HomeMy WebLinkAbout17 - Design Report - South University District Ph 3 - Sewer
Sewer Main Extension Engineer’s Report
South University District Phase 2
June, 2017
Submitted to:
City of Bozeman Engineering Department
20 East Olive
Bozeman, MT 59715
Montana Department of Environmental Quality Permitting and Compliance Division
Public Water and Subdivisions Bureau
PO Box 200901
Helena, MT 59620-0901
Prepared by:
Stahly Engineering and Associates 851 Bridger Drive, Suite 1
Bozeman, MT 59715
(406) 522-9526
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Engineer’s Report
Contents
Note: The Engineer’s Report format follows DEQ-2 organization. Additional
information required by the City of Bozeman Design Standards is added where
required. Report Narrative
Chapter 10 – Engineering Reports & Facility Plans
11.1 Engineering Report - General Information 11.11 Problem Defined 11.12 Design Conditions
11.13 Impact on Existing Wastewater Facilities
11.14 Project Description
11.15 Drawings 11.16 Design Criteria 11.17 Site Information
11.18 Alternate Selection/Analysis
11.19 Environmental Impacts
Figures and Tables
Figure 1. Vicinity Map
Figure 2.a Sewer Site Plan (included separately)
Figure 2.b Sewer Site Plan (included separately) Figure 3 Sewer Capacity Analysis Map (included separately)
Table 1. SUD Phase 2 Sewer Flow Estimates
Table 2. Capacity of 8” SDR 35 PVC Sewer Main Table 3. Capacity of 10” SDR 35 PVC Sewer Main – Kagy to Lincoln Table 4. Areas Used to Analyze Impacts on Existing Wastewater
Facilities
Table 5. Capacity of 10” SDR 35 PVC Sewer Main - Lincoln
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11.1 Engineering Report
The South University District - Phase 2 is a subsequent minor subdivision
of Lot 3, SUD Subdivision Phase 1. The subsequent division will provide
right of way dedications for South 14th Avenue, South 11th Avenue, and an
additional street on the south side (currently un-named). This subdivision will create a 16.05-acre lot for subsequent development.
Phase 2 is located within the City of Bozeman south of Campus
Boulevard, between South 11th and South 14th Avenues. Phase 2 is
located south of Phase 1 (completed). Site development on the Phase 2 lot is anticipated to be an 887-bed student housing project.
The developer’s contact information is:
Capstone Collegiate Communities, LLC. 431 Office Park Drive
Birmingham, AL 35223
Water supply and wastewater treatment will be provided by the City of Bozeman’s municipal systems. The system owner’s contact information
is:
City of Bozeman Public Service Department
PO Box 1230 Bozeman, MT 59771-1230
The location of the South University District - Phase 2 is shown on the
Vicinity Map in Figure 1.
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Figure 1. Vicinity Map, Bozeman, Montana
11.11 Problem Defined
Currently, there are no sewer mains that can provide service to the lot
without the construction of additional off site infrastructure. The sewer
mains within SUD Phase 1 do not have capacity to serve all of SUD Phase 2. Therefore, to provide sewer service to Phase 2, a 10” offsite sewer main is proposed, extending from the intersection of Willow Way
and West Lincoln Street. The proposed main extension would head south
in Willow Way to Kagy Blvd. and then south through the existing SUD park
to Campus Blvd. The 10” main would extend south in S. 14th Avenue to serve future development south of SUD Phase 2. This proposed sewer main size and configuration is in accordance with the 2015 Bozeman
Wastewater Collection Facilities Plan Update. Furthermore, the capacity
expanding costs of this trunk main is included in the Capital Improvements
Plan. From this trunk main, 8” mains are proposed to extend along Campus
Blvd, the unnamed Street on the south side of the lot, and throughout the
interior of the Phase 2 site. The location of the proposed sewer mains
within SUD Phase 2 site are shown in Figure 2, and the proposed location of the offsite sewer main is displayed in Figure 3 at the end of this report.
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11.12 Design Conditions
The projected sewer flow rates from South University District - Phase 2
was determined with several different methods.
