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HomeMy WebLinkAbout006_Water Sewer Storm Design ReportJOB NO. B21-099 MONTANA | WASHINGTON | IDAHO | NORTH DAKOTA | PENNSYLVANIA SEPTEMBER 2022 406.586.0277 tdhengineering.com 234 East Babcock Street Suite 3 Bozeman, MT 59715 CLIENT ENGINEER Lake Flato Architects 311 Third Street San Antonio, TX 78205 TD&H Engineering 234 East Babcock Street, Suite 3 Bozeman, MT 59715 Engineer: Ahren Hastings, PE WALLACE WORKS BOZEMAN, MONTANA BASIS OF DESIGN REPORT Image courtesy of Lake Flato Architects B21-099 NEST DEVELOPMENT Page 1 of 3 NEST DEVELOPMENT DESIGN REPORT SEPTEMBER 2022 Purpose and Introduction The purpose of this report is to explain how water, sanitary sewer, and storm drainage improvements will be designed to meet the City of Bozeman requirements and Montana Public Works Standard Specifications (MPWSS) to provide service to the Nest Development proposed at 801-803 North Wallace Avenue. The report will provide information on the detailed design of the above-mentioned infrastructure. The project is located at 801-803 North Wallace Ave between East Aspen Street and East Tamarack Street. The property is described as Lots 2 & 3 of Plat C-23-A18, Lot 2 of Plat C-23-A16, and Tract 1 of Minor Sub. No. 3 located in the SE ¼ of S06, T02 S, R06 E, Gallatin County, Montana and is collectively 1.475 acres in size. The property is currently undeveloped, is within zoning district NEHMU, and is designated as community commercial per the 2020 Community Plan Boundary. Proposed site improvements include the construction of two new multi-story, multi-use buildings; new multi-story rowhouses; and a new multi-story parking garage with associated landscape, hardscape, utility services, and stormwater management systems. Off-site infrastructure improvements are proposed for the 6-inch vitrified clay sanitary sewer line running west-to-east along East Aspen Street to serve the development. Existing sanitary sewer pipe and sanitary sewer manholes will be abandoned/removed from the southern edge of the project site to a new connection at existing sewer manhole E0325 located at the intersection of Front Street and East Aspen Street. Design information and specifications for the East Aspen sewer replacement will be provided in a separate public infrastructure improvement review. Design Report Water No existing water stubs exist within the development. New domestic water services will be extended to all new buildings from the existing 8-inch main in East Tamarack Street and the existing 10-inch main in North Wallace Avenue. Sizes of these services are shown on the plans as determined by the MEP Engineer. Fire services (size TBD, assumed 4-inch at time of report) will be extended to the parking structure, northeast- most building, and restaurant/bodega from the existing water mains. Final service sizing will be verified by the mechanical engineer. The services will be Type K Copper (2-inch and smaller) and Class 51 ductile iron (larger than 2-inch) and be installed per the City of Bozeman Design Standards and Modifications to Montana Public Works Standard Specifications (MPWSS). The