HomeMy WebLinkAbout11.0 108 West Babcock - Swr-Wtr Demand Calcs 108 W. Babcock 3/14/2025
The following calculations are provided to estimate the peak-hour sanitary sewer
demand and the average and maximum daily domestic water demands for the
proposed Office/Residential Building located at 108 West Babcock. The new .
building is replacing an existing 2,485 sf office building. „ :'`''�i�;'=�J������z"z,
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Estimate of Peak Hour Sewer Demand
. 1.
Average Daily Wastewater Flow (in gallons per minute) �, • ��
COMMERCIAL
Net Floor Area of Office/Retail Space: 5,118 sf
Use 1 employee per 200 sf: 5,118 sf_200 sf/emp. = 25.6 employees
Using MT DEQ Circular 4, Table 3.1-1:
Typical Flow (in gallons per day) for Office = 13 gpd/employee
Q Ave(com) = 25.6 emp. x 13 gpd per emp. = 333 gpd
RESIDENTIAL
Number of Residential Dwelling Units: 4 du
Using COB Design Standards Section V.B:
Ave. Daily Flow Rate = 2.11 people/dwelling unit & 89 gal/capita/day
Q Ave(Res) = 4 du. x 2.11 people/du x 89 gpcd = 751 qpd
Average hourly flow shall be determined for a 16-hour day:
Q Ave(Total) = (333 gpd + 751 gpd) _ (16 hours per day x 60 min. per hour) = 1.1 gpm
Total Peak Wastewater Flow (in gallons per minute)
POPULATION
Commercial: 25.6 employees
Residential: 2.11 people/du x 4 du = 8.4 residents
Population: 25.6 emp + 8.4 residents = 34 34 persons
PEAKING FACTOR
Using COB Design Standards Section V.B.6:
Peaking Factor(PF)
= Q Max y Q Ave
_ [18+(34/1000).-9] _ [4+(34/1000)-6] = 18.18 T 4.18 = 4.35
Q Peak(Total) = Q Ave(Total)x PF = 1.1 gpm x 4.35 = 4.8 gpm (Protect Total)
108 W. Babcock 3/14/2025
PROJECT INCREASE: Subtract Existing Commercial Use Flow
Q Peak(Increase)
= Q Peak(Total) - Q Ave(Extg Com)X PF
= 4.8 gpm —{(((2,000 sf= 200 sf/emp.) x 13 gpd per emp) i (16 hr x 60min/hr)] x
4.35)
= 4.8 gpm —0.6 gpm = 4.2 qpm (Proiect Increase)
Estimate of Average & Max Day Domestic Water Demand + Fire Demand
Average Day Water Demand
The Average Daily Water Demand Estimate is found by adding 15% to the average daily
wastewater generation.
Average Daily Demand = (333 gpd + 751 gpd) x 1.15 = 1,247 gpd
Or in GPM:
Average Daily Demand = 1,247 = (16 hrs x 60 min) = 1.3 gpm
Peaking Factor
Typical peaking factors for calculating maximum day water demands range from 1.5 to
3.5. Per COB Design Standards Section V.A.4, a peaking factor of 2.3 shall be used for
this calculation.
Maximum Day Water Demand
The Maximum Day Demand is found by applying the peaking factor of 2.3 to the
Average Daily Demand.
Maximum Daily Demand = 1,247 gpd x 2.3 = 2,868 gpd
Or in GPM:
Maximum Daily Demand = 2,868 _ (16 hrs x 60 min) = 3.0 gpm
Fire Flow Demand
Reference 2021 International Fire Code (IFC) Appendix B, Tables 13105.1(1) &
(2) for buildings with Automatic Sprinklers.
Building Square Footage: 13,752 sf
Building Construction Type: V-B
Minimum Fire Flow: % x 3,250 gpm = 1,625 gpm
Flow Duration: 1 hour
Calculations and Estimates performed by Melanie Dyba, PE, Bridger Engineers, Inc.