About Groundwater
Monitoring
 Seventy-five percent of all Iowans rely on
groundwater as their drinking water source. Groundwater is one of the better understood
water resources in Iowa, yet much remains unknown. The objective of the
groundwater monitoring network is to describe and measure groundwater quality throughout Iowa,
characterize aquifers in different hydrogeological environments, and measure
water quality changes and identify trends in Iowa's aquifers. The
information gathered through this program can be used to assess the groundwater resource, project future
conditions of supply, address contamination concerns, and provide the
information necessary to effectively manage the resource.
Information about Iowa's groundwater is being gathered through a
groundwater level network, a ground water quality network,
development of a monitoring well network, and private well-water monitoring.
Groundwater
Level Network
Since 1982, the Iowa Department of Natural Resources
and the U.S. Geological Survey have cooperatively conducted the Iowa Groundwater Level Network. The
objectives of the groundwater level network are: to collect data
documenting any change in groundwater storage over time in the principal
aquifers; to provide both long-term and short-term data necessary to assess
and predict the response of hydrologic systems to natural climatic variations
and human-induced stresses; to quantify the hydrologic characteristics of
aquifers including transmissivity, hydraulic conductivity, and specific
capacity; and to provide historical baseline data for studies of Iowa's
aquifers.
The current groundwater level network in Iowa
consists of 175 wells completed in the principal bedrock and surficial
aquifers that supply groundwater to numerous users throughout the state. The advantage of the groundwater level network
is that static water levels for principal aquifers can be monitored through time,
generally under non-pumping conditions. Water levels are measured on a quarterly to monthly basis and entered into the
USGS Groundwater Site Inventory database. The majority of wells are
monitoring wells, while some are municipal wells. Each year, a selected aquifer
and its respective wells are reevaluated to determine which wells to continue to
monitor and whether additional wells in that aquifer should be included in the
groundwater level network. The Devonian Aquifer water-level
network was evaluated during the 1999-2000 water year, and the Mississippian
Aquifer will be
evaluated in 2000-2001. Other aquifers that have been evaluated in recent
years include the Cambrian-Ordovician (statewide), the Silurian (northeast
Iowa), and the Dakota (northwest Iowa).
Network data collected from all
aquifers are compiled and published in the annual U.S. Geological Survey
Water-Resources Data, Iowa report. The U.S. Geological Survey Open-File
Report 92-27 titled "The Ground-Water-Level Monitoring Network in
Iowa" was published in 1992 and describes in detail the groundwater level
network in Iowa. To request a copy of the publication, contact the U.S.
Geological Survey at (319)337-4191.
Groundwater Quality Network
Since 1982, the Iowa Department of Natural Resources, U.S. Geological
Survey, and University of Iowa Hygienic Laboratory have conducted the Iowa
groundwater quality monitoring program. The purpose of the program is to provide
consistent and representative data describing the chemical water quality of the
principal aquifers in Iowa and to determine possible spatial or temporal trends in water
quality.
The groundwater monitoring program was initiated to continue a program begun
in 1950 by the State Health Department that consisted of periodic, nonspecific
sampling of untreated water from municipal water supply wells. Each year,
approximately 250 wells, primarily municipal supply wells, were randomly selected for
sampling between April and November. Between 1985 and 1989, the program
focused on the concentration of nitrate and herbicides in wells less than 200 feet
deep. Because of the random
pattern of sampling, both spatially (different wells each year) and seasonally
(different times during the year), trends in groundwater quality were difficult
to determine from the data. In 1990, the focus of the program was changed to provide year-to-year
continuity of data and a more statistically sound basis for the study of
long-term, water-quality trends. The sampling strategy was changed to a random selection
of wells weighted by aquifer vulnerability. Aquifer
vulnerability was determined by the frequency of atrazine detections in water
samples collected from wells in the respective aquifers. In 1990 and 1991,
a fixed network of 50 wells was selected to be sampled annually, and
approximately 200 wells continued to be selected on a rotational basis.
