HomeMy WebLinkAbout20 - Design Report - Headwaters Academy - Water, HydrantHeadwaters Academy – Water Main Extension 19-024
MDEQ Water Report August 28, 2020
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1 Engineers Report
The following provides the required information for the Engineers Report as outlined by
Montana Department of Environmental Quality Circular 1 – Standards for Water Works.
1.1 General Information
The existing water system is part of the City of Bozeman public water system. A water facility
plan dated July 2017 is available for the additional information related to the system. Maps from
the facility plan are included with the attachments showing the location of the project site
relative to the system.
Water and Sewer Department City of Bozeman Engineering Department
John Alston – Superintendent Shawn Kohtz – City Engineer
814 North Bozeman 20 East Olive St.
Bozeman, Montana 59715 Bozeman, MT 59715
1.2 Extent of Water Works System
The improvements under review include the extension of an existing water main and installation
of a new fire hydrant. The hydrant will be located within the Headwaters Academy property, a
private middle school. An easement for the hydrant is being dedicated to the COB. The service
area will not be expanded as part of this project, as the water system already serves this area.
1.3 Alternative Plans
The alternatives are limited for the proposed improvement. A new fire hydrant located adjacent
to the proposed structure will minimize the distance to a municipal hydrant. One possible
alternative would be to not install a new hydrant; however, spacing required by the Fire
Department would not be met. Fire suppression systems within each structure could be proposed
as an alternative.
1.4 Site Conditions
A Geotechnical Investigation Report was completed by Allied Engineering Services, Inc. for the
project site addressing foundation preparations and concerns. The upper 1.25 to 1.5 feet
consisted of silty organic topsoil. The topsoil layer was underlain by fine-grained sandy silt/clay
deposits to a depth of four to five feet below the ground surface. Below the fine-grained deposits
was found to be alluvial deposits of dense sandy gravel with rounded cobbles. In general, the
foundation will be mass excavated to native gravels; imported pit-run will be used to bring the
site up to grade. During the subsurface investigation, groundwater was not encountered in any of
the three test pits (each 8.5 feet in depth). However, an increase in moisture content was
observed starting at eight feet below the ground surface, indicating groundwater is nearby. A
groundwater monitoring well was installed and monitored from early May to the end of June.
The monitor well extended to a depth of 7.73 feet, no groundwater was observed. If found to be
necessary during construction, a dewatering permit will be obtained as necessary for dewatering
operations through MDEQ. The water main is anticipated to be installed in the gravel soils;
however, proper bedding materials will still be required.
Headwaters Academy – Water Main Extension 19-024
MDEQ Water Report August 28, 2020
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1.5 Water use data
The City of Bozeman water system providing service to the proposed site serves roughly 43,405
people based on the 2017 Water Facility Plan (WFP). Additional usage information is provided
in the WFP. The proposed site will consist of the existing house being converted for use along
with a new classroom building. Site usage is estimated for a maximum of 90 students, the size of
the school is anticipated to be capped at this time. Based on MDEQ Circular 4, the demand for a
school with cafeteria, gym, and showers is 25 gallons per day per student. The average daily
flow is then 2,250 gallons per day. From the City of Bozeman Design Standards and
Specifications, the maximum hour to average day ratio is 3:1. The maximum day to average day
ratio is 2.3:1.
Average daily flow: 2,250 gpd; 1.6 gpm
Max hour: 6,750 gpd; 4.7 gpm
Max day: 5,175 gpd; 3.6 gpm
Table 5.7 in the COB WFP lists the required fire flow for a commercial use as 3,000 gpm.
Leakage for the current water services has not been tracked for this project. An old water service
will be abandoned and capped at the existing water main, reducing potential for leakage.
1.6 Flow Requirements
The 2017 COB WFP includes hydrant flow data that was used for the following analysis. Test
hydrant 41 is located near the project site just south of Durston Road on 15th Ave. The elevation
of the hydrant is near the same as the project site. Supporting excerpts from the WFP are
included with the attachments.
