HomeMy WebLinkAbout011 2-7_water -sewer usage_Lot 6_resubmittal
190 NORTHSTAR LANE
BOZEMAN, MT 59718
406‐581‐5730
www.headwatersmt.net
Page 1 of 2
The Ridge
Lot 6 of Amended Plat J‐456 of the Ridge Athletic Club Subdivision
Resubmittal 02/02/2022
Sanitary Sewer Usage
The proposed project includes 6 residential apartments and roughly 7,560 square feet of commercial space on
approximately 0.344 acres. Average day residential flows were calculated using the City of Bozeman standard of 2.17
persons per residential unit at 64.4 gpd per person. Utilizing the wastewater flow for Neighborhood Commercial from
Tab V‐2 of the City of Bozeman Design Regulations, the estimated commercial flow is 1,200 gallons per acre per day.
Average Residential Daily Flowrate = (6 units) x (2.17 people/unit) x (64.4 gpd/person) = 838 gpd
Average Commercial Daily Flowrate = 1,200 gal/acre/day x 0.344 acres = 413 gpd
Total Average Daily Sewer Flow = 1,251 gpd
The City of Bozeman standard 2.17 persons per residential unit was multiplied by 6 units to determine an equivalent
residential population of 13 people plus the estimated commercial equivalent of 32 people (13 gpd per employee per
DEQ Circular 4). The total population of 45 people yielded a peaking factor of 4.32. 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 4.32 and adding the City’s infiltration allowance of 150 gallons per acre per day resulted in a
combined peak hourly flowrate of 8,837 gpd.
Peak Hourly Flowrate = ADF x PHF + 150 gpd/acre
Peak Hourly Flowrate = 1,251 gpd x 4.32 + 150 gpd x 0.344 ac = 5,461 gpd
5,461 gpd / 1,440 min/day = 3.79 gpm
According to the 2007 Design Report submitted by C&H Engineers, the peak sewer flow generated by the “R‐O zoned
portion of the north end of the property,” which is now Lot 6 and surrounding common open space, was estimated as
follows:
2.23 acres x 12.19 persons per acre x 72 gallons per capita per day = 1,957 gpd
Peaking hour factor used = 3.97 per the 2007 Design Report
Assumed infiltration = 2.23 acres x 150 gal/acre/day = 334.5 gpd
Peak Flow Rate = 1,957 gpd x 3.97 + 334.5 gpd = 8,105 gpd / 1,440 min/day = 6.14 gpm
The revised sewer flow for Lot 6 is less than the 2007 Design Report had estimated. The 2007 Design Report showed
that the 8” PVC sewer pipe heading north on Eagle Creek is only about 29.5% full. No new sewer flow will be added
compared to the 2007 Design Report Estimate.
Water Usage
The proposed project includes 6 residential apartments and roughly 7,560 square feet of commercial space on
approximately 0.344 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 1.54 gallons per minute. Utilizing a commercial
rate of 10,000 gallons per 1,000 square foot of commercial area per year results in 0.14 gpm. Using the City’s max day
flow factor of 2.3, results in a maximum daily demand of 3.87 gpm. Multiplying the average daily flow by the City’s peak
hour factor of 3, results in a peak hour demand of 5.04 gpm.
190 Northstar Lane, Bozeman, MT 59718 (406) 581‐5730 www.headwatersmt.net Page 2 of 2
Average Residential Daily Flowrate = (6 units) x (2.17 people/unit) x (170 gpd/person) = 2,213 gpd
2,213 gpd /1,440 min per day = 1.54 gpm
Average Commercial Daily Flowrate = 10,000 gallons per year /1,000 square feet x 7,560 sf / 365 days=
207 gpd = 0.14 gpm
Total Daily Flowrate = 1.68 gpm
Maximum Daily Flowrate = ADF x 2.3 = 1.68 gpm x 2.3 = 3.87 gpm
Maximum Hour Flowrate = ADF x 3 = 1.68 gpm x 3 = 5.04 gpm
Calculations completed by Garrett Schultz, P.E.
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