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Ammon Foothill MPC_WWCollectImpactStdy_JUB_2021-9-29FINAL BCP DEVELOPMENT, INC. Wastewater Collection System Impact Study for Ammon Foothill Master Planned Community Ammon, ID September 2021 J-U-B ENGINEERS, Inc. 275 S. 5th Avenue, Suite 220 Pocatello, ID 83201 208-232-1313 Ammon WW Collection System Impact Study iii Table of Contents Overview .......................................................................................................................................... 1-1 Background ........................................................................................................................... 1-1 Objective of Collection System Impact Study ....................................................................... 1-1 Model of Existing Ammon System ................................................................................................... 2-1 Scope of Analysis ................................................................................................................... 2-1 Existing System Layer ............................................................................................................ 2-1 Existing Model Flow Generation Layer ................................................................................. 2-1 Existing Model Analysis ......................................................................................................... 2-2 Level of Service (LOS) ............................................................................................... 2-2 Existing Depth of Flow over Diameter of Pipe (d/D) ................................................ 2-2 Existing Reserve Capacity ......................................................................................... 2-3 Existing Model Conclusions ...................................................................................... 2-4 Model of Impacts to Ammon’s System ........................................................................................... 3-1 Future System Layer .............................................................................................................. 3-1 Future Model Flow Generation Layer ................................................................................... 3-1 Future Model Analysis .......................................................................................................... 3-1 Summary of Needed Improvements ..................................................................................... 3-2 Impacts to EIRWWA Interceptor ..................................................................................................... 4-1 Summary of Analysis ............................................................................................................. 4-1 Projected Flows ..................................................................................................................... 4-1 AFMPC Flows ............................................................................................................ 4-1 City of Ammon Flows ............................................................................................... 4-1 EIRWWA Flows ......................................................................................................... 4-1 Projected Eastern Interceptor Flows ....................................................................... 4-1 Capacity Summary ................................................................................................................ 4-2 Appendices .................................................................................................................................................... 1 List of Figures Figure 2-1: Depth of Flow (d) to Pipe Diameter (D) or d/D ........................................................................ 2-3 Figure 2-2: Negative Reserve Capacity Illustration .................................................................................... 2-4 List of Tables Table 4-1 – Projected Flows in Eastern Interceptor ................................................................................... 4-2 Table 4-2 – Eastern Interceptor Capacity Summary .................................................................................. 