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HomeMy WebLinkAbout2040 Chapter 09 - Water SupplyCity of Prior Lake Water Supply 2040 Comprehensive Plan Page 689 CHAPTER 9, WATER SUPPLY 9.1 Executive Summary The purpose of this plan is to evaluate and update the City of Prior Lake’s water system plan. This plan will evaluate future design considerations with regards to water system planning and infrastructure, as well as current and future water demands. The existing facilities and infrastructure are discussed along with the condition of the facilities. Future improvements are discussed in this report with the intent of updating the water model to reflect how future improvements will impact average day and maximum day pressures along with maximum day fire flows in newly developed areas based on the City’s future land use planning. The design period for this report is 20 years, yielding a design year of 2037. Future projections for water usage are based on Metropolitan Council population projections and the 2005 through 2016 historical water usage for the City of Prior Lake. Historically, from 2005 to 2016, the City of Prior Lake saw an increase in population served of 16.5%, from 21,395 in 2005 to 25,616 in 2016. Population is a driving factor in water demands and the per capita demand for a community. Historically for Prior Lake, the residential demand and total per capita demands have averaged 70 and 95.3 gallons per capita per day (gpcd) from 2005 through 2016, respectively. Average day demand has remained relatively consistent over the 10-year historical period. The historical average of the average day demand is 2.20 MGD. Maximum day demand has seen a more significant decline since 2005. Two major peaks occurred in 2007 and 2012, which correspond to years with drought and thus increased water usage for activities like lawn irrigation. In 2007, the maximum day demand was 7.03 MGD, while in 2012 the maximum day demand reached 6.61 MGD. Overall, the maximum day demand shows a steadily decreasing demand. The average maximum day demand over the previous 10 years is 5.58 MGD. Evaluation of the categorical water usage indicates that residential water accounts for 76% of the total water used. Irrigation accounts for the second largest use category with 10% of the total water. The City water usage is third at 5% of the total water usage. Commercial water use comes in fourth at 4% of the total water, followed by unaccounted for water (3%) and lastly institutional water (2%). Water demand projections indicate that by the design year of 2037, the average day demand is expected to be 3.13 Million Gallons per Day (MGD) with a maximum day demand of 7.42 MGD. The current Water Treatment Facility (WTF) is designed to handle 7.5 MGD, and the maximum day demand is encroaching the current WTF capacity. Water storage is another important factor in evaluation of the infrastructure. Currently, there is enough storage for current demands however by the year 2040 there will be at a small deficit in storage. However, any clearwell storage from SMSC water treatment facilities is not accounted for in this report. no longer be enough storage for the average gallons per day. Analysis of the storage capacity for future demands indicates that by the design year of 2037, there will be a surplus in storage capacity of approximately 117,000 gallons. AWWA recommends that the storage capacity be equal to or greater than the average day demands. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 690 With a storage capacity of 3.25 million gallons (MG), Prior Lake currently is within this recommendation’s limits. Water supply for Prior Lake is from 7 municipal wells and from two interconnections. The City has two interconnections, one with the Shakopee Mdewakanton Sioux Community (SMSC) and one from the City of Savage. With these two interconnections, the City is provided with a sufficient water supply. However, if these two interconnections are not included, the addition of well 10 is required by 2028 to maintain a firm well capacity (capacity with the largest well out of service) greater than the maximum day demand. Historical water model figures, which are found in Section 9.2 of this report, were used to evaluate the distribution system to ensure it has adequate pressures and fire flows. The water model indicates that the City maintains a pressure of greater than 30 – 40 psi throughout the system at average and maximum day flows. It is recommended by Ten States Standards to maintain at least 35 psi in the system at any one time. The City currently exceeds this recommendation. The City currently has fire flows that exceed 3,500 gallons per minute (gpm) throughout most of the City. The Insurance Service Office (ISO) has recommendations for fire flows based in residential areas. Using these recommendations, the City of Prior Lake was determined to have exceeded the recommended fire flows. Future improvements are based on the future land use map found in Appendix A. The updated water model figures include maps showing: future improvements and infrastructure, average day pressure, maximum day pressure, and maximum day fire flows. The goal for the water model update was to evaluate how future development will affect the pressures and fire flows throughout the system and to determine what new infrastructure and watermains are required to maintain 40 – 50 psi at average day flows throughout the future land use areas. The main improvements to the system include looping new watermains and extending existing watermains to maintain adequate pressure. Future capital improvements along with preliminary costs are presented at the end of this report. This report should be continually updated and modified as the City of Prior Lakes’ water system changes and as water demands change through the design year of 2037. 9.2 Water System Design Criteria A. GENERAL This Section of the Plan develops the performance criteria under which the water system will be evaluated and/or designed. This involves an evaluation of historical population and future growth, water use patterns and projections, water storage requirements, required fire flows, and the distribution system pressure requirements. This section will form the design basis of the Water Plan. The water model for the City of Prior Lake will be instrumental in developing future design criteria guidelines related to the distribution system. B. DESIGN PERIOD Typically, water systems and the infrastructure are designed on a 20-year design period, as there are significant capital improvements required after 20 years to improve hydraulic capacity, efficiency, or by replacing process components. Therefore, the design period for this water plan update will go through 2037. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 691 Future projections for water usage are based on Metropolitan Council population projections and the 2005 through 2016 historical water usage for the City of Prior Lake. The 2005 through 2016 water usage is used as a basis to justify demand projections. It does not mean that the current trends will be exact in future years, but the trends are accurate enough that any departure from projected assumptions is considered minor and will not impact the timing of any recommendations proposed throughout the design period of this report. This plan should be revisited and updated as necessary to ensure that the system implementation is keeping pace with development, and forecasted population and water demands. Generally, every 10 years the recommendations and capital improvements should be refined based on new data and population projections. Another tool that is useful for water use planning purposes is the Minnesota Department of Natural Resources (MN DNR) Water Supply Plan (WSP). The WSP is required every 10 years by each community serving more than 1,000 people. The WSP must be approved by both the MN DNR and the Metropolitan Council as required by law. Since the WSP is required every 10 years, it is recommended to update this Comprehensive plan and the WSP at the same time. The most current Prior Lake Third Generation Water Supply Plan was submitted on October 4, 2017. C. PLANNING AREA The planning area for this report is identified by the City and includes existing land use and future land use for Prior Lake through 2040. The existing and future land use maps are found in Appendix A. The future land use map indicates that there is sufficient land to meet the anticipated growth needs for the City of Prior Lake through 2037. D. POPULATION AND WATER USE Population projections are based on the Metropolitan Councils population projections through 2040. These projections take into account historical population trends, current land use, and future land use to predict populations. 1. Historical Population and Water Use Population is associated with water use more than any other factor. Once a per capita demand is established, it is possible to predict future populations and future water demands using that data. The per capita demand is typically determined based on historical data over the last 10-years omitting extremely high or low demands as they can skew the data and make future projections unrealistic. Table 9.1 shows the 10- year historical population and water demands for the City of Prior Lake. