HomeMy WebLinkAbout009-water -sewer usage
190 NORTHSTAR LANE
BOZEMAN, MT 59718
406-581-5730
www.headwatersmt.net
Page 1 of 2
Urban Villas
Lot 3A, Block 2 of Phase 3 of Cattail Creek Subdivision
Sanitary Sewer Usage
The proposed project includes 16 existing and 48 proposed residential apartments on approximately 2.44
acres. Average day residential flows were calculated using the City of Bozeman standard of 2.11 persons per
residential unit at 89 gpd per person.
Average Residential Daily Flowrate = (64 units) x (2.17 people/unit) x (64.4 gpd/person) = 8,944 gpd
The City of Bozeman standard 2.17 persons per residential unit was multiplied by 64 units to determine an
equivalent residential population of 139 people. The total population of 139 people yielded a peaking factor of
4.21. The peaking factor, PF, was calculated by the following formula, where P = population (thousands):
PF = 18 + P0.5
4 + P0.5
Using a peak hour factor of 4.21 was and adding the City’s infiltration allowance of 150 gallons per acre per day
resulted in a combined peak hourly flowrate of 38,020 gpd.
Peak Hourly Flowrate = ADF x PHF + 150 gpd/acre
Peak Hourly Flowrate = 8,944 gpd x 4.21 + 150 gpd x 2.44 ac = 38,020 gpd = 26.4 gpm
Per the design report for Phase 3 of Cattail Creek. The original sewer demand was calculated at 1 unit per 3000 sf. The
Urban Villas site is 106, 266 sf, resulting in 36 units planned. Utilizing the planned 2.54 persons per units and 72
gallons/capita/day results in a ADF of 6,584 gpd flow planned. The planned peak hour flowrate would 28083 gpd or
19.5 gpm. This shows the proposed peak hour flow is only 6.7 gpm higher than master planned. Per correspondence with Cody Flammond, the City does not have any downstream capacity issues in the sewer infrastructure in this area.
Water Usage
The proposed project includes 16 existing and 48 proposed residential apartments on approximately 2.44
acres. Using the City of Bozeman empirical data of 170 gpd/person for residential flows, Headwaters estimates
a total residential average daily demand (ADD) of 16.4 gallons per minute. Using the City’s max day flow factor
of 2.3, results in a maximum daily demand of 37.7 gpm. Multiplying the average daily flow by the City’s peak
hour factor of 3, results in a peak hour demand of 49.2 gpm. Local landscape watering is included in the
empirical data and therefore makes these results conservative since landscape watering for this project will be
supplied by an existing onsite well.
Average Residential Daily Flowrate = (64 units) x (2.17 people/unit) x (170 gpd/person) = 23,610 gpd
23,610 gpd /1440 min per day = 16.4 gpm
Total Daily Flowrate = 16.4 gpm Maximum Daily Flowrate = ADF x 2.3 = 37.7 gpm
Maximum Hour Flowrate = ADF x 3.0 = 49.2 gpm
Per the design report for Phase 3 of Cattail Creek. The original water demand was calculated at 1 unit per 3000 sf. Per
the “Water Demand Spreadsheet” within the design report, this lot (formerly lots 3 & 4 of block 2) was anticipated to
have and average daily flow of 18,288 gpd and a max day flow of 45,720 gpd or 31.75 gpm. This shows the proposed
190 Northstar Lane, Bozeman, MT 59718 (406) 581-5730 www.headwatersmt.net Page 2 of 2
max day flowrate is only 6 gpm higher than master planned. Per correspondence with Cody Flammond, the City does
not have any capacity issues in the water infrastructure in this area. No new fire hydrants are proposed for the site. The
Bozeman Water Department conducted a fire flow test from an existing hydrant on Catalyst Street (hyd # 1889). The
test results were 1555 gpm at 86 psi. This results in roughly 5000 gpm at 20 psi. Static pressures in this area exceeded
100 psi, therefore no pressure or flow issues are anticipated.
________________
Jeremy May, P.E.
Headwaters Engineering, Inc.
www.headwatersmt.net
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