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The Lumberyard Flats Phase 1 Development
Site, Water, Sewer, Storm Water Engineering Report
November 10, 2023, Site Plan
Prepared for: Virga Ventures 1 LLC
Prepared by: Stahly Engineering and Associates
Engineer of Record: Cordell D. Pool, PE
Quality Control Reviewer: Zach Lowe, PE
Introduction
The Lumberyard Flats is a phased site development project located on Lots 1A and 2A, Block 3, of
PT Land Phase 2 Amended Subdivision Plat. Subdivision street and utility construction was
completed in 2023, and the lots are currently vacant. An affordable housing project is in progress on
Lot 1, Block 2, of PT Land Phase 2 Amended Subdivision Plat, just to the west of Lumberyard Flats.
The Lumberyard Flats site is bounded by Tschache Lane to the north, North 11th Avenue to the east,
Patrick Street to the south, and North 14th Avenue to the west. The project consists of two phases.
Phase 1 is the 5.36 acre western lot (Lot 2A). Phase 2 is the 3.27 acre eastern lot (Lot 1A).
Figure 1 – Lumberyard Flats Project Vicinity
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The Lumberyard Flats site development is shown on Figure 1 above, with Phase 2 in light gray.
Phase 1 contains 3 apartment buildings and a clubhouse. Phase 2 contains 2 more identical
apartment buildings and will share the clubhouse with Phase 1. The apartment buildings have
16,209 sf footprints and are 4-story featuring 33 one-bedroom studio apartments, 17 two-bedroom
residential units and 8 three-bedroom residential units (58 units total in each building). The
Clubhouse Building contains amenities for the residents including a lounge, mailroom, work rooms,
fitness and spa, storage, and a pet wash.
Civil Specifications and Design Standards
The civil specifications for the project are the Montana Public Works Standard Specifications
(MPWSS) and the City of Bozeman Modifications to MPWSS (COB Mods). Construction plans are
developed in accordance with the City of Bozeman Design Standards.
Site Conditions
The site is generally flat, gently sloping to the north and east. Mandeville Creek exists to the east
and north of the site, crossing 11th Avenue diagonally at the intersection with Tschache Lane.
Previously wetlands existed in the northeast corner of the site, but the previous landowner obtained
Army Corps of Engineering permits to fill wetlands within the PT Lands subdivision. Currently there
are no wetlands are on the Lumberyard Flats property. The 50’ watercourse setback from
Mandeville Creet and existing wetlands does not extend beyond the existing street rights-of-way of
11th or Tschache. There is no FEMA mapped floodplain for Mandeville creek, previous studies
conducted with the PT Land Subdivision showed no 100-year inundation on the Lumberyard Flats
site.
A geotechnical investigation was conducted in 2022 by Allied Engineering. The investigation found
conditions typical of west Bozeman, with 4-8 feet of fine-grained soil over gravel, and a shallow
groundwater table. Groundwater monitoring was conducted throughout 2022 and found depth to
groundwater approximately 3’-4’ below existing ground. Soil sampling conducted with the
geotechnical investigation found non-corrosive soils.
The site is located within the Bozeman Solvent Site Controlled Groundwater Area, which prohibits
the use of on-site irrigation wells.
Completed Subdivision Improvements
PT Land Phase 2 subdivision improvements were originally installed in 2008. However, the Phase 2
Amended Plat required additional off-site street improvements, which were completed in 2023. The
completed subdivision improvements consist of water, sewer, storm drainage, street, and lighting
improvements in adjacent streets. The subdivision improvements also provided stormwater
detention for all subdivision streets lot areas. The subdivision Stormwater Design Drainage Report
conducted by KLJ Engineering is included with this submittal. Previous subdivision improvements
also included some on-site water, sewer, and storm drain mains. Water and sewer mains were
installed in a 40-foot public utility easement overlying the property line between Lot 1A and Lot 2A.
Additionally, the storm drain serving the east end of Patrick Street runs in a 25-foot on-site easement
along the east side of Lot 1A.
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Proposed Site Improvements
Site improvements for the Lumberyard Flats will be constructed in two phases, with Phase 1 being
the western lot and Phase 2 being the eastern lot. In accordance with previous approvals, a mid-
block drive aisle connecting Patrick Street and Tschache Lane is proposed in Phase 1 to satisfy the
block length requirements between 11th and 14th Avenues. Two other site access are proposed from
14th Avenue. Due to collector street access spacing requirements, no access is proposed onto 11th
Avenue.
The site development proposes buildings lining the perimeter streets and interior parking lots.
