Water evaporation rate from underground tank

[Bribyk]

I've got two connected underground concrete water storage tanks that are losing water at what seems to be a high rate. There is limited airflow through these tanks as there are only small breather holes in the lids (8 X .25" dia), connected drain piping to an evap tower and two submerged turbine pumps. The system has not been run since filling the tanks around the beginning of May 2008 (to 5800 gal) and today the tanks show only 3700 gal.

Does this seem like a reasonable amount of evaporation for a "closed" tank (~1000 gal per month)? Or do I have a leak? I realize this could be calculated but it would be difficult to measure the air velocity across the water's surface (if there is any).

 

[vpl]

Bribyk

No it does not seem reasonable for evaporation. Especially since you say the tanks are underground.

I'd be looking for leaks.

Patricia Lougheed

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[BigInch]

I hope the concrete is lined with a waterproof coating, otherwise you have no chance. Concrete is full of capillary channels that will draw the water out of the tank.

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[Bribyk]

No dice on the coating. I knew there would be some seepage but I didn't expect this amount. I'm not worried about the water loss as much as where it's going and what it's doing to the foundation and soil below. Time to talk to the designers about this...

 

[BigInch]

You must have a liner or a coating, if you want to keep the water in it. Plain concrete soaks up water better than a Marriott towel. Concrete dams often have thick interior clay barriers to stop water from flowing straignt though them.

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[Bribyk]

The tanks are a precast concrete water cistern and the manufacturer assures me they don't seep. Looks like we may have a leak in the pipe connecting the two tanks.

 

[BigInch]

Perhaps.

Do you have any details on type of concrete used?

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[Bribyk]

No. They're rated for potable water so I'd think there would be a low-porosity standard for this application. The manufacturer is coming tomorrow to inspect the tanks.

 

[Bribyk]

All I have on the concrete is that it is 35 or 40 MPa (assuming the tank is the same as the lid).

 

[Bribyk]

We pumped out the tanks today and had the manufacturer inspect. It would appear the installer neglected a 1 1/4" plug near the bottom of one of the tanks. Our connecting pipe seal looks okay but we're gonna put a heavy coat of Plug-n-Patch around, to be safe.

 

[BigInch]

About par for the course as they say.

Good thing it was only water in them.

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[hydtools]

Things that make you go "Hmmmmmm".

Ted

 

[BigInch]

I said par for the course, 'cause there was a "hole in one."

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