Discharge Monitoring Reports and Recordkeeping Requirements

What Is a Discharge Monitoring Report?

A Discharge Monitoring Report (DMR) is the official document a permitted facility uses to report effluent monitoring data to the regulatory authority, typically the state environmental agency or the U.S. Environmental Protection Agency (EPA). If your facility holds a National Pollutant Discharge Elimination System (NPDES) permit, you are legally required to submit DMRs on the schedule your permit specifies—usually monthly, quarterly, or semi-annually. Submitting an inaccurate or late DMR is a permit violation and can result in fines or enforcement action. An unfiled DMR is treated the same as a violation.

Key Fields on a DMR Form

Every DMR form contains several standard fields you must understand before you can complete one correctly.

Permit Number and Outfall Number: These identify exactly which permit and which discharge point the data covers. Copy them directly from your permit—any mismatch can cause a submission to be rejected or misfiled.

Parameter Name and Units: Each pollutant you must monitor is listed as a parameter (for example, BOD₅, TSS, pH, fecal coliform). Units must match those in your permit exactly. Reporting milligrams per liter when the permit states micrograms per liter is a significant error.

Monitoring Frequency: Your permit states how often you must sample—daily, weekly, or monthly. The number of samples you collect during the reporting period must meet or exceed this requirement. If you collected fewer samples than required, note the shortfall; failing to meet the minimum monitoring frequency is itself a violation.

Quantity or Loading vs. Concentration: Some parameters are reported as concentration (mg/L), others as mass loading (lbs/day), and some as both. Mass loading is calculated from concentration and flow. Know which your permit requires for each parameter.

Monthly Average and Daily Maximum: Most NPDES permits set two limit types. The monthly average limit applies to the arithmetic mean of all samples collected in the calendar month. The daily maximum (or instantaneous maximum) limit applies to any single sample result. Both must be compared to permit limits separately.

Exceedance Notation: If any reported value exceeds the permit limit, you must clearly mark it as an exceedance on the DMR. Many forms use an asterisk or a separate exceedance column. Never leave this blank or unmarked—intentionally hiding an exceedance can result in serious legal consequences.

Calculating Monthly Averages

To find the monthly average for a parameter, add all valid sample results for that parameter collected during the month and divide by the number of samples. Only use results from samples collected and analyzed under your permit's approved methods. If a result is reported as a non-detect below a laboratory method detection limit, consult your permit or state guidance on how to handle it—common practice is to substitute half the detection limit or zero, but your permit or state rules govern.

What Happens When You Find an Exceedance?

Identifying an exceedance on a DMR triggers a specific set of obligations beyond simply marking the form.

1. Immediate oral notification: Most permits require you to notify the regulatory agency by phone within 24 hours of becoming aware of a violation that causes or threatens to cause harm, or within the timeframe your permit specifies.

2. Written report: A written report describing the violation, its cause, and corrective actions taken is typically required within a short window—often five days—though your specific permit controls the deadline.

3. Root cause investigation and corrective action: Document what caused the exceedance and what you are doing to prevent recurrence. Regulators look favorably on proactive corrective action.

4. Mark the DMR accurately: Sign and submit the DMR on time even if it shows violations. Late submission on top of a violation compounds your compliance problems.

Recordkeeping Requirements

NPDES regulations generally require that monitoring records, including lab reports, chain-of-custody forms, calibration logs, and copies of all DMRs, be retained for a minimum of three years from the date of the report or the date the data were collected. Your state may require a longer retention period, and your permit may specify additional requirements—always check both. Store records in a way that keeps them legible, organized, and retrievable during an inspection. Inspectors can and do request records from prior years.

Best practice is to keep hard copies in a labeled binder organized by parameter and date, and to back up digital records in a secure location. Never alter a monitoring record after the fact; falsification of records is a federal and state crime.

Compliance Calendar

A compliance calendar is a simple scheduling tool that lists every reporting and sampling deadline required by your permit for the entire year. It should include DMR due dates, sampling dates, inspection dates, and records retention milestones. Post it in the control room and review it at the start of each month. Missing a deadline is far easier to prevent than to explain after the fact.

Safety Reminder

When collecting effluent samples near discharge points or wet wells, always wear appropriate PPE: chemical-splash safety glasses, nitrile or chemical-resistant gloves, and slip-resistant boots. Be aware of slippery surfaces and confined-space hazards near wet wells. Never enter a confined space for sampling without following your facility's confined-space entry program, including atmospheric testing and a trained attendant outside.