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Home My WebLink About08 - Design Report - Gallatin County Detention Center - Sewer 1. Sewer Main Extension Engineer's Report Gallatin County Detention Center December 2008 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 7585 Shedhorn Drive Bozeman, MT 59718 (406) 522-9526 OO N TA'k EST. v STAH LY ALEGENDER O RAGENOVICH 9424ES � � J NDLP� 0 Engineer's Report Contents Note: The Engineer's Report format for the Gallatin County Detention Center Sewer Main Extension 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 11.11 Problem Defined 11.12 Design Conditions 11.13 Impact on Existing Wastewater Facilities 11.14 Project Description 11.15 Design Criteria 11.16 Site Information 11.17 Environmental Impacts Figures and Tables Figure 1. Vicinity Map Figure 2. Sewer System Map Figure3. 10" Sewer Service Area Table 1. Estimated Water Use Data Table 2. Predicted Flow in 10" Trunk Sewer Main Table 3. Capacity of 10" Trunk Sewer Main - S. 15 th Ave. Table 4. Capacity of 10" Sewer Main connecting to S 15 th Ave. Sewer Mains 1 12/22/2008 11.1 Engineering Report The proposed new Gallatin County Detention Center is located within the City of Bozeman at 615 South 16t Ave. The site is comprised of three tracts of land owned by Gallatin County with a total acreage of 18.9 acres. The site is currently occupied by the existing 40-bed Detention Center, the Law and Justice Center housing City and District Courts, and the Gallatin County Sheriff and Bozeman Police Departments. The proposed Detention Center has a 160-bed capacity that can be increased to 200-bed without additional construction. Eventual long-term expansion may increase the facility to 300 beds. The property owner's contact information is: Gallatin County c/o Larry Watson Grants and Projects Administration 311 West Main 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 Debra Arkell, Director PO Box 1230 Bozeman, MT 59771-1230 The location of the Gallatin County Detention Center is shown on the Vicinity Map in Figure 1. 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Vicinity Map (1:1000) Bozeman, Montana - 11.11 Problem Defined City of Bozeman sewer mains currently exist on the property. However, the location of the proposed Detention Center requires relocation of these existing mains. The location of the existing mains and proposed relocations in relation to the existing sewer system are shown in Figure 2, a large map included separately. A 10" trunk sewer main flows from south to north along the eastern portion of the property. An 8" sewer main provides service to the existing Law and Justice Center and flows into the 10" trunk sewer. The proposed Detention Center foot print requires the 10" trunk sewer main to be moved approximately 35 feet to the east, where it will run along the eastern side of the detention center. The 8" sewer main serving the Law and Justice Center will be moved approximately 120 feet to the south, where it will run along the southern side of the new Detention Center. Two new sewer services will be provided for the new Detention Center, and 3 existing services will be provided for the existing Law and Justice Center. Sewer Mains 3 12/22/2008 The existing Detention Center is served by a 6" service to an 8" main flowing from south to north along the western property line. This service will be temporally utilized by the existing DUI processing center (a modular building) during construction. After construction of the new Detention Center is completed, this 6" service will be abandoned as part of the demolition of the existing Detention Center. 