Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology

Transcription

1 Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology Phillip La Mori Elgin Kirkland Harlan Faircloth Robert Bogert Mark Kershner Thermal remediation of contaminated soils and groundwater by injection of hot air and steam using large-diameter auger in situ soil mixing effectively remediates volatile and semivolatile organic compounds. This technology removes large amounts of contamination during the early treatment stages, but extended treatment times are needed to achieve high removal percentages. Combining thermal treatment with another technology that can be injected and mixed into the soil, and that continues to operate after removal of the drilling equipment, improves removal efficiency, and reduces cost. Using field-determined pseudo first-order removal rates, the cost of the combined remediation of chlorinated volatile organic compounds (CVOCs) by thermal treatment followed by reductive dechlorination by iron powder has been estimated as 57 percent of the cost of thermal treatment alone. This analysis was applied to a case-study remediation of 48,455 cubic yards, which confirmed the cost estimate of the combined approach and showed over 99.8 percent removal of trichloroethene and other chlorinated VOCs. Oc 2010 Wiley Periodicals, Inc. INTRODUCTION Thermal remediation of contaminated soils and groundwater by injection of hot air and steam using large-diameter auger (LDA) in situ soil mixing is an effective way to remove source-zone volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), and petroleum hydrocarbon (PHC) contamination. Like other in situ and ex situ thermal methods, this technology relies primarily on the volatilization of the compounds treated (HLA, 1989; U.S. Environmental Protection Agency [US EPA], 1991). The in situ soil mixing technology operates one treatment cell at a time by advancing a single 7- to 10-foot-diameter auger, or dual 5- to 8-foot-diameter augers, to depths of over 70 feet. During active mixing, the permeability increases, permitting the soil and groundwater to be treated evenly by the injected high-pressure hot air and steam. Steam and hot air injected from ports on the auger heats the contaminated soil and groundwater to a temperature of approximately 75 to 95 C, thermally desorbing the VOCs and volatilizing the nonadsorbed VOCs, while the air conveys the volatilized off-gas contamination to the ground surface for capture and treatment. Typically, the in situ thermal technology using steam and hot air has removal efficiencies of 90 to 99 percent for VOCs and 50 to 90 percent for SVOCs. The removal efficiency for any chemical generally decreases as its boiling point temperature increases. c 2010 Wiley Periodicals, Inc. Published online in Wiley Interscience ( DOI: /rem

2 Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology Features common to previous implementations of this technology include: Combining the thermal treatment with another technology that can be injected and mixed into the soil, and that continues to operate after removal of the drilling equipment, has been found to be an effective way to improve removal efficiency and reduce cost when compared to thermal treatment alone. The treatment agents are well mixed into the contaminated soil and groundwater. The technology is applicable to both the vadose and saturated soil zones. Real-time monitoring of off-gas contamination permits field decisions for focused treatment at all depth levels to predetermined contaminant concentrations. Monitoring provides real-time control of all important treatment parameters, increasing efficiency and lowering cost. Monitoring of off-gas contamination quantifies the amount removed and provides tangible proof of remediation. Additional treatment agents can be applied sequentially or simultaneously for additional remediation. The surface and subsurface must be free of structures and obstructions. The thermal removal of contaminants appears to follow pseudo first-order kinetics. Thus, it is very effective in removing a large percentage of nonaqueous-phase liquid (NAPL) and dissolved contamination during the early treatment stages, but extended treatment times are needed to achieve high removal percentages of the adsorbed material (i.e., there is a diminishing return for thermal treatment over time versus cost). Combining the thermal treatment with another technology that can be injected and mixed into the soil, and that continues to operate after removal of the drilling equipment, has been found to be an effective way to improve removal efficiency and reduce cost when compared to thermal treatment alone. The second technology is applied during or immediately after the thermal treatment and mixed into the soil by the augers. An example of this approach is the mixing and injection of iron powder (i.e., zero-valent iron, or ZVI) into the soil and groundwater for continued chlorinated VOC and SVOC removal (Moos, 1998). The implementation and demonstration of the combined LDA thermal and ZVI for remediation of chlorinated dense nonaqueous-phase liquid (DNAPL) source zones has been a major improvement to the thermal soil mixing technology over the last five years. This approach takes advantage of the strengths of both thermal treatment and reductive dechlorination. For thermal treatment, the effective removal of large amounts of contamination occurs quickly, and the ZVI, combined with the mixing, distribution, and dissolution of the DNAPL, promotes continued degradation of residual mass without continued equipment expenses. The dual-treatment approach can achieve removal efficiencies of over 99.5 percent for chlorinated VOCs, and can result in significant cost savings when compared to thermal treatment alone. REMOVAL RATES Implementing site remediation using the combined thermal and ZVI technology requires knowledge of (1) the effectiveness of the thermal remediation for the specific contamination and (2) the amount of the ZVI required. The first determines the cost of the drilling equipment (thermal treatment time) and the second the cost of the iron powder (material). Combining this information will assist in optimizing the treatment plan and reducing cost. 10 Remediation DOI: rem c 2010 Wiley Periodicals, Inc.

