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HomeMy WebLinkAbout4_Icon Apartments Flow Monitoring and Analysis Memo_pg1-11_05-13-2019memo Page 1 TO: Shawn Kohtz, PE Bob Murray, Jr., PE FROM: James Nickelson, PE DATE: May 13, 2019 – Revision 1 JOB NO.: 5305.005 RE: Icon Apartments – Flow Monitoring and Analysis CC: Kevin Jacobsen, PE - MMI Will Ralph, PE – Blackridge Companies Urgent For Review Please Comment Please Reply For Your Use Wastewater flow monitoring and a capacity analysis was required by the City of Bozeman in support of future phases of the Icon Apartment project. The project is located on West Babcock Street to the east of Cottonwood Road. The overall project has received master site plan approval and as part of that approval process it was determined that there existed potential sewer line capacity issues downstream of the project. The purpose of this memorandum is as follows: 1. Provide information on the flow monitoring that was done in late 2018 2. Provide a review of additional nearby flow monitoring data 3. Summarize the 1998 Valley West Trunk Sewer Line Report and compare the design parameters utilized in the report to current standards 4. Analyze existing and buildout wastewater flows for property within the Valley West Trunk Sewer Line service area 5. Provide the findings of existing conditions scenario 6. Provide the findings of the future conditions scenario 7. Provide the implications on the Icon Apartment Project 8. Summary of Findings 1. 2018 Flow Monitoring – Manhole L-0313 – Flanders Mill Road City of Bozeman provided equipment and staff to set a HACH Flow Meter in Manhole L-0313, located in Flanders Mill Road approximately 1,100 feet north of Durston Road, and Morrison Maierle staff assisted in the set up and data logging. The meter was set on October 19, 2018 and data was collected through December 23, 2018. Due to lack of data caused by meter and battery issues during some of the monitoring period a period from October 20, 2018 through December 5, 2018 was reviewed. The following summarizes flow and depth readings through this period: Icon Apartments – Flow Monitoring and Analysis Page 2 Parameter Average Reading High Reading (1) Low Reading (2) Normal Daily High Reading Flow (gpm) 258 505 92 412 Depth (inch) 3.34 4.75 2.16 4.58 Note 1: The extreme level was 18” for an 8 minute period which was likely due to a downstream blockage. Note 2: The likely blockage also resulted in reverse flow readings. The flow data is presented graphically in Figure 1. Data was collected at 2 minute intervals and the graph presents the data with this averaged to 15 minute time periods. Figure 1 Flanders Mill Flow Data Manhole L-0313 The flow pattern is typical of an area that is predominantly residential. Flows begin rising about 6:00 AM, peak around 8:00 AM, remain relatively constant from 9:00 AM to 5:00 PM, start raising from 5:00 PM to 8:00 PM and then taper off to a low flow from midnight to 6:00 AM. Figure 2 below shows flow during a typical weekday. Icon Apartments – Flow Monitoring and Analysis Page 3 Figure 2 Flow on November 13, 2018 During the low flow hours the introduction of pumped flow into the system becomes obvious. The flow increases approximately 60 gpm and results in an observed increase in volume of approximately 700 to 800 gallon. The Laurel Glen Lift Station has a design pumping capacity of 620 gpm based on the 2006 C & H Engineering Design Report. The C & H Engineering plans show an 8 foot diameter manhole. Data from the Bozeman Water Department indicates that the distance between pump on and pump off limits is 1.8 feet. Therefore during low flow periods the minimum amount of flow pumped per pump cycle is approximately 680 gallons. The design pumped volume is similar to what is computed from the flow data. The station is cycling about 15 times between midnight and 6:00 AM which is approximately 2.5 times per hour. In Figure 3 this information is presented graphically. The SCADA data from the Bozeman Water Department was reviewed to confirm that the number of cycles from the lift station generally conforms to this data. Figure 3 Flow the morning of November 13, 2018 In summary, the flow monitoring shows that flows are consistent throughout the monitoring period, that the daily flow pattern is typical of what is expected in a predominantly residential area, and that flows rise as expected with the introduction of flow from the upstream lift station. 