Which scenario represents a high-risk non-point source site?

Which scenario represents a high-risk non-point source site?

• A. Steep agricultural field draining to stream without buffer
• B. Urban parking lot with stormwater controls
• C. Flat pasture with buffer strip
• D. Rural woodland with narrow riparian zone

Answer: (A)

The main idea is that runoff risk rises when water from land has a direct, untreated path to a stream and there’s little to stop sediment, nutrients, and contaminants from being carried along. In this scenario, a steep agricultural field drains straight into a stream with no buffer strip. Rainfall quickly runs down the slope, eroding soil and carrying fertilizer, pesticides, and sediment straight into the water because there’s nothing vegetation or soil to slow, filter, or infiltrate the runoff. That combination—steep slope plus no vegetative filter and direct channel to a waterbody—creates high potential for non-point source pollution. Compared to the other situations, the urban parking lot with stormwater controls has mechanisms to trap or treat runoff, reducing risk; the flat pasture with a buffer strip provides vegetation that helps trap sediment and absorb nutrients, lowering risk; and the rural woodland with a narrow riparian zone still offers some natural filtration and shade, though not as protective as a wider buffer. The lack of a buffer and steep slope in the first case makes it the highest-risk scenario.

The main idea is that runoff risk rises when water from land has a direct, untreated path to a stream and there’s little to stop sediment, nutrients, and contaminants from being carried along. In this scenario, a steep agricultural field drains straight into a stream with no buffer strip. Rainfall quickly runs down the slope, eroding soil and carrying fertilizer, pesticides, and sediment straight into the water because there’s nothing vegetation or soil to slow, filter, or infiltrate the runoff. That combination—steep slope plus no vegetative filter and direct channel to a waterbody—creates high potential for non-point source pollution.

Compared to the other situations, the urban parking lot with stormwater controls has mechanisms to trap or treat runoff, reducing risk; the flat pasture with a buffer strip provides vegetation that helps trap sediment and absorb nutrients, lowering risk; and the rural woodland with a narrow riparian zone still offers some natural filtration and shade, though not as protective as a wider buffer. The lack of a buffer and steep slope in the first case makes it the highest-risk scenario.