HomeMy WebLinkAbout12 Preliminary Sewer Engineer's Report 03122021
Preliminary Engineering Report
Sewer Main Extension
Community First Griffin Place
March 2021
Submitted to:
City of Bozeman Engineering Department
20 East Olive
Bozeman, MT 59715
Prepared by:
Stahly Engineering and Associates
851 Bridger Drive, Suite 1
Bozeman, MT 59715
(406) 522-8594
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Preliminary Engineering Report
Contents
Note: The Engineering Report format follows DEQ-2 organization. Additional
information required by the City of Bozeman Design Standards is added where
required.
Report Narrative
Chapter 10 – Engineering Reports & Facility Plans
11.1 Engineering Report - General Information
11.11 Problem Defined
11.12 Design Conditions
11.13 Impact on Existing Wastewater Facilities
11.14 Project Description
11.15 Drawings
11.16 Design Criteria
11.17 Site Information
11.18 Alternate Selection/Analysis
11.19 Environmental Impacts
Figures and Tables
Figure 1. Vicinity Map
Figure 2. Sewer Plan
Table 1. Wastewater Generation from North and South Buildings
Table 2. Wastewater Peak Hour Flows
Table 3. Sewer Main and Services Conveyance Capacity
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11.1 Engineering Report – General Information
The proposed Community First Griffin Place is located southeast of the intersection
of Manley Road and Griffin Drive. Community First Griffin Place is a planned two
building development designed to provide a plethora of community-focused
programs and services focused on members of the community facing challenges
with housing, hunger, and other hardships. The project is located on an
undeveloped 5.24-acre lot.
The proposed development includes two buildings, referred to as the North
Building and the South Building. The North Building will function as a Food
Resource Center providing a new home for both the Gallatin Valley Food Bank as
well as the Fork and Spoon, a “pay what you can” restaurant, while the South
Building will provide emergency housing. Both buildings will contain additional
office space for staff members.
Sewer service for the site will be provided by extension of the 8” sewer main that
currently terminates at the intersection of Griffin Drive and Industrial Drive. There is
a Griffin Drive Improvement project currently underway, which in addition to
widening the road will extend the main in Griffin Drive and stub a connection to the
Community First Griffin Place property line. From here, an 8” main will run in an
easement along the drive access on the property. Individual service connections
will be made to both of the buildings.
The developer’s contact information is:
HRDC
Heather Grenier
32 South Tracy Ave.
Bozeman, MT 59715
Water supply and wastewater treatment will be provided by the City of Bozeman’s
municipal systems. The system owner’s contact information is:
City of Bozeman Public Service Department
PO Box 1230
Bozeman, MT 59771-1230
The location of the Community First Griffin Place site is shown on the Vicinity Map
in Figure 1.
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Figure 1. Vicinity Map, Bozeman, Montana
11.11 Problem Defined
Sanitary sewer service will be provided by a new 8” main extension serving
the property. The proposed main will extend approximately 375’ west from
the existing manhole at the intersection of Griffin Drive and Industrial Drive.
This portion of the extension is currently underway as part of an ongoing
Griffin Drive Improvements project. As part of this project, the main will be
stubbed to the Community First Griffin Place property line.
From this point the main will extend south approximately 260’ along the
eastern drive aisle. A service connection will be made along this stretch of
main serving the North Building. A final segment of main will extend 81’
west, to facilitate service connection to the South Building. Both buildings
will have grease interceptors to provide pretreatment for kitchen waste prior
to sewer discharge. The proposed sewer system improvements are shown
on the Sewer Plan (Figure 2) attached at the end of this report.
New sewer mains will be in a 30’ combined water and sewer easement.
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11.12 Design Conditions
Sanitary sewer service will be provided by the City of Bozeman Municipal
system. This project is located within the planned service area of the City’s
system.
Estimated wastewater generation for Community First Griffin Place has
been determined utilizing values provided in City design standards and
Facility Plans and is shown in Table 1. For sewer main sizing, typical City
design flows are utilized.
The estimation of wastewater generation of each building is based on
proposed building use, utilizing standard City of Bozeman design values for
the majority of calculations. Additional analysis was required to determine a
design value for the emergency beds, which is the primary use of the South
Building. City-provided meter readings from the former Skate Palace, which
currently operates as emergency housing for the homeless, has been used
to estimate a flow rate per bed. Meter readings revealed a remarkably low
use per emergency bed of 7.3 gpd/unit, though there is only month of meter
readings available. To be conservative, a value 50 gpd/unit has been
applied in the wastewater generation estimate.
Table 1 – Wastewater Generation from North and South Buildings
Average Daily Flow Annual Use
North Building
Area
(sf)
#
Units
gpd/1000
sf
Gpd/
Unit Gpd AF/yr
Warehouse / Food Processing
Kitchen 16867 100 1,687 1.89
Accessory to Warehouse / Food
Processing 4326 30 130 0.15
Accessory Retail 3282 30 98 0.11
Restaurant Indoor Seating Area 1297 500 649 0.73
Restaurant Outdoor Seating Area 664 500 332 0.37
Offices 1776 30 53 0.06
Accessory Spaces 6894 30 207 0.23
Subtotal 35106 3,156 3.53
South Building
Area
(sf)
#
Units
gpd/1000
sf
Gpd/
Unit Gpd AF/yr
Emergency Beds 170 27 4,590 5.14
Office Space 3878 30 116 0.13
Common Areas 2729 30 82 0.09
Circulation, mechanical, walls 10319 0 0 0.00
Storage 2175 0 0 0.00
Bathrooms 3534 30 106 0.12
Subtotal 4,894 5.48
Building Summary Total
(gpd) 8,050 Annual Total
(AF/yr) 9.02
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It is unlikely that adjacent property will be served by further extension of
Community First Griffin Place’s sewer mains. Readily accessible sewer
mains exist to the north in Griffin Drive. A standard value of 150 gpd/acre
has been applied to the site to account for infiltration and inflow into the
sewer collection system. Applying a peaking factor of 6, produces a peak
hour flow of 36.8 gpd. Peak hour flows are a critical design condition for
sizing pipes, to ensure adequate capacity exists to convey peak flows.
