INEEL geoscientist to present NAPL contaminant modeling advance at AGU Meeting

December 08, 2002

DOE News Release Embargoed for release December 6, 2002 INEEL geoscientist to present NAPL contaminant modeling advance at AGU Meeting By modifying the mathematical theory describing the relationship between permeability, saturation, and pressure in a multiple fluid system, researchers can now more accurately predict the movement of non-aqueous phase liquid (NAPL) contaminants in the subsurface. New calculations account for residual NAPL that remains in the vadose zone-forming a long-term source for groundwater contamination, and also explain how part of this residue can be flushed into groundwater during rainstorms or flooding.

This research, funded through U.S. Department of Energy's Idaho National Engineering and Environmental Laboratory's Subsurface Science Initiative (SSI), supports the DOE's mission in environmental science.

Hydrologist Robert Lenhard of the INEEL, has resolved a critical contamination modeling problem by refining current constitutive theory - theory describing relations among fluid relative permeabilities, saturations, and pressures. His new model predicts the distribution of residual NAPL based on the prior fluid wetting and drying cycles in the subsurface. Lenhard will present his work at the American Geophysical Union meeting in San Francisco, CA, on December 8, 2002 during the Hydrology session.

"If you run existing multiphase flow models long enough, the results show that NAPL will completely drain from a vadose zone, which is contrary to field and experimental observations" said Lenhard. Better constitutive theory is needed for developing accurate computer models. "The lack of well-founded constitutive theory may be the foremost element impeding the development of accurate predictive multiphase flow models," he adds.

Lenhard's modeling advance represents a shift in researchers' conceptual understanding of NAPL behavior by recognizing that some NAPL becomes immobilized in pore spaces or as thin films on soil solids. Nowadays, subsurface contamination by NAPLs is almost ubiquitous. As a result of DOE's efforts to develop, test, manufacture, and maintain nuclear weapons for national security purposes, the DOE has very complex contamination problems with NAPLs that are denser than water. Additionally, an estimated 60 percent of Superfund (DOE, industrial and municipal) sites have NAPL contamination.

Lenhard and colleagues conducted pilot-scale (mesoscale) experiments in the laboratory to study how NAPLs behave under different conditions. NAPLs can move through the vadose zone as liquid, vapor, or carried along as dissolved droplets within a moving stream of water. His experiments indicate that residual NAPL will generate pulses of contamination during heavy rainstorms or flooding, especially at arid sites. A better understanding of how residual NAPLs contribute to contamination could influence environmental remediation choices.

Most NAPLs, such as fuels and degreasing solvents, are petroleum based. Predicting the movement of NAPLs in the subsurface is challenging because NAPLs can be either lighter or heavier than water and don't mix with water. Light NAPLs accumulate above the water table, and can depress the water-saturated region. Heavy or dense NAPLs sink below the water table and are very difficult to locate and clean up.

In order to predict the subsurface movement of multiple fluids, it is very important to know how the fluids are distributed throughout the pore spaces. The sizes of the pores containing the fluids will affect how rapidly these fluids can move downward to groundwater. If the fluids contain compounds harmful to humans and the environment, then by knowing how fast and in what quantities these compounds will reach the groundwater, effective remediation strategies can be developed using computer modeling. Lenhard has spent much of his career developing new techniques for measuring subsurface NAPL behavior and developing mathematical models for describing multi-fluid flow constitutive theory, which is needed to predict the flow behavior of multiple fluids in porous media. He is a leader in multiphse flow constitutive theory and his models are used worldwide by many scientists to predict air-NAPL-water flow behavior.

Martinus Oostrum of the DOE's Pacific Northwest National Laboratory, who has worked with Lenhard, plans to use Lenhard's new methodology to enhance the accuracy of the STOMP model- a numerical computer program for predicting Subsurface Transport Over Multiple Phases (STOMP). It is expected that the improved computer model will be used to help address NAPL contamination at DOE sites. Lenhard is also interested in employing his constitutive models in other multiphase flow computer codes.
-end-
This research was funded through the INEEL's discretionary research and development program.

The INEEL is a science-based, applied engineering national laboratory dedicated to supporting the U.S. Department of Energy's missions in environment, energy, science and national defense. The INEEL is operated for the DOE by Bechtel BWXT Idaho, LLC.

Technical contact: Robert Lenhard, (208) 526-4767, or lenhrj@inel.gov

Media contact: Deborah Hill, (208) 526-4723, or dahill@inel.gov

Visit our web site at www.inel.gov

DOE/Idaho National Laboratory

Related Groundwater Articles from Brightsurf:

Majority of groundwater stores resilient to climate change
Fewer of the world's large aquifers are depleting than previously estimated, according to a new study by the University of Sussex and UCL.

Monitoring groundwater changes more precisely
A new method could help to track groundwater changes better than before.

Cause of abnormal groundwater rise after large earthquake
Abnormal rises in groundwater levels after large earthquakes has been observed all over the world, but the cause has remained unknown due to a lack of comparative data before & after earthquakes.

Shrub encroachment on grasslands can increase groundwater recharge
A new study led by Adam Schreiner-McGraw, a postdoctoral hydrology researcher at the University of California, Riverside, modeled shrub encroachment on a sloping landscape and reached a startling conclusion: Shrub encroachment on slopes can increase the amount of water that goes into groundwater storage.

River-groundwater hot spot for arsenic
Naturally occurring groundwater arsenic contamination is a problem of global significance, particularly in South and Southeast Asian aquifers.

Groundwater, a threatened resource requiring sustainable management
The WEARE group at the University of Cordoba analyzed a case of aquifer recovery and concluded that supervision, governance and use of water for high value crops are some of the keys to guaranteeing sustainability of these reserves

Co-occurring contaminants may increase NC groundwater risks
Eighty-four percent of the wells sampled in the Kings Mountain Belt and the Charlotte and Milton Belts of the Piedmont region of North Carolina contained concentrations of vanadium and hexavalent chromium that exceeded health recommendations from the North Carolina Department of Health and Human Services.

Fresh groundwater flow important for coastal ecosystems
Groundwater is the largest source of freshwater, one of the world's most precious natural resources and vital for crops and drinking water.

Natural contaminant threat to drinking water from groundwater
Climate change and urbanisation are set to threaten groundwater drinking water quality, new research from UNSW Sydney shows.

Switching to solar and wind will reduce groundwater use
IIASA researchers explored optimal pathways for managing groundwater and hydropower trade-offs for different water availability conditions as solar and wind energy start to play a more prominent role in the state of California.

Read More: Groundwater News and Groundwater Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.