July 1997

Southeastern Technology Center Tests Aerobic System at Georgia Landfill

by Milton Gorden, STC

Southeastern Technology Center (STC) reports that early data from a demonstration of an aerobic biodegradation system at a landfill in Columbia County, GA, indicate that methane levels can be reduced by 50-90%, biological oxygen demand in the leachate can be reduced by more than 50%, and metal contamination of the leachate can be prevented. STC is a non-profit organization that facilitates the transfer of commercially viable technologies from the government sector to the private sector to promote economic growth regionally and nationally.

STC conducted the demonstration project under a cooperative agreement with the U.S. Department of Energy-Savannah River (DOE-SR) to commercialize innovative technologies developed by the agency. Columbia County, GA, and American Technologies Inc. of Grovetown, GA, also participated in the demonstration program. DOE-SR personnel provided technical support for these demonstrations.

The aerobic system STC tested at the Columbia County Landfill is designed to reduce or eliminate problems associated with the anaerobic ("dry tomb") technology commonly used in design, construction, and closure of municipal landfills. Disadvantages of the traditional anaerobic process include the production of methane, leaching of metals, formation of toxic compounds, slow stabilization, and odor. Conversion of the Columbia County Landfill to an aerobic system involved the injection of air into the subsurface through horizontal pathways. The injected air provided oxygen to aerobic microorganisms located in the overlaying waste mass, thereby promoting microbial population growth and activity. This system involves the return of leachate collected from the landfill to the top of the waste mass, where it is allowed to percolate down into the waste, providing moisture for microorganisms. The stimulated aerobic microorganisms promote the decay of carbon compounds into carbon dioxide and water.

Under the DOE cooperative agreement, STC also managed development of the HaloSnifTM fiber-optic spectrochemical sensor, the BaroBallTM technology using pressure differentials in gas venting wells, depth-discrete sampling ports for multiple depth sampling in a single well, and the PHOSterTM system (described in the March issue of Tech Trends). For additional information, contact James Ullery (STC) at 706-722-3490.

Studies Focus on Reducing Lead Bioavailability at Superfund Site

by Mark Doolan, EPA Region 7, and Stan W. Casteel, Ph.D., University of Missouri

EPA Region 7 is supporting field tests to determine the effectiveness of various forms of phosphorous ame reducing the bioavailability of lead in soil from the Oronogo-Duenweg Mining Belt Superfund Site in Jasper County, MO. The amendments include phosphoric acid, triple super phosphate, rock phosphate, iron-rich material, and compost material. Methods of treatment with these amendments include rototilling, surface aeration, and pressure injection.

In conjunction with the field studies, University of Missouri researchers are testing a new method for determining lead bioavailability using immature swine dosed with lead-contaminated soil from the site. Researchers selected swine for the bioavailability testing because immature swine are physiologically similar to young children, on which EPA's lead-uptake model is based. Dosing trials with phosphorous-amended, lead-contaminated soil indicate that a 50% or greater reduction in lead bioavailability may be possible.

These tests will help EPA regulatory officials determine whether using phosphate to treat lead-contaminated soil will modify existing cleanup levels. An existing contingent Record of Decision (ROD) for the site calls for excavation and replacement of top soil for 2,400 residential properties with lead contamination levels as high as 10,000 ppm. At properties where phosphate amendment is successful in significantly reducing bioavailability rates, excavation and replacement of the soil may be greatly reduced.

EPA anticipates completion of the Oronogo-Duenweg Mining Belt Site lead studies in early 1998.

Results of previous swine studies using lead-contaminated soil reinforce the usefulness of site-specific bioavailability measurements in setting priorities or determining remedial needs. For example, in one study conducted with lead-contaminated soils taken from the Smuggler Mountain Superfund Site in Aspen, CO, 50 juvenile male pigs were dosed orally with varying amounts of lead-contaminated soil over a 15-day period. Post-mortem analysis of liver, kidney, and bone tissues (weighted) indicated relative bioavailability values of 63-64%. These results differed significantly from the lower absorption rates measured in studies involving high doses administered to animals with physiologies unlike humans, such as adult rodents.

Other studies involved dosing juvenile swine with lead-contaminated soil samples from widely diverse sites across the country. In these studies, relative bioavailability of lead varied substantially among sources, with absolute bioavailability rates ranging from 15% to 45%.

