Bunds for pool chemicals (TN35)

PWTAG Technical notes are updates or new material for the standards and guidance given in the PWTG book, Swimming Pool Water and the PWTAG Code of practice and should be read in association with these publications.

All liquid pool chemicals should be stored in bunds, to prevent any leaks or spillage spreading. The specifications in this technical note are for sodium hypochlorite, but they are a guide too for hydrochloric acid and other liquids.

Construction and specification

Bunds can be reinforced concrete, concrete block or brick. They must have a lining resistant to water and the chemicals stored – therefore the lining may be epoxy resin, PVC, welded polypropylene or GRP. The lining should cover all walls within the bunded area up to minimum 100mm above the bund wall height. The lining should lap over the top of the bund wall. The floor of the lining should be non-slip.

Ideally, prior to any lining application, the floor of the bunded area should be finished with a self-levelling screed/compound. Uneven construction surfaces can result in flexing of the lining materials and eventually lead to failure.

The bund must be capable of containing at least 110% of the capacity of the bulk tank (which can be 1,000-3,000 litres), and the day tank if this is within the same bund. The height of the bund wall and its distance from containers should be enough to contain a jet of liquid from a puncture.

Partitions between adjacent bunds should be at least 800m high. Acids and alklalis (including hypochlorites) should not be in adjacent bunds– ideally, not in the same store room. It is risky to store any substances that can react together too near each other especially if they are flammable, explosive or give off toxic fumes.

These considerations about the size of bunds should also take into account the weight of containers being lifted over bund walls. (Special lifting arrangements may be necessary.) Inspect your containers and drums at least once a week to check they’re not damaged or leaking and put a procedure in place to replace or repair damaged or leaking containers. If the planned height of bund walls may be reduced for lifting, then the 110% capacity can be retained by increasing the overall internal area of the bund.

For jerricans, the volume of the bund must be at least 50% of the total capacity of the maximum number of containers stored at any one time. The bund should be tank tested for any leakage, using water. If the lining is PVC welded, joints should also be spark tested.

The bund should have a shallow sump capable of receiving a hand transfer pump to empty in the case of spillages, which should be discharged safely by trained personnel.

You must make sure sumps and bunds don’t become contaminated, cracked or blocked as this may cause them to leak.

The bulk tank should be installed on a concrete or suitably coated steel frame plinth. The bottom of the bulk tank should be above the fill level of the day tank, so that the bulk tank can be completely drained.

The entrance doors to the store need to consider potential future replacement of bulk tanks.

For bulk liquids a connecting fill point is required. The positioning of the fill point is site specific, but they can be external to the stores within a locked cabinet or within the store itself.


The majority of chemical spills and incidents arise from operators changing/cleaning injectors. They should therefore be inside the bunded area but easily accessible for maintenance purposes. With the chemical loop system the loop(s) can be taken above the bund area thus enabling the injector(s) to be located above the bund and be accessible from outside the bund for maintenance.

The fill valve from the bunk tank to the day tank should be installed over the bund but not within the bund flood zone. The valve should be dead man’s handle-type. Ideally the plinth design should allow transfer from bulk to day tank by gravity. If not, a transfer pump will be necessary, either manual or electric. If electric, it should incorporate a high-level switch to stop the pump when the tank is full. This transfer system should not be confused with the fill line for the bulk tank.