Physical/Chemical Properties of Sediments. 



Sedimentological properties of the samples are summarized in Table 10. Samples 1, 2, 3, 

 13, 14, and 15 had similar and relatively high clay and TOC content. Clay content was 

 relatively low and sand content was relatively high in samples 7, 8, and 9. The percent 

 gravel content was unusually high in samples 8 and 11. TIC was highest in samples 7 and 8. 



Trace Metals in Sediments 



Sample numbers 1, 2, and 3 had the highest concentrations of a variety of trace metals, 

 notably, silver, cadmium, copper, mercury, lead, and zinc (Table 11). Many of the elements 

 were nearly an order of magnitude higher in concentration in samples 1, 2, and 3 than in all 

 the others. Relative to the differences in concentrations of these metals between samples 1, 

 2, and 3 together, and the other 12 samples, the differences in concentrations of metals among 

 the other 12 samples were small. Sample number 8, which had a high gravel content, had 

 relatively low concentrations of many metals, e. g., cadmium, chromium, copper, and mercury. 

 Arsenic was most highly concentrated in samples 7 and 9. Samples 13 and 15 had among the 

 lowest concentrations of silver, arsenic, copper, lead, and zinc, but had among the highest 

 concentrations of chromium and nickel. 



Organic Compounds in Sediments 



Four classes of organic compounds were markedly more concentrated in samples 1, 2, and 3 

 than in all the others (Table 12). The concentration of total measured polynuclear aromatic 

 hydrocarbons (ZPAH) in sample 1 was elevated by a factor of 20 over the concentration 

 observed in sample number 15; EDDT was elevated by a factor of 50, total pesticides by a 

 factor of about 40, and £PCB by a factor of about 73. All four classes of organic compounds 

 were least concentrated in samples 13, 14, and 15 compared to the others. Relative to 

 samples 1, 2, and 3 and samples 13, 14, and 15; the concentrations of the organic classes were 

 intermediate in samples 4 through 12. The relative concentrations of some organic compounds 

 varied among samples. For example, the ratio of 2PAH concentrations to EDDT 

 concentrations was lower in samples 13, 14, and 15 than in the other samples. Coprostanol 

 concentrations were similar in most of the 15 samples (Appendix B). 



Chemical Ratios to Reference 



The individual trace metal and organic chemical data were merged to form a cumulative 

 index of overall contamination by the mixtures of quantified chemicals in each sample. 

 Ratios-To-Reference (RTR) values (Chapman et al, 1987) were calculated by dividing the 

 concentrations observed for the various metals and organics in each of the samples by the 

 respective mean values calculated for the three samples (13, 14, and 15) from the rural area, 

 Tomales Bay. Then, averages of these RTR values for each of the samples were calculated. 

 These average ratios indicated that samples 1, 2, and 3 were most contaminated relative to 

 the others; samples 13, 14, and 15 were least contaminated; and samples 4 through 12 were 

 intermediate in contamination. 



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