HomeMy WebLinkAboutSanitary Sewer Memo 1
Sewer
This section is a response to the requirements of the City of Bozeman Unified Development
Ordinance Section 38.220.060 relative to Water and Sewer. The original Sanitary Sewer Design
Report provides analysis for the entire PUD. The sewer main in Fowler/Avenue serves roughly
the west two-thirds of the Bozeman East Subdivision including Phase 5. The remainder of the
subdivision is served by a connection just south of the Huffine Lane/College intersection.
Flows from Phase 5 are designed to flow east to the existing sewer main in Fowler Avenue. Per
the original design report the sanitary sewer segment for Phase 5 is termed “1W”. With the
design of Lot 1 & 2, the layout has been revised so that the flows are split into “1.1W” and
“1.2W” (see updated sewer main exhibit). “1.1W” will be sewer flow from Lot 2 that flow east
via Technology Boulevard West. “1.2w” will be sewer flow from Lot 1 that will flow via a sewer
service directly into the sewer main in Fowler Road.
Appendix A “The Bozeman Gateway” Sewer Flow Spreadsheet-West Drainage Basin, indicates
that the with a design flow rate of 3495 gpd/ac, that the peak flow from Phase 5 will be 85.1gpm.
More broadly, the table from Appendix A indicates that the total peak flow from the west side of
Bozeman Gateway is 435.3gpm.
Since the report was written, the City of Bozeman Design Standards and Specifications have
been revised to reflect a lower required flow rate for B-2 zoning, decreasing from 3495
gal/ac/day to 2000 gal/ac/day. Based on the Sewer Facility Plan’s revised flow of 2000
gal/ac/day, the wastewater produced by Phase 5 as well as the total flows from the west side of
the subdivision is calculated as follows:
Sewer Flow - Phase 5
Assumptions:
- Phase 5 Area – 6.9 acres
- Design Flow Rate – 2000gpd/ac
- Proposed Hotel has 138 rooms
- Proposed Hotel guest occupancy rate of 1.5 guests per room = 207 guests
- Proposed Hotel will have approximately 15 employees
Phase 5 Average Flow Rate 6.9 acres x 2000gpd/ac = 13,800gpd = 0.02cfs = 8.98gpm
Population = 207 guests + 15 employees = 222 people
Peaking Factor (PF) = (18+(population/1000)^0.5)/(4+(population/1000)^0.5) = 4.13
Peak Flow = 13,800gpd (avg daily flow) x 4.13 = 56,994gpd
Infiltration = 150 gpd/acre x 6.9 acres = 1,035gpd
2
Total Peak Flow Phase 5 = 56,994gpd + 1,035gpd = 58,029gpd = 0.09cfs = 40.3gpm
Sewer Flow – Western Side of Bozeman Gateway
Assumptions:
- Western Side Area - 48.7 acres
- Design Flow Rate – 2000gpd/ac
- Peaking Factor – 3.53
West Side Average Flow Rate = 48.7 acres x 2000gpd/ac = 97,400gpd
Peak Flow = 97,400gpd (avg daily flow) x 3.53 = 343,822gpd
Infiltration = 150 gpd/acre x 48.7 acres = 7,305gpd
Total Peak Flow West Side = 343,822gpd + 7,305gpd = 351,127gpd = 0.54cfs = 243.9gpm
Impact on Existing Wastewater Facilities
The manhole located at the intersection of Fowler and Technology Blvd was dipped on
12/30/2019 and was found to have a sewage depth of 0.2’. Due to the timing of this measurement
during the holiday season, it is conservatively assumed that the average existing flow depth is
0.5’. The outlet pipe has a diameter of 21”. At a depth of 0.5’ the pipe is approximately 29% full
and flowing at a rate of 1.06cfs (475.8gpm), see attached Existing Pipe Flow report. Assuming a
minimum slope of 0.1%, the 21” pipe has a capacity flowing full of 6.3cfs (2,827.6gpm), see
attached 21in PVC Flowing Full report.
The contribution of 0.09cfs from Phase 5 will increase the flow to 1.15cfs (516gpm) which
equates to a pipe depth of 0.53 or 30.3%, see attached Proposed Pipe Flow Report. The existing
sewer mains 21” pipe in the vicinity of the project can handle the increase in flows based on the
information in the original Sanitary Sewer Design Report, the reduction in B-2 design flow rates
and the existing measured flow.
