Nitrate in well water

You cannot see it, taste it or smell it, boiling makes it worse rather than better, and in an agricultural county it is the contaminant most likely to be in your well without anybody knowing.

Why this county in particular

Nitrates from hog and poultry waste, and from fertiliser on crops, are the top chemical contaminants in shallow agricultural aquifers across North Carolina. Robeson County is farming country at a scale worth stating plainly. From the 2022 USDA Census of Agriculture, this county holds:

• 331,520 hogs and pigs, eighth in the state by sales.
• 9,348,864 broilers and other meat chickens.
• 196,425 acres of cropland, mostly soybeans, corn and wheat, all of which are fertilised.

Robeson ranks fourth in North Carolina for the total value of agricultural products sold, and 81 percent of that is livestock and poultry rather than crops. That is the ground your well draws through.

The nearest hard measurement comes from Duplin County rather than this one. A monitoring study there found 26 percent of 84 shallow groundwater wells around sprayfields exceeded the EPA drinking water standard of 10 milligrams per litre. Duplin is a different county with its own geology, so that figure is not a prediction about your well. It is a reason to find out about your well.

What it does

The 10 mg/L standard was not set for taste or for adults. It was set to prevent infant methemoglobinemia, known as blue baby syndrome, in which nitrate interferes with the blood's ability to carry oxygen. It is acute and it can be fatal. Babies under six months are the group at risk, and pregnancy is the other reason health guidance says to test.

Which wells are most exposed

• Shallow wells. Nitrate travels down from the surface, so the shallower the well the more exposed it is. This is Coastal Plain sand aquifer country, where wells are generally shallower than in the rest of the state, which is convenient when you are paying to drill one and less convenient here.
• Wells near cropland, sprayfields or animal operations.
• Older wells, and wells with damaged casing or a poor seal, where surface water gets in near the top rather than filtering down.
• Wells that have been flooded, which is a separate problem arriving through the same opening. See what to do if your well flooded.

Testing

Nitrate is not part of every standard well test, so ask for it by name. Private well testing in Robeson County goes through county environmental health, and fees and available panels vary from county to county, so they are the ones to ask rather than a page on the internet.

Worth testing when: someone is pregnant or there is an infant in the house, you have never tested, it has been more than a year, the well has been flooded, or you have bought the property and are taking somebody else's word for it.

If the result is over the limit

Nitrate is not fixed by chlorination, by a carbon filter, or by boiling. Treatment that does work means reverse osmosis, ion exchange or distillation, and which one suits depends on the level and the household. Sometimes the better answer is not treatment at all but a deeper or better-sealed well, and that is a conversation with a contractor rather than a filter salesman.

What that costs is on the cost page.

Sources: North Carolina private well nitrate research and groundwater monitoring around sprayfields in Duplin County; EPA drinking water standard for nitrate and its basis in infant methemoglobinemia; USDA Census of Agriculture 2022 county profile for Robeson County. Figures describe the region, not your well. Only a test does that.