I will just start off by saying, I am really really pleased to be here.
Because about 20 years ago I first raised the issue of septic tanks
contaminating surface waters, actually Bassenthwaite Lake in the Lake District.
Talked to a community about as large as this.
It was followed by stunned silence.
And then somebody came up to me afterwards and said, don't ever try to publish that. It's rubbish.
I am hoping we have got a little bit more of a sympathetic audience today.
I was asked to talk about the impact of onsite sewage treatment systems
on river water quality in UK catchments.
And I am going to for short, because that's quite a mouthful, call them septic tanks.
But it also includes other site specific systems.
And because I am a freshwater ecologist,
and most of the problems that are caused by septic systems on ecology
are caused by phosphorus, and I don't have time in 20 minutes to cover
absolutely everything, we are going to focus on phosphorus as an example.
The outline of the talk really, I have divided it into five different parts.
Talking about the numbers and locations of tanks in the first place.
What the estimated phosphorus export to the environment is.
What the impacts on water quality are.
And then look at some remediation issues.
But I know they are being looked at in much more detail tomorrow.
Not so much on that. And some conclusions.
If we start off with the numbers and locations,
we are perhaps a little bit behind what we have been hearing about in Ireland today.
Basically we think, in the UK,
there's about 1.4m septic tank systems or similar systems, onsite systems.
But the official figures that we have suggest that there are only 200,000.
We know that many many of them are very close to water systems.
And you can see in that top diagram the septic tank inspection cover
in the foreground and the stream just at the back of it.
A lot of them actually discharge directly into watercourses,
and have been put in under old regulations or no regulations at all.
And as I say the exact number and locations are unknown.
I am just going to run you through some of the ways in which
we have tried to estimate the numbers, to raise the issue.
One of the first things that was done was to look at some large area statistics,
to look at the number of unsewered properties
in relation to the density of properties in a particular area.
And as you can see from this diagram, by the time you get down to about 10 or less,
certainly down to one property per square kilometre,
then there's no centralised sewage system.
And septic tanks or similar are the main source of sewage treatment.
That allows us to scale up to the UK, just to get a rough idea how many tanks there are.
But obviously can't be used for site specific detail.
It's very very difficult to find out how many septic tanks there are.
And I spent one very wet Sunday afternoon looking at some aerial photography
and trying to decide for some particular catchments
how many septic tanks we didn't know about, though a small number are registered.
Basically using this aerial photography, going over it, just very very slowly,
and identifying all domestic properties…
and I defined domestic properties as those properties that had a chimney,
because farm buildings don't have chimneys…
had garden paths, and obvious parking areas for cars, as far as I could.
And the upshot of that was that the number of registered septic tanks
in this particular area, in the upper Hampshire Avon,
was less than 11% of the actual number that was estimated from the aerial photography.
I repeated that for the Norfolk Broads, and there it was only 5%.
All the calculations that we do for the impact of septic tanks on water bodies
in catchment statistics are based on the consented ones,
not the 95% that aren't consented and that nobody knows about.
And from that we conclude that there isn't a problem.
If you include all of the septic tanks in this particular catchment
the amount of phosphorus that they are putting out is
roughly equivalent to a sewage works serving 10,000 people.
Cumulatively at the catchment scale there can be quite a big problem.
There are other ways of doing it.
And one is to take a dataset called the address point system.
Which actually has a point on it for every building and domestic residence all over the UK.
And you can take out of it anywhere that you know that there's a sewage pipe.
This particular dataset, that I am showing now,
is actually the number of properties….
the blue dots are the number of properties that are more than 30m from a sewer pipe.
It comes to a very large number.
But there are major issues in terms of the Data Protection Act
in getting this information in the first place.
And in fact Anglian Water put this together for me.
But they would only put it together as a hard copy map,
not as digital information that we could do anything with.
Because of the problems of being able to identify people from the data that they hold.
There's some issues there to be sorted out if we are going to take this much further forward.
Improved registration is probably the best way.
And we saw some examples of how this is happening in Ireland.
Scotland started relatively early in terms of the UK.
And from April 2006 onwards they decided that all new discharges required authorisation.
