Ever feel a strong need to know what happens to stuff you pour down the drain? I didn’t think so. But if your water comes from a well and your waste goes to a septic tank, this may be of interest to you.
A while back, my job dealt with groundwater contamination (cleaning it, not causing it). When polluted groundwater is found in the vicinity of a domestic well, it’s standard practice to place test wells between the pollution and the house. A test well is a sort of early warning device in case pollutants migrate toward a home. Water from new ‘sentinel’ wells is analyzed to prove it’s clean to begin with.
Sadly, now and then we found harmful chemicals unrelated to the problem at hand in a new test well. Chemicals from paint thinner and degreasers were common, as well as from auto fluids and household cleaners. It was a case of what went down to the septic tank came back up to the tap—and people were drinking it. As you might expect, fecal coliform bacteria were often present in the water, too.
Nearly a quarter of US households—even more in the North Country—have septic systems. Sewage flows into a septic tank where solids settle out and are partially broken down by bacteria. Liquid flows out the top to the leach, or drain field where it percolates into the soil, a critical element in septic systems. The ideal soil is deep loam with enough porosity for “good guy” bacteria to get oxygen they need but not so coarse that liquid flows away too fast for bacteria to break down remaining waste.
Unless you’re building your own house, you can’t choose the soil for the drain field. But it’s good to know that clay soil or very coarse soil reduces the effectiveness of a septic system, potentially allowing sewage effluent to leach—and be washed by rain—down to groundwater.
If a drain field in clay or gravel soil needed replacing, one could expand it to improve septic system performance.
Water use greatly impacts septic system function. The less water a household uses, the better the system works and the less likely it is unwanted stuff will make it to groundwater. Also, as water use increases, so does the area (zone of influence) from which the well draws. Say 500 gallons/ day lowers the water table in a thirty-foot radius and 5,000 gallons/ day draws down 200 feet away. If the well is 100 feet from the drain field, groundwater beneath the field is constantly moving toward the well.
A word on wells. OK, several. Deep wells are less vulnerable to contamination than shallow ones, but none are immune. Well bores are “preferential flow pathways.” Water (like me) takes the path of least resistance. It’ll flow merrily down the outside of a casing no matter how deep it goes. And no one has a well in “solid rock.” They’d have a very skinny, very dry hole in the ground if that was true. Groundwater flows through fractures in rock to reach a well, in some cases traveling miles per week.
The most important thing you can do to protect your well is to avoid putting chemicals down the drain, because what goes down could come up.
Paul Hetzler is a natural resource and horticultural educator with Cornell Cooperative Extension of St. Lawrence County