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5-9 three stormwater sedimentation/detention basins (see Section 7.3). The site's hydrology is also discussed in Section 7.6.2. 5.2.6.2 Erosion Control/Soil Loss Analysis Temporary berms, straw mulch, or other erosion -control measures may be used to prevent erosion damage of soil covered areas when weather conditions inhibit complete repairs. All completed WMUs, cut and fill slopes, and portions of the landfill that will be exposed for more than 180 days will be covered to minimize erosion and downstream sedimentation as discussed in Section 7.6.3. Proposed landfill slopes for the three major areas of the Forward Landfill were evaluated using the Universal Soil Loss Equation (USLE) (see Drawing 10). A copy of the soil loss analysis (BAS, 2001) is included in Appendix I The evaluation method determines the potential for soil erosion based on the rainfall and runoff factor, the soil erodibility factor, the topographic factor derived from the slope gradient and length, the cover and management factor, and the support practice factor. The evaluation indicates that the average soil loss is determined to be approximately 1.0 tons/per acre/per year for each area evaluated. This is below the two tons/per acre/per year industry standard. The vegetative layer of the final soil cover will be seeded with native grasses to protect the upper layer of soil and to minimize erosion. 5.2.6.3 Realignment of Littlejohn's Creek The North Fork of South Littlejohn's Creek was realigned to the north and west of the landfill in 2002, as shown on Drawing 2, in order to place it outside the footprint of potential floodplain and the refuse fill areas. The North Fork realignment was designed to carry the 100 -year flood flows. 5.2.7 Landfill Gas Management As discussed in Section 7.5, the landfill gas extraction system was recently combined into a single system, as shown on Drawing 11. Under the combined system, the landfill gas is routed to the existingflare station. The existingflare station is shown on Drawing 11. As the landfill develops, it is anticipated that landfill gas extraction wells will be added/abandoned, as needed. As the landfill expands, it is anticipated that most of the system will be installed, with the balance of the system completed as part of closure. During closure construction, the system will be taken off line in phases as the final cover system is installed; the system will be modified, as necessary, and will then be reconnected. As discussed earlier, an intermediate liner system is being constructed over the Austin Road Units. Horizontal collectors, spaced at approximately 200 feet on center, have been installed to collect landfill gas generated below the liner. The horizontal collector consists of perforated HDPE pipe installed in a gravel pack below the liner system. A geotextile fabric will be installed in the gravel trench to prevent fine materials from entering and clogging the collector pipe. Additionally, the existing vertical landfill gas wells will be cut about 5 feet Forward Landfill SWT Engineering Joint Technical Document - April 2014 z:\projects\allied waste\forward\five year permit rvw 2013\itd-5 yr pr 2013\text\sec 5_final.doc