estimated domestic water demands for the development are summarized in Table 1 below with supporting assumptions and calculations in accordance with C.O.B. DSSP Section V.A.4 provided in Appendix A. B21-099 NEST DEVELOPMENT Page 2 of 3 Table 1: Estimated Water Demands Average Day Max. Day Peak Hour Parking Building 3,944 gpd 9,070 gpd 8.22 gpm Northeast Mixed- Use Building 4,242 gpd 9,757 gpd 8.84 gpm Rowhouses w/ 6 Dwelling Units 1,127 gpd 2,592 gpd 2.35 gpm Rowhouse w/ 5 Dwelling Units 939 gpd 2,160 gpd 1.96 gpm Bodega/Restaurant 821 gpd 1,888 gpd 1.71 gpm TABLE 1:Estimated domestic water demands. Calculations can be found in Appendix A. The irrigation system water source is proposed as a new exempt well on the site and will not use the public water supply. Sewer New 4-inch and 6-inch sewer services (size determined by MEP Engineer) are proposed from each building, with sewer cleanouts at maximum 100-foot intervals and changes in horizontal alignment. Sewer services for the rowhouses and bodega/restaurant will connect to the proposed 8-inch sewer main running west-to-east in East Aspen, while the services for the parking building and northeast mixed-use building will connect to the existing 24-inch sewer main in East Tamarack Street. The new 4” sewer service lines will be SDR-26 PVC and will be installed per the City of Bozeman Design Standards and Modifications to Montana Public Works Standard Specifications (MPWSS). The estimated sewer demands for the development are calculated in accordance with C.O.B. DSSP Section V.B. and using information from the City’s 2015 Wastewater Facilities Plan and C.O.B. Design Standards. The estimated sewer demands are summarized in Table 2 below with assumptions and supporting calculations provided in Appendix B. Table 2: Estimated Sewer Demands Average Day (gpd)Peak Hour (gpm) Parking Building 3,944 - Northeast Mixed-Use Building 4,242 - Rowhouses w/ 6 Dwelling Units 1,127 - Rowhouse w/ 5 Dwelling Units 939 - Bodega/Restaurant 821 - Infiltration 221 - Sewer Demand 11,293 32.8 TABLE 2: Estimated sanitary sewer demands, calculations can be found in Appendix B. B21-099 NEST DEVELOPMENT Page 3 of 3 Storm Drainage The existing project site consists of a vacant field that slopes generally to the north and east. The proposed site development includes new multi-story buildings, new concrete sidewalks, hardscape patios, new parking areas, and new landscaping. Existing concrete sidewalk at the corner of North Wallace Ave and East Tamarack Street currently has grades over 5% and will be replaced to maintain grades below maximum. Site stormwater will be conveyed to the existing 30” PVC stormwater main in East Tamarack Street and the existing 24” PVC stormwater main in North Wallace Avenue. From the stormwater mains, site stormwater is conveyed to the receiving water of Bozeman Creek as it crosses East Tamarack Street between North Rouse Avenue and North Wallace Avenue. The proposed site grading directs all on-site runoff to storm inlets directed into sub- surface infiltration chambers. At the lowest point of the parking garage building, a floor drain will direct runoff to a sub-surface