HomeMy WebLinkAbout2015-12-09 PACKET 05.1.Minnesota Department
�1 of Agriculture
INITIAL TOWNSHIP TESTING OF NITRATE
IN PRIVATE WELLS
WASHINGTON COUNTY 2014 SUMMARY
November 2015
Minnesota Department of Agriculture
Pesticide and Fertilizer Management Division
In accordance with the Americans with Disabilities Act, this information is available in alternative forms of
communication upon request by calling 551-201-6000. TTY users can call the Minnesota Relay Service a 711.
The MDA is an equal opportunity employer and provider.
MDA PRIMARY AUTHORS
Kimberly Kaiser, Nikol Ross
CONTRIBUTORS AND REVIEWERS
MDA Staff: Heather Johnson, Annie Felix-Gerth, Larry Gunderson, gill Van Ryswyk,
Michael MacDonald, Bruce Montgomery and Dan Stoddard.
Washington County Staff: Stephanie Grayzeck Souter
FUNDING
Project dollars provided by the Clean Water Fund (from the Clean Water, Land and
Legacy Amendment).
t7 m
MINNESOTA I1 1: 11
DEPARTMENT OF LAN N 1) K
AGRICULTURE',!
2014 Summary Washington County Township Sampling 12
Acknowledgements ..........................................
Table of Contents .............................................
Executive Summary .........................................
Introduction.......................................................
Background.......................................................
Methods.............................................................
Results...............................................................
Summary...........................................................
FutureWork ......................................................
References........................................................
Appendix A: Private Well Survey Questions
Appendix B: Private Well Survey Answers..
Figure 1. Statewide Geomorphology Layer, Sediment Association, Washington County ............................9
Figure 2. Bedrock Geology of Washington County.....................................................................................10
Figure 3. Water Table Aquifer Vulnerability for Washington County..........................................................11
Figure 4. Washington County Pollution Sensitivity Rating of the Water Table Aquifers .............................13
Figure 5. Townships with Vulnerable Groundwater and Row Crop Production..........................................16
Figure 6. Washington County Private Well Township Sampling Results 2014 ..........................................19
2014 Summary Washington County Township Sampling 13
LIST OF ■:
Farming on Property ...............................
Table 1. Vulnerability Ratings Based on the Geomorphology of Minnesota, Sediment Association Layer12
Distance to an Active or Inactive Feedlot
Table 2. Aquifer Type Distribution of Wells in the County Well Index........................................................15
Distance to Septic System ......................
Table 3. Township Households, Sample Kit Distribution and Return Rate................................................17
Distance to Agricultural Field ..................
Table 4. Washington County Township Sampling Summary Statistics, Does Not Include Known Hand
Drinking Water Well ................................
DugWells....................................................................................................................................................20
Treatment System Present .....................
Table 5. Township Nitrate Results Summary Related to Vulnerable Groundwater and Row Crop
Last Tested for Nitrate ............................
Production...................................................................................................................................................21
Last Nitrate Test Result ..........................
Table 6. Nitrate Concentration within Sampled Groundwater Aquifers......................................................23
Table 7. Property Setting for Well Location................................................................................................28
Table8. Well Construction Type.................................................................................................................28
Table 9. Age of Well ................................
Table 10. Depth of Well ...........................
Table 11. Unique Well ID Known ............
Table 12. Livestock Located on Property
Table 13. Fertilizer Stored on Property...
Table 14.
Farming on Property ...............................
Table 15.
Distance to an Active or Inactive Feedlot
Table 16.
Distance to Septic System ......................
Table 17.
Distance to Agricultural Field ..................
Table 18.
Drinking Water Well ................................
Table 19.
Treatment System Present .....................
Table 20.
Last Tested for Nitrate ............................
Table 21.
Last Nitrate Test Result ..........................
28
29
29
29
30
30
30
31
31
31
32
32
32
2014 Summary Washington County Township Sampling 14
In 2014, one township and one city in Washington County, Minnesota, were selected for
private well nitrate sampling in support of the Nitrogen Fertilizer Management Plan. This
selection was based on historically elevated nitrate conditions, aquifer vulnerability and
row crop production. Samples were collected from private wells using homeowner
collection and mail -in methods. Well log information was obtained when available and
correlated with nitrate results.
Information collected indicated approximately 96 percent of wells in Cottage Grove and
Denmark Township were finished in the Paleozoic sedimentary deposits. Samples were
collected from 526 wells in these two communities representing a 39 percent response
rate from homeowners.
Results showed that across the two communities, 22 percent of private wells sampled
were above the health standard of 10 mg/L for nitrate as nitrogen (nitrate -N). In Cottage
Grove, 28 percent were above 10 mg/L, and in Denmark 14 percent of the private wells
tested were above the 10 mg/L standard for nitrate -N. The maximum nitrate values
ranged from 20.9 to 34.1 mg/L. The 90th percentiles ranged from 11.8 to 15.8 mg/L and
the mean nitrate values found were 3.8 to 6.0 mg/L for Denmark Township and Cottage
Grove, respectively.
This initial testing was followed by a second sampling offered to homeowners with wells
that had a detectable nitrate result. This work will be discussed further in a follow-up
report in 2016.
