JW Clark Sewerage Treatment Plants & Septic Tanks

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JW Clark Ltd are approved contractors for Marsh Industries, manufacturers of Treatment Plants.

We Supply and Install

  • Septic Tanks,
  • Cesspits,
  • Sewerage pumping stations.

From small new build or replacement, to a full-scale development.

Are you Compliant?

Under the GBRs, anyone with a septic tank discharging into a watercourse must have replaced or upgraded it by 1 January 2020. Don“t worry if you haven“t yet, we can help.

Call  01933 650904 to discuss your project, we are happy to answer any questions!

Customer Testimonials

JW Clark installed a new septic tank in Overstone Park. This required careful handling as all the equipment had to be taken round Overstone Park Golf Course and all the work was adjacent to the Golf Course.The work was done efficiently and completed to our satisfaction, without receiving any complaint from the Golfers. They also did some work that was in addition to the contract without charge.

David Fuller
Overstone Park Residence

FAQ's - Section 1

They are for discharging into a watercourse, yes. They haven’t been ‘legal’ in this respect as far as Building Regs are concerned for a few years now. But as of 1st January 2020, it will be illegal to use and own one as such even if you inherited it or if it was already installed many years ago. Septic tanks don’t treat sewerage sufficiently to discharge into a watercourse - some of them not all. For a quote for installation of new treatment plant click here.

>4 bedrooms

6 ‘population’ treatment plant

5 bedrooms

8 ‘population’ treatment plant

6 bedrooms

8 ‘population’ treatment plant

7 bedrooms

10 ‘population’ treatment plant

For a 3-bedroom house a ‘5 population’ tank should be installed, also known as a ‘5 person’, ‘5pop’ or ‘5pp’. Treatment plants generally start at ‘6 population’. For every bedroom extra to a 3-bedroom house, an extra ‘population’ is required, so a ‘6 population’ for a 4-bedroom house, a ‘7 population’ for a 5-bedroom house and an ‘8 population’ for a 6-bedroom house, and so on. These are based on average volumes though, so if your usage is particularly high – for example if everybody is having a bath every day – then it won’t hurt to install the next model up. You may also want to plan for any future development or extension to the property. And just to confuse things, treatment plants tend to start at ‘6 population’, there isn’t a 5 population. After 6 population they go up to 8, 10, 12 and then 16 and 20 after that.

They should be serviced as per manufacturer’s guidelines, which is normally once a year. Sorry, this isn’t a service we supply but please click here for a list of companies who service treatment plants.

The Environment Agency’s take on this is that a sewage treatment plant “must be installed and operated in accordance with manufactures guidelines”. And most manufacturers recommend once a year. Make sure your chosen service provider is British Water accredited click here

A standard compressor blower the same as a 50w bulb, the equivalent to about £50/year.

All of our treatment plants are fitted with carbon vents to help minimize smells, so as long as you have the correct size tank, you service it regularly and empty it when required, you shouldn’t normally be able to smell hardly anything at all.

It’s a bit of a case of how long a piece of string is really. There are so many variables, including size of tank required, access to the site, drainage field required or distance to the watercourse. For a quote please click here.

A treatment plant will normally always be ‘full’, in so far as liquid is concerned. So if you lift the lid and it’s full to within 18 inches of the lid, then that’s normal, that doesn’t mean it needs emptying. It’s the sludge that needs emptying (de-sludging). As long as you have the right size tank, as long as you’re using it correctly and not putting any nasties in there and long as you’re not putting rainwater or surface water into it then it should only need emptying once a year, twice at the most.

Absolutely not! No! Never!

Why? A sewage treatment plant is designed to treat ‘foul’ wastewater. If you add rainwater into the mix this increases the flow beyond the size required for the size of the house. The tank will be unlikely to cope during a downpour, causing sewerage to back up due to the increased volume, it will play havoc with the treatment process and it’s illegal under Part H of Building Regulations, which states that foul and rainwater should be discharged separately!

In the event that your rainwater and foul currently go to the same place, we can separate them prior to installation of a new treatment plant. The rainwater should ideally be diverted to soakaways or to a watercourse, with only the foul going into the new Treatment Plant. For a quote click here.

