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Home My WebLink AboutMONTAVA - PHASE E - TOWN CENTER RESIDENTIAL - BDR220003 - MONTAVA SUBMITTAL DOCUMENTS - ROUND 2 - OTHER WATER AND OR SANITATION DISTRICTS (2)Montava – Phase E Sanitary Sewer Analysis Sanitary Sewer Analysis For Montava – Phase E submitted to: City of Fort Collins , Colorado November, 2022 Montava – Phase E Sanitary Sewer Analysis Sanitary Sewer Analysis – Montava Phase E, Fort Collins, Colorado Purpose The purpose of this analysis is to determine the effluent produced by Montava Phase E based upon the proposed site plans and to determine whether the existing infrastructure can accept the adjusted flows from all sources. Existing Conditions The analysis performed by Martin/Martin, documented by their report Montava – Phase G – Sanitary Sewer Modeling dated April 22, 2022 and previously approved by the Boxelder Sanitation District was used to establish expected flows and expected densities for offsite effluent contributions. Per information provided in the Montava – Phase G – Sanitary Sewer Modeling report, the Storybrook Subdivision was expected to contribute 75 gal/day/person, with an estimate of 3 people to a single-family unit. It was estimated that 142 single family residences were contained within the Storybrook Subdivision, resulting in an approximate average daily flow of 22.19 gal/minute (gpm). As noted in the report, a property to the south of Mountain Vista Drive was determined to contribute flow to the system with a density of 5 dwelling units/acre over an approximate 20 acres, ultimately contributing an approximate daily average flow of 15.625 gpm. Design Criteria The Fort Collins Utilities Water and Wastewater Design Criteria Manual, adopted on May 2, 2017 was used to design the alignment, elevations, and sizing of internal sewer systems for Phase E, with the exception of the portion of sewer system that was already designed by Martin/Martin, as documented in Montava – Phase G – Sanitary Sewer Modeling. The plan set Utility Plans for Montava Subdivision Phase G Roadway and Infrastructure, submitted on November 17, 2022 and prepared by Martin/Martin was also used to help establish proposed alignment, elevations, and sizing of sewer infrastructure for the remainder of the Phase E infrastructure not previously designed by Martin/Martin. Further coordination on final alignment and elevations for Martin/Martin’s “San Line X” and TST’s “EX. SS-03”, “SS-01” and “SS-03” sewer lines will need to be coordinated for future submittals to ensure continuity and design adequacy. The calculations provided in Appendix B are based off of information provided in the Montava – Phase G – Sanitary Sewer Modeling report, which references City and County of Denver design criteria. It should be noted that the suggested sizing provided in Appendix B adheres to City and County of Denver Design Criteria, but that the sizes shown in the Utility Plans for Montava Subdivision Phase G Roadway and Infrastructure plan set have been upsized due to the use of a significantly higher peaking factor. Please refer to Martin/Martin and the Montava – Phase G – Sanitary Sewer Modeling report for the engineering associated with the upsized piping. The portion of sewer mainline designed by Martin/Martin for Phase E reflects what is shown in Utility Plans for Montava Subdivision Phase G Roadway and Infrastructure, submitted on November 27, 2022 to allow for TST to design to the most recently proposed infrastructure. Montava – Phase E Sanitary Sewer Analysis Proposed Conditions The current sanitary system for the proposed Phase E, proposed Phase G, proposed Phase H, existing offsite Storybrook Subdivision, and existing offsite property to the south, will feed into an existing 21” Boxelder gravity main to the east of all three phases and offsite areas. This analysis will include calculations for the flows in each zone, previously established by flow calculated in Montava – Phase G – Sanitary Sewer Modeling, to determine the effluent going to the existing gravity main and to determine if the additional capacity can be accepted. The location of the existing sanitary main and approximate overall areas that drain to proposed infrastructure can be seen in Appendix A. It