HomeMy WebLinkAbout008 BIG406MOB Water Sewer Storm Design ReportJOB NO. B20-041
MONTANA | WASHINGTON | IDAHO | NORTH DAKOTA | PENNSYLVANIA
JANUARY 2022
406.586.0277
tdhengineering.com
234 East Babcock Street
Suite 3
Bozeman, MT 59715
CLIENT ENGINEER
Bechtle Architects
4515 Valley Commons Drive, #201
Bozeman, MT 59718
TD&H Engineering
234 East Babcock Street, Suite 3
Bozeman, MT 59715
Engineer: Ahren Hastings, PE
BIG406LLC MEDICAL OFFICE BUILDING
BOZEMAN, MONTANA
BASIS OF DESIGN REPORT
Image courtesy of Bechtle Architects
B20-041 BIG406LLC MEDICAL OFFICE BUILDING Page 1 of 3
BIG406LLC MEDICAL OFFICE BUILDING – PHASE I
DESIGN REPORT
JANUARY 2022
Purpose and Introduction
The purpose of this report is to explain how water, sanitary sewer, and storm drainage
improvements will be designed to meet the City of Bozeman requirements and Montana
Public Works Standard Specifications (MPWSS) to provide service to Phase I of the new
BIG406LLC Medical Office Building proposed in Lot 4 of the Sundance Minor
Subdivision at the corner of Galloway St. and Davis Ln. The report will provide
information on the detailed design of the above-mentioned infrastructure.
The project is located at along the western edge of the right-of-way of Davis Lane
between Galloway Street and Equestrian Lane north of Baxter Lane. The parcel is
described as Lot 4 of Minor Subdivision 509, located in the SE ¼ of S34, T01 S, R05 E,
Gallatin County, Montana and is 3.247 acres in size. The property is currently
undeveloped and is within zoning district B-2. Proposed site improvements include the
construction of a new multi-story, commercial medical office building with associated
parking, landscape, hardscape, utility services, and stormwater management systems.
No off-site infrastructure improvements are proposed to service this development.
Project construction is proposed to be performed in two phases. Phase I is the subject of
this site plan and will include construction of a new 3-story medical office building with an
approximate footprint of 8,345 square-feet and a total floor space of 25,038 square-feet.
Phase I will also include 101 new parking spaces, new water and sewer services, and an
on-site stormwater management system.
Phase II will be submitted at an undetermined date under a separate site plan and is
anticipated to include expansion of the 3-story medical office building constructed in
Phase I. Phase II will also include construction of an additional new parking spaces, as
well as the landscape and hardscape associated with the additional parking. The
proposed water, sewer, and storm management systems for Phase I are being sized
and designed to service the finished site after completion of Phase II.
Design Report
Water
The project lot has an existing water stub at the northwest corner that was installed to
accommodate a future main extension to multiple buildings on Lot 4. However, only one
building is proposed on this lot and therefore this stub won’t be needed and is proposed
to be abandoned.
A new 4-inch domestic water service and a fire service line (Size TBD) will be extended
to the new building from the existing 8-inch main in Galloway Street. Final service sizing
will be verified by the mechanical engineer. The services will be Class 51 ductile iron
and be installed per the City of Bozeman Design Standards and Modifications to
Montana Public Works Standard Specifications (MPWSS).
The estimated domestic water demands for the Phase 1 of the project are summarized
B20-041 BIG406LLC MEDICAL OFFICE BUILDING Page 2 of 3
in Table 1 below with supporting assumptions and calculations in accordance with
C.O.B. DSSP Section V.A.4 provided in Appendix A.
Table 1:
Estimated Water Demands
Average Day Max. Day Peak Hour
Phase 1
Building Demand 7,310 gpd 16,813 gpd 15.23 gpm
TABLE 1: Estimated domestic water demands based on an equivalent population of 43 people and a unit rate
of 170 gpcd. Calculations can be found in Appendix A.
The irrigation system water source is proposed as a new exempt well on the site and will
not use the public water supply.
