Borehole Annulus-Filling Materials and Enrichment of Heavy Metals in Eocene-Palaeocene Aquifer Systems in Awka, Southeast Nigeria

Abstract

Contamination of groundwater resources is more often associated with the infiltration of pollutants from anthropogenic activities such as waste dump sites and industrial effluents. Similar to this, reported results may be limited in its accuracy by poor sampling and analytical techniques. This study is interested in the role of geologic materials. Geologic materials, whether in-situ host rock or transported materials play a massive role in determining the quality of groundwater in any geosystem. A time-lapse evaluation of groundwater quality in Awka shows a progressive deterioration as a result of increasing enrichment in heavy metals. It is noted that Vanadium, Manganese, Arsenic and Copper increased the most over the 1993 to 2013 period under consideration. Host-rock geochemistry discounts the dominant Imo Shale as a source of the contaminants. While recognising the likely infiltration of pollutants from other common sources, it is here suggested that the high concentration of heavy metals can also be the effect of weathering products and leachates that are being derived from heavy-metal-rich igneous rock aggregates that are commonly used as annulus-filling materials in borehole construction. This calls for a more in-depth study to understand the pollution network in order to evolve a coordinated approach to protect the groundwater system and save the populace from looming health and environmental hazards.