HomeMy WebLinkAbout1.b. Water Supply
Water Supply Chapter
2040 Comprehensive Plan
Rosemount, Minnesota
ROSEM 146456 | September 7, 2018
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Water Supply Chapter
2040 Comprehensive Plan
Prepared for City of Rosemount, Minnesota
1 Introduction
The City of Rosemount municipal water system consists of nine (9) active water supply wells, four
(4) elevated storage tanks, and approximately xxx miles of transmission and distribution water
mains, ranging in size from four (4) inches up to 16 inches in diameter. The distribution system is
comprised of two pressure zones (East and West) with pressure maintained by the water level in
the elevated storage tanks.
Rosemount provides potable water to multiple large and small-scale industrial customers and
numerous commercial and residential customers. With proper planning and coordination, the
municipal water system facilities will be prepared for short-term and long-term community needs.
The City is expecting continued growth and development throughout the planning period.
Therefore, proper planning is essential to coordinate the expansion of municipal water system
facilities to meet the short-term and long-term needs of the community.
1.1 Purpose
Sound engineering and long range planning have guided the development and expansion of
Rosemount’s municipal water system since its inception. Prior reports have provided detailed
engineering evaluations, resulting in the orderly, efficient, and cost effective expansion of
Rosemount’s water system. A complete review of the entire water system was last conducted in
2007. Numerous focused updates to the 2007 plan have been made to address more specific
pending development. In 2016, the City undertook a thorough review of the Eastern Service
Area.
The City’s 2016 Local Water Supply Plan (Appendix A) meets the minimum planning
requirements of the Minnesota Department of Natural Resources and the Metropolitan Council.
The 2016 Water Supply Plan details historic and projected water use, the adequacy of the
existing water system, water conservation, resource sustainability, and emergency preparedness.
The purpose of this Water Supply Chapter is to summarize the results of previous engineering
studies and the 2016 Water Supply Plan in light of Rosemount’s 2040 Local Comprehensive
Plan.
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2 Existing Water System Facilities
The City’s drinking water system provides water for domestic and fire protection uses. The water
system f acilities operated and maintained by the City include:
Nine (9) active groundwater wells;
Four (4) elevated water storage tanks;
Water system controls; and
Water transmission and distribution system.
The water system consists of two interconnected pressure zones. The West Service Area serves
the majority of the City, including the downtown area. The West Service Area operates at a high
water (overflow) elevation of 1105.0 ft above mean sea level (AMSL).
Rosemount's East Side water system (refer to Existing System map in Appendix xx) was
originally constructed by the University of Minnesota, consisting of Rural Wells 1 and 2, and a
looped distribution system of 6 inch and 4 inch water mains. The original system provided
domestic water use only.
The University of Minnesota’s rural system was connected to the City of Rosemount’s system in
2001 with the addition of 16 inch mains and a new 500,000 gallon East Side elevated reservoir.
Trunk water mains extended along US 52 and STH 55 provide water service to Flint Hills
Resources and some of the adjacent industrial customers. Since the ground elevations in eastern
Rosemount are lower than the west side, a new pressure zone was created in the east side. The
high water (overflow) elevation of the East Side water tower is 1050.0 AMSL. Water can flow
from the west side service area to the east side service area via a pressure reducing valve
located near Rural Wells 1 and 2.
The general location and layout of the water system facilities are illustrated on the Proposed
Trunk Water System Map in Appendix xx. This section presents a summary of the design and
operating characteristics of the existing water system components.
2.1 Supply
2.1.1 Groundwater Resources
Water is supplied from nine (9) municipal wells located in separate well fields. The water supply
wells vary in depth ranging from 400 to 507 feet, and draw water from the Jordan aquifer. Table 1
summarizes well data for each of the City’s active production wells.
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Table 1 – Existing City Water Production Wells
Well Name
Unique
Well
Number
Depth
(ft)
Capacity
(gpm)
Capacity
(MGD) Service Area Aquifer
RR #1 457167 400 500 0.72 East Jordan
RR #2 474335 400 500 0.72 East Jordan
Well No. 7 112212 490 1000 1.44 West Jordan
Well No. 8 509060 498 1100 1.58 West Jordan
Well No. 9 554248 481 1200 1.73 West Jordan
Well No. 12 706804 475 1500 2.16 West Jordan
Well No. 14 722623 485 1300 1.87 West Jordan
Well No. 15 753663 487 1300 1.87 West Jordan
Well No. 16 805374 507 2000 2.88 West Jordan
Total 10,400 15.0
Firm Capacity 7,900 11.4
The firm capacity listed in Table 1 is defined as the system capacity minus the capacity of the
largest pump in each well field. This is the capacity that can be provided consistently, even during
maintenance when a well pump might be out of service.
