HomeMy WebLinkAbout04_CONREngineeringComments-Responses-Application 21139_06082021
MEMORANDUM
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TO: Susana Montana, Senior Planner
FROM: Karl Johnson, Engineer I
RE: APPLICATION NO 21139 - North Central Block 3.4 Concept Review
DATE: April 21, 2021
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ENGINEERING COMMENTS:
Easements
1. BMC 38.410.060 Easements - Front setback utility easements must be ten feet wide, and must
always be provided unless written confirmation is submitted to the community development
department from all utility companies providing service indicating that front setback easements
are not needed.
The applicant is working with Northwestern Energy to determine the final design of site utilities
and required easements. Once this design is finalized written confirmation of the solution will
be provided to the City regarding required easements.
2. DSSP V.D - Permanent structures or significant landscaping may not encroach on utility
easements or be within 10 feet of utility mains and services.
Acknowledged. All proposed structures or landscaping will not encroach into the
utility easement.
Stormwater
1. Montana Post-Construction Storm Water BMP Design Guidance Manual The applicant must
demonstrate that seasonal high groundwater will not impact the function or maintenance of the
proposed facilities. Industry guidance recommends a three-foot minimum separation from the
bottom of the proposed facility to the underlying groundwater table. The applicant must
provide local seasonal high groundwater elevations to support the proposed design.
Groundwater monitoring was conducted by the geotechnical engineer in 2018 and 2019. The
groundwater monitoring results are provided in the geotechnical report included with this
submittal. The storm chamber is located approximately halfway between two groundwater
monitoring sites, Borehole’s #2 and #3. Based on these measurements, the seasonal high
groundwater is located approximately 13’ below ground surface at an elevation of 4786.58’.
The seasonal high groundwater elevation is shown on the plans and is anticipated to be
approximately 8.5’ below the bottom of the stormwater retention system.
CONR COMMENTS & RESPONSES | ENGINEERING
SPR SUBMITTAL
BLOCK 3.4
THE HENRY
THE HENRY | BLOCK 3.4 | LOTS 1-6 OF BLOCK 3 OF BEALL’S THIRD ADDITION SECTION 07, PLAT C-44-A
2. BMC 404.04.500 Requirement To Control and Reduce Stormwater Pollutants – Provide a
stormwater drainage/treatment grading plan and maintenance plan for a system designed to
treat the first 0.5 inch of stormwater to remove solids, silt, oils, grease, and other pollutants
must be provided to and approved when the Site Plan application are submitted. The plan must
demonstrate adequate site drainage (including sufficient spot elevations), storm water
detention/retention basin details (including basin sizing and discharge calculations, and
discharge structure details), storm water discharge destination, and a storm water maintenance
plan. The approved stormwater maintenance plan must be incorporated into the Owners
Association Documents and a copy must be submitted prior to Site Plan approval.
The Engineering Report included with this submittal addresses stormwater mitigation proposed
for this project. The proposed Building 3-4 stormwater mitigation system is designed to
infiltrate in excess of the first 0.5” of rainfall. In order to reduce impacts to existing stormwater
infrastructure, the system is designed to completely retain and infiltrate storms up to 0.98”, a
98th percentile storm. Larger, infrequent storms will discharge to City stormwater lines after
the retention is exceeded, at a lower rate than pre-construction. The plans included with this
submittal display all required stormwater and site grading design for City review. The
Engineering Report included with submittal contains a draft storm water maintenance plan, to
be incorporated into the Owner’s Association Documents after final review and acceptance.
3. BMC 38.540.020 - The applicant must identify snow storage areas on the Site Plan for the
parking area. Snow removal storage areas must be sufficient to store snow accumulation on
site. Such areas shall not cause unsafe ingress/egress to the parking areas, shall not cause snow
to be deposited on public rights-of-way, shall not include areas provided for required parking
access and spaces, and shall not be placed in such a manner as to damage landscaping.
Acknowledged. The Civil Site Plan displays proposed snow storage locations.
4. Overflow paths for stormwater must be shown that demonstrates that no structures will be
flooded during a 100-year storm event.
Stormwater overflow is directed underground to City of Bozeman storm sewer. This is
achieved by an overflow pipe connecting the storm mitigation system manhole to the new
storm sewer main in Tracy. The hydraulic capacity of this overflow piping is adequate for
the 100-year storm for not only Building 3-4, but also the entirety of Block 3. The adequate
hydraulic capacity conveying this runoff to storm sewer underground ensures no structures
will be flooded during the 100-year storm event.
5. BMC 38.410.080 (D) Grading and drainage - Stormwater ponds must be provided in a storm
water easement and must be maintained by a property owners’ association.
