HomeMy WebLinkAbout04 Evergoods Eng Report
Engineering Report
Evergoods
Lot 2A Glen Lake Commerce Subdivision
Bozeman
Gallatin County, Montana
January, 2025
Prepared By:
Hyalite Engineers, PLLC
161 W Haley Spring Road Ste 101
Bozeman, MT 59718
ENGINEERING REPORT – EVERGOODS
Table of Contents January 2025 Page ii
Version 1/24/2025
Table of Contents
Table of Contents ........................................................................................................................ ii
List of Tables .............................................................................................................................. ii
List of Figures ............................................................................................................................ iii
List of Appendices ...................................................................................................................... iii
1 Introduction ......................................................................................................................... 4
1.1 Purpose of Report ...................................................................................................... 4
1.2 Scope ......................................................................................................................... 4
2 Location and Site Information ............................................................................................. 4
3 Land Use ............................................................................................................................ 5
3.1 Existing ....................................................................................................................... 5
3.2 Proposed .................................................................................................................... 5
4 Potable Water Improvements .............................................................................................. 5
4.1 Building Water Use ..................................................................................................... 5
5 Sanitary Sewer Improvements ............................................................................................ 8
5.1 Proposed Improvements ............................................................................................. 8
6 Storm Water Improvements ................................................................................................ 9
6.1 Existing Conditions ..................................................................................................... 9
6.2 General Design ........................................................................................................... 9
6.3 Hydrologic Methodology ............................................................................................. 9
6.4 Basin A Retention Chamber ......................................................................................10
6.5 Basin B Retention Chamber ......................................................................................11
6.6 Basin C Retention Pond ............................................................................................11
6.7 Inlets & Storm Sewer .................................................................................................11
6.8 Groundwater ..............................................................................................................11
6.9 System Maintenance .................................................................................................11
6.10 Erosion Sediment Control ..........................................................................................12
6.11 Flooding.....................................................................................................................12
List of Tables
Table 1 - Fixture Table ……………..……………………………………………………………………6
Table 2 - Runoff coefficients used. ............................................................................................10
ENGINEERING REPORT – EVERGOODS
List of Figures January 2025 Page iii
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List of Figures
Figure 1 - Vicinity map. .............................................................................................................. 4
List of Appendices
A) Post-development Drainage Basins
B) Pond Calculation & Summary
C) Madison Engineering Stormwater Design Report
ENGINEERING REPORT – EVERGOODS
Introduction January 2025 Page 4
Version 1/24/2025
1 Introduction
1.1 Purpose of Report
This report is intended to serve as the design document for site/civil improvements associated
with the construction of a new commercial building near the intersection of Iron Horse Road and
Manley Road, in Bozeman, MT.
1.2 Scope
Sanitary sewer service, fire and potable water service, and storm water design are within the
scope of this report. All improvements analyzed in this report are within the property. No off-site
improvements are expected.
2 Location and Site Information
The property occupies 1.06 acres and is located within the north side of the City of Bozeman
northwest of the intersection of Manley Road and Iron Horse Road, in the SW ¼ of Section 31,
Township 1S, Range 6E, P.M.M., Gallatin County, MT. The existing zoning and the nearby
surrounding zoning is M-1. The property is within the service area for municipal water and sewer
from the City of Bozeman.
Figure 1 - Vicinity map.
ENGINEERING REPORT – EVERGOODS
Land Use January 2025 Page 5
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3 Land Use
3.1 Existing
An 8-inch City of Bozeman water main exists along Iron Horse Road. The main was installed in
2018 and City of Bozeman GIS information does not make any note of deficiencies in the area.
The existing property is a vacant site that has 3 water services (2-inch) and 3 fire services (4-
inch) stubs to the lot. Lot 2A was previously 3 lots that were combined to create lot 2A as part of
Amended plat J-642A, hence why the lot has 3 water, fire and sewer services.
An 8-inch diameter City of Bozeman sewer main exists along Iron Horse Road with three 4-inch
sewer services that are stub into the property. The existing 8-inch main is PVC and laid at 0.98%
slope. The main was installed in 2018. The existing main ultimately gravity flows along the railroad
tracks to the Bozeman Wastewater Treatment Facility.
Currently no storm water facilities exist for the site, however, there is an existing storm pond as
part of the original Glen Lake Subdivision stormwater design that did account for approximately
2,015 cubic feet of storm storage for this lot once it was developed.
