1e. Well Nos. 12 & 13
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
WINI.ci .chanhassen .mn. us
.:i~
MEMORANDUM
TO:
Todd Gerhardt, City Manager
""'? D.
Paul Oehme, Director of Public Works/City Engineer c.
()~.
FROM:
DATE:
October 22, 2007
SUBJ:
Well Nos. 12 & 13, Project Nos. 08-04 & 08-05: Approve
Consultant Contract for Future Well Improvements
REQUESTED ACTION
The City Council is recommended to approve a consultant contract with Barr
Engineering Company for improvements to Well Nos. 12 and 13.
DISCUSSION
Wells 12 and 13 are recommended to replace the lost well production of Wells 5
and 6. Wells 5 and 6 are in the drift aquifer and were the cause of the lost well
production that was experienced this summer. These wells cannot be relied on for
municipal water production anymore. The new wells would be Jordan aquifer
producing wells. Staff has identified several sites which could be used for these
wells. Well Alternate Sites 2 and 4 are the preferred locations as shown on the
attached drawing. The water for these wells will be treated at the East Water
Treatment plant. The raw watermain for the wells is proposed to be directionally
drilled to reduce the amount of disturbed areas. The consultant contract includes
preliminary and final design services. It also includes time for a neighborhood
meeting to gain support for the project from the local residents. The consultant
would be responsible for construction administration and observation services.
On September 28, 2007, staff received two proposals for the well improvement.
Barr SEH, Inc.
Engineering
Submitted prior to the ./ ./
deadline
Proposal format ./ ./
Transmittal letter submitted ./ ./
with required information
Members of the consultant ./ ./
team identified
Understanding of project ./ ./
Fee $155,610 $210,100
The City of Chanhassen · A growing community with clean lakes, quality schools, a charming downtown, thriving businesses, winding trails, and beautiful parks. A great place to live, work, and play.
Paul Oehme
Well Nos. 12 & 13: Approve Consultant Contract
October 22, 2007
Page 2
Both proposals cover the basic scope of services as identified in the Request For
Proposal. Barr also included extra time in their proposal to complete a
groundwater model for the school well. This modeling is necessary to see if the
school well can be converted into a municipal producing well.
Due to the nature and scope of the work, the project will be on a tight timeline in
order to have the wells in operation prior to the beginning of 2008 peak irrigation
season.
Staff anticipates the following project schedule:
Neighborhood Meeting
Complete Final Design, Approve Plans and
Specifications and Authorize Ad for Bid
A ward Construction Contract
Substantial Completion of Construction
November, 2007
December, 2007
January, 2008
May, 2008
The work will be contracted on a time and materials bases with a not-to-exceed
amount. As with all City engineering contracts, the consultant must submit
periodic invoices that staff will review before processing. The consultant will be
required to submit timesheets verifying the hours worked on the project and
expense sheets. Staff will review the invoices and expense sheets for accuracy
and conformance to the contract.
RECOMMENDA TION
Staff recommends the Council approve a consultant contract with Barr
Engineering Company in the amount of $155,610 for engineering services for
Well Nos. 12 & 13 and to complete groundwater modeling for the school well.
Attachments
g:\eng\public\_2008 projects\08-04 well no. 12\102207 approve consultant contract.doc
Hydrogeologic Evaluation of Reduced Well
Capacities in the Lotus Lake Well Field
City of Chanhassen
Preparedfor City of
City of Chanhassen
September 2007
BARR
4700 West 77'h Street
Minneapolis, MN 55435-4803
Phone: (952) 832-2600
Fax: (952) 832-2601
Iili:Wi.Mii'fJ:.:t11&Ji'<2Jllki'W&;t;;::w..a
Hydrogeologic Evaluation of Reduced Well Capacities in the Lotus
Lake Well Field
Table of Contents
1.0 Introduction...... .............................................................................. ........................... ................... .......... 1
1.1 Scope...................................................... ............................................................................... ...... 1
1.2 Our Understanding of the Problem .............................................................................................1
1.3 Possible Causes of Loss of Well Yield ............................................................................ ........... 1
2.0 Hydrogeologic Evaluation of the Lotus Lake Well Field ......................................................................4
2.1 Extent and Nature of the Unconfined Sand and Gravel Aquifer................................................. 4
2.2 Recharge Mechanisms for the Sand and Gravel Aquifer............................................................ 5
2.3 Conceptual Model of Pumping and Hydraulic Head Changes ...................................................6
2.4 Prognosis for Future Production from the Sand and Gravel Aquifer.......................................... 7
3.0 Conclusions and Recommendations ..... ...................................... ............ .................................... 8
I hereby certify that this report was prepared by
me or under my direct supervision and that I am
a duly Licensed Professional Geologist under the
laws of the state of Minnesota.
