Use of artificial and natural tracers for the estimation of urban groundwater contamination by chemical grout injections

In many urban areas grout injections have been used to seal porous soil within the last decades. Especially the silica hydrogels have been applied in foundation engineering practice due to their various applicabilties and economical advantages. For example in the City of Berlin from 1990 to 1995 about 100.000 m3 of silica gels have been injected within porous aquifers. Therefore the environmental authority of Berlin insisted on detailed investigations of potential groundwater contamination risks. This paper presents the use of artificial and natural tracers as well as transport modelling to quantify potential changes in groundwater chemistry and to predict both longevity and toxicity of silica grouts.