What is thermal pollution?

• Thermal pollution involves anthropogenically changing the temperature of a natural body of water, such as a lake or stream
• Historically, thermal pollution has been associated with discharges from power plant cooling towers and other industrial facilities

How is stormwater runoff involved?

• Especially during the summer months, stormwater runoff can reach temperatures well above those seen in a natural environment
• High temperatures and flows associated with stormwater runoff can increase the temperature of streams or rivers

What causes thermally polluted runoff?

• Paved surfaces capture incoming solar radiation and store this energy as heat
• During a rainfall event, heat is transferred from the pavement surface to stormwater runoff
• A flash animation illustrating the basic process can be found below

Why is thermally polluted runoff a concern?

• Increasing the temperature of a creek or pond can disrupt the aquatic ecosystem and kill fish like trout
• With an estimated 1.3 million people fishing in North Carolina, spending over $1 billion each year, protecting stream quality is not only important ecologically, but economically as well. (source)

How are stormwater BMPs involved?

• While not initially designed with thermal pollution in mind, stormwater BMPs do have an impact on runoff temperature
• Because stormwater BMPs are being integrated into urban watersheds, it is important to understand whether these structures impact runoff temperature in a positive or negative manner