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Home My WebLink About012 Sewer Design Report Allison Sub PH IV A - The Boötes WASTEWATER DESIGN REPORT FOR: ALLISON SUBDIVISION PHASE IV BOZEMAN, MT Prepared By: Madison Engineering 895 Technology Drive, Suite 203 Bozeman, MT 59718 (406) 586-0262 SEPTEMBER 2020 ALLISON SUBDIVISION PHASE IV WASTEWATER SYSTEM DESIGN REPORT A. General This design report will give an overview of the proposed sewer main extension for the 48.21 acre development of Allison Subdivision Phase IV (Section 24, Township 02S, Range 5E, Plat J- 608A) located at the intersection of Arnold Street and S. 11th Avenue in Bozeman. Phase 4 of the subdivision is split into Phase IV A, B, and Future. The developed area in Phase IV A will be approximately 21.09 acres, with approximately 27.12. acres remaining in Phase IV B and Phase IV Future. There will also be a future Phase V of about 48.65 acres that will drain into the proposed Phase IV sewer mains. This report focuses on Phase IV A as well as including calculations for full build out of the remaining Phase IV and Phase V areas. It is not anticipated that any other future development outside of The Allison Subdivision Phase IV and V will flow into the proposed mains, as they are within different City of Bozeman Sewer Drainage Basins and/or serviced by other existing city mains. The report includes a description of the proposed sewer main and design parameters. The proposed Phase IV A improvements are anticipated to be constructed during 2020 and 2021. Once the sewer mains are constructed and approved, the mains will become a part of the City of Bozeman system. The following references were used in the wastewater facilities design and capacity analysis: a. COB Design Standards and Specifications Policy, 2004, Addendum #6 b. COB Modifications to Montana Public Works Standard Specifications (MPWSS), Addendum #3 c. City adopted MPWSS and Adopted Addenda d. COB Wastewater Facility Plan, 2015 e. Circular DEQ- 2 f. City of Bozeman Zoning Map g. City of Bozeman Infrastructure Viewer 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. B. Capacity Analysis The subdivision falls in the Spring Creek Drainage Basin in Bozeman, MT. The capacity was calculated for full buildout of the remaining phases, Phase IV and Phase V, of Allison Subdivision, approximately 96 acres, as well as for the current Phase IV A, about 21.61 acres. The effluent generated from the proposed subdivision will flow north into the existing City of Bozeman sanitary sewer manhole located in Opportunity Way, then east in an existing 8” main, eventually reaching the existing 10” main in S 3rd Ave. Future Phase V will also flow through the Phase IV mains. An exhibit showing the proposed mains and existing mains near the project is included in the appendix, as well as the 2015 Wastewater Facilities plan Sewer Basin Exhibit which shows the City’s sewer infrastructure. It is not anticipated that any other future development outside of Phase IV and V will flow into the proposed mains, as they are within different City of Bozeman Sewer Drainage Basins and/or served by other existing sewer mains. 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-1, R-2 and R-3 zoning. City of Bozeman's Design Standards specify an average daily flow rate of 730 gal/acre/day for R-1 development, 980 gal/acre/day for R-2 development, and 1,220 gal/acre/day for R-3 development. The proposed sewer mains have been sized to flow at no more than 75- percent of full capacity at peak hour conditions of full build out, and a Manning coefficient of 0.013 was used for PVC pipe. The average daily flow based on the estimated wastewater flows is shown in Table 1 below, a basin exhibit is included in the appendix: Table 1 Average Daily Flow Rates Basin Allison Sub Phase Zoning Area (acres) Wastewater Loading (gpd/acre) Average Flow Rate (gpd) 1 4 A R-1 11.44 730 8,351 R-2 5.12 980 5,018 R-3 4.53 1,220 5,527 2 4 B & 4 Future R-2 4.71 980 4,616 2 4 B & 4 Future R-1 22.42 730 16,367 3 5 Future R-1 48.65 730 35,515 Total 96.87 75,394 The infiltration was determined based on 150 gpd/acre multiplied by the acreage per the City of Bozeman Design Standards. 