2. Nearby Flow Monitoring Available nearby flow data was reviewed. The most current and applicable data that was found was data obtained as part of the 2015 Wastewater Facilities Plan Update. The Valley West Trunk Sewer drains to the Baxter Interceptor which was monitored for the 2015 Wastewater Facilities Plan Update from April 8, 2014 to June 10, 2014. The period of monitoring would pick up periods of lower groundwater levels in April and also annual high groundwater levels in May in June. The flow monitoring data showed a dry weather average weekday peak flow at this location of 736 gpm and an average flow of 518 gpm. The wet weather peak flow from the flow monitoring was during a rain event. The monitoring data is shown in Figure 4 and the data indicates a relatively constant peak and low flow over the monitoring period. Icon Apartments – Flow Monitoring and Analysis Page 4 Figure 4 - Flow Data - 2015 Wastewater Facility Plan Based on the peak wet weather flow data there is not a significant amount of inflow in the basin from precipitation events. Additionally the data indicates that the infiltration from rising levels of groundwater are not a large contributor to flow in this basin. The average flow at this monitoring location is approximately twice what was monitored in the Flanders Mill Road manhole. This is reasonable as the Baxter Lane manhole has a considerable larger service area. There are also additional connections to consider between the 2014 and 2018 monitoring periods. 3. Valley West Trunk Sewer Line Design Basis The Valley West Trunk Sewer was designed in 1998 at the time the property in the area was annexed into the City of Bozeman. The service area included 726 acres and the design was based on the findings in the 1997 Wastewater Facility Plan. The following key design parameters were utilized: Population Density 13.3 people per acre Wastewater Generation 117 gpd/capita Infiltration 150 gpd/acre Peaking Factor Ten State Standards Formula (DEQ Standard) Mannings Coefficient 0.013 Maximum Pipe Flow 100% 0 100 200 300 400 500 600 700 800 900 1000 4/8/14 4/18/14 4/28/14 5/8/14 5/18/14 5/28/14 6/7/14 gp m Baxter Interceptor Icon Apartments – Flow Monitoring and Analysis Page 5 With the exception of some specific areas, such as Bronken Park and Heritage Christian School, the standard population values noted above were utilized for the design. The design designated the area into 26 drainage zones which were combined to size the sewer line for 11 specific segments. Current design standards vary from those utilized in the 1998 design. These are noted below based on the 2015 Wastewater Facilities Plan Update values: Population Density Variable based on zoning Wastewater Generation reduced to 64.4 gpd/capita Maximum Pipe Flow 75% - based on depth The Valley West Sewer Trunk Line Design Report is included as an attachment to this memo. After construction of the Valley West Sewer, the Laurel Glen Subdivision was approved to connect to the line to utilize some of the excess capacity in the line. This connection point is at the intersection of Durston and Cottonwood Roads. The average flow for the service area was computed to be 727 gpm and the peak flow 2,253 gpm. 4. Valley West Trunk Sewer Line Current Design Flows and Buildout Design Flows Estimate The service area for the Valley West Trunk Sewer Line was reviewed and analyzed under two scenarios. The first scenario was to determine the existing projected flows utilizing current design standards for the developed area within the service area. The second scenario was to add in the vacant and undeveloped land into the equation. The service area is shown and the average flow information is summarized in Exhibit 1. The two scenarios are explained below. The existing estimated design flows were developed using the following parameters: • Residential The residential portions of the service area were determined by using an aerial image dated 2018, Montana Cadastral data to determine the number of condominiums, and Google Street View to confirm findings. Where single family homes were found with accessory dwelling units the lot was counted as two residential units. • Bronken Park, Schools and Churches Design flows were estimated based on literature values and estimates of use and student populations. • Commercial Areas Design flows were estimated based on utilizing the