INTRODUCTION
The Minnesota Department of Agriculture (MDA) has recently updated the 1990
Nitrogen Fertilizer Management Plan (NFMP), which is the state's blueprint for
prevention or minimization of the impacts of nitrogen fertilizer on groundwater. One of
the goals of the NFMP is to minimize or mitigate the source of pollution from nitrogen
fertilizer. Updating the NFMP provided an opportunity to restructure the County's and
the State's strategies for reducing nitrate contamination of water resources, with more
specific, localized accountability for nitrate contamination associated with row crop
agricultural production.
To effectively manage nitrate contamination of water resources, it is appropriate to
focus on areas of greatest risk. Testing private wells for nitrate is one method for
identifying areas and wells at greatest risk. For this, the MDA has developed the
"Township Testing Program". In the Township Testing Program (TTP) the MDA works
2014 Summary Washington County Township Sampling 15
with local partners (counties and Soil and Water Conservation Districts) to collect and
analyze water samples from private drinking water wells within townships that either had
high nitrate results or exist in an area with high aquifer vulnerability and a high
percentage of row crop production.
This testing conducted in Washington County will be used to guide future work as the
MDA plans to offer nitrate tests to approximately 70,000 private well owners (within 250-
350 townships) between 2014 and 2019. As of spring 2015, 60 townships in
eight counties have been completed.
For further information on this program, please visit the project webpage at:
http: //www . m d a. state. m n. us/protecting/cl eanwaterfu n d/gwdwp rotecti on/town sh i ptesti ng . aspx
ir_KrRniiNn
In many rural areas of the state, nitrate is one of the most common contaminants in
Minnesota's groundwater. In some areas of the state, a significant number of wells have
high nitrate levels.
Nitrate is a naturally occurring, water soluble molecule that is made up of nitrogen and
oxygen. Although nitrate occurs naturally, it typically originates from man-made sources
such as fertilizer, animal manure, and human waste. Nitrate is a concern because it can
have a negative effect on human health at elevated levels. The U.S. Environmental
Protection Agency (USEPA) has established a drinking water Maximum Contaminant
Level (MCL} of 10 mg/L for nitrate as nitrogen (nitrate -N) (U.S. EPA, 2009) in municipal
water systems. Minnesota Department of Health (MDH) has also established a Health
Risk Limit (H RL) of 10 mg/L for private drinking water wells in Minnesota.
Nitrogen present in groundwater can be found in several forms including nitrite and
nitrate. Nitrite concentration is commonly less than the reporting level of 0.01 mg/L,
resulting in negligible contribution to the nitrate plus nitrite concentration (Nolan and
Stoner, 2000). In the environment, nitrite rapidly converts to nitrate, which means nitrite
occurs very rarely in groundwater. Measurements of nitrate plus nitrite as nitrogen and
measurements of nitrate as nitrogen will hereafter be referred to as "nitrate".
NITRATE FATE AND TRANSPORT
Nitrate is considered a conservative anion and is highly mobile in many shallow coarse-
textured groundwater systems. Once in groundwater, nitrate is often very stable and
can move large distances from its source. However in some settings, nitrate in
groundwater may be converted to nitrogen gas in the absence of oxygen and the
presence of organic carbon, through a natural process called denitrification.
Denitrification occurs when oxygen levels are depleted and nitrate becomes the primary
2014 Summary Washington County Township Sampling 16
oxygen source for microorganisms. Shallow groundwater in coarse-textured soils
(glacial outwash) generally has low concentrations of organic carbon and is well
oxygenated, so denitrification is often limited in these conditions. Areas with glacial
outwash and intensive row crop agriculture are particularly vulnerable to elevated nitrate
concentrations. However, geochemical conditions can be highly variable within an
aquifer or region and can also change over time (MPCA, 1998).
2014 Summary Washington County Township Sampling 17
GEOLOGY AND HYDROGEOLOGY
The surficial geology in Washington County is dominated by Quaternary glacial deposits
such as outwash, till, drift and terrace deposits (Figure 1). Glacial outwash is relatively
coarse-textured compared to other glacial deposits such as till and drift deposits.
Outwash material in Southern Washington County consists primarily of sand, loamy
sand and gravel that was deposited by melt water that flowed from the Superior Lobe
deposit in Cottage Grove and the Keewatin deposit in Denmark Township (Swanson
and Meyer, 1990). The terrace deposits are also comprised of sand and gravel. Coarse-
textured deposits often allow contaminants from the surface to travel rapidly to the water
table aquifers. Statewide geomorphological mapping conducted by the Department of
Natural Resources, Minnesota Geological Survey (MGS) and the University of
Minnesota at Duluth (MDNR, MGS, and UMD, 1997) indicates the extent of glacial
deposits in Washington County as presented in Figure 1.
The bedrock geology consists of early Paleozoic sedimentary deposits (Figure 2). The
St. Peter Sandstone is the uppermost deposit and is present in the northern part of the
two communities. Beneath the St. Peter lies the Prairie du Chien Group which is
comprised of dolostone. The Prairie du Chien outcrops in bluffs along the St. Croix and
Mississippi Valley. The Jordan Sandstone underlies the Prairie du Chien and consists of
medium to coarse grained sands in the upper portion and finer grains toward the bottom
(Swanson and Meyer, 1990).
Water table aquifers and buried Quaternary aquifers occur in locations throughout the
county where quaternary deposits of sand and gravel occur. These aquifers are not
spread uniformly over the county and have varying thickness.
