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Storm Sewer The existing storm sewer system has been reviewed by City and Bonestroo staff. Please refer to Figures 3-7 for a graphic depiction of the layout of the existing system and the proposed improvements. PROPOSED PIPE INSTALLATIONS There are a number of places where it has been determined that additional pipe and storm sewer structures are needed, These improvements will help surface drainage which will in-turn add to the durability of the street surface. Subsurface drainage improvements are also proposed with th€ use of draintile either in front of the curb, if it is being salvaged or behind the curb in areas of full street reconstrudion. STORM SEWER CROSSING ISSUES The City of Centerville has been experiencing some serious problems due to heaving of fat clays and other moisture laden subgrade soils around existing storm sewer crossings. This annual heaving and settling from freeze-thaw cycles produces uneven roadways and often leads to deteriorated pavements, It is recommended that all storm sewer crossings be excavated and restored with suitable material in order to reduce movement of the future roadway. Figure 8 illustrates the cross sedion of these proposed improvements. PROPOSED STORM WATER MANAGEMENT The proposed project area lies within the Rice Creek Watershed District (RCWD). Therefore, the District will have permit authority over the projed and the storm water management within the project. In order to meet the infiltration requirements of the District, it will be necessary to install infiltration basins (rain gardens), swales or other Best Management Practices (BMPs) throughout the reconstrudion project areas. While the RCWD rules require these BMPs to be installed when street reconstruction projects are undertaken, the district understands the inherent difficulty of retrofitting a fully developed neighborhood with space consuming and grade-dependent facilities, In an effort to fully understand the watershed's requirements and to give them first hand knowledge of the projed and its challenges, Bonestroo staff, along with City staff met, on-site with watershed staff and consultants to walk the project streets. While the watershed would not offer official stances on specific project issues, they did provide helpful direction and guidance on where the letter of the rule would be enforced and where we would be able to demonstrate that there are not viable solutions available, Some neighborhoods such as the Royal Meadows development along 20th Ave. simply did not have adequate space to accommodate retrofitted rain gardens or the like. Other more spacious neighborhoods were, in the opinion of the watershed, more apt to allow the construction of these BMPs. In the attached Appendix A, potential BMP sites are identified (Figures 1.1-1.4), It is important to note that these locations were chosen based on topography and guidance from the watershed during our on-site meetings, Final locations will need to be adjusted as more information is collected. While some BMPs will be able to be constructed within the existing right-of-way and adjacent easements, others will require additional easements, The council should consider whether or not to compensate City of Centerville 2009 Street and Utiljty Improvement Project # Bonestroo Project No: 616-07-1580 Page II