ARCHIVED REPORTS_1993_1 - Laserfiche WebLink

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III. Environmental Setting, Impacts,and Mitigations F. Vegetation and Wildlife The following discussion provides a more detailed analysis of the proposed project's potential effects on the biotic environment currently present within the project area,and proposes mitigation measures to reduce these impacts to below the threshold of significance. In this analysis,the significance criteria outlined above was used to determine the level of significance of impacts to individual biotic resources. Impact F.I. Implementation of the proposed project would fill and relocate approximately 4.5 acres of the North Fork of the South Branch of Little Johns Creek. (SIGNIFICANT) As part of the proposed project,Little Johns Creek would be relocated along the northern and western boundaries of the existing landfill with a minimum fifteen foot floodplain easement extending to either side of the relocated Creek(total width of thirty feet plus the width of the new channel). The new channel would then intersect the original channel along the western site boundary(see Figure II.3). As shown in proposed project plans,the replacement channel would primarily consist of a maximum 45-foot wide,7-foot deep trapezoidal channel,with approximately 15-foot wide,Moot deep floodplain easement to either side of the new channel traversing the site for approximately 6,790 lineal feet(approximately 7.0 acres). The new creek channel would also have a geomembrane liner overlain with dirt and rip rap(R.W. Beck and Associates, 1992). A more detailed drainage relocation plan/setback vegetation plan,including vegetation establishment and maintenance programs,was not available for review during preparation of this EIR. The reasons for the Creek realignment are as follows: • To eliminate floodplain areas from the horizontal expansion areas, • To provide surface water run-on control for the horizontal expansion phases by eliminating the primary potential run-on source; • To allow maximum capacity development of the site by allowing refuse filling between the horizontal and vertical expansion phases; • Lining the creek channel will eliminate the potential of subsurface water migration into the existing landfill waste;and • Lining the creek will eliminate the potential of groundwater and landfill gas into the surface water of Little John Creek(R.W. Beck and Associates, 1992). Additionally,the project proposes to create a landfill surface water detention facility to collect run-off(surface water)from the expanded landfill and to detain 100-year flood flows on the site. i III.F.21