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GALLATIN COUNTY FA IRGROUNDS
SURFACE IMPROVEMENTS
STORM DRAINAGE REPORT
BOZEMAN , MONTANA
CERTIFICATION
I hereby state that this Final Drainage Report has been prepared by me or under my supervision and
meets the standard of care and expertise which is usual and customary in this community of
professional engineers. The analysis has been prepared utilizing procedures and practices specified by
the City of Bozeman and within the standard accepted practices.
____________________________________________ ___________________________
Mike Russell, P.E. Date
04/01/2020
April 1, 2020
Project No. BOZ 13005.04
STORM DRAINAGE PLAN FOR
GALLATIN COUNTY FAIR GROUNDS “SURFACE IMPROVEMENTS ” PROJECT
GALLATIN COUNTY FAIR GROU NDS
901 NORTH BLACK AVEN UE
BOZEMAN, MONTANA 59715
OVERVIEW NARRATIVE
The purpose of this drainage plan is to present a summary of calculations to quantify the stormwater
runoff for the Gallatin County Fairgrounds “Surface Improvements” project. All design criteria and
calculations are in accordance with The City of Bozeman Design Standards and Specifications Policy , dated
March 2004. The site stormwater improvements have been designed with the intent to meet the
current City of Bozeman drainage regulations for the entire site to the extent feasible.
The site is located south of Oak Street and north of Tamarack Street. The entire Gallatin County
Fairgrounds lot is approximately 64.7 acres. The intent of this surface improvements project is to use
an on-site stockpile of recycled asphalt pavement material to “clean up” the identified areas.
Stormwater facilities proposed in the previous “Asphalt Pathways” project were sized conservatively,
assuming the entire area upstream (to the south) could be improved to asphalt paving. Calculations
from the previous “Asphalt Pathways” project are included in this submittal.
The existing surfaces that are being improved (and project extents) primarily consist of compacted
gravel surfacing. The proposed improvements consists of re-surfacing the compacted gravel surfaces
with recycled asphalt pavement to clean up exhibit areas and other areas with higher pedestrian and
vehicle traffic. The retention pond constructed with the ‘Asphalt Pathways’ project was sized to store
and retain the 25-year design event runoff from both the pathways project and this surface
improvements project. An additional gravel swale with a subsurface boulder pit constructed along the
southern boundary will intercept runoff flowing from the south and address concerns of runoff that
has historically drained off-site to the Oak Street R.O.W.
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I. Design Approach
The modified rational method was used to determine peak runoff rates and volumes. The
rational formula provided in The City of Bozeman Standard Specifications and Policy was used to
calculate the peak runoff rates on site, time of concentration, rainfall intensities, etc. To be
conservative, we treated most watersheds as if they were predominately impervious cover,
therefore we assumed a time of concentration of 5-minutes. For gravel surfaces, a runoff
coefficient of 0.6 was assumed. For recycled asphalt pavement, a runoff coefficient of 0.8 was
assumed.
II. Proposed Watershed Descriptions
For the following sections, please refer to Appendix A of this report, which graphically
shows and labels the watersheds as well as the proposed drainage and conveyance
facilities. The previous ‘Asphalt Pathways’ Storm Drainage Report has also been
appended to this report for reference. No percolation rates have been included in these
calculations to be conservative.
West Grandstand Improvements
The west grandstand improvements include re-surfacing the existing compacted gravel surface
with recycled asphalt pavement. Increased runoff to the west of the grandstand will be directed
towards the existing drainage swale located along the southern and western edge of the
proposed improvements. The 10-year pre-developed site detention is 420 ft 3, and the 10-year
post-developed site detention is 560 ft 3, which results in increased runoff of 140 ft 3. The swale
located along the southern and western edge of these improvements is approximately 450 L.F.
by 4 feet wide by 1 foot deep and provides approximately 1,800 ft 3 of runoff. Adequate storage
is provided for the West Grandstand improvements.
East Grandstand Improvements
The east grandstand improvements include re-surfacing the existing compacted gravel surface
with recycled asphalt pavement. Increased runoff to the east of the grandstand will be directed
towards the existing drainage swale located along the eastern edge of the proposed
improvements. This existing drainage swale drains to the existing retention pond that was
constructed with the ‘Asphalt Pathways’ project. For the surface improvements, the 10-year
pre-developed site detention is 267 ft 3, and the 10-year post-developed site detention
is 356 ft 3, which results in increased runoff of 89 ft 3. The swale located along the eastern
edge of these improvements provides approximately 405 ft 3 of runoff and the retention pond
was conservatively sized to provide 11,662 ft 3, which is 2,468 ft 3 more than the required 9,194
ft 3 (see attached ‘Asphalt Pathways’ storm drainage calculations for Watershed 2). Adequate
storage is provided for the East Grandstand improvements.
West RV Parking Improvements (Between 1 st and 2 nd Entrance)
The west RV parking improvements include re-surfacing the existing compacted gravel surface
with recycled asphalt pavement. Historically, runoff in this area sheet flows across the gravel
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surface and will either infiltrate or evaporate. The 10-year pre-developed site detention
is 365 ft 3, and the 10-year post-developed site detention is 486 ft 3, which results in
increased runoff of 121 ft 3. This additional runoff will sheet flow across an area equal to
approximately 31,000 ft 2. This results in a very nominal increase in water depth across this
area, and this increased runoff will continue to sheet flow across the gravel surface and
infiltrate or evaporate.
East RV Parking Improvements (Between 3 rd and 4 th Entrance)
The east RV parking improvements include re-surfacing the existing compacted gravel surface
with recycled asphalt pavement. Historically, runoff in this area sheet flows across the gravel
surface and will either infiltrate or evaporate. The 10-year pre-developed site detention
is 268 ft 3, and the 10-year post-developed site detention is 357 ft 3, which results in
increased runoff of 89 ft 3. This additional runoff will sheet flow across the Tamarack Lot,
which is an area equal to approximately 93,000 ft 2. This results in a very nominal increase in
water depth across this area, and this increased runoff will continue to sheet flow across the
gravel surface and infiltrate/evaporate.
Main Entrance ADA Parking Improvements
The main entrance ADA parking improvements include re-surfacing the existing compacted
gravel surface with virgin asphalt pavement. The 10-year pre-developed site detention is 169
ft 3, and the 10-year post-developed site detention is 267 ft 3, which results in increased
runoff of 98 ft 3. Historically, runoff in this area sheet flows into the landscaping/swale to the
north and east of the parking area where the runoff infiltrates or evaporates. Increased runoff
due to the improvements will continue to sheet flow into the landscaping to the north and
infiltrate/evaporate.
Exhibition Area
The exhibition area improvements include re-surfacing the existing compacted gravel surface
with recycled asphalt pavement. The previous ‘Asphalt Pathways’ project constructed a
boulder pit that was sized assuming all of the area to the south would be paved with virgin
asphalt. Runoff will be captured by a gravel swale and two standpipe area inlets connected by
a 12-inch perforated storm drain pipe. See attached ‘Asphalt Pathways’ storm drainage
calculations for Watershed 1B.
The area located between Tamarack and the Exhibit building historically sheet flows across
the gravel surface into the landscaping area to the northeast where it infiltrates/evaporates.
This area between Tamarack and the Exhibit building is 13,085 ft 2 and has a 10-year pre-
developed site detention of 529 ft 3. The post-developed site detention is 705 ft 3, which results
in increased runoff of 176 ft 3. A proposed drywell will be installed in this area sized to account
for the runoff increase. Post-development site detention assuming a full pave-out results in
838 ft 3, so the drywell was sized conservatively to store 310 ft 3 (838 ft 3 – 529 ft 3). No infiltration
has been considered in these calculations. See Sheet C4.2 for the grading plan in this area,
and see Sheet C5.0 for the drywell detail.
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III. Water Quality
The City of Bozeman Design Standards and Specifications Policy states the requirement to
capture or reuse the runoff generated from the first 0.5 inches of rainfall from a 24-hour storm.
We meet this requirement by retaining all storm runoff on site with no discharge into
the City storm drain system.
IV. Outlet Structures
All runoff will be captured and retained/infiltrated on site. There are no outlet structures
proposed for this project.
V. Appendices
Appendix A – Watershed Map
Appendix B – Hydrology Calculations
Appendix C – Surface Improvements O&M Plan
Appendix D – ‘Asphalt Pathways’ Storm Drain Report w/ Attachments
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Appendix A
WATERSHED MAP
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Appendix B
HYDROLOGY CALCULATIONS
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
10386 0.238 0.6 1 0.60 0.60 0.143057851
1 0.00 0.00 0
1 0.00 0.00 0
1 0.00 0.00 0
1 0.00 0.00 0
10386 0.2384 0.1431
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.14
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 1.31
5 3.22 0.46
10 2.05 0.29
15 1.58 0.23
20 1.31 0.19
25 1.13 0.16
30 1.00 0.14
35 0.91 0.13
40 0.83 0.12
45 0.77 0.11
50 0.72 0.10
55 0.68 0.10
60 0.64 0.09
75 0.55 0.08
90 0.49 0.07
105 0.44 0.06
120 0.41 0.06
150 0.35 0.05
180 0.31 0.04
360 0.20 0.03
720 0.13 0.02
1440 0.08
420.10 ft3 0.46 (ft3/s)
Gravel
RATIONAL METHOD FOR RUNOFF CALCULATIONS
WEST GRANDSTAND - PRE-IMPROVEMENT CONDITIONS
Surface Type
Totals
= 0.6000 Cwd x Cf =0.60
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
78.64 0.00 78.64
138.13 0.00 138.13
176.05 0.00 176.05
202.90 0.00 202.90
224.39 0.00 224.39
242.62 0.00 242.62
258.60 0.00 258.60
272.94 0.00 272.94
286.00 0.00 286.00
298.03 0.00 298.03
309.23 0.00 309.23
319.72 0.00 319.72
329.61 0.00 329.61
356.38 0.00 356.38
379.86 0.00 379.86
400.92 0.00 400.92
420.10 0.00 420.10
454.23 0.00 454.23
484.16 0.00 484.16
617.09 0.00 617.09
786.52 0.00 786.52
1002.46 0.00 1002.46
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
10386 0.238 0.8 1 0.80 0.80 0.19
1 0.00 0.00 0.00
1 0.00 0.00 0
1 0.00 0.00 0
1 0.00 0.00 0
10386 0.2384 0.1907
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.19
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 1.75
5 3.22 0.61
10 2.05 0.39
15 1.58 0.30
20 1.31 0.25
25 1.13 0.22
30 1.00 0.19
