It’s a no-brainer that acing a physics exam won’t affect one’s grade in history class, yet it’s frequent to assume that a water test, not otherwise specified, covers all the potential bases. A common water test is for coliform bacteria, the presence of which would indicate a leaking septic field, or/ and manure runoff. If the lab gets back to you with a result of ND or “non-detect,” it’s great news, but it is by no means a clean bill of health.
Wells, no matter how deep, are vulnerable to contaminants that originate on the surface. Pesticide residues, nitrates from commercial fertilizers, benzene and other dissolved-phase petroleum compounds, and commercial degreasers are but a few of the things that can end up spewing from our faucets.
Across northern NY State, around 40% of residents rely on wells for drinking water. We are very fortunate in our little corner of the planet to have such easy access to fresh water. Broadly speaking, aquifers in our region are shallow, with the water table less than 50 feet below ground. In fact, dug wells still exist at some rural homes.
By contrast, it’s often necessary to drill 300 feet or deeper to find water in parts of the Southwest and Midwest. Another blessing is that our aquifers are replenished annually. In some Midwestern states, aquifers are being depleted faster than they can recharge, and it’s not uncommon for wells to run dry and need replacement or overdrilling to deepen them.
While no well is pollution-proof, a dug well is at higher risk for contamination. A drilled well is more secure, but regardless of depth, it’s still vulnerable to surface pollutants near the wellhead. There’s no such thing as a well in “solid rock,” which by definition is a dry hole in the ground. Water flows into boreholes at various depths through bedding planes in sedimentary formations, and joints and fissures in all rock types. Contaminants are sometimes drawn into wells along these channels.
There are three general categories of water-quality measurements: biological, inorganic, and organic. A typical biological marker for potential water-borne pathogens is the presence of coliform bacteria. Some coliforms are harmless, occurring naturally in soil, but fecal coliform bacteria live only in the digestive tracts of warm-blooded animals. Their presence indicates pollution from septic systems or animal manure.
Contaminants such as lead, arsenic, cadmium, and copper are called inorganic. So are nitrates, which can sicken or kill infants, as well as indicating that pesticides could be getting into the water. Many older pesticides contained lead and arsenic, which do not break down, and some farms still have high levels of these metals in the soil. Cadmium and chromium, released from smelting operations and when colored paper is burned, can leach into the groundwater too.
Hardness (from calcium and magnesium), as well as iron, chloride and sulfur are natural inorganics that can leave deposits and stains, or cause a bad smell or taste. At very high levels, some of these elements can be toxic.
“Organic” is a misleading term, because while organic food is good, consuming organic chemicals is definitely not. Pesticides, degreasers, gas, oil, antifreeze, and many paints are all organic chemicals. How do these get into our water? It’s shockingly easy to pollute groundwater here in the Northeast where it rains a lot and the distance to groundwater is relatively small. Leaky fuel tanks, tank overfills, garage floor drains, and even surface spills can contaminate wells.
We’re told oil and water don’t mix, but that’s a partial truth: they don’t mix much, but enough to badly pollute water. Benzene, a constituent of gas and diesel, is 0.018% water soluble. Given that the allowable limit of benzene in drinking water is 0.07 parts per billion (ppb), the concentration of benzene near a gas spill could be something like 180,000 ppb! Fortunately, the odor threshold for benzene is 50-100 ppb, so one would never drink benzene at that concentration.
Paint thinners and degreasers that get washed down home drains easily enter groundwater through septic fields and find their way into kitchen sinks. Many chlorinated solvents like dry-cleaning fluids have high odor thresholds, meaning one could drink high levels over time without knowing it. Fuel oil spilled in a garden could disappear in one season if one added manure and rototilled often, but underground with little oxygen, chemicals take decades, even generations, to break down.
Because groundwater is always (slowly, in general) flowing, contamination often takes months or years to show up. A corollary to that is the fact that contamination from one property can and does migrate onto others’ properties.
Testing for organics is complicated: for example, checking for solvents, pesticides, and antifreeze all require different tests. It can also be expensive. The cost of testing for oil and most solvents varies, but may be in the $50-$60 range. For pesticides, though, it can run many times that amount.
Many contaminants can be removed with the right filtration system, but upkeep is expensive. Occasionally, drilling a new well upgradient from the contaminated area is more cost-effective, and safer, than perpetual filtration.
The take-home message is that anything that goes onto the ground or down the drain can into our drinking water. National Groundwater Awareness Week is March 7-13, 2021, and World Water Day is March 22. Let’s work together to keep our well water – and that of our neighbors – well.
A former Cornell Extension educator, Paul Hetzler’s well is drilled in coarse-grained igneous rock. He takes clean water from granite, but never for granted.