HomeMy WebLinkAbout018 - Appendix N - Sewer Report
MEADOW BRIDGE SUBDIVISION
Project 05021.28
Bozeman, MT
JANUARY 2025
January 2025
Project No. 05021.28
SANITARY SEWER DESIGN REPORT
FOR
MEADOW BRIDGE SUBDIVISION BOZEMAN, MONTANA
11.1 PROBLEM DEFINED
This report describes the existing and proposed sanitary sewer mains which have been
proposed to serve the new Meadow Bridge Subdivision in Bozeman, MT. The water and
sanitary sewer infrastructure to serve the proposed development is from the City of
Bozeman and is located within the right-of-way surrounding the project site. A new
sanitary sewer main extension within the proposed Alley A will serve the lots adjacent
to Alley A and will connect to the existing sanitary sewer main on Parkway Avenue. A
new sanitary sewer main extension within Last Loop Drive and south to Alley B will
serve the lots adjacent to Last Loop Drive and Alley B. Lastly, a sanitary sewer main
extension within South 23rd Avenue will serve the lots adjacent to that road. The other
lots will have services extended from existing sanitary sewer mains within South 23rd
Avenue and Last Loop Drive.
11.12 DESIGN CONDITIONS
The anticipated existing and proposed hydraulics are discussed in Section 11.24
Hydraulic Capacity. The capacity of the proposed gravity sewer main extension will be
based on the estimated demands per the estimated additional dwelling units (DU)
and people per DU utilizing City of Bozeman Design and Construction standards
(Draft 7/1/2024).
11.13 IMPACT ON EXISTING WASTEWATER FACILITIES
The proposed sewer main extension will convey sewage away from the proposed lots
and into the City of Bozeman’s sanitary sewer collection system for further
conveyance and ultimately treatment.
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11.14 PROJECT DESCRIPTION
The proposed site will utilize existing 8-inch PVC sanitary sewer mains within South
23rd Avenue, Last Loop Drive, and Parkway Avenue. A new 8-inch PVC sanitary sewer
main is proposed to extend within city right-of-way within Alley A, Alley B, Last Loop
Drive, and South 23rd Avenue, to serve the lots adjacent to those alleys/roads. The new
8-inch sanitary sewer main in Alley A will connect to the existing sanitary sewer main
within Parkway Avenue with a new manhole connection. The new 8-inch sanitary sewer
main in Last Loop Drive and Alley B will extend from an existing manhole in Last Loop
Drive. The 8-inch sanitary sewer main extension in South 23rd Avenue will extend from
an existing manhole in South 23rd Avenue which is immediately conveyed east within
an existing alley. The existing sanitary sewer mains and proposed extensions will serve
the proposed subdivision. The sanitary sewer collection system and treatment will be
provided by the City of Bozeman.
11.15 DRAWINGS
Enclosed are copies of the technical plans and specifications.
11.16 DESIGN CRITERIA
The sanitary sewer main extensions have been designed, and will be installed, in
accordance with the criteria set forth in the City of Bozeman Design and Construction
standards and Circular DEQ-2. The sanitary sewer main extensions have been sized to
flow at no more than 75-percent of full capacity at peak hour conditions. Minimum
main line slopes, complying with Circular DEQ-2, have been assumed to be
conservative and a Manning’s friction factor of 0.013 has been utilized per the City of
Bozeman requirements. The design flow is based on the City of Bozeman guidelines for
residential areas of 64.4 gallons per capita per day (gpcd) at 2.17 people/DU. A base
infiltration rate of 150-gallons/acre/day has been applied to the gross area of the
development. Hydraulic calculations have been included in Section 11.24 Hydraulic
Capacity.
11.17 SITE INFORMATION
The existing project site is approximately 25.32-acres and is currently undeveloped.
The site is located within Gallatin County and is surrounded by existing developments.
There are no known sources of pollution that may influence the quality of water supply
or interfere with the effective operation of the water works or sanitary sewer collection
system.
There are no known or confirmed geologic hazards/unusual features for this site.
