United States National Risk Management Environmental Protection Research Laboratory Agency Cincinnati, OH 45268 Research and Development EPA/600/SR-96/042 April 1996 & EPA Project Summary Assessing UST Corrective Action Technologies: In Situ SVE-Based Systems for Free Product Recovery and Residual Hydrocarbon Removal Milovan Beljin, Roy Chaudet, Duane Graves, Jeff Schubert, and Joe Tyburski The objective of the report summa- rized recovery and soil-vapor-extrac- tion (SVE)-based systems. The SVE- based systems examined include soil vapor extraction, bioventing, and air sparging. In addition, an overview of natural attenuation/biodegradation is also provided. The full report is in- tended to provide assistance in devel- oping a conceptual understanding of the factors influencing hydrocarbon migration and retention in the subsur- face and to identify key process pa- rameters that are used to select, de- sign, and monitor corrective action sys- tems. A common approach to correc- tive action may involve the use of a favored technology, which alone does not fully achieve the remedial goals. When corrective action options are evaluated, the different contaminants present in different matrices and in dif- ferent physical states must be consid- ered along with their location, amount, and mobility. Therefore, the use of mul- tiple corrective action technologies in an integrated system may be needed to effectively remove these contami- nants from locations of concern. This Project Summary was developed by EPA's National Risk Management Research Laboratory, Cincinnati, OH, to announce key findings of the re- search project that is fully documented in a separate report of the same title (see Project Report ordering informa- tion at back). Introduction Over the past several years, since pro- mulgation of the final underground stor- age tank (UST) regulations by the U.S. Environmental Protection Agency (EPA), the number of sites with confirmed re- leases from USTs has far exceeded the resources of both industry and regulatory agencies to clean up and close them out. Delays in initiating corrective action allow mobile contaminants to migrate further from the source, thereby increasing the likelihood of more severe environmental impacts and ultimately higher cleanup costs. A variety of conventional and emerging technologies are being proposed to ad- dress sites with confirmed releases. A common approach to corrective action typi- cally involves implementing one or two technologies during a particular stage of the cleanup. For example, the use of free product "pump-and-treat" systems has tra- ditionally been a favored conventional cor- rective action technology. At many sites, a properly designed pump-and-treat sys- tem may in fact be the most effective technology. After the recovery of free prod- uct is completed, soil vapor extraction (SVE) is sometimes installed as a supple- mentary technology. Biodegradation oc- curs as part of the SVE process but is ------- often not considered in the overall design and operation of SVE systems. More re- cently, SVE has been used in combina- tion with in situ air sparging. The purpose of the full report is to pro- vide information for evaluating several cor- rective action technologies that can be used either individually or in combination. It is intended as a resource document that can serve as a starting point in under- standing the appropriate selection and use of the technologies discussed. The manual provides the following: • A conceptual understanding of the fac- tors influencing hydrocarbon migra- tion and retention in the subsurface. • Identification of process parameters that are used in the selection and design of nonaqueous phase liquid (NAPL) and SVE-based corrective action systems. • An overview of approaches and tools used in system design for these tech- nologies. • An example of the types of monitor- ing requirements that may be needed to determine system effectiveness. • An example of cost estimates for se- lected corrective action technologies. Methodology The full report focuses on (1) site char- acterization, approaches, and techniques for obtaining the data needed for making corrective action decisions; (2) the funda- mental considerations for free product mi- gration and recovery; (3) the remediation of residual organics using soil vapor ex- traction; (4) bioventing and intrinsic biore- mediation; (5) in situ air sparging; and (6) relative cost comparison between product recovery, SVE, and air sparging-SVE sys- tems. Chemical properties of organic con- taminants typically encountered are also provided. Results The approach for examining the tech- nologies in this manual is based on an understanding of the characteristics of the porous media and the contaminants, and the distribution of the contaminant phases at various locations in the subsurface. Hy- drocarbon contaminant releases from leak- ing USTs into a porous media will be distributed among four phases: (1) NAPLs or the "immiscible phase," (2) the soil mois- ture or "dissolved phase" in interstitial wa- ter, (3) the "adsorbed phase," and (4) the "vapor phase." The distribution of con- taminants into the different phases is de- pendent on the chemical and physical characteristics