James Roper, Infrastructure Segment Manager for GPS PE Pipe Systems, discusses the complexities around installing barrier pipe within contaminated land
With increasingly more brownfield sites being redeveloped to allow a greater volume of housing to be constructed, reliable pipelines are required to transport large volumes of drinking water for new homes. However, with contaminants often present in the ground, there is lots of debate around the best solutions to ensure a safe drinking water supply is maintained.
With the UK government expecting 60% of all new housing developments to be built on brownfield sites by 2021, the resulting increased requirement to convey water supplies has prompted some pipeline manufacturers and suppliers to look for ways to capitalise on this opportunity. GPS PE Pipe Systems is warning housebuilders, developers and contractors of the dangers that can come with installing water pipe that is not proven as safe for use in contaminated land.
Contamination risk
When considering pipework materials and systems to use for water supplies in brownfield sites it is important to determine whether the land is at risk of contamination. UK Water Industry Research (UKWIR) offers guidance in the form of its ‘Guidance for the Selection of Water Supply Pipes to be used in Brownfield Sites’ published in 2011.
The publication is for use by water companies, self lay organisations, developers and contractors during the planning, designing and construction of water mains and/or services in brownfield sites, with the aim of ensuring the correct materials are selected for below-ground water pipes.
The previous use of the site will provide a good indication of whether contaminants are likely to be present in the ground, but costly soil analysis will need to be undertaken to clarify whether the ground contains any harmful substances. However, when investigating brownfield sites, it is crucial that developers and contractors work closely with the water utilities, as they will ultimately need to approve any pipework material for a new water supply system.
The majority of water authorities now stipulate that brownfield sites need to be assessed under the UKWIR method, which includes desktop studies, site walkover and site investigation including multiple soil samples. Utilities will then assess all data provided by the contractor to confirm the pipe material to be used, based on the defined trigger levels in the Pipe Selection Table within the UKWIR document.
Pipe material
It is vital that the correct pipe material is selected as hydrocarbons, such as petrol, diesel, heating fuel and white spirits, often used in industrial processes can permeate through standard plastic pipes and pollute the drinking water being transported. Hydrocarbons can also damage the pipes causing them to fail due to environmental stress cracking or corrosion in metal pipes. Pipe pollution and failure is not only a danger to the public and surrounding environment, but could also result in hefty fines for the water utility, developer and contractor.
The only way to ensure the public is protected, and any contaminants remaining in brownfield sites cannot permeate into the water supply, is to use a material, which is not permeable to hydrocarbons. The Pipe Selection Table included within the UKWIR guidance outlines the pipe materials that are safe for use with various contaminants identified in the site investigation.
Standard polyethylene (PE) and PVC plastic pipes are not resistant to permeation of many contaminants and should only be used if remediation work is undertaken to remove all contaminated soil. However, the high costs to remove contaminated soil, along with associated completion sampling and analysis, would significantly increase project costs.
While wrapped steel, wrapped ductile iron, copper and PE barrier pipe with an aluminium barrier layer (PE-Al-PE) all provide an effective barrier to the majority of contaminants, a PE-Al-PE barrier pipe is the only material tested to provide a safe barrier against all known contaminants including those of inorganic nature.
Site investigation
This leads to a lot of debate among water authorities, developers and contractors regarding whether site investigation and soil analysis is required if a barrier pipe is installed. Although there is no definitive statement for how water authorities should deal with this, UKWIR offers the following guidance: “The UKWIR project steering group has decided that a PE-Al-PE barrier pipe would provide sufficient protection for the supply of drinking water in all brownfield sites. If barrier pipes are specified, there is no need to carry out soil sampling and analysis and this maybe the most cost effective solution in some cases. It is therefore reasonable to expect all water companies will accept the use of a barrier pipe in all situations as a blanket approach.”
While each water authority has its own individual process, the majority do accept PE-Al-PE barrier pipe being installed without a site investigation. However, it is left to the contractor or developer to decide whether a site investigation is preferred, with a pipe selection made based on the findings of the report. There is a strong argument that if the cost of site investigation exceeds the cost of installing a barrier pipe, then specifying barrier pipe for all brownfield sites, regardless of site specific levels of contaminants, would be the most cost effective solution.
Installation issues
With safety the number one priority on brownfield sites, the selection of the most appropriate pipe for the site conditions is vital, but there are other factors to consider for contractors, such as installation techniques and processes, maintenance requirements and longevity of the system.
While metal materials do offer a robust barrier against most hydrocarbons, they cannot offer the same installation benefits as PE-Al-PE barrier pipe systems. The lightweight nature of PE pipe, combined with the quicker and easier electrofusion jointing process, saves significant time and costs on site. While the smooth bore of PE resists corrosion, ensuring flow is not restricted over the lifetime of the system, offering optimum operational efficiency over the lifetime of the system.
The simpler and quicker jointing technique offers clear benefits, however the correct installation of the system cannot be underestimated to ensure there are no weak points or leak paths in the system. Every barrier pipe system is different and therefore it is good practice for contractors to ensure that any installers working on brownfield sites attend a manufacturer training session, to ensure they are fully equipped to install that particular system.
With the government’s increased priority on re-developing brownfield sites, many pipe systems are now promoted for use in contaminated environments. Therefore, it is important developers, housebuilders, contractors and utilities clarify the previous successful experience of barrier pipe systems to ensure the integrity of the water supply is not compromised through the selection of inappropriate pipe.