Signature: ~. J~
Date: September 26, 2007
Ray W. Wuolo
Reg. No. 19897
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List of Figures
Figure 1 Location of Chanhassen Water Supply Wells
Figure 2 Schematic Cross Section Depicting Groundwater Levels Without Pumping, With Low Rates
of Pumping, and With Higher Rates of Pumping
Figure 3 Locations of Cross-Sections A-A' and B-B'
Figure 4 Cross-Section A-A' (West to East)
Figure 5 Cross-Section B-B' (South to North)
Figure 6 Map of the Thickness of the Sand and Gravel Aquifer
Figure 7 Conceptualization of Sequenced of Hydraulic Head Changes in Aquifer Systems
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11
1.0 Introduction
1.1 Scope
Barr Engineering Company was retained by the City of Chanhassen to evaluate the possible causes
for recent reductions in well yields from City of Chanhassen Wells 2, 5, and 6. These wells are
located near the eastern edge of the City in the so-called Lotus Lake well field, as shown on Figure 1.
Four additional wells (plus one back-up well at the junior high school) are located in the western
portion of the City in the so-called Galphin Boulevard well field.
1.2 Our Understanding of the Problem
It is our understanding that City Wells 2, 5, and 6 began to experience significantly reduced yields
(i.e. lower maximum pumping rates) during the Summer of 2007. The City implemented temporary
restrictions for lawn watering in order to compensate for the reduced pumping capacity. Those
restrictions were lifted in August 2007.
City staff found that static (i.e. non-pumping) water levels in Wells 2, 5, and 6 had dropped
significantly below historical levels. As of this writing (September 2007), they have not shown any
appreciable rebound. This is an unusual circumstance for any pumping well and for these wells, such
a failure for water levels to rebound has never before occurred. City staff verified SCADA system
data on water levels with hand-instrument measurements and confirmed that the water-level
measurements in the wells were reliable.
City wells 5, 6, and 11 are screened in an unconsolidated sand and gravel aquifer. Wells 2 and 10
completed in Prairie du Chien-Jordan aquifer - a bedrock unit that is the primary water supply for
most suburban communities in the Twin Cities. Thus, the problem of reduced well yield did not
appear to be restricted to a single aquifer.
1.3 Possible Causes of Loss of Well Yield
Wells can experience reduced yield (i.e. capacity) for a number of reasons. Common causes for well
yield loss include the following:
1) Failure of pumping equipment
2) Obstructions in the discharge line
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3) Clogging of the well screen, filter pack, or open-hole portion of a well by precipitation or
bacterial flocculation
4) Collapse of the well screen or open-hole portion
5) Reductions in available drawdown, cause by:
a) Interference effects from the pumping of nearby wells
b) Regional lowering of the poteniometric surface (i.e. aquifer pressure) caused by regional
pumping or long-term reductions in recharge
c) Dewatering of storage from the aquifer
The first four common causes of well yield loss are related to the well itself. These causes can be
remedied by repair of the pump or redevelopment of the well. In extreme cases, a well may need to
be replaced (i.e. re-drilled). Reductions in available drawdown can be much more problematic
because that have nothing to do with reparable infrastructure.
Groundwater, like surface water, flows "downhill." In order for groundwater to flow to a well, there
has to be a "downhill" gradient from the aquifer to the well. When a well is pumped, the water level
in the well is lowered, inducing a "downhill" gradient toward the well from all directions and water
flows into the well at the same rate that it is pumped from the well. If the pumping rate increases, the
water level in the well is lowered even further and the gradient becomes steeper - steeper gradients
allow more water to flow into the well to meet the pumping demand. This concept is illustrated in
Figure 2.
