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Please can I borrow your canoe?

Earlier this year, Nuevas Esperanzas met with representatives of the World Health Organisation to propose a project to investigate the causes and affects of arsenic contamination which had been detected in several wells at the foot of Volcán Telica.  Funding was also requested from several other organisations and while proposals were being submitted and grant applications made, the team began work sampling water sources in the area in order to identify the extent of the problem.

It was a great opportunity to benefit from the expertise of two visiting board members, Liz Buchanan, a hydrologist from the UK, and Josiah Engblom, a hydrogeologist from the US.  Liz and Josiah are used to offering technical advice on our projects from afar so they were both keen to get their feet wet, quite literally, and help get the arsenic investigation underway.  As the work sampling wells moved away from the range of volcanoes and further down the river basin, small ditches and land drains were found where groundwater emerges at the surface.  Arsenic had been discovered in springs flowing into the river system so it was decided that it would be a good idea to check the rivers themselves.  Our experts expected to find that the arsenic would be so diluted by surface runoff that it would not be found at significant levels in the rivers. They were surprised to find that this was not the case.  Arsenic concentrations of over 100 parts per billion (ppb), were recorded in some rivers; the limit for drinking water is 10 ppb.

Liz was the first of our visitors to don her boots and wade in the river to take samples.  But our investigation took us further downstream to the point where the increasingly wide and deep Estero Real river enters the tidal reaches, flanked by mangroves on the river banks.  Here, Josiah made use of his excellent canoeing skills, much to the amusement of a local fisherman, rowing out into the middle of the river at low tide to take a sample.  Even within the tidal reaches, concentrations of over 50 ppb of arsenic were recorded.  Arsenic was also detected in the brackish water of the estuary as far downstream as Puerto Morazán, where the Estero Real flows out into the Gulf of Fonseca.

These discoveries opened up a new line of enquiry for the hydrogeological study.  Having started as a groundwater investigation, sampling of surface water had not originally been included in the project design.  However, our team realised that if we not only measured the arsenic concentrations in river samples but also the river flow, then it would be possible to determine the arsenic 'flux', that is the amount of arsenic flowing through a given section of river.  This addition to the study has helped us to build up a picture of how much arsenic is flowing from the aquifer, through the river system, and out into the Pacific Ocean.  We realised that if we calculated the combined arsenic flux from the different tributaries which flow into the river and compared this total with the arsenic flux downstream it would be possible to find out if there was any arsenic ‘missing’ (assuming that there are no sources or 'sinks' for the arsenic in the river itself).  More than 10 kg of arsenic per day flows out of the area through the Estero Real.  Sure enough, the combined flux of arsenic flowing into the river from the tributaries could not account for the total we measured downstream.  This observation helped to direct our investigation towards parts of the catchment where we had not previously looked for arsenic.

Funding for the investigation has now been approved by the Pan American Health Organisation, Grupo Pellas, Pantaleón, Friends of Students for 60,000 and the Oxford León Association and Trust, and it has been possible to begin a larger, more comprehensive monitoring programme.  From the data gathered, we hope to produce a map showing concentrations of arsenic which can be used to assess the risk to water supplies and help with the prioritisation of future interventions.

The question remains, where is all this arsenic coming from?  While we do not yet have conclusive evidence, by tracing the distribution of arsenic back up the catchment, our investigation has led us to a geothermal field, north of San Jacinto.  Many of the higher concentrations of arsenic recorded during our research so far have been from hot water sources (up to 50 degrees centigrade).  It appears that the arsenic rich water is rising up through geological faults at the foot of Volcán Telica, the volcano which erupted in May.  While our research during the last few months has brought us a long way towards understanding the extent of the arsenic problem in this area, there is still a great deal to be done.  Our technical investigations are continuing with the social impact of this problem never far from our minds.

30/08/11