4-2 Ammon WW Collection System Impact Study iv Appendices Appendix A – Figures Ammon WW Collection System Impact Study 1-1 Overview Background The Ammon Foothill Master Planned Community (AFMPC) will discharge wastewater to the City of Ammon’s collection system which will convey the flow to Eastern Idaho Regional Wastewater Authority’s (EIRWWA) Eastern Sewer Interceptor. This interceptor will convey the flow to EIRWWA’s Oxbow Water Reclamation Facility (WRF) is located west of Shelley, Idaho for treatment. The approximate footprint of the AFMPC is shown on the figures included in Appendix A. Objective of Collection System Impact Study This Collection System Impact Study will address anticipated impacts from the AFMPC to Ammon’s wastewater collection system and EIRWWA’s Eastern Sewer Interceptor. The impacts of AFMPC on EIRWWA’s Oxbow WRF are not addressed in this study but will be addressed in a separate “Treatment Impact Study”. Ammon WW Collection System Impact Study 2-1 Model of Existing Ammon System Scope of Analysis The analysis of Ammon’s existing collection system included only the portion that conveys flow to the EIRWWA interceptor. Ammon’s entire collection system was not analyzed. The Existing Model was developed using Innovyze’s InfoSWMM modeling software and the City’s GIS data. Existing System Layer The Existing Model System Layer for the City of Ammon’s collection system is comprised of manholes, gravity sewer pipes, force mains, and lift stations. A map of the Existing System Layer and study area is depicted on Figure A1 in Appendix A. The City’s GIS was used as the main source of information for rim elevations, invert elevations, pipe sizes, and pipe lengths. A review of the GIS data was completed to identify missing or questionable rim elevations, invert elevations, or pipe sizes for the major trunk lines that may be affected by the AFMPC. Missing or questionable data were reviewed with the City to determine the appropriate action to resolve the data gap. The City provided updated GIS datasets with the data gaps resolved. All manholes and pipes in the model have notes documenting the source for both rim and invert elevations. Sources include KA (Keller Associates) survey, Engineering Drawings, City GIS files, or assumed values from interpolation or straight grading. Existing Model Flow Generation Layer The Existing Model Flow Generation Layer was compiled using flow meter data from multiple temporary meter sites included in the 2013 Wastewater Collection System Master Plan (WCSMP). These data were used to determine sewer drainage basins and the locations where they inject into the modeled trunk. The average metered flows were multiplied by an hourly peaking factor of 2.5 found in the 2013 WCSMP to approximate the 2013 peak flows. The 2013 average flows were compared to the 2021 flows measured by the permanent flow meter that is located just west of Hitt Road on 65th South (York Road) that measures and collects flow data for Ammon’s total system. The City provided data from the flowmeter recorded every 15 minutes from May 3, 2021 through August 26, 2021. Earlier data were not available due to calibration issues with the flowmeter. The existing flows in the model were increased by 1.07 million gallons per day (mgd) to match the current average flows recorded by the permanent meter. This increase is likely due to growth that has occurred Ammon WW Collection System Impact Study 2-2 since completion of the 2013 WCSMP. The resulting total peak model flow at the permanent meter location is 2.85 mgd (4.41 cfs) using the 2.5 peaking factor. During the period of data, the permanent meter flows averaged 1.76 cubic feet per second (cfs) with a minimum of 0.83 cfs on May 31st and an instantaneous peak of 2.38 mgd (3.68 cfs) on July 31st during a rain event. This is significantly less than the peak value estimated above for the model, but because the window of data collection is so small, it is likely that higher peak events were not captured. One other note is that Ammon’s 2013 WCSMP (Table 4.4) projected the following total system, peak instantaneous flows for the city: • 2015 – 3.39 cfs • 2020 – 3.54 cfs • 2030 – 5.22 cfs • 2054 – 10.0 cfs Based on this, the current peak flow should be approximately 3.7 cfs. However, the 2013 WCSMP appears to have used an annual growth rate of 1.0% for the period between 2015 and 2020. Actual population growth in the Ammon area has been significantly higher than this which likely explains the higher flows observed from the current service meter data. In summary, a total peak flow of 2.85 mgd (4.41 cfs) was used for the existing model. Existing Model Analysis Figures A2 and A3 show Depth over Diameter (d/D) and Reserve Capacity for the Existing Model, which can be used to identify locations where insufficient capacity issues