Table 2 – Wastewater Peak Hour Flow
Estimated Sewer Use and Demands
On-site Structures Gallons/day
North Building 3,156
South Building 4,894
Total Domestic Use 8,050
Sewer Infiltration Area (acres) Infiltration (gal/ac) Gallons/day
Onsite 5.24 150.00 786.0
Off-site 0.00 150.00 0.0
Total Sewer Design Flow 8,836
Average Day Demand (gpm) 6.14
Peaking Factor 6.0
Peak Hour Flow Rate (gpm) 36.8
Table 3 – Sewer Main and Services Conveyance Capacities
Sewer Main and Services Capacities
Status Proposed Proposed Proposed
Location Site Main N. BLDG S. BLDG
Pipe Material 8" SDR 35 PVC 4" SDR 35 PVC 6" SDR 35 PVC
Minimum Pipe Diameter (in) 8 6 6
Minimum Pipe Slope (ft/ft) 0.004 0.02 0.02
Coefficient of Roughness (n) 0.013 0.013 0.013
Depth in Pipe at 75% Full (in) 6 4.5 4.5
Depth of Flow (ft) 0.5 0.375 0.375
Pipe Radius (in) 4 3 3
Pipe Radius (ft) 0.33 0.25 0.25
Wetted Perimeter 1.40 1.05 1.05
Area of Flow (ft2) 0.28 0.16 0.16
Hydraulic Radius 0.20 0.15 0.15
Velocity (ft/sec) 2.48 4.58 4.58
Maximum Pipe Flowrate (gpm) 312.8 324.8 324.8
Peak Hour Flow (gpm) 210.0 88.0 122.0
Peak Flow % of Max Capacity 67.13% 27.09% 37.56%
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Table 3, above, shows that an 8” sewer main has a 75% flow depth capacity
of 313 gpm installed at a minimum slope of 0.4%. An 8” sewer main at
minimum slope (0.4%) has sufficient capacity to provide sewer service for
Community First Griffin Place.
11.13 Impact on Existing Wastewater Facilities
A review of the City of Bozeman 2015 Wastewater Facility Plan identifies
future capacity limitations in the collection system downstream of this
project impacting a large portion of Bozeman. This limitation is not directly
caused by this project, and upgrades to this interceptor sewer are currently
planned for FY 2023 in the City’s Capital Improvements Plan.
11.14 Project Description
The project description is provided at the beginning of the Engineering
Report.
11.15 Drawings
Please see Figure 2, the Sewer Plan, at the end of this report, which shows
the proposed sewer improvements. Plan and profile drawings will be
submitted with the infrastructure design submittals.
11.16 Design Criteria
The Community First Griffin Place sewer main extensions will be designed
in accordance with Montana Department of Environmental Quality Circular
2, and the City of Bozeman Design Standards and Specifications Policy.
Construction specifications will be Montana Public Works Standards and
Specifications (MPWSS), and the City of Bozeman Modifications to
MPWSS.
11.17 Site Information
The Community First Griffin Place project is located on the south side of
East Griffin Drive at the intersection of Griffin Drive and Manley Road. The
site was previously occupied by a single-family residence and associated
outbuildings. They have since been demolished. The site is currently being
used as a staging and storage area for construction equipment, and a
gravel drive access has been constructed to facilitate this use. The site is
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generally flat within the project limits, with some moderately sloped terrain
around drainage ditches in the northeast of the site and along a tree stand
running north and south across the property.
A geotechnical evaluation was conducted and is provided in a separate
appendix of this submittal. The soils on the site are variable. Geotechnical
investigation revealed that the central and western thirds of the site were
historically used for ponds that have since been filled. Boring logs reveal
encountering this highly variable fill material to a depth of approximately 19’.
The eastern third of the site is predominantly native soils, with some limited
fill encountered that is typically associated with demolition of historic
structures. Groundwater monitoring performed as a portion of the
geotechnical investigation found groundwater depths ranging from 7.3’ to
13.3’ below existing grade in the area proposed for development. Full
geotechnical evaluation results are available in the attached appendix.
The site is not located within a 100-year floodplain.
11.18 Alternative Selection/ Analysis
Due to the project’s location within the City of Bozeman, extension of public
mains was the only sewer collection alternative.
11.19 Environmental Impacts
Continued use and new extensions of City of Bozeman municipal sewer
mains has the least environmental impact. No new environmental impacts
will be caused by these sewer main extensions.
GRIFFIN DRIVEPROJECT SITE5.24 ACRESNORTH BUILDING27,086 SF FOOTPRINT202 E. GRIFFIN DR.SOUTH BUILDING14,500 SF FOOTPRINT206 E. GRIFFIN DR.MONTANA RAIL LINKPHASE 1PHASE 2C3.0SEWER PLANPROFESSIONALENGINEERS &SURVEYORSCOMMUNITY FIRST
GRIFFIN PLACE STAHLYENGINEERING& ASSOCIATESHRDC
202 & 206 EAST GRIFFIN DR.
BOZEMAN, MT