Analytical precision was determined by periodically analyzing replicate 
aliquots taken from a single sample. Coefficients of variation shown in 
table 2 indicate that the standard deviation is typically less than 10 percent 
of the mean value, except for concentrations at or near the detection limit of 
the method. 
To maintain our internal quality control and to provide typical sample 
material for interlaboratory comparisons, four sediment standards representing 
different textural types were prepared from large samples of Georges Bank 
sediment. The levels of trace metals are being established by several 
analytical methods. Splits of these materials are available to _ those 
interested in cross-calibration studies. 
RESULTS AND DISCUSSION 
Sediment texture 
The texture of the surface sediments sampled in the third year of 
monitoring (appendix table 3A) is very similar to the texture measured in the 
first two years (fig. 2) as defined by the average mean $ values at each 
station for a given year. Low yearly variability of the mean > grain sizes 
occurs, as demonstrated by the close match of the data patterns. Mean $6 
values range from about 1 $ (coarse sand) at station 5-l to about 6.3 $ 
(medium silt) at station 13A located south of Martha's Vineyard. The error 
bars (standard deviation about the mean of samples from each of four seasons) 
indicate that the within-station variability is much smaller than the between- 
station variability. 
The sediments on Georges Bank are typically greater than 95 percent sand 
and contain minor amounts of gravel, silts, and clays. The sand is primarily 
medium to coarse grained, and ranges in coloration from a clear or 
20 
