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generator and automatic transfer switch will be installed at the site to maintain <br />operation during power outages. <br />Likely Construction Cost — $725005000 <br />Table 2 depicts the cost breakdown used to estimate the cost of this alternative. A <br />major factor in pricing this alternative is the uncertain amount of effort required to <br />excavate the rock subgrade. In order to develop the cost estimate for this alternative, <br />the following assumptions were made: <br />• 8 -inch diameter minimum sewer size <br />• 0.34% minimum design slope <br />• 4.0 feet cut at uppermost manhole <br />• i00% cost premium for rock excavation <br />• Grade in the area is essentially flat <br />• Drop manholes are not considered <br />It Drops through manholes are not included in the cost estimate <br />• The cost of lateral (service) line was included <br />• Annual average daily wastewater flow estimated as 300 gpd per connection <br />• 3.7 -peak factor was used to estimate the design flow <br />• The cost includes 20% for contingencies and administrative <br />• The cost includes 10% for engineering and planning fees. <br />Discussion of Benefits and Disadvantages — <br />The gravity system alternative might not be feasible due to the rock layer restriction <br />that is reflected in the cost estimate. This is the major impediment to implementing this <br />system and most likely why it was not originally implemented when the current system <br />was installed. Of related concern is the possible damage to existing structures due to <br />translated vibration during excavation through the existing rock layer. <br />A gravity flow system should decrease problems related to flood conditions. The <br />current system's individual wet wells, installed flush with grade, will no longer be <br />needed. The new gravity lines, initially installed to limit leaks, may experience <br />increased infiltration problems over time, but the pump station should be sized to <br />handle the expected peak conditions. <br />A gravity flow system has comparatively low maintenance since maintenance is limited <br />to a single site. There is very little maintenance required for the gravity lines once <br />properly installed. <br />This alternative requires reversal of the sewer line from the back of most houses to <br />the front. This, along with the depth of excavation required, will result in a higher <br />impact on customers both in construction activities and disturbance to existing <br />property. <br />Page 4 of 7 <br />FAUtilities\UTILITY - ENGB ERINGIPmjeeu -Utility Can tinction Pe uVRC - Rcxk dge Scwa FEMA Mitigation UCP W 2521VBSU Engineeedng Repon\Tech Memo <br />RocWdge - Vxuum Option. doc <br />