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.