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HomeMy WebLinkAbout005 22003 Design Report Digital SANITARY SEWER Proposed construction on Lot 3, Block 16 of Baxter Meadows Subdivision includes two structures each containing 4392 square feet of ground floor commercial/office space and 1, 3-bedroom apartment and 2, 1-bedroom apartments on the second level. Sanitary sewer service for each structure will be provided by extending the existing 4-inch sewer service stub that was provided to the Lot with the original subdivision infrastructure as well as a new 4-inch sewer service extending to the 8-inch main within Caballo Avenue. Average daily flows from each building were estimated based on number of employees and average daily residential flows from the City of Bozeman Design Standards. It was estimated that each unit would have 10 employees, each 1- bedroom apartment would house 1 person, and the 3-bedroom apartment would house 2 people. Total Lot Infiltration Rate 150 gallons/acre/day infiltration Lot area: 15,246 ft2 (0.35 acres) (150 /day)(0.35 acres) = 52.50 gallons/day Infiltration Estimated Average Daily Sewer Flow 8,785 sq ft of office space = 20 employees @ 13 gpd/employee = 260 gallons per day 4x1 BR Apt = 2.11 people/dwelling unit @ 89 gallons per capita/day = 751 gallons per day 2x3 Br Apt = 2.11 people/dwelling unit @ 89 gallons per capita/day = 376 gallons per day Total Lot 3 Wastewater Generation Rate = 1,387 gallons per day Peaking Factor 2 structures(10 employees + 2.11 people/dwelling unit (6 dwelling units)) = 45.32 people = ! (P = Population in thousands) Peaking Factor = (#.#!%&’) !(#.#!%&’) = 4.32 Maximum Daily Flow Peaking Factor x Average Daily Flow + Infiltration = Maximum Daily Flow 4.32(1,387 gallons/day) + 52.50 gallons/day = 6,044.34 gallons/day (0.0094 cfs) The Baxter Meadows subdivision was designed using design flow rates outlined in DEQ Circular WQB 4 and the 2001 City of Bozeman Design Standards. Applying the same design method to Lot 3, the average daily flow rate would be calculated as: Residential flow: 6 units(2.54 occupants/unit)(72 gallons/day) = 1,097.28 gallons/day Office Flow: 2 units(50 occupants/unit)(14.5 gallons/day) = 1450.00 gallons/day Total Average Daily Wastewater Flow = 2,547.28 gallons/day Therefore, the proposed construction is within the original Baxter Meadows Subdivision design sewer flows. WATER SYSTEM Water service for the project will be provided by a 1.5-inch water service line from the 8-inch water main within Caballo Avenue. Attached in Appendix A is a copy of the City of Bozeman Water Service Calculation Worksheet showing that the 1.5-inch meter and service are adequately sized to supply the proposed structures. Estimated Average Daily Water Flow per Structure Residential Flows 1 dwelling unit @ 2.11 persons per dwelling unit 170 gallons/day/capita water flow (6 dwelling units)(2.11 ) *+,)(170 ),./day) = 2,152.20 gallons/day Residential Industrial/Office Flows 20 employees @ 15 gallons/day/employee = 300 gallons/day Commercial/Office Total Average Daily Water Flow (2,152.20 + 300)23 = 2,452.20 gallons/day Average (1.70 gpm) Maximum Day and Peak Hour Demands Peaking Factors (from City of Bozeman Design Standards, dated July 2017): -Maximum Day Demand (Peaking Factor = 2.31) -Peak Hour Demand (Peaking Factor = 3.00) Maximum Day Demand = 2,452.20 gpd x 2.31 = 5,664.58 gpd (3.93 gpm) Peak Hour Demand = 2,452.20 gpd x 3.00 = 7,356.60 gpd (5.12 gpm) The Baxter Meadows subdivision was designed using the Bozeman Water Facility Plan and the Bozeman Design Standards in 2004. Applying the same design method to Lot 3, the average daily water flow, maximum daily demand, and peak hour demand would be calculated as