HomeMy WebLinkAbout15 - Design Report - Unitarian Universalist Fellowship (325 N 25th) - Stormwater STORMWATER DESIGN REPORT
for
UNITARIAN UNIVERSALIST
FELLOWSHIP FIRST HOME
at
325 N. 25th AVENUE
BOZEMAN, MONTANA
Prepared for:
Kasmer Properties, LLC
325 North 25th Avenue
Bozeman, MT 59718
Prepared by:
C&H Engineering and Surveying, Inc.
1091 Stoneridge Drive
Bozeman, MT 59718
(406) 587-1115
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Project No.: 15455
DECEMBER 2015
INTRODUCTION
325 N. 251h Avenue is located at the southwest corner of the intersection of W. Villard Street and
N. 25t" Avenue in Bozeman, Montana. The site lies on Lot 6 and Lot 7, Kahle Subdivision and
currently has a 2,000 square foot church building and gravel parking lot. This project will include
the construction of a 3,000 square foot addition to the existing church building, an asphalt parking
lot to replace the gravel lot, and associated infrastructure. A combination of site grading, curb and
gutter, and on-site retention via a retention pond and underground StormTech infiltration system
will be used to handle stormwater runoff from the site.
DRAINAGE AREAS
The proposed site was divided into two drainage areas as seen on the Drainage Area Exhibit in
Appendix A. Drainage Area #1 consists of the asphalt parking lot, the sidewalk that borders the
parking lot along the south edge, the adjacent landscaped areas, the shed roof in the southwest
corner of the site, and the north half of the church roof. Drainage Area#1 is the only drainage area
on the proposed site that contributes to the underground StormTech infiltration system located
under the parking lot beneath the north row of parking spaces.
Drainage Area #2 consists of the south half of the church roof, the small shed at the southeast
corner of the existing church building, and the landscaped areas in the south and east portions of
the lot. Drainage Area#2 contributes stormwater runoff to the retention pond located in the south
yard behind the church.
DESIGN CRITERIA AND METHODOLOGY
The site is designed so that stormwater runoff from a 10-year, 2-hour storm is retained and
infiltrated as required by the Bozeman Design Standards and Specifications Policy (DSSP),
Section II.C.The StormTech MC-3500 chambers were sized accounting for infiltration during the
10-year, 2-hour storm. An infiltration rate of 0.50 inch/hour was used based on a percolation rate
of 10 min./inch for soil texture similar to medium sand, sandy loam (Table 8-1, DEQ Circular 4).
This is considered a conservative estimate of the infiltration rate of the soils on site. The soil type
found at 3 ft below ground surface(bgs) to 13 feet bgs was Poorly Graded Gravel with Sand and
Cobbles during a soils investigation on November 4, 2015 conducted by C&H Engineering. The
bottom of the StormTech chamber is set at approximately 6.5 feet bgs, so that it lies within the
Poorly Graded Gravel with Sand and Cobbles layer and is approximately 2 feet above the
historical high ground water table. The retention pond that collects stormwater runoff from
Drainage Area#2 was also designed for the 10-year,2-hour storm.All calculations can be found in
Appendix B.
It should be noted that neither the StormTech chambers nor the retention pond were sized to
accommodate the first half inch of rainfall from a 24-hour storm per Bozeman DSSP, Section
II.A.4. This is because the site is less than one acre; therefore, an analysis of the first half inch of
rainfall is not required.