The relationship between the lowering of the water level in the well due to pumping (called
"drawdown") is referred to as the well's "specific capacity". At low and moderate levels, this
relationship is generally linear - as pumping rate increases, drawdown increase proportionally (i.e.
linearly). However, as drawdown becomes a greater percentage of the non-pumping water level, this
linear relationship between drawdown and pumping begins to break down. The well is said to
become "less efficient". What this simply means is that the aquifer cannot keep up with the pumping
demand in the well because it is trying to "squeeze" too much water into too thin of an zone around
the well. As a general rule of thumb, a well is approximately 90% efficient if drawdown is about 1/3
of the total available drawdown. As pumping rates increase beyond this level, drawdown increases to
higher percentages of total available drawdown with only a marginal increase in total pumping.
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2
The key issue here is the total available drawdown in a well. The total available drawdown is the
length of the column of water from the bottom of the well to the non-pumping (static) water level in
the well. If the total available drawdown is large, more water can be pumped before the well becomes
very inefficient. If that total available drawdown is reduced for some reason, well inefficiency is
reached at lower rate of pumping. As this report discusses, we suspect that this phenomenon is
responsible for low well yields in Wells 5 and 6.
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2.0 Hydrogeologic Evaluation of the lotus lake Well
Field
2.1 Extent and Nature of the Unconfined Sand and Gravel Aquifer
The unconsolidated sand and gravel aquifer is pumped from three wells in the Lotus Lake well field:
Well 5, Well 6, and Well 11. As part of this study, well logs that are maintained by the Minnesota
Geological Survey's County Well Index (CWI) for evaluated. Geologic cross sections through these
wells were developed. The locations of the cross sections are shown on Figure 3. Cross-Section A-
A' (shown on Figure 4) is approximately south to north, through the Lotus Lake well field. Cross-
Section B-B' (shown on Figure 5) is approximately east to west through the Lotus Lake well field.
Well logs from CWI were used to construct a map of the thickness of the sand and gravel aquifer that
Wells 5, 6, and 11 are screened in (Figure 6). This thickness map suggests that the sand and gravel
aquifer trends approximately north south along the eastern margin of Chanhassen and thins
considerably to the east (into Eden Prairie) and to the west. Throughout most of the aquifer, the
thickness is less than 25 feet. The sand and gravel aquifer is thicker than 100 feet in the immediate
vicinity of Wells 5, 6, and 11 but, as the map on Figure 6 shows, the thick portion of the aquifer is
very limited in extent (about 3,000 feet by 3,000 feet). The aquifer also becomes less permeable
north of Wells 5, 6, and 11, where sand and gravel grades into fine sand and silt.
The total volume in the sand and gravel aquifer of "accessible water" (i.e. water that can likely flow
under a gradient, such as pumping) is approximately 6.5 billion gallons. This is the approximate
volume of water that is stored within the pores of the aquifer. If this storage could not be replenished
by recharge, one well pumping continuously at 1,000 gallons per minute (gpm) would exhaust this
storage in about 12.3 years.
These cross sections and the thickness map indicate the following:
. The sand and gravel aquifer generally trends north-south but is of limited areal extent,
especially to the east and west.
. The sand and gravel aquifer is generally less than 25 feet thick over most of its aerial extent.
It is greater than 100 feet in thickness only in the immediate vicinity of Wells 5, 6, and 11.
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. The sand and gravel aquifer is overlain by a thick (100 to 200 feet), continuous layer of low-
permeability glacial till composed of yellow clay (near the surface), blue clay below the
yellow clay, and sandy or gravelly clay. These thick till units likely transmit very little
recharge, either from infiltrating precipitation or leakage from surface water bodies.
. The sand and gravel aquifer is separated from the underlying Prairie du Chien Group
dolomite by a basal sandy and gravelly clay till that is typically 25 to 100 feet thick. In some
locations, the basal portion of the St. Peter Sandstone overlies the Prairie du Chien Group.
The basal portion of the St. Peter Sandstone is a low-permeability shale.
