HomeMy WebLinkAboutItem 06.jI ty evill e
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Date: 14 November 2013
Item No.
ACCEPTANCE OF THE WATER TREATMENT FACILITY EXPANSION STUDY
Proposed Action
Staff recommends adoption of the following motion: Move to accept the Water Treatment
Facility Expansion Study.
Overview
During the latter half of 2012, the City commissioned Black & Veatch to review and update the
Water Treatment Facility (WTF) expansion study. Black & Veatch completed the original
expansion study in 2000 which was used as a guide for the expansion of the facility in 2001
and as a planning and budgeting tool for future expansion.
With changes to population, growth, and water use, the original expansion study became less
and less effective as a planning guide for the budgeting and timing facility enhancements to
meet resident needs. This expansion study updated the City's water use characteristics,
developed water use projections, prepared a schedule for facility expansion, and provided
estimates of project costs for an expansion.
Based on this study and a concurrent filter loading study, the City remains in a position to
meet both resident and emergency needs in the near term. Some enhancements are needed
to be able to handle the facility's higher capacity; that higher capacity enables the City to
delay an expansion for several years.
Primary Issues to Consider
• Did the study add value to the City's planning and budgeting process? Yes, the expansion
study enabled the City to test filter loading and subsequently increase the peak capacity
from 20 million gallons per day (mgd) to 26.5 MGD. This allows the City to better evaluate
the need for expansion against water demand.
Supporting Information
• A copy of the WTF Expansion Study is attached.
Christo er J. Petree
Public Works Director
Financial Impact:
Related Documents (CIP, ERP, etc.):
Budgeted: Source:
Notes:
LAKEVILLE WATER TREATMENT FACILITY
EXPANSION STUDY
B &V PROJECT NO. 179946
CITY OF LAKEVILLE PROJECT NO. 12 -14
PREPARED FOR
AICIL
City of Lakeville, Minnesota
AUGUST 2013
I hereby certify that this report was prepared by me or
under my direct supervision and that I am a duly
Licensed Professional Engineer under the laws of the
State of Minnesota.
Scott D. Fronek
Date: 8/20/13 BLACK & VEATCH
License Number: 45419 01 Building a world of difference:
4 '. PA City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
Table of Contents
1
Introduction ......................................................................................... ..............................1
1.1 Project Purpose ........................................................................................ ..............................1
1.2 Background ................................................................................................ ..............................2
1.3 Abbreviations ............................................................................................ ..............................4
2
Basis of Analysis .................................................................................. ..............................5
3
Population Projections ..................................................................... ..............................6
4
Commercial Development ............................................................... ..............................9
5
Water Use Characteristics ............................................................. .............................10
6
Average Day and Maximum Day Design Flows ...................... .............................13
7
Well Water Production ................................................................... .............................17
8
Water Treatment Facility Capacity ............................................ .............................19
9
Water Storage Volume .................................................................... .............................20
10
Treated Water Pumping Capacity ............................................. ...............................
23
11
Water Treatment Facility Improvements ................................ .............................26
12
Opinion of Probable Project Cost .............................................. ...............................
29
13
Conclusions and Recommendations .......................................... .............................30
13.1 Conclusions .............................................................................................. .............................30
13.2 Recommendations .............................................................................. ...............................
31
BLACK & VEATCH CORPORATION I Table of Contents
Alink
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
1 Introduction
1.1 PROJECT PURPOSE
The City of Lakeville experienced rapid growth in development in the previous two decades.
Growth slowed significantly during the 2008 economical recession. Planning for the City's water
treatment and supply system was historically based on the population forecasts prepared by the
Twin Cities Metropolitan Council and reflected the aggressive growth. A Water Treatment Facility
(WTF) Expansion Study was completed in 2000 to assess water use characteristics from 1990 -1999
and to develop an implementation schedule for expansion of the Lakeville WTF, wells and storage
facilities.
Following the 2000 WTF Expansion Study, the City initiated a program to encourage residents to
adhere to an alternate- day /time -of -day watering schedule. In 2007, the City of Lakeville
implemented a new tiered water billing structure that increased the customers' water rate for
consumption above a preset level. These efforts were established to reduce the volume of water
per capita consumed in Lakeville and lower the peak water consumption rates.
After 2005 the rate of development declined due to less favorable economic conditions. The
economic recession of 2008 caused further decline in development. The 2010 National census
indicated the City's population was lower than forecasted by the Metropolitan Council.
While the rate of growth has decreased since the previous WTF Expansion Study, the community
continues to grow, and the City expects the WTF will require expansion at a future time. To
determine when the City of Lakeville will need additional water system capacity, the City's water
supply and treatment capacity requirements were analyzed using population projections from the
Metropolitan Council and population and water use data from the previous twelve years.
The purpose of this report is to:
Update Lakeville's water use characteristics since 2000;
Update water use projections using historical population data and the Metropolitan Council
population forecasts;
Prepare an implementation schedule for expansion of the Lakeville WTF to accommodate the
updated demand projections;
BLACK & VEATCH CORPORATION I Introduction
Water Treatment Facility Expansion Study I City of Lakeville, Minnesota
Identify the facilities required at the facility for the expansion;
Develop an opinion of probable project cost for expansion of the facility.
1.2 BACKGROUND
A Comprehensive Water System Plan Update was completed for the City of Lakeville in 1992 and an
addendum to the plan was prepared in 1995. The purpose of the study was to address the needs of
the City in the areas of raw water supply, treatment, storage, and distribution. The most significant
treatment need identified by the water quality evaluation was the high concentrations of iron and
manganese. To minimize the problems associated with the iron and manganese, the City had
sequestered these contaminants by adding polyphosphates at the well sites. Although sequestering
reduced the problem associated with the high levels of iron and manganese in the City's well water,
the City frequently received complaints from consumers regarding the quality of the water despite
an aggressive flushing program.
