When two become one. Replacing two failing septic tanks with an eco efficient sewage treatment plant

The challenge? To upgrade the wastewater treatment at a Devon longhouse served by not one but two failing septic tanks.

The property owners contacted WCI in search of a possible upgrade to a sewage treatment plant after a routine desludging showed some problems with their existing system. With most of the house served by an old septic tank and the kitchen and one bathroom served by a Klargester onion with broken baffles, we tasked ourselves with finding a solution that would be compliant, cost effective and future proof.

After an initial site survey WCI proposed the upgrade of one septic tank to a GRAF One2Clean 7Pe sewage treatment plant owing to its low running costs and excellent discharge treatment quality. The sewage treatment plant would be sited in a disused pond at the request of the customer and discharge to a surface water gulley linking to the watercourse. The second septic tank had backed up and would need our attention too. We identified the possible conversion of the second tank to a pump chamber to transfer wastewater to the treatment plant – and keep costs down in the process. Since the second tank lay under decking and a greenhouse, we also costed for the installation of a new packaged pump chamber should its condition prove unviable upon inspection.

Work commenced in May 2024 and one of the first tasks was to inspect the second tank. Regrettably it was deemed unsuitable for adaption to a pump chamber and a new pump chamber would need to be installed in its place as per plan B.

We then partially excavated the garden pond that was to house the treatment plant. Satisfied there was no ground water present, the team then excavated to full depth and installed the Graf One2Clean as per manufacturer’s instructions. Once in place, the team ballasted the tank with water, backfilled the hole to ground level and sited the manufacturer’s kiosk within reach of the treatment plant.

The next step was to dig trenches to install a not insignificant pump line around the house to link the sewage treatment plant to the pump chamber. The effluent would be pumped to the watercourse via a culvert under the road. The pump line was installed around to the outfall and connected to the sewage treatment plant. With the electrics hooked up and the new plant ready to go, it was commissioned by a WCI British Water accredited service engineer and the old septic tank was decommissioned and the hole filled with gravel.

We then set about remedying the mess we’d made! Excavated soil was redistributed in the chicken pen as requested, the affected plot was levelled with imported topsoil and reseeded and any disturbed patio slabs were replaced and secured. A full final documents pack was presented to the owner which detailed all the work undertaken and they signed up to an annual service plan for WCI to maintain their new system.

A note from the property owners:

“A friend of ours had used WCI for a replacement sewage plant installation and recommended them to us. We had a relatively complex requirement to install a system to replace two septic tanks that had/were failing. WCI responded promptly to a request for a site survey and recommendation and talked us through all the steps. When on site they were very organised and took time to consult with us before undertaking works. Although it is impossible not to have an impact on the garden with such an extensive installation, they took care to minimise damage and we were pleasantly surprised at how well the site was restored.  It’s early days to comment on the system effectiveness but we are reassured by the equipment and workmanship guarantees that WCI provide.”

Philip, East Devon