The URL can be used to link to this page

Home My WebLink About20 - Design Report - Tinworks - Water, Sewer TINWORKS FINAL DRAINAGE REPORT BOZEMAN, MONTANA CERTIFICATION I hereby state that this Final Water and Sewer Design Report has been prepared by me or under my supervision and meets the standard of care and expertise which is usual and customary in this community of professional engineers. The analysis has been prepared utilizing procedures and practices specified by the City of Bozeman and within the standard accepted practices. ____________________________________________ ___________________________ Mike Russell, P.E. Date 11-04-2020 November 4, 2020 Project No. 06002.07 WATER AND SEWER FINAL PLANNED UNIT DEVELOPMENT DESIGN REPORT FOR TINWORKS MIXED USE DEVELOPMENT LOTS 5-28, BLOCK 105, NORTHERN PACIFIC ADDITION, BOZEMAN MT SITE NARRATIVE The following report summarizes the water and sewer design calculations for a mixed-use development located on Lots 5 through 17, Block 105 of the Northern Pacific Addition Subdivision (and portion of vacated alley) in northeast Bozeman, Montana. The project is bound by East Aspen Street to the north, Ida Avenue to the east, East Cottonwood Street to the south and existing commercial parcels to the west that front on North Wallace Avenue. The subject parcel is approximately 2.1 acres of mixed-use consisting of residential apartments, ground floor artisan manufacturing spaces, an office building and renovation of an existing building with a proposed restaurant use. The approximate northern half of the development will be built over a new partially- below-grade parking garage. WATER Currently the municipal water system adjacent to the site consists of a 6-inch water main in East Cottonwood Street at the south boundary of the site. This main will be replaced with an 8-inch main from the Cottonwood and North Wallace intersection to the East Cottonwood and Ida Avenue intersection. There will also be a new 10-inch water main installed in East Aspen Street from North Wallace to Front Street. There are existing fire hydrants at North Wallace and East Aspen intersection, the North Wallace and East Cottonwood intersection and at the East Cottonwood and Ida intersection. A new hydrant will be set at the East Aspen and Ida intersection and the existing hydrant located at the East Cottonwood and Ida intersection will be relocated to the corner of East Cottonwood and Ida giving an east/west spacing of approximately 450 feet and a north/south spacing of approximately 320 feet. 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 1760 gpm. Water for the proposed development will be served by one domestic and one fire service for each of the new individual buildings. Meter sizes were provided by the Mechanical Engineer for the project. Irrigation flow of Tinworks Mixed Use P:06020_07_PUDF_Utility_Design_Report 2 (6/23/20) MTR approximately 8gpm is assumed to be provided through the existing well at the northeast corner of the site. For water main sizing, the peak hourly flow plus the fire flow will be used. The flows are separated to services coming off of the East Cottonwood 8-inch main and the East Aspen 10-inch main. The residential flows are based on the City of Bozeman Design Standards and Specifications Policy; 2.11 people per dwelling unit, an average daily usage of 170 gallons per day per person, and a maximum hour to average day ratio of 3:1. The commercial and office flows are more difficult to estimate. DEQ 4 circular estimates that there is a usage of 13 gallons per day per employee. The maximum day demand available fire flow for the purpose of design is assumed to be 1500 gpm at 20 psi. 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 to each main are as follows: East Aspen Peak Hourly Domestic Water Demand Average Daily Flow(res) = 67 units x 2.11 persons/unit x 170 gpd/person = 24,033 gpd Average Daily Flow(comm) = 15 employees x 13 gpd/person = 195 gpd Total Avg Daily Flow = 24,228 gpd Total Avg Daily Flow = 24,228 gpd / 1440 min/day = 16.8 gpm Peak hourly Flow Rate = 16.7 gpm x 3 = 50.4 gpm Peak Hourly Flow Rate + Maximum Fire Flow Rate = Total Demand 50.4 gpm + 1500 = 1550.4 gpm East Cottonwood Peak Hourly Domestic Water Demand Average Daily Flow(res) = 6 units x 2.11 persons/unit x 170 gpd/person = 2,152 gpd Average Daily Flow(comm) = 78 employees x 13 gpd/person = 1,014 gpd Total Avg Daily Flow = 3,166 gpd Total Avg Daily Flow = 3,166 gpm / 1440 min/day = 2.2 gpm Peak hourly Flow Rate = 2.2 gpm x 3 = 6.6 gpm Peak Hourly Flow Rate + Maximum Fire Flow Rate = Total Demand 6.6 gpm + 1500 gpm = 1506.6 gpm The assumed fire flow of 1500 gpm plus the highest peak hourly demand flow of 50.4 gpm makes the total peak hourly demand flow 1550.4 gpm. Per the City of Bozeman requirements the water velocity cannot exceed 15fps. Appendix B