11.12 Design Conditions Wastewater flows from the new Detention Center are assumed to be similar to estimated water use. Water use for the existing 40-bed Detention Center has been determined from the last three years of water meter readings. Existing water use averages approximately 3,600 gpd during the fall, winter, and spring. Existing water use increases to a maximum of 4,800 gpd for a short time in summer. Based on the non- irrigation water use the existing Detention Center has an average day wastewater generation of approximately 90 gpd/bed. The existing Detention Center does not have an on-site kitchen/cafeteria. Future wastewater flow estimates were determined from MDEQ values provided in Table 5-1 of DEQ-4 for prisons. This table provides average day water use of 115 gpd/inmate and 10 gpd/staff. Estimated flows from the new Detention Center are shown in Table 1. These flows do include a kitchen/cafeteria facility. TABLE 1. Estimated Water Use-Gallatin County Detention Center User Class Proposed Future Expansion 200-Bed Facility to 300-Bed Facility Max Inmate Population 200 300 Average Day Flow(gpd/inmate) 115 115 Subtotal Inmate Water Use 23,000 34,500 Staff Population 62 90 Avera a Day Flow(gpd/staff) 10 10 Subtotal Staff Water Use 620 900 -Average Day Flow d 23,620 35,400 These estimates are compared to the 90 gpd/bed metered water use from the existing 40-bed Detention Center. Extrapolating existing water use to a 200-bed facility yields an estimated waste water production of 18,000 gpd. Kitchen/cafeteria facilities can add approximately 7 gpd per meal served, or 21 gpd per bed, for a total of 4200 gpd. The comparison of DEQ suggested water use (23,620 gpd) and the extrapolation of measured water use with the addition of approximate kitchen uses (18,000 + 4200 =22,200 gpd) indicates that DEQ suggested design values are reasonable flow estimates. Sewer Mains 4 12/22/2008 11.13 Impact on Existing Wastewater Facilities Expected Sewer Flows Future obligated wastewater flow in the 10" trunk sewer main located in South 15th Avenue was determined by considering population densities based on land use and zoning within the sewer main's service area. The service area of this main consists of 109 acres of Montana State University property zoned PLI, 20 acres of residential property zoned R-3 and R-O, and 12 acres of the Law and Justice property zoned PLI as shown on Figure 3. The Montana State University facilities in the service area include the Roskie Hall and Hedges dormitory complex, family housing, and Howard, McCall, Cheever, and Haynes Halls. The Residential areas include townhomes and condominiums bounded by College Street, 15th Avenue, and the Detention Center, as well as townhomes and condominiums along 15th Avenue north of Koch Street. I+rF'1I,� 4 t �g P �k .• � fr I tii ,I� `'`1��ffAarr `�i �.r ?:� � �-- f�trF?.�{v �� f r �J f{ r z •.A �,4 j 1 .9, + •" '+ + '+'"• 7H_ PRE fT �7te"i 5s� p,� I ... f N't r ,1 r`i �.IA.. S7 41�r�T,T ..,+ 3.Y tn �'' ,.. !. r � ice'"��t + �,�...�j•�F•17- j�h�p tF"�}� + t�rj-? S$ Yt s.• lh. 1 �; �, ��•� r r ' 1.�� t' �1� (�$T.,.'��T i�''�,�,'� ,fvhrt:i. tt�f 15� � � ;,tl �� 1 � ,j�1'�.r�'�u.r'1r�j /11,'(�r °�'1Ft'y1fr�7�r��•�x .M`, f F" 1 I •., - J a � ds"jl is�L�N 1 �Y"-$ _ ►�R't � 'qr` �� r,�.��a � • � Fa. '•�., Y.. �' r'r �� ,•� t( .,tiT;I•�t�'y"� '(f i.�:.tr V�i.��ri�� •rF r.Jm lr-.} �y r.� _.��_Z r CiOLLEGE 8TREV1'-7r1k- _ QEf q " tl t i.i C rc rrrrr. Y, rrr/ r' _ f! fr ' r6 'F ,v1RY - rrrlUr Mrirr•+ S �+ Pro RE FRI •. r' I r r `.I I r .r �,..5'..-,f.;. Figure 3. 