3 At NAPL sites, the contamination exists as pure phase, vapor, dissolved, and adsorbed material forms. Each material form will have a different removal rate response to the heat input as measured by its concentration in the produced vapor. The rotating auger(s) may encounter any form or all forms simultaneously, as it rotates and travels vertically through the contaminated volume. The pure phase, vapor, and dissolved material will be volatilized relatively quickly, while the adsorbed material will be removed more slowly. It is probable that at the low temperatures applied with this technology (e.g., less than 100 C), not all the adsorbed material will be removed. Thus, the concentration of the contamination in the off-gas vapor versus time will be initially high, quickly drop to low numbers, and eventually become asymptotic. It is possible that these several combined removal rates might be observed as pseudo first-order. There is a limited amount of data available to determine contaminant removal rates of thermal treatment. The reason for this is that obtaining the data requires stopping the treatment several times to obtain time-based samples for chemical analysis. The cost and logistics of stopping the treatment and moving the drilling rig off the treatment cell and then bringing in a direct-push technology (DPT) sampling rig to sample a location with hot and unconsolidated soil are considerable. The limited sampling that has occurred used a special smaller remediation drilling rig (2-foot-diameter auger) designed for pilot testing, and was performed in the 1990s (Novaterra, Inc., 1993; O Shea Parsons and Associates, 1994). Chemical analyses versus time from five separate sites tested with this equipment indicated that the observed thermal removal can be expressed by the following first-order equation, ln C = ln C o kt,wherec is the concentration at time t and C o is the initial concentration, t is time in consistent units, and k is the rate constant; k has the units of 1/time. Exhibit 1 is an example plot of field test results showing the concentration of tetrachloroethene (PCE) and trichloroethene (TCE) versus time for three locations at one of the five sites (O Shea Parsons and Associates, 1994). It is typical of all the thermal removal rate data in that a straight line is an adequate representation of the data on a log concentration versus time plot. Thus, the PCE thermal removal data for three locations appears to be pseudo first-order with an average k value of 0.049/min. This k value means that it takes about 14 minutes to reduce the PCE concentration by 50 percent and that it would take about 99 minutes to remove 99 percent of the contamination. Exhibit 1 also shows that the removal rate of TCE appears as pseudo first-order. A limited amount of data is also available for the removal of TCE by ZVI powder after completion of thermal treatment. These data come from a proof of concept field project completed at Argonne National Laboratory (ANL) in 1997 using dual 5-foot diameter augers to compare the ability of three methods to remove TCE from heavy clay soils. One method was the use of ZVI combined with thermal removal (Moos, 1998). Ten tests were run at ANL to evaluate the combined remediation concept. The tests indicated that the combined technology was successful but did not determine the removal rate of TCE. The results of the four key tests of the use of the combined technology have been re-evaluated here to determine if the removal of TCE by ZVI is pseudo first-order. Exhibit 2 shows that pseudo first-order removal of TCE by ZVI powder is a fair representation of the data up to about 40 days. Since the data were taken using the same iron and soil under very closely controlled conditions, it was postulated that if the data were normalized for the initial concentration of TCE all the data would fit on a single curve. This plot is shown in Exhibit 3. Exhibit 3 The cost and logistics of stopping the treatment and moving the drilling rig off the treatment cell and then bringing in a direct-push technology sampling rig to sample a location with hot and unconsolidated soil are considerable. c 2010 Wiley Periodicals, Inc. Remediation DOI: rem 11

4 Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology Exhibit 1. Thermal removal of PCE and TCE Exhibit 2. Removal of TCE by ZVI 12 Remediation DOI: rem c 2010 Wiley Periodicals, Inc.

