New 2013
Q. I’d like to know more about your comments in submodule 6B p1 Construction of Underground Tanks; Specifically:
Soil chemistry: pH, sulfide, resistivity, water table and soil moisture
Nearby metallic structures
Backfill: special bedding (coating of tank), compaction (especially lower quadrant)
Do you have some of the equations governing these principles? Especially functions for the design aspects of anchor and lower quadrant compaction.
A.
In reverse order: The anchor is straightforward – just assume the tank is in water and provides enough weight to hold it down. The steel tanks have anchor points that are strong enough, so it’s a matter of concrete design. The compaction refers to settlement around and above the tank. It is difficult to compact under the lower quadrant of the tank, especially if the excavation hole is not wide enough. Insufficient compaction in this area can lead to pipes being torn from their sockets and other problems – besides a hole in the pavement. Large and Sharp rocks can damage the coating, so sand is sometimes specified near the tank, but with modern epoxy coatings, small gravel is OK. The rest all refers to corrosion protection. That topic would be a separate course, enough to realize it is important in some soils. Some nearby electrical devices can bleed current and cause corrosion (maybe) but surely mess up an impressed current cathodic protection system and test leads.
New 2009
** Q. At work, I have had a few calls from clients wondering if my company does any “tank testing.” Honestly, I’ve never really been sure what they meant by that, so I always say no. I like the way you broke down the components of what is needed to make a “good tank.”You mention that ASTs are the way to go with regards to environmental stewardship, since they are easier to monitor for leaks. But what about issues that occur with cold weather- does the extreme cold break them down more than USTs? And what about fire hazards? I don’t think I would want a raging brushfire near my AST. I guess there are tradeoffs between the two.
A. That’s it, a tradeoff. Since the history of AST’s for small units is less, we don’t know if they are more prone to corrosion or damage, just that we will see it. Note that large ASTs must be drained from time to time and the floor inspected for leaks – which is not easy to do.
OLD
**Q. I know there are different tanks used for different purposes. Could you tell me how different are tanks to store petroleum products from hazardous materials? I mean what kind of tanks they use and lining they used from inside? Could you please direct me a site, which gives the information in detail?
A. It depends almost completely on the nature of the hazardous material. Usually the biggest threat is corrosion, so the chemical nature of the material is most important.
* Q. From the material provided in the submodule it is clear that aboveground tanks are far more easier to monitor. Even if real estate is taken into consideration I think above ground tanks are a winner. What is the value of the land which has an underground tank containing hazardous material?
I also think aboveground tanks can contain hazardous material in far more convenient way than underground tanks and also they might have lighter regulations.
* Q. It seems to me that most of the hazardous materials are stored in underground tanks. But why?
A. The trend it towards above ground tanks for the future. The only real benefit of them is that it is easier to monitor leaks, but that is a large benefit.