MTBE Performance Summary for 21 Completed Pumpand Treat Projects

Technology(ies)

Pump-and-treat only

(groundwater) Pump-and-treat with air sparging and SVE Pump-and-treat with other technologies

Number of Projects Minimum

Initial MTBE Concentration (mg/L)

Final MTBE Concentration (mg/L)

1200

Median Project Duration

Median Maximum Minimum Median Maximum (months)

1800

8000

11,000 475,000

2070 68,400

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04-009, United States Environmental Protection Agency, Washington, DC, May 2004.

TABLE 24.18

MTBE Performance Summary for 62 Ongoing Pump-and-Treat Projects

MTBE Concentration Range

Greater than 100,000^g/L

Greater than or equal to 10,000 ng/L but less than 100,000 ^g/L Greater than or equal to 1000 ng/L but less than 10,000 ^g/L Greater than or equal to 100 ng/L but less than 1000 ^g/L Greater than or equal to 50 ng/L but less than 100 ^g/L Less than 50 ng/L

Number of Projects Reporting Initial MTBE Concentrations

4 11

Number of Projects with Last Reported MTBE Concentrations

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04—009, United States Environmental Protection Agency, Washington, DC, May 2004.

The data presented in Table 24.17 for 21 completed pump-and-treat projects (either alone or in combination with other technologies) show that MTBE concentration reductions in groundwater of >99% have been achieved in several projects. The median project duration for the 21 completed sites ranged from 1.5 to 5.5 years.

Treatment performance data for ongoing projects are shown in Tables 24.18 and 24.19, for pump-and-treat and drinking water treatment projects, respectively. Both types of projects treated groundwater with relatively high initial MTBE concentrations (>100,000 ^g/L). The available data show that 10 of 11 drinking water treatment projects achieved treated MTBE concentrations of <50 |ag/L, while the results for pump-and-treat were more widely distributed.

Table 24.20 provides a summary of treatment performance data for nine pump-and-treat projects that provided performance data for TBA. Initial TBA concentrations were as high as 17,000 ^g/L,

TABLE 24.19

MTBE Performance Summary for 12 Ongoing Drinking Water Treatment Systems

MTBE Concentration Range

Greater than 100,000^g/L

Greater than or equal to 10,000 ng/L but less than 100,000 ^g/L Greater than or equal to 1000 ng/L but less than 10,000 ^g/L Greater than or equal to 100 ng/L but less than 1000 ^g/L Greater than or equal to 50 ng/L but less than 100 ^g/L Less than 50 ng/L

Number of Projects Reporting Initial MTBE Concentrations

Number of Projects with Last Reported MTBE Concentrations

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04—009, United States Environmental Protection Agency, Washington, DC, May 2004.

TABLE 24.20

TBA Performance Data for Nine Pump-and-Treat Projects

Concentration Range

Greater than 100,000^g/L

Greater than or equal to 10,000 ng/L but less than 100,000 ^g/L Greater than or equal to 1000 ng/L but less than 10,000 ^g/L Greater than or equal to 100 ng/L but less than 1000 ^g/L Greater than or equal to 50 ng/L but less than 100 ^g/L Less than 50 ng/L

Number of Projects Reporting Initial Concentrations

Number of Projects with Last Reported Concentrations

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04—009, United States Environmental Protection Agency, Washington, DC, May 2004.

with most after-treatment concentrations <50pg/L. Due to the additional interest in TBA, a review of data for the 390 projects in the database as of April 2004 showed a total of 15 pump-and-treat projects reporting performance data for TBA. Most of these projects reported using the HiPOx process for the treatment of extracted groundwater, with additional projects using GAC treatment.

24.9.6 Costs of Pump-and-Treat for Treatment of MTBE

Project cost data were reported for 43 of the 100 pump-and-treat projects in the dataset; these include data for both ongoing and completed projects. In most cases, the components that make up the project costs were not reported. However, it is likely that these costs incorporate different components, such as treatment, monitoring, design, oversight, and health and safety. Table 24.21

TABLE 24.21

Cost Summary for 43 Pump-and-Treat and Drinking Water Treatment Projects (2004 USD)a

TABLE 24.21

Cost Summary for 43 Pump-and-Treat and Drinking Water Treatment Projects (2004 USD)a

Total Cost Range (USD)

Median Total

Number of

Reported Cost

Technologies

Projects

Minimum

Maximum

(USD)

Pump-and-treat only

15

71,900

1,120,000

500,000

Pump-and-treat with air sparging and SVE

9

96,400

567,000

327,000

Pump-and-treat with air sparging

1

672,000

672,000

672,000

Pump-and-treat with SVE

7

160,000

624,000

339,000

Pump-and-treat with other technologies

1

65,000

65,000

65,000

Drinking water treatment

10

119,000

4,000,000

245,000

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04—009, United

States Environmental Protection Agency, Washington, DC, May 2004. a 2009 USD = 1.11 x 2004 USD.