As described in the water system engineer’s report, water meter readings from SUD Phase 1 were analyzed. Phase 1 does not use City water for
irrigation, so the sewer flows would be the same as the water use. Based
on the meter readings the average annual water use is 40 gallons per day
(gpd) per person. This flow rate is used to determine impacts to the City’s wastewater treatment facility and thus sewer impact fees.
For regional sewer flow analysis a sewer flow rate of 64.4 gpd/person was
used in accordance with the 2015 Bozeman Wastewater Collection
Facilities Plan Update. This flow rate was used to assess off-site capacity of sewer mains.
For design of on-site sewer mains a design flow of 89 gpd/person was
used in accordance with the City of Bozeman Design Standards.
All analyses include an infiltration rate of 150-gallons/acre/day, and a
peaking factor depending on population served in accordance with the
City of Bozeman and MDEQ Design Standards.
The average annual flow and on-site design sewer flow estimates for Phase 2 are shown in Table 1, below.
Table 1 SUD Phase 2 Sewer Flow Estimates Average Annual Flow On-site Design Flow
Total Site Area (gross area in acres) 19.37 19.37
I&I rate gpd/acre 150 150
I&I Flow (gpd) 2905.5 2905.5
Student Housing Residents 887 887
Per capita flow (gpd)* 40 89
Student Housing Flow (gpd) 35,480 78,943
Total Daily Flow (gpd) 38,385.5 81,848.5
Total Daily Flow (gpm) 26.7 56.8
Peaking Factor N/A 3.83
Peak flow (gpm) N/A 217.9
*Note: Average Annual Per Capita Flow obtained from water use data from Phase 1 of the South
University District Project was found to be 38 .02 gpd/resident
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An 8” sewer main at minimum slope has sufficient capacity to provide sewer service for Phase 2. Table 2 shows that an 8” main has a 75% flow
depth capacity of 312.8 gpm installed at a minimum slope of 0.4%. See
Table 2 below for the parameters used in the SUD PH 2 sewer capacity
calculation.
Table 2 Capacity of 8" SDR 35 PVC Sewer Main Status Proposed
Location Phase 2
Pipe Material 8” SDR 35 PVC
Pipe Diameter (in) 8
Minimum Pipe Slope (ft/ft) 0.004
Coefficient of Roughness (n) 0.013
Depth in Pipe at 75% Full (in) 6
Depth of Flow (ft) 0.5
Pipe Radius (in) 4
Pipe Radius (ft) 0.33
Wetted Perimeter 1.40
Area of Flow (ft2) 0.28
Hydraulic Radius 0.20
Velocity (ft/sec) 2.48
Flowrate (cfs) 0.70
Maximum Pipe Flowrate (gpm) 312.8
Peak Flow % of 75% Flow Depth Capacity 69.6%
In accordance with the 2015 Bozeman Wastewater Collection Facilities
Plan Update a 10” trunk line is proposed to serve this drainage area. The
capacity of this line was analyzed to determine if a 10” main has adequate
capacity to serve this area. This proposed trunk line would serve future
development along Willow Way, future development along Kagy, SUD Phase 2, SUD Phase 3, SUD Phase 5 and undeveloped property to the
south of the South University District.
Sewer loading on this 10” trunk line was based on planned zoning,
existing zoning, and planned development density in accordance with the 2015 Bozeman Wastewater Collection Facilities Plan Update. The area
served by this main provides a planned peak flow of 490 gpm. The
proposed 10” trunk line has a 75% flow depth capacity of 695 gpm when
installed at a slope of 0.6%, a reasonable minimum slope for a north-south
main. Initial analysis shows this line should be a 10” to at least the south boundary of SUD Phase 2. See Table 3 below for the parameters used in
the 10” Trunk line sewer capacity calculation.
