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Home My WebLink About006 - Appendix E - Off Site Water and Sewer Report August 22, 2024 Project No. 06020.11 WATER AND SEWER PRELIMINARY SITE PLAN DESIGN REPORT FOR BOZEMAN YARDS OFFSITE IMPROVEMENTS BOZEMAN, MONTANA Introduction The following report summarizes the water and sewer design calculations for a mixed-use development located on lots 11 and 17, Block 104 of the Northern Pacific Addition Subdivision in northeast Bozeman, Montana. The project is bound by East Aspen Street to the south, Front Street to the east, East Tamarack Street to the north and existing commercial parcels to the west. The subject parcel is approximately one and a half (1.5) acres of mixed-use consisting of residential apartments and ground floor commercial spaces. Water Currently the municipal water system adjacent to the site consists of a 12-inch ductile iron water main in East Tamarack Street and Front Street on the north and east boundaries of the site. North Wallace Avenue has a ten (10) inch ductile iron water main which connects to the water main in Tamarack. There is no water main in the undeveloped portion of East Aspen Street on the south boundary. This project will install a new ten (10) inch water main within East Aspen Street from North Wallace Avenue to Front Street. There are existing fire hydrants at North Wallace and East Aspen intersection, Front Street and East Aspen intersection, North Wallace and East Tamarack Street, and midblock on East Tamarack Street between North Wallace and East Aspen. A new hydrant will be set at the East Aspen and Ida intersection. There are no known capacity issues on the adjacent water mains and fire flows are sufficient for current standards. The City of Bozeman conducted a fire hydrant flow test at the corner of Ida and Cottonwood on May 12, 2017. The static pressure at the time of the test was 147 psi, with a residual pressure of 110 psi at 1,760 gpm. M O NTANA PROFE SSIONAL E N G INEERLICENS E D JOHN CHASE EATON No. 76203 PE P:06020_11_Water Sewer Report 2 Water services for the proposed development will be served by one (1) four (4) inch domestic and one (1) six (6) inch fire service. Meter sizes were provided by the Mechanical Engineer for the project. Irrigation flow estimate was provided by the on-site engineer as 1,000-gpd. For water main sizing, the peak hourly flow plus the fire flow will be used. The proposed domestic and fire sprinkler services are connected to the proposed East Aspen ten (10) inch water main. The residential flows are based on the City of Bozeman Design Standards and Specifications Policy; 2.17 people per dwelling unit, an average daily usage of 170-gallons per day (gpd) per person, and a maximum hour to average day ratio of 2.3:1 based on the peaking factor formula. The commercial demands were based on DEQ 4 circular estimates of ten (10) gpd per employee and six (6) gpd per customer for a coffee shop which is the assumed occupant. The maximum day demand available fire flow for the purpose of design is assumed to be 1,500 gpm at 20 psi residual. The fire suppression system will be fully designed for this project by others and will meet all appropriate required codes. The peak hourly flow rate is as follows: Block 104 South Building Peak Hourly Domestic Water Demand Average Daily Flow(res) = 40 units x 2.17 persons/unit x 170 gpd/person / 2.31 = 6,387.9 gpd Average Daily Flow(comm) = 4 employees x 10 gpd/person = 40 gpd Average Daily Flow(comm)= 200 customers x 6 gpd/person = 1,200 gpd Total Avg Daily Flow = 7,627.9 gpd Total Avg Daily Flow = 7,627.9 gpd / 1440 min/day = 5.3 gpm Maximum Daily Flow = 5.3 gpm x 3 = 15.9 gpm Maximum Daily Flow + Maximum Fire Flow Rate = Total Demand Total Demand = 15.9 gpm + 1,500 gpm = 1,516 gpm The assumed fire flow of 1,500 gpm plus the highest peak hourly demand flow of 15.9 gpm makes the total peak hourly demand flow 1,516 gpm. Per the City of Bozeman requirements, the water velocity cannot exceed 15 fps. Appendix A shows calculations for the four (4) inch domestic service line, six (6) inch fire service, and ten (10) inch water main. The proposed services and ten (10) inch water main fall below the 15 fps and thus are adequately sized. Sanitary Sewer Currently the municipal sanitary sewer system adjacent to the site consists of a 6-inch clay main in East Aspen Street at the south boundary of the site, a 10-inch vitrified clay pipe, and a 24-inch main in Front Street and East Tamarack Street to the east and north. Flow moves east under Aspen Street before connecting into the main in Front Street where it flows north to P:06020_11_Water Sewer Report 3 Tamarack. The sanitary sewer in East Aspen will be replaced with an eight (8) inch PVC main from the middle of North Wallace Avenue west of the site to a point approximately 620-feet to the east where it will tie into an existing manhole at the furthest east end of Aspen Street. This existing manhole has a 24-inch main outfall that flows to the north. A new manhole