To improve the water quality, the 10 million gallon per day (MGD) Lakeville Water Treatment
Facility was constructed and brought on -line in 1998. Rapid population growth in the Lakeville
area triggered an expansion of the facility to 20 MGD by the year 2001. Additional wells and
treated water storage facilities were added to support the community's growth.
The first Water Treatment Facility Expansion Study was completed in 2000 to provide the City
guidance for making decisions about the WTF capacity. The study indicated the City should plan to
increase capacity incrementally until reaching the 30 MGD ultimate WTF build -out in 2018. The
City followed many of the recommendations given in the 2000 WTF Expansion Study and
introduced two water conservation initiatives. During the same period the community's growth
rate decreased. Growth began to increase again in 2010. The changes in water consumption and
the unexpected growth pattern prompted the City to reevaluate the WTF expansion needs through
an updated WFT Expansion Study.
Review of the water demand data from the previous 12 years indicated the maximum demand was
approaching the design capacity of the existing WTF but only for a week or two each year. The City
questioned whether an expansion of the WTF would be the only way to meet the high demand
during the brief periods. Two options were identified to send the additional water through the
plant.
AUGUST 20, 2013
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
The first option was to use the filter by -pass that was installed on the influent pipe during the
previous plant expansion in 2001. Raw water would flow into the plant for disinfection and then be
sent directly to the treated water reservoirs. The water would meet primary drinking water
standards but would have higher iron and manganese concentrations than the filter effluent. The
City preferred not to use this option except in an emergency since it would result in decreased
water quality as compared with what is typically produced.
The other alternative was to load the existing eight filters at 4 gallons per minute per square ft
(gpm /sf) instead of the previous loading rate of 3 gpm /sf, which was the original design basis. This
alternative would allow a higher flow to be treated through the existing facility. A pilot study was
developed to test the performance of the filters under the increased loading rate. The pilot study
demonstrated the filters could be loaded to 4 gpm /sf with no adverse effects to filtered water
quality or the plant hydraulic profile. A separate report summarizes the results of the pilot study,
and concluded that based on the results of the pilot study the capacity of the WTF could be
increased to 26.5 mgd without adding additional filters. The ultimate capacity of the WTF could
also be increased from 30 mgd in the original expansion plan to 40 mgd with increased filter
loading.
This document is an update to the 2000 Lakeville WTF Expansion Study. Population projections,
water demand and treatment capacity requirements were updated to reflect the recent historical
data. The methods used to calculate the water supply and treatment needs were consistent with the
previous expansion study. The recommendations for expansion were updated to reflect the
additional capacity allowed through a higher filter loading rate.
SLACK & VEATCH CORPORATION I Introduction
Water Treatment Facility Expansion Study ( City of Lakeville, Minnesota
1.3 ABBREVIATIONS
Abbreviations used in this report are as follows:
Approx
Approximate
Avg
Average
GPCD
Gallons per capita per day
gpm
Gallons per minute
Max
Maximum
MCL
Maximum Contaminant Level
MDH
Minnesota Department of Health
MG
Million gallons
MGD
Million gallons per day
mg /l
Milligrams per liter
No.
Number
SCADA
Supervisory Control and Data Acquisition
WTF
Water Treatment Facility
Yr
Year
AUGUST 20, 2013
Aim
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
2 Basis of Analysis
To ensure adequate raw water supply, treatment, and treated water pumping and storage facilities,
the City must have a plan for incrementally expanding the existing facilities. The years 2020, 2030
and 2040 have been selected as "design years" for planning purposes. Projected water demands for
intermediate years were determined by straight -line analysis. The projected water demands, or
design flows, for each year will be used to determine when incremental expansions of the City's
water system facilities are required. Modeling of the City's distribution system was not within the
scope of this study. Therefore, it was assumed that the capacity of the City's distribution system
would be sufficient to convey the design flows.
BLACK & VEATCH CORPORATION I Basis of Analysis
Water Treatment Facility Expansion Study I( City of Lakeville, Minnesota qu
3 Population Projections
Lakeville has been one of the fastest growing communities in Minnesota. While the economic
conditions since 2000 have been volatile throughout the United States, Lakeville has continued to
grow. Lakeville's population growth rate was about 3 percent annually until it peaked at 5.4% in
2005. It then began to fluctuate between 0.3 percent and 2.9 percent. The Twin Cities Metropolitan
Council estimated the population of Lakeville in the year 2012 was 57,048 people.
Population forecasts were used in this study to develop the incremental increases in the water
treatment facility capacity required to meet the water demand of the community. Figure 3 -1 shows
the population of Lakeville since 2000 and the band of projected population developed for this
Expansion Study.
AUGUST 20, 2013
city of Lakeville, Minnesota Water Treatment Facility Expansion Study
Lakeville Population Projections
120000
110000
100000
90000
80000
70000
60000
50000
40000
30000
I -
i
I i
I I E
I
i
2000 2005 2010 2015 2020 2025 2030 2035 2040
-i- -2% growth —A--MCES 2010 Projection Actual population
Figure 3 -1. Lakeville F cpulutian Data & Projections
Planners often project population growth as 1- percent, 2- percent or 3- percent growth, with 3-
percent growth being very aggressive. The typical growth rate for Midwest communities is about
2- percent. The Twin Cities Metropolitan Council population forecasts in the 2010 Metropolitan
Area Master Water Supply Plan projected a growth rate closer to 3- percent. The City and the
Metropolitan Council agree that these projections may be too aggressive for the actual population
growth rate experienced in Lakeville since 2005. The Metropolitan Council is in the process of
revising the population forecasts for the Metro area. Preliminary forecasts are expected in August
of 2013.