10" Sewer Service Area (1:1000) Bozeman, Montana Sewer Mains 5 12/22/2008 Future development average daily flows to the 10" trunk sewer line east of the Detention Center were determined from the population density using an flow rate of 72 gallons per day per capita from the City of Bozeman Design Standards. The future Montana State University population density is considered to be 36.5 people per gross acre. This value is higher than typical PLI densities due to the presence of existing and future very high density university housing. The density value corresponds to the City of Bozeman Wastewater Facility Plan (COBWWFP) suggested wastewater flow rate of 2780 gallons per gross acre per day (Table 2-18, COBWWFP) for Montana State University east of South 19t" Ave. R-O and R-3 Residential areas have a future population density of 12.19 people per acre (Table V-1, City of Bozeman Design Standards). Future wastewater flows from the Law and Justice Property were determined from the typical PLI population densities in addition to estimated flows from the proposed expanded 300-bed Detention Center. The calculations of the total estimated future obligated flow in the 10" trunk sewer main are shown below in Table 2. Table 2. Predicted Flow into 10" Trunk Sewer Main. Sewer Main Capacity Calculation Peak Hour Flow Calc Sewer Main Service Area 141 Acres MSU Subarea 109 Acres Population Density 36.5 People/Gross Acre Subarea Population 3978.5 People Per Capita Flow 72 GPD/ Person Subarea Average Daily Flow 286,452 GPD Residential and R/O Subarea 20 Acres Population Density 12.19 People/Gross Acre Subarea Population 243.8 People Per Capita Flow 72 GPD/ Person Subarea Average Daily Flow 17,554 GPD Law and Justice Center Subarea 12 Acres Population Density 12.19 People/Gross Acre Subarea Population 146.3 People Per Capita Flow 72 GPD/Person L&J Average Daily Flow 23,620 GPD Detention Center Population 300 People Detention Center Flow 35,400 GPD Subarea Average Daily Flow 59,020 GPD Total Service Area Pop 4668.6 People I&I Rate 150 GPD/ACRE I&I Flow 21150 GPD Total Ave Day Flow with 1&1 257.7 GPM Total Ave Day Flow 371,088 GPD Ave Day to Peak Hour Peaking Factor 3.272 from DEQ 2 Peak hour flow 809.8 GPM Sewer Mains 6 12/22/2008 Based on this analysis, existing and potential future development on MSU property accounts for 81.6% of the total obligated flow. The new Detention Center accounts for 9.5% of the total obligated flow. Nearby residential uses and additional public institutions on the Law and Justice property account for the remainder. Sewer Capacity Sewer capacity for the 10" trunk sewer main located in S 15th was determined using data obtained from the City of Bozeman Wastewater Facility Plan (COBWWFP). The 10" trunk sewer main is constructed of vitrified clay pipe. The pipe slope most constraining to capacity was taken from the COBWWFP as 0.01 ft/ft on pipes P-2806 (between manholes H0542 and H0543) and P-2808 (between manholes H0546 and H0576). Downstream of these pipes the sewer changes to 12" and has greater capacity. The 12" sewer main was not analyzed as part of this report. Pipe capacity calculations are shown below in Table 3. Table 3. Ca acit of 10" Trunk Sewer Main — S. 15t"Ave. Status Existing Location S 15th Manhole#'s(COBWWFP) H0542-HO543 Pipe Material 10" Vitrified Clay Pipe Diameter(in) 10 Minimum Pipe Slope(ftlft) 0.0100 Coefficient of Roughness (n) 0.013 Depth in Pipe at Max Flow(in) 9.40 Depth of Flow(ft) 0.78 Pipe Radius(in) 5.00 Pipe Radius (ft) 0.42 Wetted Perimeter 2.21 Area of Flow(ft) 0.53 Hydraulic Radius 0.24 Velocity (fUsec) 4.4 Maximum Pipe Flowrate m 1057.8 Avgcit Flow%of Max Ca a 24% Peak Flow% of Max Ca acit 77% A portion of the 10" trunk sewer running from west to east on the north side of the Detention Center property (H0538 to H0542) is slip-lined and has a slightly smaller diameter. This pipe was also analyzed for capacity. A pipe slope of 1.0% was obtained from the COBWWFP for this pipe. Pipe capacity calculations are shown below in Table 4. Sewer Mains 7 12/22/2008 Table 4.