No abstract

Natural attenuation of MTBE and BTEX compounds in a petroleum contaminated coastal aquifer in the Tel-Aviv area was investigated. Significant decrease in MTBE concentration and complete disappearance of BTEX compounds occur within 100 m groundwater flow. Highly anaerobic conditions were determined in the close vicinity to the spill source. In order to examine the contribution of microbial degradation to the attenuation process at anaerobic conditions, compound-specific carbon isotope ratio analysis was employed. Carbon isotope enrichment of toluene up to 2.4% along with the drop in its concentration up to 80% was observed within 20 cm below the water table. The lack of isotope fractionation despite the significant concentration decrease for other studied compounds indicates significant contribution of abiotic processes to the natural attenuation.

The Jurassic Kidod shales, which reach a thickness of up to 300 m., are found throughout the subsurface of central Israel at depths ranging from 1,200 m to over 2,300 m. Data derived from the study of bitumen and kerogen extracted from these shales were used to evaluate its source potential and depositional regime. Methods used included liquid and gas chromatography, microanalysis, δ13C determination, U V spectroscopy, electron spin resonance (ESR), thermal analysis (DTA and GTA), pyrolysis and vitrinite reflectance. The data indicate that the shales were deposited in a normal open‐shelf environment under oxic conditions. This conclusion, considered with the thickness trends of the shales and their diachronous progradation from west to east, points to a marine rather than, as previously proposed, a fluvio‐deltaic provenance for the shales. The implication of this interpretation is that truncation rather than lateral facies relationships accounts for the abrupt termination of the shales to the west over the north‐soth trending sturctural highs of Be'eri–Helez–Ashdod. From quantitative source‐rock evaluation a reasonable source potential is assumed. The presence of significant volumes of exploitable oil derived from the Kidod shales is, however most unlikely, because of its low maturation stage.