- Copyright ©2010. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.
This article examines environmental concerns at the site of a Los Angeles, California, high school known as Belmont Learning Center (BLC) during its construction. A part of the site on which the school was to be built is a largely depleted oil field in the center of Los Angeles, close to a heavily populated area. Located nearby are another high school and an elementary school, each constructed more than 70 yr ago atop the same oil field. Prior to and during construction at the BLC site, which began in 1990, methane (CH4) and hydrogen sulfide (H2S) were detected in deep soil borings and monitoring wells. After the building construction began, a stratigraphic offset was also detected and interpreted as a fault line, which could be traced beneath one of the nearly completed buildings. This resulted in a decision to demolish that building and an adjacent one and to temporarily suspend all construction activity. Additional analytical measurements showed that the highest concentrations of both CH4 (>5% atmospheric concentration) and H2S (>100 ppmv) occurred only in the deeper samples, and that only traces of these environmentally hazardous gases were present at or near the soil surface. In this article, we use carbon, hydrogen, and sulfur stable isotope data, as well as 14C measurements to describe the sources and natural processes of CH4 and H2S removal.
The interpretations offered in this article will hopefully be useful in assisting environmental professionals and government officials who evaluate hazardous soil gas concentrations to make decisions during the process of issuing or denying construction permits.
Isaac R. Kaplan is a professor emeritus in geology and geochemistry at the University of California at Los Angeles, and was the former president of Global Geochemistry Corp. He received his Ph.D. from the University of Southern California in 1961. His career research interests have been directed to biogeochemical problems in marine sediments, origin of petroleum and natural gases, characterization of carbon compounds in atmospheric aerosols and meteorites, and currently in forensic environmental geochemistry.
John E. Sepich is a consulting professional engineer specializing in soil vapor mitigation. He received a BSCE from the University of Illinois in 1970 and is the owner and president of Brownfield Subslab, LLC, in San Antonio, Texas. He has worked on numerous construction projects in areas of active hydrocarbon gas seepage and has several patents in the field. He has also served as an expert witness in litigation disputes.