United States Environmental Protection Agency Solid Waste and Emergency Response (5102W) EPA 542-N-94-002 March 1994 SEPA Ground Water Currents Developments in innovative ground water treatment Hydrodynamic Cavitation Oxidation Destroys Organics By Richard Eilers, Risk Reduction Engineering Laboratory The CAV-OX® technology destroys organic contaminants (including chlorinated hydro- carbons) in water. The process uses hydrogen peroxide, hydro- dynamic cavitation and ultra- violet (UV) radiation to photolyze and oxidize organic compounds present in water at parts per million to nondetect- able levels. Ideally, the end products of the process are wa- ter, carbon dioxide, halides and-in some cases-organic acids. The CAV-OX® technol- ogy was evaluated at a SITE (Superfund Innovative Tech- nology Evaluation) demonstra- tion at Edwards Air Force Base Site 16 in California. Ground Water at Site 16 is contami- nated with volatile organic compounds (VOCs), primarily trichloroethene (TCE) and BTEX compounds (benzene, toluene, ethylbenzene and xylenes). Almost 8,500 gallons of contaminated ground water were treated during a two-week period. Initial contaminant concentrations were 1,475 to 2,000 parts per billion (ppb) TCE, 240 to 500 ppb benzene, 8 to 11 ppb toluene and up to 100 ppb xylene. The CAV-OX® systems achieved removal efficiencies of up to >99.9% for TCE and BTEX compounds. The major components of the CAV-OX® system are the cavitation chamber, UV reactor and control panel unit. Prior to entry into the cavitation chamber, ground water was pumped from three monitoring wells into a 7,500 gallon equalization tank. A bladder tank was used as the equalization tank to minimize variability in influent charac- teristics. From the equaliza- tion tank, the water was transferred to an influent holding tank, where hydro- gen peroxide was added. The water was then pumped to the cavitation chamber. Cavitation occurs when a liquid undergoes a dynamic pressure reduction while un- der constant temperature. The hydrodynamic cavitation is induced through the shape of the cavitation chamber, which causes pressure varia- tions in a flowing liquid. A pressure reduction causes gas bubbles to suddenly develop, grow and then collapse. This cavitation decomposes water into extremely reactive hy- drogen atoms and hydroxyl radicals, which recombine to form hydrogen peroxide and molecular hydrogen, which help oxidize the organic com- pounds. Flow can be recycled through the cavitation cham- ber to control the hydraulic retention time before it is transferred to the UV reactor. The UV reactor houses low-pressure mercury-vapor lamps that generate UV radiation, which further oxi- dize the organic compounds. Each lamp is housed in a UV-transmissive quartz tube, which is mounted entirely within the UV reactor. Hydroxyl and hydroperoxyl radicals are produced by direct photolysis of hydrogen perox- ide at UV wavelengths. During the SITE demonstra- tion, no scaling of the quartz tubes was observed. Treated ground water was stored in an effluent storage tank prior to disposal. Magnum Water Technolo- gy manufactures both low-en- ergy and high-energy UV systems, both of which were evaluated during the SITE demonstration. The low-ener- gy CAV-OX® I system con- tains six 60-watt lamps per reactor. The high-energy CAV-OX® II system contains two UV reactors with one UV lamp each and can operate at 2.5, 5, 7.5 or 10 kilowatts (kW). Flow capacity is esti- mated to be less than 3 gal- lons per minute (gpm) for the low-energy system and less than 5 gpm for the high-ener- gy system. Three configura- tions of the CAV-OX® tech- nology were demonstrated during the SITE evaluation: the CAV-OX® 1 system oper- ating at 360 watts and the CAV-OX® II system operating at both 5 kW and 10 kW. The demonstration consisted of 15 runs for each configuration of the CAV-OX® technology. The high-energy system was first operated with the UV re- actor at 10 kW and then at 5 kW. Ground water samples were collected before and after treatment during each run to determine the technology's ef- fectiveness in removing VOCs from ground water. The prin- cipal operating parameters— hydrogen peroxide dose, pH and flow rate-were varied during the demonstration to evaluate the technology's per- formance under different conditions. For more information, con- tact Richard Eilers at EPA's Risk Reduction Engineering Laboratory at 511-569-7809. An "Applications Analysis Report and a Technology Evaluation Report" will be available in the summer of 1994. This Month in Currents UV Oxidation Biosparging Update Surfactant Research Ground Water Models Recycled/Recyclable Printed with Soy/Canola ink on paper that contains at least 50% recycled fiber ------- RESEARCH UPDATE Biosparging Documented in Fuel Remediation Study By Don Kampbell, Robert S. Kerr Environmental Research Laboratory E PA's Robert S. Kerr Envi- ronmental Research Laborato- ry (RSKERL), through a three-year research study, has documented subsurface aera- tion (biosparging) remedia- tion of an aviation gasoline spill at the U.S. Coast Guard Air Station site in Traverse City, Michigan. This case study has shown that fuel vol- atilization by aeration and va- dose zone biodegradation of vapors is a convenient way to remove dissolved hydrocar- bons from ground water in sit- uations where large amounts of spilled fuel have moved downward through a porous vadose zone and formed a plume in the aquifer. Sparge aeration can cleanse the water of fuel hydrocarbons to meet ground water quality stan- dards. However, sparge cleans- ing of the plume water is a short-term solution unless there is further remediation of the aquifer. This