HomeMy WebLinkAbout26D Sanitary Sewer Report
THE LAKES AT VALLEY WEST
PLANNED UNIT DEVELOPMENT
WASTEWATER DESIGN REPORT
NOVEMBER 17, 2014
1
Table of Contents
Introduction .................................................................................................................................................. 2
Wastewater Flows ........................................................................................................................................ 2
Infrastructure within the Boundaries of the Planned Unit Development .................................................... 2
Offsite Infrastructure .................................................................................................................................... 2
Phases 1 and 2 .............................................................................................................................................. 3
Summary ....................................................................................................................................................... 3
Appendix A
Appendix B
2
Introduction
The Lakes at Valley West Planned Unit Development is projected to have approximately 300
dwelling units and will be completed in multiple phases. Wastewater service will be provided by
the City of Bozeman through a combination of existing infrastructure and newly constructed
infrastructure primarily located within the boundary of the Planned Unit Development. The
purpose of this report is to identify the capacity of the existing system, conceptual improvements
for the Planned Unit Development and specific improvements required for Phases 1 and 2 of the
PUD.
Wastewater Flows
The full build out of the PUD will have up to 300 dwelling units. Based on the City of Bozeman
Design Standards the total average daily wastewater flow will be 56,337 gallons per day. (89
gpdpc x 2.11 people per unit x 300 units) In addition, based on the Design Standards, the PUD
will contribute 9,750 gpd of infiltration. (65 acres x 150 gpd/acre) The total average daily flow is
computed to be 66,087 gpd and the peak flow from the PUD is computed to be 230,591 gpd
based on a peaking factor of 3.92. (56,337 gpd x 3.92 + 9,750 gpd)
Phase 1 and 2 consists of 59 dwelling units and 19.8 acres of property. Average daily
wastewater flow is computed to be 11,080 gpd. Infiltration is computed to be 2,970 gpd. Peak
flow is computed to be 49,728 gpd based on a peaking factor of 4.22.
Infrastructure within the Boundaries of the Planned Unit Development
The existing wastewater infrastructure within the boundary of the PUD consists of an 8” main
stub located at the intersection of Westgate Avenue and Durston Road and a forcemain that
provides service to the Norton Lift Station located south of the PUD.
All wastewater from the PUD will gravity flow to the existing sewer main stub located at the
intersection of Westgate Avenue and Durston Road. The new infrastructure located within the
boundary of the PUD will include sewer mains and sewer services. The sewer mains will all be
8” in diameter and services will primarily be 4” in diameter. The actual sewer service sizes will
be determined during each phase based on the detailed layout developed during that phase of
the project.
The proposed 8” sewer mains will have a peak flow of 230,591 gpd (160.1 gpm). The capacity
of an 8” main at minimum slope (0.004 ft/ft) and flowing at 75% depth utilizing an n factor of
0.013 is 313 gpm. Thus the proposed 8” mains will have adequate capacity for all phases.
Offsite Infrastructure
Wastewater will flow from the PUD through sewer mains, a lift station and a forcemain
constructed as part of the Laurel Glen Subdivision located immediately to the north of the PUD.
The Laurel Glen forcemain discharges into a sewer main constructed by the original Valley
West Subdivision and flows from that point through interceptors to the City of Bozeman’s Water
Reclamation Facility.
This existing offsite infrastructure has dedicated capacity of 49,088 gpd of wastewater flow on
an average day basis and an additional 6,600 gpd of infiltration capacity. These values are from
3
the design reports for the Laurel Glen Lift Station and are document in the memorandum
located in Appendix A.
This dedicated offsite capacity provides a total of 55,688 gpd average day flow capacity. For
The Lakes at Valley West PUD this will be utilized for 65 acres of infiltration capacity (9,750
gpd) with the remainder utilized for wastewater flow. Since the infiltration allowance is not
utilized with a peaking factor a review of the peak flow is required. The 49,088 gpd average day
wastewater flow equates to a peak flow of 166,899 gpd utilizing the peak factor of 3.40 that has
been established for the lift station. The allotted peak flow for wastewater is therefore 163,749
gpd. (166,899 gpd less additional infiltration requirement of 3,150 from the original allotment)
The resulting average day flow allotted for wastewater flow is therefore 48,161 gpd. The
available wastewater capacity is therefore 256 dwelling units based on 2.11 people/unit and 89
gpdpc.
