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Technical Memorandum
Subject: Highlands Apartments - Concurrence with Subdivision Traffic, Water, and Sewer
Plans
Date: July 23, 2025
The Highlands is a proposed affordable multifamily housing development to be located on Lots 1
and 2 of Block 2 of the Aaker Subdivision (City of Bozeman Master Site Plan Project #22381). The
subdivision completed a Traffic Impact Study, a Water Engineer’s Report, and a Sewer Engineer’s
Report for the entire subdivision. This memorandum is to verify the proposed design of the
Highlands is in concurrence with the Subdivision reports. Aaker Subdivision assumed 250 housing
units on the lots for the proposed multifamily housing. The proposed project contains 149 housing
units. For traffic, water, and sewer, this reduction in units means that the designs proposed by the
subdivision will be adequate. Each is discussed in detail below.
Traffic
The proposed design for Highlands, with a reduction to 149 units from the 250 units anticipated
with subdivision approval, will generate less trips than assumed by the Traffic Impact Study. Any
upgrades or changes proposed in the approved traffic study for Aaker subdivision will be adequate
to accommodate the traffic from the proposed multifamily housing development. According to the
City of Bozeman Design and Construction Standards, a development previously included in a
Transportation Impact Study only requires a new one if the trip generation exceeds the assumed
values, or if the original is more than 5 years old. The Aaker Subdivision Traffic Study was
completed two years ago in 2023.
Water
The City of Bozeman Design and Construction Standards (COBDCS) were updated in 2024 after the
Aaker Subdivision Master Site plan was approved. The revisions affect the calculation of water and
sewer demand by changing the assumptions of capita per unit and the gallons per day (GPD) per
capita. A comparison of the water demand for these lots by the subdivision developer under the old
standards with the proposed design under the new standards is summarized in Table 1 below.
Table 1 – Water Demand Comparison
Calculation Source Units Capita/
unit Population GPD/Capita Residential
Demand (GPD)
Subdivision Calculation
(Prior COBDCS) 250 2.11 527.5 89 46,948
Proposed Design
(COBDCS, 2024) 149 2.17 323.3 135 43,650
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The revised COBDCS yield a higher demand per unit, but with the reduction in units in the proposed
design, the overall demand remains below the subdivision master plan assumption. All designs for
the water distribution for the subdivision are adequate.
Sewer
The updates to the COBDCS between the subdivision approved design and the design of the
proposed project include updates to the assumptions of capita per unit and gallons per day per
capita, similar to the water demand updates. A sewer base infiltration rate is now added to the
demand. The base infiltration rate adds an additional 150 gallons/acre/day. Lots 1 and 2 where
Highlands will be built contain 4.30 acres, which will result in an additional 645 GPD.
Table 2 – Sewer Demand Calculation
Calculation Source Units Capita/
unit Population GPD/
Capita
Base
Infiltration
Rate (GPD)
Residential
Demand
(GPD)
Subdivision Calculation
(Prior COBDCS) 250 2.11 527.5 89 0 46,948
Proposed Design
(COBDCS, 2024) 149 2.17 323.3 64.4 645 21,468
The reduction in units and the changes in calculation result in a lower residential demand for
sewer, so sewer infrastructure designed by the subdivision will be adequate to serve the proposed
multifamily housing development.
For any additional comments or need for information please contact the undersigned.
Zack Graham
Graham Engineering LLC
406.624.2686
zack@grahameng.com