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HomeMy WebLinkAbout17 - Design Report - South University District Ph 2 - Sewer Sewer Main Extension Engineer's Report South University District Phase 2 Subdivision Infrastructure February, 2017 Submitted to: City of Bozeman Engineering Department 20 East Olive Bozeman, MT 59715 Montana Department of Environmental Quality Permitting and Compliance Division Public Water and Subdivisions Bureau PO Box 200901 Helena, MT 59620-0901 Prepared by: Stahly Engineering and Associates 851 Bridger Drive, Suite 1 Bozeman, MT 59715 (406) 522-9526 ��1N EEAfy X\\0 NT A At ru/1U���i STAH LY CORDELL D. POOL KIPIP1R =�: N0. 11645PE ;iu Engineer's Report Contents Note: The Engineer's Report format follows DEQ-2 organization. Additional information required by the City of Bozeman Design Standards is added where required. Report Narrative Chapter 10 — Engineering Reports & Facility Plans 11.1 Engineering Report - General Information 11.11 Problem Defined 11.12 Design Conditions 11.13 Impact on Existing Wastewater Facilities 11.14 Project Description 11.15 Drawings 11.16 Design Criteria 11.17 Site Information 11.18 Alternate Selection/Analysis 11.19 Environmental Impacts Figures and Tables Figure 1. Vicinity Map Figure 2.a Sewer Site Plan (included separately) Figure 2.b Sewer Site Plan (included separately) Figure 3 Sewer Capacity Analysis Map (included separately) Table 1. SUD Phase 2 Sewer Flow Estimates Table 2. Capacity of 8" SDR 35 PVC Sewer Main Table 3. Capacity of 10" SDR 35 PVC Sewer Main — Kagy to Lincoln Table 4. Areas Used to Analyze Impacts on Existing Wastewater Facilities Table 5. Capacity of 10" SDR 35 PVC Sewer Main - Lincoln Sewer Mains 1 2/1/2017 11 .1 Engineering Report The South University District - Phase 2 is a subsequent minor subdivision of Lot 3, SUD Subdivision Phase 1. The subsequent division will provide right of way dedications for South 14th Avenue, South 11th Avenue, and an additional street on the south side (currently un-named). This subdivision will create a 16.05-acre lot for subsequent development. Phase 2 is located within the City of Bozeman south of Campus Boulevard, between South 11th and South 14th Avenues. Phase 2 is located south of Phase 1 (completed) and Phase 1 B (in progress). Site development on the Phase 2 lot is anticipated to be an 887-bed student housing project. The developer's contact information is: Capstone Collegiate Communities, LLC. 431 Office Park Drive Birmingham, AL 35223 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 South University District - Phase 2 is shown on the Vicinity Map in Figure 1. Sewer Mains 2 2/1/2017 •L• If .i s 1 ' Figure 1. Vicinity Map, Bozeman, Montana 11.11 Problem Defined Currently, there are no sewer mains that can provide service to the lot without the construction of additional off site infrastructure. The sewer mains within SUD Phase 1 do not have capacity to serve all of SUD Phase 2. Therefore, to provide sewer service to Phase 2, a 10" offsite sewer main is proposed, extending from the intersection of Willow Way and West Lincoln Street. The proposed main extension would head south in Willow Way to Kagy Blvd. and then south through the existing SUD park to Campus Blvd. The 10" main would extend south in S. 14th Avenue to serve future development south of SUD Phase 2. This proposed sewer main size and configuration is in accordance with the 2015 Bozeman Wastewater Collection Facilities Plan Update. Furthermore, the capacity expanding costs of this trunk main is included in the Capital Improvements Plan. From this trunk main, 8" mains are proposed to extend along Campus Blvd, the unnamed Street on the south side of the lot, and throughout the interior of the Phase 2 site. The location of the proposed sewer mains within SUD Phase 2 site are shown in Figure 2, and the proposed location of the offsite sewer main is displayed in Figure 3 at the end of this report. Sewer Mains 3 2/1/2017 