To account for the uncertainty in the forecasted population of Lakeville, the future population is
depicted as a band of potential population in Figure 3 -1. The upper boundary of the band is the
BLACK & VEATCH CORPORATION I Population Projections
Water Treatment Facility Expansion Study I City of Lakeville, Minnesota
Metropolitan Council's projected population for Lakeville. The lower boundary of the band is the 2-
percent growth line, which levels off at the maximum build -out population of 88,800. The
population through 2040 is expected to fall somewhere within the population band. This expansion
study was conducted based upon the population projections resulting from both growth patterns.
AUGUST 20, 2013
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
4 Commercial Development
Lakeville experienced moderate industrial /commercial /institutional (ICI) development in the years
2000 -2011. Like residential customers, ICI customers rely on a steady, reliable water supply. Table
4- 1Table 4 -1 depicts the number and increase in ICI connections since 2000.
Table 4 -1. Industrial /Commercial /Institutional Water Use
2000 312
209
13
2001 318
6
218
12
2002 327
9
195
12
2003 351
24
226
11
2004 393
42
213
11
2005 409
16
255
14
2006 444
35
301
14
' 1 007 476
32
279
12
2008 480
4
283
12
2009 499
19
276
12
2010 503
4
254
13
2011 504
1
274
13
Data provided by the City of Lakeville.
The general trend of additional ICI connection is very similar to the trend of residential connection
additions. The number of ICI connections increased rapidly until 2007. Growth then slowed due to
the economic recession. As shown in Table 4 -1, the ICI water consumption is between 11 and 14
percent of the total water consumption in the City. The number of ICI connections is expected to
grow at roughly the same pace as the growth in population in the community.
BLACK & VEATCH CORPORATION I Commercial Development
Water Treatment Facility Expansion Study I City of Lakeville, Minnesota
5 Water Use Characteristics
Two methods are commonly used to summarize historical water consumption and estimate the
design flow rates for future years. One method differentiates between water consumption by
residential users and the water consumption for industrial, commercial and institutional (ICI)
water users. The other method does not consider the classifications of water users, focusing
instead on total community water use.
The previous Water Treatment Facility Expansion Study evaluated both methods to determine the
best method for Lakeville. The previous study concluded that historic ICI consumption accounted
for about 15 percent of the total water consumption in the community. Residential consumption
was about 85 percent of the total. The future residential water consumption was projected, and the
future ICI was calculated by multiplying the projected residential water consumption by 1.15. This
method assumes the proportion of community water demand contributed by ICI remains constant
through 2040. Any conservation measures or decline in residential growth would be assumed to be
consistent across both user classifications. This method would be effective for Lakeville
considering the relatively small percentage of ICI use as compared to residential consumption.
However, a similar result can be determined through the more simplistic method of projecting the
community water use as a whole.
This Expansion Study assessed historical water consumption and estimated the future design flows
in the system based on the total water use in the community. Table 5 -1 presents the population of
Lakeville, the average daily water production at the Lakeville WTF and the per capita water
consumption for the years 2000 -2012. To determine the average daily per capita water demand
the total number of gallons used in the City over one year was divided by 365 days and divided
again by the City s population that year. As indicated in the table the per capita water demand for
years 2000 through 2012 ranged from 100 gallons per capita per day (GPCD) to 135 GPCD.
AUGUST 20, 2013
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
Table 5 -1. Population and Water Consumption for Years 2000 -2011
2000
43,128
118
2001
44,751
123
2002
46,285
100
2003
47,53
128
2004
49,097
115
2005
51,722
111
2006
52,323
126
2007
53,829
135
2008
54
123
2009
55
118
2010
55,954
104
2011
56,534
111
2012
57,048
122
The general trend of water consumption in the City is best displayed graphically. Figure 5 -1 shows
the increase in the community's population and the trend of water consumption over the eleven
year study period. Water consumption peaked in 2007, and then declined for three years before
rising again. The highest consumption occurred consistently during the summer months. Summer
water use was typically between three and five times higher than usage during the rest of the year.
BLACK & VEATCH CORPORATION I Water Use Chi racteristics
Water Treatment Facility Expansion Study I city of Lakeville, Minnesota
Water Consumption
140
O
I a 130 -- –
C
0
x120— i
d
CL
d
110
M a
3
0 100
m
W
m
90
L
d
a'
80
2000 2002 2004 2006 2008 2010 2012
Year
Figure 5 -1. !Water ccnsumption in gallons per person per day (GPCD) Lakeville
The City implemented three water conservation measures to encourage residents and businesses to
conserve water and attempt to lower the maximum day demand during warm weather. The City
initiated public outreach activities to increase public awareness of the importance of water
conservation and to educate the public about conservation methods. In 2004 the City began an
alternate - day /time -of -day watering initiative. Though not legally enforceable, the City asked
residents and businesses to water landscaping only every other day and never between 11 AM and
5 PM. To support these efforts the Lakeville City Council adopted an ordinance in December 2007
requiring citizens to observe the alternate- day /time -of -day watering schedule. The same year the
City introduced a tiered water rate structure to assess higher water rates as usage increased. Water
consumption decreased after 2007, though the economic recession may have contributed to the
reduced consumption. Figure 5 -1 indicates the water conservation measures have helped to
decrease the consumption rate of water in Lakeville. However, other factors may also play a role in
the decrease. A more precise argument could be made if monitoring continued.
