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Posted by Dave Collins on April 30, 2008, 10:25 am

The following is a summary on the water situation in La Manzanilla written recently by Mark Cable Rains, Assistant Professor of Ecohydrology, Department of Geology, University of South Florida. Mark is part of a research team headed by the Great Basin Institute who has been conducting environmental research in the greater La Manzanilla area since 2001. I have translated this information and am passing it on to Morgan, our water master. Further questions about these issues can be directed to Mark at:

There are four major water-supply wells in La Manzanilla. Two of these wells are owned and operated by La Manzanilla, while two of these wells are owned and operated by Tamarindo. When wells are pumped, groundwater levels drop and groundwater flows towards the wells from all directions. This is not a problem if the wells are located in a large basin filled with fresh water. This can be a problem, however, if the wells are located in a small basin close to the coast, because salt water from the ocean and/or lagoons and mangroves at the edge of the ocean can flow into the aquifer and eventually into the wells. This can become a bigger problem if groundwater pumping is increased. We call this salt-water intrusion, and it is a problem throughout the world in coastal communities that rely on groundwater for their water-supply needs.

Salt-water intrusion may be occurring in La Manzanilla. I emphasize the use of the word "may", because our results are preliminary and have not been fully explored. The background salinity of water in the aquifer is approximately 0.5, while the background salinity of the ocean is approximately 35. The salinity in the primary water-supply well for La Manzanilla was approximately 0.5 in January 2007 and January 2008. However, the salinity in the secondary water-supply well for La Manzanilla, which is closer to the mangrove and closer to the water-supply wells for Tamarindo, was greater than 1.0 in January 2007 and greater than 2.5 in January 2008. These higher salinities may be due to salt-water intrusion, and this increase in salinity may be due to increasing salt-water intrusion. Again, I emphasize the use of the word "may", because our results are preliminary and have not been fully explored. Nevertheless, these results suggest that our work on this issue is timely and necessary if we are maintain clean water for the community of La Manzanilla. In this regard, we are continuing our work and are regularly communicating with Morgan to ensure that he has current information about the La Manzanilla water resources.


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