HomeMy WebLinkAbout1.0 Data Elements and Assessment
1.0 Data Elements and Assessment
In accordance with Minnesota Rules Chapter 4720.5200, the data elements and their assessments
required to be included in the Wellhead and Source Water Protection Plan for the City of Prior Lake
(Public Water Supply 1700007) are presented in this section. Data elements related to the physical
environment, land use, water quantity, and water quality required for this Wellhead and Source
Water Protection Plan (the Plan) for the City of Prior Lake were specified in the May 4,2006
Scoping Decision Notice No.2 from the Minnesota Department of Health (MDH).
The City of Prior Lake operates Well 3 (unique no. 207308), Well 4 (unique no. 110452), Well 5
(unique no. 420954), Well 6 (unique no. 603083), and Well 7 (unique no. 655913) to provide the
City's drinking water. Wells 8 (unique no. 686263) and 9 (unique no. 686264) were put into service
as this Plan was being prepared. As such, Wells 8 and 9 are not included in this Plan. Minnesota
unique well numbers for Wells 3, 4, 5, 6, and 7 are shown in Table 1. Wells 3, 4,5, and 7 are located
in a well field in the eastern portion of the City and Well 6 is located in a well field in the western
portion of the City (Figure 1). Wells 3, 4, 5, and 6 are completed in the Jordan Sandstone aquifer.
Well 7 is completed in the Franconia Formation-Ironton Sandstone-Galesville Sandstone (FIG)
aquifer.
City of Prior Lake Wells 3, 4, and 5 were classified as being vulnerable to contamination in Part 1
of this Plan while Prior Lake Wells 6 and 7 were classified as being not vulnerable to contamination
(Barr, 2005). Vulnerability to contamination of the Jordan Sandstone aquifer (the City's main source
water aquifer) within the eastern Drinking Water Supply Management Area (DWSMA) associated
with Wells 3, 4, and 5 was determined to range from low to high. Since Prior Lake wells 6 and 7
have been classified as "not vulnerable" it was not necessary to assess the vulnerability of the
aquifers in the DWSMAs associated with these wells (Barr, 2005). A copy of the Part 1 report can
be found in Appendix A.
The eastern well field DWSMA associated with Wells 3, 4, 5, and 7 is found in Township 115N,
Range 22W, Section 36; Township 114N, Range 22W Sections 1 and 12; and Township 114N, Range
21W, Sections 6 and 7. The western well field DWSMA associated with Well 6 is found in
Township 115N, Range 22W, Sections 33 and 34 and Township 114N, Range 22W, Section 3.
Portions of the DWSMA identified in the wellhead protection area delineation study (Barr, 2005) for
the eastern well field extend into Credit River Township and Spring Lake Township (Figure 1). The
City of Prior Lake will begin discussions with the Boards of Supervisors for Credit River and Spring
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Lake Townships regarding cooperation between the City and the Townships in safeguarding the Prior
Lake source water aquifers.
1.1 Physical Environment Data Elements
Data elements discussed in this section include precipitation, geology and hydrogeology, soils, and
water resources.
1.1.1 Precipitation
Since the some of the Prior Lake municipal wells and a portion of the Jordan Sandstone aquifer
within the eastern DWSMA are classified as vulnerable to contamination, precipitation must be
evaluated to determine if it could potentially apply to the Plan.
As shown on the map and in the table in Appendix B, there is one National Oceanic and Atmospheric
Administration (NOAA) climate observing station in Scott County. This station is located in Jordan.
The station location is identified by latitude and longitude in the Station Index table in Appendix B.
There are additional cooperative weather observing stations in Scott County maintained by
volunteers that do not appear on the map. Appendix B also includes tables of monthly and annual
precipitation for various locations in Scott County, including Prior Lake, for the period 2002 through
2006.
As described in the Part 1 report (Barr, 2005), the Jordan Sandstone aquifer (i.e., the City's main
source water aquifer) is under leaky-confined hydrogeologic conditions under Prior Lake, except in
areas where a buried bedrock valley is cut into/through the Jordan Sandstone. Based on the aquifer
vulnerability assessment results, issues related to precipitation may potentially have an affect on the
management strategies developed for the eastern DWSMA. In areas of high aquifer vulnerability,
precipitation can act as a transport mechanism through infiltration or, possibly, runoff. A
contaminant could be transported from the surface toward the source water aquifer via infiltration. A
contaminant could also be displaced through the municipal storm sewer system, or across
impermeable surface features during or after precipitation events.
1.1.2 Geology and Hydrogeology
The regional and local geology and hydrogeology of the Prior Lake area are described in detail by
Barr Engineering Company (Barr) (1999a; 2002; and 2005) and the geology and hydrogeology in the
vicinity of the DWSMAs is summarized below.
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The regional groundwater flow system includes four aquifers that were considered in the
development of the Prior Lake wellhead protection plan: the glacial drift/St. Peter Sandstone, the
Prairie du Chien Group, the Jordan Sandstone, and the FIG aquifer. Aquifers deeper than the FIG
were considered to have negligible interaction with overlying aquifers, based on available
information. A leaky aquitard lies between each of the aquifer units. Between the glacial drift/St.
Peter aquifer and the underlying Prairie du Chien Group the aquitard consists of the basal portion of
the St. Peter Sandstone (where present) and glacial till. Between the Prairie du Chien Group and the
Jordan Sandstone, a resisting aquitard layer is present that combines the leakage resistance effects of
vertical anisotropy of hydraulic conductivity and lower hydraulic conductivity conditions in the basal
portion of the Oneota Formation (Prairie du Chien Group). Between the Jordan Sandstone and the
Franconia Formation (the uppermost unit in the FIG aquifer) is the St. Lawrence Formation. The St.
