4th EEGS Meeting

The new introduced method for the soil contamination survey is based on the analysis of the soil gas or vapour. This newly developed method offers fast andreliable location of contaminant sourees and trajectories of the contaminant spread. Gas from the pore space in soil and rock formations is commonly known as soil vapour. The composition of this phase, in particular the présence and concentration of organic compounds, reveals vital information about pollution of the subsurface environment. Organic compounds constitute a group of contaminants which impact severely on groundwater resources. The presence and distribution of such pollutants can be detected by a new established technique known as a Soil Vapour Analysis ("SVA") or Soil Vapour Survey ("SVS").

In 1994 we applied the satellite positioning method to environmental monitoring (Camus et al., 1994, Cefalo P.,1996). A Carbon Monoxide electrochemical sensor was mounted on a car together with a GPS positioning sensor. The car was driven along the streets of Trieste center and the concentration of this gas was measured every two seconds. By properly choosing the urban route with crossing streets, the data were processed in the form of contour levels, so allowing a mapping of the CO concentration. The data were also processed as street pollution profil es. The sensor has a delayed response of about 9 seconds. Moreover, the CO concentration as measured outside a vehicle suffers a lot of transient peaks due to the exhaustion of any car or motorbyke close to the sensor. Nevertheless immediatly repeated passages on the same street displayed the same concentration within 20%, which is quite a significant result if the measurement campaign is devoted to alert authorities and people of the dangerous pollution.

A combined geophysical survey was carried out in a oil refinery to study the complex hydrocarbon contamination of the soil and the near surf ace aquifer, resulting from several years of leakage of hydrocarbon products. A near surf ace level characterized by a strong reflector was weIl detected using Ground Penetrating Radar; lateral changes of the strength of the reflection and the subsequent drilling confirmed the existence of a free phase of hydrocarbon in the vadose zone above the water tabIe. Because of the limited thickness of the layer embedded with the residual oil, the geoelectrical resistivity measurements were not effective for detecting this level. The resistivity measurements pointed out very low values in the upper zone of the aquifer; this effect can be associated to complex chemical reactions between the dissolved hydrocarbon phase and the aquifer system. These effects were investigated using high resolution geoelectrical tomography. Soil data resulting from several boreholes confirmed the reliability of the geophysical response. Geochemical and physical analysis of the soil and groundwater samples, combined with the geophysical investigation, allowed the definition of a reliable model ofthe polluted area.

To enable an effectice proteetion of near surface groundwater reservoirs against pollution from agriculture, industry or waste disposals the protective qualities of the unsaturated layers on top of the aquifer must be quantified. On that basis the risk of groundwater contamination can be mapped and endangered regions can be protected be governmental regulations. A mean for the protective qualities can be the percolation time from the surface to the groundwater saturated zone. While groundwater is moving through the unsaturated layer the concentration of contaminants is reduced by biological and chemical processes. These processes are time consuming, and as a rule of thumb a percolation time of at least 10 years can offer an effective proteetion of our groundwater resources.

The aim of this research is to find the class and the quantity of pollutants in soils and rocks on the bases of the different electrical behaviour of organic compounds and metallic ions at the solid-liquid interface, as function of electrical frequency in the DC-.;-.200kHzrange. This research started from previous laboratory studies of the polluted sample electrical responses. The electrical behaviour of these samples has been analysed following the method of Losito et al.(1985) pointed out to investigate the phyllosilicate electrical properties. The method starts from the waveform analysis of the electrical signals, that are strongly distorted by the double-layers of clay minerals. The classical THD% (% Total Harmonie Distortion) and the HD%(co) parameters, used in this analysis, are also strictly dependent of the pollutant molecular size and give an "electrical signature" ofthe pollutant-mineral interaction. On the base of the said laboratory results, a Geoelectrical Integrated Method (GIM) has been performed and tested to investigate and monitor the presence of chemical and organic pollutants near riverbed, water tables, and urban waste deposits.

The national radon survey in Lithuania started in 1995. Measurements have been performed in 400 randomly selected detached houses. Two separate used by inhabitants rooms used to be selected for measurements. E-PERM electrets by Rad Elec Inc were used for registration of indoor radon concentrations. The measurements were performed during heating season for 3 or more weeks. The results indicate dependenee of indoor radon concentrations on location of house. Five regions have been detected with average indoor radon concentrations exceeding the national level (55 Bq m") by almost two times. Houses with indoor radon concentrations higher than internationally recommended and nationally adopted levels of action (400 Bq m-3 for existing and 200 Bq m-3 for new houses) have been detected during the survey. One more region with elevated indoor radon concentrations has been identified in the karstic area near Birzai. For identification of this region the data available in the Lithuanian Geological Survey have been used because the measurements in randomly selected houses have been unable to disclose uniquity of this region. Analysis of results shows with small exceptions that the main souree of indoor radon in Lithuania is soiI. Since it is necessary to create the system of radon risk mapping selective measurements of radon concentrations in the soil air have been performed. Electrical tomography measurements were also included in order to get a possible correlation between distribution of radon concentration in soil gas and apparent resistivity anomalies of subsurface.

Here are reported the results obtained from the application of the georadar method for the detection ofLNAPL (Light Non-Aqueous Phase Liquids) when they are floating on the water table. In order to do this study it was necessary to fust consider the georadar response on a theoretical model, which would respond in the closest possible manner to the actual case, and then move on to the field data. The studies on the theoretical model and on the field data have shown that it is not possible to individuate the presence of light hydrocarbons floating on the water table without resorting to the evaluation of attributes. Among the numerous attributes, in this work, only the instantaneous amplitude, phase and frequency were taken into consideration. Among these attributes, the instantaneous amplitude and frequency allow detection of hydrocarbons, while the instantaneous phase gives only a better lateral continuity of reflectors.

SoH contamination caused by hydrocarbons is a problem for the reorganisation of closed factories and tank farms. It is necessary to determine the kind and content of the contaminants. Soil samples lead to reliable results but the detailed investigation of an area requires a large number of boreholes, which are usually quite expensive. Radiomagnetotellurics (RMT) is comparable to the known VLF-R method but uses a broader frequency range (10-240 kHz). Electromagnetic sounding is possible by using several radio transmitters with different frequencies. The horizontal electric field in the direction of the radio transmitter and the horizontal magnetic field perpendicular to this direction are observed. From the ratio of the amplitudes of these fields the apparent resistivity is derived. The phase between the two fields yields the second measured value.

The City of Edinburgh Council is currently redeveloping the West Granton area in north Edinburgh, Scotland. The area has accommodated heavy industrial use for the past 150 years and consequently has numerous possible contaminant sources. A major concern for potential groundwater pollution is the emergence of contaminants on the neighbouring foreshore. This paper concentrates on the sites of two former oil distribution terminals that have been acquired for remediation and redevelopment. Figure 1 locates the old installations used for the storage of various hydrocarbons. By 1987, all the storage tanks and surface structures were dismantled to ground level. Contaminated made ground was cleared from the eastern most site which was awarded a certificate of remediation.

A geophysical survey, based on unconventional geoelectrical prospecting methods, was carried out in a controlled test site located in Montalto Uffugo (CS), Southem Italy. The main objective of the study is to outline the complex geological features of subsurface and to gain information about the hydrogeological features of the investigated area. Subsequently, the geoelectrical measurements will be used to control the time evolution and spatial distribution of contaminants and to analyze the correlation between the soil resistivity and the hydraulic characteristics of aquifer.