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Septic tanks on limestone

grahams

Well-known member
Around here (Grange-over-Sands) we have several large new housing developments. Rather than connecting into existing (inadequate) foul water systems, the developers are saving money by using a septic tanks system (one per site) which, in extreme conditions, dumps the overflow into limestone fissures. As there are no surface streams, no water testing, other than squirting water down the fissures and watching it disappear, has been performed to my knowledge.

The housing developments are on limestone hills with considerable gradients and undulations, resulting in the need for extensive earthworks.

Has anyone any knowledge or experience of the use of septic tanks on limestone?
 

grahams

Well-known member
Thanks Alastair.
Just to be clear, the septic tanks systems service considerable numbers of houses - 43 in one case and over 200 plus industrial in the other case.
 

adam

Member
Septic tanks need a soakaway - a large area of grassland for the dirty water to drain to. It sounds like this probably isn't the case there, and being on a limestone hill, it wouldn't be possible to construct underground soakaways anyway.

Is it possible they're installing package sewage treatment plants? These supposedly treat the water to a sufficient standard to discharge straight back to a watercourse, so should in theory be ok to discharge to limestone. However they need to be maintained and periodically emptied to work well, otherwise they'll start discharging untreated sewage.

I'd expect the EA will have been consulted on the development and consented the plans for wastewater treatment. Even so, it's a lot easier for them to monitor a single public sewage treatment plant than several hundred private ones. It's surprising that they haven't insisted on connection to the mains. Individual systems for each house seems a crazy way of doing things.
 

Ed

Active member
alastairgott said:
grahams said:
considerable numbers of houses

Yes, I guess that'll make a difference, one or two bums vs 243x2.5=608 bottoms dropping anchor.


It isn't the actually occupancy number but the potential maximum ie 2x double bedroom = 4 people. 

BS6297 this is the formula:

C= (150 P + 2,000) 
C is the size of the septic tank in litres. This is litres per day capacity

P is the population to be served - this is potential not actual inhabitants.

Planning can ask for a hydraulical study to be undertaken on large developments

It wil lalso need an Environmental Permit  from the EA
 

alastairgott

Well-known member
guess that the 2000 is for the water already in the tank.

2.5 was a guesstimate on the number of potential inhabitants.

Please do not be offended by wild assumtions when you consider that if the population is primarily composed of Elderly (retired) Residents then you could expect that to be a high use of the toilets (ie in the house all day), wheres a house comprised of professionals may have a lower use of the toilets (due to spending most of their time outside of the house).

I guess with new housing you may expect to see higher occupancy, however Grange over sands is quite close to the Lakes, so could have a bias towards some people taking up houses for retirement.

British standards are all well, but this is a generic formula, and probably errs on the side of caution.

I've just been out to Miami-dade county in florida, there are a large number of Septic tanks serving the locality and most of the water which the population uses comes from subterranean aquifers. some which have a high flow, in the region of 7000gallons per day.
http://miamidade.floridahealth.gov/programs-and-services/environmental-health/onsite-sewage-disposal/index.html

Clearly there is a huge threat to the environment out there, but as far as I know the Mangroves make more stench than the sewage does. I even went paddling in the water near a sewage treatment site, no smell there!
 

Simon Wilson

New member
For a new development of 200 houses the Environment Agency will have been well involved in the provisions for sewage from the planning stage.
 

grahams

Well-known member
No problem Alastair - oldish folks like me never take offense at anything  8).

The smaller of the two developments (for 43 houses) is almost complete. At its lower end the development has a small area of wild grass and scrub which acts as a soakaway. Whilst I have no way to confirm this, I would guess that the builders have followed the regulations (thanks for the link Simon) regarding the size of the soakaway but I was surprised to discover that the overflow is to a fissure, the water tracing of which appears to be inadequate. It could be that the procedures specified in the Gov. waste guidelines have not been followed correctly - out of sight, out of mind, until the waste pops up under someone's house.

Downslope from the new development is an area of older housing which extends almost to the salt marsh. The 8 inch sewer pipe is known to be inadequate and frequently dumps sewerage on the road by Kents Bank Station. It is likely that the builders chose the septic tank method as upgrading the current pipe would be very expensive. But it could be that there are Gov. directives which require that new developments are self contained.

Regarding the larger development of 200 houses plus industrial the building of which has not yet started, a similar septic tank/soakaway/overflow method is proposed. As similar water tracing problems exist on the larger site but on a much greater scale, a proper solution for dealing with overflow will be needed.
 

adam

Member
I've just been perusing the foul & surface water drainage strategy for the 43 house development (sad times). It shows the foul water connecting to the nearest mains sewer. The soakaways are for surface drainage which is then discharged to the estuary. I thought it was unlikely that such a development would want, or be permitted, to use septic tanks.
The 200 house development doesn't seem to have a planning application yet but I wouldn't worry about that one either. Sounds like UU will need to upgrade their sewage works though.
 

Tommy

Active member
Alastair, As someone who grew up nearby...

Grange-Over-Rated is the definition of God's waiting room.

Now the waiting room has improved toilet facilities!
 

alastairgott

Well-known member
Topimo said:
God's waiting room.

Is that in referance to its proximity to the lakes and also gods own country (yorkshire) or just that theres always a phantom with a scythe nearby to harvest the ripened people?
 

droid

Active member
alastairgott said:
Topimo said:
God's waiting room.

Is that in referance to its proximity to the lakes and also gods own country (yorkshire) or just that theres always a phantom with a scythe nearby to harvest the ripened people?


The youth of today..... ::)
 

grahams

Well-known member
GoS has easy access to God's Own County, to the Lakes, to the local hills and to the North Pennines so it keeps an old crock like me happy. Too many other oldies and not enough pubs though.

I've found a supplement to the South Lakes planning documentation that states that the foul drainage on the larger of the two sites is to be into the sewerage system with a soakaway for surface water. The smaller site has a soakaway and a vented septic tank beneath the 'biodiversity area' at the lowest point on the site. If the sewerage is disposed of via the already overloaded pipe, the problems at Kents Bank station are going to be exacerbated.
 

grahams

Well-known member
Thanks Simon but the planning docs don't usually go into such detail. Some of the larger and more environmentally sensitive sites have planning supplements which specify requirements such wildlife corridors, drainage and preservation of drystone walls. The smaller of the two development sites does not appear to have one of these supplements so I'm going to ask the builder, Russel Armer.
 

AR

Well-known member
The planning application should have been accompanied by a pretty hefty Environmental Impact Assessment (EIA) and if that didn't cover wider drainage impacts given it's on limestone then I'd be very surprised. It'd be worth your while talking to John Gunn about it as he does consultancy work on limestone hydrology as well as his academic role.

Septic tanks are not uncommon round here in the White Peak, my own house has one and even the small sewage works for the villages generally discharge the final effluent into soakaways after it's been through the reed beds.
 
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