Pedestrian circulation is provided throughout the site both east-west and north-south. The
clubhouse is centrally located fronting Tschache Lane. Generally, the site and buildings will be
elevated above existing grade to improve drainage and separation to groundwater.
Site improvements consist of on-site water and sewer mains and services, storm drainage piping,
franchise utilities, parking, hardscape, landscape, and site lighting improvements. Civil site
improvements are shown in detail on the Civil Plans.
Figure 2 – The Lumberyard Flats Master Plan Phase 1 Civil Layout
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Water
Existing 8” DI and 12” DI City of Bozeman water mains run in adjacent streets and on-site. The site
is located at the intersection of three of Bozeman’s pressure zones. Patrick Street to the south is the
downstream end of the Sourdough (main town) pressure zone. Pressures in this zone are
approximately 165 psi in this area. To the northeast is the Lyman (northeast) pressure zone with
approximately 120 psi in this area. Tschache Land and 14th Avenue to the north and west are within
the Northwest pressure zone where pressure is reduced from the two higher zones to approximately
75 psi.
During the concept plan review the City Engineering Department strongly encouraged this
development to utilize the lower (northwest) pressure zone to supply the buildings and site. 8” Water
main extensions are proposed from the existing water mains in the lower pressure zone to provide a
looped system from Tschache Lane and 14th Avenue. This loop will provide service to all of the
proposed buildings and internal fire hydrants. One new fire hydrant is proposed on Patrick Street at
the site access.
The City of Bozeman 2017 Water Facility Plan Update did not identify any fire protection limitation in
this area of town. Several fire hydrants are located adjacent to the site. Furthermore, as part of the
2017 Water Facility Plan Update, a fire flow test was performed on a hydrant approximately 1,250
feet away along Sacco Drive. The results for this test (test number 3) are included with this report.
The static water pressure is approximately 81.9 psi. Two adjacent hydrants were opened
simultaneously at a 2.5” diameter nozzle, the hydrant nearest to the site flowed at 1,215 gpm while
the other flowed at 1,235 gpm for a combined flowrate of 2,450 gpm. These flows resulted in a 19.1
drop in psi at the residual test hydrant, for a residual pressure of 62.8 psi. This indicates that
reasonable urban fire flows can be met in the area. Specifically, each of the nearby hydrants could
be expected to provide similar flows, resulting in approximately 2,500 gpm of fire flow available to
The Lumberyard Flats Development.
Building water and fire services will be provided from existing and new on-site mains. The proposed
Flats Building services are 4” domestic water services and 6” fire services. The water service sizing
is based on the fixture counts performed for the site plan submittal. The water fixture unit count for
The Flats Building type is 691.5 units, corresponding to a peak flow of 160 gpm and which requires a
4” service and 3” meter. The water fixture unit count for The Clubhouse Building is 52.5 units,
corresponding to a peak flow of 53 gpm which requires a 2” service and meter.
The estimated water use for The Lumberyard Flats Development is provided in Table 1. Due to the
lack of City design standards for multi-family buildings, domestic water use estimates are based on
the typical wastewater generation rate of 89 gallons per day (gpd) per person with an estimated 2.11
persons per unit, plus the estimated irrigation demand. The landscaping is designed to be water
conserving. Irrigation water supply will be provided from each building’s domestic water service.
Preliminary irrigation demands were provided by the landscape architect. Irrigation is anticipated to
occur over an approximately 100-day season resulting in a total annual water use of 519,557
gallons, or 1.59 ac-ft. The average daily irrigation flow is 5,196 gpd during summer. The average
daily irrigation water use estimate of 5196 is equivalent to only 8.5 gallons per day per resident
during summer, much less than historical single-family residential use. The estimated annual water
use for the entire Lumberyard Flats project is anticipated to be approximately 54,459 gpd, with a
peak hour demand of 163 gallons per minute (gpm).
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Table 1. The Lumberyard Flats Estimated Water Use
Cash-in-lieu-of water rights are assessed within the City of Bozeman based on estimated annual
average water use for a project. Currently, a $6,000 fee is assessed per acre-ft/year. Cash-in-lieu
amounts will be determined by the City during the Site Plan review.
Existing and proposed water mains and services are shown in the civil plans. All water mains and
services will be installed in Phase 1 of the development. A 30’ public water and sewer easement will
be provided for all new on-site water mains, with “bump-outs” provided for fire hydrants.
