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Identifjring, testing, and implementing innovative technologies will be required in order to meet the expectations identified in the Ten Year Plan. The Portsmouth Gaseous Diffusion Plant (PORTS) has hosted and funded many technology demonstrations. The cooperative working relationship with the regulator community, a history of successfblly moving fiom the demonstration stage to remediation of an existing unit, and the available technical support have combined to make PORTS an ,ideal site for field demonstrating new ideas.Many individuals and organizations have contributed to the successll completion of this project. Without the hancial support and management assistance of the U.S.

1This report has been reproduced directly from the best available copy. 4-7(a) Binding energies of the Pd 3d3,2 and the Pd3d, peaks in the x-ray photoelectron spectrum of elemental Pd deposited on the iron surf-ace. 4.8. 4.9.5.1. 5.2.5.3.6.1. 7-4Tc (pCi/g) distribution in Fe columns 580,000 gal of water treated . . . 7-6 Number of times influent TCE concentration was reduced by % as it passed through the Pd/Fe treatment columns. Laboratory research conducted at ORNL and the UofA led to the discovery that zero-valence iron treated with a trace of palladium (pd) (nominally 0.05%) rapidly dechlorinated a wide range of hydrocarbons. Other research at ORNL and elsewhere has shown that many metals and radionuclides either precipitate or are adsorbed by zero-valence iron. Technetium (Tc) is particularly amenable to treatment of this type. Consequently, a combined approach using zero-valence iron for Tc and palladized iron (Pd/Fe) for trichloroethene (TCE) was applied to a groundwater waste stream at the PORTS facility.Laboratory research preparatory to the field tests demonstrated that Pd/Fe dechlorinated TCE one to two orders of magnitude faster than untreated iron. Further studies examined the nature of the Pd/Fe surface and evaluated the reaction mechanism. Work with x-ray photoelectron spectroscopy demonstrated that Pd attaches to the iron surface in a two-step process whereby a Pd-oxygen bond forms first with Pd in the +2 oxidation state. The Pd is then rapidly fbrther reduced to the elemental state as it plates on the Fe surface.Mechanistic studies have demonstrated that Pd/Fe reduces chlorinated hydrocarbons by hydrogenation. Hydrogen gas, formed because of the corrosion of Fe, is absorbed by the Pd. The chlorinated hydrocarbon adsorbs to the iron and is then reduced by hydrogen at the Pd/Fe interface.Laboratory studies with zero-valence iron revealed a very high capacity for immobilization of Tc. In a column study, approximately an order of magnitude more Tccontaminated water could be treated by the iron as compared to a conventional ion xiii exchange resin. The primary removal mechanism is believed to be reductive precipitation.In the field test, approximately 600,000 gal of water were treated. Treatment was straightfonvard and completely effective for Tc. The influent concentration of Tc was lower than anticipated (<20 pCi/L). Nevertheless, all of the Tc contained in the treated water was adsorbed by approximately 12 in. of a coarse zero-valence iron.

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Extensive hydrodynamic testing was performed as part of a program to evaluate horizontal recirculation as a means of removing contaminants from thin, interbedded aquifers. Two test sites, each containing a pair of horizontal recirculation wells, were evaluated using various hydraulic tests. Results of these evaluations showed that ground water was intercepted more than 100 feet beyond the wells, and that the hydraulic gradient increased by more than two orders of magnitude. Aquifer heterogeneity, however, controlled the efficiency and uniformity of ground water flow. Heterogeneity was assessed with a variety of techniques. Bromide tracer tests and the colloidal borescope provided the most useful data. For example, at an uncontaminated site, the leading edge of the bromide tracer traversed the 100 feet between the injection and extraction wells in 21 hours, and the peak bromide concentration was observed in 2.6 days, compared with the four days predicted by a pumping test. The resulting maximum velocity calculation was consistent with measurements made with the borescope in preferential flow zones. Data obtained from a highly contaminated location indicated that assessments of aquifer heterogeniety are further complicated by the presence of DNAPL. Very low flow occurred in a highly contaminated zone, despite the fact that lithologic descriptions indicated that this region contained permeable sand and gravel.