GLSSWD Existing Gravity Filter Rehabilitation

The existing filters consist of four cell “Centrol” type of gravity filters. Each cell is 10 ft. x 10 ft. This project consists of rehabilitation of three of the four cells. One cell has been rehabilitated previously (Filter No. 3). Filters 1 and 2 can be taken out service simultaneously for rehabilitation. The two filter cells should be in operation at any given time. 1. Remove the filter media from the filters to be rehabilitated. Filter cells 1 and 2 can be rehabilitated simultaneously. Filter No. 4 shall be rehabilitated as an Add Item as listed in the Bid Schedule. 2. Remove the existing filter underdrain blocks and grout from the filter cell being rehabilitated. 3. Remove the grout bedding from the floor and level the floor for new underdrain installation. 4.Modify the existing J-risers in the air wash system to the required height recommended by the underdrain manufacturer. 5. Install the new low profile underdrain system as per manufacturer’s recommended procedure. 6. Install reverse graded gravel system above the underdrain blocks. 7. Install filter sand media and skim the media as specified. 8. Install anthracite media and skim the media as specified. 9. Revise the drawdown siphon pipe height inside filter as shown in the drawings and attach a flange at the end of the pipe. 10. Disinfect the filter cell and put it back into service after passing bacteriological tests. 11.Add Item as listed in the Bid Schedule: remove and replace four, 10” backwash waste valves with extended shaft and pneumatic actuators in the Centrol Column. 12. Add Item as listed in the Bid Schedule: furnish and install four (4) manual override control stations for bypassing the 14” filter effluent valves with pneumatic actuators with I/P converters.

Division 33 -	Utilities, Sanitary Sewerage Utilities, Sanitary Utility Sewerage Piping, Sanitary Utility Sewerage Force Mains, Sanitary Utility Sewerage Structures.
Division 46 -	Water and Wastewater Equipment, Filtration Equipment, Filter Media.