The main source of groundwater in Washington County is the Prairie Du Chien -Jordon
Aquifer. The Prairie du Chien -Jordon Aquifer is composed of the Prairie du Chien Group
and Jordon Sandstone. These two bedrock aquifers have distinctly different
compositions. In many areas they function as a singular aquifer because there is no
confining unit between them. This aquifer complex underlies most of Washington
County and is the most commonly utilized aquifer in the county. The aquifer is not used
much in the northwest corner and along the eastern edge of the county because of low
yields, but in the southwest this aquifer is more permeable and can yield more water
(Swanson and Meyer, 1990).
The statewide geomorphological mapping also classified the state into aquifer sensitivity
ratings. There are three ratings for aquifer sensitivity: low, medium, and high (Figure 3).
The ratings are based upon guidance from the Geologic Sensitivity Project Workgroup's
report, "Criteria and Guidelines for Assessing Geologic Sensitivity in Ground Water
Resources in Minnesota" (MDNR, 1991). Sensitivity ratings are described in Table 1.
2014 Summary Washington County Township Sampling 18
Washington County
Geomorphology -Sediment Association
jrrf
y� Forest rake Scandia
F
- r 7'
Marine on Saint Croix
tl�
$__H go May
Stillwater
Grant. r
Mahtomedi '
f �
f
ti
1
Baytown—,;
Lake Elmo West
Oakdale Lakeland
j Woodbury Afton {
Newport 4+
11,E Cottage Grove
1 �
z
Denmark
Sediment Association
Alluvium
Ice Contact
Lacustrine
Outwa sh
- Peat
Supraglacial Drift Complex
Terrace
Till Plain
Undifferentiated
N
Miles wF
a 2 4 8
5
MINNESOTA DEPARTMENT
OF AGRICULTURE
Figure 1. Statewide Geomorphology Layer, Sediment Association, Washington County.
2014 Summary Washington County Township Sampling 19
Bedrock Geology of Washington County
(Adapted from Mossler.
John H- 2013)
Forest Lake n fa
rrjir<s
Manneon Saint Croix
Hua ay�,�
1
Stil lwate"
Grant --
Bedrock
Decorah Shale
Stlffwatef
Platteville Formation and Glenwood Formation
C}aK rfs Heights
St. Peter Sandstone
Q8yt04Yn
Prairie du Chien Group
Jordan Sandstone
La a FJmo
Oakdale
St Lawrence Formation
.We Lakeland •-.
Tunnel City Group
Wonewoc Sandstone
Eau Claire Formation
Mt. Simon Sandstone
Woodbury on�,
.-,}.
,>
� e14
a E
Miles
` .rr
0 2 4 a
• tta Grove Denma
Minnesota l Department
Aynculture
Figure 2. Bedrock Geology of Washington County.
2014 Summary Washington County Township Sampling 1 10
Figure 3. Water Table Aquifer Vulnerability for Washington County.
2014 Summary Washington County Township Sampling 1 11
Water Table Aquifer
Vulnerability
Rating for Washington County
Based on Reclassification of the Sed iment Association Layer (DNR, MGS,UMID, 1997)
Forest I ake4
S radia
Mar ne on'Saint Croix
Ilk
f�Hugo
i
Stillwater" Ff
Grant
Mahtomedi
Aquifer Vulnerability Rating
High
Medium
Low
BatownWater Features
00
Elmo West
OakLake
dale
Lakeland
Woodbury
Alton Miles W N b
Newport*
° a s
I
t
i
Cottage Grove
J
,Den mark
MINNESOTA DEPARTMENT
of AGRICULTURE
Figure 3. Water Table Aquifer Vulnerability for Washington County.
2014 Summary Washington County Township Sampling 1 11
Table 1. Vulnerability Ratings Based on the Geomorphology of Minnesota, Sediment Association
Layer.
Sediment Association
SensitivityNulnerability Rating
Alluvium, Outwash, Ice Contact, Terrace, Bedrock:
Igneous, Metamorphic, and Sedimentary
High
Su ra lacial Drift Complex, Peat, Lacustrine
Medium
Till Plain
Low
GEOLOGIC ATLAS
The County Geologic Atlas examines a county's geology and groundwater aquifers. The
atlas describes bedrock and surficial geology, hydrogeology of the aquifer and the
connection of land surface to groundwater (MGS, 2015). This information is an
important resource for groundwater management. It can aid in activities such as
monitoring, appropriation, permitting, remediation, and well construction.
A complete geologic atlas typically consists of two parts:
• Part A (prepared by MG S), which includes the water well database and
1:100,000 scale geologic maps. These maps focus on the geology of the county,
and
• Part B (developed by the Minnesota MDNR Division of Ecological and Water
Resources) contains maps on hydrogeology; including aquifer sensitivity to
pollution, groundwater chemistry and aquifer delineations.
The geologic atlas for Washington County was completed in 1990 and was not divided
into these two parts. However, this atlas still contains much of the data that can typically
be found in Parts A and B. An important analysis provided in the Atlas is called the
Sensitivity of Ground -Water Systems to Pollution. This map has a rating system based
on the estimated time for water to travel from the land surface to the water table system
(Figure 4). The water table aquifer vulnerability map (Figure 3) is somewhat similar to
the pollution sensitivity map when comparing at a one-dimensional level. The MDNR
pollution sensitivity map has a higher level of detail and rates all of Denmark Township
at some level of "high" sensitivity, while the water table vulnerability map, rates some of
the same area as "Iowa'. Since the MDNR pollution sensitivity map is mapped at a higher
resolution it is likely a better representation of sensitivity/vulnerability to groundwater.
