Density against water content curves (standard Proctor energy unless stated otherwise): (a) biosolids and sewage sludge; (b) alum WTRs. Note: zero air voids (saturation) curves in Figures 4(a) and 4(b) based on mean G _S values of 1·55 and 1·92, respectively (†from forthcoming article entitled ‘Shear strength of biosolids for monofill design’ by Oettle, O’Kelly and Ramos)