HomeMy WebLinkAboutAppendix C - Water and Sewer Design Report - Flanders Mill
DESIGN REPORT
WATER AND SEWER
FLANDERS MILL SUBDIVISION
Prepared for:
Flanders Mill, LLC
235 Greenhills Ranch Road, Bozeman, MT 59718
Prepared by:
C&H Engineering and Surveying, Inc.
1091 Stoneridge Drive, Bozeman, MT 59718
(406) 587-1115
Project Number: 13067
April 2014
Design Report - Page 2 of 10
INTRODUCTION
The proposed Flanders Mill Subdivision is a major residential subdivision located on a
136.75-acre parcel legally described as Tract 1 of Certificate of Survey No. 2834 located in the
East Half of the West Half of Section 3, Township 2 South, Range 5 East of P.M.M., City of
Bozeman, Gallatin County, Montana. It is bordered by Baxter Lane to the north, Ferguson Avenue
to the east, and Flanders Mill Road to the west. The subdivision will connect to existing City of
Bozeman water and sewer mains.
The proposed subdivision includes 292 single family lots on 55.33 acres (zoned R-3) and two
multi-family lots on 5.42 acres (zoned R-4). This report assumes that the multi-family lots will
contain 57 dwelling units assuming 10.4 dwelling units per acre for R-4 zoning (Table V-1, City of
Bozeman Design Standards and Specifications Policy).
WATER DISTRIBUTION SYSTEM
Current water mains and stubs in the area utilized for this project include: the 12-inch ductile iron
pipe (DIP) located in Baxter Lane at the north subdivision boundary, the 10-inch DIP in Oak Street
at the east central portion of the subdivision, and 8-inch DIP stubs on the west side of Ferguson at
the intersections of Moonstone Drive, Sunstone Street, Annie Street, Renova Lane, and Tanzanite
Drive.
A WaterCAD analysis is enclosed (Appendix A of this report) analyzing all mains installed with
this project. The connections to the existing system are modeled as two pumps representing the
connections near the south (Ferguson) and north (Baxter) ends of the subdivision with
characteristics matching pressure/flow data measured by the City of Bozeman Water Department.
Water Distribution System Demands
The design parameters used herein are according to the City of Bozeman Design Standards and
Specifications Policy (DSSP) dated March 2004.
Design Report - Page 3 of 10
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 (349 dwelling units)
Average Day Demand = 349 d.u. x 2.11 persons/d.u. x 170 gpcpd = 125,186 gpd = 86.94 gpm
Maximum Day Demand = 7.47 gpm x 2.3 = 199.95 gpm
Peak Hour Demand = 7.47 gpm x 3.0 = 260.81 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 subdivision. The peaking factor for each
case is 1.0, 2.3 and 3.0 respectively.
Design Report - Page 4 of 10
Static, residual and pitot pressures were measured by the City of Bozeman Water Department for
the 8-inch water main in Andalusian Avenue north of Equestrian at Hydrant #2485 and the 8-inch
water main stub near the intersection of Ferguson Avenue and Sunstone Street. The measurements
at the Ferguson/Sunstone hydrant were taken on the low pressure side of the existing pressure
reducing valve (PRV) in Ferguson. The Hydrant Pressure/Flow Result Forms are attached in
Appendix A of this report. The results are shown below:
JUNCTION
NODE
# OF
UNITS
AVG.
DAY
(GPM)
MAX. DAY
(GPM)
PEAK
HOUR
(GPM)
Design Report - Page 5 of 10
Location Hydrant # Static Pressure Pitot Pressure Residual Pressure
Andalusian near
Kimberwicke
2485 107# 94#
Andalusian 2484 80# (1500 gpm)
Ferguson/Sunstone 2278 81# 75#
Ferguson/Moonstone 2279 65# (1350 gpm)
This flow/pressure information was used to develop relationships between static head and flow at
the tie in points. This relationship was simulated in the WaterCAD model using pumps at the
connection points. The pumps are connected to reservoirs which act as a source of water. The
elevations of the reservoirs are fixed at the elevation of the pumps, which is also equivalent to the
elevation of the tie in point. The reservoir does not create any head on the system; the head is
generated entirely by the pumps. The input data and the pump curves 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 subdivision. The modeled connection point (pump) at Baxter Lane supplied
sufficient pressure to the system which forced the modeled connection pump at Ferguson to shut
off. The lowest pressure observed in the model was 80.97 psi at Junction #264 near the southwest
boundary of the subdivision. The proposed 8-inch and 10-inch DIP water mains provide
adequate capacity to serve the development. 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 at fire hydrant locations. The model shows that all hydrant junctions
satisfy fire flow constraints (residual pressure > 20 psi, flow rate > 1500 gpm), while providing
service to lots at peak hour. The results of the analysis at peak hourly flow are given in Appendix A
of this report.
Design Report - Page 6 of 10
SANITARY SEWER SYSTEM
Sewer main lines will be installed in nearly all streets in the subdivision and will connect to two
trunk/interceptor mains: the Valley West Trunk Main/Baxter Interceptor and the Ferguson Trunk
Main/27th Avenue Cattail Creek Interceptor.
Sanitary Sewer Design Load
The flow rates used herein are according to the City of Bozeman Design Standards and
Specifications Policy, March 2004 (COB DSSP). The peaking factor for the design area is
determined by calculating the equivalent population and inserting the population into the Harmon
Formula. An 8-inch main is the minimum diameter allowed within the City of Bozeman. The
proposed mains within the subdivision will be 8-inch. All new sewer lines shall be sized to flow at
no more than 75% of capacity for peak hour conditions.
The city average of 2.11 persons per household is used to calculate the equivalent population for
the service area.