Lawrence Formation is a dolomitic shale and siltstone that ranges in thickness from approximately 55
to 80 feet in Scott County (Runkel and MossIer, 2006).
As noted above, most of the City of Prior Lake municipal wells are completed in the Jordan
Sandstone aquifer while Well 7 is completed in the FIG aquifer. Well construction information for
the Prior Lake municipal wells is summarized in Table 1 and copies of the MDH well records are
presented in Appendix C.
The surficial geologic unit in the vicinity of the DWSMAs consists mainly of unconsolidated glacial
drift deposits including sand, gravel, and clay. Based on the well logs for the Prior Lake municipal
wells, these unconsolidated glacial drift deposits are approximately 105 to 210 feet thick within the
DWSMAs (Appendix C).
The uppermost bedrock within the DWSMAs varies with location and includes the Prairie du Chien
Group, Jordan Sandstone, St. Lawrence Formation, Franconia Formation, and IrontonlGalesville
Sandstone (Figure 2). Information from well logs in the Minnesota Geological Survey County Well
Index (CWI) indicates that the Prairie du Chien Group dolomite in the area of the DWSMAs ranges
in thickness from approximately 140 feet to 200 feet. Depth to the top of the Jordan Sandstone
ranges from approximately 260 feet to 300 feet within the DWSMAs. Thickness of the Jordan
Sandstone varies between approximately 80 feet and 100 feet within the DWSMAs.
The two primary major sources of water to the glacial drift/St. Peter Sandstone aquifer are
recharge from infiltration and seepage from surface water bodies. The primary source of
water for the Prairie du Chien Group, Jordan Sandstone and FIG aquifer is leakage from
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adjoining aquifer units. Discharge is to the major streams; the Minnesota River, the
Mississippi River, the Vermillion River, and the Cannon River. Pumping wells also remove
water from the aquifer units.
Lakes, especially in northern Scott and Dakota Counties, are generally perched above the
water table and leak water down into the aquifer as a function of the resistance of the lake's
bottom sediment and the unsaturated drift material below the lakes. Upper portions of the
Vermillion and Credit Rivers also leak water (losing stream) in the glacial drift.
A buried bedrock valley cuts through the Prior Lake area trending north-northeast. This valley is
filled with glacial till. The Franconia Formation subcrops along the axis of this valley (Runkel and
Mossier, 2006). To the southwest of Prior Lake, this buried bedrock valley opens into a wide area
where the Jordan Sandstone and overlying bedrock units have been removed by erosion and bedrock
units below the Jordan Sandstone subcrop. There are also small tributary valleys beneath the City of
Prior Lake (Figure 1).
Prior Lake Wells. 3,4,5, and 6 are all completed in the Jordan Sandstone. The Jordan Sandstone is
stratigraphically between the Prairie du Chien Group and St. Lawrence Formation. As noted above,
the basal portion of the Oneota Formation in the Prairie du Chien Group is the resisting aquitard
between the Prairie du Chien Group and Jordan Sandstone. However, the degree of hydraulic
connection between the Prairie du Chien Group and the Jordan Sandstone is known to vary, at least
on a local basis. Accordingly, MDH staff used draft guidance (MDH, April 2005) for delineating
WHP As in fractured and solution-weathered bedrock to assess the need for additional analysis ofthe
capture zones for the Prior Lake wells (the delineation of the capture zones is described in this Barr,
2005). The assessment of the Prairie du Chien Group and Jordan Sandstone using volume
calculations based on pumping volumes and the groundwater modeling results indicated that the
leakage between the Prairie du Chien and Jordan is sufficiently small so as to obviate the need for a
more extensive fracture flow analysis. This result is substantiated by the isotope data from the city's
wells. The tritium result observed in the sample from Well 6 is below 0.8 t.u. and is 1.3 t.U. in the
sample from Well 3. Neither of these results is indicative of large-scale recharge to the Jordan from
overlying materials.
Groundwater in the glacial drift aquifer in Scott County generally flows from a high point in the
southeast to the north and west towards the Minnesota River (Kanivestsky and Palen, 1982).
Groundwater flow in the bedrock aquifers, where present, generally mimics flow in the water table
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system, with flow being generally towards the north and west. The Minnesota River is a discharge
zone for the bedrock aquifers.
1.1.3 Soils
Since Prior Lake Wells 3,4, and 5 and a portion of the associated DWSMA are classified as
vulnerable to contamination, surficial soil characteristics must be evaluated to determine if they
could potentially apply to the Plan. Review of available information from the Scott County soil
survey indicates that there are a variety of surficial soil types within the DWSMAs. These soils have
a range of infiltration characteristics. There are no known eroding lands causing sedimentation
problems within the DWSMAs.
Based on the aquifer vulnerability assessment results, issues related to surficial soil characteristics or
the surficial soil types may potentially have an affect on the management strategies developed for the
DWSMAs. Surficial geologic materials in the City of Prior Lake consist of sand, gravel, and clay in
soils of varying permeabilities. Soil classifications and permeability distributions are shown on
Figures 3 and 4, respectively. The City is well aware that land development and land use activity
may have an impact on the source water aquifer in areas of high aquifer vulnerability within the
eastern DWSMA associated with permeable soil types.
1.1.4 Water Resources
Since Prior Lake Wells 3, 4, and 5 and portions of the associated DWSMA are classified as
vulnerable to contamination, surface water resources must be evaluated to determine if they could
potentially apply to the Plan.
Flow directions and boundaries of watersheds in the area do not indicate any reasons for concern.
