support engineered structures. Section 3.2.5(C) of the Regulations discusses the various possible barrier layers of the liner system and natural lithology is part of the liner design criteria. The least robust prescriptive liner design might consist of natural lithology (minimum 20 feet thickness with hydraulic conductivity less than 1x10 -5 cm /sec) with the upper 12- inches recompacted to a conductivity less than 1x10 -7 cm /sec. The proposed liner system design is a very robust design that will provide additional protection of the environment. The liner system proposed consists of a double synthetic liner with leachate collection and a leak detection system. Any precipitation that falls within a cell can be removed through the leachate collection drain/sump and thereby relieving any buildup of liquid on the primary (upper) synthetic liner. A leak detection system situated between the synthetic liners can detect any failure in the primary liner and, should a leak develop in the primary liner, it can be utilized as a drain also relieving any fluid head buildup on the secondary liner. Section 3.1 of the Regulations provides criteria for "location restrictions and site standards" and the proposed site meets these criteria. Considering the proximity to and elevation above the White River, the issues identified include: facility and site stability and the potential for seepage to the White River. The Department plans to recommend additional information and possibly design changes to the Application with regards to these issues. For Section 3.1.4 of the Regulations a facility should be designed to resist the maximum horizontal acceleration in lithified earth material for the site. We will request an evaluation of the facility using these criteria to document that the proposed design will remain intact during an earthquake even though the site is not located in a seismic impact zone. For Section 3.1.5 of the Regulations we will request additional review of published information or a site field investigation to identify any geomorphic features that may be associated with historically unstable areas not only on the proposed site but on nearby land with a similar setting. Section 3.1.8 of the Regulation states that landfills shall isolate waste from the public and the environment and applicants shall utilize Section 3.2 (Design Requirements) to justify that wastes and potential leachate will be controlled within the fill area. For the proposed facility the Department will request that the sub -grade slope away from the steep slope such that any liquids in the leachate collection and in the leak detection are directed away from the edge and are located as far from the steep slope, and the White River, as possible. In addition we may request that the sub -grade be constructed with moderately low permeability material such that the secondary liner will be a more robust composite liner. The sub -grade fill will in -fill any fractures or joints in the bedrock, directly beneath