Sewer
An existing 8-inch sewer stub was extended to the northwest corner project site that was
intended for a future main extension to connect multiple buildings on Lot 4. Since there
will only be one building on Lot 4, a sewer main stub is no longer needed. A new 6-inch
sewer service is proposed from the building, with 6” sewer cleanouts at maximum 100-
foot intervals. It is proposed to use the existing sewer stub as a service connection by
means of connecting with an 8x6 inch reducer. The new 6” sewer service line will be
SDR-26 PVC and will be installed per the City of Bozeman Design Standards and
Modifications to Montana Public Works Standard Specifications (MPWSS).
The estimated sewer demands for Phase 1 of the project are calculated in accordance
with C.O.B. DSSP Section V.B. and using information from the City’s 2015 Wastewater
Facilities Plan and DEQ circular 4. The estimated sewer demands for Phase 1 are
summarized in Table 2 below with assumptions and supporting calculations provided in
Appendix B.
Table 2:
Estimated Sewer Demands
Average Day (gpd) Peak Hour (gpm)
New Building Demand 2,800 -
Lot Infiltration 480 -
Total Sewer Demand 3,280 8.75
TABLE 2: Estimated sanitary sewer demands based on an average daily building occupancy of 280 people and
a unit flow rate of 10 gpcd. Calculations can be found in Appendix B.
The latest approved Sundance Minor Subdivision engineering design report allocated
2,000 gal/day/acre domestic sewer flow plus 150 gal/day/acre Infiltration flows for Lot 4
based on future anticipated land use. This equates to an allocated 6,981 gpd allocated
daily demand for Lot 4 which more than covers the estimated Phase 1 average day
demand and leaves an estimated 3,701 gpd available for Phase 2.
B20-041 BIG406LLC MEDICAL OFFICE BUILDING Page 3 of 3
Storm Drainage
The existing project site consists of a vacant field that slopes generally to the north. The
proposed site development includes a new multi-story building, new concrete sidewalks,
hardscape patios, new parking areas, and new landscaping. An existing drainage ditch
north-to-south along the west edge of the site, and an existing public storm water pond
occupies an easement in the southeast corner of the lot. The drainage ditch is the
closest outfall location and is proposed to be regraded within the drainage easement
along the western property line to accommodate a new sidewalk. Stormwater from the
site and subdivision is conveyed north via this drainage ditch to a receiving tributary
south of Cattail Street.
The proposed site grading directs all on-site runoff to a new stormwater pond at the
northwest corner of the site. At the lowest point of the site parking and hardscape, a
drainage chase will direct runoff to the combination detention/retention pond with an
outfall structure discharging to the adjacent drainage ditch. To accommodate the storm
runoff from the buildings, a series of roof drains and drainage chases will direct runoff to
the parking lot which will also drain to the stormwater pond.
The pond is designed to fully retain/infiltrate the flow from the first half inch of rainfall
from site impervious areas. As this will be the only stormwater feature for both phases of
the project, the pond has been sized for the full phase 2 buildout of the site. Runoff
volumes greater than the first half inch will be allowed to flow to the drainage ditch via a
pond outfall structure with a weir positioned above the retention volume elevation
designed to restrict flows to pre-development flow rate. The ultimate stormwater
destination will be to the receiving tributary south of Cattail Street, with the first half inch
of rainfall retained on-site and the overflows flows being restricted to the pre-
development runoff rate for the design storm.
A geotechnical excavation investigation was conducted at the site on October 25th, 2021.
Groundwater was observed from depths of approximately 5 to 7.5 feet below existing
grade in test pits with depths of 6.2 to 8.5 feet. Therefore, it is anticipated that
groundwater will be sufficiently deep to allow for a retention/infiltration strategy to be
successful at this site using an extended detention surface pond per the Montana Post-
Construction Stormwater BMP Design Guidance Manual. Perforated pipe in subgrade
drains is proposed along the entire length of the pond bottom for settlement of pollutants.
The subgrade drains will direct flow to the outfall structure which will have a slot
designed to drain the first half inch of rain over a minimum of forty-eight hours to provide
time for pollutants to settle prior to discharge. The subgrade drains will allow seasonally
high groundwater to drain from the pond bottom and prevent water from stagnating.
APPENDIX A
Water Calculations
BIG406LLC Medical Office Building
Galloway St. & Davis Ln.