There are several surface water bodies in the City that have a shoreland management classification
(see Section 1104.20 I of the City Code) and are designated as public lakes by the Minnesota
Department of Natural Resources. Markley Lake (DNR ill no. 70-2l W) and Blind Lake (DNR ill
no. 70-53) are the only surface water bodies with shoreland management classifications within the
eastern DWSMA. Arctic Lake (DNR ill no. 70-85) is the only surface water body with a shoreland
management classification within the western DWSMA. A portion of Markley Lake lies within the
boundary of that portion of the eastern DWSMA that has been identified as highly vulnerable to
contamination. As noted in the Prior Lake 2030 Comprehensive Plan (Prior Lake 2005a), the City
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enforces both shoreland and floodplain management ordinances within 1,000 feet of any lake in the
City.
Based on the aquifer vulnerability assessment results, issues related to surface water resources may
potentially have an affect on the management strategies developed for the DWSMAs. Geologic
conditions in and around the City's eastern DWSMA result in areas of high aquifer vulnerability.
Due to these conditions, surface water (including storm water) management is critical for
maintaining a water supply of high quality. The quality of the source water is dependent on the
quality of its recharge. Recharge sources/mechanisms are noted above. Surface water management
will be conducted so as to reduce the potential negative effects that surface waters may have on the
source water aquifers. Management strategies in this Plan will address current and future surface
water quality in the area so that aquifer recharge and water availability does not become an issue for
the City.
1.2 land Use Data Elements
Land use and public utilities within the DWSMAs are discussed in this section. Parcels in the City of
Prior Lake and in Credit River and Spring Lake Townships were used to delineate the DWSMAs and
are shown in the Wellhead Protection Area Delineation Report (Appendix A).
1.2.1 land Uses
Current and historical land uses are discussed in this section.
1.2.1.1 Current Land Use
Since Prior Lake Wells 3, 4, and 5 and portions of the associated DWSMA are classified as
vulnerable to contamination, current land use must be evaluated to determine if it could potentially
apply to the Plan. Figure 5 shows the DWSMAs superimposed over a map of current (as of 2005
obtained from the Metropolitan Council) land use. Numerous land uses are found within the
DWSMAs, including agricultural, farmsteads, golf course, industrial and utility, institutional, parks
and recreation, retail and other commercial, residential, and undeveloped. Figure 6 shows the
DWSMAs superimposed over a map showing current zoning in the City of Prior Lake.
A potential contaminant source inventory (PCSI) was conducted within the DWSMAs. Information
on potential contaminant sources was obtained from Scott County, MDH, and Minnesota Pollution
Control Agency (MPCA) databases. Properties identified as potential sources of contamination
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during the PCSI are listed in Tables 2 through 7. A portion of this information was field verified
during development of this Plan. Methods used to verify the PCSI information for different
included windshield surveys of properties and direct contact of property owners. Some of the
information related to the locations of potential contaminant sources that was obtained from the
public databases was determined to be inaccurate during the verification process. The inaccurate
information was updated as necessary. Public database information that was not verified
development of this Plan will be verified as part of Plan implementation. Verified properties are
identified in Tables 2 through 7. Results of this inventory indicate the presence of several potential
contaminant sources within the DWSMAs. Locations of these potential contaminant sources are
shown on Figures 7 through II. These potential contaminant sources have been considered, as
appropriate based on aquifer vulnerability, in the development of the management strategies for the
DWSMAs.
Information from the MPCA and Scott County indicates there are contaminant spill/release sites
within the DWSMAs. These spill/release sites have been addressed under oversight by the
Minnesota Pollution Control Agency (MPCA). Available information indicates that these sites have
been closed. That is, no further remedial action is needed at the sites. Because of the potential for
contaminant spills, transportation corridors represent an additional potential source of contamination,
particularly in areas of high aquifer vulnerability. These potential contaminant sources have been
considered in the development of the management strategies for the DWSMAs.
Data obtained from Scott County, the Minnesota Geological Survey (MGS) County Well Index
(CWI), and the Minnesota Department of Natural Resources (MDNR) State Water Use Database
(SWUDS) during the PCSI indicates that there are a number of private wells within the DWSMAs
(Figure 10). Table 5 lists the wells that were identified in the DWSMAs and indicates the aquifer in
which each well is completed (if known) and the date the well was completed (ifknown).Private
wells located within the DWSMAs, particularly those wells completed in the lower half of the Prairie
du Chien Group and in the Jordan Sandstone have the potential for being a pathway for
contamination to reach the Jordan Sandstone aquifer and the Prior Lake municipal wells. Available
information indicates that there are no private wells within the eastern DWSMA completed in the
Jordan Sandstone and that one private well in the western DWSMA is open to the Jordan Sandstone.
Available information also indicates that there are .no private wells open to the FIG aquifer in the
eastern DWSMA. Wells that were not properly installed or have not been adequately maintained
may provide a conduit for contaminants to reach the main source water aquifer (i.e., the Jordan
Sandstone).
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Several individual sewage treatment systems (ISTS) have been identified within the eastern DWSMA
(Table 6 and Figure 11). While three ISTS have been identified in the western DWSMA (Table 6
and Figure 11), none of these are large systems serving more than 20 people. Section 705.300 of the
City Code requires that:
"The owners of all houses, buildings, or properties used for human occupancy, employment,
recreation or other purpose, situated within the City and abutting on any street, alley or right of
way in which there is now located or may in the future be located a public sanitary sewer of the
City is hereby required at their expense to install a suitable toilet facility therein, and to connect
such facilities directly with the proper public sewer in accordance with the provisions of this
Section. ..".
