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HomeMy WebLinkAbout012 Sanitary Sewer Lift Station Analysis 1091 Stoneridge Drive • Bozeman, Montana • Phone (406) 587-1115 • Fax (406) 587-9768 www.chengineers.com • E-Mail: info@chengineers.com Civil/Structural Engineering and Surveying May 28, 2019 Anna Russell, P.E. City of Bozeman Engineering Department 20 E. Olive Street Bozeman, MT 59718 RE: Sanitary Sewer Analysis for Jennifer Place Condominiums MASP (COB #19-153); Dear Ms. Russell, This letter is to provide an analysis of the capacity allocated in the Laurel Glen Lift Station for Lot 1, Block 9 of Laurel Glen Subdivision Phase 1. Several reports have been done to analyze the available capacity in the Laurel Glen Lift Station. This letter will make reference to the original 2002 Lift Station Design Report done by Allied Engineering, and the 2018 Lift Station Analysis completed by C & H Engineering. In the original 2002 report Lot 1, Block 9 was given a sewer designation zone of B-1. Based on the 2002 report B-1 was given a design flow of 3,495 gallons per acre. The 2002 report was done prior to the approval of the final plat of Laurel Glen Subdivision Phase 1, the 2002 report estimated the area of Lot 1, Block 9 to be 3.03 acres. The 2002 report did not account for right of way deductions in the contributing areas, which is why there is a discrepancy in the report lot areas versus the platted lot areas. Because this discrepancy is caused by city right of way the 2002 lot area can be used for the capacity analysis of the subject property. Based on this information Lot 1, Block 9 was allocated the following: 3.03 acres x 3,495 gallons per acre = 10,590 gallons per day (gpd) = 7.35 gallons per minute (gpm) (Average) The original design report assumed a peaking factor of 3.52 based on the anticipated populations of the subdivision. Therefore, the peak hour flow allocated for Lot 1, Block 9 is: 7.35 gpm x 3.52 = 25.8 gpm (Peak) The proposed layout for the Jennifer Place Condominiums consists of (10) 2- Unit Condominiums, or 20 dwelling units total. The City of Bozeman Design Standards and Specifications Policy estimates an average of 2.11 people per dwelling unit and 89 gpd per capita of wastewater production. Using these numbers, the proposed development will contribute the following to the Laurel Glen Lift Station: 2.11 people per d.u. x 10 d.u. = 42.2 people Civil/Structural Engineering and Surveying 42.2 peopole x 89 gpd per capita = 3,756 gpd = 2.61 gpm (Average) Using the Harmon formula, the peaking factor for the development can be estimated as follows: F=(18+P0.5)/(4+P0.5) Where: P = Population in thousands F = Peaking factor F=(18+ 0.0420.5)/(4+0.0420.5)=4.33 Therefore, the peak hour flow entering the lift station from this development is: 2.61 gpm x 4.33 = 11.3 gpm (Peak) Based on this information there is adequate capacity in the Laurel Glen Lift Station to handle peak hour flow from the proposed development. Infiltration was left out of this analysis since it was accounted for in the original report, and the City of Bozeman DSSP uses the same rate (150 gpd per acre). The 2018 analysis prepared by C & H Engineering confirms the allocated wastewater rates for Lot 1, Block 9. The report also provides an analysis of the contributing areas of the Laurel Glen Lift Station to confirm that there is still adequate capacity based on the original allocations. Relevant portions of the 2002 & 2018 reports are included with this letter. If you have any questions or need any more information please give us a call at 406.587.1115. Thank You, Reviewed By: Drew Cater, E.I. Matt Hausauer, P.E. Civil/Structural Engineering and Surveying Appendix A Allied Engineering Report Section (2002) Civil/Structural Engineering and Surveying Appendix B Sewer Zone Map (2002) Boulder CreekWESTBROOKFIGURE 4LAUREL GLEN PHASES 1 & 2 Civil/Structural Engineering and Surveying Appendix C C & H Engineering Report (2018) Table 1 Dwelling Units Acres Population Average Daily Flow (gpd) Average Flow (gpm) Dwelling Units (Ex./Prop.)Population3 Average Daily Flow (gpd) Average Flow (gpm) Traditions (Rosa Subdivision)1 Block 1 19 48.26 3474.72 2.41 ND4 --2.41 Block 2 27 68.58 4937.76 3.43 27 58.59 3808.35 2.64 Block 3 18 45.72 3291.84 2.29 18 39.06 2538.90 1.76 Block 4 46 116.84 8412.48 5.84 44 95.48 