infiltration chamber. To accommodate the storm runoff from the buildings, a series of roof drains and drainage chases will direct runoff to the hardscaped open spaces to drain to storm inlets and the sub-surface infiltration chambers. The volume of off-site runoff produced by post-development Basin 3 that does not flow to on-site infiltration chambers is accounted for by retaining extra volume in the on-site infiltration chambers equal to the volume flowing off site. The sub-surface infiltration chambers are designed to fully retain/infiltrate the flow from the first half inch of rainfall from site impervious areas. Runoff volumes greater than the first half inch will be allowed to flow to the existing stormwater mains via the sub-surface infiltration systems with the overflows flows being restricted to the pre-development runoff rate for the design storm. Flow restriction will be performed by weirs in storm drain manhole outlet structures. A geotechnical excavation investigation was conducted at the site on March 5th, 2020. Groundwater was observed from depths of approximately 14 feet below existing grade in test pits with depths of 15.1 to 20.9 feet. Further groundwater monitoring was performed from March 16th, 2020 to July 22nd, 2020, seasonally-high groundwater was found to peak at 9.8 feet below existing grade during this observation period. Therefore, it is anticipated that groundwater will be sufficiently deep to allow for a full retention/infiltration strategy to be successful at this site. APPENDIX A Water Calculations WALLACE WORKS Date: 09.14.2022 Domestic Water Demands Domestic Water Demand - Parking Building: Residential Use: Wastewater Flow Rate =89.0 GAL./PERSON/DAY (Per C.o.B. Design Standards) Total Dwelling Units=21.0 UNITS (from architect plans) Total Dwelling Residents=44 PEOPLE (2.11 people per dwelling unit per COB Design Standards) Residential Flow=3,944 GPD Peak Hour Demand: Average Day Demand =3,944 GPD (All Uses) Average Day Demand =2.74 gpm (GPD / 1,440 minutes) Maximum Day Demand =6.30 gpm (Ave. Day x Peaking Factor = 2.3) Peak Hour Demand =8.22 gpm (Ave. Day x Peaking Factor = 3) Domestic Water Demand - Northeast Mixed-Use Building: Residential Use: Wastewater Flow Rate =89.0 GAL./PERSON/DAY (Per C.o.B. Design Standards) Total Dwelling Units=22.0 UNITS (from architect plans) Total Dwelling Residents=46 PEOPLE (2.11 people per dwelling unit per COB Design Standards) Residential Flow=4,131 GPD Commercial Use: Office Space=4,038.0 SF (from architect plans) Commercial Flow=111 GPD (10,000 gal/yr/1,000sf - Unit Water Demand for Office) Peak Hour Demand: Average Day Demand =4,242 GPD (All Uses) Average Day Demand =2.95 gpm (GPD / 1,440 minutes) Maximum Day Demand =6.78 gpm (Ave. Day x Peaking Factor = 2.3) Peak Hour Demand =8.84 gpm (Ave. Day x Peaking Factor = 3) Domestic Water Demand - Rowhouse with 6 Dwelling Units: Residential Use: Wastewater Flow Rate =89.0 GAL./PERSON/DAY (Per C.o.B. Design Standards) Total Dwelling Units=6.0 UNITS (from architect plans) Total Dwelling Residents=12.7 PEOPLE (2.11 people per dwelling unit per COB Design Standards) Residential Flow=1,127 GPD