study found that complete remediation of contaminants was prevented by fuel globules trapped in capillary pores of sand gran- ules that protected them from the sparge aeration. These oily globules can recharge and maintain the contaminant plume once sparging ceases. At the Traverse City site, about 36,000 gallons of gaso- line had spilled in 1969 as a result of a flange failure of an underground transfer line. During the next 20 years a plume 1,200 feet long down gradient was formed. The wa- ter table is at a depth of ap- proximately 15 feet with an oily phase smear of almost five feet, due to fluctuations in water depth resulting from climatic changes. During the study period about one-third of the smear zone was in the vadose zone and two-thirds were at or below the water ta- ble. Both the aquifer and the vadose zone were composed of relatively uniform beach sand. Prior to the field-scale study, an eight-month bio- venting pilot-scale demonstra- tion was conducted. At its completion in 1991, the sys- tem's performance showed that 99% of the fuel hydrocarbons in the vadose zone were re- moved, with only minimal surface emissions. Upon com- pletion of the pilot study, aera- tion wells were installed in the same plot to a depth of 10 feet below the water table. The rate of aeration was the same as for the pilot-scale (SEE BIOSPARGING, PAGE 3) Surfactant Flushing Research to Remove Organic Liquids from Aquifers By Linda M. Abriola and Kurt D. Pennell, University of Michigan Organic liquids, such as gas- oline and industrial solvents, are a major source of ground water contamination through- out the United States. Through the Great Lakes/ Mid-Atlantic Hazardous Sub- stances Research Center, re- searchers at the University of Michigan have combined de- tailed laboratory experiments with the development of mathematical models to in- vestigate the potential useful- ness of surfactant flushing as an aquifer-remediation technology. The specific ob- jectives of this research were to: (1) screen and select sur- factants that will enhance the solubility of organic liquids in water; (2) measure the solubil- ity of dodecane and tetrachlo- roethylene (PCE) in aqueous surfactant solutions; (3) quan- tify the ability of selected sur- factants to recover entrapped dodecane from soil columns; and (4) develop and evaluate numerical models capable of predicting surfactant-en- hanced solubilization and mobilization of organic liq- uids in ground water systems. First, commercially avail- able surfactants were screened based on their toxicity, bio- degradability, molecular structure and potential to sol- ubilize organic compounds. The screening process led to the selection of three nonion- ic surfactants for experimen- tal testing with two organic liquids, dodecane and PCE, as model compounds. The re- searchers found that adding these surfactants to water increased the aqueous solubili- ty of PCE and dodecane by 200 times and one million times, respectively. The large enhancement in solubility re- sults from the incorporation or partitioning of organic com- pounds within surfactant mi- celles (colloidal-size clusters). Surfactant molecules aggregate to form micelles above a spe- cific concentration, the criti- cal micelle concentration (CMC). The micelles possess a (SEE SURFACTANT FLUSHING, PAGE 4) Ground Water Currents ------- NEW FOR THE BOOKSHELF Compilation of Ground-Water Models EPA'S Robert S. Kerr Envi- ronmental Research Laborato- ry has published a report, "Compilation of Ground-Wa- ter Models" (Document No. EPA/600/R-93/118). This re- port is a review of ground wa- ter models and is based on information gathered by the International Ground Water Modelling Center (IGWMC) under a research and technol- ogy transfer cooperative agree- ment with the EPA. The IGWMC was established as an international clearinghouse and technology transfer center for ground water modelling. Ground water modelling, as a computer-based methodolo- gy for mathematical analysis, is a tool for investigating and managing the mechanisms and controls of ground water systems. Models are playing an important role in the de- termination of the physical and economical effects of proposed ground water protec- tion policy alternatives and thus the protection of human and ecological health. Com- puter models are important tools in the screening of alter- native remediation technolo- gies and strategies in cleaning up ground water systems pol- luted in the (recent) past, in the sound design of ground water resource development schemes for water supply and for other land use modifica- tions affecting ground water systems. The model selection pro- cess for appropriate computer codes is a vital step to con- ducting these investigative and management alternatives for ground water systems. To be able to select a computer code appropriate for the type of analysis to be performed, ground water modelers need to have an overview of avail- able computer codes and their characteristics. These model- ling codes are used for the evaluation of policies, actions and designs that may affect such systems. This report pre- sents the methodology used by the IGWMC to classify, eval- uate and manage descriptive information regarding ground water modelling codes for the purpose of model selection. Furthermore, the report pro- vides an overview of available ground water modelling codes and their major characteris- tics. A section is included that defines ground water model- ling, presents the classifica- tion approach taken by the IGWMC and discusses differ- ent types of models and the mathematical approaches in- voked for developing the models. Separate sections