should be noted that the infrastructure shown as “Potential Future Sewer Alignment” has not yet been designed or calculated and serves only as a suggestion of potential locations for additional infrastructure. In doing so, it can be noted that the infrastructure proposed within Phase E should carry only effluent produced by Phase E users and site pad owners, and that it is unnecessary for this infrastructure to route effluent produced by any of the areas labeled for “Future Development.” Infrastructure routed through the areas labeled as “Future Development” should be able to be routed separately, also minimizing the number of tie-in points to the existing 21” Boxelder Sanitation District mainline. This would be made possibly by using the suggested tie-in point for this eastern portion of proposed development, as it is the same manhole that the infrastructure discussed in this analysis ties in to. The existing 21” Boxelder sanitary main will receive effluent flows from the Storybrook Subdivision, approximately 20 acres of residential development to the south of Mountain Vista Drive, approximately 38 acres of residential development in proposed Phase G, approximately 36 acres of mixed-use development in proposed Phase E, and approximately 16 acres of mixed-use development in proposed Phase H. These plans also show the expected average daily flows from the aforementioned areas to be approximately 264 gpm which was used in the Montava Phase E flow calculations. The same design strategy utilized in Martin/Martin’s Montava – Phase G – Sanitary Sewer Modeling report was also used in the calculations shown in Appendix B, wherein the total flow assumed for each phase, with the exception of Phase G, was applied at the most upstream manhole in each phase. Though the effluent flow will tie into multiple locations along the pipe, this conservative approach ensures that the entire sewer pipe contained within each phase will be sized to carry the expected flow for the entire phase. The average daily flows for the following types of land occupation were established in the Montava – Phase G – Sanitary Sewer Modeling report: • A single-family unit and multi-family unit was assumed to produce an average of 75 gal/capita/day with an assumed occupancy of 3 capita/unit for both single-family and multi-family units. This resulted in a calculated flow of 225 gal/unit/day for both single- family and multi-family units (75 gpd/person x 3 people/unit = 225 gpd/unit). • A mixed-density single family residence (specific to Phase G) was assumed to produce an average of 75 gal/capita/day with an assumed average occupancy of 3.7165 Montava – Phase E Sanitary Sewer Analysis capita/mixed-density single-family unit. It should be noted that this average daily flow rate and density assumption was not noted in Martin/Martin’s Montava – Phase G – Sanitary Sewer Modeling report, but the average daily flow was assumed to be the same as a single-family and multi-family unit, and other information for Phase G usage provided in Montava – Phase G – Sanitary Sewer Modeling was used to back-calculate an approximate density for a mixed-density single family unit. This resulted in an assumed flow of 278.7375 gal/unit/day for mixed-density single-family units (75 gpd/person x 3.7165 people/unit = 278.7375 gpd/unit). • A commercial user (specific to Phase E and H) was assumed to produce an average of 500 gal/day/acre, as noted in the Montava – Phase G – Sanitary Sewer Modeling report. The average daily flow for each area was peaked using a peaking factor (PF) calculated by specifications established by the City and County of Denver Department of Public Works in their Sanitary Planning Criteria. The maximum peaking factor was calculated by the following equation: PF = 2.6 x Q average daily, cfs-0.16. Therefore, the total peaked effluent flows into the existing 21” pipe are expected to be approximately 747 gpm (PF = 2.6*(0.59)-0.16 = 2.83 -> 263.79 gpm x 2.83 = 747 gpm), which is different from the peaking factor used in Martin/Martin’s Montava – Phase G – Sanitary Sewer Modeling report, but is referenced by the City and County of Denver Department of Public Works Sanitary Planning Criteria. Conclusion The effluent produced by the offsite areas and proposed phases discussed above is expected to be adequately captured by the existing 21” Boxelder Sanitation District mainline, due to the conclusions previously established in the Montava – Phase G – Sanitary Sewer Modeling report accepted by the Boxelder Sanitation District. Ultimately, the existing and proposed infrastructure should be able to adequately capture the effluent flows from these sources. Montava – Phase E Sanitary Sewer Analysis References 1. Montava – Phase G – Sanitary Sewer Modeling, April 22, 2022. 