Early detection of groundwater contamination from waste disposal facilities is challenging in karst terranes. First, one needs to demonstrate that the groundwater system at the study site is monitorable. Both springs ...Early detection of groundwater contamination from waste disposal facilities is challenging in karst terranes. First, one needs to demonstrate that the groundwater system at the study site is monitorable. Both springs and wells are potential monitoring locations if they are effectively connected to the groundwater system, and they are not impacted by any other disposal facilities. Second, due to dynamic responses to recharge events, particularly discharge and chemical constituents at karst springs, multiple-parameter, long-term, and high-frequency monitoring may be required to collect background data. Sampling and analysis plans should be designed to reflect the unique characteristics of the monitoring locations. Characterization of the natural variations in water quality may require sampling efforts under different flow conditions. Third, evaluation of the potential impact of waste disposal units on the groundwater system requires an effective statistical evaluation program. Due to heterogeneity of karst aquifers, intra-locational comparison is generally preferred to inter-locational comparison. Sufficient groundwater monitoring data prior to construction of waste disposal units are required to develop the intra-locational statistical evaluation. In the case study presented in this paper, procedures to address these above-mentioned challenges were presented for two springs using seven dye tracing tests, two spring instrumentations, nine background sampling, flow-weighted concentrations, and an innovative statistical evaluation method were presented. These procedures were developed to evaluate potential contaminant release from a solid waste disposal facility constructed in a relatively isolated karst terrane. Although the specific procedures may not be duplicated, the overall technical approaches discussed in the paper may shed light on groundwater monitoring programs in other karst areas.展开更多
Dilution and attenuation factor (DAF) has a major influence on soil-to-groundwater screening level calculation for protection of contaminant migration from soil into groundwater at solid waste management units (SWMUs)...Dilution and attenuation factor (DAF) has a major influence on soil-to-groundwater screening level calculation for protection of contaminant migration from soil into groundwater at solid waste management units (SWMUs). Risk assessment guidance prepared by U.S. Environmental Protection Agency for site investigation and remediation suggests a default DAF of 20. If the base assumptions included in the default DAF are recognized to be not representative of site conditions at a SWMU, calculation of site-specific DAF is recommended when sufficient data are collected to justify using a different DAF value for development of soil screening levels. Commonly used methods of calculating DAF include analytical and numerical simulations that often require too many parameters to be obtained in practice. This paper proposes a probability method to develop site-specific DAF. The approach uses data that are readily available through field reconnaissance and site-specific investigation. A case study is presented in which the probability method was applied to an actual SWMU, and the calculated DAF is compared with that calculated from a dilution method. The probability-based DAF is 67 at 90% probability percentile, which is comparable to the dilution-based DAF of 76. Based on the calculated site-specific DAFs, SSLs could be developed for the contaminants of potential concern and used for evaluation of migration pathways from a contamination source through soil to groundwater. .展开更多
文摘Early detection of groundwater contamination from waste disposal facilities is challenging in karst terranes. First, one needs to demonstrate that the groundwater system at the study site is monitorable. Both springs and wells are potential monitoring locations if they are effectively connected to the groundwater system, and they are not impacted by any other disposal facilities. Second, due to dynamic responses to recharge events, particularly discharge and chemical constituents at karst springs, multiple-parameter, long-term, and high-frequency monitoring may be required to collect background data. Sampling and analysis plans should be designed to reflect the unique characteristics of the monitoring locations. Characterization of the natural variations in water quality may require sampling efforts under different flow conditions. Third, evaluation of the potential impact of waste disposal units on the groundwater system requires an effective statistical evaluation program. Due to heterogeneity of karst aquifers, intra-locational comparison is generally preferred to inter-locational comparison. Sufficient groundwater monitoring data prior to construction of waste disposal units are required to develop the intra-locational statistical evaluation. In the case study presented in this paper, procedures to address these above-mentioned challenges were presented for two springs using seven dye tracing tests, two spring instrumentations, nine background sampling, flow-weighted concentrations, and an innovative statistical evaluation method were presented. These procedures were developed to evaluate potential contaminant release from a solid waste disposal facility constructed in a relatively isolated karst terrane. Although the specific procedures may not be duplicated, the overall technical approaches discussed in the paper may shed light on groundwater monitoring programs in other karst areas.
文摘Dilution and attenuation factor (DAF) has a major influence on soil-to-groundwater screening level calculation for protection of contaminant migration from soil into groundwater at solid waste management units (SWMUs). Risk assessment guidance prepared by U.S. Environmental Protection Agency for site investigation and remediation suggests a default DAF of 20. If the base assumptions included in the default DAF are recognized to be not representative of site conditions at a SWMU, calculation of site-specific DAF is recommended when sufficient data are collected to justify using a different DAF value for development of soil screening levels. Commonly used methods of calculating DAF include analytical and numerical simulations that often require too many parameters to be obtained in practice. This paper proposes a probability method to develop site-specific DAF. The approach uses data that are readily available through field reconnaissance and site-specific investigation. A case study is presented in which the probability method was applied to an actual SWMU, and the calculated DAF is compared with that calculated from a dilution method. The probability-based DAF is 67 at 90% probability percentile, which is comparable to the dilution-based DAF of 76. Based on the calculated site-specific DAFs, SSLs could be developed for the contaminants of potential concern and used for evaluation of migration pathways from a contamination source through soil to groundwater. .
