Carlos Grangeia

An investigation into the use of geophysical methods in the study of aquifer contamination by graveyards

Graveyards are the traditional way of dealing with the deceased and often their location is unsuitable so that there is a potential contamination danger for local aquifers and soils. Such a contamination is complex as organic, inorganic and biological pollutants will be present. This problem has been studied by direct methods, i.e. boreholes. However borehole location can be difficult and so it is proposed here to use geophysical multiparameter surveys, as well as hydrochemistry studies, to investigate the contamination in the vicinity of two graveyards located in very porous and permeable formations. Based on the geophysical interpretation, two shallow boreholes were drilled and groundwater sampling confirmed local aquifer contamination. The geophysical response is shownto depend on the water table depth, and when this is close to the ground surface, it is demonstrated that geophysical methods can be used to map contamination plumes originated in the graveyards and, therefore, assist borehole location.

The use of gravity methods in the internal characterization of landfills - a case study.

Some examples of the use of gravity exploration methods in landfills were published recently. However, density contrast between the landfill and the host media as well as the cost involved may be limiting factors to the application of gravimetry to this problem. Herein a case study of the application of gravity methods to the internal characterization of a sealed landfill is presented. This landfill is installed in recent low-density quaternary sand formations. Two north–south gravity profiles were carried out. The first profile crossed the landfill at its centre, whilst a second profile was done some distance away from the landfill to provide general regional information. The first profile was modelled in order to obtain lateral variations of density within the landfill that might be caused by different types of waste and/or the age of the waste deposits. Gravity modelling and interpretation were supported with data from resistivity profiles carried out in the immediate vicinity of the gravity measurements, i.e. the resistivity profiles interpretation results constrained the thickness of landfill deposits.

A multi-method high-resolution geophysical survey in the Machado de Castro museum, central Portugal

Restoration of historical buildings is a delicate operation as they are often built over more ancient and important structures. The Machado de Castro Museum, Coimbra, Central Portugal, has suffered several interventions in historical times and lies over the ancient Roman forum of Coimbra. This building went through a restoration project. These works were preceded by an extensive geophysical survey that aimed at investigating subsurface stratigraphy, including archeological remains, and the internal structure of the actual walls. Owing to the needs of the project, geophysical data interpretation required not only integration but also high resolution. The study consisted of data acquisition over perpendicular planes and different levels that required detailed survey planning and integration of data from different locations that complement images of the surveyed area. Therefore a multi-method, resistivity imaging and a 3D ground probing radar (GPR), high-resolution geophysical survey was done inside the museum. Herein, radargrams are compared with the revealed stratigraphy so that signatures are interpreted, characterized and assigned to archeological structures. Although resistivity and GPR have different resolution capabilities, their data are overlapped and compared, bearing in mind the specific characteristics of this survey. It was also possible to unravel the inner structure of the actual walls, to establish connections between walls, foundations and to find older remains with the combined use and spatial integration of the GPR and resistivity imaging data.

Examples of the Use of Non-Invasive Techniques for the Evaluation of Stone Decay in Portugal

Today experts agree that precise damage diagnosis is the key to comprehensive characterization, interpretation, rating and prediction of stone damage. It provides vital information for monument conservation and sustainable preservation. Better understanding of the stones used in monuments and the factors, processes and characteristics involved in stone decay is therefore essential to the sustainable preservation of cultural heritage. A frequent and major obstacle to studying stone decay in monuments is the impossibility of touching or obtaining samples for study in the laboratory or even in-situ. The aim of this paper is to present the results of three non-invasive geophysical (3-D electrical resistivity and seismic refraction) and geochemical (soluble salts typology and distribution) techniques, that were used to diagnose stone damage in case studies involving Portuguese cultural heritage. Different techniques were applied based on decay typology or observed phenomena.

Sedimentary structure of the Nazaré coastal dunes (Portugal)

The internal structure of costal dunes located south of Nazaré was analyzed using Ground Penetrating Radar. These coastal dunes comprise stabilized dunes, located in the inner part of the dune field, and foredunes, both separated by a dry dune slack. The radargram analysis allowed the identification of five bounding surfaces that define six main aeolian sand units. The Units I, II, III and IV correspond to the progradation of foredunes seaward (NW), while Units V and VI represent the migration of a parabolic dune and a blowout, respectively, to southeast. A strong reflector separating Units I, II and III from Unit V is interpreted as a paleosoil, suggesting a break in aeolian sedimentation of unknown duration, but with sufficient time for soil development. The absent of the paleosoil over the Unit IV leave some doubts in relation to its relative age, although is indicative of the occurrence of an erosive event. Radar stratigraphic analysis provided a relative chronology of units that will be used as a framework for selecting sampling points for future absolute dating and sedimentological studies.

High Resolution Geophysics Inside Machado de Castro Museum – Coimbra, Centre Portugal

Geophysics has been used inside Machado de Castro Museum buildings (Coimbra, Portugal) to guide archeological surveys and to help building restoration. The high resolution geophysical work consisted on GPR and Resistivity survey. Data was gathered on the floor of the so called Renaissance room and on the Cryptoporticus wall, that is, perpendicular to the plane of the Renaissance room floor. Restoration works in old buildings is a sensitive task as they often lay over older buildings. Therefore, high accuracy is demanded to non invasive exploration works. Hence, the geophysical survey was designed in order to obtain very high accuracy. Both the geophysical data/interpretation and the archeological findings were organized in a GIS to provide a full picture of the area under investigation. Archeological excavations confirmed the geophysical findings as well as the accuracy obtained.

A geophysical survey on the Panasqueira mine tailings

Mine tailings can be a major environmental problem because of the large quantities and volumes, high slope instabilty and leaking that can threaten nearby rivers and water supply. The Panasqueira Mine (Central Portugal) has been a major wolfram producer of the westem world since the early decades of the twenty century.