Suspended solids and metals are recognized as key pollutants in stormwater runoff. Thus, stormwater treatment systems have become increasingly vital components of urban infrastructure, playing a key role in reducing pollutant loads entering receiving water bodies. This thesis focuses on evaluating the treatment of solids and metals in stormwater systems, through both controlled laboratory experiments and field-based assessments.

Synthetic stormwater is widely used as a substitute for real runoff in both laboratory and field experiments. Its main advantages are the ability to control influent quality and quantity, as well as to improve the repeatability of experiments. However, no standardized formulation currently exists. A critical review which was conducted to evaluate the use of synthetic stormwater in experimental stormwater research revealed substantial variation among studies. Based on these findings, a narrower set of pollutant concentration ranges was suggested to enhance the comparability, repeatability, and reproducibility of future experiments.

The experiments evaluating design parameters of a suggested Bottom Grid Structure demonstrated that hydraulic modifications of settling areas in the stormwater treatment systems could enhance sedimentation, though the results were not directly scalable to field conditions. Among the variable factors in the experiment, inclined cell walls of the Bottom Grid Structure had the strongest effect, increasing sedimentation by up to 22% compared to control runs. Column studies showed peat and bark to be the most effective filter materials for dissolved Zn removal, although the use of peat is associated with significant drawbacks regarding other pollutants and uncertainties about its long-term performance. Evaluated zeolite filter system treating copper roof runoff achieved high removal of Cu (49–85%) and Zn (48–94%) but exhibited declining performance over time.

A field study examining the performance of two EcoVault facilities revealed relatively low TSS removal (40–46%), substantially below both previous EcoVault studies and manufacturer claims. Dissolved metals were inadequately removed, likely due to elevated hydraulic loading rates and progressive filter clogging. Sedimentation was identified as the dominant treatment mechanism, while the zeolite filter cassettes provided negligible additional metal removal.

The field experiments underscored the importance of site-specific design of stormwater treatment systems, especially in cases where the influent is dominated by dissolved metals. Despite their limited performance, underground treatment systems remain a practical solution in densely built urban environments where surface space is constrained. However, targeted design improvements are essential to enhance treatment efficiency. Furthermore, comparisons with commonly used models for the prediction of the performance of stormwater treatment systems revealed that actual removal rates were approximately 50% lower than estimated values, highlighting the need for additional field-based data to improve model calibration and support the development of more reliable and context-sensitive stormwater treatment strategies.