-Capacity of 10" Sewer Main Connecting to S 15th Ave. Status Existing Location DC - 15th Ave Manhole#'s (COBWWFP) H0538-H0542 -Pipe Material 10" Lined Vitrified Cla Pipe Diameter(in) 9.5 Minimum Pipe Slope (ft/ft) 0.0100 Coefficient of Roughness (n) 0.013 Depth in Pipe at Max Flow(in) 8.93 Depth of Flow(ft) 0.74 Pipe Radius (in) 4.75 Pipe Radius (ft) 0.40 Wetted Perimeter 2.10 Area of Flow(ft) 0.48 Hydraulic Radius 0.23 Velocity(ft/sec) 4.3 Maximum Pipe Flowrate m 922.6 -.Avg Flow% of Max Capacity 28% Peak Flow% of Max Ca acit 88% Discussion of Capacity Calculations Based on the future obligated flows estimated, and the pipe capacity calculations, the downstream 10" sewer main has capacity to accept the additional flows produced by the new Detention Center. The downstream 10" sewer main is at 77% of capacity at peak hour flows in South 15th Avenue, and at 88% of capacity at peak hour flows where slip-lined on the Law and Justice Center property. The adequacy of this sewer main to transport future obligated flows depends most on MSU future development. Future MSU residence halls or other high-rise high-density student residences would exceed the flow estimates considered in this report. Due to the potential inconvenience of reconstruction of the sewer main under newly constructed Detention Center site improvements, a 12" sewer main is proposed where the existing 10" sewer main is being relocated. At this time this upsizing is a low-cost upgrade that could help reduce the impact of potential future infrastructure improvements on the site. Should future construction on the Law and Justice property require additional relocation of the existing 10" main, it too could be upgraded to a 12" main. The anticipated peak flows are only 17% and 53% of a 12" sewer pipe capacity at average and peak hour flows. Sewer Mains 8 12/22/2008 x- 11.14 Project Description The project has been adequately described in previous sections. Complete Plans and Specifications for the project are included with the submittal showing the proposed sewer main relocations. 11.15 Design Criteria The Gallatin County Detention Center sewer service and relocated sewer main 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. 11.16 Site Information The site is typical of Bozeman with fine grained soils overlying gravel deposits. Geotechnical borings have determined the depth to gravel ranges from 4 to 20 feet. Estimated depth to groundwater obtained from the geotechnical borings is 4-8 feet. If mains are installed during high groundwater times dewatering may be required. 11.17 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 12/22/2008 i Legend 4Hxa" r ® Manholes ... • Cleanouts / • Lampholes 7 Caps add s c a� �� Taps W i nt.s. ts. n7s. a o� _ WN, R tiUB Pf� Tees 1, Opd C.O.S.924 � Wyes C' 77 Sewer Mains(by material) flinch �° �� / Asbestos Concrete rrmNWOn s A G vow Q� 6 S os.isv off` O > Cast Iron Iry-Irv- C),: = 3 �* B inch ` U PB inch os� �\ 05� o og /�/Cement GI` N of r r _. 0 C in T /V Clay ZLU m N Ductile Iron W C Z Cj < - PVC W >BD f erex�En Dx- /i�Tile Zad 0 /V Vitrified Clay Z O o 0 N E -- - //// W a r ne a 3 s > Slip Lines N w` 3 U .a� t CbNO Parcels J V) As �a 00 a a x Roads 00 Oa�w ' F I C Rh, RANs Parks BD 'ISION a" yry a inch l=== w i ru sT h- a 10Ihl City Limits E rrI evl— rn ,N.�T_te 3SnR � 13 B 1 5� ti e -& A/z 2 a N EW PVC SEWER- 9 A m m ---- srcmxsr -- -- N 3 REMOVED- EXISTING CLAY SEWER E REMOVED - ��Ii - - Wj'� E o o ' - � I e " �9 inch i o - — �. , -8 _n 1)ICk`ERStYfFST _.___.______ _ r__ ____ -. _ 14 Ga \ W H s = EXISTING CLAY SEWER S -� W a T' ----� FB H-s GB � m w ro' ti \ _ Z Z 0,.S.309 ._......--__ y®VITE SE—RI: _ coia.r(,r; stBDIvisic)N r SW1/4Sectiion12 T25 R5E O N O QZ m -4L 1'PS'I'- it�RnP.CE_JT3A ,fp y - N' I J LL 1 L¢j� KNOW/m/m, H-5 v DESIGNED BAR DRAWN BAR CHECKED AOR s -- I inch equals 200 feet 200 100 0 200 Feet SHEET 7 - FIGURE 2