A comparison of XRFS and ICP-OES methods for soil trace metal analyses in a mining impacted agricultural watershed.

Field portable X-ray fluorescence spectroscopy (XRFS) has become increasingly prevalent for in situ detection of trace metals, as it is both rapid and cost effective. The accuracy of in situ XRFS analyses has been questioned due to possible interferences from elevated soil moisture and organic content. In this study, three metal analysis protocols (Cd, Pb, Zn) were compared for surface soil samples collected near the Tar Creek Superfund Site in northeastern Oklahoma. The protocols included the use of a field portable XRF spectrometer for in situ analyses and on homogenized, pulverized, air-dried soil samples sieved to < 250-µm fraction in the laboratory. A subset of soil samples was also analyzed after microwave-assisted hot HNO3 digestion followed by inductively coupled plasma-optical emission spectrometry (ICP-OES) analyses. Moisture content and loss-on-ignition (as a surrogate for organic matter) were determined for each sample. Soil moisture exceeding 10% in situ caused underreporting of field XRF readings when compared to the laboratory XRF readings. Relationships between concentrations determined by laboratory XRFS and ICP-OES for Pb (r2 = 0.96) and Zn (r2 = 0.91) were not statistically different (p < 0.025 for both analytes). A strong relationship between ICP-OES analyses of Zn and Cd (r2 = 0.93) allowed prediction of Cd concentrations for additional samples not analyzed by ICP-OES. This study recommends that XRFS field readings be used for initial screening only and that samples analyzed via field portable XRFS be homogenized, air dried, sieved and re-analyzed in the laboratory to yield the most accurate results.

Remediation of NAPL source zones: lessons learned from field studies at Hill and Dover AFB.

Innovative remediation studies were conducted between 1994 and 2004 at sites contaminated by nonaqueous phase liquids (NAPLs) at Hill and Dover AFB, and included technologies that mobilize, solubilize, and volatilize NAPL: air sparging (AS), surfactant flushing, cosolvent flooding, and flushing with a complexing-sugar solution. The experiments proved that aggressive remedial efforts tailored to the contaminant can remove more than 90% of the NAPL-phase contaminant mass. Site-characterization methods were tested as part of these field efforts, including partitioning tracer tests, biotracer tests, and mass-flux measurements. A significant reduction in the groundwater contaminant mass flux was achieved despite incomplete removal of the source. The effectiveness of soil, groundwater, and tracer based characterization methods may be site and technology specific. Employing multiple methods can improve characterization. The studies elucidated the importance of small-scale heterogeneities on remediation effectiveness, and fomented research on enhanced-delivery methods. Most contaminant removal occurs in hydraulically accessible zones, and complete removal is limited by contaminant mass stored in inaccessible zones. These studies illustrated the importance of understanding the fluid dynamics and interfacial behavior of injected fluids on remediation design and implementation. The importance of understanding the dynamics of NAPL-mixture dissolution and removal was highlighted. The results from these studies helped researchers better understand what processes and scales are most important to include in mathematical models used for design and data analysis. Finally, the work at these sites emphasized the importance and feasibility of recycling and reusing chemical agents, and enabled the implementation and success of follow-on full-scale efforts.

Field demonstration of surfactant-enhanced solubilization of DNAPL at Dover Air Force Base, Delaware.

This study reports on a surfactant-based flood for tetrachloroethylene (PCE) removal from a control test cell at the Dover National Test Site. The surfactant formulation (sodium dihexyl sulfosuccinate (Aerosol-MA or AMA), isopropanol and calcium chloride) was able to achieve a high concentration of PCE in swollen micelles (supersolubilization) without vertical PCE migration. The hydraulic system included eight screened wells that were operated in both vertical circulation and line drive configurations. After 10 pore volumes of flushing, the overall PCE removal was 68% (65% of which corresponded to the surfactant flooding alone). In addition, the residual PCE saturation was reduced from 0.7% to 0.2%, and the concentration of PCE in the groundwater was reduced from 37-190 mg/L before the flushing to 7.3 mg/L after flooding. Recycling the surfactant solution reduced the required surfactant mass (and thus cost, and waste) by 90%. Close to 80% of the total PCE removal was obtained during the first five pore volumes which were operated in an upward vertical circulation flow scheme. No free oil phase was observed during the test. Further analysis of multilevel sampler data suggests that most of the trapped oil remaining in the cell was likely localized in secluded regions of the aquifer, which helps explain the lower PCE groundwater concentration after remedial activities. In summary, this field study demonstrated the feasibility of surfactant-enhanced remediation to reduce the mass in the source zone and significantly reduce the PCE aqueous concentration and therefore the risk associated with the contaminant plume.

Distal revascularization-interval ligation: a durable and effective treatment for ischemic steal syndrome after hemodialysis access.

PURPOSE: The treatment of hemodialysis access-induced ischemic steal syndrome is challenging. Despite promising early results with the distal revascularization-interval ligation (DRIL) procedure, the operation has not been widely adopted because of concerns about its complexity and long-term efficacy. The purpose of this report was to determine the efficacy and durability of the DRIL procedure in relieving hand ischemia and in maintaining access patency in the setting of hemodialysis access-induced ischemia. METHODS: A retrospective review was performed of all patients who underwent the DRIL procedure for access-induced ischemia. Demographic information was compiled, as were data regarding access and bypass patency, limb salvage, and patient survival. Arteriovenous access and brachial artery bypass patency rates were determined with life-table methods. RESULTS: Between 1995 and 2001, we performed 55 DRIL procedures in 52 patients (35 women and 17 men; mean age, 60.8 years; range, 30 to 86 years). The indications for surgery were ischemic pain in 27 patients, tissue loss in 20 patients, loss of neurologic function in four patients, and pain on hemodialysis in one patient. Most patients (92%) had diabetes. The mean interval from access placement to DRIL was 7.4 months (range, 1 to 84 months). The mean follow-up interval was 16 months (range, 1 to 67 months). The brachial artery bypass primary patency rate was 80% at 4 years, and the arteriovenous access primary patency rate was 83% at 1 year. Forty-seven of 52 patients (90%) had substantial or complete relief of ischemic hand symptoms, and 15 of 20 patients with digital ischemic lesions have healed completely. CONCLUSION: DRIL is a durable and effective procedure that reliably accomplishes the twin goals in the treatment of angioaccess-induced ischemia: persistent relief of hand ischemia and continued access patency.