ABSTRACT:

This paper presents the results obtained with two geophysical methods – ground penetrating radar (GPR) and resistivity applied at a site in Rio De Janeiro, Brazil, where the soil and groundwater were contaminated by an organochloride pesticide called HCH – hexachlorocyclehexane, and by metabolotes. Detailed hydrogeological and some geological information is available for the site and is summarized in this report. The geophysical survey was carried out in order to map as precisely as possible the site stratigraphy. It is well know that details of the stratigraphy can have a considerable influence in the fate of the contaminant. The obtained results showed that high resolution profiles of shallow stratigraphic units can be obtained with GPR sections. It was also possible to define regions where particular reactions between HCH and lime were taking place.

INTRODUCTION

The purpose of a ego-environmental investigation is to characterize soil and groundwater pollution problems in sufficient detail to facilitate the design of a cost-effective corrective action program. Geologic, hydrologic and chemical data must be acquired and integrated to define the nature and extent of soil and groundwater contamination, as well as the potential migration of these contaminants within the natural groundwater flow system. The characterization of geological heterogeneity is one of the most difficult problems in such investigations. Inadequate knowledge of the position of the boundaries between lithologies (for example, between sand and clay, stratigraphic processes, physical properties and hydrologic units all create uncertainties in modeling. Drilling does not adequately solve this characterization problem as it only yields data for points on the surface of the earth and lines of data as a function of depth. Surface geophysical methods can aid in such investigations by providing continuous information about physical and chemical properties in the earth in both Arial and depth extent, noninvasively, remotely, safely and inexpensively.

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