HomeMy WebLinkAboutVarianceRequest_StormwaterPipe_07262021
109 E Main Street, Ste B, Bozeman, MT 59715 I OFFICE 406.728.4611 I EMAIL wgm@wgmgroup.com
July 26, 2021
City of Bozeman
Engineering Department
20 East Olive Street
Bozeman, MT 59718
RE: Variance Request – City of Bozeman Design Standards and Specifications Policy
Section V.D.4.b – Storm Sewer Mains
Dear City of Bozeman:
The above referenced section of the City of Bozeman DSSP states: Storm sewer mains shall have a
minimum depth of cover of two (2) feet below final grade, provided that the pipe material shall
withstand the design load.
The applicant is requesting a variance to this standard as it related to the creation of Rogers Way in
Annie Subdivision Phase 4.
The applicant is requesting that storm drain pipe which crosses the proposed road (Roger’s Way)
near the north-center portion of the site be allowed to be buried to a minimum 12 inches deep. This
bury depth helps accommodate stormwater design and pipe installation between the road and the
open space lot and detention pond, to keep the detention pond elevation high enough that the pipe
and pond are safely elevated above potential flooding or backwater associated with the adjacent
stream/ditch. Keeping the storm drain pipe relatively high in elevation also helps ensures that
backwater does not come back into the pipe, thus having the chance to freeze or have other
maintenance issues.
The proposed pipe crossing the road is 18-inch diameter RCP sloped at 0.4%. The pipe is shown on
the storm pipe profile on plan sheet STM3 in the stormwater design report. The pipe would be buried
about 12-inches (minimum) along the edges of the road, and deeper in the middle of the crowned
road. The RCP pipe will be capable of withstanding the design traffic loads. The RCP will also be
capable of replacing the bottom portion of the design road section, per approval from the geotechnical
engineer.
This variance would not be contrary to and will serve the public interest, in that it makes the
stormwater facilities more efficient, functional, and have less future maintenance. The buried pipe
also will not adversely impact the road or other utilities. This design is necessary due to the unique
property conditions, including the road horizontal layout, which is the most sensible and efficient
layout, and due to the road vertical profile, which is also the natural and sensible profile for traffic and
pedestrian use, and due to the future site finished grading, which will include smooth, even terrain
mildly sloping toward the new road.
City of Bozeman Planning Department
July 26, 2021
Page 2 of 2
Sincerely,
WGM Group, Inc.
Gary Fox
PROJECT ENGINEER
W:\Projects\201016\Docs\Subdivision Submittal\Preliminary Plat Submittal\Response to DRC Comments - July 2021\VarianceRequest_StormwaterPipe_07262021.docx