If they were greater than 15 people they required a discharge licence.
And they brought into place a rule that said that if you sell your house
and it's got a septic tank it then has to be registered.
And there was a cost associated with that.
And to encourage people to register early they waived the registration fee
and asked people to register their septic tanks voluntarily.
The upshot of that was that well over 50,000 people tried to register their septic tanks
in a very short period of time
and actually caused a bit of a backlog in the registration process.
But it just goes to show how many there are.
In England and Wales they have started to do registration much later.
And the idea was that all of these discharges should be registered,
but somebody complained to their local MP that this increased their red tape.
And in England at least they have suspended that registration pending a review.
And that as far as I know is still ongoing.
In Wales they decided to carry on with it and they are still collecting data.
And we will see some of that in a moment.
But one of the things I would like to just illustrate is in my favourite catchment,
the one I normally work in, in Scotland, in Lough Leven,
is a phosphorus sensitive catchment.
Lough Leven is very very sensitive to phosphorus going in.
It causes algal blooms.
And there's many millions of pounds are being spent upgrading the lough
and its catchment over the last 20 years.
And the local planning authorities there, they use what they call the 125% rule.
What that says, it's part of the planning process.
And if you want to introduce a new source of phosphorus into the catchment
you have to calculate how much that will be,
then calculate what 125% of that will be,
and apply mitigation to somewhere else in the catchment
to remove that phosphorus from the catchment of someone else's septic tank
or something similar to compensate for that.
And you can't get your planning consent until you do that.
I don't know how clear that is, but
the outcome of the improved registration in Wales is actually illustrated in this map.
And the small red circles are the consented tanks
or the registered tanks that they already knew about before the registration process started.
The greeny coloured ones are the ones that have been added since,
as people have started to register their tanks.
You can see that that information suggests that this 95% of them not known about
before the registration is actually probably true.
We need to have a look at how much phosphorus comes out of these systems.
There are obviously other pollutants and there are issues with pathogens and things.
But just for this 20 minutes we will focus on phosphorus.
If we say that there's 1.4m septic tanks or similar in the UK,
and we look at roughly how much phosphorus comes out of each one of them,
and sum it for the UK we get 1,810 tonnes per year of total phosphorus.
Now if we compare that to fertiliser derived phosphorus leaving a catchment,
that's 123,000 tonnes.
You would think that it's a very very small percentage.
And you would be absolutely right, if you are looking at the UK scale.
The problem is that most of these systems are in very sensitive upland systems,
where there are headwater streams and where this phosphorus is really very important.
It isn't right to just compare the amount coming from farmland generally
across the UK with the amount from septic tanks and dismiss it.
Because the local problems in headwater streams where things are very sensitive
can be quite serious.
You should also think as well that only about 50% of what comes off farmland is soluble phosphorus.
A lot of it is particulate, some of which becomes available. But a lot of it doesn't.
Whereas what comes out of a septic tank, 98% of it is soluble
and very biologically available phosphorus,
that promotes things like algal blooms and the growth of macrophites
and downgrading of water quality.
Here is an example, similar to one we saw this morning,
in fact, of a septic tank that had a problem.
It was poorly designed and we tend to think that poorly designed
septic tanks are the older ones.
This one was built in just 2002.
And when we looked into it in detail, somebody said, can you come and have a look,
see what's wrong with it, we had a look and I think the builders had the plans upside down.
Because they are supposed to mound the system,
because of the height of the water table there.
Build a mound of about a metre of soil and put the pipes in at the top.
What they did was, they put the pipes in at the bottom and
built the mound over the top of it.
And this caused these sorts of problems.
It had gone through all the planning and approval and everything.
Don't be absolutely sure that your more recent ones are behaving properly.
System discharge leads to direct discharges to water and storm run off,
and these sorts of things obviously where if it rains it all washes into ….
you can see it's causing its own algal bloom at the bottom anyway.
But it then runs off into local water bodies. They can be incorrectly sited.
They can be poorly managed. And we will come back to that in a moment.
What is very often true is that if there's a problem with a septic tank it will smell.
And that's when really to look for a problem.
