HomeMy WebLinkAbout008 - Appendix H - On-site Engineering Report• • www.seaeng.com Engineers and Land Surveyors 851 Bridger Drive, Suite 1, Bozeman, MT 59715 | phone: 406-522-8594 | fax: 406-522-9528 Bozeman Yards South aka Block 104 South Building Site, Water, Sewer, Storm Water Engineering Report August 23, 2024, Site Plan RC February 23, 2024, Site Plan Prepared for: Jackadoo LLC Prepared by: Stahly Engineering and Associates Engineer of Record: Cordell D. Pool, PE Quality Control Reviewer: Zach Lowe, PE Introduction The Bozeman Yards South is an infill redevelopment project located on Lots 17-26, Block 104, of Am. Northern Pacific Addition. The lot size is 35,364 square feet. Existing conditions on the site consist primarily of a gravel parking lot, with some minimal landscaping and an existing one-story building with a raised loading dock. As part of development, the lots will be aggregated so the building is contained within its own single lot. Figure 1 – Bozeman Yards South Project Vicinity
Page | 2 The location of the Bozeman Yards South project can be seen in Figure 1. The Bozeman Yards South site development and related private improvements are proposed to be completed in conjunction with off-site public street improvements on Aspen Street and Front Street. The Proposed Building is a 5-story residential building featuring a mix of 1, 2 and 3-bedroom condominiums. The building also contains basement level parking with 41 parking spaces, and 7 on-street parking spaces along the Aspen Street frontage. The proposed building and site improvements are shown on Figure 2. Civil Specifications and Design Standards The civil specifications for the project are the Montana Public Works Standard Specifications (MPWSS) and the City of Bozeman Modifications to MPWSS (COB Mods). Construction plans are developed in accordance with the City of Bozeman Design Standards. Off-site Street and Improvements Adjacent to Site Off-site infrastructure improvements are part of a separate project to be constructed concurrently with the on-site building improvements. Off-site improvements consist of new water and sewer mains in Aspen Street, new street and storm drainage improvements on Aspen Street and Front Street, conversion of Ida Avenue between Aspen and Front streets to open space/park, Triangle Park improvements, sidewalks, and lighting. The franchise utilities currently located within adjacent streets will be relocated underground in new utility easements fronting the Bozeman Yards (Block 104) streets. The alley running through Bozeman Yards (Block 104) will be completed with the on-site project. The off-site project will bring needed street and utility improvements to the area as part of a long-term vision for improving pedestrian and vehicular circulation to the neighborhood. Site Demolition The existing building, parking lot, and utility services on the Bozeman Yards South site will be demolished. The existing building north of the alley will remain and be used for construction offices and staging area. Site Improvements Site improvements consist of site hardscape improvements, alley improvements, franchise utility services, building water and sewer services, and stormwater mitigation. On-site parking is provided underground within the basement of the building. The basement parking is proposed to be accessed from the alley. Basement parking provides 41 parking stalls, with an additional 7 on-street spaces available. Access to the basement parking is provided from the improved alley. To accommodate building access concrete bands are added to the alley to provide 24’ of travel width and/or pedestrian pathways. Trash is collected and stored within the building and rolled out to the alley for loading. The trash access and basement ramp are heated. Site hardscape consists of ground level patios and entry plazas with sidewalk, steps, and ADA ramp accesses to the building. The hardscape will provide private areas and seating nooks separated by landscape amenities. Residents are provided with interior bike storage and exterior bike racks are provided for visitors and commercial customers.
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Figure 2 – Bozeman Yards South Site Layout
Gas, communication, and power building services are proposed to be run from Tamarack Street
along the west property line to the south in a proposed 10’ utility easement on the north and south
properties. Utility meters are proposed along the west wall of the building, and a backup generator
will be housed in the northwest corner of the building.
Water and Sewer
New water and sewer main improvements will be installed in Aspen Street as part of a separate off-
site project. Engineering analysis will be conducted with the off-site project to show that adequate
capacity exists to supply Bozeman Yards South with water supply, fire protection, and sewer service.
Based on hydrant flow test #45 in the City of Bozeman 2017 Water Facility Plan, the water pressure
is estimated to be approximately 145 psi. This test also shows a fire flow available in this area of
town to be over 3000 gpm, indicating adequate water supply for fire protection.
