What are we doing?
Why?
The existing pipes are a combination of those installed by the National Trust in the 1970s and some which are even older. Surveys have shown that some of these pipes are now leaking because of damage from settlement and tree roots.
The septic tanks are reaching the end of their life and need replacing with a system better able to cope with the needs of the restaurant and visitor numbers. We investigated a number of different options and this is a cost-effective use of our charity’s funds and will see us safely exceed the requirements of new legislation introduced by the Environment Agency which comes into force in 2020.
The sewage treatment plant
We're installing a KEE bio-disc sewage treatment plant. This system has been tried and tested and proven to be a cost-effective and environmentally sound way of treating sewage.
It has four chambers through which the sewage passes, becoming cleaner and freer from nitrates as it goes.
1= Septic tank – The foul waste drains into this chamber first
2= A biodisk system admits air into the liquid waste which helps natural bacteria grow and treat the sewage. Around 200 disks turn in the liquid, aerating it.
3 = Sewage from the 1st biodisk chamber moves into the second where it is treated again by the same process.
4 = By the time the sewage has been treated in the 3rd biodisk chamber it has lost its smell and is cloudy rather than muddy. The nitrate content is now well below that advised as safe by the Environment Agency.
Doing it right
Conservation is always at the forefront of our thinking. To ensure the work doesn’t damage the architecture and environment on the Cotehele site, the following checks are in place:
Looking after the trees
Our arboricultural watching brief ensures we do not cause harm to Cotehele’s trees.
Our re-designed drains bring together the House drain and the Barn drain and run them to the new sewage treatment plant. As the drains have to be laid to fall, the only practical design goes through the woodland.
To avoid harming trees we can’t use large diggers within the root system, which is usually one and a half times the tree canopy, so we’re mostly digging the drain trenches by hand. We can use a small digger and dumper on ground protection boards, which prevent the soil being compacted underneath, with hand digging around the tree roots.
The new drain will run under the tree roots and any roots larger than 20mm need to be retained. We wrap them in hessian and keep them moist to protect them until they are re-buried.