The relationship between wastewater treatment plants and nutrient impaired surface water bodies in seven northern states
Discharges from wastewater treatment plants (WWTPs) contribute significantly to nutrient loading of surface water bodies and to water body impairments in specific systems. As a result attention has been focused on the control of discharges from these point sources. However, the relationship between nutrient impairment and WWTP discharge on a broader scale is unclear. To investigate this relationship we examined the following factors in seven northern states: 1) the percentage of nutrient impaired water bodies that receive discharges from WWTPs directly or via tributaries 2) the percentage of WWTPs with advanced treatment to remove phosphorus (P) 3) the proportion of Total Maximum Daily Loads (TMDLs) for nutrients identifying WWTPs as significant sources of phosphorus and the fraction of the phosphorus load attributable to WWTPs. The results of this study suggest that on a state and regional scale WWTPs represent a small fraction of the P loading to impaired water bodies. However, in specific systems they may be the most important P source.