35 0.91 0.17
40 0.83 0.16
45 0.77 0.15
50 0.72 0.14
55 0.68 0.13
60 0.64 0.12
75 0.55 0.11
90 0.49 0.09
105 0.44 0.08
120 0.41 0.08
150 0.35 0.07
180 0.31 0.06
360 0.20 0.04
720 0.13 0.02
1440 0.08 0.02
560.14 ft3 0.61 (ft3/s)
1048.69 0.00 1048.69
1336.62 0.00 1336.62
645.54 0.00 645.54
822.78 0.00 822.78
560.14 0.00 560.14
605.64 0.00 605.64
506.48 0.00 506.48
534.56 0.00 534.56
439.47 0.00 439.47
475.17 0.00 475.17
412.31 0.00 412.31
426.29 0.00 426.29
381.33 0.00 381.33
397.38 0.00 397.38
344.80 0.00 344.80
363.92 0.00 363.92
299.19 0.00 299.19
323.49 0.00 323.49
234.74 0.00 234.74
270.53 0.00 270.53
104.85 0.00 104.85
184.17 0.00 184.17
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
= 0.8000 Cwd x Cf =0.80
Runoff Volume Discharge Volume Site Detention
=
Totals
Recycled Asphalt Pavement
RATIONAL METHOD FOR RUNOFF CALCULATIONS
WEST GRANDSTAND - POST-IMPROVEMENT CONDITIONS
Surface Type
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
6600 0.152 0.6 1 0.60 0.60 0.090909091
1 0.00 0.00 0
1 0.00 0.00 0
1 0.00 0.00 0
1 0.00 0.00 0
6600 0.1515 0.0909
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.09
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 0.83
5 3.22 0.29
10 2.05 0.19
15 1.58 0.14
20 1.31 0.12
25 1.13 0.10
30 1.00 0.09
35 0.91 0.08
40 0.83 0.08
45 0.77 0.07
50 0.72 0.07
55 0.68 0.06
60 0.64 0.06
75 0.55 0.05
90 0.49 0.04
105 0.44 0.04
120 0.41 0.04
150 0.35 0.03
180 0.31 0.03
360 0.20 0.02
720 0.13 0.01
1440 0.08
266.96 ft3 0.29 (ft3/s)
Gravel
RATIONAL METHOD FOR RUNOFF CALCULATIONS
EAST GRANDSTAND - PRE-IMPROVEMENT CONDITIONS
Surface Type
Totals
= 0.6000 Cwd x Cf =0.60
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
49.97 0.00 49.97
87.78 0.00 87.78
111.88 0.00 111.88
128.93 0.00 128.93
142.59 0.00 142.59
154.18 0.00 154.18
164.33 0.00 164.33
173.44 0.00 173.44
181.74 0.00 181.74
189.39 0.00 189.39
196.51 0.00 196.51
203.17 0.00 203.17
209.45 0.00 209.45
226.47 0.00 226.47
241.39 0.00 241.39
254.77 0.00 254.77
266.96 0.00 266.96
288.65 0.00 288.65
307.67 0.00 307.67
392.14 0.00 392.14
499.81 0.00 499.81
637.04 0.00 637.04
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
6600 0.152 0.8 1 0.80 0.80 0.12
1 0.00 0.00 0.00
1 0.00 0.00 0
1 0.00 0.00 0
1 0.00 0.00 0
6600 0.1515 0.1212
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.12
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 1.11
5 3.22 0.39
10 2.05 0.25
15 1.58 0.19
20 1.31 0.16
25 1.13 0.14
30 1.00 0.12
35 0.91 0.11
40 0.83 0.10
45 0.77 0.09
50 0.72 0.09
55 0.68 0.08
60 0.64 0.08
75 0.55 0.07
90 0.49 0.06
105 0.44 0.05
120 0.41 0.05
150 0.35 0.04
180 0.31 0.04
360 0.20 0.02
720 0.13 0.02
1440 0.08 0.01
355.95 ft3 0.39 (ft3/s)
Recycled Asphalt Pavement
RATIONAL METHOD FOR RUNOFF CALCULATIONS
EAST GRANDSTAND - POST-IMPROVEMENT CONDITIONS
Surface Type
Totals
= 0.8000 Cwd x Cf =0.80
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
66.63 0.00 66.63
117.03 0.00 117.03
149.17 0.00 149.17
171.91 0.00 171.91
190.12 0.00 190.12
205.57 0.00 205.57
219.11 0.00 219.11
231.26 0.00 231.26
242.32 0.00 242.32
252.52 0.00 252.52
262.01 0.00 262.01
270.90 0.00 270.90
279.27 0.00 279.27
301.96 0.00 301.96
321.86 0.00 321.86
339.70 0.00 339.70
355.95 0.00 355.95
384.86 0.00 384.86
410.22 0.00 410.22
522.86 0.00 522.86
666.41 0.00 666.41
849.38 0.00 849.38
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
9019 0.207 0.6 1 0.60 0.60 0.1242
0 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
9019 0.2070 0.1242
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.12
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 1.14
5 3.22 0.40
10 2.05 0.25
15 1.58 0.20
20 1.31 0.16
25 1.13 0.14
30 1.00 0.12
35 0.91 0.11
40 0.83 0.10
45 0.77 0.10
50 0.72 0.09
55 0.68 0.08
60 0.64 0.08
75 0.55 0.07
90 0.49 0.06
105 0.44 0.06
120 0.41 0.05
150 0.35 0.04
180 0.31 0.04
360 0.20 0.02
720 0.13 0.02
1440 0.08
364.81 ft3 0.40 (ft3/s)
Gravel
RATIONAL METHOD FOR RUNOFF CALCULATIONS
WEST RV PARKING - PRE-IMPROVEMENT CONDITIONS
Surface Type
Totals
= 0.6000 Cwd x Cf =0.60
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
68.29 0.00 68.29
119.95 0.00 119.95
152.88 0.00 152.88
176.19 0.00 176.19
194.86 0.00 194.86
210.68 0.00 210.68
224.57 0.00 224.57
237.01 0.00 237.01
248.35 0.00 248.35
258.81 0.00 258.81
268.53 0.00 268.53
277.64 0.00 277.64
286.22 0.00 286.22
309.47 0.00 309.47
329.86 0.00 329.86
348.15 0.00 348.15
364.81 0.00 364.81
394.44 0.00 394.44
420.43 0.00 420.43
535.87 0.00 535.87
683.00 0.00 683.00
870.52 0.00 870.52
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
9019 0.207 0.8 1 0.80 0.80 0.166
1 0.00 0.00 0.000
1 0.00 0.00 0
9019 0.207 0.166
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.17
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 1.52
5 3.22 0.53
10 2.05 0.34
15 1.58 0.26
20 1.31 0.22
25 1.13 0.19
30 1.00 0.17
35 0.91 0.15
40 0.83 0.14
45 0.77 0.13
50 0.72 0.12
55 0.68 0.11
60 0.64 0.11
75 0.55 0.09
90 0.49 0.08
105 0.44 0.07
120 0.41 0.07
150 0.35 0.06
180 0.31 0.05
360 0.20 0.03
720 0.13 0.02
1440 0.08 0.01
486.41 ft3 0.34 (ft3/s)
RATIONAL METHOD FOR RUNOFF CALCULATIONS
WEST RV PARKING - POST-IMPROVEMENT CONDITIONS
Surface Type
Recycled Asphalt Pavement
Totals
= = 0.8000 Cwd x Cf =0.80
Runoff Volume Discharge Volume Site Detention
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
91.05 0.00 91.05
159.93 0.00 159.93
203.84 0.00 203.84
234.92 0.00 234.92
259.81 0.00 259.81
280.91 0.00 280.91
299.42 0.00 299.42
316.02 0.00 316.02
331.14 0.00 331.14
345.08 0.00 345.08
358.04 0.00 358.04
370.18 0.00 370.18
381.63 0.00 381.63
412.63 0.00 412.63
439.82 0.00 439.82
464.20 0.00 464.20
486.41 0.00 486.41
525.92 0.00 525.92
560.58 0.00 560.58
714.49 0.00 714.49
910.66 0.00 910.66
1160.69 0.00 1160.69
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
6624 0.152 0.6 1 0.60 0.60 0.091239669
1 0.00 0.00 0
1 0.00 0.00 0
1 0.00 0.00 0
1 0.00 0.00 0
6624 0.1521 0.0912
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.09
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 0.84
5 3.22 0.29
10 2.05 0.19
15 1.58 0.14
20 1.31 0.12
25 1.13 0.10
30 1.00 0.09
35 0.91 0.08
40 0.83 0.08
45 0.77 0.07
50 0.72 0.07
55 0.68 0.06
60 0.64 0.06
75 0.55 0.05
90 0.49 0.04
105 0.44 0.04
120 0.41 0.04
150 0.35 0.03
180 0.31 0.03
360 0.20 0.02
720 0.13 0.01
1440 0.08
267.93 ft3 0.29 (ft3/s)
Gravel
RATIONAL METHOD FOR RUNOFF CALCULATIONS
EAST RV PARKING - PRE-IMPROVEMENT CONDITIONS
Surface Type
Totals
= 0.6000 Cwd x Cf =0.60
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
50.15 0.00 50.15
88.10 0.00 88.10
112.28 0.00 112.28
129.40 0.00 129.40
143.11 0.00 143.11
154.74 0.00 154.74
164.93 0.00 164.93
174.08 0.00 174.08
182.40 0.00 182.40
190.08 0.00 190.08
197.22 0.00 197.22
203.91 0.00 203.91
210.22 0.00 210.22
227.29 0.00 227.29
242.27 0.00 242.27
255.70 0.00 255.70
267.93 0.00 267.93
289.70 0.00 289.70
308.79 0.00 308.79
393.57 0.00 393.57
501.63 0.00 501.63
639.35 0.00 639.35
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
6624 0.152 0.8 1 0.80 0.80 0.122
1 0.00 0.00 0.000
1 0.00 0.00 0.000
1 0.00 0.00 0.000
1 0.00 0.00 0
6624 0.152 0.122
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.12
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 1.11
5 3.22 0.39
10 2.05 0.25
15 1.58 0.19
20 1.31 0.16
25 1.13 0.14
30 1.00 0.12
35 0.91 0.11
40 0.83 0.10
45 0.77 0.09
50 0.72 0.09
55 0.68 0.08
60 0.64 0.08
75 0.55 0.07
90 0.49 0.06
105 0.44 0.05
120 0.41 0.05
150 0.35 0.04
180 0.31 0.04
360 0.20 0.02
720 0.13 0.02
1440 0.08 0.01
357.24 ft3 0.25 (ft3/s)
668.83 0.00 668.83
852.47 0.00 852.47
411.72 0.00 411.72
524.76 0.00 524.76
357.24 0.00 357.24
386.26 0.00 386.26
323.03 0.00 323.03
340.93 0.00 340.93
280.29 0.00 280.29
303.06 0.00 303.06
262.96 0.00 262.96
271.88 0.00 271.88
243.21 0.00 243.21
253.44 0.00 253.44
219.91 0.00 219.91
232.10 0.00 232.10
190.81 0.00 190.81
206.32 0.00 206.32
149.71 0.00 149.71
172.54 0.00 172.54
66.87 0.00 66.87
117.46 0.00 117.46
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
= 0.8000 Cwd x Cf =0.80
Runoff Volume Discharge Volume Site Detention
=
Totals
Recycled Asphalt Pavement
RATIONAL METHOD FOR RUNOFF CALCULATIONS
EAST RV PARKING - POST-IMPROVEMENT CONDITIONS
Surface Type
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
4172 0.096 0.6 1 0.60 0.60 0.057465565
0.000 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
4172 0.0958 0.0575
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.06
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 0.53
5 3.22 0.18
10 2.05 0.12
15 1.58 0.09
20 1.31 0.08
25 1.13 0.06
30 1.00 0.06
35 0.91 0.05
40 0.83 0.05
45 0.77 0.04
50 0.72 0.04
55 0.68 0.04
60 0.64 0.04
75 0.55 0.03
90 0.49 0.03
105 0.44 0.03
120 0.41 0.02
150 0.35 0.02
180 0.31 0.02
360 0.20 0.01
720 0.13 0.01
1440 0.08
168.75 ft3 0.18 (ft3/s)
Gravel
RATIONAL METHOD FOR RUNOFF CALCULATIONS
ADA PARKING - PRE-IMPROVEMENT CONDITIONS
Surface Type
Totals
= 0.6000 Cwd x Cf =0.60
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
31.59 0.00 31.59
55.49 0.00 55.49
70.72 0.00 70.72
81.50 0.00 81.50
90.14 0.00 90.14
97.46 0.00 97.46
103.88 0.00 103.88
109.64 0.00 109.64
114.88 0.00 114.88
119.72 0.00 119.72
124.22 0.00 124.22
128.43 0.00 128.43
132.40 0.00 132.40
143.16 0.00 143.16
152.59 0.00 152.59
161.05 0.00 161.05
168.75 0.00 168.75
182.46 0.00 182.46
194.48 0.00 194.48
247.88 0.00 247.88
315.94 0.00 315.94
402.68 0.00 402.68
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
4172 0.096 0.95 1 0.95 0.95 0.091
1 0.00 0.00 0.000
1 0.00 0.00 0.000
1 0.00 0.00 0.000
1 0.00 0.00 0
4172 0.096 0.091
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.09
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 0.83
5 3.22 0.29
10 2.05 0.19
15 1.58 0.14
20 1.31 0.12
25 1.13 0.10
30 1.00 0.09
35 0.91 0.08
40 0.83 0.08
45 0.77 0.07
50 0.72 0.07
55 0.68 0.06
60 0.64 0.06
75 0.55 0.05
90 0.49 0.04
105 0.44 0.04
120 0.41 0.04
150 0.35 0.03
180 0.31 0.03
360 0.20 0.02
720 0.13 0.01
1440 0.08 0.01
267.19 ft3 0.19 (ft3/s)
Asphalt Pavement
RATIONAL METHOD FOR RUNOFF CALCULATIONS
ADA PARKING - POST-IMPROVEMENT CONDITIONS
Surface Type
Totals
= 0.9500 Cwd x Cf =0.95
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
50.02 0.00 50.02
87.85 0.00 87.85
111.97 0.00 111.97
129.05 0.00 129.05
142.72 0.00 142.72
154.31 0.00 154.31
164.48 0.00 164.48
173.59 0.00 173.59
181.90 0.00 181.90
189.55 0.00 189.55
196.67 0.00 196.67
203.35 0.00 203.35
209.63 0.00 209.63
226.66 0.00 226.66
241.60 0.00 241.60
254.99 0.00 254.99
267.19 0.00 267.19
288.90 0.00 288.90
307.93 0.00 307.93
392.48 0.00 392.48
500.24 0.00 500.24
637.58 0.00 637.58
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
13085 0.300 0.6 1 0.60 0.60 0.18023416
0.000 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
13085 0.3004 0.1802
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.18
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 1.65
5 3.22 0.58
10 2.05 0.37
15 1.58 0.28
20 1.31 0.24
25 1.13 0.20
30 1.00 0.18
35 0.91 0.16
40 0.83 0.15
45 0.77 0.14
50 0.72 0.13
55 0.68 0.12
60 0.64 0.12
75 0.55 0.10
90 0.49 0.09
105 0.44 0.08
120 0.41 0.07
150 0.35 0.06
180 0.31 0.06
360 0.20 0.04
720 0.13 0.02
1440 0.08
529.27 ft3 0.58 (ft3/s)
Gravel
RATIONAL METHOD FOR RUNOFF CALCULATIONS
EXHIBITION AREA - PRE-IMPROVEMENT CONDITIONS
Surface Type
Totals
= 0.6000 Cwd x Cf =0.60
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