Date: 1.21.2022
Phase 1 Water Demands
Domestic Water Demand - New Medical Office Building:
Equivalent Population= 43 people (sewer flow / 64.4 gpcd - from 2015 Wastewater Plan)
Average Day Demand = 7,310 GPD (170 gppd per COB Design Standards)
Peak Hour Demand:
Average Day Demand = 7,310 GPD (All Uses)
Average Day Demand = 5.08 gpm (GPD / 1,440 minutes)
Maximum Day Demand = 11.68 gpm (Ave. Day x Peaking Factor = 2.3)
Peak Hour Demand = 15.23 gpm (Ave. Day x Peaking Factor = 3)
APPENDIX B
Sewer Calculations
BIG406LLC MEDICAL OFFICE BUILDING
Galloway St. & Davis Ln.
Date: 01.21.2022
Phase 1 Sewer Flow Calculation
Average Daily Flow:
Wastewater Flow Rate = 10.0 GAL./PERSON/DAY (10 gppd for Hostpital, Medical-Employee per MT DEQ-4)
Daily medical providers = 14.0 PEOPLE (from architect plans)
Daily building staff = 42.0 PEOPLE (3 staff per provider per architect plans)
Daily Patients = 224.0 PEOPLE (estimated 16 outpatients per provider per day)
Average Total Daily Occupancy = 280.0 PEOPLE
Average Daily Flow = 2,800 GPD
Infiltration:
Property Size = 3.2 acres
Infiltration Flow = 480 GPD (150 gpd/acre per COB Design Standards)
Peak Sewer Flow:
Average Day Demand = 2,800 GPD (total domestic flow)
Equivalent Population = 43 Persons (total flow / 64.4 gpcd - from 2015 Wastewater Plan)
P = 0.0435 (population/1,000)
Peaking Factor = 4.33
Peak Domestic Sewer Demand = 12,114 GPD (avg. day demand)*(peaking factor)
+ Infiltration Flow = 480 GPD (not peaked)
Total Peak Flow = 12,594 GPD (peaked domestic flow + infiltration)
Peak Sewer Flow = 8.75 GPM (peak flow)/(24 hrs/day)/(60 min/hr)
௫ ௩
= 18 + ℎ ଵ/ଶ
4 + ℎ ଵ/ଶ
BIG406LLC MEDICAL OFFICE BUILDING
Galloway St. & Davis Ln.
Date: 01.21.2022
6" Sewer Service Pipe Capacity
Input Values
d = 0.50 ft = 6"
y = 0.375 ft = 75%
Calculated Values (Equations from Fluid Mechanics by Chow)
Theta (Θ) 4.19 rad 2*arccos(1-y/(d/2))
Area (A) 0.16 ft2 (1/8)*(Θ-sinΘ)d2
Wetted Perimeter (P) 1.05 ft 0.5Θd
Hydraulic Radius (R ) 0.15 ft (.25)*(1-(sinΘ)/Θ)d
Top Width (T) 0.43 ft (sin 0.5Θ)d
Mannings Equation (Equation from Fundamentals of Mechanics by Munson)
n = 0.013 (per COB Design Standards)
S0 = 0.0100 ft/ft (1.0% Min. Slope)
Q = 0.51 cfs Q = 1.49/n*A*R2/3*S0
0.5
Q = 230.3 gpm Q gpm = (Q cfs)(7.48 gal/ft3)(60 sec/min)
V = 3.25 ft/s V = Q/A
Results A 6" diameter sewer service flowing 75% full at the min. slope of 1.0%
has a carrying capacity of 230.3 gpm.
JOB NO. B13-016
GREAT FALLS, BOZEMAN, KALISPELL & SHELBY, MT | SPOKANE, WA | LEWISTON, ID | WATFORD CITY, ND | MEDIA, PA
JUNE 2018
406.586.0277
tdhengineering.com
234 East Babcock Street
Suite 3
Bozeman, MT 59715
CLIENT ENGINEER
Baxter Meadows Land Partners TD&H Engineering
234 East Babcock Street, Suite 3
Bozeman, MT 59715
Engineer: Ahren Hastings, PE
WATER, SEWER, PAVING AND STORM DRAINAGE
IMPROVEMENTS
SUNDANCE SUBDIVISION PHASES A & C
INFRASTRUCTRE IMPROVEMENTS
BOZEMAN, MONTANA
DESIGN REPORT
7-24-18
Ammeded 5.11.2020
to include Equestrian
Lane extension to
Davis Lane
Latest approved Sundance Minor Subdivision
Engineering Design Report
3
Each lot in the subdivision has or will have at least an 8-inch sewer stubbed out to the lot.