The City Code does not regulate ISTS on any properties within the City that cannot connect to the
sanitary sewer as per the requirements of Section 705.300. For any such properties and for properties
outside the City limits, the City relies upon Scott County Individual/Community Sewage Treatment
Ordinance No.4 and Minnesota Rules chapter 7080.
An evaluation of the potential presence of Class V wells within the DWSMAs was done as part
of the PCSI. Typical land uses associated with the presence of Class V wells include automobile
service stations and repair shops. During the PCSI, it was determined that three businesses typically
associated with Class V wells are present within the eastern DWSMA (see Table 7) and no
businesses typically associated with Class V wells are present within the western DWSMA. It was
not determined if Class V wells are actually present on any of these properties. However, the
information obtained during the PCSI indicates that one of the three businesses within the eastern
DWSMA is no longer in operation (Table 7). Field verification confirmed that the business is no
longer in operation at the location listed in the database.
As previously mentioned, the PCSI was conducted using information provided by Scott County,
MDH, and the MPCA. For future updates of this Plan the City will access available data sources and
maintain as accurate and up to date as possible potential contaminant source database in its wellhead
protection file.
1.2.1.2 Historical Land Use
Since Prior Lake Wells 3,4, and 5 and a portion of the associated DWSMA are classified as
vulnerable to contamination, historical land use must be evaluated to determine if it could potentially
apply to the Plan.
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Prior Lake was incorporated as a village in l891. Prior to the 1960s, Prior Lake experienced low to
moderate growth and the area around Prior Lake was mainly farmland (e.g., Figure 12). Note that
metadata associated with ArcView shapefiles of pre-l 997 land use maps available from the
Metropolitan Council indicate that the maps are not considered reliable for determining land use of
individual properties but are adequate for determining general land use categories in an area. Using
available information, historical land uses that might significantly affect the management strategies
for the DWSMAs that are not currently present within the DWSMAs were not identified.
While it is possible that buried features such as old farm wells that were not properly sealed or
unused underground storage tanks not listed in any available database could be present within the
DWSMA, available information does not suggest the presence of such features. Thus, there is no
basis for a concerted search for such buried features with in the DWSMAs. If any such, currently
unknown, features are to be located in the future it would most likely occur only if they are
encountered during redevelopment of a property.
1.2.2 Public Utilities
Since Prior Lake Wells 3, 4, and 5 and portions of the associated DWSMA are classified as
vulnerable to contamination; public utilities must be evaluated to determine if they could potentially
apply to the Plan.
The Prior Lake municipal wells have open-borehole completions, mainly in the Jordan Sandstone. As
noted above, Wells 3, 4,5, and 6 are open to the Jordan Sandstone aquifer while Well 7 is open to
the FIG aquifer. Well construction information for these Prior Lake municipal wells is summarized
in Table 1. Copies of the MDH Well Records for these wells are presented in Appendix C.
As shown on Figure 13, no petroleum or natural gas pipelines cross the DWSMAs. However, there
are natural gas pipelines in the general vicinity of the City of Prior Lake.
Stormwater management in Prior Lake is discussed in chapter 7 of the City's 2030 Comprehensive
Plan. Maps showing the existing and proposed elements of the Prior Lake stormwater system are
presented on Figures 7.4 through 7.9 of the 2030 Comprehensive Plan. Based on the aquifer
vulnerability assessment results, issues related to stormwater management may potentially have an
affect on the management strategies developed for the eastern DWSMA.
A municipal storm sewer and surface water drainage system plays a significant role in the
management of stormwater and can be an important part of management strategies developed for a
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wellhead protection plan. An improperly designed or maintained storm sewer and surface water
drainage system may increase the chance for the spread of a contaminant into environmentally
sensitive areas, such as protected wetlands, lakes, and rivers or allow infiltration of contaminants in
areas of high aquifer vulnerability within the eastern DWSMA that could potentially reach the main
source water aquifer. The City of Prior Lake has developed plans for stormwater management (see
Prior Lake 2005a; 2005b) to address issues regarding water quality and treatment of the stormwater
and consideration is given to the management of stormwater in later portions of this Plan.
Figure 14 shows the relationship between the City's storm sewers and the Inner Wellhead
Management Zone (IWMZ) specified in Minnesota Rules 4720.5100. As indicated on Figure 14,
storm sewers are present within the IWMZ for Wells 3 and 6. The vulnerability of the source water
aquifer underlying only a very short segment of the storm sewer within the IWMZ for Well 3 is
classified as "High" (Figure 14A).
Another component of surface water management in the vicinity of Prior Lake is the County's
judicial ditch system. The Scott County judicial ditch system is shown on Figure 15. Comparison of
the ditch locations shown on Figure 15 to the DWSMA boundaries indicates that none of the ditches
in this system are in the high vulnerability portion of the eastern DWSMA.
The City's sanitary sewer system is discussed in chapter 8 of the City's 2030 Comprehensive Plan.
A map showing the existing and proposed elements of the Prior Lake sanitary sewer system is
presented on Figure 8.1 of the 2030 Comprehensive Plan. Based on the aquifer vulnerability
assessment results, issues related to sanitary sewers may potentially have an affect on the
management strategies developed for the eastern DWSMA.
An improperly designed or maintained sanitary sewer system may increase the chance for the release
of untreated sewage into environmentally sensitive areas, such as protected wetlands, lakes, and
rivers or allow infiltration of untreated sewage within areas of high aquifer vulnerability within the
eastern DWSMA that could potentially reach the main source water aquifer. The City of Prior Lake
has an ongoing maintenance program to insure the integrity and proper operation of the sanitary
sewer system.
