What is the primary requirement for analytical methods used in sampling according to regulatory guidelines?

The primary requirement for analytical methods used in sampling according to regulatory guidelines is that they must be approved by the DEQ (Department of Environmental Quality). This approval is essential because it ensures that the methods being used are reliable, validated, and meet specific standards necessary for assessing environmental impacts and compliance. Regulatory bodies like the DEQ set forth guidelines to maintain consistency and accuracy across various sampling and testing procedures, which ultimately helps protect public health and the environment.

While the other options might present important considerations in specific contexts, such as safety for on-site conditions or cost-effectiveness, they are not the primary regulatory requirement. Approval by the DEQ indicates that the method meets all necessary criteria, including reliability and accuracy, which are crucial for regulatory compliance and decision-making processes.