HomeMy WebLinkAbout2-2 Sewer Report
2695 Tschache Lane Project
City of Bozeman
Sewer Main Extension
DEQ Circular-2
Engineering Report
Prepared By:
1055 Mount Avenue
Missoula, MT 59801
MMI #: 10093.001
February 2023
Table of Contents
Introduction ................................................................................................................................ 3
1.1 Problem Defined .......................................................................................................... 3
1.2 Design Conditions ........................................................................................................ 3
1.3 Impact on Existing Wastewater Facilities ..................................................................... 4
1.4 Project Description ....................................................................................................... 4
1.5 Drawings ...................................................................................................................... 4
1.6 Design Criteria ............................................................................................................. 4
1.7 Site Information ............................................................................................................ 5
1.8 Alternative Selection/Analysis ...................................................................................... 5
1.9 Environmental Impacts ................................................................................................ 5
1.10 Operation & Maintenance ............................................................................................ 5
Conclusion ................................................................................................................................. 5
ATTACHMENTS:
Will Serve Letter from City of Bozeman (To be provided upon review/acceptance)
Retainage of professional engineering services letter from The Voyager Company
Written By: CCF Checked By: TBM
Approved By: WEH
Project No.: ____10093.001
INTRODUCTION
The Voyager Company contracted with SCB Architects and Morrison-Maierle to design the 2695
Tschache Lane Project. The proposed new development requires improvements for the sanitary
sewer facilities. There are currently no wastewater facilities serving the project as the subject
property is undeveloped. There is an existing 24-inch asbestos concrete sewer main located to
the north of the proposed development beneath Baxter Lane. There are also existing 8-inch and
10-inch sewer main stubs located within Trade Wind Lane. To provide sanitary sewer service to
the new development, two new 8-inch SDR 35 PVC sewer mains will be connected to the
existing sanitary sewer main stubs. These improvements and modifications will ensure that the
new development and all existing buildings continue to be served by the City of Bozeman sewer
system.
1.1 Problem Defined
a. The Developer plans to construct a new housing development consisting of 3 Apartment
buildings, 46 townhouses, 3 single-family units, a clubhouse and a gear garage. The
proposed development will be served through two 8-inch main extensions. Both
extensions will be gravity flow. The first will tie into the existing 10-inch PVC sewer main
located within Trade Wind Lane and will then run south below proposed N 25th Ave, run
west below Turbulence Lane and run south to the southeast corner of the development.
The second extension will tie into the existing 8-inch PVC sewer near the middle of
Trade Wind Lane and will then run south to the southwest corner of the development.
Connection to the City’s wastewater system will utilize the two existing sanitary sewer
manholes. Sanitary sewer service to the existing buildings to the north will not be
interrupted, as these services are down-grade of the proposed main extensions.
Sewer facilities included in this project will be designed in accordance with the Montana
Department of Environmental Quality (MDEQ) Circular-2 Regulations. Adequate
capacity will be provided to allow for some growth in areas adjacent to the actual project
area. However, a majority of the property surrounding the development is developed or
currently being developed and therefore additional capacity is not a considerable issue.
1.2 Design Conditions
a. The sewer main extensions for the 2695 Tschache Lane Development will serve all
proposed buildings. The added capacity from the development is not anticipated to
overwhelm the existing infrastructure or the City’s wastewater system and treatment
facilities. Hydraulic calculations based on the proposed development and existing main
are summarized below:
Assumptions:
• 2.11 persons/dwelling
• 89 gallons/capita/day
• 150 gallons/acre/day
Total Population = 343 DU x 2.11 person/DU = 724 persons
Total Population Flow = 724 persons x 89 gallons/capita/day = 64,436 gallons/day
Peaking Factor (based on 724 persons) = 3.89
Wastewater Flow Rate = 64,436 gallons/day x 3.89 = 250,656 gallons/day
Infiltration = 150 gallons/acre/day x 14.428 acres = 2,164 gallons/day
Total Peak Flow = 250,656 gallons/day + 2,164 gallons/day = 252,820 gallons/day
(175.6 gallons/minute)
The constricting pipe for the proposed development is an 8-inch PVC sewer main
running at 0.55% slope.
8-inch PVC Sewer (0.55% slope, 75% full) = 366.8 gpm > 175.6 gpm
1.3 Impact on Existing Wastewater Facilities
a. The proposed and existing mains have adequate capacity to serve the development and
account for the additional flows. A “Will Serve” Letter from the City of Bozeman will be
provided upon review of the proposed storm water design.
1.4 Project Description
a. The sewer main extensions for the 2695 Tschache Lane Project includes the installation
of approximately 1,894 lineal feet of 8” SDR 35 PVC sanitary sewer main and ten 48-
inch diameter manholes. Existing development surrounding this project will not have
their service interrupted as they are downstream of the proposed sewer main
extensions. Bury depth ranges from approximately 5-feet to 9.5 feet. All sewer main that
does not meet bury depth requirements will be insulated with 1” of blue board insulation
for every foot less than the required bury depth (minimum of 2”).
