WATER-MOVEMENT AND SOLUTE TRANSPORT THROUGH SAPROLITE

Many soils are underlain by saprolite. The purpose of this study was t o assess the potential for preferential movement of pollutants through one soil and two saprolites in the Piedmont region of North Carolina. At one site (Site 1), two 100 by 100 by 100 cm intact blocks were iso lated in situ in the Bt horizon and underlying saprolite, and a soluti on containing KBr, NH4NO3, a blue dye, and a red dye was applied to th e top of each block. At a second location (Site 2), a 120 by 120 by 10 0 cm intact block of saprolite was similarly prepared. Acid red dye po wder (5 g) was placed in four small holes (3 cm deep) bored into the s urface of the block, and the block was leached with a solution contain ing only KBr and NH4NO3. After drainage, each block was dissected laye r by layer (5 or 10 cm thick), and the middle 80 by 80 by 100 cm volum e was divided into 768 samples and analyzed for K+, Br-, NH4+, and NO3 -, as well as dye content. The visible patterns of the dyes, and extra cted solute concentrations, al Site 1 indicated that preferential move ment was more pronounced in the at horizon than in the saprolite. At S ite 2, the red dye and solutes moved vertically with little lateral de viation. Our results suggest that vertical water movement in the two s aprolites occurs mainly through matrix pores with little preferential movement via the visible features inherited from respective parent roc ks.