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Page 41 liner and directly below the leachate collection trenches,providinga second containment trenches and sumps. secondary t beneath the Erosion Control Proposed erosion control measures for landfill surfaces and soil'stockpiles in the landfill design include Y 4 r minimizing slope and runoff distance,providing vegetative cover,contour furrowing the surface, increasing the organic content of the soil,and using mulch,erosion control blankets,terraces on steep t slopes,sediment basins,and silt fences or straw bales. In addition, the City of Stockton completed a Wet Weather Operations Plan and an Erosion Control Plan in 1998,implementing a mitigation measure in the 1994 EIR. As discussed in IV.K.Water Quality, Impact K.1, these measures have been implemented for portions of the existing landfill,and could also control erosion of landfill surfaces and soil stockpiles at the expansion area. , ` Surface Water Control r- Stormwater run-off from the working face of the landfill may contact refuse. This wastewater would be collected in a perimeter drainage system afthe edge of the landfill and be directed to the perimeter leachate collection trenches. ' Surface water control includes protecting the landfill from flooding of the North Branch of the South Fork of Little Johns Creek and from surface water run-on, and properly handling surface water run-off'from the landfill closure areas. The existing and proposed landfill would have a perimeter surface water ditch system to route landfill run-off to a detention facility and intercept any surface water run-on that could be directed towards the expansion areas. The surface water detention facility would be located in the southwest corner of the site,and pump its discharge to the North Branch of the South Fork of Little Johns Creek. The ditch system and detention facility would be designed for capacity of the.100-year,24-hour storm. The North Branch of the South Fork of Little Johns Creek ,which currently flows between the existing landfill and the 45-acre borrow pit,would be realigned to the north and west of the existing landfill,to exit the landfill at the same location at which it now exits (see Figure 3). The creek,along with associated wetlands and upland habitat along the banks of the channel,occupies approximately 4.5 acres. Of this,the U.S. Army Corps of Engineers has determined that there are 2.895 acres of jurisdictional waters-of the U.S.,including 0.859 acre of jurisdictional wetlands,which would be filled as part of the project. The EIR assessed a creek realignment with a relatively narrow channel (approximately 40 feet wide at its surface). That realignment plan included lining the creek with a geomembrane liner covered �` with soil and riprap. Following certification of the 1994 EIR,a revised creek realignment plan was I 1 completed,the"Wetland Mitigation and Monitoring Plan for the Austin Road Landfill Expansion"(see Appendix D). The U.S. Army Corps of Engineers authorized the creek relocation specified in the new Fplan on May 12, 1997,subject to certain terms and conditions,including adherence to-the revised creek realignment plan. (See N.F. Biological Resources for discussion of the impacts of the creek realignment). The current realignment plan follows an alignment similar to that assessed in the EIR,with an increased length of 200 lineal feet compared to the existing creek,but with a much wider integrated Fi flood plain(approximately 200 feet)planted with bands of riparian vegetation and with no geomembrane liner, as shown in Appendix D,Figure 3.2. This would result in.a more natural-appearing stream channel and provide habitat superior to the 1994 plan. t GRASSETTI ENVIRONMENTAL CONSULTING Ff