Effective solubility assessment for organic analytes in liquid samples, BKK class I landfill, West Covina, California, 2014–16

Abstract

Executive Summary The U.S. Geological Survey assessed the effective solubilities of organic analytes at the BKK Class Ⅰ Landfill site, West Covina, California, in cooperation with the California Department of Toxic Substances Control, using available data for liquid samples collected within (in-waste) and below (sub-waste) the landfill in 2014–16. The primary purpose of the effective solubility calculations was to determine the likely presence or absence of dense non-aqueous phase liquids (DNAPLs), which is important for understanding the sources, persistence, and movement of the leachate contaminants. Percent effective solubility (a measure of the degree of deviation of a measured liquid concentration of a compound from the aqueous effective solubility) greater than 1 percent is the threshold that commonly has been used to infer the presence of DNAPLs or mixed DNAPLs in aqueous monitoring results. In the present study, however, thresholds higher than 1 percent were used because of elevated temperatures and concentrations of cosolvents in the liquid samples—thresholds of 10 percent or 100 percent, respectively, were used for liquid and solid (at 25 degrees Celsius) organic compounds for potential non-aqueous phase liquid presence. Overall, the effective solubility calculations indicate the likely presence of DNAPLs or mixed DNAPLs in some samples for a range of compounds, including tetrachloroethene, trichloroethene, 1,1-dichloroethene, vinyl chloride, 1,2,4-trichlorobenzene, 1,4-dichlorobenzene, 1,2-dichlorobenzene, naphthalene, toluene, ethylbenzene, and xylenes. Samples with the highest calculated percent effective solubilities for chlorinated ethenes, ethanes, and benzenes were from a location where liquid in the waste prism is known to be in contact with the groundwater beneath the landfill. Trends in the effective solubilities for the chlorinated ethenes and ethanes were generally consistent between the in-waste and sub-waste samples, supporting a similar source composition for these liquids. Percent effective solubilities were less than 10 for the chlorinated ethanes in all the in-waste and sub-waste samples, indicating that DNAPL of these compounds is not present. Percent effective solubilities of chlorinated benzenes, ethylbenzene, and xylenes exceeded the 10-percent effective solubility threshold in more of the sub-waste samples than the in-waste liquid samples. Volatilization also may influence the patterns in the calculated effective solubilities but were not included in this study.