Friday, November 8, 2013

Polluted wells

It’s hard to think of something closer to a personal threat than pollution in the water you drink. It’s also hard to comprehend that several billion people on this planet do not have safe water to drink. When a natural disaster hits, cholera frequently follows – because water sources are compromised. They can be compromised biologically or chemically. The following is an example query in this area of direct personal impact.

Q: Hi,
I'm trying to understand the concept and possible problems with groundwater and thought of a few questions,

So first, say there is a contamination in the groundwater and people notice it in their well, now what would a heavy spring rains do to this? Would it further contaminate it? 

What happens in case of drought, would you think the contamination would wear off?
Thanks.  - Banion

A: Good questions, and like all good questions, the answer(s) fall into an "it depends" range. That is to say, there are a lot of unknowns not clear from your question.

Let me try to answer via possible scenarios:
- A shallow well vs. deep well;
- Fracking may or may not be an issue;
- The pollutant was introduced externally, as opposed to via the well itself;
- The groundwater is recharged or not - a rainy vs. an arid environment;
- The pollutant is chemical (DNAPL/LNAPL/PAH), or it is Biologic.

Keep in mind that mitigation of a groundwater pollutant could fill at least a book by itself; with rare exceptions like some PAH's (Polycyclic Aromatic Hydrocarbons), water pollution rarely "wears off".

Here are just some possible scenarios with comments:

1. The well is shallow, and the pollution does not come from the well itself - in other words it was not introduced via the well:
    If you are just beginning to notice the pollution the odds are that a lead element of a pollution plume has just intersected the well. Continued drawing from the well will just pull more of the plume towards the well-head. In short: it will only get worse. The well may be lost, depending on the nature of the pollutant. If you can identify the source and it can be localized, there are steps you can take to isolate and mitigate the problem - but these steps are usually expensive and complicated.

2. The well is shallow, and the pollution was something inadvertently or deliberately dumped into it:
    Pumping will reduce the concentration gradually - but then you need to dispose of the polluted water that you draw up. If you simply dump it on the ground, it will eventually seep back to the water table, which in many environments is recharged from rain. The earth can function as as filter just so far.

3. The pollutant is biologic in nature (E. coli, for instance):
    Biological systems tend to equilibrate - and persist. If there is something like phosphates and nitrogen for the E. coli to feed on, it will grow. If no support is available (materials to feed on, warm temperatures to propagate in) then the biologics may go dormant - but they can be very long-lived as they wait around for a more favorable growth environment. If the biologic was introduced via the well itself, you would likely have to "shock" it with a chemical like chlorine (think of a complicated swimming pool), then pump until the well water passed a biological safety test - and treat the water that was pumped out, before it is disposed of. If the biologics arrive via the groundwater from a nearby feedlot, say, you may have to abandon the well. Industrial-scale pig farms are a true biological time-bomb.

4. The pollutant is a DNAPL, LNAPL, or PAH:
    A DNAPL (Dense Nonaqueous Phase Liquid) is one of a group of organic substances that are relatively insoluble in water - they will sink in water, are immiscible in but will not dissolve in water. An example would be a ruptured diesel fuel tank. A NAPL or LNAPL is similar, but not denser than water, and tend to remain shallow. These can all be really serious problems, though generally localized, and always very expensive to deal with.
    Instead of writing about this for a few days, let me instead point you at some useful links:

5. The pollutant is radioactive:
    Now we are talking about a Super Fund site, and the billions of dollars being poured into the World War II-era Hanford site in south-central Washington State is an example of this. During and following the World War, radioactive waste was buried in the ground in barrels, and dumped into single-walled tanks at Hanford and other sites around the country. This has happened all over the world. There is a vast region of the Caucasus in Russia and another near Chernobyl in the Ukraine that are both off-limits to human occupation, and the Great Tohoku tsunami of 2011 has made a significant area on the Sendai coast of Japan a dangerous wasteland. Plutonium may be the most toxic metal in the entire periodic table: micrograms can kill. At one point, plutonium was at detectable levels downstream from Hanford in the nearby Columbia River where I occasionally kayak.

6. Deep wells: 
    The water you are drawing is likely fossil - that is the recharge is slow at best, and that water has already been there for a long time (centuries or millennia). The groundwater may or may not be recharged. If you live in Saudi Arabia or Central Arizona, it's the latter case, and the well will eventually dry up. The ground itself will subside (damaging roads and buildings), and any pollution will likely stay with the water wherever it ends up. If you live in the Pacific Northwest of the USA, the groundwater is constantly being recharged via rain and snow. Any pollution will likely reach a steady state and then decline over time as it is diluted, but you may still have to abandon a polluted well. Most municipalities take extensive precautions to protect their reservoir watersheds for this reason.

7. Fracking:
    Fracking is hydraulic fracturing of "tight" geologic formations (like shale) to open them up and release trapped hydrocarbons. The process is technically complex, and involves injecting water and sand - as well as "proprietary" chemicals - at very high pressure into these tight formations. I might add here that if fracking is taking place anywhere near your water well, then your water is only protected as long as the fracking is deep, and the horizon being exploited is not connected to your groundwater - something that is nearly impossible to guarantee. It goes without saying that the fracking wells must be assiduously cemented and sealed - and subsequently monitored. We've all seen the videos of people turning on water in their kitchen sinks and literally igniting them with a match or lighter. 


No comments:

Post a Comment