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 75,394 gpd and a wastewater flow rate of 65 gpcd, the total equivalent population is 1,160 persons. With this equivalent population, the peaking factor is 3.76. The calculated peaking factor is included in the appendix of this report. The peak flow rate anticipated from the development at full build out based on an average daily flow of 75,394 gallons per day, plus an infiltration rate of 150 gpd/acre is: Peak Flow Rate = (Average Flow Rate x Peaking Factor) + Infiltration Peak Flow Rate = (75,394 gpd x 3.76) + (150 gpd/ac x 96.87 ac) = 298,012 gpd = 207 gpm = 0.46 cfs The proposed Allison Subdivision Phase 4 plus future phase peak design flow is 0.46 cfs or 207 gpm. The Allison Sub Phase 4 A total design flow is 18,896 gpd, and at a flow rate of 65 gpcd, this equates to 298 persons. With this equivalent population, the peaking factor is 4.08. The calculated peaking factor is included in the appendix of this report. The peak flow rate anticipated from the development at full build out based on an average daily flow of 18,896 gallons per day, plus an infiltration rate of 150 gpd/acre is: Peak Flow Rate = (Average Flow Rate x Peaking Factor) + Infiltration Peak Flow Rate = (18,896 gpd x 4.08) + (150 gpd/ac x 21.09ac) = 80,260 gpd = 56 gpm = 0.124 cfs The Allison Subdivision Phase 4 peak design flow is 0.124 cfs or 56 gpm. The sewer main size for the development will be an 8-inch, based on minimum required pipe size and slope. An 8- inch PVC sewer main at 0.4% slope has a capacity of 0.70 cfs at ¾ pipe depth which has adequate capacity for the proposed peak flow of 0.46 cfs effluent generated from the 96-acre site. Calculations are provided in the appendix of this report. C. Proposed Collection System PVC pipe meeting COB specifications will be used for all the sewer mains. The maximum manhole spacing will be 400 feet for the 8-inch main with a manhole barrel size of 48-inches. Manholes will be constructed according to COB specifications. All sewer services will be 4-inch PVC installed at 2% minimum grade. Sewer services will connect into the main with in-line gasketed wyes. A 4-inch sewer service with a grade of 2.0% can convey approximately 60 gpm at 50% capacity. The sewer main will be located within a 60-foot wide Right of Way and maintain a minimum separation of 10-feet from the proposed public water main. D. Future Development Wastewater Demands The full-buildout of the Allison Phase IV & V subdivision is anticipated to have a peak flow rate of 0.46 cfs per the calculations above. The Allison Phase 4 & 5 developments lie within the “Spring Creek” sewer drainage basin. A City of Bozeman sewer drainage basin exhibit taken from the 2015 Wastewater Facilities Plan that shows the City’s sewer system is included in the appendix. It is not anticipated that any other future development outside of Phase IV and V will flow into the proposed mains, as they are within different City of Bozeman Sewer Drainage Basins and/or serviced by other existing city mains. Therefore, the proposed 8” sewer main improvements for the Allison Phase IV & V subdivisions are adequate to meet project and future demands. E. Downstream Capacity Analysis The City of Bozeman has provided a letter indicating that capacity exists in the sewer collection system to provide service for the subdivision. The letter is included with this report. F. Groundwater, Soil Conditions, and Floodplain Information According to an exploratory soil test pits on site, the soil consists of topsoil to a depth of 1.0’, followed by lean clay (brown, medium stiff, silt lenses) to a depth of 7.5’, followed by well graded gravel (multi colored, very dense to medium dense) to a depth of 17.0’. Groundwater was observed in spring and summer of 2019 and 2020, and the highest (shallowest) groundwater measurement was 3.17’ of the surface. The average seasonal high groundwater depth at the six (6) wells was 5.32’ from the surface. Buoyancy calculations were conducted and indicate that the proposed manholes are adequate for the design, buoyancy calculations are included in the Appendix. The soil and groundwater found on site are suitable for this project. Figgins creek borders the west side of the project and it has a FEMA delineated 100-year floodplain. The proposed development will have restrictions on development in the floodplain