For more information on the phosphate amendment studies at the Oronogo-Duenweg site, contact Mark Doolan (EPA Region 7) at 913-551-7169. For more information on bioavailability testing in swine, contact Stan W. Casteel, Associate Professor of Toxicology (College of Veterinary Medicine, University of Missouri) at 573-882-6811.

Phase III of DoD's UXO Demonstration Program Completed

by Kelly Rigano, U.S. Army Environmental Center

The U.S. Department of Defense (DoD) Army Environmental Center (USAEC), in partnership with the Naval Explosive Ordnance Disposal Technology Division, has completed Phase III of the Unexploded Ordnance (UXO) Technology Demonstration Program. The U.S. Army Jefferson Proving Ground in Madison, IN, hosted 15 demonstrations of various technologies at a 16-hectare, controlled test site containing a known baseline of emplaced, inert ordnance.

Phase III results indicate that UXO technologies show continued improvement in detection performance since the initial Phase I demonstrations in 1994. Improvements to the capabilities for discriminating UXO from background clutter, however, need a focused effort. Additionally, performance of excavation technologies has not improved significantly. Results also show that technology for remote excavation is feasible, but slow and inefficient.

The detection technologies demonstrated in Phase III utilized electromagnetic induction, gradiometers, magnetometers, and ground penetrating radar sensors. Top performers detected over 95% of the emplaced ordnance targets. Corresponding false alarms (demonstrator target reports that do not correspond to baseline ordnance targets) exhibited by all demonstrators were high. For optimum performers, the false alarm (FA) ratios (the number of FAs/number of detected ordnance) ranged between 1.91 and 5.18. This means that 2-5 targets were identified for every baseline ordnance target detected. These results show that demonstrator detection performance was dependent not only on the type of sensor used, but on each demonstrator's entire technical process for collecting, processing, and reporting data.

In its Phase III final report, UXO Technology Demonstration Program at Jefferson Proving Ground, Phase III, April 1997, DoD recommends establishment of target discrimination goals and standard formats for raw sensor data, identification of discrimination factors, and availability of raw sensor data to technology developers. DoD also recommends further funding for development of innovative and high-risk technologies and the availability of a test area at the Jefferson Proving Ground for technology development. For further information, contact Kelly Rigano (USAEC) at 410-612-6868.

Polyurea Spray Elastomer Used for Containment

by Carol J. Miller, Ph.D., P.E., Wayne State University

Researchers recently found that a polyurea elastomeric material is highly effective in forming a continuous, seam-free landfill liner. Experts from Wayne State University, Drexel University, and Foamseal collaborated to develop the elastomer as an alternative to the materials conventionally used for landfill liner and cover systems.

The elastomer consists of an isocyanate-terminated prepolymer reacted with an amine-terminated resin. These liquids are pumped by a two-component dispense unit at 2000 psi and 155š F and sprayed through a mechanical purge gun in a fan-shaped pattern. Application of the elastomer is performed by hand or with automated equipment utilizing a transversing spray gun. Completed chemical reaction occurs within minutes of application. A color coding system is used to reflect varying thickness of the liner needed for differing site conditions, ranging from red, for a thickness of 165 mil, to green, for 105 mil. By uniquely coloring base materials, field personnel responsible for spraying the elastomer are guided in achieving the required thickness and controlling uniformity of the spray. Complete coverage with the spray is achieved when base materials lose color.

Laboratory testing of mechanical and hydraulic properties of the polyurea spray indicated a tensile strength, at maximum stress, of 20.8 MPa, tear resistance of 4.0 N/mm, and puncture resistance of 16.6 N/mm. Water vapor transmission occurred at 7.1 x 10-10 cm/sec. Direct shear testing results showed a friction angle and cohesion of 38.7š and 2 psi, respectively, when the elastomer was sprayed onto soil; 14.5š and 0 psi when sprayed onto geotextile material; and 37.4š and 0 psi when combined with geotextile material and sprayed on soil. Product cost is competitive with more traditional landfill liner material options. The application cost for a typical 60 mil liner is estimated as $10/yd2.

An alternative use for the spray elastomer as a clay liner desiccation inhibitor was field tested on a limited scale; this application would have widespread use in arid and semi-arid climates where desiccation cracking of clay liners is a major threat. For more information, contact Carol Miller, Ph.D., P.E., (Wayne State University) at 313-577-3876 or Rick Tanis (Foamseal) at 810-628-2587.