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Home My WebLink About20 - Design Report - Four Points Ph II - Wastewater WASTEWATER DESIGN REPORT FOR: FOUR POINTS SUBDIVISION PHASE II BOZEMAN, MT Prepared By: Madison Engineering 895 Technology Drive, Suite 203 Bozeman, MT 59718 (406) 586-0262 DECEMBER 2020 FOUR POINTS SUBDIVISION PHASE 2 WASTEWATER SYSTEM DESIGN REPORT A. Engineering Report This design report will give an overview of the proposed sewer main extension for the 36.36 gross acre development of Four Points Subdivision Phase 2 (SE ¼, Section 34, Township 01S, Range 05E) located at the intersection of Cattail St and Davis Ln in Bozeman. The developed area in Phase 2 will be approximately 13.79 acres, which is zoned for high density residential (R- 4) development, and the remaining 22.57 acres will be dedicated to wetland areas or common open space areas. The report includes a description of the proposed sewer main and design parameters. The proposed improvements are anticipated to be constructed spring of 2021. Once the sewer mains are constructed and approved, the mains will become a part of the City of Bozeman system. The procedures and parameters outlined in the COB Design Standards and Specifications Guide were used in the design of the sewer infrastructure for the proposed development. The developer’s contact information is: Four Points MT LLC 5 Rimani Dr Mission Viejo, CA 92692 Sewer service will be provided by the City of Bozeman. The system owner’s contact info is: City of Bozeman Public Service Department PO BOX 1230 Bozeman, MT 59771 The location of the Subdivision is shown on the vicinity map in the figure below: B. Problem Defined The goal of this report is to document capacity within the existing City of Bozeman sewer system to serve the proposed lots and to verify that the proposed sewer extensions are adequately sized for the effluents of the proposed development. The existing sewer mains, lift station, and proposed sewer mains and services within the project vicinity are displayed on the Sewer Exhibit included in the Appendix. In general, the proposed mains and services flow into existing sewer mains, and then into an existing nearby lift station. For reference, the overall City of Bozeman sewer system from the 2015 Wastewater Facilities Plan is included in the Appendix. At the time of this report, the City is constructing a 30” sewer interceptor along Cattail St and Ferguson Ave. It is anticipated that the interceptor will be completed in early 2021. The City indicated that the 30” interceptor would switch to the primary sewer transmit service for the area, and would be allocated on a first come first serve basis. The new interceptor will reduce the flows into the existing Baxter Meadows lift station. Since the proposed development utilize existing sewer mains that flow into the lift station, the development will utilize the Cattail St lift station, and not the 30” interceptor. C. Design Conditions The wastewater demands from the proposed subdivision were estimated based on a per gross acre basis for zoned areas. The wastewater loading densities per zoned areas were obtained from Table V-1 of the City of Bozeman Design Standards and Specifications for R-4 zoning. City of Bozeman's Design Standards specify an average daily flow rate of 1,950 gal/acre/day for R-4 development, plus an infiltration flow rate of 150 gal/acre/day. The average daily flow based on the estimated wastewater flows is shown in the table below: Proposed Developable Lot Area (acre) Loading gpd/acre Avg Flow gal/day Lot 2 Block 1 2.68 1,950 5,226 Lot 1 Block 2 1.62 1,950 3,159 Lot 4 Block 2 3.05 1,950 5,948 Lot 2 Block 3 2.33 1,950 4,544 Lot 3 Block 3 2.32 1,950 4,524 Lot 4 Block 3 1.79 1,950 3,491 Subtotal 13.79 Subtotal 26,891 A peaking factor for the entire subdivision including future phases was calculated based on the following formula: Qmax / Qave = (18 + P0.5) / (4 + P0.5) (P = Population/thousands) Based on a total flow of 26,891 gpd and a wastewater flow rate of 65 gpcd, the total equivalent population is 414 persons. With this