The main constituents of GRC are based on the naturally occurring earth oxides that are used in the manufacture of cement and glass fibres. These are not generally regarded as pollutants. Wash water from the manufacturing process contains cement and this is alkaline. It is normal for factories to have settlement tanks so that solids are not put into the drainage system.
The environmental effects of the drainage channels are shown in Figure 1 and Figure 2. They indicate that the decreases in environmental effects due to reductions of glassfibre content, from a 3% baseline, were small and dependent upon the particular environmental indicator.