5 Exhibit 3. Normalized removal of TCE by ZVI shows that the first-order removal of TCE by ZVI has a half-life (i.e., the time required to reduce the concentration of TCE 50 percent) of 7.53 days. Exhibit 3 also has two data points at two months and one data point at three months after treatment that are not included in Exhibit 2. These three data points suggest that, in some cases, the ZVI activity was slowed after 40 days. This fact was noted during the analysis of the ANL results (Moos, 1998). The cause was not firmly determined but based upon microscopic analysis of the iron powder recovered from the treatment cells, it was suggested that the decrease in the reactivity of iron occurred from corrosion found on its surface. In any case, it appears that for the ANL test, the iron maintained its reactivity for over one month, or about five 50 percent removal cycles and, in some cases, longer but at a reduced rate. APPLICATION EXAMPLE Although the removal rate information is limited, it provides a basis to evaluate various combinations and costs of the combined thermal and powdered iron treatment to achieve a desired remediation goal. For example, it takes about 45 minutes of application of 9,000 pounds of 166 C steam and 15,000 cubic feet of 66 C air to reduce the concentration of TCE in the off-gas by 50 percent from a soil column 8 feet in diameter and 35 feet in length. Using the first-order equation of ln C = ln C o kt, k has a value of per minute. Assuming first-order kinetics holds, it will take 1.5 hours of thermal treatment using the LDA to achieve 75 percent reduction. Setting a goal of over 98 percent removal of TCE, this goal could be accomplished by 4.23 hours (254.0 minutes) of thermal treatment (ln(.02)/(.0154) = (254.0/60)) = 4.23 hours. c 2010 Wiley Periodicals, Inc. Remediation DOI: rem 13

6 Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology The cost comparison of using the two approaches can be determined based upon the volume treated, the cost of the equipment, and the cost of the iron. This 98 percent removal might also be achieved by combining 1.5 hours of thermal treatment achieving 75 percent removal, followed by one month of remediation by ZVI powder, where the iron has a TCE removal rate of 50 percent in 7.5 days. The cost comparison of using the two approaches can be determined based upon the volume treated, the cost of the equipment, and the cost of the iron. The volume of soil treated is about 65.2 cubic yards (yd 3 ) per treatment cell, which amounts to about 195,500 pounds, where the soil weighs 3,000 pounds per yd 3. Because the auger creates a treatment circle, a 17 percent area overlap is required to achieve 100 percent areal coverage; this reduces the effective treatment volume to 54.1 yd 3 per cell. A typical LDA thermal treatment operation might cost $35 (+/ $5) per minute. Thus, the cost to thermally remove 98 percent of the contamination is estimated to be 4.23 hr 60 min/hr $35/min = $8,890. This calculates to about $ per effective cubic yard treated. The injection and mixing in of 1 percent by weight (1,950 lbs) of iron powder that costs $0.50/pound will take about 30 minutes at an injection cost of about $30/min. Thus, the cost of 1.5 hours of thermal treatment plus iron will be 90 min $35/min + $0.50/lb 1,950 lb + $30/min 30 min = $5,018. The estimated cost of the combined approach is $92.90 per effective cubic yard treated. Thus, the savings for a combined approach of thermal plus iron compared to thermal alone to remediate to over 98 percent removal is estimated at about $71.40 per cubic yard. This results in an estimated savings of $3,862 per treatment cell, approximately 43 percent of the estimated cost of thermal treatment. In addition, if the powdered iron remains reactive for more than one month, the removal of additional chlorinated VOCs will occur. When this happens, removal efficiencies of 99.8 percent or greater can occur, as was found in the case-study test results described in the next section. FULL-SCALE REMEDIATION CASE STUDY Project Description The remediation summarized in this case study details part of the Corrective Measures Implementation (CMI) for Space Launch Complex 15 (SLC-15), Solid Waste Management Unit C030 located at Cape Canaveral Air Force Station in Cape Canaveral, Florida (BEM Systems, Inc., 2006). SLC-15 was constructed in 1957 for the United States Air Force Titan I Missile Program but was utilized as a waste storage and disposal area from 1958 until approximately The storage and disposal of wastes adversely impacted soil and groundwater quality at SLC-15. Several Interim Measure (IM) activities were performed to address issues with vadose-zone soils, sediment, and surface water. A Corrective Measure Study (CMS) and a Corrective Measure Design (CMD) were developed specifically to address groundwater and saturated soil impacted with chlorinated VOCs. Chlorinated VOCs, including TCE, cis-1,2-dichloroethene, vinyl chloride, PCE, trans-1,2-dichloroethene (cis-1,2-dce), 1,1-dichloroethene (1,1-DCE), and 1,1,2-trichloro-1,2,2-trifluorethane (Freon 113), were present in dissolved, sorbed, and DNAPL forms in the surfical aquifer. Freon 113 was the most abundant contaminant, even though it was not a chemical of concern (COC). The saturated subsurface groundwater (water table at about 6 feet below ground surface) that had TCE concentrations at or above 10 mg/l (i.e., approximately 1 percent of the solubility) was considered as the source contamination zone, requiring remediation 14 Remediation DOI: rem c 2010 Wiley Periodicals, Inc.

