Assessment of 1992 Wisconsin Atrazine Rule (Ag 30): Final Report

Atrazine has been detected in groundwater in parts of North America. Despite a downward trend in atrazine use over the past decade (WASS, 1991), Wisconsin has not escaped the environ­mental risk associated with this herbicide. Three factors contribute to the scope of the problem: 1) the long-standing popularity of atrazine as an inexpensive, reliable herbicide, 2) the amount of com planted, and 3) atrazine’s leaching charac­teristics. Data from a series of Wisconsin ground­water quality surveys, representing a wide range of soil and hydrologic conditions, has led to the conclusion that atrazine has the potential to be present in all areas of the state where it is used (DATCP, 1992). Based on earlier experience with aldicarb (Gustafson, 1991) and a desire to create a structured approach for managing antic­ipated threats to groundwater, Wisconsin adopted a Groundwater Law in 1983 (Chapter 160, Wisc. stats). This law along with the subsequent adop­tion of a set of human-health-based contaminant standards (NR 140, Wis. Admin. Code) required the Wisconsin Department of Agriculture, Trade and Consumer Protection (D ATCP) to address the emerging patterns of atrazine detections (Belluck, 1988). DATCP’s response, as required under law, was the promulgation of Ag 30, the Atrazine Rule, the nation’s most restrictive atr­azine policy.

In a context of broad uncertainty regarding the relative contributions to groundwater atrazine detections from non-point sources, point sources, and quasi-point sources (Hallberg, 1986; Fawcett, 1990) as well as “recent” versus “historic” atrazine, DATCP elected to restrict field applica­tion of atrazine beyond the federal standards beginning in the 1991 growing season. The restrictions represent a three-tiered structure: a statewide set of rules; a more restrictive set of rate restrictions applied to a series of Atrazine Man­agement Areas (AMAs) and the designation of a series of Atrazine Prohibition Areas (AP As) in which atrazine use is not allowed under any circumstances. Duringthe 1992 growing season, the area designated as AMA totaled approxi­mately 290,000 ha in five counties, and 11 dis­tinct areas totalling approximately 9700 ha were designated as APAs.

This tiered structure is a result of the differ­ential responses available to DATCP to address a groundwater problem under state law. According to the Groundwater Law, where detections exceed the atrazine Preventive Action Limit (PAL) of 0.35 ppb, DATCP must take steps to prevent further degradation. Because of the diffuse pat­tern of detections, the decision was made to create statewide restrictions. In those areas where the density and intensity of detections warranted a stronger response, AMA designation was made. When the detections are found to exceed 3. 0 ppb, the Enforcement Standard (ES), DATCP is di­rected to prohibit use, hence the AP As. It should be noted that despite this formulaic representa­tion of the atrazine rule-making process, the uncertainty of groundwater contamination pro­cesses in the context of the Groundwater Law has required interpretation and compromise by DATCP and other participant groups.

The rules limit field application of atrazine on the basis of soil surface texture, last year’s usage, and AMA designation (See Table 1 ). Under the rules, atrazine applications are limited to the period between April 15th and July 31 “; all han­dlers and applicators must be certified by the state; non-crop uses are prohibited; irrigation restrictions apply; and detailed records must be kept for all applications.