Remediation of Ground Water and Soil Affected by Acid-Rock Drainage at a Chemical Manufacturing Facility

In support of the redevelopment of a 100-year old, 86-acre, former chemical manufacturing facility, LFR developed and implemented a Conceptual Remedial Plan that included chemical treatment, physical encapsulation, and a permeable reactive barrier (PRB). The site included a saltwater marsh and freshwater lagoons with a landfill composed primarily of waste roasted iron pyrite ore. The waste pyrite ore is a byproduct of the sulfuric acid manufacturing that was conducted on the site until the 1970’s. Elevated dissolved concentrations of copper, cadmium, nickel and zinc in the shallow groundwater were the primary concern at the site. Groundwater pH was as low as 3 standard units. Acid was generated from the oxidation of waste pyrite ore used as shallow fill at the site. The acid leached metals from the ore and further enhanced their transport to groundwater. Remedial measures included:

• neutralization and stabilization of 300,000 cubic yards of waste pyrite ore with dolomitic limestone to prevent leaching of metals;

• treatment of metals in acidic shallow groundwater by direct injection of over 140,000 gallons of calcium polysulfide, an alkaline reducing agent;

• installation of a PRB to provide a polishing step in dissolved metals treatment and minimize metals loading to the adjacent tidal marsh; the PRB is composed of compost material to create chemically reducing conditions, limestone to provide pH buffering, and chemically reduced sediment to provide sulfate-reducing bacteria; and,

• installation of a site cap to prevent erosion and reduce infiltration through the neutralized roasted pyrite ore on site.

The majority of the remediation took place between 2000 and 2002. Groundwater conditions were significantly improved, with metals concentrations decreasing by 1 to 3 orders of magnitude in most areas. The PRB continues to create reducing conditions and concentrations of key metals in the PRB have remained below target levels.