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Alcatraz Mound Downsizes

A bay bottom bulge off Alcatraz that posed a navigational hazard has diminished in size, according to monitoring done by the Army Corps between March and August 1993. Officials attribute the reduction to tighter management procedures aimed at increasing dispersion of dredged materials dumped at the site. Procedures included a limit on total disposal to 400,000 cubic yards per month, of which only 150,000 could be from clamshell operations. Clamshell dredges release solid sediments, while hopper dredges dispose of a more easily dispersed slurry. New procedures also restricted disposal to areas deeper than approximately 60 feet, and away from the mound. Hydrographic surveys showed that the overall dispersion rate for the site and surroundings ranged from 85-99 percent.

Contact: Al Mathiesen (415)744-3359

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