A. Review Groundwater Well Study and Water Quality Improvement Options
CITY OF
CHANHASSEN
7700 Market Boulevard
PO Box 147
Chanhassen, MN 55317
Administration
Phone: 952.227,1100
Fax: 952.227.1110
Building Inspections
Phone: 952.227,1180
Fax: 952.227.1190
Engineering
Phone: 952,227.1160
Fax: 952.227.1170
Finance
Phone: 952,227,1140
Fax: 952.227.1110
Park & Recreation
Phone: 952,227.1120
Fax: 952.227,1110
Recreation Center
2310 Coulter Boulevard
Phone: 952.227.1400
Fax: 952,227,1404
Planning &
Natural Resources
Phone: 952.227,1130
Fax: 952,227.1110
Public Works
1591 Park Road
Phone: 952.227.1300
Fax: 952.227.1310
Senior Center
Phone: 952,227,1125
Fax: 952.227.1110
Web Site
www.ci.chanhassen.mn.us
MEMORANDUM
TO:
Todd Gerhardt, City Manager
10.
. Paul Oehme, Director of Public Works/City Engineer ·
FROM:
DATE:
January 12, 2009
~
SUBJ:
Review Groundwater Well Study and Water Quality Improvement
Options for Well #4 - Project No. 09-02
BACKGROUND
The City of Chanhassen has recently experienced several significant events
related to the adequacy and reliability of its potable drinking water supply. In the
summer of 2007, two of its shallower wells, Wells 5 and 6, experienced rapidly
decreasing water levels and became unusable. They have not recovered since that
time and remain out of service. Other wells in Chanhassen's and nearby Eden
Prairie's well supply network have seen declining water levels in recent years
which translates into declining yields.
The Metropolitan Council Environmental Services has been working on a
regional water supply model and master plan that identifies issues each city in the
area must consider when planning water appropriations. Part of that planning
process suggested the possibility of significant additional drawdown in the
aquifers supplying Chanhassen and the potential to impact nearby natural
resources with future withdrawals. Significant additional drawdown in the City's
main aquifer could result in the loss of additional wells.
Finally, Well 4 has elevated levels of radium, a naturally occurring contaminant,
which are within the Minnesota Department of Health guildeline levels, however,
higher than what we would like to see.
As a result of these issues, the City has undertaken this well siting study and water
quality improvement options for Well #4.
OVERVIEW
The purpose of this study was to guide the City in planning out its future water
supply in general and provide specific guidance for future well locations in its
East and West wellfields that will be able to supply water to the city as it grows.
The planning period for this study runs to ultimate build out of the city water
system which will occur when the city reaches ultimate population. The following
specific elements were addressed in this study:
Chanhassen is a Community for Life - Providing for Today and Planning for Tomorrow
A
~.'
Todd Gerhardt
Review Groundwater Well Study
January 12,2009
Page 2
. Aquifer Yield Assessment. Provide a qualitative assessment of whether or not the Jordan
aquifer alone can supply all of the city's future water needs. Provide a similar qualitative
assessment of the Franconia Ironton Galesville (FIG) aquifer's ability to augment the
City's current well network and serve as an average day water source.
. Well Locations. The study is intended to help the City estimate the amount of new wells
necessary to meet peak summer demands and plan for the approximate locations of new
wells in and near the two existing wellfields while also meeting safe yield requirements
listed in the State Rules. This includes an evaluation that will take into account receding
water levels that may occur in the Chanhassen wells as appropriations in the area
mcrease.
. Potential Contaminants. For this element, a preliminary review of MPCA and related
resources will be conducted to locate known potential sources of contamination located in
or near enough to Chanhassen to be of concern. This is limited to known releases and
documented groundwater contamination in the aquifers of concern.
. Well 4 Water Quality Improvements. A recommendation for water quality
improvements.
RECOMMENDATIONS
Aquifer Yield Assessment. After performing the modeling and reviewing past studies, the
following conclusions were reached regarding the aquifers in the city:
1. The shallow sand and gravel aquifer of Wells 5, 6 cannot be considered a viable
source for the future unless some form of augmentation is planned such as aquifer
storage and recovery (this is a process where water from another source is treated and
then pumped down into the aquifer and stored for later reuse). Well 11 is also in the
gravel aquifer however currently has 200 ft of static water level over the pump.
While the city will continue to use Chanhassen Well 11 the City will need to monitor
this well closely to see ifit will be a long term viable municipal source of water.
2. The Prairie du Chien-Jordan aquifer appears to be able to supply the City the water it
needs both now and into the future but localized drawdown conditions at specific
wells will continue to be a problem. New wells will be needed to meet future
demands and those wells should be sited carefully and as far apart as reasonable to
limit interference. Due to the trends of lowering water levels, it is recommended that
the City pursue wells in another aquifer as a hedge against potential future problems.
It is recommended that the City consider at least one FIG well in each major
wellfield. If drawdown continues to be a concern in the Jordan then it is possible that
additional FIG wells could be added as needed to augment the City supply.
3. The Franconia-Ironton-Galesville aquifer could not be studied in depth for this
evaluation since little geological information is available about the aquifer in this
area; however a preliminary review of the data available suggest that the aquifer
should be able to support two 500- to 600-gpm wells, even considering future
drawdowns likely to be caused by growing communities to the west of Chanhassen.
The modeling performed for this report included a preliminary look at the FIG
g:\eng\public'-2009 projects\09-02 well #4 water quality improvements\09-02 ws bkgd feasiblity report review. doc
Todd Gerhardt
Review Groundwater Well Study
January 12,2009
Page 3
aquifer. Model results show static water levels at least 300 feet of water above the
top of the FIG aquifer in most all parts of Chanhassen even after drawdown from
future growth is considered. Even with the poor yields common in the FIG, yields of
500- to 600-gpm or more could be expected depending on specific local aquifer
characteristics. Questions remain concerning the properties of the FIG aquifer in the
Chanhassen area and the degree of hydraulic connection between this aquifer and the
overlying Prairie du Chien-Jordan aquifer which would need to be addressed before
committing to municipal wells in the FIG aquifer. For this reason, before any FIG
well is considered a testing well should be drilled and a pump test should be
completed.
Well Locations. Five new wells will be required to provide firm capacity at peak summer
demand in 2030. Based on this report, an additional well may be necessary between 2025 and
2030 to provide firm capacity at peak summer demands. This new well should be added into the
2009 rate structure between years 2025 and 2030. A total of 14 potential well sites were
reviewed for this report. The groundwater modeling suggests that each of the 14 potential well
sites will likely be able to support a new 1,000 gpm Prairie du Chien-Jordan well. A map of the
well sites is shown on the attached figure. Sites 2 and 10 are very near the eroded edge of the
Jordan Sandstone. If those sites are chosen, exploratory borings should be performed in advance
of the well drilling to ensure that they are viable sites. Sites that performed very well include 2,
7,8, and 10. Sites that performed well include 5, 6, 12, and 14. Sites that performed adequately
include 1, 3,4,9 (this is the proposed Well 14 site), 11, and 13.
Chanhassen Well 4 Water Quality Improvements and Future Well 14 Planning. Two
alternatives related to the treatment of Chanhassen Well 4 raw water were detailed in this report.
The first option is to pipe the raw water from the well to the East Treatment Plant and the other
option is to construct an on-site package plant for treatment. A cursory review was also
completed of sealing the most probable geological area which is most likely causing the water
quality problems. This option was not recommended or reviewed further in any great detail
because it would most likely reduce the production of the well as much as half. Converting this
well to an ASR well was also reviewed but not recommended because of government agency
reviews and approvals that would be required and because of concerns for likelihood of success.
Drilling a new well was also considered but deemed not cost effective.
Based on this analysis, it was determined more cost effective to connect Chanhassen Well 4 to
the East Treatment Plant than to construct an on-site treatment plant for iron, manganese and
radium removal. Piping Well 4 to the East Treatment Plant would cost an estimated $700,000 to
$920,000 while constructing and on-site package treatment plant would cost approximately $1.1
to $1.5 million. A benefit of constructing a pipe from Well 4 to the East Water Treatment Plant
is this pipe can also be used for a future well along the corridor.