may exist from existing peak flows. Level of Service (LOS) The City has selected the following criteria for the collection system level of service based on percent full relative to the full pipe capacity: the percent of full capacity must be less than 75% for all pipes during the peak instantaneous flow. Existing Depth of Flow over Diameter of Pipe (d/D) The d/D figure can be used as a quick way to identify the extent of surcharging, if any does occur. This figure includes the effects of backwater from downstream pipe segments, so it shows how full a pipe may get under the modeled conditions. The illustrated pipe shown in Figure 2-1 below represents a pipe flowing less than half full. Ammon WW Collection System Impact Study 2-3 Figure 2-1: Depth of Flow (d) to Pipe Diameter (D) or d/D A pipe that is full would have a d/D value of 1.0. While a pipe flowing half full would have a d/D value of 0.5. Larger pipes can handle more flow than smaller pipes at equivalent d/D values. Also, larger pipes have more reserve capacity per increment of d/D value. The InfoSWMM modeling software reports d/D values based on the hydraulic grade line throughout the collection system. If there is a downstream choke point in the collection system that causes the water to back up and raise the hydraulic grade line to levels above the top of a pipe, InfoSWMM reports a d/D value of 1.0. The d/D values typically vary along the length of pipe segments. Some pipe segments have flows that transition between full or partially full. The d/D values recorded in this report are at the upstream end of each pipe segment in the model and are found in Figure A2. Existing Reserve Capacity An equally important measure of system capacity is reported in the InfoSWMM output as reserve capacity. Reserve capacity is a measure of how much additional flow (mgd) can be added to any given pipe segment based strictly on the Manning’s open channel flow equation. The reserve capacity is individually calculated for each pipe segment without taking into account any backwater that may be present from a downstream choke point; therefore, it does not indicate whether or not surcharging will occur. The reserve capacity figure can be used to identify individual pipes that could be the root cause of surcharging or limited capacity. It is possible in the future as more flows are added to the system that short pipe segments can be identified by the model as having negative capacity even though the flows never fill the pipe to the top. This happens if there are short flat segments of pipe in the system that do not have enough slope to convey the flows based on the Manning’s equation. However, because the pipe segments are short and the downstream pipe segments are steeper, the hydraulic grade line never reaches the top of the pipe. This flow condition is illustrated in Figure 2-2 below. Ammon WW Collection System Impact Study 2-4 Figure 2-2: Negative Reserve Capacity Illustration The pipe segment between the two manholes is so flat that the water is beginning to back up. This is because the capacity of the pipe, based on the Manning’s equation, is less than the peak flow. If the flat pipe segment was much longer, the hydraulic grade line would rise above the top of the pipe. In InfoSWMM, the middle pipe segment gets reported as a pipe with negative reserve capacity even though the water surface never reaches the top of the pipe. Existing Model Conclusions The Existing Model analysis shows no surcharging (i.e., d/D > 1.0) and no insufficient capacity issues (i.e., reserve capacity < 0.0). Ammon WW Collection System Impact Study 3-1 Model of Impacts to Ammon’s System Future System Layer The Future System Layer was developed to take advantage of existing and future public right-of-way where possible and the low-lying areas along natural drainages. The Future System Layer also accommodated LEI Engineering’s anticipated injection locations of the AFMPC development to Ammon’s future system. During the development of the Future System Layer, the following generalized criteria were taken into consideration: • Recommended future routing and pipe sizing from the 2013 WCSMP; • The Hillside Canal is the prevailing topographic feature in the study area. The remaining study area generally slopes to the southwest, away from the east bench area; • Location of where current and future right-of-way is expected to be along section lines, quarter section lines, and extension of existing roads. • Future pipe slopes were planned to be minimum grades as required by 10-States Standards. Sizing of