7 because it is considered as a potential indication of DNAPL. TCE was present in the groundwater up to 500 mg/l and in the soil up to 1,800 mg/kg (see pretreatment data in Exhibits 5 through 8). Two source areas (Launch Stand [LS] and Deluge Basin [LB]) were identified as having greater than 10 mg/l of TCE from depths of 20 to 55 feet below ground surface, containing approximately 48,500 cubic yards of contaminated soil and groundwater. The CMS recommended combined in situ thermal treatment and ZVI of soil and groundwater by the application of LDA soil mixing technology. The mixing equipment was designed to deliver injected fluids (i.e., steam, hot air, and iron slurry) to the subsurface contaminants to facilitate treatment and removal. Hot air and steam used to volatilize the COCs were emplaced using a 10-foot-diameter auger in a batch process that treated one column at a time. ZVI slurry was also co-injected with air into every column to continue the remediation after cessation of the thermal treatment. During active steam and air treatment, a vacuum was applied to a 14-foot-diameter shroud at the ground surface to collect vaporized contaminants that were subsequently treated in a gas conditioning system, and then destroyed in a flameless thermal oxidizer. The vaporized contaminants were continuously sampled, and the concentration of contamination removed during treatment was measured by a flame ionization detector (FID) in the off-gas stream. The gas composition was measured by an in-line gas chromatograph (GC). These measurements, when combined with contaminated off-gas flows and temperatures, permitted the calculation of the estimated amount of each COC and Freon 113 removed during thermal treatment. Project Goal The goal of the remedial implementation was to reduce the identified source area TCE mass by at least 80 percent or more, so that natural attenuation of the remaining contamination would meet the objective of reaching the Florida Groundwater Cleanup Target Level (GCTL) for TCE in less than 68 years. This goal was based on fate-and-transport modeling. Because the source-area TCE mass could not be accurately and credibly defined due to the presence of DNAPL, the amount of material to reach 80 percent removal could not be determined. Thus, the objective of the project was to achieve as much removal as possible, greater then 80 percent, as determined from pretreatment and posttreatment soil and groundwater chemical samples. The goal of the remedial implementation was to reduce the identified source area TCE mass by at least 80 percent or more, so that natural attenuation of the remaining contamination would meet the objective of reaching the Florida Groundwater Cleanup Target Level for TCE in less than 68 years. RESULTS Sampling and Chemical Analysis Pretreatment and posttreatment DPT soil and groundwater samples for chemical analysis were collected on 40-foot orthogonal grids at 22 LS locations and at 21 DB locations, specifically for the purpose of performance evaluation. Post-treatment sampling occurred three to six months after treatment. Since the sampling grids extended slightly beyond the contaminated areas, the pretreatment evaluation samples also served the purpose of confirming and refining the conceptual site model. Thermal treatment and iron powder injection occurred between 20 and 55 feet below the ground surface. Both soil and groundwater samples were taken for chemical analysis nominally at seven depths (10, 20, c 2010 Wiley Periodicals, Inc. Remediation DOI: rem 15

8 Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology Exhibit 4. Number of analytical samples in treatment zone Groundwater Soil Medium Location Launch Stand Deluge Basin Launch Stand Deluge Basin Total # DPT # DPT in Remediation Zone Potential Total # of Samples = = = = Actual # Samples Pretreatment Actual # Samples Posttreatment Total # Pre- and Posttreatment Analysis Samples # DPT with Post Samples > QL # of Post Samples with TCE > QL Total # of Analyses by Medium Note: The 2 indicates that DPT samples are obtained pre- and posttreatment. QL means Analyte analyzed for but undetected at the corresponding quantification limit." 30, 40, 45, 50, and 60 feet below the ground surface, five depths were in the treatment zone). The purpose of the 10-foot sample above the treatment zone was to confirm that the remediation did not contaminate it, and the purpose of the 60-foot sample below the treatment zone was to confirm no downward migration of the contamination was caused by the treatment. Because the sampling grids extended outside of the contaminated source areas, only 16 of the pretreatment LS DPT locations and 17 of the DB DPT locations were in the remediated source areas. This resulted in 5 16 = 80 and 5 17 = 85 potential preand posttreatment samples in the two source areas to evaluate the remediation of both the groundwater and soil. Exhibit 4 provides a summary list and breakdown of the sampling activities, including the potential samples and the actual samples recovered for analysis. Exhibit 4 indicates that the summary results presented below come from 299 pre- and posttreatment groundwater samples recovered out of a potential 330 samples and 329 pre- and posttreatment soil samples recovered out of a potential 330 samples. Each of the samples was analyzed by US EPA Method 8260 for the seven chlorinated VOCs listed above. Exhibit 4 indicates the large amount of analytical data that needed to be evaluated, understood, and presented. The presentation of this much data could be difficult and lengthy. Fortunately, the remediation results either met or exceeded expectations in that less than 5 percent ((14/628) 100 = 4.5 percent) of the posttreatment TCE results were above the quantification limit of the analysis defined as analyte analyzed for but undetected at the corresponding quantification limit. This fact itself is an important result in that it shows that the technology is capable of removing almost all of the contamination and that the iron remains reactive long enough to achieve results below the quantification limit. The fact that only 14 of the posttreatment samples were greater than the quantification limit also means that most of the posttreatment DPT samples showed complete removal at all five sample points in the treatment zone. This suggested that the 16 Remediation DOI: rem c 2010 Wiley Periodicals, Inc.