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04—009, United

States Environmental Protection Agency, Washington, DC, May 2004. a 2009 USD = 1.11 x 2004 USD.

summarizes the cost information from these 43 projects, broken down by type of other technologies used in conjunction with pump-and-treat.

Another source reported the unit costs of pump-and-treat (based on only capital cost) as <USD5.28/m3/yr (USD20/1000 gallons/yr) for projects treating >75,700m3/yr (20MG/yr) of groundwater, and unit costs (based on O&M cost) as <1.32m3/yr (USD5/1000 gallons/yr) for projects treating >75,700 m3/yr (20MG/yr) of groundwater.87 These unit costs represent treatment costs for the use of pump-and-treat in general, and are not specific to the treatment of MTBE and other oxygenates. In another source, the cost of pump-and-treat is generally considered to be worse than the average of the costs for remediation technologies for treatment of contaminated groundwater.34

24.9.7 Factors That Affect the Performance and Cost of Oxygenate Treatment Using Pump-and-Treat

Because of the high water solubility of oxygenates, groundwater extraction may be effective in removing a significant mass of these contaminants. Key factors that affect the performance and cost of the extraction component of a pump-and-treat system include

1. The depth and accessibility of the plume; site hydrogeologic characteristics, such as aquifer permeability.

2. The hydraulic conductivity and flow gradient.

3. Remedial goals for the site.

4. The presence or prior removal of the contaminant source.

If groundwater contamination is deep underground or is beneath areas (such as buildings and rail lines) where conventional vertical wells cannot be placed, innovative drilling techniques or more powerful extraction pumps may be required. Alternatively, shallow and accessible groundwater may be easily extracted using simple collection trenches. Hydrogeologic characteristics will define the number, design, and spacing of extraction points, with tighter formations typically requiring more extraction points for a given area. Groundwater flow characteristics and the number and spacing of wells will be the basis for determining the flow rate of groundwater that needs to be extracted to achieve the desired capture zone. Cleanup goals are also a factor. On-site containment goals may require only pumping from the downgradient edge of a plume, whereas a goal of complete aquifer restoration may require more well points pumping at a higher extraction rates.

One of the most significant factors that affect cost and performance is whether the contaminant source area at a site is present. If a contaminant source area is allowed to continue to contribute to the groundwater plume, groundwater extraction may be required for much longer periods of time than if the contaminant source is removed or treated prior to beginning groundwater pump-and-treat. Because they are relatively water soluble, oxygenates tend to dissolve in groundwater rather than form NAPL. When they do form NAPL, they float rather than sink, and thus form an LNAPL. Thus, removal or treatment of MTBE and other oxygenate source areas can be more straightforward than for other contaminants such as chlorinated solvents.

24.9.8 Advantages and Limitations

The advantages of applying pump-and-treat are as follows3440:

1. The properties of MTBE (high water solubility and low organic/water partition coefficient) make it amenable to groundwater extraction.

2. Pump-and-treat can be used to remediate an aquifer or to provide for hydraulic containment.

The limitations to applying pump-and-treat are as follows34,40:

1. Long-term operation may be required to achieve remediation goals for large plumes, complex hydrogeologies, or if an active source remains in place.

2. The cost of constructing, operating, and maintaining treatment systems is considered to be relatively high.

3. Biofouling or mineral precipitation in extraction wells or treatment processes can reduce system performance.

24.9.9 Example Projects

The following two project descriptions incorporate examples of completed, full-scale applications of pump-and-treat technology to MTBE-contaminated sites.

24.9.9.1 Pump-and-Treat at Christy Station, North Windham, Maine

MTBE was detected in groundwater at Christy Station, located in North Windham, Maine, soon after the fuel station was constructed in 1997. Between May and June 1998, a full-scale cleanup was performed using a pump-and-treat system that consisted of two extraction wells operating at a combined 3 gpm. The extracted groundwater was treated using shallow tray aeration followed by GAC, and the treated groundwater was disposed off-site. Initial concentrations of MTBE in groundwater were as high as 6000 pg/L, but MTBE concentrations stabilized at 300 pg/L with the operation of the pump-and-treat system. The goal was to reduce MTBE in the aquifer to concentrations <500pg/L. Following aeration, MTBE in the extracted groundwater was reduced to concentrations ranging from 10 to 30pg/L, and following GAC adsorption, MTBE was reduced to concentrations of <2 pg/L. A performance standard for extracted groundwater was not identified. The cost assessment for the remediation was USD200,000, the capital cost for the pump-and-treat system was USD60,000, and the O&M cost was USD11,000 for 1 month of operation.91

