ABSTRACT
A sequentia l ex trac tio n p ro ced u re developed to identify and quantify th e s tru c tu ra l co m p o n en ts o f aqu ifer sedim ents th a t bind chrom ium and o th e r heavy m etals ind icated th a t m ost o f th e heavy m etals are tightly bou n d to th e soil m atrix . T h e exchangeab le fractions and o rgan ic bound fractions w ere found to be sta tistica lly th e sam e at th e tw o locations (T able I). This w as ex p ected since th e soil a t th e tw o locations w as o f th e sam e geo log ic fo rm ation , and co n tained sim ilar am o u n ts o f o rgan ic m atter. H ow ever, th e o x ide-bound and residual frac tio n s w ere statistically different. H igher concen tra tions o f ch rom ium w ere o b se rv ed in soil sam ples obta ined closer to th e sou rce o f th e co n tam ination , as co m p ared to th o se ob ta ined d ow ngrad ien t from th e source. T he variability o f accum ulation in th e ox ide and residual fractions betw een th e tw o locations resu lted from th e soils near th e facility experiencing a longer ex p o su re tim e to th e con tam inan ts; they had a longer o pportun ity to diffuse in to th e p artic le m atrix. T h e fact th a t a significant am ount o f chrom ium w as tigh tly bound n ear th e sou rce su g g ests th a t a slow , k inetically-contro lled a ttenua tion m echanism w as also influencing heavy m etal m obility at th e site. The streng th o f th e ex trac tan ts used in th e A sikainen and N ikolaid is study indicated tha t only a fraction o f th e to ta l
P hysical C haracteristics C hem ical C haracteristics Soil p H 5.63 B arium , m g/K g 95.1 D ry D en sity , g /m l 1.57 C adm ium , m g/K g 2 8 .9 S a tu ra te d D ensity , g /m l 1.90 C hrom ium , m g/K g 5 20 .5 P o ro s ity 0.33 C o p p er, m g /K g 55.3 S pecific G rav ity 2 .35 Iron , m g/K g 14321 .2 d lO , m m 0.14 L ead , m g /K g 2 6 .2 d 6 0 , m m 2.70 M anganese , m g /K g 241.1 Soil O rg an ic M a tte r C o n ten t 0 .82 N ickel, m g /K g 156.1 S u rface A re a (B E T ), m 2 /g 2.7 Z inc, m g /K g 6 4 .8
