A recent application by a steel-manufacturing plant to obtain a permit for an industrial landfill on abandoned soda ash waste beds near the city of Syracuse, New York, resulted in an extensive hydrogeologic and geochemical investigation. This investigation was initiated because of (1) previous disposal of waste by the metal manufacturer at this site and (2) the unique location of the landfill on top of preexisting waste beds on the shores of Onondaga Lake. The waste beds cover approximately 1 473 000 m2 to a depth of 20 m and consist of hydraulically placed hydroxides, salts, and residues, all byproducts of soda ash production. The metals-manufacturing wastes have been placed as a thin (0.5 to 2 m) layer over an area of 69 000 m2 on the soda ash waste beds during the past ten years. The primary leachate contaminant of concern has been hexavalent chromium.
The groundwater monitoring program and investigations included installation of 76 monitoring points including wells, piezometers, lysimeters, and seepage galleries. The hydrogeologic investigation included 30 permeability tests, over 600 water quality samples, and development of a three-dimensional, seven-layer groundwater model of the site. A significant groundwater mound was identified within the waste beds. Groundwater flows predominantly downward through the soda ash wastes into thick underlying alluviolacustrine and glaciolacustrine deposits and ultimately into Onondaga Lake. The results of groundwater monitoring over a one-year period indicate no detectable chromium from the metal-waste leachate escaping through the soda ash wastes. Retention of hexavalent chromium within the underlying highly alkaline soda ash wastes by adsorption, reduction, and precipitation suggests a viable means for in situ treatment of several metals-manufacturing waste products.