***Q. It seems like there have been several cases in Fairbanks where contaminated soil has been discovered and the strategy has been to haul it somewhere and cover it with black visqueen… What's up with that? After reading up on bioremediation of hydrocarbons, it seems really simple to encourage "bugs" to rather quickly eat up the contaminants. Is this impression incorrect? I know that cold weather hampers things, but in several of the studies I read, reductions of >90% was achieved in a matter of 3 - 4 months.
A. There are several reasons for the piles of hydrocarbon-contaminated soil. Contamination might be discovered during an excavation or if it might be excavated on purpose. Either way, it must be covered to minimize infiltration and placed on a liner to keep leachate out of the groundwater. If it was to be sent off site, it may be loaded directly into trucks or railcars. Why not just treat on site? This takes time, real estate, and permission of the regulators. A plan must be approved and the plan will always call for periodic monitoring. It will also define the final cleanup levels that are acceptable. Some hazardous components, such as lead, will not degrade. Just spreading the contaminated soil, and "landfarming" it by tilling, will reduce hydrocarbons, especially if they are below a certain level already. Finally, adding certain nutrients will speed the process. If your original sin was small, and you are allowed to do this in situ, it is usually economical. There the trick would be getting a permit and this would involve a risk assessment. If there are higher levels of contamination, or the risk assessment was not favorable, you would be required to place the soil on a liner before you do all that. If you can get a permit, the only real question is economics. However for governments and sometimes industry if they have insurance, the initial costs are "free money" from grants or settlements and often-free money that has to be spent this fiscal year. While the ongoing costs of maintaining and monitoring a site are "real money" that must come out of a maintenance budget.

Q. I guess that I'm a bit confused by the idea of one sample being done on a pile of soil to determine whether or not it is contaminated. It seems like a large volume to be approximating with one tiny sample. (Then again, I've thought about it, and I can't think of a better way to do it.)
A. Usually the permitting agency will set a standard, so many samples per so many cubic yards or per pile. They often do not allow statistics, but use the highest value for the pile.

Q. I would like to know how regulatory agencies decide if natural attenuation is an acceptable form of treatment. I'm sure that many companies forced to take remedial action to reduce contaminant levels would love to say just leave it, natural attenuation will take care of everything. I guess I'm just wondering what protocol is used to decide if it is or isn't a viable treatment alternative.
A. That is set by regulation, but almost all of them permit a risk assessment. What levels are “acceptable” may be set by regulation, but more often is the judgment of the regulators. Sometimes it is impractical to remediate a site, and sometimes it will take so long to get the money and do a remediation, that natural attenuation will reduce the levels about as well.

* Q. I have a question about the addition of special microbes to the soil population for the removal of contaminants. Wouldn't the addition of a foreign organism to a environment be a potential ecological hazard? For example, that organism will out-compete the resident population due to substrate specificity. Right? But what if that organism were to invade neighboring soils and outcompete the population adjacent to the treatment location for the resident substrate.
A. Could be a good plot for a science fiction novel. The organisms in the soil have been out competing other organisms for a long time. They are specialized for that soil, pH, moisture, local organics, etc. The problem is usually just the opposite; you can't get the fancy bugs to grow because the locals out compete them.

* Q. Natural attenuation, my site remediation topic, seems alot like a do nothing alternative, but the literature goes out of the way to describe it as otherwise. What's the difference? Monitoring type(s)? I was a little dissapointed when I started doing my reading on the process - I was hoping for something with a little more action (natural doesn't necessarily have to mean passive, as it seems to in this sense).
A. You bring up an interesting issue regarding "do nothing" versus "natural attenuation." The regulators and the affected public will almost never accept a polluter "doing nothing." But they will sometimes approve "natural attenuation with monitoring."