Because they really shouldn't have a smell associated with them.
If they are not working properly then you get reduced processing of the effluent
that comes out of it and blocking of the biomat,
increased surface run off and direct discharges often over land to watercourses.
Now we started looking at developing some guidance to reduce the risk.
And this study here, which is very very recent, looked at 48 septic tanks,
and particularly asked the owners a lot of information about them.
One of which was the age of their system.
Interestingly 54% were over 20 years old.
And 14% were over 50 years old, of the septic tanks that they looked at.
Very large numbers of very old systems, put in under virtually no regulations,
many of them cracked. And we will look at that in a moment.
This report also put together a flow chart to assess the impact of a septic tank
on a local watercourse.
And it's got a series of…you may not be able to see that it's rather small…
but a series of yes and no answers. Has it been regulated?
Was the system installed since 2001 etc.?
And then it goes through to a low, medium or high impact box,
which are the green, orange and red boxes.
But we really really have to be very careful about how we assess impact,
because if you manage your septic tank properly and it's functioning properly
it very very efficiently turns particulate phosphorus into soluble phosphorus
and puts it out of the outflow.
Most of the regulations and information that you can get hold of
is to treat other pollutants and not phosphorus.
It's possible that by telling people to manage them properly
and take the sludge out of them and so on
that we actually are creating more soluble phosphorus being discharged into the environment.
Why haven't we dealt with this before?
I guess it's because they are hidden.
We look at these lovely rural landscapes and there's no obvious water quality issues.
And they are hidden underground, so we can't see them.
But if you look in more detail, and we saw some pictures like that this morning,
there are pipes with sewage fungus growing out of them,
smelly pipes and things emptying into watercourses all over the place.
But because they are hidden, in the UK at least, and by the sound of it in Ireland,
we have taken this sort of three wise monkey approach to it.
You see no evil, you speak no evil, you hear no evil.
But I think there should have been another monkey that was called smell no evil.
Because they couldn't have ignored it then.
And it's really really important that they realise what they have been doing.
Impacts on water quality, I will just quickly skim through this.
But people say, well, OK, but there's not much impact on water quality.
Here's one example in the Wyre catchment in England.
And you can see the side of the septic tank, how much the phosphorus goes up.
It goes up from 50 micrograms per litre, which is highish anyway, but not incredibly high,
to 400 micrograms per litre, which is four times the Water Framework Directive targets,
or more than that in rural areas.
Again in the Eye Brook you can see again, the blue being the upstream of these systems
and the red being the downstream.
And the two graphs here, the top is total phosphorus,
the bottom is soluble reactive phosphorus.
You can see how much of the soluble reactive bio-available increases downstream of these systems.
I am not sure if you can see the numbers,
but it goes up from about 50 micrograms per litre to 250 in that case.
We can also look across catchments. We can look at hotspots.
And this is one that I did at Hornsea Mere where there was a big problem
with phosphorus affecting the lake there.
And we found that all over those large red blobs are concentrations
in the drainage system there, that are more than 300 micrograms per litre,
more than three times…probably more than that of the target concentrations.
In actual fact the very bottom one was over 2 mg/litre phosphorus in the stream there.
And these were contributing to a massive in-lake phosphorus concentration of 1.2mg/litre,
which is way above what it should be.
Another discharge here, the Chitterne Brook, which is down in the Hampshire Avon in England.
And you can see there it's what they call a winter born stream, fed by groundwater.
And in the winter the groundwater rises and flushes out the septic systems.
And you can tell that by the increased phosphorus there.
You can tell it by the fact that boron goes up at the same time.
That's found in detergents.
You can also tell because a local newsletter called ‘Chit Chat',
they have an item every February,
complaining that their septic tanks have overflowed into the river.
Some more detailed data shows how this happens.
When there is low flows there's dilution of the waste with higher flows,
and then as the flow increases it starts to wash out what's in the soak away
and what is in the tank.
And then you get an increase with flow of phosphorus concentrations in the water.
Some more information from Northern Ireland,
showing that higher densities of septic tanks then the phosphorus concentrations
in the streams that they are close to are more likely to
exceed phosphorus concentration targets if there are more septic tanks.