No! It can’t! It should be preferably discharged into a watercourse (stream/river etc) or alternatively into a drainage field/land drainage. If a watercourse is not available, a calculation (percolation test) must be done to ascertain the amount of land drainage required. At this point, it often becomes apparent that the cost of the land drainage will be similar in cost to the installation of the actual treatment plant itself, sometimes more. And so the land drainage often gets skimped on, and often by installing a soakaway instead. But soakaways don’t work, no matter how big they are, and even if they are built with crates. Once they are full, they are full, they are full! Except in the most amazingly draining ground, they will get full very quickly and stay full. Lack of land drainage installed for a treatment plant is one of the main reasons they don’t work. If you have an existing septic tank or treatment plant and the effluent isn’t draining away quickly enough, it’s most likely because of insufficient land drainage. For a quote for any such remedial work click here.

The structure of the treatment plant itself is guaranteed for 25 years. On most types of treatment plants the only moving/serviceable part will be the ‘compressor blower’, this is guaranteed for 2 years. In reality the compressor blower will last for many years, but when it comes to replacing it, cost will normally be about £200 for a new compressor blower.

Yes, you must apply to local Building Control prior to installing a new Treatment Plant, and everything must conform to Drainage and Waste Disposal 2002 edition Part H-H2. However, Building Control will only normally need a few days’ notice prior to the start of the job. The homeowner can instruct Building Control, otherwise we can take care of instructing them and paying their fees etc. For a quote click here.

FAQ's - Section 2

As a domestic customer you are likely to be exempt from obtaining a permit from the Environment Agency as long as you can abide by their ‘General Binding Rules for Small Sewage Discharges’. For the full document click here.

For a summary see below:

The sewerage must be from ‘domestic’ use. For commercial sewerage you will need to apply to the Environment Agency for a permit. However, some small domestic-type businesses can be included in the General Binding Rules, such as a pub or a small nursing home. In this instance the waste would normally be in proportion to that of a domestic property.

You must not pollute the surface water or groundwater or stream, and this is generally achieved by having a treatment plant installed properly, and which conforms to BS EN 12566, as our works do. For a quote for a new installation click here.

The system should be installed in accordance with the manufacturer’s specification, and the system should be maintained as per the manufacturer’s specification.

The treatment plant should be emptied in accordance with the manufacturer’s specification and should be emptied by a competent company. For more info click here.

If you sell your property you must give any prospective or actual purchaser full written details of the treatment plant fitted, and notify them that they will be discharging sewerage under the General Binding Rules for Small Sewerage Discharges’

You must not discharge effluent within 30 metres of a public sewer. However, if there is a public sewer within 30 metres, then you shouldn’t be installing a treatment plant anyway, except for under exceptional circumstances. We also carry out sewer connections onto public sewers, for a quote for a connection to the public sewer click here.

Your old septic tank must be emptied and decommissioned and should not be left in a state whereby it could continue to pollute the watercourse.

As well as adhering to all of the rules above, the two sets of rules below are as important. One set deals with treatment plant which discharge into a drainage field/land drainage, the second set deal with a treatment plant that discharges into a watercourse (river or stream).

Treatment plants which discharge into drainage field/land drainage:

You must not discharge more than 2,000 litres (2 cubic metres) per day into the ground. To put this into perspective, emptying a bath into the treatment plant will normally generate about 80 litres of discharge from the treatment plant, and flushing the toilet will normally generate about 10-5 litres. A 4-bedroom house will normally generate about 900 litres a day, a 6-bedroom house 1,200 litres a day and a 10-bedroom house about 1,800 litres a day.

The treatment plant should discharge into a suitable drainage field/land drainage

The treatment plant must not discharge within a groundwater Source Protection Zone 1 [SPZ1] and must not be within 50 metres of a well, spring or borehole that is used to supply water for domestic consumption.

The treatment plant must not discharge within 50 metres of a Special Area of Conservation, a Special Protection Area, a Ramsar site or a Biological Site of Special Scientific Interest.

The treatment plant must not discharge into ancient woodland.

Treatment plants which discharge into a watercourse (river or stream)

You must not discharge more than 5,000 litres per day into a watercourse. 

