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Oxfam Tank Liner damaged by Insects

Hey, we constructed several Oxfam water tanks, 70 and 90m3, on 2m and 3m elevated platforms. The platform consists of a round brick wall back-filled with brick-chips and sand. On top of the tank platform we erected the tanks. Inside on top of the platform there is at 4 inch sand layer to protect the tank liner. Now we discovered in two tanks over 60 small holes in the tank liner, caused by probably termites, only from the bottom into the tank, no holes in the walls. The termites must have been in the back-fill material and might eat holes into the liner to reach the comfortable stable and cool temperatur of the tank. How would you get rid of the insects? Concrete layer between liner and platform as a physical barrier? What about insecticides as a chemical measure, but that might not be the greatest option regarding the proximity of drinking water? Any advice or ideas? :-) Thanks!

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Dear Luderix,

We would be Interested to know what lining system you have used for the Oxfam tanks (rubber or plastic), as we have been manufacturing Oxfam tanks and lining systems for over 45 years, and we have never heard of a incident with termites. We would normally recommend a concrete base for tanks over a T95, and and compacted sand for smaller tanks and we would also suggest a geo-textile disc to protect the liner.

Best wishes Craig Butyl Products Group

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There are several approaches to termite protection, none of which are mutually exclusive (so you can try all and any of them). The first is the barrier method, where you insulate your vulnerable structure with other structures that resist attack. The second is poisoning and the third is setting traps.

From what you describe, it seems that you may have already imported some infestation in the tank fill material, so it will only be possible to use barriers on future constructions. This might be difficult anyway because of the need to achieve an absolute seal between the fill and the tank liner. One approach might therefore be to sterilise the fill material before use it, e.g by roasting over a fire or by spreading out thinly in bright daylight (termites don't like daylight).

The simplest and cheapest non-persistent and non toxic termite poisons are vinegar and borax. The existing structures could be sprayed with these - probably several times before the tank is filled. The best trap is apparently wet cardboard. This is like caviar to termites, so a management strategy might be to leave pieces of wet cardboard in the vicinity of the tanks and regularly take them out and burn them before replacing with new. There is a range of of commercial termite trapping systems, many of which have to be set out around the area and buried in the ground ( a bit like slug traps).

Hope some of this is helpful.

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Dear Keith, thanks a lot for answer and advice! Very much apreciated. I posted the challenge also in SuSanA forum and had some interesting comments, have a look... Tarsheets used for roofs could work as well. Nevertheless, our plan is now to remove steel or plastic roofs, remove the liner, dig the sand layer out, down to the platform, seal the platform with a 2 inch concrete slab, refill 4 inch of sieved or treated sand to protect the liner and reinstall liners and roofs...

luderix gravatar imageluderix ( 2019-06-30 14:31:50 +0100 )edit
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Good stuff. Sounds like a sensible approach. K

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We opened the tank walls on two sides by removing one metal sheet. We lofted the liner instead removing steel roof and liner. We digged the sand layer out. We placed a 3 inch concrete slab on top of the platform. We covered the slab with a 3 inch sand layer. The sand was sieved to make sure no insects (termites/ants) are back-filled and the sand was treated with a 1% chlorine solution inside the tank. Liner down, metal sheets back. Only tricky remaining part is that the screws of the metal sheets should be holded manually from inside while closing the nuts from outside and the corners of the metal sheets need to covered by solid black tape to prevent liner damages...

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Just a comment - you have presumed the damage is due to termites, but you may want to consider other options. Are there any other signs of termites such as actual sightings or tunnels in the sand layer?

Other causes may be damage during construction or transport. Are people standing in the tank during construction or cleaning? Is the sediment in the tank gritty? Was the protective sand layer soft like sand for mortar or harder like sand for concrete?

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Just a comment - you have presumed the damage is due to termites, but you may want to consider other options. Are there any other signs of termites such as actual sightings or tunnels in the sand layer?

Other causes may be damage during construction or transport. Are people standing in the tank during construction or cleaning? Is the sediment in the tank gritty? Was the protective sand layer soft like sand for mortar or harder like sand for concrete?

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