Which monitoring element is described as being used "as needed" under the CGP?

• A. Visual monitoring
• B. Non-visible pollutant monitoring
• C. Flow monitoring
• D. Visual monitoring and non-visible pollutant monitoring, as needed

Answer: (D)

In the CGP, stormwater monitoring uses two elements: visual monitoring of the discharges to catch obvious issues (color, turbidity, odor, sheen, etc.) and non-visible pollutant monitoring to detect contaminants that can’t be seen with the eye. The non-visible pollutant monitoring is described as being used “as needed”—you perform these tests when visual observations or site conditions suggest a potential problem or when verification is required. Visual monitoring provides routine, ongoing assessment, while non-visible monitoring is invoked selectively to confirm or investigate suspected issues. That combination is why the best answer is the one that pairs both monitoring types with the note that non-visible monitoring is used as needed.