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HomeMy WebLinkAbout20 - Design Report - Bridger View PUD - WaterEngineering Report Water Main Extension Bridger View PUD October 2020 Submitted to: City of Bozeman Engineering Department 20 East Olive Bozeman, MT 59715 Prepared by: Stahly Engineering and Associates 851 Bridger Drive, Suite 1 Bozeman, MT 59715 (406) 522-8594 Water Mains 1 10/7/2020 Engineering Report Contents Note: The Engineering Report format follows DEQ-1 organization. Additional information required by the City of Bozeman Design Standards is added where required. Report Narrative 1.1.1 General Information 1.1.2 Extent of water works system 1.1.3 Alternate plans 1.1.4 Site conditions 1.1.5 Water use data 1.1.6 Flow requirements 1.1.7 Sources of water supply 1.1.8 Proposed treatment processes 1.1.9 Sewage system available 1.1.10 Waste disposal 1.1.11 Automation 1.1.12 Project Sites 1.1.13 Financing 1.1.14 Future Extensions Figures and Tables Figure 1. Vicinity Map Figure 2. Water Plan Appendices Hydraulic Analysis Exhibit Water Mains 2 10/7/2020 1.1.1 General Information The proposed Bridger View Planned Unit Development (PUD) is located southwest of the intersection of Bridger Drive (MT 86) and Story Mill Road. Bridger View PUD is a 62-home neighborhood consisting of modest homes with a compact, urban design. This project is located on approximately 8 acres which was formerly occupied by 40 mobile homes within the Bridger View Trailer Park. The trailer park was served by a privately-owned, on-site water supply. The proposed individual lots are compact with small yards and common open spaces. Houses will be constructed by the developer (HRDC) and range in size from 1, 2, and 3 bedrooms roughly proportioned at 25%, 50% and 25% respectively. The subdivision will create 52 residential single-household lots and 5 duplex lots. A common house is also proposed for community functions. Five common garages are proposed which will not have water or sewer facilities. The project will be served by extension of City of Bozeman water and sewer mains throughout the project. Individual service lines will be provided to each residential lot and the common house. City of Bozeman water and sewer mains currently exist along Bridger Drive to the north of the project. The previous water and sewer lines serving the trailer park do not meet City standards and will be abandoned during construction. The trailer park water supply wells in the northern portion of the site will be used for irrigation of the project. The developer’s contact information is: HRDC. Heather Grenier 32 South Tracy Ave. Bozeman, MT 59715 Water supply and wastewater treatment will be provided by the City of Bozeman’s municipal systems. The system owner’s contact information is: City of Bozeman Public Service Department PO Box 1230 Bozeman, MT 59771-1230 The location of the Bridger View PUD is shown on the Vicinity Map in Figure 1. Water Mains 3 10/7/2020 Figure 1. Vicinity Map, Bozeman, Montana 1.1.2 Extent of Water Works System Water supply to the area is from an existing 12” diameter water main running along the south side of Bridger Drive. This project will provide 8” water mains looping from and back to, the existing 12” main in Bridger Drive. Additionally, a water main will be stubbed to Story Mill Road to allow connection to a future water main in that street. The proposed water system improvements are shown on the Water Plan (Figure 2) at the end of this report. The Bridger View PUD water main extensions have been designed in accordance with Montana Department of Environmental Quality Circular 1, and the City of Bozeman Design Standards and Specifications Policy. Construction specifications will be Montana Public Works Standards and Specifications (MPWSS), and the City of Bozeman Modifications to MPWSS. New water mains will be in water and/or water and sewer easements