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HomeMy WebLinkAbout5. Additional Supplements Additional Subdivision Preliminary Plat Supplements Page 1 f 6 Additional Subdivision Preliminary Plat Supplements Flanders Mill Subdivision 1. Surface Water This site contains significant wetland areas and two non-wetland waterways, the Unnamed Tributary of Baxter Creek (UT Baxter) and the Baxter-Border Stream. Modifications to the existing surface water channels and wetlands are proposed with this subdivision. A detailed description of the existing on-site surface waters/wetlands and proposed alterations is provided in the enclosed 404 Permit Application (Appendix A). The UT Baxter is a perennial stream that flows south to north from Durston Road along the eastern part of the property before being diverted west under Flanders Mill Road. The current stream bed is approximately two feet wide and is a low-functioning stream with low sinuosity, includes no woody vegetation, and flows have little access to a wetland floodplain adjacent to the stream. The channel receives two sources of surface water: from a seep along Ferguson Lane and irrigation waste water from the Maynard-Border diversion structure on the south side of Durston. It is suspected that the UT Baxter also conveys groundwater. This proposal includes realigning this stream from its current channel to a proposed 30-ft wide meandering wetland floodplain corridor. The new stream corridor will run south to north through the entire subdivision, cross under Baxter Lane, and confluence with the restored reach of the Baxter-Border stream on the north side of Baxter. The Baxter-Border stream flows perennially east to west through the northeast corner of the property. The stream enters the property from dual culverts under Ferguson Lane directly south of the Baxter/Ferguson roundabout and exits the property through dual culverts running north under Baxter Lane. This stream is proposed to be diverted south approximately 30 feet to allow for the full construction of Baxter Lane (the north half of Baxter has been constructed). Detailed information of the on-site surface water and wetlands, including all maps, alteration proposals, permits, and descriptions is provided in Appendix A. 2. Floodplains (Waived) There are no designated floodplains on or immediately adjacent to this site. 3. Groundwater (Waived) Groundwater levels are known and will be accounted for with proposed construction. Public City of Bozeman sanitary sewer and water are proposed for the project, minimizing potential groundwater degradation. Surface runoff will be controlled by channeling flows into stormwater facilities. These facilities will filter sediments and oil, which will reduce the potential for contamination of downstream aquifers. Additional Subdivision Preliminary Plat Supplements Page 2 f 6 4. Geology, Soils, Slopes Geologic Hazards The surface geology covering the subject property has been mapped as older alluvium of braid plains by the Montana Bureau of Mines and Geology. This formation is described as Well-rounded, moderately to well-sorted, bouldery gravel with interbedded silt, see Geologic Map in Appendix B. This correlates well with the tests pits that C&H Engineering has observed across the subject property. In the test pits, Poorly Graded Gravel with Sand and Cobbles was encountered at relatively shallow depth, within 3 to 5 feet of the surface. No geologic hazards such as rock falls, landslides, or subsurface subsidence are associated with the underlying geologic formation. The only geologic hazard that would potentially affect the proposed subdivision is seismic activity, which is discussed in the following paragraphs. The Bozeman area is located in an earthquake zone known as the intermountain seismic belt, which is a zone of earthquake activity that extends from northwest Montana to southern Arizona. In general, this zone is expected to experience moderately frequent, potentially damaging earthquakes. The USGS and Montana Bureau of Mines and Geology (MBMG) have compiled a map of Quaternary Class A faults and earthquake epicenters in western Montana (see Appendix B). A Class A fault is one that is associated with at least one large magnitude earthquake within the last 1.6 million years. The earthquake epicenters shown on the map (yellow circles) are associated with earthquakes of magnitude 2.5 or greater, with stars indicating epicenters of earthquakes with a magnitude greater than 5.5. A review of this map indicated that there are 4 Class A faults located within 20 miles of the subject property and 15 earthquake epicenters have been recorded within 10 miles of the subject property. The four faults mapped near the subject property are the Central Park Fault, Bridger Fault, Elk Creek Fault, and the Gallatin Range Fault. Each of these faults is described as a normal