Projects

Development of a Statistically Valid Program for Monitoring Pesticides in Ground Water in the State of Indiana—Overview

Overview by Denver Harper, Sally Letsinger, Greg Olyphant, and Alex Zlotin

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PROJECT SUMMARY

In cooperation with the Indiana Department of Environmental Management (IDEM) and Office of the Indiana State Chemist (OISC), the Department of Geological Sciences of Indiana University (IU) and the Indiana Geological Survey (IGS) have undertaken a project to write statistical software that is interfaced with a database management system in order to provide a statistically valid basis for evaluating data regarding pesticide concentrations in monitoring wells of the Indiana Baseline Monitoring Program (IBMP). The initial phase of the project was from October 1, 1997, to September 30, 1999. Additional work is being conducted from January 1 to December 31, 2001.

MONITORING NETWORK

The purpose of the project is to develop a statistically valid basis for extrapolating pesticide data from domestic water wells in the IBMP to aquifers throughout the state. The relevant chemical analytes were determined by the personnel of the OISC in consultation with personnel of IDEM.

Hydrogeologic settings of Indiana (left), and the subset of settings that were chosen for monitoring (right). The maps are derived from A. H. Fleming and others, 1995, Atlas of hydrogeologic terrains and settings of Indiana, Open-File Report 95-7, Final Report to the Office of the Indiana State Chemist, Contract No. E005349-95-0, Indiana Geological Survey, Bloomington, Ind.

The plan for selection of actual monitoring wells consisted of the following steps:

1. Representative hydrogeologic settings within the state of Indiana were selected by a special subcommittee of the Ground Water Task Force to comprise 22 monitoring subnetworks.
2. Because a sample size of 20 sampling points per monitoring subnetwork was considered to be the minimum number necessary for statistical analysis, the special subcommittee of the Ground Water Task Force determined that the IBMP should include a total of 440 wells.
3. Within the area of each subnetwork, coordinates of geographic points were randomly generated by personnel of the Indiana Geological Survey (IGS) using a numerical algorithm.
4. The randomly generated points were digitally plotted by IGS on 1:100,000-scale maps that were provided to personnel of IDEM.
5. Personnel of IDEM, using records from the water well database of the Indiana Department of Natural Resources, were to identify wells that were as close as possible to the randomly generated points.
6. Having compiled a list of potential sampling sites, personnel of IDEM conducted a field survey and made arrangements for inclusion of specific wells and springs into the sampling-point networks. All 440 sampling points have been selected. Of these 440 points, locations for 267 have been verified using GPS (global positioning system) equipment.

STATISTICAL ANALYSIS

Statistical analysis of pesticide data was proposed to detect trends in the presence and quantity of pesticides in ground water. In particular, the following questions are addressed:

1. In any given year, which categories and (or) subcategories of aquifers have occurrences and concentrations of pesticides that are above U.S. EPA National Primary Drinking Water Standards?
2. Has there been a statistically significant (95 percent confidence level) increase or decrease in the occurrence and (or) concentration of pesticides in any of the categories or subcategories of aquifers over the past year? If so, are the differences associated with a particular season?

The interface of a computer application that was created to allow nontechnical users to view chemical data and to undertake interactive statistical analyses.

Average values of each analyte within each of the monitoring networks will be calculated, and statistical comparisons will be made to determine whether the average values are above EPA standards and (or) whether statistically significant differences exist between the various hydrogeologic settings. A computer application has been created to allow nontechnical users to view the chemical data and to undertake interactive statistical analyses as new data are incorporated into the chemical database. After a complete set of actual data becomes available, the application will undergo final testing and revision by personnel of IGS, and the application will be provided to appropriate personnel of OISC and IDEM.

For a more detailed technical report on the investigation, go to the Pesticides Web page. NOTE: Because it contains a number of graphics with large file sizes, the technical report is best viewed with a high-speed internet connection.

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For additional information, contact:

• Greg Olyphant (e-mail: olyphant@indiana.edu) at the Department of Geological Sciences, Indiana University, Bloomington, IN 47405
• Sally Letsinger (e-mail: sletsing@indiana.edu) at the Indiana Geological Survey, 611 N. Walnut Grove, Bloomington, IN 47405