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• Mr. Greg Basso -2- 11 July 1989 Mr. Tom Woodward The proposed landfill liner design does not cover the sidewalls of the unit. Although this design has commonly been used at Forward in the past, Subchapter 15, Title 23, California Code of Regulations (Subchapter 15) clearly requires that all natural geologic materials must be separated from waste by a liner where a liner is used in a waste management unit. This deficiency in the design needs to be corrected. The design report states that the compacted soil liner will be sloped at 20 to the leachate collection and removal system (LCRS) trenches located in the base of the swales. Without a drainage layer (e.g. gravel blanket) over the soil liner, you need to provide engineering calculations that demonstrate that the 20 slope is sufficient to promote transmission of leachate through the refuse to the trenches with no buildup of hydraulic head on the liner. Our inspections of WMU D88 raised the concern that soil used to cover asbestos waste discharged along the western margin of the D88 unit may have blinded the northern leachate sump to the remainder of the landfill. Section 2543(f) of Subchapter 15 requires that where a dendritic LCRS is used in a Class III landfill, only wastes which have a permeability which approximates that of subdrain material (e.g. gravel) may be placed adjacent to the liner. This waste must remain permeable throughout the active life and post -closure maintenance period of the landfill. The D89 design report needs to specify the type of waste that will be placed next to the liner and compare its estimated permeability with that of a blanket -type leachate collection system. The design report needs to provide information on the maximum anticipated daily volume of leachate from the waste manage- ment unit and engineering calculations to demonstrate that the LCRS is designed to collect and remove twice that volume. The method of annual LCRS testing, as required by Subchapter 15, also needs to be specified in the design report. The design drawings show that the leachate transfer pipe in the LCRS trenches will be underlain by compacted soil, but we cannot determine the clay thickness. The drawing of "typical trench cross section" on Sheet 7 shows 4 feet of compacted soil beneath the transfer pipe. This drawing needs to be reconciled with the "profile views" on Sheets 5 and 6 which show 1 foot of compacted soil beneath the transfer pipe. The