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Idol& AM KLEINFELDER Attachment 1 Response to Regulatory Comments Cove Contractors Landfill January 4, 1996 California Integrated Waste Management Board Comments and Response 1. Conceptual final cover design is acceptable to CIWMB staff provided the following is addressed. (a)provide final cover cross section and plan map clearly showing extent of proposed FML (Drawing 2 is not clear with regard to FML extent in the pit area), (b) provide justification for not including drainage or gas collection layers, and (c)provide more detailed description of final cover design in the pit area, in particular along the side slopes. a) Drawing 2 has been revised to show more clearly the extent of the area that will be capped (see Appendix A of this document). Cross-sections taken across the area to be capped are shown in Drawing 2a(see Appendix A). b) Neither drainage or gas collection layers were added to the cap because they are not required by either Title 23, Title 14 or Subtitle D. In addition, the effectiveness of these layers is questionable given the unique configuration of the landfill cap at the Cove Contractors landfill site. As shown in the closure plan drawings, the cap will be placed over an excavation and will assume the shape of a bowl (as opposed to a dome which is typical for landfills). Installation of a drainage layer poses difficult design problems for the drainage layer outlet. Water intercepted by the drainage layer will flow to the pit area and at that point will have to be routed from beneath the vegetative layer to the surface before the point where impounded water is encountered. While such a design is not impossible, it is our opinion that any benefits that may be offered by the drainage layer are offset by the difficulty of design, difficulty of installation, and cost. In a regular landfill, gas can collect under the dome-shaped cap and is best vented especially if a geomembrane is used. At the Cove Contractors landfill, the cap is in the shape of a bowl and not a dome and it will not collect landfill gas in the same way that a dome shaped cap will. Landfill gas that may be generated at the landfill will be intercepted by the cap but instead of being trapped at that point, the gas will probably move laterally along the geomembrane to the edge of the cap and then vent to the atmosphere. Given that Cove Contractors landfill is filled primarily with inert waste (lower potential for gas generation than with municipal waste) and the auto-venting capability of the cap, it is Kleinfelder's opinion that a landfill gas layer in the cap is unnecessary. C) Lining the pit area is complicated by the presence of the steep, soil face at the northern end of the pit. In preparation of the pit for placement of the liner, this soil face will require some form of resloping and stabilization. For this size of project, there are three reasonable options for resloping and stabilization: 1. Slope Layback - This involves removing soil from the top of the steep soil face and replacing it at the base to form a shallower slope, most likely 2:1. The problem with this approach is that it requires encroachment onto the adjacent property. For this reason, it is not feasible. 2. Slope Buttressing - Soil would be imported and placed against the soil face to form a wedge of soil supporting the soil face. This wedge would likely be 2:1. 23-481399-A00/TL960001 Pagel of 5 January 4, 1996 Copyright 1996 Kleinfelder,Inc.