HomeMy WebLinkAbout16723 Laurel Glen Lift Station Capacity Analysis w.Attachments_opt 2021-02-12 LAUREL GLEN LIFT STATION
CAPACITY ANALYSIS
DESIGN REPORT
Prepared for:
Rosa Construction, Inc.
125 Central Ave., Unit 1A, Bozeman, MT 59718
Prepared by:
T
EC IM616.N- il
Engineering and Surveying Inc.
1091 Stoneridge Drive • Bozeman, MT 59718
Phone (406] 587-1115 • Fax (406) 587-9768
www.chengineers.com • info@chengineers.com
Project Number: 16723.7 "
IARK A,
`
May 3, 2020
INTRODUCTION
With the previous phase of the Rosa Apartments project in 2018,C&H Engineering and Surveying
provided a capacity analysis of the Laurel Glen Lift Station (LGLS) to determine if there was
additional capacity remaining in the lift station to allow for the construction of the next phase of
the Rosa Apartments project. To complete this analysis the City agreed to allow C&H Engineering
to evaluate the contributing area to the LGLS using the 2018 city design standards of 2.17 people/
DU, and average daily flow rate of 65 gpcd.
This original analysis (included in Appendix A for reference) was completed as part of an
alternative to upgrading the LGLS with the understanding that, in the future, a portion of the
contributing area to the LGLS would be diverted to the Norton East Ranch Interceptor(NERI) in
Cottonwood Road. This diversion would then provide the additional capacity in the lift station
necessary to finish development of several projects in the LGLS contributing area.
Now, with downstream construction of the Davis Lane lift station scheduled, C&H Engineering
has prepared the following design report to support the proposed diversion to the NERI, and detail
the additional capacity that will be available to the LGLS as a result of the diversion.
The proposed diversion will be made on the 8"sanitary sewer main in Flanders Way, 1 block south
of Oak Street, and will divert 33 acres of Flanders Creek Subdivision to the NERI through Lot 3,
Block 5 Flanders Creek Subdivision. C&H Engineering has submitted a site plan application for
this lot on behalf of Vision Development, LLC. for construction of 12 dwelling units around a
central drive access. Since this project already proposes a sanitary main extension off of Flanders
Way, and proposes an east/west drive access with a public access and utility easement, installing
the sanitary sewer main diversion through this drive access does not negatively impact the
proposed project. This project is also currently on hold at the city until additional sewer capacity in
the LGLS is provided.
UPDATES TO TABLE 1
Table 1 was created with the previous 2018 lift station capacity analysis to compare the originally
allocated design sewer flows from each development contributing to the lift station to how each
development was actually built out. This was completed on a block by block basis with the total
original and actual design flows from each block being compared to determine if any excess
capacity remained in the lift station after build-out of these developments.A complete explanation
of how Table 1 was developed can be found in the 2018 capacity analysis in Appendix A.
In the 2018 analysis,the original flow allocations for blocks that were not yet fully constructed, or
were vacant were reserved, and those blocks were marked as "Not Developed" (ND) in the 2018
flow estimate column of the table. Since then several of these vacant lots have been built out, and
several have approved site plans,so we can now estimate what density of dwelling units is planned
for these lots. The following explanations discuss which blocks were changed between the Table 1
provided in the 2018 capacity analysis, and the Table 1 provided with this report. The blocks that
were updated are shown in red text in the 2020 column of Table 1.
Traditions—Block 1
Block 1 consists of 19 townhouse lots.At the time of this analysis 14 of the 19 townhouse lots have
been constructed. Since the original Block 1 allocation in the LGLS was for 19 units(refer to Table
2 in the 2018 Lift Station Capacity Analysis), and 14 of them have been constructed, Block 1 was
updated in Table 1 to list 19 dwelling units at full buildout.
Traditions—Blocks 5 and 6 (Rosa Apartments)
Since the intent of this analysis is to determine whether there is sufficient capacity in the lift station
for the full-buildout of Rosa Apartments, Blocks 5 and 6,which represent Rosa Apartments,were
updated to show the proposed unit count at full build-out, 194 units. 108 of the proposed 194
dwelling units are currently approved and constructed.
