Fig. 4. (a) Early breakthrough curves of Cu passed though untreated aquifer material in the presence of low and high molecular weight fractions of dissolved organic matter (DOM). (b) Breakthrough curves of Cu in the presence of hydrophilic acid compounds of two molecular-weight (MW) fractions. (c) Breakthrough curves of Cu in the presence of hydrophobic DOM compounds of two MW fractions. The Cu breakthrough curve in the absence of DOM is repeated in each graph for purposes of comparison. Arrows indicate when the influent was switched to KClO₄.