1.3 Water Quantity Data Elements
Surface water and groundwater quantity are discussed in this section.
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1.3.1 Surface Water Quantity
Since Prior Lake Wells 3,4, and 5 and a portion of the associated DWSMA are classified as
vulnerable to contamination, surface water quantity must be evaluated to determine if it could
potentially apply to the Plan.
Surface water features within the DWSMAs include lakes, ponds, stormwater basins, and wetlands.
As noted above, there are lakes within the DWSMAs that meet the definition of public waters in
Minnesota Statutes Section 103G.005, subdivision 15 and have shoreland classifications pursuant to
Minnesota Statutes Sections 103F.201 to 103F.221. Several ofthe surface water features are listed in
the City's stormwater management plan (see Prior Lake 2005a). There are wetlands within the
DWSMAs. Some of these wetlands are associated with other surface water features such as lakes.
The majority of these wetlands within the DWSMAs are small in size (i.e., <2 Yz acres.) and are not
definable by the Minnesota Statute for Public Waters Wetlands (i.e., Section 103G.221 to
103G.2373). Prior Lake does not have an appropriation permit to withdraw water from any surface
water feature within the DWSMAs.
Cleary Lake is located in the southeastern portion of the eastern DWSMA. Underlying aquifer
vulnerability in this portion of the DWSMA is "Low". The MNDR's SWUDS database indicates that
under appropriation permit 786042, water is pumped from Cleary Lake for golf course irrigation.
The annual permitted withdrawal from the lake is 33 million gallons with an instantaneous maximum
pumping rate of 600 gallons per minute. This is the only permitted surface water withdrawal within
the DWSMAs shown in the SWUDS database.
As indicated above in Section 1.1.4, infiltration of low quality surface water could adversely affect
the main source water aquifer. This is particularly true in areas of high aquifer vulnerability within
the eastern DWSMA. Thus, management of the vulnerable source water aquifer within the eastern
DWSMA may potentially be affected by issues related to surface water resources.
1.3.2 Groundwater Quantity
Since Prior Lake Wells 3,4, and 5 and a portion of the eastern DWSMA are classified as vulnerable
to contamination; groundwater quantity must be evaluated to determine if it could potentially apply
to the Plan.
Prior Lake Well 7 went into operation in 2003. Since that time, the Jordan Sandstone aquifer has
supplied approximately 79% to 96% of the water pumped by the City of Prior Lake to meet its public
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water demand. The remainder of the water pumped by the City has been from the FIG aquifer. The
Jordan Sandstone aquifer can yield a sufficient quantity of water to meet the City of Prior Lake's
current public water demand. Supplementing withdrawals from the Jordan Sandstone aquifer with
pumping from the FIG aquifer provides the City with additional capacity to meet future water
demands.
Prior Lake's projected water demand used for the WHP A delineation is 1,150,718,600 gallons per
year (Barr, 2005). Under Minnesota Department of Natural Resources (MDNR) Appropriation
Permit No. 756201, the City of Prior Lake currently has a permitted annual groundwater
appropriation of 700 million gallons per year (MGY). The City was in the process ofrequesting an
increase in their annual appropriation as this Plan was being prepared.
Population in Prior Lake has steadily increased since 1980 as discussed in the Prior Lake
Comprehensive Plan (Prior Lake, 2005a). In 1980, the population of Prior Lake was 7,284. Prior
Lake's population had grown to 11,482 in 1990 and 15,917 in 2000. The Comprehensive Plan
estimates that Prior Lake's population will reach approximately 26,500 by 2010 and will increase to
approximately 40,000 by 2030.
Water demand is discussed in both the 2030 Comprehensive Plan and the Water Emergency and
Conservation Plan (Prior Lake, 2005a and 2006, respectively). Water demand in Prior Lake has
continued to grow along with the population. From 1996 to 2000 Prior Lake's water demand
increased approximately 32% and from 2000 to 2005 Prior Lake's water demand increased
approximately 15%. The City's population increased approximately 49% between 1996 and 2005.
Available information from the MDNR's SWUDS database indicates that there are no high capacity
wells (i.e., wells with annual appropriations of more than I million gallons) other than City of Prior
Lake municipal wells within the DWSMAs and only two high capacity wells within one mile of the
DWSMAs (Figure 10 and Table 8).
Construction of other high capacity wells in or near the DWSMAs may influence groundwater flow
in the source water aquifers and the groundwater quantity available to the municipal system. Such
wells could potentially affect the boundaries of the DWSMAs, which would require the City to
update the current wellhead protection plan. Issues regarding changes in appropriations resulting
from additions or deletions to the current list of water appropriations in the area will be addressed in
the management portion of this Plan.
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Persistent drought conditions during the growing season may also prove to be a threat to the quantity
of groundwater available to the municipal system. For this reason, Prior Lake has a permanent
conservation program for outside water usage (see City Ordinances section 704). This program consists
of an odd/even water use system with a daily outdoor water use restrictions from 11 a.m. to 5 p.m. that is
in effect beginning May 1 and extending through September 1 and it applies to all property within the
City of Prior Lake. The program restricts users to watering lawns and gardens or otherwise using an
outdoor hose before 11 a.m. or after 5 p.m. on either odd or even days of the month, depending on .J::::--
the property address. The only exceptions to the restrictions are for new sod, seed, or landscaping for the
first 30 days after planting. To qualify for the exceptions, a property owner must complete and submit a
Sprinkling Permit Form which is available from the City. The City ordinance also gives the City
Manager the authority to declare a water emergency and ban all outdoor water use if the Manager is
notified by the Public Works Director that specific conditions exist that may result in the City being
unable to meet water demand.