Hydrant Flow Test
o Static pressure: 139 psi
o Residual pressure: 136.8 psi
o Flow Rate: 1,878 gpm
The existing water system is looped and the project site served from an existing 10-inch main
located in Durston Road. The flow test demonstrates minimal pressure drop during the flow
event of over 1,800-gpm. The looped system and relatively small pressure drop during the flow
test was used to make assumptions in development of a simple model in EPANET. The model
assumes a reservoir at the connection to the existing main in Durston Road with a pressure head
of 130-psi. The model will be unconservative in that additional system pressures would drop at
the assumed reservoir. A lower residual of 130-psi was assumed for this reason (the residual
during the hydrant flow test was almost 137-psi). The assumptions for the model and results are
outlined below. The model does conservatively assume the entire 3,000-gpm demand will be
achieved via the one proposed hydrant. Realistically, other hydrants in the area could be utilized
concurrently during a fire event.
8” pipe
o C = 130
o Length = 270-ft
6”
o C = 130
Headwaters Academy – Water Main Extension 19-024
MDEQ Water Report August 28, 2020
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o Length = 20-ft
130-psi static in reservoir; 300-ft
3,000-gpm
Results:
o Residual pressure of 108-psi (250-ft) during flow of 3,000 gpm
The model and assumptions are very simplified and do not include other system flows or losses.
Based on the observed flow test and minimal reduction in pressure, along with the high residual
pressure from the EPANET model; it appears that the system has adequate capacity to provide
the required fire flows without dropping system pressures below 20-psi. Domestic flows for the
site are relatively small compared to the overall system and are anticipated to have minimal
impact to the system capacity.
1.7 Sources of Water Supply
Water is supplied by the COB public water system. The main sources are Hyalite/Sourdough and
Lyman Spring. Additional information is addressed in the COB WFP.
1.8 Proposed Treatment Processes
The Hyalite/Sourdough Water Treatment plant provides water treatment for the municipal
system. This is a large-scale microfiltration plant providing the bulk of the water for the city. The
Lyman Spring water is chlorinated prior to discharge to the reservoir.
1.9 Sewage System
Sanitary service for the site will be accomplished via two service connections to the existing
COB sanitary sewer system. A municipal sanitary treatment plant provides treatment for the
system. Additional information is provided in the City of Bozeman Wastewater Facility Plan.
1.10 Water Disposal
Disposal from the project site will be to the municipal system. A major wastewater treatment
plan is managed by the City of Bozeman with discharges monitored and addressed by the
Wastewater Facility Plan.
1.11 Automation
There will be limited components to monitor for the private site. The COB has been working to
upgrade metering systems to assist with quickly identifying any water leaks on the customs side
of the meter.
1.12 Project Sites
The project site is located near the existing high school and a residential area of town. It is
anticipated that a portion of students will be able to commute to the site via walking/biking. A
commercial area is located east of the site along North 7th. This has been considered by the
ownership group. Water is sanitary sewer service is provided from the municipal system
reducing the concern for on-site components.
1.13 Financing
Financing will be accomplished through private capital.
1.14 Future Extensions
Future expansions for the project site are not anticipated at this time.
1
8
2
6
2 3
1
Diameter
6.00
8.00
24.00
36.00
in
Day
EPANET 2 Page 1
1
22
113.64
3
108.73
1
0.00
Pressure
25.00
50.00
75.00
100.00
psi
Day
EPANET 2 Page 1
Network Table - Links
Length Diameter Roughness Velocity
Link ID ft in fps
Pipe 1 270 8 130 19.15
Pipe 2 20 6 130 34.04
EPANET 2 Page 1
Network Table - Nodes
Elevation Demand Head Pressure
Node ID ft GPM ft psi
Junc 2 0 0.00 262.27 113.64
Junc 3 0 3000.00 250.93 108.73
Resvr 1 300 -3000.00 300.00 0.00
EPANET 2 Page 1