Sewer
Sewer service is provided by the 8” PVC sewer main located in Tschache Lane. Subdivision
improvements provided two 8” stubs to the property. Sewer mains will be extended onsite from
these two stubs. Wastewater fixture counts have determined that the apartment buildings require 8”
services, and the Clubhouse requires a 6” service. Manholes are provided where the apartment
sewer services join the sewer main. The clubhouse is served by extending an existing 6” service on-
site.
Daily wastewater generation was determined utilizing City design average day flows of 89 gallons
per day (gpd) per person, with an average population of 2.11 people per unit. Infiltration and Inflow
(I&I) is 150 gpd/acre. Applying this value with the inflow and infiltration estimate results in an
average daily flow for the project of 55,754 gpd. A peaking factor of 3.93 based on City Design
Standards, the peak hour wastewater flow for the entire Lumberyard Flats project is estimated at 152
gallons per minute (gpm). This value is used for the design of on-site sewer mains. These values
and demands are summarized in Table 2.
Lumberyard Flats Overall Estimated Water Use
Units Capita/Unit Population GPD/Capita Water Use (gpd)
Phase 1 -Lot 2A 174 2.11 367 89 32,675
Phase 2 -Lot 1A 116 2.11 245 89 21,784
Total 290 612 54,459
Site Area - Lots and
ROW (ac)8.63
Average Day Water Use [Equal to Wastewater Flow](gpd) 54,459
Irrigation (gpd)5,196
Max Day Water Use [Average Day Use + Irrigation] (gpd)59,655
;P = Pop. ÷ 1,000 Peaking Factor (PF)3.93
Water Use Peak Hour Flow (gpm)163
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Table 2. The Lumberyard Flats Estimated Wastewater Flow
Impact to existing sewers were analyzed by estimating total flow from all existing and proposed
users of the existing 8” sewer main in Tschache Lane. This sewer provides service to existing
commercial buildings located in Phase 1(Block 1) of the PT Land subdivision, the proposed
affordable housing project located in Block 2 of the subdivision, and the Lumberyard Flats project.
The Kenyon Noble property is served from 11th Avenue sewer main.
The estimated wastewater flow was determined by zoning designation (for commercial uses) or
actual proposed residential units. Block 1 of the PT land subdivision consists of approximately 6.77
acres of commercial development, zoned B-2. A wastewater flow generation rate of 2000 gpd/acre
was applied to this use. Block 2 has a proposed use of 155-unit affordable housing project. In
accordance with the methodology utilized in the Bozeman Wastewater Facility Plan, a per capita flow
of 64.4 gpd/unit is used for community wastewater generation. City standard methods determined a
peaking factor of 3.75, resulting in a peak hour flow of 200 gpm in the Tschache Lane sewer. These
calculations are summarized in Table 3.
The 8” sewer main is Tschache Lane is installed at 0.4% slope. At 75% flow depth (6”) the capacity
of this sewer is 313 gpm, which is greater than the estimated wastewater flow in this pipe. The
capacity calculations are shown in Table 4.
Existing and proposed sewer mains and services are shown in the civil plans. All sewer mains and
services will be installed in Phase 1 of the development. A 30’ public water and sewer easement will
be provided for all new on-site sewer mains.
Lumberyard Flats Overall Estimated Wastewater Flow
Units Capita/Unit Population GPD/Capita Wastewater
Flow (gpd)
Phase 1 -Lot 2A 174 2.11 367 89 32,675
Phase 2 -Lot 1A 116 2.11 245 89 21,784
Total 290 612 54,459
Site Area (ac)8.63
Inflow & Infiltration (gal/ac/day)150
Inflow & Infiltration (gpd)1,295
Wastewater Flow + Inflow & Infiltration (gpd)55,754
;P = Pop. ÷ 1,000 Peaking Factor (PF)3.93
Wastewater Peak Hour Flow (gpm)152.1
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Table 3. Tschache Lane Estimated Wastewater Flow
Table 4. Offsite Sewer Capacity Calculations
Tschache Lane 8" Sewer Drainage Area
Development Area Area #Units Population GPD/Capita Wastewater
ac or GPD per Acre per unit gpd
Block 1, PT Land Ph. 1 Sub'd (Existing B-2)6.77 2000 13,538
Lot 1, Block 2, Am. PT Land Ph. 2 Sub'd (B-2M)3.11 155 2.11 64.4 21,062
Lot 2A, Block 3, Am. PT Land Ph. 2 Sub'd (Phase 1)5.36 174 2.11 64.4 23,644
Lot 1A, Block 3, Am. PT Land Ph. 2 Sub'd (Phase 2)3.27 116 2.11 64.4 15,763
Total Wastewater Flow 18.51 74,006
I&I at 150 gpm/acre 2,776
Total Wastewater Flow with I&I 76,782
Equivalent Population (flow/64.4gpdpc)1,192
;P = Pop. ÷ 1,000 Peaking Factor (PF)3.75
Peak Hour Flow (gpm)200
*Kenyon Noble drains into 11th Ave Sewer
Sewer Main
Location Tschache
Pipe Diameter (in)8
Minimum Pipe Slope (ft/ft)0.004
Coefficient of Roughness (n)0.013
Depth in Pipe at 75% Full (in)6
Depth of Flow (ft)0.5
Pipe Radius (in)4
Pipe Radius (ft)0.33
Wetted Perimeter 1.40
Area of Flow (ft2)0.28
Hydraulic Radius 0.20
Velocity (ft/sec)2.48
Maximum Pipe Flowrate (gpm)313
Peak Hour Flow (gpm)200
Peak Flow % of Max Capacity 64%
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Storm Water
The existing site is undeveloped but served by adjacent subdivision drainage improvements.
