Almost every month there are announcements of yet more areas of the world that face hazards from natural contamination of groundwater by release of arsenic from whichever minerals host it in sediments. In Bangladesh alone, the WHO estimates that tens of million people are at risk. Although large tracts of the US and other rich countries do have arsenic levels in groundwater that are above the maximum recommended for safety, the crisis is one that most severely affects some of the world’s poorest and most populous countries. To help solve this massive public health problem, the National Academy of Engineering is offering the Grainger Challenge Prize for Sustainability, a sum of US$1 million, to the individual or individuals who design and create a workable and cheap water treatment system that anyone can use for arsenic-contaminated groundwater in Bangladesh, India, Nepal, and other developing countries. The most likely cheap remedy lies in the use of iron hydroxide as a means of absorbing dissolved arsenic, but several other candidates, including coal fly ash and limestone, together with biological precipitation, have recently begun tests.
Incidentally, the action in the UK against the Natural Environmental Research Council, for negligence in failing to analyse for arsenic in Bangladesh groundwater in the early 1990s, on behalf of 400 Bangladeshis affected by arsenic poisoning, recieved the legal go ahead to appeal against an earlier decision by a British court to throw out their case. My thanks to John McArthur of University College London for this news.
Drilling into the San Andreas Fault?
It seems that in order to really get a feel for the physical and chemical processes involved in faulting, drilling into an active one is a good idea, or at least that seems to be the driving motive behind the SAFOD (San Andreas Fault Observatory at Depth) project of the US Geological Survey (Cohen, P. 2005. Journey to the centre of a quake. New Scientist, 5th February 2005 issue, p. 42-45). It might make sense, because pressures of pore fluids near active faults seem likely to exert some influence over whether a fault segment moves or not. Overpressured fluids can serve to lubricate the otherwise sticky fault surface. In the case of the San Andreas, activity is fragmented. Detailed monitoring of microseismicity near Parkfield, California revealed that a mere 100 x 100 metre patch on the fault plane was responsible for much of the activity. It lies about 3 km down, just within reach of oil-drilling technology. In fact the Parkfield segment is one of the shallowest active zones on the whole fault.. There are already holes in place, drilled to 2 km to host monitoring instruments, and new drilling methods eventually will allow sideways puncturing of the fault plane so as to install more. But even sophisticated drilling is still largely a blind operation, which inevitably hits snags, and there have been several in the SAFOD project. One severed communications with existing instruments. The general idea behind SAFOD is that fault displacements propagate from small “nucleation” sites. The length of the fault that undergoes displacement during one movement is generally correlated with the magnitude of the resulting earthquake. Parkfield seems to be such a nucleation site, but since the earthquakes associated with it are of small magnitude chances are that interfering with it will not accidentally release a large one. The benefits, set against the risks and undoubtedly high costs, are mainly that even the tiniest motions can be monitored. Surface monitoring of course cannot investigate pore fluids and other phenomena, and nor can it detect events less than magnitude 0.5, whose energy is absorbed by rock before it can reach the surface. By monitoring what happens in events with a range of small magnitudes, it ought to be possible to develop earthquake theory to the point where at least the role of fluid pressures, the feedback between earth vibrations set off by one event and movements on a later one, and the effects of mineralogy on friction that resists movement can be assessed. Whatever, once in place, the wait for useful results to accumulate could be a long one, so SAFOD is planned for a 15 year lifetime
More information on SAFOD is available at http://www.earthscope.org/safod/index.shtml