Water laws & technology

Issue 4 > Meet the Managers > Water quality issues: Water laws & technology
Stream in the Smokies.

TMDLs will let Park managers know how much sulfate and nitrate can come into the Park and not harm streams.

NPS photo.

The Clean Water Act and TMDLs
The Clean Water Act of 1977 requires that streams have a pH of at least 6.0. If the level drops below that, the Environmental Protection Agency lists the stream as “impaired” (also referred to as "on the 303(d) list). In 2006, the state of Tennessee listed 41 miles of high elevation streams in the park as impaired. The act mandates that the park “fix” the streams by making them less acidic. If it doesn’t, it will face legal consequences. To fix the streams, managers have to target the source of the pollution—primarily vehicles and power plants outside the park—and reduce the amount that comes into Smoky Mountain streams.

Knowing just how much air pollution must be reduced to bring stream pH levels up to 6.0 isn’t easy. The key amount is called the Total Maximum Daily Load, or TMDL. The EPA defines TMDL as “a determination of the amount of a pollutant from point, nonpoint, and natural background sources, including a margin of safety (MOS), that may be discharged to a water quality-limited water body.”

Figuring out the TMDL takes a lot of calculations, including where the pollution is coming from, and how rain brings the pollution to different parts of the park. There are two classes of pollutants that scientists have to take into consideration. Point sources include pollutants dumped directly into the water from a single source (we don't have many of those in the park), or pollutants that come from single, identifiable sources such as coal-fired power plants. Non-point sources include all sources of pollution that we can't pinpoint, or that move, such as cars and other vehicles that release exhaust into the air.

To figure out what the TMDL is, the Park is working with researchers at Syracuse University, who will model different scenarios of pollution, climate trends, and resulting stream pH. Final numbers will let the Park, state representatives, and federal lawmakers mandate reductions in sulfate and nitrate emissions from power plants and vehicles. This action may be the first of many to link known impacts in streams to laws mandating cleaner air and energy.

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