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2.4.3.3 Sediment Grain Size, Total Organic Carbon, and Moisture Content 



Grain size analysis was conducted by both the MAXIM laboratory (1997) and 

 GeoTesting Express (1998) using American Society for Testing and Materials (ASTM) 

 Method D422-63. A sieve analysis was performed in which the sample was separated into 

 size fractions of greater than 62.5 mm (<4 phi; sand and gravel), and less than or equal to 

 62.5 mm (>4 phi; silt and clay). The wet sieve and dry sieve fractions less than 62.5 mm 

 (silt and clay) were combined for each sample. The silt and clay fraction was then 

 subdivided using a pipette technique in 1997 (Plume/phi) and a hydrometer technique in 

 1998 (ASTM/mm). Both of these techniques are based upon differential settling rates of 

 particles. The data on grain size were converted from their respective units (phi or mm) to 

 units of gravel and sand, silt, and clay. 



Although the reported percent of fine sediment seemed accurate in the 1997 results, 

 the independent percentages of silt and clay did not correspond to visual observations of the 

 core samples prior to shipment to the laboratory. In addition, the measured silt-clay 

 percentages were also not consistent with observations of sediment cores collected in 1998 

 over the mound and results of the 1998 grain size analysis, which suggested a much higher 

 percentage of clay. This may be an artifact of the two different variations employed for 

 differentiation of the fine-grained material. Results are reported as percent fines (silt + clay). 



Total organic carbon (TOC) analyses were performed using EPA SW-846 Method 

 9060 (USEPA 1997). In this method, organic carbon is measured using a carbonaceous 

 analyzer that converts the organic carbon in a sample to carbon dioxide (C0 2 ) by wet chemical 

 oxidation. The C0 2 formed is then measured directly by an infrared detector. The amount of 

 C0 2 in a sample is directly proportional to the concentration of carbonaceous material in the 

 sample. Results expressed in this report are on a dry weight basis. 



Moisture content was determined gravimetrically using ASTM Method D2216. Prior 

 to initiating grain size analysis, a sub-sample (approximately 5-20 g) was taken for 

 determination of total solids (%). Total solids in a sediment sample is a measurement of the 

 water content of the sediment. This value is used to normalize chemical data to the actual 

 dry weight of the sample. Wet weights were obtained gravimetrically and recorded prior to 

 drying the samples at 103° C. The percent moisture in each sample was calculated by the 

 following equation: 



(g sediment wet weight) - (g sediment dry weight) , .. 



water content (%) = — & & ^- L x 100 



(g sediment dry weight) 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



