Colloidal Transport in Saturated Gravel Columns: A Focus on Parameters Influencing Filtration Behaviour to Understand Upscaling Challenges

Abstract

Upscaling colloid filtration tests from laboratory scale to real field conditions remains a major challenge. Results obtained in laboratory experiments often differ strongly from those observed in the field, which can lead to incorrect assumptions. This may result, for example, in poorly designed protection zones or misleading assessments of groundwater quality. Therefore, it is important to identify the parameters that influence the attachment and release of contaminants, in order to understand which aspects need special attention when designing laboratory tests. This thesis investigates how flow rate and column height affect the transport and retention of microspheres in saturated soil samples. For this purpose, laboratory experiments were conducted using different flow rates and column lengths, while keeping the soil material identical. The results show that flow rate had no clear influence on the breakthrough curves or on retention behaviour. Higher flow rates did not lead to lower retention. Likewise, different column heights did not significantly affect retention. However, it was demonstrated that upscaling becomes possible when a power-law approach is applied. Using this approach, attachment factors determined at small scales in centimetre-scale columns of 30 to 50 cm can be transferred to larger scales, such as metre-scale lysimeter experiments. This is crucial for translating laboratory results to field conditions and for applying them to practical tasks such as the design of protection zones or groundwater risk assessments.