fault, indicating that one side of the fault will move downward into the earth relative the other side during an earthquake. Protective Measures It is important that any structures constructed within the subdivision be designed to withstand horizontal seismic accelerations that may be induced by such an earthquake, as is required by the International Building Code. The USGS has estimated the peak horizontal ground acceleration for the subject property during an earthquake with a 10 percent probability of being exceeded in 50 years to be 0.1500g (15.00 percent the acceleration of gravity) (USGS, 2002). Structural design of any structures constructed within the subdivision need to comply with Section 1613 of the 2009 International Building Code (IBC). Based on the subsurface soils encountered during the field investigation and the surface geologic mapping of the site, the Site Class is D. Additional Subdivision Preliminary Plat Supplements Page 3 f 6 Unusual Features The groundwater elevation across the subject property is relatively high, within a few feet of the surface across most of the subdivision. This is common across much of the Bozeman area and most earthwork contractors are properly equipped to deal with this issue. The fine grained soils overlying the alluvial gravel have not been subjected to significant overburden pressures and have low shear strength. They will need to be removed from beneath any foundation footings for structures constructed on the site or be mechanically reinforced. This issue can be addressed on a site by site basis by a competent geotechnical engineer when homes are constructed within the subdivision. This process is required by the City of Bozeman Building Department, which currently requires a geotechnical report with subgrade improvement recommendations in order to issue a building permit for any structure constructed within the city limits. Soils Map The subdivision layout has been overlain onto a NRCS soils map of the area, see Appendix B. The required soils reports, including physical properties, engineering properties, soil limitations for building and site development, water features, and hydric soils, are included in Appendix B. A wetland delineation report completed by a certified consultant is included in Appendix A. Cuts and Fills No unusual geological features or significant topographic changes are present on the subdivision site. No substantial cut or fill areas are proposed throughout the development. 5. Vegetation (Waived) A wetlands delineation was completed for the property and wetland creations and disturbances are proposed for the development. The associated permitting is currently in process, a copy of the wetland permit application is provided in Appendix A. 6. Wildlife (Waived) No critical wildlife species or habitats are found on this property. Montana Fish, Wildlife & Parks was informed of the proposed development. Their comments are included in Appendix G. 7. Historical Features (Waived) No structures exist on site; the property is actively being cultivated. 8. Agriculture Approximately 85 acres of the property are being used for growing alfalfa/livestock feed. No other agricultural uses exist on the site. Adjacent land uses include residential subdivisions to Additional Subdivision Preliminary Plat Supplements Page 4 f 6 the north and east, a regional park to the east, two church properties to the south, and agricultural land to the west of Flanders Mill Road. The agricultural land west of Flanders Mill Road recently received City of Bozeman Commission approval to be purchased and developed as a City sports complex including several turf athletic fields. 9. Agricultural Water User Facilities The UT Baxter Creek is a natural stream channel, and it was only used to convey water to this specific property, not additional Farmers Canal members. Farmers Canal does not own the stream but have easement rights and accompanying secondary easement rights for inspecting, maintaining and repairing. Farmers indicated they do not clean and maintain those ditches that are not part of their main canals. The Baxter-Border Ditch entering the property from the 100-acre park is part of the Farmer's Canal system. A 20-foot wide easement has been provided in the proposed location. Permission will be sought from Farmers Canal before relocating the ditch as proposed; the City of Bozeman has requested that the ditch be piped or moved outside of the Baxter Lane right-of-way for safety reasons. 