of the hydrocarbon, the de- gree of weathering that has occurred, and the characteristics of the porous media. The contaminant distribution will change as the contaminant moves from the un- saturated zone to the saturated porous and fractured media. At many sites where NAPL is present, the initial cleanup efforts are removing the NAPL sources, if possible. For NAPLs that cannot be removed directly or that remain as residuals, the contaminant mass may be partly removed by volatilization and dissolution into groundwater. Biodegrada- tion processes may be a cost-effective option for attenuation of groundwater plumes, or for decreasing contaminant con- centrations to acceptable levels in both the saturated and unsaturated zones. The remedial action will use a correc- tive action technology based on the sub- surface properties and contaminant mass, phases, locations, and mobility. Once a technology is selected, designed, and implemented, the performance of the sys- tem is monitored to determine if remedia- tion goals can be met by using the se- lected technology. If the goals are not met, then a reassessment of the remedial system, site condition, and remedial goals (if necessary) may be needed. Conclusions Sites with subsurface contamination vary greatly in terms of complexity, physical and chemical characteristics, and in the risk that they may pose to human health and environmental resources. In determin- ing appropriate action for addressing pe- troleum releases, three-dimensional site characterization is required to provide a sufficient contaminant definition of behav- ior and to support corrective action deci- sions. Based on an understanding of the phase locations and the mechanisms af- fecting the movement and disposition of the contaminants, appropriate technolo- gies can be identified and selected as part of a corrective action strategy. For larger spill volumes or shallower water tables, light nonaqueous phase liq- uid (LNAPL) may reach the groundwater, where it will spread laterally. Initial reme- diation steps involve controlling and re- moving free product by pumping it from trenches or wells to limit the spread. Pump- ing rates should be selected to maintain hydraulic gradient control. Higher rates will lead to lower overall product recovery as NAPLs are smeared over a larger cone of depression in the water table and become trapped by capillary forces as residual hy- drocarbons. Careful placement and de- sign of free product recovery systems can have a major impact on recovery efficiency. Soil vapor extraction (SVE) based tech- nology primarily includes soil vapor ex- traction, bioventing, and a combination of soil vapor extraction and air sparging. This technology removes volatile contaminants and to a lesser extent semivolatile con- taminants from the vadose zone and up- per part of the saturated interval (primarily in the case of air sparging). SVE can be used to biovent the soil and to deliver oxygen for enhanced biodegradation. Bioventing is an emerging technology that combines features of SVE and in situ bioremediation. The technology permits the in situ treatment of vadose zone soil im- pacted with any biodegradable contami- nant. An attractive treatment strategy for contaminated vadose zone soil and groundwater involves bioventing and in- trinsic bioremediation. Bioventing in source areas can be an effective approach to eliminate the dissolution, diffusion, and leaching of contaminants into the ground- water. Without a constant recharge of con- taminants, intrinsic bioremediation in the groundwater can limit plume migration and ultimately reduce contaminant levels to acceptable or even nondetectable levels. A combined treatment strategy has the potential to be expedient and cost-effec- tive. In situ air sparging is a recently intro- duced technology that utilizes in situ vola- tilization to remove volatile components from residual NAPL or dissolved-phase contaminants present below the water table. As with SVE, air sparing has broad appeal because it is simple to implement and capital costs are moderate. Air sparging technology is still in its infancy, however. A limited number of air sparging operations and pilot tests have been evalu- ated; some of these were effective, while several were not. The full report was submitted in partial fulfillment of Contract No. 68-C2-0108, Work Assignment No. 6, by IT Corpora- tion, under the sponsorship of the U.S. Environmental Protection Aqencv. 2 ------- Milovan Beljin, Roy Chaudet, Duane Graves, Jeff Schubert, and Joe Tyburski are with IT Corporation, Cincinnati, OH 45246. Chi-Yuan Fan is the EPA Project Officer (see below). The complete report, entitled "Assessing UST Corrective Action Technologies: In Situ SVE-Based Systems for Free Product Recovery and Residual Hydrocarbon Removal," (Order No. PB96-163605; Cost:$49.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: National Risk Management Research Laboratory U.S. Environmental Protection Agency Edison, NJ 08837 United States Environmental Protection Agency National Risk Management Research Laboratory (G-72) Cincinnati, OH 45268 BULK RATE POSTAGE & FEES PAID EPA PERMIT NO. G-35 Official Business Penalty for Private Use $300 EPA/600/SR-96/042 ------- |