How to meet EU lead standards by 2003

Neil Tarbet from WRc takes a look at the problem of lead pipes and how to choose an appropriate technique, such as trenchless pipe pulling or lining.


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The revised EU drinking water directive (1998) includes a requirement to

reduce the amount of lead present in supplies.

A stepped approach is allowed in recognition of the enormity of the task –

there are an estimated 7-10M properties currently receiving water via lead

pipes in the UK alone.

At the same time the directive recognises that water utilities do not have

full control over pipes within customers’ properties and it could be

difficult for a government to introduce legislation forcing customers to

remove their lead pipes.

A get-out clause has therefore been introduced which says that the

requirements of the directive have been met, provided the water supply

complies with its requirements at the final point of the distribution system

over which the utility has control; the boundary stop-tap.

However this get-out clause does not apply to Œpremises and establishments

where water is supplied to the public, such as schools, hospitals and

restaurants’.

The problem is therefore how the requirements of the directive can be met,

given these restrictions. In the majority of cases it will be possible to

meet the interim 25µg/l limit by water treatment and in favoured areas it

may be possible to meet the final 10µg/l value. However it is likely that

for most waters, pipe replacement or rehabilitation will be necessary.

TRENCHLESS systems

Various systems for the renovation or removal of lead pipes have been

developed, in addition to traditional open-cut trenching. Open cut trenching

does not require special skills or equipment but is very disruptive and

costly. Other than for the replacement of the short-side supply pipe, it is

generally considered as as a last resort.

For long-side supply pipes, installation of a new pipe by Œpneumatic impact

moling¹ is the most common method. However, impact moling cannot be used in

all situations, particularly where the ground is non-compressible, rocky or

congested by other services.

If the length to be installed is greater than 10m, intermediate digs may be

required.

The more innovative pipe replacement techniques fall into two types; pipe

pulling and pipe splitting. The basic principle common to pipe pulling is

simple ­ the lead pipe is gripped and pulled from the ground by a mechanical

device, whilst at the same time a new service pipe is pulled in behind the

lead pipe.

The mechanical device used to pull out the lead pipe may be a winch,

hydraulic jack or even a backhoe mechanical digger. The key difference

between the methods is the system used to grip the pipe.

The simplest systems use a bullet-shaped tool. The pulling cable is fed from

the pulling device, through the lead pipe and connected to the nose of the

bullet, which engages into the end of the lead pipe. The new service pipe is

attached to the tail of the bullet. As the cable is tensioned, the bullet

pushes the lead pipe out of the ground and the new pipe is pulled into the

space vacated by the lead pipe.

The bullet technique was originally developed to remove galvanised steel

pipe. However, lead is much more flexible and malleable than steel and often

laid with bends and loops rather than in a straight line. Applying pulling

force at the end of the pipe can therefore cause it to distort and buckle,

making it difficult or impossible to remove.

Methods have been devised to overcome this (see left). Feeding a cable

through a heavily encrusted or convoluted pipe can prove difficult and the

thicker the cable, the more difficult it is to feed through ­ but the

greater the pulling force that can be applied.

Hard, dry ground conditions also make it more difficult to pull out lead

pipe. The main benefits of pipe pulling are that it works relatively quickly

and it can be used in congested service areas as the new pipe is installed

along the line of the old.

For pipe splitting, the tool is pulled through the pipe by a cable. The

split pipe is forced apart because there is insufficient space for the

replacement pipe, which is connected to the tail end of the splitting tool.

There is also a risk that adjacent services, e.g electricity cables, may be

damaged if the cutter drifts out of the lead pipe at bends.

An alternative to removal is the renovation of the lead pipe by thin wall

lining. A thin wall tube is inserted to provide a physical barrier between

lead and water. This approach has several advantages. It is rapid, is not

affected by ground conditions, suitable for lining through to the consumer’s

stop tap and helps to reduce leakage.

Unfortunately it may not be possible to insert the liner into a convoluted

or distorted pipe.

The diameter of the pipe is reduced by the liner, although the improved

hydraulic performance of the lined pipe generally compensates for the

reduction in diameter.

The long-term performance of the lining depends to some extent upon the

condition of the pipe. There are two processes available in the UK, the

Neofit PET lining technique (£4-5/m) and the cheaper folded Polyline

Microliner (£1.50/m) which is pulled through and then inflated using

compressed air.

Choice of the most appropriate method will depend upon a range of technical

and economic factors.


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