Historical Trends of Metals in the Sediments of San Francisco Bay, California:
Core data from San Pablo Bay, Grizzly Bay, Richardson Bay, and Central Bay
by Michelle I. Hornberger, Samuel N. Luoma, Alexander van Geen, Christopher Fuller, and Roberto Anima, USGS
based on article published in Marine Chemistry, 1999. V. 64, pp 39-55.

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Methods: Sample Locations

Preliminary analyses of 0.6N HCl-extractable metals were conducted on 14 cores from a group of 273 gravity cores collected in 1990 and 1991. Detailed analyses were conducted on six of the 14 cores and, for comparison, on one core from Tomales Bay. Tomales Bay is 45 km north of San Francisco Bay and is neither industrialized nor urbanized, although there is a small, inactive mercury mine in its watershed. The six cores from San Francisco Bay included replicate cores from two major regions of the Bay. All six had bimodal depth profiles of HCl -extractable metal concentrations (higher concentrations in the near surface sediments than at depth) and were from locations of net sediment deposition, as indicated by differences in bathymetry between 1955 and 1990 (Ogden Beeman & Assoc., 1992)

Core RB92-3 was collected at the mouth of Richardson Bay, a 2-km wide, wind-protected embayment near the mouth of San Francisco Bay. A ship building facility was operational during World War II within Richardson Bay; otherwise, local sources of contaminants are minimal. Richardson Bay sediments should integrate contamination from both North and South Bay (Krone, 1979), but are probably also strongly influenced by marine processes (Conomos, 1979). Cores CB90-9 and CB90-12 were from Central Bay which is also strongly influenced by marine inputs (Conomos, 1979). In addition, these sites are approximately 6 km from the Alcatraz Island dredge spoil dumping site, where dredging waste has been deposited since 1975 (AHI and Williams Associates, 1990). Three cores from further landward in the estuary were analyzed in detail; two from San Pablo Bay (SP90-2 and SP90-8) and one from the Grizzly Bay arm of Suisun Bay (GB90-6). Together these are termed North Bay cores. Water chemistry and sediment transport in these locations are influenced by inputs from the San Joaquin and Sacramento Rivers (Conomos, 1979). Salinities less than 1 can occur during the highest river flows; low flow salinities are typically 17 to 24 in northern San Pablo Bay. Previous studies have documented enriched concentrations of Cr, Ni, V, Cu, and Cd in water and bivalves in Suisun and northern San Pablo Bay as a result of a variety of industrial discharges (Flegal et al., 1991; Abu-Saba and Flegal, 1995; Brown and Luoma, 1995).