Phosphorus Discharge

The City of Burlington is committed to protecting the water quality of Lake Champlain. Excess phosphorus has negatively affected the water quality and there is now a cap on the amount allowed into the lake. The cap is known as the Total Maximum Daily Load (TMDL), and is regulated by the State of Vermont. 

Pounds of Phosphorus
< 5173

To bring phosphorus levels below water quality targets, Vermonters in the Lake Champlain Watershed need to reduce phosphorus export from all sources.  Wastewater Treatment Plants play an important role in reducing phosphorus by efficiently treating sanitary waste from homes and businesses.  Burlington’s Wastewater Plants have consistently met (or discharged well under) previous permit limits (0.8 mg/L monthly average, 0.6 mg/L annual average).  Though Wastewater Plants are only 4% of the overall phosphorus loads entering the Lake, the Lake Champlain TMDL requires more stringent limits (0.2 mg/L annual average) of these facilities, largely because they are “easier” to regulate than other sources.  While Burlington has not yet been issued permits with new phosphorus limits, we are holding ourselves to what will eventually be the new limit through chemical optimization. 

On the Wastewater Treatment Plant side, chemical optimization shows promise (see 2016 results).  However, due to the influence of rain events in 2017 on our Main Wastewater Treatment Plant combined sewer system, even though we have reduced concentrations of phosphorus in the outflow, the volume of outflow is much greater. This means that we will possibly discharge more pounds of phosphorus than our self-imposed 2017 target. Burlington Water Resources is currently undertaking a large scale planning effort to determine our overall strategy for cost effectively reducing phosphorus export from all of our sources, including the combined sewer system and our separate storm sewer system, as well as the Wastewater Treatment Plants (since optimization may not get us all the way to our eventual permit targets).  The results of the study will help determine where investments will be made throughout the City.

Samples are taken of the Wastewater effluent (outflow).  The measured concentrations (mg/L units of  mass/volume) are multiplied by the volume (millions of gallons), and after some conversions, yield a mass in pounds.  Our official TMDL limits are in metric tons (2204.62 lbs = 1 mT)