will be included within the stretch of main at the Aspen and Ida intersection. Sanitary sewer wastewater from the proposed building will flow to the new sewer main in East Aspen. The building will be served by two (2) six (6) inch services. The design flow rates are calculated below for both the residential and commercial uses to determine the impact to the City of Bozeman municipal sanitary sewer system. The residential flows are based on the City of Bozeman Design Standards using an average daily flow rate of 89 gpd/person using 2.17 persons per unit. The commercial flow rates are calculated the same as they were as described above in the water section. The flow rates also include an infiltration rate of 150 gpd/acre. The residential and commercial flows to each of the mains is summarized below: East Aspen Sanitary Sewer Bozeman Yards Development Residential Avg Daily Flow = 45 units x 2.17 persons/unit x 64.4 gpd/person = 6,289 gpd Commercial Avg Daily Flow = 4 employee x 10 gpd/employee = 40 gpd Commercial Avg Daily Flow = 200 customers x 6 gpd/person = 1,200 gpd Total Avg Daily Flow (with no infiltration) = 7,529 gpd Infiltration Flow = 1.5 ac x 150 gpd/ac = 225 gpd Total Avg Daily flow w/ infiltration = 225 gpd + 7,529 gpd = 7,754 gpd Total Avg Daily Flow Rate = 7,754 gpd / 1440 min/day = 5.4 gpm Peaking Factor = (18+.290 0.5)/ (4+.290 0.5 ) = 4.08 Peak Hourly Flow Rate = (4.08 x 7,754 gpd)/ 1440min/day) = 21.97 gpm Total Area In addition to the Bozeman Yards development, the proposed sewer will connect to Wallace Works and other adjacent properties. The Walla ce Works sewer demand is an average day demand of 11,293 gpd with a peak hour of 32.8 gpm. Additionally, there are 4.8 acres of land with un-known sewer demands bordering the proposed sewer replacement. All 4.8 acres are in zoned in the Northeast Historic Mixed-Use District, therefore the assumed domestic flow is: Domestic Flow (gpad) (470 +150) x 4.8 = 2,976 gpd or 2 gpm. P:06020_11_Water Sewer Report 4 In all, the new sewer main has a peak hour flow rate of 56.8 gpm. Using Manning’s Equation, we have concluded that the maximum capacity of an eight (8) inch sanitary sewer main at half (0.5) a percent slope flowing 50 percent full is approximately 188 gpm which is significantly more than the maximum 23.0 gpm flow from the worst-case building, therefore, an eight (8) inch sanitary sewer main is sufficient. Sanitary Sewer Service Line Sizing (maximum flow from building) As shown above, the peak hourly flow rate from the Bozeman Yards development project is roughly 22 gpm. Using Manning’s Equation, the maximum capacity of a six (6) inch sanitary sewer service at two (2) percent slope flowing 50 percent full is approximately 178 gpm which is significantly more than the maximum 22 gpm flow from the building, therefore, the six (6) inch sanitary sewer services have adequate capacity. CONCLUSION Upgrading the municipal water system and sanitary sewer system and installing the service sizes as described above will provide adequate capacity to meet the minimum design standards from the City of Bozeman and the Montana Department of Ecology using the flows rates provided in this report. The new utility improvements and flows will be modeled by the City of Bozeman to confirm the standards are met. Modifications may be required to the assumed utility improvements if said modeling shows any system inadequacies. APPENDICES Appendix A – Water Line Sizing Calculations Appendix B – Sanitary Sewer Sizing Calculations Appendix A WATER LINE SIZING CALCULATIONS Q (flow) gpm Q (flow) CF/min A (area of 4" service pipe), in2 A (area of 4" service pipe) SF v (velocity, Q/A) fps, MAXIMUM VELOCITY PER C.O.B. STANDARDS = 15 FPS 25.00 3.34 12.57 0.09 0.64 Q (flow) gpm Q (flow) CF/m A (area of 6" main pipe), in2 A (area of 6" main pipe) SF v (velocity, Q/A) fps, MAXIMUM VELOCITY PER C.O.B. STANDARDS = 15 FPS*1067.50 142.70 28.27 0.20 12.11 Q (flow) gpm Q (flow) CF/m A (area of 10" main pipe), in2 A (area of 10" main pipe) SF v (velocity, Q/A) fps, MAXIMUM VELOCITY PER C.O.B. STANDARDS = 15 FPS 1525.00 203.86 78.54 0.55 6.23*WATER MAINS AND SERVICES SIZING CALCULATIONS Water service lines assume a 70/30% split of the total flow coming through the line during peak hourly demand flow. P:06020_11_Water Sewer Report 6 Appendix B SANITARY SEWER SIZING CALCULATIONS Block 104 Offsite Improvements Project No. 06020.11 February 22, 2024 8-inch Diameter Main Pipe Diameter, D (ft)0.66 Minimum Slope, S (ft/ft)0.005 Manning's Roughness Coefficient, n 0.013 USCS Unit Constant, Co 2.16 Flow in Full Pipe (cfs)0.84 Flow Full Capacity (gpm)376 Half Full Capacity (gpm)188 Velocity in Pipe (ft/sec)2.43 6-inch Diameter Services Pipe Diameter, D (ft)0.50 Minimum Slope, S (ft/ft)0.02 Manning's Roughness Coefficient, n 0.013 USCS Unit Constant, Co 2.16 Flow in Full Pipe (cfs)0.79 Flow Full Capacity (gpm)356 Half Full Capacity (gpm)178 Velocity in Pipe (ft/sec)4.04 Sanitary Sewer Calculations Flow Full and Velocity in Sewer Pipe at Minimum Slope