HomeMy WebLinkAbout16 Water & Sewer Report Updated 8-21-20
WATER & SEWER MAIN
DESIGN REPORTS
FOR:
2131 GRAF
MULTI-UNIT
RESIDENTIAL DEVELOPMENT
BOZEMAN, MT
Prepared By:
Madison Engineering
895 Technology Drive, Suite 203
Bozeman, MT 59718
(406) 586-0262
AUGUST 2020
2131 GRAF MULTI-UNIT RESIDENTIAL DEVELOPMENT
SEWER SYSTEM DESIGN REPORT
A. General Project Description
This report will give an overview of the proposed wastewater collection system for the
development of the Icon Apartment Homes at 2131 Graf multi-unit residential development Lot
2 of minor sub 235 located in S23, T20S, R05E P.M.M, located south of Stucky Road and north
of Graf Street in Bozeman, MT. The zoning for the 25.99 acre area is listed as R-4, residential
high density. The proposed apartment buildings are designed as three (3)-3 plex (Type A), nine
(9)-32 plex (Type B), and five (5)-32 plex (Type C) for a total of 457 units in the residential
development. The improvements for Phase 1 of the development are anticipated to be
constructed during the Fall of 2020.
Included in this report is a description of the proposed wastewater collection system and design
parameters. Once the wastewater system is constructed and approved, the system will become a
part of the City of Bozeman (C.O.B.) system. The following references were used in the
wastewater facilities design and capacity analysis:
a. COB Design Standards and Specifications Policy, 2017. Addendum #7
b. COB Modification to Montana Public Works Standard Specifications (MPWSS)
c. City adopted MPWSS and adopted Addenda
d. COB Wastewater Facility Plan, 2017
e. MDEQ Circular No. 2
f. City of Bozeman Zoning Map
The procedures and parameters outlined in the COB Design Standards and Specifications Guide
were used in the design of the sewer infrastructure for the proposed development.
B. Capacity Analysis
The proposed wastewater collection system consists of 2,714 linear feet (0.51 miles) of new 8”
sewer main and will provide service to the multi-unit residential development. The effluent
generated from the proposed apartment buildings will be collected by the wastewater collection
system and ultimately flow north to Lantern Lane and west to an existing COB SSMH.
The wastewater demands from the proposed subdivision were estimated based on a flow per capita
basis, which provided a more conservative flow than a per zoned acre basis. (COB Table V-1
specifies an average daily flow rate of 1,950 gal/ac-day for R-4 zoning, resulting in 49,901 gpd =
25.59ac x 1,950 gal/ac-day).
The proposed sewer mains have been sized to flow at no more than 75-percent of full capacity at
peak hour conditions of full build out, and a Manning coefficient of 0.013 was used for PVC pipe.
The average daily flow is based on the number of units, 2.11 residents per unit, and 89 gallons per
capita per day, the latter two values based on COB design standards:
൬457 units ∗ 2.11 residents
unit ∗ 89 gallons
capita/day ൰ = 85,820 gpd
An approximate population for the project at full build out is calculated as:
457 units ∗ 2.11 residents
unit = 964 persons
This is a more realistic population value compared to utilizing the 10.4 units per acre (Table V-1
from COB design standards) applied to 25.99 acres, which only results in 570 persons.
This equivalent population can be utilized to determine a peaking factor:
൬𝑄௫
𝑄௩
൰ =18 +𝑃.ହ
4 +𝑃.ହ =18 +.964.ହ
4 +.964.ହ = 3.81
(P = Population/thousands)
Based on a total population of 964 people, a peaking factor of 3.81 was calculated. The peak flow
rate anticipated from the development based on an average daily flow of 85,820 gallons per day
is:
Peak Flow Rate = (85,820 gpd x 3.81) = 326,974 gpd
= 227 gpm
= 0.51 cfs
Additionally, an infiltration flow of 3,839 gpd (150 gal/acre/day x 25.59 acres) has been added to
the flow, resulting in a total flow of 330,813 gpd (0.51 cfs).
The sewer main size for the development will be an 8-inch, based on minimum required pipe size
and designed at a 0.40% slope. An 8-inch PVC sewer main at 0.40% slope has a capacity of 0.64
cfs at ¾ pipe depth, which has adequate capacity for the proposed peak flow of 0.52 cfs effluent
generated from the site. Calculations are included in the end of this report.
In addition, two of the proposed buildings will utilize the existing 8” sewer main in Graf St. The
total number of units using this sewer is 64 units. The resultant flow rate is 12,019 gpd, or 0.02
cfs. The peak flow rate is 45,792 gpd, or 0.07 cfs.
C. Proposed Collection System
PVC pipe meeting COB specifications will be used for the sewer mains. The effluent from the
development will drain into a proposed 8-inch diameter sanitary sewer main via 4-inch or 6-inch
sewer services. The effluent in the 8-inch wastewater collection system will then flow north to
Lantern Drive and west to an existing manhole and existing 8” sewer main in Lantern Drive. The
maximum manhole spacing will be 400 feet for the 8-inch main. Manholes will be constructed
according to COB specifications. Sewer services will be 4-inch to 6-inch PVC installed at 2%
minimum grade. Sewer services will connect into the main with in-line gasketed wyes. The sewer
main will maintain a minimum separation of 10-feet horizontally and 18-inches vertically from
any proposed or existing public water mains.
D. Downstream Capacity Analysis
The sanitary sewer mains were designed in conformance with the City of Bozeman Wastewater
Improvement Plan. The sewer effluent from the proposed development will flow into the existing
Meadow Creek Trunk Sewer which was designed for this property. A capacity letter from a City
Engineer will be required prior to DEQ approval of the system.
