The final stage for ammonia discharge improvements occurred in 2004. The biological aerated filter (BAF) system allows for year-round nitrification of wastewater. In 2004, Metro's annual ammonia discharge was reduced to 152 metric tons and by 2005, the annual discharge fell to 21 metric tons. The ACJ also led to the creation of an ambient monitoring program (AMP) to track the effectiveness of the improvements made to the wastewater collection and treatment infrastructure. The AMP is designed to identify sources of materials to the lake, evaluate in-lake water quality conditions, and examine the interactions between Onondaga Lake and Seneca River. Since 2007, Onondaga Lake has been in full compliance with the ambient water quality standards for ammonia. It was officially de-listed for that particular parameter in the State's 2008 list of impaired bodies of water.