2.1.2 Emergency Interconnections
During emergencies, water can also be supplied to the City of Rosemount through system
interconnect with the City of Apple Valley. Closed valves at the interconnect locations prevent
water from passing between the two systems under normal operation. During an emergency, the
valves could be opened in order to maintain adequate water supply.
2.2 Treatment
The United States Environmental Protection Agency (USEPA) has set primary (enforceable)
standards, for drinking water. Rosemount’s water is tested regularly and is in conformance with
primary standards. The USEPA also has set secondary standards (non-enforceable
recommendations) for aesthetic water quality. The secondary standards are set to minimize the
potentially negative aesthetic qualities (such as color, taste, odors) of water containing high levels
of these contaminants. The secondary standard for iron and manganese in drinking water is set
at 0.3 milligrams per liter (mg/L) and 0.05 mg/L, respectively. Water from some of Rosemount’s
wells exceed the secondary standards for iron and manganese, however the City has managed
to minimize customer complaints by blending water from the wells and adding polyphosphates
(for sequestering iron and manganese) at the supply wells. Rosemount currently disinfects the
source water by chlorination at the well sites. Additional treatment includes fluoride (to prevent
tooth decay).
Treatment is discussed in more detail in the Adequacy of Facilities section of this report.
Appendix xx provides a summary of the current EPA Water Quality Requirements.
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2.3 Distribution
The City water distribution system provides a means of transporting and distributing water from
the supply sources to customers and other points of usage. The distribution system must be
capable of supplying adequate quantities of water at reasonable pressures throughout the
service area under a range of operating conditions. Furthermore, the distribution system must be
able to provide not only uniform distribution of water during normal and peak demand conditions,
but must also be capable of delivering adequate water supplies for fire protection purposes. The
current water main size inventory is summarized in Table 2.
Table 2 – Existing Water Distribution System Summary
Pipe Size Length (ft) Length (Miles) % of total
4-inch
6-inch
8-inch
10-inch
12-inch
16-inch
20-inch
24-inch
Total 5,000 10.0 100%
Notes: Hydrant leads not included
Source: Rosemount GIS
The Rosemount water system is comprised of about xxx miles of water main ranging in size from
4 inches up to 16 inches in diameter. The existing distribution system is shown in the map in
Appendix F at the end of this report
2.4 Storage
The Rosemount water distribution system is currently operated using elevated storage tanks.
Water from these facilities is fed into the system by gravity. The City currently has four elevated
storage tanks that have a combined storage volum e of 3,500,000 gallons. Table 3 summaries the
water storage facilities within the Rosemount water system.
Table 3 – Existing Water Storage Facilities
Facility Name Year Constructed Total Volume
(gallon)
Usable Volume
(gallon)
Overflow
Elev. Style
Chippendale Tower 1972 500,000 500,000 1105 Elevated
Connemara Tower 1988 1,000,000 1,000,000 1105 Elevated
Bacardi Tower 2007 1,500,000 1,500,000 1105 Elevated
East Side Tower 1998 500,000 500,000 1050 Elevated
Total 3,500,000 3,500,000
Water storage facilities are important to water systems, as they help supply water during peak
hour demands. During times of peak demand, water is withdrawn from the storage tanks to
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provide adequate pressures throughout the system and to minimize the pumping capacity
required and the size of transmission mains throughout the City. Water stored in elevated tanks
also provides system reliability during power outages, fire events, and well pump outages.
3 Population and Community Growth
In order to understand the requirements of the future water system, anticipated water use
characteristics must be determined. This involves first understanding how water is currently used
and then developing an estimate of how water might be used in the future. This section
summarizes the primary assumptions regarding future growth of the City’s water service area.
