HomeMy WebLinkAbout10.0 108 West Babcock - Stormwater Report108 West Babcock 7/11/2024
Storm Water Drainage & Maintenance Plan 2 of 2
Design The proposed project consists of completely replacing the existing building, parking lot and landscaped and hardscaped areas. The new building and parking lot have been designed to direct all stormwater runoff to a system of underground Stormtech retention chambers under the
parking lot. The flat roofs will contain a system of gutters and downspouts which will capture the runoff and send it to an underground pipe to the Stormtech catch basin. The carport roof will slope to the south. The south edge will contain a gutter and downspouts to direct runoff to the asphalt parking lot where it will flow overland to the catch basin. The parking lot will be graded to the north where a catch basin will be located. This catch basin will contain a 12” sump to collect sediment and debris before entering the chambers. This catch basin will also be the access point
for future maintenance and cleaning of the chambers. Six (6) SC-710 Stormtech Chambers will be installed in two rows of three to provide the required retention volume for the property. Details of the retention chamber system are provided on Sheet
C2.3.
Retention & Sizing Calculations The retention chambers have been sized to collect runoff for the 10-yr 2-hr storm event as required by the City of Bozeman Design Standards & Specifications Policy. The retention calculations are provided on the sheet titled Stormwater Retention Calculations included in Appendix A of this report. The effective lot area (the total lot minus the 6 feet of alley along the west property boundary which does not drain onto the site) was used for the area in the retention calculations This area consists of 8,151 sf which consists mostly of the building and asphalt parking lot. Using this area, a 0.8 runoff coefficient, and the 0.41 in/hr rainfall intensity, the required storage volume is 442 CF. The six chambers with the surrounding stone provides an actual storage volume of 449 CF.
Details & Specifications Included with the Grading & Drainage Plan is a Storm Water Detail Sheet (C2.3) which contains details and specifications of the underground chambers.
Maintenance Plan A Stormwater Maintenance Plan is included in Appendix B of this report.
APPENDIX A
RETENTION CALCULATIONS
Stormwater Retention Calculations
Project:108 West Babcock
Date:7/11/2024
Engineer:M. Dyba, Bridger Engineers
C (weighted C factor):see table
I (Intensity):0.41 in/hr (per COB for 10 yr, 2 hr storm)
A (area):in acres
UNDERGROUND STORAGE (Runoff from the Entire Site)
Land Use sf A (acres)C A*C
Effective Lot Area 8151 0.187 0.8 0.150
0 0.000 0.8 0.000
0 0.000 0.2 0.000
Totals:0.187 0.150
C ave (A*C /A):0.800
Q (CIA):0.061 cfs
V (Qx7200):442 cf REQUIRED STORAGE VOLUME
Stormtech Chamber SC-740:
Height:30 in 2.5 ft
Width:51 in 4.25 ft
Length: (per chamber)90.7 in 7.6 ft
Length: (installed)85.4 in 7.1 ft
Storage/chamber*:74.9 cf *
Storage/additional inch of stone**:1.13 cf **
Additional inch(es) of stone foundation:0 in
*Value provided by manufacturer assuming 6" stone above, below & between chambers & 40% stone porosity.
** Add 1.13 cf of storage for each additional inch of stone foundation.
Req'd # of chambers:5.9 (Req'd storage volume / storage/chamber)
Chamber Sizing:
Use 2 rows with 3 chambers each
Total number of chambers: 6
Actual Storage Volume:449 cf (# of chambers x storage/chamber)
APPENDIX B
STORMWATER MAINTENANCE PLAN
7/11/2024
Stormwater Maintenance Plan 1 of 1
Stormwater Maintenance Plan 108 West Babcock
Prepared for: Papillon, LLC 102 N. Broadway Ave. Bozeman, MT 59715
Prepared by: Bridger Engineers, Inc. 2150 Analysis Drive, Ste. B Bozeman, MT 59718
Ownership & Maintenance Responsibility Stormwater facilities for the 108 West Babcock project consist of those listed below. They are owned, funded and maintained by the Property Owner or Property Owner’s Association. These facilities should be inspected bi-annually with maintenance measures performed on an as-needed
basis. StormTech® Underground Stormwater Retention Chambers A system of StormTech underground storm water retention chambers are buried beneath the building slab. These chambers are accessed by a concrete catch basin with a cast iron grate lid
and an 18” diameter connecting pipe from the catch basin to the chambers. The first row of chambers is installed as an “isolator row” for cleaning. StormTech.com provides an inspection and maintenance manual (attached to this document) for the process of cleaning the chambers. This manual should be used to perform bi-annual inspections and maintenance as required. Cleaning of the chambers is accomplished by using a flusher nozzle as described in the attached manual. A JetVac process may be used, as the chamber row is installed as an isolator row, lined
with an AASHTO Class 1 Woven Geotextile. Catch Basin A concrete catch basin with grate lid is located at the north end of the parking lot to collect surface runoff from the new asphalt parking lot. The catch basin contains a removable grate inlet cover and 12” sump for collecting sediment. The catch basin should be inspected bi-annually for debris and sediment build-up and cleaned as needed. Roof Gutters The building contains gutters which will capture and direct stormwater from the roof to the subsurface drainpipe. Ensure that the gutters are free of debris and inspected annually. The drainpipe may be cleaned out by flushing as needed. Attachment See attached StormTech Inspection & Maintenance Manual obtained from www.stormtech.com.
