What initially was thought to be an isolated contamination incident at Sudbury sewerage scheme, is now suspected of being a more widespread underground problem - and sewage is not the culprit!
Three-phase contamination, probably with historically related sources, was first encountered in an excavation for a stormwater connection. The sump acted as a collection pool for darkly contaminated and oily seepage water which was disposed of by dewatering to foul sewer. The receiving Anglian Water STW could treat this short-term chemical oxygen demand (COD) 'spike' but reportedly there was raised concern that the plant may have to cope with elevated COD loads over an extended period. Ongoing geotechnical investigative boreholes have revealed further evidence of contamination, and this has raised concern that the contamination is likely to be more widely spread than previously envisaged.
A F Howland Associates, geotechnical engineers and chief advisers contracted to Anglian Water have begun investigating the problem. A desktop study will aim to identify historical activities, likely contaminative sources and other general environmental factors. Primary concern will be potential risk of exposure of workers and construction materials to contaminants in soils and groundwater during development. The desktop study will be used as a decision-making tool to design and implement a sampling and testing strategy to chemically characterise the contamination.
Because it is not a full-blown contamination investigation, the sparse spread of boreholes for geotechnical investigative purposes, which will be used for contamination sampling, will not allow accurate delineation of contamination plumes, but will ensure that strategic positions on the scheme will be characterised. A F Howland will use properties of soils and the geohydrological regime, together with chemical nature of the contaminants, to infer potential migration and behaviour of contaminants below the scheme. From this information predictions can be made and precautionary measures taken confidently.
Howland's phased approach is favoured because it facilitates continual project feedback, ensuring well-informed decisions on necessary precautions, where ground contamination issues are concerned, can be taken.