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SEC77ON J -LANDFILL EXPANSION ISSUES Page 1-2 Lastly, there is another parcel, approximately 6.5 acres is size, which the City will either acquire or for which they will obtain an easement. This parcel is located in the northeast comer,between Austin Road and the landfill access road, and is roughly triangular in shape. The Northem California Youth Authority currently owns it. The parcel would be used for flood plain containment during the 100 year storm event. No waste facilities or waste placement would be sited on this parcel. The proposed Site Plan, Preliminary Phasing Plans, and associated details and sections for the proposed Austin Road Landfill Expansion are referenced here as Drawings P1 through P7. These plans are conceptual in nature and show the intended methods of sequencing the fill operations and the layout of facilities on the site. The expansion is proposed to be developed in a series of major stages referred on the conceptual design drawings as Phases I - VI. Phases I through IV are located south of the existing landfill area and Little Johns Creek and will be referred to as the horizontal expansion phases. The liner for the horizontal expansion phases will be installed over native soil with the liner elevation set no lower than 20 feet mean sea level (MSL). All six phases will be taken to 150 feet MSL at closure. Phases I through IV are projected to last until approximately 2024. Phases V and VI will be referred to as the vertical expansion phases; they are anticipated to provide another 21 years capacity for waste disposal, until approximately 2045. At the time that Phase I is opened, the existing landfill will be closed and receive a final cover of two feet foundation material, one foot of compacted soil with a permeability less than 1 x 10'8 cm/sec, and one foot of soil for vegetation. After closure of the existing landfill, soil will be stockpiled on this surface, which will preload the future vertical expansion area to accelerate the settlement rate and maximize the opportunity for a stabilized foundation for the Phase V and VI liner and leachate collection systems. A primary concern about vertical expansion concepts is the possible detrimental effect of settle- ment on liner and leachate collection systems. This concern is complicated by two factors: 1) insufficient data on landfill compaction and settlement rates, and 2) lack of design history and standards for vertical expansions. In the past few years, a number of facilities have been expanded using liners over existing refuse grades. It is expected that over the next 20 years the , case histories of these facilities coupled with the evolution of geosynthetic technology will provide a better basis for vertical expansion designs than Is currently available. The design philosophy for completing the horizontal expansion phases prior to the vertical expansion phases is to allow maximum settlement of the existing landfill, to provide the longest possible period for settlement monitoring, and to take full advantage of improvements in geosynthetic technology over the next 20 years. Actual phase construction may be sequenced somewhat differently than shown in this preliminary design. In particular, the vertical expansion phases may be subdivided into a series of smaller expansions. Also, it may be advantageous to progress the horizontal expansions in a different sequence than shown on the conceptual design drawings for reasons unforeseen at this time. However, all the horizontal expansion phases will be completed prior to the development of the vertical expansion phases and all phases will be contained within the final footprint of the lined landfill as shown on the drawings. R.W.Back and Associates City of Stamm 1811.002