CONTAMINATED GROUND AND CONTAMINATED ESTUARY SEDIMENT ILLUSTRATED BY 2 CASE-HISTORIES

Contaminated ground forms a problem in all of the industrialized count ries of the world. Contaminated ground may give rise to hazards and th at implies a degree of risk which also involves a problem of definitio n. The investigation of a site which is suspected of being contaminate d differs somewhat from a routine site investigation. Sampling of soil , groundwater and gas-producing material may be required. Various prec autions may be necessary to do this and personnel may have to wear pro tective clothing. The first case history considered involves a site in vestigation for a relief sewer in Glasgow. As the site investigation p rogressed it ran into made-ground which contained chemical waste. The presence of this waste meant that the nature of the investigation chan ged and much more stringent safety precautions had to be taken. It als o meant that the initial location of the sewer tunnel had to be reposi tioned at greater depth in uncontaminated sandstone rather than in the superficial deposits above. The other case history considers the cont amination of sediments in the Forth Estuary. When trace metals are rel eased into the water column they can be transferred rapidly to the sed iment phase by adsorption onto suspended particulate matter, followed by sedimentation. Intertidal flats may be considered as important trac e metal sinks since they accumulate large amounts of suspended matter. Hence, in polluted estuaries the deposition of suspended particles on intertidal flats may thus cause severe contamination. The Forth Estua ry has unique contamination for British estuaries; it is experiencing significant Hg pollution. In addition, due to the presence of a nuclea r submarine base in the Forth Estuary, Co-60 is detectable in the inte rtidal sediments. Temporal and spatial contamination patterns were ana lysed in relation to historical and present pollution point sources. T he effect of fluvial and marine sediment mixing on trace metals and ot her processes controlling contaminant levels is reviewed. Preliminary results on quantifying sediment accretion rates using Caesium levels a re discussed.