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Table 3 Capacity of 10" SDR 35 PVC Sewer Main
Status Proposed
Location Phase 2 & Full Build-out
Pipe Material 10” SDR 35 PVC
Pipe Diameter (in) 10
Minimum Pipe Slope (ft/ft) 0.006
Coefficient of Roughness (n) 0.013
Depth in Pipe at 75% Full (in) 7.5
Depth of Flow (ft) 0.625
Pipe Radius (in) 5
Pipe Radius (ft) 0.42
Wetted Perimeter 1.75
Area of Flow (ft2) 0.44
Hydraulic Radius 0.25
Velocity (ft/sec) 3.53
Flowrate (cfs) 1.55
Maximum Pipe Flowrate (gpm) 694.6
Peak Flow % of 75% Flow Depth Capacity 70.5%
Building sewer services can be sized at 4”, however, 6” services may be
used for easier maintenance. Services will be sized in accordance with
the Uniform Plumbing Code.
11.13 Impact on Existing Wastewater Facilities
The existing 10” sewer main along West Lincoln Street was examined to
determine if the main is adequately sized to handle additional impacts
from the development of SUD Phase 2. At the minimum slope of 0.28%,
the existing 10” main has a flow capacity of 475 gpm at 75% flow depth of the pipe as required by the City of Bozeman Design Standards and
Specifications Policy. The peak flow for SUD Phase 2 and the existing
developments that are served by this main is calculated to be 398 gpm,
within the pipe’s capacity (See Table 5)
However, peak flows during MSU football games add a significant flow to
the sewer. During the MSU 2011 fall semester, flow measurements were
obtained showing an additional 90 gpm during football games. Accounting
for this additional flow increases the peak flow to the existing 10” sewer
main on Lincoln to 488 gpm, slightly exceeding the 75% flow depth capacity (this flow results in a 77% flow depth). Please note that this
capacity exceedance would occur only during home football games
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(typically 6 per year), and is only an exceedance of the 75% flow depth, not the full pipe capacity.
The areas used for the calculation of the peak flow within this pipe are
graphically shown in Figure 3 at the end of this report. See Table 4 and 5 below for the parameters used in the SUD Phase 2 and existing developments flow capacity calculation.
Table 4 - Areas Used to Analyze Impacts on Existing Wastewater Facilities
Acres
Wastewater Flow Rate
(gal/acre/day)
Total Flow
(gpd)
Receiving
Manhole Description
Lincoln to Kagy
Residential R4.a 1.75 1456 2,548 H0609 Existing Fourplex S. of Lincoln
Residential R2 4 728 2,912 H0608 Existing Duplex Development
Residential R1 2 1456 2,912 H0608 Lincoln Residential Redveloped to R4
Residential RS 1.5 1456 2,184 H0606 Lincoln Residential Redeveloped to R4 Community Commercial B1 10 1000 10,000 H0603 11th and Lincoln Commercial
Residential R4 10 1456 14,560 H0603 Bird House Apartments and Offices
Kagy to Stucky
Business Park RO 16 728 11,648 H0603 Stadium Center
MSU Stadium 18.4 500 9,200 H0603 Existing Loading Estimate
SUD Phase 1 14 2433 34,069 H0603 Loading based on planned density
SUD Phase 1B 6 2324 13,944 H0603 Loading based on planned density
SUD Phase 2 24 2480 59,530 H0605 Loading based on planned density
Totals 108 163,507 gpd
114 gpm
3.503
peaking
factor
398 gpm
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Table 5 Capacity of 10" SDR 35 PVC Sewer Main - W. Lincoln St. Status Existing - W. Lincoln
St.
Location PH 2 & Ex.
Developments
Pipe Material 10” SDR 35 PVC
Pipe Diameter (in) 10
Minimum Pipe Slope (ft/ft) 0.0028
Coefficient of Roughness (n) 0.013
Depth in Pipe at 75% Full (in) 7.5
Depth of Flow (ft) 0.625
Pipe Radius (in) 5
Pipe Radius (ft) 0.42
Wetted Perimeter 1.75
Area of Flow (ft2) 0.44
Hydraulic Radius 0.25
Velocity (ft/sec) 2.41
Flowrate (cfs) 1.06
Maximum Pipe Flowrate (gpm) 474.5
Peak Flow % of 75% Max Capacity 83.9%
Looking ahead, once all future development that will utilize the sewer main
along W. Lincoln Street is complete, the peak flow will be approximately
841 gpm. This volume will require the sewer main between Willow Way
and S. 19th Ave to be sized at 15”, which will also be suitable to handle the increased peak flows from MSU football games.