99.08 0.00 99.08
174.02 0.00 174.02
221.80 0.00 221.80
255.62 0.00 255.62
282.70 0.00 282.70
305.66 0.00 305.66
325.81 0.00 325.81
343.87 0.00 343.87
360.32 0.00 360.32
375.48 0.00 375.48
389.59 0.00 389.59
402.80 0.00 402.80
415.26 0.00 415.26
448.99 0.00 448.99
478.58 0.00 478.58
505.11 0.00 505.11
529.27 0.00 529.27
572.27 0.00 572.27
609.97 0.00 609.97
777.45 0.00 777.45
990.91 0.00 990.91
1262.97 0.00 1262.97
=
Project: Gallatin County Surface Improvements
Project #: BOZ_13005.04
Date: 4/1/2020
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
13085 0.300 0.95 1 0.95 0.95 0.285
1 0.00 0.00 0.000
1 0.00 0.00 0.000
1 0.00 0.00 0.000
1 0.00 0.00 0
13085 0.300 0.285
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.29
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 2.61
5 3.22 0.92
10 2.05 0.59
15 1.58 0.45
20 1.31 0.37
25 1.13 0.32
30 1.00 0.29
35 0.91 0.26
40 0.83 0.24
45 0.77 0.22
50 0.72 0.21
55 0.68 0.19
60 0.64 0.18
75 0.55 0.16
90 0.49 0.14
105 0.44 0.13
120 0.41 0.12
150 0.35 0.10
180 0.31 0.09
360 0.20 0.06
720 0.13 0.04
1440 0.08 0.02
838.02 ft3 0.59 (ft3/s)
Asphalt Pavement
RATIONAL METHOD FOR RUNOFF CALCULATIONS
EXHIBITION AREA - POST-IMPROVEMENT CONDITIONS
Surface Type
Totals
= 0.9500 Cwd x Cf =0.95
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
156.87 0.00 156.87
275.54 0.00 275.54
351.19 0.00 351.19
404.74 0.00 404.74
447.61 0.00 447.61
483.97 0.00 483.97
515.86 0.00 515.86
544.46 0.00 544.46
570.51 0.00 570.51
594.52 0.00 594.52
616.85 0.00 616.85
637.77 0.00 637.77
657.49 0.00 657.49
710.90 0.00 710.90
757.75 0.00 757.75
799.75 0.00 799.75
838.02 0.00 838.02
906.09 0.00 906.09
965.79 0.00 965.79
1230.96 0.00 1230.96
1568.94 0.00 1568.94
1999.70 0.00 1999.70
=
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 7/9/2018
TABLE I-1: Runoff Coefficients for Use in the Rational Method
LAND USE RUNOFF COEFFICIENTS, C
Open Land 0.2
Low to Medium Density Residential 0.35
Dense Residential 0.5
Commercial Neighborhood 0.6
Commercial Downtown 0.8
Industrial 0.8
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 7/9/2018
Design Standards and Specifications Policy
City of Bozeman, March 2004 as Amended
RAINFALL INTENSITY-DURATION CURVES (Figures I-2, I-3)
Time 2 5 10 25 50 100
(min)(in/hr)(in/hr)(in/hr)(in/hr)(in/hr)(in/hr)
1 4.20 7.15 9.16 10.72 13.72 15.69
5 1.60 2.55 3.22 3.83 4.74 5.34
10 1.05 1.64 2.05 2.46 3.00 3.35
15 0.83 1.26 1.58 1.89 2.30 2.56
20 0.70 1.05 1.31 1.58 1.90 2.11
25 0.61 0.91 1.13 1.37 1.64 1.82
30 0.55 0.81 1.00 1.22 1.45 1.61
35 0.50 0.73 0.91 1.10 1.31 1.45
40 0.46 0.67 0.83 1.01 1.20 1.33
45 0.43 0.63 0.77 0.94 1.11 1.22
50 0.40 0.58 0.72 0.88 1.04 1.14
55 0.38 0.55 0.68 0.82 0.97 1.07
60 0.36 0.52 0.64 0.78 0.92 1.01
75 0.31 0.45 0.55 0.68 0.79 0.87
90 0.28 0.40 0.49 0.60 0.70 0.77
105 0.26 0.36 0.44 0.55 0.64 0.69
120 0.24 0.33 0.41 0.50 0.58 0.63
150 0.21 0.29 0.35 0.43 0.50 0.55
180 0.19 0.26 0.31 0.39 0.45 0.48
360 0.12 0.17 0.20 0.25 0.28 0.30
720 0.08 0.11 0.13 0.16 0.18 0.19
1440 0.05 0.07 0.08 0.10 0.11 0.12
Storm Recurrence Interval
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 7/9/2018
Design Standards and Specifications Policy
City of Bozeman, March 2004 as Amended
Zoning District/Design Storm Requirement
Zoning Type
Design Rainfall
Frequency
Open Land 2-year
Residential 10-year
Commercial 10-year
(p. 28, Table I-3)
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 7/9/2018
STORMWATER MANAGEMENT MANUAL
TABLE 2-5 FREQUENCY FACTORS FOR THE RATIONAL FORMULA
Recurrence Interval Adjustment Factor
(Years)Cf
2 1.00
5 1.00
10 1.00
25 1.10
50 1.20
100 1.25
* C X Cf should not exceed 1.0
V:13005_04_2020-04-01_DRAINAGE REPORT 7 (04/01/20) JAZ/mr
Appendix C
SURFACE IMPROVEMENTS O&M PLAN
April 1, 2020
Project No. BOZ 13005.03
STORM DRAINAGE FACILITY MAINTENANCE PLAN
FOR
GALLATIN COUNTY FAIR GROUNDS SURFACE IMPROVEMENTS
BOZEMAN, MONTANA
OVERVIEW NARRATIVE
The purpose of this maintenance plan is to outline the necessary details related to ownership,
responsibility and cleaning schedule for the storm drainage facilities for the Gallatin County
Fairgrounds. This plan has been completed in accordance with The City of Bozeman Design Standards
and Specifications Policy , dated March 2004. The site stormwater improvements have been designed
with the intent to meet the current City of Bozeman drainage regulations for the entire site to the
extent feasible.
Specific site information and criteria are described below:
I. Ownership of Facilities
Gallatin County Fairgrounds
Gallatin County Fairgrounds will own all stormwater facilities which includes the dry wells,
conveyance ditches and the detention basin.
II. Inspection Thresholds for Cleaning
Basin
If the average depth of sediment exceeds 6 inches, clean basin
Conveyance Ditches
If the average depth of sediment exceeds 2 inches, clean entire ditch
Dry Wells
If sediment in sump exceeds 5 inches or grate is more than 25% clogged with debris, clean
grate and/or structure
V:13005_04_O&M 2 (04/01/20) JAZ/mr
III. Cleaning
Basin
Excavate or dig sediment out of basin and dispose of excess sediment
Conveyance Ditches
Excavate or dig sediment out of basin and dispose of excess sediment
Dry Wells
To clean grate of structure, remove and dispose of debris clogging the grate. To clean
structure, use catch basin vacuum to remove sediment and debris
IV. Schedule
Basin
Inspection: Every 6 months
Clean Basin: Every 5 years or as needed based on inspection
Conveyance Ditches
Inspection: Every 6 months
Clean Ditches: Every 5 years or as needed based on inspection
Dry Wells
Inspection: Every 6 months
Vacuum Drywells: Every 5 years or as needed based on inspection
V. Responsible Party
Gallatin County Fairgrounds
The Gallatin County Fairgrounds will be responsible for the inspection and maintenance of
all stormwater facilities located within the project limits
I agree to the above operation, maintenance and replacement schedule detailed above.
Signature : __________________________________________
Gallatin County Fairgrounds Representative
Checklist continued on next page
INSPECTOR’S NAME:DATE:NAME & ADDRESS OF STORMWATERFACILITY:GENERAL OBSERVATIONS (IS WATERFLOWING?):WEATHER:Checked? (Y/N)Maintenance Needed? (Y/N)Observations and Remarks
Look for debris, trash and sediment blocking catch basin grate. If found, remove. Replace grate if damaged.Inspect filter if installed. Change if torn or clogged.Look for sediment and trash in catch basin sump. Clean out if sediment fills 60% of the sump or comes within 6” of a pipe.Look for damage or cracks to frame, grate, basin walls or bottom. If found, repair or replace.Check integrity of ladder rungs, cleanout gate, and orifice plate. If bent or obstructed, take appropriate action.
Check for undercutting, scouring, and slumping. If found, repair or maintain.Remove all trash and loose sediment. Remove sediment if it will impede water flow or clog downstream structures.Remove vegetation that impedes water movement. Remove vegetation over 9” in height, and all trees and shrubs impeding flow.Repair check dams as necessary.Remove any dumped yard waste.In ditches and swales, check for integrity of grass, check dams, inlets, and outlets. Remove shrubs and trees.
CATCH BASINS AND INLETS
CONVEYANCES
Stormwater System Inspection Checklist
G-6 | Page
Checked? (Y/N)Maintenance Needed? (Y/N)Observations and Remarks
Inlets and outlets: remove vegetation and debris. Fix erosion and scouring. Fix cause of sediment found below outlet.Remove vegetation and debris from trash rack.Add rock to energy dissipater if missing.If necessary, repair rock on spillway. Remove trees, shrubs, and vegetation over 4”. If piping or erosion is visible, consult engineer.
Check for slumping or sloughing of walls. If over 4” of slumping, consult with an engineer. Fix any erosion or scouring. If leaks, piping or soft spots are found, consult with an engineer.If liner visible on bottom, check for holes or replace.Clean any oil sheen from water with oil-absorbent pads or vactor truckChecksediment depth near inlet.If more than one footexists,or there is build upnear inlet,the pond needs to becleaned.
On the pond walls, mow grass to 4 – 9”. Remove clippings. Reseed bare areas.On pond surface, emergent vegetation over 50% of the area indicates sediment removal needed.On pond bottom, remove tree seedlings.Around the pond,remove trees and shrubs that shadesidewallgrassorthatmighthaveproblemrootsnearpipes and structures.Remove invasive and poisonous plants.Remove algae if over 10% of surface.Check integrity of access ramp; ensure stable and clear for heavy equipment.Check integrity and operation of all fences, gates, and locks. Repair as needed for ease of access.Remove rodents and insects if evidence found.Remove vegetation on fences.
POND
COMPONENTS OF THE POND
ACCESS AND SAFETY
VEGETATION
G-7 | Page
POST CONSTRUCTION BMP INSPECTION CHECKLIST
MonthlySchedule/Frequency
AnnuallyAnnually
Inspect pond area, sidewalls, and shoreline for erosion, settlement, and rodent damage
Inspect exterior of catch basins
AnnuallyAnnuallyAnnually
QuarterlyMonthly and after storm events
Quarterly and after storm eventsQuarterly, and after storm eventsQuarterly and after storm events
Quarterly
Inspect ditches, check dams, and all visible pipes and culverts for trash, obstructions and other problems
Inspect bioswales for vegetation cover and bare areasInspect fences, gates and locks Quarterly
Prepared by RESources for Sustainable Communities for the Birch Bay Watershed & Aquatic Resources Management (BBWARM) District. This project was been funded wholly or in part by the U.S. Environmental Protection Agency under assistance agreement WS-96073401 to Whatcom County. The content of this document do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendations for use.
Inspect pond area for oil sheens or trash
Inspect access ramps for ease of heavy equipment access
Inspect inside catch basins, including flow restrictor/orifice plate
Inspect spillway for vegetation overgrowth and ease of heavy equipment access
Inspect interior of catch basins for debris and sediment
Pond area sediment accumulation (pond bottom)
Inspect pond area for undesirable or poisonous vegetation and noxious weedsInspect water levels in the pondInspect trash racks, debris barriers, and energy dissipaters
Inspect inlets and outlets for trash, obstructions, and vegetation
Activity
Semi-annually, during growing seasonAfter storm events
G-5 | Page
V:13005_04_2020-04-01_DRAINAGE REPORT 8 (04/01/20) JAZ/mr
Appendix D
‘ASPHALT PATHWAYS’ STORM DRAINAGE REPORT W/ ATTACHMENTS
December 17, 2019
Project No. BOZ 13005.03
STORM DRAINAGE PLAN
FOR
GALLATIN COUNTY FAIR GROUNDS “ASPHALT PATHWAYS” P ROJECT
GALLATIN COUNTY FAIR GROU NDS
901 NORTH BLACK AVEN UE
BOZEMAN, MONTANA 59715
OVERVIEW NARRATIVE
The purpose of this drainage plan is to present a summary of calculations to quantify the stormwater
runoff for the Gallatin County Fairgrounds “Asphalt Pathways” improvements project. All design
criteria and calculations are in accordance with The City of Bozeman Design Standards and Specifications
Policy , dated March 2004. The site stormwater improvements have been designed with the intent to
meet the current City of Bozeman drainage regulations for the entire site to the extent feasible.
