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Chao-Li Liu

Publications and source records attributed to Chao-Li Liu.

6 recordsLinked to original sources
USGS2005

Hydrochemistry of the Mahomet Bedrock Valley Aquifer, East-Central Illinois: Indicators of recharge and ground-water flow

A conceptual model of the ground-water flow and recharge to the Mahomet Bedrock Valley Aquifer (MVA), east-central Illinois, was developed using major ion chemistry and isotope geochemistry. The MVA is a “basal” fill in the east-west trending buried bedrock valley composed of clean, permeable sand and gravel to thicknesses of up to 61 m. It is covered by a thick sequence of glacial till containing thinner bodies of interbedded sand and gravel. Ground water from the MVA was found to be characterized by clearly defined geochemical regions with three distinct ground-water types. A fourth ground-water type was found at the confluence of the MVA and the Mackinaw Bedrock Valley Aquifer (MAK) to the west. Ground water in the Onarga Valley, a northeastern tributary of the MVA, is of two types, a mixed cation-SO 4 2- type and a mixed cation-HCO 3 type. The ground water is enriched in Na + Ca 2+ , Mg 2+ , and SO 4 2- which appears to be the result of an upward hydraulic gradient and interaction of deeper ground water with oxidized pyritic coals and shale. We suggest that recharge to the Onarga Valley and overlying aquifers is 100% from bedrock (leakage) and lateral flow from the MVA to the south. The central MVA (south of the Onarga Valley) is composed of relatively dilute ground water of a mixed cation-HC0 3 type, with low total dissolved solids, and very low concentrations of Cl - and SO 4 2- . Stratigraphie relationships of overlying aquifers and ground-water chemistry of these and the MVA suggest recharge to this region of the MVA (predominantly in Champaign County) is relatively rapid and primarily from the surface. Midway along the westerly flow path of the MVA (western MVA), ground water is a mixed cation-HCO 3 - type with relatively high Cl - , where Cl - increases abruptly by one to two orders of magnitude. Data suggest that the increase in Cl - is the result of leakage of saline ground water from bedrock into the MVA. Mass-balance calculations indicate that approximately 9.5% of recharge in this area is from bedrock. Concentrations of Na + , HCO 3 - , As, and TDS also increase in the western MVA. Ground water in the MAK is of a Ca 2+ -HCO 3 2- type. Mass-balance calculations, using Cl - as a natural, conservative tracer, indicate that approximately 17% of the ground water flowing from the confluence area is derived from the MVA.

Groundwater↗
USGS2005

Environmental Isotope Characteristics of Landfill Leachates and Gases

The isotopic characteristics of municipal landfill leachate and gases (carbon dioxide and methane) are unique relative to the aqueous and gaseous media in most other natural geologic environments. The δ 13 C of the CO 2 in landfills is significantly enriched in 13 C, with values as high as +20 ‰ reported. The δ 13 C and δD values of the methane fall within a range of values representative of microbial methane produced primarily by the acetate-fermentation process. The δD of landfill leachate is strongly enriched in deuterium, by approximately 30 ‰ to nearly 60 ‰ relative to local average precipitation values. This deuterium enrichment is undoubtedly due to the extensive production of microbial methane within the limited reservoir of a landfill. The concentration of the radiogenic isotopes, 14 C and 3 H, are significantly elevated in both landfill leachate and methane. The 14 C values range between approximately 120 and 170 pMC and can be explained by the input of organic material that was affected by the increased 14 C content of atmospheric CO2 caused by atmospheric testing of nuclear devices. The tritium measured in leachate, however, is often too high to be explained by previous atmospheric levels and must come from material buried within the landfill. The unique isotopic characteristics observed in landfill leachates and gases provide a very useful technique for confirming whether contamination is from a municipal landfill or some other local source.

Groundwater↗
USGS1999

Isotopic identification of the source of methane in subsurface sediments of an area surrounded by waste disposal facilities

The major source of methane (CH4) in subsurface sediments on the property of a former hazardous waste treatment facility was determined using isotopic analyses measured on CH4 and associated groundwater. The site, located on an earthen pier built into a shallow wetland lake, has had a history of waste disposal practices and is surrounded by landfills and other waste management facilities. Concentrations of CH4 up to 70% were found in the headspace gases of several piezometers screened at 3 different depths (ranging from 8 to 17 m) in lacustrine and glacial till deposits. Possible sources of the CH4 included a nearby landfill, organic wastes from previous impoundments and microbial gas derived from natural organic matter in the sediments. Isotopic analyses included ??13C, ??D, 14C, and 3H on select CH4 samples and ??D and ??18O on groundwater samples. Methane from the deepest glacial till and intermediate lacustrine deposits had ??13C values from -79 to -82???, typical of natural 'drift gas' generated by microbial CO2-reduction. The CH4 from the shallow lacustrine deposits had ??13C values from -63 to -76???, interpreted as a mixture between CH4 generated by microbial fermentation and the CO2-reduction processes within the subsurface sediments. The ??D values of all the CH4 samples were quite negative ranging from -272 to -299???. Groundwater sampled from the deeper zones also showed quite negative ??D values that explained the light ??D observed for the CH4. Radiocarbon analyses of the CH4 showed decreasing 14C activity with depth, from a high of 58 pMC in the shallow sediments to 2 pMC in the deeper glacial till. The isotopic data indicated the majority of CH4 detected in the fill deposits of this site was microbial CH4 generated from naturally buried organic matter within the subsurface sediments. However, the isotopic data of CH4 from the shallow piezometers was more variable and the possibility of some mixing with oxidized landfill CH4 could not be completely ruled out.

Applied Geochemistry↗
USGS1988

Microbial methane in the shallow Paleozoic sediments and glacial deposits of Illinois, U.S.A.

Methane formed by the microbial decomposition of buried organic matter is virtually ubiquitous in the groundwaters of Illinois. Chemical and carbon isotopic compositions are reported for gas samples collected from over 200 private and municipal water wells and from 39 small gas wells completed in glacial deposits (drift-gas wells). Carbon and hydrogen isotopic data for methane, carbon dioxide and water show that these gases were formed by the carbon dioxide reduction pathway, the same mechanism which has been previously shown to be responsible for microbial methane formation in the marine environment. The isotopic composition of methane in these samples can be closely correlated with the chemical composition of the gas and with water chemistry. The data are interpreted as indicating that isotopically very light methane is found in waters where the residence time of groundwater in the methanogenesis zone was very short relative to the methane production rate. ?? 1988.

Chemical Geology↗
USGS1987

Use of stable sulphur isotopes to monitor directly the behaviour of sulphur in coal during thermal desulphurization

A method has been developed using stable sulphur isotope analyses to monitor the behaviour of sulphur forms in a coal during thermal desulphurization. In this method, the natural stable isotopic composition of the pyritic and organic sulphur in coal is used as a tracer to follow their mobility during the desulphurization process. This tracer method is based on the fact that the isotopic compositions of pyritic and organic sulphur are significantly different in some coals. Isotopic results of pyrolysis experiments at temperatures ranging from 350 to 750 °C indicate that the sulphur released with the volatiles is predominantly organic sulphur. The pyritic sulphur is evolved in significant quantities only when pyrolysis temperatures exceed 500 °C. The presence of pyrite seems to have no effect on the amount of organic sulphur evolved during pyrolysis. The chemical and isotopic mass balances achieved from three different samples of the Herrin (No. 6) coal of the Illinois Basin demonstrate that this stable isotope tracer method is quantitative. The main disadvantage of this tracing technique is that not all coals contain isotopically distinct organic and pyritic sulphur.

Illinois, Indiana, Kentucky↗