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WASTE DISCHARGE REQUIREMENTS ORDER NO.R5-2002-0219 -2- FOR COUNTY OF SAN JOAQUIN FOR CONSTRUCTION AND OPERATION OF NORTH COUNTY RECYCLING CENTER AND SANITARY LANDFILL FACILITY, SAN JOAQUIN COUNTY specified at the time (1991) in Title 23, Subchapter 15, Section 2510 prior to RCRA, Subtitle D requirements. A geonet with an overlying geotextile, and perforated HDPE collection pipes with drain rock in collection trenches,were installed on the bottom liner as the LCRS. 5. On April 17,2001 the Board's Executive Officer issued a letter to solid waste landfill owners and operators requiring a liner performance appraisal for any liner system to be constructed after January 1, 2000,regardless of any liner expansion previously authorized in waste discharge requirements. The performance appraisals were required to include a demonstration that liner systems to be constructed will comply with Title 27 performance standards. 6. The Discharger proposes to construct an engineered alternative liner system for Module 4 and subsequent modules. Module 4 will be constructed as soon as possible to allow discharge of municipal solid waste to an area of 15 acres south of the existing Module 3. The proposed primary engineered alternative liner system incorporates a composite 60- mil HDPE geomembrane over a GCL. The proposed engineered alternative is based on a Liner Performance Demonstration Report dated May 14, 2002 which concluded that, 0 based on site specific unsaturated zone modeling the designed engineered alternative composite liner system meets the Title 27 performance criteria for Class III waste disposal units. SITE DESCRIPTION 7. The sediments underlying the Unit based on the boring logs of the monitoring wells consist of interbedded sands, silts and clays with occasional gravelly layers. The measured hydraulic conductivity of the native soils within the unsaturated zone underlying the Unit ranges between 1 x 104 and 2 x 10-7 cm/sec. These unsaturated zone hydraulic conductivity results are based on insitu tests and laboratory tests conducted on undisturbed soil samples. The depth of the tested soil varies from 30 to 60 feet below the ground surface. Three tests were conducted on silty sand layers with hydraulic conductivity results ranging from 1 x 10-4 and 8 x 10-6 cm/sec. Two tests were conducted on interbedded silt, clay and sand layers with hydraulic conductivity results ranging from 3 x 10'7 and 2 x 10-7 cm/sec. The measured hydraulic conductivity of the native soils within the saturated zone underlying the Unit is 9 x 10-3 cm/sec based on a slug test conducted at monitoring well G-1. (See Table 3 and Drawing 1 of the Geologic and Hydrogeologic Report,January 1988). 8. The site-specific seismic hazard report prepared for NCRCSL in December 1994 was reviewed by the author in 2002 and verified to be still applicable for site conditions. The