E. Conclusion
As outlined above, a proposed 8-inch sanitary sewer collection system serving the residential
development has the capacity for the effluent generated from the subdivision. The wastewater
sewer collection system was designed on a conservative premise for future development. This
project will require the approval of the City of Bozeman Engineer and MDEQ.
2131 GRAF MULTI-UNIT RESIDENTIAL DEVELOPMENT
WATER SYSTEM DESIGN REPORT
A. General
This design report will give an overview of the proposed water main extension for the development
of the “2131 Graf” Multi-Unit Residential Development Infrastructure Improvements. The
proposed Phase 1 improvements are anticipated to be constructed during the fall of 2020. Once the
water main is constructed and approved, the main will become a part of the City of Bozeman
system.
The following references were used in the preparation of this report:
a. COB Design Standards and Specifications Policy, 2017. Addendum #7
b. COB Modifications to Montana Public Works Standard Specifications (MPWSS).
c. MDEQ Circular No. 1
d. City of Bozeman Zoning Map
e. City of Bozeman Water Facility Plan
f. 2015 International Fire Code
Existing System
The proposed water main extension will be served by the existing City of Bozeman water
distribution system, which will be looped. The two connection locations are at Lantern Drive and
at the intersection of Graf Street and S 21st Avenue. There will also be a connection on S 21st Ave
with the Nexus Point project to the north. The following information was obtained by the City of
Bozeman at the intersection of Lantern Lane and Enterprise Boulevard.
Fire Hydrant: 2077
Static Pressure: 65 psi
Pitot Pressure: 56 psi
Residual pressure: 57 psi
Hydrant discharge: 1,250 gpm from 2.5” port
Distribution Main Capacity – Fire flow at minimum residual pressure
Qr = Qt[(Ps – Pm)/(Ps – Pt)]0.54
Qr = 1,250 [(65 –20)/(65 – 56]0.54
Qr = 2,981 gpm at 20 psi
Qt = Hydrant Discharge during Test
Qr = Fire Flow at Residual Pressure
Ps = Static Pressure
Pm = Minimum Residual Pressure = 20 psi
Pr = Residual Pressure
Pt = Pitot Pressure
B. Proposed Water System
The proposed water main extension for the project consists of approximately 4,060 linear feet of
8” ductile iron pipe that will connect to the existing water main in Graf St at S 21st Ave and the
existing main at Lantern Drive. The layout of the proposed water main meets the COB design
criteria and will be located within the easements/right of way and separated from the proposed
sanitary sewer main by a minimum of 10 feet horizontally. Fire hydrants will be installed within
COB design criteria and will not exceed the recommended distance.
C. Capacity Analysis
The water main extension is proposed for the development of the 18 buildings comprised of 460-
units, which sits on an estimated 25.99 acres of R-4 (Residential High Density) zoned land. An
estimation of the water flow rate was based on the City of Bozeman’s design standards and
specification policy, which suggests using an average daily flow rate of 2.11 people per dwelling
unit and 170-gallons per capita per day. Applied to the 460 units, the required water flow rate is
calculated:
൬457 units ∗ 2.11 residents
unit ∗ 170 gallons
capita day ൰ = 163,926 gpd
Based on these parameters, the 457-unit development at full build out will have an estimated water
usage of 163,926 gpd (113.84 gpm). The main will connect to the existing City of Bozeman system
and will serve the future Graf Street apartment buildings.
In addition to the average daily demand, the water main extension must account for peak periods
of daily use. Peaking factors are applied to the demand and account for these peak periods in daily
use. The peaking factors used are maximum daily use and peak hour and are obtained from the
City of Bozeman Design Standards. Table 1 shows the peaking factors and the resultant flows
from those factors when applied to the average daily demand of 113.84 gpm.
TABLE 1
PEAKING FACTORS
Flow Designation Peaking Factor Flow (gpm)
Average Day Demand 1 113.8
Maximum Day Demand 2.3 261.8
Maximum Hour
Demand
3 341.5
Based on communication with the architect, there will be three types of buildings that will consist
of four (4)-3 plex (Type A), nine (9)-32 plex (Type B), and five (5)-32 plex (Type C) for a total of
18 individual buildings. The square footage for each type of building are as follows: Type A =
5,072sf, Type B = 32,647sf and Type C = 38,647sf. The units will be V-A and V-B type
construction with fire sprinklers. A Type V-A 38,227sf building requires 3,500 gpm for a 3-hour
flow duration per the 2015 International Fire Code, Table B105.1(2). The flow capacity for the
largest apartment building was chosen to be more conservative. Based on the 2015 International
Fire Code’s Table B105.2, the 3,500 gpm fire flow can be reduced but shall not be less than the
minimum of 1,500 gpm.
D. Results
Based on the analysis outlined above, the required minimum fire flow is 1,500 gpm and with the
maximum hour demand of 341.5 gpm, a maximum hour flow of 1,841.5 gpm is required. The flow
analysis attached states a required fire flow of 1,500 gpm, which includes an additional max hour
demand of 341.5 gpm is analyzed throughout the system. The flow analysis shows that an 8-inch
DI pipe can provide the development with the required flow of 1,841.5 gpm and remain above the
minimum pressure of 20 psi. See attached flow analysis for calculations.
E. Conclusion
Based on this analysis, the proposed 8-inch ductile iron water main serving the Graf residential
development extension provides adequate service to meet the 457-unit peak hour demand and fire
flows requirements for the development. The water main was designed on conservative premise
for future development. The water main design is consistent with the City of Bozeman Water
Facility Plan.
This project will require the approval of the City of Bozeman Engineer and MDEQ.
Appendix:
Capacity Calculations
WaterCAD Fire Flow Report