Future improvements will be required to serve the PUD beyond the 256 dwelling units of
capacity that currently exist. A review of the available capacity of sewer mains between the
PUD and the Laurel Glen Lift Station has been completed and summarized in a memorandum
located in Appendix B. The memorandum documents adequate capacity to serve the PUD from
the point of connection to the lift station. Improvements to the lift station will most likely be
required when the PUD exceeds 256 dwelling units. Improvements downstream of the lift
station maybe required at that point. It is recommended as the PUD is developed that the
number of dwelling units be tracked. Depending on the actual number of dwelling units
eventually contemplated offsite infrastructure improvements may or may not be required.
Phases 1 and 2
The Lakes at Valley West, Phases 1 and 2 will be served by an 8” sewer main that begins at the
Intersection of Westgate Avenue and Durston Road, extends through future phases of the
Lakes at Valley West and contuse through the Phase 1 and 2 Subdivision to provide sewer
service to each lot within the development. Adequate capacity is available in the existing City of
Bozeman wastewater infrastructure and the proposed 8” mains will provide adequate capacity
for the development.
Summary
The existing City of Bozeman wastewater infrastructure in addition to the proposed 8” sewer
mains with the development will provide adequate capacity to serve 245 dwelling units in The
Lakes at Valley West Planned Unit Development. At this time, only 59 of the potential proposed
300 dwelling units have been fully defined. During the detailed future design of the project the
total number of dwelling units will be fully developed. If at that time, the number of units begin to
approach the documented 256 dwelling unit capacity, additional analysis will be required and it
is probable that offsite improvements will be needed.
Appendix A
Appendix B
TO: Greg Stratton
FROM: Jodie Binger and James Nickelson
RE: Valley West – Wing Lake Property
Existing Sewer Capacity Through Laurel Glen Subdivision to Lift Station
DATE: March 17, 2014
The existing 8” and 10” sewer mains within the Laurel Glen Subdivision were analyzed
to determine if the mains have adequate capacity to convey expected flows from the
proposed Valley West Subdivision. Existing flow was determined based on currently
built units and zoning classifications. Expected flow was determined based on the City
of Bozeman Design Standards. Both of the existing line sizes were shown to have the
capacity to include the proposed flows. Flow calculations and Figures are attached to
support these findings.
Based on a maximum number of units of 300 on the Valley West property the expected
flow from Valley West is 0.36 CFS. After build out of the Laurel Glen Subdivision, the 8”
outfall line has 0.61 cfs of capacity and the 10” outfall line has 0.71 cfs of capacity.
Thus adequate capacity exists to serve Valley West through these sewer mains.
Attachments: 8” Calculations with Supporting Map
10” Calculations with Supporting Map
Record Drawings of Laurel Glen Sewer
memo
Services 145.33 units
People 2.11 people
units
Flow 89 gal
person day
B1 zoning 6.53 acres
1000 gal
acre day
Infiltration 150 gal
acre day
Area 33.32 acres
Wastewater Flow (based on asbilts and plat)
average flow:145.33 units 2.11 people 89 gal -27292 gal
(units)units person day -day
average flow:6.53 acres 1000 gal -6530 gal
(B1)acre day -day
population:145.33 units 2.11 people -307 people
units -
0.31 people in thousands
peak flow:(18+P^.5)18.5537565 4.07 peaking factor
