THE LONG-TERM WEATHERING OF PFA AND IMPLICATIONS FOR GROUNDWATER POLLUTION

Borehole samples of weathered PFA were taken from an ash disposal moun d at a major British power station. The oldest ash studied was deposit ed in 1975. XRD and SEM investigation of weathered PFA showed no subst antial changes in mineralogy, such as the formation of secondary clay minerals, as the result of weathering. However, element concentrations in porewater and PFA varied as a function of depth indicating (a) rea ction of PFA with infiltrating porewaters and attainment of equilibriu m (Ca, SO42-, Ba, Sr), (b) reaction without attainment of equilibrium (Mg, Na, K, B, Mo) and (c) elements infiltrating into the PFA from the surface (Cl-, NO3-). The depth trends were used to assess mobility an d migration of elements in the PFA mound and thus to produce informati on on leachate evolution in older PFA disposal sites in which leachate s could either enter surface waters or pass downwards into groundwater .