October 1997

Energy Dispersive X-Ray Fluorescence for Expedited Site Characterization by Roger Henderson, U.S. Army Corps of Engineers

The U.S. Army Corps of Engineers (USACE) has achieved considerable time and costs savings in site characterization by using a field-portable energy dispersive x-ray fluorescence (EDXRF) system in conjunction with a global positioning system (GPS). The combined system enabled the USACE to fully characterize both the vertical and horizontal extent of heavy metal contamination on eight firing ranges at the Presidio of San Francisco within five weeks, under a single field mobilization. In contrast, the USACE estimates that a typical site characterization approach using a fixed-based laboratory and traditional investigation methods would have required 2-3 field mobilizations spread out over 1.5 years. The USACE realized a cost savings of $50,000-75,000 by using the EDXRF/GPS approach.

Basic x-ray fluorescence analysis entails the bombardment of soil samples by an x-ray source, which results in an increased excitement of atoms in the sample. Each metal contained in the sample re-radiates x-rays of a unique wavelength, and these wavelength emissions are picked up by an x-ray detector. At Presidio, the USACE used the Spectrace 9000 to analyze multiple metals (lead, zinc, antimony, copper, and barium) in each sample. Developers of the Spectrace 9000 participated in a recent CSCT verification project on which final results will be issued later this year.

Field staff collected samples from a 40-ft. x 40-ft. sampling grid at selected locations based on information from historic maps, traditional range usages, and experience from other firing range sites, and located specific sample points through use of a portable GPS. The system produced quantitative analytical results within 20 minutes of sample receipt and immediately posted the results on computerized maps, which dictated the vertical and horizontal location of the following sample. This process complied with decision criteria requiring that each sample in which more than 400 mg/kg of lead were detected be followed by additional samples (each 1 foot deeper and 10-15 feet farther out than the previous) until levels fell to less than 400 mg/kg.
The USACE concluded this effort in record time, and collected and analyzed over 400 soil samples, which is far more sampling than would have been completed under traditional methods.

This iterative approach to site characterization, coupled with on-site real time analysis, provides distinct advantages over traditional methods, including its extreme flexibility for both sample collection and analysis. At the eight Presidio firing ranges, the USACE completed site characterization at a cost of approximately $77,000, while a traditional approach may have cost over $162,000. For more information on the use of EDXRF/GPS technology used at the Presidio, contact Roger Henderson (USACE, Sacramento District) at 916-557-5378.

The USACE is committed to informing, encouraging, and supporting the consideration and use of effective innovative technologies for environmental investigation and remediation. Since 1989, the USACE Innovative Technology Advocate Program has empowered USACE districts and divisions, laboratories, and the Hazardous, Toxic and Radioactive Waste Center of Expertise with direct responsibility for innovative technology development and application. During fiscal year 1997, the USACE conducted more than 250 innovative technology projects under this program. For more information on innovative technologies within the USACE, contact Innovative Technology Advocates Dr. Donna Kuroda at 202-761-4335, Johnette Schockley at 402-697-2558, or Jeff Breckenridge at 402-697-2577.

Expedited Site Characterization (ESC) at Soil Sites

by Albert Bevolo, Ph.D., Ames Laboratory

Conventional site characterization practice is typified by multiple field investigations managed and performed by various groups that focus on contaminant distribution using off-site analytical services. The cost of this approach is high, because it can takes year to accomplish compared to expedited site characterization (ESC).

ESC is a proven methodology that utilizes in-field decision-making, a dynamic work plan, and real-time data acquisition and interpretation. ESC incorporates several key principles:

• an experienced, multidisciplinary core team of hands-on professionals that plans the project and manages the field investigations,
• a dynamic work plan that uses on-site data processing and interpretations by these senior technical experts to ensure effective decision-making,
• a Phase I that focuses on the hydrogeologic portion of the conceptual site model (CSM) and utilizes multiple methods, such as geophysical tech- niques, borehole logging, and direct push technologies (DPT), and
• a Phase II, which begins only after the hydrogeologic portion of the CSM is complete, that focuses on the chemical contaminant portion of the CSM.

Since 1993, the Ames Laboratory ESC team, supported by the DOE Office of Environmental Management (EM), has implemented soil and ground-water projects involving contaminants such as polycyclic aromatic hydrocarbons (PAHs), volatile organics, petroleum products, dense non-aqueous phase liquids (DNAPLs), pesticides, radioactive isotopes, and RCRA metals. The team's biggest success to date occurred at the Savannah River Site (SRS) D Area oil seepage basin assessment. This project involved 13 contaminants, an extensive hydrogeology investigation, three on-site laboratories, and a 14-day ground- water investigation, and resulted in regulatory acceptance of ESC. Based on these SRS results, DOE plans to use ESC for all future SRS site assessments, currently budgeted at $650,000,000.

The ASTM standard guide (PS 86-96) contains a comprehensive explanation of ESC. At several demonstration sites, ESC has resulted in cost savings of 30-50% and savings in time of 30-80%. Regulators are accepting ESC because of DOE's proactive, open strategy to involve them and ESC's demonstrated ability to move the cleanup ahead of schedule, while providing for improved data quality to support better remedial decisions.

Soil contamination was recently investigated at the DOE Central Nevada Test Area. Most of the surface structures had been decommissioned, but surface and subsurface drilling mud pits and shaker pads were left for assessment. A geophysical investigation used electromagnetic surface geophysical measurements, combined with percussive electrical conductivity probing, to optimize the sampling strategy. Depth-specific mud layers in covered pits and shaker debris runoff could be located. Total petroleum hydrocarbon (TPH) diesel and hexavalent chromium (Cr) were the contaminants of potential concern. Nearly 1,000 soil samples were taken with percussive DPT to depths of 20 feet in the sandy high-desert soils over a period of 22 days.

One mobile lab tracked TPH diesel using U.S. EPA Method 8015A. Early gas chromatography (GC) results indicated the presence of a motor oil component of TPH. Having senior decision-makers in the field made it easy to incorporate the additional measurements. Eight sites would have been misidentified as below regulatory concern without consideration of the TPH motor oil.

The second mobile lab tracked total Cr by flame atomic absorption and x-ray fluorescence and hexavalent Cr by wet chemistry. The latter techniques allowed a quick determination that eight sites with high total Cr were actually below the hexavalent Cr preliminary action level.
For additional information, contact Dr. Albert Bevolo (Ames Laboratory, Ames, IA) at 515-294-5414, 515-294-6963 (fax), or e-mail bevolo@ameslab.gov.