(4+P^.5)4.55375653
4.074385 33821.521 gal -137802 gal
day -day
infiltration:150 gal 33.316791 acres -4998 gal
acre day -day
total flow 137801.9 gal +4997.5186 gal -142799 gal
day day -day
99 gal
min
0.22 cfs
pipe flow (assume greater than 1/2 full)pipe flow (assume less than 1/2 full)
d 8 in d 8 in
n 0.013 n 0.013
k 1.486 k 1.486
s 0.003 ft/ft s 0.003 ft/ft
r 0.333 ft r 0.333 ft
h 0.402 ft h 0.265 ft
theta 3.557 rad theta 2.727 rad
A 0.129 ft^2 A 0.129 ft^2
P 0.909 ft P 0.909 ft
R 0.142 ft R 0.142 ft
q 0.22 cfs q 0.22 cfs
flow<1/2
Note: h>r therefore less than 1/2 full
Existing Flow in 8" Laurel Glen Sewer Line
Laurel Glen Pipe Flow Conditions
pipe flow
d 8 in
n 0.013
k 1.486
s 0.003 ft/ft
r 0.333 ft
h 0.167 ft
theta 2.094 rad
A 0.281 ft^2
P 1.396 ft
R 0.201 ft
q 0.60 cfs
0.38 cfs
172 gal
min
Services 300 services
People 2.11 people
service
Flow 89 gal
person day
Infiltration 150 gal
acre day
Area 65 acres
Wastewater Flow (based on proposed Valley West Subdivision)
average flow:300 services 2.11 people 89 gal -56337 gal
service person day -day
population:300 services 2.11 people -633 people
service -
0.63 people in thousands
peak flow:(18+P^.5)18.795613 3.92 peaking factor
(4+P^.5)4.79561297
3.919335 56337 gal -220804 gal
day -day
infiltration:150 gal 65 acres -9750 gal
acre day -day
total flow 220803.6 gal +9750 gal -230554 gal
day day -day
160 gal
min
0.36 cfs
Existing Line WILL Convey Flow From Proposed Valley West Addition
Allowable Future Flow (75% pipe full flow)
Q (allow from
Valley West)
Flow Expected From Valley West Proposed
Services 443.67 services
People 2.11 people
service
Flow 89 gal
person day
B1 zoning 6.53 acres
1000 gal
acre day
Infiltration 150 gal
acre day
Area 68.76 acres
Wastewater Flow (based on asbilts and plat)
average flow:443.67 services 2.11 people 89 gal -83317 gal
service person day -day
average flow:6.53 acres 1000 gal -6530 gal
(B1)acre day -day
population:443.67 services 2.11 people -936 people
service -
0.94 people in thousands
peak flow:(18+P^.5)18.9675452 3.82 peaking factor
(4+P^.5)4.96754519
3.818293 89846.789 gal -343061 gal
day -day
infiltration:150 gal 68.76322 acres -10314 gal
acre day -day
total flow 343061.4 gal +10314.483 gal -353376 gal
day day -day
245 gal
min
0.55 cfs
pipe flow (assume greater than 1/2 full)pipe flow (assume less than 1/2 full)
d 10 in d 10 in
n 0.013 n 0.013
k 1.486 k 1.486
s 0.004 ft/ft s 0.004 ft/ft
r 0.417 ft r 0.417 ft
h 0.467 ft h 0.366 ft
theta 3.385 rad theta 2.898 rad
A 0.231 ft^2 A 0.231 ft^2
P 1.208 ft P 1.208 ft
R 0.191 ft R 0.191 ft
q 0.55 cfs q 0.55 cfs
flow<1/2
Note: h>r therefore less than 1/2 full
Existing Flow in 10" Laurel Glen Sewer Line (phase 1 and 2)
pipe flow
d 10 in
n 0.013
k 1.486
s 0.004 ft/ft
r 0.417 ft
h 0.208 ft
theta 2.094 rad
A 0.439 ft^2
P 1.745 ft
R 0.251 ft
q 1.26 cfs
0.71 cfs
318 gal
min
Services 300 services
People 2.11 people
service
Flow 89 gal
person day
Infiltration 150 gal
acre day
Area 65 acres
Wastewater Flow (based on proposed Valley West Subdivision)
average flow:300 services 2.11 people 89 gal -56337 gal
service person day -day
population:300 services 2.11 people -633 people
service -
0.63 people in thousands
peak flow:(18+P^.5)18.795613 3.92 peaking factor
(4+P^.5)4.79561297
3.919335 56337 gal -220804 gal
day -day
infiltration:150 gal 65 acres -9750 gal
acre day -day
total flow 220803.6 gal +9750 gal -230554 gal
day day -day
160 gal
min
0.36 cfs
Allowable Future Flow (75% pipe full flow)
Q (allow from
Valley West)
Flow Expected From Valley West Proposed
Existing Line WILL Convey Flow From Proposed Valley West Addition