Description: This report considers the various forms of wall construction, both past and present, discusses the probable causes of past failures, draws attention to the general design considerations, and recommends parameters on which future designs should be based. A study has been made of the physical properties of all types of conventional and plastic filter media, and an assessment has been undertaken of the effect of biological film growth and effluent retention on these properties. Cantilever and ring tension walls are considered, and recommendations are made on the calculation of wall loadings. These are given for the various filter media, together with active pressure and passive resistance coefficients for the different forms of construction. Since the investigation was essentially a desk study, field work was confined to a general visual examination of filter walls and media and did not involve any experiments. However, it is evident from this study that information on certain aspects is very sparse (in some cases non-existent), and reference is made to those areas where further research work would be of benefit. The conclusions include suggestions on remedial actions which can be taken where filter walls are showing signs of failure or where collapse is imminent.