The 127,000 gallon tank is generally in very good shape. It was inspected by the manufacturer, Mount Baker Silo, and a licensed structural engineer who tested the integrity of the concrete and verified the rebar was installed per spec. There is seepage along many of the joints, which is typical of this type of construction. There is one area about 24′ up on the South side where soil was mixed in with the concrete. Over the years this area has had excessive leakage. Several attempts to patch the inside and outside.
More pictures of the tank are shown below.
Conclusion and Plan
- With routine maintenance we expect several decades of operation from the tank.
- Continue to monitor the condition of the tank in general and the known weak areas.
- Prepare the small tank for regular operation.
- Develop a plan to meet the chlorine contact time (CT) requirements, and have the plan approved by the state dept of health before putting the small tank in operation.
- If the seepage increases again:
- Test approved alternate CT plan
- Clean and disinfect the small tank
- Bring the small tank online
- Drain and dry the large tank,
- Pressure wash the inside of the large tank
- Sand blast the interior areas to be repaired
- Roto hammer suspect joints and cracks to enable solid repair
- Seal areas of concern
- Refill, disinfect and bring back online in an approved manner.
New storage for increased capacity is a different issue, and should be funded primarily by the new members.
These pictures were taken in the spring of 2007 in preparation for repairing the large tank. The plan was to bring the small tank online during the repair process. At the last moment we realized that we did not have a good plan for maintaining the required CT.
The small tank was drained, cleaned, and sanitized.
The small tank prior to draining:
The small tank was surprisingly clean. The water was clear with only a slight collection of dust on the surface. There is some sediment visible in the top left corner of the picture. Mark should be there Wednesday at 9 or 10 to finish draining it, then start cleaning. He wondered if it might have been partially refilled. We will know tomorrow for sure. I don’t see how we could partially fill it without overflowing.
The big tank, looking down at a patch on patch on patch:
(click on any image to super size it)
This shot was taken while standing on the lid, prior to lowering the level. The electrodes used to control the pumps are dangling on the wires. The hardware holding the breather pipe on the contact culvert is corroded, or has iron deposits.
Here are 3 or 4 different materials used in attempted patches. The wider area epoxy was probably the last attempt, but it does not appear to overlap the earlier one. The black rubbery stuff pulled off very easily exposing bare concrete. The epoxy pulled off in small pieces and felt soft, but seemed to be on top of slime, not concrete. The four pictures above are a crude panoramic. The one on the far right has a fine vertical crack that we should consider grinding out for an inch or so.
This shows the 2″ drain hole in the distance, just below the lid, and the electrical conduit that floods the plant when the tank overflows. Sorry for the different perspectives.