Attachments
g:\eng\public\_2009 projects\09-02 well #4 water quality improvements\09-02 ws bkgd feasiblity report review. doc
Barr Engineering Company
4700 West 77th Street. Minneapolis, MN 55435-4803
Phone: 952-832-2600 . Fax: 952-832-2601 · www.barr.com An EEO Employer
BARR
Minneapolis, MN . Hibbing, MN . Duluth, MN . Ann Arbor, MI · Jefferson City, MO · Bismarck, ND
Technical Memorandum
To:
From:
Subject:
Date:
Project:
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22, 2008
23101001
Background
The City of Chanhassen has recently experienced several significant events related to the adequacy
and reliability of its potable drinking water supply. In the summer of 2007 two of its shallower wells,
Wells 5 and 6, experienced rapidly decreasing water levels and became unusable. They have not
recovered since that time and remain out of service. These wells supplied the recently completed
East Water Treatment Plant so their loss not only reduced total supply but also the treated supply
which was the highest quality water produced in the City.
Even before these wells failed the City's wells were operating near capacity during peak summer
pumping. Other wells in Chanhassen's and nearby Eden Prairie's well supply network have also seen
declining water levels in recent years. In addition to this, two of the City's remaining wells have
other issues that must be addressed to ensure long term reliability. Well 4 has elevated levels of
radium, a naturally occurring contaminant, that occasionally exceed water quality standards. In
addition to this, during a recent attempt to rehabilitate Well 3 an old drill bit was found to be stuck in
the hole which limits the work that can be done to the well and in turn lowers its reliability.
Finally, the Metropolitan Council Environmental Services has been working on a regional water
supply master plan that identifies issues each city in the area must consider when planning water
appropriations. Part of that planning process suggested the possibility of significant additional
draw down in the aquifers supplying Chanhassen and the potential to impact nearby natural resources
with future withdrawals. Significant additional drawdown in the City's main aquifer could result in
the loss of additional wells. As a result of these issues the City has undertaken this well siting study.
P:\Mpls\23 MN\10\23 10100100 Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo]inal.doc
To:
From:
Subject:
Date:
Page:
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
2
Introduction
The purpose of this study is to assist the City of Chanhassen in planning out its future water supply in
general and provide specific guidance for future well locations in its East and West Well Fields that
will be able to supply water to the city as it grows. The planning period for this study runs to ultimate
build out of the city water system which will occur when the city reaches ultimate population. The
following specific elements will be addressed in this study:
. Well Locations. The study is intended to help the City plan the approximate locations of new
wells in and near the two existing well fields that will meet ultimate water demands while
also meeting safe yield requirements listed in the State Rules. This includes an evaluation that
will take into account receding water levels that may occur in the Chanhassen wells as
appropriations in the area increase.
. Potential Contaminants. For this element a preliminary review of MPCA and related
resources will be conducted to locate known potential sources of contamination located in or
near enough to Chanhassen to be of concern. This is limited to known releases and
documented groundwater contamination in the aquifers of concern.
. Well 4 and Well 14 Planning. Provide specific guidance related to connecting existing
Well 4 to the city's East Water Treatment Plant along a route that includes a site for future
Well 14.
. Aquifer Yield Assessment. Provide a qualitative assessment of whether or not the Jordan
aquifer alone can supply all of the city's future water needs. Provide a similar qualitative
assessment of the Franconia-Ironton-Galesville (FIG) aquifer's ability to augment the City's
current well network and serve as a backup supply source.
In order to cover these items the report will be broken down into four main sections including:
I. Water System Constraints
II. Well Siting Modeling
III. Existing Well 4 and Future Well 14 Considerations
IV. Conclusions and Recommendations
The first section, Water System Constraints, will briefly define the conditions of the existing and
future system for which the well siting modeling will be done. This section will include a summary of
the wells that are currently utilized by the city, followed by a discussion of known aquifer
contamination that might impact well locations. This section will conclude with a look forward that
will summarize the future average and peak day demand that will be used in modeling. Barr will use
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To:
From:
Subject:
Date:
Page:
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December22~,2008
3
data provided by the City in the current comprehensive planning effort to identify an annual and
instantaneous amount of water that the City will need to appropriate in order to adequately supply
water to its residents and other costumers.
The second section, Well Siting Modeling, will describe the modeling work that went into the well
siting portion of this effort. This section will include a summary of model purpose and scope,
modeling assumptions and the model refinement effort. This will be followed by a description of the
model runs including a simulation of the ultimate average pumping conditions and a simulation of the
projected maximum water. The section will conclude with a summary of the modeling results and
cover the qualitative assessment of the Jordan aquifer. Barr will use the recently completed metro
area groundwater model prepared for the Metropolitan Council to estimate the impacts of new wells
on the Jordan aquifer in Chanhassen and to site wells in the city's two well fields.
The third section, Existing Well 4 and Future Well 14 Considerations will deal specifically with
connecting existing Well 4 to the East Treatment Plant. Included in this section will be a qualitative
assessment of the treatment needed at Well 4 along with cost estimates comparing an on site package
plant to connecting the well to the existing East Treatment Plant.
The fourth and final section, Conclusions and Recommendations, will summarize the findings in
the previous sections in the form of recommendations of action that the City of Chanhassen should
take. A summary of the aquifer yield assessment mentioned above will be included in this section of
the memorandum.
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To:
From:
Subject:
Date:
Page:
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
4
Water System Constraints
In any well siting plan it is critical to identify constraints that will shape the effort. A constraint is
defined as a condition that must be met in order for a proposed well site to be considered. The goal of
this effort is to identify well sites, which will meet these constraints. As the need arises for a new
well the City can then select from these well sites using project-specific criteria that might not be
known at this time or might change from what they are today. The constraints that will be used in
determining well sites that will be modeled include:
. Only well sites proposed by the city will be considered.
. Wells will only be modeled in the Jordan Aquifer.
. Only current city supply wells considered reliable will be used in future projections
. Existing wells will be modeled at sand free (A WW A standards) sustainable pumping rates.
This means the starting point for well pumping rates in the model may not match what the
City normally considers the rate for a given well to be. This will be further explained below.
. The total yield of the wells modeled must equal the ultimate peak day demand for the city.
. The configuration of the future well fields must be set up to feed two water treatment plants,
the existing East Treatment Plant and the proposed West Treatment Plant.
Existing Wells
The city currently has infrastructure for 12 wells in place; including Wells 2 througb 13. Well 1 was
the City's original well and has since been abandoned and sealed. All of the existing wells are
completed in one of two aquifers the regional Prairie du Chien Jordan aquifer or a shallower local
sand and gravel aquifer located in the glacial drift. Two of the wells completed in this shallower sand
and gravel aquifer, Wells 5 and 6, are no longer in service since water levels in them dropped to a
point where they could not be used in the summer of 2007. A third well located in this same aquifer,
Well 11, will be excluded from long-term consideration since it cannot be considered a reliable
source given what happened to Wells 5 and 6. In addition to this Well 3 was recently partially
rehabilitated and found to have an old drilling bit stuck down in the open hole limiting its sand free
pumping rate to 800 gpm. The remainder of the wells produce water at various rates as shown in the
Table 1. Note that there are two different rates listed, the Comprehensive Plan Rate and the Modeling
Rate. This is done simply to maintain consistency with other planning efforts. The Comprehensive
Plan Rate is that rate listed in Appendix D of the City's current Comprehensive Plan, which is the
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From:
Subject:
Date:
Page:
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
5
Department of Natural Resources-Division of Waters and Metropolitan Council Water Emergency
and Conservation Plans work sheet. The Modeling Rate is that rate used in the computer model for
calculating drawdown and well interference and assessing the viability of future well sites. These
rates are nominal well production rates that represent a reasonable estimate of anticipated long term
sustainable rates at the wells. The rates are allowed to vary within the model depending upon the
water level within the aquifer so it is not critical that they represent the exact current actual well
capacity. Furthermore, actual well production rates vary depending upon a number of circumstances
including, but not limited to; hydrogeologic well interference, hydraulic pump interference,
operational settings, weather patterns such as drought, and the condition of the pumping equipment.
Table I summarizes the well rates and notes which water plant they would serve. The different water
plants are further described below in the Future System Description subsection of this memo.
Table 1
Existing Well Capacities
Comprehensive Modeling Plant
Well # A uifer Plan Rate Rate Served
2 Jordan 850 1,000 m East Side
3 Prairie du Chien/Jordan 800 m 800 m West Side
4 Prairie du Chien/Jordan and 950 gpm 1,000 gpm East Side
FIG
5 Drift 0 0 m East Side
6 Drift 0 0 m East Side
7 Jordan 1,100 1,000 m West Side
8 Jordan 1,000 1,000 m West Side
9 Jordan 1,000 1,000 m West Side
10 Jordan 1,000 1,000 m East Side
11 Drift 1,000 0 m East Side
12 Prairie du Chien/Jordan 1,000 1,000 m East Side
13 Prairie du Chien/Jordan 900 1,000 m East Side
In addition to the wells owned and operated by Chanhassen, the City also has permission to use a
well owned by a school on the west side of town under emergency conditions. The City considered
converting it to a permanent well when Wells 5 and 6 failed. However, it was subsequently
discovered that it was not constructed to current code and would require significant, costly, and time
consuming repairs to convert the well into a permanent City well. Because of this efforts have been
focused on siting new wells and adding treatment to Well 4 to bring it back into regular use.
