Spatial mapping of groundwater quality in the municipality of Santa Ignacia, Tarlac, Philippines

Abstract The municipality of Santa Ignacia in the Province of Tarlac is highly dependent on groundwater as its major water supply for various purposes, but there is inconsistency in monitoring groundwater quality in the area which may impact the health of consumers. This study presented the preliminary assessment of groundwater quality through the application of spatial mapping. Out of 6,815 wells in the municipality, groundwater samples were collected from 274 hand pump wells. The measurements of selected groundwater quality parameters such as pH, conductivity, nitrate, nitrite, and iron of groundwater samples were determined on-site. The geographical coordinates of sampled wells and measurements of groundwater quality parameters were used in Geographic Information System software, QGIS, to construct the spatial distribution and spatial variation maps. The values of measured parameters were interpolated using the inverse distance weighted technique to predict the parameters at other sites in Santa Ignacia. Spatial variation maps revealed that the groundwater quality parameters varied in the municipality. All measured parameters, except the nitrite content, were within the acceptable limits set by the World Health Organization for drinking water. The high level of nitrite content in groundwater may be attributed to the application of fertilizers during agricultural activities. The nitrite content of groundwater, which exceeded the permissible limit, may cause long-term public health problems. Hence, an upscale evaluation and monitoring of groundwater quality and existing anthropological activities in the municipality are highly recommended. The identification of other possible source(s) of nitrite is necessary to lessen possible contamination risk and to protect the groundwater sources in the municipality. The results of this preliminary study would be useful in prospect studies of groundwater quality in the study area and in other provinces in the Philippines.