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Dec 31 2019
Existing Pipe Flow
Circular
Diameter (ft) = 1.75
Invert Elev (ft) = 100.00
Slope (%) = 0.10
N-Value = 0.011
Calculations
Compute by: Known Depth
Known Depth (ft) = 0.50
Highlighted
Depth (ft) = 0.50
Q (cfs) = 1.061
Area (sqft) = 0.57
Velocity (ft/s) = 1.86
Wetted Perim (ft) = 1.98
Crit Depth, Yc (ft) = 0.37
Top Width (ft) = 1.58
EGL (ft) = 0.55
0 1 2 3
Elev (ft)Section
99.50
100.00
100.50
101.00
101.50
102.00
Reach (ft)
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Sunday, Dec 29 2019
21in PVC Flowing Full
Circular
Diameter (ft) = 1.75
Invert Elev (ft) = 100.00
Slope (%) = 0.10
N-Value = 0.011
Calculations
Compute by: Q vs Depth
No. Increments = 10
Highlighted
Depth (ft) = 1.58
Q (cfs) = 6.312
Area (sqft) = 2.28
Velocity (ft/s) = 2.77
Wetted Perim (ft) = 4.38
Crit Depth, Yc (ft) = 0.93
Top Width (ft) = 1.05
EGL (ft) = 1.69
0 1 2 3
Elev (ft)Section
99.50
100.00
100.50
101.00
101.50
102.00
Reach (ft)
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Thursday, May 14 2020
Proposed Pipe Flow
Circular
Diameter (ft) = 1.75
Invert Elev (ft) = 100.00
Slope (%) = 0.10
N-Value = 0.011
Calculations
Compute by: Known Q
Known Q (cfs) = 1.15
Highlighted
Depth (ft) = 0.53
Q (cfs) = 1.150
Area (sqft) = 0.62
Velocity (ft/s) = 1.85
Wetted Perim (ft) = 2.05
Crit Depth, Yc (ft) = 0.39
Top Width (ft) = 1.61
EGL (ft) = 0.58
0 1 2 3 4
Elev (ft)Depth (ft)Section
99.50 -0.50
100.00 0.00
100.50 0.50
101.00 1.00
101.50 1.50
102.00 2.00
Reach (ft)
OPEN SPACE 2
OPEN SPACE 3
OPEN SPACE 4
COMMON AREA 1ALOT 1A1
LOT 3A
LOT 1A LOT 4 LOT 5
LOT 6
LOT 7
LOT 5
OPEN SPACE 5COMMON AREA 2A
OPEN SPACE 6
LOT 14A COMMON AREA 3A LOT 16A
COMMON AREA 4A
LOT 17A
LOT 25A
LOT 22B
LOT 46
LOT 45
COMMON AREA 12
LOT 48
COMMON AREA 7
COMMON AREA 6A
LOT 24A
LOT 23A
OPEN SPACE 10
LOT 1
LOT 2
LOT 3
LOT 4
LOT 1A
LOT 5
LOT 6
LOT 3 LOT 4
OPEN SPACE 1
LOT 1
LOT 6
LOT 7
COMMON AREA 5A LOT 19A
LOT 2A1
LOT 4A
LOT 35
LOT 36
COMMON AREA 11
LOT 37
LOT 38
COMMON AREA 10
LOT 40
LOT 41
LOT 42
COMMON AREA 14 COMMON AREA 13
LOT 44 LOT 43
OPEN SPACE 1B
COMMON AREA 8
OPEN SPACE 1A
LOT 2
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CONNECTION POINT
EXST. MH JO516
CONNECTION POINT
EXST. MH JO602
2W
1.1W
3W
5W
4W
1E
2E
3E
4E
1W ANALYZED SANITARY SEWER SEGMENT
SEE APPENDIX A & B
PROPOSED SANITARY
SEWER MAIN
PROPERTY BOUNDARY
LEGEND
SSWWWW W
W
SSSS
1.2W
BOZEMAN GATEWAY
SEWER LAYOUT