The URL can be used to link to this page

Home My WebLink About05 - Design Report - Valley West Ph 3 - Sanitary Sewer Valley West Subdivision—Phase#3 Sanitary Sewer Design Report Introduction This report provides a basis for design of the Valley West Subdivision—Phase#3 sanitary sewer collection system. A comprehensive design report evaluating the capacity of the existing sewer facilities serving the entire Valley West Subdivision Planned Unit Development(PUD) is provided in the Preliminary Plan submittal for the PUD. The PUD report does not identify any capacity problems for the existing collection piping to serve the development. The sewer system serving Valley West Subdivision—Phase#3 will be designed and constructed in accordance with WQB Circular No. 2; Montana Public Works Standard Specifications (MPWSS); City of Bozeman modifications to the MPWSS; and the Uniform Plumbing Code; and the City of Bozeman Wastewater Facility Plan. In accordance with the City of Bozeman Design Standards and Specifications Policy this report is being submitted for approval by the City of Bozeman prior to the plan and specification submittal. The applicant intends to utilize the self-certifications process provided for in these design standards. Deviation Requests Utility Design Criteria A deviation from the requirement to use zoning densities identified in Table V-1 of the City of Bozeman Design Standards and Specifications Policy is requested. The underlying zoning for the property is R-3. Table V-1 identifies and allowable density of 12.19 dwelling units per acre for the property. The Valley West Subdivision Planned Unit Development identifies development densities for the entire subdivision area. These planned densities are considerably less than the maximum densities allowed by zoning. Designing for densities identified in Table V-1 will result in over conservative pipe design for the subdivision. We request that the densities identified in the Valley West Planned Unit Development Preliminary Plan submittal be used for design. City of Bozeman Standard Pipe Locations A second deviation is related to the sewer main location in the public right-of-way. This deviation is needed in order to transition from the standard location constructed with prior phases to the new standard location for roads with widths less than35 feet. This standard calls for locating the sewer 5.5 feet south and east of the centerline. The deviation is needed where the sewer transition begins and ends. Peak Flows Peak hour flows are calculated using the peaking formula provided in the City of Bozeman Design Standards and Specifications Policy. PF = 18 +P"2 4+P1/2 (P =Population in thousands) Table 2 represents peak flows based on the average daily flow calculated in the previous paragraph. Table 2 Peak Hour Flows —Valley West PUD Densities Drainage Basin Ave. Daily Flow (gpm) Peaking Factor Peak Flow N,-nni) Area 1 (total) 57 3.8 216 Area 1 (Phase 3) 33.7 3.9 131 Area 3 (total) 38.2 3.9 149 Sanitary Sewer Pipe Desilln Wastewater Drainage Area 1 Using the approved densities presented in the Valley West Planned Unit Development and the peak flows provided in Table 2, the sewer pipes transporting wastewater from the Valley West Subdivision — Wastewater Drainage Area 1 will need to convey a peak flow of 216 gpm. The capacity of an 8" diameter sewer pipe installed at a slope of 0.4% can be calculated as follows: Manning's Equation Q = (1.49/n) AR2J3S1I2 A Manning's friction factor of 0.013 will be used as required by the City of Bozeman Design Standards. Per the City of Bozeman Design Standards, new sewers will be sized to flow at 75% of full capacity during peak hour conditions upon full build-out of the development. Using Appendix A in "Open Channel Hydraulics" by Chow, the maximum capacity of an 8" diameter PVC sewer pipe will occur under the following conditions: y/do = 0.75; Using Appendix A the corresponding AR2J3 = 0.2840 do8/3 Calculating AR2i3 = (0.2840) (0.67813) = 0.09645 DeSiLm Specifics: All manholes will be 48-inch diameter with eccentric cone top section. If drop manholes are necessary, the drop will be constructed inside the manhole and a 60-inch diameter manhole will be used. Manholes will have full-depth channels. Manhole spacing will be at maximum intervals of 400'. All sewer mains will be 8-inch diameter PVC pipe. Sewer services shall be 4-inch or 6-inch diameter connected to the main with in-line wyes. Service line stubs will be extended to 8' inside the property line. Service lines will be located 15-feet from the downstream lot line. A 12' wide gravel access road will be constructed to provide access to sanitary sewer manholes not located within a paved roadway or alley. Easements will be provided where sewer mains are located outside the area to be platted. i 1 . 1 L340 {EXISTING OURST NROPD SANITARY S£WETRUtJ425 LF 18" SS 375 LF 18" SS 255 LF 18" SS 255 LF 18" F S' 390 LF OF S" 400 LF OF 9" Il® 0.187._ �� ® 0_27._ p0.18_ L ® 0.1$.: 0,. _ ssO0.4s7. � — 9f - - -T. , yl- 1 DURSTON ROAD I { 1 VALLEY WEST PUD / I 370 LF t2" 1 WASTEWATER DRAINAGE I / SS ® 1.057. 1 AREA 3 BOUNDARY 7 I \ I•' I ALLEY WEST PUD S ASTEWATER DRAINAGE PTF9REA 1 BOUNDARY I I T a1O LF T 2"." SS 0 0.63.� ' , i 1 I) 1T5 LF T2- I . SS .10 0.777; 7 3M LF 12- F— I I ••�SS 0 2.35= 300 LF I I-� '� �u I I � I I — —� — —O— — '—' — — EXISTING SANITARY SEWER TRUNK SYSTEM SS 0 1.66= 1 d! I I —�� u• PROPOSED SANITARY SEWER COLLECTION SYSTEM e I 1 i I o IAS E�...�TE N. CE E S UD /ASTEW ` WASTEWATER DRAINAGE AREA 1 BOUNDARY o . I I I I 400 LF 12" / I P4 ° { SS a 1.0% I J \ CASCADE STREET-Npr WASTEWATER DRAINAGE AREA 2 BOUNDARY G WASTEWATER DRAINAGE AREA 3 BOUNDARY 0 NEW A.A t 0 400 LF 12` ' ^� SS a I.0% / IT200 0 IUD 200 J I (IN FEET) Ir£ST BABCOCX STREET _ 1 I I EXISTING 'COTTONYpOOD ROADF SANITARY SEVER TRUNK T 141QRRISON VALLEY WEST =i MAIERLE,mc. PHASE 3 SEWER EXHIBIT CUENT.ASPP£H FA7FAPPIS£5 02/18105 PLOTTED DATE: Feb/18/2005 FIELD WORK DATE: DRAWNG NAME: DRAWN BY: SMR SCALE: H\3384\019\I \EMHI9DS\PA S.°.r a.El g Ilk, I S I} CHECKED BY.W PROJ q:3384.019 SHEET __l_OF 1 1