Field Demonstration in Situ Fenton's Destruction of DNAPLS I ~ "I *.

by K. M. Jerome Westinghouse Savannah River Company Savannah River Site Aiken, South Carolina 29808

6. 6. Looney

I 7,. J t '

RECORDS ADMINISTRATION

I

J. Wilson Geo-Cleanse International, Inc. NJ USA

INFOR v

A document prepared for FIRST INTERNATIONAL CONFERENCE ON REMEDIATION OF CHLORINATED AND RECALCITRANT COMPOUNDS at Monterey, CA, USA from 5/18/98 - 5/21/98.

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WSRC-RP-98-00011

I FIELD DEMONSTRATION OF IN SITU FENTON'S DESTRUCTION OF DNAPLS

Karen M. Jerome (Westinghouse Savannah River Company (WSRC), Aiken, SC USA)

Brian B. Looney (WSRC, Aiken, SC USA) Jim Wilson (Geo-Cleanse International, Inc. Kenilworth, NJ USA)

ABSTRACT: A collaborative effort between Geo-Cleanse International, Inc. and WSRC in 1997 resulted in demonstration of in situ oxidation based on Fenton's chemistry. The technology treatment yielded an approximate 90 % destruction of a 600 pound dense non-aqueous phase liquid (DNAPL) pool located 155 ft below ground surface. Factors to be considered in selecting this technology are volume of DNAPL, other compounds which may be oxidized under similar conditions, geochemical makeup of the treatment zone, and tightness of treatment zone. Economic evaluation of this technology indicated the costs are sensitive to both depth and DNAPL quantity. Based only on economic considerations, large DNAPL volumes (e.g. lOOO's of pounds) are needed to make the technology viable. Positive attributes of this technology are the end products are innocuous materials, no waste is generated from the treatment process and no material is brought to the surface.

INTRODUCTION At large industrial sites where contamination resulted from release of

chlorinated solvents to the ground, a significant barrier to clean up is treatment of the undissolved DNAPL in the soil and groundwater. Chlorinated solvents, such as trichloroethylene (TCE) and tetrachloroethylene (PCE) , are more dense than water and migrate downward through the vadose zone and into the groundwater. The migration path is influenced by geology, hydrology, and solvent physicalkhemical characteristics. Data collected at the Savannah River Site (SRS) over the past 15 years indicate that DNAPL below the water table occurs as relatively diffuse ganglia and/or a thin layer on the top of aquitards. DNAPL acts as a reservoir that will continue to generate contaminant levels far above remediation concentration goals well into the future. In an effort to achieve remediation goals and reduce future costs, technologies that will recycle or destroy DNAPL are being developed and demonstrated.

A demonstration of one such destruction technology was conducted at the Savannah River Site in April of 1997. This demonstration evaluated an in situ oxidation technology based on Fenton's chemistry to destroy DNAPL below the water table. Westinghouse Savannah River Company (WSRC) worked in cooperation with Geo-Cleanse International, Inc. in conducting this test, sponsored by the Department of Energy (DOE).

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WSRC-RP-98-00011

Objective. The objective of this demonstration is to evaluate a technology in the general class of DNAPL destruction technologies. This was accomplished by determining a destruction efficiency and preparing a cost analysis of the demonstration. The goal is to identify a DNAPL recycling or destruction technology to incorporate into the existing suite of technologies being used in the A/M Area of SRS to remediate a 1500 acre groundwater plume resulting from four major DNAPL sources.

Site Description. A/M Area, a former metals fabrication facility within the DOE’S Savannah River Site, located in Aiken, South Carolina, was chosen for the location of this demonstration. Three and a half million pounds of solvents, primarily TCE and PCE, were discharged to the soils and groundwater in A/M- Area from 1958 until 1985. Typical of the Atlantic Coastal Plain, sediments beneath A/M-Area are interbedded sands, silts and clays deposited during periods of fluctuation in sea level and modified by erosion during intervening times. Clay rich confining intervals are interspersed with more transmissive, sandier intervals. The uppermost significant clay beneath the water table, termed “Green Clay”, is at an approximate elevation of 200 ft msl (35 ft below the water table and 150 ft bgs).

MATERIALS AND METHODS The demonstration was conducted in three phases: pre-test

characterization, technology test, and post-test characterization. Pre- and post- test characterization consisted of collecting continuous soil cores from which soil samples were taken and analyzed by GC headspace method to measure TCE and PCE concentrations. Rotosonic drilling was used to collect soil cores and to install all wells for the test. By comparing post-test characterization data to pre- test characterization data the destruction efficiency of the treatment technology was determined. The test of the Geo-Cleanse@ process, based on Fenton’s chemistry, was conducted over a 6 day period.

