Water storage tank: Tear it down or upgrade?
Should you try to extend the life of an existing water tank or start over with a new one? It’s a question those responsible for public water systems often face.
There are options that will stretch the life of a tank regardless of whether there is enough system-wide capacity and/or hydraulic grade line limitations posed by the current tank. It is possible to extend its usability quite a few years by getting it up to current standards, and thus improve operations.
Recently I worked with a client in the greater Seattle area faced with this dilemma. Mead & Hunt was asked to evaluate two cast-in-place potable water storage tanks constructed in the 1970s. I’m proud to report that based on our recommendations, the life of the tanks should be extended by 15-20 years. This delayed a multi-million dollar investment for complete tank replacement. We also estimated that 50 percent of the appurtenance improvements will be useful for future tanks at this same site, making the project even more successful.
How did we do it?
We have a process we recommend, but in short begin by gathering all the available background data on the tank. Be sure to include as-built drawings, specs, standard operating procedures and past maintenance records.
Next, we’ll pick the brains of the folks familiar with the tanks, most importantly the operators. Each investigation may vary slightly based on the type of tank – concrete, steel or other style.
Here are some questions we typically use in our research. Each has a unique set of options to consider for resolution.
- Are there any water quality complaints in the service area?
- Is this tank in an area susceptible to seismic activity?
- Can the tank be adequately isolated?
- Did the Department of Health identify any deficiencies?
- Are there any changes in pumping capacity that are impacting the appurtenance design?
- Are there any security concerns? Example: children climbing on the tanks.
- Is there any means of de-chlorinating the water when it’s drained?
- Are there any leaks or structural concerns?
- Are air gap requirements met for cross connection?
Now it’s time to get our hands dirty with field investigation. But before we begin, make sure the confined space entry requirements are met.
Complete a thorough investigation of both the interior and exterior of the tank. Observe any distinct differences with the as-built documentation on-file. For concrete tanks, areas of cracking and spalling should be noted. Check steel tanks for coating deficiencies. Compare the appurtenance design to Health Department requirements.
To replace or repair
Once the evaluation is complete, we can provide a 30 percent cost estimate. Now it will be clear to you whether upgrading the tank will be cost effective. Also, we’ll help you consider what improvements might be used and useful for a future tank at the same site.
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