Case study


Contaminated waste: A walk in the park


Zero Waste is the ultimate aspiration for any reclamation project. Inevitably, achieving this ideal entails overcoming environmental, technical, and financial challenges. Yet this is exactly what specialist remediation contractor VHE achieved in Jersey on a heavily contaminated site in a residential district. Steve Stiff reports.


Steve Stiff Managing director of VHE


T


HINK OF Jersey and the island’s distinctive brown cows and delicious ice cream spring to mind. Rolling green hills encapsulate the natural splendour of the island.


Farming, and latterly finance and tourism, are the mainstays of Jersey’s economy. But like its English neighbour to the North, Jersey has an industrial presence with an associated environmental legacy. In Jersey’s capital, St Helier, the island’s


gasworks were located in what is now the town centre North quarter. Bordered on all sides by residential and commercial properties the gasworks plant relocated in 1991 and the buildings were demolished to ground level. Any contamination from the works was sealed beneath tarmacadam surfacing and the area was used as two adjacent public car parks, split by a public road. Momentum soon grew for the site to


become a town park with the redevelopment forming a key part of the area’s regeneration strategy. Removing the contamination was fundamental to the protection of public health and its long term viability as a public park. VHE was appointed in July 2009 to undertake the remediation contract while the park design was still being developed (as the States of Jersey was committed to opening the park in late 2011). The resulting £6m contract was the largest remediation project ever undertaken on the island. “The scheme started with a public


petition in 1996 to create a park on the former gas works,” said Quintin Murfin, principal engineer for the States of Jersey. “We have now overcome the difficulties


presented by the site and are moving forward with a unique scheme to provide a family park that meets local community needs.”


Reuse of site material Jersey has no facility to treat contaminated material on island so the key feature of the remediation was the reuse of existing site material. The scheme was therefore engineered to be zero waste. Four streams for material disposal were


developed by VHE and designers, Parsons Brinckerhoff, and were agreed with the head of waste regulation for the States of Jersey. The tarmacadam surface and underlying


hardcore base was recycled at La Collette, the island’s commercial waste processing centre, where it was turned into aggregates. Excavated material from foundations and


underground structures was screened on site to remove the ‘hard’ material which was also sent to La Collette for recycling. The inert soils were sent to La Collette for reuse to reclaim land along St Helier’s foreshore. Contaminated material that could be


satisfactorily treated on site was retained for re-use while a solution was devised for the remaining material that could not be viably treated.


Contamination hot spots During earlier site investigations hot spots of contamination with the heaviest coal tar- based material had been identified. One of these, the gas holder base, provided an ideal location for the treatment of the more heavily contaminated material. The material was stabilised with lime,


excavated from the tank and placed in a treatment area where further biophysical treatment was undertaken. Screening removed oversize fractions and the remaining 1,500 tonnes of material was sealed in one tonne bulk bags before being transported by barge to Holland for reprocessing. The material was incinerated at high temperature and the cooled ash converted into suitable fill material for use in the construction industry. The original remediation design was to provide a 600mm capping layer above a


An environmental concern was leach prevention: this was solved by laying an impermeable liner across the site The environmental impact of the scheme


300mm drainage layer, both placed above a geosynthetic clay liner. With the very early development of the design requiring a greater depth of material to be excavated and removed from site, VHE proposed an alternative to the 300mm drainage layer thereby reducing the off-site disposal by approximately 3,600m³ of material. During the course of the project


approximately 18,000m³ of material was excavated on the site. All underwent some form of treatment


including bioremediation, stabilisation and screening before either being reused on site or treated off site as described above.


Leach prevention One environmental concern was leach prevention which was solved by an impermeable liner laid across the site. As well as providing a barrier to prevent the mixing of capping material and existing soil, the liner incorporates a bespoke drainage system to harvest rainwater. Any rainwater is ‘captured’ and channelled through a contractor-designed drainage system to a pumping station where it is pumped to an underground storage tank for re-use as part of the park’s irrigation system. The 500,000 litre underground storage


tank was constructed within the gas holder base used to treat material during the remediation phase of the works. This stored water is used by with the site’s


irrigation system which comprises 5,400m of underground pipe work and over 6,000m of drip irrigation tube to water the grassed areas, trees and shrubs. Excavated material was also used to


The gas holder base provided an ideal location for the treatment of the more heavily contaminated material 8 March 22 2012


stabilise the underlying ground conditions on the site which did not provide the required bearing capacity that the various proposed park structures required. The ground improvement was carried out by excavating geotechnically unsuitable material and backfilling the void with hard material recovered from the general excavation works, crushed on site to provide a well graded material and compacted in layers.


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has been minimised at every stage, bearing in mind that this was in the midst of a residential area. There were more than 3,000 lorry movements to carry out the remediation but comprehensive traffic management ensured there was no disruption on the island’s roads, many of which are quite narrow. Noise, dust and vapour emissions were all strictly monitored and controlled.


Finished result At the time of the tender the sequence of works envisaged was such that the remediation works would be completed before construction of the park began. However, as the town park design


developed, this was not possible given the complexity of the project and the need for phased handover of the works. VHE therefore also undertook all the hard and soft landscaping works for the park. In place of a stark car park Jersey now


has a vibrant, healthy public open space, designed by landscape architects Burns + Nice. Two dramatic water features are key features of the park; a 9m x 3.5m polished stainless steel water curtain and a water jet field, with all the water being continuously recycled. Around the hard and soft play areas 150 trees up to 10m tall have been planted along with 10,000 shrubs and plants. The construction was completed in


October 2011; 42 weeks from the start of the project and three weeks ahead of programme. Over 2,000 people attended the opening ceremony and many more are now enjoying the benefits of St Helier’s latest public amenity. Chris Sampson, the director at transport


and technical services who is leading the project for the States of Jersey says: “The team has now completed the contemporary park which the local community has been waiting for over a decade. The community are now benefiting from this much needed space for leisure and relaxation within the town and the regeneration of the area is already being initiated.”


& WA S T E W O R L D


RWW Recycling


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