Case Study 01

The use of PFA in land restoration.

The creation of the Millennium Coastal Park at Llanelli in South Wales has led to the transformation of the old Carmarthen Bay power station site. In the year 2000 this was the site of the internationally famous Eisteddfod. In addition a number of civic amenity sites have been created for the local population and tourists. Pulverised Fuel Ash (PFA), or fly ash1 as it is known in many countries, from the old power station lagoons has been utilised for a number of applications including:

• Ground remediation – capping of contaminated industrial sites in the Burry Port area.
• Landscaping – for creation of earth sculpture and a community woodland.
• Lightweight engineering fill – for backfill to land bridges and promenades.
• Lime / cement stabilised PFA – for subbase in temporary roads and cycle ways.

At Llanelli the old power station lagoons provided a readily available source of material, which was used as growing medium for landscaping many parts of the site. A series of pools, woodland, footpaths, cycle ways and general green and wooded areas have all been formed along a four miles stretch of the coastline using PFA blended with fertilisers. Both sewage sludge and silt extracted from Burry Port harbour have been used to provide a source of nutrients for such landscaping work. The harbour silt was used as a growing medium once the salts had been washed out through natural processes, e.g. rain. In many areas trees have been planted to form the Burry Port Community Woodland. Natural re-vegetation occurred so quickly that the grasses and wild plants were in danger of overwhelming the trees – showing the benefits of using PFA as a safe material for landscaping and remediation.

Approximately 300,000 tonnes of PFA was used as a lightweight engineering fill for the two bridges on site, which span the railway. They provide access to seaward land on the site. The bridges are segmental precast units that contain PFA, as a cementitious addition, to give added strength and durability to the structures – see UKQAA Datasheet 1 “Pulverised Fuel Ash for Concrete”. They are the largest of their type built with the UK. The backfill to these bridges was PFA placed and compacted to form a lightweight fill – see UKQAA Datasheet 2 “Pulverised Fuel Ash for Fill”.

PFA has many potential uses for remediation and ameliorating industrial landscapes. Weathered PFA can be used as a suitable topsoil media when blended with a source of fertiliser. This may consist of nitrogen rich chemical fertilisers or nutrient rich materials like sewage sludge, chicken litter, etc. In the Millennium Coastal Park project sewage sludge has been used with great success. 

* In excess of 400,000 tonnes of PFA used in landscaping and fill.

* A wide range of materials have been successfully recycled on the project:

• Silts from the harbour.
• Sewage sludge.
• Building materials from demolished structures on site.
• Glass reinforced pipes recycled as drainage pipes.
• Timber piles to be used on the Pembrey link and harbour.
• River gravel’s and subsoil’s as capping for Eisteddfod caravan site.
• Approximately 150,000 to 200,000 tonnes of colliery waste, from a nearby tip, will be used as a general fill.

Acknowledgements.

UKQAA would like to thank the Millennium Coastal Park Project, for their co-operation in preparing this case study.