11.14 Project Description
The SUD Phase 2 project is a student housing project to the south of the
recently completed Stadium View Apartments. The project falls within the
Master Planned SUD Residential Emphasis Mixed Use (REMU) zoning district.
268 student residential units are proposed within the project. Altogether,
the development of SUD Phase 2 will provide 887 student bedrooms.
11.15 Drawings
Please see attached Figure 2 showing proposed locations of the on-site
sewer mains.
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11.16 Design Criteria
The South University District – Phase 2 sewer main extensions were designed in accordance with Montana Department of Environmental Quality Circular 2, Montana Public Works Standards and Specifications,
City of Bozeman Modifications to Montana Public Works Standards and
Specifications, the Uniform Plumbing Code, and the City of Bozeman
Wastewater Facility Plan.
11.17 Site Information
The SUD Phase 2 site is typical of Bozeman with fine grained soils
overlying gravel deposits. Geotechnical borings have determined the
depth to gravel ranges from 8 to 10.5 feet. Estimated depth to
groundwater from the geotechnical borings is 8.5 to 12 feet. If mains are installed during high groundwater times dewatering may be required.
11.18 Alternative Selection/ Analysis
Due to the project’s location within the City of Bozeman, extension of
public mains was the only sewer supply alternative.
11.19 Environmental Impacts
Continued use and new extensions of City of Bozeman municipal sewer
mains has the least environmental impact. No new environmental impacts
will be caused by these sewer main extensions.
Calculation Sheet 2
South University District
Sewer Main Hydraulic Analysis
Existing Pipes with all potential Future Flows including all of SUD and offsite development
Sewer Loads
Area Breakdown by Zoning or Planned Land Use
Lincoln to Kagy
(sf)(ac)(gal/ac/day)(gpd)
1 R4 90,036 2.1 1950 4,031
2 R1 88,716 2.0 730 1,487
3 RS 65,449 1.5 1220 1,833
4 R2 181,359 4.2 980 4,080
5 County A 834,350 19.2 730 13,982
6 County B 992,386 22.8 1456 33,171
7 B1 460,873 10.6 1000 10,580
8 R4 463,928 10.7 1950 20,768
9 RO 676,957 15.5 980 15,230
10 MSU Stadium 799,299 18.3 500 9,175
11 SUD Phase 1B 252,977 5.8 2246 13,043
12 SUD PH 1 557,933 12.8 2660 34,069
Infiltration 125 150 18,816 13.07
13 REMU Willow Way 625,319 14.4 1456 20,901
14 R4 Willow Way 225,119 5.2 1950 10,078
15 SUD PH 2 Willow Way 843,741 19.4 3073 59,520
16 LOT 1 PH 3 Willow Way 458,500 10.5 1456 15,325
17 LOT 2 PH 3 Willow Way 495,062 11.4 1456 16,548
18 LOT 3 PH 3 Willow Way 932,671 21.4 1456 31,175
19 LOT 4 PH 3 Willow Way 615,844 14.1 1950 27,569
Infiltration 96.3 150 14,450 10.03
Totals 347 342,563 gpd
238 gpm
Sewer Capacity Calculations
Existing
Pipe
Size
Slope
(dh/dl)
Total
Daily Flow
(gpd)
Peaking
Factor
Peak Flow
(gpm)
Infiltration
(gpm)Total
Peak Flow
(gpm)
depth
of
flow
(in)
coeffic
ient of
rough
ness
(n)
radius
(in)
radius (ft)depth of
flow (ft)
wetted
perime
ter (ft)
area of
flow
(ft2)
hyd radius Velocity
(ft/sec)
75% Depth
Capacity
Flowrate
(gpm)
% Capacity
Q/Q 75
Lincoln 15 0.21%342,563 3.22 856 13.07 869 11.25 0.013 7.5 0.625 0.9375 2.62 0.99 0.38 2.7 1,212 72%
Willow 10 0.97%181,115 3.47 436 10.03 446 7.5 0.013 5 0.417 0.625 1.75 0.44 0.25 4.5 883 49%
Area Water Usage Rates1