From Ground Water Currents, January 1996, Issue No. 14

In Situ Remediation -- Status Reports

EPA has identified six abiotic technologies that are emerging as possible cleanup remedies. These technologies are: thermal enhancements, surfactant enhancements, treatment walls, hydraulic fracturing/pneumatic fracturing, cosolvents and electrokinetics. For each technology, EPA has produced a separate IN SITU REMEDIATION TECHNOLOGY STATUS REPORT. The purpose of each report is to identify research projects and to describe recent field demonstrations and commercial applications of the technology. The technologies contained in the reports either treat ground water and soil in place or increase the solubility and mobility of contaminants so that pump-and-treat remediation of the contaminant is improved.

These emerging technologies grew out of a need identified by researchers and regulators who recognize that the source of much ground water contamination is dense non-aqueous phase liquids and other compounds that migrate downward into aquifers, creating pools of subsurface contamination. Thus, pump-and-treat systems can only treat the symptom, not the cause. Technologies such as the ones discussed in these reports are emerging to treat the cause and improve pump-and-treat efficiency.

The reports do not cover trends in the use of bioremediation. EPA has other resources summarizing the progress of bioremediation technologies. A brief summary of the technologies and report contents follows. Thermal enhancement technologies include: (1) the injection of hot water or steam or (2) the use of radio frequency or electrical resistance heating to increase the mobility, solubility or volatilty of organic contaminants, particularly immiscible compounds. Physical site conditions, not chemical reactions, are the major controlling factors on the use of this technology. The thermal enhancement status report discusses 16 completed, ongoing or future demonstrations. The 11 completed demonstrations provide some cost and performance information. Most of the demonstrations treated volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs) and the BTEX compounds (i.e., benzene, toluene, ethylbenzene and xylene). However, two demonstrations were designed to treat polyaromatic hydrocarbons (PAHs) from wood treating sites; and, one treated pesticides.

Surfactants increase the solubility of the contaminant in water. They also directly mobilize the contaminant by reducing interfacial tension between the contaminant and the soil matrix. The report contains nine research projects, six ongoing or future demonstrations, three completed demonstrations and one commercial application. The target contaminants were VOCs, SVOCs, BTEX and PCBs. Continued surfactant research is important. There are a variety of surfactants available to be tested; the effectiveness of each of these to treat a specific contaminant in a specific geochemical environment is usually unknown until laboratory and bench scale treatability tests are conducted. Treatment walls are vertical treatment zones installed across the flow path of a contaminant plume to treat the contaminants as the plume passes through the zone. These mechanically simple barriers may contain metal-based catalysts for degrading volatile organics, chelators for immobilizing metals or nutrients and oxygen to enhance bioremediation. There are 11 research projects, nine ongoing or future demonstrations, two completed demonstrations and one commercial application. Four of the 11 ongoing or completed demonstrations are using or have used in situ metal-enhanced dehalogenation; and, the patent for this technology is held by the University of Waterloo. The remaining demonstrations are testing the use of O2 nutrients for bioremediation and chemical reactants to reduce Cr+6 The ten research projects are divided between the treatment of metals and organics.

Hydraulic fracturing/pneumatic fracturing consists of the injection of pressurized water or air to increase the size and number of fractures in a consolidated material or relatively impermeable unconsolidated material. The enlarged fractures provide more treatment area for an in situ technology or more pathways to remove solubilized or mobilized contaminants. There are two ongoing or future demonstrations and ten completed demonstrations discussed in the report.

Cosolvents are a form of in situ flushing that involves the injection of a solvent mixture (e.g., water plus a miscible organic solvent such as alcohol) that enhances the solubility of organic contaminants. The use of cosolvents is in the very early stage of development. One research project was completed in 1991; and, there are three ongoing or future demonstrations. No vendors were identified who are marketing the technology. The three planned demonstrations will be conducted by a partnership between a federal laboratory, a military base and a university.

Electrokinetics has as its basis that positively-charged organic or inorganic contaminants can be made to migrate in an electric field to a collection point for removal by pumping. There are ten research projects, five ongoing or future demonstrations and one completed demonstration. There are a relatively large number of universities conducting research in electrokinetics many supported by DOE.

The full status reports can be ordered from EPA's National Center for Environmental Information and Publications (NCEPI). You can order the reports by mail or by FAX. The FAX number is 513-489-8695. The mail address is: NCEPI, 11305 Reed Hartman Highway, Suite 219, Cincinnati, OH 45241. Please refer to the document number when ordering. The individual report document numbers are: Thermal Enhancements (EPA542-K-94-009); Surfactant Enhancements (EPA542-K-94-003); Treatment Walls (EPA542-K-94-004); Hydraulic Fracturing/Pneumatic Fracturing (EPA542-K-94-005); Cosolvents (EPA542-K-94-006); and Electrokinetics (EPA542-K-94-007).