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Small‐Scale Retrospective Ground Water Monitoring Studies for Agricultural Chemicals: Study Design and Site Selection
Author(s) -
De Martinis James M.
Publication year - 1989
Publication title -
groundwater monitoring and remediation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 47
eISSN - 1745-6592
pISSN - 1069-3629
DOI - 10.1111/j.1745-6592.1989.tb01026.x
Subject(s) - hydrogeology , groundwater , scale (ratio) , environmental science , site selection , agriculture , vulnerability (computing) , environmental monitoring , water resource management , environmental resource management , environmental engineering , engineering , geography , computer science , cartography , geotechnical engineering , archaeology , computer security , political science , law
A small‐scale retrospective ground water monitoring study is designed to determine if, after years of normal usage, an agricultural chemical has leached to ground water. These studies are conducted on actively planted fields in hydrogeologically vulnerable areas. Because the results of such studies may have larger ramifications for the particular agricultural chemical over much broader hydrogeologic and geographic areas, care must be exercised in selecting particular fields to be monitored and in establishing site‐specific ground water monitoring networks. The U.S. Environmental Protection Agency, Office of Pesticide Programs, has established draft guidelines and suggested field protocols for such studies. These guidelines serve as a baseline for such studies, though many other hydrogeologic and agronomic factors play significant roles. Small‐scale retrospective studies are ordinarily broken into a series of tasks that lead to the selection of a suitable test site(s) by determining on a national scale where to monitor; meeting minimum hydrogeologic and agronomic criteria; and establishing a ground water monitoring program. A detailed hydrogeologic vulnerability analysis is conducted in product use areas for the chemical being studied. A series of screening steps results in a subset of moderate‐ to high‐use counties that are underlain by permeable soils and vulnerable to ground water impacts from agricultural chemicals. Once these counties are determined, suitable test fields can be selected. The individual site selection criteria can be exhaustive. However, these criteria in combination with one another are necessary to ensure that the selected sites will yield information as to whether or not the chemical has leached through the soil profile and the unsaturated zone to ground water. The following criteria are considered essential to a particular site: flat topography; “workable” field size; documented history of use of the chemical being monitored; avoidance of regional and farm‐specific point sources; typical irrigation and farm practices for the crop on which the chemical is applied; farmer cooperation; field accessibility; permeable soils and unsaturated zone; and shallow water table. There are also other hydrogeologic and agronomic parameters that need to be assessed prior to site selection. The hydrogeologic and agronomic criteria are not always easily met. For example, the topography and shallow water‐table criteria could eliminate key agricultural areas in the United States where the agricultural chemical to be monitored may be used. However, the data generated during these field‐scale retrospective studies, when properly conducted, can provide information regarding whether or not a particular agricultural chemical has leached to ground water under worst‐case conditions.