AUGUST 20, 2013
City of Lakeville, Minnesota � Water Treatment Facility Expansion Study
6 Average Day and Maximum Day Design Flows
The design flows for years 2020, 2030 and 2040 were developed based on the historical water
consumption data provided by the City of Lakeville and the band of predicted populations
calculated for this study. Well pumping and WTF production data collected by the City's
Supervisory Control and Data Acquisition System (SCADA) was analyzed to determine the average
day and maximum day demand. Average day demand for years 2000 -2012 ranged from 4.65 MGD
to 7.15 MGD. The average day demand was determined by dividing the total water use for each
year by 365 days per year. The maximum day demand for years 2000 -2012 ranged from 13.2 MGD
to 20.4 MGD. The maximum day demand for each year was highest quantity of water used in one
day in a given year.
The data was then used to calculate the per capita water consumption and the peaking factor, or
maximum day /average day ratio. The average per capita water consumption was determined by
dividing the average day demand by the population for each year. The peaking factor was
calculated by dividing the maximum day demand by the average day demand for each year. Table
6 -1 presents the water demands and peaking factors.
BLACK & VEATCH CORPORATION I Average Day and Maximum Day Design Flows
Iffater Treatment Facility Expansion Study I City of Lakeville, Minnesota
Table 6 -1. Water demand in Lakeville from 2000 -2011
2000
5.1
118
16.3
3.2
2001
5.5
123
20.2
3.7
2002
4.6
100
13.4
2.9
2003
62
128
16.9
2.7
2004
5.6
115
15.6
2.8
2005
5.7
111
18.1
3.1
2006
6.6
126
18
2.7
2007
7.2
135
20.4
2.9
2008
6.7
123
20.2
3.0
2009
6.6
118
17.1
2.6
2010
5.8
104
13.2
2.3
2011
5.3
111
15
2.4
2012
4Hi+P�Tr�
6.9
122
17.2
2.7
i +�i v.�rars.�.�.�saa
The flow data in Table 6 -1 formed the basis for calculation of the future design flows. The average
per capita water consumption was one key component of the projection. The 2000 WTF Expansion
Study used 113 GPCD to predict future design flows. This was based upon the guidance provided in
the 1992 Comprehensive Water System Plan Update, which took into account pumping records and
population from 1970 -1990 as well as water conservation activities in Lakeville. Based on the
consumption trend indicated in Table 6 -1 and in Figure 5 -1,113 GPCD appears to be too low to
estimate the future water consumption of the City.
Instead, 118 GPCD was selected as the best per capita water consumption rate to predict future
design flows. Two different analyses were considered to select the per capita consumption rate.
First, the per capita water consumption for 2008 -2012 was averaged to account for the affect of the
water conservation initiatives. The average for those years was 116 GPCD. This average, however,
was not used further in this analysis because it eliminated the years when the community was
AUGUST 20, 2013
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
growing fastest. Rapid growth might occur again because Lakeville has plenty of land open for
development. In addition, the data set for years 2008 -2012 was considered too small to be a good
representation of the demand characteristics of the community.
The other predictive method allowed consideration of the complete set of per capita flow demand
data since 2000. The highest and lowest per capita demands were considered outliers and were
removed from the analysis. The remaining demands were averaged for a per capita consumption
rate of 118 GPCD. This is slightly more conservative than using the average of only the last five
years. It is also higher than the per capita demand used in the previous WTF Expansion Study, but
it provides the best fit to the water consumption patterns of the last 12 years. The results of this
calculation are shown in Table 6 -2.
Table 6 -2. Design f6ows calculated for both population growth scenarios.
2020
7.9
28.9
9.1
27.4
2030
9.6
31.4
10.5
31.4
2040
10.S
31.4
12.8
38.4
The maximum day demand for the design years, as shown in Table 6 -2, was calculated based on the
peaking factor. The historical peaking factor for years 2000 -2012 are shown in Table 6 -1. Similar
to the previous WTF Expansion Study, the 90th percentile of the historical peaking factor was
considered appropriate to use for determining the design flows. To account for the conservation
measures enacted by the City the projected peaking factor was calculated from the historical
peaking factors in 2004 -2012. The 90 percentile of the peaking factors for this period was 3.0.
The peaking factor was multiplied by the average day demand to determine the maximum day
demand for the design years. Because the maximum day demand is used as the design flow for the
WTF, the resulting max day demand represents a ten percent chance the maximum demand will
exceed the capacity of the water production and treatment facilities. The historical water demands
and the projected water demands are summarized in Figure 6 -1.
BLACK & VEATCH CORPORATION I Average Day and Maximum Day Design Flows
Ach
Water Treatment Facility Expansion Study I City of Lakeville, Minnesota
Water Demand to Community Build-out
30
Ta 25
E
0 "
a
E
0 20
0
is
10
5
0 1
2000
2005 2010 2015 2020 2025 2030 2035 2040
Year
SAD -2% -WP-AD-MCES -*- MD - 2 % MGD) -4-- MD - MCES -N(---Averap daily demand � Maximum day demand
Figure 6-1. Average and maximum day demand. Actual demand to 2012; predicted demand to 2040.