The site is located south of Oak Street and north of Tamarack Street. The entire Gallatin County
Fairgrounds lot is approximately 64.7 acres. However, the project will disturb only ~2.74 acres of the
site and increase the impervious area by ~0.95 acres. The intent of the stormwater design is to mitigate
runoff from the asphalt pathways improvement project limits through a small series of dry wells and
the proposed retention pond. All stormwater runoff generated from this project will be
retained/infiltrated on site.
The existing surfaces that are being improved (and project extents) primarily consist of compacted
gravel surfacing. The proposed development consists of an asphalt access pathway to assist with
internal circulation of pedestrian and vehicular traffic. The retention pond will be sized to store and
retain the 25-year design event runoff from the proposed surface improvements. An additional gravel
swale with a subsurface boulder pit has been added to this project along the southern boundary to
intercept runoff flowing from the south and addressing concerns of runoff that has historically drained
off-site to the Oak Street R.O.W.
V:13005_03_2019-12-17_Storm_Drainage_Plan 2 (12/17/19) MTR
I. Design Approach
The modified rational method was used to determine peak runoff rates and volumes. The
rational formula provided in The City of Bozeman Standard Specifications and Policy was used to
calculate the peak runoff rates on site, time of concentration, rainfall intensities, etc. To be
conservative, we treated most watersheds as if they were predominately impervious cover,
therefore we assumed a time of concentration of 5-minutes. For gravel surfaces, a runoff
coefficient of 0.6 was assumed.
II. Proposed Watershed Descriptions
For the following sections, please refer to Appendix A of this report, which graphically
shows and labels the watersheds as well as the proposed drainage and conveyance
facilities.
Watershed 1A flows into existing dry wells located south of the existing hockey rink
building. These dry wells are called out and identified within Appendix A. Excess runoff that
cannot enter the existing dry wells will overtop into Conveyance Swale 1 (called out in
Appendix A) and outfall into Watershed 2. A detail for the existing drywells from the As-Built
construction drawings dated 12/15/2014 is attached to this report. Based on the dimensions
shown in the detail, we have calculated that each of the four dry wells located on site provide
approximately 469 ft 3 of storage, or a total of 1,876 ft 3. The required 25-year, 2-hour storm
storage for Watershed 1A was calculated to be 1,493 ft 3 using a conservative percolation rate
of 6.8 in/hr, which is the minimum rate for poorly graded sandy gravels according to USCS
Soil Classifications.
Watershed 1B runoff will be intercepted by a proposed gravel swale (shown in Appendix
A), located along the southern edge of asphalt of the new paved pathway. A new proposed
boulder pit will be installed below the proposed swale along with two Type IV area inlets and
12-inch perforated storm drain pipe. The proposed boulder pit was sized with the assumption
that further paving improvements will be constructed. Based on the Watershed 1B limits
shown in Appendix A and the breakdown of future pervious and impervious areas, the
required storage for this watershed is 6,932 ft 3. The boulder pit was sized to provide 8,113 ft 3,
to be conservative and to account for future improvements of changing gravel to pavement
upstream of the gravel swale.
Watershed 2 is conveyed to the north Conveyance Swale 1 and Conveyance Swale 2, into
Basin 1 (a newly proposed retention pond). The conveyance swales have the capacity to
convey the 25-year storm event to Basin 1 . The 25-year design event requires a storage of
9,194 cubic feet, and Basin 1 has the capacity to retain 11,662 cubic feet to store runoff, to
be conservative. Additionally, Conveyance Swale 2 directly south of Basin 1 provides 405
cubic feet of storage. Sanderson Stewart conducted percolation/infiltration rates at the
location of the proposed Basin 1 retention pond after 24-hours of saturation of the soils
resulting in a percolation rate of 1.38 inches per hour. Percolation rates were measured
between approximately three to four feet in depth in soils that could be classified as lean
clays with sand. The proposed retention pond shows a final depth of approximately of six
to seven feet in depth below existing grade. Historical exploratory bores ~600’ south
V:13005_03_2019-12-17_Storm_Drainage_Plan 3 (12/17/19) MTR
indicated a “poorly-graded gravel with sand and clay,” lens of soils at depths ranging from 2-
3’ at the shallowest and 10’ at the deepest (where test pits were not excavated deeper.)
(Geotechnical Report completed by TD&H Engineering in October 2012 created for the
New Ice Hockey Pavilion Expansion project, See Appendix E.) In the event that these
poorly-graded gravels are exposed during excavation, the pond should not need to be
excavated any deeper. A note on Sheet C4.2 indicates that the contractor shall inform the
Engineer of the depth of the existing gravel layer. Additional percolation through the
“poorly-graded gravel with sand and clay” was accounted for with a conservative rate of 6.8
in/hr as the proposed depth of the pond will expose approximately 1,454 ft 2 of that gravel
lens to provide a larger area of percolation.
Watershed 3 sheet flows into two new dry wells which will capture and retain runoff from
minor storm events. Each drywell provides approximately 400 ft 3 of storage, for a total of
800 ft 3. During larger storm events runoff will pond over the dry wells and overtop into the
adjacent fairground area. Excess runoff from the most easterly dry well may eventually drain
to Basin 1 but will first experience percolation into surrounding soils as it has, historically.
Excess runoff from the western dry well will drain into the adjacent existing swale to the
west shown in Appendix A. This existing swale is approximately 400 feet long, 3-feet wide,
and 1 foot deep. This swale will provide an additional 1,200 ft 3 of storage. The calculations
for Watershed 3 show a required storage of 1,268 ft3, so adequate storage is provided
including the dry wells and drainage swale, not counting for percolation. The underlying soils
that the dry wells and basin will tie into are poorly graded gravel with sand and clay based on
the Geotechnical Report completed by TD&H Engineering in October 2012 created for the
New Ice Hockey Pavilion Expansion project. Percolation through this “poorly-graded gravel
with sand and clay” lens was accounted for with a conservative rate of 6.8 in/hr. In all,
Watershed 3 has sufficient storage and is conservatively designed to retain the design storm
event.
III. Proposed Storage and Conveyance Facilities
Basin 1
Basin 1 is located to the north of the project limits within an existing drainage swale designed
to convey runoff from the existing gravel road. A new, larger swale (Conveyance Swale 2) will
be constructed to convey runoff to the new basin. The basin will be constructed in line with
the existing swale and any excess runoff from the basin will overtop the north edge of the
basin into the existing swale.
The basin is designed to have 4:1 side slopes and a maximum water depth of 1.5 feet.
Infiltration was considered as part of the design based on the underlying soil layers shown in
the Geotechnical Report bore logs. The stage storage volume calculations for the proposed
basin are attached to this report. Basin 1 and Conveyance Swale 2 will be seeded in order to
limit the potential for erosion.
Conveyance Swale 1
V:13005_03_2019-12-17_Storm_Drainage_Plan 4 (12/17/19) MTR
As mentioned above, Conveyance Swale 1 is used to convey excess runoff from Watershed 1
to Watershed 2. The 25-year, 5-minute peak flow from Watershed 1 is 4.57 cfs and
Conveyance Swale 1 has the capacity to convey 5.66 cfs. The maximum velocity through the
channel is 1.06 ft/s. The channel will be cut into the existing gravels on site. The swale will be
seeded for grass to prevent any erosion, but the low velocity rate should help minimize the
potential for erosion. The Bentley Flowmaster swale capacity calculations are included in the
appendix.
Conveyance Swale 2
As mentioned above, Conveyance Swale 2 is used to convey excess runoff from Watershed 1
and 2. The 25-year, 5-minute peak flow from both watersheds is 8.07 cfs and Conveyance
Swale 2 has the capacity to convey 8.14 cfs. The maximum velocity through the channel is
2.83 ft/s. The channel will be cut into the existing gravels on site. The swale will be seeded for
grass to prevent any erosion, but the low velocity rate should help minimize the potential for
erosion. The Bentley Flowmaster swale capacity calculations are included in the appendix.
Dry Wells
The new drywells on site are designed to capture runoff for minor storms and allow larger
storms to pond up over the dry well and eventually infiltrate through the dry wells perforations.
Any excess runoff will overtop into the fairgrounds area, then eventually into Basin 1 (to the
east) or to the existing drainage swale (to the west).
IV. Water Quality
The City of Bozeman Design Standards and Specifications Policy states the requirement to
capture or reuse the runoff generated from the first 0.5 inches of rainfall from a 24-hour storm.
We meet this requirement by retaining all storm runoff on site with no discharge into
the City storm drain system.
V. Outlet Structures
All runoff will be captured and retained/infiltrated on site. There are no outlet structures
proposed for this project.
V:13005_03_2019-12-13_Storm_Drainage_Plan 6 (12/13/19) MTR
Appendix A
WATERSHED MAP
WA
T
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S
H
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D
1
A
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D
1
B
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2
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3
DI
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C
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N
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A
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F
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PR
O
P
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E
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DR
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W
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DR
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1
NE
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V:13005_03_2019-12-13_Storm_Drainage_Plan 7 (12/13/19) MTR
Appendix B
HYDROLOGY CALCULATIONS
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 12/13/2019
Design Storm Frequency =25 years
Area of perc
(ft^2)Perc rate (in/hr)
Perc rate
(ft/sec)
974 6.80 0.0001574
Discharge Rate, d =0.15 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
15529 0.356 0.8 1.1 0.88 0.88 0.314
16965 0.389 0.95 1.1 1.05 1.00 0.389
0 1.1 0.00 0.00 0
32494 0.746 0.703
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.72
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 10.72 7.72
5 3.83 2.76
10 2.46 1.77
15 1.89 1.37
20 1.58 1.14
25 1.37 0.98
30 1.22 0.88
35 1.10 0.79
40 1.01 0.73
45 0.94 0.68
50 0.88 0.63
55 0.82 0.59
60 0.78 0.56
75 0.68 0.49
90 0.60 0.43
105 0.55 0.39
120 0.50 0.36
150 0.43 0.31
180 0.39 0.28
360 0.25 0.18
720 0.16 0.11
1440 0.10 0.07