It's logical but people didn't really believe that in the past.
And here, this is to do with a cracked septic tank.
Basically we were looking at the inflows to Loweswater in Cumbria.
And you can see that big peak in the graph at the bottom.
That was coming from a septic tank on this stream here,
which turned out, a) to be cracked, and b) to take roof run off.
When you had really high rainfall it just flushed the whole lot out into Loweswater.
The inputs from septic tanks to that lake we estimated
to be about 14% of the phosphorus load.
And here there's a big issue because they only use consented systems
to do the calculations for catchment.
You can see on the left here, and we will just talk about the top left,
because we are running out of time.
6% of phosphorus in the downstream is predicted to come from septic tanks,
and 94% from agriculture on a balancing basis.
If you take into account all the tanks, the ones that I found from the aerial photography,
that balance changes.
And it's 40% from tanks and only 60% from agriculture,
because they do this by difference.
They look at the amount in the stream and they take away what they know about,
and the rest of it must be agriculture.
That's enough to fail Water Framework Directive targets on its own.
Remediation, not too much on this.
But one of the things the cheap and easy things is to start giving people good,
well-founded public information.
And I will just read what it says here,
this is news releases from the Lough Leven catchment.
Don't be a septic sceptic.
Do your bit to help Lough Leven, was one of the things that we sent out.
And septic leaks thwart lough clean up.
We said to people, look, we are spending millions of pounds reducing inputs
from agriculture and sewage, you need to sort out your septic tanks as well.
Because they are contributing.
The impact has been massive.
And Lough Leven has recovered.
But that's another very long story that I am not going to do now.
But a simple thing, which the Scottish Environment Protection Agency tried,
was to make these teatowels which say to people, make the link with your sink.
You know, what goes down your sink goes into the septic tank,
ends up producing phosphorus and contaminating the environment.
And there are other similar sorts of things.
Every time someone is at the sink doing their washing up,
they pick up their teatowel and they may remember.
The problem actually though is that it's dishwashers…
dishwasher detergent that contains a lot of phosphorus.
And you don't often use a teatowel if you have got a dishwasher.
There are other ways. We also talk to the local community.
We also go into the schools. And that's for another talk really.
The impact of these sorts of lifestyle changes is actually unknown.
We don't really know what a difference it makes if you use phosphate free detergents.
But there's some evidence that phosphate free detergents is important.
We also know that the local shops often don't stock them.
That makes it difficult for people to get hold of.
But one interesting thing is that the phosphate that comes out of your septic tank
is probably half as high if you all go vegetarian.
That's something to think about.
OK, so again people say, well does it really come from septic tanks?
I just want to show you this example. And I really am on my last slide now.
Just to show you the River Chew, where they had a lot of septic tanks.
And then they introduced a first-time sewerage scheme.
And the water quality dropped, in terms of phosphorus concentration
dropped enormously from an average of 250 micrograms per litre to 86 micrograms per litre.
Now I have to say we were cheating a wee bit there.
Because the first-time sewerage scheme actually plumbed the phosphorus
from the sewage works that they put in into another river.
However, it was very much lower and this actually does demonstrate
what the impact is of the septic tanks themselves.
We shouldn't just write it off as a silly example.
We can see that most like came from septic tanks.
There are very few other places we can demonstrate that.
Conclusions, lots of mounting evidence.
Discharges can occur under high and low flows.
They affect nutrient concentrations, and may be incorrectly attributed to agriculture.
And I think that's quite an important issue.
Catchments with high densities are most vulnerable.
Removing or upgrading septic tanks appears to improve water quality.
But we need to be very careful that we know by how much.
And the phosphorus discharge is highly biologically available.
There's high risk of ecological impacts.
We still don't understand them terribly well. We need a better process understanding.
Because the information that we give out to people
should inform best management practices properly,
not give them a whole load of other stories that actually aren't true.
And I am going to stop there. Thank you very much
0:00:00 / 0:00:00
Dr. Linda May (CEH, Edinburgh)
The impact of on-site sewage treatment systems on river quality in UK catchments