HomeMy WebLinkAbout007 SANITARY DEMAND MEMOSanitary Sewer Demand Memo 04/11/2025
Allied Engineering Services, Inc. Memo Page 2
For the 549-ft2 bakery, an average wastewater flow rate of 6 gallons per day per customer and 10 gallons
per day per employee was assumed as outlined for a “Coffee Shop” in MDEQ-Circular 4 Table 3.1-2
“Typical Wastewater Flows from Recreational Facilities”.
An infiltration rate of 150 gal/acre/day was added to the flow demand calculations per the Section 6.3
Technical Memorandum 5.0 of the COB Wastewater Collection System Facility Plan – 2024 Update.
Please see the attached calculations for additional information. A summary is provided below.
2020 COB Design Standards - Residential Dwelling Units:
Number of Dwellings = 13
Assumed Occupancy Rate = 2.11 people/unit
Wastewater Flow Rate per Capita = 89 gallons/capita/day
Average Day Demand = 2,441 gallons/day
2024 COB Design Standards - Residential Dwelling Units:
Number of Dwellings = 13
Assumed Occupancy Rate = 2.17 people/unit
Wastewater Flow Rate per Capita = 64.4 gallons/capita/day
Average Day Demand = 1,817 gallons/day
1,375-ft2 Office:
Number of Employees = 10
Average Wastewater Flow Rate per Employee = 13 gallons/employee/day
Average Day Demand = 130 gallons/day
549-fts Bakery:
Number of Employees = 4
Average Wastewater Flow Rate per Employee = 10 gallons/employee/day
Number of Customers = 100
Average Wastewater Flow Rate per Customer = 6 gallons/customer/day
Average Day Demand = 640 gallons/day
Total Wastewater Demand:
Gross area of site = 0.143 acres
Infiltration rate = 150 gpad (0.10 gpam)
Total with 2020 COB Design Standards
Total average day demand + Infiltration = 3,233 gpd (2.24 gpm)
Peaking factor (P=0.141) = 4.20
Peak hour demand + Infiltration= 13,506 gpd (9.38 gpm)
Total with 2024 COB Design Standards
Total average day demand + Infiltration = 2,608 gpd (1.81 gpm)
Peaking factor (P=0.142) = 4.20
Peak hour demand + Infiltration= 10,882 gpd (7.56 gpm)
Please contact Wyatt Alt, Cole Oshiro-Leavitt and/or Rory Romey at 406-582-0221 or
walt@alliedengineering.com; coshiro-leavitt@alliedengineering.com; rromey@alliedengineering.com
with any questions or if additional information is required.
Sanitary Sewer Demand Memo 04/11/2025
Allied Engineering Services, Inc. Memo Page 3
2020 COB Standards Residential Dwelling Units: Number of Dwellings: 13 Units
Assumed Occupancy Rate: 2.11 People/Unit
Wastewater Flow Rate per Capita: 89 Gallons/Capita/Day
Average Day Demand: 2441.27 Gallons/Day
2024 COB Standards Residential Dwelling Units: Number of Dwellings: 13 Units
Assumed Occupancy Rate: 2.17 People/Unit
Wastewater Flow Rate per Capita: 64.4 Gallons/Capita/Day
Average Day Demand: 1816.72 Gallons/Day
1,375-ft2 Office: Number of Employees: 10 Employees
Average Wastewater Flow Rate per Employee: 13 Gallons/Employee/Day
Average Day Demand: 130 Gallons/Day
549-ft2 Bakery: Number of Employees: 4 Employees
Average Wastewater Flow Rate per Employee: 10 Gallons/Employee/Day
Number of Customers: 100 Customers
Average Wastewater Flow Rate per Customer: 6 Gallons/Customer/Day
Average Day Demand Employees: 40 Gallons/Day
Average Day Demand Customers: 600 Gallons/Day
Average Day Demand Bakery: 640 Gallons/Day
Total Wastewater Demand: Gross Area of Site: 0.143 Acres
Infiltration Rate: 150 Gallons/Day/Acre
Average Site Infiltration Rate: 21.45 Gallons/Day
2020 COB Standards Total Average Day Demand: 3211.27 Gallons/Day
Total Average Day Demand + Infiltration: 3232.72 Gallons/Day
Total Average Day Demand + Infiltration: 2.24 Gallons/Minute
Total Site Population: 141.43 Persons
Peaking Factor: 4.20 Peak Hour Demand + Infiltration: 13506.27 Gallons/Day
Peak Hour Demand + Infiltration: 9.38 Gallons/Minute
2024 COB Standards Total Average Day Demand: 2586.72 Gallons/Day
Total Average Day Demand + Infiltration: 2608.17 Gallons/Day
Total Average Day Demand + Infiltration: 1.81 Gallons/Minute
Total Site Population: 142.21 Persons
Peaking Factor: 4.20 Peak Hour Demand + Infiltration: 10881.71 Gallons/Day
Peak Hour Demand + Infiltration: 7.56 Gallons/Minute