and street rights-of-way running through the property. Where water and sewer are running together the easements are 30’ wide. Where water mains run individually, a 20’ easement is proposed. These 20’ easements are narrower than City standards but are located adjacent to common open Water Mains 4 10/7/2020 space with a public access easement, which can provide additional access to the water main. A deviation from the City standard is requested for the 20’ wide water main easements. This deviation allows trees to be planted in the common open space just outside of the easement. No trees are proposed within the water and sewer easements, or within 10’ of water and sewer mains. New 8” water mains are looped with the exception of a short dead end main in the center of the project. This main is 120 feet long and will have a 2” blow-off hydrant at the end; this short dead end complies with City standards. Each lot will have an individual 1” water service from the main to the front of the structure, with a curb stop located on the easement or right-of-way line. Due to the small lot size, a deviation is requested to have 5’ separation between water and sewer services and between services and trees. This deviation will allow for the trees to be planted in the front yards of the lots and in common open spaces. Without this deviation, very few trees could be planted on lots and in common open spaces. To avoid conflicts with water and sewer services; power and communication lines are typically run in easements at the rear of the lots. 1.1.3 Alternate Plans Due to the project’s location within the City of Bozeman, extension of public mains was the only water supply alternative. Distribution alternatives were explored, and the proposed design was selected to increase looping and minimize dead ends. Lastly, during alternative review it was decided to utilize the existing trailer park wells in the northern portion of the site for irrigation of the common open spaces and private lawns. This reduces the impact on the City’s water supply and provides consistent water conservation throughout the project. 1.1.4. Site Conditions The Bridger View PUD site is located on the former site of the Bridger View Trailer Park. The trailer park was served by private sewer mains connected to the City system and with a privately-owned, on-site water supply. The existing sewer mains and water lines will be abandoned with site construction. The trailer park had some minor cut/fill grading to establish level trailer sites; but previous site work did not significantly impact the soils since the mobile homes did not have foundations. Beyond the minor site grading, the soils are typical of the Bozeman area. A geotechnical evaluation was Water Mains 5 10/7/2020 conducted and is provided in a separate appendix of this submittal. The soils can generally be described as a deep topsoil overlaying a fine- grained subsoil, with gravelly sand material at a depth of approximately 8 feet. Because basements are proposed for the new homes, groundwater monitoring was conducted throughout the summer of 2019. Monitoring results are provided with the geotechnical report. Groundwater depths were generally greater than 10 feet and should not impact homes or utilities. The underlying gravelly sand material will provide a suitable foundation material for pipes and basements. 