• Toxic pollutants are grouped into organics and metals.
• Nonpoint sources are diffuse sources of pollution while point sources are specific points of discharge.

The Environmental Protection Agency (EPA) identifies conventional pollutants as those that may be controlled through effluent guidelines. These pollutants are contained in the sanitary wastes of households, businesses, and industries. Conventional pollutants include:

• Biochemical oxygen demand (BOD),
• Total suspended solids (TSS),
• Fecal coliform,
• Oil and grease,
• pH, and
• Other pollutants as determined by EPA.

EPA identifies 65 pollutants and classes of pollutants as toxic pollutants; of those, EPA designates 126 specific substances as “priority” toxic pollutants, and the list of priority toxic pollutants can be found at 40 CFR 423, Appendix A. Toxic pollutants are particularly harmful to animal or plant life, and they are primarily grouped into:

• Organics (including pesticides, solvents, polychlorinated biphenyls (PCBs), and dioxins); and
• Metals (including lead, silver, mercury, copper, chromium, zinc, nickel, and cadmium).

All other pollutants are classified as nonconventional pollutants. These are any additional substances that are not conventional or toxic that may require regulation, including nutrients such as nitrogen and phosphorus.

Nonpoint sources vs. point sources

Think of nonpoint sources (NPS) of pollution as “diffuse sources” of pollution. The discharge does not originate from a specific point, outfall, pipe, or other specific place. It can result from land runoff or seepage or be deposited from the atmosphere. Snowmelt that picks up contaminants as it moves over and through the ground can be a type of NPS pollution. Eventually, the runoff deposits contaminants into surface waters, such as lakes, rivers, wetlands, and coastal waters. Examples of NPS include:

• Excess fertilizers, herbicides, and pesticides from farms and lawns;
• Oil, grease, and toxic chemicals from industrial sites and energy production;
• Sediment from improperly managed construction sites;
• Crop lands, forests, and eroding streambanks;
• Bacteria and nutrients from animal waste and faulty septic systems; and
• Atmospheric deposits from hydromodification (e.g., dams).

Point sources, on the other hand, are specific “points” of discharge. Common points of discharge include pipes, tunnels, channels, etc. Typical point sources include factories and sewage treatment plants. Sources may discharge one or more pollutants, or “effluents,” to a surface water. Some sources discharge directly into a waterbody, while others treat the effluent before releasing it. In addition, sources may send their wastewater to a sewage treatment plant for treatment.