2014 Summary Washington County Township Sampling 112
Washington County Geologic Atlas:
Nater Table Sensitivity to Pollution
Information Adapted from C-05 Geologic Atlas of Washington County, Minnesota (Meyer, 1990)
Water Table Sensitivity to Pollution
- Very High
- High
High -Moderate
Moderate
Low
Water features
N
Miles wF
0 2 4 8
5
MINNESOTA DEPARTMENT
OF AGRICULTURE
Figure 4. Washington County Pollution Sensitivity Rating of the Water Table Aquifers.
2014 Summary Washington County Township Sampling 1 13
COUNTY WELL INDEX
The County Well Index (CWI) is a database system developed by the MCS and the
MDH for the storage, retrieval, and editing of water well information. The database
contains basic information (e.g. location, depth, static water level) for wells drilled in
Minnesota. The database also contains information on the geology and the well
construction for many private drinking water wells. The CWI is instrumental in the
development of the County Geologic Atlas described in the previous section. The CWI is
the most comprehensive Minnesota well database available, but contains only
information for wells in which a well log is available. It is important to note that most
records in the CWI are for wells drilled after 1974, when water well construction code
required well drillers to submit records to the MDH. The CWI does contain data for some
records obtained by the MGS for wells drilled before 1974 (MGS, 2015).
The CWI was used to gather information about the two communities, Cottage Grove
and Denmark Township, in Washington County included in this Pilot Study.
Table 2 summarizes the general aquifer types, while the following section is a brief
summary of the major aquifer types with the average well depth. According to the
information from the CWI (MDH, 2015):
In the two communities, there are 917 documented wells
• Approximately one percent of wells are completed in the shallow Quaternary
Water Table Aquifer (QW -FA) and are 119 feet deep on average.
o QW -FA wells are defined as having less than ten feet of confining material
(clay) between the land surface and the well screen (MPCA, 1998). When
there is less than ten feet of clay, it allows surface contaminants to travel
more quickly to the water table aquifers. In general, shallower wells
completed in the OWTA may be more susceptible to nitrate contamination.
• One percent of the wells are completed in a Quaternary buried aquifer and are
163 feet deep on average.
o Buried aquifer wells have more than ten feet of confining material (typically
clay) between the land surface and the well screen.
2014 Summary Washington County Township Sampling 114
• In both communities, the Paleozoic aquifers (over 90 percent) are utilized the
most frequently. These bedrock wells average 248 feet deep.
o In Washington County the majority of the used Paleozoic aquifers are part
of the Prairie du Chien Group or the Jordan Sandstone complex. These
aquifers are confined by the shaley base of the St. Peter Sandstone
(Swanson and Meyer, 1990), which provides protection from pollution to
these aquifers.
Table 2. Aquifer Type Distribution of Wells in the County Well Index.
* Represents a total
NITRATE PROBABILITY MAPPING
In many areas, nitrate probability maps have been developed by the MDH to assist in
local water quality planning efforts. These maps identify areas of a county with relatively
high, moderate, and low probability of having elevated nitrate concentrations in
groundwater. The goal of nitrate probability mapping is to help protect public and private
drinking water supplies, to help prevent further contamination by raising awareness and
to assist in local planning and prevention. The nitrate probability map is similar in
appearance compared to the updated aquifer vulnerability map; however it shows less
area categorized in the high rating. Washington County's report was published in 2002
and can be accessed here:
http:llwww . h ealth . state. m n. usld ivslehlwaterlswpinitratelrep orts12011 m eth odlwashi n Mon. P df
2014 Summary Washington County Township Sampling 115
Aquifer Type
Community
Wells
Quaternary
Water Table
Buried
Paleozoic
Undesignated
Other
Cottage
501
2%
1%
94%
2%
<1%
Grove
Denmark
416
<1%
<1%
97%
2%
<1%
Township
Average
917*
1 %
1 %
96%
2%
<1%
* Represents a total
NITRATE PROBABILITY MAPPING
In many areas, nitrate probability maps have been developed by the MDH to assist in
local water quality planning efforts. These maps identify areas of a county with relatively
high, moderate, and low probability of having elevated nitrate concentrations in
groundwater. The goal of nitrate probability mapping is to help protect public and private
drinking water supplies, to help prevent further contamination by raising awareness and
to assist in local planning and prevention. The nitrate probability map is similar in
appearance compared to the updated aquifer vulnerability map; however it shows less
area categorized in the high rating. Washington County's report was published in 2002
and can be accessed here:
http:llwww . h ealth . state. m n. usld ivslehlwaterlswpinitratelrep orts12011 m eth odlwashi n Mon. P df
2014 Summary Washington County Township Sampling 115
TOWNSHIP TESTING
The MDA has recently updated the 1990 NFMP which is the state's blueprint for
prevention or minimization of the impacts of nitrogen fertilizer on groundwater. Updating
of the NFMP provides an opportunity to restructure county and the state strategies for
reducing nitrate contamination of groundwater, with more specific, localized
accountability for nitrate contamination from agriculture. In order to effectively reduce
nitrate contamination of groundwater resources, it is necessary to identify areas of
concern. Areas of concern tend to be fairly localized, so township and city boundaries
were selected for nitrate testing. Factors such as aquifer vulnerability, row crop
production, and previous nitrate results are being used to prioritize townships for
sampling. Townships with at least 30 percent of the area characterized with vulnerable
groundwater and at least 20 percent of the area in row crop production are shown in
Figure 5. This map serves as a starting point for planning sample locations and is
modified based on local expertise.
