Preliminary Results of Demonstration Capping Project in Hamilton Harbour

Abstract

Abstract Placement of a pilot-scale sand cap occurred in Hamilton Harbour between July 31 and September 20, 1995. The harbour site is at a location where contamination of the bottom sediments is of concern. One ha of contaminated finegrained sediments was covered with 6,600 tonnes of clean sand to an average thickness of 30 cm. A very accurate positioning system was required and placement with adequate accuracy was possible up to wind speeds of about 30 km/h. Initial readings of settlement gauges taken in September 1995 show the ultimate settlement due to primary consolidation to range between 6 and 8 cm. Preliminary results indicate that the suspended material found in the water column during cap placement was almost entirely composed of fines associated with the cap sand. Vibracores showed a sharp interface between the sand cap and sediments with no signs of extensive mixing. Based on multibeam echo sounding results and other supporting data collected at the site, the sand cap was successfully placed in the designated area without any significant sediment disturbance. Some horizontal spreading of sand fines occurred beyond the site boundary.