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HomeMy WebLinkAboutNarrative Response to Engineering Comments10-28-2020 1091 Stoneridge Drive • Bozeman, Montana • Phone (406) 587-1115 • Fax (406) 587-9768 www.chengineers.com • E-Mail: info@chengineers.com Civil/Structural Engineering and Surveying October 30, 2020 Lance Lehigh, P.E. City of Bozeman Engineering Department 20 E. Olive Street Bozeman, MT 59718 RE: Response to Westside Flats Master Site Plan Review Comments Concept Plan Review Comments (#20224) Dear Mr. Lehigh: This letter is to provide a narrative response to the Engineering Review provided on September 2, 2020. Responses to comments are in italics below. Concurrent Construction 1. Bozeman Municipal Code (BMC) 38.230.100.A.12 - As presented, the phasing plan is difficult to follow given the complexity and scale of the development. Please provide a detailed phasing plan accompanied with exhibits that show how the development intends to build out prior to Master Site Plan approval. The phasing plan should clearly show sanitary sewer, water, storm, street, buildings, trails, and other critical infrastructure that is needed to support the development. C1.1 is now included with the submittal that shows infrastructure to be installed with the three phases of the site plan. The water and sewer mains will be installed with Phase 1 of the Development. A 24’ all weather access road will be provided for maintenance through Phases 2 and 3 prior to their construction. The linear trail system along the east side of the property will also be installed with Phase 1. Easements 1. Bozeman Municipal Code (BMC) 38.410.060 - Please provide a standalone existing survey, which identifies all easements, right-of-way, property lines, etc. In addition, provide a separate exhibit identifying all proposed easements that would be provided with the master site plan (i.e. utility, public access, public street and utility). The standalone survey is provided that shows the existing easements on the property. The proposed easement exhibits are included with easement drafts. Civil/Structural Engineering and Surveying 2. BMC 38.410.060 - All public easements must be provided with the master site plan submittal in a clean draft format for review. Easements will be deemed inadequate if they are not in a final draft format (signatures are not required for the draft review). Easements must be stamped by a licensed professional surveyor. If for any reason a public easement must be modified based on review of subsequent site plan submittals, the applicant must request a release and reconvey of any portion of the dedicated easements. This item is noted. These Easements for the trail, public access and utility and the utility easement are included with this submittal. It is our understanding that these easements are to be provided with the Subdivision Exemption Application for the amended plat for this project. However, since the easement pertain mostly to the proposed improvements with this master site plan, we’ve included them with this submittal as well. The applicant understands that that a release and reconveyance may be necessary during subsequent site plan submittals. 3.BMC 38.410.040.D Rights-of-way for pedestrians - Thirty foot Public Access easements are required for the two east/west trails through the property from May Fly Street and the open space lot between May Fly Street and Dragon Fly Street. The easements may not contain parking stalls or structures within them. The easements will extend north and south to encompass the proposed trail. This item is noted. The thirty‐foot public access easements were updated to encompass the trails and do not contain any parking stalls or structures. 4. BMC 38.410.060.B.2.b Easements - 10 foot utility easements are required for dry utilities on the Master Plan submittal. Contact Dylan Swanson with Northwestern Energy for utility easements – dylan.swanson@northwestern.com, 406-497-3663. A draft of the proposed 10‐foot utility easement is included for review with the submittal. Floodplain 1. The West Side Flats Flood Hazard Evaluation report was reviewed. Comments are attached to the end of this memorandum and must be addressed prior to Master Site Plan approval. This item is noted. We are updating the flood hazard evaluation to address the attached comments. The updated flood hazard evaluation report is forthcoming. 2. BMC 38.600.090.B.4.a Requires the flood hazard evaluation be certified by a Professional Engineer registered in the state of Montana. This item is noted. The forthcoming report will be certified by a Professional Engineer registered in the state of Montana. Lighting Civil/Structural Engineering and Surveying 1. (DSSP) Section XII Lighting Design Criteria - Designers shall submit to the City a calculation summary table for each calculation grid and City of Bozeman Standard Specifications for Lighting Materials and Installation Revision March 2020 include the average illuminance or luminance, maximum illuminance or luminance, minimum illuminance or luminance, and Avg:Min ratio. Calculated values may vary from criteria by no more than 10% above or below. a. Missing streetlights along Fallon and West Babcock Lights along Fallon and Babcock have been added to the Master Site Plan to be completed with Phase 1. The spacing of the lighting was based on the streets local and collector designations respectively. Stormwater 1. DSSP II.B. Storm Drainage Plan -The applicant must include a drainage system design and maintenance plan with the Master Site Plan application given the groundwater complexity associated with the Site. The City's requirements are contained in the Design Standards and Specifications Policy and the City modifications to Montana Public Works Standard Specifications. The drainage plan must also address stormwater comments 2-5. A stormwater management report is included with the submittal per the City’s requirements. A draft of the stormwater maintenance plan is also included with this submittal. 