2. Fort Collins Utilities Water and Wastewater Design Criteria Manual, May 2, 2017. 3. Utility Plans for Montava Subdivision Phase G Roadway and Infrastructure, submitted November 17, 2022. 4. City and County of Dener Department of Public Works Sanitary Sewer Design Technical Criteria Manual, revised March, 2008. Appendix A Appendix B Table 1. Node Summary Node 0 263.79 0.59 2.83 746.74 1.664 66%15 Node 1 204.37 0.46 2.95 602.64 1.343 80%12 Node 2 94.38 0.21 3.34 314.93 0.702 60%10 Node 3 37.81 0.08 3.86 146.06 0.325 42%8 Node 4 22.19 0.05 4.21 93.34 0.208 27%8 Table 2. Pipe Capacities - 86% Full Pipe Diam. (in)Pipe Radius, r (ft)A (ft2) (full) P (ft) (full) = 2*PI*r R (ft) (full)S (ft/ft)Qfull (cfs)Q86% (cfs)Q86% (gpm) 8 0.333 0.3491 2.094 0.1667 0.0040 0.7663 0.659 296 10 0.417 0.5454 2.618 0.2083 0.0028 1.1625 1.000 449 12 0.500 0.7854 3.142 0.2500 0.0022 1.6756 1.441 647 15 0.625 1.2272 3.927 0.3125 0.0015 2.5086 2.157 968 Table 3. Node Contributions Node 1 204.37 0.46 2.95 602.64 1.343 Phase H 59.422 0.13 3.59 213.51 0.476 TOTAL 263.79 0.59 2.83 746.7 1.664 Attenuation Factor:1 Node 2 94.38 0.21 3.34 314.93 0.702 Phase E 109.99 0.25 3.26 358.13 0.798 TOTAL 204.37 0.46 2.95 602.64 1.343 Attenuation Factor:1 Node 3 37.81 0.08 3.86 146.06 0.325 Phase G 64.10 0.14 3.55 227.55 0.507 TOTAL 94.38 0.21 3.34 314.93 0.702 Attenuation Factor:0.9261 Node 4 22.19 0.05 4.21 93.34 0.208 Unknown S Property 15.625 0.03 4.45 69.52 0.155 TOTAL 37.81 0.08 3.86 146.06 0.325 Attenuation Factor:0.99993 Storybrook Subdivision 22.19 0.05 4.21 93.34 0.208 TOTAL 22.19 0.05 4.21 93.34 0.208 Attenuation Factor:1 Base Flow (cfs) Base Flow (cfs) Base Flow (cfs) Base Flow (cfs) Base Flow (cfs) Base Flow (gpm) Peak Flow (cfs) Peaking Factor Peak Flow (gpm) Base Flow (gpm) Peak Flow (cfs) Peak Flow (cfs) Node 0 Peak Flow (cfs) Peak Flow (gpm) Peaking Factor Base Flow (gpm) Node 4 Base Flow (gpm) Peaking Factor Peak Flow (cfs) Peak Flow (gpm) Node 2 Peaking Factor Base Flow (gpm) Peaking Factor Pipe Capacities (80% depth ~= 86% capacity*City of Denver Design Criteria, minimum slope) using Manning' Eqn (Q = A*1.49/n*R2/3*S1/2) w/ n = 0.013 Montava Sanitary Sewer Analysis Pipe Flow Capacity (Max = 86%) Peak Flow, Qp (gpm) Peak Flow, Qp (cfs) Base Flow, Qavg (gpm) Required Pipe Size (in) Base Flow, Qavg (cfs) Node 1 Node 3 Peak Flow (gpm) Peaking Factor Peak Flow (gpm) Model Assumptions: 0.013 Peaking factorSewer System = 2.6 * Qaverage daily, cfs -0.16 1 cfs =448.8 gpm 1 acre =43,560 sf Existing Condition Assumptions: Storybrook Subdivision (info from M/M & Boxelder San. District): 142 SFR 75 gal/capita/day 3 capita/SFR =0.156 gal/SFRE/minute Average Daily Flow 22.19 gpm =31,950 gpd Property Upstream of Phase G (info from M/M 7 Boxelder San. District): 5 DU/Acre 20 Acre 100 DU 75 gal/capita/day 3 capita/DU Average Daily Flow 15.625 gpm =22,500 gpd Phase E Assumptions (info from M/M & Boxelder San. District): 217 SFR 482 MFR 75 gal/capita/day, SFR or MFR 3 capita/SFR or MFR 97,000 ft2 Commercial 500 gal/day/acre Average Daily Demand, total 109.99 gpm =158,388 gpd Phase G Assumptions (info from M/M & Boxelder San. District): 202 Mixed-density SFR 160 MFR 75.00 gal/capita/day, Mixed-density SFR 3.7165 capita/Mixed-density SFR 75 gal/capita/day, MFR 3 capita/MFR Average Daily Flow 64.10 gpm =92,305 gpd Phase H Assumptions (info from M/M & Boxelder San. District): 31 SFR 270 MFR 75 Mixed Use Units 3 capita/SFR or MFR or Mixed Unit 84,295 ft2 Commercial 500 gal/day/acre Average Daily Demand, total 59.422 gpm =85,568 gpd gpm0.773Average Daily Demand, commercial gpm109.22Average Daily Demand, residential gpm0.672Average Daily Demand, commercial gpm58.75Average Daily Demand, residential gal/capita/day, SFR or MFR or Mixed Use Units75 n =