future planned lines was based on the previous 2013 WCSMP sizing, as shown in Figure A4. Some of the study area has sufficient slope to allow trunk lines to be constructed at steeper than minimum grade, possibly with reduced trunk line sizes. However, if trunks are designed and installed at reduced size and steeper slope than identified in this study, care must be taken to ensure future capacities or serviceability are not reduced. Since the exact location of future sewer lines is unknown, a “meander” factor was added to allow for alignment flexibility as development occurs. This safety factor allows each trunk line to “meander” from the location where the AFMPC connects to Ammon’s system and allows for adding up to 20 percent of its length. Future Model Flow Generation Layer The Existing Model Flow Generation Layer was used as the base for the Future Model Flow Generation Layer. New flows added to the Future Model were provided to J-U-B by LEI Engineering. These flows were added to the future model at the two injection locations identified by LEI Engineering. The first injection location will inject a peak flow of 50.5 gallons per minute (gpm) into the existing 8- inch sewer line running parallel to 21st South near Manhole L21-001. The second injection location will inject a peak flow of 998 gpm into a new 18-inch trunk line near the intersection of 1st Street and 52nd East. These injection locations can be seen in Figure A4. Future Model Analysis The Future Model analysis shows the results if all of the future flows are developed without the addition of any relief lines or correction of existing system deficiencies. This helps identify the priorities for Ammon WW Collection System Impact Study 3-2 needed improvements. Figures A5 and A6 show d/D and Reserve Capacity for the existing pipes in Future Model, identifying potential capacity issues in the existing collection system. Summary of Needed Improvements The Future Model analysis shows no surcharging (i.e., d/D > 1.0) in the existing system, but there are two potential bottleneck areas with possible capacity issues (i.e., reserve capacity < 0.0). Both potential bottlenecks occur on Sunnyside Road with the first occurring west of the Crowley Road intersection, and the second at the Dal Avenue intersection. These two potential bottlenecks show a negative reserve capacity but no surcharging. This is the result of a flat pipe in both instances. The maximum d/D is 0.38 ft/ft and 0.39 ft/ft, respectively. Both sections have significant capacity in the upstream and downstream pipes, so they will likely not lead to surcharging under the future AFMPC flow conditions. To serve the entire AFMPC area a new trunk line consisting of 18-inch (3,000 lf), 21-inch (4,550 lf), and 30-inch (5,150 lf) pipes will need to be constructed. This new trunk line will continue north from the existing 30-inch pipe on Crowley Road to 21st South and then east to Ballagio Drive. From Ballagio Drive, the trunk will continue north and then east, crossing to 52nd East and finally north to 1st Street, as shown in Figure A4. This new trunk line will allow for the future abandonment of the The Villas Lift Station, which will be a benefit for the City of Ammon. The existing 30” trunk line on Sunnyside Road and Crowley Road has sufficient capacity to handle the AFMPC flows. The AFMPC does reduce the total capacity of the existing 30” trunk line by approximately 21%. Based on this analysis, no other needed improvements to Ammon’s collection system were identified to provide capacity for the AFMPC. However, it should be noted that this analysis is an approximation based on information that is currently available. The analysis did not include a system-wide evaluation of Ammon’s entire collection system nor did it include master planning for growth beyond the AFMPC. It is possible that the main trunk line may need to be upsized at some future date to serve the AFMPC and other future areas that will develop. In addition, significant information and assumptions were obtained from the 2013 WCSMP which may need to be updated as significant growth and changes to the collection system have occurred since this master plan was completed. When the master plan is updated, this impact study should be refined, and the results updated accordingly. Ammon WW Collection System Impact Study 4-1 Impacts to EIRWWA Interceptor Summary of Analysis The portion of the City of Ammon’s collection system that conveys flow from the AFMPC connects to EIRWWA’s Eastern Interceptor on Sunnyside Road just west of Taylorview Lane. From