The present and future needs and characteristics of the identified service area have a direct
impact on the need for expansion or reconfiguration of water system facilities. Therefore, the
conclusions discussed in this section were used as a primary basis for projecting future water
needs, evaluating the adequacy of existing water system facilities, and identifying needs for
future water system improvements.
3.1 Population and Relationship to 2040 Comprehensive Plan
In many cases, there is a close relationship between a community's population and total water
consumption. As such, f uture water sales can be expected to reflect future changes in service
area population. Similarly, commercial and industrial water consumption will tend to vary
proportionately with the growth of the community. However, proportionally increased water use
and population growth can vary greatly depending on the specific characteristics of a community.
For the purposes of water system planning, City staff estimated the population served with
municipal water in each service area as shown in Table 4. These projections through 2040 are
consistent with Rosemount’s 2040 Comprehensive Plan. For water system planning purposes,
City staff estimated potential service areas beyond the formally adopted 2040 Plan. The following
projections assume growth to occur within both the East Side and West Side Service Areas. The
projected population served by municipal water for the City of Rosemount is summarized in
Table 4.
Table 4 – Projected Served Population
Year
Total
City
Population
Total
Population
Served (1)
East Side Only
Service Area
Population
Served (2)
West Side Only
Service Area
Population
Served (1)
2016 23,544 60 23,484
2017 23,857 60 23,797
2018 24,210 60 24,150
2019 25,011 60 24,951(3)
2020 25,380 60 25,320
2025 28,562 60 28,502
2030 36,421 500 35,921
2040 46,843 1,000 45,843(4)
Ultimate 98,000 28,000 70,000
Notes:
(1) Source: City Estimates
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(2) Assume 20 homes currently served by U of M Rural Water System, but not served by municipal
sanitary sewer system
(3) Assumes Umore development begins
(4) 38,100 per Met Council, plus Umore Phases 1 -5
4 Water Requirements
Projections of customer demands and service area serve as the basis for capital improvement
planning. Several standard methods were used in this study to project water supply and storage
needs based on estimates of population and community land use growth. This section
summarizes the methodology used and the results of these projections.
4.1 Variations in Customer’s Demand & Pumpage
Water demands are variable and change throughout the day, month, and year. Typically, two
water demand days are used for water system planning – average day and maximum day.
Average Day Demand is defined as the total volume of water pumped throughout the
year divided by the number of days in the year. It is typically recommended that a water
system’s available water storage be equal to or exceed the average daily demand.
Maximum Day Demand is defined as the maximum volume of water pumped during a
single day in a given year.
The maximum day demand conditions typically occur during the summer, when outdoor water
use is at its highest level of the year. A summary of recent MD levels is summarized in Table 5.
The maximum day demand is defined as the amount of water pumped during a single day of the
year with the highest water usage, and is often expressed as a ratio of the annual average day
pumpage. The maximum day pumpage is of particular importance to water system planning,
because water supply facilities are sized to meet this demand.
4.2 Water Consumption History
An analysis of past water consumption characteristics is performed by reviewing historical water
use data. The data analyzed includes historical pumping records as well as select historical water
billing data.
Average Day (AD) water use was analyzed to develop overall water use trends. Maximum Day
(MD) water consumption was analyzed for the previous 10 years to develop an understanding of
maximum day peaking factors (refer to July 2016 Water Supply Plan contained in Appendix C).
Peaking factors are defined as the ratio of the maximum day water use to the average day water
use. Projections of future water requirements are based on the results of this analysis coupled
with estimates of population and community growth and future land use.
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Table 5 – Recent Historical Water Use
Year Population Served Total Water Pumped (MGY) Water Average Day Water Pumped (MGD) Max Day Water Pumped (MGD) MD/AD Ratio Avg Day Per Capita Water Use (gpd) Max Day Per Capita Water Use (gpd) 2007 22,474 937.5 2.57 na Na 114 na
2008 22,750 910.4 2.49 6.6 2.66 110 292
2009 23,244 937.9 2.57 6.5 2.52 111 278
2010 23,350 825.6 2.26 5.2 2.32 97 224
2011 22,239 855.8 2.34 6.3 2.67 105 281
2012 22,432 973.1 2.67 6.9 2.58 119 307
2013 22,711 880.6 2.41 6.4 2.64 106 280
2014 23,044 815.0 2.23 6.4 2.86 97 278
*2015 23,244 804.0 2.20 6.1 2.75 95 260
2016
2017
*Note: 2015 figures are estimates except for Max Day.