Design Report-Page 2 of 3
SUMMARY OF STORMTECH DESIGN
Four StormTech MC-3500 chambers and two end caps have a storage capacity of 808 cubic feet,
which is adequate to retain and infiltrate the runoff from the design storm. The runoff from the
10-year, 2-hour storm is 810 cubic feet. During that 2 hour storm duration, 208 cubic feet are
infiltrated, leaving a remainder of 602 cubic feet to be retained in the StormTech system. The
StormTech underground system receives stormwater runoff via the combination manhole/curb
inlet located in the northeast portion of the parking lot. This inlet also serves as a sand-oil
separator, as required by the Bozeman DSSP, Section II.A.2. The inlet has a 9 inch sump depth to
capture sediment.The oil is separated by using a 3M,T-240 oil-absorbent floating pillow.Also,an
additional oil-separation measure is in the design of the outlet pipe. A 90 degree pipe fitting is
attached to the outlet pipe extending down into the manhole 1.5 feet (see Detail 8/C2.0 on civil
drawing set). Because oil is less dense than water and floats on the surface, this outlet pipe design
will prevent oil from collecting on the surface of the stormwater trapped in the sump,then spilling
out through the outlet pipe into the StormTech chambers. The 90 degree downward bend
extending downward into the sump will minimize the ability of trapped oils to exit the manhole
and enter the StormTech system. The sand-oil separator manhole will require maintenance and
replacement of the oil absorbent pillow when necessary by the owner.
Also, for ease of maintenance of the underground StormTech chambers, a manhole, per City of
Bozeman Detail 02720-3, will be installed on the east side of the system. This manhole will be
connected to the StormTech system by a 24 inch HDPE pipe sloped at 2%.
Design Report-Page 3 of 3
DRAINAGE AREA EXHIBIT
LEGEND W. VILLARD STREET EXISTING EDGE OF U)
PAVEMENT Ln
DSO ROOF DOWNSPOUT P T_REET SIGN®
6
PROPERTY BOUNDARY LINE UE131. BL Sheet'of I
[N89'29'5TE]
DRAINAGE AREA LINE 135.71 08729'5T
cc)
PROPOSED SPILL CURB X X
INSP-_CTION
I 1p MANH
7a
0
0 PROPOSED CATCH CURB C
W
V11 En >
fi CURB INLET
RIM ELEv.=99.75- lu afli
C
SITE DAT PROPOSED ASPHALT PAVEMENT
A LO
0 7LP LOT 7
cv
DRAINAGE AREA fil SUMMARY
CONCRETE =8,528 S.F.
STORM ER HASE TIED
ROOF =,3,540 S.F.
V-=,`7
NTO R( OF DO' NSPO T�,,
I
LANDSCAPE =4,873 S.F.
SEE �7AIL__ /C2.6`
TOTAL AREUr
WAT
E N F)
SECTION
CTIO 0
WELDED BAR"--'GRATING. AMICO 19
A=16,941 S.F. INSTALL 4' WIPE SECTION OF
SIMILAR).
PRODU_ (OR SIMILAR) GRADE! BREAK."-
Runoff from Drainage Area #1 flows an inlet in the north curb
F
flow line of the proposed asphalt parking lot. unoff flows from
the inlet to a Stormtech underground retention system. BIKE PRO OSED 5- SIDEWALK
I
RACKS 0
RAINAGE AREA #2 SUMMARY o 0 o D 0 -10 PROPOSE REE
JNCRETE =0 S.F. GRADE BRJ 0 b
ROOF =1,698 S.F. PROPERTY 0.
b ii—lun)
LANDSCAPE =3,080 S.F. P$jb S_ 0
V z F b o >
TOTAL AREA=4,778 S.F. ",to
b BUILDING ADDITION
z to
Runoff from Drainage Area #2 flows to a landscaped retention
pond on the south side of the building. SIGN
FL
GRASS—LINED SWALE,/
TO IFON—
F t* 9 .4'
ROOF DOWDRAINNSftUT
/r
THROUGH CURB ''�UT.
SEE LANDSCAPE
`,6
<
EXISTING
SHED
REMOVE EX. SHED
EXIFIIV 'WATER SPIGOT
' a
EXISTING
SHED
EXISTING FENCE
Ln
Scale O Feet TO REMA NPROPOSED RETENTION PONVOL. @ 1.5' DEPTH=135 C. M-a"Pate.12-01-5
20 20
SS
W
SS
3"][S89-24- JLAF-A
6 0 6 DRAINAGE AREA EXHIBIT V) M
Scale In Meters E
Contour Intervals: 1 Foot EX1 SCALE: 1 10' #1 5455EX1 I
STORMWATER CALCULATIONS
Post-development Runoff Coefficient Calculation
Drainage Area 1
Determine Weighted C Coefficient for the north half of the roof,parking tot and landscaped areas.
