HomeMy WebLinkAbout18 - Design Report - PT Lands Ph 3 - Water, Sewer
PT Land Subdivision
Phase 3
Public Utilities Design Report
June 2018
PT Land Subdivision Phase 3
Public Utilities Design Report i
TABLE OF CONTENTS
Introduction ............................................................................................................... 1
Project Description .................................................................................................. 1
Construction Drawings ............................................................................................... 1
Design Criteria ........................................................................................................ 1
Evaluation of Potential Impacts - Sanitary Sewer .................................................................. 1
Proposed Wastewater Flow ......................................................................................... 1
Lot 1 – Hotel/Banquet Center Design Flow .................................................................... 1
Lot 2/Block 4 & Lot 4/Block 3 – Projected Design Flows .................................................... 2
Infiltration Rate .................................................................................................... 2
Evaluation of Potential Impacts - Water Main ....................................................................... 4
Flow Requirements ................................................................................................... 4
List of Figures and Tables
Table 1: Estimated Average Day Flow ............................................................................... 3
Appendices
Appendix A: Hydrant Pressure Tests
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INTRODUCTION
This report includes the sanitary sewer and water main design information for the PT Land Phase 3
Subdivision and the proposed Embassy Suites – Hampton Inn development. The information is intended
to illustrate the impacts of the proposed sewer and water utilities on the City of Bozeman’s existing
systems.
Project Description
The proposed PT Land Phase 3 Subdivision is a subsequent minor subdivision of Lot 6A of PT Land Phase
2 Subdivision. This 32.51-acre lot is proposed to be divided into five (5) new lots for the purposes of
constructing a phased commercial development consisting of a hotel and a mixed-use complex with
retail, restaurant and commercial uses. The Phase I development will be a new Embassy Suites – Hampton
Inn hotel along with parking lots to meet parking requirements associated with Phase I, which will be
constructed on Lots 1 and 2 of Block 4. Phases II, III and future phases will include retail and restaurant
spaces to be constructed on Lot 2 of Block 4 and Lot 4 of Block 3. The proposed subdivision is generally
bound by Baxter Lane to the north, Tschache Lane and Patrick Street to the south, N. 15th Avenue to the
west and N. 11th Avenue to the east. The proposed land use for PT Land Subdivision Phase 3 is outlined
below:
Block 4
Lot 1 – Hotel/Banquet Center
Lot 2 – Undeveloped - Potential Future Uses Include Restaurant/Retail
Block 3
Lot 4 – Undeveloped – Future Use Not Known, anticipated as mixed commercial
Block 5
Common Open Space 1 and 2 – Undevelopable - Wetland/Storm Drainage Pond/Open
Space
Construction Drawings
Construction drawings for the project, including location and alignments, can be found attached as part
of this submittal package.
Design Criteria
Design criteria is in accordance with Montana DEQ Circular 2 - Design Standards for Public Sewage Systems
and Circular 4 – Montana Standards for Subsurface Wastewater Treatment Systems as well as City of
Bozeman Design Standards and Specifications Policy.
EVALUATION OF POTENTIAL IMPACTS - SANITARY SEWER
Proposed Wastewater Flow
Lots 1 and 2 of Block 4 and Lot 4 of Block 3 will be the only lots contributing sanitary flows for the
finished development. With future developments not fully known, Lot 2 of Block 4 and Lot 4 of Block 3
will be designed using Table V-1 Wastewater Flow Rate for Zoned Undeveloped Areas found in the City
of Bozeman Design Standards and Specifications Policy (COB-DSSP).