9 Exhibit 5. Summary TCE removal efficiency (RE) Launch Stand Groundwater Soil Pretreatment Posttreatment Pretreatment Posttreatment DPT Max Max Max Max Sample TCE (mg/l) TCE (mg/l) Difference TCE (mg/kg) TCE (mg/kg) Difference Location # QL varies QL = (mg/l) RE (%) QL varies QL = 0.1 (mg/kg) RE (%) , , , , Average Note: QL means Analyte analyzed for but undetected at the corresponding quantification limit." Average RE calculated from average values. posttreatment chemistry for each DPT location could be represented by a single value, either the quantification limit, or as the maximum value of the contamination at 20, 30, 40, 45, or 50 feet below ground surface, thus simplifying the data evaluation. This meant that in the few cases where the remediation did not achieve the quantification limit, the actual result would also be fairly represented. Thus, the pretreatment value used for comparison was also chosen as the maximum value in that DPT location. This evaluation approach, shown in Exhibit 5 through Exhibit 8, uses the maximum pretreatment and posttreatment values to calculate removal efficiency (RE). RE is defined as the maximum posttreatment value or quantification limit divided by the maximum pretreatment value in soil or groundwater in each soil boring times 100. This definition means that the best value of RE is limited by the posttreatment quantification limit, which was usually mg/l for groundwater and 0.1 mg/kg for soil in the posttreatment samples. While the objective of the project was to reduce the TCE in the contaminated source areas by a minimum of 80 percent, as determined by chemical analysis of pre- and posttreatment soil and groundwater samples, the remediation reduced all the chlorinated VOCs. Therefore, the results of both the TCE remediation and the total chlorinated VOC remediation are presented separately. c 2010 Wiley Periodicals, Inc. Remediation DOI: rem 17

10 Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology Exhibit 6. Summary TCE removal efficiency (RE) Deluge Basin Groundwater Soil Pretreatment Posttreatment Pretreatment Posttreatment DPT Max Max Max Max Sample TCE (mg/l) TCE (mg/l) Difference TCE (mg/kg) TCE (mg/kg) Difference Location # QL varies QL = (mg/l) RE (%) QL varies QL = 0.1 (mg/kg) RE (%) na na na Average Note: QL means Analyte analyzed for but undetected at the corresponding quantification limit." na = not applicable. Average RE calculated from averages. Launch Stand TCE Results Exhibit 5 lists the summary pre- and posttreatment LS TCE soil and groundwater analytical data for the 20- to 55-foot treated depth interval. Exhibit 5 shows that the groundwater has an overall TCE removal efficiency of percent for remediated cells. The exhibit also shows that the soil TCE RE was percent for remediated cells. The test results for posttreatment analyses of 10 of 16 groundwater DPT locations and 15 of 16 soil DPT locations have, as the highest concentration, the quantification limits of mg/l and 0.1 mg/kg, respectively. This demonstrates that the combined thermal and ZVI technology has removed almost all the TCE. Deluge Basin TCE Results Exhibit 6 lists the summary pre- and posttreatment DB TCE soil and groundwater analytical data. The posttreatment analytical results maximum for both media are at the 18 Remediation DOI: rem c 2010 Wiley Periodicals, Inc.