equivalent population, the peaking factor is 4.02. The developed lots flow into one of two locations, “Interceptor 2” or “Interceptor 3” of the Baxter Meadows Sewer Design report, as described later in this report. Interceptor 2 also joins with Interceptor 1 at the intersection of Cattail St and Gallatin Green Blvd. The peak flows, including infiltration, split out by downstream interceptor are summarized below: Description Avg Flow gal/day Peak Flow gal/day Infiltration gpd/acre Infiltration Flow gpd Peak + I&I gal/day Peak + I&I gpm Interceptor 2 Lots (These Lots Flow to Interceptor 2 & Subsequently Interceptor 1) Lot 2 Block 1 5,226 20,983 150 402 21,385 15 Subtotal 21,385 15 Interceptor 3 Lots (These Lots Flow to Interceptor 3) Lot 1 Block 2 3,159 12,684 150 243 12,927 9 Lot 4 Block 2 5,948 23,880 150 458 24,338 17 Lot 2 Block 3 4,544 18,243 150 350 18,592 13 Lot 3 Block 3 4,524 18,165 150 348 18,513 13 Lot 4 Block 3 3,491 14,015 150 269 14,283 10 Subtotal 88,653 62 Grand Total 110,038 76 The total peak hour flow plus infiltration is 110,038 gpd or 76 gpm. The proposed 8” sewer main extension, at the minimum design slope of 0.4%, has a capacity of 313 gpm flowing at 75% full, exceeding the peak plus infiltration flow. It is not anticipated that any other future development outside of Four Points Phase 2 will flow into the proposed mains, as those areas are serviced by other existing city mains. The sewer services will be either 4” or 6”, sized in accordance with the Uniform Plumbing Code. D. Impact on Existing Wastewater Facilities At the time of this report, the City is constructing a 30” sewer interceptor along Cattail St and Ferguson Ave. It is anticipated that the interceptor will be completed in early 2021. The City indicated that the 30” interceptor would switch to the primary sewer transmit service for the area, and would be allocated on a first come first serve basis. The new interceptor will reduce the flows into the existing Baxter Meadows lift station. Since the proposed development utilize existing sewer mains that flow into the lift station, the development will utilize the Baxter Meadows lift station, and not the 30” interceptor. The proposed project lies within the original Baxter Meadows Subdivision. The original Baxter Meadows Subdivision Wastewater design report by Robert Pecca & Associates (RPA) was evaluated to confirm that the proposed effluents do not exceed the original design capacity of the existing sewer mains. The original report included in it’s effluent calculations the areas of the proposed lots. Per the report, the proposed lots are serviced via two interceptors, “Interceptor 2 and Interceptor 3”. Interceptor 2 subsequently joins with Interceptor 1 at the intersection of Cattail St & Gallatin Green Blvd. Excerpts from the Baxter Meadows Wastewater report, including calculations for and exhibits that show the interceptors and the associated drainage basins, are included in the Appendix. Lot 1 of Block 2 will flow into Interceptor 2 which runs within an alley and roadway along Gallatin Green Blvd. The RPA report defined the required capacity of Interceptor 2 to be 0.36 cfs or 162 gpm, and recommended an 8” sewer main. However, a 10” main was installed instead. The existing 10” main adjacent to and down gradient of the proposed Lot 1 of Block 2 was installed at a minimum slope of 0.816%, which has a capacity of 810 gpm at 75% full. Therefore, it is anticipated that the 10” has the capacity to handle the Lot 1 Block 2 peak hour flow of 15 gpm. Interceptor 2 subsequently flows into Interceptor 1 in Cattail St. The RPA report defined the required capacity of Interceptor 1 to be 1.64 cfs or 736 gpm, and recommended a 15” sewer main in its northern reach. However, an 18” main was installed instead. The existing 18” main, Interceptor 1, was installed at a minimum slope of 0.368%, which has a capacity of 2608 gpm at 75% full. Therefore, it is anticipated that the 18” has the capacity to handle the Lot 1 Block 2 peak hour flow of 15 gpm. The remaining developable lots will flow into Interceptor 3, which is located