Water, fire, and sewer service to Bozeman Yards South will be by extension of service stubs
installed with the off-site street improvement project from E. Aspen Street. Services are sized in
accordance with plumbing and fire code and fixture counts. Water fixture counts are estimated to be
1,042 units, corresponding to an instantaneous flow of 220 gpm and which requires a 4” water
service and meter. The fire service will be 6”. To reduce piping conflicts in the basement, two 6”
sewer services are proposed.
Irrigation water supply will be provided through the domestic water service. Irrigation demands were
provided by the landscape architect. Irrigation is anticipated to occur over an approximately 100-day
season resulting in a total annual water use of 62,823 gallons, or 0.19 ac-ft. The maximum daily
irrigation flow is 628 gpd.
Page | 4 The estimated water use calculations for Bozeman Yards South are based on a usage rate of 89 gpd/capita with an estimated 2.17 persons per unit for residential units. Commercial water use estimates are based on MT DEQ-4 wastewater generation values for a Coffee Shop. These values represent the upper end of water use for the commercial space. The estimated annual water use for the entire building is anticipated to be approximately 8,739 gallons per day (gpd), with a peak hour demand of 25.0 gallons per minute (gpm). The Bozeman Yards South anticipates water use that is lower than typical city design flow estimates. There is not currently an established methodology for estimating water use in this kind of urban, high-density residential use where per capita landscape irrigation is much less than typical residential single household units. Table 1 – Bozeman Yards South building Annual Domestic Water Use Cash-in-lieu-of water rights will be required for domestic use and on-site irrigation. Daily wastewater generation was determined utilizing the same residential unit estimate and commercial estimates described in the water use estimate, but with infiltration and inflow and without the irrigation demand. Applying these values results in an average daily flow for the Bozeman Yards South building of 8,233 gpd, and a peak hour flow of 23.5 gpm. Table 2 – Bozeman Yards South building Estimated Sewer Use and Demands Bozeman Yards South building Estimated Water UseResidential UseUnits Capita/Unit Population GPD/Capita Water Use (gpd)
Apartment Units422.1791898,111Commercial UseEmployees4141040Customers200120061,200Total2462468,111Site Area - Lot (ac)0.81Average Day Water Use [Equal to Wastewater Flow](gpd) 8,111Irrigation (gpd) 628Max Day Water Use [Average Day Use + Irrigation] (gpd) 8,739 ;P = Pop. ÷ 1,000 Peaking Factor (PF) 4.11Water Use Peak Hour Flow (gpm) 25.0
Page | 5 Storm Water The existing site conditions consist of a building and a gravel parking lot with some minor landscaping areas without any stormwater mitigation. Currently, runoff from the site is directed north or east, towards the undeveloped alley or Ida Avenue, eventually running into the City storm sewer in Tamarack Street. The development is required to provide on-site stormwater mitigation to manage stormwater originating from the lot development. The original concept for Bozeman Yards (aka Block 104) had independent subsurface stormwater systems located on each lot, and a separate permeable paver system for the alley. The developer now prefers to have a single shared stormwater sub-surface system serving both building sites and the alley located within the alley right-of-way. This is more cost efficient to build and maintain compared to separate systems. A utility occupancy permit will be required to allow the use of City-owned alley right-of-way for stormwater mitigation. Because existing and proposed franchise utilities run along street frontages, there are no existing or proposed utilities within the alley to conflict with the subsurface stormwater system. The system is designed to accommodate typical alley traffic over the top of it. Existing and post development stormwater runoff volumes were determined by the Rational Method with a weighted coefficient determined for the building’s rooftop, pavement area, gravel parking area, sidewalks, patios, and landscaped areas. Areas were tabulated for the Bozeman Yards South (aka Block 104 South Building), Bozeman Yards North and alley sub-areas, and the total combined site of approximately 1.5 acres as shown on Exhibit 1 at the end of this report. Storm runoff calculations for the entire combined site are shown in Table 3. The post development runoff coefficient is higher than the existing conditions, producing approximately 60% more runoff than the existing conditions. Runoff flow rates are provided for the highest intensity (short duration) events for a range of storm frequencies. Runoff volumes are provided for the different storm frequencies and precipitation depths. Note runoff flow rate and volume are not related. Peak runoff flow rate only depends on rainfall intensity at the time of concentration and the frequency of the event. Runoff volume depends only on the storm duration and precipitation depth. For example, the 10-year, 2hr and 10-year, 24hr storms have the same peak flow, but different runoff volumes due to the different precipitation depths. The Bozeman Yards (Block 104) development is proposed to have a shared subsurface retention system located in the alley between the buildings. The retention system consists of a gravel bed with one row of Stormtech chambers beginning and ending with inlet/access manholes. The site runoff (mostly rooftop) from each building will be directed through building storm drain outlets and into the chambers via connection to the infiltration chamber. The alley will drain in an asphalt swale towards any of three slotted drain inlets and drop into the retention system. A groundwater monitoring well was installed near the stormwater retention system and groundwater levels were monitored through the summer of 2023. The highest groundwater elevation is approximately 8’ below finished grade, and greater than 3 feet below the infiltration chambers. The retention system is sized to contain runoff from the 10-year, 2-hour storm event which is a 0.82” storm event. This storm event represents the 96th percentile storm event in Bozeman and produces approximately 3,476 cubic feet (cf) of storm runoff for the combined sites and alley. To reduce post-development runoff leaving the site from larger storm events to below existing flows, a retention volume of 4,386 cubic feet is proposed. Table 3 shows that stormwater from the design event (10-year, 2-hour storm) is completely retained and the estimated reduction of runoff from larger storm events.
