Which of the following is often a standard procedure in wastewater sampling?

Using sealed containers is a standard procedure in wastewater sampling because it helps prevent contamination and ensures the integrity of the sample. By sealing the containers, any potential external factors that could alter the sample's composition, such as exposure to air or environmental contaminants, are minimized. This is crucial for obtaining accurate and reliable test results when the samples are analyzed in a laboratory.

Additionally, sealed containers help preserve the chemical and biological characteristics of the sample during transport and storage until testing occurs. This practice is essential in maintaining the sample's properties, which can be affected by factors like evaporation, light exposure, and microbial growth.

Other procedures, such as conducting tests on-site, may also be standard in specific circumstances, but they are not universally applicable to all types of wastewater sampling. Air drying samples or decreasing the sample size are not standard practices, as they can compromise the accuracy of the analysis by either altering concentrations or not representing the wastewater adequately.