Sewerage improvement works at Cotehele
Looking after Cotehele properly isn't all about conservation of tapestries, woodland management and habitat restoration. One vital piece of work we're currently undertaking is to improve the sewerage facilities by the house.
What are we doing?
We’re digging trenches and laying new pipes to drain foul waste water away from the house and Barn restaurant.
We’re installing a new Sewage Treatment Plant to replace two existing septic tanks
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:
Listed buildings consent
Archaeological watching brief
Arboricultural watching brief
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.
Caring for our heritage
The archaeological watching brief is in place to look for any archaeology that might be uncovered during the digging.
Past excavations at Cotehele have unearthed very little archaeology – not even broken pottery and rubbish that you’d expect to find on a site like this.
So, where is all the ‘rubbish’? It’s possible that we’ll discover a medieval rubbish tip when we begin digging the pipeline channels in the woodland. If we do, digging will stop while archaeologists move in to excavate the area, which will be very exciting, but will slow down our drainage work.
Toilets through time at Cotehele
Not all the methods used to deal with human waste during Cotehele’s history have been as efficient or environmentally sound as this new sewage treatment plant.
The earliest toilets at Cotehele were latrines with chutes which let waste fall down into a pit by the house walls. These pits were emptied by Night Soil Men, who took the waste away to large dumps for use as fertilizer. These men also removed waste from seat-and-bucket latrines and chamber pots.
Specially designed furniture hid chamber pots within rooms. In the South Room a night cupboard conceals a pot within a mahogany cabinet (c.1790) and in King Charles’s Room there is a pot inside the ornately carved 19th-century bed steps.
The later Victorian water closets installed at Cotehele flushed waste straight into the storm drainage system, which was designed as a channel to drive rain water away from the house and down the valley to the River Tamar.
This combined storm and foul drainage system continued to be used at Cotehele until the 1970s when the National Trust had ownership of the site and separated the drains, installing two septic tanks to treat foul waste.