CWEA Grade 4 Practice Test

The identification of plating bath rinses and stormwater runoff as common sources of dilute solutions discharged to the pretreatment system is rooted in their particular characteristics. Plating bath rinses typically contain trace amounts of heavy metals and other chemicals used during metal treatment processes. These rinses are essential to manage properly because they can significantly impact water quality if they enter the wastewater stream without prior treatment.

Stormwater runoff is another common source, especially in industrial areas. Rainwater can wash away pollutants from surfaces, including metals, oils, and other chemicals, leading to a diluted mixture that must be treated before being discharged into the environment. This runoff often contains lower concentrations of pollutants, hence the term "dilute solutions," but still requires appropriate handling to avoid contaminating natural water bodies.

In contrast, choices like pulp waste and cleaning agents, agricultural chemicals and household waste, and industrial solvents and food processing waste consist of either more concentrated solutions or types of waste that are specifically regulated under different protocols, often involving distinct treatment processes for various contaminants.