flows from the Valley West Sewer Trunk Line Design Report and prorated on what portions of the property were developed. The future estimated flows were developed using the following parameters: • Residential For residential areas that have been platted and the buildout density could be determined by the number of approved lots or units the actual number of future units was utilized in Icon Apartments – Flow Monitoring and Analysis Page 6 the analysis. For undeveloped residential areas the value from the Valley West Sewer Trunk Line Design Report was utilized with the exception of the Icon Apartments where the full buildout of the approved Master Site Plan was utilized based on the flow values in that approval. • Bronken Park, Schools and Churches The future flows were estimated based on literature values for the park. To be conservative and to account for the undeveloped portions of the Petra Academy, Christ the King Lutheran Church, and Springhill Presbyterian Church that would be developed, the entire parcels were assumed to be based on the per acre design flows from the Valley West Sewer Trunk Line Design Report. In addition it was assumed that the Heritage Christian School would connect to the sewer line as was contemplated in the Valley West Sewer Trunk Line Design Report. • Commercial Areas Future flows were based on the Valley West Sewer Trunk Line Design Report. The following table summarizes the computed existing design flows and the future buildout flows utilizing the above procedures. The flows are provided on an average and peak basis for the entire service area and near the location on Flanders Mill Road where the flow monitoring was completed. Peak flows were computed by taking the average daily flow and calculating an equivalent population using 64.4 gpd per capita and applying the standard City of Bozeman peaking factor formula. Existing Projected Flows Future Project Flows Location Average Flow (gpm) Peak Flow (gpm) Average Flow (gpm) Peak Flow (gpm) Valley West Basin 435 1,127 736 1,879 Near Flanders Mill (L-0313) 369 975 648 1,691 5. Valley West Trunk Sewer Line Existing Conditions Findings The existing flows from the Valley West Trunk Sewer Line basin are less than what is projected utilizing the methods outlined above. The average and peak flows from the flow monitoring and the calculations are summarized in the following table: Location Average Flow (gpm) Measured Average Flow (gpm) Computed Peak Flow (gpm) Measured Peak Flow (gpm) Computed Flanders Mill (L-0313) 258 369 505 975 The averaged measured flow is approximately 70% of the computed flow and the peaking factor based on the flow monitoring is 2.0 and the peaking factor utilized based on the design standards is 3.0. For the full Valley West Trunk Sewer Line basin the modeled peak flow from the 2015 Wastewater Facility Plan Update was 500 gpm (Chapter 5 Overall Improvements Figure) which is in the range of the peak flow of 505 gpm monitored in 2018. Icon Apartments – Flow Monitoring and Analysis Page 7 The flow monitoring that was completed as part of the 2015 Wastewater Facility Plan Update on Baxter Lane included a larger drainage basin then the Valley West Trunk Sewer Line but the data shows that measured flows are less than those derived from computations and that the actual peaking factors are less than those derived from the peaking factor formula. The difference between the measured flow and the computed flow for the Valley West Trunk Sewer Line can be attributed to the following: • The 140 gpd per dwelling unit value developed with the 2015 Wastewater Facility Plan Update is based on a percentage of overall residential flow to the Water Reclamation Facility so includes some infiltration. This value is also a city wide average so includes older portions of the community that have older and less water efficient fixtures than the dwelling units served by the Valley West Trunk Sewer Line. Based on winter time meter residential data, the per capita water use is 45.6 gpd (overall city residential data) which is 29% less than the 64.4 gpd figure from the 2015 Wastewater Facility Plan. All of these factors would suggest that the computed flow value would be higher than the measured flow value. • The computed flows for commercial areas were computed using conservatively high assumptions. 