10. Water and Sewer Water Supply Water for domestic use and fire protection will be provided by connections to the City of Bozeman water system. The proposed water mains will connect to existing water mains in Ferguson Avenue and Baxter Lane. Please see the Water and Sewer Design Report in Appendix C for more information. Water rights, or cash-in-lieu thereof, will be transferred with final plat. Sanitary Sewer Sanitary sewer service will be provided through connection to the City of Bozeman’s existing sanitary sewer collection system. An existing sanitary sewer main runs north in Ferguson Avenue. Another existing trunk main runs north up Flanders Mill Road, east on Annie Street (future), then jogs north before continuing east on Renova Lane (existing and future). Sanitary sewage from the subdivision will be conveyed to theses existing mains. From there, sanitary sewage will be conveyed to and treated at the City of Bozeman’s Water Reclamation Facility. Please see the Water and Sewer Design Report in Appendix C for more information. 11. Stormwater Management Stormwater will be collected using curb inlets and conveyed via storm sewer pipes to retention and detention ponds located in the park and open space areas. Please see the Stormwater Management Design Report in Appendix D for more information. Additional Subdivision Preliminary Plat Supplements Page 5 f 6 12. Streets, Roads, and Alleys The proposed Flanders Mill Subdivision has legal access onto Ferguson Avenue, Baxter Lane, Oak Street, and Flanders Mill Road. No lots front directly onto Baxter Lane. A one- foot “no access” strip has been provided along Oak Street. As well as interior local streets, this project involves extending Ferguson Avenue from Oak Street to Baxter Lane, completing the south side of Baxter Lane, extending the south half of Oak Street from Ferguson Avenue to Flanders Mill Road, and working with neighboring property owners to improve Flanders Mill Road. Flanders Mill Road will be moved west from its current location so that the road centerline runs along the west boundary of the property. Stormwater design will address treatment of stormwater runoff. Sidewalks and an extensive trail network will provide pedestrian circulation within the subdivision (see Park Master Plan). Alternative compliance is being requested for block length and width. Please refer to the Alternative Compliance Narrative in Section IV. 4. Typical pavement sections have been designed based on soil conditions on the site. Please refer to the Pavement Design Report in Appendix F for more information. A traffic impact study was conducted by Marvin and Associates in November 2013. Please refer to Appendix E. Road maintenance for all streets will be provided by the City of Bozeman after the improvements have been accepted by the City. Erosion and siltation control will be exercised during construction by using the appropriate best management practices as outlined in “Montana Sediment and Erosion Control Manual” (May 1993) prepared by the MDEQ Water Quality Bureau. 13. Utilities Letters requesting comments on their ability to service this subdivision have been sent to the following service providers: Republic Services of Montana (formerly Allied Waste), American Medical Response, Bozeman Deaconess Hospital, Bozeman Public School District, Charter Communications, NorthWestern Energy, CenturyLink (formerly Qwest Communications), Streamline Transit, the U.S. Postal Service, and Montana Fish Wildlife & Parks. Response letters from all of those who chose to comment are enclosed in Appendix G. NorthWestern Energy provided a response stating that they are willing and able to provide gas and electric service to the proposed subdivision. Charter indicated interest in providing telephone/internet/TV. Republic Services stated that they will provide standard curbside residential garbage and/or recycling services. A private utility plan will be submitted with construction drawings. Standard 10’ front yard utility easements will be provided. Additional Subdivision Preliminary Plat Supplements Page 6 f 6 14. Educational Facilities A letter was sent to Kevin R. Barre, Director of Facilities, Bozeman Public Schools. This letter and a response from Mr. Barre are enclosed in Appendix G. 15. Land Use Flanders Mill Subdivision is proposed as a 295-lot major subdivision with 292 single-family residential lots, 2 multi-family lots (zoned R-4), and one lot for the existing NorthWestern Energy substation (zoned PLI). 16. Parks and Recreation Facilities Please see the Park Master Plan. 17. Neighborhood Center Plan The Neighborhood Center will be located in the north park. Please see the Park Master Plan for further details. 18. Lighting Plan A Special Improvement Lighting District will be created after preliminary plat approval and before the final plat application. A preliminary lighting layout is included in Appendix H. 19. Affordable Housing (Waived) The Workforce Housing Ordinance has been suspended until further notice. 20. Miscellaneous No additional impacts or hazards are anticipated. 21. Stormwater Management Permit Application A Stormwater Pollution Prevention Plan (SWPPP) will be submitted to the Montana Department of Environmental Quality prior to construction.