1.6 Colorado Discharge Permit System (Regulations 61/62), DMRs & Biosolids Reporting

The Clean Water Act reaches the operator through a permit

A drinking water operator answers to Regulation 11. A wastewater operator answers to a permit. Colorado holds delegated authority from EPA to run the National Pollutant Discharge Elimination System, and the state version is the Colorado Discharge Permit System (CDPS), created by Regulation 61 (5 CCR 1002-61). Every domestic and industrial facility that discharges pollutants to state surface waters must hold either an individual CDPS permit or coverage under a general permit.

Two companion regulations set the numbers the permit writer starts from:

• Regulation 31 (Basic Standards and Methodologies for Surface Water) establishes statewide criteria and the methodology for deriving standards.
• Regulation 38 and the other basin regulations assign use classifications (aquatic life, recreation, water supply, agriculture) and numeric standards to specific stream segments.
• Regulation 62 contains the effluent limitations that apply directly to categories of discharges.

Your permit number, your outfall numbers, and the receiving stream segment appear on the permit's first pages. Knowing the segment matters because two identical plants discharging to different segments can carry very different ammonia or metals limits.

Two kinds of effluent limit

Technology-based effluent limits (TBELs) reflect what a properly operated treatment technology can achieve, regardless of the receiving water. For publicly owned treatment works, the federal secondary treatment standard is the familiar baseline:

Water-quality-based effluent limits (WQBELs) are calculated backward from the stream standard. The permit writer takes the standard for the segment, applies the low-flow design condition, accounts for available dilution, and derives the end-of-pipe number needed so the standard is met outside the mixing zone. Ammonia, total residual chlorine, metals, temperature, and nutrients are the parameters most often controlled this way. When both a TBEL and a WQBEL exist, the more stringent one becomes the permit limit.

Colorado's Regulation 85 adds nutrient management controls, and many domestic permits now carry total nitrogen and total phosphorus limits or monitoring requirements that drive the biological nutrient removal operation covered later in this guide.

Reading limit types correctly

• Daily maximum — the highest single measurement allowed on any day.
• 7-day (weekly) average — the arithmetic mean of samples taken in a calendar week.
• 30-day (monthly) average — the arithmetic mean of samples in a calendar month; for bacteria this is usually a geometric mean.
• Mass loading (lbs/day) — concentration converted through the pounds formula. A plant can meet a concentration limit and still violate a mass limit if flow rises, which is why operators track both.

Monitoring, records, and discharge monitoring reports

The permit's monitoring table specifies, for each outfall and parameter, the sample type (grab or 24-hour composite), the frequency, and the analytical method. Composite samples are required for most conventional pollutants because they represent the day; grab samples are required for parameters that change or degrade fast — pH, temperature, dissolved oxygen, total residual chlorine, and bacteria.

Discharge monitoring reports (DMRs) are the legal record of compliance. Colorado permittees submit them electronically through NetDMR, generally by the deadline stated in the permit (commonly the 28th day of the month following the monitoring period). A DMR must be signed by a responsible official — a principal executive officer, a ranking elected official, or a duly authorized representative — under a certification that carries penalties for false statement. The operator in responsible charge is the person who verifies that the bench sheets, flow records, and laboratory reports behind the DMR are accurate before it is signed.

Records retention is a permit condition: monitoring records, calibration and maintenance records, original strip chart recordings, and copies of all reports are kept for at least three years, extended automatically if enforcement is pending.

Bypass, upset, and noncompliance reporting

• Bypass means intentionally diverting waste streams around any portion of the treatment facility. Bypass is prohibited unless it is unavoidable to prevent loss of life, personal injury, or severe property damage, there is no feasible alternative, and the permittee gives notice — 10 days in advance for an anticipated bypass, and within 24 hours for an unanticipated one.
• Upset is an exceptional incident causing unintentional and temporary noncompliance from factors beyond reasonable control. It is an affirmative defense only if the permittee identifies the cause, shows the facility was being operated properly, gives the required 24-hour notice, and takes remedial action.
• 24-hour reporting. Any noncompliance that may endanger health or the environment — including any unanticipated bypass or upset that exceeds an effluent limit, and violation of a maximum daily limit for a parameter the permit lists for 24-hour reporting — must be reported orally within 24 hours of becoming aware of it, with a written submission within five days.
• Sanitary sewer overflows are reported under both the permit and Colorado's spill reporting requirements.

Regulation 64: biosolids

Regulation 64 (5 CCR 1002-64) is Colorado's biosolids rule and implements the federal 40 CFR Part 503 framework. Operators of any facility that treats sewage sludge for land application need to know:

• Site approval and notification. Land application sites must be approved by the Division, with buffer distances from residences, surface water, and wells, and notification before application begins.
• Metals. Ceiling concentrations and cumulative or annual pollutant loading rates apply to arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc.
• Pathogen reduction. Class A biosolids meet density limits for fecal coliform or Salmonella and one of the listed alternatives; Class B biosolids meet a fecal coliform geometric mean limit or a Process to Significantly Reduce Pathogens, and carry site restrictions on crop harvest, grazing, and public access.
• Vector attraction reduction. At least one of the listed options, most commonly 38 percent volatile solids reduction through digestion.
• Annual report. Preparers generally submit an annual biosolids report to the Division by March 1 covering the prior calendar year's quantities, quality, and application sites.

For the exam, connect the pieces: the permit sets the number, the laboratory produces the data, the DMR reports it, and the ORC is accountable for the truth of all three.