follows: Total Average Daily Water Flow 8 units(2.54 occupants/unit)200 gallons/day = 4,064 gallons/day Average (2.82 gpm) Maximum Day and Peak Hour Demands Peaking Factors (from City of Bozeman Design Standards 2004): -Maximum Day Demand (Peaking Factor = 2.50) -Peak Hour Demand (Peaking Factor = 3.00) Maximum Day Demand = 4,064 gpd x 2.50 = 10,160 gpd (7.06 gpm) Peak Hour Demand = 4,064 gpd x 3.00 = 12,192 gpd (8.47 gpm) Therefore, the proposed construction is within the original Baxter Meadows Subdivision design water demands. STORM WATER OVERVIEW Stormwater runoff from the full development of Lot 3 was accounted for in the sizing of the Baxter Meadows Subdivision storm water infrastructure. The storm water infrastructure installed with the subdivision includes roadway and adjacent parking asphalt, curb and gutter, underground storm sewers, storm water retention/detention facilities. LOT 3 STORM WATER MANAGEMENT Attached in Appendix B are relevant sections of the Stormwater Design Report prepared for Baxter Meadows Subdivision, Phase 2A. The project site is located within Drainage Basin #6 and highlighted on the “Phase II – Drainage Basins & Detention Locations” map. The original Detention Basin #6 calculations are also attached highlighting the post- development runoff coefficient assumed for the site. Lot 3 contains a gross area of 15,404 square feet. The proposed development of Lot 3 will include: Roof Area (C=0.85) = 8,152 sq ft Concrete/Asphalt Area (C=0.90) = 3,848 sq ft Landscaping (C=0.30) = 3,403 sq ft The Composite C coefficient for the proposed developed area is: C = (0.85(8,152) + 0.90(3,848) + 0.30(3,403)) C = 0.74 The proposed site development includes a higher impervious area than that which was assumed with the original Baxter Meadows Phase 2A infrastructure design report (C of 0.74 vs. C of 0.57). Attached in Appendix B is a “Stormwater Design Calculations” spreadsheet comparing the 10-year storm water volumes for the assumed site runoff (C=0.57) and the proposed site runoff (C=0.74). The calculations show that a minimum on-site retention volume of 179 cubic feet is required to limit the off-site flows to the original projection. The proposed on-site storm water facilities are to be maintained by the Lot 3 owners. Attached in Appendix B is a copy of the “Stormwater Maintenance Plan” outlining the owner’s maintenance responsibilities for the on-site retention pond. The existing off-site stormwater conveyance and detention facilities are to continue to be maintained by the Baxter Meadows Subdivision property owner’s association. The owner’s association maintenance responsibilities are spelled out in the subdivision covenants and homeowners association documents. Appendix A - City of Bozeman Water Service Calculation Worksheets 2.5 X X ¾” 20 19 17 14 11 ¾” 39 36 33 28 23 1” 1” 39 39 36 30 25 ¾” 1¼” 39 39 39 39 39 1” 78 76 67 52 44 1½” 1¼” 78 78 78 66 52 1” 1½”/2” 85 85 85 85 85 1½” 151 151 151 128 105 2” 151 151 151 150 117 1½” 370 340 318 272 240 2” 1½” 370 370 370 368 318 1” ¾” 2” 2” 1½” 1¼” UPC Table 610.3 Standard Design Water Supply Fixture Units Fixture Units # of Fixtures Total 4.0 X ________ = ________ 10.0 X ________ = ________ 2.0 X ________ = ________ 4.0 X ________ = ________ 1.5 X ________ = ________ 2.5 X ________ = ________ 1.0 X ________ = ________ 0.5 X ________ = ________ 3.0 X ________ = ________ 1.0 X ________ = ________ 1.5 X ________ = ________ 1.5 X ________ = ________ Appliances and Fixtures Bathtub/Combination Tub/Shower Soaker Tub Shower (per head) Clothes washer Dishwasher Hose Bibb Additional Hose Bibb (each) Drinking Fountain Service / Mop Basin Lavatory Sink Kitchen Sink Laundry Sink Water closet (1.6 GPF) 2.5 X ________ = ________ Water closet (1.6 GPF – Flushometer tank) X ________ = ________ = ________ Water closet (flushometer valve) Urinal (flushometer valve) = ________ Table Values ________ Table Values ________ Total Number of Fixture Units ________ First identify the length in feet to the farthest fixture and applicable service. Then, cross reference the number of fixtures, based on the Total Number of Fixture Units above to determine the appropriate Meter & Service, and Supply & Branch size. UPC Table 610.4 Maximum Allowable Length in feet - 46-60 PSI Meter & Supply & 150’ 200’ Service Branches If count is over 370 fixtures, water demand does not meet table 610.4 submitted by a registered Montana mechanical engineers design, signed and stamped. March 2023 Commercial (2021 UPC) City of Bozeman Water Service Calculation Worksheet Project Address: ___________________________________ Pr operty Owne r: ______________________________ General Contractor: _______________________________________________________________________________ Permit Number: _______________ Proposed Water Meter Size: _______________ *As a substitute for this form you can utilize Appendix M in Uniform Plumbing Code. The calculator results, as well as all of the fixtures that will be used on this proje ct will need to be submitted in lieu of this form. Sec . 610 .1 Sec. 6 10.1 100’ 80’ 60’ *Appendix M requires the property to be identified as a water conservation Building. 2.5 X X ¾” 20 19 17 14 11 ¾” 39 36 33 28 23 1” 1” 39 39 36 30 25 ¾” 1¼” 39 39 39 39 39 1” 78 76 67 52 44 1½” 1¼” 78 78 78 66 52 1” 1½”/2” 85 85 85 85 85 1½” 151 151 151 128 105 2” 151 151 151 150 117 1½” 370 340 318 272 240 2” 1½” 370 370 370 368 318 1” ¾” 2” 2” 1½” 1¼” UPC Table 610.3 Standard Design Water Supply Fixture Units Fixture Units # of Fixtures Total 4.0 X ________ = ________ 10.0 X ________ = ________ 2.0 X ________ = ________ 4.0 X ________ = ________ 1.5 X ________ = ________ 2.5 X ________ = ________ 1.0 X ________ = ________ 0.5 X ________ = ________ 3.0 X ________ = ________ 1.0 X ________ = ________ 1.5 X ________ = ________ 1.5 X ________ = ________ Appliances and Fixtures Bathtub/Combination Tub/Shower Soaker Tub Shower (per head) Clothes washer Dishwasher Hose Bibb Additional Hose Bibb (each) Drinking Fountain Service / Mop Basin Lavatory Sink Kitchen Sink Laundry Sink Water closet (1.6 GPF) 2.5 X ________ = ________ Water closet (1.6 GPF – Flushometer tank) X ________ = ________ = ________ Water closet (flushometer valve) Urinal (flushometer valve) = ________ Table Values ________ Table Values ________ Total Number of Fixture Units ________ First identify the length in feet to the farthest fixture and applicable service. Then, cross reference the number of fixtures, based on the Total Number of Fixture Units above to determine the appropriate Meter & Service, and Supply & Branch size. UPC Table 610.4 Maximum Allowable Length in feet - 46-60 PSI Meter & Supply & 150’ 200’ Service Branches If count is over 370 fixtures, water demand does not meet table 610.4 submitted by a registered Montana mechanical engineers design, signed and stamped. March 2023 Commercial (2021 UPC) City of Bozeman Water Service Calculation Worksheet Project Address: ___________________________________ Pr operty Owne r: ______________________________ General Contractor: _______________________________________________________________________________ Permit Number: _______________ Proposed Water Meter Size: _______________ *As a substitute for this form you can utilize Appendix M in Uniform Plumbing Code. The calculator results, as well as all of the fixtures that will be used on this proje ct will need to be submitted in lieu of this form. Sec . 