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Characterization of the Study Areas for the Pilot Study: Agricultural Chemicals in Rural, Private Wells in Illinois

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Title: Characterization of the Study Areas for the Pilot Study: Agricultural Chemicals in Rural, Private Wells in Illinois
Author(s): Mehnert, Edward; Barnhardt, Michael L.; Ray, Chittaranjan; Greenpool, M. R.; Dey, W. S.; Vaisanen, U.; Kempton, J. P.; Curry, B. B.
Contributor(s): Barnhardt, Michael L.; Mehnert, Edward; Ray, Chittaranjan; Schock, Susan C.
Subject(s): Hydrogeology Groundwater -- Illinois Agricultural Chemicals in Groundwater
Abstract: The Illinois Groundwater Protection Act of 1987 (PA 85-863) mandated that the impact of pesticides on groundwater be evaluated. Because pesticide use is widespread in rural areas and groundwater is the major source of drinking water in rural areas, the Illinois State Geological Survey (ISGS) and the Illinois State Water Survey (ISWS) developed recommendations for a statewide survey of agricultural chemicals in rural, private water wells in Illinois (McKenna et al. 1989). This pilot study was undertaken to develop and evaluate field, analytical, and database management methodologies that would be applied in a statewide survey. Such an evaluation of the research design would assist in streamlining and making more economically feasible the statewide survey recommended by McKenna et al. (1989). Specifically, the pilot study evaluated the validity of using the potential for contamination of shallow aquifers as the stratification variable by assessing the occurrence of agricultural chemicals in rural, private wells in representative hydrogeologic settings in Illinois (McKenna et al. 1989). Additional objectives included field testing well selection procedures; conducting well user interviews; training Illinois Department of Agriculture (IDOA) and Illinois Department of Public Health (IDPH) personnel in sampling procedures; and establishing and evaluating techniques for database management, laboratory management, and quality assurance/quality control. The results of the pilot study could be used in a statewide survey to determine the number of wells necessary for characterizing the quality of water pumped from rural, domestic wells, while at the same time maintaining an acceptable level of statistical reliability and analytical precision. This report summarizes the land use, agricultural, geologic, and hydrologic characterizations of the five representative settings in the pilot study. A companion report, Pilot Study: Agricultural Chemicals in Rural, Private Wells in Illinois (Schock et al. 1992), discusses the project design, sampling methodology, and statistical analysis and interpretation of the chemical analyses. Schock et al. (1992) also present recommendations for conducting a statewide survey and propose modifications in the sampling and chemical analysis protocols. The volume of the characterization material warranted publication as a separate document. Both reports should be reviewed concurrently to fully understand the objectives, methodologies, and results of the pilot study. Characterizing the geologic materials of target areas is a major component in assessing the potential for contamination. McKenna et al. (1989) identified four hydrogeologic settings that occur in Illinois on the basis of their interpretation of the stack-unit geologic map of Illinois (Berg and Kempton 1988). The distance from the land surface to the top of the uppermost deposit of aquifer material was used to differentiate the four groups. The four study areas chosen for the pilot study represent these four hydrogeologic groups and are located in the following counties: (1) Mason (aquifer material within 5 feet of land surface), (2) Kankakee (between 5 and 20 feet of land surface), (3) Livingston (between 20 and 50 feet of land surface), and (4) Piatt (aquifer material greater than 50 feet from land surface). A fifth study area in Effingham County was chosen because large-diameter, dug or bored wells are the predominant well type and no well-defined significant aquifer system is present within 50 feet of land surface. The other four areas contain predominantly small-diameter, drilled or driven wells. For each study area, all available topographic, geologic, and soil survey maps were used to create a database on the Geographic Information System (GIS). Selected cultural, topographic, geologic, hydrologic, and soil survey information was digitized and used to provide the data for various base maps produced using the GIS. The location of each water well in each study area was verified, and the available drillers' logs for each well were interpreted. For each area, a . number of maps was produced, including a stack-unit map to a depth of 50 feet, and bedrock 1 topography, drift thickness, parent materials/soils, and terrane maps. Because some of these maps are quite similar to one another, not all individual maps are presented for each area. In some cases, a single map could convey the necessary information for a given study area. Such streamlining to eliminate redundancy was desirable because one of the objectives of the pilot study was to evaluate the economic feasibility of a statewide survey. The land use, agricultural, geologic, and hydrologic maps produced for the pilot study serve dual