1,493.46 ft3 1.77 (ft3/s)
RATIONAL METHOD FOR RUNOFF CALCULATIONS
Watershed 1A Peak Flows
Surface Type
Gravel
Asphalt/Concrete/Roof
Totals
= = 0.8783 Cwd x Cf =0.97
Runoff Volume Discharge Volume Site Detention
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
463.47 9.20 454.27
827.27 45.99 781.28
1061.75 91.99 969.76
1228.61 137.98 1090.63
1362.67 183.98 1178.69
1476.66 229.97 1246.68
1576.83 275.97 1300.86
1666.81 321.96 1344.85
1748.89 367.96 1380.93
1824.64 413.95 1410.69
1895.18 459.94 1435.23
1961.33 505.94 1455.39
2023.74 551.93 1471.81
2193.02 689.92 1503.10
2341.79 827.90 1513.89
2475.42 965.88 1509.54
2597.32 1103.87 1493.46
2814.58 1379.83 1434.75
3005.51 1655.80 1349.71
3857.35 3311.60 545.75
4950.63 6623.20 -----
6353.77 13246.40 -----
=
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 12/13/2019
Design Storm Frequency =25 years
Area of perc
(ft^2)Perc rate (in/hr)
Perc rate
(ft/sec)
5337.5 6.80 0.0001574
Discharge Rate, d =0.84 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
32968 0.757 0.15 1.1 0.17 0.17 0.125
18260 0.419 0.8 1.1 0.88 0.88 0.369
37685 0.865 0.95 1.1 1.05 1.00 0.865
91878 2.109 0.95 1.1 1.05 1.00 2.109
0 1.1 0.00 0.00 0
180791 4.150 3.468
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =3.60
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 10.72 38.61
5 3.83 13.78
10 2.46 8.84
15 1.89 6.82
20 1.58 5.68
25 1.37 4.92
30 1.22 4.38
35 1.10 3.97
40 1.01 3.64
45 0.94 3.38
50 0.88 3.16
55 0.82 2.97
60 0.78 2.81
75 0.68 2.44
90 0.60 2.17
105 0.55 1.96
120 0.50 1.80
150 0.43 1.56
180 0.39 1.39
360 0.25 0.89
720 0.16 0.57
1440 0.10 0.37
6,931.88 ft3 8.84 (ft3/s)
24742.53 36295.00 -----
31755.20 72590.00 -----
15021.12 9073.75 5947.37
19278.50 18147.50 1131.00
12981.04 6049.17 6931.88
14066.86 7561.46 6505.40
11703.93 4536.88 7167.05
12371.79 5293.02 7078.77
10114.37 3024.58 7089.79
10960.40 3780.73 7179.67
9471.82 2520.49 6951.34
9802.46 2772.53 7029.92
8740.69 2016.39 6724.31
9119.29 2268.44 6850.85
7880.76 1512.29 6368.47
8330.46 1764.34 6566.12
6810.44 1008.19 5802.25
7380.11 1260.24 6119.87
5306.45 504.10 4802.36
6140.41 756.15 5384.26
2316.35 50.41 2265.94
4134.60 252.05 3882.55
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
= 0.7890 Cwd x Cf =0.87
Runoff Volume Discharge Volume Site Detention
=
Gravel
Concrete/Roof
Asphalt Pavement
Totals
Landscape
RATIONAL METHOD FOR RUNOFF CALCULATIONS
Watershed 1B Peak Flows
Surface Type
=
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 12/13/2019
Design Storm Frequency =25 years
Area of perc
(ft^2)Perc rate (in/hr)
Perc rate
(ft/sec)
Percolation Rate (GRAVEL), d =0.23 cfs 1454 6.80 0.0001574
Percolation Rate (SSC), d =0.14 cfs 4329 1.38 3.194E-05
Percolation Rate (Total), d =0.37 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
116649 2.678 0.9 1.1 0.99 0.99 2.65
41823 0.960 0.6 1.1 0.66 0.66 0.63
0 1.1 0.00 0.00 0
0 1.1 0.00 0.00 0
0 1.1 0.00 0.00 0
158472 3.6380 3.2848
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =3.28
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 10.72 35.21
5 3.83 12.57
10 2.46 8.07
15 1.89 6.22
20 1.58 5.18
25 1.37 4.49
30 1.22 3.99
35 1.10 3.62
40 1.01 3.32
45 0.94 3.08
50 0.88 2.88
55 0.82 2.71
60 0.78 2.56
75 0.68 2.22
90 0.60 1.98
105 0.55 1.79
120 0.50 1.64
150 0.43 1.43
180 0.39 1.27
360 0.25 0.81
720 0.16 0.52
1440 0.10 0.34
9,194.41 ft3 8.07 (ft3/s)
22563.72 15861.22 6702.50
28958.86 31722.44 -----
13698.38 3965.31 9733.07
17580.85 7930.61 9650.24
11837.94 2643.54 9194.41
12828.14 3304.42 9523.72
10673.29 1982.65 8690.64
11282.34 2313.09 8969.24
9223.71 1321.77 7901.94
9995.24 1652.21 8343.03
8637.74 1101.47 7536.27
8939.26 1211.62 7727.64
7971.00 881.18 7089.82
8316.25 991.33 7324.92
7186.78 660.88 6525.90
7596.88 771.03 6825.85
6210.72 440.59 5770.13
6730.22 550.74 6179.49
4839.17 220.29 4618.88
5599.69 330.44 5269.25
2112.37 22.03 2090.35
3770.51 110.15 3660.36
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
= 0.8208 Cwd x Cf =0.90
Runoff Volume Percolation/Infiltration Site Detention
=
Gravel
Totals
Impervious
RATIONAL METHOD FOR RUNOFF CALCULATIONS
Watershed 2 Peak Flows
Surface Type
=
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 12/13/2019
Design Storm Frequency =25 years
Area of perc
(ft^2)Perc rate (in/hr)
Perc rate
(ft/sec)
Discharge Rate, d =0.16 cfs 1000 6.80 0.0001574
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
11123 0.255 0.9 1.1 0.99 0.99 0.25
27298 0.627 0.6 1.1 0.66 0.66 0.41
0 1.1 0.00 0.00 0
0 1.1 0.00 0.00 0
0 1.1 0.00 0.00 0
38421 0.8820 0.6664
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.67
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 10.72 7.14
5 3.83 2.55
10 2.46 1.64
15 1.89 1.26
20 1.58 1.05
25 1.37 0.91
30 1.22 0.81
35 1.10 0.73
40 1.01 0.67
45 0.94 0.62
50 0.88 0.58
55 0.82 0.55
60 0.78 0.52
75 0.68 0.45
90 0.60 0.40
105 0.55 0.36
120 0.50 0.33
150 0.43 0.29
180 0.39 0.26
360 0.25 0.17
720 0.16 0.11
1440 0.10 0.07
1,268.28 ft3 2.55 (ft3/s)
4577.61 6800.00 -----
5875.02 13600.00 -----
2779.05 1700.00 1079.05
3566.71 3400.00 166.71
2401.62 1133.33 1268.28
2602.50 1416.67 1185.84
2165.34 850.00 1315.34
2288.90 991.67 1297.23
1871.26 566.67 1304.59
2027.78 708.33 1319.45
1752.38 472.22 1280.16
1813.55 519.44 1294.10
1617.11 377.78 1239.33
1687.16 425.00 1262.16
1458.02 283.33 1174.68
1541.21 330.56 1210.66
1260.00 188.89 1071.11
1365.39 236.11 1129.28
981.74 94.44 887.30
1136.03 141.67 994.37
428.55 9.44 419.10
764.94 47.22 717.72
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
= 0.6869 Cwd x Cf =0.76
Runoff Volume Discharge Volume Site Detention
=
Gravel
Totals
Impervious
RATIONAL METHOD FOR RUNOFF CALCULATIONS
Watershed 3 Peak Flows
Surface Type
=
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 12/13/2019
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
41415 0.951 0.6 1 0.60 0.60 0.570454545
0.000 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
41415 0.9508 0.5705
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.57
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 5.23
5 3.22 1.84
10 2.05 1.17
15 1.58 0.90
20 1.31 0.75
25 1.13 0.64
30 1.00 0.57
35 0.91 0.52
40 0.83 0.48
45 0.77 0.44
50 0.72 0.41
55 0.68 0.39
60 0.64 0.37
75 0.55 0.32
90 0.49 0.28
105 0.44 0.25
120 0.41 0.23
150 0.35 0.20
180 0.31 0.18
360 0.20 0.11
720 0.13 0.07
1440 0.08
1,675.19 ft3 1.84 (ft3/s)
Gravel
RATIONAL METHOD FOR RUNOFF CALCULATIONS
Pre-Project Runoff Volume
Surface Type
Totals
= 0.6000 Cwd x Cf =0.60
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
313.58 0.00 313.58
550.80 0.00 550.80
702.02 0.00 702.02
809.06 0.00 809.06
894.77 0.00 894.77
967.45 0.00 967.45
1031.20 0.00 1031.20
1088.36 0.00 1088.36
1140.44 0.00 1140.44
1188.43 0.00 1188.43
1233.08 0.00 1233.08
1274.90 0.00 1274.90
1314.33 0.00 1314.33
1421.09 0.00 1421.09
1514.73 0.00 1514.73
1598.70 0.00 1598.70
1675.19 0.00 1675.19
1811.27 0.00 1811.27
1930.62 0.00 1930.62
2460.69 0.00 2460.69
3136.30 0.00 3136.30
3997.40 0.00 3997.40
=
Project: Gallatin County Roadway Improvements
Project #: BOZ_13005.03
Date: 12/13/2019
Design Storm Frequency =10 years
Discharge Rate, d =0.00 cfs
Input values for runoff coefficients from appropriate tables.
Area Area
Runoff
Coefficient
Frequency
Factor
Calculation
Value
A A/(43560 ft2/acre)C Cf C x Cf C' C' x A
(ft2)(Acres)=(C x Cf) < or = 1 (Acres)
41415 0.951 0.9 1 0.90 0.90 0.855681818
0.000 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
0 1 0.00 0.00 0
41415 0.9508 0.8557
Weighted Runoff Coefficient, Cwd SCjAj
SAj
Cwd x Cf x SAj =0.86
Where Cj is the adjusted runoff coefficient for surface type j
and Aj is the area of surface type j
Rainfall Rainfall Peak Flow
Duration, t Intensity, i = Cwd x SAj x i
(min) (in/hr)(ft3/s)
1 9.16 7.84
5 3.22 2.75
10 2.05 1.76
15 1.58 1.35
20 1.31 1.12
25 1.13 0.97
30 1.00 0.86
35 0.91 0.78
40 0.83 0.71
45 0.77 0.66
50 0.72 0.62
55 0.68 0.58
60 0.64 0.55
75 0.55 0.47
90 0.49 0.42
105 0.44 0.38
120 0.41 0.35
150 0.35 0.30
180 0.31 0.27
360 0.20 0.17
720 0.13 0.11
1440 0.08 0.07
2,512.78 ft3 2.75 (ft3/s)
Impervious
RATIONAL METHOD FOR RUNOFF CALCULATIONS
Post-Project Increase in Impervious Cover
Surface Type
Totals
= 0.9000 Cwd x Cf =0.90
Runoff Volume Discharge Volume Site Detention
=
= Cwd x SAj x i x t = d x t = Runoff Volume - Discharge Volume
(ft3) (ft3) (ft3)
470.37 0.00 470.37
826.19 0.00 826.19
1053.03 0.00 1053.03
1213.60 0.00 1213.60
1342.15 0.00 1342.15
1451.18 0.00 1451.18
1546.80 0.00 1546.80
1632.55 0.00 1632.55
1710.66 0.00 1710.66
1782.65 0.00 1782.65
1849.62 0.00 1849.62
1912.36 0.00 1912.36
1971.49 0.00 1971.49
2131.64 0.00 2131.64
2272.10 0.00 2272.10
2398.05 0.00 2398.05
2512.78 0.00 2512.78
2716.90 0.00 2716.90
2895.92 0.00 2895.92
3691.03 0.00 3691.03
4704.44 0.00 4704.44
5996.10 0.00 5996.10
=
V:13005_03_2019-12-13_Storm_Drainage_Plan 8 (12/13/19) MTR
Appendix C
HYDRAULICS CALCULATIONS
Project Description
Friction Method Manning Formula
Solve For Discharge
Input Data
Roughness Coefficient 0.033
Channel Slope 0.00500 ft/ft
Normal Depth 0.40 ft
Left Side Slope 25.00 ft/ft (H:V)
Right Side Slope 40.00 ft/ft (H:V)
Results
Discharge 5.66 ft³/s
Flow Area 5.20 ft²
Wetted Perimeter 26.01 ft
Hydraulic Radius 0.20 ft
Top Width 26.00 ft
Critical Depth 0.29 ft
Critical Slope 0.03040 ft/ft
Velocity 1.09 ft/s
Velocity Head 0.02 ft
Specific Energy 0.42 ft
Froude Number 0.43
Flow Type Subcritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 0.40 ft
Critical Depth 0.29 ft
Channel Slope 0.00500 ft/ft
Critical Slope 0.03040 ft/ft
Worksheet for Conveyance Ditch 1
7/9/2018 10:12:15 AM
Bentley Systems, Inc. Haestad Methods Solution Center Bentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 1of 1Page
Swale 1
Project Description
Friction Method Manning Formula
Solve For Discharge
Input Data
Roughness Coefficient 0.032
Channel Slope 0.01300 ft/ft
Normal Depth 0.80 ft
Left Side Slope 5.00 ft/ft (H:V)
Right Side Slope 4.00 ft/ft (H:V)
Results
Discharge 8.14 ft³/s
Flow Area 2.88 ft²
Wetted Perimeter 7.38 ft
Hydraulic Radius 0.39 ft
Top Width 7.20 ft
Critical Depth 0.73 ft
Critical Slope 0.02159 ft/ft
Velocity 2.83 ft/s
Velocity Head 0.12 ft
Specific Energy 0.92 ft
Froude Number 0.79
Flow Type Subcritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 0.80 ft
Critical Depth 0.73 ft
Channel Slope 0.01300 ft/ft
Critical Slope 0.02159 ft/ft
Worksheet for Conveyance Ditch 2
7/9/2018 10:12:43 AM
Bentley Systems, Inc. Haestad Methods Solution Center Bentley FlowMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 1of 1Page
Swale 2
V:13005_03_2019-12-13_Storm_Drainage_Plan 9 (12/13/19) MTR
Appendix D
MAINTENANCE PLAN
December 13, 2019
Project No. BOZ 13005.03
STORM DRAINAGE FACILITY MAINTENANCE PLAN
FOR
GALLATIN COUNTY FAIR GROUNDS ROADWAY IMPR OVEMENTS
BOZEMAN, MONTANA
OVERVIEW NARRATIVE
The purpose of this maintenance plan is to outline the necessary details related to ownership,
responsibility and cleaning schedule for the storm drainage facilities for the Gallatin County
Fairgrounds. This plan has been completed in accordance with The City of Bozeman Design Standards
and Specifications Policy , dated March 2004. The site stormwater improvements have been designed
with the intent to meet the current City of Bozeman drainage regulations for the entire site to the
extent feasible.
Specific site information and criteria are described below:
I. Ownership of Facilities
Gallatin County Fairgrounds
Gallatin County Fairgrounds will own all stormwater facilities which includes the dry wells,
conveyance ditches and the detention basin.
