TRANSPORT OF HEAVY-METALS THROUGH ACCUMULATED SEDIMENTS IN WET PONDS

Nine detention ponds in Florida were selected to investigate heavy-met al accumulation in their bottom sediments. Core sediment samples were collected from each pond, frozen and divided into six layers. The tota l metal content and extractable metal by toxicity characteristic leach ing procedure (TCLP) were determined for each sediment layer in each p ond. The fractions of extractable metals using TCLP exhibited an expon ential decline with increasing fine particles (less than 0.062 mm diam eter) and organic content. Most of these metals are tightly bound to t he bottom sediments, and their transport is very slow. It is feasible to remove the accumulated sediments saturated with metals from the bot tom of the ponds for periodic maintenance at relatively long periods, averaging 25 years, to avoid seepage and potential contamination of gr oundwater beneath the pond.