Page | 6 Table 3 – Bozeman Yards (Block 104) Combined System Stormwater Calculations The combined retention system storage calculations are shown in Table 4, accounting for both the chamber and gravel storage. The proposed storage volume exceeds the runoff generated from the 10-year, 2-hour design storm event. The retention system is sized without consideration of infiltration, which provides significant additional capacity and a comfortable margin of safety. With infiltration considered, the retention system is capable of fully containing the 100-yr, 24hr storm runoff. Land Classification CRooftops 0.9Pavement 0.9Gravel Alley 0.5Sidewalk 0.9Gravel Parking 0.5Landscape 0.2TotalWeighted Runoff Coeff. (C )Design Storm 10y 2hr 10-Year 25-Year 50-Year 100-YearDrainage Area (acres) 1.543 1.543 1.543 1.543 1.543Drainage Area (sf) 67,196 67,196 67,196 67,196 67,196Slope (%) 2 2 2 2 2Time of Concentration (min) 5.0 5.0 5.0 5.0 5.024 Hour Precipitation Volumes (in) 0.82 1.84 2.16 2.42 2.67Design Storm 10y 2hr 10-Year 25-Year 50-Year 100-YearIntensity at Tc (Figure I-2 pg. 29) (in/hr) 0.41 3.22 3.83 4.74 5.34Peak Runoff Rate at Tc (Q = CIA) (cfs) 0.30 2.32 2.75 3.41 3.84Runoff Volume (cf) 2,142 4,807 5,643 6,323 6,976Design Storm 10y 2hr 10-Year 25-Year 50-Year 100-YearIntensity at Tc (Figure I-2 pg. 29) (in/hr) 0.41 3.22 3.83 4.74 5.34Peak Runoff Rate at Tc (Q = CIA) (cfs) 0.48 3.76 4.47 5.54 6.23Runoff Volume (cf) 3,476 7,800 9,156 10,258 11,318Design Storm10y 2hr 10-Year 25-Year 50-Year 100-YearRunoff Volume Increase (cf) 1,334 2,992 3,513 3,936 4,342Retention Volume (cf) 4,386 4,386 4,386 4,386 4,386Net Runoff Volume Post Mitigation (cf) -910 3414 4770 5872 6932% Decrease in Runoff from Existing 100% 29% 15% 7% 1%Event Retained 10-y,2-hr 10y,4.5-h 25-y, 2.25-h 50-y,1.41-h 100-y,1.08-hDuration Retained (min) N/A 240.0 135.0 85.0 65.0Intensity at Time of Overflow (in/hr) N/A 0.3 0.5 0.7 1.0Peak Post Retention Overflow Rate (cfs) N/A 0.3 0.5 0.91.1% Decrease in Peak Flow from Existing N/A 87% 80% 75% 71%Post Dev Peak Flow CalculationsMitigation Calculations67,196 67,1960.47 0.76Design Storm InformationExisting Peak Flow Calculations22,577 026,990 13,7273,000 0Site StatisticsExisting Area (sf) Post Dev Area (sf)12,369 43,1210 4,0222,260 6,326
Page | 7 Table 4 – Bozeman Yards (Block 104) Combined Retention System Calculations Similar calculations were done for each sub-area to determine the peak flow rate and conveyance capacity of the piping. For the purposes of conveyance of building and site runoff, a 100-year storm was used. Table 5 – Bozeman Yards (Block 104) Sub-Area Peak Flow Calculations Each building has multiple storm drain pipes running into the system, but no less than one 10” and one 8” pipe run at a 2% slope. The combined capacity of these pipes is 4.39 cfs, which exceeds the 100-year peak flow from either building. The alley has a peak flow of 0.54 cfs, which equates to a flow depth of approximately 1”. However, there are 3 inlets in the alley so flow depths will be much less. Subsurface Chamber SystemChambers Length (ft) 140Number of chambers 20Storage per chamber 45.9Chambers Storage (cf)918Gravel Bed Length (ft) 155Gravel Bed Width (ft) 23Gravel Bed Depth (ft) 3.5Cube Volume (cf) 12477.5Net Gravel Volume (cf) 11559.5Gravel porosity 0.30Total Gravel Storage (cf)3468Total Storage 4,386Sub-area Sub Area 1 Sub Area 2 Sub Area 3Land Classification C Boz Yards