HomeMy WebLinkAboutHaggerty Multi-Family Water_Sewer MemoMEMORANDUM PAGE 1 OF 4 FEBRUARY 2026
MEMORANDUM
To: City of Bozeman Engineering Department
From: Bobby Egeberg, PE
Date: 02/27/2026
Reference: Water and Sewer Demand Calculations – Haggerty Multi-Family
We have evaluated the projected water and sewer demands for the Haggerty Multi-Family project, a
0.47-acre property within Bozeman, MT. The owner of the project plans to develop two residential
buildings with a total of 10 units. The legal description for the project is defined as: Lot 2A1 of Minor
Sub 16B, S08, T02S, R06E, Rear Elks Club Property. The City of Bozeman Design and Construction
Standards (October 2024) were utilized in evaluating the projected water and sewer demands for the
project.
WATER DEMAND
Existing water demands for the site are zero as it is an undeveloped property. Proposed water
demands were determined per Section 4.2.4 & 4.2.6 of the City Standards. Since there are known
development plans, demand calculations were completed using an average daily domestic flow
rate of 135 gallons per capita per day at 2.17 people per dwelling unit for the proposed project site.
Average Day Demand (ADD):
Per Building: 5 units x 2.17 people per unit x 135 gpcd = 1,465 gpd
Total: 2 buildings x 1,465 gpd per building = 2,930 gpd = 2 gpm
Maximum Day Demand (MDD):
Per Building: 2.3 x 1,465 gpd = 3,369 gpd
Total: 2 buildings x 3,369 gpd = 6,738 gpd = 4.7 gpm
Peak Hour Demand (PHD):
Per Building: 3.0 x 1,465 gpd = 4,395 gpd
Total: 2 buildings x 4,395 = 8,790 gpd = 6.1 gpm
MEMORANDUM PAGE 2 OF 4 FEBRUARY 2026
SEWER DEMAND
During the construction of the two residential buildings, it is proposed that the existing 10-inch
PVC sewer main that runs southeast to northwest across the northern half of the property be
plugged and abandoned. It is also proposed that the existing 8-inch PVC sewer main that runs
along the eastern edge of the property be relocated approximately 5 feet further east with three
new manholes. Rather than continuing to drain along the west side of Haggerty Lane, we propose
crossing Haggerty Lane to the north with a new 8-inch sewer main and connecting to the existing
18-inch sewer main with a new manhole. A new 4-inch sewer service will serve the west building
and connect to the existing 10-inch PVC sewer main west of the property via a new manhole. A new
4-inch sewer service will serve the east building and connect to the relocated 8-inch PVC sewer
main on the east property boundary. The new sewer main constructed under Haggerty Lane has
been sized to meet the sewer demand from the proposed property, the property directly to the east
(currently Ulu Wellness), and the Bozeman Softball Complex directly to the south. The following
sections summarize the projected demand calculations.
Existing sewer demands for the site are zero as it is an undeveloped property. Proposed sewer
demands were determined per Section 5.2.4 of the City Standards. Since there are basic
development plans, demand calculations were completed using an average daily domestic flow
rate of 64.4 gallons per capita per day at 2.17 people per dwelling unit for the proposed project site.
Average Daily Domestic Flow:
64.4 gpcd x 10 dwelling units x 2.17 people per dwelling unit = 1,398 gpd
Base Infiltration Rate:
150 gallons/acre/day x 0.47 acres = 71 gpd
Average Domestic Flow + Base Infiltration Rate:
1,398 gpd + 71 gpd = 1,469 gpd
A peaking factor of 4.38 was determined from the peaking factor formula in Section 5.2.5.
Peaking Factor x (Average Domestic Flow + Base Infiltration) (gpd):
4.38 x 1,469 gpd = 6,434 gpd = 4.5 gpm
MEMORANDUM PAGE 3 OF 4 FEBRUARY 2026
Current sewer demands for the property directly to the east (currently Ulu Wellness) are unknown
to Sanbell, therefore demand calculations were computed using the B-2M Zoning within Table
5.2.1:
Average Domestic Flow (2800 gpad):
0.65 acres x 2800 gpad = 1820 gpd
Average Domestic Flow + Base Infiltration (2950 gpad):
0.65 acres x 630 gpad = 1918 gpd
The peaking factor for Ulu Wellness property was assumed to be the same as the proposed
property based off the lots having similar sizes. The peaking factor is also greater than the
minimum peaking factor of 2 as described by DEQ Circular Two.
Peaking Factor x (Average Domestic Flow + Base Infiltration) (gpd):
4.38 x 1918 gpd = 8,401 gpd = 5.8 gpm
Current sewer demands for the property directly to the south, Bozeman Softball Complex, are
unknown to Sanbell, therefore demand calculations were completed using the PLI Zoning within
Table 5.2.1:
Average Domestic Flow (50 gpad):
26 acres x 50 gpad = 1,300 gpd
Average Domestic Flow + Base Infiltration (200 gpad):
26 acres x 200 gpad = 5,200 gpd
It was assumed that the maximum usage for the Bozeman Softball Complex would be 300 people.
A peaking factor of 4.08 was determined from the peaking factor formula in section 5.2.5:
Peaking Factor x (Average Domestic Flow + Base Infiltration) (gpd):
4.08 x 5,200 gpd = 21,216 gpd = 14.7 gpm
The total peak sewer demand for the three properties that would be utilizing the proposed sewer
line would be 32,850 gpd or 22.8 gpm. The proposed 8-inch sewer main capacity at 75 percent full
MEMORANDUM PAGE 4 OF 4 FEBRUARY 2026
is 258 gpm with a slope of 0.004 ft/ft. The existing 18-inch sewer main capacity at 75 percent full
is 6,333 gpm using the existing pipe slope of 0.0319 ft/ft.
Appendices
Appendix A – Hydraulic Calculations
Appendix B – Site Map
HAGGERTY MULTI-FAMILY
Project # 250389.01/.02 APPENDIX A HYDRAULIC CALCULATIONS
Project: 250389 Haggerty Multi-Family
Date: 2/27/2026
8-INCH
Capacity Calclulations .004 FT/FT Slope
8" Pipe Flowing Full Capacity 0.77 cfs
8" Pipe Flowing Full Capacity 344 gal/min
Q/Qfill @ 75% full 0.75 per nomograph
Capacity @ 75% full 258 gal/min
Total Peak Hourly Flow plus Infiltration 22.80 gal/min
Result
Q/Qfull based on peak hour 0.09
Percent Full for 8" From Nomograph at peak hour 25%
Project: 250389 Haggerty Multi-Family
Date: 2/27/2026
Capacity Calculations .0319 FT/FT Slope
18" Pipe Flowing Full Capacity 18.81 cfs
18" Pipe Flowing Full Capacity 8444 gal/min
Q/Qfill @ 75% full, 0.75 per nomograph
Capacity @ 75% full 6333 gal/min
Total Peak Hourly Flow plus Infiltration 22.80 gal/min
Result
Q/Qfull based on peak hour 0.00
Percent Full for 18" From Nomograph at peak hour 2%
HAGGERTY MULTI-FAMILY
Project # 250389.01/.02
APPENDIX B SITE MAP
EXHIBIT A015SCALE:1" = 30'3015