In recent years Japan has had an opportunity to develop a strategy to control diffused pollution of agrochemicals in watersheds upstream of drinking water intakes. Three types of approaches to controlling probable pollution have been examined. These are (1) risk based assessment approach, (2) regulatory approach supported by standard setting and (3) planning based guide to land use. In this paper, based on the results of pilot studies in several golf links, the practical procedures of these approaches are systematically structured.
First, risk-based assessment approach includes typical exposure assessment and quantitative risk assessment (QRA) coupled with fate analysis of runoff into reservoirs. The basic process of QRA of indicative herbicides, insecticides and fungicides, generated the result that additional cancer risk would be around minus 5-6 order of life time risk for citizens to drink water from reservoirs receiving contaminated river water.
Second, appropriate standard setting enhances a reasonable regulatory approach. In 1990, concentration of twenty agrochemicals in effluents from golf links and rivers at receiving outlets from golf links were evaluated in a nation-wide program in terms of the ratios of samples having higher concentrations than the tentative quality standard. Both seasonal change of observed concentration in dry weather and high concentration in rainfall events are evaluated.
Concerning a planning based guide to land use, zoning of forest conservation districts for water resources conservation would be responsible for appropriate land use management and water quality control. The author proposed the skeleton of a water resources conservation plan for safe drinking water supply for a local government as a client, especially emphasizing land use suitability mapping, development guides and mitigation techniques.