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LCRS Design - Area 2B Foothill Sanitary Landfill when using the GDN (0.059 inches) is much less than regulatory limit of 12 inches, thus satisfying both state and federal regulations for LCRS design. Should the County decide to increase the waste fill height of up to 300 feet, Odes of the GDN should be tested at 25,000 psf, in lieu of 11,000 psf, and have a minimum transmissivity of 3.5x10-4 m2/s. A review of available GDN materials indicate that under the critical leachate generation condition (i.e. limited waste thickness [15 -foot scenario]) the transmissivity of GDNs that meet project strength requirements (see Section 5.2) are generally of the same order of magnitude as the 9 -inch -thick drainage material specified for previous module construction. As such, there are currently available products that meet project transmissivity requirements, and that do not substantially reduce the engineering properties of the blanket layer LCRS component. 5.2 Compressive Strength The required strength of the geocomposite should be at least 1.5x the maximum expected vertical stress that the GDN will be exposed to. Assuming a maximum waste thickness of 145 feet over the base liner based on the current master plan, and an assumed unit weight of 75 pcf, the vertical stress the GDN is expected to experience is about 11,000 psf. Assuming a 1.5 factor of safety for material compressive strength, the GDN should have a minimum compressive strength of 16,500 psf. Products are currently available that meet this compressive strength criteria. Should the County decide to increase the waste fill heights at the FSLF in the future up to a maximum fill height of 300 feet, the selected GDN should have a minimum compressive strength of 38,250 psf. The compressive strength for the increased fill is based on a waste unit weight of 85 pcf, which is appropriate for thicker waste fills, and a factor of safety of 1.5 Products are currently available that meet this compressive strength requirement. 5.3 GDN Geotextile The geotextile portions of the GDN should have a minimum mass per unit area of 8 oz/yd2 with an apparent opening size (AOS) equivalent to a number 80 sieve screen (0.180 mm) to provide adequate retention of the overlying operations soil. Products are currently available that meet this geotextile mass per unit area and AOS requirement. 5.4 Conclusion GDNs have become widely used and accepted in the landfill industry, particularly in cases where suitable drainage materials are not readily available or where higher flows need to be accommodated. The LCRS system proposed for Area 213, based on the calculations presented herein, meets the federal and state requirements for such as discussed in Section 2 of this report. Additionally, the proposed base liner LCRS system meets the WDR requirements for being considered as an EAD under the FSLF's current MRS as the proposed design includes all LCRS components required by the WDRs, does not significantly reduce engineering properties of the components, and is at least as protective of water quality as the currently approved EAD. Project No. AU 17.1254 1 LCRS Design 9 May 2018