Florida Wastewater Practice Test 2025 – 400 Free Practice Questions to Pass the Exam

A fixed sample in laboratory testing is specifically defined as a sample that has been purposely spiked by the lab technician for Quality Assurance/Quality Control (QA/QC) purposes. This process involves adding a known quantity of a substance to the sample to evaluate the accuracy and precision of the testing methods being used. By spiking a sample, the technician can monitor the recovery rates of the added substance, thereby ensuring that the testing procedures are effective and that the analysis yields reliable results.

Other options do not fit this definition. A randomly collected sample does not have the controlled conditions necessary to be considered fixed; it lacks the intentional manipulation that characterizes a fixed sample. A sample tested without analysis cannot be classified as a fixed sample because it implies that no quality verification is being performed. Finally, while a sample from the treatment plant effluent is related to wastewater sampling, it doesn't inherently imply any spiking or QA/QC activity unless specified. Thus, the correct choice captures the essence of purposeful manipulation for quality assurance in laboratory settings.