3.2 Proposed
The proposed development will consist of 1 commercial building, parking lot, stormwater facilities
and service extensions to the building. As mentioned above the site has 2 additional water, fire
and sewer services that service the site. The additional water and fire services are to be
terminated at the main within Iron Horse, leaving Lot 2A with 1 2-inch water service and 1 4-inch
fire service that will be extended to service the building. The 2 additional sewer services are to be
capped and abandoned at the property line per City of Bozeman Standards. Again, leaving the
lot with just 1 sewer service that will be extended to the building. All stormwater storage for the
parking lot will utilize underground infiltration systems and a retention pond in the northeast corner
of the site that will collect run off from the building. All storm water is to be retained on-site.
4 Potable Water Improvements
4.1 Building Water Use
Domestic Service Sizing
1 commercial building with 20 employees = 20 employees at 13 gpd (per DEQ 4) = 260 gpd
Maximum Day Flow
Peaking factor = 2.3 (per City of Bozeman Design Standards)
260 gpd (2.3) = 598 gpd
Max day flow = 598 gpd / 1440 = 0.42 gpm
ENGINEERING REPORT – EVERGOODS
Potable Water Improvements January 2025 Page 6
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Peak Hour Demand
Peaking factor = 3.0 (per City of Bozeman Design Standards)
260 gpd (3.0) = 780 gpd
Peak hour flow = 780 gpd / 1440 = 0.54 gpm
The building will consist of multiple fixtures that are illustrated in the table below. As a check
to the above flow, the number of fixture units were estimated as outlined in Table 1 below:
Table 1 – Fixture Table
Appliance Fixture Units X # Fixtures = Total
Shower (per head) 2 1 = 2
Hose Bidd 2.5 1 = 2.5
Additional Hose Bibb 1 3 = 3
Service / Mop Basin 3 3 = 9
Lavatory Sink 1.0 5 = 5
Kitchen Sink 1.5 1 = 1.5
Water Closet 2.5 6 = 15
Total = 38
Based on the above fixture units (2021 Uniform Plumbing Code - Chart A 103.1(1)), the peak
design flow is estimated around 40 gpm. The proposed 2” copper pipe is capable of flowing 40
gpm at approximately 4.1 ft/s.
ENGINEERING REPORT – EVERGOODS
Potable Water Improvements January 2025 Page 7
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As part of Madison Engineering’s “Water & Sewer Main Extensions Design Report” for the original
Glen Lake Subdivision, they showed that the City of Bozeman’s fire hydrants 1215 and 1216 had
a discharge of 1,695 gpm out of a 2.5” port with 128 psi of residual pressure when tested. Madison
Engineering’s calculated that the fire flow at residual pressure (20 psi) is 3,154 gpm using the
following information and equation.
Fire Hydrants – 1215 & 1216
Static Pressure, Ps = 140 psi
Pitot Pressure, Pt = 102 psi
Residual Pressure, Pr = 128 psi
Hydrant discharge during testing, Qt = 1,695 gpm
Fire flow at minimum residual pressure equation
Qr = Qt*((Ps-Pt)/(Ps-Pt))0.54
Qr= 1,695*((140-20)/(140-102))0.54 = 3,154 gpm
Irrigation Demand
The DNRC provides an acre-foot usage of water for landscape/lawn area of 2.5 AF/acre. This
translates to approximately 1” per week of irrigation usage. The proposed irrigation use for this
site will be provided by the City of Bozeman. Below is the estimate flow rate for the project
based on the total landscape square footage.
Assumed 1”/week for irrigation of turf areas and 4-month irrigation season.
Total irrigated turf/landscaped areas = 19,540 sqft = 0.45 acres
1”/week (16 weeks) = 1.33 ft of irrigation over 0.45 acres
Total irrigation = 0.52 acre-feet/year = 25,988 cu.ft. ( 7.48 gal/cu.ft.) = 194,392 gal./year
Over 120-day irrigation season, 15 hours of irrigation per day
194,391 gals./year (1 year/120 days) ( 1 day/15 hrs) (1hr/60 min) = 1.8 gpm
In conclusion based on the above fixture units (2021 Uniform Plumbing Code - Chart A 103.1(1)),
the peak design flow is estimated around 40 gpm and the irrigation demand peak design flow is
estimated around 1.8 gpm for a total of 41.8 gpm. The proposed 2” copper pipe is capable of
flowing 41.8 gpm at approximately 4.27 ft/s.
ENGINEERING REPORT – EVERGOODS
Sanitary Sewer Improvements January 2025 Page 8
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5 Sanitary Sewer Improvements
5.1 Proposed Improvements
A simple service connection is the only sanitary sewer improvement required. The proposed
service design can be summarized as follows:
Length = 82 feet
Slope = 2%
Nominal Diameter = 4-inch
Minimum Depth = 5
Maximum Depth = 7 feet
Pipe Material = SDR 26 PVC (0.013 Roughness Coeff.)