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 692 Table 9.1: Historical Water Demand Year Population (1) Average Demand (MGD) Max Day Demand (MGD) Residential Per Capita Usage (gpcd) Total Per Capita Usage (gpcd) 2005 21,395 1.93 5.66 61.3 90.3 2006 21,542 2.27 5.98 72.7 105.2 2007 22,111 2.44 7.03 80.9 110.5 2008 22,917 2.32 6.42 73.8 101.1 2009 23,335 2.41 5.78 75.0 103.1 2010 22,796 2.11 4.54 68.1 92.6 2011 23,010 2.22 5.00 71.1 96.6 2012 23,385 2.49 6.61 79.8 106.6 2013 24,223 2.25 6.12 69.6 92.7 2014 24,911 2.02 5.10 62.4 81.2 2015 24,732 2.00 4.25 62.3 81.0 2016 25,616 2.12 4.52 62.7 82.7 Average 2.22 5.58 70.0 95.3 (1) Population estimates are from the MN State Demographer From 2005 to 2016, the City of Prior Lake saw an increase in population served of 16.5%, from 21,395 in 2005 to 25,616 in 2016. The population trend has steadily increased over the last 10 years. Based on the historical population, it is anticipated that the projected population will follow similar growth trends. Residential per capita demand is calculated based on the volume of water used by residential customers. The majority of water used within the City is for residential use and is discussed below. The residential per capita demand has averaged 70.0 gallons per capita per day (gpcd) from 2005 through 2016. Typically, it is desirable to maintain a residential demand less than 75 gpcd. Prior Lake’s conservation utility billing and educational efforts will help to keep the residential demand below this threshold. The total per capita demand averages 95.3 gallons per capita per day (gpcd) from 2005 through 2016. When the data from 2011 through 2016 is evaluated, the average day demand is 87 gpcd. This decrease in average per capita demand reflects water conservation measures the City has been implementing for the last several years. The per capita demand had a peak in 2012 due to a relatively moderate drought that occurred that year. This peak does not represent the trend in per capita demand and is considered an outlier in the data set from 2011 through 2016. Future water usage was based on the 2001 through 2016 average per capita demand. Overall, per capita demand shows a decreasing trend over the last 10 years as water conservation measures were implemented and education about water conservation becomes more public and easier to find. Starting in 2014, the City began purchasing water from SMSC. Based on the data in Table 9.1, when the City began purchasing water, the total per capita demand decreased from the previous year’s demands. This could also be attributed to increased rainfall in the Metropolitan region during those years. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 693 Average day demand has remained relatively consistent over the 10-year historical period. The historical average of the average day demand is 2.20 MGD. Similar to the per capita demand, 2012 saw a slight peak in average day demand due to drought conditions that persisted during the summer months. Overall, there have not been any major fluctuations in average day demand. However, the demand has slightly decreased since 2012, which could be represented by increased precipitation and efforts by the City to implement water conservation techniques and programs. Maximum day demand has seen a more significant decline since 2005. Two major peaks occurred in 2007 and 2012, which correspond to years with drought and reduced precipitation. In 2007, the maximum day demand was 7.03 MGD, while in 2012, the maximum day demand was 6.61. Overall, the maximum day demand shows a steadily decreasing demand. The average maximum day demand over the previous 10 years is 5.58 MGD. As the demand continues to decrease, this drives the peaking factor down since the max day demand becomes closer to the average day demand. The most significant decrease in max day demand occurred from 2012 to 2016, which is similar to the average day demand and the total per capita demand over the same timeframe. Maximum day demands are most likely decreasing due to the implementation of water conservation measures and education about conserving water being more easily accessible to customers. The graph below represents the trends in average and maximum day demands from 2005 through 2016. Average Day Demand Max Day Demand 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 2004 2006 2008 2010 2012 2014 2016 2. Water Use by Category One way to analyze water consumption and historical demands is to observe who uses the water. Categorizing water use within a community can provide insight on where to prioritize water conservation efforts and provides valuable information when making future water demand projections. The average water consumption by category for residential, commercial, industrial, and other uses is shown below. Demand (MGD) City of Prior Lake Water Supply 2040 Comprehensive Plan Page 694 As discussed above, residential water usage is the largest category in the City of Prior Lake. The land use promotes residential development driving the water use up in this category. There is limited commercial and industrial development in Prior Lake making these water use categories much smaller than the residential demand. The residential demand consists of typical household uses including lawn and garden watering, flushing toilets and taking showers, running washing machines, cooking, cleaning, and all other household water uses. As shown in Table 9.1, the residential per capita demand is 70.0 gpcd and according to chart above, residential water accounts for 76% of the total water. Irrigation accounts for the second largest use category with 10% of the total water. The City water usage is third at 5% of the total water usage. This category includes water used by the City for hydrant flushing, ice-skating rinks, vehicle washing, backwashing at the Water Treatment Facility and any other water used by the City for daily operations. Commercial water use comes in fourth at 4% of the total water, followed by unaccounted for water (3%) and lastly institutional water (2%). 3. Seasonal Water Use Seasonal water use was evaluated for Prior Lake with results found in Table 9.2. The table shows total volume of water used in the summer months compared to the winter months. For the purpose of this evaluation, summer months were considered May through September and winter months were October through April. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 695 Table 9.2: Average Seasonal Water Demands Year Population Summer Usage (MG) Winter Usage (MG) Summer Per Capita Demand (gpcd) Winter Per Capita Demand (gpcd) 2005 21,395 406 298 52.0 38.2 2006 21,542 515 311 65.6 39.6 2007 22,111 580 312 71.9 38.6 2008 22,917 532 314 63.6 37.5 2009 23,335 561 317 65.9 37.3 2010 22,796 430 341 51.7 41.0 2011 23,010 474 338 56.4 40.2 2012 23,385 579 331 67.8 38.8 2013 24,223 499 320 56.5 36.2 2014 24,911 422 316 46.5 34.7 2015 24,732 409 322 45.3 35.7 2016 25,616 457 316 48.9 33.8 Average 489 320 57.7 36.7 Results indicate that summer demand is on average 33% greater than winter demands. This is evident by looking at the total water usage between the seasons and by looking at the summer per capita demand versus the winter per capita demand. One key reason for larger summer demands is lawn irrigation. Lawn irrigation is commonly a large water use category during summer months that can drive up the total volume of water used during that season. Conserving water with respect to lawn irrigation is discussed in Section 9.4 of this report. The purpose of evaluating seasonal demands is to determine if the City has sufficient infrastructure to handle peak demands. As indicated in Table 9.1, historical maximum day demands are commonly above 5.5 MGD. Evaluating seasonal demands will ensure that consideration is given for planning future improvements to handle the seasonal variations in water demand. The winter usage provides a good baseline water usage while summer water usage provides key design details that should be considered with future planning. Based on the above table, the City has sufficient infrastructure to handle peak summer month flows. However, as the population continues to grow and housing with lawn irrigation expands, this will drive up the summer demands to a point where additional infrastructure may need to be discussed. 4. Projected Population and Water Use Historic water use (average and maximum day demands) and population projections can be utilized to help make future water projections. It is also important to consider changing trends in the amount of growth expected in the industrial and commercial sectors. These consumers can use large volumes of water for process and general operation of industry. Expansions of this sector can greatly influence future water demands. Historically, the City of Prior Lake does not have a large industrial or commercial water demand. Based on 2016 data, the largest commercial or industrial water user required only 0.4% of the total annual water delivered to the distribution City of Prior Lake Water Supply 2040 Comprehensive Plan Page 696 system. There are no known anticipated large volume water users planning on locating in Prior Lake. Commercial and industrial use is anticipated to follow historical trends and grow as population increases. Residential demand will drive future water projections. The future demand forecast is shown in Table 9.3. Table 9.3: Water Demand Forecast Year Projected Total Population (1) Projected Population Served Projected Total Per Capita Water Demand (GPCD) Projected Average Daily Demand (MGD) Projected Maximum Daily Demand (MGD) (2) 2016 25,616 25,616 83 2.12 4.52 2017 25,941 25,941 87 2.25 5.43 2018 26,401 26,401 87 2.29 5.53 2019 26,951 26,951 87 2.34 5.64 2020 27,500 27,500 87 2.39 5.76 2021 28,000 28,000 87 2.43 5.86 2022 28,500 28,500 87 2.48 5.97 2023 29,000 29,000 87 2.52 6.07 2024 29,500 29,500 87 2.56 6.18 2025 30,000 30,000 87 2.61 6.28 2030 32,500 32,500 87 2.82 6.77 2037 (3) 36,070 36,070 87 3.13 7.42 2040 37,600 37,600 87 3.27 7.67 (1) Total Population Projections based on Metropolitan Council population projections (2) Peaking Factor based on historical data (3) Design Year Water demand projections in Table 9.3 were based on historical trends and the increase in population. Metropolitan Council System Statements were used to for population projections through 2040. It is assumed that the projected service population will equal the projected total population as all future residents will be required to connect to the City’s distribution system. The historical total per capita demand from 2011 through 2016 (excluding 2012) of 87 gallons per capita per day (gpcd) was used to make water demand projections through 2040. This excludes 2012, which was a dry year, which led increased water usage and a much higher per capita demand over the previous two years and following four years. It can be acceptable to omit years with extreme drought or extreme precipitation as outliers as they can skew the data and make future projections unrealistic. Based on historical trends in per capita demand and future population projections, it is likely that the total per capita demand will remain consistent around 87 gpcd through 2040. The reason 2011 through 2016 data was used (excluding 2012) was that the City has implemented water conservation measures over the last several years and the per capita demand reflects those efforts. It is important to consider these water conservation measures when making projections as they can help make accurate projections with regards to the City’s plan of conserving water and reducing per capita demands. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 697 The projected average day demand was calculated by multiplying the projected total per capita demand of 87 gpcd by the projected service area population. The projected average day demand shows a slightly increasing demand because the average day demand is calculated based on population. As the population increases and the per capita demand remains constant, the average day demand will slightly increase. By the design year of 2037, a projected average day demand of 3.13 MGD is expected. The projected maximum day demand was calculated by multiplying the average day demand by a peaking factor. The peaking factor used to calculate the projected maximum day demand is the average peaking factor from 2011 through 2016 of 2.41. This peaking factor was used to project maximum day demands up to 2030. Ten States Standards has recommendations for peaking factors using an empirical equation that calculates peaking factors based on a community’s population. Based on Ten States Standards recommendations, as the population increases, the peaking factor will decrease. Therefore, as Prior Lakes’ population continues to increase, they should theoretically see a decreasing peaking factor. Using Ten States Standards recommendations, the peaking factor for 2030 and 2040 are 2.40 and 2.35 respectively. Reducing the peaking factor also accounts for improved technology and more water efficient appliances and water conservation programs that may be implemented in the City. Using these criteria, a projected maximum day demand of 7.42 MG is projected in the design year of 2037. 5. Future Water Storage Requirements AWWA recommends that the storage capacity should equal or exceed average day demands. Considerations for improving storage capacity are based on the existing infrastructure and the ability to maintain a storage capacity equal to or greater than the future water use projections found above. Table 9.4 presents the future storage capacity requirements necessary for Prior Lake. Year Service Area Population Average Day (GPD) Existing Elevated Storage (gallons) Existing Ground Storage (gallons) Storage Excess/ Deficit (gallons) 2016 25,616 2,117,797 1,750,000 1,500,000 1,132,203 2017 25,941 2,253,084 1,750,000 1,500,000 996,916 2018 26,401 2,293,037 1,750,000 1,500,000 956,963 2019 26,951 2,340,807 1,750,000 1,500,000 909,193 2020 27,500 2,388,490 1,750,000 1,500,000 861,510 2021 28,000 2,431,917 1,750,000 1,500,000 818,083 2022 28,500 2,475,344 1,750,000 1,500,000 774,656 2023 29,000 2,518,771 1,750,000 1,500,000 731,229 2024 29,500 2,562,198 1,750,000 1,500,000 687,802 2025 30,000 2,605,625 1,750,000 1,500,000 644,375 2030 32,500 2,822,760 1,750,000 1,500,000 427,240 2037 (1)36,070 3,132,830 1,750,000 1,500,000 117,170 2040 37,600 3,265,717 1,750,000 1,500,000 -15,717 (1) Design Year Table 9.4: Storage Capacity Requirements City of Prior Lake Water Supply 2040 Comprehensive Plan Page 698 Based on the table above, by the design year of 2037, an excess storage capacity of 117,170 gallons are expected. There is enough storage capacity through the design year of 2037. The existing ground storage is included in the capacity because a backup generator is located at the site which can run pumps to convey water into the distribution system during a power failure. Currently, there is enough storage for current demands. However, by the year 2040 there will be at a small deficit in storage. However, any clearwell storage from SMSC water treatment facilities are not accounted for in this report. no longer be enough storage for the average gallons per day. E. DISTRIBUTION SYSTEM REQUIREMENTS 1. Watermain Sizing Requirements Ten States Standards recommends the minimum size of watermain for providing fire protection and serving fire hydrants to be 6-inches in diameter, with larger mains required if necessary. In addition, velocities in long watermain segments should be between 2 and 10 feet per second (fps) with average flows less than 5 fps, with 10 fps being acceptable during emergency withdrawals for short durations. 2. Pressure Requirements Water pressures are subject to individual preference. What some may view as adequate pressure may be viewed as too much or too little pressure. Municipalities are challenged with balancing pressure with demand and capacity of the system along with conservation of water. Typically, higher pressures equate to higher flow rates, but increases the volume of water lost through crack and broken pipes. Ten States Standards recommends the minimum working pressure in the distribution system should be 35 psi with normal working pressures ranging from 60 – 80 psi. The Minnesota Department of Health (MDH) along with Ten States Standards requires the system to maintain a minimum pressure of at least 20 psi at ground level at all points in the distribution system under all flow conditions. This ensures that there is adequate water pressure in the event of a long-term power failure or during an emergency. The City of Prior Lake desires to have at least 40 – 50 psi in the distribution system for normal operation. Future consideration should be given to new developments to maintain pressures greater than 40 – 50 psi. 3. Water Distribution Model The water model for Prior Lake was updated for this report to show the impacts of future improvements to the system. Future improvements are discussed in Section 9.3 of this report. The model was updated based on future zoning within the City of Prior Lake. The projected water model including an updated anticipated distribution system map, anticipated average and maximum day pressure maps, and an anticipated maximum day fire flow map are provided in Section 9.3. The improvements relate to improving fire flow where possible and adding new watermain into areas that are slated for future development. The water model should be used as a tool to evaluate if additional infrastructure is required in the distribution system. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 699 9.3 Existing Water System Facilities and Infrastructure A. General The City of Prior Lake water system consists of seven (7) active wells (includes one well used for peak demands only), two (2) elevated storage tanks, one (1) booster station, one (1) pressure service area, four (4) pressure reducing valves, and a system of trunk and lateral watermains varying in sizes from 6 inches to 24 inches. Existing trunk watermain and major water system infrastructure are presented in Figure 9.1. B. Water Supply 1. Wells The City of Prior Lake’s water supply currently consists of seven wells. A summary of the existing well data and pumping capacities is presented in Table 9.5. Table 9.5: Prior Lake Well Information Well No. 3 4 5 6 7 8 9 Year Installed 1973 1975 1988 2001 2003 2006 2007 Inner Casing Dia. (in.) 16 16 24 & 16 30 & 24 12 24 N/A Total Depth (ft) 364 345 372 410 640 402 N/A Capacity (gpm) 1200 1100 1000 1200 450 1200 450 Capacity (MGD)(1) 1.44 1.32 1.20 1.44 0.54 1.44 0.54 (1) Assumes wells pump for 20 hours per day Wells 7 and 9 are the lowest producing wells available, with each having a capacity of 450 gallons per minute (gpm). Wells 3, 6, and 8 are the largest capacity wells, each capable of producing 1,200 gpm. However, well number 6 is not connected to the City’s Water Treatment Facility (WTF) and is only used to supplement the water supply to meet maximum day demands. All the wells pump water from the Prairie du- Chein Jordan Aquifer. One way to evaluate the pumping capacity and the ability of the wells to meet maximum day demands, it to evaluate the total and firm well capacities. The total well capacity is the total capacity of all the wells pumping together to supply water. The firm well capacity is the pumping capacity of all the wells without the largest producing well in service. Typically, firm well capacity is used to measure whether there is enough supply to meet demands. If the firm well capacity is not greater than or equal to the maximum day demand, then there is insufficient water supply to provide enough water to meet demands. Table 9.6 presents the total and firm well capacities for the Prior Lake wells based on pumping for 20 hours per day or 24 hours per day. Using 20 hours per day for well pumping is typical, as it allows for pump maintenance, partial aquifer recharge, and pump cycling based on elevated storage tank levels. Pumping for 24 hours represents an emergency in which the City is trying to supplement an City of Prior Lake Water Supply 2040 Comprehensive Plan Page 700 extremely large demand by running the wells constantly. Table 9.6: Prior Lake Well Pumping Capacity to WTF Item 20-Hour Pumping (1) 24-Hour Pumping (1) Firm Capacity Total Capacity Firm Capacity Total Capacity Well Capacity (gpm) 4,200 5,400 4,200 5,400 Well Capacity (MGD) 5.04 6.48 6.05 7.78 (1) Firm and Total Capacities do not include Well No. 6 as this well is available for emergency use only City of Prior Lake Water Supply 2040 Comprehensive Plan Page 701 Water Modeling City of Prior Lake Figure 9.1: Existing Water Distribution System March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 702 2. Interconnections To supplement water supply and to make up for deficits in pumping capacity during maximum day demands, the City of Prior Lake has agreements with the Shakopee Mdewakanton Sioux Community (SMSC) and with the City of Savage to purchase water to supplement the City’s water supply. The agreement with Savage allows the City to use up to 1 million gallons of water per day. The current agreement between SMSC and Prior Lake allows Prior Lake to purchase up to 2.2 million gallons of water per day. As the population of SMSC grows and water use increases, the total volume of water the City can utilize decreases to 1.5 million gallons. However, the City will always be able to use up to 1.5 million gallons of water per day in the future from SMSC per the agreement. Table 9.7 shows the total capacity including the amounts available from SMSC. Table 9.7: Prior Lake Well Pumping and SMSC Capacity Item 20-Hour Pumping (1) 24-Hour Pumping (1) Firm Capacity Total Capacity Firm Capacity Total Capacity Well Capacity (MGD) 5.04 6.48 6.05 7.78 SMSC Capacity (MGD) 1.5 1.5 2.2 2.2 Total Capacity (MGD) 6.54 7.98 8.25 9.98 (1) Firm and Total Capacities do not include Well No. 6 as this well is available for emergency use only The City began using the interconnection with SMSC in 2014. Since then, they have purchased 159, 231, and 270 million gallons of water in 2014, 2015, and 2016, respectively. The interconnections with SMSC and Savage have helped provide a supplemental water source to meet the City’s maximum day demands. 