Townships with Vulnerable Groundwater and Row Crap Production
Lac Qui
Legerld
®� 20%Vul n arable Crounc6vater
30°% Vulnerable GW & 20% Rnw Crops
"% of Township in Row Craps
M-20%
21%-30%
3196-40%
41%-50%
-51%-9295. ,
Me-
a 125 n 50 '!5 105
Figure 5. Townships with Vulnerable Groundwater and Row Crop Production.
2014 Summary Washington County Township Sampling 116
The City of Cottage Grove and Denmark Township, two communities from Washington
County, were chosen for sampling based on the following criteria: local expertise from
Washington County and Washington Conservation District, past high nitrate results,
vulnerable groundwater, and row crop production.
The goal of this program is to characterize current nitrate conditions at the highest
density level possible. Most households with private wells received an invitation letter
from the local partner to participate in the free nitrate testing supported by MDA.
Homeowners with private wells were sent a water sample kit (by a certified lab) which
included a survey about their well, sample bottle, sample instructions, and a pre -paid
return mailer. All costs of the kit are paid by the MDA using Clean Water Funds.
Homeowners were asked to complete the well survey, fill the sample bottle, and mail
the sample to the certified lab in the prepaid mailer. Once the sample was analyzed, the
lab sent homeowners their results in the mail. Table 3 presents the responses received
from the homeowners.
Table 3. Township Households, Sample IGt Distribution and Return Rate.
* Estimate provided by Washington County.
2014 Summary Washington County Township Sampling 1 17
Estimated
Approximate
Water Samples
Community
Number of
Number of Test
returned to Lab
Return
Households on
Kits Sent
(not including QA or
Rate
Private Wells*
extra kit requests)
Cottage Grove
800
780
300
38%
Denmark Township
625
567
226
43%
Total
1425
1347
526
39%
* Estimate provided by Washington County.
2014 Summary Washington County Township Sampling 1 17
Homeowners returned 526 water samples for analysis across the two communities
(Figure 6). On average, 39 percent of households responded to the free nitrate test
offered by the MDA (Table 3). The results of the township nitrate sampling are displayed
in Figure 6.
The summary statistics for all well construction types except known hand dug wells are
shown in Table 4. Hand dug wells are often very shallow, typically just intercepting the
water table, and therefore are much more sensitive to local surface runoff contamination
(feedlot runoff), point source pollution (septic system effluent), or chemical spills. The
following paragraphs provide a brief discussion of the statistics presented in Table 4,
which does not include hand dug wells.
The minimum values of nitrate -N for each community were less than the detection limit,
which is 0.03 mg/L. The maximum values ranged from 20.9 to 34.1 mg/L, with Cottage
Grove having the highest result. The 90th percentiles range from 11.8 to 15.8 mg/L, with
Cottage Grove having the higher 90th percentile. The mean nitrate -N values found were
3.8 to 6.0 mg/L for De n ma rk T own s h i p and Cottage Grove, respectively. Results from
the sampling revealed that in Denmark Township and Cottage Grove 10 percent or
more of the wells were over 10 mg/L nitrate -N. These results contrast findings from a
2010 USG report on nitrate concentrations in private wells in the glacial aquifer
systems across the upper United States in which less than five percent of sampled
private wells had nitrate concentrations greater than 10 mg/L (Warner and Arnold,
2010).
The data collected in the TTP are similar to the historical results from the Washington
County well water program. This program has a database that contains historical
sampling results from over 14,000 well samples collected by Washington County from
1978 to 2013. These results show the mean nitrate -N level in Washington County is
2.05 mg/L. The historical database results also show that the southern communities had
higher groundwater nitrates than other parts of Washington County (PHE, 2014).
Table 5 shows township results compared with percent of the area in row crop
production and in vulnerable geology.
2014 Summary Washington County Township Sampling 1 18
Washington County Township Testing Results 2014
Forest Lake I Scandia
r -7,i
Marine on Saint Croix
I
Muga May
Stillwater
I` -1 Grant
Mahtomedi
P g
f w..
Baytown
Lake Elmo,. West
ale, I Lakeland
Newport
Private Well Results Nitrate -N mgfL
0=3
n 310
?10
Water Features
Vulnerable Township
N
Miles wF
a 2 4 8
5
MINNESOTA DEPARTMENT
OF AGRICULTURE
Figure 6. Washington County Private Well Township Sampling Results 2014.
2014 Summary Washington County Township Sampling 1 19
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Table 5. Township Nitrate Results Summary Related to Vulnerable Groundwater and Row Crop
Production.
