David Plumb keeps pollution out (cont.)

The ‘barrier’ was then constructed by laying overlapping, strong plastic sheets against the trench plates, down to a depth of 2.5m; a depth calculated by the environmental consultants to be deep enough to stop contamination seeping under. To give the sheets rigidity, they were sandwiched between layers of fibreboard. To further guard against seepage, the base of the membrane was sealed with a layer of clay and the rest of the barrier was held in place by the clean material used as backfill.

The whole process was made more complicated by the area’s high water table, which meant the excavation had to be pumped out first thing in the morning, lunch time and last thing at night. In total, 3,000 gallons of water per day had to be pumped out and put through David Plumb’s mobile water interceptor. This removes any contaminants from the water. The contamination is sent to an approved wet waste site and the cleaned water is discharged down the foul sewer; after being cleared by the local water company, which analyses the scrubbed water to ensure it is safe.

To ensure any water can be dealt with easily in the future, five capped wells will be left on the site.

23 August 2006

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