6206.20 4.31 Block 5 2.7024 32.97 2373.84 1.65 ND4 --1.65 Block 6 3.6481 44.51 3204.72 2.23 ND4 --2.23 Block 7 8 1.0331 32.92 2370.24 1.65 8 17.36 1128.40 0.78 Block 8 21 53.34 3840.48 2.67 18 39.06 2538.90 1.76 Block 9 4 0.571 17.13 1233.36 0.86 ND4 --0.86 Total 23.01 Total 18.41 Flanders Creek2 Block 1 2.7198 33.18 2388.96 1.66 41 88.97 5783.05 4.02 Block 2 14 35.56 2560.32 1.78 14 30.38 1974.70 1.37 Block 3 14 35.56 2560.32 1.78 ND4 --1.78 Block 4 32 81.28 5852.16 4.06 32 69.44 4513.60 3.13 Block 5 6.8889 84.04 6050.88 4.20 ND4 --4.20 Block 6 40 101.6 7315.20 5.08 32 69.44 4513.60 3.13 Total 18.56 Total 17.64 Boulder Creek3 R-3A Zoning (2002)16.66 203.09 14622.48 10.15 ND4 - 14622.48 10.15 R-4 Zoning (2002)7.01 85.45 6152.40 4.27 ND4 - 6152.40 4.27 Total 14.43 Total 14.43 Westbrook3 Phases 1-3 21.54 179.03 12890.16 8.95 62 134.54 8745.10 6.07 Phase 4 (The Nest)6.17 75.21 5415.12 3.76 ND4 -5415.12 3.76 Total 12.71 Total 9.83 Laurel Glen Phase 1 & 23 Block 1 & 2 (R-3)6.08 74.12 5336.64 3.71 60 130.20 8463 5.88 Block 3 (R-2)3.30 25.15 1810.8 1.26 10 21.70 1411 0.98 Block 4 (B-1)6.18 21599 15.00 31 67.27 4373 3.04 Block 5 (R-3)1.84 22.43 1614.96 1.12 18 39.06 2539 1.76 Block 6 (R-4)5.47 66.68 4800.96 3.33 68 147.56 9591 6.66 Block 7 (R-3)5.40 65.83 4739.76 3.29 40 86.80 5642 3.92 Block 8 (R-2)4.97 37.87 2726.64 1.89 20 43.40 2821 1.96 Block 9 (B-1)3.03 10590 7.35 ND4 --7.35 (R-3A)1.10 13.41 965.52 0.67 6 13.02 846 0.59 Block 10 (R-3A)1.17 14.26 1026.72 0.71 6 13.02 846 0.59 Block 11, 12, 13 & 14 (R-2)3.64 27.74 1997.28 1.39 (R-3A)5.39 65.7 4730.4 3.29 (R-3)4.24 51.69 3721.68 2.58 Block 15 & 16 (R-2)3.84 29.26 2106.72 1.46 (R-3A)4.1 49.98 3598.56 2.50 (R-3)2 24.38 1755.36 1.22 Block 17 & 18 (R-3)6.27 76.43 5502.96 3.82 (R-4)4.35 53.03 3818.16 2.65 Block 19 (R-4)4.13 50.34 3624.48 2.52 24 52.08 3385 2.35 Block 34 - Creekstone (R-3)4.86 59.24 4265.28 2.96 43 93.31 6065 4.21 Total 62.73 Total 60.74 Valley West From 2003 Allied3,5 R-3 Zoning 40 487.6 35108 24.38 B-1 Zoning 4 13980 9.71 Total 34.09 Total 34.09 Total Avg. Design Flow (gpm) 165.53 Total Avg. Daily Flow (gpm) 155.13 Total Peak Flow (gpm) 562.80 Total Peak Flow (gpm) 518.13 Total Peak Flow Including 32 gpm Infiltration (gpm)594.80 Total Peak Flow Incl. Infiltration (gpm) 575.88 Lift Station Design Capacity (Per 2006 Design Report)(gpm) 598.1 Total Excess Flow (gpm)22.22 67.9 2018 Flow Estimation Development Original Flow Allocations (2006) 71 154.07 10015 6.95 47 101.99 6629 4.60 Excess Dwelling Units 14246 9.89 ND4 - 49088 34.09 101 219.17 Factor Year Value 2006 2.54 2017 2.11 2018 2.17 2002 72 2006 72 2017 89 2018 65 2002 3.52 2006 3.4 2018 3.34 B-1 Wastewater Use (gal / acre) 2002 3495 R-2 Population Density (ppl / acre) 2002 7.62 R-3 Population Density (ppl / acre) 2002 12.19 R-3 Population Density (ppl / acre) 2002 12.2 R-3A Population Density (ppl / acre) 2002 12.19 R-4 Population Density (ppl / acre) 2002 12.19 NOTES 3. Boulder Creek, Westbrook, Laurel Glen, and Valley West flow allocations under "Original Allocations" were derived from 2002 Laurel Glen Subdivision Sewer Zone Map so that flow allocations match original lift station design. 4. The constructed dwelling units for the 2018 Flow Estimates were surveyed using final plat records, aerial imagery, and confirmed with a site visit by C&H Engineering. If a portion of the contributing area to the lift station has not yet been constructed, then a "Not Developed" (ND) was placed in that row under 2018 Flow Estimates, and the original flow allocation for that block was preserved. 1. Traditions (Rosa) Subdivision block numbers under "Original Allocations" are labeled based on the preliminary plat of Rosa Subdivision so that dwelling unit estimates per block match what was allocated in the 2006 Lift Station Upgrade Report. See Attached. 2. Flanders Creek block numbers under "Original Allocations" are labeled based on the preliminary plat of Flanders Creek so that dwelling unit estimates per block match what was allocated in the 2006 Lift Station Upgrade Report. Input Table People per D.U. Gallons Per Capita Per Day Peaking Factor (per design report) 5. Per instruction by the City of Bozeman, this analyis assumed that The Lakes at Valley West Subdivision used all of, but not greater than it's flow capacity as allocated by the 2002 Laurel Glen Lift Station Design Report.