* Represents an average
WELL SETTING AND CONSTRUCTION
WELL OWNER SURVEY
The well owner survey, sent out with the sampling kit, requested additional information
about private wells that were to be sampled. The survey included questions about the
well construction, depth and age, and nearby land use. A blank survey can be found in
Appendix A. It is important to note that well information was provided by the well owners
and may be approximate or potentially erroneous. The following section is a summary of
information gathered from the well owner survey (complete well survey results are
located in Appendix B at the end of this document, Tables 7-21).
The majority of wells in each township were identified by the homeowner as "rural'
property. Approximately 82 percent of sampled wells are drilled construction and two
percent are sand point wells. There were no hand dug wells sampled.
Sand point (drive -point) wells are typically completed at shallower depths than drilled
wells. Sand point wells are also usually installed in areas where sand is the dominant
geologic material and where there are no thick confining units such as clay. This makes
sand point wells more vulnerable to contamination from the surface.
Most of the sampled wells are greater than 100 feet deep, with the majority between
100 and 299 feet below ground surface.
2014 Summary Washington County Township Sampling 121
Total
Percent of Land
Percent of Land
Percent of Wells
90th
Community
in Row Crop
in Vulnerable
Nitrate -N
Percentile
Wells
Production
Geology
? 10 mg/L
mg/L
Cottage
Grove
300
27%
36%
29%
15.8
Denmark
Township
226
47%
23%
13%
11.8
Total
526
37%-
30%-
21 %*
14.2
* Represents an average
WELL SETTING AND CONSTRUCTION
WELL OWNER SURVEY
The well owner survey, sent out with the sampling kit, requested additional information
about private wells that were to be sampled. The survey included questions about the
well construction, depth and age, and nearby land use. A blank survey can be found in
Appendix A. It is important to note that well information was provided by the well owners
and may be approximate or potentially erroneous. The following section is a summary of
information gathered from the well owner survey (complete well survey results are
located in Appendix B at the end of this document, Tables 7-21).
The majority of wells in each township were identified by the homeowner as "rural'
property. Approximately 82 percent of sampled wells are drilled construction and two
percent are sand point wells. There were no hand dug wells sampled.
Sand point (drive -point) wells are typically completed at shallower depths than drilled
wells. Sand point wells are also usually installed in areas where sand is the dominant
geologic material and where there are no thick confining units such as clay. This makes
sand point wells more vulnerable to contamination from the surface.
Most of the sampled wells are greater than 100 feet deep, with the majority between
100 and 299 feet below ground surface.
2014 Summary Washington County Township Sampling 121
POTENTIAL NITRATE SOURCE DISTANCES
The following response summary relates to isolation distances of potential point sources
of nitrate that may contaminate wells. This information was obtained from the well
surveys completed by the homeowner.
• On average, farming takes place on twelve percent of the properties.
• Agricultural fields are greater than 300 feet from wells at 64 percent of the
properties.
• Only two percent of the well owners across the communities responded that they
have livestock (greater than ten head of cattle or other equivalent) on their
property.
• Most wells (75 percent) are more than 300 feet from an active or inactive feedlot.
• Very few well owners (less than one percent) store more than 500 pounds of
fertilizer on their property.
• A small minority of wells (six percent) are less than 50 feet away from septic
systems.
2014 Summary Washington County Township Sampling 1 22
WELL LOGS
In some cases, well owners were able to provide Unique Well Identification Numbers
(Unique ID) for their wells. When the correct Unique IDs are provided, a well log can be
used to obtain well construction information and to identify the aquifer that the well
withdraws water from. In this study, 85 wells were identified in the CWI and the well logs
were obtained (Table 6). This represents 16% of the sampled wells in this township
testing.
According to the well logs, the most commonly utilized aquifers were from the Paleozoic
aquifers. This reflects the overall findings for all documented wells in the focus area
(Table 2). Only one of the documented wells was in the Quaternary water table aquifer.
Table 6. Nitrate Concentration within Sampled Groundwater Aquifers.
Aquifer
Total
Wells
Ave
Depth**
Number
Percent
<3 3<10 ?10
<3 3<10 ?10
(Feet)
Nitrate -N mg/L
Quaternary
Water Table
1
157
1
0
0
100%
0%
0%
Paleozoic
84
258
66
13
5
79%
15%
6%
Total
85
257*
67
13
5
79%*
15%*
6%*
* Represents a weighted average value.
** The depths were obtained from well logs in the CWI database.
2014 Summary Washington County Township Sampling 123
The City of Cottage Grove and Denmark Township were chosen for sampling based on
the following criteria: local expertise from Washington County and Washington
Conservation District, past high nitrate results, vulnerable groundwater, and row crop
production.
Samples were collected from private wells using homeowner collection and mail -in
methods. Samples were collected from 526 wells in these two communities
representing a 39 percent response rate from homeowners.
According to the well logs and CWI, the most commonly utilized aquifers were from the
Paleozoic aquifers. Specifically, the Prairie Du Chien -Jordon Aquifer is the main source
of groundwater.
Results showed that across the two communities, 22 percent of private wells sampled
were above the health standard of 10 mg/L for nitrate as nitrogen (nitrate -N). In Cottage
Grove, 28 percent were above 10 mg/L, and in Denmark 14 percent of the private wells
tested were above the 10 mg/L standard for nitrate - N.