In 1992, investigation of water-quality trends became the primary focus
of the program, and a 10-year work plan was designed to eliminate spatial and
seasonal variance, yet allow flexibility within the schedule to address
additional data needs. In 1992, the well
inventory was divided into categories based on aquifer type and again on well
depth for surficial aquifers, and into categories designated "vulnerable to
contamination" and "not vulnerable to contamination" based on the
map Groundwater Vulnerability Regions of Iowa (Hoyer, B.E., and Hallberg,
G.R., 1991, Special Map Series 11: Iowa Department of Natural Resources,
scale 1:500,000) for bedrock aquifers. Geologic and soil data,
thickness of Quaternary cover (unconsolidated sediments), proximity to agricultural drainage wells and
sinkholes through which contaminants can be introduced to the aquifer, and
evaluation of historical groundwater quality and well contamination were all used to
determine the vulnerability of each well. A total of 90 wells were selected for sampling from a well inventory comprised of
approximately 1,640 public water supply wells. From the 90 sites in the fixed
network, 45 wells from two surficial aquifer types were selected to be sampled
annually. These surficial aquifer types were alluvial and
Pleistocene. The other 45 wells (from the bedrock aquifer types) were selected to
be sampled on a rotational schedule based on aquifer vulnerability to
contamination. The wells determined to be vulnerable to
contamination would be sampled every 2 years, and those wells categorized as not
vulnerable to contamination would be sampled every 4 years. All 90 wells
were sampled in the first 2 years (1992 and 1993) and the sampling rotation
began in 1994.
Currently, in addition to the
sampling of the core 90 municipal wells, 60 other municipal wells from
particular aquifers are rotated into the sampling routine each year. The
rotating wells will allow an in-depth investigation into the water quality of
each primary aquifer in the state. In 2002, the 60 rotating wells were from the
Mississippian and Cretaceous aquifers (32 Mississippian wells and 28 Cretaceous
wells). The rotating wells for 2003 are from the Silurian/Devonian Aquifer. All
of the aquifers in the state will be covered over a period of five years
Ambient (Dedicated) Groundwater Monitoring Network
A monitoring well network will be developed throughout the
state to evaluate the ambient or background quality of aquifers in Iowa. The target is to develop 60 well-nest sites, or about 180
monitoring wells. (A well nest is two or more wells located in close
proximity to each other where each well is completed to a different
depth.) These will be developed at different depths to tap
specific aquifers used in the region. In most instances, this will include one
or more bedrock sources, but will also include glacial drift, alluvial, or buried
alluvial sources. Annually, two to five well-nest sites will be developed
through contracts with drilling companies. Water will be age dated from each
well to indicate vulnerability. Annually, each well will have the mineral content analyzed and
common parameters assessed. For
the first year after the wells are constructed, water levels will be measured
continuously to characterize each aquifer and the hydraulic connection of that
particular aquifer to aquifers located above and below it. After year one, water levels will be measured less frequently.
Development of monitoring wells will provide important information
for the overall management of groundwater in Iowa. Pump tests and
geophysical tests will
assess aquifer characteristics. A continuous rock core will be obtained from each
site as part of a lithologic and stratigraphic reference collection. This
information will enhance our understanding about the distribution and
variability of rock units throughout the state, and their potential as future or
expanded sources of groundwater for Iowans.
The advantage of a monitoring well network is that
the well
construction is well known, the rock core provides detailed information about
the sequence of bedrock in the subsurface, allows determination of aquifer
properties and water quality from a specific aquifer
under non-pumping conditions.
Rural Well Water Survey
The State-Wide Rural Well-Water Survey (SWRL) was a one-time,
statistically based sampling of 686 private wells across Iowa to evaluate the quality of
private drinking-water supplies used by rural Iowans. The survey,
completed in 1988 and 1989, addressed
two questions: (1) What proportion of private wells in rural Iowa are
affected by various environmental contaminants? (2) What proportion of
rural Iowa residents are utilizing well water containing these environmental
contaminants? The survey was conducted as part of the implementation of
the Iowa Groundwater Protection Act of 1987. Water sampling was conducted by the Iowa Department of
Natural Resources and the University of Iowa Center for Health Effects of
Environmental Contamination. Results provide a 'snapshot' of the condition of the private
well-water supplies in Iowa and some insight into the condition of Iowa's
groundwater resource. It also serves as a baseline for measuring future
trends and changes in groundwater and rural private drinking-water
quality. The well-water was analyzed for an extensive
list of parameters, including pesticides, bacteria, inorganic chemicals, and
radionuclides. An inventory questionnaire was completed for each household
and a health assessment questionnaire was completed for each individual in the
household.
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