1.1.5. Water Use Data Domestic water will be provided by the City of Bozeman Municipal system. This project is located within the planned service area of the City’s system. Estimated water use for the Bridger View PUD has been determined utilizing values provided in City design standards and Facility Plans. Due to the small, efficiently designed homes with well-supplied irrigation, the water use is anticipated to be lower than typical. However, for water main sizing, typical City design flows are utilized. Because the water system will not supply irrigation, the estimated residential water use is based on the City of Bozeman design standards for wastewater generation. Typical design flow water use is 89 gallons per day (gpd) per capita, with an average population of 2.11 people per home. Again, because the water system will not supply site irrigation, large summer peaks are not anticipated. A peaking factor of 4.2:1 was used to determine the peak hour flow rate. For design purposes, the common house was estimated to have the same water use as a typical home, for a total of 63 users. The estimated total project design flow is 11,831 gpd with a peak flow of 35 gpm. For estimating annual water use, an average of 64.4 gpd/capita was used based on values provided in the City of Bozeman Wastewater Facility Plan. Due to the small, efficiently designed homes, actual use may be significantly lower. This average water use results in an annual water use of 9.86 acre-feet of water. Payment of cash-in-lieu of water rights will be used to provide water rights for this project. Site irrigation water will be provided by the existing trailer park wells located in the northern portion of the site. Irrigation lines will provide water to common open spaces and individual lots. Irrigation systems will be maintained by the owners’ association. Drought tolerant plants and drip irrigation systems are proposed to conserve water. It is estimated that a total of approximately 2.1 acres of turf will be spray irrigated and the Water Mains 6 10/7/2020 remaining planting beds and trees will be drip irrigated. The systems will be “high efficiency” and annual water use is estimated at 3.35 acre- feet/year. This water use is within the combined water right exemption of 10 acre-feet. 1.1.6. Flow Requirements As stated previously, the peak hour water demand is estimated to be 25 gallons per min (gpm). Fire flows have not been determined yet but will be in accordance with the Uniform Fire Code. It is anticipated that a fire flow of 1500 gpm will be required. The fire flow requirement will be the dominant design constraint for system design. This test reported static water pressure of 127 psi, and a flow rate of 2,500 gpm with a residual pressure of 86 psi. This test indicates that the water system network in this area can provide fire flows and peak domestic demand with very little impact on the system pressures. Phase 1 of the development includes three new fire hydrants with Phase 2 adding one more fire hydrant and Phase 3 introduces more looping within the distribution system. A nearby hydrant flow test conducted, and this test reported static water pressure of 127 psi, and a flow rate of 2,500 gpm with a residual pressure of 86 psi. This test indicates that the water system network in this area can provide fire flows and peak domestic demand with very little impact on the system pressures. The flow test was performed on two existing fire hydrants as shown on the figure below. Water Mains 7 10/7/2020 WaterCAD modeling was used to predict available fire flows for the new hydrant with the completion of each Phase. The WaterCAD model and results are provided at the end of this report. The WaterCAD model was calibrated to the existing hydrant flow test. To achieve calibration, the model reservoir elevation was lowered 11’ to account for friction losses in the supply line from the reservoir affecting the static pressure available. The model under predicted the residual pressure measured during the flow test. However, the flow meter was maxed out at 2,500gpm and the model appears calibrated if the hydrant flow was increased to 2,625gpm. The model predicted fire flows over 2,800 gpm for the new fire hydrants in the development, due to the high static pressures in this area. The 2017 Water Facility Plan did not contemplate a lower pressure zone for this area, so the water pressure is unlikely to change. This fire flow results in velocity over 26 feet per second (fps) in the 6” water mains. The City of Bozeman Design Standards limit design flow velocity to 15 fps in mains. This velocity limitation would result in a fire flow of about 1400 gpm. 1.1.7. Sources of Water Supply This section is not applicable. 