11 quantification limit, except for DPT sample location 13 groundwater, which has a TCE concentration of 9.9 mg/l in the sample taken from a depth of 30 feet, and mg/l in the sample taken at a depth of 40 feet. These are the only results in 299 posttreatment TCE groundwater analyses (LS and DB) that are not less than mg/l. A review of all the 299 posttreatment TCE groundwater results indicates that only 13 analyses are greater than the quantification limit of mg/l. A careful review of the specific analysis with the chemical analyst did not reveal any problems or potential errors with the location 13 sample. The possibility exists that the result was caused because the ZVI was not mixed in well enough, or that there was a problem with the ZVI slurry injection for this cell. A review of the recorded operational data of ZVI slurry flow did not reveal any problems but that is not conclusive. At this point, the most likely reason for this 9.9 mg/l result and even the 40-foot mg/l result appears to be in the injection and/or mixing processes. Unfortunately, neither the 45-foot nor the 50-foot groundwater samples were recovered from this DPT location, so they cannot be used to assist in the evaluation. The soil samples, which come from a separate DPT, provide no information except that the analysis is below the quantification limit. Including DPT 13, Exhibit 6 shows an overall RE of percent for TCE from the DB groundwater. Launch Stand Total Chlorinated VOC Results Exhibit 7 lists the summary pre- and posttreatment LS total chlorinated VOC analytical data for soil and groundwater. The overview of the test results is similar to that found with TCE alone, in that the posttreatment data are almost always nondetect for the 20- to 50-foot treated depth interval. This exhibit shows that the groundwater has an overall total chlorinated VOC removal efficiency of percent. The exhibit also shows that the soil total chlorinated VOC RE was percent. Deluge Basin Total Chlorinated VOC Results Exhibit 8 lists the summary pre- and posttreatment DB total chlorinated VOC analytical data for soil and groundwater. The overview of the results is similar to that found with TCE, in that the posttreatment chemistry analyses values are almost always at the quantification limit for the 20- to 50-foot treated depth interval (i.e., in 11 DPT locations, all samples were nondetects for groundwater, and in 16 DPT locations, all samples were nondetect for soil). Exhibit 8 shows chlorinated VOC removal efficiencies of percent for groundwater (not including DPT 13) and percent for soil, close to the maximum possible, using the detection limit as the default value. A review of all the 299 posttreatment TCE groundwater results indicates that only 13 analyses are greater than the quantification limit of mg/l. Sampling Results Above and Below the Treatment Zone The 0 to 20 feet of overburden above the target treatment interval were not included in the treatment plan because this interval did not show TCE concentrations greater than 10 mg/kg. Pretreatment sampling indicated the presence of lower concentrations of TCE as well as lower concentrations of the other COCs and Freon 113. It was expected that actions relating to treating the targeted treatment interval would result in the treatment of the COCs and Freon 113 from this interval. Exhibit 9 lists the summary average pre- and posttreatment analytical data for the 10-foot depth interval for total chlorinated VOC for c 2010 Wiley Periodicals, Inc. Remediation DOI: rem 19

12 Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology Exhibit 7. Summary total chlorinated VOC removal efficiency (RE) Launch Stand Groundwater Soil Pretreatment Posttreatment Pretreatment Posttreatment DPT Max Max Max Max Sample 7 VOC (mg/l) 7 VOC (mg/l) Difference 5 VOC (mg/kg) 5 VOC (mg/kg) Difference Location # QL varies QL = (mg/l) RE (%) QL varies QL = (mg/kg) RE (%) , , , , , , , , Average Note: QL means Analyte analyzed for but undetected at the corresponding quantification limit." 5VOCs= TCE, PCE, VC, cis-1,2-dce, and Freon VOCs= 5VOC+ 1,1-DCE + trans-1,2-dce. Average RE calculated from averages. QL = = due to interferences. both groundwater and soil. For both the LS and DB, for the great majority of the samples, the data show a significant reduction of total chlorinated VOCs. The LS had about a 90 percent reduction in total chlorinated VOCs. This occurs in spite of very limited actual remediation directed to this interval. The overburden was treated with hot air during the first pass to assist the drilling into the cell and the last pass out of the cell, and often had steam applied during the last pass. Some treatment of the overburden is also assumed to occur during the source treatment activity, as air and steam possibly pass through the loose soil adjacent to the surface. The DB, which was remediated last, shows over 99 percent total chlorinated VOC removal because there was a conscious effort to apply the remediation to the 0- to 20-foot zone during passage through it. The result of the above described remediation activities on the overburden contamination is that the preand posttreatment analytical results for the 10-foot interval indicate that there is a measurable reduction of the total chlorinated VOCs caused by the treatment activities 20 Remediation DOI: rem c 2010 Wiley Periodicals, Inc.

