NSWC/WOL/TR 75-35 



which responds linearly to methane. The detector output is 

 integrated and displayed in milligrams per liter (mg/1) on the 

 digital meter. 



4.3.4 Sediment 



4.3.4.1 Metals 



Metals in the sediment samples can be determined by a simple 

 procedure essentially described by Iskandar and Keeney.28 Each sedi- 

 ment sample is mixed thoroughly, and a subsample is dried at 105°C 

 in a forced-air oven. The dried sample after discarding large 

 pebbles, twigs, shells, bugs, etc, is ground with a porcelain mortar 

 and pestle until fine ( 100-mesh) . 



A subsample (1-2 grams) is placed in a 70-ml Pyrex digestion 

 tube and predigested at room temperature for 16 hours by reaction 

 with 5-10 ml of concentrated HNO3 . Subsequently, the sample is 

 digested on an hot plate at 120°C for 3 hours. After it is cooled, 

 3 ml of concentrated HCIO4 are added, and the mixture is heated at 

 210-220°C until HCl fumes are evolved. The cooled digest is then 

 filtered through a 0.45u Millipore filter and brought to a 2 5-ml 

 volume with distilled water. The metals in the solution are 

 determined by atomic absorption. 



4.3.4.2 Explosives 



The analyses of explosives in sediment samples are generally 

 more involved than in water samples. First, the explosives are 

 extracted from the sediment with the appropriate solvent. Then, the 

 explosives in the extract are separated by thin- layer chromatography 

 and finally analyzed by gas chromatography. 



TNT, RDX, Tetryl 



Seventy-five to 100 grams of the sediment sample are stirred 

 with 50 ml of benzene. The benzene extract is decanted into a 100-ml 

 round-bottom flask for vacuum evaporation. 



28 



Iskandar, K. I., Keeney, D. R., "Concentration of Heavy Metals in 



Sediment Cores from Selected Wisconsin Lakes", Environ. Sci. 



Technol., 8, 165 (1974). 



56 