II. Inspection Thresholds for Cleaning
Basin
If the average depth of sediment exceeds 6 inches, clean basin
Conveyance Ditches
If the average depth of sediment exceeds 2 inches, clean entire ditch
Dry Wells
If sediment in sump exceeds 5 inches or grate is more than 25% clogged with debris, clean
grate and/or structure
V:13005_03_2019-12-17_Storm_Drainage_Plan 8 (12/17/19) MTR
Appendix E
GEOTECHNICAL REPORT
Great Falls • Bozeman • Kalispell, Montana
Spokane, Washington • Lewiston, Idaho
REPORT OF GEOTECHNICAL INVESTIGATION
ICE HOCKEY (HAYNES) PAVILION EXPANSION
GALLATIN COUNTY FAIRGROUNDS, BOZEMAN, MONTANA
October 2012
CLIENT: Bozeman Amateur Hockey Association
PO Box 6414
Bozeman, MT 59771
Contacts: Julie Keck (406) 586-5557
Rob Pertzborn (406) 582-8988
ENGINEER: TD&H Engineering
234 E. Babcock Street, Suite 3
Bozeman, MT 59715
Contact: Kyle Scarr, P.E. (406) 586-0277
Job No. B12-060
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10/5/12
ICE HOCKEY PAVILION EXPANSION Table of Contents
GALLATIN COUNTY FAIRGROUNDS i
TABLE OF CONTENTS
1.0 INTRODUCTION ............................................................................................................... 1
1.1 PURPOSE AND SCOPE ................................................................................................. 1
1.2 PROJECT DESCRIPTION .............................................................................................. 1
2.0 SITE CONDITIONS ............................................................................................................ 3
2.1 GEOLOGY AND PHYSIOGRAPHY ............................................................................. 3
2.2 SURFACE CONDITIONS .............................................................................................. 3
2.3 SUBSURFACE CONDITIONS ....................................................................................... 3
3.0 ENGINEERING ANALYSIS .............................................................................................. 6
3.1 INTRODUCTION ............................................................................................................ 6
3.2 SITE GRADING AND EXCAVATIONS ....................................................................... 6
3.3 SHALLOW SPREAD FOOTING FOUNDATION ........................................................ 6
3.4 FLOOR SLABS AND EXTERIOR FLATWORK .......................................................... 7
4.0 RECOMMENDATIONS ..................................................................................................... 8
4.1 SITE GRADING AND EXCAVATIONS ....................................................................... 8
4.2 SHALLOW SPREAD FOOTING FOUNDATION ........................................................ 9
4.3 FLOOR SLABS AND EXTERIOR FLATWORK ........................................................ 10
4.4 CONTINUING SERVICES ........................................................................................... 11
5.0 SUMMARY OF FIELD AND LABORATORY STUDIES ............................................. 12
5.1 FIELD EXPLORATIONS ............................................................................................. 12
5.2 LABORATORY TESTING ........................................................................................... 12
6.0 LIMITATIONS .................................................................................................................. 14
ICE HOCKEY PAVILION EXPANSION Table of Contents
GALLATIN COUNTY FAIRGROUNDS ii
APPENDIX
Site Plan (Figure 1)
Logs of Exploratory Test Pits (Figures 2 through 4)
Laboratory Test Data (Figures 5 and 6)
Soil Classification and Sampling Terminology for Engineering Purposes
Classification of Soils for Engineering Purposes
ICE HOCKEY PAVILION EXPANSION Introduction
GALLATIN COUNTY FAIRGROUNDS 1
GEOTECHNICAL REPORT
ICE HOCKEY (HAYNES) PAVILION EXPANSION
GALLATIN COUNTY FAIRGROUNDS
1.0 INTRODUCTION
1.1 PURPOSE AND SCOPE
This report presents the results of our geotechnical study for the Ice Hockey Pavilion Expansion
(Haynes Pavilion) located at the Gallatin County Fairgrounds in Bozeman, Montana. The
purpose of the geotechnical study is to determine the general surface and subsurface conditions
at the proposed site and to develop geotechnical engineering recommendations for support of the
proposed structure and design of related facilities. This report describes the field work and
laboratory analyses conducted for this project, the surface and subsurface conditions
encountered, and presents our recommendations for the proposed foundations and related site
development.
Our field work included excavating three soil test pits beneath the proposed addition. Samples
were obtained from the test pits and returned to our materials testing laboratory for testing.
Laboratory testing was performed on select soil samples to determine engineering properties of
the subsurface materials. The information obtained during our field investigations and laboratory
analyses was used to develop recommendations for the design of the proposed foundation
systems. The test pits excavated during our site investigation were intended to validate the
subsurface soils information and testing performed in July of 1999, also by TD&H Engineering,
for the original Haynes Pavilion building geotechnical report titled “Ice Hockey Pavilion,
Gallatin County Fairground, Bozeman, Montana.”
This study is in general accordance with the proposal submitted by Mr. Kyle Scarr, P.E., of our
firm dated June 26, 2012. Our work was authorized to proceed by Ms. Julie Keck, of the
Bozeman Amateur Hockey Association (BAHA) by her signed acceptance of our proposal.
1.2 PROJECT DESCRIPTION
It is our understanding that the proposed project consists of, in part, a single-story, steel-framed,
metal structure approximately 36,400 square feet in area and being approximately 223 by 163
ICE HOCKEY PAVILION EXPANSION Introduction
GALLATIN COUNTY FAIRGROUNDS 2
feet. The expansion will be located west of the existing Haynes Pavilion. The new addition is
proposed to be supported on conventional shallow spread footings incorporating slab-on-grade
construction. The interior slab will include a refrigeration system to maintain ice conditions. It
is also our understanding an under-slab heating system is being considered to prevent potential
frost related problems associated with year-round use of the facility as an ice rink. Structural
loads had not been provided for our use at the time of this report. For the purpose of our study,
we have assumed that wall loads will be less than 4 kips per lineal foot (kpf) and column loads
will be less than 100 kips. This is consistent with the design structural loads for the original
Haynes Pavilion. If loadings, locations or conditions are significantly different from those
described above, we should be notified to reevaluate the recommendations contained in this
report. Site development will most likely include landscaping and exterior concrete flatwork.
The
ICE HOCKEY PAVILION EXPANSION Site Conditions
GALLATIN COUNTY FAIRGROUNDS 3
2.0 SITE CONDITIONS
2.1 GEOLOGY AND PHYSIOGRAPHY
The site is geologically characterized as consisting of thin, surficial deposits of late Pleistocene-
aged loess (eolian origin) which varies in thickness and is comprised of silt, sand and clay. In
general, the fine-grained soils overlie alluvial fan and valley floor deposits of the Pleistocene
age. The coarse alluvial-fan and valley deposits consist of poorly-graded, subrounded to
rounded gravel with sand and cobbles with minor amounts of silt. Fan deposits are generally
thin in a downslope direction with local thicknesses up to 165 feet reported. The alluvial fan
deposits overlie Tertiary-aged strata.
The appropriate 2009 International Building Code (IBC) seismic design parameters for the site
include site coefficients of 1.102 and 1.571 for F a and F v, respectively. The Site Class for this
site is C and the mapped spectral response accelerations at short periods (SM s) and at 1-second
period (SM 1) are 0.821 and 0.360, respectively.
The likelihood of seismically-induced soil liquefaction or settlement for this project is low and
does not warrant additional evaluation.
2.2 SURFACE CONDITIONS
The proposed project site is located at the Gallatin County Fairgrounds in Bozeman, Montana,
and presently consists of a gravel parking lot and landscaped areas. Based on background
information, site observations, and topographic survey, the site slopes downward toward the
north at slopes ranging from 1.0 to 1.5 percent. The topography is best described as nearly level.
The proposed building foot print area is currently used as gravel parking areas, asphalt pathways,
and lawn areas.
2.3 SUBSURFACE CONDITIONS
2.3.1 Soils.
The subsurface soil conditions appear to be relatively consistent based on our exploratory
excavating and soil sampling. In general, the subsurface soil conditions encountered
ICE HOCKEY PAVILION EXPANSION Site Conditions
GALLATIN COUNTY FAIRGROUNDS 4
within the test pits consist of approximately 0.5 to 1.0 feet of fill (topsoil and gravel
surfacing) over 1.8 to 2.4 feet of lean clay with sand. The lean clay with sand overlies
poorly-graded gravel with sand and clay which extends to a depth of at least 10.0 feet,
which was the maximum depth investigated. In general, the subsurface soils encountered
are relatively consistent with those observed during the 1999 investigation by TD&H
Engineering.
The subsurface soils are described in detail on the enclosed test pit logs and are
summarized below. The stratification lines shown on the logs represent approximate
boundaries between soil types and the actual in situ transition may be gradual vertically
or discontinuous laterally.
FILL SOILS
Fill across the site includes 1.5-inch minus gravel surfacing (TP-1 and TP-3) and lean
clay with sand to gravelly lean clay (TP-2). The gravel surfacing appeared medium
dense based on observation of the test pit wall and the relative difficulty to excavate. The
natural moisture content of the material sampled from TP-3 was 2%.
LEAN CLAY WITH SAND
The lean clay with sand appeared soft to firm based on observation of the test pit wall and
the relative ease to excavate. A sample of the material obtained from TP-2 contained
trace gravel, 27 percent sand, and 72 percent silt and clay. The lean clay with sand
exhibited a liquid limit of 33 percent and a plasticity index of 14 percent. The natural
moisture content varied from 18 to 22 percent and average 20 percent. The lean clay
with sand is likely compressible based on testing performed on similar soils. The upper 1
to 2 inches of this material appeared to be remnants of topsoil that was not completely
removed prior to fill placement.
POORLY-GRADED GRAVEL WITH SAND AND CLAY
The poorly-graded gravel with sand and clay appeared very dense based on observation
of the test pit wall and the relative difficulty to excavate. In situ moist densities range
from 124.8 to 132.2 pounds per cubic foot (pcf) and dry densities range from 117.7 to
127.7 pcf based on in place field density testing using a nuclear densometer. The natural
moisture content varied from 3 to 6 percent and averaged 5 percent. Sub-rounded to sub-
angular rock particles on the order of 12-inches in diameter were abundant throughout the
material. A decrease in clay content with depth was observed in all test pits.
ICE HOCKEY PAVILION EXPANSION Site Conditions
GALLATIN COUNTY FAIRGROUNDS 5
2.3.2 Ground Water
Ground water was not encountered within the test pits to the maximum depth investigated
(10.0 feet). The absence of observed ground water may be directly related to the time of
the subsurface investigation. Numerous factors contribute to seasonal ground water
occurrences and fluctuations, and the evaluation of such factors is beyond the scope of
this report.
ICE HOCKEY PAVILION EXPANSION Engineering Analysis
GALLATIN COUNTY FAIRGROUNDS 6
3.0 ENGINEERING ANALYSIS
3.1 INTRODUCTION
The primary geotechnical concern regarding this project is the presence of weak compressible
lean clay soils, uncontrolled fill, and lenses of topsoil beneath the proposed slab-on-grade
construction. Each of these can create a potential for settlement if not considered in design or
removed. These materials should not pose significant risk to conventional shallow spread
footings if the below recommendations are followed.
3.2 SITE GRADING AND EXCAVATIONS
The ground surface at the project site is nearly level and slopes between 1.0 and 1.5 percent
down to the north. Based on our field work and depending on the final finished floor elevation,
lean clay with sand and poorly-graded gravel with sand and clay will be encountered in
foundation excavations to the depths anticipated. Based on the test pits, ground water should be
below the anticipated depths of footing and utility excavations.
3.3 SHALLOW SPREAD FOOTING FOUNDATION
Considering the subsurface conditions encountered and the nature of the proposed construction,
the structure can be supported on shallow spread footing foundations bearing on native poorly-
graded gravel with sand and clay or on properly compacted structural fill extending down to
native poorly-graded gravel with sand and clay.
Based on our experience and using an allowable bearing pressure of 4,000 pounds per square
foot (psf), we estimate the total settlement for footings will be less than ¾-inch. Differential
settlement across the structure should be on the order of one-half this magnitude.
The lateral resistance of spread footings is controlled by a combination of sliding resistance
between the footing and the foundation material at the base of the footing and the passive earth
pressure against the side of the footing in the direction of movement. Design parameters are
given in the recommendations section of this report.
ICE HOCKEY PAVILION EXPANSION Engineering Analysis
GALLATIN COUNTY FAIRGROUNDS 7
New spread footings placed adjacent to the existing structure should bear at approximately the
same elevation as the existing footings and should be separated from the existing footings by a
lateral distance greater than at least one footing width of the new or existing footing (whichever
is widest) to avoid adverse stresses on the subgrade, footings, and stem walls.
3.4 FLOOR SLABS AND EXTERIOR FLATWORK
The natural on-site soils, exclusive of all fill and topsoil, are suitable to support lightly to
moderately loaded, slab-on-grade construction. A leveling course of granular fill directly below
the slab is recommended to provide a structural cushion, a capillary-break from the subgrade,
and a drainage medium.
ICE HOCKEY PAVILION EXPANSION Recommendations
GALLATIN COUNTY FAIRGROUNDS 8
4.0 RECOMMENDATIONS
4.1 SITE GRADING AND EXCAVATIONS
1. All topsoil and organic material, asphalt, concrete and related construction debris,
and should be removed from the proposed building areas and any areas to receive
site grading fill. All existing and abandoned utilities should be relocated or
removed from within the building footprint. Stripping depths should extend
through all fill and topsoil lenses which were observed up to two feet below
existing ground. Required stripping depths will vary across the site.