AUGUST 20, 2013
r
VVTFCapacitV when filters loaded to 4 9pm/sf (2 MGD)
- - - - - - - - - - - - - - - -
- - - - - -
- - - - - - - - - - - - I
- - - - - -
0
WTF Capacity 20 MGD
AUGUST 20, 2013
W . City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
7 Well Water Production
The City of Lakeville water system is served by 17 wells. Six wells (Wells 14 -19) have been
constructed since 2000. The rated pumping capacity of each well is identified in Table 7 -1. During
the summer months, when pumping is highest, the City pumps less than the rated capacity to avoid
problems caused by drawdown within the aquifer. The summer pumping rates are also shown in
Table 7 -1.
Table 7 -1. Lakeville wells, rated pumping capacity and actual pumping capacity during the summer
6
1,325
1,125
8
1,350
1,050
9
1,350
1,100
10
1,600
1,000
11
1,300
11050
12
1,300
900
13
1,300
975
2
1,000
850
4
1,300
1,050
7
1,275
1 =)
3
1,300
1,040
14
1,300
1,050
15
1,300
1,100
16
1,300
1,175
17
1,300
1,150
18
S00
500
19
1,300
1,100
BLACK & VEATCH CORPORATION I Well Water Production
Water Treatment Facility Expansion Study I City of Lakeville, Minnesota
1. Well capacity and summer pumping capacity provided by the City of Lakeville.
2. Well 7 is capable of producing 1,100 gpm in the summer months, but the City does not
typically use this well.
Well Number 7 is located on the edge of the City boundary. It is not connected to the Lakeville
treatment facility. In the past, it was slated for connection to a future treatment facility, but that
plan is no longer in place. The City has not used this well in approximately five years and is
considering abandoning the well.
Well number 3 is a satellite well and is used only a few days each year to supplement high demand.
It is in a low pressure zone, so the water cannot flow to the WTF. The well has a history of causing
taste and odor issues in the business district served by the well. In addition, MDH has concluded
the geologic materials surrounding the well do not offer substantial resistance to downward
groundwater flow, making the well susceptible to contamination. For these reasons well 3 is used
only when absolutely necessary.
Well 12 is rated at 1300 gpm but is never run above 900 gpm. The aquifer surrounding the well
casing is loose causing the pump to pull up sand if it is operated above 900 gpm.
The City will need to develop several new wells by 2020 to meet the maximum day demand and
have additional capacity for waste streams (plate settler sludge, equipment washing water, etc.)
within the water treatment process. Additional wells will be needed as the population of Lakeville
approaches maximum build -out. The implementation schedule will be based on the firm capacity of
all wells, or the total capacity of the wells with the largest out of service.
AUGUST 20, 2013
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
8 Water Treatment Facility Capacity
The Lakeville Water Treatment Facility was designed as a 10 MGD facility to reduce iron and
manganese concentrations present in the well water. Tests performed by MDH indicated the WTF
also reduced radium levels by approximately 40 percent, though the facility influent does not
exceed Federal Regulations for radium. The facility capacity was increased to 20 MGD through the
addition of four 2.5 MGD filters and a 1 MGD reservoir in 2001. The loading rate of the filters was 3
gpm /sf. The recent pilot study indicated the WTF can successfully operate up to 26.5 MGD by
loading each of the eight existing filters at 4 gpm /sf or 3.3 MGD.
The Lakeville WTF ultimate treatment capacity was initially planned to be 30 MGD with the
addition of four filters identical to the previous eight. With the increased filter loading construction
of four new filters will expand the WTF capacity to 40 MGD. Figure 6 -1 depicts the projected
maximum day demands for each year through 2040. As shown in the Figure, the 26.5 MGD capacity
is adequate for current water demand, but expansion of the WTF will be needed to meet the
maximum day demand between 2019 and 2025. Similar to the previous expansion, it is not
economical to construct each filter individually to meet the City's immediate needs. Instead all four
filters should be constructed at the same time. Expansion to 40 MGD will provide the City enough
water treatment capacity to meet the community's needs beyond the ultimate build -out population
of 88,800 residents. It is recommended the City carefully track the population and water use
changes to narrow the expected time period for expansion and beginning planning for an expansion
as flows approach 26.5 MGD.
BLACK & VEATCH CORPORATION I Water Treatment Facility Capacity
Water Treatrnent Facility Expansion Study a City of Lakeville, Minnesota
9 Water Storage Volume
Water storage facilities serve a number of purposes including flow equalization and fire flow
reserve. Without storage facilities, the supply and treatment facilities would need to be sized to
meet the instantaneous peak demands. Designing a water system in this way would be impractical
and expensive. The amount of equalization storage required is based upon the demand
characteristics of the water system and the capacity of the major system components. Water
supply and treatment facilities are typically sized to meet the maximum day demand. It is common
for maximum demand to occur for several days in a row because maximum demand often occurs
during a run of hot days in the summer or early fall. Water equalization storage is then sized to
meet demands in excess of the maximum day demand. For most water systems this approach
results in a system that can meet the maximum demand, will have additional water available for fire
flow and can maintain a reasonable water age to minimize the loss of the chlorine residual. The
volume of treated water stored is the sum of the volume stored in the reservoirs at the water
treatment facility and the elevated storage volume.
The volume of storage in the WTF reservoirs has a direct impact on the degree of operational
flexibility. In general, the more storage available at the WTF, the more flexible the WTF operations
can be. Without sufficient operational flexibility it would be difficult to optimize the WTF
operations. The WTF storage volume is currently 3.1 MG, which is equivalent to 16 percent of the
facility capacity. Therefore, for every 10 MGD increase in the WTF capacity the treated water
storage volume must be increased by 1.6 MG to maintain the current level of operational flexibility.
The years when additional reservoir volume will be needed for each population growth scenario
are shown in Table 9 -1. Additional high service pumping capacity must also be provided to
accommodate the additional volume of stored water.
