HomeMy WebLinkAboutWater Sewer Memo 2026.01.26
714 Stoneridge Drive · Suite 3 · Bozeman, MT 59718 · (406) 586-5599 · www.alpinesurveying.net
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January 26, 2026
City of Bozeman Engineering Department
20 E. Olive Street, 1st Floor
Bozeman, MT 59715
RE: Water & Sewer Demand Memo – Delta Gamma Site Alteration
Lot 1 – 4, BLOCK 34, CAPITOL HILL ADD, S13, T02 S, R05 E
To Whom it May Concern,
The intent of this memo is to outline the anticipated water and sanitary sewer demands for the
proposed Delta Gamma Site Alteration on Lots 1-4 of Block 34, Capitol Hill Addition. The 0.39-
acre site is located on the northeast corner of the intersection of W. Garfield St and S. 4th Ave. it
is currently zoned R-2.
1.0 Overview
The project site was previously developed as an additional parking lot for the neighboring Delta
Gamma sorority, so domestic services were not provided to the lot. There are existing water and
sewer mains running along the property in W. Garfield St and S. 4th Ave. The proposed site
alteration will include the construction of a new building that includes a single dwelling unit and
additional space for support activities for the neighboring sorority. New service connections are
proposed from the adjacent mains to serve the new structure.
The existing water main in W. Garfield St. is 12” diameter and the main in S. 4th Ave is 6” diameter,
both mains are ductile iron. A 6” diameter vitrified clay sewer main exists in S. 4th Ave. The
proposed unit will have a new 4” sanitary sewer service and 1” domestic water service extended
to it. There is an existing irrigation service with a separate meter pit on the property that will remain
unchanged through the development of this site and will continue to be used for irrigation.
2.0 Water Demand
In order to be consistent with the sanitary sewer estimates, the water demand calculations for the
proposed project were computed using 2.17 people per dwelling unit, based on 2024 City of
Bozeman Design and Construction Standards (COB DCS). Per the DCS the average daily
residential demand was defined as 135 gallons per capita per day (gpcd). Table 4.2.3 in the DCS
also uses a maximum day to average day ratio of 2.3 and a peak hour ratio of 3.0. fire suppression
is not proposed for the new structure. However, existing hydrants are located approx. 300 ft west
714 Stoneridge Drive · Suite 3 · Bozeman, MT 59718 · (406) 586-5599 · www.alpinesurveying.net
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of the project site at the Garfield & S. 5th Ave. intersection, another hydrant approx. 230 ft east of
the project site at the Garfield & S. 3rd Ave intersection. The below table provides the estimated
water demands based on be above assumptions.
410 W GARFIELD ST -WATER DEMAND ESTIMATES
Phase Dwelling
Units Population Average Day
(GPD)
Average
Day (GPM)
Max Day
(GPM)
Peak Hour
(GPM)
410 W GARFIELD ST 1 2.2 293.0 0.20 0.47 0.61
Total 1 2.170 292.9 0.20 0.50 0.61
Assumptions
Population / Dwelling Unit 2.17 City of Bozeman DCS (2024)
Water Demand Rate 135 City of Bozeman DCS (2024)
Max. Day To Avg. Day Ratio 2.30 City of Bozeman DCS (2024)
Peak Hour Peaking Factor 3.00 City of Bozeman DCS (2024)
3.0 Sanitary Sewer Demand
There are several ways to estimate Sanitary Sewer flows for a given project, including standards
set forth by the Montana DEQ Circular 2, Montana DEQ Circular 4, and the COB DCS. However,
the projected wastewater flows in this memo are calculated using the values provided in the City
of Bozeman DCS. This document provides an estimate of 2.17 persons per dwelling unit with a
daily wastewater generation rate of 64.4 gallons per persons per day. A peaking factor based on
the Harmon Formula & an infiltration rate of 150 gallons per acre per day were also applied to the
project, both as outlined in the COB DCS. Based on these criteria, the estimated demands from
the proposed project are included in the table below. The capacity of the proposed on-site 4” PVC
sewer service was verified using Manning’s formula for open channel flow in a circular pipe and
a Manning’s n-value of 0.013 per the COB DCS requirements. The design requirements state that
new sewer lines shall be sized to flow at no more than 75-percent full capacity. Pipe calculations
are included below.
714 Stoneridge Drive · Suite 3 · Bozeman, MT 59718 · (406) 586-5599 · www.alpinesurveying.net
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Please feel free to contact me with any questions at (406) 586-5599, or by email at
ecote@alpinesurveying.net.
Sincerely,
Ethan Cote, P.E 60593
Phase Dwelling Units Population
Average Day
GPD
Peaking
Factor
Peak Hour
Flow (GPM)
Total Infiltration
(GPM)
Design Flow
Rate (GPM)
Design Flow
Rate (cfs)
410 W GARFIELD ST 1 2.2 139.7 4.46 0.43 0.04 0.47 0.00
Total 1 2.2 139.7 4.46 0.43 0.04 0.47 0.00
Assumptions
2.17
64.4
0.39
150
58.50
0.04
Pipe Capacity
Pipe Pipe Size (in) Flow Depth - d (in) Slope (ft/ft) Manning's n Flow (CFS)
4" PVC 4 3 0.02 0.013 0.25
GPM
Total Infiltration
Total Infiltration
410 W GARFIELD ST - Overall Sanitary Sewer Demand Estimate
Population / Dwelling Unit
Wastewater Generation Rate
Total Lot Area
Infiltration Rate
PPL (per COB DSSP 2024)
GPD per person (per COB DSSP 2024)
Acres
Gal./Acre/Day (per COB DSSP 2024)
GPD
4" PVC Pipe