6. Valley West Trunk Sewer Line Future Conditions Findings The future computed flows for the Valley West Sewer Trunk Line are lower than what the Valley West Sewer Trunk Line Design Report was based on. The computed future peak flow for the overall basin is 1,879 gpm while the Valley West Sewer Trunk Line Design Report listed a peak flow of 2,253 gpm. The capacity of the sewer line varies based on pipe size and pipe slope. At the lower end of the basin the pipe is 21” PVC with a minimum slope of 0.124%. Based on full pipe flow the capacity of the line is 2,504 gpm and at 75% flow depth the capacity is 2,283 gpm. Both of these values are higher than the peak flow for the overall basin so the 21” pipe has capacity to serve the buildout of the area including the Icon Apartment Project. The 21” pipe transitions to an 18” pipe near where the flow monitoring location was conducted at and at the location where the flow was calculated in the above tables. The future peak flow at this location is computed to be 1,691 gpm. The minimum slope of this portion of the 18” line is at 0.131%. Based on full pipe flow, the capacity of the line is 1,706 gpm and at 75% flow depth the capacity is 1,556 gpm. These these values are near the computed future peak flow which could indicate capacity concerns. An 18” pipe at 75% flow depth would need to have a slope of 0.187% to provide for flow of 1,858 gpm and if flowing at 100% depth would need to have a slope of 0.155%. The capacity limiting sections if the 100% depth standard is used a length of 513 feet of pipe is undersized (Manhole 5.0 to 5.2 as listed in Figure 5). If the 75% depth standard is used a length of 872 feet of pipe is undersized (Manhole 4 to 5.2 as listed in Figure 5). Icon Apartments – Flow Monitoring and Analysis Page 8 Figure 5 – Manhole 4 to 5.2 In order to check capacity in other portions of the Valley West Trunk Sewer Line that will serve the Icon Apartments the future flow entering the manhole from the west at Flanders Mill and Durston was computed. The future peak flow was calculated to be 1,402 gpm. The pipe line in this area is 18” PVC with a minimum slope of 0.179%. This limiting section of pipe as a capacity of 1,818 gpm at 75% depth and thus has adequate capacity to serve the buildout of the basin. Another area that was checked is the capacity of the most northern portions of the sewer line in Cottonwood Road. The future peak flow in this line at the point it enters the Durston Road line is computed to be 981 gpm. This line is 12” PVC and the limiting section has a slope of 0.362%. This line has a full depth capacity of 962 gpm. The next flattest segment of this 12” line has a slope of 0.59% which results in a full pipe capacity of 1,228 gpm and a 75% depth capacity of 1,119 gpm. The next flattest section of the pipe is at 0.696% which results in a 75% flow depth capacity of 1,216 gpm which can handle the future computed flow. If the 75% flow depth parameter is used the upsizing of 300 feet of pipe (Manhole 8 to 8.1 as listed in Figure 6) would be required to meet the capacity requirements of the computed future flow. Icon Apartments – Flow Monitoring and Analysis Page 9 Figure 6 – Manhole 8 to 8.2 City Engineering Staff is planning on constructing a project this summer that will change the future condition flows for the Valley West Basin. The project includes installing a new sewer line in Cottonwood Road which will divert a portion of the Valley West flow to the Baxter Lift Station. The proposed sewer line will divert all flow from the existing sewer main in Cottonwood south of Babcock to flow in the new sewer line to the Baxter Lift Station. The area that will be diverted is shown in yellow highlighting in Figure 7. Figure 7 - Cottonwood Sewer Project This project will divert 60 gpm of future flow based on an average flow basis. This value was calculated by utilizing the flow values from the Valley West Sewer Trunk Line Design Report with the exception of the TBP Condominium project. The condominium project has a higher density and higher projected flows than was contemplated in the Valley West Sewer Trunk Line Design Report and as such the higher flow value was utilized. Reducing the average flow by 60 gpm reduces the peak flows for the scenarios reviewed with the revised peak flows summarized in the following table: TBP Condominiums Icon Apartments – Flow Monitoring and Analysis Page 10 Location Revised Future Peak Flow Amount Reduced Valley West Basin 1,730 gpm 149 gpm 18” – Near