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To:
From:
Subject:
Date:
Page:
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
6
Water Levels
Water levels in all of the City's wells have declined over the years, Similar declines in water levels
have been observed in nearby communities such as Eden Prairie. Some of the declines in
Chanhassen's wells have resulted in significant problems including the failure of Wells 5 and 6 and
the need to deepen pump settings in other wells. Most of the reasons for the declines are related to
increasing population and the climate. As a population grows so does its' demand for water. When
dry cycles hit the region the increased population produces higher and higher peak demands during
summer months when lawn irrigation is greatest. Whenever these dry cycles run for extended periods
the source aquifer becomes more stressed than it in the past due to the greater demand. Levels in
individual wells can drop down to the pump causing reduced yield or even pump failure.
In the past, water levels would drop during heavy summer use then rebound to normal levels in the
winter when demand diminished. During these times winter water levels would be close enough to
that of the previous year so as not to raise any concern. In recent years even winter water levels have
been lower than those recorded in previous winters. Some of this may be attributable to recent
drought conditions which have reduced aquifer recharge. However, the significant increase in
population and related increase in water use has likely been the most significant cause.
The water level fluctuation in Chanhassen is not entirely unexpected given the increase in water
demand and the recent drought conditions. However, because of the proximity of the Prairie du Chien
to the surface in Chanhassen the fluctuation is of greater concern since it is resulting in water levels
closer to the top of the source aquifer and is often close to pump setting elevations. There are three
things that are of concern, first the trend has been decreasing levels year over year, second there is
evidence that since about the year 2000 the magnitude of fluctuation between summer and winter has
been more severe, and third the summer drop has been bad enough to require lowering pump settings
and in some cases is approaching the lowest levels that the well can support. All of the wells lowest
readings have all occurred in the last eight years and Wells 5 and 6 failed during this time.
The groundwater flow model used in the well siting work is described later in this report and was
calibrated to existing data which shows the fluctuations. The City should continue to carefully
monitor water levels noting monthly and annual minimum and maximum static and pumping water
levels for each well. This data should be reviewed regularly to determine if water levels are
continuing to decline to a point where additional action will be needed.
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To:
From:
Subject:
Date:
Page:
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
7
Known Contamination
The city has one well with a known contamination issue related to a naturally occurring contaminant.
In the past, Well 4 has tested positive for radium. The regulatory limit for this contaminant is 5 pCi/l
and the well has tested as high as 6.8 pCi/l. Radium is naturally occurring and usually associated with
sandstone aquifers. In the Metro area it is more commonly found in the Mt. Simon Hinckley
formation but occasionally shows up in some Jordan wells. It can also occur in portions of the FIG
aquifer and the open hole portion of this well extends into that formation. Past studies of this
contaminant show no discernable pattern to the occurrence of this contaminant. Because of this well
sites will not be screened to limit the possibility of encountering this contaminant.
Maps showing the potential contaminant source inventory are shown on Figures 1 and 2. There are no
significant issues that would result in eliminating any of the potential well sites considered in this
study. The only caveat to this is for potential Well sites 3, 4, 11 and 12 which are in the northwestern
part of the City, down gradient and relatively close to several MPCA multi-sites. Should one of these
sites be selected for a future well Barr recommends that the status of those sites be verified. If
concern arises then a groundwater sample should be collected and tested prior to committing to a new
well. Figure 1 shows the potential contaminant sources with respect to the city's existing wells, while
Figure 2 shows the same information with respect to the potential well sites. This map is a
compilation of known and reported contamination sources. It is a compilation of the regulatory data
that are readily available. Barr Engineering Co. cannot guarantee that the aquifers under investigation
are free of contamination. However, it is important to note that the City has completed a well head
protection plan as required by the State and according to City staff none of the wells were considered
vulnerable. This does not guarantee that Chanhassen's wells cannot be contaminated from surface
sources but it does suggest that contamination is not likely. This is largely due to the significant
layer of clay present in this area that separates the surface from the source aquifers.
Future Average and Peak Day Demand
The well siting model utilizes both the average and peak day demand for Chanhassen as well as
surrounding communities. The Metropolitan Council Environmental Services has compiled projected
water demand data for all of the communities in the metropolitan area. The data is used in the model
to represent the water demand for each of the surrounding communities for the year 2030. The
ultimate day demand data for the city of Chanhassen was taken from the water section of City's
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From:
Subject:
Date:
Page:
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
8
current Comprehensive Plan. In that document the ultimate peak day was determined to be
17.3 MGD or roughly 12,400 gpm. The peaking factor used in planning was 3.1 therefore the average
day demand is projected to be 5.8 MGD or 4,000 gpm. While not identical they are in line with what
MCES is projecting for ultimate demand in Chanhassen in the year 2050.
Future System Description
The current plan for Chanhassen is to construct a second water treatment plant on the west side of
town. The plan is for the current East Side treatment plant and the Future West Side treatment plant
to each produce 6,000 gpm of finished water. The well siting modeling effort recognizes this plan by
dedicating each existing well to one of these two plants. Under this plan the current wells can supply
a total of 5,000 gpm of water to the East Plant assuming that Well 4 is connected to the plant and
Well 11 is excluded from future consideration, and 3,800 gpm to the future West Side plant. Under
the final three modeling scenarios future wells are modeled that approximately "fill out" the
remaining supply to each plant up to at least 6,000 gpm.
Well Siting Modeling
Purpose and Scope
This section of the technical memorandum summarizes the results of groundwater-flow modeling to
verify if the proposed future water-supply well locations provided by the City of Chanhassen will be
able to supply water for the city to ultimate build out. The City of Chanhassen provided Barr
Engineering Co. with a list of 14 possible well locations for consideration which are shown on Figure
2. These are sites that are either already owned by the City or are potentially available for purchase.
These 14 sites were evaluated in the newly developed Metro Model groundwater-flow model
(developed by Barr for the Metropolitan Council) by using the model to simulate pumping conditions
during peak regional demand periods that the Metropolitan Council projects for the year 2030. For
this study, the proposed wells at all 14 sites were assumed to be completed in the Prairie du Chien
Group and or Jordan Sandstone (Prairie du Chien-Jordan aquifer), with construction similar to the
recently installed Chanhassen Wells 12 and 13. However, the model does have the capability of
evaluating wells in other aquifers (such as the FIG aquifer).
The sustainable capacity (or "yield") of a well is dependent upon how the well is constructed and the
hydrogeologic conditions surrounding the well (e.g., the permeability of the aquifer). The sustainable
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From:
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Date:
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
9
capacity of a well is also dependent on the "available drawdown", which is controlled by the regional
groundwater levels in the aquifer. Regional groundwater levels can change over time in response to
changing climatic conditions. but the primary cause of changes in regional groundwater levels in the
metro area is increased pumping by municipal wells. As population increases, water demand
increases, along with the installation of more high-capacity wells and more pumping. The so-called
"cone of depression" of each pumping well intersects the cone of depression of other wells, causing
an additive decrease in water levels.
The Metropolitan Council has made projections of future water demand on a community-by-
community basis for the Seven-County Metropolitan Area on la-year increments to the year 2050.
These demand projections include both average daily demand and maximum peak (summer) demand.
Some water conservation is factored into these estimates. In general, demand is projected to be near
maximums by 2030-this is the date that is often used to evaluate full build-out conditions in the
metro area (although this may vary from community to community). For this study, we used projected
average and peak demands at 2030 to estimate pumping conditions for the communities in Hennepin
and Carver Counties-those areas that most likely will have a meaningful impact on Chanhassen' s
groundwater availability in the future. As noted above Chanhassen' s pumping conditions were set
based on Section 9 of the City's current Comprehensive Plan.
The analysis described herein uses the following assumptions concerning future water demand:
· The simulated condition for evaluating demand limitations is a 2-week peak summer
condition in 2030 during which all existing and proposed city wells are assumed be running
continuously.
· Chanhassen Well 11 (completed in the glacial drift aquifer) is assumed to not be available to
meet future water demands.
· Chanhassen Well 4 is assumed to be pumping and connected to the East Water Treatment
plant.
· The maximum pumping rate for existing and future wells is 1,000 gallons per minute (gpm).
