How Does Agriculture Pollute Private Wells?

Key Takeaways:

• Runoff is the primary way agricultural pollutants enter well water supplies. Farming practices can contaminate well supplies with:
  • Nitrates
  • Bacteria
    
  • Heavy metals
  • Pesticides
• To understand your risks from potential agricultural pollution as well as what to do about it, you should test your well water.
• Depending on your well water’s specific contaminants, activated carbon filters, nanofiltration, and reverse osmosis can help treat water with agricultural contaminants

What Is Agricultural Runoff? 

Agricultural runoff is water from irrigation, rain, or snowmelt that does not soak into the soil but instead travels along its surface into streams and other water sources, collecting all sorts of contaminants in the process.

Agricultural contaminants also leach or seep into the soil and penetrate down to groundwater sources, like aquifers. Wells draw their water from aquifers.

What Are Biosolids?

When wastewater is processed, solids are separated from liquids, with the solids then being treated to produce a nutrient-rich biosolid. They often sell this “sewage sludge” to farms to be used as fertilizer. 

Wastewater treatment plants in rural areas also dump a lot of contaminant-rich sewage sludge directly into potential water sources like rivers and streams.

Drinking Water Contaminants from Agricultural Pollution

Agricultural activity can pollute well water with the following contaminants:

• Nitrate (from fertilizer and manure)
• Coliform bacteria (in areas near livestock operations)
• Pesticides
• Emerging contaminants (like PFAS from biosolid applications)
• Heavy metals (often found in pesticides and fertilizers)
  

Nitrates (& other nutrients)
High nitrate levels can be harmful, particularly to infants and pregnant women. Nitrogen and phosphorus-rich fertilizers make up a large part of the runoff that leaches into water sources and elevates nitrate levels in drinking water supplies.

Surveys by the USGS found that one quarter of the shallow wells tested underneath or nearby heavily farmed areas were contaminated above the EPA limit (10 PPM). Almost three quarters of the communities with nitrate levels in drinking water at or above 10 PPM are found in only five states: Arizona, California, Kansas, Oklahoma, and Texas.[1]

Coliform Bacteria
In addition to nutrients like nitrates and phosphorus, livestock waste from sprawling animal feed farms can potentially introduce harmful coliform bacteria into well water supplies.

Heavy Metals
Heavy metals (like cadmium, arsenic, lead, etc.) enter well water sources largely due to their presence in certain fertilizers. Analytical testing of some industrial-grade fertilizers have revealed concerning levels of arsenic, cadmium, and lead.[2] Lithium is also found in fertilizers and potash mixtures.

Analytical testing of both glyphosate-based and non-glyphosate-based pesticides revealed elevated levels of arsenic, chromium, cobalt, lead, and nickel—heavy metals all linked with toxic effects in humans.

Pesticides (incl. herbicides, insecticides, & fungicides)
Pesticides can contaminate groundwater sources by seeping into the soil. They spread easily too, and end up in water sources through rain, runoff, and wind. These chemicals can stay in groundwater for decades, even if efforts are made to reduce pesticide use above ground.

Traditionally, insecticides have been considered more harmful to humans than herbicides because of the biological differences between humans and plants. Nevertheless, organophosphate pesticides (which include both herbicides, like glyphosate, and insecticides, like chlorpyrifos) are considered the most harmful pesticides to humans.[3] Some of the more concerning pesticide compounds include:

• 1,2-Dibromo-3-chloropropane (dibromochloropropane or DBCP, discontinued but environmentally persistent)
• Atrazine
• Acephate
• Chlormequat (a recently introduced pesticide)
• Chlorpyrifos
• Dimethoate
• Glyphosate (or RoundUp, an organophosphate)
• Paraquat
• Phosmet

Emerging Contaminants (like PFAS and PPCPs)
PFAS (per- and polyfluoroalkyl substances) end up in wastewater streams nationwide due to their presence in our everyday lives. Because the biosolids that are commonly sold to large farming operations are a product of wastewater treatment, PFAS (which are prohibitively costly to fully remove) are introduced into the soil that grows the food we eat, and into ground and surface waters we drink.

Other emerging contaminants, including PPCPs (pharmaceuticals and personal care products) end up in wastewater streams, which are then used to make biosolids. Likewise, hormones and antibiotics used in the rearing of livestock can find their way into drinking water supplies.

Other Concerns
These include total suspended solids (TSS)—or sediment. TSS can carry bacteria and other contaminants.

Agricultural practices also impact water chemistry: pH variations, which can lead to acidic or alkaline conditions, can affect water quality and the effectiveness of water treatment.

Which Agricultural Contaminants Should I Be Most Concerned About?

Protecting well water from agricultural pollution is a chief concern, namely because wells are unregulated and solely the responsibility of the well owner.

Testing your water once a year is highly recommended. If you live close to factory farms, you should consider testing for:

• Nitrate (especially with newborns and small children in the home)
• Coliform bacteria
• Heavy metals
• PFAS 
• Volatile organic compounds (VOCs), like DBCP
• Sediment (which can overwhelm catchments, promote bacterial growth, and carry other contaminants)

Be sure these contaminants are available in your chosen testing kit. Volatile Organic Compounds (VOCs) are also a contaminant class to test for as some pesticides are considered VOCs. VOCs will volatilize from surface water sources, but some VOC pesticides are persistent in soil and can make their way to groundwater.