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GDN within the graded valleys. GLA reviewed available products to establish if GDNs were available meeting the strength requirements to withstand the loading from the final buildout of the FSL, and to establish if products meeting the strength requirements have adequate transmissivity characteristics to meet the CCR Title 27 and WDR drainage requirements. Additionally, a hydraulic evaluation of landfill performance (HELP) analysis was completed using GDN properties to estimate the peak daily amount of leachate that would need to be handled by the GDN drainage layer. The evaluation of the GDN drainage layer is presented in the LCRS Engineered Alternative Design Report — Foothill Sanitary Landfill Area 2B attached to this letter (Attachment 1). Based on the results of the analysis included in Attachment 1, GDNs are currently available that meet the site specific structural and transmissivity requirements of the FSL to allow the LCRS to maintain a hydraulic head of less than 12 inches and handle a minimum of 2 times the anticipated maximum daily leachate flows. The HDPE piping system was also evaluated for structural and flow capacity and was found to be adequate with respect to both. Additionally, based on our experience with similar liner systems, GLA believes that the proposed LCRS will be acceptable from a slope stability perspective. It should be noted that the EAD proposed by GLA in the attached report is consistent with similar base LCRS blanket drainage systems proposed on other landfills within California. Most recently GLA was able to assist Kern County Public Works Department in negotiating with the Central Valley Regional Water Quality Control Board (CVRWQCB) to change from a 1 -foot -thick base liner gravel drainage layer to a GDN at the Bena Sanitary Landfill in Bakersfield, California. The conditional approval letter from the CVRWQCB is included as Attachment 2. Many other facilities within California have incorporated the use of a GDN as the base liner blanket collector including the American Avenue Disposal Site and the City of Clovis Landfill in Fresno County, Johnson Canyon Landfill in Monterey County, and California Street Landfill in Redlands, CA. Upon your concurrence with the information provided in this letter, which is further detailed in Attachment 1, GLA will update: the Area 2B slope stability analysis, the LCRS design in the Construction Drawings and Technical Specifications, and then modify the Engineer's Cost Estimate accordingly. If you have any questions about the information included in this letter, or the attached, please do not hesitate to contact me at 530.272.2448 GLA PN AU17.1254.00 I Alternate Leachate Collection and Removal System May 8, 20181 RevO 2