AUGUST 20, 2013
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
Table 9 -1. Treated water reservoir volume for each increase in WTI= capacity.
2014
20
3.1
20
3.1
2015
20
3.1
26.5
4.1
2016
26.5
4.1
26.5
4.1
2017 -2019
16.5
4.1
26,5
41
2020
26.5
4.1
40
5.1
2021 -2025
26.5
4.1
40
5.1
2026 40 5.1 40 5.1
Assumed capacity of plant and reservoir was available on the first day of the year.
The City currently has 5.75 MG of elevated storage. Approximately 1.5 MG of additional elevated
storage should be constructed to provide adequate water storage. The City's current plan is to
construct the additional elevated storage in 2016.
Although it is important to have sufficient storage to meet maximum hour demands, the effects of
having too much storage must be considered. Storing too much water extends the water age and
results in reduced chlorine residuals within the distribution system and taste and odor problems.
To prevent these problems the average detention time within the distribution system should not
exceed approximately three days. Detention time within the distribution system was not modeled
for this study. However the detention time within the storage facilities could be determined by
dividing the projected treated water storage volume by the projected average day flow. Table 9 -2
identifies the projected storage volume, average day flow for the design years and the storage
facility detention time. For the purposes of this study the detention time for the finished water in
the distribution system beyond the storage facility was assumed to be much lower than the
detention time within the storage facility.
BLACK & VEATCH CORPORATION I Water Storage Volume
Water Treatment Facility Expansion Study { City of Lakeville, Minnesota
Table 9 -2. Projected Detention Time within Finished ;Prater Storage Facilities
2020
11.35
7.9
1.44
12.35
9.1
1.36
2030
12.35
9.6
1.29
12:35
10.5
1.27
2040
12.35
10.5
1.22
12.35
12.8
1.04
As indicated in Table 9 -2, the detention time ranges from 1.04 days to 1.44 days, well under the 3
day maximum. Therefore, the City should not experience difficulties maintaining the chlorine
residual or taste and odor problems as a result of excessive detention times.
AUGUST 20, 2013
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
10 Treated Water Pumping Capacity
The City of Lakeville can store 3.1 MG, or 35 percent of the 8.85 MG total treated water storage
volume, below ground at the WTF. The ground reservoir is an important part of the available water
during maximum hour events, and the capacity of the high service pumping station must be
adequate to support the maximum demand. The pumping station must be capable of pumping half
of the reservoir storage volume in a 4 hour period in addition to meeting the maximum day
demand. Therefore, the firm pumping station capacity must increase when the WTF capacity
increases.
The high service pumping station currently houses four high service pumping units, including two 4
MGD pumps, an 8 MGD pump and a 14 MGD pump. The pumping station also houses a backwash
pump dedicated to filter backwash. The ultimate capacity of the high service pumping station is 48
MGD.
Table 10 -1 and Table 10 -2 summarize the required firm high service pumping requirements for
both population growth scenarios, which were calculated by adding the flow rate required to pump
half of the reservoir volume in 4 hours to the flow rate of the maximum day. An improvement
schedule was developed to maintain the total firm high service pumping capacity slightly higher
than the required firm high service pumping capacity. Future upgrades will include installing a 14
MGD unit with a VFD in the blank space, replacement of one 4 MGD pump units with a 14 MGD unit
and replacement of the remaining 4 MGD unit with a 12 MGD unit. The existing 8 MGD unit will
remain in service through the ultimate build -out of the high service pumping station.
BLACK & VEATCH CORPORATION I Treated Water Pumping Capacity
Ank
Water Treatment Facility Expansion Study I City of Lakeville, Minnesota
Table 10 -1. Increases in High Service Pumping Capacity for 2% population growth scenario.
2013
20
19.5
3.1
28.8
16
26.5
2014
20
201
3.1
29.4
30
Add 14 MGD
36.5
2022
26.5
24.7
4.1
37.0
PUMP.
2015
20
20.7
3.1
30
30
25.7
2016
20
21.3
4.1
33.6
30
38.6
2017
26.5
21.9
4.1
34.2
40
Replace a 4 with
203 4-2040
40
31..5
5 -6
48.3
48
a 14 MGD.
2018 26.5 225 4.1 34.8
2019
26.5
23.1
4.1
35.4
2020
26.5
23.7
4.1
36
2021
26.5
24.2
4.1
36.5
2022
26.5
24.7
4.1
37.0
2023
26.5
25.2
4.1
37.5
2024
26.5
25.7
4.1
38.0
2025
26.5
26.3
4.1
38.6
2026
40
26.8
5.1
42.1
40 Now have a 14,
14,14,4 and 8
MGD pumps.
40
40
40
40
40
40
40
48 Replace 4 pump
with 12 MGD
pump.
2027
40
27.3
5.1
42.6
48
2028
40
27.8
5.1
43.1
48
2029
40
28.3
5.1
43.6
48
2030
40
28.8
5.1
44.1
48
2031
40
29.5
5.1
44.8
48
2032
40
29.7
5.1
45.0
48
2033
40
30.0
5.1
45.3
48
203 4-2040
40
31..5
5 -6
48.3
48
�a
AUGUST 20, 2013
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
Table 10 -2. Increases in high service pumping capacity for Met Council population growth scenario.
2013
20
20.0
3.1
29.3
16
2014
26.5
21.0
31
33.3
16
2015
26.5
22.1
4.1
34.4
40
Add a 14 mgd
pump & replace a 4
mgd with a 14 mgd
2016
26.5
23.2
4.1
35.4
40
2017
26.5
24.2
4.1
36.5
40
Have a 4, 8, 14,14
and 14 mgd.
