Rapid growth of economics and society has driving force in continuously mining natural resources and discharging pollutant to environment. Thus, environment is suffered seriously impacts. Although there is 「Environmental Imapct Assessment Act」to request a new developing project to proceed environmental impact assessment, traditional regulations lack of ability to include cumulative impacts and thus may violate environmental carrying capacity. It could cause environmental degradation. To maintenance environmental sustainability, cumulative impacts should not exceed environmental carrying capacity. To achieve the goal, the management measures is to meet allowable total maximum loads which are allocated to each single user as their limits. The water quality indicator of BOD is used as an example in this study. According to hydraulic and hydrologic characteristics of a stream and its water quality standard, assimilation capacity of a stream or total maximum load for each subregion can be determined. The total maximum loads of each subregion are further divided by its area to obtain allowable unit pollutant load. A developing project needs to meet the limit of unit pollutant load, and then total pollutant discharge from all projects within the same region will not exceed total allowable discharge of the region. Furthermore, cumulative pollutant discharge from all regions along a stream will not exceed assimilation capacity. Unit pollutant load is used to be a standard for a new developing project and to evaluate reducation rates of current pollutant discharges. The Touchie and Keya ceek watersheds are used as case studies. Results indicate that cumulative pollution from domestic, inductrial and agricultural sources have exceed stream assimilation capacity in both creeks now. How to apply unit pollutant load to improve water quality is then addressed in this report. This research also collects water quality information of EIA reports accepted by Environmental Prote

Cumulative environmental impact assessment,Total mass control,Geographic Information System