Site Area(Sq.Ft.) Area(acre) *C FACTOR
Concrete/Asphalt 8528 0.1958 0.95
Roofs 3540 0.0813 0.95
Landscape 4873 0.1119 0.10
Total 16941 0.3889
Weighted C= 0.71
Drainage Area
Determine Weighted C Coefficient for the south half of the roof and landscaped area south of the church.
Site Area(Sq.Ft.) Area(acre) *C FACTOR
Roof 1698 0.0390 0.95
Landscape 3080 0.0707 0.10
Total 4778 0.1097
Weighted C= 0.40'
"Runoff coefficients from Table 3-1 of the"Design and Construction of Sanitary and Storm Sewers",ACSE.(See Appendix C)
Runoff calculations for 10 year, 2 hour storm
Runoff Calculations - 10 year,
2 hour storm
Drainage Area 1
Calculate runoff in cfs for the design storm (10 year, 2 hour event)
Q = CiA
Where:
C = Rational Method Runoff Coefficient 0.71
i = rainfall intensity 0.41 in./hr.
A=Area 0.39 acres
Q = Runoff(cfs) 0.11 cfs
Calculate volume of runoff for a 2 hour duration event to be retained underground Stormtech.
V=Volume (ft) 810 ft3
Drainage Area 2
Calculate runoff in cfs for the design storm (10 year, 2 hour event)
Q = CiA
Where:
C = Rational Method Runoff Coefficient 0.40
i= rainfall intensity 0.41 in./hr.
A=Area 0.11 acres
Q = Runoff(cfs) 0.02 cfs
Calculate volume of runoff for a 2 hour duration event to be retained in retention pond.
V=Volume (ft) 130 W
StormTech sizing calculations
Select Storm Tech MC-3500 Chamber
*Installed storage volume per chamber 178.9 cf
*End cap storage volume 46.0 cf
Estimate approximate number of chambers required
Required storage volume(D.A.#1) 810 cf
Storage volume of 4 chambers and 2 end caps 808 cf
Determine the effect infiltration will have on the design Check whether 3 chambers will provide adequate storage
Estimated percolation rate of soils on site 10 min./inch (From Table 8-1 DEQ Circular 4,see Appendix C)
Convert to perc. rate to infiltration rate 0.50 ft./hr.
Footprint of MC-3500 chamber width= 77 inches (See Civil Drawing C3.0)
installed length= 86 inches
area= 46.0 sq.ft.
Footprint of MC-3500 cap width= 77 inches
installed length= 22.5 inches
area= 12.0 sq.ft.
Volume of water infiltrated during 2hr storm per chamber 46.0 cf
Volume of water infiltrated during 2hr storm per end cap 12.0 cf
Total volume infiltrated during 2 hour storm(3 chambers) 162 cf
—Required storage volume after infiltration(3 chambers) 648 cf
Storage volume of 3 chambers and 2 end caps 629 cf
629cf<648cf;therefore,3 chambers will not provide adequate storage when accounting for infiltration.
Verify that 4 chambers is adequate
Volume of water infiltrated during 2hr storm per chamber 46.0 cf
Volume of water infiltrated during 2hr storm per end cap 12.0 cf
Total volume infiltrated during 2 hour storm(4 chambers) 208 cf
Required storage volume after infiltration(4 chambers) 602 cf
Storage volume of 4 chambers and 2 end caps 808 cf
808cf>602cf;therefore,4 chambers will provide adequate storage when accounting for infiltration.
*Includes 9 inch depth of stone foundation.(See Appendix C)
**This calculation uses the infiltration rate spread over just three chambers,to check if three chambers could be used.
REFERENCE MATERIALS
Table 3-1. Recommended Runoff Coefficients.