All new sewer mains will be 8-inch diameter SDR 35 PVC. The sewer mains have been
sized for the development based upon the following values from the City of Bozeman
Design Standards and Specification Policy, Revised 3/31/2011:
Residential
2.11 people / unit
188 Units
89 gallons / capita / day
150 gallons / acre / day infiltration
2000 gallons per acre per day average (commercial)
25 gallons per acre per day average (park)
New sewer mains will be designed to roughly parallel the road centerline grades. A
capacity check on 8-inch sewer main using the minimum slope of 0.4% and a Manning’s
friction factor of 0.013 indicates new wastewater flows from the subdivision will not
exceed the pipe’s capacity assuming 75% of the maximum capacity.
8-inch sewer mains will be able to adequately handle the flows as described above.
However, since this subdivision falls within the Baxter Meadows Lift Station zone
adequate capacity must be present in the lift station to support these flows. From the
original Baxter Lift Station design report, for B2 zoning, 3,495 gpd/ac was used. This
project falls entirely within B-2 zoning and the size of Lots 2, 3, 4, Sundance Park and R2
make up a total of 23.9 acres.
Allocated capacity within the lift station is calculated as follows:
3,495 gpd/ac x 23.9 ac = 83,531 gpd / 1440 min/day = 58.0 gpm
150 gpd/ac x 23.9 ac = 3,585 gpd / 1440 min/day = 2.5 gpm
Peaking factor from original lift station design report = 3.01
(58.0x3.01)+2.5 = 177.1 gpm (allocated flow in lift station)
Estimated flow for this subdivision is calculated as follows:
Lots 3, 4 and R2 are commercial and total 11.89 acres
2,000 gpd/ac x 11.89 ac = 23,780 gpd / 1440 min/day = 16.5 gpm
Sundance Park total 2.83 acres
25 gpd/ac x 2.83 ac = 70.75gpd / 1440 min/day = 0.05 gpm
150 gpd/ac x 14.72 ac = 2,208 gpd / 1440 min/day = 1.5 gpm
Peaking factor from original subdivision design report = 4.1
(16.5 x4.1)+2.5 = 70.2 gpm
Lots 2 is 188 residential units and 0.67 acres (29,397 SF) of commercial
2,000 gpd/ac x 0.67 ac = 1,340 gpd / 1440 min/day = 0.9 gpm
188 x 2.11 x 89 = 35,305 gpd / 1440 min/day = 24.5 gpm
Sewer flow rates
allocated for Lot 4:
2,000 gpd/ac Domestic
+150 gpd/ac Infiltration
Appendix C
Storm Water Calculations
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B20-041 DRAINAGE
DRAINAGE BASIN & RETENTION FACILITY SIZING
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C4.1
TRB
CJC
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SHEET
DESIGNED BY:
QUALITY CHECK:
JOB NO.
