This report presents results of a study to evaluate the formation of hydrazine during the chloramination of water and wastewater. Hydrazine is the product of the reaction between chloramine and free ammonia and is classified by the EPA as a "probable human carcinogen" with a 10-6 cancer risk level of 10 ng/L in drinking water. Model simulations were performed to predict hydrazine formation under a variety of water and wastewater treatment and distribution conditions.