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

follows:a. Sand drying filters may be used to process waste filter wash water andsettling basin residuals from treatment units that have automatic residualremoval facilities. Sand filters shall have the following features:1. Total filter area, regardless of the volume of water to be handled,should be no less than 100 square feet. Unless the filter is smallenough to be cleaned and returned to service in one day, two or morecells are required;2. Filters shall have sufficient capacity to contain, above the level ofthe sand, the entire volume of wash water produced by washing ofall the production filters in the plant;3. Sufficient filter surface area should be provided so that, during anyone filtration cycle, no more than two feet of backwash water willaccumulate over the sand surface;4. The filter shall not be subject to flooding by surface runoff or floodwaters. Finished grade elevation shall be designed to facilitatemaintenance, cleaning and removal of surface sand as required;5. The filter media shall consist of a minimum of twelve inches of sand,three to four inches of supporting small gravel or torpedo sand andnine inches of gravel in graded layers. All sand and gravel shall bewashed to remove fines;6. Unless the design engineer submits information justifying differentsand sizes, filter sand shall have an effective size of 0.3 to 0.5 mmand a uniformity coefficient not to exceed 3.5;7. Each filter shall be provided with an adequate under drain system topermit satisfactory discharge of filtrate;8. Provision shall be made for the sampling of each filter effluent;9. Overflow devices from the filters shall not be permitted;10. Where freezing is a problem provisions should be made for coveringthe filters during winter months;11. Filters shall not have a common wall with a compartment storingfinished water but shall be separate structures. Filter piping shall notcreate an unprotected cross-connection; and12. The provisions for the final disposal of the residuals shall beprovided in the submittals to the department and the equipment orcontractor arrangements necessary to remove and haul the sludgeshall be specified.b. Lagoons may be used to temporarily store residuals until they can beremoved for final disposal. Lagoons shall have the following features:1. Be designed with a volume 10 times the total quantity of wash waterdischarged during any 24-hour period;2. A minimum usable depth of five feet;3. Length four times width and the width at least three times the depth,as measured at the operating water level;4. Outlet to be at the end opposite the inlet;5. Velocity to be dissipated at the inlet end; andAug. 29, 2003Page 91