3. Impacts on Aquifer Pumping Levels The City of Prior Lake monitors their supply wells with their SCADA system. The SCADA system collects readings on the well water levels every 15 minutes. The data that is collected can be used to view trends in the water levels to adjust the well to optimize pumping or to determine if there is an issue with the supply in the well. The resulting well hydrographs are presented in Appendix B. It is important to note that the data is presented as the monthly average well water level. The hydrographs show that well water levels are either stable or show an increasing trend. An increasing trend means that the water levels are rising over the monitoring period. Based on the hydrographs, wells 3, 5, 6, 7, and 9 show stable trends in water levels. Even though the well water levels appear to fluctuate significantly through the monitoring period, as can be seen for Well No. 7, the overall trend remains stable. Wells 4 and 8 show an increasing trend in water levels over the monitoring period. One piece of data that can be collected from the hydrographs is the feet of fluctuation of the water levels. Observing the seasonal variation of water level can help determine City of Prior Lake Water Supply 2040 Comprehensive Plan Page 703 if there are times of the year when a well has limitations or if there is an issue if pumping capacity becomes limited. Overall, none of the wells for Prior Lake fluctuate significantly. During the drought in 2012, almost all wells have a significant drop in water level elevation. 2012 was the summer that put extreme stress on the water system as peak day demands became very large. Even with the higher than normal usage in 2012, the well water levels recovered to previous levels within the next couple of years. Prior Lake’s wells appear to be stable with no significant concerns over water levels at each well. Gaps in the data indicate a time when the SCADA measurement system was not properly calibrated, or it was non-functional. C. WATER TREATMENT FACILITIES Prior Lake has a single Water Treatment Facility (WTF) with a design capacity of 7.5 MGD. The WTF was constructed in 2009 with the intent of removing iron (Fe) and manganese (Mg) from the raw well water. Water quality data is discussed later in the Section. The facility has an aerator to oxidize the iron and manganese in the water. Water then flows into a detention tank to allow the oxidized particles to settle. The detention time is approximately 30 minutes. After detention, the water enters one of six gravity filters. The filters are dual media filters comprised of a silica sand under anthracite coal. There is approximately 30 inches of media in each filter (15 inches of each material). Potassium permanganate is added prior to the water entering the filters. The purpose of the potassium permanganate is to oxidize any remaining manganese in the water. The filtered water is collected in a 1.5-million-gallon water reservoir. Water is transferred to the distribution system by the High Service Pumps (HSP). Chemical additions and their purpose include: • Chlorine – used for disinfection • Fluoride – used to help prevent tooth decay • Polyphosphate – used to prevent corrosion in the distribution pipes The WTF is operated by a Supervisory Control and Data Acquisition (SCADA) system. A large diesel generator serves as a backup to run the WTF in the event of a power failure. The WTF is designed based on a 20-year design period and is capable of handling current average and max day flows as determine by the analysis in Section 9.2 for future demands. With proper maintenance and upkeep and with the data provided in Table 9.3, the WTF has adequate capacity. D. WATER DISTRIBUTION SYSTEM The water distribution system consists of all the components necessary to convey water from the wells or storage facilities to customers in the system. 1. Piping Network/Watermain Routing The City of Prior Lake water distribution piping consists of 6 inch through 20-inch diameter cast or ductile iron pipe. The larger (16 – 20 inch) pipes run under large trunk highways. These pipes convey large volumes of water throughout the City until smaller lateral pipes (less than 16 inch) convey water in neighborhoods. The majority of watermain in the City ranges from 6 inch to 10 inch. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 704 The watermains are looped within the City as to not have a dead-end pipe, which could create water quality concerns. The watermains loop around and connect so the water flows in a path. Parts of the system do have branched systems that are not looped. Consideration should be given to looping larger diameter watermains with future expansion. Extending watermain to future developments and providing looping can help with maintaining adequate system pressure. Hydrant flushing is an important maintenance activity to clean out dead end watermains. The City has been proactive in performing hydrant flushes on critical watermains. The water distribution-piping network has been well maintained and will continue to serve the customers of Prior Lake. 2. Pressure Service Areas Prior Lake is served by a single pressure service area from two elevated storage tanks and one reservoir at the WTF. Four (4) Pressure Reducing Valves (PRV’s) on the northern edge of town help by regulating pressures in neighborhoods whom could otherwise have extremely high or low pressures. There are two booster stations in the City. One serves one area in the northwestern side of town near the Wilds golf course and the other serves the Summit Preserve area just north of Co. Rd. 42 and east of Co. Rd. 18. 3. System Pressures As discussed above, the City of Prior Lake is served by a single pressure service area. Both elevated towers and the ground reservoir serve the entire City. Figure 9.2 presents the existing average day pressures throughout the distribution system. Based on the figure, a majority of the City has pressures greater than 50 psi. Around the lake, (typically areas with the lowest elevation) pressures are in excess of 70 psi. This covers the downtown area of Prior Lake as well. Areas on the far southern and western areas of the City have pressures that dip down into the 40 – 50 psi range. Only areas that are near the city limits have pressures in the 30 – 40 psi range. However, development is limited in these areas. The area around the Wilds golf course has pressures ranging from 50 – 70 psi. The system appears to have adequate pressures to supply water at average day demands throughout the City. Figure 9.3 presents the existing system maximum day pressure. This is the pressure throughout the system during maximum day demands. When compared to Figure 9.2, the maximum day pressures slightly decrease throughout the City. Areas around the lake (typically the lowest portions of the City) maintain a similar system pressure around 70 – 80 psi (within 10 psi of average day pressures). The greatest impacts during maximum day are on the South side of the City where in some neighborhood’s pressures drop from 70 – 80 psi down to 50 – 60 psi. The downtown area of Prior Lake still maintains adequate pressures during max day demands with pressures ranging from 50 – 70 psi. Even though these are impacted the most, the system pressure is still adequate throughout the City. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 705 Figure 9.5 shows the existing Hydraulic Grade Line (HGL) throughout the City as indicated by the model. The HGL is consistent between 1,000 – 1,200 feet for a majority of the City. On the outskirts of town, in areas where development is limited, the HGL begins to decrease. This is due to less water infrastructure in these areas and the limited development. The majority of the City maintains a sufficient HGL according to the water model. Figure 9.6 indicates that the HGL ranges from 950 – 1,200 feet during maximum day demands. Again, on the western and southern edges of the City where development is limited and there is less infrastructure, the HGL begins to decrease in elevation. Even still, the majority of the area in City limits maintains an adequate HGL during maximum day demands. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 706 Water Modeling City of Prior Lake Figure 9.2: Existing Average Daily Pressure March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 707 Water Modeling City of Prior Lake Figure 9.3: Existing Maximum Day Pressure March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 708 E. WATER DISTRIBUTION FACILITIES 1. Pressure Reducing Valves Four (4) Pressure Reducing Valves (PRV’s) are used on the norther edge of the City to help maintain adequate pressures. The PRV’s are operated and maintained by the City. These stations help prevent excess pressures in the areas around the Wilds golf course. The PRV’s are in good condition. In addition, there is a check valve located downstream of the Summit Preserve neighborhood at the intersection of Kensington and Co. Rd. 42. The check valve is meant to keep high pressure flow from moving south of Co. Rd. 42. However, should the Summit Preserve booster station fail or be taken off line for some reason, water would still be able to flow into the Summit Preserve neighborhood through the check valve. 