underground storage taNks

Installing an underground water storage tank is simple when you have the right tools for the job. In this article, you will learn a simple 6-step installation method that includes an explanation of the recommended materials and machinery to be used. Using the correct backfill material to bury a polyethylene tank is particularly important as it will lengthen the life of the tank significantly. Because these tanks are getting buried, you must also be extra cautious about where you are installing them. The geographical  elements of certain areas may require you to consider extra cautionary steps.

Backfill Material Instructions:

Using the correct backfill material will minimize the possibility of the tank collapsing. This is an extremely critical part of installation and must be followed. A one-to-six ration of river and cement mix is required to encapsulate the tank. If the geographical area is prone to high water table levels during the raining season this ratio may be increased. When mixed care should be taken not to ad water and make a wet mix, it should be a dry mix for filling the bottom of the hole and around the tank. It is important that all material must be free of sharp objects that could cause damage to the tank.

7-Step Installation Guide for Underground Water Storage Tanks:

1. Excavate – Measure the length and width of the tank. Add at least 250mm on both ends and sides of the tank and mark those dimensions on the ground. Excavate to a depth that will provide a minimum of 200mm and a maximum of 350mm of cover over the top of the tank. Topsoil may be placed over the filling after the filling have been lightly compacted and hardened.
2. Prepare Base – Remove any roots and rake the bed flat. The preferred tank bedding material is the filling material described above. After measuring and filling in the base layer of 250mm of filling, lightly compact and level before setting the tank. Ensure there are NO SHARP OBJECTS mixed filling. This could puncture the tank without you knowing.
3. Set the Tank – Place the tank in the middle of the hole. Begin pushing the tank back and forth to allow the base filling to fill in the ribs along the bottom of the tank. If you are lowering the tank in the hole using a crane or excavator, level the tank before removing the straps in case further excavation is needed.
4. Install Connections – Install bulkhead fittings in tank. You MUST plumb with a flexible hose directly from the bulkhead fitting. This prevents any movement that could break the fitting and put extra stress on the tank. Extra fittings that are installed in this tank are the responsibility of the owner. Underground tanks must be vented to prevent them sucking in when water is being pumped out.
5. Add Risers – Remove lid and gasket that is supplied with the tank. A RotoTank™ riser varying from 300mm to 900mm may be installed on top of the tank to secure access to the tank. More risers may be added to accommodate the depth of the hole. Add lid and gasket to the top riser installed.
6. Backfill – Begin filling in the space around the tank with the recommended filling material and compact in layers of 200-300mm. Make sure all gaps under the tank are completely filled. ALWAYS COMPACT EVENLY AROUND THE ENTIRE TANK. Make sure to compact backfill under pipes. Carry on layering the filling until a layer of at least 200mm is lightly compacted over the tank.
7. Finishing off the installation – Once the tank is installed in the ‘sand/cement powder mix’ it can be finished off by adding topsoil over the tank. The vent or risers should be properly secured.
   

   Quick Summary:

   Now you have a basic idea of how to install an underground water storage system, you’re set to go! Regular checks of an under-ground tank is recommended to ensure nothing out of the ordinary has happened. If you are using your underground tank for drinking or potable water, you should also make an effort to monitor the water quality to be sure no debris has entered through the tank lid.