Lot 1 – Hotel/Banquet Center Design Flow
According to the Montana Department of Environmental Quality (DEQ) Circular 2, average daily sanitary
flow for hotels can be estimated using 50 gallons-per-capita-per-day (gpcd) for guests and 13 gpcd for
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Public Utilities Design Report Page 2 of 5
employees. The hotel is anticipated to have 214 rooms and 30 employees maximum per shift. For a
conservative estimate, it is assumed there will be three (3) guests per room. Calculations for the
estimated average day flow can be seen below:
Population
o (214 Rooms x 3 People/Room) = 642 people
o 30 employees
Average Daily Flow
o 642 people x 50 gpcd = 32,100 gpd
o 30 employees x 13 gpcd = 390 gpd
o Total = 32,490 gpd
Using Section 11.243.b, the peak hourly demand resulting from estimated average day demand and an
equivalent population for the hotel use is 90.4 gpm. This is assuming the worst-case population of 672
people (all the rooms booked and all shift employees present).
Peak Flow
o 642 guests + 30 employees = 672 people
o (22.6 gpm) x [18+.672.5)/(4+.672.5)] = 88.25 gpm
Lot 2/Block 4 & Lot 4/Block 3 – Projected Design Flows
As stated earlier, since these Lots 2 and 4 are planned for future undetermined uses, Table V-1
Wastewater Flow Rate for Zoned Undeveloped Areas of the COB-DSSP, will be used to estimate design
flows. According to the table, areas zoned B-2 and B-3 have an estimated flowrate of 2,000 gpd/acre
and 3,000 gpd/acre, respectively. For the purposes of this report, estimated flows were assumed to be
2,500 gpd/acre. Calculations for the estimated average day flow of Lots 2 and 4 can be seen below:
Lot 2/Block 4 Developable Acreage = 2.49 acres
Lot 2/Block 4 Average Day Flow = 2.49 acres x 2,500 gpd/acre = 6,225 gpd
Lot 4/Block 3 Developable Acreage = 11.74 acres
Lot 4/Block 3 Average Day Flow = 11.74 acres x 2,500 gpd/acre = 29,350 gpd
Infiltration Rate
According to the COB, an infiltration rate of 150 gallons/acre/day must be accounted for in the design
of new sanitary sewer main. As Lots 1 and 2 of Block 4 and Lot 4 of Block 3 have approximately 20 acres
of combined developable land, an additional 3,000 gpd has been added to the estimated wastewater
generation.
The following table, Table 1: Estimated Average Day Flow illustrates the resulting wastewater flows for
the overall development.
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Table 1: Estimated Average Day Flow
Acreage Standards Average Daily
Flow (gpd)
Average Daily
Flow (gpm)
Lot 1
Block 4
5.757 acres
(250,784 ft2)
DEQ 2 – 50 gpcd
per 642 people
and 13 gpd per
30 employees
32,490 22.56
Lot 2
Block 4
2.494 acres
(108,645 ft2)
COB Table V-1
2,500 gpd/acre 6,225 8.65*
Lot 3 11.74 acres
(511,394 ft2)
COB Table V-1
2,500 gpd/acre 29,350 40.76*
Infiltration
Rate
20 acres
(total) COB 3,000 2.08
Total 71,065 74.05
*GPM calculated assuming 12-hour day for daily operating hours of anticipated use.
As can be seen in the table above, the estimated average daily wastewater flow from the overall
subdivision is 71,065 gpd (74.05 gpm). Using the same peaking factor calculated above for the hotel use,
3.90, and applying it to the total estimated average daily flow for the entire subdivision, the estimated
peak flow is 288.80 gpm.
Proposed sanitary sewer main extensions will be 8” PVC, which has a minimum slope of 0.40%. To ensure
this minimum allowable slope will adequately convey the design peak flow for the subdivision, Manning’s
Equation was used with the following City of Bozeman design criteria.
Design Criteria
o New sewer lines shall be sized to flow at no more than 75% of full capacity at peak-
hour conditions upon full development.
o A Manning’s friction factor of 0.013 shall be used in designing new sewers.
