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Extremely alkaline ground water has been found underneath many shuttered steel mills and slag dumps and has been an impediment to the cleanup and economic redevelopment of these sites because little is known about the geochemistry. A large number of these sites occur in the Lake Calumet region of Chicago, Illinois, where large-scale infilling of the wetlands with steel slag has created an aquifer with pH values as high as 12.8. To understand the geochemistry of the alkaline ground water system, we analyzed 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 [Ca.sup.2+] and O[H.sup.-] in equilibrium with Ca(OH)[.sub.2]. Where the alkaline ground water discharges in springs, atmosphere C[O.sub.2] 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 and have not accumulated in large concentrations in the ground water. Calcite precipitated at the springs is rich in a number of heavy metals, suggesting that metals can move through the system as particulate matter. Air sparging appears to be an effective remediation strategy for reducing the toxicity of discharging alkaline water., Introduction Extremely alkaline ground water has not been extensively studied because it is observed only rarely in natural water, and then only in distinctive geological settings, such as thermal springs [...]

A total of 176 wells in sand-and-gravel glacial aquifers in central Illinois were sampled for arsenic (As) and other chemical parameters. The results were combined with archived and published data from several hundred well samples to determine potential sources of As and the potential geochemical controls on its solubility and mobility. There was considerable spatial variability in the As concentrations. High concentrations were confined to areas smaller than 1 km in diameter. Arsenic and well depth were uncorrelated. Arsenic solubility appeared to be controlled by oxidation-reduction (redox) conditions, especially the presence of organic matter. Geochemical conditions in the aquifers are typically reducing, but only in the most reducing water does As accumulate in solution. In wells in which total organic carbon (TOC) was below 2 mg/L and sulfate (S[O.sub.4.sup.2-]) was present, As concentrations were low or below the detection limit (0.5 µg/L). Arsenic concentrations >10 µg/L were almost always found in wells where TOC was >2 mg/L and S[O.sub.4.sup.2-] was absent or at low concentrations, indicating post-S[O.sub.4.sup.2-] reducing conditions. Iron (Fe) is common in the aquifer sediments, and Fe oxide reduction appears to be occurring throughout the aquifers. Arsenic is likely released from the solid phase as Fe oxide is reduced., Introduction Arsenic (As) is well known for its acute toxicity, and As in drinking water can also cause serious dermatological conditions and affect the respiratory, gastrointestinal, cardiovascular, and nervous systems [...]

Abstract: The conservative nature of chloride (Cl−) in groundwater and the abundance of geochemical data from various sources (both published and unpublished) provided a means of developing, for the first time, a representation of the hydrogeology of the Illinois Basin on a basin‐wide scale. The creation of Cl− isocons superimposed on plan view maps of selected formations and on cross sections across the Illinois Basin yielded a conceptual model on a basin‐wide scale of recharge into, groundwater flow within and through the Illinois Basin. The maps and cross sections reveal the infiltration and movement of freshwater into the basin and dilution of brines within various geologic strata occurring at basin margins and along geologic structures. Cross‐formational movement of brines is also seen in the northern part of the basin. The maps and cross sections also show barriers to groundwater movement created by aquitards resulting in areas of apparent isolation/stagnation of concentrated brines within the basin. The distribution of Cl− within the Illinois Basin suggests that the current chemical composition of groundwater and distribution of brines within the basin is dependent on five parameters: (1) presence of bedrock exposures along basin margins; (2) permeability of geologic strata and their distribution relative to one another; (3) presence or absence of major geologic structures; (4) intersection of major waterways with geologic structures, basin margins, and permeable bedrock exposures; and (5) isolation of brines within the basin due to aquitards, inhomogeneous permeability, and, in the case of the deepest part of the basin, brine density effects. [ABSTRACT FROM AUTHOR]

Large-scale nitrate contamination of ground water is often observed in irrigated areas where the soils are generally permeable, and nitrate plumes have been reported to occur at shallow depths in unconfined aquifers. It has been hypothesized that these nitrate plumes can be captured by the pumping action of irrigation wells and recycled at the field site. This paper presents results from a field and modeling study investigating the distribution of nitrate in an unconfined sand aquifer in an irrigated system. Results from tracer tests under both natural and forced gradients indicate that irrigation pumping has minor but measurable effects on solute transport. Hydrological and solute transport modeling using various pumping schedules suggests that, in most cases, the influence of irrigation pumping on solute transport will be minimal, even on local scales.

Extremely alkaline ground water has been found underneath many shuttered steel mills and slag dumps and has been an impediment to the cleanup and economic redevelopment of these sites because little is known about the geochemistry. A large number of these sites occur in the Lake Calumet region of Chicago, Illinois, where large-scale infilling of the wetlands with steel slag has created an aquifer with pH values as high as 12.8. To understand the geochemistry of the alkaline ground water system, we analyzed 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- in equilibrium with Ca(OH)2. 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 and have not accumulated in large concentrations in the ground water. Calcite precipitated at the springs is rich in a number of heavy metals, suggesting that metals can move through the system as particulate matter. Air sparging appears to be an effective remediation strategy for reducing the toxicity of discharging alkaline water.