Acknowledged. As seen in the North Central Master Plan, the stormwater mitigation system
constructed with Building 3-4 is a “temporary” mitigation structure that will be replaced by a
multi-user stormwater mitigation system serving all proposed development in Block 3. This
communal stormwater mitigation structure will be located within a stormwater easement and
will be maintained by a property owners situation. The proposed temporary mitigation
structure will also be located within a stormwater easement.
CONR COMMENTS & RESPONSES | ENGINEERING
SPR SUBMITTAL
BLOCK 3.4
THE HENRY
THE HENRY | BLOCK 3.4 | LOTS 1-6 OF BLOCK 3 OF BEALL’S THIRD ADDITION SECTION 07, PLAT C-44-A
6. Sand/oil separators must be utilized in all parking structures.
In subsequent discussions with the City, sand/oil separators are no longer required for the
projects within the North Central Master Plan. Documentation of this decision is available to be
provided at the City’s request.
Water and Wastewater
1. 38.410.070. and DSSP.V.A and B – The applicant must provide an estimate of the peak-hour
sanitary sewer demand as well as the average and max day demands of domestic water usage
for the proposed site development. The estimates must be certified by a professional engineer.
Certified estimates for water and sewer demand and usage have been provided in the
Engineering Report included with this submittal.
2. DSSP V.A.6.h Services - Existing water services or stubs that are not utilized for service upon
development of the lot must be properly abandoned at the water main.
Acknowledged. Demolition notes shown on the “Existing Conditions” plan outline these
requirements.
3. DSSP V.A.8 Hydrants - Two fire hydrants are shown on the intersections of Villard and North
Tracy. Only one hydrant is required at each intersection. The applicant should contact the city
fire department to determine if additional hydrants are appropriate.
Acknowledged. The two fire hydrants were shown in anticipation of Fire Department
requirements to provide fire hydrants within 100’ of each FDC for this type of construction.
Initially, the FDC location was more than 100’ away from the existing hydrant, necessitating the
installation of a new fire hydrant. After design progression the FDC is now located within 100’
of the existing hydrant and the new hydrant is no longer required. This design element has
been removed from the project.
4. The existing water and sewer services to the existing 1-story building on the south side of the lot
are shown on sheet C1.0 but are not shown on sheet C1.2. It would appear there is a conflict
with the proposed interim storm water chambers and the sewer service that drains to North
Tracy. Please update drawings with sewer services and address separation issues with sewer
service.
The existing sewer service serving the Medical Arts building is located 40’ south of the storm
mitigation chamber. The sewer service shown in C1.0 “Existing Conditions” serving the Same
Day Sewer is demolished and abandoned at the main as described in the Site Demolition Notes.
No conflicts between storm mitigation and sewer services exist on the site.
5. The applicant is advised that the downstream sewer main located within Tracy Ave from W
Peach St to W Cottonwood St is a 6-inch Vitrified Clay Pipe. Upon future development, the
existing sewer main servicing the subject property must be upsized and replaced. The exact
extent and size of the sewer main replacement will be determined based on the peak-hour
sanitary sewer demand and existing upstream and downstream sewer slopes.
CONR COMMENTS & RESPONSES | ENGINEERING
SPR SUBMITTAL
BLOCK 3.4
THE HENRY
THE HENRY | BLOCK 3.4 | LOTS 1-6 OF BLOCK 3 OF BEALL’S THIRD ADDITION SECTION 07, PLAT C-44-A
The applicant is advised to contact the City’s engineering department to discuss the upgrade
prior to site plan submittal.
Acknowledged.
Transportation
1. The proposed building appears to encroach upon the vision triangle. The building may not
encroach on the vision triangle.
Acknowledged. The building design has been revised to address this conflict.
2. 38.400.090. Access- The proposed basement parking access on to N Tracy Ave does not meet
access requirements.
Acknowledged. The design has been updated for basement parking access to be on to West
Villard Street.
ENGINEERING ADVISORY COMMENTS:
Water Rights
1. BMC 38.410.130 (A) (1) Water rights - The applicant must contact Griffin Nielsen with the City
Engineering Department to obtain a determination of cash-in-lieu of water rights (CILWR).
CILWR must be paid prior to respective site plan approvals.
Acknowledged. An estimate using methodology provided by Griffin Nielsen for other projects
within the North Central Master Plan has been provided in the Engineering Report included
with this submittal.
Water and Wastewater
1. Existing water wells are shown in existing plan. If wells are to be abandoned they must be
abandoned in accordance with DEQ requirements.
Acknowledged. The existing wells on site provide heating and cooling for the Medical Arts and
Tower buildings. No wells are proposed for abandonment with this project.
2. New curb stops must be located within the road r-o-w or utility easement.
Acknowledged.
CONR COMMENTS & RESPONSES | ENGINEERING
SPR SUBMITTAL
BLOCK 3.4
THE HENRY
THE HENRY | BLOCK 3.4 | LOTS 1-6 OF BLOCK 3 OF BEALL’S THIRD ADDITION SECTION 07, PLAT C-44-A