Manning’s Equation:
ܳൌ 1.49
݊ ܣܴଶଷܵଵଶ
Where:
n = 0.013 (Manning’s friction factor)
A = 0.280 ft2
o Calculated cross-sectional area based on 75% full, 8” nominal pipe diameter
R = 0.201 ft
o Calculated hydraulic radius based on 75% full, 8” nominal pipe diameter
S = 0.004 ft/ft = 0.40% (minimum slope for 8” main)
Q = 0.696 cfs = 312.36 gpm
o Calculated flow capacity of 8” main at 75% full.
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As can be seen in the above calculation, the flow capacity for extension of new 8” sanitary sewer mains
is 312.36 gpm, which will provide adequate capacity to convey the estimated peak flow of 288.80 gpm
for the anticipated build out conditions of the new subdivision.
EVALUATION OF POTENTIAL IMPACTS - WATER MAIN
The following water main analysis evaluates proposed water use data as well as flow requirements at the
site to determine the impacts, if any, on the City of Bozeman’s existing distribution system as a result
of the overall development.
Flow Requirements
The City of Bozeman requires a minimum working residual pressure of 20 psi at all points in the system
under maximum day demands plus fire flow conditions. Currently, based on pressure testing completed
at nearby fire hydrants, there is approximately 72 psi of residual pressure (see Appendix A).
The ratio of average day demand to maximum day demand typically ranges from 1.2 for larger systems
to 3.0 for smaller systems. As this is a very small system, it is assumed that maximum day demand is
equivalent to three times the average day demand.
The proposed water main planned for construction of the subdivision will extend north from Tschache
Lane along N. 15th Ave., then east across Lot 1/Block 4 and then south along the proposed private drive
to loop back into the existing water main in Tschache Lane. This looped branch will primarily serve Lots
1 and 2 of Block 4 and a portion of Lot 4 of Block 3. For conservative analysis, the pressure loss for this
proposed looped extension was calculated, using Hazen-Williams, as a dead-end extension providing the
max day demand plus fire flow requirement for the estimated developed conditions of the subdivision.
The anticipated pressure losses for the developed conditions are calculated below for each segmented
extension as described above.
Ploss = 4.52 x L x [(Q/C)1.85 / (D)4.87]
Branch 1 - Tschache Lane to Baxter Lane along North 15th Ave. – 11.82 psi pressure loss
o L = 553 ft
o Q= 1,500 gpm(fire flow condition) + 71.97 gpm x 3(maximum day demand) = 1,716 gpm
o C = 130, DI pipe
o D = 8 in
Branch 2 – Parking Lot (east/west) Water Main – 12.36 psi pressure loss
o L = 578 ft
o Q= 1,500 gpm(fire flow condition) + 71.97 gpm x 3(maximum day demand) = 1,716 gpm
o C = 130, DI pipe
o D = 8 in
Branch 3 – Private Drive (north/south) Water Main – 9.82 psi pressure loss
o L = 459 ft
o Q= 1,500 gpm(fire flow condition) + 71.97 gpm x 3(maximum day demand) = 1,716 gpm
o C = 130, DI pipe
o D = 8 in
Total water main extension loss = 11.82 + 12.36 + 9.82 = 34 psi
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As can be seen, the pressure loss from the maximum design flow conditions is not expected to adversely
impact the existing system and will not cause residual pressures to drop below the City’s requirement of
20 psi. The pressure losses presented provide a conservative analysis based on a single water main
extension acting like a dead end main. The actual losses experienced by the proposed system extension
would be significantly less, due to making the proposed looped connections to the existing 12” main in
Tschache Lane. KLJ requests that the City enter the flow demands presented into their working water
model for more detailed analysis, as necessary.
Appendix A: Hydrant Pressure Tests
CITY OF BOZEMAN
HYDRANT PRESSURE/FLOW REQUEST FORM
Date: 4/21/17
Location Hydrant # Static Pressure Pitot Pressure Residual Pressure
Tshache Ln 439 60
Tshache Ln 2253 78 72
Requested By: Shane Strong
Fax #
Nozzle Size Flowed: 2.5”
Done By: ES / TH
Comments: 1300 GPM