Origin of methane and sources of high concentrations in Los Angeles groundwater
Journal of Geophysical Research: Biogeosciences
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Abstract
In 2014, samples from 37 monitoring wells at 17 locations, within or near oil fields, and one site >5 km from oil fields, in the Los Angeles Basin, California, were analyzed for dissolved hydrocarbon gas isotopes and abundances. The wells sample a variety of depths of an aquifer system composed of unconsolidated and semiconsolidated sediments under various conditions of confinement. Concentrations of methane in groundwater samples ranged from 0.002 to 150 mg/L—some of the highest concentrations reported in a densely populated urban area. The δ13C and δ2H of the methane ranged from −80.8 to −45.5 per mil (‰) and −249.8 to −134.9‰, respectively, and, along with oxidation‐reduction processes, helped to identify the origin of methane as microbial methanogenesis and CO2 reduction as its main formation pathway. The distribution of methane concentrations and isotopes is consistent with the high concentrations of methane in Los Angeles Basin groundwater originating from relatively shallow microbial production in anoxic or suboxic conditions. Source of the methane is the aquifer sediments rather than the upward migration or leakage of thermogenic methane associated with oil fields in the basin.
Suggested Citation
Kulongoski, J.T., McMahon, P.B., Land, M., Wright, M., Johnson, T., and Landon, M.K., 2018, Origin of methane and sources of high concentrations in Los Angeles groundwater: Journal of Geophysical Research: Biogeosciences, v. 123, no. 3, p. 818-831, https://doi.org/10.1002/2017JG004026.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Origin of methane and sources of high concentrations in Los Angeles groundwater |
| Series title | Journal of Geophysical Research: Biogeosciences |
| DOI | 10.1002/2017JG004026 |
| Volume | 123 |
| Issue | 3 |
| Publication Date | March 11, 2018 |
| Year Published | 2018 |
| Language | English |
| Publisher | American Geophysical Union |
| Contributing office(s) | California Water Science Center |
| Description | 14 p. |
| First page | 818 |
| Last page | 831 |
| Country | United States |
| State | California |
| City | Los Angeles |
| Other Geospatial | Los Angeles Basin |