Natural Attenuation – Teil 1

Monitoringverfahren und Sanierungskonzepte – ein Fortschrittsbericht

Die Berücksichtigung des biologischen Schadstoffabbaus (natural attenuation) war in den vergangenen zwei Dekaden ein vielbeachtetes The ma in der Altlastensanierung. Der fol gende Übersichtsartikel beschreibt Praxiserfahrungen aus zwölf Jahren Altlastenmonitoring zur Bewertung des natürlichen Schadstoffabbaus, der Erfolgskontrolle von in situ Sanierungsmaßnahmen oder der forensischen Aufklärung von Schadensereignissen. Er stellt die Bedeutung und Anwendungshäufigkeit von zehn wichtigen Untersuchungsverfahren in verschiedenen Sanierungsphasen und -konzepten dar. Die zukünftigen Sanierungstechnologien werden variabel und komplex sein. Damit erhöht sich der Untersuchungsbedarf zum Verständnis der biologischen und hydrochemischen Prozesse in einer Schadstofffahne.

The proof and characterization of natural attenuation processes is one of the most important aspects in the development of nature based remediation strategies. Remediation concepts as well as monitoring tools have advanced to complex practice within the last 20 years. However, stakeholders require better know-how in the application of adequate monitoring of bio logical activity at contaminated sites. For this purpose, we present a statistical overview on innovative monitoring tools for the assessment of biodegradation that were applied at 233 contaminant sites throughout Europe within the last 12 years. The investigations targeted the validation of long-term self purification (MNA, 80 % of cases) or success control of stimulated biodegradation (ENA, 8 %) sometimes in combination with forensic objectives (source identification, 12 %). Compound-specific isotope analysis (¹³C/¹²C-CSIA) of pollutants evolved as the key method to quantify degradation of chlorinated ethenes (CE), BTEX or MTBE (within 221 monitoring campaigns), while in situ microcosms (24 ×) and metabolite analysis (28 ×) were the major tools to prove PAH degradation. Further methods such as qPCR analysis of gene markers (19 ×), CSIA analysis of redox compounds (20 ×), GC/MSscreening (10 ×) or enantiomer analysis (2 ×) were used for more detailed and specific objectives (e. g. environmental forensic or proof of pesticide degradation). Laboratory experiments (7 ×) are recently used to evaluate an efficient enhancement of biodegra dation by specific reagent mixtures. When natural attenuation is accepted as a relevant option for remediation, detailed studies on biodegradation processes and plume development are mandatory. At 111 sites, multiple-lineof-evidence approaches provided independent and differentiated information on the microbial elimination of contaminants. The combination of methods depended mainly on dominant pollutants and optional use of in situ treatment. As a case study, we describe that CSIA, qPCR and laboratory microcosms improved the application of MNA at a TCE contaminated site. Moreover, a multi-method-approach is presented for the evaluation of natural and stimulated ETBE biodegradation based on carbon and hydrogen CSIA as well as in situ microcosms (BACTRAPS) at a fuel contaminated field site. In a nutshell, nature based remediation will only be viable by understanding biological, chemical and hydrogeological processes at a contaminant site. Adequate and cost-efficient monitoring tools are available to fulfil this challenge and they are still considerably improved by research efforts. Though recent and future remediation strategies are highly complex, they will be facilitated by process-oriented investigations.