HomeMy WebLinkAboutPeak Hour Sewer Demand_GMS_2024-06-20_stampedGreg Matthews Studio Post 14 Office Building 6/20/2024
PAGE 1 OF 2
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 GMS Post 14 Office Building located on Lot 2, Block 3 of the Ferguson Farm Subdivision (formerly Lot 4 of the Spring Creek Village Resort Subdivision).
The estimates provided have been compared to the estimates provided in the Lot 4 Spring Creek Village Resort Subdivision Sewer and Water Management Design Report which was used for sizing the infrastructure of the Ferguson Farm Subdivision. Estimates for the proposed building are shown to be well within the original estimates provided for this lot.
Estimate of Peak Hour Sewer Demand Estimated Number of Employees
Approx. Net Floor Area of Office Space: 4,024 sf Use 1 employee per 200 sf: 4,024 sf ÷ 200 sf/emp. = 21 employees Average Daily Wastewater Flow Using MT DEQ Circular 4, Table 3.1-1: Typical Flow (in gallons per day) for Office = 13 gpd/employee Q Ave. Day = 21 emp. x 13 gpd per emp. = 273 gpd
Average Hourly Wastewater Flow (in gallons per minute)
Average hourly flow shall be determined for a typical 8-hour day. Q Hourly = 273 gpd ÷ (8 hours per day x 60 min. per hour) = 0.57 gpm
Peaking Factor Typical peaking factors for calculating peak sewer demand range from 3 to 5. An average value of 4 shall be used for this calculation. Peak Flow
Q Peak = 0.57 gpm x 4 = 2.3 gpm
Greg Matthews Studio Post 14 Office Building 6/20/2024
PAGE 2 OF 2
To size the sewer mains, the Lot 4 Spring Creek Village Resort Subdivision Sewer and Water Management Design Report calculated an estimated Average Daily Wastewater Flow using Table V-1 with the B-2 Zoning Flow Rate of 2,000 gallons/acre/day. Using this value for this lot, the Average Daily Wastewater Flow is 2,000 gallons/acre/day x 0.3331 acres = 666 gallons/day.
The Q Ave. Day of 273 gpd for this project is well under the estimated flow of 666 gpd for a lot this size which was used to size the infrastructure.
Estimate of Average & Max Day Domestic Water Demand
The Average Daily Water Demand Estimate is found by adding 15% to the average daily wastewater generation.
Average Daily Demand = 273 gpd x 1.15 = 314 gpd
Or in GPM: Average Daily Demand = 314 ÷ (8 hrs x 60 min) = 0.65 gpm The Maximum Day Demand is found by applying a peaking factor of 2.3 to the Average Daily Demand. Maximum Daily Demand = 314 gpd x 2.3 = 722 gpd Or in GPM: Maximum Daily Demand = 722 ÷ (8 hrs x 60 min) = 1.5 gpm
The estimated Average Daily Demand (ADD) & Maximum Daily Demand (MDD) of domestic water usage for the proposed office building is well within the estimates used in the Lot 4 Spring Creek Village Resort Subdivision Sewer and Water Management
Design Report used for sizing the infrastructure of the Ferguson Farm Subdivision. The Lot 4 Spring Creek Village Resort Subdivision Sewer and Water Management Design Report calculated an estimated ADD of 29.11 gpm and an estimated MDD of 66.95 for 21 Commercial Lots averaged over a 24-hour period. The estimate calculations above use a more conservative duration of eight hours for a typical workday. Calculations and Estimates performed by Melanie Dyba, PE, Bridger Engineers, Inc.