This rate is assumed to relate to well construction and aquifer permeability. The model
analysis further imposes a potential demand restriction that reduces available draw down due
to regional pumping.
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
10
.
The minimum allowable water level during pumping of any of the existing or future
Chanhassen wells is equal to 10 feet above either the top of the pump intake or the top of the
Prairie du Chien Group!. The Minnesota Department of Natural Resources (MDNR) does not
permit pumping levels to drop below the top of a confined aquifer and generally requires a
buffer of about 10 percent of the aquifer thickness above the top of the aquifer. Note that
MCES is in the process of developing additional "Water Supply Issue Responses" that will
shape future well siting in the Metropolitan area. They are not yet final and only became
available in draft form recently. The implication of those issue responses is not accounted for
in this modeling run but will affect the City when new wells are requested.
.
In the modeling analysis, an existing or future well is allowed to pump at a continuous rate of
1,000 gpm until such time that the pumping water level in the aquifer drops to a
predetermined point. At this time the model computes a new pumping rate for the well that is
less than 1,000 gpm. This continues in an effort to simulate operations that would occur to
maintain a safe water level in the wells as pumping water levels approach the pump intake or
the top of the aquifer. If the model predicts a pumping rate that is less than 500 gpm, the well
is shut off and pumping is set to zero. This last condition is imposed with the assumption that
if conditions only permit a well to operate at rates less than 500 gpm, the well location
probably is inadequate.
Five new Jordan wells, pumping at 1,000 gpm each, will be required along with existing
wells pumping at 1,000 gpm each to provide firm pumping capacity at peak summer demand
in 2030. That is a total of 13,800-gpm of supply or l2,800-gpm of firm supply which meets
the peak projected demand of 12,400-gpm (17.3 MOD). Ultimately a sixth new well may be
needed to ensure firm capacity to each treatment plant.
.
1 Assuming a 100% efficient well.
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Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December22~,2008
11
Overview of Methods
Model Refinement
The "northwest sub-regional model" of the Metropolitan Council's Metro Model was used as a
starting point for this evaluation. The finite-difference grid for this model was refined in the vicinity
of Chanhassen to improve numerical accuracy for this evaluation. Model parameters (e.g., aquifer
thickness, permeability, etc.) remained unchanged.
The model covers all of Hennepin and Carver Counties, as well as portions of Wright County and a
small portion of Scott County that is adjacent to the Minnesota River. Other areas of the metro region
were not included because the Mississippi and Minnesota Rivers are significant hydrologic barriers to
flow for the Prairie du Chien-Jordan aquifer. The model includes layers for all major aquifers and
aquifers from the ground surface down to the deepest regional aquifer - the Mt. Simon-Hinckley
aquifer. As part of developing this model for the Metropolitan Council, the model underwent
substantial calibration.
The model was first used to simulate "current" pumping conditions. A steady-state simulation of
current pumping conditions was performed using annualized average pumping rates for 2006. The
purpose of this simulation was to: (1) verify the appropriateness of the model grid's refinement and
(2) provide some baseline for comparing results of future conditions.
Simulation of 2030 Average Pumping Conditions
Before proceeding with the peak period simulation, average pumping conditions for 2030 needed to
be simulated. The simulation of 2030 average pumping conditions provides starting groundwater
levels for a 2-week simulation period of maximum 2030 demand (which is the primary indicator of
how future wells will perform). This required assigning new pumping rates for the wells in the
surrounding communities, based on projected demands estimated by the Metropolitan Council. For
purposes of this simulation, not every community in the model domain needed to be considered-
only those in close proximity to Chanhassen.
The Metropolitan Council's estimates for future demand are listed on Table 2. Some communities,
such as Edina, Eden Prairie, and Minnetonka are projected to experience slight reductions in average
demand in 2030, compared to 2004 and almost no change in peak demand. The reduced demand
projections made by the Metropolitan Council reflect some assumed conservation measures. Growing
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Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
12
communities, such as Chaska, Minnetrista, and Victoria are projected to have substantially increased
average and peak day demands in 2030.
Table 2
Average and Peak Water Demand (MGD) for Communities Near Chanhassen in 2004 and 2030
(from Metropolitan Council)
2004 Avg Day 2004 Max Day 2030 Avg Day 2030 Max Day
Community Demand (MGD) Demand (MGD) Demand (MGD) Demand (MGD)
Chanhassen ** 2.643 5.90 5.74 *** 17.8 ***
Chaska 2.819 9.217 4.256 14.089
Eden Prairie 8.422 25.131 7.828 25.2
Edina 7.345 21.772 7.179 21.888
Hopkins 2.605 4.673 2.835 5.086
Long Lake 0.102 0.842 0.123 0.98
Maple Plain 0.281 0.574 0.35 0.715
Minnetonka 7.999 22.119 7.483 21 .48
Minnetonka Beach 0.077 0.267 0.075 0.264
Minnetrista 0.211 0.646 1.351 3.794
Mound 0.698 3.569 0.741 3.816
Plymouth 9.66 26.257 9.653 27.475
Richfield 3.386 7.23 4.424 9.447
Shorewood 0.496 2.195 0.508 1.559
Spring Park 0.219 0.391 0.268 0.477
S1. Bonifacius 0.235 0.626 0.294 0.783
S1. Louis Park 6.115 11.554 7.137 13.485
Victoria 0.48 1.979 1.865 9.741
Wayzata 0.847 2.631 0.872 2.706
* Metropolitan Council projection
** Data from Chanhassen's 2008 Comprehensive Plan
*** These are ultimate demand numbers not necessarily 2030
It is worth noting that the Prairie du Chien-Jordan aquifer is not present in Minnetrista, and only a
very small portion of Jordan is present in the southernmost tip of Victoria and the western part of
Chaska. The Jordan Sandstone that is present in these locations is disconnected from the Jordan in
which Chanhassen's wells are completed. Minnetrista and Victoria will have to rely heavily on the
drift and FIG for their future supply. This is significant because the majority of the other
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Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
13
communities near Chanhassen that do rely upon the Jordan Sandstone for their water supply are
already at or very close to ultimate build out, meaning that there is a limited amount of new
appropriations expected from the Prairie du Chien-Jordan aquifer in the future from cities other than
Chanhassen.
For lower growth communities, future demand will likely be met using existing wells. For growing
communities, future demand will likely require the installation of new wells. Some communities may
have water supply plans that identify future well locations, but many may not. In either case, it is
beyond the scope of this study to include new well locations for communities other than Chanhassen
into the model to meet 2030 demand. The approach taken in this evaluation was to apply a percentage
increase over existing pumping rates for each existing well in a community in order to meet 2030
average and maximum day demands. This approach assumes that existing wells will be able to meet
future demands-an assumption that is likely not true for many growing communities. However, this
assumption is both useful and valid for the groundwater model and accounts for the effects of future
pumping since the total supply is still coming from the source aquifer of interest.
For the average 2030 pumping conditions, it was assumed that the existing wells (not including
Well 11) would be the only wells pumping to meet average demand for Chanhassen. This was done
to establish initial groundwater levels for simulating a 2-week period of maximum demand. This
approach also will focus future demand on the existing wells to help identify if any of them are likely
to be a problem in the future as new wells are added. The 2030 average demand conditions were
simulated as a steady state.
Simulation of Maximum Water Use for 2030
Projected 2030 peak demands for communities near Chanhassen are listed in Table 2. Peak demand is
typically substantially higher than average demand. Most communities design their well systems to
meet peak day demands. Therefore, during most of the year, communities have excess well capacity.
Peak demands typically take place during the summer when irrigation is most prevalent. If these peak
demands were simulated in the model as occurring continuously (i.e., simulated as a steady-state
condition), the results would likely be a gross overestimate of draw down and well-interference
effects. Simulating peak pumping as occurring over a short duration (e.g., days or weeks) is more
realistic and captures the phenomenon of taking groundwater out of aquifer storage. This approach
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Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
14
results in more a more accurate representation of conditions in the aquifer, showing the significant
drawdown that does occur during short-term peak pumping but less draw down over the long term
when pumping returns to average levels. For this evaluation, we assumed the following:
. Groundwater levels predicted for average 2030 demand conditions are the starting condition
for the simulation.
. For a 2-week period, pumping would be increased in the surrounding communities to equal
peak demand projections for 2030. Pumping for the entire community would be distributed
over the existing wells in these communities.
. A specific storage value of 0.000135 is assumed for the aquifer system and a specific yield
value of 0.25 is assumed. These are values obtained from a controlled aquifer test in
Lakeville and are believed to be representative of the Prairie du Chien-Jordan aquifer in the
metro area.
