Introduction

This Fact File provides detail on five conventional pollutants identified by EPA and addressed in effluent guidelines. If your organization discharges wastewater, you must control these pollutants to maintain compliance and avoid enforcement penalties. Best Conventional Pollutant Control Technology (BCT) helps control these pollutants from existing industrial point sources, and BCT limitations are established after EPA considers a two-part “cost-reasonableness” test. Conventional pollutants may also be controlled and regulated through Best Practicable Control Technology Currently Available (BPT) and, for new direct discharge sources, New Source Performance Standards (NSPS). These standards and guidelines factor heavily into National Pollutant Discharge Elimination System (NPDES) permits issued to direct dischargers by EPA and the states.

Background

Section 304(a)(4) of the Clean Water Act (CWA) designates conventional water pollutants, and they are listed at 40 CFR 401.16. These pollutants are separate from the 65 pollutants and classes of pollutants identified by EPA as “toxic pollutants.” All other pollutants that are not conventional or toxic but may require regulation are known as “nonconventional pollutants.” While EPA can designate additional conventional pollutants, the most recent addition to the list was made in 1979. The five conventional pollutants are:

• Biochemical oxygen demand (BOD)
• Total suspended solids (TSS)
• pH
• Fecal coliform
• Oil and grease

Each of these conventional pollutants is subject to limits in NPDES permitting. They are controlled through proper monitoring, sampling, and treatment of wastewater.

Biochemical oxygen demand (BOD)

Biochemical oxygen demand (BOD) is a measure of the amount of oxygen consumed by aerobic bacteria and other microorganisms as they break down organic materials in a facility’s wastewater. This is important to water quality because the relatively small amount of oxygen in waterways, known as dissolved oxygen (DO), is crucial to supporting aquatic life. When a wastewater causes an aquatic ecosystem to begin consuming more oxygen than it produces, DO levels fall and local plant and animal life are negatively impacted. BOD may also be affected by temperature as well as organic material since warmer water (such as thermal wastewater discharges from cooling processes) lowers DO levels.

Total suspended solids (TSS)

Total suspended solids (TSS) are particles that are found in wastewater that may be collected by a filter and exceed two microns in size (smaller particles would be considered total dissolved solids). TSS are mostly inorganic materials such as clay, silt, sediment, or metals, but they may also include organic material such as bacteria, plankton, or algae. While some particles eventually settle, TSS are those that float (i.e., are suspended) either on the water’s surface or somewhere between the water source’s bottom and its surface. In addition to pollutants resulting from industry, erosion and stormwater runoff can contribute to TSS totals. High concentrations of TSS adversely affect drinking water clarity and quality and may serve as carriers of other toxic pollutants that impact human health and the environment.

pH

pH measures how acidic or basic a solution is on a scale of 0 to 14. A lower number indicates greater acidity, a higher number indicates greater basicity, and a pH of 7 is neutral. EPA suggests a pH range of 6.5 to 9 in its criteria for good freshwater quality. Wastewater discharges that cause the pH of a water source to become too high or low can have negative impacts on aquatic life, including increased mortality and reduced biodiversity.

Fecal coliform

Fecal coliforms are bacteria that may indicate sewage contamination and potentially harmful pathogens in a body of water. They come from the feces of humans and warm-blooded animals. Poorly treated municipal sewage, stormwater runoff, and septic systems are common sources of fecal coliform pollutants. The most well-known species of coliform is Escherichia coli, or E. coli for short. Fecal coliform presents health risks related to drinking water, swimming, and eating aquatic organisms, especially shellfish (which are often eaten undercooked or raw). Fecal coliform can also contribute to increased biochemical oxygen demand, another conventional pollutant.

Oil and grease

Oil and grease pollutants may vary greatly in their physical, chemical, and toxicological makeups and can be discharged from many different industries and sources. In addition to the oil and gas industry, common sources of these contaminants include vegetable oil and meat processing facilities. Limits on this pollutant are very strict — in fact, oil and grease is the second most enforced conventional pollutant, behind pH. Method 1664A from EPA is used for testing wastewater for oil and grease contaminants using n-hexane as an extraction solvent.

Applicable laws & regulations

Clean Water Act (CWA) section 304(a)(4)

40 CFR 400–471 — Effluent guidelines and standards

40 CFR 401.16 — Conventional pollutants

Related definitions

Effluent guidelines: Wastewater discharge standards based on the types of contaminants that are common for a particular industry. Effluent guideline standards for direct dischargers are technology-based regulations and are incorporated into NPDES permits issued by federal EPA or the state in which the organization is located.

Point sources: Specific points of pollutant discharge, common examples of which include pipes, tunnels, or channels. Typical point sources include factories and sewage treatment plants. Some sources discharge directly into a waterbody, while others treat the pollutant, or “effluent,” before releasing it.

Key to remember

Conventional pollutants (biochemical oxygen demand (BOD), total suspended solids (TSS), pH, fecal coliform, and oil and grease) factor into NPDES permitting and are contained in the sanitary wastes of households, businesses, and industries. They are regulated by BCT, BPT, and NSPS levels of control under effluent guidelines.

Real world examples

Failing to effectively control effluents such as conventional pollutants can lead to monetary penalties. Two cities in Idaho were subject to $15,000 penalties each after an EPA inspection and records review revealed that the cities’ wastewater treatment plants regularly discharged pollutants into nearby waterways in excess of their CWA permit limits. In addition to the fines, both cities were required to develop and implement new facility plans to ensure future compliance with effluent limitations and requirements.

EPA also recognizes the proactive pollution prevention efforts of water programs. A Kansas processor of milk ingredients was selected to receive a Pollution Prevention Award from the agency for its plant effluent treatment project, which included the construction of an irrigation pond to hold treated water that was previously discharged. This pond further controlled pollutants while also conserving well water resources.