Waste discharge regulations can be concentration- or mass-based except for?

Waste discharge regulations are typically established to control the level of pollutants that can be released into the environment through various mediums, primarily water. Regulations can be based on either the concentration of pollutants, typically measured in terms of parts per million (ppm), or on mass-based limits, which take into account the total quantity of a pollutant being discharged over a given timeframe.

pH and temperature are unique in that they are not regulated based on concentration or mass in the same way as many other pollutants. Instead, they have specific thresholds that must not be exceeded to protect aquatic ecosystems. These thresholds refer to the acceptable levels that maintain the health of water bodies rather than measuring how much of these parameters are contributed by the discharge in a concentration or mass basis. If the pH or temperature goes beyond these limits, it can result in significant harm to aquatic organisms, hence the regulatory focus on maintaining them within safe ranges.

In contrast, pollutants like phosphorus, heavy metals, and organic compounds often come under both concentration and mass-based regulations, allowing for flexibility in compliance approaches based on the nature of the discharge. Therefore, the focus on maintaining specific levels for pH and temperature differentiates them from other pollutants, highlighting why they stand apart from the concentration or mass-based regulatory framework