U.S. Geological Survey (USGS) scientists used a mass–balance solute–transport model to enhance an understanding of factors affecting chlorinated ethene (CE) concentrations in a public supply well. They found that long–term simulated and measured CEconcentrations were affected by dense nonaqueous phase liquid (DNAPL) volume, composition, and by the bioavailability of organic carbon that drives biodegradation.
Chlorinated ethenes are one class of chlorinated solvents that are among the most common organic contaminants found in public supply wells in the United States. CEs measured and modeled in this study include tetrachloroethene, commonly referred to as perchloroethene (PCE), and trichloroethene (TCE), cis–1,2–dichloroethene (DCE), and vinyl chloride (VC). The presence of CEs in public supply wells provides evidence that there are one or more contaminant source areas, which may include DNAPLs.
The mass–balance solute–transport model was built by telescoping a calibrated regional three–dimensional MODFLOW model to the capture zone of a public supply well that has a history of CEcontamination. The local model, using the Sequential Electron Acceptor Model in three dimensions (SEAM3D) code, was then used to simulate the interactions between naturally occurring organic carbon that acts as an electron donor, and dissolved oxygen , CEs, ferric iron, and sulfate that act as electron acceptors. This study advances the SEAM3D technology by introducing the concept of using dissolution of a DNAPL source area as boundary and initial conditions for delivering CEs to groundwater.
This study builds upon other USGS studies to refine the understanding of CE transport in groundwater using simulated and measured long–term trends of CE concentrations at a public supply well. Previous USGS efforts using a mass balance modeling approach quantified in model output the effects of assumed particulate organic carbon concentrations, dissolved oxygen concentrations, the source of contamination, and factors affecting water movement.
Public supply wells are required to monitor concentrations of primary and secondary contaminants, including CEs present in treated and finished water that is delivered for distribution to the public. In the case of supply wells that produce groundwater containing CEcontaminants, such as the well described in this study, substantial costs are associated with treating the water. That being the case, having information concerning the expected long–term trends of contaminant concentrations in the raw untreated groundwater can be relevant to deciding whether water treatment costs are likely to increase or decrease over time, and whether it is more cost effective to abandon water production at particular wells rather than to invest in water treatment.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology).
Below are other science projects associated with this featured science activity.
Drinking Water and Wastewater Infrastructure Science Team
Drinking Water and Wastewater Infrastructure Science Team
Below are publications associated with this featued science activity.
Modeling long-term trends of chlorinated ethene contamination at a public supply well
Modeling the effects of naturally occurring organic carbon on chlorinated ethene transport to a public supply well
A framework for assessing the sustainability of monitored natural attenuation
- Overview
U.S. Geological Survey (USGS) scientists used a mass–balance solute–transport model to enhance an understanding of factors affecting chlorinated ethene (CE) concentrations in a public supply well. They found that long–term simulated and measured CEconcentrations were affected by dense nonaqueous phase liquid (DNAPL) volume, composition, and by the bioavailability of organic carbon that drives biodegradation.
USGS Hydrologist sampling a public supply well for chlorinated ethene contaminants. Photo Credit: Bruce Campbell, USGS Chlorinated ethenes are one class of chlorinated solvents that are among the most common organic contaminants found in public supply wells in the United States. CEs measured and modeled in this study include tetrachloroethene, commonly referred to as perchloroethene (PCE), and trichloroethene (TCE), cis–1,2–dichloroethene (DCE), and vinyl chloride (VC). The presence of CEs in public supply wells provides evidence that there are one or more contaminant source areas, which may include DNAPLs.
The mass–balance solute–transport model was built by telescoping a calibrated regional three–dimensional MODFLOW model to the capture zone of a public supply well that has a history of CEcontamination. The local model, using the Sequential Electron Acceptor Model in three dimensions (SEAM3D) code, was then used to simulate the interactions between naturally occurring organic carbon that acts as an electron donor, and dissolved oxygen , CEs, ferric iron, and sulfate that act as electron acceptors. This study advances the SEAM3D technology by introducing the concept of using dissolution of a DNAPL source area as boundary and initial conditions for delivering CEs to groundwater.
This study builds upon other USGS studies to refine the understanding of CE transport in groundwater using simulated and measured long–term trends of CE concentrations at a public supply well. Previous USGS efforts using a mass balance modeling approach quantified in model output the effects of assumed particulate organic carbon concentrations, dissolved oxygen concentrations, the source of contamination, and factors affecting water movement.
Public supply wells are required to monitor concentrations of primary and secondary contaminants, including CEs present in treated and finished water that is delivered for distribution to the public. In the case of supply wells that produce groundwater containing CEcontaminants, such as the well described in this study, substantial costs are associated with treating the water. That being the case, having information concerning the expected long–term trends of contaminant concentrations in the raw untreated groundwater can be relevant to deciding whether water treatment costs are likely to increase or decrease over time, and whether it is more cost effective to abandon water production at particular wells rather than to invest in water treatment.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology).
- Science
Below are other science projects associated with this featured science activity.
Drinking Water and Wastewater Infrastructure Science Team
The team studies toxicants and pathogens in water resources from their sources, through watersheds, aquifers, and infrastructure to human and wildlife exposures. That information is used to develop decision tools that protect human and wildlife health.Drinking Water and Wastewater Infrastructure Science Team
The team studies toxicants and pathogens in water resources from their sources, through watersheds, aquifers, and infrastructure to human and wildlife exposures. That information is used to develop decision tools that protect human and wildlife health. - Publications
Below are publications associated with this featued science activity.
Modeling long-term trends of chlorinated ethene contamination at a public supply well
A mass-balance solute-transport modeling approach was used to investigate the effects of dense nonaqueous phase liquid (DNAPL) volume, composition, and generation of daughter products on simulated and measured long-term trends of chlorinated ethene (CE) concentrations at a public supply well. The model was built by telescoping a calibrated regional three-dimensional MODFLOW model to the capture zoAuthorsFrancis H. Chapelle, Leon J. Kauffman, Mark A. WiddowsonModeling the effects of naturally occurring organic carbon on chlorinated ethene transport to a public supply well
The vulnerability of public supply wells to chlorinated ethene (CE) contamination in part depends on the availability of naturally occurring organic carbon to consume dissolved oxygen (DO) and initiate reductive dechlorination. This was quantified by building a mass balance model of the Kirkwood-Cohansey aquifer, which is widely used for public water supply in New Jersey. This model was built by tAuthorsFrancis H. Chapelle, Leon J. Kauffman, Mark A. WiddowsonA framework for assessing the sustainability of monitored natural attenuation
The sustainability of monitored natural attenuation (MNA) over time depends upon (1) the presence of chemical/biochemical processes that transform wastes to innocuous byproducts, and (2) the availability of energy to drive these processes to completion. The presence or absence of contaminant-transforming chemical/biochemical processes can be determined by observing contaminant mass loss over timeAuthorsFrancis H. Chapelle, John Novak, John Parker, Bruce G. Campbell, Mark A. Widdowson