A 21-acre parcel in the east coast region of the United States hosted several industrial operations from 1907 to 1982. Groundwater at a pH of 5 SU and containing as much as 30 mg/L of zinc discharges to a small stream on one edge of the facility. The site surface was remediated and redeveloped into an apartment complex. Groundwater remediation was not a requirement at the time that the apartment complex was built. Subsequent ecological studies indicated that surface water impacts were occurring from zinc discharging from groundwater, and therefore remediation was required. In situ stabilization technologies that could be applied to groundwater with minimal interference with site use were evaluated in bench-scale and in-field pilot tests. The bench scale testing using site soil and groundwater samples determined that a 4 weight percent (wt. %) slurry of magnesium hydroxide [Mg(OH)2] reduced zinc concentrations from 14.7 to 0.013 mg/L. Multiple extractions found a pH of 8.5 SU and a zinc concentration of 0.088 mg/L of zinc following about 1,200 aquifer pore volumes of leaching, equivalent to 400 years at the site groundwater flow rate. Pilot testing was completed with direct-push injection methods. Approximately 7.3 tons of reagent slurried in 4,205 gallons of water was injected at six points. Temporary well samples within the injection zone had post-injection zinc concentrations of <0.020 mg/L. A monitoring well downgradient of the injection zone yielded 21 mg/L of zinc prior to the injection. Within two weeks the concentration had decreased to 10 mg/L and at 8 months following injection the zinc concentration was 0.99 mg/L and the pH was 9.3 SU. The proposed remedial design took the form of a reactive zone at the edge of the facility, which treats groundwater prior to its discharge to surface water. Regulatory approval for the full-scale implementation was received in July 2007 and injection was begun in August 2007.
Rehm, Bernd W.; Kondelin, Robert; and Markesic, Steve
"In Situ Stabilization Of Zinc In Soil And Groundwater,"
Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy:
Vol. 13, Article 19.
Available at: http://scholarworks.umass.edu/soilsproceedings/vol13/iss1/19