Author: George Stewart Roadcap

Publisher:

Published: 2004

Total Pages: 124

ISBN-13:

Large-scale infilling of the wetlands in the Lake Calumet region of Chicago, Illinois with steel slag has created an aquifer with extremely alkaline ground water, the pH of which can range up to 12.8. To understand the geochemistry of this aquifer, we examined samples of ground water and the associated slag and weathering products from four sites. We also considered several potential remediation schemes to lower the pH and toxicity of the water. The principal cause of the alkaline conditions is the weathering of calcium silicates within the slag. The resulting ground water at most of the sites is dominated by Ca2+ and OH, which form a temperature-sensitive pH buffering system. Where the alkaline ground water discharges in springs, atmospheric CO2 dissolves into the water and thick layers of calcite form. Iron, manganese, and other metals in the metallic portion of the slag have corroded to form more stable low-temperature oxides and sulfides. Fe and Mn in the slag, as well as steel additives such as Ni and Mo, react to form insoluble phases; these metals did not accumulate in large concentrations in the ground water. Calcite precipitated at the springs is rich in a number of heavy metals, suggesting that the metals moved through the system as particulate matter. Air sparging appears to be an effective remediation strategy for reducing the toxicity of discharging alkaline waters. Microbiologists have long believed that highly alkaline conditions are poorly supportive of microbial life, in part because an environment lacking in hydrogen ions (H+) is likely to interfere with the proton motive force needed by most respiring organisms to synthesize ATP, and with the need to maintain a circum-neutral intracellular pH (Horikoshi and Akiba, 1982). Here I describe a diverse microbial community that inhabits extremely alkaline (pH ~ 12-13) ground water from the Lake Calumet region. Using microbial culturing, genetic sequencing, and microcosm experiments, I confiimed the presence and growth of a variety of alkaliphilic ß-Proteobacteria, Bacillus, and Clostridium species at pH up to 13.2. Many of the bacterial sequences most closely matched other alkaliphiles found more moderately alkaline waters around the world. Oxidation of dihydrogen produced by reaction of water with steel slag is likely a primary energy source to the community. These results extend upward the known range of pH tolerance for a microbial community by as much as two pH units. The microbial community may provide a source of novel microbes and enzymes that can be exploited under alkaline conditions.