Fig. 4. Distribution of Fe in the original aquifer solids. The fractions removed with these extractants are operationally defined as iron associated with (1) surface exchangeable sites, (2) carbonates, (3) organic matter, (4) Mn oxides, (5) non-crystalline Fe oxides, (6) crystalline Fe oxides, and (7) the residual fraction. Error bars are 95% CI of triplicate extractions.