There are currently no known water use conflicts or interference complaints associated with pumping
from the Prior Lake municipal wells.
At this point in time, the City of Prior Lake's current water supply meets the demand of its
consumers. Prior Lake's 2030 Comprehensive Plan includes a recognition that the municipal water
supply system will need to be expanded in the future to meeting growing water demand. The City is
confident that the municipal water supply system will continue to have the capability of meeting
future demand.
1.4 Water Quality Data Elements
Surface water and groundwater quality are discussed in this section.
1.4.1 Surface Water Quality
Since Prior Lake Wells 3,4, and 5 and a portion of the eastern DWSMA are classified as vulnerable
to contamination, surface water quality must be evaluated to determine if it could potentially apply to
the Plan.
There are lakes/ponds that meet the definition of public waters within the DWSMAs. As noted
above, wetlands are also present within the DWSMAs.
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Stormwater management in Prior Lake is addressed in the City's Surface Water Management
Plan/Wetland Inventory & Management Plan (Prior Lake, 2005b) and the 2030 Comprehensive Plan.
The stormwater management plan was developed to address the issues of water quality, water
quantity, and rate control. The goals and policies of the plan have been developed for the City
concerning water quality, water quantity, recreation, fish and wildlife management, groundwater
enhancement, education, wetlands, and erosion. The plan acts as a guideline for current and future
urban development.
As noted above, infiltration of low quality surface water could adversely affect the main source water
aquifer. This is particularly true in areas of high aquifer vulnerability within the eastern DWSMA.
Thus, issues related to surface water quality may potentially have an affect on the management
strategies developed for the eastern DWSMA.
1.4.2 Groundwater Quality
The MDH has an ongoing program to monitor quality of municipal water supplies. Prior Lake's
municipal wells are sampled at least once every year for parameters that may include selected metals,
other inorganic compounds, organic compounds, and bacteria as part of this program (note that
samples may not be analyzed for all the monitoring parameters each year). To date, reported
concentrations of all monitoring parameters meet the regulatory levels specified by the U.S. EP A as
part of the Safe Drinking Water Act. The most recent sampling of Prior Lake's municipal wells by
the MDH for which results are available at the time this Plan was prepared occurred in 2006 (see
Appendix D). In addition to the MDH sampling program, the City of Prior Lake routinely tests water
at various locations in the municipal water distribution system for fluoride, polyphosphate, free
chlorine, and total chlorine. A copy of Prior Lake's May 2007 Consumer Water Quality Report is
available on the City's website (http://www.cityofpriorlake.comlpublic_works_ drinking_ water.shtml). A
copy of the May 2007 Consumer Water Quality Report is presented in Appendix D. Copies of the
City's routine water quality measurements for January - November 2006 are also presented in
Appendix D.
As noted in Prior Lake's 2030 Comprehensive Plan, sampling results for the City's water supply
indicate that iron and manganese exceed the National Secondary Drinking Water Standards. These
secondary standards address drinking water aesthetics (e.g., taste and odor). As a result, the City of
Prior Lake is planning to build a water treatment facility to remove iron and manganese from the
water in the municipal water supply system. The May 2007 Water Quality Report (see Appendix D)
indicates that the planned completion date for the water treatment facility is January 2009.
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The City does not have any additional water quality data for the source water aquifers within the
DWSMAs beyond that obtained by the MDH and City sampling programs. The 2002 through 2005
Water Quality Reports are available on the City's web site and groundwater quality data for years
prior to 2006 are also available from the City upon request.
According to information gathered during the PCSI, there are leaking underground storage tank
(LUST) locations within the eastern DWSMA in Prior Lake (Figure 8). Available information
indicates that all of these sites are closed and that no additional remedial actions are needed.
Information gathered during the PCSI indicates that there are currently no known spills/contaminant
releases within the DWSMAs that require remedial actions. To date, no impacts on the City's water
supply resulting from the presence of old LUST or spill/release sites has been observed.
The presence of these sites within the eastern DWSMA is a reminder that spills/releases of
contaminants could potentially occur within the DWSMAs. It is important to consider groundwater
quality when determining management strategies for the land uses within the DWSMAs. Since the
City currently enjoys good water quality, the City will develop management strategies in the later
portions of this Plan aimed at maintaining the groundwater quality in the source water aquifer.
1.5 Assessment of Data Elements
1.5.1 Use of the Municipal Wells
Prior Lake currently has been operating 5 wells (Wells 3, 4, 5, 6, and 7) in the municipal water
supply and distribution system for public water supply 1700007 since 2003. Two wells (Wells 8 and
9), were added to the system as this Plan was being prepared. Wells 3, 4, 5, and 7 are in the eastern
well field (Figure 1). Well 6 is in the western well field (Figure 1). Wells 3, 4,5, and 6 are
completed in the Jordan Sandstone aquifer. Well 7 is completed in the FIG aquifer. Construction
details for the Prior Lake municipal wells are summarized in Table 1 and copies of the MDH well
records are presented in Appendix C.
Population in Prior Lake has steadily increased, as discussed in the City of Prior Lake 2030
Comprehensive Plan (Prior Lake, 2005a). In 1940, the population of Prior Lake was 349. By 1960,
the population of the City had increased to 848. In 1980, the population of Prior Lake was 7,284.
Prior Lake's population had grown to 11,482 in 1990, and to 15,917 in 2000. In 2005, the population
of Prior Lake was 21,395. The 2030 Comprehensive Plan estimates that Prior Lake's population will
reach approximately 26,500 by 2010 and approximately 40,000 by 2030.