mitigation. Currently, runoff from the site is directed north to Tschache Lane, where it is collected in
the streets and conveyed to the existing detention basin north of Tschache Lane. The subdivision
Stormwater Design Drainage Report conducted by KLJ Engineering is included with this submittal.
The subdivision detention basin was designed as a wet-pond due to the presence of shallow
groundwater. Within the drainage report the Lumberyard Flats property was estimated to have a
runoff coefficient of 0.90.
The runoff coefficient for the Lumberyard Flats was determined based on the planned buildings,
parking, hardscape, and landscaping, as shown in Table 5. The runoff coefficient of the Lumberyard
Flats is 0.79, resulting in less runoff than estimated with the subdivision design. Therefore, the
existing detention basin has adequate capacity to serve the proposed Lumberyard Flats project.
Table 5. The Lumberyard Flats Runoff Coefficient Calculations
Two storm drain mains, a 15” and a 24”, were extended to the property with the subdivision street
improvements. Also, the existing 18” storm drain running on-site along 11th Avenue will serve Phase
2. New on-site 15”, 18” and 24” storm drains will be extended from these pipes to collect and convey
storm runoff on-site. Building roof drains will be piped into the storm drainage system. Existing and
proposed storm drainage facilities are shown on the civil plans. Storm drainage improvements will
be installed per phase.
Storm drains are designed in accordance with the City of Bozeman’s Design Standards. Storm
runoff is estimated using the Rational Method with a weighted coefficient determined for the site’s
building rooftops, pavement areas, sidewalks, and landscape areas. Storm drain piping is sized to
convey the 25-year event.
Lumberyard Flats Site Areas and Runoff Coefficient C
Land Classification C Post Dev Area (sf)
Rooftops 0.9 88,230
Pavement 0.9 150,359
Sidewalk 0.9 35,192
Landscape 0.2 50,753
Total 324,534
Weighted Runoff Coeff. (C )0.79
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Conveyance Capacity
For conveyance capacity the site was divided into 6 sub-areas each contributing to the collection
system shown on the Storm Water Area Figure (Figure 1 attached). The 25-year storm runoff was
calculated for each sub-area as shown in Table 6.
Table 6. Drainage Area Peak Flow Calculations for Pipe Conveyance
The sub-area storm runoff calculations are used to size the individual storm drain pipe segments, as
shown in Table 7.
Table 7. Storm Drain Pipe Capacity Calculations
Sub-area 1A connects directly to the 15” storm drain stubbed to the property. Sub-area 1B, 1C, and
1D combine to discharge to the 24” stub. Sub-area 2A and 2B will connect to the 18” storm drain
running on-site along 11th Avenue. Table 7 shows that all pipes have adequate capacity to convey
the 25-year event. The minimum pipe size for any lateral feeding one of these pipes is 15”.