11.12 Design Conditions The projected sewer flow rates from South University District - Phase 2 was determined with several different methods. As described in the water system engineer's report, water meter readings from SUD Phase 1 were analyzed. Phase 1 does not use City water for irrigation, so the sewer flows would be the same as the water use. Based on the meter readings the average annual water use is 40 gallons per day (gpd) per person. This flow rate is used to determine impacts to the City's wastewater treatment facility and thus sewer impact fees. For regional sewer flow analysis a sewer flow rate of 64.4 gpd/person was used in accordance with the 2015 Bozeman Wastewater Collection Facilities Plan Update. This flow rate was used to assess off-site capacity of sewer mains. For design of on-site sewer mains a design flow of 89 gpd/person was used in accordance with the City of Bozeman Design Standards. All analyses include an infiltration rate of 150-gallons/acre/day, and a peaking factor depending on population served in accordance with the City of Bozeman and MDEQ Design Standards. The average annual flow and on-site design sewer flow estimates for Phase 2 are shown in Table 1, below. Table 1 SUD Phase 2 Sewer Flow Estimates Average Annual Flow On-site Design Flow Total Site Area (gross area in acres) 19.37 19.37 I&I rate gpd/acre 150 150 I&I Flow(gpd) 2905.5 2905.5 Student Housing Residents 887 887 Per capita flow(gpd)* 40 89 Student Housing Flow(gpd) 35,480 78,943 Total Daily Flow(gpd) 38,385.5 81,848.5 Total Daily Flow (gpm) 26.7 56.8 Peaking Factor N/A 3.83 Peak flow (gpm) N/A 217.9 *Note:Average Annual Per Capita Flow obtained from water use data from Phase 1 of the South University District Project was found to be 38.02 gpd/resident Sewer Mains 4 2/1/2017 An 8" sewer main at minimum slope has sufficient capacity to provide sewer service for Phase 2. Table 2 shows that an 8" main has a 75% flow depth capacity of 312.8 gpm installed at a minimum slope of 0.4%. See Table 2 below for the parameters used in the SUD PH 2 sewer capacity calculation. Table 2 Capacity of 8" SDR 35 PVC Sewer Main Status Proposed Location Phase 2 Pipe Material 8" SDR 35 PVC Pipe Diameter(in) 8 Minimum Pipe Slope (Tft) 0.004 Coefficient of Roughness (n) 0.013 Depth in Pipe at 75% Full (in) 6 Depth of Flow(ft) 0.5 Pipe Radius (in) 4 Pipe Radius (ft) 0.33 Wetted Perimeter 1.40 Area of Flow(ft) 0.28 Hydraulic Radius 0.20 Velocity(ft/sec) 2.48 Flowrate (cfs) 0.70 Maximum Pipe Flowrate(gpm) 312.8 Peak Flow% of 75% Flow Depth Capacity 69.6% In accordance with the 2015 Bozeman Wastewater Collection Facilities Plan Update a 10" trunk line is proposed to serve this drainage area. The capacity of this line was analyzed to determine if a 10" main has adequate capacity to serve this area. This proposed trunk line would serve future development along Willow Way, future development along Kagy, SUD Phase 2, SUD Phase 3, SUD Phase 5 and undeveloped property to the south of the South University District. Sewer loading on this 10" trunk line was based on planned zoning, existing zoning, and planned development density in accordance with the 2015 Bozeman Wastewater Collection Facilities Plan Update. The area served by this main provides a planned peak flow of 490 gpm. The proposed 10" trunk line has a 75% flow depth capacity of 695 gpm when installed at a slope of 0.6%, a reasonable minimum slope for a north-south main. Initial analysis shows this line should be a 10" to at least the south boundary of SUD Phase 2. See Table 3 below for the parameters used in the 10" Trunk line sewer capacity calculation. Sewer Mains 5 2/1/2017 Table 3 Capacity of 10" SDR 35 PVC Sewer Main Status Proposed Location Phase 2 & Full Build-out Pipe Material 10" SDR 35 PVC Pipe Diameter(in) 10 Minimum Pipe Slope (ft/ft) 0.006 Coefficient of Roughness (n) 0.013 Depth in Pipe at 75% Full (in) 7.5 Depth of Flow(ft) 0.625 Pipe Radius (in) 5 Pipe Radius (ft) 0.42 