Recent geotechnical borings indicate that topsoil exists in depths from zero (0) inches
to twelve (12) inches throughout the site. The topsoil layer is underlain by poorly graded
Sanitary Sewer Design Report Page 3 of 5 January 2025
gravel at an average depth of one (1) foot. Groundwater was encountered during the
geotechnical exploration and subsequent groundwater monitoring at an average
depth of 6 feet. The approximate groundwater flow is northerly.
11.18 ALTERNATIVE SELECTION/ANALYSIS
No alternatives were considered as the property is within the Bozeman City limits and
conventional gravity sanitary sewer collection is feasible.
11.19 ENVIRONMENTAL IMPACTS
The environment is improved by connecting to the City of Bozeman sanitary sewer
collection system rather than individual or combined onsite disposal systems which
have the potential to impact ground and surface waters.
11.24 HYDRAULIC CAPACITY
11.24.1 FLOW DEFINITION AND INDENTIFICAITON
An Excel spreadsheet has been prepared to analyze the existing and proposed sanitary
sewer mains.
The average daily demand (ADD) is based on the average daily usage of 64.4 GPCD and
2.17 people/DU. Dwelling units per lot were assumed based on lot sizes and feasibility
of construction based on setbacks and allowed lot coverages. Lots greater than 9,000
square feet (SF) were assigned 3 DU, lots between 6,000 SF and 9,000 SF were assigned
2 DU, and lots less than 6,000 SF were assigned 1 DU.
Peaking factors, based on the formula below, were applied to the calculated ADD to
calculate the Peak Hour Demand (PHD).
The sanitary sewer demand for the subdivision is summarized in Table 1 below and
additional calculations are provided in Appendix A.
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Table 1. Sanitary Sewer Demand Summary
Sanitary Sewer Discharge Location ADD
(gpm)
PHD
(gpm)
Alley A 3.60 14.29
Alley B 0.63 2.52
Last Loop Drive 4.58 18.10
S 23rd Ave 0.64 2.53
Existing Alley 1.05 4.19
Total 10.49 41.62
11.24.2 HYDRAULIC CAPACITY FOR WASTEWATER FACILITIES TO SERVE EXISTING
COLLECTION SYSTEM
This section is not applicable.
11.24.3 HYDRAULIC CAPACITY FOR WASTEWATER FACILITIES TO SERVE NEW
COLLECTION SYSTEM
The designated flows calculation in section 11.24.1 Flow Definitions and Identification
will be conveyed from to the City of Bozeman’s sanitary sewer collection system via
gravity. The capacity of the existing/proposed 8-inch sewer mains at the minimum
0.4 percent design slope is 344-gpm. Assuming the pipe does not exceed 75 percent
of full flow capacity, then the available capacity at 75 percent of full flow is 258-gpm.
The available pipe capacity exceeds the calculated peak hour demand at every
discharge location, so the existing/proposed sewer mains are appropriately sized to
convey the anticipated sewer demands. See Appendix B for pipe hydraulic capacity
calculations.
The City of Bozeman will convey the designated flows to their wastewater facility
within their wastewater collection system. Inflow and Infiltration (I&I) is assumed to
be minor relative to the sewage flows since the proposed sewer main extension will
utilize standard PVC push-on joints. However, to be conservative, 150 gal/acres/day
demand has been added to the available main capacity to account for potential I&I.
Manholes will not be installed in low points where surface water has the potential to
pool above the rim and seep into the sewer collection system.
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Should you have any questions, I can be reached at 406-922-4308 to further discuss
this report.
