== 4) Sludge production. The lime-soda ash soften- ing process produces chemical sludge composed princi- pally of calcium carbonate and magnesium hydroxide. As withdrawn from sedimentation basins equipped for mechanical sludge removal, the proportion of dry sol- ids in the sludge will generally fall within the range of 2 to 10 percent. The weight of dry solids produced by softening reactions will average approximately 2.5 times the weight of commercial quicklime used. For hydrated lime, softening solids produced will be rough- ly twice the weight of commercial hydrated lime em- ployed. Fairly accurate values of total solids produc- tion at an operating plant can be developed utilizing a mass balance which takes into consideration the sus- pended solids in the raw water, ==