HomeMy WebLinkAbout012 Sanitary Sewer Lift Station Analysis 1091 Stoneridge Drive • Bozeman, Montana • Phone (406) 587-1115 • Fax (406) 587-9768
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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.