. Following this modeling a long term peak pumping scenario will be run to estimate the
ability of the aquifer to sustain peak pumping over extended periods. This will be discussed
in a separate section below.
Both existing city of Chanhassen wells and potential future city of Chanhassen wells were simulated
using the Multi-Node Well package (MNW) in MODFLOW2000 (the groundwater flow code used in
this study). MNW wells allow for the setting of a pumping rate, along with the minimum acceptable
pumping level and the minimum acceptable pumping rate (below which, the well is shut off). By
using MNW wells in the model, the effects of regional lowering of groundwater levels on pumping
rates in the Chanhassen wells are better simulated. Six scenarios, each featuring combinations of five
potential future well sites, were simulated, as summarized on Table 3.
Scenarios I and 2 concentrate pumping stress on the east well field Scenario 3 concentrates demand
on the west well field and Scenarios 4 through 6 divide the demand between both well fields. This
split of demand will help in estimating the potential impacts to each well field by in effect over
stressing that field in the first three scenarios. The final three represent a more true division of
demand that would occur to feed the existing East Treatment Plant and the future west plant.
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
15
Condition Pumping Rates
Current 2008
2030 Average 2030 Average
Scenario 1 E 1000 gpm
Scenario 2 E 1000 gpm
Scenario 3 W 1000 gpm
Scenario 4 B 1000 gpm
Scenario 5 B 1000 gpm
Scenario 6 B 1000 gpm
lExcept Chanhassen 11
Table 3
Summary of Model Scenarios
Wells Operating during Simulation
All Existing Chanhassen Wells 1
All Existing Chanhassen Wells 1
All Existing Chanhassen Wells \ Site 1, Site 7, Site 8, Site 9, Site 14
All Existing Chanhassen Wells \ Site 5, Site 6, Site 7, Site 8, Site 14
All Existing Chanhassen Wells\ Site 2, Site 3, Site 10, Site 11, Site 12
All Existing Chanhassen Wells\ Site 1, Site 2, Site 5, Site 12, Site 14
All Existing Chanhassen Wells \ Site 4, Site 6, Site 7, Site 9, Site 10
All Existing Chanhassen Wells 1, Site 2, Site 3, Site 6, Site 11, Site 13
The MNW package's specified minimum level for terminating pumping is shown on Table 4. The
limiting values for all wells in the modeling runs were determined to be approximately 10 feet above
the top of the Prairie du Chien Group. Modeling results are reported relative to these limiting water
levels. The locations of the potential future wells (labeled Site 1, Site 2, etc.) are shown on Figure 3.
Model simulations were conducted for six different pumping scenarios. These were simulated using a
2-week transient model with regional wells operating at their respective projected peak pumping rates
for 2030. Results for the transient models were taken at the end of the two-week period to represent
the maximum expected draw down at the wells. The peak rates were modeled for six scenarios during
which Chanhassen's existing wells and five different potential wells were each pumping at
1,000 gpm. Pumping for Chanhassen 11 was set to zero for all model simulations.
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
16
Table 4
Limiting Water Levels assigned in the Multi-Node Well Package
Well 10 Limiting Water Level, 1t
Chanhassen 2 731.86
Chanhassen 3 694.09
Chanhassen 4 667.88
Chanhassen 7 732.84
Chanhassen 8 694.06
Chanhassen 9 681.56
Chanhassen 10 750.89
Chanhassen 12 731.86
Chanhassen 13 738.88
Site 1 732.94
Site 2 644.69
Site 3 747.54
Site 4 764.11
Site 5 727.03
Site 6 720.14
Site 7 648.29
Site 8 643.37
Site 9 692.26
Site 10 659.45
Site 11 747.54
Site 12 736.55
Site 13 727.69
Site 14 707.68
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
17
<..,.,.-
Results
The results of this modeling evaluation predict that the aquifer will be able to meet the water demand
for the city of Chanhassen under current conditions, average projected conditions for the year 2030,
and peak projected conditions for the year 2030 but that concerns related to individual wells do exist.
Both the existing Chanhassen pumping wells and potential future wells were analyzed. Table 5 shows
the pumping levels in the wells under these conditions relative to the limiting water level for each
well. Wells with head levels in bold red are wells that were running during the given scenario.
Positive values indicate the pumping level for a given well was above the limiting water level and the
well was able to supply the pumping demand simulated (1,000 gpm for future wells). Negative values
would indicate the water level in a given well fell below the limiting water level and flow from the
well was terminated - there are no wells with predicted negative water levels. Figures 4 through 7
depict the information contained in Table 5. The water levels predicted by the model are for the
groundwater immediately outside of the casing of a given pumping well. No well is 100 percent
efficient and as water enters the open hole or screen there is some additional head loss that will result
in a slightly lower level in each of the wells than what is shown in Table 5.
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Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December22~,2008
18
Table 5
Simulated head levels relative to limiting water level
2030 Scenario Scenario Scenario Scenario Scenario Scenario
WelllD Current Average 1 2 3 4 5 6
Chanhassen 2 101.96' 92.39 83.62 83.64 84.39 84.14 84.16 84.36
Chanhassen 3 151.16 144.65 133.83 133.90 132.17 133.56 133.49 132.58
Chanhassen 4 154.20 148.05 131.27 132.98 135.05 133.30 133.34 134.88
Chanhassen 7 124.88 116.97 110.00 110.01 106.05 108.23 109.77 107.80
Chanhassen 8 162.74 152.08 137.73 137.74 136.29 136.95 137.57 136.83
Chanhassen 9 166.11 152.84 136.14 136.23 134.63 135.90 135.17 135.62
Chanhassen 10 82.39 61.71 42.75 42.80 43.61 43.25 43.40 43.59
Chanhassen 12 107.71 96.97 90.46 90.42 90.97 90.82 90.76 90.92
Chanhassen 13 93.37 82.52 75.16 75.18 75.51 75.35 75.42 75.50
Site 1 106.98 103.65 93.92 104.68 105.38 95.05 104.52 104.54
Site 2 209.61 206.79 206.73 206.73 193.91 194.24 206.46 194.20
Site 3 122.89 119.45 120.56 120.56 108.69 120.09 120.54 109.14
Site 4 94.83 91.19 93.01 93.04 92.53 92.90 88.01 92.66
Site 5 129.82 126.56 128.81 89.80 128.89 92.64 126.07 126.11
Site 6 136.00 132.70 135.06 93.06 135.11 132.42 95.76 95.79
Site 7 194.14 190.09 164.43 164.86 192.49 191.80 167.80 192.39
Site 8 195.31 191.02 152.52 153.01 193.23 192.15 190.49 193.13
Site 9 136.51 133.40 114.64 133.17 134.16 133.15 115.91 133.50
Site 10 182.84 179.79 179.69 179.75 155.12 179.44 155.43 179.32
Site 11 108.65 103.96 104.01 104.04 87.63 103.38 103.59 88.28
Site 12 126.99 122.61 123.24 123.24 112.64 113.63 123.08 122.23
Site 13 107.15 104.33 103.69 105.31 105.46 104.53 104.72 93.31
Site 14** 120.83 116.76 103.00 103.68 117.95 104.57 117.10 11 7.86
* Pumping wells are indicated by bold red numbers
** Site of proposed future Well 14
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Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
19
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Figure 4
. Chan hassen 2
. Chan hassen 3
. Chan hassen 4
.. Chanhassen 7
. Chanhas5en 8
Simulated Head Levels in Chanhassen Wells Relative to the Limiting Water Level
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Scenario 4
Scenario 5
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-25
. Chanha55en 9
. Chanhas5en 10
. Chanha55en 12
. Chanha55en 13
Figure 5
Simulated Head Levels in Chanhassen Wells Relative to the Limiting Water Level
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Figure 7
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22"d, 2008
20
275
225
25
.Sitell
.Site 2
.Site 3
.Site 4
.Site S
. Site 6
.Site 7
Simulated Head Levels in Potential Future Wells Relative to the Limiting Water
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. Site 11
. Site 12
. Site 13
. Site 14
Simulated Head Levels in Potential Future Wells Relative to the Limiting Water
Level
P:\Mpls\23 MN\IO\231 0 1 00 1 00 Chanhassen Well Siting Study\WorkFiJes\modeJing_report\Well Siting Memo_Final.doc
Current
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-25
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
21
All wells were able to operate at their assigned pumping rates without falling below the limiting
water level. In particular, Chanhassen 8 performed particularly well. On average, wells maintained
pumping water levels around 122 feet above the limiting water level. The 2030 average pumping
water levels in all wells remained essentially the same compared to the current imposed pumping
rates. The 2030 peak pumping conditions, however, resulted in somewhat lower pumping water
levels for wells that were pumping during a given simulation compared to Current or 2030 Average
pumping conditions. It is important to note that the predicted water levels are for the groundwater
levels in the aquifer immediately adjacent to the well - water levels in the well can expect to be lower
as a result of well losses that lead to less than 100% efficient wells.