. In one area immediately south of Wells 5 and 6, well logs indicate that the basal till layer is
absent. In this area, the sand and gravel aquifer is in direct hydraulic connection with the
underlying Prairie du Chien Group. This "window" in the basal till layer is one location
where there would tend to be higher rates of flow between the underlying Prairie du Chien
Group and the sand and gravel aquifer.
2.2 Recharge Mechanisms for the Sand and Gravel Aquifer
Given the limited aerial extent of the sand and gravel aquifer and the overlying thick sequence of
low-permeability glacial till, it appears likely that the primary mechanism for recharging the sand
and gravel aquifer is by upward flow from the Prairie du Chien Group into the sand and gravel
aquifer. Recharge would likely be through the "windows" in the basal till but would also take place
(at much lower rates) through the basal till itself.
Recharge of the sand and gravel aquifer by the Prairie du Chien Group would take place when the
hydraulic head in the Prairie du Chien Group is higher than the head in the sand and gravel aquifer.
Prior to modern development of this portion of the Twin Cities metropolitan area, pressure heads in
the Prairie du Chien Group would have been well above the top of the sand and gravel unit and the
head pressures within the two units would have reached an equilibrium.
In recent years, it appears likely that regional pumping of the Prairie du Chien-Jordan aquifer system
has resulted in a lowering of pressure heads in the Prairie du Chien Group, at least for a portion of
most years. In response to this lowering of pressure head in the Prairie du Chien Group, there has
likely been a disequilibrium between heads in the Prairie du Chien Group and the sand and gravel
aquifer, with higher heads in the sand and gravel aquifer. This likely resulted in a condition in which
the sand and gravel aquifer actually was recharging a portion of the Prairie du Chien Group via
leakage through the basal till "windows" and to a lesser extent, through the basal till itself. In other
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words, pumping in the Prairie du Chien Group not only stops the recharge of the sand and gravel
aquifer, it induces downward leakage from the sand and gravel aquifer.
2.3 Conceptual Model of Pumping and Hydraulic Head Changes
A conceptual model of how hydraulic head has changed in the sand and gravel aquifer in responds to
pumping is shown sequentially in Figure 7. The aquifer geometry, as shown on Figure 7, has been
simplified for clarity.
In illustration 1 of Figure 7, the hydraulic heads in the Prairie du Chien Group and the sand and
gravel aquifer are shown in a condition that likely was present before widespread pumping in
southeastern Caver and southwestern Hennepin Counties began (early 1960's). The hydraulic head of
the two aquifer systems were likely nearly equal to one another and the sand and gravel aquifer was
fully saturated. There likely was little leakage between the two aquifer systems because there was no
hydraulic gradient.
In illustration 2 of Figure 7, the hydraulic head of the Prairie du Chien Group is lowered in response
to pumping of Chanhassen Well 2 and other pumping in the region. The lowering of hydraulic head
in the Prairie du Chien Group causes downward leakage from the sand and gravel aquifer, with the
largest rate of leakage likely taking place through the "windows" in the basal till. In response to this
leakage, the hydraulic head in the sand and gravel begins to drop. When the hydraulic head reaches
the top of the sand and gravel aquifer, water that is stored in the pore spaces of the aquifer begins to
drain, causing dewatering of the top of the aquifer. Replenishment via recharge from the overlying
till is likely minimal.
In illustration 3 of Figure 7, Wells 5, 6, and 11 are installed and are pumping in the sand and gravel
aquifer. Well 2 continues to pump. Pumping of Wells 5, 6, and 11 further deplete storage in the sand
and gravel aquifer and the hydraulic head drops further. Regional pumping in the Prairie du Chien
Group, combined with pumping of Well 2, further lowers the hydraulic head in the Prairie du Chien
Group and prevents the Prairie du Chien Group from recharging, from below, the sand and gravel
aquifer.
Illustration 4 of Figure 7 represents the current situation. The hydraulic head in the Prairie du Chien
group has dropped to near the level of the pump intake in Well 2, resulting in a substantial drop in
specific capacity of this well. The sand and gravel aquifer has been dewatered to a level where the
hydraulic head for this aquifer is slightly above the pump intakes for Wells 5 and 6 - these wells,
also have substantially reduced capacity because there is very little available drawdown left. Well 11,
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6
which is about 500 feet from the other wells and is screened slightly deeper in the sand and gravel
aquifer, continues to have sufficient available drawdown to continue to operate. However, much of
the sand and gravel aquifer has had its storage depleted.
