A compost cap consisting of biosolids and wood ash was applied to the surface of Pb mine tailings that had been impounded in a wetland near Smelterville, ID since the 1920s. The primary risk associated with elevated Pb is direct ingestion of sediment by waterfowl. Total Pb in the sediment ranged from 15.45 to 49.78 g kg-1. The compost cap was applied in 1998 with the goals of providing 1) a barrier to the contaminated sediment for fertile plant growth and limit migration of Pb to the barrier surface and, 2) a zone of reducing conditions to change the mineral form and subsequently the extractability of Pb in the underlying contaminated sediment. Cores were taken from the wetland in 2005 and analyzed for Pb speciation using X-ray absorption fine structure (XAFS) spectroscopy to identify Pb mineral forms and physiologically-based extraction test (PBET) to access Pb bioaccessibility. Cores were separated into the depth immediately below and 15 cm below the compost cap - contaminated sediment interface. There was increased concentration of PbS in the horizon directly below the compost. Lead bioaccessibility decreased with increasing concentration of PbS and increased with increasing concentration of PbCO3. Plant roots were confined to the fertile compost cap horizon. Both total Pb and extractable Pb in the compost cap horizon was very low (total Pb < 240 mg kg-1, PBET Pb < 5%) indicating that incidental ingestion of the compost cap material would not cause any detrimental effects to waterfowl. These results suggest that this type of remedial approach offers an environmentally friendly and cost effective remedial option for Pb contaminated sediments.