■i:
Well owners with detectable nitrate results from this township testing were offered a free
pesticide sample and a follow-up nitrate sample taken by MDA staff. At the time of this
resampling, a well site visit is performed (when possible) in order to rule out well
construction issues and likely point sources of nitrate. In preparation for the well site
visits, every effort is made to obtain well log information so that nitrate results and the
aquifer designation can be compared in a more comprehensive fashion. Washington
Conservation District offers to meet with homeowners to discuss potential well
construction issues and possible nitrogen point sources on the homeowner property.
This work will be discussed further in a follow-up report in 2016.
The testing conducted in Washington County will be used to guide future work as the
MDA plans to offer nitrate tests to approximately 70,000 private well owners (within 250-
350 townships) between 2014 and 2019. As of spring 2015, 60 townships in
eight counties have been completed.
2014 Summary Washington County Township Sampling 124
Minnesota Department of Health. (2002). Washington County Nitrate -Nitrogen
Probability. On-line PDF Retrieved March 25, 2015, from
http:llwww. health. state. mn. u sld ivslehlwaterlswpin itratelreports12011 method/wash
ington.pdf
Minnesota Department of Health. (n. d.) County Well Index website. Retrieved March 11,
2015, from http://vvww.health.state.mn.us/divs/eh/cwi/
Minnesota Department of Natural Resources. (1991). Geologic Sensitivity Project
Workgroup. Criteria and guidelines for assessing geologic sensitivity of ground
water resources in Minnesota, Minnesota Department of Natural Resources,
Division of Waters, St. Paul, Minn., p. 122.
Minnesota Pollution Control Agency. (1998). Baseline Water Quality of Minnesota's
Principal Aquifers, Region 2, North Central Minnesota.
Minnesota Geological Survey, MDNR and University of Minnesota —Duluth. (1997).
Geomorphology of Minnesota, geomorphology data describing a wide variety of
conditions related to surficial geology within a hierarchical classification scheme
that was devised for use within Minnesota, Scale 1:100,000.
Minnesota Geologic Survey. (n.d.) Minnesota Geological Survey County Geological
Atlas Program. Retrieved March 17, 2015, from
http://vvww.mnqs.umn.edu/county atlastcou ntyatlas. htm
Mossler, John H. (2013). M-194 Bedrock Geology of the Twin Cities Ten -County
Metropolitan Area, Minnesota. Retrieved from the University of Minnesota Digital
Conservancy: http://purl.umn.edu/154925
Nolan, BT., and Stoner, J.D. (2000). Nutrients in Groundwaters of the Conterminous
United States, 1992-95: Environmental Science and Technology, 34(7),
1156-1165.
Swanson, L., and Meyer, G. N. (1990). C-05 Geologic atlas of Washington County,
Minnesota. Minnesota Geological Survey. Retrieved from the University of
Minnesota Digital Conservancy: http://Purl.umn.edu/58492
U.S. Environmental Protection Agency. (2009). National Primary Drinking Water
Regulations list, On-line PDF Retrieved February 2, 2015, from
http://water.epa.gov/drink/contaminantstupload/mcl-2.pdf
Warner, K. L., and Arnold, T. L. (2010). Relations that Affect the Probability and
Prediction of Nitrate Concentration in Private Wells in the Glacial Aquifer System
in the United States, A USGS National Water -Quality Assessment Program
Scientific I nvestigations Report 2010.
2014 Summary Washington County Township Sampling 1 25
Washington County Department of Public Health & Environment [PHE]. (2014). The
Washington County Groundwater Plan 2014-2024. On-line PDF Retrieved March
27, 2015, from http://www.co.washington.mn.us/DocumentCenter/View/794
2014 Summary Washington County Township Sampling 1 26
Private Well Survey Questions
1. What setting did the water sample come from? Please choose only one.
Answers choices: Sub -division, Lake Home, River Home, Country, Municipal/city, or
Other.
2. Are there livestock on this properly? Yes or No
3. Do you mix or store fertilizer (500Ibs or more) on this property? Yes or No
4. Does farming take place on this property? Yes or No
Well Information Section
5. Does your well have a Unique Well ID number? Yes or No
6. If yes, what is the Unique ID?
(6 digit number found on a metal tag attached to your well casing)
7. Type of well construction?
Answer choices: Drilled, Sand point, Hand dug, Other, Other, and don't know.
8. Approximate age (years) of your well?
Answer choices: 0-10 years, 11-20 years, 21-40 years, and over 40 years old.
9. Approximate depth of your well
Answer choices: 0-50 feet, 51-99 feet, 100-299 feet, and 300 or more feet.
10. Distance to an active or inactive feedlot
Answer choices: 0-50 feet, 51-99 feet, 100-299 feet, and 300 or more feet.
1 1 . Distance to a septic system
Answer choices: 0-50 feet, 51-99 feet, 100-299 feet, and 300 or more feet.
12. Distance to an agricultural field
Answer choices: 0-50 feet, 51-99 feet, 100-299 feet, and 300 or more feet.
13. Is this well currently used for human consumption? Yes or no
14. Please check any water treatment you have other than a water softener.
Answer choices: None, Reverse osmosis, distillation, filtering system and other.
15. When did you last have your well tested for nitrates?
Answer choices: Never, with the last year, within the last 3 years, the last 10, or 10 or
more.
16. What was the result of your last nitrate test?
Answer choices: 0<3, 3< 10, 10 or greater, or don't know.
