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WASTE DISCHARGE REQUIREMENTSORDER NO. 115-2003-0020 -7- FOR COUNTY OF SAN JOAQUIN FOR CONSTRUCTION, OPERATION, CLOSURE AND EVALUATION MONITORING FOOTHILL SANITARY LANDFILL, MUNICIPAL SANITARY LANDFILL SAN JOAQUIN COUNTY calculations assume that there will be one geomembrane defect of a centimeter diameter hole per acre of liner placed. This geomembrane defect assumption was based on current state -of - practice construction quality assurance for landfill liners. Based on these conditions, a leak rate of 0.0005 gal/acre-day was estimated using the HELP -3 computer model. The calculated leakage rate for the prescriptive liner 60 -mil HDPE/24-inch clay with a hydraulic head of 12 inches (Subtitle D) was 0.81 gal/acre-day. 42. The VLEACH model was used to determine the potential for groundwater contamination from a leak in the liner system. VLEACH simulates the movement of potential contaminants among three phases: (1) gas phase; (2) liquid phase; and (3) as an adsorbed compound on the solid phase (soil). The maximum concentration of modeled constituents in groundwater after the modeling period of 100 years was calculated to be below 0.1 ppb, which is below the laboratory detection limits for the modeled constituents. The modeled constituents included, but were not limited to, benzene, 1,2-dichloroethane, chloride, and hexavalent chromium. 43. The Construction Quality Assurance (CQA) manual incorporates specific testing protocols, inspection, and documentation requirements in accordance with Section 20324 of Title 27, to provide evidence that the construction proceeds in accordance with the design plans and specifications, and that the system will meet or exceed the design intent and regulatory performance standards. 44. The Discharger will perform a state -of -practice geoelectric liner leak detection survey for the GCL. The leak testing enables location of defects, which might impact groundwater and the unsaturated zone, and construction contractor repair of the defects prior to the acceptance of the liner construction project. CONSTRUCTION AND ENGINEERED ALTERNATIVE 45. On 17 June 1993, the State Water Resources Control Board adopted Resolution No. 93-62 implementing a State Policy for the construction, monitoring, and operation of municipal solid waste landfills that is consistent with the federal municipal solid waste regulations promulgated under Title 40, Code of Federal Regulations, Part 258 (Subtitle D). 46. Resolution No. 93-62 requires the construction of a specified composite liner system at new municipal solid waste landfills, or expansion areas of existing municipal solid waste landfills, that receive wastes after 9 October 1993. 47. Resolution No. 93-62 also allows the Board to consider the approval of engineered alternatives to the prescriptive standard. Section 1H.A.b. of Resolution No. 93-62 requires that the engineered alternative liner systems be of a composite design similar to the prescriptive standard. 48. Section 20080(b) of Title 27 allows the Board to consider the approval of an engineered alternative to the prescriptive standard. In order to approve an engineered alternative in