2.4 Prognosis for Future Production from the Sand and Gravel
Aquifer
It is likely that the combined effects of pumping out of the sand and gravel aquifer (Wells 5, 6, and
11) and downward leakage induced by the pumping of Well 2 and regional pumping in the Prairie du
Chien Group has substantially dewatered the sand and gravel aquifer. According to DNR water
appropriations records, Chanhassen has pumped about 4 billion gallons of water from the sand and
gravel aquifer. That volume of water is about 60 percent of the available storage (based on the
volume of the aquifer, as previously discussed).
In September 2007, the City staff measured the static (non-pumping) water levels in the Lotus Lake
well field wells and also measured changes in water levels when Well 11 was turned on and off. It
was found that the static water levels in all of the wells were at about the same elevation. It was also
found that water levels responded to cessation of pumping, but not at the level one might normally
expect (i.e. only a couple feet at most). This lack of response is likely the result of unconfined
conditions within the sand and gravel aquifer. Sand and gravel aquifers are slow to respond to
changes in pumping because of the high values of storage.
Over the winter, water levels in the Prairie du Chien Group may rise and begin to recharge the sand
and gravel aquifer from below. It is unlikely that the upward vertical flow into the sand and gravel
aquifer will be sufficient to replenish much of the depleted storage. In the Spring, when demand
increases, Wells 5 and 6 may be operational but only for a very short time. There is likely insufficient
time during the winter to realize much in the way of replenished storage. In fact, it would likely take
many years of no pumping in the sand and gravel aquifer combined with high water levels in the
Prairie du Chien Group to result in substantially resaturation of the sand and gravel aquifer.
Well 11 may continue to produce water. However, it is reasonable to assume that eventually Well 11
could experience decreased specific capacity. Wells 5 and 6 should not be counted on for future
production.
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3.0 Conclusions and Recommendations
Based on this hydrogeologic evaluation, the following are concluded:
1. The sand and gravel aquifer of the Lotus Lake well field is of limited aerial extent. Much of
the aquifer is less than 25 feet in thickness. Assuming a specific yield of 0.2, the total volume
of water stored in the aquifer is about 6.5 billion gallons.
2. The entirety of the sand and gravel aquifer is overlain by a thick sequence of low-
permeability glacial till that greatly inhibits recharge from infiltrating precipitation and
leakage from surface-water bodies. Recharge, while likely not zero, is something very close
to zero through the overlying till.
3. A gravelly clay till underlies the sand and gravel aquifer in most locations and separates the
sand and gravel aquifer from the underlying Prairie du Chien Group. The Prairie du Chien
Group, combined with the Jordan Sandstone, is the primary aquifer system for water supply
in the Twin Cities (exclusive of surface-water sources). There is at least one "window" in the
this basal till unit that allows for a direct hydraulic connection between the sand and gravel
aquifer and the Prairie du Chien Group. Upward flow from the Prairie du Chien Group into
the sand and gravel aquifer through these "windows", as well as diffuse leakage through the
basal till, is the primary mechanism for recharging the sand and gravel aquifer.
4. Pumping from Prairie du Chien-Jordan Well 2, combined with regional pumping in the
Prairie du Chien-Jordan aquifer, likely has resulted in lower hydraulic heads in the Prairie du
Chien Group underneath the Lotus Lake well field. These lower heads have effectively
reduced or stopped upward recharge of the sand and gravel aquifer.
5. Pumping of the sand and gravel aquifer by Wells 5, 6, and 11 has caused much of the sand
and gravel aquifer to become dewatered as storage has been removed. It is estimated that
over 60 percent of the available storage of the sand and gravel aquifer has been pumped by
these wells.