Source: DNR Water Use Records, City Records
Based on this analysis, the existing MD demand is determined to be xxx MGD (million gallons per
day), or xxx gpcd (gallons per person per day), based on a service population of xxx.
4.3 Hourly Demand Fluctuations
Water demands are variable throughout the day and can vary depending on common use among
users. Over the course of a given day, water uses often follow a diurnal demand distribution.
Table 6 represents a typical daily demand distribution for residential water use. Commercial and
industrial uses are usually more constrained and predictable. The residential demand graph
depicts low water demand during the late evening and early morning periods. As the morning
progresses, there is an increase in demand as indoor water use increases when people are
preparing for the day. During the summer this morning demand is also impacted by automatic
lawn sprinkler systems that are typically operated in the morning. During late morning to early
afternoon there is a slight recovery prior to a second peak use in the early evening after people
arrive home from their daily routine.
Most water systems are designed to meet the maximum daily demand rate with supply facilities
such as wells, treatment processes, and pumping facilities. Storage reservoirs are used to
supplement the supply of treated water during the peak usage hours within each day. During
lower usage periods, the system is able to produce water in excess of the demand. This excess
is used to fill the storage reservoirs. When the demand rate exceeds the production rate, the
stored water in the reservoirs is used to make up for the deficit.
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Table 6 – Typical Diurnal Demand Curve
Time Demand
Multiplier Time Demand
Multiplier
12:00 AM 45% 12:00 PM 110%
1:00 AM 40% 1:00 PM 103%
2:00 AM 45% 2:00 PM 103%
3:00 AM 50% 3:00 PM 105%
4:00 AM 70% 4:00 PM 110%
5:00 AM 115% 5:00 PM 120%
6:00 AM 155% 6:00 PM 118%
7:00 AM 165% 7:00 PM 110%
8:00 AM 160% 8:00 PM 100%
9:00 AM 145% 9:00 PM 90%
10:00 AM 130% 10:00 PM 75%
11:00 AM 115% 11:00 PM 63%
Source: AWWA M32, Computer Modeling of Water Distribution Systems,
2012, American Water Works Association
4.4 Water System Demand Projections
Estimates of future water use are established through a review of future land use and population
projections. For the purposes of this study, City staff provided estimates of served population in
the East, West, and UMORE areas to aid in water system capital improvement planning.
Future water use projections are made using population projections and historic per capita water
usage (Table 5). Historic per capita useage is then adjusted based on future land uses. This land
use adjustment is especially important in the East Side Service Area, where the City is planning
for a higher percentage of commercial/industrial uses.
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4.4.1 Summary of Projected Water Demands
Table 7 provides a summary of the projected water demand.
Table 7 – Projected Water Demand
Year Population
Served
Average Day
Demand
(MGD)
Max Day
Demand
West Side1
(MGD)
Max Day
Demand
East Side2
(MGD)
Total
Maximum Day
Demand
(MGD)
2018 24,210 2.72 8.84 0.23 9.07
2020 25,380 2.93 9.50 0.27 9.77
2025 28,562 3.52 11.3 0.42 11.7
2030 36,421 4.12 13.1 0.60 13.7
2035 41,632 4.76 13.1 0.90 14.0
2040 46,843 5.40 13.8 1.20 15.0
Ultimate 98,000 13.7 21.1 13.1 34.2
Source: DNR Water Use Records, City of Rosemount
Notes: 1Source: WSB Tech Memos, SEH Tech Memo
2Source: SEH 2016 East Side Utilities Study
4.5 Water Needs for Fire Protection
In addition to the water supply requirements for domestic, commercial, and industrial
consumption, water system planning for fire protection requirements is an important
consideration. In most instances, water main sizes are designed specifically to supply adequate
fire flow.
Guidelines for determining fire flow requirements are developed based on recommendations
offered by the Insurance Services Office (ISO), which is responsible for evaluating and classifying
municipalities for fire insurance rating purposes. When a community evaluation is conducted by
ISO, the water system is evaluated for its capacity to provide needed fire flow at a specific
location and will depend on land use characteristics and the types of properties to be protected.