Drainage Subarea Basin #1A 1B 1C 1D 2A 2B
Drainage Area (acres)1.69 1.30 1.52 1.07 1.43 1.47
Drainage Area (sf)73780 56825 66007 46558 62504 64070
Slope (%)1.5 1.5 1.5 1.5 1.5 1.5
Runoff Coefficient 0.79 0.79 0.79 0.79 0.79 0.79
Frequency Adjustment Factor, Cf 1.1 1.1 1.1 1.1 1.1 1.1
Basin Length (ft)320 320 320 320 320 320
Time of Concentration (min)6.8 6.8 6.8 6.8 6.8 6.8
Peak Flow Calculations
Design Storm 25yr 25yr 25yr 25yr 25yr 25yr
Time of Concentration (min)6.8 6.8 6.8 6.8 6.8 6.8
Intensity at Tc (Figure I-2 pg. 29) (in/hr)3.16 3.16 3.16 3.16 3.16 3.16
Peak Runoff Rate at Tc (Q = CIA) (cfs)4.22 3.25 3.78 2.67 3.58 3.67
Drainage Subarea #1A 1B 1C 1D 2A 2B
Pipe Material PVC PVC PVC PVC PVC PVC
Pipe Size (in)15.00 15.00 18.00 18.00 15.00 15.00
Manning's "n" (PVC)0.013 0.013 0.013 0.013 0.013 0.013
Area (ft2)1.23 1.23 1.77 1.77 1.23 1.23
Wetted Perimeter (ft)3.93 3.93 4.71 4.71 3.93 3.93
Hydraulic Radius (ft)0.31 0.31 0.38 0.38 0.31 0.31
Slope (ft/ft)0.0050 0.0050 0.0100 0.0100 0.0100 0.0100
Full Flow Capacity (cfs)4.58 4.58 10.53 10.53 6.48 6.48
Velocity (ft/sec)3.73 3.73 5.96 5.96 5.28 5.28
Contributing Drainage Basin 1B 1C
Stormwater Flow (cfs)4.22 3.25 7.03 9.70 3.58 3.67
% Capacity 92%71%67%92%55%57%
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Storm Water Maintenance:
General Information
The PT Land Subdivision utilizes storm water detention basins to mitigate storm water impacts from
subdivision lots and streets. The stormwater detention basins are located in planned open space
and are to be maintained by the PT Land Property Owners’ Association. Stormwater is collected
and conveyed to the detention systems by storm drainage pipes located on-site and within City
streets. The City is responsible for maintaining storm piping within City rights-of-way. The
Lumberyard Flats Property Owners’ Association is responsible for monitoring and maintaining on-site
storm drainage facilities on the Lumberyard Flats property as described herein.
The on-site and subdivision storm water facilities are designed to operate without excessive
maintenance. However, like all infrastructure, periodic monitoring and maintenance will prevent
costly repair and replacement. This Maintenance Plan has been prepared in accordance with City of
Bozeman guidelines. Over time, recommended maintenance guidelines may evolve. Please
contact the City of Bozeman Storm Water Division if any questions arise.
Storm Water Facilities Maintenance Schedule
1. Site Housekeeping. (Continuously as needed)
The main cause of storm water facility damage is poor site housekeeping. Sediment tracked
onto pavement can be washed into storm water appurtenances and damage these facilities.
Trash can clog conveyance structures, potentially causing property damage.
• Keep sidewalk and parking areas clean.
• Pick up trash.
• Restore damaged landscaping in order to prevent sediment runoff.
2. System Monitoring. (Quarterly, except in winter)
The storm water facilities shall be inspected quarterly to quickly identify small issues before
expensive damage can occur. In addition to regular monitoring, the best time to inspect the
performance of storm water facilities is during runoff events.
• Observe system during runoff. Look for ponding on inlet structures. This can indicate
a clogged conveyance structure.
• Inspect Inlets, Manholes, and Pipes
3. Curb, Inlet, and Storm Drain Piping Maintenance. (Annually as required)
All storm water conveyance structures can acquire sediment and debris buildup. If this
sediment and debris is not periodically removed, it can cause undesired ponding and
clogging. These conveyance structures need to be inspected and cleaned if required.
• Ensure pipe entrances and exits are free of trash and debris
• Remove sediment or debris in the structures if present.
• Check for damage, repair as needed.
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UGESD SDSUB AREA 1A73,780 SF1.69 ACSUB AREA 1B56,825 SF1.30 ACSUB AREA 2A62,504 SF1.43 ACSUB AREA 2B64,070 SF1.47 ACSUB AREA 1C66,007 SF1.52 ACSUB AREA 1D46,558 SF1.07 ACFIGURE 1STORM WATERAREA FIGURE1 4/29/2022 OVERALL CONCEPT PLAN CDP
2 11/10/2023 COB SITE PLAN SUBMITTAL CDP ZWL PROFESSIONALENGINEERS &SURVEYORSTHE LUMBERYARD FLATSTSCHACHE LANE STAHLYENGINEERING& ASSOCIATESVIRGA VENTURE 1 LLCBOZEMAN, MT