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Water demand is discussed in both the 2030 Comprehensive Plan and the Water Emergency and
Conservation Plan (Prior Lake, 2005a and 2006, respectively). Water demand in Prior Lake has
continued to grow along with the population. From 1996 to 2000 Prior Lake's water demand
increased approximately 32% and from 2000 to 2005 Prior Lake's water demand increased
approximately l5%. The City's population increased approximately 49% between 1996 and 2005.
Using the projected water demand in the Water Emergency and Conservation Plan, it is estimated
that in the year 2015 Prior Lake's water demand will be approximately 39% higher than it was in
2005.
As noted above, Prior Lake Wells 8 and 9 were put into service as this Plan was being prepared. In
addition, the City is in the process of identifying locations for new municipal wells. As discussed in
the 2030 Comprehensive Plan, the Jordan Sandstone and other aquifers are potential targets for these
wells.
The 2030 Comprehensive Plan anticipates that Prior Lake will need a total of approximately 16 wells
to meet the City's water demand by 2020. The plan envisions future wells being completed in the
Jordan Sandstone aquifer and, possibly, other aquifers. The Comprehensive Plan also envisions that
the majority of future wells will be installed in the western portion of the City. This projected total
number of wells represents an increase of up to nine municipal wells beyond those currently in
operation. The Prior Lake 2030 Comprehensive Plan projects a population of 33,300 in the year
2020 and 40,000 in the year 2030.
While the City's water meets all primary water quality criteria, iron and manganese concentrations in
the water supply are above aesthetic criteria. Thus, the City is planning to construct a treatment plant
to address these aesthetic water quality issues. Currently, the City treats the water at the wellhead
via chlorination, fluoridation and sequestering of iron and manganese.
Prior Lake currently has 1,750,000 gallons of elevated water storage consisting of a 750,000 gallon
tank located on the south side of town along Tower Street (Tower No.1) and a 1,000,000 gallon tank
located on the north side of town along Cedarwood Street (Tower No.2). The 2030 Comprehensive
Plan describes proposed expansion of the City's water storage capacity.
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1.5.2 Wellhead Protection Area Criteria
Information/criteria used to perform the groundwater flow modeling for the Prior Lake
WHP AJDWSMA delineations (Barr, 2005) is discussed in the WHP A study report (Part 1 of this
Plan) and summarized below. A copy of the WHPA study report is included in Appendix A.
1.5.2.1 Time of Travel
A 10-year time of travel was used for the WHP A delineation for each of the Prior Lake municipal
wells. The maps in the Part 1 report show the combined 10-year time of travel WHP As for the wells
in the eastern and western portions of the City. In addition, the one-year time of travel zone for each
Prior Lake municipal well is also shown on the maps in the Part 1 report.
1.5.2.2 Aquifer Transmissivity
Aquifer transmissivity for the Jordan Sandstone aquifer was determined from the results of an aquifer
test conducted in Prior Lake Well 3 during the period May 7-8, 1998 by MDH staff. In addition,
aquifer transmissivity for the FIG aquifer was determined from the results of an aquifer test in
Savage Well 8 (unique number 582627) conducted during the period March 8-26, 1999 by Barr
Engineering Company (Barr, 1999b).
The mean transmissivity for the Jordan Sandstone based on the aquifer test in Prior Lake
Well 3 is 4,940 ft2/day (459 m2/day). At Prior Lake Well 3 the Jordan Sandstone is 97 feet thick
(Appendix C). Available well logs indicate that the thickness of the Jordan Sandstone in the Prior
Lake area is somewhat variable. This variation is reflected in the groundwater flow model used to
delineate the WHP As.
The transmissivity of the FIG aquifer determined from the Savage Well 8 aquifer test is 701 ft2/day
(65.1 m2/day). At Savage Well 8, the FIG aquifer is 205 ft (62.5 m) thick. Thus, the aquifer test
results indicate a hydraulic conductivity of 3.42 ft/day (1.04 m/day). Average thickness of the FIG
aquifer in the vicinity of Prior Lake and Savage is approximately 197 ft (60 m). In the calibrated
groundwater flow model used in the delineation of the WHP A, a hydraulic conductivity for the FIG
aquifer of 1.04 m/day was used. Thus, a transmissivity of 62.4 m2/day was used for the FIG aquifer
in the area around Prior Lake.
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1.5.2.3 Daily Volume of Water Pumped
Daily volume of water pumped from each of Prior Lake's municipal wells was determined by using
the highest recorded or projected pumping volume for each well. Determination of the daily volume
of water pumped for each well used in the groundwater flow models is discussed in detail in the Part
1 report (Appendix A).
1.5.2.4 Flow Boundaries
To accurately delineate the WHP As, it is necessary to assess the affects that nearby wells, rivers,
lakes, and variations in geologic conditions may have on groundwater flow directions and velocities.
The WHPAs for the City of Prior Lake wells were delineated using two separate multi-aquifer
groundwater flow models.
The Twin Cities Metropolitan Area Groundwater Model (a.k.a, the Metro Model) developed by /
the Minnesota Pollution Control Agency (e.g., Seaberg, 2000) was used to delineate the WHPA for \ 1L~ '/4
Well 7 in the FIG aquifer. This model uses the analytic element method approach to grOundwater\ ~~ ~ V
modeling as implemented in the software code MLAEM developed by Strack Consulting, Inc. .rS\.'t:::J ~~~ .f"V
(Strack, 1989; Strack, 1998). " ~ ,\:-,?J
The Scott-Dakota County Groundwater Model developed by Barr (1999a; 2001) for the MDH was
used as a starting point for the model used to delineate the WHPAs for Wells 3, 4,5, and 6 (the
Jordan Sandstone aquifer wells). This model uses the finite difference method approach to
groundwater modeling as implemented in the software code MODFLOW developed by the United
States Geological Survey. (McDonald and Harbaugh, 1988; Harbaugh and McDonald, 1996).