13 Exhibit 8. Summary total chlorinated VOC removal efficiency (RE) Deluge Basin Groundwater Soil Pretreatment Posttreatment Pretreatment Posttreatment DPT Max Max Max Max Sample 5 VOC (mg/l) 5 VOC (mg/l) Difference 4 VOC (mg/kg) 4 VOC (mg/kg) Difference Location # QL varies QL = (mg/l) RE (%) QL varies QL = (mg/kg) RE (%) Average Note: QL means Analyte analyzed for but undetected at the corresponding quantification limit. 5VOCs= TCE, PCE, VC, cis-1,2-dce, and Freon VOCs= TCE, VC, cis-1,2-dce, and Freon 113 Average RE calculated from average values. directed toward the source. Therefore, this indicates no sign of upward migration or condensation of COCs. Exhibit 9 presents the summary average results for 31 of 32 posttreatment analytical data for the 60-foot depth interval groundwater and soil samples from both the LS and DB. These posttreatment concentrations actually show a statistical decrease in concentration from the pretreatment concentrations. In this they are consistent with preand posttreatment results from 12 DPT locations taken from nontreated areas (data not shown). However, one posttreatment soil value not included in the statistical analysis, 3,063 mg/kg, for DB sample location 7 is significantly increased from the pretreatment value of 0.2 mg/kg. The compound causing the 3,063-mg/kg increase is Freon 113, which was not a COC. The US EPA (1994) has evaluated the solubility of Freon 113 in water and recommends 170 mg/l as the solubility at 25 C. Because the 3,063 mg/kg in soil greatly exceeds the solubility of 170 mg/l, it is believed that this posttreatment soil sample contained undissolved Freon 113 (i.e., DNAPL). The pre- and posttreatment c 2010 Wiley Periodicals, Inc. Remediation DOI: rem 21

14 Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology Exhibit 9. Average pre- and posttreatment analysis of samples at 10 and 60 feet Total Chlorinated VOCs Groundwater (mg/l) Soil (mg/kg) QL = QL = Samples Pre Post Pre Post Launch Stand % Removed # DPT Samples # Samples at QL Deluge Basin # DPT Samples # Samples at QL Samples Pre Post Pre Post Launch Stand % Removed # DPT Samples # Samples at QL Deluge Basin % Removed # DPT Samples # Samples at QL QL = quantification limit. samples come from two separate DPT locations whose locations can be up to six feet apart. Thus, the cause of this single high value cannot be determined as downward migration from the treatment, or a preexisting DNAPL condition not present in the pretreatment soil sample. Based upon the analytical results for the 29 groundwater samples and the 29 other soil samples, the preponderance of evidence supports the hypothesis of a preexisting condition, and little likelihood of downward contaminant migration caused by the treatment. However, this result would then suggest that, in at least one location, the contamination extends deeper than was previously known. Estimated Amount Removed Using the GC Data The method used to estimate the approximate amount of VOCs removed during thermal treatment integrated the continuous off-gas total FID readings and flow rate of the off-gas to calculate the amount removed. The approach used the GC data for each cell to calculate the amount of each compound present and removed by the treatment. The procedure for calculating the amount removed was to average each treatment cell s two to four GC readings for each compound, and input them into the calculation algorithm. The limited number of GC readings means that the calculated removal amounts are only 22 Remediation DOI: rem c 2010 Wiley Periodicals, Inc.

15 Exhibit 10. Calculated thermal removal of chlorinated VOCs in pounds Vinyl Dichloro- Chloride ethylene Freon 113 TCE PCE Other Total Launch Stand 1, ,495 3, ,719 Deluge Basin , ,554 Total 1,426 1,009 6,231 4, ,272 approximate. The following analytes were identified during the GC analysis: vinyl chloride, cis-1,2-dce, TCE, PCE, Freon 113, and Other Compounds. The category of Other Compounds was present in minute amounts (less than 2 percent) and was assigned a molecular weight of 133 for the calculation. As shown in Exhibit 10, the calculated approximate removal was 13,272 lbs of chlorinated VOCs, which includes 4,235 lbs of TCE and 6,231 lbs of Freon 113. COST (2004 DOLLARS) The remediation contractor was paid $4.634 million to remediate 48,455 cubic yards, or $95.64 per cubic yard. This project was performed in Florida and was impacted by three hurricanes during the 2004 hurricane season. The project was also shut down for ten hours due to missile and shuttle launches. These facts resulted in delays, the cost of which is included in the $4.634 million. The cost for the time lost due to both causes is $284,731. This reduces the actual cost of construction to $4.349 million, or $89.76 per cubic yard. The $89.76 did not include any project oversight management or cost of the extensive analytical effort. CONCLUSIONS Based on field studies, it has been shown that the in situ thermal removal rate of TCE and other chlorinated VOCs from soil during thermal treatment using LDAs can be expressed as pseudo first-order. This fact explains the long remediation times required to achieve 98 percent or more removal by thermal treatment. It has also been shown that the removal rate of TCE and other chlorinated VOCs from soil by ZVI is also pseudo first-order and the iron is reactive for over one month and perhaps longer. Using the pseudo first-order removal rates obtained from field studies, an estimate of the cost of treatment of a TCE DNAPL site using the combined thermal and ZVI treatment was obtained and compared with the cost of thermal treatment alone. The combined approach was shown to cost about 57 percent of the thermal treatment alone. This result was then applied to an actual site remediation at Cape Canaveral Air Force Station in 2004 (see the Case Study section). The estimated cost of the construction part using the combined remediation was $92.90 per cubic yard. The actual construction cost was $89.76 per cubic yard for a 48,455-cubic-yard site. The close agreement between the estimate and actual cost demonstrates the usefulness of the approach and its application to real projects. c 2010 Wiley Periodicals, Inc. Remediation DOI: rem 23

