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Competency Area 7: Non-point source pollution AEM

PO 70. Distinguish between agricultural and non-agricultural NPS pollution and Point Source pollution and the extent and importance of each.

Non-point source pollution is pollution having no well defined source, such as that originating from diffuse land surface areas or the atmosphere. Agricultural non-point sources include things like:

  • Soil erosion (sediment) and runoff and leaching losses of fertilizer nutrients (P, N) and pesticides from intensively cropped land
  • Nutrients, pathogens, and BOD (Biological Oxygen Demand) loss from land receiving manure applications or when livestock have access to streams
  • Spray drift from manure and pesticide applications (e.g., causing odor issues or damage to non-targeted plant foliage).

Non-agricultural sources of NPS pollution result from urban and suburban residential and commercial activities and would include:

  • Sediments, nutrients, pesticides, and petrochemical losses in storm water runoff from impervious surfaces (streets, roads, parking lots)
  • Nutrient and pesticide losses from lawns, gardens, golf courses
  • Nutrient and pathogen losses from on-site sewage disposal systems
  • Sediment losses from active logging areas and construction activities
  • Various chemical and drift losses from traffic and other diffuse commercial activities and dump areas

Sediment from soil erosion and other non-agricultural source losses constitutes the largest non-point pollutant loading on a mass basis and is the most frequently cited cause of surface water quality impairment. Phosphorus and pathogens (Fecal-type coliforms, Cryptosporidium, Giardia) are also frequently the cause of surface water impairments. Although many pesticides are detected at more than 10% frequency in surface water (atrazine, simazine, metalochlor), the concentrations rarely exceed drinking water maximum contaminant level (MCL) limits. Simazine and diazinon are frequently detected in urban areas.

Elevated levels of nitrates (above the MCL of 10 ppm) are frequently found in groundwater, with some vulnerable areas reporting 10 to 20% of wells exceeding the MCL. The percentage of wells exceeding the MCL for nitrate is generally higher in intensively farmed agricultural areas, but can also be high in densely populated urban areas where on-site systems are used on permeable soils. Pathogens are reported more frequently than pesticides in groundwater. Atrazine is the most commonly detected pesticide in groundwater in agricultural areas, whereas simazine occurs more frequently in urban areas.