\
\ IJ\. I/\.
\\.S'1't S\
e 'CfJ \J
~
Both groundwater models take into account regional flow boundaries and the effect of other hig
capacity wells. High capacity well locations were taken from Barr (1999a) except for the Pro r Lake
municipal wells. The City of Prior Lake provided the coordinates for these wells.
(( ~5{;
::;::bi~:'Od~:~;O:t:: :::::::r flow ill the Jordan Sandstone aquifer was estimated based on 1Jt{~
piezometric maps from the Scott County Geologic Atlas {Kanivetsky and pa~, 1982) to be to the
north and northwest. The ambient direction of groundwater flow in the FIG aquifer was estimated
based on piezometric maps from the Scott County Geologic Atlas (Kanivetsky and Palen, 1982) to
range from approximately north to approximately west. These flow directions are consistent with the
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flow directions determined with the regional groundwater flow models used to delineate the Prior
Lake WHP As.
1.5.3 Quality and Quantity of Water Supplying the Public Water Supply Well
As noted above, four of the five Prior Lake municipal wells addressed by this Plan are open to only
the Jordan Sandstone. Well 7 is open to the FIG aquifer. Thus, the Jordan Sandstone aquifer is the
major source water aquifer for the City of Prior Lake. While the City of Prior Lake pumps a
significant volume of water from the FIG aquifer each year this aquifer is not considered vulnerable
to contamination within the eastern DWSMA (Barr, 2005). Therefore, references to the source water
aquifer or major source water aquifer in this Plan refer to the Jordan Sandstone aquifer.
Static water level measurements in the Prior Lake municipal wells and water level measurements in
nearby MDNR observation wells completed in the Jordan Sandstone indicate that there is no long-
term decline in the potentiometric surface in the Jordan Sandstone aquifer. Since Well 7 was
installed in the FIG aquifer, static water level measurements in the well have indicated no long-term
decline in the potentiometric surface in the FIG aquifer.
There are no known well interference complaints or water use conflicts associated with operation of
the Prior Lake municipal wells.
Available information from the MDNR's SWUDS database indicates that there are no high capacity
wells other than the Prior Lake municipal wells within the DWSMAs and there are only two high
capacity wells within 1 mile of the DWSMAs (Table 8). According to the SWUDS database, these
wells are used for golf course irrigation.
The proximity of the Savage Fen to the City of Prior Lake requires that potential impacts to the Fen
from pumping in the Jordan Sandstone be considered as the municipal water supply system expands
in the future. Potential adverse impacts on the Savage Fen could affect the quantity of water
available to Prior Lake from the Jordan Sandstone aquifer in the future. The City of Prior Lake is
working with the MDNR to determine what, if any, affect future increases in pumping by the Prior
Lake municipal water supply system may have on the Savage Fen.
As discussed above, results of sampling of the Prior Lake municipal wells by the MDH indicate that
the water pumped by the wells meets the applicable primary drinking water quality standards.
However, iron and manganese exceed the secondary (i.e., aesthetic) drinking water quality standards.
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As a result, the City is in the planning process for a water treatment facility that will remove the iron
and manganese from the municipal water supply.
There is no known groundwater contamination in the Jordan Sandstone aquifer or in the FIG aquifer
in the vicinity of the DWSMAs that adversely affects the source water aquifers.
Based on the available information, the only potential groundwater quantity issue for Prior Lake is
the potential affect future increases in pumping from the Prior Lake municipal water supply system
might have on the Savage Fen. There are no known groundwater quality issues that will have any
significant impact on the management of the DWSMAs associated with the Prior Lake municipal
wells. While it is possible that high capacity wells completed in the Jordan Sandstone aquifer in the
vicinity of Prior Lake or within the DWSMAs could affect the quantity of groundwater available,
there are currently no known water use conflicts or well interference complaints related to the
municipal wells or corresponding DWSMAs. Clearly, as Prior Lake installs additional wells in the
future DWSMA boundaries will need to be adjusted. New wells constructed within the 10-year time
frame of this Plan will be incorporated by means of Plan amendments with the help of the Wellhead
Protection Consultant.
1.5.4 land and Groundwater Uses in the DWSMAs
A portion of the DWSMA associated with Prior Lake municipal wells 3, 4,5, and 7 has been
determined to be highly vulnerable to contamination. Land uses within this portion of the DWSMA
could affect source water protection efforts or the management of the DWSMA.
Privately-owned wells, particularly those that are completed in or penetrate the City's source water
aquifers, will be considered when developing the management strategies for all vulnerability zones in
the Prior Lake DWSMAs. Unmaintained, damaged, poorly-constructed, or unused/abandoned wells
could provide a direct route for contaminants to enter the source water aquifers.
Potential contaminant sources within the DWSMAs identified through the PCSI include storage tank
sites, hazardous waste generators, contaminant release sites, ISTS, and properties where businesses
typically associated with Class V wells operate( d). These potential contaminant sources will be
considered when developing the management strategies for the DWSMAs based on aquifer
vulnerability as specified in the April 25, 2006 Scoping Decision Notice No.2 the City received from
the MDH.
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As previously noted, no non-municipal wells that extend into the Jordan Sandstone aquifer or the FIG
aquifer within the DWSMAs have been identified.
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