and creek setbacks. The proposed setbacks within the Phase IV A areas are displayed on the Sewer Drainage Basin Exhibit included in the appendix. G. Environmental Impacts The proposed project is not anticipated to have any adverse environmental impacts. The required Floodplain, 310, 318, and 404 permits have been obtained for the Phase IV A improvements within the Figgins Creek areas. A SWPPP will be completed and put in place for the Phase IV A project in accordance with City and State requirements. Future phases may require additional permits, and they will be obtained in compliance with federal, state, and local agencies as required. H. Conclusion As outlined above, the 8-inch sanitary sewer main serving Phases IV & V of Allison Subdivision will have the capacity for the effluent generated the residential subdivision. In addition, there is adequate capacity in the system to serve Allison Subdivision. This project will require the approval of the City Engineer and MDEQ. Appendix 1. Wastewater Main Capacity Analysis 2. Peaking Factor Calculation 3. Sewer Drainage Basin Exhibit 4. Sewer System Exhibit 5. 2015 Wastewater Facilities Plan Exhibit 6. Manhole Buoyancy Calculations 7. City of Bozeman Capacity to Serve Letter APPENDIX Pipe Capacity Project Description Friction Method Manning Formula Solve For Discharge Input Data Roughness Coefficient 0.013 Channel Slope 0.40 % Normal Depth 6 in Diameter 8 in Results Discharge 0.70 ft³/s Flow Area 0.28 ft² Wetted Perimeter 1.40 ft Hydraulic Radius 2 in Top Width 0.58 ft Critical Depth 0.39 ft Percent Full 75.0 % Critical Slope 0.00773 ft/ft Velocity 2.48 ft/s Velocity Head 0.10 ft Specific Energy 0.60 ft Froude Number 0.63 Maximum Discharge 0.82 ft³/s Discharge Full 0.76 ft³/s Slope Full 0.00333 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0 in Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0 in Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % Normal Depth Over Rise 75.00 % Downstream Velocity Infinity ft/s 8-inch PVC Pipe Capacity 1/16/2014 8:28:10 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page GVF Output Data Upstream Velocity Infinity ft/s Normal Depth 6 in Critical Depth 0.39 ft Channel Slope 0.40 % Critical Slope 0.00773 ft/ft 8-inch PVC Pipe Capacity 1/16/2014 8:28:10 PM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of2Page Peaking Factor Calculation Sewer Main Extension Allison Subdivision Full Buildout Peaking Factor Total Flow = 75,394 gpd Flow Rate = 65 gpcd Equivalent Population = 1,160 people =Q(max)= 18 + P 0.50 P = Population/thousands Q(ave)4 + P 0.50 Peaking Factor = Allison Subdivision Phase 4 A Peaking Factor Total Flow = 18,896 gpd Flow Rate = 65 gpcd Equivalent Population = 291 people =Q(max)= 18 + P 0.50 P = Population/thousands Q(ave)4 + P 0.50 Peaking Factor = 3.76 Peaking Factor Peaking Factor 4.08 Drawings & Exhibits EMEM DRAINAGE BASIN 3 DRAINAGE BASIN 2 PHASE V PHASE IV B & FUTURE DRAINAGE BASIN 1 PHASE IV A EMEM S.S. BASINSMADISON ENGINEERING 895 TECHNOLOGY BLVD, STE 203, BOZEMAN, MT 59718 PHONE (406) 586-0262 ALLISON SUBDIVISION PHASE 4 SEWER DRAINAGE BASINS BOZEMAN,MT 1 inch = 0 SCALE 300 feet 600'150'300' EMEM ALLISON PHASE V 48.65 AC R-1 ALLISON PHASE IV B & FUTURE 22.42 AC R-1 4.71 AC R-2 ALLISON PHASE IV A 11.44 AC R-1 5.12 AC R-2 4.53 AC R-3 S.S. SYSTEMMADISON ENGINEERING895 TECHNOLOGY BLVD, STE 203, BOZEMAN, MT 59718PHONE (406) 586-0262ALLISON SUBDIVISION PHASE 4EXISTING SEWER SYSTEMBOZEMAN,MT1 inch = 0 SCALE 500 feet 1000'250'500' Figure 5-1 – Drainage Basins within the Bozeman Community Plan 5-3 Manhole Buoyancy Calculations Bozeman Capacity to Serve Letter Allison Subdivision Phase IV A Wastewater System Design Report The Boötes Addendum I - August 2023 Wastewater Daily Flow Analysis The Boötes Residential Development Average Daily Flow No of Units 71 Residents/unit 2.11 Gallons per Capita/day 89 Average Daily Flow 13,333 gpd Peaking Factor Calculations Zoning Density (residents/unit) Total Popoulation R3 2.11 150 =Q(max)=18 +P 0.50 P = Population/thousands = 84/1000 = 0.150 Q(ave)4 +P 0.50 Peaking Factor = Peak Hour Sewer Demand Average Daily Flow 13,333 gpd 555.5 gph 9.3 gpm Peaking Factor 4.19 Peak Hour Sewer Demand 2328.4 gph 38.8 gpm 311.28 cfh 5.19 cfm 0.086 cfs 4.19 Peaking Factor Units/AcreAcres 3.63 19.6