NAPL Contamination Evaluation Using GIS
Continued...

Figure 5: NAPL saturations across the site

Results of the analysis indicate that the NAPL mobility varies spatially across the site. NAPL saturations in the aquifer range from less than 5 percent to approximately 90 percent, as shown in Figure 5. Four of the five NAPL plumes were determined to have low mobility (i.e., less than one foot per day) and were essentially stable with low migration potential. One plume, which consists primarily of diesel fuel and is located in the sandy portion of the aquifer, was determined to have mobility of 20 to 50 feet per day. Because GIS analysis was conducted on a refined grid, mobile plumes could be characterized into different mobility zones.

Figure 6: This final map shows mobility across the site. The light brown plume is the only mobile plume among the five plumes.

By evaluating NAPL mobility, stability, and recoverability spatially using GIS, it was possible to determine the migration potential for each NAPL plume. Spatial analysis enabled an assessment of the potential risk derived from the mobility of the NAPL plume and the potential of NAPL to be recovered from the aquifer. These results enabled more efficient and effective use of resources and considerable savings in addressing the contamination at the facility, because of focused remediation efforts rather than sitewide remediation efforts.

For more information about how GIS can be used in NAPL characterization and risk assessment, contact
Pramod R. Thota
Environmental Systems and Technologies (A Division of GES)
3708 South Main Street, Suite D
Blacksburg, Virginia 24060
Tel.: 540-552-0685
Fax: 540-951-5307
Web: www.esnt.com

About the Authors

Jeffrey A. Johnson is a principal scientist at Environmental Systems and Technologies (ES&T), a division of Groundwater & Environmental Services, Inc. (GES), and an Esri business partner. He holds a doctorate in geology from the University of California, Berkeley and is a certified and registered professional geologist and a licensed remediation specialist. He specializes in applying computer technology to better characterize and remediate contaminated environmental sites.

Pramod R. Thota is a project engineer with Environmental Systems and Technologies, a division of Groundwater & Environmental Services, Inc. He has experience in developing GIS applications for use in NAPL characterization and risk assessment. He manages the development of three-dimensional visualization, software programming, and Internet/Intranet GIS applications. He holds a master's degree from Virginia Polytechnic Institute and State University in civil and environmental engineering with a specialization in GIS.