The treatment plant must not discharge within 500 metres of a Special Area of Conservation, Special Protection Area, Ramsar site, Biological Site of Scientific Interest, freshwater pearl mussel population, designated bathing water or protected shellfish water. Nor within 200 metres of an aquatic local nature reserve, or 50 metres of a chalk river or aquatic local wildlife site.

The watercourse must be flowing at all times of year, not just in the winter. However, the watercourse may occasionally run dry in times of exceptionally dry weather.

You must not discharge into an enclosed lake or pond. It must be a watercourse which has ‘flow’.

When discharging into a watercourse, you must also discharge partially into a drainage field/land drainage within 10 metres of the watercourse, to aid with drainage during seasonal changes.

FAQ's - Section 3

Don’t put solid or non-biodegradable items down the toilet, or into anything from which it will work its way to the treatment plant. That includes sanitary towels, tampons, disposable nappies, baby wipes, cotton wool, incontinence pads, cotton buds etc.

Don’t pour fat or any cooking oils down the sink, the treatment plant will really struggle with these

Don’t have a traditional wash day or do all of your washing in a short period, spread it throughout the week if you can.

Don’t forget that you have a treatment plant, and don’t treat it like a bin! Unlike when you are connected to the ‘mains’ drainage, nothing is going to ‘go away’, everything you put down the toilet or down the sink is going to end up in your expensive treatment plant.

Don’t allow bleach or other strong cleaning chemicals to make their way into the plant

Don’t use washing powders, use liquid instead

DO continue to educate other members or tenants of the property as to what they can and can’t put down the toilet and the sink. Especially in the case of tenants, you might want to consider possibly putting signs up in the bathrooms and in the kitchen.

DO Try to use the same cleaning products and liquids, try not to change brands too often

Treatment Plant

Latest Case Study

Naseby Treatment Plant

Key Tasks:

  • Dig out and install 16 person treatment plant
  • Set in concrete and surround with 10mm gravel
  • Lay new sewerage pipes from house to new tank
  • Lay pipe from tank to existing manhole 
  • Fill in old tank with spoil already on site
  • Backfill and reinstate as found, leaving no mess

Treatment Plant

A recent customer from Naseby was having problems with his sewerage treatment plant and it needed replacing. After being awarded the job, we got in touch with our friends at Marsh Industries, who specialise in tanks of all shapes and sizes. We ordered a 16 person treatment plant to replace the old one, and a dug a pit  with enough room around the edges to set the tank in `Gen 3` concrete. We laid a 4 inch drainage pipe from the house to the tank, where the sewerage can be broken into two parts, leaving eventual wastewater to run out through an outlet and into an existing manhole at the bottom of the garden, some 30 metres away.  We managed to dispose of the original tank and lose some spoil in the hole, saving our customer some money. We then reinstated to leave the grass as green as when it started!

Here is what the customer said:

It took me months of evaluation to decide how to replace my failed sewage plant, I found JW Clark LTD as a highly recommended installer through the equipment Manufacturer.

They gave me very clear Information on the timing of the project and all the time during installation our needs for minimal disruption were considered, the job was completed in a timely manner with consideration and least area damage on our soft ground, which after a month is nearly back to normal grassland. Although not the cheapest Supplier they offered very fair Value , and we are completely satisfied and also confident if any problems arise they'll be dealt with efficiently.

Why Use JW Clark?

Our Reputation

Over the last 18 years, JW Clark Ltd have built many trusted relationships with all members of the trade, ensuring our work load is filled by repeat and one off customers.

Our forward thinking, innovitive and hard working approach has kept us in touch with the latest ideas and ensures we always find solutions, not problems.

Whatever project you are planning,  with JW Clark you will receive an honest service, at a competitive price with people you can trust.


Our Team

All of our groundwork employees are employed by us, we do not use subcontractors. They drive vehicles with our sign-writing on and wear our uniform. All employees are courteous and polite and are trained and briefed as to the level of customer service we want to deliver.

Operatives hold the relevant qualifications & accreditations for the work they are carrying out, and are trained and qualified for the machinery they operate.

Our Plant & Machinery

Most plant & machinery we use is owned by us and maintained to the highest standards.

All plant & machinery is checked every day by our operatives prior to starting work in the morning, and documentation is kept in the machines at all times to this effect.

Road Haulage Association
Environment Agency - Registered Waste Carrier
New Roads and Street Works Act

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