Flanders Creek—Blocks 1, 2, 3, 4, and 6
Since the proposed sanitary sewer main diversion would divert all flow from Blocks 1, 2, 3, and 4
of Flanders Creek to the NERI, the proposed dwelling unit counts in the 2020 Flow Estimate
Column contributing to the LGLS were changed to zero. The 12 units on the eastern side of Block
6 would also be diverted to the NERI, so only 20 of the 32 units in Block 6 would continue to
contribute to the LGLS.
Flanders Creek—Block 5
Block 5 of Flanders Creek Subdivision was originally allocated 4.20 gpm to the LGLS. Several of
these lots have since been built out with multiple residential units, and 3 of them are still vacant.
The diversion to the NERI would also take place in Block 5, and would divert 5 of the 8 parcels
away from the LGLS. Since 2 of the 3 remaining lots have not yet been developed, this analysis
conservatively keeps all of the originally allocated 4.20 gpm of sewer flow for Block 5 allocated to
these remaining 3 lots in Block 5.
Boulder Creek Subdivision
The 2018 lift station capacity analysis determined that only 147 of the proposed dwelling units in
Boulder Creek Subdivision from the platted residential lots and the multi-family lots could be
developed at that time. Boulder Creek was platted with the understanding that the individual
residential lots could be built out, but that the multi-family project could not be fully constructed
until additional sewer capacity was provided. The proposed unit counts at full buildout of Boulder
Creek were added to Table 1 in this analysis to determine if there is sufficient capacity in the LGLS
for full buildout of the multi-family project (R-4 Zoning) in Boulder Creek. Full Build-out of
Boulder Creek Subdivision has the potential for construction of up to 118 dwelling units on the
individual residential lots, and the multi-family project is currently under review at the city for the
construction of 114 residential units.
Westbrook Phase 4 (The Nest)
The Nest PUD has been approved for the construction of 45 dwelling units. The original capacity
allocation in the LGLS for that parcel would only allow for approximately 36 dwelling units. In
order to allow for the build-out of all 45 units, excess capacity from The Lakes at Valley West
Subdivision was dedicated to The Nest project to account for the remaining 9 units. The
correspondence regarding this allocation of 9 dwelling units is included in Appendix B for
reference. Since the Nest is only using 36 dwelling units of its originally allocated capacity, this
value was added to Table 1.
Laurel Glen Block 9 (Jennifer Place Condominiums)
A site plan application for Block 9 of Laurel Glen called the Jennifer Place Condominiums is in the
final stages of review at the City of Bozeman Planning Department. This site plan includes the
construction of 20 residential condominium dwelling units. In anticipation of the approval and
construction of the Jennifer Place Condominiums, Block 9 was updated to show 20 dwelling units
in Table 1.
Valley West Subdivision including the Lakes at Valley West
The original allocation from the 2003 Allied lift station analysis is maintained in Table 1. Also
see the 2018 lift station capacity analysis.
PEAKING FACTOR
Similar to the 2018 Capacity Analysis, in order to calculate the peaking factor for this analysis,the
population of the contributing area to the LGLS was estimated by dividing the total contributing
flow to the lift station (gallons per day)by the 65 gallons per capita per day as listed in the 2018
design standards.
160.90 gpm (Table 1) 231,696 gpd Average Daily Flow to Lift Station
231,696 gpd/65 gpcd = 3,565 people = 3.57 P(Population in Thousands)
This value was then entered into the City's peaking factor calculation to determine the peaking
factor for the lift station.
Qmax 18+PI12
Peaking Factor = ------- _ --------- (P =Population in thousands)
Qave 4+P1/2
Peaking Factor=3.38
INFLOW& INFILTRATION
The 2006 design for the upgrade of the LGLS used the City's design standard estimate of 150
gallons/acre/day of inflow and infiltration(I/I) and applied it to the entire contributing area of the
lift station (Laurel Glen, Flanders Creek, Rosa, and Lakes at Valley West subdivisions). This
resulted in an estimated 32.0 gpm of I/I to be accounted for in the design of the LGLS. During
review of the 2018 Lift Station Capacity Analysis, the City Engineering Department reviewed its
SCADA data for the LGLS and estimated that the actual flow of UI contributing to the lift station is
50 gpm. Therefore, C&H Engineering was instructed to use this new estimate while analyzing
capacity in the lift station, and to provide for additional infiltration resulting from the buildout of
the remaining contributing areas to the lift station. C&H Engineering was also instructed to
account for possible future I/I due to degradation of the area's sewer infrastructure.
