Media Change Out Procedures Luke AFB.pdf

Media Change Out Procedures

A. Preparations of treatment system prior to media extraction:

1. Isolate all manual vessel valves and lock the well off from operating automatically

2. Drain the system down through the lowest outlet point the day/ evening prior to the media change out event. A drain valve is located at the base of the tank. A hose can be attached to the tank and opened. The hose must discharge to a low point below the base of the vessel.

The vent valve on the side of the vessel will also need to be opened to allow air into the vessel for draining.

B. Media Extraction:

1. Remove side manway and top hatch covers and allow the vessel to ventilate adequately.

2. Place plastic sheeting around the side manway area to retain any media that may fall out when opening the side manway.

3. Cover the base of the side manway with a blanket or other thick covering to prevent manway coating damage from the vacuum hose.

4. Perform confined space procedures including air monitoring, PPE, and the proper trained personnel for the confined space entry.

5. Vacuum all media out through the side manway. Ideal vacuum hose size is 4”-6” to prevent clogging. All components in the vessel should not be bare metal and be insulated to protect metal to vessel coating contact which results in damage. Open the side manway and start vacuuming, moving across the vessel. Vessel entry is required to assure damage to the vessel does not occur. Vacuum media until the lower Gravel under-bedding is reached. The vacuum hose must have a “stinger” or other component to break up the media before vacuuming it up otherwise the vacuum hose will clog.

6. Inspect vessel walls for Oxidation or Holidays that may have occurred during operation or from media removal. Vessel coating damage will be fairly obvious with rust staining in a vertical line on the vessel sidewalls.

7. Repair if necessary using FC-22 NSF epoxy and allow for adequate time for curing.

Demobilization and Remobilization may be necessary to provide time for the proper surface preparation and curing time of approximately 18-24 hours depending on temperature and humidity.

C. Media filling and Recommissioning of treatment system:

8. For change outs only requiring top-off of gravel under-bedding, replenish any lost under-bedding gravel, typically a 1” layer is provided for incidental removal during the media extraction. If scope requires all gravel under-bedding to be extracted; fill vessel ½ of the overall sidewall height of the vessel with water, install gravel through top opening manway until all the required gravel under-bedding has been loaded. Once the gravel under-bedding has been loaded, drain the water in the vessel down as described in section A-2 . Gravel layer should be a minimum of 3”-4” above the collector system or equal to the sidewall/lower dish weld of the vessel. When leveling gravel, water can be used to identify any low areas. Fill vessel from the bottom to identify low and high spots in gravel. Do not level gravel with shovels or bare metal equipment to protect vessel from damage. Use a new sanitized 2” x 6” x 4’ piece of wood for best results.

9. Seal side manway with new gasket and Anti-seize on the bolts. Torque bolts in an alternating pattern.

10. Chlorination will occur during several points of the media loading process. 1 gallon of 12.5%

NaOCl is required per 50 cu/ft. to assure a minimum of 400 ppm solution is in the vessels during the 12-hour (Overnight) soak period to allow full disinfection and adsorption of the chlorine (media adsorbs 17g of free chlorine per cuft of media).

11. Add 1 gallon of chlorine per 100 cu/ft. to the gravel bed before filling with water

12. Fill the vessel 2/3 full of water from the bottom of the vessel, not the top inlet, prior to any media. This can be done from an alternate source water or by opening the supply side of the system and filling through the lower outlet as when the system is in backwash.

Alternatively, treated water may be able to be used and flow in reverse from the treated water tank using the appropriate valve on the vessel, used for treated discharge during service.

13. Water must be above the side manway to test the sealing of the side manway gasket before adding more chlorine or any media.

14. Once water level is above the side manway and no leaks present, add 1/3rd of the total chlorine required while filling the vessels to 2/3 to allow a proper mixing.

15. Untie to sack bottom trunk lower tie and put in the top vessel opening. Then untie the tip sack truck tie and allow media to flow into the vessel. Direct the media into the center of the vessel to prevent mounding before all media is put in the vessel. CAUTION – media fines will be present and exit the vessel top manway. Propper PPE is required to prevent inhalation of media dust.

16. Once all media is loaded, fill the vessel from the top vessel inlet through the appropriate valve. Add the remaining chlorine after all media is submerged.

17. Close the top air relief isolation ball valve to prevent media fines from getting into the air relief unit. Install the top manway, open the vent valve on the side of the vessel, and complete filling the tank until all air is out.

18. Pressurize the vessel and confirm no leaks are present in top or side manway. With vessel under operating pressure, tighten top and side manways as the gasket will compress when vessel put under pressure.

19. Soak media overnight for a minimum of 12 hours, per AWWA disinfection guidelines to ensure proper chlorine saturation and disinfection occurs. The vessel should be at a minimum of 25 ppm chlorine residual after the 12-hour soak is completed. Chlorine test strips or the reagent calorimeter test are difficult to read due to the red coloring of the water used to sample the residual.

20. Put the system into Backwash slowly increase the flow from starting at 1/3 the backwash flowrate to allow al air to be discharged and media to slowly expand. The flowrate of the vessel should be 1/3rd of the normal operating backwash flow. After 15 minutes increase the flowrate to 2/3rd full flow, allowing more media fluidization. After an additional 15 minutes, increase flow to normal backwash full flow rate, for virgin media backwashing.

21. This full flow backwash process typically takes 15-30 minutes. Some fines will still be present however water turbidity will be low and water will be clear/transparent in color.

22. Open air relief isolation valve and rinse the vessel one at a time until waste water is clear.

This may take 3-5 minutes for turbidity to clear. An initial spike in color may occur as media bed settles. Rinse media until free chlorine residual is 1ppm-2ppm. Residual above 2 ppm will prevent a Bac-T sample from being effective.

23. Pull Bac-t sample in accordance to local / state requirements. Bac-T sampling completed by

Utility or subcontractor.

24. Once Bac-t results pass, place system back into service allowing air to escape through vent line until water is present. Close the vent lines and observe full system operation.