Fenton’s Chemistry. H. J. H. Fenton developed a chemistry which oxidized malic acid through use of hydrogen peroxide and iron salts in the 1890s. This chemistry has been, and is still widely used by the waste water industry for treatment of organic wastes. Hydrogen peroxide is the active ingredient in oxidation of organic compounds by this methodology. The hydroxyl radical is the reactive species in this process.

The chemistry of Fenton’s reagent (1) is well documented as a method for producing hydroxyl radicals by reaction of hydrogen peroxide and ferrous iron (Fe’2). Hydroxyl radicals are very powerful, effective and nonspecific oxidizing agents, approximately lo6 to lo9 times more powerful than oxygen or ozone alone.

H,O, + Fe2+ 3 Fe3+ + OH- + OH* (1)

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WSRC-RP-98-00011

During the optimum reaction sequence and when the catalyst is iron, ferrous iron (Fe") is converted to ferric iron (Fe+3). Ferrous iron is soluble in water at pH 5 to 6 and is necessary for generation of the hydroxyl radical, but ferric iron will not generate the hydroxyl. radical and is less soluble at pH 5 to 6. Under properly controlled and buffered conditions, ferric iron can be regenerated back to ferrous iron by a subsequent reaction with another molecule of hydrogen peroxide (2).

H20, + Fe3' u Fe2' + H' + HO,' (2)

The iron will remain available in ferrous form as long as pH is properly buffered and there is sufficient hydrogen peroxide. As hydrogen peroxide is consumed, some iron will precipitate out as ferric iron (if pH is moderate).

Many reactions occur during the oxidation of a contaminant, but as shown by equation (3) a contaminant (RHX), hydrogen peroxide, and ferric iron, as a catalyst, are consumed to produce water and carbon dioxide. RHX represents an organic compound and X represent a halide (such as chloride). If the compound is non-halogenated (no X), then the hydrogen ion and halide anion are not formed in the overall reaction.

+ H,O, w H,O + CO, + H' + X- (3) RHX Fe+2

Geo-Cleanse@' Technology Description. Geo-Cleanse' technology, an in situ destruction technique, utilizes Fenton's reagent to convert organic contaminants to water and carbon dioxide. Hydrogen peroxide and catalyst are injected into the groundwater zone where DNAPL contamination is located. The injection process is proprietary and Patents #5,525,008 and #5,611,642 have been issued.

The injector contains a mixing head which is utilized for mixing reagents and has components to stimulate circulation of groundwater to promote rapid reagent diffusion and dispersion. Thus, all reagents are injected into the subsurface through the injectors. Upon start of the injection process, air with catalyst solution is injected to ensure the injector is open to the formation prior to injection of peroxide and catalyst solution. When an acceptable flow has been established, peroxide and catalyst will be injected simultaneously. This ensures that catalyst and peroxide will not mix together in a sealed system. The injector is designed with a check valve and constant pressure delivery system ensures safety in field operations.

The number of injectors installed and volume of injectate is based on the source area size. Injection of catalyst solution adjusts the groundwater pH to between 4 and 6, where metals, specifically iron, will be at the optimal electron state, +2. This is followed by the simultaneous injection of hydrogen peroxide and catalyst. Mixing of catalyst and hydrogen peroxide in the subsurface will generate heat as the reaction with organic contaminants progresses. Monitoring is conducted during the treatment phase for water vapor; carbon dioxide gas, hydrogen peroxide, the contaminants to be destroyed, pH , conductivity, and

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dissolved oxygen. process to maintain groundwater pH within the range of 4 to 6 .

Catalyst solution may be added throughout the injection

Test Site. The selected test site is in a bowl shaped surface depression approximately 50 feet square. It is located within a suspected subsurface trough in the Green Clay along which DNAPL is migrating. Soil concentrations of PCE in the test are ranged from 10 to 150 pg/g. Highest concentrations were found in a zone at approximately 140 ft below ground surface (bgs). An injector was installed in the center of the test zone with 3 additional injectors and 3 monitoring wells installed radially outward at distances of 17 and 27 feet, respectively (Figure 1). Also installed were 4 vadose zone piezometers.