Wetted Perimeter 1.75 Area of Flow(ft) 0.44 Hydraulic Radius 0.25 Velocity(ft/sec) 3.53 Flowrate (cfs) 1.55 Maximum Pipe Flowrate(gpm) 694.6 Peak Flow% of 75% Flow Depth Capacity 70.5% Building sewer services have not been sized yet, but will likely be 4" and 6" depending upon the building fixture units. Services will be sized in accordance with the Uniform Plumbing Code. 11.13 Impact on Existing Wastewater Facilities The existing 10" sewer main along West Lincoln Street was examined to determine if the main is adequately sized to handle additional impacts from the development of SUD Phase 2. At the minimum slope of 0.28%, the existing 10" main has a flow capacity of 475 gpm at 75% flow depth of the pipe as required by the City of Bozeman Design Standards and Specifications Policy. The peak flow for SUD Phase 2 and the existing developments that are served by this main is calculated to be 398 gpm, within the pipe's capacity (See Table 5) However, peak flows during MSU football games add a significant flow to the sewer. During the MSU 2011 fall semester, flow measurements were obtained showing an additional 90 gpm during football games. Accounting for this additional flow increases the peak flow to the existing 10" sewer main on Lincoln to 488 gpm, slightly exceeding the 75% flow depth capacity (this flow results in a 77% flow depth). Please note that this capacity exceedance would occur only during home football games Sewer Mains 6 2/1/2017 (typically 6 per year), and is only an exceedance of the 75% flow depth, not the full pipe capacity. The areas used for the calculation of the peak flow within this pipe are graphically shown in Figure 3 at the end of this report. See Table 4 and 5 below for the parameters used in the SUD Phase 2 and existing developments flow capacity calculation. Table 4-Areas Used to Analyze Impacts on Existing Wastewater Facilities Wastewater Total Flow Rate Flow Receiving Acres (gal/acre/day) pd Manhole Description Lincoln to Kaav Residential R4.a 1.75 1456 2,548 H0609 Existing Fourplex S.of Lincoln Residential R2 4 728 2,912 H0608 Existing Duplex Development Residential R1 2 1456 2,912 H0608 Lincoln Residential Redveloped to R4 Residential RS 1.5 1456 2,184 H0606 Lincoln Residential Redeveloped to R4 Community Commercial B1 10 1000 10,000 H0603 11th and Lincoln Commercial Residential R4 10 1456 14.560 H0603 Bird House Apartments and Offices Kagy to Stuck Business Park RO 16 728 11,648 H0603 Stadium Center MSU Stadium 18.4 500 9,200 H0603 Existing Loading Estimate SUD Phase 1 14 2433 34,069 H0603 Loading based on planned density SUD Phase 1 B 6 2324 13,944 H0603 Loading based on planned density SUD Phase 2 24 2480 59,530 H0605 Loading based on planned density Totals 108 163,507 gpd 114 gpm peaking 3.503 factor 398 gpm Sewer Mains 7 2/1/2017 Table 5 Capacity of 10" SDR 35 PVC Sewer Main -W. Lincoln St. Status Existing -W. Lincoln St. Location PH 2 & Ex. Developments Pipe Material 10" SDR 35 PVC Pipe Diameter(in) 10 Minimum Pipe Slope (ft/ft) 0.0028 Coefficient of Roughness (n) 0.013 Depth in Pipe at 75% Full (in) 7.5 Depth of Flow(ft) 0.625 Pipe Radius (in) 5 Pipe Radius (ft) 0.42 Wetted Perimeter 1.75 Area of Flow(ft) 0.44 Hydraulic Radius 0.25 Velocity(ft/sec) 2.41 Flowrate (cfs) 1.06 Maximum Pipe Flowrate (gpm) 474.5 Peak Flow% of 75% Max Capacity 83.9% Looking ahead, once all future development that will utilize the sewer main along W. Lincoln Street is complete, the peak flow will be approximately 841 gpm. This volume will require the sewer main between Willow Way and S. 19t" Ave to be sized at 15", which will also be suitable to handle the increased peak flows from MSU football games. 11.14 Project Description The SUD Phase 2 project is a student housing project to the south of the recently completed Stadium View Apartments. The project falls within the Master Planned SUD Residential Emphasis Mixed Use (REMU) zoning district. 