3.2 Surface Sediments (Atlas, University of Louisville) 



The frequency of sampling for surface sediment (0-3 cm) is shown 

 in Table 5. Ten primary locations were sampled repeatedly (Fig. 3.7). 

 Results of total hydrocarbon determinations for the ten stations, as 

 these concentrations varied with time, are presented in Figures 3.8 

 through 3.12. Also included in these figures are source evaluations 

 for each sample hydrocarbon assemblage, based on GC information. The 

 biogenic (B) category indicates that terrigenous odd chain n-alkanes 

 dominate the f^ GC trace. The pyrogenic (P) category signifies an 

 important abundance of combustion-related polynuclear aromatic hydro- 

 carbons (PAH) in the f2 fraction as well as the presence of some 

 unresolved material (UCM) in both the f^ and f2» In those samples 

 labeled B or B/P the primary sources of hydrocarbons are as indicated 

 although a small fraction of the hydrocarbons may consist of petroleum. 

 Figure 3.13 summarizes these source criteria. Only GC/MS analysis of 

 each sample would definitely eliminate the small chance of a false 

 negative (i.e. not finding AMOCO oil where there were traces). 



The error bars in the figures indicate that two determinations 

 were made for the December 1978 samples (Table 6) . All other determin- 

 ations were based on one replicate. Note that the coefficient of 

 variation ranges from .01 (1%) to .94 (94%). The higher variability is 

 observed in samples with the lowest and highest (^1000 ppm) absolute 

 concentration levels, the former due to natural patchiness, the latter 

 owing to "pooling" of oil in heavily impacted stations. 



GC/MS results are available for stations 3, 5 and 7 throughout the 

 study period and are presented graphically in Figures 3.14 through 

 3.33. These semi-log plots illustrate quantitatively the aromatic 

 composition of all samples normalized to C3 dibenzothiophene or where 

 C3DBT is absent to pyrene. C3DBT was used to normalize the data as it 

 is assumed that these compounds are the slowest to weather of all of 

 the aromatic hydrocarbons. 



All AMOCO CADIZ-impacted stations illustrate a normal weathering 

 sequence (i.e. see Fig. 3.1). However, fresh inputs of petroleum were 

 observed to impact the region of stations 7 and 8 in the form of tar 

 chips during November 1979 and stations 2, 11 and 12 in the form of oil 

 from the TANIO spill in August of 1980 (Fig. 3.34). 



Although a wide range of residual oil concentrations appear in the 

 various samples, several trends in the data seem apparent. Stations 1, 

 9, and 10 remain unimpacted by the spill throughout the study. Station 

 2 remains unimpacted until a secondary petroleum input influences its 

 hydrocarbon chemistry in November of 1979 (the timing of the secondary 

 tar impact at stations 7 and 8 also is probably related to leakage from 

 the sunken tanker) and again in August of 1980, the latter relating to 

 the TANIO spill, also readily detected at Stations 11 and 12 at this 

 time. Through March of 1980 weathered AMOCO CADIZ oil is readily 

 detected at Stations 3, 4, 5, 6, 7 and 8. However, the results of the 

 August 1980 samplings indicate that inputs of non-AMOCO CADIZ hydro- 

 carbons (i.e. background) at Stations 6 and 8 become dominant. At 

 stations 3 and 7 where GC/MS data exists, the main AMOCO CADIZ aromatic 



50 



