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WASTE DISCHARGE REQUIREMENTS -9- FORWARD INC.,FORWARD LANDFILL SAN JOAQUIN COUNTY Landfills 35. The containment features of existing landfill units are described in Finding 8. Starting with WMU D-93 and all future landfill units in WMU D ('including those which overlie existing landfill units) and WMU K the liner design is proposed to meet RCRA Subtitle D and Chapter 15 Class Il landfill requirements. These landfill units will include a composite liner overlain by a blanket LCRS. The composite liner includes at least two feet of compacted soil with a permeability of 10-'cm/s or a geosynthetic clay liner(GCL) overlain by a geosynthetic liner at least 40 mil in thickness (minimum 60 mil if HDPE). The clay liner is generally constructed from native soil mixed with imported clay because native soils alone do not meet the permeability requirement. The blanket LCRS consists of either a one-foot thick layer of gravel or a geosynthetic drainage net(GDN). Where the liner of a Class H landfill overlaps waste in an older Class III unit, the composite liner system typically consists of GCL+HDPE+GDN. This interface liner is typically underlain by several feet of engineered fill to prevent differential settlement in underlying waste from affecting the liner system. An operations layer is placed over the liner system to prevent overlying waste from damaging it- Impoundments ents 36. The liner in the interim WMU F is currently a single clay liner that will be removed before leachate reaches the outer one foot of the liner. The final design for future liner systems in WMU F will be submitted prior to construction and will meet or exceed the requirements of Chapter 15. A GCL is an approved Engineered Alternative to the prescriptive outer clay liner component in the double liner option. CERTIFICATION 37. A certified engineering geologist certified in the October 1987 Report of Waste Discharge that WMUs C, D t7 and E meet the siting and construction requirements in Chapter 15. Design and construction certifications are provided for each additional unit or module as it is constructed. CEQA AND OTHER CONSIDERATIONS 38. The action to revise WDRs for this facility is exempt from the provisions of the California Environmental Quality Act, (Public Resources Code, Section 21000, et seq.), in accordance with Title 14, CCR, Section 15301.