Pesticide contamination of groundwater has been linked to intensive agricultural activity. Several federal legislations have been applied to protect groundwater quality from on-farm pesticide contamination, but results have not been notable. The environmental protection agency has mandated that states develop management plans based on area-specific differences in groundwater use, value, and vulnerability. The Michigan Department of Agriculture (MDA) has been structuring its programs based on a combination of aquifer sensitivity and groundwater impact potential; and attempting to estimate aquifer sensitivity based on soil type and sub-surface geology. This paper is to define the method to estimated total mass of "likely to leach" pesticides applied in each county in Michigan. Survey data collected from Michigan Agricultural Statistics Service, National Agricultural Statistics Service, Michigan County Food and Agricultural Development Statistics, and pesticide-use-site codes were used to identify pesticide use site type and distribution. The pesticide use activities and practices which may contaminate groundwater were also identified. Seventy-two site types have been identified. Two types of matrices describing the magnitude of each site type in a county and the available pesticide use information associated with each site type were developed. An estimate of the total mass of likely to leach pesticides applied in each county were computed by combining these matrices, and the missing information was also identified. The possible methodology of completing the prototype matrices and the potential uses of matrix was discussed.