Call StormTech at 860.529.8188 or 888.892.2694 or visit our website at www.stormtech.com for technical and product information.26
12.0 Inspection and Maintenance
12.1 ISOLATOR ROW INSPECTION
Regular inspection and maintenance are essential to assure
a properly functioning stormwater system. Inspec tion is
easily accomplished through the manhole or optional
inspection ports of an Isolator Row. Please follow local
and OSHA rules for a confined space entry.
Inspection ports can allow inspection to be accomplished
completely from the surface without the need for a con-
fined space entry. Inspection ports provide visual access
to the system with the use of a flashlight. A stadia rod
may be inserted to determine the depth of sediment.
If upon visual inspection it is found that sediment has
accumulated to an average depth exceeding 3" (76 mm),
cleanout is required.
A StormTech Isolator Row should initially be inspected
immediately after completion of the site’s construction.
While every effort should be made to prevent sediment
from entering the system during construction, it is during
this time that excess amounts of sediments are most
likely to enter any stormwater system. Inspection and
maintenance, if necessary, should be performed prior
to passing responsibility over to the site’s owner. Once
in normal service, a StormTech Isolator Row should be
inspected bi-annually until an understanding of the sites
characteristics is developed. The site’s maintenance
manager can then revise the inspection schedule based
on experience or local requirements.
12.2 ISOLATOR ROW MAINTENANCE
JetVac maintenance is recommended if sediment has
been collected to an average depth of 3" (76 mm) inside
the Isolator Row. More frequent maintenance may be
required to maintain minimum flow rates through the
Isolator Row. The JetVac process utilizes a high pressure
water nozzle to propel itself down the Isolator Row while
scouring and suspending sediments. As the nozzle is
retrieved, a wave of suspended sediments is flushed back
into the manhole for vacuuming. Most sewer and pipe
maintenance companies have vacuum/ JetVac combi-
nation vehicles. Fixed nozzles designed for culverts or
large dia meter pipe cleaning are preferable. Rear facing
jets with an effective spread of at least 45" (1143 mm)
are best. The JetVac process shall only be performed
on StormTech Rows that have AASHTO class 1 woven
geotextile over the foundation stone (ADS 315ST or
equal).
Looking down the Isolator Row.
A typical JetVac truck. (This is not a StormTech product.)
Examples of culvert cleaning nozzles appropriate for Isolator Row
maintenance. (These are not StormTech products.)
27 Call StormTech at 860.529.8188 or 888.892.2694 or visit our website at www.stormtech.com for technical and product information.
12.0 Inspection & Maintenance
STORMTECH ISOLATOR™ROW - STEP-BY-STEP
MAINTENANCE PROCEDURES
Step 1)Inspect Isolator Row for sediment
A) Inspection ports (if present)
i. Remove lid from floor box frame
ii. Remove cap from inspection riser
iii. Using a flashlight and stadia rod, measure
depth of sediment
iv. If sediment is at, or above, 3" (76 mm)
depth proceed to Step 2. If not proceed
to Step 3.
B) All Isolator Rows
i. Remove cover from manhole at upstream
end of Isolator Row
ii. Using a flashlight, inspect down Isolator
Row through outlet pipe
1. Follow OSHA regulations for confined
space entry if entering manhole
2. Mirrors on poles or cameras may be
used to avoid a confined space entry
iii. If sediment is at or above the lower row of
sidewall holes [approximately 3" (76 mm)]
proceed to Step 2. If not proceed to Step 3.
Step 2)Clean out Isolator Row using the JetVac process
A) A fixed floor cleaning nozzle with rear
facing nozzle spread of 45" (1143 mm) or
more is preferable
B) Apply multiple passes of JetVac until back-
flush water is clean
C) Vacuum manhole sump as required during
jetting
Step 3) Replace all caps, lids and covers
Step 4)Inspect and clean catch basins and manholes
upstream of the StormTech system following local
guidelines.
4
21) B)1) A)
Figure 20 –StormTech Isolator Row (not to scale)
Please contact StormTech’s Technical Services
Department at 888-892-2894 for a spreadsheet to
estimate cleaning intervals.
12.3 ECCENTRIC PIPE HEADER INSPECTION
Theses guidelines do not supercede a pipe manufac-
turer’s recommended I&M procedures. Consult with the
manufacturer of the pipe header system for specific I&M
procedures. Inspection of the header system should
be carried out quarterly. On sites which generate higher
levels of sediment more frequent inspections may be
necessary. Headers may be accessed through risers,
access ports or manholes. Measurement of sediment
may be taken with a stadia rod or similar device. Clean -
out of sediment should occur when the sediment volume
has reduced the storage area by 25% or the depth
of sediment has reached approximately 25% of the
diameter of the structure.
12.4 ECCENTRIC PIPE MANIFOLD MAINTENANCE
Cleanout of accumulated material should be accom-
plished by vacuum pumping the material from the head-
er. Cleanout should be accomplished during dry weath-
er. Care should be taken to avoid flushing sediments out
through the outlet pipes and into the chamber rows.
Eccentric Header Step-by-Step MaintenanceProcedures
1.Locate manholes connected to the manifold system
2.Remove grates or covers
3.Using a stadia rod, measure the depth of sediment
4.If sediment is at a depth of about 25% pipe volume
or 25% pipe diameter proceed to step 5. If not
proceed to step 6.
5.Vacuum pump the sediment. Do not flush sediment
out inlet pipes.
6.Replace grates and covers
7.Record depth and date and schedule next inspection
1, 2, 6
3, 4, 5
Figure 21 –Eccentric Manifold Maintenance