Intrinsic vulnerability assessment of the Sébaco Valley aquifer, Nicaragua, to contamination using the DRASTIC method

Abstract

This article deals with the vulnerability to contamination of the Sébaco valley aquifer, Nicaragua with a study area of 263 km2
, using the
DRASTIC method created by the United States Environmental Protection Agency (Aller et al., 1987). The DRASTIC method is a tool that
allows us to make maps of vulnerability to identify which areas of the aquifer are susceptible to contamination or can be adversely affected by
a contaminant regardless of the type of agent. This method depends on seven hydrogeological parameters described below; 1) Depth of
groundwater, with ranges ranging from 3 - 30 meters. 2) net recharge, where the average annual recharge from the rains is of the order of 70
mm. 3 and 4) mean of the aquifer and the impact of vadose zone, of the geology present in the aquifer, as well as data of lithological records.
5) type of soil, with vertisols in an area 209.7 km2
, 79.7% of the surface of the aquifer. 6) topographic slope coming from 5 – 80 % and 7)
hydraulic conductivity where the predominant range in the aquifer is the conductivity between 10-30 m / day.
Based on the analysis of the obtained information, the variables evaluated were reclassified according to the DRASTIC methodology,
establishing the ranges of high, moderate and low vulnerability to pollution, with a moderate vulnerability to pollution in the aquifer of the
Sébaco valley of 138 km2
, 52 % of the surface of the aquifer, located in the central part of the valley. The low vulnerability to contamination of
the aquifer lies in the Northwest and Nor-east, corresponding to 49 km2
, 19 % of the surface of the aquifer. The zone of high vulnerability to
pollution, with 76 km2
, 29 % of the surface of the aquifer located to the south-east and at the ends of the aquifer.