within the proposed Veronica Way street. The RPA report defined the required capacity of Interceptor 3 to be 0.97 cfs or 436 gpm, and recommended a 15” sewer main. The existing 15” sewer main, Interceptor 3, adjacent to the remaining developable lots was installed at a minimum slope of 0.7%, which has a capacity of 2,212 cfs at 75% full. Since the capacity of the existing 15” main greatly exceeds the original design capacity, it is anticipated that the 15” has the capacity to handle the remaining developable lots peak hour flow of 62 gpm. The lift station was designed by Allied engineering and the lift station design report was evaluated to determine the pumping capacity. The lift station consists of three 13-horsepower submersible pumps sized to handle a peak hourly flow of 1380 gpm with any two pumps, while the average daily flow of 502 gpm will be handled with a single pump. Since the 30” interceptor will reduce the flows into the lift station, it is anticipated that it will have the capacity for the proposed development peak hour flows of 77 gpm. As stated previously, the lift station was sized to include the flows from the areas of the proposed development. Excerpts from the lift station report demonstrating the flow rates and capacities of the pumps are included in the appendix. The City of Bozeman will need to provide a letter certifying that they have adequate capacity to serve the proposed subdivision. E. Project Description This proposed project is intended to be a residential development within the City of Bozeman. The developable lots of the project are zoned R-4, or Residential High Density District. At the time of this report, the design of the interior lots has not been completed. The proposed subdivision streets will provide the necessary water, sewer, and transportation infrastructure to provide utility service and legal and physical access to the lots. F. Drawings The proposed sewer improvements within the proposed roadways are displayed on the Sewer Exhibit provided in the Appendix. Construction drawings and specifications with sewer plan and profiles will be submitted with any agency review submittal accompanying this report. G. Design Criteria The following design criteria were used in the wastewater facilities design and capacity analysis: a. COB Design Standards and Specifications Policy, 2004, Addendum #7 b. COB Modifications to Montana Public Works Standard Specifications (MPWSS), Addendum #3 c. Montana Public Works Standard Specifications d. COB Wastewater Facility Plan, 2015 e. Circular DEQ- 2 f. Uniform Plumbing Code H. Site Information The Four Points subdivision lies in northeast Bozeman, contains delineated wetlands which have been declared restricted wetland and common open space areas, and has slopes falling northward between 1% and 2%. There are no delineated floodplains in the subdivision. A geotechnical report was conducted for the entire Four Points Phase 2 Development in 2015 by Allied Engineering. In general, soil conditions consist of a layer of topsoil 1.0 to 3.5 ft thick followed by a layer of silts and clays between 3.0 and 13.5 ft depths, followed by alluvial sandy gravel. Groundwater was monitored on the site and seasonal high groundwater levels were observed between 2 and 5 ft below the existing surface. It is anticipated that significant dewatering efforts will be required for utility construction. Manhole buoyancy calculations have been provided in the appendix. I. Alternative Selection/Analysis The only viable alternative for this project is to utilize the existing City of Bozeman sanitary sewer system. J. Environmental Impacts The proposed wastewater improvements have the least adverse environmental impact as they utilize the existing City of Bozeman wastewater facilities. It is not anticipated that any adverse environmental impacts will occur from the development. The phase 2 development will only occur in non-wetland areas. The contractor will be required to implement a stormwater pollution prevention plan (SWPPP) during construction. K. Future Development Wastewater Demands It is not