16 Combined Thermal and Zero-Valent Iron In Situ Soil Mixing Remediation Technology For the depths that were treated, the LDA soil mixing using hot air and steam followed by ZVI had an average removal efficiency of 99.8 percent of the TCE and chlorinated VOCs from both the soil and groundwater at SLC-15 at the Cape Canaveral Air Force Station, using the quantification limit as the best value. In most cases, the posttreatment analyses were nondetect at the method quantification limit of 0.1 mg/kg for soil and mg/l for water, suggesting close to complete removal. Over 95 percent of the results met the Florida groundwater target cleanup levels (GTCLs) and soil target cleanup levels (STCLs) for all COCs. The remediation appears to confirm the approach of using combined thermal and ZVI technology to significantly improve the results and reduce the cost of remediation of chlorinated DNAPL source zones. The percent average RE in groundwater (DPT 13 location excluded) and percent RE in soil for TCE in the treated areas demonstrates that the remedy met the 80 percent removal criterion required to achieve soil cleanup target levels and a groundwater cleanup target level of mg/l for TCE within 68 years as stated in the CMS. REFERENCES BEM Systems, Inc. (2006). Remediation by In-Situ Steam and Iron Enhanced Soil Mixing Space Launch Complex 15, Solid Waste Management Unit C030 Cape Canaveral Air Force Station, Florida. Corrective Measures Implementation Report. HLA. (1989, March 8). Volume I Baseline Calibration and Testing Annex Terminal Site San Pedro, California. HLA Job No. 4273,020.11, Joseph R. Morabito and Donald W. Quigley. Moos, L. P. (1998, October). Optimization of soil mixing technology through metallic iron addition. Presented at the Tenth National Technology Information Exchange (TIE) Workshop, Willowbrook, Illinois. Novaterra, Inc. (1993). Final report to FMC, P. O. Number CA O Shea Parsons and Associates. (1994, November 28). Field pilot demonstration of the applicability of hot air/steam stripping for in-situ soil treatment of voc contaminated soils, Methode Plant, Harwood Heights, Illinois. Final Report, Novaterra Inc. U.S. Environmental Protection Agency (US EPA). (1991). Toxic treatments, in situ steam/hot-air stripping technology. Applications Analysis Report U.S. Environmental Protection Agency, EPA/540/A5-90/008. U.S. Environmental Protection Agency (US EPA). (1994). Chemical summary for Freon 113. Retrieved November 2, 2009, from freon.txt Phillip La Mori, PhD, is a senior scientist with FECC Corporation of Orlando, Florida, where he provided technical leadership for the combined LDA thermal and ZVI remediation project at SLC-15, Cape Canaveral AFS. He has spent the last 23 years working on the development of the LDA thermal remediation technology. Dr. La Mori has a BS in chemistry and an MA in geology from UCLA, and a PhD in materials science from Northwestern University. He has an MBA from Pepperdine University. Elgin Kirkland is a project engineer with FECC Corporation of Orlando, Florida, where he was responsible for the design, implementation, and operational procedures for the combined LDA thermal and ZVI remediation project at SLC-15, Cape Canaveral AFS. Kirkland has a BS in electrical engineering from the Georgia Institute of Technology. 24 Remediation DOI: rem c 2010 Wiley Periodicals, Inc.

17 Harlan Faircloth is the vice president of CORE Engineering & Construction, Inc. of Winter Park, Florida. His focus area associated with environmental remediation has been associated with chlorinated solvents, specifically DNAPL, for the last 15 years. He is currently working on several projects funded by the U.S. Air Force. Faircloth received his BS in civil engineering from Florida State University. Robert Bogert is a principal engineer with HydroGeologic, Inc. in Orlando, Florida. Bogert s focus is in the area of groundwater remediation, with emphasis on chlorinated hydrocarbons. Bogert received his BS and MS in environmental engineering from the University of Central Florida. Mark Kershner is a project manager for the USAF at Cape Canaveral Air Force Station. His main objective is to restore facilities at the installation where ground water and soil contamination has occurred through past operational practices. Kershner received his BS and MS in biological sciences from the University of Central Florida. c 2010 Wiley Periodicals, Inc. Remediation DOI: rem 25