Description of Area Runoff Coefficient
Business
Downtown 0.70 to 0.95
Neighborhood 0.50 to 0.70
Residential
Single-family 0.30 to 0.50
20,000 sq ft 0.49
10,000 sq ft 0.52
8,500 sq ft 0.57
Multi-units, detached 0.40 to 0.60
Multi-units, attached 0.60 to 0.75
Residential(suburban) 0.25 to 0.40
Apartment 0.50 to 0.70
Industrial
Light 0.50 to 0.80
Heavy 0.60 to 0.90
Parks, cemeteries 0.10 to 0.25
Playgrounds 0.20 to 0.35
Railroad yard 0.20 to 0.35
Unimproved 0.10 to 0.30
Character of Surface
Pavement
Asphalt and Concrete 0.95
Brick 0.85
Roofs 0.95
Lawns, Sandy soil
Flat, 2% 0.05 to 0.10
Average,2 to 7% 0.10 to 0.15
Steep, 7%+ 0.15 to 0.20
Lawns, Heavy soil
Flat, 2% 0.13 to 0.17
Average,2 to 7% 0.18 to 0.22
Steep, 7%+ 0.25 to 0.35
Source: Design and Construction of Sanitary and Storm Sewers, ASCE and the
Water Pollution Control Federation, 1969.
�' O
Circular DEQ 4
Page 34 of 97
8.4.2 For determining absorption system sizing, the following formula may be used:
Wastewater Flow from Chapter 5 (gpd) divided by the application rate in Table 8-
1 or Table 8-2(gpd/ft2) =Absorption system length (ft2 ) or expressed as a
mathematical formula:
gam_= ft2
gpd/ft2
TABLE 8-1 (Residential)
Texture Square feet for three bedroom Estimated Application
(ft2) Pere rate rate
(min/in) ( d/ft)
Gravelly sand or very coarse sands (a) 375 <3 a) 0.8 a
Loamy sand, coarse sand 375 3 - < 6 0.8
Medium sand, sandy loam 500 6 - <10 0.6
Fine sandy loam, loam, silt loam 600 10- <16 0.5
Very fine sand, sandy clay loam 750 16 - <31 0.4
Clay loam, silty clay loam 1000 31 - <51 0.3
Sandy clay, clay, or silty clay 1500(b)(c) 51 - <121 0.2
Clays, silts, silty clays (soil is reported 2000(d) > 121 0.15
throughout the soil profile) (USE EVTA
BED)
Clays or silts,pan evaporation rates do not > 121 NP
allow for EVTA use
(a) If the soil for 3 feet below the infiltrative surface is gravelly sand or very coarse sands,or there is less than 6
feet separation between the bottom of the trench and a limiting layer,the trench must be pressured-dosed or
other treatment provided as approved by the reviewing authority. If the soil for 3 feet below the infiltrative
layer is very gravelly sand or coarser textured,the trench also must be sand-lined or other treatment as approved
by the reviewing authority.
(b) Pressure distribution will be required if more than 500 lineal feet(or 1000 square feet)of distribution line is
needed.
(c) Comparison of soils profile report,percolation rate,and USDA soils report will be used to select applicable
square footage.
(d) Square footage is increased because the trench sidewall is not available in EVTA bed systems.
NP—Not permitted
2004 Edition
StormTech MC-3500 Chambt�.
Storage Volume Per Chamber/End Cap ft'(m') Volume of Excavation Per Chamber/End Cap in yd'(m')
Bare Chamber/End Cap and Stone _ Stone Foundation Depth _
Unit Volume-Stone Foundation 9"(230 mm) 12"(300 mm)15"(375 mm)18"(450 mm)
Storage Depth in.(mm) _
ft' 9 - 12 _- 15 18 MC-3500 12.4(9.5) 12.8(9.8) 13.3(10,2) 13,8(10.5)
(m') (230) (300) (375) (450) End Cap 4.1(3.1) 4.2(3.2) 4.4(3.3) 4.5(3.5)
MC-3500 109.9 178.9 184.0 189.2 1943 NOTE.,Assumes 9'(230 mm)of separation between chamber rows
Chamber (3.11) (5.06) (5.21) (5.36) (5.5) and 24'(600 mm)of cover. The volume of excavation will vary as the
MC-3500 14.9 46.0 49A 51.1 depth of cover increases.
