2005-02-02 P&R Packet - Laserfiche WebLink

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,/ ,I Ms. Kim Stephan, Park and Recreation Liaison City of Centerville January 12, 2005 Page 4 Wetlands Based on a site visit and review of the National Wetland Inventory (NWI) maps, it appears that there are several designated wetlands within the proposed trail alignment west of County Road 54. The implications of wetland impacts are varied, but the two basic responses are avoidance and mitigation. Impacts may be avoided by establishing alternate trail alignments around the wetland or constructing the trail on boardwalk. Mitigation would entail the creation of new wetland at a nearby site within the local watershed to offset the impact of trail construction. Wetland impacts may also be minimized by constructing retaining walls adjacent to the wetlands to minimize the extent of impact. While impacts to wetlands do not preclude the construction of a trail, wetland mitigation and boardwalks both have the potential to add significant cost. Wetland delineations will be required to determine the full extent of wetland impact along the trail corridor. Permitting will also be required through the Rice Creek Watershed District. Soils Based on review of the Anoka County soil survey, the entire trail corridor is located within the Nessel-Dundas-Webster soil association which suggests a higher concentration of organic soils that have high water retention and are poorly drained which could pose a moderate to severe limitation for the development of the trail in some areas. The presence of these soils suggest that it may be necessary to excavate and remove these organic soils in some areas or construct the alternate pavement section as discussed in the Design Criteria section. While the presence of these soils do not preclude the construction of trails, the potential for soil removal or alternate construction methods could add to the cost of construction. This report assumes that approximately 350 linear feet of trail may need to be constructed near wetland areas using the alternate cross-section. Further investigation of the existing soils in the area is suggested to help identify other areas within the trail corridor that are located within poor soil areas. ESTIMATED CONSTRUCTION COST A preliminary estimated construction cost for the proposed trail segment is based on the alignment shown in Figure 1. The total construction cost of the proposed trail is approximately $287,000. The total project cost assumes construction in 2006 and includes the addition of a 10 percent contingency. Indirect costs of 5 percent for survey, geotechnical, wetland delineation and permitting and 10 percent for design, inspection, and administration are included for planning purposes. The estimate does not include costs for wetland mitigation and utility relocation. A more detailed estimate for the construction costs of the trail segments can be found in Appendix A. As noted in the previous section, several factors that can contribute significantly to the cost of the project are relative unknowns at this point. These factors include mitigation requirements for wetland impacts, soil corrections due to poor soils, and the acquisition of additional trail right-of-way.