2014 Summary Washington County Township Sampling 1 27
APPENDIX B: PRIVATE WELL SURVEY ANSWERS
A
Table 7. Property Setting for Well Location
Properly Setting
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Setting
Percent
Country
48.0%
74.9%
59.1%
Lake
0.0%
0.9%
0.4%
River
11.3%
7.5%
9.7%
Sub -division
27.3%
9.7%
19.8%
Other
6.3%
3.1%
4.9%
Not Available
7.0%
4.9%
6.1%
Table 8. Well Construction Type
Well Construction Type
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Well Type
Percent
Drilled
79.0%
85.4%
81.7%
Sand Point
2.0%
11.3%
1.7%
Other
1.0%
0.0%
0.6%
Not Available
18.0%
13.3%
16.0%
Table 9. Age of Well
Well Age
Community Cottage Grove
Denmark Township
Total
Total Wells 300
226
526
Age Percent
a 10 years 4.7%
12.8%
8.2%
11-20 years 18.0%
23.9%
20.5%
21-40 years 51.0%
37.2%
45.1%
Over 40 years 21.3%
19.5%
20.5%
Not available 5.0%
6.6%
5.7%
2014 Summary Washington County Township Sampling 1 28
Table 10. Depth of Well
Well Depth
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Depth
Percent
0-50 feet
1.0%
0.9%
1.0%
51-99 feet
5.7%
4.4%
5.1%
100-299 feet
56.7%
47.3%
52.7%
Over 300 feet
19.0%
28.3%
23.0%
Not available
17.7%
19.0%
18.3%
Table 11. Unique Well ID Known
Does the Well Have a Unique I D
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Unique ID
Percent
No
22.0%
20.4%
21.3%
Yes
15.7%
18.8%
18.8%
Not Available
63.3%
55.4%
59.9%
Table 12. Livestock Located on Property
Livestock on Properly
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Livestock
Percent
No
93.0%
92.9%
93.0%
Yes
1.7%
2.7%
2.1%
Not Available
5.3%
4.4%
4.9%
2014 Summary Washington County Township Sampling 1 29
Table 13. Fertilizer Stored on Property
Fertilizer Stored on the Property
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Fertilizer
Percent
No
95.0%
94.7%
94.9%
Yes
0.0%
0.9%
0.4%
Not Available
5.0%
4.4%
4.8%
Table 14. Farming on Property
Does Farming Take Place on the Property
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Farming
Percent
No
91.3%
72.6%
83.3%
Yes
3.7%
23.0%
12.0%
Not Available
5.0%
4.4%
4.8%
Table 15. Distance to an Active or Inactive Feedlot
Distance to Feedlot
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Feedlot
Percent
0-50 feet
3.0%
7.1%
4.8%
51-99 feet
2.3%
2.2%
2.3%
100-299 feet
1.7%
5.8%
3.4%
Over 300 feet
78.0%
69.9%
74.5%
Not available
15.0%
15.0%
15.0%
2014 Summary Washington County Township Sampling 1 30
Table 16. Distance to Septic System
Distance to Septic System
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Septic
Percent
0-50 feet
7.3%
4.0%
5.9%
51-99 feet
35.0%
23.5%
30.0%
100-299 feet
44.3%
54.9%
48.9%
Over 300 feet
7.7%
9.3%
8.4%
Not available
5.7%
8.4%
6.8%
Table 17. Distance to Agricultural Field
Distance to Agriculture Field
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Distance to Field
Percent
0-50 feet
1.3%
6.2%
3.4%
51-99 feet
4.7%
6.6%
5.5%
100-299 feet
16.3%
25.7%
20.3%
Over 300 feet
72.0%
53.5%
64.1%
Not available
5.7%
8.0%
6.7%
Table 18. Drinking Water Well
Is the Well Used for Drinking Water
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Drinking Water
Percent
No
0.7%
4.9%
0.6%
Yes
94.0%
94.7%
94.3%
Not Available
5.3%
4.9%
5.1%
2014 Summary Washington County Township Sampling 1 31
Table 19. Treatment System Present
Treatment System Used for Drinking Water
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Treatment System
Percent
None
45.3%
48.7%
46.8%
Filtering System
26.7%
22.7%
24.5%
Reverse Osmosis
21.7%
19.0%
20.5%
Distillation
0.0%
0.4%
0.2%
Other
0.7%
0.4%
0.6%
Not Available
5.7%
9.7%
7.4%
Table 20. Last Tested for Nitrate
When was the Well Last Tested for Nitrate
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Last Tested
Percent
Within the last year
3.3%
3.5%
3.4%
Within the last 3 years
14.0%
16.4%
15.0%
Within the last 10 years
20.7%
20.8%
20.7%
Greater than 10 years
15.3%
17.3%
16.2%
Never Tested
18.3%
18.1%
18.3%
Not Sure
1 25.0%
19.5%
22.6%
Not Available
1 3.3%
4.4%
3.8%
Table 21. Last Nitrate Test Result
What was the Last Nitrate Result
Community
Cottage Grove
Denmark Township
Total
Total Wells
300
226
526
Last Nitrate -N Result
Percent
<3 mg/L
9.0%
13.7%
11.0%
3< 10 mg/L
9.0%
9.3%
9.1%
mgL
4.7%
3.1%
4.0%Available
ENoot
77.3%
73.9%
75.9%
2014 Summary Washington County Township Sampling 1 32