However, in high value districts, fire flow requirements of up to 3,500 gpm can be expected.
Therefore, for the purposes of this study, a basic fire flow requirement of 3,500 gpm for three
hours was used for establishing water supply and storage requirements. Based on current
insurance classification guidelines, this basic fire flow requirement is not expected to change over
the planning period.
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Other typical fire flow requirements based on land use are outlined in Table 8.
Table 8 – Typical Fire Flow Requirements
Land Use
Building
Separation
(feet)
Available fire flow
@ 20 psi (gpm)
Single & Two Family Residential >100 500
Single & Two Family Residential 30-100 750
Single & Two Family Residential 11-30 1000
Single & Two Family Residential <10 1500
Multiple Family Residential Complexes - 2,000 to 3,000+
Average Density Commercial - 1,500 to 2,500+
High Value Commercial - 2,500 to 3,500+
Light Industrial - 2,000 to 3,500
Heavy Industrial - 2,500 to 3,500+
Source: Insurance Services Office
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5 Adequacy of Existing Water System
Water systems are analyzed, planned, and designed primarily through the application of basic
hydraulic principles. Some important factors that must be considered when performing this
analysis include:
Location and capacity of supply facilities;
Location, sizing, and design of storage facilities;
Location, magnitude, and variability of customer demands;
Water system geometry and geographic topography;
Minimum and maximum pressure requirements; and,
Land use characteristics with respect to fire protection requirements.
The system was evaluated based on the following standard water industry criteria:
Pressure;
Flow Capacity;
Reliability;
Supply; and,
Storage.
Prior engineering studies have evaluated the Rosemount water system in detail to determine the
adequacy of the system to supply existing and future water needs and to supply water for fire
protection purposes. The following comments regarding the adequacy of the existing water
system are drawn from those reports. In general, the existing water system operates well. The
City has adequate well supply and treatment capacity, and the existing piping network and
storage facilities generally provide adequate flows and pressures.
5.1 Water Supply, Storage and Distribution Relationship
Water demands over the course of a Maximum Day event are met from a combination of water
supplied from the wells and water drawn from the water towers. Tower levels are drawn down
during the day, when the demand is highest, and are refilled at night, when demands are lowest.
Typically, water supply must equal 100% of the Maximum Day Demand, and the storage
reservoirs must have sufficient capacity to supply the peak hour demands.
The water distribution system pipes must be sized to convey a wide range of flow rates; such as
tank filling, peak hour demands, and fire flows.
5.2 Supply (Wells and Pumps)
5.2.1 Supply Capacity
The firm capacity of the existing wells (11.4 MGD) exceeds the expected 2018 MD demand (9.1
MGD). Therefore, the City has adequate well capacity to meet existing water demands. Since
siting, design, permitting, and construction of new water supply wells and storage can take two
(2) years, the City has a policy of adding wells and storage facilities concurrent with development.
This policy provides the City with a safety factor to know that adequate supply is available (or
under construction) for all platted parcels – whether or not they are immediately connected to the
water system.
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5.2.2 Water Quality
The water quality from all wells meets all enforceable EPA Primary Drinking Water Standards,
and is regularly tested by City staff and Minnesota Department of Health. Water from Wells 12,
14, 15, and 16 contain iron and manganese in excess of the recommended Secondary Standard.
Although not a health hazard, iron and manganese levels in excess of the Secondary Standards
can result in customer aesthetic complaints (red, or black colored water, staining of fixtures or
clothing). The City currently manages the iron and manganese in these wells through
“sequestering” agents (polyphosphates). These polyphosphates keep the iron and manganese in
suspension, thus preventing the iron and manganese from settling out in the distribution system.
In the future, if polyphosphate treatment is ineffective, the City may consider adding a water
filtration system to remove iron and manganese.
The City has completed and continues to actively implement a Wellhead Protection Plan
(WHPP). The goal of the WHPP is to prevent contaminants from entering the area that
contributes to the aquifer where the City’s water supply is withdrawn. The WHPP is updated
every 10 years, or when a new well is added.
5.2.3 Resource Sustainability
Static and pumping aquifer water levels are recorded and trended at each of the City’s supply
wells (refer to Water Supply Plan for details). Long term trends indicate a potential declining
aquifer level in the region. Regional planning summarized in the Metropolitan Council’s Mater
Water Supply Plan suggests the following long-term concerns for a sustainable water supply in
the Rosemount area:
Potential for water use conflicts between Public and private wells.