End Cap (0.42) (1.33) :47.7
1,35) (1.40) (1.45)
NOTE.•Assumes 9'(230 mm)row spacing,40%stone porosity, 12'
i
(300 mm)stone above and includes the bare chambedend cap vol- _
ume.End cap volume assumes 6"(150 mm)stone perimeter. r
Amount of Stone Per Chamber
ENGLISH
Stone Foundation Depth
---
tons Nd') 9" 12" 15" 18"
MC-3500 9.1(6.4 yd') 9.7(6.9 yd') 10A(7.3 yd')I 11.1(7.8 yd')
End Cap 4.1(2.9 yd') 4.3(3.0 yd3) 4.5(3.2 yd') 4.7(3.3 yd3)
METRIC kg(m') 230 mm 300 mm 375 mm 450 mm
MC-3500 8220(4.9 m') 8831(5.3 m') 9443(5.6 m1 10054(6.0 m')
End Cap_ 3699(2.2 m1) 3900(23 m') 4100(2.5 m')
NOTE Assumes 12'(300 mm)of stone above,and 9'(230 mm)row T
spacing,and 6'(150 mm)of perimeter stone in front of end caps.
General Cross Section
CHAMBERS SHALL BE DESIGNED IN ACCORDANCE WITH ASTM F2787
"STANDARD PRACTICE FOR STRUCTURAL DESIGN OF THERMOPLASTIC
CORRUGATED WALL STORMWATER COLLECTION CHAMBERS".
CHAMBERS SHALL MEET ASTM F2418"STANDARD GRANULAR WELL-GRADED SOIL/AGGREGATE MIXTURES,<35%FINES,
SPECIFICATION FOR POLYPROPLENE(PP)CORRUGATED COMPACT IN 12-(300 mm)MAX LIFTS TO 95%STANDARD PROCTOR
WALL STORMWATER COLLECTION CHAMBERS". DENSITY,SEE THE TABLE OF ACCEPTABLE FILL MATERIALS.
ADS GEOSYNTHETICS 601T NON-WOVEN GEOTEXTILE ALL
AROUND CLEAN,CRUSHED,ANGULAR STONE IN A&B LAYERS PAVEMENT LAYER
i
'TO BOTIOM OF F-B LE PAVEMENT.FOR UNPAVED 9'INSTALLATIONS-RE RUTTING FROM VEHICLES MAY OCCUR
ING E C vERTOT71M.F 24., (MAX'm)
7
y.=.'. .,r�...-y :.-._ (600 MIN
>s 12"(300 mm)MIN
-
PERIMETER STONE (1140 mm)
EXCAVATION WALL I I 1
(CAN BE SLOPED
-
OR VERTICAL)
DEPTH OF STONE TO BE
6'(150 mm)MIN
__I - DETERMINED BY DESIGN
- ENGINEER 9"(230 mm)MIN
MC-3500 9.. (795 mm)-- I
END CAP / (230 mm)MIN 77" 0 I�12'(300 mm)TYP
DESIGN ENGINEER IS RESPONSIBLE FOR J
ENSURING THE REQUIRED BEARING
CAPACITY OF SUBGRADE SOILS
"FOR COVER DEPTHS GREATER THAN 8.0'PLEASE CONTACT STORMTECH
THE INSTALLED CHAMBER SYSTEM SHALL PROVIDE THE LOAD FACTORS SPECIFIED IN THE AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS
SECTION 12.12 FOR EARTH AND LIVE LOADS,WITH CONSIDERATION FOR IMPACT AND MULTIPLE VEHICLE PRESENCES.
3 Call StormTech at 860.529.8188 or 888.892.2694 or visit our website at www.stormtech.com for technical and product information.