Shallow Groundwater Wells Network - Background
The Illinois State Water Survey operates two observation well networks to
collect data on shallow groundwater levels across the state. The observation
wells typically are located in areas remote from pumping so only natural
fluctuations in the water table, undisturbed by pumping, are measured. These
data allow scientists to assess both short-term and long-term trends in the
water table. This information is useful for understanding the effects of
climate on Illinois’ hydrologic cycle.
Illinois’ shallow observation well network was established by William C. Walton
in the 1950s as a result of the drought of the early to mid-50s. Walton’s
observation well siting criteria included: 1) siting at least one well in each
physiographic division of Illinois (keeping in mind a reasonable geographic
distribution), 2) siting them near weather stations, 3) siting them in areas
easy to access where opportunities for vandalism were limited, and 4) placing
them in areas where the groundwater level fluctuations reflected natural
changes in the water table rather than changes caused by domestic or industrial
well pumpage (R. Peppler, 4/27/93).
Originally, there were 21 wells in the network, but by 1992, only 19 remained
operational. Groundwater levels are monitored continuously with Stevens Type-F
paper chart recorders. Water Survey groundwater staff or local “Well-Watcher”
volunteers replace the recording charts and measure the depth to water in each
well on a monthly basis. In the late 1980s, the
Water and Atmospheric Resources Monitoring (WARM)
program was initiated to coordinate pre-existing ISWS hydrologic data
collection efforts. Thereafter, the wells in this network became known as the
WARM wells and the network was called the WARM observation well network.
Around 1989, the Water Survey initiated a 19-station climate network (the Illinois
Climate Network, ICN) to collect predominantly atmospheric-related data using modern digital
recording equipment. These data are remotely downloaded on an hourly basis. A
goal was subsequently set to install a shallow observation well at each ICN
station. Drilling at the 19 climate stations was conducted during late 1996 and
early 1997. Shallow 4-inch diameter wells were constructed at each location.
Hand measurements of depth-to-water were collected initially, but eventually
each ICN well was outfitted with a pressure sensor that sends data to a station
datalogger. Hourly water level observations are recorded and transmitted back
to the ISWS each night for subsequent digital processing.
Consequently, there are two groups of shallow observation wells at the Water
Survey: the WARM wells and the ICN wells. They are presently generally
distinguished by their method of measurement. The WARM wells are visited
monthly and water level data are recorded on a paper chart with a Stevens
Type-F recorder. Currently, only the month-end hand measurements are recorded
digitally. The ICN wells are visited less often, and on an irregular basis,
with downloads of hourly digital-recorded measurements.