As proposed, the 4” service has a hydraulic capacity of 40 GPM at only 1.8” (45% full). This can
be compared to the instantaneous building water demand of 40 GPM. For the purposes of
estimating downstream system impact, from Section 4.1, the average day sewer flow is estimated
to be 260 gallons per day. The peak hour flow can be estimated using a peaking factor approach
where
Peak Hour Flow = Average Day Flow × Peaking Factor,
Peaking Factor = (18 + √P)/(4 + √P).
where P denotes population in thousands (“Circular DEQ-2 Design Standards for Public Sewage
Systems” 2016). The expected total population of the site is 20 employees, yielding a peaking
factor of 4.35 and a peak hour flow of 47.1 gallons per hour.
ENGINEERING REPORT – EVERGOODS
Storm Water Improvements January 2025 Page 9
Version 1/24/2025
6 Storm Water Improvements
This section provides a design basis and hydraulic calculations for sizing stormwater facilities for
Evergoods commercial site. The City of Bozeman Design Standards and Specifications Policy
and the Montana Post-Construction Storm Water BMP Design Guidance Manual (Peterson,
Savage, and Heisler 2017) were used as the primary guidelines for this stormwater drainage
design.
6.1 Existing Conditions
The existing site is native grasses, that slopes 0.5% to 1.5% to the northwest. There is an existing
storm pond located on Lot 9, Block 2 of the Glen Lake Subdivision. This existing storm pond was
designed to hold a 10-year 2-hour storm event, within Madison Engineering calculations for this
storm pond they accounted for a C value of 0.65 for all lots which includes lot 2A. The storm
storage accounted for within the original subdivision design for this lot is 2,015 cubic feet if the C
value of 0.65 is used (see appendix C for Madison Engineering stormwater design report).
6.2 General Design
The proposed development will be a 9,025-sf structure and an asphalt paved parking lot. There
has been multiple geotechnical investigations and reports for this site, the most recent
geotechnical report has been referenced for this site. 4 soil test pits were excavated during the
geotechnical investigation and the results show that the site consists of 1 foot of fill material with
1.5 feet of topsoil and sandy lean clay below, followed by poorly graded gravels to the bottom of
the test pits (8 feet). Groundwater wasn’t encountered in all of the test pits. Due to having poorly
graded gravels 2.5 to 3 feet below the existing ground surface, infiltration is feasible for this site.
The storm pond and the CMP infiltration system will capture the entire first ½” of rainfall so the
design will incorporate low impact development by treating the stormwater runoff.
6.3 Hydrologic Methodology
The rational method was used to determine peak runoff rates. The rational formula provides a
peak runoff rate which occurs at the time of concentration.
Q = CfCiA
Where C = Weighted C Factor
Cf = correction factor for infrequent storms
i= Storm Intensity (in/hr)
A = Area (acres)
Q = Runoff (cfs)
The storm intensities were developed from table 6.5.2 of the City of Bozeman Design Standards
and Specifications. Runoff coefficients for each basin were calculated using a weighted percentile
of impervious and pervious area. The coefficient used are shown in the table below.
ENGINEERING REPORT – EVERGOODS
Storm Water Improvements January 2025 Page 10
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Table 1 - Runoff coefficients used.
RUNOFF COEFFICIENTS
Asphaltic and Concrete 0.95
Heavy Soil (flat) 0.17
Heavy Soil (average) 0.22
Drives, Walks and Roofs 0.95
Time of concentration was determined using the following equation:
Tt = .√
.
Where Tt = Sheet flow travel time (min)
n= roughness coefficient
L= Flow length (ft)
P2= 2-year, 24-hour rainfall depth (inch)
S= Slope of Basin, (ft/ft)
Ku= Unit conversion constant, 0.42 in CU
The modified rational method approach was used to compute runoff volume. This method can
be used for storm durations equal or greater than the time of concentration. This method assumes
the maximum runoff rate occurs at the time of concentration and continues to the end of the storm.
Maximum runoff rates for durations greater than the time of concentration are less than the peak
runoff rate because average storm intensities decrease as duration increases. The total runoff
volume is computed by multiplying the duration of the storm by the runoff rate.
Retention volumes were calculated using the modified rational method. The modified rational
method uses peak flow rates to determine volume. The peak flow rate is determined using the
rational method, that peak flow rate is conservatively held constant for the duration of the storm.
