HomeMy WebLinkAbout19 - Design Report - Southbridge Condominiums - Water, Sewer DESIGN REPORT
WATER AND SANITARY SEWER
SOUTHBRIDGE CONDOMINIUMS
Prepared for:
JW Roylance Construction, Inc.
343 Middle Road
Sheridan, MT 59749
Prepared by:
Engineering and Surveying Inc.
1091 Stoneridge Drive • Bozeman, MT 59718
Phone (406) 587-1115 • Fax(406) 587-976B
www.chengineers.com • info@chengineers.com
Project Number: 190104
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Revised: October 23 2019
INTRODUCTION
The proposed Southbridge Condominium project includes the construction of 11 condominium
units in two 4-plex buildings and one 3-plex building on Lot 1, Block 4 of Southbridge
Subdivision, Phase 1. The 1.08-acre property is located within the City of Bozeman limits and is
currently zoned R3 Residential. The property is located on the NW corner of the intersection of S.
191h Ave and Southbridge Drive and will be accessed by a paved drive entrance off of Southbridge
Drive.
Water and sanitary sewer mains are located in Southbridge Drive in front of the subject property.
An 8" sewer main stub was extended into the property with the underlying subdivision
infrastructure, and a 4" water main stub was extended into the boulevard in front of the property.
This 8" sewer main stub will be extended into Lot 1 beneath the paved drive entrance, and an 8"
water main will be extended off of the existing water main in Southbridge Drive.
WATER DISTRIBUTION SYSTEM
As mentioned previously, an 8" D.I.P. water main will be tied into the existing 8" water main in
Southbridge Drive and extended 139 linear feet into Lot 1 beneath the paved drive entrance. The
8" main will dead-end with a cap and permanent blow-off assembly. 1.5" copper water services
will be extended off of this 8" water main to Building # 1 and Building # 2. The water service for
Building#3 will be extended off of the end of the existing 4"water stub located in the boulevard in
front of the lot.
A WaterCAD analysis is enclosed (Appendix A of this report) analyzing the main installed with
this project. The connection to the existing system in Southbridge Drive is modeled as a pump
with characteristics matching pressure/flow data from the existing hydrant at the intersection of
Southbridge Drive and S. 201h Ave. This existing flow data,provided by the City of Bozeman,was
used to approximate the pressure and flow for the water main the project area.
Design Report-Page 2 of 7
Water Distribution System Demands
The design parameters used herein are according to the City of Bozeman Design Standards and
Specifications Policy (DSSP) dated May 2017.
Average Daily Residential Usage = 170 gallons per capita per day
Average Population Density = 2.11 persons/dwelling unit
Minimum Fire Hydrant Flow = 1,500 gpm
Residual Pressure Required = 20 psi for Fire Flow
Average Day Demand (Peaking Factor= 1.0)
Maximum Day Demand (Peaking Factor=2.3)
Peak Hour Demand (Peaking Factor= 3.0)
Water Demands (11 dwelling units)
Average Day Demand= 11 d.u. x 2.11 persons/d.u. x 170 gpcpd= 3,946 gpd= 2.74 gpm
Maximum Day Demand =2.74 gpm x 2.3 = 6.30 gpm
Peak Hour Demand =2.74 gpm x 3.0 = 8.22 gpm
Water Distribution System Hydraulic Analysis
A water distribution model was created using WaterCAD Version 6.5 for demand forecasting and
describing domestic and fire protection requirements. In order to model the system, each junction
node of the water distribution system was assessed a demand based on its service area. The table
shown below quantifies the demands placed at the junction nodes and calculates the demands for
Average Day, Maximum Day and Peak Hour within the project. The peaking factor for each case
is 1.0, 2.3 and 3.0 respectively. Refer to the site layout in Appendix A for node locations.
JUNCTION # OF AVG. DAY MAX. DAY PEAK HOUR
NODE UNITS (GPM) (GPM) (GPM)
5 4 1.00 2.29 2.99
3 7 1.74 4.01 5.23
Total 11 2.74 6.30 8.22
Static, residual and pitot pressures were provided by the City of Bozeman Water Department for
Design Report-Page 3 of 7
Hydrant #2459 on the 8" water main in S. 20th Ave. at the NW corner of the intersection with
Southbridge Drive. Email correspondence with the City of Bozeman Water Department regarding
the hydrant data is provided in Appendix A of this report for reference.
Static Pitot Residual
Location Hydrant#
Pressure Pressure Pressure
S. 20th Ave/ Southbridge
2459 50 # 36 # 48 #
Drive
This flow/pressure information was used to develop relationships between static head and flow at
the tie in point to the existing water main. This relationship was simulated in the WaterCAD model
modeled as a pump with characteristics matching pressure/flow data from the existing hydrant.
The pump was placed in Southbridge Drive,west of the tie in point of the proposed water main and
is connected to a reservoir which acts as a source of water. The elevation of the reservoir is fixed at
the elevation of the pump. The input data and the pump curve are included in Appendix A of this
report.