2018
26.5
25.3
4.1
37.6
40
2019
26.5
26.3
5.1
38.6
48
Replace 4 with 12
mgd pump
2020
40
27.4
5.1
417
48
2021
40
27.8
5.1
43.1
48
2022
40
28.2
S.1
43.5
48
2023
40
28.6
5.1
43.9
48
2024
40
29
51
44.3
48
2025
40
29.4
5.1
44.7
48
2026
40
29.8
5.1
45.1
48
2027
40
30.2
5.1
45.5
48
2028
40
30.6
5.1
45.9
48
2029
40
31
5.1
46.3
48
2030
40
31.4
5.1
46.7
48
2031
40
32.1
5.1
47.4
48
2032
40
32.8
5.1
48.1
48
2033
40
33.5
5.1
48.8
48
Additional HSP
capacity needed.
2034
40
34.2
5.1
49.5
48
2035
40
34.9
5.1
50.2
48
2036
40
35.6
5.1
S0.9
48
2037
40
36.3
5.1
51.6
48
2038
40
37
5.1
52.3
48
2039
40
37.7
5.1
53
48
2040
40
38.4
5.1
53.7
48
BLACK & VEATCH CORPORATION I Treated Water Pumping Capacity
Water Treatment Facility Expansion Study I City of Lakeville, Minnesota up
11 Water Treatment Facility Improvements
The existing WTF has a capacity of 20 MGD, with a 3.1 MG reservoir and a high service pumping
station capacity of 30 MGD (16 MGD firm). Additional loading of the filters will increase the capacity
to 26.5 MGD. The ultimate capacity of the WTF is 40 MGD, with a 6.1 MG reservoir and high service
pumping station capacity of 48 MGD. Table 11 -1 presents a schedule for expansion of the treatment
capacity, reservoir storage volume and treated water pumping capacity through ultimate build -out
of the Lakeville WTF to ensure that projected water demands can be met. For the purposes of long -
range planning, the schedule of improvements was developed as a conservative plan based on the
Met Council population growth scenario. The improvements should be complete by the year
indicated in Table 11 -1.
Table 11 -1. Water Treatment Facility Improvement Schedule
Construct 4 Filters (3.3 MGD each)
X
Treated Water Reservoir X X
Add High Service Pumping Capacity X
IY
Expand Chlorine Storage & Feed X X
System
Backwash Air Blower X
Backwash Pump X
Expand Orthophosphate Storage & X
Feed System
Expand Compressed Air System X
Packaged Gravity Plate Settler X
Washwater Recovery Pump X
Emergency Generator X
Expand Plant Intake Capacity X
na.sa.�..�.a..as�- rte.. r - m�rer -. s+ - ���n �- +a. — a,�
AUGUST 20, 2013
i City of Lakeville, Minnesota I Water Treatment Facility Expansion Study
Expand High Service Pump Effluent X
Miscellaneous Improvements X
The following paragraphs provide a detailed description of each of the WTF improvements
identified in Table 11 -1.
Filters. New filters will be identical to the existing filters and have a capacity of 3.3 MGD each. The
constant rate dual media filters will be equipped with air -water backwash. Filter installation will
include the required SCADA programming to monitor and control the new filters. It is
recommended the City fill and equip all filters during filter construction.
Treated Water Storage Reservoir Additional treated water reservoir volume will be added in 1 MG
increments. To maintain the current level of operational flexibility while accommodating the
increased filter loading,1 MG of reservoir volume will be needed before the new filters are
constructed. A new 1 MG reservoir structure will be constructed by 2020 during expansion of the
WTF to 40 MGD in treatment capacity. If possible, the influent pipeline for the new storage
reservoirs will connect to the existing reservoir influent pipeline. A new influent pipeline will be
constructed if necessary. A common effluent pipeline will be constructed to convey the water from
the new reservoirs to the high service pumping station wetwell.
High Service Pumping Station Capacity Expansion The first capacity expansion of the high service
pumping station will install a 14 MGD VFD unit in the area currently filled with a blank. Each
subsequent expansion will include upgrading the two existing 4 MGD vertical diffusion vane
pumping units with a 14 MGD pumping unit and a 12 MGD pumping unit. Each expansion of the
high service pumping station will include the required SCADA programming to monitor and control
the new equipment.
Chlorine Storage and Feed System Expansion When planning for the WTF expansion it is
recommended the City consider alternatives to chlorine gas for disinfection. If chlorine gas is
selected by the City for continued use, the chlorine storage and feed system expansion will include
four additional chlorine scales and two chlorine feeders.
In addition, chlorine storage and feed capacity will need to increase in the near term to
accommodate the additional filter loading to 26.5 MGD. The WTF is currently nearing the
chlorination capacity when producing less than 20 MGD and will not be sufficient for 26.5 MGD.
BLACK & VEATCH CORPORATION I Water Treatment Facility Improvements
Water Treatment Facility Expansion Study 1 City of Lakeville, Minnesota w' a
Orthophosphate Storage and Feed System Expansion Orthophosphate is added to the treated
water to inhibit corrosion of the copper pipe within the distribution system. The orthophosphate
storage and feed system expansion will include the upgrade of the existing chemical metering
pump, if necessary and installation of a larger bulk chemical storage tank if needed to meet
capacity.
Compressed Air System Expansion The compressed air system expansion will include the
installation of an additional air receiver, air dryer, oil separator, and associated valves, piping, and
appurtenances. The expansion of the compressed air system is required to accommodate
additional pneumatic filter valves.
