Fig. 6. Cemented areas of the permeable reactive barrier (PRB): (a) backscatter electron (BSE) analysis of an undisturbed sample collected after the first 15 mo of operation at the shallow up-gradient interface of Core A showing Fe⁰ filings cemented together by Fe (oxy)hydroxides, Fe₂O₃, aragonite, and FeS; (b) map showing the distribution of the different minerals in (a); (c) BSE of an undisturbed sample collected 30 mo after installation at the shallow up-gradient interface from Core 1 showing the buildup of precipitation on an Fe⁰ surface; and (d) map showing the different minerals in (c). (Note the layering of mineral sequences, the transformation of calcite from aragonite, and the goethite crystals on the surface.)