The analysis resulted in an expected future I/I flow rate of 57.75 gpm contributing to the LGLS. A
complete explanation of how this value was calculated can be found in the enclosed 2018 Lift
Station Capacity Analysis.
This flow rate of 57.75 gpm is used in the following calculations to determine how much I/I is to be
diverted away from the LGLS with this proposed sewer main diversion.
Contributing area to LGLS(Per 2006 Design Report) = 306.76 acres
57.75 gpm = 83,160 gpd of I/I
83,160 gpd/306.76 acres = 271 gpd/acre of I/I
Contributing area diverted to NERI= 33 acres
33 acres x 271 gpd/acre = 8,943 gpd = 6.21 gpm of M diverted to NERI
Remaining III Contributing to LGLS after diversion = 57.75 gpm— 6.21 pm = 51.54 gpm
CONCLUSION
Based on the Table 1 analysis, if the proposed diversion to the LGLS were to be made, the total
remaining average daily flow that will contribute to the lift station at full buildout is 160.90 gallons
per minute. When this is converted to peak flow and the infiltration rate of 51.54 gpm is included,
the total Peak Flow to the lift station is as follows:
160.90 gpm x 3.38 peaking factor = 543.84 gpm Peak Flow
543.84 gpm +51.54 gpm (Infiltration Rate) = 595.38 gpm Total Peak Flow to Lift Station
The current design capacity of the LGLS is 598.1 gpm based on the 2006 design report. Therefore,
based on this analysis,the proposed sanitary sewer main diversion from Flanders Way to the NERI
in Cottonwood Road would provide sufficient capacity in the LGLS for the full buildout of the
194-unit Rosa Apartments project, and the 114-unit multi-family development in Phase 1 of
Boulder Creek Subdivision. Similarly, since the proposed 12-unit site plan on Lot 3, Block 5 of
Flanders Creek Subdivision will be diverted the NERI, sewer capacity for this project will be
provided as well.
Construction of this diversion cannot be completed until the Davis Lane Lift Station and its
associated trunk main are completed in late 2020, early 2021. It is also understood that the excess
capacity provided by the buildout of the Jennifer Place Condominiums likely cannot be used until
construction of that project is complete. However, the proposed dwelling units for Jennifer Place
Condominiums were added to Table 1 to show that with completion of that proposed condo project
and this proposed sanitary sewer diversion; full buildout of the remaining projects in the LGLS
contributing area is feasible.
ATTACHMENTS
Input Table
Factor Year Value
2006 2.54
People per D.U. 2017 2.11
2018 2.17
2002 72
Gallons Per Capita Per Day 2006 72
2017 89
2018 65
Peaking Factor (per 2002 3.52
design report) 2006 3.4
2020 3.38
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) 1 2002 1 12.19
NOTES
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.
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 2020 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.
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.