2. All fill and backfill should be non-expansive, free of organics and debris and
should be approved by the project geotechnical engineer. All fill should be placed
in uniform lifts not exceeding 8 inches in thickness for fine-grained soils and not
exceeding 12 inches for granular soils. All fill and backfill shall be compacted to
the following percentages of the maximum dry density determined by a modified
proctor test which is outlined by ASTM D1557 or equivalent (e.g. ASTM D4253-
D4254).
a) Below Foundations or Spread Footings ............................................. 95%
b) Below Slab-on-Grade Construction................................................... 92%
c) Below Streets, Parking Lots, or Other Paved Areas .......................... 92%
d) General Landscaping or Nonstructural Areas ................................... 90%
e) Utility Trench Backfill, To Within 2 Feet of Surface ........................ 92%
3. Imported structural fill, if needed, should be non-expansive, free of organics and
debris, and selected per the following gradation requirements:
Screen or Sieve Size Percent Passing by Weight
3-inch 100
1½-inch 80 – 100
¾-inch 60 – 100
No. 4 25 – 60
No. 200 10 maximum
ICE HOCKEY PAVILION EXPANSION Recommendations
GALLATIN COUNTY FAIRGROUNDS 9
4. Develop and maintain site grades which will rapidly drain surface and roof runoff
away from foundation and subgrade soils; both during and after construction.
5. Downspouts from roof drains should discharge at least 10 feet from the buildings
or convey directly to a storm drain system.
6. Site utilities should be installed with proper bedding in accordance with pipe
manufacturer’s requirements.
7. It is the responsibility of the Contractor to provide safe working conditions in
connection with underground excavations. Temporary construction excavations
greater than four feet in depth, which workers will enter, will be governed by
OSHA guidelines given in 29 CFR, Part 1926. For planning purposes, subsoils
encountered in the test pits classify as Type B for the lean clay with sand and
Type C for the poorly-graded gravel with sand and clay.
4.2 SHALLOW SPREAD FOOTING FOUNDATION
The design and construction criteria below should be observed for a spread footing foundation
system. The construction details should be considered when preparing the project documents.
8. Both interior and exterior footings should bear on properly compacted native
poorly-graded gravel with sand and clay or on properly compacted structural fill
(meeting the requirements of Items 2 and 3) extending down to gravel. Footings
should be designed for a maximum allowable soil bearing pressure of 4,000 psf
provided settlements as outlined in the engineering analysis are acceptable. The
limits of over-excavation and replacement with compacted structural fill should
extend downward and outward laterally from the bottom edges of the footings at a
1:1 (horizontal to vertical) projection.
9. Soils disturbed below the planned depths of footing excavations should either be
recompacted or be replaced with suitable compacted backfill approved by the
geotechnical engineer.
10. Footings should have a minimum width of 16 inches for wall footings and 24
inches for column footings.
ICE HOCKEY PAVILION EXPANSION Recommendations
GALLATIN COUNTY FAIRGROUNDS 10
11. Exterior footings and footings beneath unheated areas should be placed at least 48
inches below finished exterior grade for frost protection.
12. The bottom of the footing excavations should be free of cobbles and boulders to
avoid stress concentrations acting on the base of the footings.
13. Lateral loads are resisted by sliding friction between the footing base and the
supporting soil and by lateral pressure against the footings opposing movement.
For design purposes, a friction coefficient of 0.50 and a lateral resistance pressure
of 400 psf per foot of depth are appropriate for the poorly-graded gravel with sand
and clay.
14. New footings placed adjacent to the existing structure should bear at the same
approximate elevation and should be separated from the existing footings by a
distance greater than one footing width (new or existing footing, whichever is
widest).
15. A representative of the project geotechnical engineer should observe all footing
excavations and backfill phases prior to the placement of concrete formwork to
ensure they are in compliance with our recommendations.
4.3 FLOOR SLABS AND EXTERIOR FLATWORK
16. For normally loaded, slab-on-grade construction, a minimum 6-inch cushion
course consisting of free-draining, crushed gravel should be placed beneath the
slabs and compacted to a minimum of 92 percent density per ASTM D1557 (or
equivalent per ASTM D4253-D4254). This material should consist of minus 3/4-
inch aggregate with no more than 10 percent passing the No. 200 sieve. Prior to
placing the cushion course, the upper six inches of subgrade should be compacted
to 92 percent of maximum density per ASTM D1557.
17. The results of our field exploration indicate that existing fill and buried topsoil
lenses will be encountered in the building area. The existing fill and topsoil
should be removed below all slab areas. If over excavation is required to remove
all existing fill and topsoil below the slab, structural fill meeting the requirements
of Item 2 and 3 above should be used as backfill.
ICE HOCKEY PAVILION EXPANSION Recommendations
GALLATIN COUNTY FAIRGROUNDS 11
18. The lean clay with sand is considered to have high frost susceptibility (frost group
F3) according to National Cooperative Highway Research Program (NCHRP). A
thermal analysis should be performed to model the maximum depth of sustained
frost penetration. The results of the thermal analysis should be used to provide
subgrade improvement recommendations. Without a thermal analysis, the only
positive way to prevent potential frost heave is to excavate the fine-grained soils
below the ice rink down to the gravel and backfill with compacted nonfrost-
susceptible granular fill or as previously mentioned, placement an under-slab
heating system below the refrigerated slab to prevent freezing of the subsurface
soil.
19. Geotechnically , an underslab vapor barrier is not required.
4.4 CONTINUING SERVICES
Three additional elements of geotechnical engineering service are important to the successful
completion of this project.
20. Consultation between the geotechnical engineer and the design professionals
during the design phases is highly recommended. This is important to ensure that
the intentions of our recommendations are incorporated into the design, and that
any changes in the design concept consider the geotechnical limitations dictated
by the on-site subsurface soil and ground water conditions.
21. Observation, monitoring, and testing during construction is required to document
the successful completion of all earthwork and foundation phases. A geotechnical
engineer from our firm should observe the excavation, earthwork, and foundation
phases of the work to determine that subsurface conditions are compatible with
those used in the analysis and design.
22. During site grading, placement of all fill and backfill should be observed and
tested to confirm that the specified density has been achieved. We recommend
that the owner maintain control of the construction quality control by retaining the
services of a construction materials testing laboratory. We are available to
provide construction inspection services as well as materials testing of compacted
soils and the placement of Portland cement concrete.
ICE HOCKEY PAVILION EXPANSION Summary of Field and Laboratory Studies
GALLATIN COUNTY FAIRGROUNDS 12
5.0 SUMMARY OF FIELD AND LABORATORY STUDIES
5.1 FIELD EXPLORATIONS
The field exploration program was conducted on August 23, 2012. A total of three test pits were
excavated to depths ranging from 9.3 to 10.0 feet at the locations shown on Figure 1 to observe
subsurface soil and ground water conditions. The tests pits were excavated using a Takeuchi TB
250 excavator. The subsurface exploration and sampling methods used are indicated on the
attached test pit logs. The test pits were logged by Mr. Kyle Scarr, P.E. of TD&H Engineering.
The approximate locations and surface elevations of the exploratory test pits are shown on Figure
1. Logs of all soil test pits, which include soil descriptions and sample depths are presented on
the Figures 2 though 4. No evidence of ground water was encountered.
5.2 LABORATORY TESTING
Samples obtained during the field exploration were returned to our materials laboratory where
they were observed and visually classified in general accordance with ASTM D2487, which is
based on the Unified Soil Classification System. Representative samples were selected for
testing to determine the engineering and physical properties of the soils in general accordance
with ASTM or other approved procedures.
Tests Conducted: To determine:
Natural Moisture Content Representative moisture content of soil at the time of
sampling.
Grain-Size Distribution Particle size distribution of soil constituents describing the
percentages of clay/silt, sand and gravel.
Atterberg Limits A method of describing the effect of varying water content
on the consistency and behavior of fine-grained soils.
UU Shear Strength (Field) The undrained, unconfined shear strength (s u) of cohesive
soils as determined in the field by a pocket penetrometer.
ICE HOCKEY PAVILION EXPANSION Summary of Field and Laboratory Studies
GALLATIN COUNTY FAIRGROUNDS 13
The laboratory testing program for this project consisted of five moisture-visual analyses, one
sieve (grain-size distribution) analysis, and one Atterberg Limits analysis. The grain-size
distribution curves and Atterberg limits are presented on Figures 5 and 6. In addition, in place
field density tests using a nuclear densometer were conducted. The results of field density
testing, field shear strength testing, and water content analyses are presented on the test pit logs.
ICE HOCKEY PAVILION EXPANSION Limitations
GALLATIN COUNTY FAIRGROUNDS 14
6.0 LIMITATIONS
This report has been prepared in accordance with generally accepted geotechnical engineering
practices in this area for use by the client for design purposes. The findings, analyses, and
recommendations contained in this report are based on site conditions encountered and further
assume that the results of the exploratory test pits are representative of the subsurface conditions
throughout the site, that is, that the subsurface conditions everywhere are not significantly
different from those disclosed by the subsurface study. If during construction, subsurface
conditions appear different from those encountered during our study, this office should be
advised at once so we can review these conditions and reconsider our recommendations, when
necessary.
Unanticipated soil conditions are commonly encountered and cannot be fully determined by a
limited number of soil test pits and laboratory analyses. Such unexpected conditions frequently
require that additional expenditures be made to obtain a properly constructed project. Therefore,
some contingency fund is recommended to accommodate such potential extra costs.
If substantial time has elapsed between the submission of this report and the start of work at the
site, or if conditions have changed because of natural causes or construction operations at or
adjacent to the site, we recommend that this report be reviewed to determine the applicability of
the conclusions and recommendations considering the time lapse or changed conditions.
If you desire, we will review those portions of the plans and specifications which pertain to
earthwork and foundations to determine if they are consistent with our recommendations. In
addition, we are available to observe construction, particularly the placement and compaction of
all fill, preparation of all foundations and quality control testing of Portland cement concrete.
This report was prepared for the exclusive use of the owner and architect and/or engineer in the
design of the subject facility. It should be made available to prospective contractors and/or the
contractor for information on factual data only and not as a warranty of subsurface conditions
such as those interpreted from the test pit logs and presented in discussions of subsurface
conditions included in this report.
Prepared by: Reviewed by:
Kyle L. Scarr, P.E. Craig R. Nadeau, P.E.
Geotechnical Engineer Geotechnical Engineer
QUALITY CHECK:
DESIGNED BY:
DRAWN BY:
CAD NO.
JOB NO.
DATE:
B12-060 FIG 1
MONTANAWASHINGTON
IDAHO
GREAT FALLS-BOZEMAN-KALISPELL
LEWISTONSPOKANE
Engineering
tdhengineering.com
HAYNES PAVILION EXPANSION
BOZEMAN, MONTANA
APPROXIMATE TEST PIT LOCATIONS
KLS
NA
NA
10/3/12
B12-060
FIGURE
1
Log of Test Pit TP-1
Figure No.
Sheet of
2
1 1
GR
A
P
H
I
C
LO
G
0 10 20 30 40 50
0
0 10 30 40 5020
SA
M
P
L
E
DE
P
T
H
WA
T
E
R
GR
O
U
N
D
SOIL DESCRIPTION
LEGEND
DE
P
T
H
(F
E
E
T
)
Haynes Pavilion Expansion
Bozeman, Montana
THOMAS, DEAN & HOSKINS, INC.
ENGINEERING CONSULTANTS
AUGUST 23, 2012 B12-060
(F
E
E
T
)
1
8
12
9.3
Gr
o
u
n
d
w
a
t
e
r
N
o
t
E
n
c
o
u
n
t
e
r
e
d
Du
r
i
n
g
E
x
c
a
v
a
t
i
o
n
Well-graded GRAVEL with sand and silt, relatively medium
dense, dry, brown to gray, 1.5" minus gravel surface course
APPROXIMATE SURFACE ELEVATION:
SURFACE:
Logged By: Kyle L. Scarr, P.E.Excavated By:Earth Surgeons
Takeuchi TB 250
Gravel surfaced parking lot
4797.5 Feet
2
3
4
5
6
7
9
10
11
13
14
15
16
Lean CLAY with sand, relatively soft to firm, dry, brown to tan,
upper 2" appears to have been topsoil
Poorly-graded GRAVEL with sand and clay, relatively very
dense, slightly moist, brown variegated, less fines with depth,
cobbles and boulders up to 1' in diameter
Bottom of Test Pit
3.0
0.6
Average qu = 2.5 tsf
5.0' - 6.0'
Wet density: 129.2 pcf
Dry density: 125.6 pcf
Moisture: 2.9%
Log of Test Pit TP-2
Figure No.
Sheet of
3
1 1
GR
A
P
H
I
C
LO
G
0 10 20 30 40 50
0
0 10 30 40 5020
SA
M
P
L
E
DE
P
T
H
WA
T
E
R
GR
O
U
N
D
SOIL DESCRIPTION
LEGEND
DE
P
T
H
(F
E
E
T
)
Haynes Pavilion Expansion
Bozeman, Montana
THOMAS, DEAN & HOSKINS, INC.
