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Home My WebLink AboutAppendix F Sewer and Water Flow Capacities 1-24-19COTTONWOOD + IDA RESPONSE & RESUBMITAL II || JANUARY 2019 APPENDIX F SEWER AND WATER FLOW CAPACITIES SECTION 8 April 3, 2018 Project No. 06002.03 WATER AND SEWER PRELIMINARY DESIGN REPORT FOR COTTONWOOD + IDA MIXED USE DEVELOPMENT LOTS 5-28, BLOCK 105, NORTHERN PACIFIC ADDITION, BOZEMAN MT SITE NARRATIVE The following report summarizes the water and sewer design 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. Almost all of the development will be built over a new 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 8-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 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 building. For purposes of sizing the water meter and domestic service, the AWWA M22 fixture unit calculation is used with an assumed pressure of 100 psi. Irrigation flow of 8 gpm is assumed through the service to the existing building at the southwest corner of the site. The total estimated fixture units, peak flow and recommended meter sizes for each building are summarized below: Cottonwood Mixed Use V:16020_03_Utility_Design_Report 2 (4/3/18) TRP For water main sizing, the peak hourly flow will be used. The flows are separated to services coming off of the East Cottonwood 8-inch main and the East Aspen 8-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. Based on the 88 parking spaces for the office and artisan manufacturing spaces (prior to reduction), you could assume for estimating purposes that each space is an employee. DEQ 4 circular estimates that there is a usage of 13 gallons per day per employee. This peak hourly flow rate to each main are as follows: East Aspen Peak Hourly Domestic Water Demand Average Daily Flow(res) = 63 units x 2.11 persons/unit x 170 gpd/person = 22,598 gal/day Average Daily Flow(comm) = 84 employees x 13 gpd/person = 1,092 gal/day Total Avg Daily Flow = 23,690 gal/day Total Avg Daily Flow = 23,690 gal/day / 1440 min/day = 16.5 gal/min Peak hourly Flow Rate = 16.5 gal/min x 3 = 49.5 gal/min Cottonwood Mixed Use V:16020_03_Utility_Design_Report 3 (4/3/18) TRP East Cottonwood Peak Hourly Domestic Water Demand Average Daily Flow(res) = 30 units x 2.11 persons/unit x 170 gpd/person = 10,761 gal/day Average Daily Flow(comm) = 5 employees x 13 gpd/person = 65 gal/day Total Avg Daily Flow = 10,766 gal/day Total Avg Daily Flow = 10,766 gal/day / 1440 min/day = 7.5 gal/min Peak hourly Flow Rate = 7.5 gal/min x 3 = 22.5 gal/min 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 replace 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 describe above in the water section. The flow rates also included is an infiltration rate at 150 gpm/acre infiltration rate. The residential and commercial flows to each of the mains is summarized below: East Aspen Sanitary Sewer Residential Avg Daily Flow = 63 units x 2.11 persons/unit x 89 gpd/person = 11,830 gpd Office Avg Daily Flow = 84 employee x 13 gpd/employee = 1,092 gpd Total Avg Daily Flow (with no infiltration) = 12,922 gpd InfiltrationFlow = 1.05 ac x 150 gpd/ac = 158 gpd Total Avg Daily flow w/ infiltration = 158 gpd + 12,922 gpd = 13,080 gpd Total Avg Daily Flow Rate = 13,080 gpd / 1440 min/day = 9.1 gpm Cottonwood Mixed Use V:16020_03_Utility_Design_Report 4 (4/3/18) TRP Peaking Factor = (18+0.133 0.5 )/ (4+0.133 0.5 ) = 4.21 Peak Hourly Flow Rate = (4.21 x 12,922gpd + 158 gpd )/ 1440min/day) = 37.9 gpm East Cottonwood Sanitary Sewer Residential Avg Daily Flow = 30 units x 2.11 persons/unit x 89 gpd/person = 5,634 gpd Commercial Avg Daily Flow = 5 employee x 13 gpd/employee = 65 gpd Total Avg Daily Flow (with no infiltration) = 5,699 gpd InfiltrationFlow = 1.05 ac x 150 gpd/ac = 158 gpd Total Avg Daily flow w/ infiltration = 158 gpd + 5,699 gpd = 5,857 gpd Total Avg Daily Flow Rate = 5,857 gpd / 1440 min/day = 4.1 gpm Peaking Factor = (18+0.063 0.5 )/ (4+0.063 0.5 ) = 4.29 Peak Hourly Flow Rate = (4.29 x 5,699gpd + 158 gpd )/ 1440min/day) = 17.1 gpm Sanitary Sewer Service Line Sizing (maximum flow from building #1 base on 45 units) Residential Avg Daily Flow = 45 units x 2.11 persons/unit x 89 gpd/person = 8,451 gpd Total Avg Daily Flow Rate = 8,451 gpd / 1440 min/day = 5.9 gpm Peaking Factor = (18+0.095 0.5 )/ (4+0.095 0.5 ) = 4.25 Peak Hourly Flow Rate = 4.25 x 5.9 gal/min = 25.1 gpm The maximum capacity of a 6-inch sanitary sewer service at 2% slope flowing 0.75% full is approximately 287 gpm which is significantly more than the maximum 25.1 gpm flow from the worst case building , therefore, the sanitary sewer services for each building shall be 6- inch. CONCLUSION Upgrading the municipal water system and sanitary sewer system and installing the service sizes as described above is assumed to 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. These changes will be reflected in the final engineering report.