anticipated that any other future development outside of Four Points Phase 2 will flow into the proposed mains, as those areas are serviced by other existing city mains. Therefore, the proposed wastewater system for the subdivision is adequate to meet project and future demands. The City of Bozeman is providing relief to the lift station, as they are building a new 30” interceptor in Cattail St and Ferguson Ave. The interceptor will reduce the flows to the existing lift station, and future upgradient sewer flows that would have gone to the existing lift station will be re-routed to the new 30” interceptor on a first come first serve basis. A capacity to serve letter is included in the Appendix. Appendix 1. Sewer System Exhibit 2. 2015 Wastewater Facilities Plan Exhibit 3. Wastewater Main Capacity Calcs 4. Excerpts from Baxter Meadows Sewer Report 5. Excerpts from Lift Station Report 6. Manhole Buoyancy Calculations 7. Capacity to Serve Letter APPENDIX Sewer System Exhibits PROPOSED LOT 1 BLK 2 70,767 SF 1.62 ACRES PROPOSED LOT 2 BLK 2 179,501 SF 4.121 ACRES (WETLANDS) PROPOSED LOT 1 BLK 1 75,992 SF 1.74 ACRES (WETLANDS) PROPOSED LOT 4 BLK 3 78,120 SF 1.79 ACRES PROPOSED LOT 6 BLK 3 487,175 SF 11.18 ACRES (WETLANDS) EXISTING LOT 1 MINOR SUB 475 PUBLIC PARK 233,438 SF 5.359 ACRES ZONING: R3 PROPOSED COMMON OPEN SPACE LOT 5 BLK 3 24,009 SF, 0.55 ACRES (Detention Basin) PROPOSED LOT 7 BLK 372,136 SF1.66 ACRES(LINEAR PARK) PROPOSED COMMON OPEN SPACE LOT 3 BLK 2 30,430 SF, 0.70 ACRES (Detention Basin) PROPOSED LOT 1 BLK3 9,914 SF 0.23 ACRES (Lift Station)VERONICA WAYBLONDIE STREET CATTAIL STREET KIMBERWICKE STREETMILKHOUSE AVEVAQUERO WAYCASPIAN AVEDAVIS LANEFERGUSON AVEKIMBERWICKE STREET EXISTING LOT 2 MINOR SUB 475 115,826 SF 2.659 ACRES ZONING: R3 EXISTING LOT 3MINOR SUB 475123,623 SF2.838 ACRESZONING: R4 PROPOSEDLOT 4 BLK 2132,995 SF3.05ACRES PROPOSED LOT 2 BLK 1 116,759 SF 2.68 ACRES PROPOSEDLOT 3 BLK 3101,002 SF2.32 ACRES PROPOSED LOT 2 BLK 3 101,437 SF 2.33 ACRES GREENWAY BLVDLEGEND 1" = 0 SCALE 100' 20050100 EXHIBITMADISON ENGINEERING 895 TECHNOLOGY BLVD, STE 203, BOZEMAN, MT 59718 PHONE (406) 586-0262 FOUR POINTS PHASE 2 SANITARY SEWER EXHIBIT Figure 5-1 – Drainage Basins within the Bozeman Community Plan 5-3 Sewer Capacity Calculations Sewer Main Capacity Calculations Status Proposed - 8" Sewer Location Blondie St Pipe Material 8” SDR 35 PVC Pipe Diameter (in) 8 Minimum Pipe Slope (ft/ft) 0.004 Coefficient of Roughness (n) 0.013 Depth in Pipe at 75% Full (in) 6 Depth of Flow (ft) 0.5 Pipe Radius (in) 4 Pipe Radius (ft) 0.33 Wetted Perimeter 1.40 Area of Flow (ft2)0.28 Hydraulic Radius 0.20 Velocity (ft/sec) 2.48 Flowrate (cfs) 0.70 Maximum Pipe Flowrate (gpm)312.8 Status Existing - Interceptor 1 Location Cattail St Pipe Material 18” SDR 35 PVC Pipe Diameter (in) 18 Minimum Pipe Slope (ft/ft) 0.00368 Coefficient of Roughness (n) 0.013 Depth in Pipe at 75% Full (in) 13.5 Depth of Flow (ft) 1.125 Pipe Radius (in) 9 Pipe Radius (ft) 0.75 Wetted Perimeter 3.14 Area of Flow (ft2)1.42 Hydraulic Radius 0.45 Velocity (ft/sec) 4.09 Flowrate (cfs) 5.81 Maximum Pipe Flowrate (gpm)2608.0 Status Existing - Interceptor 2 Location Greenway Blvd Alley Pipe Material 10” SDR 35 PVC Pipe Diameter (in) 10 Minimum Pipe Slope (ft/ft) 0.00816 Coefficient of Roughness (n) 0.013 Depth in Pipe at 75% Full (in) 7.5 Depth of Flow (ft) 0.625 Pipe Radius (in) 5 Pipe Radius (ft) 0.42 Wetted Perimeter 1.75 Area of Flow (ft2)0.44 Hydraulic Radius 0.25 Velocity (ft/sec) 4.11 Flowrate (cfs) 1.80 Maximum Pipe Flowrate (gpm)810.1 Status Existing - Interceptor 3 Location Veronica Way Pipe Material 15” SDR 35 PVC Pipe Diameter (in) 15 Minimum Pipe Slope (ft/ft) 0.007 Coefficient of Roughness (n) 0.013 Depth in Pipe at 75% Full (in) 11.25 Depth of Flow (ft) 0.9375 Pipe Radius (in) 7.5 Pipe Radius (ft) 0.63 Wetted Perimeter 2.62 Area of Flow (ft2)0.99 Hydraulic Radius 0.38 Velocity (ft/sec) 4.99 Flowrate (cfs) 4.93 Maximum Pipe Flowrate (gpm)2212.0 Excerpts from Baxter Meadows Sewer Report Excerpts from Lift Station Report Manhole Buoyancy Calculations Capacity to Serve Letter