2. DSSP Section (A) (4) Water Quality - The applicant must include a drainage plan with post- construction storm water management controls that are designed to infiltrate, evapotranspire, and/or capture for reuse the post-construction runoff generated from the first 0.5 inches of rainfall from a 24-hour storm preceded by 48 hours of no measurable precipitation. For projects that cannot meet 100% of the runoff reduction requirement, the remainder of the runoff from the first 0.5 inches of rainfall must be either: a. Treated onsite using post-construction storm water management control(s) expected to remove 80 percent total suspended solids (TSS); b. Managed offsite within the same sub-watershed using post- construction storm water management control(s) that are designed to infiltrate, evapotranspire, and/or capture for reuse; or c. Treated offsite within the same subwatershed using post- construction storm water management control(s) expected to remove 80 percent TSS. a. The existing stormwater facility (Detention Pond #4) has standing stagnant groundwater that does not drain. Please explain how the facility meets the water quality requirements The updated stormwater design will not contribute runoff to the existing Detention Pond with the exception of a small area of open space surrounding the pond. In our discussions with you regarding this pond it was decided that if the proposed development did not contribute runoff to the proposed pond then the pond would not need to be upgraded with this project. Civil/Structural Engineering and Surveying The stormwater runoff generated on site will meet the water quality requirement by retaining all runoff onsite in a series of retention ponds. The facilities are designed to evapotranspiration and /or infiltrate the entire design storm runoff volume. 3. DSSP Section (C) Water Quantity - The applicant must provide on-site detention with release rates limited to predevelopment runoff rates. Retention ponds must be sized based on a 10- year, 2-hour storm intensity. a. The applicant must confirm that the design satisfies on-site detention with release rates limited to predevelopment runoff rates. Retention ponds must be sized based on a 10- year, 2-hour storm intensity. Currently, the existing facility (Detention Pond #4) has standing water and cannot drain. The master site plan storm water design report will no longer utilize the existing pond. The proposed stormwater facilities are all retention ponds. The required release rate no longer applies. 4. Montana Post-Construction Storm Water BMP Design Guidance Manual Seasonal High Groundwater - The proposed project is located in an area that is known to have seasonally high groundwater. Engineering recommends that the applicant confirm that 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. a. The applicant must confirm groundwater elevations throughout the development. b. Existing stormwater infrastructure located throughout the Norton Ranch Development is significantly impacted to local high groundwater conditions. The applicant is encouraged to utilized low-impact-development stormwater solutions given the extremely high groundwater conditions located throughout the development. The stormwater management report addresses the groundwater concerns. Observations from projects surrounding West Side Flats are included to show that stormwater facilities will not be negatively affected by high groundwater. The bottom of all of the retention facilities are designed to be 1.5’ or less below existing grade to avoid groundwater inundation. 5. DSSP Section (D) Discharge Structures – Ponds shall be designed so as to avoid long-term standing water in the pond. a. The existing facility has long-term standing water which can create water quality issues such as increases in downstream temperatures as well as an incubator for bacteria and parasites. The proposed facilities need to be able to drain or an alternative solution should be proposed. The proposed retention facilities are designed to infiltrate runoff and will not have a release or drain component to them. However, as mentioned previously, the proposed facilities are set above the assumed high groundwater table to avoid inundation with groundwater. Civil/Structural Engineering and Surveying 6. BMC 40.04.700.A.4.a Requirements. Runoff from untreated snow storage cannot be discharged offsite. Ensure the snow storage areas slope to areas that are treated. The snow storage areas are in areas that flow to proposed retention ponds. Transportation 1. BMC 38.220.080 (A) 2.g Traffic Generation - The applicant must submit a peak hour trip generation value to the City to determine whether a traffic impact study (TIS) is required prior to Master Site Plan approval. Peak hour trip generation numbers were provided the City of Bozeman engineering staff via email on 3 separate occasions to determine if a TIS would be required for this project. At the time of this submittal we have not received a response regarding the need for a TIS, or whether a waiver would be granted. The Trip generation calculations for the proposed project are provided below. Please review and let us know if these calculations warrant a TIS for this project, or if a waiver can be granted. 