ENGINEERING CONSULTANTS
AUGUST 23, 2012 B12-060
(F
E
E
T
)
1
8
12
10.0
Gr
o
u
n
d
w
a
t
e
r
N
o
t
E
n
c
o
u
n
t
e
r
e
d
Du
r
i
n
g
E
x
c
a
v
a
t
i
o
n
FILL: Lean clay with sand, relatively soft, dry, brown
APPROXIMATE SURFACE ELEVATION:
SURFACE:
Logged By: Kyle L. Scarr, P.E.Excavated By:Earth Surgeons
Takeuchi TB 250
Lightly grassed lawn area
4799.0 Feet
2
3
4
5
6
7
9
10
11
13
14
15
16
FILL: Gravelly lean clay, relatively firm, dry, brown, gravel up
to 3" in diameter
Poorly-graded GRAVEL with sand and clay, relatively very
dense, slightly moist, brown variegated, less fines with depth,
cobbles and boulders up to 1' in diameter
Bottom of Test Pit
3.4
0.5
4.0'- 5.0'
Wet density: 132.2 pcf
Dry density: 127.7 pcf
Moisture: 3.5%
1.0
Lean CLAY with sand, relatively soft to firm, slightly moist,
brown to tan, upper 1" appears to have been topsoil
Log of Test Pit TP-3
Figure No.
Sheet of
4
1 1
GR
A
P
H
I
C
LO
G
0 10 20 30 40 50
0
0 10 30 40 5020
SA
M
P
L
E
DE
P
T
H
WA
T
E
R
GR
O
U
N
D
SOIL DESCRIPTION
LEGEND
DE
P
T
H
(F
E
E
T
)
Haynes Pavilion Expansion
Bozeman, Montana
THOMAS, DEAN & HOSKINS, INC.
ENGINEERING CONSULTANTS
AUGUST 23, 2012 B12-060
(F
E
E
T
)
1
8
12
10.0
Gr
o
u
n
d
w
a
t
e
r
N
o
t
E
n
c
o
u
n
t
e
r
e
d
Du
r
i
n
g
E
x
c
a
v
a
t
i
o
n
Well-graded GRAVEL with sand and silt, relatively medium
dense, dry, brown to gray, 1.5" minus gravel surface course
APPROXIMATE SURFACE ELEVATION:
SURFACE:
Logged By: Kyle L. Scarr, P.E.Excavated By:Earth Surgeons
Takeuchi TB 250
Gravel surfaced parking lot
4799.5 Feet
2
3
4
5
6
7
9
10
11
13
14
15
16
Lean CLAY, relatively firm, slightly moist, dark brown to black,
trace sand, appears to have been topsoil
Poorly-graded GRAVEL with sand and clay, relatively very
dense, slightly moist, brown variegated, less fines with depth,
cobbles and boulders up to 1' in diameter
Bottom of Test Pit
2.3
0.5
5.0' - 6.0'
Wet density: 124.8 pcf
Dry density: 117.7 pcf
Moisture: 6.0%
Tested By: SSS Checked By:
9-4-2012
(no specification provided)
PL= LL= PI=
D90= D85= D60=
D50= D30= D15=
D10= Cu= Cc=
USCS= AASHTO=
*
Lean CLAY w/sand
3/8"
#4
#10
#20
#40
#60
#80
#100
#200
100.0
99.3
98.3
96.8
93.9
90.0
86.8
84.8
72.0
19 33 14
0.2507 0.1529
CL A-6(8)
Report No: A-6178-206
Intrinsik Architecture
Haynes Pavilion Geotech
B12-060
Material Description
Atterberg Limits
Coefficients
Classification
Remarks
Location: TP
Sample Number: A-6178 Depth: 2'-2.5'Date:
Client:
Project:
Project No: Figure
SIEVE PERCENT SPEC. *PASS?
SIZE FINER PERCENT (X=NO)
PE
R
C
E
N
T
F
I
N
E
R
0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0001 0.001 0.01 0.1 110 100
% +3" Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 0.0 0.7 1.0 4.4 21.9 72.0
6
i
n
.
3
i
n
.
2
i
n
.
1½
i
n
.
1
i
n
.
¾
i
n
.
½
i
n
.
3/
8
i
n
.
#4 #1
0
#2
0
#3
0
#4
0
#6
0
#1
0
0
#1
4
0
#2
0
0
Particle Size Distribution Report
5
Bozeman Amateur Hockey Association
Tested By: TJR Checked By:
Lean CLAY w/sand 33 19 14 93.9 72.0 CL
B12-060 Intrinsik Architecture
MATERIAL DESCRIPTION LL PL PI %<#40 %<#200 USCS
Project No. Client: Remarks:
Project:
Figure
Location: TP Depth: 2'-2.5'Sample Number: A-6178
PL
A
S
T
I
C
I
T
Y
I
N
D
E
X
0
10
20
30
40
50
60
LIQUID LIMIT
0 10 20 30 40 50 60 70 80 90 100 110
CL-ML
C L o r O L
C H o r O H
ML or OL MH or OH
Dashed line indicates the approximate
upper limit boundary for natural soils
47
LIQUID AND PLASTIC LIMITS TEST REPORT
Report No: A-6178-207 Haynes Pavilion Geotech
Bozeman Amateur Hockey Association
6
Great Falls, Kalispell, Bozeman, Montana
Spokane, Washington, Lewiston, Idaho
THOMAS, DEAN & HOSKINSEngineering Consultants SOIL CLASSIFICATION AND
SAMPLING TERMINOLOGY
FOR ENGINEERING PURPOSES
12" 3" 3/4" No.4 No.10 No.40 No.200 <No.200
SILTS & CLAYSBOULDERSCOBBLESGRAVELSSANDS
PARTICLE SIZE RANGE
(Distinguished By
Atterberg Limits)FineCoarse FineMediumCoarse
Sieve Openings (Inches)Standard Sieve Sizes
CL - Lean CLAY
ML - SILT
OL - Organic SILT/CLAY
CH - Fat CLAY
MH - Elastic SILT
OH - Organic SILT/CLAY
SW - Well-graded SAND
SP - Poorly-graded SAND
SM - Silty SAND
SC - Clayey SAND
GW - Well-graded GRAVEL
GP - Poorly-graded GRAVEL
GM - Silty GRAVEL
GC - Clayey GRAVEL
* Based on Sampler-Hammer Ratio of 8.929 E-06 ft/lbf and 4.185 E-05 ft^2/lbf for
granular and cohesive soils, respectively (Terzaghi)
STANDARD PENETRATION TEST (ASTM D1586)
RELATIVE DENSITY*RELATIVE CONSISTENCY*
Granular, Noncohesive
(Gravels, Sands, & Silts)Fine-Grained, Cohesive
(Clays)
Very Loose
Loose
Medium Dense
Dense
Very Dense
Very Soft
Soft
Firm
Stiff
Very Stiff
Hard
0-2
3-4
5-8
9-15
15-30
+30
0-4
5-10
11-30
31-50
+50
Standard
Penetration Test
(blows/foot)
Standard
Penetration Test
(blows/foot)
PLASTICITY CHART
0 10 16 20 30 40 50 60 70 80 90 100 110
60
50
40
30
20
107
4
C L o r O L
C H o r O H
ML or OL
MH or OH
CL-ML
"U - L I N E "
"A - L I N E "
LIQUID LIMIT (LL)
P L A S T I C I T Y I N D E X (P I )
For classification of fine-grained soils and thefine-grained fraction of coarse-grained soils.
Equation of "A"-line
Horizontal at PI = 4 to LL = 25.5,
then PI = 0.73 (LL-20)
Equation of "U"-line
Vertical at LL = 16 to PI = 7,
then PI = 0.9 (LL-8)
Great Falls, Kalispell, Bozeman, Montana
Spokane, Washington, Lewiston, Idaho
THOMAS, DEAN & HOSKINSEngineering Consultants ASTM D2487
CLASSIFICATION OF SOILS
FOR ENGINEERING PURPOSES
Flow Chart For Classifying Coarse-Grained Soils (More Than 50 % Retained On The No. 200 Sieve)
Flow Chart For Classifying Fine-Grained Soils ( 50 % Or More Passes The No. 200 Sieve)
<5% fines
5-12% fines
>12% fines
<5% fines
5-12% fines
>12% fines
Well-graded GRAVELWell-graded GRAVEL with sandPoorly-graded GRAVELPoorly-graded GRAVEL with sand
Well-graded GRAVEL with silt
Well-graded GRAVEL with silt and sandWell-graded GRAVEL with clay (or silty clay)Well-graded GRAVEL with clay and sand (or silty clay and sand)
Poorly-graded GRAVEL with silt
Poorly-graded GRAVEL with silt and sand
Poorly-graded GRAVEL with clay (or silty clay)Poorly-graded GRAVEL with clay and sand (or silty clay and sand)
Silty GRAVELSilty GRAVEL with sandClayey GRAVELClayey GRAVEL with sandSilty, clayey GRAVEL
Silty, clayey GRAVEL with sand
Well-graded SAND
Well-graded SAND with gravel
Poorly-graded SANDPoorly-graded SAND with gravel
Well-graded SAND with silt
Well-graded SAND with silt and gravel
Well-graded SAND with clay (or silty clay)Well-graded SAND with clay and gravel (or silty clay and gravel)
Poorly-graded SAND with siltPoorly-graded SAND with silt and gravelPoorly-graded SAND with clay (or silty clay)
Poorly-graded SAND with clay and gravel
(or silty clay and gravel)
Silty SANDSilty SAND with gravelClayey SAND
Clayey SAND with gravel
Silty, clayey SAND
Silty, clayey SAND with gravel
<15% sand>15% sand
<15% sand
>15% sand
<15% sand>15% sand
<15% sand
>15% sand
<15% sand>15% sand<15% sand>15% sand
<15% sand>15% sand<15% sand>15% sand<15% sand
>15% sand
<15% gravel
>15% gravel
<15% gravel>15% gravel
<15% gravel>15% gravel<15% gravel>15% gravel
<15% gravel
>15% gravel<15% gravel>15% gravel
<15% gravel
>15% gravel<15% gravel>15% gravel<15% gravel>15% gravel
Lean CLAYLean CLAY with sandLean CLAY with gravelSandy lean CLAY
Sandy lean CLAY with gravel
Gravelly lean CLAY
Gravelly lean CLAY with sand
Silty CLAY
Silty CLAY with sand
Silty CLAY with gravel
Sandy silty CLAYSandy silty CLAY with gravelGravelly silty CLAYGravelly silty CLAY with sand
SILT
SILT with sandSILT with gravelSandy SILTSandy SILT with gravel
Gravelly SILT
Gravelly SILT with sand
Fat CLAYFat CLAY with sand
Fat CLAY with gravel
Sandy fat CLAYSandy fat CLAY with gravelGravelly fat CLAYGravelly fat CLAY with sand
Elastic SILT
Elastic SILT with sand
Elastic SILT with gravelSandy elastic SILTSandy elastic SILT with gravelGravelly elastic SILT
Gravelly elastic SILT with sand
%sand > %gravel
%sand < %gravel
<15% gravel>15% gravel<15% sand>15% sand
%sand > %gravel
%sand < %gravel<15% gravel>15% gravel<15% sand
>15% sand
%sand > %gravel%sand < %gravel
<15% gravel>15% gravel<15% sand>15% sand
%sand > %gravel%sand < %gravel<15% gravel>15% gravel<15% sand
>15% sand
%sand > %gravel
%sand < %gravel
<15% gravel>15% gravel<15% sand>15% sand
fines=ML or MH
fines=CL or CH (or CL-ML)
fines=ML or MH
fines=CL or CH (or CL-ML)
fines=ML or MH
fines=CL or CH
fines=CL-ML
fines=ML or MH
fines=CL or CH
(or CL-ML)
fines=ML or MH
fines=CL or CH
(or CL-ML)
fines= ML or MH
fines=CL or CH
fines=CL-ML
<30% plus No. 200
>30% plus No. 200
<30% plus No. 200
>30% plus No. 200
<30% plus No. 200
>30% plus No. 200
<30% plus No. 200
>30% plus No.200
<30% plus No. 200
>30% plus No. 200
Cu>4 and 1<Cc<3
Cu<4 and/or 1>Cc>3
Cu>4 and 1<Cc<3
Cu<4 and/or 1>Cc>3
Cu>6 and 1<Cc<3
Cu<6 and/or 1>Cc>3
Cu>6 and 1<Cc<3
Cu<6 and/or 1>Cc>3
CL
CL-ML
ML
CH
MH
PI>7 and plotson or above"A" - line
4<PI<7 andplots on or above"A" - line
PI<4 or plotsbelow "A" - line
PI plots on orabove "A" - line
PI plots below"A" - line
GRAVEL%gravel >
%sand
SAND%sand >%gravel
LL>50(inorganic)
LL<50(inorganic)
GW
GP
GW-GM
GW-GC
GP-GM
GP-GC
GM
GC
GC-GM
SW
SP
SW-SM
SW-SC
SP-SM
SP-SC
SM
SC
SC-SM
<15% plus No. 20015-29% plus No. 200
%sand > %gravel
%sand < %gravel
<15% plus No. 200
15-29% plus No. 200
%sand > %gravel
%sand < %gravel
<15% plus No. 200
15-29% plus No. 200
%sand > %gravel
%sand < %gravel
<15% plus No. 20015-29% plus No. 200
%sand > %gravel
%sand < %gravel
<15% plus No. 20015-29% plus No. 200
%sand > %gravel
%sand < %gravel