A participant asked the question below:
We have an elevated water tank, 21,000 gallons, with possible holes in the roof and perhaps birds nesting on the tank, it all must be replaced. What is the good short term cheap solution?
Well that’s a very good question. If there’s a hole in the tank and there are birds at the top, that’s certainly a huge public health concern. We had some data; unfortunately I don’t have it on my fingertips at the moment. But we have some data that was taken while ago.
It used to be a lot of tanks with faulty roofs that bird droppings would get in. That many of the water disease outbreaks were caused by holes in water tanks, particularly by bird droppings.
So it is a very serious concern in terms of public health and it is something that needs to be addressed in a very very quick fashion.
Again if that’s true there are holes in the roof and there are birds up there, there is a big potential for contamination to get into the system and you don’t want anything to happen with disease outbreaks or anything like that.
So it is something of a very serious concern that should be addressed very quickly. That being said in terms of what approach is the best to repair a tank, I have to confess I don’t know repair techniques for tanks maybe Ross does, in terms of what specific techniques to be used.
I’m thinking, and I had situations like this back in the days when I work for a municipality that ran a water utility. I’d like to talk to the question perhaps a little bit more in terms of asset management principles.
Assess the condition of the asset
So what we’ve got in this question is the description of an asset. It’s going to be a reasonably expensive asset to replace; that it has some major maintenance problem. Or in fact that might just be an indicator that there are other problems up there as well and you might need to replace the whole asset.
When you want an asset management planning point of view the first thing that you want to do is get a better idea of the condition of the asset. Is it something that we can just repair by resealing the roof or sealing that particular hole? It’s just an isolated problem in other words.
You could do the same analysis on a pipe main or any other type of asset. Or is it a wider spread problem of issue?
The whole tank is actually getting quite near its (end of) life. We’re going to get more holes, more problems. Because you’re trying to make a decision there, are we going to be spending money on this tank and in its current condition that is just a waste of money – it is only going to hold us for a year?
Or is it just one isolated little problem and so if we spend a few thousand dollars fixing that hole then we’re going to get another 10 or 20 years out of the tank.
Evaluate costs and advantages of repair or replacement
So once you know that, if it’s just a simple repair then you’ve got to put the work package out and give it to your crews.
The biggest thing about elevated tanks of course is just the whole safety aspect of making sure that who’s working isn’t going to fall and all sorts of things; and maintaining the hygiene and everything else there.
Sometimes, you can take the opportunity to clean or repaint the tank while you’re doing that sort of work as well. So you could take it off line and actually do the whole job, get some more life out of it – if that’s your approach.
If it’s going to be that this tank is really right at the end of its life and we’ve looked at the pedestal and it’s got problems as well, and needs structural works, and the list goes on, and it’s getting too expensive to repair, then you’re on to replacement.
Analyze cost-benefit of replacement
Then the question is, do you go for another elevated tank or do you put some ground tanks in with some pumps. And really that’s just a straight engineering analysis on cost-benefits.
Obviously an elevated tank may or may not have additional pumping. Certainly if you’re going to put in ground tanks then you’re going to have some base pumping cost or something like that. Also you have got wear and tear on the pumps through the life of the asset, and also the energy cost and the maintenance cost of the pumps.
So you can run those numbers out and the thing is, you’re saying, what’s the life of the tank? If it’s 30-50 years, what over the same period of time is going to be the most cost-effective solution that there is?
Do a quick analysis
You can just do a quick analysis. Trade those things off against each other, the answer will drop out and then you’ll have a way forward.
The only complicating matter is if you got your authority has policies on how to handle elevated tanks. Or maybe there is a state or a city policy that trying to get rid of elevated tanks for some reason. And that might change the dynamic of your analysis.