I refer the hon. Member to the earlier responses given to the hon. Member for Portsmouth, South (Mr. Hancock) on 17 March and 31 March 2008, Official Report, column 736W and column 499W respectively regarding groundwater contamination and contaminated land.
Further to those responses, the highest levels of contamination at a particular site do not necessarily reflect the most serious risks to people or the environment. This usually depends on many factors which control the likelihood that pollutants might enter a “receptor” (e.g. a person or ecosystem) with harmful effect. Any remedial action will depend on the nature of these source-pathway-receptor relationships and the outcome of a risk assessment, as well as considerations of technical feasibility, costs and benefits. These are site-specific matters.