REMEDIAL ACTION WORK PLAN OPERABLE UNIT 2, LANDFILL ...

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\. The final cover grades (excluding the proposed 4:1 side slopes around the perimeter) will be
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increased from the regulatory minimum of three percent to not more than 10 percent. The
proposed maximum slope requirement is selected to minimize erosion rather than to minimize
slope stability concerns. Slopes over 10 percent are feasible, however additional erosion control
methods, and increasing costs, are usually required to limit soil loss.
The proposed constructibility improvement is to increase the slopes on the cover above three
percent minimum to allow for the expected settlement and eliminate the construction delay.
2.9.1.5 Storm Water Drainage
The cover storm water drainage system consists of a network of 8 and 12-inch diameter pipes
diverting drainage water to large itilltration basins adjacent to the landfill cover areas. The pipes
are situated in a 12-inch vegetative cover layer which means there is little to no cover soil over
the pipe.
The proposed constructibility improvement is to eliminate the pipes and the infdtration basins.
Storm water will run off the cover and collect in a shallow infiltration channel around the
perimeter of the landfill areas. The area of the perimeter channel will equal or exceed the
inlltration basin area so the infdtration design will not be changed.
2.9.7.6 Flexible Membrane Liner (Geomembrane)
The slope stability design in the Design Analysis (HLA, 1995a) specifies a three horizontal to
one vertical (3: 1) slope around the perimeter as the critical location. However, the
geomembrane is shown located on a 2:1 slope. The design would require importing soils to meet
the design output from the slope stability analysis. Additionally, the geomembrane extends out
further than five feet past the general fill (refuse from Area A).
The proposed constructibility improvement is to flatten the geomembrane slope to 4:1 and use
on-site soils. Another improvement is to use textured geomernbmne along the 4:1 slopes only
and reduce costs by using a smooth geomembrane on the relatively flat areas over most of the
landfill cover areas. The extent of the geomembrane perimeter will be reduced to extend no
further than five feet past the edge of refuse. Figure 2-16, Constructibility Improvements, shows
,.--.., a simplified section through the perimeter berm.
SM6-24-961SACTERCITTORD 0U21RAWP.RV1
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