2. Booster Stations Currently, Prior Lake operations one booster station located just west of the intersection of Wilds Parkway NW with Wood Duck Trail NW. The area around the Wilds golf course is at a higher elevation than a majority of the City. The existing water towers do not provide sufficient hydraulic grade to maintain adequate water pressures in this area. The booster station helps to increase water pressure and flow in this area. Based on the water model shown in Figures 9.2 and 9.3, the booster station maintains a pressure of greater than 40 – 50 psi during both average day and maximum day. The booster station is in good condition to continue to supply water for future demands. A new booster station is planned to be installed in 2018 in the Summit Preserve area. The current model for maximum day pressures (Figure 9.3) indicates that at the north side of the development, pressures drop to around 30 - 40 psi. This new booster station will increase pressure and flows to the new Summit Preserve development. F. WATER STORAGE FACILITIES 1. Types and Capacity of Storage Facilities Currently, the City of Prior Lake has three storage facilities totaling 3.25 million gallons of storage capacity. There are two elevated storage facilities with a capacity of 1.75 million gallons. In 2009, the City constructed a new Water Treatment Facility (WTF), which contains a large reservoir that has pumps and backup generator. Since there are pumps and a generator that can pump the water in the event of a power failure, the 1.5-million-gallon reservoir at the WTF is included in the total storage capacity. A summary of the storage facilities is presented in Table 9.8. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 709 Table 9.8: Water Storage Facilities Summary Structure Name Location Type of Storage Structure Year Constructed Primary Material Storage Capacity (Gallons) South Tower Tower St. SE Elevated storage 1973 Steel 750,000 North Tower Cedarwood St. SE Elevated storage 1986 Steel 1,000,000 WTP Clearwell 16335 Itasca Ave. SE Ground storage 2009 Concrete 1,500,000 Total 3,250,000 AWWA recommends that the storage capacity should equal or exceed the average day demand. Based on the historical data provided in Table 9.1, the current storage capacity is adequate for current average day demands. Using Table 9.4, the analysis of storage capacity, and the future average day projections, by 2025 there is an estimated average day demand of 2.61 MGD yielding a surplus storage capacity of 644,000 gallons. Looking at 2030, the projected average day demand is 2.82 yielding a surplus in storage of 427,000 gallons. By the design year of 2037, an excess of 117,000 gallons of storage capacity is expected. There is enough storage capacity for the City of Prior Lake through the design year. Both elevated towers are in good condition and have several more years of useful life remaining. 2. Minimum Use One way to evaluate the adequacy of storage capacity is to evaluate the minimum use to see if there is sufficient turnover of water during winter months to prevent freezing in the storage facilities. A good rule is to allow water to turnover every couple of days in the winter. Currently, the average day demand averages approximately 2.22 MGD. Utilizing the full storage capacity of 3.25 MG, the water turnover is about every 1.5 days. Using the future demands, by 2037 the average day demand is anticipated to be3.13 MGD, yielding a turnover every 1.03 days (if no extra storage facility is constructed). Based on this simple analysis, there is enough storage supply and water turnover in the City to prevent water from freezing in the towers during winter months. 3. Existing Fire Demand Requirements Water modeling can be used to evaluate available fire flows in a City. This can be beneficial for planning purposes when evaluating distribution system improvements. The guide for determining required fire flows is developed by the Insurance Service Office (ISO). When designing future improvements, it is important to account for needed fire flows. The needed fire flow differs between structures and building types such as residential, commercial, or industrial. For single-family homes, the following table should be considered for needed fire flows. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 710 Table 9.9: Needed Fire Flows for Residential Homes Distance Between Buildings (ft) Fire Flow (gpm) More than 100 500 31 - 100 750 – 1,000 11 - 30 1,001 - 1500 Less than 11 1,501 – 2,000 Continuous 2,500 Commercial and industrial needed fire flows are determined on an individual basis by evaluating the occupancy area, communication factor, exposure factor, and if a sprinkler system is installed. Typically, most systems require only 500 – 1,000 gpm of needed fire flow if a sprinkler system is installed and up to 500 gpm of additional flow if a sprinkler system is not installed. Figure 9.4 presents the City of Prior Lakes’ existing maximum day fire flows. As can be seen on the map below, a majority of the City has a fire flow greater than 3,500 gpm. Areas with less flow are found on the end runs of watermains and along runs with smaller diameter watermains. The lowest available fire flow according to the model in Figure 9.4 is between 1,000 and 1,500 gpm. Small areas around the north end of Lower Prior Lake have the lowest available fire flow. These areas are on the end of the smaller diameter watermains. However, these areas still have sufficient fire flows based on the discussion and table above. Overall, the City of Prior Lake has sufficient fire flow protection. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 711 Water Modeling City of Prior Lake Figure 9.4: Existing Maximum Day Fire Flow March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 712 Water Modeling City of Prior Lake Figure 9.5: Existing Average Daily Demand - Hydraulic Grade Line March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 713 Water Modeling City of Prior Lake Figure 9.6: Existing Maximum Daily Demand – Hydraulic Grade Line March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 714 G. WATER QUALITY 1. General The purpose of this section is to evaluate the water quality of the Prior Lake Water System and detail the treatment methods used. The section will also detail the current drinking water standards and how the Prior Lake water quality compares to these standards. 2. Water Quality and Treatment The Prior Lake water quality is considered good. The water is considered potable since it does not exceed any limits set forth in the National Primary Drinking Water Standards. However, due to iron and manganese levels present in the aquifer, the water exceeds levels above the National Secondary Drinking Water Standards. The Secondary Drinking Water Standards has limits of 0.3 mg/L for iron (Fe) and 0.05 mg/L for manganese (Mn). Excessive iron and manganese can cause red and black stains when the water is used for irrigation and other household uses. It can also create taste and odor problems and cause plumbing issues over time. Well No. 6 and 7 are the only two wells that have iron levels that exceed the Secondary Standard of 0.3 mg/L. All of the wells exceed the Secondary Standard of 0.05 mg/L for manganese. Table 9.10 identifies the well manganese levels and the respective concentrations and loads based on the well pumping capacity. Well water is typically blended from certain wells to achieve a lower overall manganese concertation entering the WTF. As seen in Table 9.10, each well (except well 7) accounts for approximately 23% of the total manganese load pumped from each well. Table 9.10: Well Water Quality Well No.(1) Well Flow (gpm) Well Flow (2) (MGD) Manganese Concentration (mg/L) Manganese Load (lbs./day) Percent of Total Manganes e Load 3 1,200 1.44 0.28 3.36 23.1% 4 1,100 1.32 0.319 3.51 24.1% 5 1,000 1.2 0.343 3.43 23.6% 7 450 0.54 0.199 0.90 6.2% 8 1,200 1.44 0.278 3.34 23.0% (1) Well No. 9 data was omitted as data was not available at the time this report was written Assumes pumping at 20 hours per day The City’s current water treatment facility (WTF) uses an aerator, chemical addition, and gravity filtration to oxidize the iron and manganese in the water and remove it from solution. Details of the treatment facility are discussed in Section 9.3 of this report. The WTF is very effective at removing iron and manganese levels to below the National Secondary Drinking Water Standards. Table 9.11 represents the average iron and manganese concentrations and loads that enter the WTF and the average effluent concentrations and loads leaving the WTF. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 715 Table 9.11: Iron and Manganese Removal Raw/Treated Constituent Average Concentration (mg/L) Mass Load (lbs./day) Raw Iron 0.22 3.92 Treated Iron 0.01 0.27 Raw Manganese 0.53 9.62 Treated Manganese 0.03 0.63 On average, 9.62 lbs/day of manganese enters the WTF in the raw water supply. The manganese load in the effluent is 0.63 lbs/day, approximately two times the load of iron leaving the filters. The mass loadings were calculated based on the average daily flow from the last six years (2010 – 2016) of 2.17 MGD. Effluent iron concentrations average 0.01 mg/L and effluent manganese concentrations average 0.03 mg/L. Overall, the filter achieves a 93% removal of iron and 93% removal of manganese producing an effluent water quality higher than the standards set in the Secondary Drinking Water Standards. a) Fluoridation Fluoride is added to the treated water before it is sent into the distribution system. Fluoride is added to aide in cavity protection for customers and prevents tooth decay. b) Chlorination The City disinfects the supply water using chlorine as a primary disinfectant. The City uses free chlorine as the source of chlorine. This is achieved by breakpoint chlorination where chlorine is added at a specific dose which oxidizes all of the natural or added ammonia in the water until all that is left is the free chlorine molecules. This type of disinfection provides a stable and powerful disinfectant that inactivates organisms in the water and provides a suitable residual in the distribution system. 