Peak Hour Demand: Average Day Demand =1,127 GPD (All Uses) Average Day Demand =0.78 gpm (GPD / 1,440 minutes) Maximum Day Demand =1.80 gpm (Ave. Day x Peaking Factor = 2.3) Peak Hour Demand =2.35 gpm (Ave. Day x Peaking Factor = 3) Domestic Water Demand - Rowhouse with 5 Dwelling Units: Residential Use: Wastewater Flow Rate =89.0 GAL./PERSON/DAY (Per C.o.B. Design Standards) Total Dwelling Units=5.0 UNITS (from architect plans) Total Dwelling Residents=10.6 PEOPLE (2.11 people per dwelling unit per COB Design Standards) Residential Flow=939 GPD Peak Hour Demand: Average Day Demand =939 GPD (All Uses) Average Day Demand =0.65 gpm (GPD / 1,440 minutes) Maximum Day Demand =1.50 gpm (Ave. Day x Peaking Factor = 2.3) Peak Hour Demand =1.96 gpm (Ave. Day x Peaking Factor = 3) Domestic Water Demand - Bodega/Restaurant: Residential Use: Wastewater Flow Rate =89.0 GAL./PERSON/DAY (Per C.o.B. Design Standards) Total Dwelling Units=4.0 UNITS (from architect plans) Total Dwelling Residents=8 PEOPLE (2.11 people per dwelling unit per COB Design Standards) Residential Flow=751 GPD Restaurant Use: Office Space=2,537.0 SF (from architect plans) Commercial Flow=70 GPD (10,000 gal/yr/1,000sf - Unit Water Demand for Office) Peak Hour Demand: Average Day Demand =821 GPD (All Uses) Average Day Demand =0.57 gpm (GPD / 1,440 minutes) Maximum Day Demand =1.31 gpm (Ave. Day x Peaking Factor = 2.3) Peak Hour Demand =1.71 gpm (Ave. Day x Peaking Factor = 3) APPENDIX B Sewer Calculations WALLACE WORKS Date: 05.02.2022 8" Sewer Main Pipe Capacity Input Values d =0.67 ft = 8" y =0.500 ft = 75% Calculated Values (Equations from Fluid Mechanics by Chow) Theta (Θ)4.19 rad 2*arccos(1-y/(d/2)) Area (A)0.28 ft2 (1/8)*(Θ-sinΘ)d2 Wetted Perimeter (P)1.40 ft 0.5Θd Hydraulic Radius (R )0.20 ft (.25)*(1-(sinΘ)/Θ)d Top Width (T)0.58 ft (sin 0.5Θ)d Mannings Equation (Equation from Fundamentals of Mechanics by Munson) n =0.013 (per COB Design Standards) S0 =0.0040 ft/ft (0.4% Min. Slope) Q =0.70 cfs Q = 1.49/n*A*R2/3*S00.5 Q =313.6 gpm Q gpm = (Q cfs)(7.48 gal/ft3)(60 sec/min) V =2.49 ft/s V = Q/A Results A 8" diameter sewer main flowing 75% full at the min. slope of 0.40% has a carrying capacity of 313.6 gpm. WALLACE WORKS Date: 09.14.2022 4" Sewer Service Pipe Capacity Input Values d =0.33 ft = 4" y =0.250 ft = 75% Calculated Values (Equations from Fluid Mechanics by Chow) Theta (Θ)4.19 rad 2*arccos(1-y/(d/2)) Area (A)0.07 ft2 (1/8)*(Θ-sinΘ)d2 Wetted Perimeter (P)0.70 ft 0.5Θd Hydraulic Radius (R )0.10 ft (.25)*(1-(sinΘ)/Θ)d Top Width (T)0.29 ft (sin 0.5Θ)d Mannings Equation (Equation from Fundamentals of Mechanics by Munson) n =0.013 (per COB Design Standards) S0 =0.0200 ft/ft (1.0% Min. Slope) Q =0.25 cfs Q = 1.49/n*A*R2/3*S00.5 Q =110.4 gpm Q gpm = (Q cfs)(7.48 gal/ft3)(60 sec/min) V =3.51 ft/s V = Q/A Results A 4" diameter sewer service flowing 75% full at the min. slope of 2.0% has a carrying capacity of 110.4 gpm. Appendix C Storm Water Calculations SSN89°14'54"E 194.92'S00°56'17"W 330.15'N00°52'45"E 180.94'S89°18'45"W 194.81'N00°58'01"E 148.99'© 2021 Lake|Flato Architects, Inc.3 1 1 T H I R D S T R E E TS A N A N T O N I O, T E X A S 7 8 2 0 5P 2 1 0. 