Using Waste Foundry Sands as Reactive Media in Permeable Reactive Barriers

Executive Summary: The objective of this study was to evaluate the potential use of waste foundry sand as an inexpensive medium for permeable reactive barriers (PRBs). Batch and column tests were conducted to evaluate the reactivity and sorptive capacity of twelve foundry sands for four groundwater contaminants: TCE, the herbicides alachlor and metolachlor, and zinc. Parameters obtained from these tests were then used to size PRBs for typical field conditions. The sizing calculations showed that foundry-sand PRBs containing at least 1% iron appear are viable under typical conditions for remediating groundwater contaminated with solvents, herbicides, and metals to concentrations below the maximum contaminant level (MCL).

The batch and column tests showed that the relatively abundant organic carbon in foundry sands results in appreciable sorption of TCE, alachlor, and metolachlor. When typical concentrations in groundwater are considered, sorption of these compounds can be described with a partition coefficient from a linear isotherm model. Foundry sands were also found to be a good sorbent for zinc. However, the partition coefficient for zinc varies significantly with solution pH.

Rate constants for reduction of TCE, alachlor, and metolachlor with foundry sand were found to be comparable to those for conventional iron media used for PRBs. Additionally, the rate constant can be normalized by the surface area to solution ratio, as is done for conventional iron media. The rate constant for zinc was found to vary within a small range (typically 0.05 — 0.20 1/hr). Higher rate constants for zinc typically were obtained at higher pH.