3. Current Drinking Water Standards The City follows all of the enforcement standards set forth in the Environmental Protection Agency’s National Primary Drinking Water Standards. These standards are enforceable limits that each public water supply system must adhere to and provide annual updates to the public. Prior Lake accomplishes this in the annual drinking water report. 4. Proposed Drinking Water Standards With the current WTF treating for iron and manganese and removals below the National Secondary Drinking Water Standards, the City is sending treated water into the distribution system that is safe and sustainable for customer use in the City. The City will continue to monitor water quality per Federal and State regulations. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 716 9.4 Water Conservation A. General The purpose of this section is to discuss how water conservation plays a key role in future water planning and how these concepts can be implemented by the City. Water conservation is becoming an important issue where water is viewed as an important resource. Conserving water may help with demand reduction and relaxes stress on the distribution system and wells during high usage months. Water conservation can include a vast range of techniques and strategies from the addition of rain barrels to capture rainfall for lawn irrigation, to drip irrigation systems for larger gardens, to even replacing regular household appliances with energy and water efficient appliances. This section will discuss concepts for reducing water use, and peak day demands along with the current water rates and the water lost throughout the system and how they relate to water conservation B. Reducing Use Reducing water use is one of the largest factors for decreasing the per capita demand and water lost through the system. Most of the water in a community goes towards residential use. As discussed earlier in this report, residential water use includes water used in all household appliances, cooking, cleaning, toilets, showers, and lawn irrigation. Seasonal usage can affect what water is used for with respect to residential demand. Typically, commercial and industrial demands remain relatively constant throughout the year, as the day-to-day operations of the facility do not change significantly. Reducing water use in these facilities involves discussion with the owner and what techniques may work for each industry or business. During winter months, a baseline demand can be established because almost all of the residential water is used for normal household uses with the exception of lawn irrigation. This baseline demand can give an estimate to how much water is required for residential customers on a regular basis with no lawn irrigation. However, during summer months when lawn irrigation is at a peak, this seasonal demand can play a large role in how much water is required for customers. The analysis of seasonal demands is discussed in Section 9.2 of this report. The analysis concludes that the summer demand is on average, 33% greater than winter demands. Seasonal peak water demands are often the result of lawn irrigation. Keeping up with peak demands requires the construction of additional water supply and storage facilities sooner than they may be otherwise warranted. If a City is treating this water that may mean expansion or addition of the Water Treatment Facility (WTF), just to keep up with these demands. With an average of 76% of water going to residential use, lawn irrigation can play a major role in the seasonal demand for this customer category. Currently, the City has sufficient water supply with the interconnections to keep with the maximum day demands and seasonal water use. However, if future water use continues to grow without any sort of water conservation measure to limit irrigation, Prior Lake may be required to add Well 10 sooner than anticipated. Reduction of lawn irrigation to help control demands is typically accomplished through odd- even day or even time-of-day watering restrictions. Prior Lake currently has an City of Prior Lake Water Supply 2040 Comprehensive Plan Page 717 ordinance for odd-even day watering that has helped reduce peak day and seasonal demands. The City has also been proactive in implementing a tiered rate structure that bills more for higher water usage. This has helped reduce water usage over the past few years as is evident in Table 9.1 (Historical Demands). The City currently bills water customers on a bi-monthly basis. The City should consider monthly billing as a method to help with conservation as customers will see and track their usage more frequently and have a chance to make changes on usage more quickly. This would require additional time by the City to put together customer bills and possibly reconfiguration of the City’s billing system/software. The water rate system is a two-tier system for usage rates. The City should consider adding a third, higher rate on high usage. Many other communities have a three-tier system with the higher tier targeting those high usage customers. Reducing water lost in the system is accomplished through leak detection and annual water audits. The City currently performs a leak detection on a third of the City each year. This means that every three years the entire City will have updated leak detection results. It is important to use the leak detection information yearly for Capital Improvement Planning to target areas where the volume of water lost in the system is greatest. Water losses can also be targeted by installing new enhanced meters and repairing and recalibrating current meters. Water conservation is a key factor in reducing water use. Conservation measures typically involve education along with an incentive and regulation to encourage water conservation. While some of these measures such as: billing inserts on water conservation or rebates for installing a water efficient appliance or grant programs for adding rain barrels, can help with reducing water use, they will not completely eliminate the need for additional wells or water storage. However, they could delay the implementation of the infrastructure or reduce the total future required capacity. C. Reducing Peak Demands Historically, the maximum day demands for Prior Lake frequently exceed 5 MGD as indicated in Table 9.1. These peak day demands typically occur in the summer months when lawn irrigation is at its highest. The water used for lawn irrigation is typically what drives maximum day demands. The volume of water devoted to lawn irrigation can be moderated by the odd-even day watering restriction. There has been moderate success in Prior Lake since this restriction has been implemented. This restriction may help reduce seasonal demands due to lawn irrigation, but it does not significantly reduce overall use. Reducing overall use involves more complex water conservation techniques as discussed above. Reducing the peak demands may help reduce stress on the water supply and distribution system. Evaluation of historical demands indicates that over the past few years, peak demands have been decreasing or slightly lower than the previous 10-year average. One contributing factor could be that Prior Lake has been dedicated to improving the efficiency of the distribution system and increasing efforts related to water conservation. One of the City of Prior Lake Water Supply 2040 Comprehensive Plan Page 718 key elements that has helped reduce peak demands is the implementation of the tiered rate system that bills more for higher water use. By continuing to manage the rate system and make changes as necessary, this may help by controlling the peak day demands experienced during summer months when water usage is greatest. D. Water Rates As stated above, the City of Prior Lake has a tiered rate system for residential customers that bills out bimonthly with the volume reported in thousands of gallons of water used. This type of billing is considered conservation billing and has helped the City reduce overall water usage since its implementation. By having water bills reported in gallons, it allows customers to easily see how much water they use in a given billing period, so they can manage their own water usage and how much they are willing to pay for water. The City currently has a two- tiered system that bills rates as follows: • $4.53 per 1,000 gallons for the first 25,000 gallons • $6.25 per 1,000 gallons for water usage over 25,000 gallons The City evaluates water rates on a yearly basis and updates them as necessary. The latest rate adjustment was made in January of 2017. E. Water Loss The City of Prior Lake has submitted their Third Generation Water Supply Plan (WSP) to the Minnesota Department of Natural Resources (DNR). In the preliminary WSP, unaccounted for water is estimated at approximately 6.9% (2005 – 2016 average). When evaluating the 6- year average (2011 – 2016), the unaccounted-for water averages 2.8%. The reason the 2005 – 2016 unaccounted for water is higher is because from 2005 – 2007 Prior Lake had unaccounted for water greater than 10% each year. Since then, the unaccounted-for water has significantly decreased and has remained less than 7% per year. The DNR has a threshold of keeping unaccounted for water less than 10%. Based on the available data, Prior Lake is well below the 10% threshold. However, over the last 11 years the 6.9% average unaccounted for water equates to approximately 55 million gallons of water lost. Lost water can attribute to leaks from the system, unmetered use (i.e. firefighting, street sweeping, ice rink flooding, hydrant flushing, construction etc.), or even unauthorized use. Water losses means lost revenue to the utility of the water is not metered or if it lost due to leaks in the system. With the addition of enhanced water meters on commercial buildings and automated meters in residential homes, this has helped reduce the amount of water that goes unmetered in the system over the last several years. Maintaining a meter change-out schedule and/or a maintenance schedule can help reduce the errors due to water meters. As stated earlier in this report, the City conducts a leak survey on a third of the City every year. This helps find and stop leaks that are occurring the City to reduce the amount of water lost. The leak detection is an important part in system maintenance that should continue yearly to stop leaks and prevent large volumes of water from leaking and not being metered. Identifying and correcting leaks early enables utilities to minimize costly City of Prior Lake Water Supply 2040 Comprehensive Plan Page 719 repairs of large watermain failures, and to avoid premature expansion to supply and treatment and storage facilities. Another important tool that can be used to help track water losses is a water audit. This can be as simple as tracking the total volume of water pumped in a year and comparing it to the volume of water billed to customers. These two numbers should be relatively close to each other. If they are significantly different, that could indicate that water is being lost in the system somewhere, which results in lost revenue. Overall, Prior Lake has a lower percentage of unaccounted for water and they have implemented and maintained a quality leak detection program. These efforts should help track water losses to keep them at a minimum. 