Water Distribution System Design Summary
The model shows that the existing water distribution system provides adequate flow and pressure
for the proposed project. The modeled connection point (pump) in Southbridge Drive supplied
sufficient pressure to the system. All of the junction nodes in the water model read 20 psi. The
proposed 8-inch, D.I.P. water main in Southbridge Drive provides adequate capacity to serve the
project. The flows and pressures within the system for the Peak Hour Demands were generated
using WaterCAD and can be found in Appendix A of this report.
The capacity of the system to meet fire flow requirements was tested by running a steady state fire
flow analysis for all junctions, including the existing fire hydrant location on Southbridge Drive in
front of the subject property. The model shows that the junction at this existing hydrant satisfies
fire flow constraints (residual pressure>20 psi, flow rate> 1500 gpm), while providing service to
the apartment buildings at peak hour. The results of the analysis at peak hourly flow are given in
Appendix A of this report.
Design Report-Page 4 of 7
SANITARY SEWER SYSTEM
An existing 8" sanitary sewer main is located in Southbridge Drive in front of the project site and
an 8" sewer main stub was extended into the SW corner of the property with the Meadow Creek
Subdivision infrastructure improvements. A new manhole will be installed on the end of this
existing stub, and a new 8" sewer main will be extended 108 linear feet into the property beneath
the paved drive entrance, terminating at a second manhole. All three proposed condo buildings
will be serviced by 4" sewer services connected to this new main.
Sanitary Sewer Design Load
The population estimates of 2.17 people per dwelling unit, and residential flow rate of 65 gpcd
used herein are according to the City of Bozeman Design Standards and Specifications. The
peaking factor for the design area is determined using the formula provided in the City of Bozeman
Design Standards and Specifications. The proposed main extension will be 8-inch and shall be
sized to flow at no more than 75% of capacity for peak hour conditions.
As stated previously, the contributing area from the Southbridge Condominium project includes
11 condo dwelling units on the 1.08-acre site. The equivalent population and assumed infiltration
rate for the contributing area is calculated as follows:
Equivalent Population: (2.17 persons/d.u.) x (11 d.u.) =24 persons
Assumed infiltration rate: (150 gal/acre/day) x (1.08 acres) = 162 gal/day
Total Design Load.-
The peak flow rate is calculated by multiplying the City's design generation rate of 65 gallons per
capita per day by the population,multiplying by the peaking factor, and adding the infiltration rate:
Peaking Factor from Meadow Creek Subdivision Design Report (Appendix B) = 3.632
Design Report-Page 5 of 7
Peak Flow Rate: (65 gal/person/day)(24 persons)(3.632) + 162 gal/day
= 5,828 gal/day
=4.05 gpm (0.009 cfs) = Qpeak
Sanitary Sewer Hydraulic Analysis.-
The capacity of an 8-inch main is checked using Manning's Equation:
Q = (1.486/n)AR2i3S1/2
8-inch PVC Pipe @ 75%Capacity
Pipe Diameter= 8 in
Manning's (n)= 0.013 (for PVC)
Min. Slope (S) = 0.004 ft/ft
A=n(r2) 0.35 ft2
P=2n r 2.09 ft
R=A/P 0.17 ft
Qf.0= 0.764 cfs
Qo.75= 0.573 cfs
Qo.75 = 0.573 cfs > Qpeak= 0.009 cfs .'. adequate
Based on these calculations, an 8-inch sewer main extension is more than adequate to carry the
design flows for the Southbridge Condominium project.
The existing sanitary sewer main stub and sewer main in Southbridge Drive were designed by
Engineering, Inc. as part of the Meadow Creek Subdivision. The "Water and Wastewater Design
Report" for Meadow Creek Subdivision by Engineering, Inc. is included in Appendix B for
reference. The existing 8" sewer main stub into the project site (Lot 1, Block 4) and the existing
sewer main stub into the property to the south of Southbridge Drive (Lot 1, Block 5) both tie into
the existing sewer main at MH #100 in Southbridge Drive. Based on the design report by
Engineering, Inc. (Appendix B)the projected peak hourly flow(including infiltration)to MH#100
from these two lots was 7.74 gpm when using the (then current) C.O.B. design standard values of
Design Report-Page 6 of 7
2.54 persons/dwelling and 72 gpcd. The design report assumed that 16 units would be constructed
between these two lots, but did not specify how many units were anticipated per lot. In order to
assure that adequate capacity is reserved for development of Lot 1, Block 5 in the future, the
following calculations are intended to show that the proposed project does not use too large of a
proportion of this original flow projection to MH#100.
The projected peak flow of 4.05 gpm from the project site would make up 52% of the original flow
projection of 7.74 gpm into MH #100 (4.04/7.74). Since the project site (Lot 1, Block 4) is 1.084
acres and Lot 1, Block 5 to the south is 0.987 acres, these two lots have a combined area of 2.071
acres contributing to MH #100. The project site makes up 52% of this combined area
(1.084/2.071).
Therefore, when comparing the total area of these two lots to the total flow anticipated from these
lots,the proposed flow from the project is proportionate to the lot area of the project. Based on this
it is assumed that there is adequate capacity available in the downstream sewer infrastructure for
the proposed project.
Design Report-Page 7 of 7