"Stagnation in the groundwater downstream of the barrier results in very little dilution occurring and a *contaminant plume* developing. In contrast, the predictions with unimpeded groundwater (no trenches) show low concentrations across the whole site area due to dilution from the incoming clean groundwater."
www.ncl.ac.uk/wrgi/wrsrl/projects/ici/ici.html

"Creosote and chlorinated phenols have been used extensively as wood preservatives throughout the United States. Contaminants leaked to the underlying aquifer through several unlined ponds and were transported toward nearby Pensacola Bay. Studies at this site have demonstrated that microorganisms can adapt to extremely harsh chemical conditions and that microbial degradation was restricting migration of the **contaminant plume**."
www.contaminatedland.co.uk/case-stu/bio-remd.htm

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Note added at 1 hr (2007-05-23 20:45:30 GMT)
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Here's a link relating to oil:

"Developing Conceptual Models of Biodegradation: Lessons Learned From a Long-Term Study of a Crude-Oil Contaminant Plume..."
http://adsabs.harvard.edu/abs/2002AGUSM.H22D..03C

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Note added at 18 hrs (2007-05-24 13:55:37 GMT)
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Şi parcă francezii îi zic "panache de polluant":

"COST-EFFECTIVE SAMPLING NETWORK DESIGN
FOR **CONTAMINANT PLUME** MONITORING UNDER
GENERAL HYDROGEOLOGICAL CONDITIONS

Présentation d’un modèle de simulation de propagation
de **panache de polluant** dans une nappe afin d’optimiser
un réseau de suivi."
http://ruisseau.oieau.fr/eaudoc/pdf/livret_ref_biblio/05mai....