Pollution control efforts at many “point sources”—wastewater treatment plants and factories that discharge into waterways through a pipe—have resulted in some of the greatest nutrient reduction efforts in the watershed.
In 1985, those point sources delivered 87.7 million pounds of nitrogen to the Chesapeake. That fell to 58.4 million pounds in 2002. Phosphorus discharges during the same period decreased from 9.2 million pounds to 4.3 million. The reductions took place even as 2.5 million additional people moved into the watershed.
When tributary strategies are fully implemented, the amount of nitrogen entering the Bay is expected to be cut by at least another 17.5 million pounds from 2002 levels, and phosphorus should be reduced by another 1 million pounds.
Of more than 350 large point sources in the watershed, more than 100 municipal and industrial facilities treat wastewater with technology to remove nitrogen. According to the EPA, this is the largest number in any of the nation’s watersheds.
Reductions in point source discharges are particularly beneficial to the Bay cleanup effort. Unlike runoff (or nonpoint) controls which take time—often years—to show results, point source upgrades produce instantaneous benefits. Nutrient reductions are realized as soon as the discharge leaves the pipe and hits the river.
Nonetheless, point source loads increased slightly in 2003, to 61.2 million pounds for nitrogen, and to 4.5 million pounds for phosphorus.
Part of the reason was that some plants that had not been included in the 2002 data were added for 2003. But most of the reason was because 2003 was the third-wettest year since 1937.
As the ground becomes saturated, water begins infiltrating into the pipes, increasing the flow going into treatment plants, especially at older systems. Also, in some cities, the stormwater system is combined with the sanitary sewer system. When it rains, street runoff is flushed to the treatment plant, dramatically increasing the amount of water being handled by the plant.
The level of treatment wastewater receives is often related to how long the plant has to treat it. That is especially true for treatment plants using biological nutrient removal technology to control nitrogen. BNR uses microbes to convert nitrogen in the wastewater to harmless nitrogen gas, which is the most common element in the atmosphere. Generally, the longer the microbes have to work, the more nitrogen they can remove. Therefore, when flows are high and a treatment plant is near its capacity it has less time—and ability—to remove nutrients.