Contaminated, Effluent-Affected Sediment on the Continental Margin near Los Angeles, California (abstract from talk): EOS Trans. AGU, 76(3), Ocean Sciences Meeting Supplement OS1, 1996.

Lee, H. J., Drake, D. E., Edwards, B. D., Hamer, M. R., Hampton, M. A., Karl, H., Kayen, R. E., and Wong, F. L.

Discharges of suspended solids and sediment-borne pollutants, including DDT and PCBs, through an ocean outfall system on the Palos Verdes shelf have produced a fine-grained, contaminated sediment deposit. Reductions in solids and contaminant discharges since 1971 have resulted in a two-layered deposit, consisting of less contaminated material overlying a horizon of heavily contaminated, organic-rich sediment at subsurface depths of 5 to 35 cm. Very-high-resolution subbottom profiling, sidescan-sonar imagery, sea-floor photography, and laboratory measurements on core samples from approximately 60 stations were conducted to map and characterize the effluent-affected sediment. Results were entered in a geographic information system (GIS) to allow manipulation of data and calculation of the bulk characteristics of deposit. The body of effluent-affected sediment has a volume of approximately 9 million cubic meters and a thickness between 5 cm and 60 cm. The body extends from approximately 35 m on the continental shelf down the continental slope to a water depth of at least 500 m. Practically all of the deposit is contaminated with DDT and PCBs. Within the deposit, concentration levels of p,p'-DDE )the dominant isomer of DDT) are typically greater than 1 ppm and range as high as several hundred ppm. The footprint of DDT-contaminated sediment, delimited at the 1 ppm concentration level of p,p'-DDE, covers a seafloor surface area in excess of 40 square kilometers. The mass of total DDT per unit area was integrated using the GIS to yield a mass of total DDT for the entire Palos Verdes Margin in excess of 100 metric tons.