Making remediation as safe as houses

Cardiff has long enjoyed a well-deserved reputation as a Renaissance city. The grand villas that line the leafy streets are testament to the wealth generated by the capital’s citizens over the centuries. The Marquess of Bute, who turned Cardiff into the world’s greatest coal exporting port, equally transformed its castle into what has been described as a ‘Welsh Victorian Camelot’.

The city’s prosperity was built on trade, and the vast natural resources in the Welsh Valleys such as coal and iron. As the trade expanded so did the port, along with manufacturing and processing industries together with the houses needed to accommodate the workers. Like many industrial cities Cardiff’s fortunes declined in the latter half of the last century but has been buoyed by major regeneration efforts.

The rejuvenation of the city centre and Cardiff Bay has spread to Grangetown, west of the city centre. A stunning new stadium has replaced Ninian Park, Cardiff City’s former ground, which is now being redeveloped into a new housing estate comprising 142 homes. The St Donat’s Road Estate lies in the heart of Grangetown and adjacent to the Ninian Park development.

Constructed during the 1930s, to relocate residents from the site of the Cradiff Bus Station, the estate comprises 110 properties accessed off a single road and constructed in on four sides of a square with two cul-de-sac roads on either side. The properties are mostly arranged in small blocks of two to four houses. The houses had been occupied for many years without incident when cracking to the exterior of some houses was observed.

Investigations revealed the cause to be settlement problems due to the houses having been built on ash. It is not clear whether the ash was imported or a by-product of one of the redundant smelting works. The ash contained traces of heavy metals, including zinc and copper, which potentially presented a threat to human health. Consequently, Cardiff City Council under the auspices of Part IIA of the Environmental Protection Act 1990, resolved to remove hazardous material from the gardens of affected properties.

Home ownership is split between private and council, but it was decided that all affected properties would be treated. Further investigation by the contaminated land officer determined that 46 of the 110 properties should be treated. The £1.5M contract was secured in competition by remediation contractor VHE who had worked with the city council previously on the capping and restoration of the Lamby Way landfill site.

Work on the estate commenced in October 2009 and is the first Part IIA contract to be undertaken by the council, with the project being overseen by its projects design and development department. The specification for each property involves the excavation and removal of contaminated material up to a depth of 500mm, the insertion of a geotextile membrane to act as a barrier and mark the extent of the excavation, and the importation of equal quantities of clean soil. This is then overlaid with hard or soft landscaping.

The scheme involves many logistical challenges with the health and safety of residents and workers being a prime concern. Other issues include access into and around the estate which is via a single road, and the access to the rear gardens of the longer terraced properties, which can only be entered by narrow driveways on either side.

To facilitate the works and reduce the overall impact to the residents the remediation works would need to be split into twelve separate sections, with some running concurrently, at different locations. The works have been successful only with the cooperation of the residents, which is achieved by daily communication between the site team and the residents, the use of a weekly drop in centre and a calling card system.

A detailed survey and photographic record was compiled of every property to be remediated. This records the condition of the house and ensures that gardens and exterior spaces are reinstated according to their previous condition. In order to complete the programme as quickly as possible, light machinery such as mini excavators and mini dumpers, are being used.

Special care is taken when using the vehicles to preserve the safety of residents and visitors, as well as traffic. Even using these is a challenge as some properties were built at an angle with rear gardens of differing angles and levels. Location of services is critical during excavation so as not to pose a threat to the safety of the contractor and to preserve continuity of supply for the resident.

Typical services include water, electricity and gas, although the location and condition of the services is not always as anticipated. Drains, especially, are prone to having been damaged by tree roots or movement and need to be replaced before work can be completed. All material generated from site is disposed off to an appropriately licensed facility under the applicable duty of care.

In order to minimise vehicle movements on the estate, non-hazardous excavated material is stockpiled at a single location before a sufficient quantity is assembled for collection and disposal at a local recycling facility. Hazardous material is taken to Wigmoor Famr landfill site, operated by Grundon Waste Management. As part of the overall regeneration of the area and to improve the urban environment, VHE will also be installing or repairing low brick walls and metal railings to the front of many houses as part of the contract.

Remediation work on a number of properties has already been finished, with the balance due for completion by the end of this month. A further boost to the area is the refurbishment of the adjacent bus depot which is being undertaken under a separate contract by one of VHE’s sister companies Britannia Construction.

Steve Stiff is managing director of VHE Construction