In advance of a planned cleanup of the contaminated site “Gaswerk Simmering”, a comprehensive appraisal of groundwater was carried out to assess and document the site’s current status. For the first time, a large scale analysis of 16 selected heterocyclic aromatic hydrocarbons (hetero-PAHs) was conducted, in addition to the characterization of a number of standard, routine parameters. The method for analytical detection of hetero-PAHs was specifically developed for this work. The decision to analyze these 16 hetero-PAHs was taken by the author based on the specific site and their assumed toxicological relevance. The microbiological potential of the contaminated site was assessed using simple indicative parameters of microbiological degradation (nitrate, sulfate and redox potential). The convenient measurements, provided by this method facilitated a rapid estimate of the oxidative and microbiological conditions of the groundwater. These observations suggest that microbiological degradation processes could be further activated by adding adequate nutrients. In addition to analytical work, assays for luminous bacteria were conducted, to add an eco-toxicological parameter to the assessment of the site as-is status. This parameter may also be used for future monitoring of the remediation success.The physico-chemical and eco-toxicological data obtained during the groundwater assay were displayed in two-dimensional format by means of special graphical software, providing a means to visualize the concentration centers of individual contaminants. In addition, statistical analysis facilitated an estimation of the total concentration distribution of the parameters observed within the sampled area. By means of the graphical analysis, two different contamination hotspots could be clearly distinguished, each showing a characteristic individual composition of pollutants. As part of the project FAMOS, IFA-Tulln conducted bio-reactor degradation tests with contaminated soil material originating from both hotspots. The samples were extensively analyzed and toxicologically monitored through chemical analysis of selected distinctive parameters and a bioassay battery especially assembled for this purpose by the author. Measurement of the selected 16 hetero-PAHs was included with other analytical parameters and in analogy with the 16 EPA-PAHs, a composite parameter Σhetero-PAHs was devised. The Σhetero-PAHs was frequently within the same order of magnitude as the ΣEPA-PAHs, which accentuates the importance of the hetero-PAHs that have hitherto only found little attention. Good agreement was found between the eco-toxicology research with the chosen bioassays (luminous bacteria, Thamnotoxkid FTM, algae and daphnia tests) and the analytically determined concentration of pollutants. In all analyzed samples, decreasing concentration of the selected contaminants (Σhetero-PAHs, ΣEPA-PAHs, ΣCyanide and ΣBTEX) was accompanied by a decrease of toxicity with the biological test systems. This suggests that, with high probability, no elevated toxicity may be expected during the degradation processes because of toxic metabolite formation and/or elevated bioavailability of pollutants. This result is also supported by data obtained by the current state evaluation which, in combination with further studies favor the application of microbiological in-situ clean up techniques. The described method is very well suited for assessing future changes in groundwater during and after a hotspot remediation and as well, for toxicological monitoring of an ongoing in-situ remediation at the site of the Gasworks Simmering. As a result of the applied combination of biological test systems and state-of-the-art analyses, even complex mixtures of contaminants can be well defined and toxicologically evaluated.