HomeMy WebLinkAboutSanitary Sewer Design Report 06-25-19 SEWER MAIN
DESIGN REPORT
FOR:
NEXUS POINT
DEVELOPMENT
BOZEMAN, MT
Madison Engineering
895 Technology Blvd Ste 203
Bozeman, MT 59718
(406) 586-0262
MAY 2019
NEXUS POINT 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 Nexus Point development on Lot I of minor sub 235 located in S23, T02S,
R05E P.M.M, located west of south 19'Avenue and north of Lantern Lane in Bozeman, MT.
The zoning for the 19.99 acre area is listed as R-O, residential office district. The proposed
buildings are designed as two (2)-multi-floor office buildings, six (6)-12 plex 2-bedroom units,
four (4)-30 plex 1 & 2-bedroom units and two (2)-24 plex 2-bedroom units along with a club
house for a total of 240 units in the residential development. The improvements for Phase I of
the development are anticipated to be constructed during the fall of 2019.
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#6
b. COB Modification to Montana Public Works Standard Specifications (MPWSS)
c. City adopted MPWSS and adopted Addenda
d. COB Wastewater Facility Plan, 2017
e. WQB 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 3,234 linear feet (0.61 miles) of new 8"
sewer main and will provide service to the multi-unit residential & office development. The
effluent generated from the proposed buildings will be collected by the wastewater collection
system and ultimately flow west and north to existing COB Manhole's located in Lantern Lane
and South 19t`Avenue.
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 980 gaUac-day for R-O zoning, resulting in 15,533 gpd =
15.85 ac x 980 gaUac-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.
Nexus Point Development
Wastewater Design Report
Page 1 of 3
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:
residents gallons l _
(240 units * 2.11 unit * 89 capita/day J — 45,070 gpd
An approximate population for the Nexus Point Multi-Unit Residential Development at full build
out is calculated as:
residents
240 units * 2.11 =unit 507 persons
This is a more realistic population value compared to utilizing the 5.2 units per acre (Table V-1
from COB design standards) applied to 15.18 acres, which only results in 79 persons.
This equivalent population can be utilized to determine a peaking factor:
(Qmax _ 18 + P` _ 18 +.507.5
QAve
4 + P,5 4 +. 507 s = 3.97
(P =Population/thousands)
Based on a total population of 507 people, a peaking factor of 3.97 was calculated. The peak flow
rate anticipated from the development based on an average daily flow of 45,070 gallons per day
is:
Peak Flow Rate= (45,070 gpd x 3.97) =178,928 gpd
= 125 gpm
= 0.28 cfs
Additionally, an infiltration flow of 2,378 gpd (150 gal/acre/day x 15.85 acres) has been added to
the flow, resulting in a total flow of 181,306 gpd(0.28 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 3/4 pipe depth, which has adequate capacity for the proposed peak flow of 0.28 cfs effluent
generated from the site. Calculations are included in the end of this report.
C. Proposed Collection System
PVC pipe meeting COB specifications will be used for the sewer mains. The effluent from the
Nexus Point multi-unit residential development will drain into a proposed 8-inch diameter sanitary
sewer main via 4-inch sewer services. The effluent in the 8-inch wastewater collection system on
Arnold Street will flow north to proposed manholes before turning east and connecting to an
Nexus Point Development
Wastewater Design Report
Page 2 of 3
existing manhole located on South 19th Avenue, the wastewater collection system on Lantern Lane
will flow west to an existing manhole. The maximum manhole spacing will be 400 feet for the fl-
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. It is anticipated that the City of Bozeman sanitary sewer system has enough
capacity to accommodate the main extension. 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.
Nexus Point Development
Wastewater Design Report
Page 3 of 3
8-inch PVC Pipe Capacity_
Project Description
Friction Method Manning Formula
Solve For Discharge
Input Data
Roughness Coefficient 0.013
Channel Slope 0.40000 %
Normal Depth 5.68 in
Diameter 8.00 in
Results
Discharge 0.64 ft/s
Flow Area 0.26 ft'
Wetted Perimeter 1.32 ft
Hydraulic Radius 2.37 in
Top Width 0.61 ft
Critical Depth 0.38 ft
Percent Full 69.8 % (93%full flow capacity x 75%flow depth)
Critical Slope 0.00748 ftM
Velocity 2.45 ft/s
Velocity Head 0.09 ft
Specific Energy 0.56 a
Froude Number 0.66
Maximum Discharge 0.82 fr/s
Discharge Full 0.76 fN/s
Slope Full 0.00278 ft/ft
Flow Type SubCrflical
GVF Input Data
Downstream Depth 0.00 in
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth O.OD In
Profile Description
Profile Headloss 0.00 ft
Average End Depth Over Rise 0.00 %
Normal Depth Over Rise 69.75 %
Downstream Velocity Infinity ft/s
Bentley Systems,Inc. Heestad Methods SolabdloelNwvMester VBI(SELECTseries 1) [08.11.01.031
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