POLLUTION OF SOIL AND GROUNDWATER FROM INFILTRATION OF HIGHLY CONTAMINATED STORMWATER - A CASE-STUDY

A surface and a sub-surface infiltration system that received runoff w ater from trafficked roads for several decades was dug up and the cont amination with heavy metals, PAH and AOX was investigated. Most measur ed solid phase concentrations exceeded background concentrations in ne arby surface soils and subsurface sediments and some even exceeded gui delines fixed to preserve the fertility of soil. However, the contamin ation decreased rapidly with depth. None of the measured metal concent rations in simulated soil solutions exceeded defined drinking water qu ality standards. Surprisingly, the surface and the sub-surface infiltr ation system seemed to be equally good at retaining pollution. This in dicates that the runoff sludge found in such infiltration systems play s an important role both as a source and a sorbent for stormwater cont aminants. The study does not point at a considerable risk for groundwa ter contamination due to stormwater infiltration, but highlights that well absorbable contaminants readily available in urban stormwater run off eventually build up in surface soils and sub-surface sediments to environmentally critical concentration levels. Thus, on the one hand s tormwater infiltration systems may act as effective pollution traps an d on the other, they may pose a potential solid waste disposal problem that future stormwater management based on local infiltration will ha ve to face. (C) 1997 IAWQ. Published by Elsevier Science Ltd.