9.5 Recommended Future Improvements A. General This section details recommended future improvements to Prior Lakes’ water system to improve the water supply, treatment, distribution system, and storage facilities. The recommended improvements are based on evaluation of the existing facilities discussed in Section 9.3 and the projected water demands evaluated in Section 9.2. This Section includes the updated water system model to show how the infrastructure improvements discussed below affect average and maximum day pressures, as well as maximum day fire flows. B. Water Supply Analysis of the water supply indicates that Prior Lake does not require additional wells at this time. However, it is desirable to maintain a firm well capacity (capacity with the largest well out of service) greater than the project maximum day demand. Currently, with operating the wells at 24 hours per day, the City has a firm well capacity of 4,200 gpm, or 6.05 MGD. Future demands indicate that sometime around 2025, maximum day demands will become greater than the firm well capacity. However, the City has the agreement with SMSC to purchase a maximum of 2.2 MGD and a minimum of 1.5 MGD and this capacity allows the City to push well 10 to 2037. The agreement with SMSC is a key component of the City’s water system and affords the City the capacity needed so no major water improvements are needed. It is noted to look at adding well 10 in 2037. It is best to evaluate the long-term water supply plan for Prior Lake to discuss if there is a desire to add well 10 or maintain the interconnections with SMSC and Savage. C. Water Treatment Facilities The current WTF has adequate capacity for current and future demands. The facility adequately removes iron and manganese from the water to below National Secondary Drinking Water Standards. No future improvements are necessary at the WTF. Proper maintenance is an important element in the operation of the WTF. Equipment and coating systems should be inspected every 20 years and replaced or repaired as needed. To ensure proper operation of the WTF filters, a filter evaluation should be done every 5 – 7 years. This will help operators understand the “health” of their filters and to help eliminate potential future problems with the media. The filter evaluation will also help City of Prior Lake Water Supply 2040 Comprehensive Plan Page 720 determine if the media should be replaced and approximately, when it should be replaced. D. Water Distribution System The following are recommended improvements to the distribution system. Improvements were based on the existing water model figures provided in Section 9.3 of this report and the existing and future land use maps in Appendix A. The goal was to try improving the ISO classification with respect to maximum day fire flows and pressures throughout the system to meet demands for future development. It was assumed that areas with residential usage would be similar to historical demands with regards for required flows and that industrial demands would be similar to historic demands. These assumptions were used only to update the water model to evaluate required watermain looping and infrastructure required for the future land use depicted in Appendix A. The actual development or infrastructure should be an integral part of the City’s planning and the water distribution system should be developed around the actually planning documents. 1. Watermain The City of Prior Lakes’ distribution system currently consists of watermains ranging in size form 6 inches up to 20 inches. As the system continues to grow (as depicted by the maps in Appendix A and this Section), the need for additional watermain increases. The new watermains should be added to the system to strengthen the existing loops or to create new loops in areas not currently served by the distribution system. Looping watermains in the most effective method for increasing average and maximum day pressures as well as increasing the fire flow in an area. Figure 9.7 depicts the anticipated future improvements to the distribution system with regards to locations for placement of new watermains. The intent is to show general locations and preferred looping routes. The actual implementation and placement of the watermains should be integrated in consideration with other utility installations and actual planned developments and roads. The main areas of focus for the addition of watermain were on the west and north sections of the City. These areas will see substantial future development according to the future land use map. To best serve these areas, future watermain additions were developed based on the watermain currently installed with sizing and looping additions used to maintain adequate pressure and fire flows. Based on Figure 9.7, the proposed watermain additions on the west side of the City include extending the 16-inch watermain that currently terminates north of highway 13, along highway 13 to the southwest. This new 16-inch watermain would serve the areas that the future land use map in Appendix A depicts as primarily industrial and urban low-density residential land use. Looping this new 16-inch watermain through these sections will provide adequate flows and pressures to these areas. In addition, extending the 20” watermain that is currently installed up to the intersection of Marschall Rd. at Belmont Ave. NW, to the west and south along Marschall Rd., will provide adequate flows and the ability to loop watermain through these areas. Additionally, more loops can be created depending on how the development in these City of Prior Lake Water Supply 2040 Comprehensive Plan Page 721 areas progresses. Some ideas for additional loops include adding 8-inch loops through residential neighborhoods and extending 10-inch or 12-inch watermains through industrial developments. The new 16-inch watermain would be connected to the existing watermain that runs around the north end of Upper Prior Lake. On the north side of the City, the projected land use is a mix of urban low-density to urban high-density housing with additional industrial land throughout. To best serve this area, the existing 16-inch watermain that runs along County Road 42 can be extended into the northwest corner of the City. This loop would serve the projected residential demand. Additionally, to help maintain adequate flows and pressure, the 16-inch watermain from the SMSC WTP, would be extended North along County Road 82 and ultimately connect to the 16-inch watermain on County Road 42. To meet demands in the north-central section of the City, the existing 12-inch watermain running along County Road 21 would be extended east and west to serve the projected residential and industrial areas. A new 12-inch watermain would also be extended north along Pike Lake Trail NE to the City limits. This 12-inch line would also have an 8-inch line running to the east. Several pressure-reducing valves are required in this scenario to help even out the pressures. The additional loops created pockets of low or high pressures that are regulated by using the PRV’s. Average day pressures throughout the City are depicted in Figure 9.8. With the addition of the new watermain loops to serve the future development areas, the City can expect to maintain an average day pressure ranging from 70 – 90 psi in the western section of the City. The pressures here would be adequate for future residential and industrial development as depicted in the future land use map in Appendix A. In the north section of the City, average daily pressures in the new land use areas range from 70 – 90 psi with some areas having pressures in the 50 – 60 psi range. As noted above, this area has several PRV’s added. The PRV’s were added to isolate the Summit Preserve development and allow the new booster station to increase the pressure, and to control pressures in the areas between County Roads 18 and 21. These PRV’s help to maintain the pressures above 70 psi for a majority of the area. Figure 9.11 indicates that the Hydraulic Grade Line (HGL) throughout the City will remain constant between 800 – 1,200 feet with the watermain additions shown in Figure 9.7. This is adequate for future average day demands. Maximum day pressures using the updated water model are found in Figure 9.6. In the western section of the City, maximum day pressures ranging from 60 – 80 psi can be expected. A majority of this area depicted in Figure 9.9 will have a pressure of approximately 70 psi. In the northern section of the City, maximum day pressures drop to around 50 psi west of County Road 21, but the majority of the area still maintains pressures greater than 50 psi. Based on Figures 9.8 and 9.9, with the addition of new watermain loops, the City can expect to maintain average day and maximum day pressures greater than 50 psi in all areas. Figure 9.12 indicates that the HGL throughout the City will be constant in most of the City between 1,160 – 1,220 feet. Areas on the North side of the City can expect to have a HGL between 1,100 – 1,160 feet. The change in HGL is due to the elevation change in the topography. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 722 Overall, the HGL is adequate for future maximum day demands. 2. Fire Flow Based on the current model, most of the Prior Lake has a fire flow greater than 3,500 gpm, with the lowest modeled fire flow of 500 gpm in small areas around Lower Prior Lake. The lowest fire flows are in areas with dead end watermains. However, these areas are directly adjacent to, or are surrounded by areas with fire flows greater than 3,500 gpm. Overall, the City already has fire flows that exceed recommendations found in Table 9.9 above. The addition of new watermain will still help increase the available fire flow in areas around the City limits and in all future development areas. The additional watermains increased the projected maximum day fire flows to greater than 3,500 gpm in all future land use areas. This indicates that the looping and sizing of watermains was adequate to provide enough fire flow to meet the criteria set up in Table 9.9. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 723 Water Modeling City of Prior Lake Figure 9.7: Anticipated Water Distribution System March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 724 Water Modeling City of Prior Lake Figure 9.8: Projected Average Daily Pressure March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 725 Water Modeling City of Prior Lake Figure 9.9: Projected Maximum Day Pressure March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 726 Water Modeling City of Prior Lake Figure 9.10: Projected Maximum Day Fire Flow March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 727 Water Modeling City of Prior Lake Figure 9.11: Projected Average Daily Demand – Hydraulic Grade Line March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 728 Water Modeling City of Prior Lake Figure 9.12: Projected Maximum Daily Demand– Hydraulic Grade Line March 2018 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 729 E. Water Distribution Facilities 1. Pressure Reducing Valves The existing pressure reducing valves (PRV’s) are in adequate condition for several more years. With proper maintenance and upkeep, they should continue to function as intended. The check valve at Kensington and Co. Rd. 42 is new and with proper maintenance will serve the City for a long time. Additional PRV’s may be necessary as shown in Figure 9.7 to control the pressure gradients on the north side of the City. The reason the PRV’s were added here was to isolate the Summit Preserve development to allow the booster station to increase the pressure. It is important to note that not all of the PRV’s may be needed depending on how future development progresses. Additional loops may be added to negate the need for some of the PRV’s. 2. Booster Stations The existing booster station near the Wilds golf course is in adequate condition for current and future demands. It is recommended to continue with proper maintenance on the station and infrastructure associated with it. One improvement that is currently in the construction phase is the addition of the Summit Preserve booster station. This booster station will be located in the Summit Preserve area and will be operational in 2018. Currently, there are several homes being constructed in this new development. There is a large elevation change in this area as well that will require additional hydraulic lift to maintain water pressures at the highest elevation. F. Water Storage Facilities 1. Storage Requirements AWWA recommends storage capacity equal to or greater than average day demand. Based on the analysis in Section 9.2 of this report, the City of Prior Lake will have approximately 117,000 gallons of excess storage capacity by the design year of 2037 per this report. There is currently enough storage capacity to meet future average day demands up until 2037. No future improvements are required for storage facilities at this time. The recommendation is to continue with proper maintenance and to evaluate the towers as needed to determine the adequacy of the coating system to ensure that it has several more years of useful life. The analysis in Section 9.3 of this report indicates that the fire storage capacity is adequate for current and future flows. However, the needed fire reserve plays a critical role in the needed storage capacity for a water system. Any type of progress that can be made, such as an ordinance requiring fire suppression systems in all new buildings, are important considerations that will help reduce the total volume of water required for fire flows and fire storage. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 730 9.6 Economic Analysis A. General This section presents the general cost estimates and Capital Improvement Planning (CIP) schedule anticipated per the discussion of this report. For watermain, the City’s policy is the developer is responsible for installing 8-inch piping and the City pays for the upsizing anything larger than 8-inch. Per our future watermain figure the lineal feet of piping and pipe sizing is determined and Table 9.12 shows the amount of future watermain and the City and developer portion of the future watermain costs. Table 9.12: Future Watermain Costs Length of Water Proposed Unit Price Main Size Water Main ($ per foot) Developer (inches) (feet) City Cost Cost Total Cost 8 28,905 $50 $0 $1,445,250 $1,445,250 10 85 $60 $850 $4,250 $5,100 12 10,230 $80 $306,900 $511,500 $818,400 16 27,940 $95 $1,257,300 $1,397,000 $2,654,300 20 6,970 $120 $487,900 $348,500 $836,400 Subtotals $2,052,950 $3,706,500 $5,759,450 The cost estimates provided in this section are preliminary cost estimates. Table 9.13 in section B presents the CIP. City of Prior Lake Water Supply 2040 Comprehensive Plan Page 731 CAPITAL IMPROVEMENT PLAN AND COST ESTIMATES 2027 Year 2028 Table 9.13: Cost and Implementation Schedule Item 2018 2019 2020 2021 2022 2023 2024 2025 2026 2029 2030 2031 2032 2033 2034 2035 2036 2037 Well 10 $800,000 Water Tower- Cleaning/ Misc. Repairs (2) $10,000 $20,000 $20,000 Water Distribution System Improvements (1) $105,000 $1,110,000 $110,000 $115,000 $100,000 $100,000 $100,000 $100,000 $100,000 $100,000 $100,000 $100,000 750 Kgal Water Tower – Coating Reconditioning $800,000 1.0 MG Water Tower – Coating Reconditioning $1,250,000 Booster Station- Summit Preserve $650,000 Water Treatment Facility: 20-year Renovations $800,000 Water Treatment Facility Filter Evaluation $15,000 $15,000 $15,000 $15,000 DNR Water Supply Plan $30,000 $30,000 Annual Total $755,000 $1,110,000 $110,000 $115,000 $15,000 $110,000 $0 $900,000 $0 $145,000 $20,000 $900,000 $1,250,000 $100,000 $15,000 $920,000 $0 $100,000 $0 $145,000 (1) 2018 – 2021 costs are from the 2017 – 2021 CIP for Prior Lake (2) Water Tower Cleaning includes the cost for cleaning both the 750 Kgal and the 1.0 MG towers together City of Prior Lake Water Supply 2040 Comprehensive Plan Page 732 C. TRUNK WATER FEE The trunk water fee is setup to pay for future watermain oversizing and for future capacity of the system and ensures the City is collecting adequate trunk water charges to pay for these future capital projects. The main future capital costs are as follows: WTP Expansion at SMSC $11,000,000 Well No. 10 $2,000,000 Watermain Oversizing $2,052,950 Total $15,052,950 D. FUNDING Several sources are available for funding the above projects. The City of Prior Lake can also choose to fund the projects by bonding themselves or using cash reserves. It may be more beneficial to receive state funding for larger projects such as WTF renovations or water tower renovations as these can cost significantly more than a watermain replacement project. For these projects, the state of Minnesota has the Public Facilities Authority that funds projects through the Drinking Water Revolving Fund. This requires placement on the Project Priority List to receive funding for drinking water projects. The City can also choose to try and receive different grants to fund the above projects if they are eligible. Appendix A: Existing and Future Land Use Maps 734 735 Appendix B: Well Hydrographs *Note: Static water level measured on 4/14/1973 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 737 Prior Lake Well No. 3 Water Elevation Well Water Elevation Static Water Level* 885.00 880.00 875.00 870.00 865.00 860.00 855.00 850.00 845.00 840.00 Water Level Elevation (ft) *Note: Static water level measured on 7/10/1995 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 738 Prior Lake Well No. 4 Water Elevation Well Water Elevation Static Water Level* 890.00 885.00 880.00 875.00 870.00 865.00 860.00 855.00 850.00 845.00 840.00 835.00 830.00 825.00 Water Level Elevation (ft) *Note: Static water level measured on 4/6/739 88 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 739 Prior Lake Well No. 5 Water Elevation Static Water Level* 925.00 900.00 875.00 850.00 825.00 800.00 775.00 750.00 725.00 700.00 Water Level Elevation (ft) *Note: Static water level measured on 8/9/740 01 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 740 Prior Lake Well No. 6 Water Elevation Well Water Level Static Water Level* 950.00 940.00 930.00 920.00 910.00 900.00 890.00 880.00 870.00 860.00 850.00 840.00 830.00 820.00 810.00 800.00 790.00 780.00 770.00 760.00 750.00 Water Level Elevation (ft) *Note: Static water level measured on 4/14/2003 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 741 Water Level Elevation (ft) Prior Lake Well No. 7 Water Elevation Well Water Level Static Water Level* 900.00 880.00 860.00 840.00 820.00 800.00 780.00 760.00 740.00 *Note: Static water level measured on 6/6/2006 City of Prior Lake Water Supply 2040 Comprehensive Plan Page 742 900.00 875.00 850.00 825.00 800.00 775.00 750.00 725.00 700.00 675.00 650.00 625.00 600.00 575.00 550.00 525.00 500.00 475.00 450.00 Prior Lake Well No. 8 Water Elevation Well Water Level Static Water Level* Water Level Elevation (ft) City of Prior Lake Water Supply 2040 Comprehensive Plan Page 743 *Note: Static water level measured on 10/12/2006 900.00 875.00 850.00 825.00 800.00 775.00 750.00 725.00 700.00 675.00 650.00 625.00 600.00 575.00 550.00 525.00 500.00 475.00 450.00 Prior Lake Well No. 9 Water Elevation Well Water Level Static Water Level* Water Level Elevation (ft)