24.9.9.2 Pump-and-Treat and sVE at service station NH-B, somersworth, New Hampshire

During inventory measurements in September 1996, a gasoline station in New Hampshire, referred to as Service Station NH-B, detected a release of 7950 L (2100 gallons) of gasoline. Soil at the site consists of 1.22-2.44m (4-8ft) of sandy fill overlying 0.61-3.97m (2-13 ft) of glacial till, with bedrock occurring at 3.04-4.58 m (10-15 ft) below the ground surface. The depth of the groundwater ranges from 1.52 to 4.58 m (5-15 ft) below the ground surface. The site is characterized by fractured bedrock and a hydraulic gradient of 30m/1000m (30 ft /1000 ft). Remedial activities included the removal of three USTs: 782T (860tons) of contaminated soil, 102 m3 (27,000gal) of groundwater containing 71.7kg (158 lb) of hydrocarbons, and 454L (120 gal) of LNAPL. A pump-and-treat system consisting of seven recovery wells screened to bedrock and operating at a total flow rate of 7.5 gpm was implemented. The extracted groundwater was treated using oil/water separation, filtration, and air stripping. The air stripper contained a 7 horse power (HP) blower that operated at 1000 scfm. Maximum concentrations in the influent to the air stripper were 1,670,000 pg/L of MTBE and 439,000 pg/L of BTEX. SVE was conducted using 11 vertical wells and 4 horizontal wells, and a 11.2kW (15 HP) blower operated at standard 8.5m3/min (300 scfm) and 89-127 mm (3.5-5 in) of mercury. No vapor treatment was performed. As of January 2000, the pump-and-treat system had removed 1950 kg (4300 lb) of hydrocarbons and SVE had removed (2976 lb) of hydrocarbons. Enhanced bioremediation is currently performed at the site. The current total remediation cost for this site is USD590,000.31

24.10 TREATMENT OF EXTRACTED GROUNDWATER USED IN

PUMP-AND-TREAT AND DRINKING WATER TREATMENT SYSTEMS

24.10.1 Ground Treatment of Extracted Groundwater

The aboveground (ex situ) treatment technologies used for extracted groundwater are applied both in pump-and-treat systems and drinking water treatment systems. In general, the methods for extraction of groundwater are not linked to or limited by the type of aboveground treatment technologies. This section focuses on aboveground treatment of extracted groundwater, for both pump-and-treat and drinking water treatment, while the previous section focuses on groundwater extraction. This section also includes specific examples of treatment applications used in pump-and-treat and drinking water treatment systems.

The general types of aboveground technologies that have been used for treating extracted groundwater that is contaminated with MTBE and other oxygenates include the following90:

1. Air Stripping—Processes in which contaminants are volatilized from water to air in an engineered system, such as a packed tower92; treatment of the resulting contaminated vapor phase may also be required.

2. Adsorption—Processes in which contaminants are adsorbed from water onto a medium, such as GAC or resin, as driven by equilibrium forces.93,94

3. Chemical Oxidation—Processes in which contaminants are sequentially oxidized to less toxic products through the introduction of chemical oxidants79 or the creation of oxidizing conditions through other means, such as using UV radiation, electrical stimulation, or cavitation.

4. Biotreatment—Processes in which contaminants are biodegraded in an engineered system, such as an attached growth9596 or an activated sludge bioreactor.97

24.10.2 Effect of the Properties of MTBE and Other Oxygenates on Treatment

The properties of MTBE and other oxygenates affect their relative treatability in extracted water using different technologies. Air stripping, adsorption, oxidation, and biotreatment technologies are technically capable of and have been used to treat water contaminated with some or all of the fuel oxygenates. However, the properties of oxygenates versus other fuel contaminants such as BTEX, and the different properties of ether-based versus alcohol-based oxygenates, are important factors to consider when selecting and designing an aboveground treatment system. The effect of fuel oxygenates properties on treatment using each of the commonly used technologies is briefly discussed below.

