9.2 Wastewater Characteristics & Abnormal Discharge Identification
Key Takeaways
- Fresh domestic wastewater is gray-brown with a musty odor; black wastewater with a rotten-egg odor indicates septic conditions and sulfide generation.
- Federal pretreatment rules prohibit discharges with a closed-cup flash point below 140 degrees Fahrenheit and discharges with a pH below 5.0.
- A petroleum odor or sheen in a manhole is an explosion hazard requiring immediate LEL monitoring, evacuation of the area, and notification.
- Illicit discharges are traced by working upstream manhole by manhole until the contamination disappears, isolating the contributing reach.
9.2 Wastewater Characteristics & Abnormal Discharge Identification
Exam Focus: Identify physical and/or abnormal characteristics of the wastewater sits in the Monitoring, Evaluation, and Adjustment content area, and ensure compliance of discharge limits… with all applicable local, state, and federal regulations sits in Security, Safety, and Administrative Procedures. In practice they are the same skill: recognize what does not belong and act on it.
Normal Domestic Wastewater
| Characteristic | Fresh domestic wastewater | Septic (stale) wastewater |
|---|---|---|
| Color | Gray to gray-brown | Black |
| Odor | Musty, earthy, slightly disagreeable | Rotten eggs (H₂S) |
| Dissolved oxygen | Present, though low | Zero |
| Sulfide | Low | Elevated |
| Temperature | Roughly 50–75 °F, warmer than groundwater | Same |
| pH | Roughly 6.5–8.0 | May drop as acids form |
The color and odor shift from gray to black and from musty to rotten-egg is the single most useful field observation an operator makes. It means dissolved oxygen has been exhausted, sulfate-reducing bacteria are active, and hydrogen sulfide is being generated — the precursor to odor complaints, crown corrosion, and an atmospheric hazard. Its usual causes are excessive detention time in a force main or wet well, low velocity and deposition in a flat gravity line, or a high-strength industrial load.
Abnormal Characteristics and What They Suggest
| Observation | Likely source | Operator concern |
|---|---|---|
| Milky white | Latex paint, dairy processing, concrete washout | High-strength load; solids and pH |
| Vivid red, blue, green | Dye works, printing, industrial process, or a dye test in progress | Illicit discharge or uncoordinated testing |
| Petroleum sheen or gasoline odor | Fuel release, service station, illegal dumping | Explosion hazard — the highest-priority abnormal condition |
| Heavy white or persistent foam | Surfactants, detergent discharge | Interferes with treatment and with visual inspection |
| Very low pH, corroded concrete | Acid discharge — plating, food processing, battery | Attacks concrete and metal; hazardous to entrants |
| Very high temperature, steam | Boiler blowdown, laundry, food processing | Accelerates sulfide generation; can deform plastic pipe |
| Blood, tissue, unusual solids | Slaughterhouse, medical facility | Pathogen and BOD loading |
| Solvent odor | Degreasing operation | Toxic and potentially flammable vapors |
The Petroleum Case Deserves Emphasis
Gasoline vapor in a sewer produces an explosive atmosphere throughout a connected reach, and manhole explosions have killed operators and members of the public. The response is not investigation first:
- Do not enter. Do not introduce any ignition source — no engines, no non-intrinsically-safe equipment, no smoking.
- Monitor LEL from the surface and evacuate the immediate area if readings are significant.
- Notify the fire department, the utility's emergency contact, and the regulator.
- Ventilate and trace the source upstream only once it is safe.
Federal Prohibited Discharge Standards
The EPA General Pretreatment Regulations (40 CFR Part 403) establish prohibitions that apply to every user of a publicly owned treatment works, whether or not a local ordinance repeats them. No user may introduce:
- Fire or explosion hazards, including any stream with a closed-cup flash point below 140 °F (60 °C).
- Corrosive material, and in no case a discharge with pH lower than 5.0 unless the works is specifically designed for it.
- Solid or viscous pollutants in amounts that obstruct flow or interfere with operation.
- Slug loads — any pollutant, including oxygen-demanding load, released at a flow rate or concentration that interferes with the works.
- Heat sufficient to inhibit biological treatment, and in no case heat that raises the treatment plant influent above 104 °F (40 °C).
- Petroleum oil, non-biodegradable cutting oil, or mineral oil in amounts causing interference or pass-through.
- Pollutants releasing toxic gases, vapors, or fumes in quantities that may cause acute worker health and safety problems.
- Trucked or hauled pollutants, except at discharge points designated by the works.
Beyond these federal prohibitions, the utility sets local limits derived from its own plant capacity, its sludge disposal method, and its receiving water. Significant industrial users hold individual discharge permits with numeric limits, sampling requirements, and self-monitoring reports.
Tracing an Illicit Discharge
When abnormal wastewater appears, the tracing method is systematic and works upstream:
- Document first. Photograph, note the time, and record the observed characteristics. Discharges are often intermittent, so if it is not documented when observed it may not be reproducible.
- Sample where the discharge is observed, following chain-of-custody if enforcement is possible.
- Work upstream manhole by manhole. The contamination is present at every manhole below the source and absent above it. The reach where it disappears contains the source.
- Narrow to the contributing connections. Within that reach, identify the service laterals and check each — dye testing individual connections is the standard confirmation.
- Consider timing. Batch discharges follow production or shift schedules; a site that is clean at 10 a.m. may discharge at shift end. Continuous or automatic samplers capture what spot checks miss.
- Refer to pretreatment staff for enforcement, and document the entire chain of observations.
The operator's role is observation, documentation, immediate safety action, and notification. Enforcement is the pretreatment program's job, but it can only act on what the field crew reports.
An operator opens a manhole and observes black wastewater with a strong rotten egg odor, where the same manhole showed gray-brown wastewater with a musty odor six months earlier. What has changed in the system?
Under the EPA General Pretreatment Regulations at 40 CFR Part 403, which discharge is specifically prohibited from any user of a publicly owned treatment works?
An operator detects a strong gasoline odor while removing a manhole cover during a routine inspection. What is the correct immediate action?