Sincerely,
Bobby Egeberg, PE
Bozeman Land Development Manager
MEADOW BRIDGE SUBDIVISION
Project 05021.28 APPENDIX A SANITARY SEWER DEMANDS
Lot Size (sf) Size (acres)Sewer Service Discharge LocationNumber of Dwelling UnitsNumber of People per Dwelling UnitSewer Demand (gpcd)Infiltration (gal/acres/day)ADD without Infiltration (gpd)ADD with Infiltration (gpd)ADD with Infiltration (gpm)PHD (gpm)111,2210.258Alley A32.1764.4150419.24457.880.321.26211,7990.271Alley A32.1764.4150419.24459.870.321.26312,8820.296Alley A32.1764.4150419.24463.600.321.27410,2000.234Alley A32.1764.4150419.24454.370.321.26510,2000.234Alley A32.1764.4150419.24454.370.321.26610,2000.234Alley A32.1764.4150419.24454.370.321.26711,6950.268Alley A32.1764.4150419.24459.520.321.2689,0170.207Alley A32.1764.4150419.24450.290.311.2698,2500.189Alley A22.1764.4150279.50307.910.210.84108,8240.203Alley A22.1764.4150279.50309.880.220.84119,0390.208Alley A32.1764.4150419.24450.370.311.261210,3720.238Alley A32.1764.4150419.24454.960.321.261314,0540.323Last Loop Drive32.1764.4150419.24467.640.321.271412,4570.286Last Loop Drive32.1764.4150419.24462.140.321.261512,5060.287Last Loop Drive32.1764.4150419.24462.310.321.261612,3960.285Last Loop Drive32.1764.4150419.24461.930.321.261712,4110.285Last Loop Drive32.1764.4150419.24461.980.321.26189,6210.221Last Loop Drive32.1764.4150419.24452.370.311.26199,5100.218Last Loop Drive32.1764.4150419.24451.990.311.26208,5120.195Last Loop Drive22.1764.4150279.50308.810.210.84218,7910.202Last Loop Drive22.1764.4150279.50309.770.220.84229,9410.228Last Loop Drive32.1764.4150419.24453.480.311.26236,6820.153Last Loop Drive22.1764.4150279.50302.510.210.84246,4790.149Alley B22.1764.4150279.50301.810.210.84256,4790.149Alley B22.1764.4150279.50301.810.210.84266,4790.149Alley B22.1764.4150279.50301.810.210.842711,9290.274Last Loop Drive32.1764.4150419.24460.320.321.26286,3130.145Last Loop Drive22.1764.4150279.50301.230.210.84294,8840.112Last Loop Drive12.1764.4150139.75156.570.110.42306,4540.148Last Loop Drive22.1764.4150279.50301.720.210.84316,1750.142Last Loop Drive22.1764.4150279.50300.760.210.84325,5270.127Last Loop Drive12.1764.4150139.75158.780.110.42335,1980.119Last Loop Drive12.1764.4150139.75157.650.110.42345,8500.134Last Loop Drive12.1764.4150139.75159.890.110.43354,0000.092S 23rd Ave12.1764.4150139.75153.520.110.42364,0000.092S 23rd Ave12.1764.4150139.75153.520.110.42374,0000.092S 23rd Ave12.1764.4150139.75153.520.110.42384,0000.092S 23rd Ave12.1764.4150139.75153.520.110.42394,0000.092S 23rd Ave12.1764.4150139.75153.520.110.42404,0000.092S 23rd Ave12.1764.4150139.75153.520.110.42416,0020.138Existing Alley22.1764.4150279.50300.160.210.84426,0020.138Existing Alley22.1764.4150279.50300.160.210.84436,0020.138Existing Alley22.1764.4150279.50300.160.210.84446,0020.138Existing Alley22.1764.4150279.50300.160.210.84458,3950.193Existing Alley22.1764.4150279.50308.400.210.84Total368,750 8.465 N/A 99 2.17 64.4 150 13835.05 15104.85 10.49 41.62Meadow Bridge Sanitary Sewer Demands
Sanitary Sewer Discharge Location ADD (gpm) PHD (gpm)Alley A3.6014.29Alley B0.632.52Last Loop Drive4.5818.10S 23rd Ave0.642.53Existing Alley1.054.19 Sanitary Sewer Demand SummaryMeadow Bridge Subdivision
