What Is Leachate?

OK – leachate is not generally thought of as small talk at cocktail parties – but it could be! And no – it is not a by-product of leeches. Leachate is basically contaminated water or liquid produced whenever a material is placed on the ground and either precipitation falls on it or it has its own liquid content. Basically, if it touches the ground it probably produces leachate. And let’s face it – everything is made of chemicals! Therefore leachate contains chemicals. So what’s the big deal? Well, there are a couple of issues here.

First, chemical contamination in leachate goes somewhere right? It just goes away. If you use Google Earth© and punch in “away” it will take you about 8,513 miles from Portland, Oregon to Away, China. But that’s probably not where your leachate will end up. Leachate generally travels either down (due to that pesky gravity) or it moves sideways due to the nature of the local soil type and geology. If it goes down, the leachate will eventually hit the groundwater table. If it moves sideways it will eventually pop out in a stream, creek, or other body of water.

Second, there can’t be that much contamination – right? The answer would be “no and yes”.  Unless you dump a lot of material or do it over a long time, a plume of contaminated leachate probably will not be created. However, like we have found in so many other situations, the cumulative effects of small amounts of contaminants can have a long term effect. As science and technology advance we are constantly increasing our ability to detect more minute concentrations of contaminants. At the same time we are constantly revising our understanding of the impacts of even trace quantities of various chemicals on humans and the environment.

So what produces leachate around the home? There are lots of sources. We will start with the most common source - yard chemicals – including the dreaded “ides”. Herbicides, fungicides, rodenticides, insecticides are all collectively known as pesticides because they all kill “pests”. Most folks work on the precept that “if a little is good a lot is better”. We have all seen the neighbor (and that could be you when viewed from across the street!) spreading fertilizer or weed and feed. There are all those little “pills” of chemicals on the sidewalk, in the barkdust, or visible in the grass. Those chemicals dissolve and move into the soil when it rains. Even when these chemicals are applied in the EPA approved amounts and conditions; they are still released into the environment. Some breakdown into other chemicals, some are metabolized by the target “pest”, and some are just plain excess.

Ah you say “but I don’t use those kinds of chemicals. I live off the grid with a septic system, compost pile, and use gray water in my garden”. Hmm. Seems to me the septic system has a drainfield that produces a leachate. In addition to the obvious wastes, the septic tank receives a huge variety of chemicals such as: personal care products (soap, shampoo, cream rinse, hair care products, deodorants, antiperspirants, toothpaste, and mouthwash), excess pharmaceuticals excreted from your body (like estrogen from birth control pills, acetaminophen, ibuprofen, antibiotics, and heart and diabetic medications), detergent, other laundry products, caffeine, heavy metals, and other goodies. Some of these chemicals stay in the sludge in the tank but most of them are designed to be water soluble and can be discharged into the soil via the drainfield leachate.

That compost pile – well, let’s look at what goes in it. Fruits and vegetables, perhaps some fibrous materials like paper napkins and coffee filters, some coffee grounds, and maybe some houseplant leaves and garden debris. As your compost pile “drains” it is actually producing leachate. The fruits and vegetables could have trace pesticides, preservatives, or ripening agents. The paper products have all the chemicals that are part of the paper making process. The coffee filter and grounds have caffeine that is definitely water soluble. The house plants, like outdoor plants, could have fertilizer or pesticide residuals.

And that gray kitchen water system will see many of the products mentioned above that are discharged in the septic drainfield such as soaps and pesticides and chemical residuals you so carefully washed off your food. If you collect bathroom sink and bath water the list gets longer. When that gray water hits the soil it is basically leachate.

So what does all this mean? Where do I go from here? The answer is “don’t panic”. Just be aware of what leachate sources you are producing. Where you can, try to reduce the total chemical load discharged into the soils. As with so much of being green and living a sustainable lifestyle, awareness is a huge part of the answer. We recognize the collective power of us all just doing a little. If you use a gas lawn mower try a little harder not to overfill the fuel tank so it will not spill on the ground. When you garden try to use just a little less chemicals and sweep up any that are on your walk or driveway. Be aware of what you are composting. Remember that essentially all commercially produced foods have some chemicals in them.

Leachate on the larger scale threatens our groundwater and surface waters. Leachate does not simply go away. Granted, there are a variety of physical and chemical processes that can trap or chemically change the contaminants in leachate. But remember the chemicals are still there or have been converted into different chemicals. All life forms are a conglomeration of chemicals. It is just that we need to take a little more effort in how we dispose of chemicals so that other life forms are not unnecessarily exposed to our waste products. So “mind your leachate!”

About the Author

Bill Renfroe is a master level certified hazardous materials manager (CHMM).  He has degrees in chemical engineering and chemistry. He has worked for the EPA, the Corps of Engineers, and Oregon Department of Environmental Quality.  Bill was the EH&S Manager for a large semiconductor manufacturer in the NW.  He was a founding member of the Oregon Association of Environmental Professionals. Bill has over 30 years experience in the environmental arena with more than 10 years of environmental consulting in Oregon and SW Washington.  He is the founder of an environmental consulting business called MyEnvironmentalConsultant.com. For more information about MyEnvironmentalConsultant.com, visit us at the Better Living Show, March 26-28, Booth #917.