By PAUL HETZLER
Here’s a recipe for success: Well-drained loam. Adequate nitrogen. Plenty of organic matter to provide good soil porosity. Yep—just the ticket to remediate an oil spill.
In a former life I cleaned up petroleum spills for a living. Although bulk-storage facilities as well as tanker semi-trucks and train cars were occasionally the source of oil or gasoline spills, it was a real eye-opener to learn how often faulty home-heating oil tanks or even the odd leaky auto gas tank led to significant soil and water contamination.
When three-fourths of “soil” is “oil” you may wonder why cleaning up an oil spill even matters. More than once I heard grumblings to the effect that oil is a natural product that comes out of the ground, so it may as well go right back in.
Granted, there’s a certain logic to that, but with precious few exceptions, oil is found deep in the ground—essentially the other “end” of the earth from the one we live on—in zones far removed from drinking water aquifers. I’m not a livestock expert, but I’m pretty sure horse apples are associated with one specific end of a horse, and real apples are the only kind that should go in the other end. It’s a coarse analogy, though a fair one. Oil comes from in the ground but should not go on the ground.
Dealing with contaminated water is complex and obscenely expensive. So it’s important to deal with oil-soaked dirt—which can be remediated by gardening (Really. More on that in a minute.) —before rain leaches dissolved-phase petroleum into groundwater.
I can hear some collective head-scratching out there (or maybe that’s everyone closing their newspapers), so I’ll clarify that petroleum does actually dissolve in water. It does so to a small degree; we’re talking in the parts-per-million range, but it’s more than enough to make your hot chocolate taste and smell like high-test gas.
In the aftermath of a big spill, petroleum-laced soil can be trucked to an incinerator facility or hazardous-waste landfill. These are costly options, but sometimes there is little choice. For the homeowner or farmer with a modest-size spill, though, it’s possible to “garden” the oil away.
Soil microbes are the engines that drive this “gardening” process, also called bioremediation. Various bacteria and fungi adapt to “run on oil,” using hydrocarbons for food, leaving only carbon dioxide and water as end products.
Oxygen is also critical. Oil breaks down infinitesimally slowly in anaerobic (without oxygen) conditions. I’ve seen the removal of buried fuel tanks that had not been used in 30 or more years, and the stench of petroleum was overwhelming. On the other hand, well-managed “gardens” of contaminated soil can be clean in one or two years.
Organic matter exponentially increases the surface area that our friendly microbes can colonize, and it helps with porosity for oxygen to get in. Finally, a little nitrogen at the beginning of the process gives the microbes a boost to get going.
Because of leaching potential, 8 to 10 inches of affected soil is spread on a foot of clean sand on heavy plastic such as bunker-silo covering. The edges need to be bermed up to prevent runofff. Soil amendments such as compost or manure are worked in, and the “garden” is then rototilled several times per season. Lab analysis, or in some cases field instruments, mark progress until at some point petroleum is no longer detected. Then the soil can be used for any purpose at all so long as it stays on the owner’s property.
Sowing cover crops like buckwheat can help speed up remediation because fungi colonize the root systems, which provide more surface area.
I should say that the New York State Department of Environmental Conservation requires all petroleum spills to be reported to its 24-hour Spill Hotline (1-800-457-7362) within two hours of discovery. Just telling you the law. Bioremediation is approved by the DEC in many instances, and they can help advise and monitor these “gardens.”
See http://www.dec.ny.gov/regulations/4636.html for more details.
Paul Hetzler is a forester and Cornell Cooperative Extension of St. Lawrence County horticulture and natural resources educator.