Sites 1 through 14 are potential future wells and did not show the same pumping water level drop for
2030 peak conditions unless they were "turned on" for a given scenario. For example, pumping was
simulated for Site 5 in Scenarios 2 and 4. Figure 6 shows lower pumping water levels for Site 5
during these scenarios when compared to the Current and 2030 Average conditions. The fact that
wells that did not have imposed pumping rates showed negligible drawdown indicates the ability of
the system to supply the current, 2030 average, and 2030 peak water demands without undue
influence on water levels throughout the aquifer.
There are three conclusions to take away from this evaluation:
1. Peak pumping, as projected by the Metropolitan Council for 2030, does not appear to induce
critical regional groundwater level drawdowns in the Prairie du Chien-Jordan aquifer in
Chanhassen. This conclusion assumes 2 weeks of continuous peak pumping.
2. The City of Chanhassen appears to have considerable leeway in selecting future well
locations from the 14 locations they have identified. All locations appear to be able to supply
1,000 gpm during the two week peak pumping conditions, assuming the information on
hydraulic parameters for the aquifer that are currently in the model accurately represent
existing conditions. Not all locations performed the same and some are very close to the
eroded edge of the Prairie du Chien Jordan formation.
The following additional comments are offered with respect to the modeled well sites. Site 2
and Site 10 are at the edge of the western extent of the Jordan Sandstone and if these sites are
selected we would recommend an exploratory boring to confirm geology in advance of
procuring a well drilling contractor to make sure the formation is present and to confirm well
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Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
22
design. The 14 sites can be categorized into three general groupings, those that performed
very well, those that performed well and those that performed adequately. Those that
performed very well had the greatest head above the limiting water level shown in Table 6.
Those that performed well had the next most head above the limiting water level and those
that performed adequately had the least head above the limiting water level. The groups are
shown in the table below. If all other factors were equal Barr would recommend selecting
sites from the higher performing groups. Note that the site being considered for City Well 14
is Site 14 in the Adequate performing sites group.
Table 6
Sites that performed
Very Well
2*,7,8 and 10*
Ranking of Future Well Sites
Sites that performed Sites that performed
Well Adequately
5,6,9, and 12 1,3,4,11,13 and 14
* These sites are at the eroded edge of the Prairie du Chien-Jordan formation.
3. Both existing conditions and the model show that water levels in Well 10 are close to the
limiting elevation near the top of the Prairie du Chien formation. The model shows that the
well should not experience additional severe drawdown conditions in the future. The entire
Prairie du Chien is cased off in this well and a screen is set only in the Jordan. The pump is
set very low in the well near the top of the screen well below the top of the Prairie du Chien.
Because of this the pump should not see water levels that prevent it from operating as
intended. However, as currently configured the well could draw water levels down below the
top of the Prairie du Chien without causing a problem for the pump. The City should monitor
water levels in this well carefully. The limiting water elevation is approximately 215 feet
below the ground at WelllO. This generally indicates that the City needs to monitor all of its
wells carefully in the future. It also points out that there still is a concern that excessive peak
pumping will have negative impacts on wells. In addition, localized variations in geology that
may not be known about and therefore not represented in the model may contribute to
drawdown not identified by the model. As a result Barr recommends that a second source
aquifer be considered in the near future along with careful monitoring of water levels in all
city Wells.
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Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
23
Extended Peak Pumping Scenarios
Following the initial model runs several extended peak pumping scenarios were run to find out how
long the wells could sustain a peak pumping scenario. Each scenario was started by running average
demand conditions for Chanhassen and surrounding communities as described above. Demands in
surrounding communities were then increased to match peak demands and all Chanhassen wells
considered in each scenario were then turned on at full capacity at left to run for 180 consecutive
days. Three different scenarios were run. They include:
1. Existing wells only excluding Well 11
2. Scenario 4 which includes existing Chanhassen wells excluding Well 11 and new wells at
Sites 1,2,5,12 and 14 (this is the site of future Well 14)
3. Scenario 5, which includes existing Chanhassen wells excluding Well 11 and new wells at
Sites 4,6, 7, 9 and 10
During the extended peak scenarios all wells were again able to supply water at the modeled rates
throughout the simulation. Water levels in the wells declined over the first few days of peak pumping
and then stabilized at various levels that were all above the limiting water levels. Water levels did not
decline further even after prolonged pumping. Water levels stabilized at elevations relatively close to
those shown in the two week pumping scenarios.
What this indicates is that using known aquifer parameters the model predicts that average recharge
rates, which are based on average precipitation, are able to be transmitted through the aquifer to
regional wells to sustain peak pumping even for extended periods. What is not accounted for is the
impact of extended drought periods that interrupt the recharge cycle of the wells. Peak pumping
almost always occurs in conjunction with drought conditions which in turn limit aquifer recharge.
The model currently assumes a continuous average rate of recharge over the region.
Actual water levels in the City's wells often decline continually over extended pumping periods. This
can happen when recharge is limited and the wells need to reach farther and farther to obtain the
water needed. The fact that the model shows the wells able to supply the City even during extended
pumping indicates that problems associated with declining water levels likely caused by dry weather
patterns and other factors that are limiting aquifer recharge and not limitations in the aquifer itself.
In other words, under average recharge conditions the aquifer is able to transmit water from the
places where it is normally recharged to the wells in Chanhassen in a quantity that would meet the
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December22~,2008
24
City's peak demands even for extended pumping periods. Pumps may have to be lowered but the
wells would not dry up due to aquifer transmissivity limitations. What will affect water levels will be
weather patterns that ultimately cannot be predicted. If aquifer recharge diminishes due to extended
drought then declining water levels will continue to be a problem. Because of this the City needs to
continue to monitor water levels and be prepared to enact sprinkling bans if continued drought
interferes with aquifer recharge. In addition to this, a secondary source such as the FIG aquifer
would provide a hedge against these problems since it is a deeper aquifer and is able to attenuate
varying recharge somewhat better.
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
25
Existing Well 4 and Future Well 14 Considerations
The purpose of this section is to conduct a brief analysis of existing Chanhassen Well 4 to determine
the most cost effective way to treat and deliver this water to the system. This section includes a
review of raw water quality data from Chanhassen Well 4 with respect to meeting primary and
secondary drinking water quality standards. Based on this review an evaluation of two alternatives
related to the treatment of Chanhassen Well 4 will be performed. A major factor contributing to this
analysis is the fact that a potential site for future Well 14 exists along a route that could be used to
connect Chanhassen Well 4 to the East Treatment Plant. If this site were to be used for future
Welll4 then a raw water main would be relatively close to the Chanhassen Well 4 site making
connecting it to the treatment plant more feasible and cost effective.
Chanhassen Well 4-Raw Water Quality Information and Review
The City provided Chanhassen Well 4 raw water quality data that is shown in Table 7. Based on the
data provided it appears that Well 4 can be pumped to the East Water Treatment Plant, blended with
raw water from Chanhassen Wells 2, and 10 through 13, and treated without any major treatment
modifications to the plant. Both iron and manganese levels in Chanhassen Well 4 water are in line
with those from the water from the other Wells being treated at the plant. The main difference is the
presence of higher levels of radium. That stated, it is recommended that before any new source is
added to an existing water treatment plant detailed studies should be performed to ensure that no
unexpected and undesirable outcomes will occur. Trace elements present in any water source can
affect existing treatment processes. However, based on what is known about the quality of water in
Well 4 only minor adjustments, if any, would be needed to add the well to the raw water supplying
the East Plant.
P:\Mpls\23 MN\IO\2310JOOIOO Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo_Fina1.doc
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
26
Table 7
Water Quality from Well 4 and Wells Supplying the East Treatment Plant
Well Source Fe mg/I Mn mg/I Sample Date
Well #4 0.321 0.091 11/14/08
Plant Influent Avg. 0.328 0.090 11/06/08
Plant Influent Range 0.220-0.400 0.070-0.144 11/06/08
Well #2 0.330 0.100 11/06/08
Well #10 0.220 0.070 11/06/08
Well #12 0.340 0.072 11/06/08
Well #13 0.400 0.144 11/06/08
In addition to this, blending of the Chanhassen Well 4 raw water with the other raw water sources
supplied to the treatment plant will result in lowering of the concentration of radium in the finished
water to levels below the regulated limit of 5 pCi/I. This is true even without considering the benefits
of treatment, the dilution alone would bring radium concentrations to levels below the regulated limit
as long as it is blended with at least one other well pumping at the same rate as Chanhassen Well 4
and that has very little or no radium.
