Design Guide for Community Water Systems - The Water, Sanitation ...

Chapter 4 -- Tre atment4.0. General.The design of treatment processes and devices shall depend on evaluation of the natureand quality of the particular water to be treated and the desired quality of the finishedwater.4.1. Clarification.Plants using conventional clarification to treat water prior to filtration shall be designedto:a. Provide at least a two-stage treatment process consisting of primary rapidmixing, flocculation and sedimentation and secondary rapid mixing,flocculation, and sedimentation, in series, to treat surface water;b. Provide at least a single stage treatment consisting of rapid mixflocculation-sedimentationfor clarification to treat groundwater under thedirect influence of surface water;c. Be constructed to permit units to be taken out of service without disruptingoperation, and with drains or pumps sized to allow dewatering in areasonable period of time;d. Have walls and interior equipment constructed of stainless steel or nonmetallicmaterials or provide duplicate parallel units;e. Avoid constructing conventional cylindrical settling units because oftheir excessive short-circuiting and poor flow characteristics;f. Be started manually following shutdown, unless otherwise approved by thedepartment where automatic monitoring control is provided;g. Be constructed to minimize hydraulic head losses between units to allowfuture changes in processes without the need for repumping; andh. Be piped so raw water cannot be discharged directly into the filters.4.1.1. Presedimentation, or raw water storage basins.a. Presedimentation basin is recommended for water systems taking waterfrom navigational rivers.b. Storage Capacity. Presedimentation basins should be sized so that the riverintake can be shut down to allow spill and/or contamination to pass beforeresuming normal operation.c. Inlet. Incoming water shall be dispersed across the full width of the line oftravel as quickly as possible; short-circuiting must be prevented.d. Bypass. Provisions for bypassing presedimentation basins shall beincluded.Aug. 29, 2003Page 47