Environmental risk assessment of a shallow aquifer in "piana campana" (ITALY): A field comparison between seismic refraction and reflection methods

The "Piana Campana", known since the Roman age for the fertility of its land, is now facing the problem of pollution of water resources. The primary cause of pollution is the discharge from numerous chemical, mechanical and thermoelectric plants. Another cause is the excessive use of chemicals in the modern agricultural practices. In order to assess the environmental risk to the main aquifer of the site, it is necessary to locate discontinuities (faults and fractures) in the Campanian Ignimbrite, a thick semi-permeable tuff bank, which partly protects the reservoir from polluted water seeping from the upper aquifers. To test the potential of seismic methods for such investigations, a reflection and a refraction survey were performed on a site near the town of Acerra. The refraction data were interpreted using the Generalised Reciprocal Method (Palmer, 1980). Comparison between reflection and refraction methods shows that: 1) both methods could detect a fault which was not noticed in the surface geological survey; 2) the seismic reflection method is more effective and direct than seismic refraction because the data required less manipulation; 3) the geological makeup of the area posed a difficult problem for the refraction survey; in fact only the superficial geological features were mapped by this survey, while the reflection method could detect the depth and the morphological trend of the Campanian Ignimbrite Formation, which was the target of this geophysical investigation; 4) the refraction survey allowed a more detailed morphological reconstruction of the shallowest horizon and a more reliable velocity determination along the profile line.