shows calculations for the 10” main, the 8” main and the 6” service lines, all of which fall below the 15fps and thus are adequately sized. Tinworks Mixed Use P:06020_07_PUDF_Utility_Design_Report 3 (6/23/20) MTR SANITARY SEWER Currently the municipal sanitary sewer system adjacent to the site consists of a 6-inch main in East Cottonwood Street at the south boundary of the site and a 6-inch main in East Aspen Street at the north boundary of the site. Both mains flow to the east. The sanitary sewer in East Cottonwood will be replaced with an 8-inch from the manhole at the southwest corner of the site to a point approximately 540 feet to the east where it will tie into an existing manhole at the furthest east end of Cottonwood Street. This existing manhole has a 10-inch main outfall that flows to the north. The sanitary sewer in East Aspen will be replaced with an 8-inch main from the manhole at the northwest corner of the site to a point approximately 480 feet to the east where it will tie into an existing manhole at Front Street. This existing manhole also has a 10-inch main outfall that flows to the north. Sanitary sewer wastewater from each of the proposed buildings will flow to the closest of the new sewer main in either East Cottonwood or East Aspen. The design flow rates 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 2.11 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 included is an infiltration rate at 150 gpd/acre infiltration rate. The residential and commercial flows to each of the mains is summarized below: East Aspen Sanitary Sewer Residential Avg Daily Flow = 70 units x 2.11 persons/unit x 89 gpd/person = 13,145 gpd Office Avg Daily Flow = 15 employee x 13 gpd/employee = 195 gpd Total Avg Daily Flow (with no infiltration) = 13,340 gpd Infiltration Flow = 1.05 ac x 150 gpd/ac = 158 gpd Total Avg Daily flow w/ infiltration = 158 gpd + 13,340 gpd = 13,498 gpd Total Avg Daily Flow Rate = 13,498 gpd / 1440 min/day = 9.4 gpm Peaking Factor = (18+0.133 0.5)/ (4+0.133 0.5 ) = 4.21 Peak Hourly Flow Rate = (4.21 x 13,340 gpd + 158 gpd)/ 1440min/day) = 39.1 gpm East Cottonwood Sanitary Sewer Residential Avg Daily Flow = 3 units x 2.11 persons/unit x 89 gpd/person = 563.4 gpd Commercial Avg Daily Flow = 78 employees x 13 gpd/employee = 1,014 gpd Total Avg Daily Flow (with no infiltration) = 1,577.4 gpd InfiltrationFlow = 1.05 ac x 150 gpd/ac = 158 gpd Tinworks Mixed Use P:06020_07_PUDF_Utility_Design_Report 4 (6/23/20) MTR Total Avg Daily flow w/ infiltration = 158 gpd + 1,577.4 gpd = 1,735.4 gpd Total Avg Daily Flow Rate = 1,735.4 gpd / 1440 min/day = 1.21 gpm Peaking Factor = (18+0.063 0.5)/ (4+0.063 0.5 ) = 4.29 Peak Hourly Flow Rate = (4.29 x 1,577.4 gpd + 158 gpd )/ 1440min/day) = 4.81 gpm Using Manning’s Equation, we have concluded that the maximum capacity of a 8-inch sanitary sewer service at 0.5% slope flowing 75% full is approximately 417 gpm which is significantly more than the maximum 39.1 gpm flow from the worst case building , therefore, the sanitary sewer mains for each building shall be 8-inch. This information is provided for the City of Bozeman’s use in their model if desired. Sanitary Sewer Service Line Sizing (maximum flow from building B base on 49 units) Residential Avg Daily Flow = 49 units x 2.11 persons/unit x 89 gpd/person = 9,202 gpd Total Avg Daily Flow Rate = 9,202 gpd / 1440 min/day = 6.4 gpm Peaking Factor = (18+0.095 0.5)/ (4+0.095 0.5 ) = 4.25 Peak Hourly Flow Rate = 4.25 x 6.4 gal/min = 27.2 gpm Again, using Manning’s Equation, the maximum capacity of a 6-inch sanitary sewer service at 2% slope flowing 75% full is approximately 287 gpm which is significantly more than the maximum 27.2 gpm flow from the worst case building , therefore, the sanitary sewer services for each building shall be 6-inch. This information is provided for the City of Bozeman’s use in their model if desired. 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 Environmental 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 Tinworks Mixed Use P:06020_07_PUDF_Utility_Design_Report 5 (6/23/20) MTR Appendix A WATER LINE SIZING CALCULATIONS Q (flow) gpm Q (flow) CF/m A (area of 6" service pipe), in2 A (area of 6" service pipe) SF v (velocity, Q/A) fps, MAXIMUM VELOCITY PER C.O.B. STANDARDS IS < 15 FPS *1085.28 2.42 28.27 0.20 12.31 *1054.62 2.35 28.27 0.20 11.97 Q (flow) gpm Q (flow) CF/m A (area of 8" main pipe), in2 A (area of 8" main pipe) SF v (velocity, Q/A) fps, MAXIMUM VELOCITY PER C.O.B. STANDARDS IS < 15 FPS 1550.40 3.45 50.27 0.35 9.90 1506.60 3.36 50.27 0.35 9.62 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 IS < 15 FPS 1550.40 3.45 78.54 0.55 6.33 1506.60 3.36 78.54 0.55 6.15 *Water service lines assume a 70/30% split of the total flow coming through the line during peak hourly demand flow. WATER MAINS AND SERVICES SIZING CALCULATIONS