FIELDBOOK
DRAWN BY:
DATE:
BIG 406 LLC MEDICAL OFFICE BUILDING
BOZEMAN, MONTANA
B20-041
01.21.22
REV DATE REVISION
Engineering
234 E. BABCOCK ST., SUITE 3 • BOZEMAN, MONTANA 59715
406.586.0277 • tdhengineering.com
SITE PLAN REVIEW
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Big 406 LLC Medical Office Building
Date: 01.21.2022
Basin RRV (First 0.5") Calculations
Rational Formula "C" Values Per
MTDEQ 8 "C"
Impervious Area/Pond Surface 0.9
Gravel Area 0.8
Unimproved Area 0.3
Lawn/landscape 0.1
Post-Development Conditions:
Basin # Description Total
Area (SF)
Total
Area (AC)
Impervious
Area (SF)
Gravel
Area (SF)
Unimproved
Area (SF)
Landscape
Area (SF)
Composite
Cave
1 Whole Site: Post-Development 128,825 2.96 97,239 0 0 31,586 0.70
Runoff Reduction Volume (First 0.5" of Rainfall):
P = 0.5 Inches (Water Quality Rainfall Depth)
Rv = 0.73 (Dimensionless Runoff Coefficient, R
v=0.05+0.9(I)
I = 75.5% (Percent Impervious Area Draining to Facility)
A = 2.96 AC (Total Drainage Area)
RRV = 0.090 AC-FT (Runoff Reduction Volume)*
3,915 CF
*RRV = PRvA/12 per Montana Post-Construction Storm Water BMP Design Guidance Manual Eq. 3-1
Big 406 LLC Medical Office Building
Date: 01.21.2022
Peak Runoff
Tc* Tc* 10 yr Flow
Slope Distance CCf t1 Slope k Velocity Distance t2 Total Cave CCf Area Total i Q
% ft min % fps ft min min ac min in/hr cfs
1.06 88 0.30 13.80 1.25 0.491 1.80 316 2.92
Tc* Tc* 10 yr Flow
Slope Distance CCf t1 Slope k Velocity Distance t2 Total Cave CCf Area Total i Q
% ft min % fps ft min min ac min in/hr cfs
1.06 88 0.70 6.83 1.25 0.491 1.80 316 2.92
*Tc minimum of 5 minutes
FHWA HEC 22, Eqn 3-4
Cf = 1.0 for 10-year storm event K=0.457 Grassed Water Way (Roadside Ditch)
K=0.619 Paved Area
K=0.491 Unpaved shallow concentrated flow
9.76 2.084 4.34
Shallow Concentrated Flow
Post-
Development
Site
9.76 0.70 0.70 2.96
TIME OF CONCENTRATION 10 YEAR FLOW CALC
Overland Flow Shallow Concentrated Flow
1.30
TIME OF CONCENTRATION 10 YEAR FLOW CALC
IDF curve equation for 10-yr storm
Tc = time to concentration in hours
Rational Method
Cf = 1.0 for 10-yr event
0.30
Pre-
Development
Site
16.72 0.30 2.96 16.72 1.468
Overland Flow
1 3
1 87 1 1
/
f
c S
. ( . CC ) D
T
-
= V = 3 . 28 × k × S ݅ଵ = 0.64 ⋅ ܶି.ହ
ܳ = ܣ ⋅ ݅ ⋅ ܥܥ
Big 406 LLC Medical Office Building
Date: 01.21.2022
25-yr Pipe Flow Calculations
25-Year Flow Calcs: Pipe Capacity Calcs (94% full):
Location Basin Size
(Acres) C
ave CCf
Tc
(min)
25 yr
i
(in/hr)
Flow
Q2
(cfs)
Pipe
Diameter (d)
(ft)
Pipe Slope
(%)
Manning's
n
94% Flow
Depth (y)
(ft)
Theta (Θ)
(rad.)
Area (A)
(ft2)
Hydraulic
Radius (R)
(ft)
Qfull
(cfs)
Pond Release Structure Overflow Pipe 2.96 0.70 0.77 9.76 2.49 5.71 1.50 0.50% 0.013 1.41 5.29 1.72 0.43 8.01
0 Manning's Eqn: Q = 1.49/n*A*R
2/3
*S0
0.5
Rational Method
Cf = 1.1 for 25-yr event
IDF curve equation for 25-yr storm
Tc = time to concentration in hours
Q = CC f × i × A
. 64
i 25 = 0 . 78 × T c -
Big 406 LLC Medical Office Building
Date: 01.21.2022
Outlet Structure Main Slot Width Calculations
Pre-Development
Peak Runoff (cfs) C (Constant)
Head above
Slot (ft)
1.30 3.33 0.5
Slot width= 1.11 ft
13.28 in
Q = Discharge (cfs)
C = Weir Coefficient = 3.33
L = Length of Weir Opening (ft)
Reference - City of Bozeman Standards H = Head (ft)
C × L × H 3 / 2 = Q weir
Big 406 LLC Medical Office Building
Date: 01.21.2022
Outlet Structure Extended Detention Slot Width Calculations
Pre-Development
Peak Runoff (cfs) C (Constant)
Head above
Slot (ft)
0.02 3.33 0.75
Slot width= 0.0106 ft
0.128 in
Q = Discharge (cfs)
C = Weir Coefficient = 3.33
L = Length of Weir Opening (ft)
Reference - City of Bozeman Standards H = Head (ft)
C × L × H 3 / 2 = Q weir
R