Gas Works, Tunbridge Wells, Kent
Background
The site, (approx 3Ha) had historically been used for gas production from the early 1890s until the mid 1970s. The previous site owner had carried out remediation as part of a risk reduction exercise, although this only met the specified site end-use of ''securely fenced vacant land ''.
The site was purchased for residential redevelopment with private gardens and open landscaped areas in 2004. A key feature included "opening up" of a culverted stream through the site to create a landscape feature, designed and managed to enhance its ecological diversity and to increase wildlife populations.
Investigation
Following consultation with the regulators in early 2004 Southern Testing undertook a detailed Site Investigation. Ground conditions encountered comprised fill over a silty laminated and fissured clay and mudstone (Wadhurst Clay). The substructure to several of the former gas works buildings / structures, including a gasholder, remained intact below ground level. The soils, and locally groundwater, were found to be contaminated with arsenic and PAH''s, TPH, BTEX compounds, phenols, cyanide and ammonia and certain solvents.
Remedial Design
Sustainable and innovative techniques were designed to meet the planning, environmental and geotechnical requirements of the site. Following successful treatability studies, specialist remediation contractors, Biogenie and May Gurney undertook remedial works comprising:
- Bioremediation of 30,000 m3 of contaminated soils, with the majority being retained for use on-site (only 1% considered untreatable, and disposed of off-site).
- Construction of an impermeable / non-reactive barrier to a depth of up to 12.5m along the northern site boundary.
- Construction of semi permeable/reactive clay barrier, to remove contaminants in the groundwater flowing off-site and to provide protection to the new stream channel.
- Re-engineering / remediation of an existing culvert stream to construct an open channel feature across the site.
Southern Testing managed the project and undertook all validation works. The project was carried out within a very commercially driven timeframe, with the whole project from initial involvement to current initial occupations taking only 18 months.
Brownfield Briefing Remediation Innovation Award 2006
In 2006, the project won a Brownfield Briefing Remediation Innovation Award for "Best Use of Combined Systems". read more
Judges Comments
" This project demonstrates tremendous collaboration. It was homogeneous and well managed bringing benifits off site as well as onsite " John Cambell
" Two tried and tested technologies brought together in a best pratice manner..a well presented submission which gives due credit to those who actually carried out the remediation " Clive Boyle
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