1.5 Drawings
a. Design drawings pertinent to the installation of the sanitary sewer main extensions are
included. Drawings are stamped and signed by a registered professional engineer in the
State of Montana.
1.6 Design Criteria
a. The following parameters were considered during the design of 2695 Tschache Project
sewer main extension:
• Proposed sewer main will be 8-inch SDR 35 PVC meeting ASTM D-3034
requirements.
• Row Homes: New 4” Schedule SDR 35 sanitary sewer service.
• Single Units: New 4” Schedule SDR 35 sanitary sewer service.
• Flats: New 8” SDR 35 PVC sanitary sewer service.
• Clubhouse: New 4” SDR 35 sanitary sewer service.
• Gear Garage: New 4” SDR 35 sanitary sewer service.
• Gear Garage: 4” Sand/Oil sanitary sewer service.
• Sand-Oil separator per City of Bozeman requirements.
• Design bury depth of 4-feet minimum.
• Where bury depth of 5’ cannot be achieved, 1” of blueboard insulation is required for
every 1” of bury depth below 5’ (minimum of 2”).
• Provide minimum 10-foot edge to edge horizontal separation between sewer main
and water and storm mains.
• All manholes spaced no more than 400 feet apart.
• Minimize vertical and horizontal bends where possible.
• Maintain 18-inch minimum vertical separation at crossings with water and storm
sewer mains.
• Project will be constructed in accordance with City of Bozeman Public Works
Standards and the 7th Edition Montana Public Works Standard Specifications
(MPWSS).
• Minimize disruption to residential and commercial services during construction.
1.7 Site Information
Soils on site consist of topsoil, silt, lean clay, and sandy gravels and cobbles per the
Geotechnical Report completed by Terracon July 29th, 2022. Topsoil is noted to be 0.5
feet in thickness. Generally, the sewer main will be laid through lean clay with sand.
The project is located North of Rose Park and outside of the floodplain. Topography of
the existing and proposed ground in the area of the main extension is generally flat
varying in elevation approximately 7 feet from the high point in the southwest corner to
the low point in the northeast corner. The eastern 1/3 of the site falls toward the adjacent
stream corridor and existing wetlands. During the geotechnical investigation
Groundwater was encountered between depths of 5.5’ and 11’ below the existing ground
surface during Terracon’s explorations. Mottling was not mentioned in the report.
Groundwater is presumed to flow northeast toward the storm pond. A majority of the site
will be filled to bring finished grades up increasing depth to groundwater.
1.8 Alternative Selection/Analysis
a. The proposed main extension was chosen as the most viable alternative based on
design and construction costs. The proposed alignment involves utilizing existing
infrastructure and two main extensions to provide service to the proposed buildings.
Alternatives considered involved one sewer main with longer service lines. Overall, it
was determined that the proposed gravity main extension and proposed alignments
were most cost effective and efficient. No additional development is proposed on the
development property as full buildout of the subject property is included with the
proposed development.
1.9 Environmental Impacts
a. There are no expected adverse environmental impacts from the installation of this sewer
main extension. The main extension alignment will be installed before any asphalt or
concrete is placed in the area. No environmental issues are known in this area. The City
of Bozeman has adequate capacity for this development. Watertight pipe will be utilized
based on high groundwater anticipated to ensure that wastewater is unable to leak out of
the proposed mains.
1.10 Operation & Maintenance
a. The proposed sewer infrastructure will be connected to the City of Bozeman public
sewer system. All new infrastructure will be owned, operated and maintained by the City
of Bozeman.
CONCLUSION
The report provided above for the 8” SDR 35 PVC sewer main extensions for the 2695
Tschache Lane Project in Bozeman, MT was prepared in accordance with Circular DEQ-2 and
City of Bozeman Standards. Construction of the main extension is anticipated to begin
construction in the Fall of 2023. Construction will be in accordance with City of Bozeman Public
Works Standards and MPWSS. The owner will retain professional engineering services through
Morrison-Maierle or other to provide certified as-built drawings within 90 days after completion
of construction and to certify installation is in accordance with approved drawings and
specifications.
2695 Tschache Lane – Water and Sewer Main Extensions
Retainage of Professional Engineering Services
In accordance with ARM 17.38.101 (10), the Owner, Bozeman Property Owner LLC, will retain
Morrison-Maierle or another licensed engineer for professional engineering certification of the
water and sewer systems for the 2695 Tschache Lane Development Project. Project is located
on the remainder of Tract 1, COS 1256 less Minor Subdivision 404 in the NE 1/4 of Section 2,
Township 2 South, Range 5 East in Bozeman, Montana.
Bozeman Property Owner LLC Date