When the benefits of iron manganese filtration are considered the picture gets even better. This is
because radium has been found to adsorb to manganese oxides. A common treatment for radium
removal is to add hydrous manganese oxides (HMO) to a treatment stream and then perform normal
iron manganese filtration (this is an oversimplified description but generally serves the discussion
here). Even without the addition of HMOs normal iron manganese filtration of water that has iron
and manganese present in it often results in a beneficial lowering of radium 226 and 228. Studies of
five iron manganese filtration plants preformed by the Minnesota Department of Health found that
without modifying their processes to optimize for radium removal the plants all produced water with
lower levels of radium in the effluent than was present in the influent streams. Removals varied from
19 to 63 percent for radium 226 and from 23 to 82 percent for radium 228. Note that the study also
found that radium removal by this method has lower threshold limits. Neither radium 226 or 228
could be completely removed from the source water by unmodified iron manganese filtration alone.
Removal rates varied depending upon a number of factors which should be studied in greater detail
before adding Well 4 water to the East Treatment plant. But even if the worst removal efficiencies
were achieved and Well 4 water were treated at the East Treatment Plant unblended with other wells
P:\Mpls\23 MN\10\2310100100 Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo]inal.doc
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From:
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Date:
Page:
Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
27
it would still likely be below regulated limits some of the time depending upon concentrations in the
influent stream. This is shown in Table 8 below which also shows the best potential removal
efficiencies that might be achieved.
Table 8
Estimated Potential Range of Radium Levels Produced by East Treatment Plant
Radium 226 &228
in Influent pCi/1
5.4
6.3
6.8
16.2
Approx. Effluent
Worst Case, pCi/1
4.3
5.0
5.4
12.9
Approx. Effluent
Best Case, pCi/1
2.1
2.4
2.5
5.0
Comments
Concentrations from 12/17/04 MDH letter
Worst case removal exceeds MCL
High radium level recorded at Well #4
Best case removal exceed MCL
Note this table is based on similar proportions of radium 226 to 228 as existed in the 12/17/04 letter
data.
What Table 8 also shows is that unmodified iron manganese filtration alone should not be relied upon
to bring Chanhassen Well 4 water down to limits below the MCL without significant bench and pilot
scale treatment studies. Chanhassen Well 4 has had radium hits as high as 6.8 pCi/1 and as the table
shows the worst case assumption for radium removal at that influent concentration results in an
effluent concentration of 5.4 pCi/l. If the raw water from Chanhassen Well 4 is to be treated at the
well location a new package treatment plant with a radium removal system will need to be further
reviewed. This would involve a pilot study to identify if a separate detention vessel and radium
removal system is needed in addition to a pressure filter system for iron and manganese removal
treatment. Alternative 2 provides preliminary costs for a package water treatment plant at Chanhassen
Well 4 that assumes some form of HOM addition will be needed to bring the water down to regulator
limits
Evaluation and Preliminary Screening of Alternatives
Two alternatives related to the treatment of Chanhassen Well 4 raw water were reviewed. One for
routing the well to the East Treatment plant and the other for constructing an on site package plant
for treatment. The following is a discussion of each alternative.
P:\Mpls\23 MN\10\23 10100100 Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo_Final.doc
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
28
Alternative 1-Connect Well 4 to the East Water Treatment Plant along with Well 14
Figure 8 provides the route used for estimating the cost of connecting Chanhassen Well 4 to the East
Water Treatment plant. This raw water main would be designed to allow for the future connection of
proposed Well 14 and would be approximately 6,100 lineal feet long. The main would be 12 inches
in diameter for 858 lineal feet running from Chanhassen Well 4 north to Lake Drive and then
16 inches in diameter from there to the point where it would connect to the existing raw water main
from Chanhassen Well 13. The larger diameter main would allow for another well from the west to
be connected to the East Treatment Plant. It is assumed minimal modifications would be needed at
the East water treatment plant to connect Chanhassen Well 4 and future Well 14 to the plant. A
preliminary estimate using the bid tabs from the Chanhassen Wells 12 and 13 raw water main bid
results in an approximate cost range of $730,000 to $950,000. The range is intended to account for
unknown conditions and variation in bids. Note we are in uncertain cost estimating times with prices
fluctuating significantly. Material prices are beginning to drop after years of steep rises.
Alternative 2-Package Water Treatment Plant at Well 4
Consideration was given to the construction of a new package style water treatment plant located at
Chanhassen Well 4. This option would allow for treatment of the raw water at Chanhassen Well 4
and subsequent connection to the existing water supply system. Construction of a water treatment
plant at Chanhassen Well 4 would require modifications to the existing well house to include a
radium treatment system comprised of a multi-cell pressure filter and additional related equipment
and tanks. Additionally, the creation of another water treatment plant would require additional
staffing time for operation and maintenance above what is needed at the East and West water
treatment plants. Those costs are not considered here since the base cost estimate already exceeds that
needed to pipe Chanhassen Well 4 to the East Treatment Plant. With a separate treatment plant at
Chanhassen Well 4 it was assumed that a HMO-style radium removal system would be needed to
ensure compliance with radium regulations. A pilot study is recommended to verify the need of
radium removal treatment if this alternative is pursued further. A preliminary cost for such a plant
I
was prepared. The cost for a package plant located at a site adjacent to Chanhassen Well 4 would fall
in the range of $1.1 to $1.5 million. This estimate includes: modifications to Wellhouse 4, a pressure
filter, a pressure detention vessel, an HMO chemical feed system, a buried backwash tank, electrical,
HV AC, and miscellaneous piping.
P:\Mpls\23 MN\IO\23 10100100 Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo]inal.doc
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December22~,2oo8
29
Analysis of Alternatives
This was only a preliminary scoping level review of the two alternatives but it is readily clear that
constructing a package plant at Chanhassen Well 4 is not a cost effective alternative costing $370,000
to $550,000 more than bringing Chanhassen Well 4 water to the East Treatment Plant. If the cost of
routing future Well 14 to the East treatment plant is eliminated from the Well 4 costs the difference is
significantly greater. Chanhassen Well 4 should be routed to the East Treatment plant using
direction ally drilled HDPE raw water main similar to how Chanhassen Wells 12 and 13 were brought
to the plant. This will utilize an asset that the City already has in Chanhassen Well 4 and improve
water quality from that well by removing iron, manganese and radium. Finally, it also adds needed
supply to the East Treatment Plant to replace other less reliable or failed supply wells.
P:\Mpls\23 MN\1O\23 10100100 Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo_Final.doc
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
30
Overall Conclusions and Recommendations
As pointed out in the Introduction the purpose of this report was four-fold. Each of those purposes
will be addressed in this section. After that a set of recommended actions will be described.
Well Locations. The groundwater modeling suggests that each of the 14 potential well sites
considered in this study should be able to support a new 1,000 gpm Prairie du Chien-Jordan well.
Sites 2 and 10 are near the eroded edge of the Jordan Sandstone. If those sites are chosen exploratory
borings should be performed in advance of the well drilling to ensure that they are viable sites. Sites
that performed very well include 2, 7, 8, and 10. Sites that performed well include 5, 6, 9 and 12.
Sites that performed adequately include 1,3,4, 11, 13 and 14 (this is the proposed Well 14 site).
Potential Contaminants. No contaminants were found that exhibited a pattern that would affect well
siting. Existing Well 4 has had occasional low level contamination caused by a naturally occurring
contaminant: radium. Four well sites, 3,4, 11 and 12, are down gradient and relatively close to
several MPCA Multi-sites. If any of these sites are selected then the status of those sites should be
verified. If concerns are raised then a testing program to verify groundwater quality at those sites
should be performed before committing to a new well at any of those locations.
Chanhassen Well 4 and Future Well 14 Planning. It is more cost effective to connect Chanhassen
Well 4 to the East Treatment Plant than to construct an on site treatment plant for iron manganese
and radium removal. Piping Chanhassen Well 4 and future Well 14 to the East Treatment plant would
cost and estimated $730,000 to $950,000 while constructing and on site package treatment plant
would cost approximately $1.1 to $1.5 million. Before connecting Well 4 to the East Treatment Plant
a more detailed water quality analysis should be performed to ensure that adding Well 4 water to the
plant does not disrupt the current treatment process.
