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WASTE DISCHARGE REQUIREMENTS ORDER R5-2015-0058-01 -23- <br />SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS <br />FOOTHILL SANITARY LANDFILL, INC. <br />FOOTHILL LANDFILL <br />SAN JOAQUIN COUNTY <br /> <br />As described in Finding 7, these WDRs classify LF-1 and LF-2 as separate landfill <br />units under Title 27. As such, these WDRs require that all future LF-2 liner <br />extensions overlapping unlined unit LF-1 meet Title 27 containment system <br />standards for a Class III, existing (i.e., pre-Subtitle D) MSW landfill (i.e., non- <br />composite compacted clay liner or equivalent). See Construction Specification <br />D.1; Title 27, sections 20330 and 20340. <br />96. Module 1’s LCRS layer included a 9-inch layer of drainage gravel on the landfill’s <br />base liner and geonet on the landfill’s interior side slopes. The gravel layer was <br />designed for sheet flow drainage (3% grade) to a collection sump constructed in the <br />southeast corner of the module. Perforated HDPE collection piping, including six, 4- <br />inch laterals and a 6-inch header, were also installed to assist drainage and minimize <br />leachate head on the liner. Five of the laterals (each cross-sloping from west to east <br />at a 2% grade) were plumbed to a header pipe installed in a gravel-filled trough along <br />the eastern side of the module. The other lateral was installed in a collection trough <br />along the southern side of the module and plumbed directly to the sump. Each end of <br />the laterals was connected to a riser extending up the side slope to allow for <br />inspection and cleaning, if necessary. <br />97. Module 1’s LCRS sump was designed as follows, from top to bottom: <br />a. A geotextile separator layer (immediately underlying the module’s LCRS); <br />b. Up to 4 feet of LCRS sump gravel; <br />c. A geotextile cushion layer; <br />d. Primary composite liner; <br />e. A secondary sump; <br />f. A secondary composite liner; and <br />g. One foot of prepared foundation soil. <br />Both the primary and secondary sump liners were constructed in accordance with the <br />EAD approved under previous WDRs. <br />98. The primary sump was constructed to a maximum depth of 4 feet (216 feet MSL) with <br />3H:1V side slopes. A dedicated submersible sump pump with a liquid level sensor <br />installed in an 18” HDPE sump collection/riser pipe to control sump liquid levels was <br />included in the design. External controls allowed for setting the pump cycle to ensure <br />that the sump is pumped off. The system also included alarms set at minimum and <br />maximum allowable liquid levels to ensure safe pump operation and to prevent head <br />buildup on the liner beyond the sump. Volume pumped was also automatically <br />recorded. <br />99. A secondary sump was also included in the design to monitor the primary sump for <br />leaks. The secondary sump consisted of a geonet blanket layer (sandwiched <br />between the primary and secondary composite liners) draining into a 2-foot deep <br />gravel-filled trench underlying the primary sump. 12-inch HDPE collection and riser <br />piping housing a bubbler line to measure liquid level were also included in the <br />secondary sump design. A submersible pump was also installed in the secondary <br />sump to pump and return any leakage to the primary sump.