Windrow and Renova 1,539 gpm 152 gpm 18” – Durston and Flanders Mill 1,244gpm 158 gpm 12” – Cottonwood and Durston 810 gpm 171 gpm This reduction in flow will provide capacity for the full buildout of the Icon Apartment Project and the buildout of the full drainage basin. The following table shows the segments of existing sewer lines that were reviewed showing the future peak flows and the capacity of the pipes at 100% and 75% flow depths. Location Revised Future Peak Flow 100% Full Depth Capacity 75% Depth Capacity Manhole 4 to 5 (18” – 359 lf – Slope 0.159%) 1,539 gpm 1,879 gpm 1,714 gpm Manhole 5 to 5.1 (18” – 244 lf – Slope 0.131%) 1,539 gpm 1,706 gpm 1,556 gpm Manhole 5.1 to 5.2 (18” – 256 lf – Slope 0.152%) 1,539 gpm 1,838 gpm 1,676 gpm Manhole 8 to 8.1 (12” – 300 lf – Min Slope 0.362%) 810 gpm 962 gpm 877 gpm Manhole 8 to 8.1 (12” – 175 lf – Min Slope 0.590%) 810 gpm 1,228 gpm 1,119 gpm 7. Implications on the Icon Apartment Project Based on the analysis completed to date the sewer lines that will serve the Icon Apartment Project have capacity to serve the buildout of the project and the drainage basin based on City of Bozeman Standards and MDEQ Circular 2 design requirements. 8. Summary The Valley West Trunk Sewer Line has capacity to serve the full buildout of the Valley West Basin including the full buildout of the Icon Apartment Project. END R-4 80 units B-1 3 acres 42 36 150 units (75 duplexes) ± 12.5 gpm future R-O 8.5 ac 3 4 2 2 2 1 1 1 1 144 4 4 4 3 3 4 73 18 64 82 40 18 2 2 2 2 2 2 2 1 1 2 12 50 current +11 future R-2 21 48 60 10 30* 13 current duplexes 2 future 32* 274331 1 1 1 2 1 21 1 43 6 R-2 10 ac 0 R-4 15.5 ac 4 4 4 4 4 4 4 4 22 2 2 22 2 2 22 2 2 22 2 24 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 22 2 2 44 32 32 2 2 2 2 36 24 32 222 5 5225* 22 current, ± 12 future 45 +5 future 1 1 11 1 1 11 1 1* 1*1*1 1 28 78 86 +4 future 5 48 +2 future 17 +1 vacant lots 18 11 +1 vacant lots 3 3 1 1 1* 1 1 1 1 12 +1 vacant lots park 27 park park 2* 2* 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 49 23 46 129 2 2 2 2 2 2 16 49 12 16 12 2 2 22 2 2 2 2 2 2 4 4 40 5 5 5 55 3 2 2 2 22 61 68 40 2 2 2 2 2 244 4 2 2 2 2 22 2 2 116 2 2 2 2 2 2 22222 2 2 2 2 4 2 2 2 2 2 1 1 1 1 1 1 95 2 2 2 2 2 2 3 2 2 2 2 2 23 68 2 2 2 2 2 2 2 2 2 22 2 76 23 current +2 future 15 3**1**91 7 102 current +6 future R-28.8 acres R-3± 8 acres 146 current +100 future park park R-2 R-3 4.2 ac R-O 8.25 ac 6 existing+8 future Avg flow = 1.8 gpm (not connected to city yet) Avg flow = 0.25 gpm B-230 acres Avg flow = 43.2 gpm from design report ± 200 seats500 studentsand teachers Avg flow = 33 gpm from design report (Estimate 22 now, + 11 future) UMU31 acres Future Avg flow = 33.5 gpm ±230 students andteachers 38 current +14 future 27 52 32 ±50 studentsand teachers 12 10.5ac BP Avg flow =11.34 gpm 36 +9 future Total Avg flow = 59.4 gpm Current = 5 gpm 55 ac x 1.08 = 59.4 gpm Future Avg flow = 3.24 gpm Avg flow = 8.5 gpm Avg flow = 1.0 gpm Icon Apps Phase 1- 216 units (21 GPM) Phase 2- 120 units (11.6 GPM) 4 gpm 1 gpm Avg flow = 43.2 gpm from design report 9 acres9.72 gmpfuture 3 acres3.3 gmp future 84 FIGURE NUMBER © PROJECT NO.DRAWN BY: DSGN. BY: APPR. BY: DATE: COPYRIGHT MORRISON-MAIERLE, INC.,2019 N:\5305\006 - Icon Apts\ACAD\Sewer Modeling\Exhibit.dwg Plotted by cooper krause on May/9/2019 engineers surveyors planners scientists MorrisonMaierle 2880 Technology Blvd West Bozeman, MT 59718 406.587.0721 www.m-m.net 5305.006 EX 1 CPK BOZEMAN MONTANA VALLEY WEST SEWER CAPACITY CPK ICON APPARTMENTS JRN 01/2019 945 CURRENT UNITS (91.7 GPM) Future Flow = 166.5 gpm (from Laurel Glen design report by C&H, 2006) 112.0 GPM CURRENT AVERAGE FLOW 186.2 GPM FUTURE AVERAGE FLOW 298.2 GPM TOTAL FLOW CURRENT DESIGN STANDARD: 2.17 PEOPLE PER UNIT 64.4 GPD PER CAPITA 0.097 GPM PER DWELLING 9.5 GPM CURRENT 23.32 GPM FUTURE 524 CURRENT UNITS (50.8 GPM) 144 FUTURE UNITS (21.3 GPM) 653 TOTAL UNITS (72.1 GPM) 711 CURRENT UNITS (69.0 GPM) 17 FUTURE UNITS + 3.24 GPM (4.89 GPM) 728 TOTAL UNITS + 3.24 GPM (73.9 GPM) FLOW MONITORING MANHOLE L-0313 Avg flow = 43.2 gpm from design report 50 current +11 future Estimated average flow per outlined area (Based on original design report) Number of units per outlined area DURSTON ROAD OAK STREET HUFFINE LANE BABCOCK STREET CO T T O N W O O D R O A D 1 2 3 4 5 2 1 3 4 5 POTENTIAL AREA TO BE REMOVED FROM VALLEY WEST TRUNK LINE AVERAGE FUTURE FLOW = 60.0 GPM