102440 - -

MOX-9 , + / . - / MOX-3V / 9 I

MbX-5 / ' MOX-2 MOX-10

MOX-7 102420 4 MOX-1

0 1 MOX-PV . + U I

MOX-4 Approximate

+ -

MOX-11 Trealrneol Zom 0 ! MOX-4V

102400 4- I

\ MOX-3

0 \ / Horizontal

Ground Water Grad tent

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MOX-a MOX-lV - -.e 0

\ 48200 48220 * 48240 48260 48280 48300

Easting FIGURE 1. Schematic of In Situ Oxidation Field Demonstration Site Layout (coordinates are a local grid in feet)

RESULTS AND DISCUSSION Success of the demonstration is based on destruction of DNAPL in the

treatment zone. The best measure of destruction is based on measurement of DNAPL globules in the sediment before and after the treatment process. Results of pre- and post- test characterization indicated a significant decrease in DNAPL concentration after the technology test, as represented in Figure 2. The estimated pre-test mass of DNAPL in the treatment zone was 600 pounds (Ibs) and the estimated post-test mass of DNAPL was 40 Ibs. Resulting in a destruction rate of approximately 90 percent for the treatment zone. The treatment zone is defined as the vertical distance between the water table

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CVOCs, Ibs per 1 Foot Reaction Zone Interval

0 25 50 75 I00

124 0 Pre-Test DNAPL 128

I32

136

140

144

148

152 156

injection Zone

FIGURE 2. Pre- and Post- Test DNAPL Mass for the In Situ Oxidation Demonstration

(124 ft bgs) and the Green Clay (152 ft bgs) and a 27 ft radius from the center injector. Contaminant mass was estimated by averaging sediment concentrations at one foot depth intervals and assuming a treatment zone of 64,000 ft3. Total destruction of all DNAPL was not achieved and can be attributed to the process not contacting all DNAPL globules in the fine grained sediments. Injected hydrogen peroxide takes the path of least resistance through areas of higher permeability, which in this case is through sandy regions of the treatment zone.

Cost Evaluation of Demonstration. This evaluation examined costs from two perspectives. First, overall cost of the demonstration is discussed in relationship to the influence of each component of the demonstration. Second, cost on a per pound of DNAPL removed basis is compared to the cost per pound of DNAPL removed for the baseline system of pump and treat using air stripping.

In evaluating the influence of each component of the demonstration on the overall demonstration cost, six categories were identified: site preparation, pre-test drilling and characterization, technology test, post-test drilling and characterization, demobilization, and documentationlproject management. The majority of costs are related to the technology test and the pre-test drilling, 36% and 30% of total costs, respectively. Breaking these two categories down into

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WSRC-RP-98-00011

their respective activities showed that drilling activities and peroxide will vary greatly dependent on depth to contamination and amount of DNAPL present.

In an effort to determine the cost effectiveness of this technology, a unit cost based on a pound of DNAPL treated or destroyed was determined and compared to the unit cost of the baseline technology. For A/M Area, the baseline technology is pump and treat using airstripping. The baseline cost is $87/lb DNAPL treated (note this is related to groundwater concentration, and the unit cost will increase over time as concentrations decrease). The break even point for in situ oxidation is dependent on depth to contamination. For the A/M Area this occurs at volumes ranging from 6,500 lbs to 9,500 lbs of DNAPL as depth to contamination increase form 60 ft to 155 ft. Unit cost of in situ oxidation at sites with small volumes of DNAPL, less than 4000 lbs, is greater than $100/lb of DNAPL. Unit costs escalate to greater than $700/lb of DNAPL for sites with approximately 1000 Ibs of DNAPL.

CONCLUSIONS During this demonstration approximately 90% of 600 lbs of DNAPL was

destroyed in a six day operating period, leaving a residual of 40 Ibs of DNAPL in the target zone. On a unit cost basis, this technology becomes cost competitive with pump and treat using airstripping ($87/lb, SRS costs) for a DNAPL pool of approximately 9,500 Ibs at a depth of 155 ft bgs. Depth is a major contributor to the overall costs when this technology is employed. For a DNAPL pool of equal volume, remediation costs will increase as depth to the DNAPL pool increases. Thus, both size of the DNAPL pool and depth to the DNAPL pool must be considered in determining when this technology becomes cost competitive with the chosen baseline technology.

Other factors contributing to the decision to use this technology include duration of treatment, and end products of treatment. Treatment is conducted in a period of days to weeks. Factors effecting the duration of the treatment would include: other compounds which may be oxidized under similar conditions, geochemical makeup of treatment zone, and tightness of treatment zone (i.e., access to DNAPL). End products of in situ oxidation are very appealing. No waste is generated from the treatment process, and no material is brought to the surface. End products of this process are carbon dioxide, water, and chloride ions. All of these compounds are considered innocuous materials.

Additional questions raised during the demonstration concerned effects of the treatment on the geochemistry and microbiology in the target zone. Work underway in 1998 will attempt to determine these effects.

REFERENCES

Jerome, K. M., €3. Riha, B. B. Looney. 1997. Final Report for Demonstration of In Situ Oxidation of DNAPL Using the Geo-Cleanse@ Technology. WSRC- TR-97-00283. Prepared for the U. S . Department of Energy

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