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WASTE DISCHARGE REQUIREMENTS ORDER R5-2015-0058-01 -27- SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS FOOTHILL SANITARY LANDFILL, INC. FOOTHILL LANDFILL SAN JOAQUIN COUNTY 115. The Discharger has adequately demonstrated that construction of a liner in accordance with the Title 27 prescriptive standard would be unreasonably and unnecessarily burdensome in comparison to the proposed engineered alternative. The Discharger has further demonstrated that the proposed engineered alternative(s) described in Attachment H, are consistent with the performance goals of Title 27’s prescriptive standard and will afford at least equivalent water quality protections. 116. According to the submitted seismic analysis, the proposed new WMU will be able to withstand the MCE seismic event described in Finding 45. (Title 27, § 20370). 117. A 1992 United States Environmental Protection Agency (USEPA) guidance document, Action Leakage Rate for Leak Detection Systems, informs theory relating to evaluation and observation of flow rates through surface impoundment containment systems with geomembrane system components. The 1992 USEPA guidance, in part, provides that the objective of a containment system is to minimize the head or pressure on the secondary liner and thereby decrease the potential for migration of constituents out of a surface impoundment should a leak occur in both the primary liner and the secondary liner. The 1992 USEPA guidance document also describes the “action leakage rate” (ALR) as the maximum design flow rate, with a safety factor, that a leak detection system can remove without the head on the secondary liner exceeding one foot. The document further provides for guidance for geomembrane containment systems where flow rates in excess of the minimum ALR indicate a major localized or general failure of a primary liner; flow rates of 1,000 gallons/acre/day or greater represent “potentially significant hole sizes that may be readily identified and repaired” for geomembrane based containment systems. The guidance recommends that the ALR for lined surface impoundments be set at no more than 1,000 gallons per acre per day (gpad) unless site-specific conditions dictate otherwise. 118. Higher ALR values above the recommended 1,000 gpad are site-specific and require Central Valley Board staff to consider design of the surface impoundment, pumping rates, and Discharger’s submitted technical ALR reports when establishing ALR values. The presence of automatic pumps at surface impoundments allow for a greater USEPA recommended volume of 1,000 gpad for each of the proposed Class II surface impoundments. 119. Central Valley Water Board staff identified that ALR values of 1,000 to 3,000 gpad have been set for other Central Valley sites. Given the above information, this WDRs, as amended by this Order, set the ALR for proposed surface impoundments at 1,000 gpad. 120. The Discharger may request alternative ALRs for existing and proposed surface impoundments. Any such request must be accompanied by technical reports supporting the proposed ALRs, for review and approval by the Central Valley Water Board.