268 student residential units are proposed within the project. Altogether, the development of SUD Phase 2 will provide 887 student bedrooms. 11.15 Drawings Please see attached Figure 2 showing proposed locations of the on-site sewer mains. Sewer Mains 8 2/1/2017 11.16 Design Criteria The South University District— Phase 2 sewer main extensions were designed in accordance with Montana Department of Environmental Quality Circular 2, Montana Public Works Standards and Specifications, City of Bozeman Modifications to Montana Public Works Standards and Specifications, the Uniform Plumbing Code, and the City of Bozeman Wastewater Facility Plan. 11.17 Site Information The SUD Phase 2 site is typical of Bozeman with fine grained soils overlying gravel deposits. Geotechnical borings have determined the depth to gravel ranges from 8 to 10.5 feet. Estimated depth to groundwater from the geotechnical borings is 8.5 to 12 feet. If mains are installed during high groundwater times dewatering may be required. 11.18 Alternative Selection/ Analysis Due to the project's location within the City of Bozeman, extension of public mains was the only sewer supply alternative. 11.19 Environmental Impacts Continued use and new extensions of City of Bozeman municipal sewer mains has the least environmental impact. No new environmental impacts will be caused by these sewer main extensions. Sewer Mains 9 2/1/2017 SUD PHASE 1B , r— SLID PHASE 1 + �I_ STAHLY �.� �f_ _ a. L,1 1.11 N CAMPUS BLVD II STAHLY y� ENGINEERING I _ -�L �I $ ASSOCIATES PROFESSIONAL II I ENGINEERS d l V II I SURVEYORS PROPOSED OFF-SI II 1 I wwwseaeng.com SEWER MAIN TO IW.p W. LINCOLN STRE I , I ( II IWAY PhOon (4 6)535D L 6594 EWISTOWN, MT 59457 II I I 3530 CENTENNIAL DR. HELENA, MT 59601 Lu 11 I Phone:(406)442-6594 _ Fox:(406)442-6557 IIQ I 051 BRIDGER DR. STE. 1 PHASE 1 PARK �> III = BOZEMAN. MT 59715 PROPOSED SE _R II Phone;(406)522-9526 MAIN (TYP) I II I Foz;(406)522-9526 I r, II I PROPOSED BUILDING- - -, I II = 11 _ ISSUE/REVISION / SERVICE (TYP) 1 1 9-027TE B16 DH DESCRIPTION II I PRELIMINARY PLAT III _ I Il II No. DATE BY II 2 1 1-31-17 1 JOS II DESCRIPTION II COB SUBMITTAL No. DATE BY ( S D.P ASE 2 J I I I 3 \� DESCRIPTION LOT - - - 8 16 e 6' __ I / — No. DATE BY \ ( � 4 DESCRIPTION V EXISTING SEWER No. DATE BY n W III NOT CONNECTED 5 J I l u III TO THIS PROJECT DESCRIPTION I U pl PROPOSED Q I II II SEWER MAIN r II III �— —t-- PROPOSED BUILDING II III - - SERVICE (TYP) I V I III O I tl II '1 I II III SEWER SITE } ) I I III PLAN PHASE 2 PARK - - _ ED III STREE-- - I Ili PHASE 2 - -UNNAM - 1 n — I SOUTH UNIVERSITY MM pi DISTRICT II COLLEGIATE I CAPSTONE STUB SEWER FOR +i FUTURE EXTENSION STUB SEWER FOR REMAINDER PARCEL STUB SEWER FOR II � COMMUNITIES LLc. FUTURE EXTENSION FUTURE EXTENSION Ili III DESIGNED: CDP DRAWN: PDH 0 50 t00 200 11 II; CHECKED: CDP DATE: 9-27-16 SCALE IN PENT II III FIGURE .I III 2.a ° 1 STAHLY 1970 ` 1 - -I STAHLY ENGINEERING L — — J— J i• r I „� ? �_�� & ASSOCIATES PROFESSIONAL ENGINEERS& SURVEYORS www.secong.com 404 W. BROADWAY / LEWISTOWN, MT 59457 Il , N i_}} Phona:(406)535-6594 ` / ) ,.� r ( + ( a¢ QQ a 3530 CENTENNIAL DR. p J g HELENA, MT 59601 a p m Phonw..(406)442-5594 �^ � - Fo:c(4D6)442-6557 I -il I BOZEMAN, 59715 SJ Phone:(406)522-9526 Fax:(406)522-9526 ISSUE/REVISION No.I DAZE I BY 1 F - \ 1 1-31-17 1 JDS DESCRIPTION COB SUBMITTAL r f -y - I No. DATE BY (n LNF- 2 _ r I DESCRIPTION I ` L No. DATE BY 3 I DESCRIPTION � No. DATE BY4 DESCRIPTION vpi No. DATE BY L J � _ _ J— J I, I 5 U .I DESCRIPTION 1 L 1 oC) o pV 2 p V > W W F 30 Do _ 0 uj i zoo3 a ��7f3 O LL V ► t°� t`I o C) X SEWER SITE 3 PLAN n n Li Li SOUTH 2 SOUTH UNIVERSITY DISTRICT L J 1 f—I r 1 If CAPSTONE —' U L r —� 1 COLLEGIATE _ I COMMUNITIES LLC. ` LJ DESIGNED: CDP I I DRAWN: PDH - 1OO ZOO 4Q� CHECKED: CDP I I DATE: 9-27-16 SCALE IN FEET FIGURE 2.b CD > art `► STAHLY 1970 _�, i .,♦ . 1Y. � ,` 4' �'v ra' STAHLY `\ �f �!+� ; +` t;• r s' z ENGINEERING ��a l( — tea . 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