Hydrologic data for a study of pre-lllinoian glacial till were collected during the 1991 water year at a site in Linn County, east-central Iowa. A hydrologic-data-collection network, consisting of a meteorological station, 22 observation wells, and a water-quality minimonitor, was installed at the site to investigate the hydraulic properties of the till. Recorders were installed on 12 of the observation wells to continuously monitor water levels.
Rainfall at the study site from October 1990 to September 1991 was 17.86 inches. The greatest monthly rainfall (4.07 inches) occurred in March. The smallest monthly rainfall (0.06 and 0.04 inch) occurred in June and July, respectively.
The highest water levels measured in 22 observation wells were recorded from March through May 1991. Water levels in three of the deeper wells, completed in the unweathered glacial till, continued to rise from the time the wells were initially installed in November 1989 until they were bailed for water-quality sampling in May 1991. One well had water levels greater than the top of the well casing for most of the period from March to mid-July.
Ten unvented, vibrating-wire pressure transducers with internal thermistors were buried in two boreholes at upgradient and downgradient locations to record hydraulic pressure and water temperature at selected depths.
A water-quality minimonitor was installed near the top of the water table to monitor temporal changes in ground-water quality. For October 1990 through September 1991, the daily mean water temperatures ranged from 7.3 to 14.9 degrees Celsius, and the daily median pH values ranged from 6.9 to 7.5 standard units.
Herbicide concentrations in rainfall ranged from 0.05 to 1.3 micrograms per liter. Herbicides detected in the largest concentrations included alachlor, atrazine, and metolachlor. Metribuzin was the only herbicide detected in ground-water samples at a concentration of 0.10 micrograms per liter in water from one observation well.