132 apartment units Daily trips = 132 x 5.44 = 718 Peak AM Trips = 132 x 0.36 = 48 Peak PM Trips = 132 x 0.44 = 58 2. BMC 38.520.040.C.5 Non-motorized circulation and design. The applicant is advised that the existing trail/proposed trail network creates a mid-block crossing on West Babcock. The applicant must install a City approved pedestrian crossing, signs, and curb paint. In addition, the applicant will need to conduct an analysis either with the TIS (if warranted) or stand- alone on what type of crossing (RRFB (Rectangular Rapid Flash Beacon) or HAWK (High- Intensity Activated crosswalk) beacon) is needed to provide safe movement across West Babcock. The crossing must be shown on the Master Site Plan application and completed with Phase 1 of development. Sanderson Stewart was contracted to provide a warrant analysis on the pedestrian crossing at West Babcock Street. Their enclosed analysis determines that a crossing signal is not warranted at this time. 3. BMC 38.400.080 (A) Sidewalks - A City sidewalk must be constructed along West Babcock and Fallon Street frontage along with Phase 1 of the development. The minimum width of a sidewalk is defined in DSSP Section IV.B.3. The sidewalks are now called out to be constructed with Phase 1 of the development to meet the minimum width of a sidewalk as defined in DSSP Section IV.B.2. Civil/Structural Engineering and Surveying Water 1. DSSP Section (V) (A) Main Size - A water design report must be prepared by a professional engineer for the proposed project. The water distribution system must be designed to meet the maximum day demand plus fire flow and the peak hour demand. A water design report was not provided with the Master Site Plan submittal. A water design report is included with the submittal. 2. BMC 38.410.070. and 38.230.100.A.12 - Each phase of development must connect to the water distribution system at a minimum of two points to allow a redundant feed (per City of Bozeman Engineering DSSP Section V.A. 5). The water main will be installed with Phase 1 of the project. The water main connects to existing water main at 3 locations (May Fly Street, Dragon Fly Street, Fallon Street) to provide redundant feed to the property. 3. Water Riser Room - The applicant is advised to appropriately size the mechanical room to fit the water service line lay length. See the attached pdf showing the recommended mechanical room sizes based on pipe size lay lengths. Please contact John Alston (jalston@bozeman.net) the City’s water and sewer superintendent if additional questions arise. The water riser rooms are dimensioned on C3.0,C3.1, and C3.2 . The water riser rooms meet the necessary dimension for the pipe lay lengths. Water Rights 1. BMC 38.410.130 - Water rights and/or payment of cash-in-lieu of water right is required prior to Phase 1 site plan approval for the demand on the City’s potable water system. The applicant is advised to contact Brian Heaston in the City’s Engineering Department to discuss the required water rights analysis. The CILWR determination has been confirmed by Brian Heaston. The email correspondence is included with this submittal. Wastewater 1. BMC 38.410.070.A - As presented, wastewater generated from the subject property will flow into the existing Norton Ranch Lift Station. The applicant will need to verify that this lot was originally allocated capacity at the lift station and that the subject property can be adequately served by the Norton Ranch Lift Station prior to Master Site Plan approval. Civil/Structural Engineering and Surveying a. Norton Ranch Lift Station - The applicant is advised that the Norton Ranch Lift Station has been designed to be reconfigured to allow for phased development of the Norton Ranch Subdivision. The exact configuration is dependent on the phase and number of dwelling units to be served. Currently, there are three pumps at the lift station with a single principal pump that can operate under different hydraulic conditions that the station experiences, specifically column separation after pumping cycles. DEQ Circular 2 requires that multiple pumps must be provided and of the same size. Units must have capacity such that, with any unit out of service, the remaining units will have capacity to handle the design peak hour flow. The Design Report for Proposed Capacity Upgrades to the Existing Norton Ranch Lift Station completed by C&H Engineering and Surveying, Inc. in July 2020 account for the Westside Flats project in the flow calculations. The proposed upgrades would provide adequate capacity and redundancy so that the lift station could serve the proposed Westside Flats projects. 2. DSSP Section (V) (B) Sanitary Sewer System Design Criteria - The applicant must provide an estimate of the peak-hour sanitary sewer demand for the different phases certified by a professional engineer for the proposed project prior to Phase 1 site plan approval. This information is used to verify downstream sewer capacity as well as keep the City’s wastewater hydraulic model updated. The estimate of peak-hour sanitary sewer flow is provided in Appendix C of the water and sanitary sewer design report. Recommended Conditions of Approval 1. If not already filed for the subject site, the applicant will need to provide and file with the County Clerk and Recorder's office executed Waivers of Right to Protest Creation of Special Improvement Districts (SID’s) for the following: a. Street improvements to Fallon Street from N Laurel Parkway to N Cottonwood Rd including paving, curb/gutter, sidewalk, and storm drainage b. Street improvements to W Babcock Street from N Laurel Parkway to N Cottonwood Rd including paving, curb/gutter, sidewalk, and storm drainage c. Intersection improvements to North Cottonwood Road and W Babcock Street d. Intersection improvements to North Cottonwood Road and Fallon Street The document filed must specify that in the event an SID is not utilized for the completion of these improvements, the developer agrees to participate in an alternate financing method for the completion of said improvements on a fair share, proportionate basis as determined by square footage of property, taxable valuation of the property, traffic contribution from the development, or a combination thereof. The applicant must provide a copy of the filed SID waiver prior to Master Site Plan approval. A draft of the waiver is included with the submittal. Civil/Structural Engineering and Surveying If you require any further information, please give me a call at (406) 587-1115. Sincerely, Ethan Cote, P.E.