2 2 7. 3 3 3 5 F 2 1 0. 2 2 4. 9 5 1 5w w w . l a k e f l a t o . c o mSET ISSUE DATESDATEISSUEPROJ. ARCHITECTDRAWN BY:L|F PROJ. NO.OWNER: NEST PARTNERS3131 SENTINEL DRIVEBOZEMAN, MT 59715THIS SQUARE APEARS 1/2"x1/2"ON FULL SIZE SHEETSCIVIL: TD&H ENGINEERING234 E. BABCOCK, SUITE 3BOZEMAN, MT 59715LANDSCAPE: DESIGN 5111 N. TRACY ST.BOZEMAN, MT 59715STRUCTURAL: IMEG108 WEST BABCOCK STBOZEMAN, MT 59715MEP: ENERGY12042 STADIUM DRIVE, SUITE 2BOZEMAN, MT 59715GARAGE: WALKER CONSULTANTS10375 PARK MEADOWS DRIVE, SUITE 425LONE TREE, CO 80124Autodesk Docs://Nest Bozeman/Nest Bozeman–LFA–Arch–Main–R22.rvt 2/25/2022 12:11:22 PMProject StatusIssue Date21043TBAMWALLACEWORKS801 N. WALLACE AVEBOZEMAN MTEngineeringtdhengineering.comDRAINAGEBASINSEX.1 WALLACE WORKS Date: 09.14.2022 Post-Development 'C' Value Calculations Rational Formula "C" Values Per MTDEQ 8 "C" Impervious Area/Pond Surface 0.9 Gravel Area 0.8 Unimproved Area 0.3 Lawn/landscape 0.1 Pre-Development Basin (C Value) Determinations: Basin #Basin Description Total Area (SF) Total Area (Acres) Impervious Area (SF) Gravel Area (SF) Unimproved Area (SF) Landscape Area (SF) Composite Cave 1 Lot North of E. Aspen 64,270 1.48 0 3004 59889 1377 0.32 0.32 Post-Development Basin (C Value) Determinations: Basin #Basin Description Total Area (SF) Total Area (Acres) Impervious Area (SF) Gravel Area (SF) Unimproved Area (SF) Landscape Area (SF) Composite Cave 1 North End of Site to N Inlets 34,688 0.80 33556 866 0 266 0.89 2 Center of Site to Central Inlet 18,310 0.42 15924 619 0 1767 0.82 3 East Side of Site to Street Inlet 11,272 0.26 6683 3557 0 1032 0.80 0.87 WALLACE WORKS Date: 09.14.2022 Basin RRV (First 0.5") Calculations Rational Formula "C" Values Per MTDEQ 8 "C" Impervious Area/Pond Surface 0.9 Gravel Area 0.8 Unimproved Area 0.3 Lawn/landscape 0.1 Post-Development Conditions: Basin #Description Total Area (SF) Total Area (AC) Impervious Area (SF) Gravel Area (SF) Unimproved Area (SF) Landscape Area (SF) Composite Cave 1 North End of Site to N Inlets 34,688 0.80 33,319 866 0 266 0.89 Runoff Reduction Volume (First 0.5" of Rainfall): P =0.5 Inches (Water Quality Rainfall Depth) Rv =0.91 (Dimensionless Runoff Coefficient, Rv=0.05+0.9(I) I =96.1%(Percent Impervious Area Draining to Facility) A =0.80 AC (Total Drainage Area) RRV =0.030 AC-FT (Runoff Reduction Volume)* 1,322 CF *RRV = PRvA/12 per Montana Post-Construction Storm Water BMP Design Guidance Manual Eq. 3-1 Post-Development Conditions: Basin #Description Total Area (SF) Total Area (AC) Impervious Area (SF) Gravel Area (SF) Unimproved Area (SF) Landscape Area (SF) Composite Cave2Center of Site to Central Inlet 18,310 0.42 15,924 619 0 1,767 0.82 Runoff Reduction Volume (First 0.5" of Rainfall): P =0.5 Inches (Water Quality Rainfall Depth) Rv =0.83 (Dimensionless Runoff Coefficient, Rv=0.05+0.9(I) I =87.0%(Percent Impervious Area Draining to Facility) A =0.42 AC (Total Drainage Area) RRV =0.015 AC-FT (Runoff Reduction Volume)* 635 CF *RRV = PRvA/12 per Montana Post-Construction Storm Water BMP Design Guidance Manual Eq. 3-1 Post-Development Conditions: Basin #Description Total Area (SF) Total Area (AC) Impervious Area (SF) Gravel Area (SF) Unimproved Area (SF) Landscape Area (SF) Composite Cave 3 East Side of Site to Street Inlet 11,272 0.26 6,683 3,557 0 1,032 0.80 Runoff Reduction Volume (First 0.5" of Rainfall): P =0.5 Inches (Water Quality Rainfall Depth) Rv =0.58 (Dimensionless Runoff Coefficient, Rv=0.05+0.9(I) I =59.3%(Percent Impervious Area Draining to Facility) A =0.26 AC (Total Drainage Area) RRV =0.006 AC-FT (Runoff Reduction Volume)* 274 CF *RRV = PRvA/12 per Montana Post-Construction Storm Water BMP Design Guidance Manual Eq. 3-1 WALLACE WORKS Date: 09.14.2022 Peak Runoff Tc*Tc*10 yr Flow Slope Distance CCf t1 Slope k Velocity Distance t2 Total Cave CCf Area Total i Q %ft min %fps ft min min ac min in/hr cfs 2.04 100 0.32 11.50 2.60 0.491 2.60 226 1.45 Tc*Tc*10 yr Flow Slope Distance CCf t1 Slope k Velocity Distance t2 Total Cave CCf Area Total i Q %ft min %fps ft min min ac min in/hr cfs 0.62 72 0.82 5.21 1.31 0.619 2.32 197 1.41 1.09 0.619 2.12 224 1.76 *Tc minimum of 5 minutes FHWA HEC 22, Eqn 3-4 Cf = 1.0 for 10-year storm event K=0.457 Grassed Water Way (Roadside Ditch) K=0.619 Paved Area K=0.491 Unpaved shallow concentrated flow IDF curve equation for 10-yr storm Tc = time to concentration in hours Rational Method Cf = 1.0 for 10-yr event 0.32 Pre- Development Site 12.95 0.32 1.48 12.95 1.734 Overland Flow TIME OF CONCENTRATION 10 YEAR FLOW CALC Overland Flow Shallow Concentrated Flow 0.82 TIME OF CONCENTRATION 10 YEAR FLOW CALC 8.38 2.300 2.79 Shallow Concentrated Flow Post- Development Site 8.38 0.82 0.82 1.48 31 11871 / f c S D)CC.(.T SkV28.3 𝑖10 = 0.64 ⋅𝑇𝑐−.65 𝑄=𝐶𝐶𝑓⋅𝑖⋅𝐴 WALLACE WORKS Date: 09.14.2022 SD MH Structures Slot Width Calculations Pre-Development Peak Runoff (cfs)C (Constant) Head above Slot (ft) 0.82 3.33 1.0 Slot width=0.25 ft 2.96 in Q = Discharge (cfs) C = Weir Coefficient = 3.33 L = Length of Weir Opening (ft) Reference - City of Bozeman Standards H = Head (ft) weirQHLC2/3 WALLACE WORKS Date: 09.14.2022 25-yr Pipe Flow Calculations 25-Year Flow Calcs:Pipe Capacity Calcs (94% full): Location Basin Size (Acres)Cave CCf Tc (min) 25 yr i (in/hr) Flow Q2 (cfs) Pipe Diameter (d) (ft) Pipe Slope (%) Manning's n 94% Flow Depth (y) (ft) Theta (Θ) (rad.) Area (A) (ft2) Hydraulic Radius (R) (ft) Qfull (cfs) SD MH#1 Structure Overflow Pipe 0.80 0.89 0.98 8.38 2.75 2.15 1.25 0.50%0.013 1.18 5.29 1.20 0.36 4.93 0 Manning's Eqn: Q = 1.49/n*A*R2/3*S00.5 Rational Method Cf = 1.1 for 25-yr event IDF curve equation for 25-yr storm Tc = time to concentration in hours AiCCQf 64. 25 78.0 cTi WALLACE WORKS Date: 09.14.2022 25-yr Pipe Flow Calculations 25-Year Flow Calcs:Pipe Capacity Calcs (94% full): Location Basin Size (Acres)Cave CCf Tc (min) 25 yr i (in/hr) Flow Q2 (cfs) Pipe Diameter (d) (ft) Pipe Slope (%) Manning's n 94% Flow Depth (y) (ft) Theta (Θ) (rad.) Area (A) (ft2) Hydraulic Radius (R) (ft) Qfull (cfs) SD MH#2 Structure Overflow Pipe 0.68 0.81 0.89 8.38 2.75 1.67 1.25 0.50%0.013 1.18 5.29 1.20 0.36 4.93 0 Manning's Eqn: Q = 1.49/n*A*R2/3*S00.5 IDF curve equation for 25-yr storm Tc = time to concentration in hours Rational Method Cf = 1.1 for 25-yr eventAiCCQf 64. 25 78.0 cTi