Obviously it will vary by soil type and rain. Let’s just say a catch tub of 6 quarts of dirty motor oil is spilled onto your backyard lawn. Your soil is a reasonably well drained standard sandy loam in a mid-Atlantic weather area. Are we talking months, years, decades? Does it eventually reach the water table?
Depends on the water table. In the Midlantic states the water table is pretty high in the lowlands. Rainwater would carry some of it down rapidly. A lot of it may run off with rain water.
I dumped two quarts on the lawn, couple years until the grass grew back … clay/loam soil, annual rainfall rates that’ll make your back teeth float.
You can see 90% biodegradation of oil in 3 months with a relatively low initial concentration (5%) and highly organic soil. Spilling 6 quarts all in one place into a sandy soil will take significantly longer to get to that point, probably more on the order of years. As noted, more of it will probably run off than the amount that degrades.
Motor oil doesn’t penetrate soil too efficiently; it binds up on any organic material in the soil. That won’t slow it down if you have pure sand, but in loamy soil with some organic content, you probably won’t see significant penetration. It might get down to some water table if it’s very shallow (a few feet in depth), but it won’t be drinking water. However, dirty oil will probably be contaminated with lighter hydrocarbons such as MTBE and BTEX (benzene, toluene, ethylbenzene, and xylenes) which move much faster in soil and are more resistant to biodegradation. Dirty oil will probably also have heavy metal contamination, which not only won’t biodegrade but will also likely inhibit biodegradation of the oil.
This popped up this morning and seemed timely.
Exposing Environmental Charlatans Rant - Wranglerstar paints his fence posts with used motor oil.
Cool video Astro. I too use old motor oil to protect machinery from rusting and on wooden posts. My father used creosote but as Wranglestar says, it isn’t easily available these days.
I don’t do it often and I do like protecting the environment so there is no wilful sloshing around and spilling oil on the ground.