24.10.2.1 Air Stripping

Similar to air sparging, air stripping relies on the volatilization of contaminants from the aqueous to the vapor phase. The property that shows the extent to which this transfer can take place during air sparging is the Henry's law constant, which represents the extent to which a contaminant will partition between the dissolved state and the vapor state under equilibrium conditions.92 A contaminant with a greater Henry's law constant is more readily stripped from water during air stripping than one with a lesser Henry's law constant. The discussion related to the effect of the properties of fuel oxygenates on air sparging is also applicable to air stripping. As discussed in that section, all common fuel oxygenates (with the possible exception of DIPE) are less readily stripped than BTEX (based on their Henry's law constants). Because of this, air stripping systems designed to treat oxygenates often are designed to allow for more air/water contact time than a system designed to treat BTEX constituents at the same concentrations. This is typically accomplished by the use of a larger stripping tower or packing material with a higher specific surface area. As an illustration, based on their ranges of Henry's law constants, ether-based oxygenates would require 5-10 times more air contact than BTEX to volatilize the same concentration of contaminant. Because of this, an air stripping system designed to treat BTEX may not be capable of adequately addressing ether-based oxygenates. Alcohol-based oxygenates are even more difficult, and in some cases impractical, to strip from groundwater.

The properties of oxygenates may also affect the applicability and design of a system to treat the contaminated vapor effluent resulting from air stripping, if one is required.

24.10.2.2 Adsorption

In adsorption processes, contaminated water is contacted with a solid adsorption medium, such as GAC or resin. Based on their equilibrium properties relative to the specific adsorption medium, contaminants will partition from the water to the solid until the system reaches equilibrium.93 The maximum concentration of a given contaminant that can be adsorbed is dependent on

1. The type of adsorption medium used.

2. The specific contaminant and its concentration.

3. Concentrations of other substances in the water that may competitively adsorb.

4. Parameters such as temperature.

Although the actual treatability of a contaminated water stream is dependent on all of these parameters, the relative treatability of MTBE and other oxygenates can be estimated based on their relative tendency to partition from water to an organic matrix. One common measure of this tendency is the organic carbon-based partition coefficient. Generally, contaminants with lower partition coefficients are less amenable to treatment using GAC or resin adsorption. Figure 24.7 shows the ranges of partition coefficients for ether- and alcohol-based coefficients and BTEX.

As shown in Figure 24.7, the average partition coefficients for ether- and alcohol-based oxygenates are much lower than for BTEX. Based on this, it would be expected that adsorption systems

Ether oxygenates

MTBE ETBE TAME DIPE

Alcohol oxygenates

Alcohol oxygenates

TBA Ethanol Methanol Benzene Toluene Ethyl- Xylenes benzene

FIGURE 24.7 Relative ranges of partition coefficients for fuel oxygenates and BTEX. (Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04-009, United States Environmental Protection Agency, Washington, DC, May 2004.)

designed only to treat BTEX may not be able to effectively address ether-based oxygenates, and that the lower molecular weight alcohol-based oxygenates would not be amenable to adsorption.

24.10.2.3 Chemical Oxidation

MTBE and other oxygenates are susceptible to degradation through oxidation reactions. If a sufficient amount and strength of oxidant and enough time are provided, all ether- and alcohol-based fuel oxygenates can be destroyed via chemical oxidation. However, the amount and type of oxidant that is necessary for the treatment of MTBE or other oxygenates at a given site will depend on numerous factors beyond the amount of contaminant present.

There are also technologies that use electrical or other forms of energy to generate oxidizing and reducing radicals in aqueous solution and thereby destroy contaminants such as MTBE and other oxygenates. These technologies include E-beams and ultrasound. High-energy E-beams induce radiolysis (radiation-driven splitting) of water to form oxidizing hydroxyl radicals (OH^) as well as reducing hydrated electrons (e-q) and hydrogen (H^). Ultrasound technology relies on the breakdown of water molecules into oxidizing and reducing free radicals (OH and H^) under the intense heat and pressures generated during ultrasound-induced cavitation. Both of these technologies have been demonstrated, on the pilot scale, in application to groundwater contaminated with MTBE.83

24.10.2.4 Biotreatment

MTBE and other oxygenates are susceptible to biodegradation. For in situ biological treatment, the primary focus is on creating conditions that are conducive (sufficient electron acceptors, nutrients, microbes, and cometabolite) to stimulate biodegradation. With aboveground biotreatment, the creation of these conditions is simpler because the treatment is occurring in a defined, controlled, and accessible system. However, the relative biodegradability of different contaminants, such as ether-and alcohol-based oxygenates, is an important consideration in the selection and design of a biotreat-ment component for a pump-and-treat system.