dis- cuss and review the different categories of ground water models: flow models, transport models, chemical reaction models, stochastic models, models for fractured rock and ground water management models. The appendices include a listing and description from the IGWMC Model Annota- tion Search and Retrieval Sys- tem (MARS) of selected models from each category. Currently this MARS data- base is installed on a micro- computer operating under MS-DOS. Detailed informa- tion on the reviewed models is presented in a series of tables, preceded by an introduction on model classification and principal characteristics of the described models. The report can be ordered from EPA's Center for Envi- ronmental Research Informa- tion at 513-569-7562. Please refer to Document No. EPA/ 600/R-93/118 when ordering. Biosparging, from page 2 bioventing—an air flow pat- tern upward that enabled the air to remain below ground for approximately 24 hours. Plume water initially contain- ing several hundred micro- grams per liter (ug/1) of BTEX compounds (benzene, toluene, ethylbenzene and xylenes) was cleansed to <1 ug/1. After one year of operation, and again after two years, rep- licate vertical profile core samples were collected from the sparged plot and from an adjacent non-sparged control in the plume. Considerable variations between replicated profiles for fuel carbon con- centrations were detected. Averaged values for total fuel carbon of replicates showed that non-sparged control sam- ples decreased by 10% while sparged replicates showed a 42% decrease. Most of the sparged decrease occurred dur- ing the first year. The ability of the system to completely eliminate contaminants was restricted because of fuel glob- ules trapped in capillary pores of sand granules which pro- tected them from the sparge aeration. For more information, call Don Kampbell at RSKERL at 405-436-8564. A history of the first year of work has al- ready been published; the ref- erence is: Kampbell, D. H., C. J. Gnffm and F. A. Blaha, "Comparison of Bioventing and Air Sparging for In-Situ Bioremediation of Fuels," Proceedings of Symposium on Bioremediation of Hazardous Wastes: Research, Develop- ment, and Field Evaluations, Dallas, Texas, 1993, pp. 61-65 (Document No. EPA/600/ R-93/054) and can he ordered from EPA's Center for Envi- ronmental Research Informa- tion at 513-569-7562. A publication on the full study is anticipated for the Fall of 1994. Ground Water Currents ------- Surfactant Flushing, from page 2 lipophilic (attracted to or sol- uble in oils) core surrounded by a hydrophilic (attracted to or soluble in water) mantle. When the concentration of surfactant exceeds the CMC, organic compounds dissolve within the lipophilic core of surfactant micelles. The most promising surfac- tant tested, polyoxyethylene (20) sorbitan monooleate (trade name Tween 80 or Witconol 2722), was used in the soil-column experiments. This is a food-grade surfactant commonly used in dietary supplements, flavoring agents, whipped toppings and short- enings. Dodecane was used as the model organic compound. Prior to surfactant flushing, dodecane was entrapped in water-saturated soil columns packed with a uniform sand. After the introduction of a 4% surfactant solution, the concentration of dodecane exiting the column increased dramatically. Removal of 10% of the residual dodecane required 0.7 liters of surfac- rant solution. Comparable re- covery of dodecane without surfactant would have re- quired approximately 130,000 liters of water. Although high, the con- centrations of dodecane mea- sured in the column effluent were seven times less than those measured in batch ex- periments. These results im- ply that the equilibrium solubility of dodecane was not reached within the soil col- umn. Subsequent column experiments conducted at several flow rates confirmed the existence of rate-limited, rather than instantaneous, solubilization of residual dodecane. Numerical models were then developed which coupled surfactant transport with the solubilization of re- sidual organic liquids. The models were used to interpret laboratory experiments, eval- uate alternative remediation strategies and investigate the factors which influence the solubilization and mobiliza- tion of organic liquids at the field scale. Using these mod- els, HSRC researchers ex- plored optimal surfactant technologies, based on the amount of flushing time and amount of surfactant so- lution required to remove re- sidual dodecane from soil columns. This research demonstrates the ability of surfactants to enhance the solubility or or- ganic liquids and to promote recovery of entrapped organic liquids from soil columns. Model simulations were shown to be valuable tools in Interpreting data and evaluat- ing alternative pumping strat- egies. The results of these projects provide a basis for further development of surfac- tant flushing as an aquifer re- mediation technology. Ongoing research efforts focus on processes influencing the solubilization and mobiliza- tion of PCE entrapped within several aquifer materials. For more information, con- tact Linda Abriola at the University of Michigan (313-764-9406). To order additional copies of Ground Water Currents, or to be included on the permanent mailing list, send a fax request to the National Center for Environmental Publications and Information (NCEPI) at 513-891-6685, or send a mail request to NCEPI, 11029 Kenwood Road, Building 5, Cincinnati, OH 45242-0419. Please refer to the document number on the cover of the issue if available. Ground Water Currents welcomes readers' comments and contributions. 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