Railways, heavy engineering workshops, coal gas production, gravel extraction and refuse tipping left their mark on Derby. Within seven minutes' walk of the city centre, in 1993 what is now Pride Park was a semi-derelict industrial wasteland. The city was losing much of its traditional heavy industry and new employers, working in non-polluting industries, were settling elsewhere on greenfield sites.
Derby City Council's vision was to rehabilitate the site to a good practice standard that would satisfy regulators and developers and, more especially, their clients and insurers. Realising that vision was estimated to involve an investment of £50M in public funding to clean up the 80ha site and attract £200M of private investment, which would in turn create long term employment for 3,500 people.
Consultant Ove Arup & Partners was brought in to analyse the problem and produce a solution that was affordable as well as acceptable. There were two obvious alternatives. The expensive one was to excavate everything deemed to be contaminated and drop it in a suitable hole somewhere else.
The cheap option would have been to put a clay cap over the site to contain the contamination insitu - where it would remain as a dubious problem that might yet have to be resolved.
Having surveyed the site, tested for 22 possible contaminants and developed a three dimensional model, Arup determined that there was a risk of groundwater pollution spreading into the adjacent River Derwentand recommended a third course of action:
Isolate the groundwater with a 3km perimeter bentonite cut off wall sunk deep into the ground around most of the site
Excavate the most seriously contaminated material and contain it in a properly engineered repository in one corner
Cap the site within the wall with a pervious layer of clean material through which rainwater will percolate into the contained ground
Pump this natural flushing water from specially installed wells and fully treat it to extract contaminants before releasing it to the river.
In the long term, by pumping for several decades, this constant cleaning process will eliminate significant contamination.
This strategy aimed at producing a 'suitable for use' site was a pioneering concept at a time when there was little in the way of guidance from regulators. The idea has since been adopted by the Department of the Environment Transport & the Regions.
Retention of two vital gasholders and a collection of listed railway buildings, which have yet to find a new function, means that Pride Park has not entirely lost the visual signsof its industrial heritage. But major employers, including Prudential, have been attracted and have redeveloped half the site. Derby is well on the way to achieving its vision.