Land-Use Studies
The primary objective of the Land-Use Studies is to assess the concentrations and distribution of water quality constituents in recently recharged ground water (generally less than 10 years old) associated with the most significant settings of land use and hydrogeologic conditions in each study unit. A closely related second objective is to understand the human and natural factors in each setting that affect ground water quality. This focus on recently recharged shallow ground water in priority settings enables direct assessment of relations between land-use activities and ground water quality.

The two land-use studies in the LIRB are row-crop (corn and soybeans) agricultural land use areas overlying glacial deposits. The first Land-Use Study (LUS1), is located in the Bloomington-Ridged subsection of the Till Plains section of the Central Lowlands Province, where there are no buried bedrock valleys. This area is characterized by shallow ground water, which is the source of the major water supply to the area. The area where wells were drilled has till that is very clayey with a few thin sand layers.

The second Land-Use Study (LUS2) is located in the Bloomington-Ridged Till Plain, which is characterized by thick glacial till deposits overlying a buried bedrock valley. The major water supply is the deep glacial-fluvial deposits within the buried valley (Mahomet aquifer). The LUS2 area, a region of agricultural land use, was originally intended to be in the Galesburg-Springfield subsection of the Till Plains Section. However, most of the wells in our study-unit survey were less than 100 feet deep in agricultural areas, making a LUS study in the area redundant. Because little new information would be found, the LUS2 area was changed to the Bloomington-Ridged subsection.

Study Unit Surveys
The first Study Unit Survey (SUS1) is composed of unconsolidated glacial aquifers in the Mahomet-Teays buried bedrock valley. Thirty domestic and monitoring wells were sampled for pesticides, organic contaminants, and volatile organic compounds (VOCs). The wells are generally 200 to 300 feet below land surface, and most tap a confined or semi-confined aquifer.

In utilizing the network design parameters (physiography, bedrock valleys, and land use), the number of wells available for sampling was reduced from 33,000 to 305. Then, using an equal-area distribution method, this subset of 305 wells was divided into 35 equal areas, from which one primary and four alternate sites were selected. We sampled ground water at 30 wells in SUS1 and had a positive response from most of the well owners for sampling. Of those sampled, 19 were the first chosen, 9 were the second chosen, and 2 were the third chosen. Twenty-six of the wells were privately owned. Other wells included 1 farm, 1 community, 1 stock, and 1 non-community public supply.

The second Study Unit Survey (SUS2) is composed of the Bloomington-Ridged Plain Mahomet buried bedrock valley and the Galesburg-Springfield Plain non-buried bedrock valley. We sampled ground water at 30 wells for SUS2 using an equal area distribution method. One primary, and four alternates were chosen. We had a slightly less positive response in this part of the basin because most supplies are shallow wells, and there is more concern about contamination. The distribution was as follows: 14 were first chosen, 5 were second chosen, 4 were third chosen, 5 were fourth chosen, 0 was fifth chosen, and 2 were alternates in the same cell. Twenty-seven wells were privately owned. Other wells included 1 stock, 1 municipal, and 1 farm.