Table 1
Original Flow Allocations(2006) 2020 Flow Estimation
Development Dwelling AverageAverage Dwelling Units Average Daily Average Flow
Acres Population Daily Flow Population;
Units (gpd) Flow(gpm) (Ex./Prop.) Flow(gpd) (gpm)
Traditions(Rosa Subdivision)'
Block 1 19 48.26 3474.72 2.41 19 41.23 2679.95 1.86
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
Block4 46 116.84 8412.48 5.84 44 95.48 6206.20 4.31
Block 2.7024 32.97 2373.84 1.65 194 420.98 27363.70 19.00
Block 6 3.6481 44.51 3204.72 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 ND' - - 0.86
Total 23.02 Total 32.98
Flanders Creek
Block 1 2.7198 33.18 2388.96 1.66 0 0.00 0.00 0.00
Block 2 14 35.56 2560.32 1.78 0 0.00 0.00 0.00
Block 3 14 35.56 2560.32 1.78 0 0.00 0.00 0.00
Block4 32 81.28 5852.16 4.06 0 0.00 0.00 0.00
Block 6.8889 84.04 6050.88 4.20 ND' - - 4.20
Block 6 40 101.6 7315.20 5.08 20 43.40 2821.00 1.96
Total 18.56 Total 6.16
Boulder Creek 3
R-3A Zoning(2002) 16.66 203.09 14622.48 10.15 118 256.06 16643.90 11.56
R-4 Zoning(2002) 7.01 85.45 6152.40 4.27 114 247.38 16079.70 11.17
Total 14.43 Total 22.72
Westbrook
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 36 78.12 5077.80 3.53
Total 12.71 Total 9.60
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 (R-2) 3.30 25.15 1810.8 1.26 10 21.70 1411 0.98
Block4 (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 (R-3) 5.40 65.83 4739.76 3.29 40 86.80 5642 3.92
Block (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 20 43.40 2821 1.96
(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 71 154.07 10015 6.95
(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
47 101.99 6629 4.60
(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 3.82 101 219.17 14246 9.89
(R-4) 4.35 53.03 3518.16 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 55.34
Valley West From 2003 Allied"'
R-3 Zoning 40 487.6 35108 24.38
B-1 Zoning 4 13980 g,71 ND' - 49088 34.09
Total 34.09 Total 34.09
Total Avg.Design Flow(gpm) 165.53 Total Avg.Daily Flow(gpm) 160.90
Total Peak Flow(gpm) 562.80 Total Peak Flow(gpm) 543.84
Total Peak Flow Including 32 gpm Infiltration(gpm) 594.80 Total Peak Flow Intl.Infiltration(gpm) 595.38
Lift Station Design Capacity(Per 2006 Design Report)(gpm) 598.2
FIGURE 1 - DWELLING UNITS SERVED
BY LAUREL GLEN LIFT STA TION
LOCATED IN THE NE 114 OF THE SE 114, SECTION 4, T. 2 S., R. 5 E. OF
P.M.M., CITY OF BOZEMAN, GALLATIN COUNTY, MONTANA
LEGEND
®
43 PRO.DWELLING UNITS 114 PRO, DWELLING UN115 VACANT/UNOCCUPIED LOT 6/43 CONSTRUCTED 0/114 CONSTRUCTED ROSA""pROARo APARTMENTS
UNITSI
�..�SUBDIVISION BOUNDARY
LOT BOUNDARY ��"�7FEE7 •T-'�•
—— AREA TO BE DIVERTED TO NORTON �,b uN4rs BLOC T.
8
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24 PRO.DWELLING UNITS NOTES A �NL�1� H4LIN
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1. DWELLING UNITS BASED ON CURRENT AERIAL PHOTOGRAPHY, 20/24 CONSTRUCTED --:.*B ^� �' PHASE 3 �S Wt.
0/12 CONSTRUCTED
SUBDIVISION PLATS, GOGGLE STREET VIEW AND SITE VISITS Y - -�-1� _ �, '� BLOCK 6 `.�
BY C&H ENGINEERING ON 1/30/2018, 4/04/2018, AND oV ; " �6 DWEWNG UNITS4 DWELu"c uN s
5/03/2020. �4 DWELLING UNITS 2. PROPERTY LINES AND SUBDIVISION BOUNDARIES ARE BASED - r _ �PWE�� �4 D:EWNG UNITS 4 DWELLING UNlrS
23 DWEWNG UNITS 12 DWEWNG UNITS
ON CITY GIS DATA AND PLATS AND ARE APPROXIMATE. L, 8NEFiW000 WAY BNERWODD w3. FLANDERS CREEK AND TRADITIONS SUBDIVISION BLOCK 32 DWELLING UNITS L // IT�T1 -�Iwl ' 2G DwewNc uNlrs
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NUMBERS ARE BASED ON NUMBERING AT TIME OF 2006 o —_ _ \ _ _ DwELLI_IN_c.,DNrrs—� TRA 1
LIFT STATION UPGRADE SO THAT CURRENT DWELLING UNIT 20 DWELLING uNl1s ; _ _ � } BO ER -LuI p
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IN 2006 LIFE STATION UP UPGRADE. t0 UNITS or �I CREW .47
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27 DWELLING UNfrS I
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Scale In Feet ! VAL Elf WEST 4 OW LING
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