Which of the following is NOT a non-point source of pollution?

Storm sewer discharges are considered point sources of pollution because they are discrete conveyances that deliver wastewater or stormwater directly to a water body. This means that the pollution can be traced back to a specific source, such as a pipe or drainage system. Non-point source pollution, on the other hand, is diffuse and comes from multiple sources across a broader area.

Agricultural runoff, septic systems, and atmospheric deposition all fit into the category of non-point source pollution. Agricultural runoff occurs when rainwater washes fertilizers, pesticides, and other contaminants from agricultural fields into adjacent water bodies. Septic systems can contribute to pollution as they release effluents over a wide area, especially when they malfunction, but they aren't directly associated with a point of discharge. Atmospheric deposition refers to pollutants that are deposited from the atmosphere, such as acid rain or particulate matter, which also come from numerous sources rather than a single identifiable discharge point.

Thus, storm sewer discharges are the only option that constitutes a clear point source of pollution.