South Boz Yards North AlleyRooftops 0.9 24,052 19,069 0Pavement 0.9 0 0 4,022Gravel Alley 0.5 0 0 0Sidewalk 0.9 2,282 2,034 2,010Gravel Parking 0.5 0 0 0Landscape 0.2 8,109 5,618 0Total 34,443 26,721 6,032Weighted Runoff Coeff. (C ) 0.74 0.75 0.90Design Storm 100-Year 100-Year 100-YearDrainage Area (acres) 0.791 0.613 0.138Drainage Area (sf) 34,443 26,721 6,032Slope (%) 2 2 2Time of Concentration (min) 5.0 5.0 5.024 Hour Precipitation Volumes (in) 2.67 2.67 2.67Design Storm 100-Year 100-Year 100-YearIntensity at Tc (Figure I-2 pg. 29) (in/hr) 5.34 5.34 5.34Peak Runoff Rate at Tc (Q = CIA) (cfs) 3.10 2.47 0.54Site StatisticsDesign StormPost Dev Peak Flow Calculations
Page | 8 Storm Water Maintenance It is the property owner’s responsibility to monitor and maintain their on-site stormwater mitigation system, and alleys are required to be maintained by adjacent property owners. The on-site stormwater retention system is designed to capture sediment and debris and requires regular monitoring and periodic maintenance to remove sediments and debris. If this sediment and debris is not periodically removed, it can cause undesired ponding and clogging. The stormwater retention system consists of manhole structures and underground chambers. These components need to be inspected quarterly, except in winter, and cleaned if required. • Inspect for sediment or debris in the manhole/inlet structure and remove if present. • Inspect infiltration chambers through inspection ports for sediment accumulation. Sediment depth less than 3” is acceptable. Sediment depth exceeding 3” requires removal by a cleaning service. • Check for damage, repair as needed. • Maintain records of quarterly inspections and cleaning and provide records to the City upon request. The alley stormwater retention system consists of permeable pavers. The pavers are designed to require only minimal maintenance with longer-term deep cleaning. The manufacturer recommends bi-monthly inspection of performance, ideally during rainstorms to verify that infiltration is still occurring. Over the long term occasional deep cleaning with compressed air or a specially equipped vacuum truck is required. Permeable pavers should not be cleaned by pressure-washing as this just pushes sediment further in. • Broom-clean the surface regularly to reduce sediment. • Check for damage, repair as needed. • Inspect for proper infiltration during storm events (bi-monthly). • Long-term cleaning with compressed air or vacuum truck as required to restore infiltration. • Maintain records of inspections and cleaning and provide records to the City upon request.
Bozeman Water DistributionSystem Model CalibrationField Test Data Sheet
Test Number: __________
Test Date: ______________
Start Time: ___________
End Time: ___________
Test By: _________
Zone: ___________________
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9 757 964RESIDUAL HYDRANT
Hydrant No. ______
HPR No. ________
Static: __________
Residual: ________
FLOW HYDRANT #1
Hydrant No. ______
HPR No. ________
Flow: ______________
FLOW HYDRANT #2
Hydrant No. ______
HPR No. ________
Flow: ______________
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4 3/13/2024 DD SET CDP ZWL
5 8/23/2024 SITE PLAN RC1 CDP ZWL PROFESSIONALENGINEERS &SURVEYORSBOZEMAN YARDS SOUTH805 N. IDA AVE STAHLYENGINEERING& ASSOCIATESJACKADOO LLCBOZEMAN, MT 0020'40'0020'40'EXHIBIT 1STORMWATERDRAINAGEEXHIBIT