Packaged Gravity Plate Settler The capacity of the new packaged gravity plate settler will be
identical to the existing unit. The new unit will be located adjacent to and east of the existing unit.
The SCADA system will be programmed to monitor and control the new plate settler.
Wash Water Recovery Pump A submersible wash water recovery pumping unit and associated
valves, piping, and appurtenances will be installed in the wash water recovery basin. The capacity
of the new pumping unit will be identical to the existing pumping units. The SCADA system will be
programmed to monitor and control the new wash water pumping unit.
Emergency Generator An emergency power generator will be installed adjacent to the existing
generator. The existing 1150 kW generator can provide enough emergency power to run the WTF
and two wells. A similar sized generator will be needed to operate the expanded WTF and
additional wells.
Influent Capacity. The existing influent pipe reduces from 30 inches in diameter to 24 inches in
diameter as it approaches the WTF. Preliminary calculations indicate the velocity of the water
through this pipe will become excessive when the flow into the plant is larger than 30 MGD. A
larger diameter plant influent pipe or duplicate plant influent pipe will be needed to accommodate
the increased influent volume.
High Service Pump Effluent Piping. The plans from the previous plant expansion indicated a future
36 -inch pipe could be added when the plant treatment capacity is increased. The expansion of the
plant to 40 MGD will require construction of the planned 36 -inch effluent pipe to maintain
acceptable velocities within all of the effluent pipes.
Miscellaneous Improvements In addition to the specific improvements described previously there
are other improvements that will bring the WTF up to current design standards and codes.
Improvements may include installation of equipment such as automatic lighting or updated
chemical metering devices. Structural repairs will be completed if needed as part of the WTF
expansion project.
AUGUST 20, 2013
City of Lakeville, Minnesota I Water Treatment Facility Expansion Study.
12 Opinion of Probable Project Cost
The budget level opinion of probable project cost to increase the capacity of the Lakeville Water
Treatment Facility from 20 MGD to 40 MGD, increase the water storage and high service pumping
capacities and double the size of the existing Truck Shop is $22,900,000. A summary of the
probable costs for the complete expansion is provided in Table 13 -1.
Table 12-1. Opinion of Probable Cost for Complete Expansion of WTF and Truck Shop.
General Requirements $ 1,400,000
Site work $950,000
Water Treatment Facility Expansion $ 15,700,000
Truck Shop Expansion $610.000
Upgrades for Safety, Redundancy and Reliability $ 200,000
Contingency (30 %) $ 5,300,000
Water Treatment Facility Expansion Study I City of Lakeville, Minnesota'
13 Conclusions and Recommendations
13.1 CONCLUSIONS
The following paragraphs summarize the study conclusions and associated recommendations.
The City experienced rapid growth during the first half of the last decade, followed by more
moderate growth. The Twin Cities Metropolitan Council's population projections continue to
indicate the potential for rapid growth until 2020.
The City's initiatives to decrease peak flow rates through incremental billing, alternate day /time
of day watering schedules and community outreach have had some impact. Other factors, such as
the economic recession, may have contributed to the decreased maximum flows.
Per capita water consumption of 118 GPCD is representative of the water consumption patterns
from the previous decade. The water consumption pattern is expected to continue into the future.
Water consumption data from 2000 -2012 indicated a maximum day to average day peaking
factor of 3.0 would represent 90% of the historical flows. This peaking factor was applied to the
projected average annual demand for the design years.
Well numbers 2 and 4 are now connected to the WTF and used regularly. Well number 3 is used
only a few days each year. Well number 7 has not been used for at least four years. The City is
considering abandoning the well. Up to ten new wells will be required to supply adequate water
to meet a 40 MGD demand.
The firm capacity of the high service pumping station is currently lower than required to meet
the emergency pumping requirements. Additional pumps will be needed as total water demand
increases.
The City's maximum day water demand is expected to reach the current WTF capacity of 20 MGD
between 2013 and 2014. The WTF can increase the loading to the filters as needed to a maximum
of 4 gpm /sf, or 3.3 MGD, which increases the WTF capacity to 26.5 MGD.
Lakeville's maximum day water demand is expected to exceed the 26.5 MGD capacity between
2019 and 2025, depending on the rate of population growth within the community.
Expansion of the WTF will add four filters that are identical to the existing filters and will
increase the treatment capacity of the plant to 40 MGD. This treatment capacity is adequate to
meet the water demand for Lakeville beyond the expected community build -out population of
88,800 people.
AUGUST 20, 2013
I City of Lakeville, Minnesota j Water Treatment Facility Expansion Study
13.2 RECOMMENDATIONS
The following actions are recommended for Lakeville based on the findings of this expansion study.
The projected maximum day demand reaches 20 MGD, the design flow of the existing facility,
between 2013 and 2014. Planning for a capacity increase to 26.5 MGD should commence.
Based on Met Council population projections, the maximum day demand is projected to exceed
the Lakeville WTF maximum treatment capacity of 26.5 MGD in 2019. Planning for the final
expansion to 40 MGD should begin in the next several years.
To maintain the current degree of operational flexibility, the existing 3.1 MG treated water
storage reservoir at the WTF should be expanded to 4.1 MG before the WTF begins treating 26.5
MGD and to 5.1 MG when the additional filters are constructed. This will increase the total
reservoir storage volume to 5.1 MG.
The capacity of the Lakeville WTF high service pumping station should be increased to 30 MGD in
2014 . to he able to meet the maximum day demand. The existing blank space in the high service
pumping station should be filled with a 14 MGD pumping unit with a VFD.
BLACK & VEATCH CORPORATION I Conclusions and Recommendations