this location, the interceptor continues generally southwest approximately 13 miles to the Oxbow WRF. The pipe diameter ranges from 30-inch to 48-inch, and the pipe material is Duromaxx HDPE (corrugated exterior with smooth wall interior). For the purposes of this impact study, a fully hydraulic computer model of the interceptor was not developed, but a high level analysis of the interceptor capacity was performed for comparison to anticipated existing and future flows. Record drawings for the interceptor were reviewed, and the interceptor was divided into five segments as designated in the record drawings and defined by pipe size. The minimum slope within each segment was identified, and the maximum hydraulic capacity of each segment was calculated using Manning’s formula based on that minimum slope. A roughness coefficient (Manning’s n) of 0.013 was used in the calculations. The capacity of each pipe segment based a d/D ratio of 0.75 was also calculated as representing a target maximum capacity with contingency for planning purposes. Projected Flows AFMPC Flows The peak flows from the AFMPC at build-out were projected by LEI to be a total of 1,048 gpm (2.33 cfs) as noted earlier in Section 3.2. It is understood that a 15 year build-out period is planned for AFMPC. City of Ammon Flows As discussed in Section 2.3, a current peak flow of 2.85 (4.41 cfs) was used for the City of Ammon (not including the AFMPC). EIRWWA Flows EIRWWA collects flow data for its entire service area from its influent flow meter at the Oxbow WRF. The EIRWWA service area includes not only the City of Ammon but also the City of Shelley and rural areas in Bonneville and Bingham Counties. Observed data from the past several years indicate peak hour flows of 3.5 mgd (5.42 cfs). Projected Eastern Interceptor Flows In the Treatment Impact Study Table 2-1, assumed growth rates for the EIRWWA service area were developed through 2041. The assumed annual rate for growth not including the AFMPC was approximately 2.5% so this rate was used to estimate future flows for the City of Ammon and from EIRWWA’s service area. Ammon WW Collection System Impact Study 4-2 The range of potential flows were estimated that may occur in the Eastern Interceptor over the next 80 years. At its upper end, the interceptor would primarily convey Ammon’s flows. At its lower end, the interceptor at the Oxbow WRF would convey flows from EIRWWA’s entire service area. The flows from AFMPC were added to the peak flows projected for Ammon and the Oxbow WRF to estimate future peak flows in the Eastern Interceptor as summarized in Table 4-1: Table 4-1 – Projected Flows in Eastern Interceptor Capacity Summary Table 4-2 summarizes the maximum available capacity in the Eastern Interceptor in the five segments identified as calculated using the methodology described in Section 4.1. Table 4-2 – Eastern Interceptor Capacity Summary As indicated in the above table: • For Segment 1, the capacity of the 30 inch interceptor between 49th and Sunnyside is 11.9 cfs (for d/D = 0.75) which could be exceeded by Ammon’s flow (including AFMPC) by 2051. • For Segment 2, Ammon’s flow (including AFMPC) may exceed the interceptor capacity of 20.6 cfs by 2074. • For Segment 3, Ammon’s flow (including AFMPC) may exceed the interceptor capacity of 29.1 cfs by 2091. • For Segment 4, Ammon’s flow (including AFMPC) would not exceed the interceptor capacity of 37.1 cfs until after 2101. Year AFMPC Ammon (w/o AFMPC) Total Ammon (including AFMPC) At Oxbow WRF (w/o AFMPC) At Oxbow WRF (including AFMPC) 2021 0.00 4.41 4.41 5.42 5.42 2036 2.34 6.39 8.72 7.85 10.19 2061 2.34 11.84 14.18 14.55 16.89 2101 2.34 31.79 34.13 39.08 41.41 Peak Flows (cfs) Pipe Segment Pipe Diam (inch) Min. Slope Full Pipe Capacity (cfs) Capacity at 0.75 d/D (cfs) 1 - 49th to Sunnyside 30 0.10%13.0 11.9 2 - 65th to 49th 42 0.05%22.6 20.6 3 - Idaho Canal to 65th 42 0.10%31.9 29.1 4 - Just east of New Sweden to Idaho Canal 48 0.08%40.7 37.1 5 - WRF to just east of New Sweden 48 0.15%55.8 50.9 Ammon WW Collection System Impact Study 4-3 • For Segment 5, the interceptor also conveys flows from the New Sweden interceptor and the City of Shelley. Flows at the Oxbow WRF (including AFMPC) would not exceed the interceptor capacity of 50.9 cfs until after 2101. Note that for Segments 2, 3, and 4, flows from developments in the counties between Ammon and Shelley will add to Ammon’s flows and have not been accounted for in the above discussion. A full hydraulic model and master plan of the EIRWWA interceptor and service area are recommended in the future to confirm the projected flows and estimates of available capacity in the interceptor. Ammon WW Collection System Impact Study Appdx 1 Appendices Appendix A – Figures "= "="= "= "= "= "= "= Ross Ave LSRich Lane LS The Villas LS Mountain Bend LS IBSD Wildwood LS Promatory Point LS Taylorview-Judy LS 1st St Community LS Figure A1Figure A1 ExistingExistingSystem LayerSystem Layer . 