Potential for significant decline in aquifer water levels.
Potential for impacts of groundwater pumping on surface water features and ecosystems.
Significant vulnerability to contamination.
Uncertainty about aquifer productivity and extent.
The City has been actively performing engineering and scientific studies and working with the
Minnesota Department of Natural Resources and Minnesota Department of Health prior to siting
new wells. As each new well is installed, new aquifer and water quality data becomes available
for further analysis for use in siting the next well.
5.3 Storage
The City’s four (4) steel elevated storage tanks are strategically located to provide adequate
pressure and fire flows to the system. The total available storage volume of 3.5 million gallons is
adequate for current needs.
5.4 Distribution System
5.4.1 Water System Pressures
Existing static water pressures are shown on the map in Appendix xx. Pressure between 50
pounds per square inch (psi) and 80 psi are generally considered desirable. Pressures lower than
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40 psi may trigger low pressure complaints, and customers with pressures above 80 psi should
be fitted with in-building pressure reducing valves to provide adequate pressure.
Pressures are generally adequate throughout the system. Portions of the northwestern area of
the City have lower pressures, while the eastern portion of the City tends to have some higher
pressure areas. Isolated areas of low and high pressures exist throughout the system, however
the City does not regularly receive water pressure complaints.
The City should identify and map customers with in-home pressure reducing valves or in-home
booster stations for future reference.
5.4.2 Available Fire Flow Capabilities
Previous reports have utilized a computer model of the water distribution system to estimate
available fire flows throughout the system. Existing fire flows are generally adequate in the
Western Service Area.
Existing fire flows in the East Service Area are generally adequate where connected to the
recently installed trunk water mains. The existing 4 inch and 6 inch pipes from the Rural System
cannot convey a significant quantity of water required for fire protection. The existing 500,000
gallon East Side water tower cannot fully provide for a 3500gpm fire for 3 hours. In the event of a
large, long duration fire in the East Side, water is available to flow from the West Service to the
East Service area through pressure reducing valves.
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6 Water System Improvements
Prior engineering planning studies have laid out a plan for the cost effective expansion of the
City’s water system to m eet future growth. The following provides a summary of proposed
improvements and triggers for implementation.
6.1 Treated Water Supply
6.1.1 Southwest and Northwest Well Fields
Wells 7, 8, 9, and 12 are in the southwestern portion of the City, while Wells 14, 15, and 16 are
near Barcardi Avenue, north of CSAH 42. Near-term plans are to continue developing the
Northwest Well Field first as new wells are needed, followed by addition of wells in the Southwest
well field.
If water treatment is needed or desired in the future, it is assumed that there would be a
northwest and southwest water treatment plant.
6.1.2 East Well Field
Prior studies have identified a potential new east well field east of State Highway 52. If water
treatment is needed or desired in the future, and eastern water treatment plant could be
constructed in the east well field.
6.1.3 Water Supply Recommendations
The following is a summary of water supply recommendations.
Continue to implement the City’s Water Conservation Plan to delay or reduce the need
for additional supply wells.
Identify and acquire property for future well sites and water treatment plant sites in
conjunction with development.
Provide corridors for raw water piping from the wells to the water treatment plant site.
Continue to monitor water levels and update groundwater analysis and planning.
Continue to implement and update the City’s WHPP to protect existing and proposed
water supply.
6.2 Storage
Additional water storage is planned for both the Eastern and Western Service Areas. Preliminary
sizing and locations of future storage has been identified to provide adequate pressures and
flows. Actual implementation of storage additions will be guided by development.
6.3 Distribution System
Expansion of the distribution system proceeds with development. The majority of distribution
system pipes added will be eight (8) inch to serve local residential needs, however some of these
pipes will be oversized to serve as the basis of a trunk pipe network that connects the water
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supply and storage facilities, and provides large flows required for tank filling, peak hourly usage,
and fire flows.
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Figures
Figure 1 – Title
Figure 2 – Title
Appendix A
MNDNR Water Supply Plan
Appendix B
Water Quality Requirements
Appendix C
Supplemental Information