610 .1 Sec. 6 10.1 100’ 80’ 60’ *Appendix M requires the property to be identified as a water conservation Building. Appendix B - Baxter Meadows - Phase II Detention Basin 6 calculations - Phase II – Drainage Basins & Detention Locations map - Stormwater Design Calculations - Stormwater Maintenance Plan Storm Water Design CalculationsDrainage Area #1 2,721 ft2Composite Runoff Coefficient CalculationProject: Lot 3 Baxter MeadowsArea (ft2)Area (acres)C factorHardscape = 780 0.02 0.90 From City of Bozeman Design Standards: Q=CIARoof = 1,135 0.03 0.85 V=7200QLandscaping = 806 0.02 0.30 Total Area = 2,721 0.06 Q = runoff (cfs)C = Weighted C factorWeighted Cw = 0.70 I = Rainfall Intensity (in/hr) based on a 10 yr, 2 hr eventA = Area (acres)For a 10 year, 2 hour storm event: V = Volume ( ft3)Area = 2,721 ft2Area = 0.06 acresRainfall Intensities (from Figures I-2 & I-3)Q10 =0.0179 cfsI10 = 0.4079 in/hr (10 yr, 2 hr event)Vrqd = 129 ft3 I25 = 0.5005 in/hr (25 yr, 2 hr event)I50 = 0.5822 in/hr (50 yr, 2 hr event)I100 = 0.6348 in/hr (100 yr, 2 hr event)Drainage Area #2 1,083 ft2RETENTION POND DESIGNComposite Runoff Coefficient CalculationOriginal Subdivision Pond Size C= 0.5682Area (ft2)Area (acres)C factorArea = 15,404ft2Hardscape = - - 0.90 Area = 0.35 acresRoof = 770 0.02 0.85 Q10 =0.082 cfsLandscaping = 314 0.01 0.30 Vrqd = 590ft3Total Area = 1,083 0.02 Post Development Pond SizeWeighted Cw = 0.69 Composite Runoff Coefficient CalculationFor a 10 year, 2 hour storm event:Area (ft2)Area (acres)C factorArea = 1,083 ft2Hardscape = 3,848 0.09 0.90 Area = 0.02 acresRoof = 8,152 0.19 0.85 Q10 =0.0070 cfsLandscaping = 3,403 0.08 0.30 Vrqd = 50 ft3 Total Area = 15,404 0.35 Weighted Cw = 0.74 For a 10 year, 2 hour storm event:Area = 15,404 ft2Area = 0.35 acresQ10 =0.1069 cfsVrqd = 770 ft3 ΔLot/Subdivision = 179 ft3 To be Retained on Lot 3 STORM WATER MAINTENANCE PLAN 3720 Galloway Street Gallatin County, Montana THE FOLLOWING PROPERTY OWNER'S RESPONSIBILITIES FOR ROUTINE INSPECTION AND MAINTENANCE ARE TO BE PERFORMED BY THE LANDOWNER OR THEIR DESIGNATED AGENT. SHOULD THE PROPERTY CHANGE OWNERSHIP THESE RESPONSIBILITIES SHALL PASS TO THE NEW PROPERTY OWNER(S). 1. Routine Maintenance Activities (1-3 month interval) • Designate no cut zones in the bottom of basins • Remove trash, leaves, grass clippings and debris from inlets, swales & ponds • Remove any obstruction to flow • Establish a chemical free zone in and around the basins • Inspect for uniform ponding, and that water disappears within three days of rain events • Inspect inlets, piping, swales & outlet structures for sediment buildup and/or evidence of erosion • Check for eroded or channelized areas. Repair immediately, find the cause and take action to prevent further erosion. • Inspect structures and pond area for oil sheens • Inspect ponds and swales for undesirable vegetation or noxious weeds 2. Annual Maintenance Activities (Annually) • Cut vegetation to 6” and remove clippings • Re-establish vegetation on eroded and barren areas • Remove excess sediment build-up in inlets, piping, swales, ponds and outlet structures. • Update maintenance plan and inspection log • Repair/Replace eroded or damaged rip rap aprons • Clear and remove accumulated winter sand in parking lots and structures 3. Long Term Maintenance Activities (5-10 year interval) • Consult a qualified professional to inspect and return storm water basin back to initial design found on the subdivision and/or site plan engineering plans. • Dredge basin if sediment buildup is greater than 6” • Re-establish vegetation • Repair or replace damaged storm water structures and/or piping • Repair/Replace eroded or damaged rip rap aprons • Re-grade swales to ensure proper drainage.