Aquifer Yield Assessment. After performing the modeling and reviewing past studies the following
conclusions have been reached regarding the aquifers currently supplying the city:
1. The shallow sand and gravel aquifer into which Chanhassen Wells 5, 6, and 11 are completed
cannot be considered a viable source for the future unless some form of augmentation is planned
such as aquifer storage and recovery (this is a process where water from another source is treated
and then pumped down into the aquifer and stored for later reuse). While the city can continue to
P:\Mpls\23 MN\lO\2310100100 Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo_Final.doc
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
31
use Chanhassen Well II it should not plan on it being a long-term viable source unless additional
information becomes available to suggest otherwise.
2. The Prairie du Chien-Jordan aquifer appears to be able to transmit water to the city wells in an
amount needed if recharge rates remain at or above average levels. This is true now and into
the future but localized draw down conditions at specific wells will continue to be a problem for
the city, especially if extended drought limits aquifer recharge. New wells will be needed to meet
future demands and those wells should be sited carefully and as far apart as reasonable to limit
interference. Due to the trends of lowering water levels, Barr recommends that the City pursue
wells in another aquifer as a hedge against future problems. Barr recommends that the City
consider at least one FIG well in each major well field. If dry weather patterns persist and
draw down continues to be a concern in the Jordan then it is possible that additional FIG wells
could be added as needed to augment the City supply though it appears that this should not be
necessary unless weather patterns continue to be dry and aquifer recharge is limited.
3. The FIG aquifer was not studied in depth for this evaluation; however a preliminary review of the
data available suggest that the aquifer should be able to support two 500- to 600-gpm wells, even
considering future draw down likely to be caused by growing communities to the west of
Chanhassen. The modeling performed for this report included a preliminary look at the FIG
aquifer. Model results show static water levels at least 300 feet of water above the top of the FIG
aquifer in most all parts of Chanhassen even after draw down from future growth is considered.
Even with the poor yields common in the FIG this should support wells of 500 to 600-gpm or
more depending on specific local aquifer characteristics. Concerns stated in the DRAFT MCES
Metropolitan Water Supply Study are not major and should not be taken as a reason to abandon
this aquifer as a potential source. Questions remain concerning the properties of the FIG aquifer
in the Chanhassen area and the degree of hydraulic connection between this aquifer and the
overlying Prairie du Chien-Jordan aquifer which would need to be addressed before committing
to municipal wells in the FIG aquifer.
Recommended actions, Barr recommends the following actions be taken by the City in response to
the this study.
1. The MDNR has not responded to the City's 10-year appropriations permit. The DRAFT MCES
metro Water Supply Study identifies some issue related to the potential to impact the Seminary
P:\Mpls\23 MN\IO\2310100100 Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo_Pinal.doc
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Paul Oehme, City of Chanhassen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
32
Fen. The City should maintain contact with the MDNR and prepare to perform additional
modeling if needed to address any concerns that they might bring up related to impacts to the fen.
3. Perform a treatability study for Well 4 to determine the impact of adding that water to the East
Treatment Plant. Finalize the selection of a site for Welll4 and have plans prepared to connect
Well 4 and future Welll4 to the East Treatment Plant.
4. During modeling existing Well lO had some of the lowest water levels with respect to its limiting
water elevation. However, the pump is set just above the screen which is set only in the Jordan.
This means that Well lO will not likely experience pump problems in the future but that, as
configured, it could draw down water levels below the regulatory limiting elevation during a
prolonged drought or extended pump runs. Barr recommends that the City carefully monitor
water levels in this well along with those in its other wells. Water levels should be set in each
well that would trigger actions such as sprinkling bans and possibly a change in the pump call
sequence to allow a given well to rest more before it is used again. In addition, frequent triggers
could also initiate a new well project to spread out the demand among more wells and lighten the
load on each. Frequent triggers could also initiate a Franconia Ironton Galesville well as
discussed more below.
5. Commit to identifying a second source aquifer to supplement the Prairie du Chien-Jordan aquifer.
Options include the FIG aquifer, the Mt. Simon-Hinckley aquifer or aquifer storage and recovery
using Chanhassen Wells 5 and 6. The FIG aquifer will be the most cost effective to pursue given
the regional ban on the use of the Mt. Simon-Hinckley aquifer and the design challenges
associated with aquifer storage and recovery. However it is not as productive as other options.
a. If the FIG aquifer is selected as the source, then a more detailed study of the FIG aquifer
should be performed to determine if it can be a supplemental source to the City and act as a
backup should wells in the Prairie du Chien-Jordan aquifer prove to be problematic. The FIG
aquifer should not be considered a source for supplying a significant portion of your peak day
demand due to its limited productivity; but it would be able to increase the City's supply
reliability. It could be used to supply average day demand thereby reducing the stress on the
Prairie du Chien-Jordan aquifer. In addition, because the FIG is separated from the shallower
aquifers by an aquitard, wells located in it can be sited right next to shallower wells without
substantially impacting their performance. This means that one new FIG well could be sited
in the existing east well field immediately adjacent to either failed WellS or 6. This new FIG
P:\Mpls\23 MN\lO\2310100100 Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo_Final.doc
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From:
Subject:
Date:
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P<\ul Oehme, City of Ch<\nh<\ssen
Ray Wuolo, Brian LeMon, and Katy Lindstrom, Barr Engineering Co.
Results of Well Location Screening Modeling
December 22nd, 2008
33
well could utilize some of the equipment originally intended for one of those wells thereby
saving installation costs. It is also worth noting that the Prairie du Chien-Jordan aquifer is
absent in parts of the City and in those areas the FIG aquifer may be more productive than in
areas where it is overlain by the Prairie du Chien-Jordan aquifer. The detailed study should
include modeling of wells sites, a field investigation including construction of a pumping
well and a long term aquifer (pumping) test. Finally, the MCES Metropolitan Water Supply
Plan identifies this aquifer as a viable source for Chanhassen.
b. If aquifer storage and recover (ASR) is to be considered, a well code variance would be
needed. This would be followed by a detailed examination of the geology of the shallow
aquifer that would include a geochemical analysis and a better definition of its connection to
the underlying aquifers in the region. This would then be followed by bench and pilot studies
to verify water chemistry needed to make a successful project. The potential up side of hits
option is the existing infrastructure at Wells 5 and 6 that could be reused and the productive
nature of the aquifer.
c. If the Mt. Simon-Hinckley aquifer is selected for further evaluation as the source, a detailed
alternative water source study will need to be performed in consultation with the MDNR.
This would likely be a long-term process with many political and technical obstacles along
the way and no guarantee of being granted permission in the end.
P:\Mpls\23 MN\1O\2310100100 Chanhassen Well Siting Study\WorkFiles\modeling_report\Well Siting Memo_Fina1.doc
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Master Water Supply Plan - Appendix 2
Community Water Supply Profiles
Chanhassen
Water Demand Projections (Note 1, 2; Ref. A) 2004 2010 2020 2030 2040 2050
Population Served 23652 27500 34500 38000 45925 50655
Annual Total (Million Gal./Yr) 1031.86 1199.76 1429.89 1492.06 1803.24 1988.97
Average Day (Million Gal./Day) 2.83 3.29 3.92 4.09 4.94 5.45
Maximum Day (Million Gal./Day) 9.39 10.92 12.94 13.30 16.07 17.73
Maximum Day, Conserving 100/0 9.825 11.64 11.97 14.47 15.96
Estimated Additional Wells 1 1 0 2 1
Current Water Supply(Ref. 8, C)
The community owns and operates their own water supply system.
2004 Permitted Appropriation: 1200 million gallons per year
Current Water Source(s)
# Wells
2004 Municipal Water Use
Multi-Aquifer
Prairie du Chien-Jordan
1
5
1
IF
iii Multi-Aquifer
. Prairie du
Chien-Jordan
Quaternary
[] Quaternary
Available Future Water Supply Source(s) (Rd. 0)
o Quaternary aquiferes)
o Prairie du Chien-Jordan aquifer
o Franconia-Ironton-Galesville aquifer
o Interjurisdictional cooperation: Victoria, Chaska, Shorewod, Eden Prairie
The following must be addressed in water supply planning and development ~ote 3; Ref. A. 8, C,
Potential for impacts to state protected trout habitat or calcareous fen
o Seminary Fen located within one mile of the community
o Assumption Creek, trout habitat, located within one mile of the community
Minnesota Department of Natural Resources and Department of Health conditions
o Conditions identified on existing and future water appropriation permits issued by the
Minnesota Department of Natural Resources
o Issues identified in Source Water Assessments, which can be found on the Minnesota
Department of Health website www.health.state.mn.usjdivsjehjwaterjswpjswaj
Notes and references can be found on the cover page.
November 3, 2008 Draft
A2 - 33