6. As storage has been depleted, hydraulic head levels in the sand and gravel aquifer have
dropped, causing reductions in available drawdown within the wells. During the summer of
2007, the available drawdown was reduced to a critical level, causing the specific capacity
and well efficiency of Wells 5 and 6 to rapidly drop. The result has been a nearly complete
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8
loss in well capacity. Well 11 continues to produce water, primarily because it is screened
slightly deeper than the other wells and has a lower pump setting. Well 11 may continue to
produce water but it may also begin to experience reduced yields, similar to Wells 5 and 6.
7. It is unlikely that the Prairie du Chien Group will be able to recharge the sand and gravel
aquifer and replenish the stored water that has been pumped. This is especially the case as
long as there is continued pumping in the sand and gravel aquifer by Well 11.
8. Regionally, the hydraulic head in the Prairie du Chien-Jordan aquifer has dropped over the
summer. The result has been a lowering of available drawdown in Well 2. The pump intake
of Well 2 is actually above the top of the Prairie du Chien Group.
Based on this evaluation, the following are recommended:
1. Lower the pump setting in Well 2. The pump intake in Well 2 is in the casing, above the
open-hole portion of the Prairie du Chien Group. This well's capacity should be able to be
restored to it's original value by lowering the pump and thereby increasing the available
drawdown. Consideration should be given to lowering the pump into the Jordan Sandstone.
2. Install two wells completed in the Prairie du Chien-Jordan aquifer to compensate for the loss
of use of Wells 5 and 6. These two new wells do not constitute a new appropriation - they are
designed to replace lost capacity. The Prairie du Chien-Jordan aquifer, while heavily used in
the region, is generally very reliable. Test wells should not be necessary. The following
additional items should be considered in the installation of these wells:
a. It is imperative that wells are separated from one another by a distance sufficient to
minimize well interference effects. As a general rule of thumb, wells should be 1,000
feet from one-another, unless they are completed in different aquifers that have little
or no hydraulic connection. Distances farther than 1,000 feet are better. Distances
closer than 1,000 feet will likely result in some overall capacity because of well
interference - therefore, there will be some trade off when considering available land
for installing wells.
b. Larger diameter wells afford the opportunity to install larger, more efficient pumps.
Larger diameter wells are generally more efficient in terms of aquifer losses,
resulting in more capacity.
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9
c. Screens can be used in bedrock aquifers. Screened wells cost more than open-hole
wells and there is some reduction in specific capacity for screened wells. Screened
wells may have lower development costs.
d. The Minnesota Department of Health has requirements for isolation distances for
wells. Department of Health staff should be consulted before finalizing locations.
e. The Minnesota Department of Natural Resources is responsible for water
appropriations and should be consulted before finalizing well locations. Department
of Health staff should also be consulted with regard to any additional evaluations that
may be required because of the City's proximity to Seminary Fen - a calcareous fen
wetland complex north of the Minnesota River in the southeastern portion of Chaska.
3. Consideration should be given to reevaluating the City's water conservation program to
minimize peak summer demand. The Minnesota Department of Natural Resources and the
Metropolitan Council offer assistance to cities in designing and implementing water
use/conservation programs. For example, some methods of implementation of lawn
sprinkling restrictions have been found to be more effective than others.
It is unlikely that the current problems with the wells in the Lotus Lake well field could have
been discovered and mitigated before they occurred. Aquifer tests (e.g., pumping tests) typically
are not run long enough nor do they pump at sufficiently high rates to disclose potential aquifer
dewatering. Unfortunately, these types of problems in unconsolidated sand and gravel aquifers
often do not manifest themselves until several years of pumping have taken place. It is unusual in
the Twin Cities metropolitan area to find wells that suddenly lose capacity, such as Wells 5 and
6. The circumstances for the loss of capacity are the result of an aquifer of limited aerial extent, a
thick covering of low permeability clayey till, and better than anticipated connection with the
underlying Prairie du Chien-Jordan aquifer.
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10
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Figure 1
Location of Chanhassen Water Supply Wells
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AQUIFER
Figure 2
Schematic Cross Section Depicting Groundwater Levels Without Pumping, With
Low Rates of Pumping, and With Higher Rates of Pumping
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(
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l?.l 10 - 25
D 25 - 50
CJ 50-100
III 100 - 200
D No Data
2000
I
o
2000
4000 Feet
Figure 6
Map of the Thickness of the Sand and Gravel Aquifer
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