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WASTE DISCHARGE REQUIREMENTS ORDER NO. R5-2009-0049 -8- SAN JOAQUIN COUNTY DEPARTMENT OF PUBLIC WORKS HARNEY LANE LANDFILL SAN JOAQUIN COUNTY 37. The approved final cover constructed for closure is.- a. s:a. Foundation Layer—Two feet of compacted soil b. Low Hydraulic Conductivity (LHC) Layer— one foot of compacted clay (k < 1 x 10-6 cm/sec) c. Erosion Resistant Layer— One foot of clean vegetative cover soil d. Vegetative Cover— native grass mix The foundation layer was compacted to a minimum of 90 percent of relative maximum dry density using onsite borrow soil and excavated soil from the detention basin. The LHC layer was constructed using a mixture of imported Ione clay and onsite borrow, and was compacted to a maximum permeability of 1 x 10-6 cm/sec. Field and laboratory permeabilities were correlated by double-ring infiltrometer tests. To achieve permeability specifications with lower relative compaction (90 percent), a higher percentage of Ione clay was used along the sideslopes. 38. The Discharger completed landfill closure in March 1994 and submitted the closure certification report for the project (April 1994 Final Documentation Report for Final Cover Foundation and Vegetation Layers, Harney Lane Sanitary Landfill, San Joaquin Public Works). Regional Water Board staff approved the closure certification report in January 1995. Grading 39. The final cover was constructed over both landfill units with an elongated (north- south oriented) central crest. On Landfill 1, the cover deck was graded from the crest (146 feet MSL) to the side slopes (126 feet MSL) at a minimum slope of 3 percent. The side slopes were graded from the rim deck to the landfill perimeter (104 feet MSL) at about 2.5H:1V, except for the northern side slope (i.e., the landfill toe), which was graded at about 15H:1V. The Landfill 2 cover deck was also graded from the crest (132 feet MSL) to the side slopes (128 feet MSL) at a minimum slope of 3 percent. The side slopes were graded to about 2.5H:1V, except at the NE corner of the unit, where the side slope was graded to about 3.5H:1 V. 40. A technical report demonstrating the stability of the cover slopes per Title 27, section 21750(f)(5) was not required for the facility because the Discharger closed the units prior to 18 July 1997 (See Title 27 sections 21090(a) and 20310(g)). A 1991 slope stability report prepared under previous Chapter 15 regulations showed factors of safety greater than 1.5 along the steepest landfill side slopes, which is what is typically required of landfills now undergoing closure. Drainage 41. Sheet flow runoff from the top decks of each landfill unit is directed via perimeter swales to 12-inch diameter, corrugated metal pipe overside drains. Unlined ditches (with "V" shape or trapezoidal profiles) along the perimeter of each landfill capture and carry discharges from the overside drains and side slope runoff through a common culvert to the detention basin in the southwest corner of the site. The