The volume of retention volume required is calculated by multiplying the peak runoff by storm
duration. City of Bozeman Standards requires both minor and major storm event be evaluated. In
this case a 10-yr 2-hr storm was evaluated for the minor storm event and both the 100-yr 2-hr and
100-yr 24-hr were evaluated for the major storm event. The intensities are developed from table
6.5.2 of the City of Bozeman Design Standards and Specifications. Runoff coefficients are taken
from Table 6.6.4. Retention volume is determined using the following equation:
V = 7200Q
Where V = Volume, cf
Q = flow rate, cfs
6.4 Basin A Retention Chamber
Basin A is located underneath the southern parking lot. Stormwater runoff from Basin A will be
conveyed via curb and gutter to 2 proposed inlets, where it will be piped to a 30” underground
storm inflation system. The 30” underground storm inflation systems will consist of 1 lateral 50’
long that is perforated with a 1 foot of gravel on all side of the pipe. Basin A is comprised of
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asphaltic and concrete, and heavy soils/landscape areas. This retention system is sized to handle
the entire volume of a 10-year, 2-hour storm event. This retention system will store runoff as it
evaporates and percolates into the existing gravels on site. The required retention storage for
Basin A is 563 cubic feet.
6.5 Basin B Retention Chamber
Basin B is located underneath the south western parking lot. Stormwater runoff from Basin B will
be conveyed via curb and gutter to a proposed inlet, where it will be piped to a 30” underground
storm inflation system. The 30” underground storm inflation system will consist of 2 lateral 55 long
that is perforated with a 1 foot of gravel on all side of the pipe. Basin B is comprised of asphaltic
concrete, roofs, and heavy soils/landscape areas. This retention system is sized to handle the
entire volume of a 10-year, 2-hour storm event. This retention system will store runoff as it
evaporates and percolates into the existing gravels on site. The required retention storage for
Basin B is 1,132 cubic feet.
6.6 Basin C Retention Pond
Basin C is located on the north side of the site. Stormwater runoff from Basin C will be flow out of
roof drain downspouts and flow to a retention pond in the northern corner of the site. The retention
pond is 93’ long by 11’ wide with 4:1 side slopes. Basin C is comprised of roof, and heavy
soils/landscape areas. This retention pond is sized to handle the entire volume of a 10-year, 2-
hour storm event. This retention pond will store runoff as it evaporates and percolates into the
existing gravels on site. The required retention storage for Basin B is 392 cubic feet.
6.7 Inlets & Storm Sewer
Using the Modified Rational Method, a contributing flow to each inlet in the system was
determined. The inlet grates were designed to accommodate the 25-year storm event without
overtopping a depth 0.15’ below the top of curb or spreading greater than 9 feet. Inlets and
manholes will have a 9” sump for sediment collection. Storm pipes were sized to accommodate
the 100-year storm event. Pipes are sloped to maintain a minimum velocity of 3 ft/s when flowing
full to prevent sediment deposit. A manning’s N of 0.009 was used for the A-2000 Storm pipe
within the model per the manufacturer’s specifications.
6.8 Groundwater
Groundwater is known to be high in this location. However, a soils investigation report was
completed for the property by C&H Engineering in 2020. The report states that groundwater or
seepage was not observed during the excavation of the test pits. Another soils investigation report
was conducted in 2003 by Allied Engineers. From this report TP-5 & TP-7 would most accurately
represent the site, these test pit logs did not note any groundwater but did indicate that soils get
moist around 8’ deep.
6.9 System Maintenance
Regular maintenance of stormwater facilities is necessary for proper function of the drainage
system. All stormwater maintenance will be the responsibility of the property owners. Maintenance
items include removing debris from inlet grates, cleaning and flushing pipes, cleaning manhole
sumps, and establishing ground cover after construction. The infiltration facilities must be
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inspected after every storm event to ensure that they are draining properly. The infiltration facilities
will be cleaned and maintained by access risers installed on the underground stormwater
retention system per “Contech Inspection and Maintenance Guide”.
6.10 Erosion Sediment Control
During construction, stormwater pollutant controls will include silt fencing, straw wattles, rock
check dams, and straw bales. Silt fence, straw waddles, or other perimeter protection will be
installed on the down gradient edge of disturbed soil. Straw wattles, straw bales, or other erosion
protection will be placed in newly installed inlets. Temporary erosion control measures will be
installed and continuously maintained for the duration of construction.
This project will require acceptance of a Stormwater Pollution Prevention Plan (SWPPP) permit
for stormwater discharge associated with construction activity prior to starting any construction.
Protection during and immediately after construction, will be controlled in accordance with this
permit and the Montana Sediment and Erosion Control Manual.
Permanent erosion control will consist of implementation of seeding disturbed areas. Any visible
sediment must be removed from the pond prior to completing construction.
6.11 Flooding
Excessive runoff from a large storm event (significantly exceeding the design storm, i.e 100-year)
will be routed such that it does not inundate buildings, drainfields or over top the roadway. The
stormwater infrastructure has been analyzed for the 100-year storm. In the event of a 100-year
storm the retention systems will be filled causing the water to over top the curb and be routed to
the existing oversized storm pond located in lot 9 block 2 of the Glen Lakes Subdivision.