Abstract: Environmental and health impact assessment of Hamadan wastewater treatment plants were studied for the treatment of wastewater produced at Hamadan, Bahar and Lalejin Cities, with the population of about one millions. In this study, a new method of EIA applied, using Leopold Matrix 3 dimensions to predict the negative and positive impacts of the project activities on environmental factors. After the data collection, processing and analyzing, Adkins and Burks check list along with new 3-dimensional Leopold Matrix were applied. This 3-dimensional method was a new method which was applied in this study for the first time in Iran. The scaling-ranking checklist was also applied which is a suitable approach for determination of intensity and importance of environmental impacts. The results obtained from this investigation showed that execution of the wastewater treatment plant could have some negative impacts, but may contain some important positive impacts particularly on the improvement of health conditions and environmental quality in the proposed project area. The mitigation measures have also been noticed for the project and in this regard some major management approaches were proposed at the construction and operational phases.