1.1.8. Proposed Treatment Process This section is not applicable. 1.1.9 Sewage System Available Sewer service is provided by new City mains extended through the site from the existing sewer main running along the northern portion of the property. Sewers will be approximately 8 feet deep and primarily cross below water mains and services. 1.1.10 Waste Disposal This section is not applicable. 1.1.11 Automation This section is not applicable. Water Mains 8 10/7/2020 1.1.12 Project Sites This section is not applicable. 1.1.13 Financing This section is not applicable. 1.1.14 Future Extensions The water system layout accommodates future water main extensions as required to complete future system improvements in this area. A water main will be extended to Story Mill Road to connect with a potential future water main in that street. Additionally, the water main located in Hillside Lane may be connected to future water mains serving undeveloped property to the south. PHASE 1PHASE 3PHASE 1PHASE 2PHASE 1PHASE 2PHASE 2PHASE 3STORY MILLSPUR TRAILSTORY MILL COMMUNITY PARKCITY OFBOZEMANPROPERTYSTORY MILL ROAD (60' ROW & 30' ESMT)BRIDGER DRIVE (Aka Hwy 86) - (110' ROW)HILLSIDE LANE(60' ESMT)HILLSIDE LANE (64' ROW)FLOURHOUSECOURTMILLWORKSCOURTLOT 56LOT 53LOT 49LOT 46LOT 21LOT 40LOT 35LOT 23LOT 13LOT 26LOT 27LOT 4LOT 16LOT 19LOT 47LOT 12LOT 44LOT 43LOT 39LOT 22LOT 38LOT 31LOT 33LOT 42LOT 2LOT 41LOT 37LOT 10LOT 9LOT 32LOT 29LOT 30LOT 5LOT 7LOT 8LOT 52LOT 55LOT 57LOT 54LOT 51LOT 50LOT 48LOT 45LOT 17LOT 25LOT 14LOT 15LOT 11LOT 20LOT 24LOT 36LOT 34LOT 1LOT 6LOT 3LOT 28HILLSIDE GREENHILLSIDE GROVEPHASE 2PHASE 3BLOCK 1BLOCK 2BLOCK 3BLOCK 4PATH TO THE "M"PARKSIDE WALKMILLWORKS ROW FLOURHOUSE WAY (30' ROW)BLUE SILOS WAY (30' ROW)BLUE SILOSCOURTMILLWORKS WAY (30' ROW)ADDITIONAL ROW 1976 SFLOT 18LOTC-1LOTC-2LOTC-4LOTC-5LOTC-3LOTC-6OS 1OS 5OS 6OS 3OS 4OS 7OS 7OS 8OS 7C2.0WATER PLANPROFESSIONALENGINEERS &SURVEYORSBRIDGER VIEW STAHLYENGINEERING& ASSOCIATESHRDC BOZEMAN MONTANA PHASE 1PHASE 3PHASE 1 PHASE 2 PHASE 1 PHASE 2 PHASE 2 PHASE 3 STORY MILLSPUR TRAILSTORY M ILL COMMUN ITY PARKCITY OFBOZEMANPROPERTYSTORY MILL ROAD (60' ROW & 30' ESMT)BRIDGER DRIVE (Aka Hwy 86) - (110' ROW) HILLSIDE LANE (60' ESMT) HILLSIDE LANE (64' R O W ) FLOURHOUSE COURT MILLWORKS COURT LOT 56 LOT 53 LOT 49 LOT 46 LOT 21 LOT 40 LOT 35 LOT 23 LOT 13 LOT 26LOT 27 LOT 4 LOT 16 LOT 19 LOT 47 LOT 12 LOT 44 LOT 43 LOT 39 LOT 22 LOT 38 LOT 31 LOT 33 LOT 42 LOT 2 LOT 41 LOT 37 LOT 10 LOT 9 LOT 32 LOT 29 LOT 30 LOT 5 LOT 7 LOT 8 LOT 52 LOT 55 LOT 57 LOT 54 LOT 51 LOT 50LOT 48 LOT 45 LOT 17 LOT 25 LOT 14 LOT 15 LOT 11 LOT 20LOT 24 LOT 36 LOT 34 LOT 1 LOT 6 LOT 3 LOT 28 HILLSIDE GREEN HILLSIDE GROVE PHASE 2 PHASE 3 BLOC K 1 BLOCK 2 BLOCK 3 BLOCK 4 PATH TO THE "M" PARKSIDE WALK MILLWORKS ROWFLOURHOUSE WAY (30' ROW)BLUE S ILOS WAY (3 0 ' ROW ) BLUE SILOS COURT MILLWORKS WAY (30' ROW) ADDITIONAL ROW 1976 SF LOT 18 LOT C-1 LOT C-2 LOT C-4 LOT C-5 LOT C-3 LOTC-6 OS 1 OS 5 OS 6 OS 3 OS 4 OS 7 OS 7 OS 8 OS 7 RESIDUAL HYDRANT STATIC PRESSURE 129 psi RESIDUAL PRESSURE 113 psi MODEL RESULT 108 psi MODEL RESULT MATCHES IF HYDRANT FLOW INCREASED TO 2625GPM 12" WATER LINE IN BRIDGER DRIVE (SUPPLY)TOWN SUPPLY MODELED AS RESERVOIR AT HGL 5027' TO CALIBRATE TO EXISTING STATIC PRESSURE AT HYD 1861 LYMAN RESERVOIR ACTUAL HGL 5038' 12" PIPE FROM LYMAN SUPPLY MAIN MODELED AT ACTUAL LENGTH OF 2625'BRIDGER DRIVE DEMAND MODELED AT 300 GPM HYDRANT FLOW TEST AT 2500 GPM NEW HYDRANT (HYD-BSW) NEW DEMAND MODELED AT 7 GPM NEW HYDRANT (HYD-HL1)NEW HYDRANT (HYD-HL2) NEW HYDRANT (HYD-MW) NEW DEMAND MODELED AT 7 GPM NEW DEMAND MODELED AT 7 GPM WATERCAD