purposes. First, the process of producing them provided the researchers the opportunity to assess the quality and quantity of the database. Because the pilot study areas are generally representative of the status of the statewide database, knowledge of problems arising during this stage of the project will aid in the evaluation of the economic feasibility of the recommended statewide survey. Second, these maps are important in interpreting the chemical and statistical results presented in the companion document (Schock et al. 1992), which presents the sampling protocols and statistical analyses of the chemical data and summarizes the results of the pilot study. Because the characterization part of the pilot study was designed to test procedures and methodologies that would be applied in a statewide survey, emphasis was placed on using all available databases (e.g., soil, stratigraphic, geographic, topographic, and hydrologic). No additional fieldwork was conducted other than the actual water sampling and selected trips to identify industrial, commercial, and agricultural activities, and to interview residents. Existing drinking-water wells were used for sampling. This design required interpretation of the existing geologic database, which consists of drill logs from private, municipal, and commercial water wells; drill logs from coal and gas borings; drill logs from highway and bridge borings; and reports, maps, and unpublished data housed at the ISGS and the ISWS. Additional information was obtained from the county soil reports of the U.S. Department of Agriculture-Soil Conservation Service (USDA-SCS). Because the selection of the five study areas was made on the basis of their hydrogeologic classification and not the amount of information currently available, the quality and quantity of data varied considerably. Some of the study areas (Mason and Kankakee) are within or near the boundaries of recently completed research projects and, therefore, more information was available concerning the hydrogeologic characteristics of the area. Conversely, considerably less geologic and hydrologic information was available for the Livingston and Effingham County study areas, and the data that are available are either dated or presented on very small-scale maps. An additional problem was caused by the different map scales used in the original sources. Source map scales ranged from the large-scale, 1:15,840-scale soil survey maps (where 1 inch equals 0.25 miles) to the small-scale, 1.250,000 state stack-unit map (where 1 inch equals 4 miles). The pilot study used 1:24,000-scale topographic maps for preliminary geologic mapping, whereas the GIS maps presented in this report range in scale from about 1:62,000 to 1:100,000. Map detail and readability are concerns because the level of detail that can be presented is directly related to map scale (larger scale maps show more detail than smaller scale maps). Because small-scale maps require more data generalization than large-scale maps of the same area, less information can be shown. The physical size of the map also controls its use because it affects scale and readability. With few exceptions, all of the working . maps produced for this project were at scales larger than the final published version. Although in some cases considerable detail was generalized for the final map, all five study areas exhibited a need for additional, accurate geologic information. The most common problem encountered was the lack of detailed, verifiable, drill logs for water wells in the study area. Often, the verifiable wells were either clustered in a small area or lacked the information necessary for a detailed geologic interpretation of the sediments. 2 Overall, the problems encountered in the characterization part of the pilot study appear to be representative of the problems that would be encountered in a statewide survey. For some study areas, there was a lack of information that would have allowed a more detailed hydrogeologic interpretation. Extrapolating from the ISGS regional glacial stratigraphic framework into areas lacking detailed geologic information assisted in identifying the geologic units present and their hydrogeologic characteristics. The accuracy and detail of the extrapolation is obviously related to the level of detail of the previous research, but sufficient information appears to be available in the current geologic database to allow for regional geologic mapping and interpretation of the geologic sediments and the potential for contamination of groundwater resources by agricultural chemicals. Due to the variability in the quality and quantity of geologic data, however, some areas selected for the recommended statewide survey may require interpretations that are based on marginal data and are, therefore, more likely to be in error. Because geologic complexity varies across Illinois, data with similar quality, quantity, and spatial density may be adequate in some areas and not in others. Neither the pilot study nor the proposed statewide survey will replace the need for detailed, site-specific studies.
Issue Date: 1992
Publisher: Illinois State Water Survey and the Illinois State Geological Survey
Series/Report: Cooperative Resources Report 15
Type: Text
Language: English
URI: http://hdl.handle.net/2142/35248
Date Available in IDEALS: 2012-11-21
 

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