Long ago I once read, for my highschool debate team, that 1 gallon of gasoline will make 10,000 gallons of water undrinkable. I’ve been trying to verify this via Google and I’m not having much luck. I’ve read that one gallon of gas can contaminate seventy-five thousand gallons of water, and I’ve read that it can contaminate 750,000 gallons of water. I’ve also read that it can contaminate 2 million to 8 million gallons of ground water. Finally, I’ve learned that MTBE increases the contamination potential by quite a bit and therefore I, being in Michigan where MTBE was banned in 2003, cannot trust the stats that may include MTBE as an additive.

So, I ask this:

Suppose a new gasoline station is opened in Michigan and gasoline leaks into the groundwater. How big of a deal is this. Obviously this depends on the size of the leak.

I’m sure I’m asking the question completely wrong. So be generous.

The question sounds reasonable, though it might need some specification of your definition of bad.

I think you could look up the EPA limits on compounds like MTBE and like the main ingredients of gasolene (benzine, toluene, ethylbenzine, and xylene), and find their fractions in gasoline (is it 1/10 xylene etc), and then divide to get the amount of water contaminated. That is, one kilogram of benzine would put 10 ppb into 100,000,000 kg of water. Sorry but i don’t feel helpful enough to do all this myself.

It is used engine oil, not gasoline. Take a look at this Google search.

I find this claim suspicious though. Engine oil is either spilled accidentally or leaking from car engines all the time. If this assertion was true, there wouldn’t be any drinkable water to be found on the planet by now.

Er…okay, so I’ve got .005 mg/liter as the EPA limit of benzene and Wikipedia tells me that 1% benzene content in gasoline is typical in the U.S. So that’s five parts per million. So I can be really sloppy and assume that 1% benzene = 10 ml/liter of benzene in gasoline and, here’s the sloppy part, if 1 mg/liter=1 ppm, I can roughly say that there’s about 10 ppm of benzene in a gallon of gasoline. (I’m moving between volume & weight, which is a no-no; however, the unit of measure won’t change the ratio.)

So if there’s 10 ppm in a gallon of gasoline and .005 ppm is the limit for the EPA, then…er…if I pour 1 unit volume w/ 1 ppm into 999 units of volume with zero ppm, then the result will be .001 ppm for the whole mix, right? So if my original volume had 5 ppm instead, then that’d give me .005 ppm for the whole mix. So one unit volume of 5 ppm will get me to approx. 1,000 units of .005 ppm.

Thus one unit of 10 ppm will give me approx. 2,000 units of .005 ppm? So one unit of gasoline will push 2,000 units of water to the EPA level of .005 ppm of benzene?

Well, it was hard to follow your math, but I think you’re off by about a factor of 1,000 (I’m guessing your mistake is that 1% is 10,000 ppm). I get 2 million gallons contaminated per gallon of gasoline, if perfectly mixed.

That’s a kind of reasonable back-of-the-envelope calculation, but of course it assumes absolutely perfect mixing of the gasoline into the water. Which doesn’t happen ever or even come close in the real world. First, as you can imagine, leaks and groundwater never get to be physically perfectly mixed-- a leak won’t be perfectly dissipated into the neighborhoods groundwater at exactly the EPA level. More importantly, on a chemical level gasoline doesn’t particularly like to mix with water (you know, like, uh, oil and water), so the leak will percolate through the soil until it hits the water table, then will kind of just sit on top of the water level

[That’s why MBTE is such a problem, by the way-- unlike benzene, MBTE loves to mix with water, so will dissipate a lot farther. It’s not that dangerous, as it smells so bad at even low concentrations that nobody is likely to drink enough to be toxic, but certainly can ruin the well]

So how bad a leak is, as you might guess, depends on the size of the leak, and where it is.

Just remember that underground spills are very hard to find and clean up, so even a small one can be expensive.