Delimitation of a hydrogeological reserve for a city within a karstic aquifer: the Merida, Yucatan example

Merida is the largest city in southeastern Mexico, where the urban supply i s obtained mainly from three wellfields outside of the urban limits in a ka rst aquifer that is particularly vulnerable to contamination. Merida, Yucat an has a population greater than 600 000 inhabitants. The city obtains its freshwater from a thin (<50 m thick) sole-source aquifer. This aquifer also supplies water to satisfy the industrial and agricultural needs of the reg ion. Ln order to help in maintaining an adequate water supply for the city, a detailed study has been conducted to determine the best area to establis h a hydrogeological reserve zone (HRZ). A polygon of 900 km(2) was chosen s outhwest of the city. This area is upgradient from Merida, no industrial ac tivity is present, and there are two natural boundaries that bound the prop osed HRZ. These are no-flow boundaries that have developed as a result of t he second boundary: a high permeability zone locally known as the ring of c enotes (ring of sinkholes). The major current obstacle to designate this ar ea as a hydrogeological reserve is an industrial landfill that is present i n within the proposed area. As part of the establishment of the HRZ, the la ndfill should be relocated, and a comprehensive ground water quality study should be conducted to determine the actual water quality of the aquifer. ( C) 2000 Published by Elsevier Science B.V.