Valley West Trunk Main/Baxter Interceptor Connection:
The 18-inch Valley West Trunk Main flows west to east through the portion of the proposed
subdivision that lies south of future Oak Street before jogging 360-ft to the north and transitioning
to a 21-inch line near the Ferguson/Renova intersection. A majority of the proposed lots south of
Oak Street will connect to the Trunk Main with two new manholes, three main connections to
existing manholes, and several direct service connections. The equivalent population and assumed
infiltration rate for the contributing area is calculated as follows:
Equivalent Population: (2.11 persons/d.u.)(92 d.u.) = 194 persons
Assumed infiltration rate: (150 gal/acre/day) (30.74 acres) = 4,611 gal/day
Total Design Load:
The peak flow rate is calculated by multiplying the City's design generation rate of 89 gallons per
capita per day by the population, multiplying by the peaking factor, and adding the infiltration rate:
Design Report - Page 7 of 10
Harmon Formula: Peaking Factor = (18 + P0.5)/(4 + P0.5)
where: P = Population in thousands
Peaking Factor = (18 + 0.1940.5)/(4 + 0.1940.5)
Peaking Factor = 4.15
Peak Flow Rate: (89 gal/person/day)(194 persons)(4.15) + 4,611 gal/day
= 76,356 gal/day
= 53.03 gpm (0.1181 cfs)
Sanitary Sewer Hydraulic Analysis:
The capacity of an 8-inch main is checked using Manning’s Equation:
Q = (1.486/n)AR2/3S1/2
For an 8-inch PVC sewer main:
Manning's n = 0.013 for PVC
Minimum Slope = 0.004 ft/ft
A = area = (3.14/4)d 2 = (3.14/4)(8/12)2 = 0.34907 ft2
P = perimeter = 2(3.14)r = 2(3.14)(4/12) = 2.0944 ft
R = hydraulic radius = A/P = 0.34907/2.0944 = 0.16667 ft
R2/3 = 0.30105 ft
S = 0.004 ft/ft
S1/2 = 0.0632 ft/ft
Qfull = (1.486/0.013)(0.34907)(0.30105)(0.0632) = 0.7592 cfs
Q0.75 = (0.75)(0.7592) = 0.5694 cfs > Qpeak = 0.1181 cfs adequate
Based on these calculations, an 8-inch sewer main is more than adequate to carry the design flows
for the subdivision. According to the 2007 Bozeman Wastewater Facilities Plan, the Baxter
Interceptor is flowing at less than 50% capacity for the peak day model. This indicates that the
Interceptor has adequate capacity to manage the additional flows from the proposed development.
Design Report - Page 8 of 10
Ferguson Trunk Main/27th Avenue Cattail Creek Interceptor Connection:
The north part of the proposed subdivision lying north of future Oak Street (including a small
portion of the south part) will connect to the existing Ferguson Trunk Main at the intersection of
Ferguson Avenue and Tanzanite Drive, and at the Ferguson/Baxter roundabout. The contributing
area includes 200 single family lots and 2 multi-family lots (5.5025 acres, zoned R-4). The
multi-family lots are assumed to have a total of 57 dwelling units assuming 10.4 dwelling units per
acre for R-4 zoning (Table V-1, COB DSSP). Therefore, the total number of contributing dwelling
units is 257 (200 + 57). The equivalent population and assumed infiltration rate for the
contributing area is calculated as follows:
Equivalent Population: (2.11 persons/d.u.)(257 d.u.) = 543 persons
Assumed infiltration rate: (150 gal/acre/day) (106.01 acres) = 15,901 gal/day
Total Design Load:
The peak flow rate is calculated by multiplying the City's design generation rate of 89 gallons per
capita per day by the population, multiplying by the peaking factor, and adding the infiltration rate:
Harmon Formula: Peaking Factor = (18 + P0.5)/(4 + P0.5)
where: P = Population in thousands
Peaking Factor = (18 + 0.5430.5)/(4 + 0.5430.5)
Peaking Factor = 3.96
Peak Flow Rate: (89 gal/person/day)(543 persons)(3.96) + 15,901 gal/day
= 206,976 gal/day
= 143.73 gpm (0.3203 cfs)
Sanitary Sewer Hydraulic Analysis:
The capacity of an 8-inch main is checked using Manning’s Equation:
Q = (1.486/n)AR2/3S1/2
Design Report - Page 9 of 10
For an 8-inch PVC sewer main:
Manning's n = 0.013 for PVC
Minimum Slope = 0.004 ft/ft
A = area = (3.14/4)d 2 = (3.14/4)(8/12)2 = 0.34907 ft2
P = perimeter = 2(3.14)r = 2(3.14)(4/12) = 2.0944 ft
R = hydraulic radius = A/P = 0.34907/2.0944 = 0.16667 ft
R2/3 = 0.30105 ft
S = 0.004 ft/ft
S1/2 = 0.0632 ft/ft
Qfull = (1.486/0.013)(0.34907)(0.30105)(0.0632) = 0.7592 cfs
Q0.75 = (0.75)(0.7592) = 0.5694 cfs > Qpeak = 0.3203 cfs adequate
Based on these calculations, an 8-inch sewer main is more than adequate to carry the design flows
for the subdivision. Downstream from the proposed connection, the Ferguson Trunk Main
transitions to an 18-inch line before entering the Baxter Meadows Lift Station. According to the
2007 Bozeman Wastewater Facilities Plan, the Ferguson Trunk Main and the 27th Avenue/Cattail
Creek Interceptor are flowing at less than 50% capacity for the peak day model, thus indicating
that the lines have adequate capacity downstream from the proposed subdivision.
Design Report - Page 10 of 10
APPENDIX A
WATERCAD MODEL &
COB HYDRANT DATA