0 2,000 4,000 ft Date: 9/29/2021 BCP Development, Inc.BCP Development, Inc. 2021 Wastewater CollectionSystem Impact Study Path: \\85-IFFILES\Public\Client Library\FlagshipHomes\GIS\Figures\A1_Existing_System Layer.mxdPipe Size (in) 6 8 10 12 15 18 24 27 30 48 Force main Manhole "=Lift Station Ammon Foothill MasterPlanned Community 1st Street 52nd East21st South Sunnyside Road Crowley RoadAmmon RoadHitt Road49th South 17th Street "= "="= "= "= "= "= "= 1st St Community LS IBSD Wildwood LS The Villas LS Ross Ave LSRich Lane LS Taylorview-Judy LS Promatory Point LS Mountain Bend LS Figure A2Figure A2 ExistingExistingDepth over DiameterDepth over Diameter . 0 2,000 4,000 ft Date: 9/29/2021 BCP Development, Inc.BCP Development, Inc. 2021 Wastewater CollectionSystem Impact Study Path: \\85-IFFILES\Public\Client Library\FlagshipHomes\GIS\Figures\A2_Existing_DepthOverDiameter.mxdDepth over Diameter 0.00 - 0.25 0.25 - 0.50 0.50 - 0.75 0.75 - 1.00 1.00 - 1.50 1.50 - 2.00 2.00 - 5.00 > 5.00 Collector Trunk Force main "=Lift Station Ammon Foothill MasterPlanned Community 1st Street 52nd East21st South Sunnyside Road Crowley RoadAmmon RoadHitt Road49th South 17th Street "= "="= "= "= "= "= "= 1st St Community LS IBSD Wildwood LS The Villas LS Ross Ave LSRich Lane LS Taylorview-Judy LS Promatory Point LS Mountain Bend LS Figure A3Figure A3 ExistingExistingReserve CapacityReserve Capacity . 0 2,000 4,000 ft Date: 9/29/2021 BCP Development, Inc.BCP Development, Inc. 2021 Wastewater CollectionSystem Impact Study Path: \\85-IFFILES\Public\Client Library\FlagshipHomes\GIS\Figures\A3_Existing_ReserveCapacity.mxdReserve Capacity Over Capacity 0.01 - 0.25 0.25 - 0.50 0.50 - 1.00 1.00 - 2.00 2.00 - 5.00 5.00 - 10.00 > 10.00 Collector Trunk Force main "=Lift Station Ammon Foothill MasterPlanned Community 1st Street 52nd East21st South Sunnyside Road Crowley RoadAmmon RoadHitt Road49th South 17th Street ! ! ! ! ! ! ! !!!!!! ! ! ! ! ! ! ! !!!! ! ! ! "= "="= "= "= "= "= "= 1st St Community LS IBSD Wildwood LS The Villas LS Ross Ave LSRich Lane LS Taylorview-Judy LS Promatory Point LS Mountain Bend LS Figure A4Figure A4 FutureFutureSystem LayerSystem Layer . 0 2,000 4,000 ft Date: 9/29/2021 BCP Development, Inc.BCP Development, Inc. 2021 Wastewater CollectionSystem Impact Study Path: \\85-IFFILES\Public\Client Library\FlagshipHomes\GIS\Figures\A4_Future_SystemLayer.mxdPipe Size (in) 6 8 10 12 15 18 24 27 30 48 Force main Manhole "=Lift Station Future Pipe Size(in) 18 21 30 !Future Manhole Ammon FoothillMaster PlannedCommunity AFMPC's Injection Location #1: 50.5 gpm AFMPC's Injection Location #2: 998 gpm1st Street 52nd East21st South Sunnyside Road Crowley RoadAmmon RoadHitt Road49th South 17th Street Ballagio Drive "= "="= "= "= "= "= "= 1st St Community LS IBSD Wildwood LS The Villas LS Ross Ave LSRich Lane LS Taylorview-Judy LS Promatory Point LS Mountain Bend LS Figure A5Figure A5 FutureFutureDepth over DiameterDepth over Diameter . 0 2,000 4,000 ft Date: 9/29/2021 BCP Development, Inc.BCP Development, Inc. 2021 Wastewater CollectionSystem Impact Study Path: \\85-IFFILES\Public\Client Library\FlagshipHomes\GIS\Figures\A5_Future_DepthOverDiameter.mxdDepth over Diameter 0.00 - 0.25 0.25 - 0.50 0.50 - 0.75 0.75 - 1.00 1.00 - 1.50 1.50 - 2.00 2.00 - 5.00 > 5.00 Trunk Collector Force main "=Lift Station Ammon Foothill MasterPlanned Community 1st Street 52nd East21st South Sunnyside Road Crowley RoadAmmon RoadHitt Road49th South 17th Street "= "="= "= "= "= "= "= 1st St Community LS IBSD Wildwood LS The Villas LS Ross Ave LSRich Lane LS Taylorview-Judy LS Promatory Point LS Mountain Bend LS Figure A6Figure A6 FutureFutureReserve CapacityReserve Capacity . 0 2,000 4,000 ft Date: 9/29/2021 BCP Development, Inc.BCP Development, Inc. 2021 Wastewater CollectionSystem Impact Study Path: \\85-IFFILES\Public\Client Library\FlagshipHomes\GIS\Figures\A6_Future_ReserveCapacity.mxdReserve Capacity Over Capacity 0.01 - 0.25 0.25 - 0.50 0.50 - 1.00 1.00 - 2.00 2.00 - 5.00 5.00 - 10.00 > 10.00 Trunk Collector Force main "=Lift Station Ammon Foothill MasterPlanned Community 1st Street 52nd East21st South Sunnyside Road Crowley RoadAmmon RoadHitt Road49th South 17th Street