MEADOW BRIDGE SUBDIVISION
Project 05021.28 APPENDIX B HYDRAULIC CALCULATIONS
Project: Meadow Bridge SubdivisionDate: 01/06/2025Capacity Calculations - Alley A8" Pipe Flowing Full Capacity0.77cfs8" Pipe Flowing Full Capacity344gal/minQ/Qfill @ 75% full, 0.75per nomographCapacity @ 75% full258gal/minSystem DemandDESIGNATIONR-3 ZoningDemandResidential Demand4751gal/day3.30gal/minPeaking Factor (per City of Bozeman formula)4.24Peak Hourly Flow13.99gal/minInfiltration at 150 gal/acres/day426gal/dayInfiltration gal/min0.30gal/minTotal Peak Hourly Flow plus Infiltration14.29gal/minResultQ/Qfull based on peak hour0.04Percent Full for 8" From Nomograph at peak hour16%Alley A Service Area
Project: Meadow Bridge SubdivisionDate: 01/06/2025Capacity Calculations - Alley B8" Pipe Flowing Full Capacity0.77cfs8" Pipe Flowing Full Capacity344gal/minQ/Qfill @ 75% full, 0.75per nomographCapacity @ 75% full258gal/minSystem DemandDESIGNATIONR-3 ZoningDemandResidential Demand838gal/day0.58gal/minPeaking Factor (per City of Bozeman formula)4.24Peak Hourly Flow2.47gal/minInfiltration at 150 gal/acres/day67gal/dayInfiltration gal/min0.05gal/minTotal Peak Hourly Flow plus Infiltration2.52gal/minResultQ/Qfull based on peak hour0.01Percent Full for 8" From Nomograph at peak hour5%Alley B Service Area
Project: Meadow Bridge SubdivisionDate: 01/06/2025Capacity Calculations - Last Loop Drive8" Pipe Flowing Full Capacity0.77cfs8" Pipe Flowing Full Capacity344gal/minQ/Qfill @ 75% full, 0.75per nomographCapacity @ 75% full258gal/minSystem DemandDESIGNATIONR-3 ZoningDemandResidential Demand6009gal/day4.17gal/minPeaking Factor (per City of Bozeman formula)4.24Peak Hourly Flow17.69gal/minInfiltration at 150 gal/acres/day583gal/dayInfiltration gal/min0.40gal/minTotal Peak Hourly Flow plus Infiltration18.10gal/minResultQ/Qfull based on peak hour0.05Percent Full for 8" From Nomograph at peak hour18%Last Loop Drive Service Area
Project: Meadow Bridge SubdivisionDate: 01/06/2025Capacity Calculations - S 23rd Ave8" Pipe Flowing Full Capacity0.77cfs8" Pipe Flowing Full Capacity344gal/minQ/Qfill @ 75% full, 0.75per nomographCapacity @ 75% full258gal/minSystem DemandDESIGNATIONR-3 ZoningDemandResidential Demand838gal/day0.58gal/minPeaking Factor (per City of Bozeman formula)4.24Peak Hourly Flow2.47gal/minInfiltration at 150 gal/acres/day83gal/dayInfiltration gal/min0.06gal/minTotal Peak Hourly Flow plus Infiltration2.53gal/minResultQ/Qfull based on peak hour0.01Percent Full for 8" From Nomograph at peak hour5%S 23rd Ave Service Area
Project: Meadow Bridge SubdivisionDate: 01/06/2025Capacity Calculations - Existing Alley8" Pipe Flowing Full Capacity0.77cfs8" Pipe Flowing Full Capacity344gal/minQ/Qfill @ 75% full, 0.75per nomographCapacity @ 75% full258gal/minSystem DemandDESIGNATIONR-3 ZoningDemandResidential Demand1397gal/day0.97gal/minPeaking Factor (per City of Bozeman formula)4.24Peak Hourly Flow4.11gal/minInfiltration at 150 gal/acres/day112gal/dayInfiltration gal/min0.08gal/minTotal Peak Hourly Flow plus Infiltration4.19gal/minResultQ/Qfull based on peak hour0.01Percent Full for 8" From Nomograph at peak hour8%Existing Alley Service Area