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WASTE DISCHARGE REQUIREMENTS ORDER NO.R5-2002-0219 -15- FOR COUNTY OF SAN JOAQUIN FOR CONSTRUCTION AND OPERATION OF NORTH COUNTY RECYCLING CENTER AND SANITARY LANDFILL FACILITY, SAN JOAQUIN COUNTY 2. Both the bottom liner and side slope liner of all new Units and lateral expansion areas of existing Units shall be constructed in accordance with one of the following composite liner designs: a. The prescriptive standard design which consists of a lower compacted soil layer that is a minimum of two feet thick with a hydraulic conductivity of 1 x 10-7 cm/sec or less and has a minimum relative compaction of 90%. Immediately above the compacted soil layer, and in direct and uniform contact with the soil layer, shall be a synthetic flexible membrane component that shall be at least 40-mil thick(or at least 60-mil thick if composed of high density polyethylene [HDPE]),which is immediately overlain with a leachate collection and removal system. A soil operations layer shall be placed above the leachate collection and removal system. b. An engineered alternative composite bottom liner system that is comprised, in ascending order, of the following: 1) A twelve-inch thick engineered soil foundation layer that shall be constructed of select fine-grained soil materials which shall be compacted in lifts of six inches or less to 90% of maximum dry density at 0%to 4%wet of optimum moisture content, in accordance with the approved construction quality assurance plan, and shall be either: a) Compacted to attain a hydraulic conductivity of 1 x 10-5 cm/sec or less; or b) Meet the following gradation criteria: (a) A maximum size of 3/8-inch; (b) At least 30%of the material,by dry weight,passing the No. 200 U. S. Standard sieve; (c) A gradation series (i.e.,well-graded)that is amenable to compaction; and 2) A nonwoven bottom geotextile, which may be part of the geosynthetic clay layer (GCL). 3) A GCL that shall exhibit appropriate strength characteristics(hydrated)to accommodate stresses associated with specific landfill design parameters, with particular attention to interface, long-term creep shear, and bearing capacity. 4) A 60-mil thick synthetic flexible membrane of HDPE.