How to track underground storage tank leaks?

A viewer asked this question on 8/18/2000:

Hi! I'm writing a mystery in which the victim is killed because he has information about shoddy construction of underground storage facilities used to store petroleum production by-products. The story takes place on the upper Texas coast, not too far away from Houston, so we're dealing with fairly swampy wetlands. The underground storage facilities are in underground salt domes (I think). How would the slow leakage of some of these by-products affect the local ecology? I'm looking for something that would work slowly, killing trees and wildlife, over a 20-year period.

What I'm looking for is general information about the impact of shoddy construction in these storage facilities on swampy wetlands.


JesseGordon gave this response on 8/21/2000:

Underground leaks would follow underground waterways, which although they're hidden from view are pretty consistent and can be tracked. The way you track them is to put a brightly-colored liquid into the tank, and then look at nearby streams for where the brightly-colored stuff comes out. If it's a very slow leak, you'd do it by some chemical taggant instead of color, and then leave chemical detectors in likely streams, instead of looking by eye.

You can also use electrical conductance meters to track underground water flow. You simply stick a metal post in the ground, attached to another metal post 100 yards away by a wire, run a charge, and measure the conductance. That tells you how much water is in the ground; wetter ground conducts better, and wetter ground means more underground flow.

Neither of those work very well in swamps. In wetlands, they'd work fine, as long as there's no standing water. But no one would ever put underground storage tanks (USTs) in wetlands anyway -- water is too corrosive. The main reason USTs fail is because they rust, as my colleague pointed out, which of course would be a much bigger risk in wetlands. Or the USTs could get punctured by some later construction project, in a wetland or not.

The local ecology would only be affected in the areas where the contents of the UST flowed. That's called "the plume", analogous to a plume of smoke from a smokestack. The plume flows underground in this case, but it always flows "downhill," just like flow on the surface. But it's harder to figure out where "downhill" is when it's underground, because it's based on how loose the dirt is, or where rock layers are, etc. But basically, the stuff would flow from the UST to some nearby waterway, and you could track that by the methods above.

If it's deeper underground, it might flow into an underground water table, which would contaminate people's wells. Wells don't use "surface water" (which isn't very clean); they go down, say, 50 feet to an "aquifer", or underground water table. That's cleaner water because it has been filtered by going through 50 feet of the ground. If the USTs are buried deeply, they could contaminate the aquifer that people's wells come from. If they're really deep, they could contaminate deeper aquifers; city wells are usually deeper than people's wells, like to the second level of underground water flow. The same flow concepts apply; it's just even harder to track the flow.

Go see the movie "Erin Brockovich" -- it's all about underground flow of contaminants.

A viewer rated this answer:

GREAT!!! I'm still in the collecting data stage, and this is wonderful information that I'll make good use of. Really appreciate your help!!

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