Which option correctly states the retention period for DMR copies kept by facility owners?

• A. 2 years
• B. 3 years
• C. 4 years
• D. 5 years

Answer: (B)

Keeping DMR copies for three years ensures there is a ready record to verify monthly or quarterly discharge data across multiple reporting periods and to support any compliance review or investigation. This retention period is the standard requirement used in many wastewater permits and aligns with common regulator audit timelines, giving both regulators and facility staff time to review trends and address any discrepancies. Two years would often be too short to cover enough reporting cycles, while four or five years goes beyond the typical mandate and can be unnecessarily burdensome. Therefore, three years is the best answer.