Framework for groundwater protection--the Managua ground water system as an example

A framework for ground water protection was developed and tested in the Eastern subarea of the Managua, Nicaraga, ground water system. The framework is a planning tool aimed at identifying areas with a high need for protection to aid future land-use decisions. The basic components of the framework are vulnerability assessment, contaminant source characterization, and assignment of a protection value. The framework is developed for a geographic information system environment. The vulnerability assessment was carried out using a modified version of the DRASTIC method. The most vulnerable parts of the study area proved to be an area with a shallow ground water table coupled with shrinking/swelling clay soils, and an area where recent porous lava flows mean high recharge and low attenuation capacity. In the contaminant sources characterization, the type of contaminant, its relative concentration, mode of deposition, duration of contaminant load, and possibility for remediation were considered. The sources characterized as emitting a high potential contamination load were concentrated in a tax-free industrial zone and three villages. The main contaminant sources were a tannery, chemical industries, and sewage water outlets. Both the ground water vulnerability and the potential contamination load were classified as high, moderate, or low. By superimposing the potential contamination load on the vulnerability map, the ground water contamination liability was evaluated by a skewed 3 x 3 matrix. A relative protection value of the ground water was calculated, based on classifications of available quantities, quality, sensitivity to changes in ground water level, and present or planned use. Together, these maps form an atlas to be used for ground water protection and land use planning.