24.10.3 Technologies Used for Aboveground Treatment of Oxygenates

One or more aboveground technologies are typically used to treat extracted groundwater before reinjection or discharge to surface water or the sewer. Multiple technologies, or treatment trains, are commonly used at sites contaminated with MTBE and other oxygenates (e.g., air stripping followed by GAC polishing). A significant amount of literature has been dedicated to the design of above-ground treatment systems. Some of the key considerations relevant to treatment of MTBE and other oxygenates in extracted groundwater are summarized below.90

24.10.3.1 Air Stripping

1. A typical volumetric ratio of air to water for the effective treatment of MTBE is at least 150-200 parts air to one part water, greater than that required to solely remove BTEX.

2. Most states require the capture and treatment of air stripper off-gas. Typical off-gas treatment technologies that are applicable to MTBE and other oxygenates are adsorption, thermal treatment, and biotreatment.

24.10.3.2 Adsorption

1. Because of their water solubility and low partition coefficients, MTBE and other oxygenates are difficult to adsorb on GAC. Other, more preferentially adsorbed, contaminants in groundwater may also reduce the capacity of GAC to remove MTBE and other oxygenates. In some cases, the more absorbable contaminants may even displace MTBE or other oxygenates that are already adsorbed. In addition, natural groundwater constituents, such as iron, manganese, or organic carbon, may also consume adsorption capacity. Because of this, two or more GAC beds are often used in series so that contaminant breakthrough can be monitored in the first bed without risking the discharge of contaminants into the effluent. 2. Certain types of adsorption media have been shown to preferentially adsorb certain contaminants. For example, research has shown that, in some cases, coconut shell-based GAC removes MTBE better than typical coal-based GAC. In addition, synthetic resins have been developed to preferentially adsorb some oxygenates, such as TBA, that are less absorbable by GAC. Often, adsorption processes also take advantage of the biodegradabil-ity of MTBE and other oxygenates by promoting bacterial growth on the adsorption.

24.10.3.3 Chemical Oxidation

1. For the ex situ treatment of groundwater contaminated with MTBE or other oxygenates using chemical oxidation, most systems rely on processes that generate hydroxyl radicals, which are capable of completely oxidizing organic material to primarily carbon dioxide and water. Approaches that have been used to generate hydroxyl radicals for the oxidation of MTBE and other oxygenates include the following:

• Combination of hydrogen peroxide and UV light.

• Combination of hydrogen peroxide and ferrous iron (Fenton's chemistry).

• Combination of ozone and UV light.

• Combination of ozone and hydrogen peroxide (such as in the HiPOx system).

• Ultrasonic cavitation (using high-energy ultrasonic vibrations to generate high temperatures and pressures).

• E-beam (using high-energy electrons to split water molecules into free radicals).

2. The incomplete oxidation of MTBE and other oxygenates may result in the generation of undesirable intermediate products, such as TBF, TBA, and acetone. The design (oxidant dosage and contact time) should be adequate to achieve complete oxidation or additional treatment processes, such as GAC, may be used to address residual contamination.

3. The presence of other oxidant-consuming constituents in the feed water, such as iron, natural organic carbon, carbonates, bromide, and other contaminants, may require pretreat-ment of the feed stream, additional oxidant dosage, or more contact time to adequately destroy the MTBE and other oxygenates.

24.10.3.4 Biotreatment

1. Biological treatment systems that incorporate mechanisms to retain sufficient biomass are generally applicable to groundwater containing lower concentrations of contaminants. These systems typically consider the limited supply of carbonaceous material (food) to sustain a viable population of degrading microbes. Attached growth bioreactors, and suspended growth bioreactors that incorporate membrane-based biomass separation systems,98 are generally appropriate for these applications.

2. Because the biological degradation rate of MTBE has been observed to be slower than for other common contaminants, such as BTEX, MTBE will typically be the rate-limiting contaminant that determines the necessary hydraulic retention time for a mixed contaminant system, since it will typically be the slowest to degrade.

3. Due to the difficulties involved in maintaining an adequate microbial mass applied to low concentrations of MTBE or other oxygenates in groundwater, treatability studies are often performed to confirm that extracted groundwater can be adequately treated in a bioreactor.

Recently, some efforts have been made to combine treatment technologies that employ adsorption and biological treatment. Biological treatment technologies that use naturally occurring microorganisms have successfully treated MTBE-contaminated groundwater. However, these microorganisms do not grow efficiently on MTBE, and thus require a microbial retention mechanism. GAC serves as an attachment medium that immobilizes microbes.93 Other retention mechanisms include permeable barrier membranes and PRBs. GAC is often promoted for its capability for absorbing on environmental pollutants. However, in the presence of BTEX, the tendency of MTBE and TBA to adsorb on carbon is lowered. Consequently, GAC may not offer substantial adsorption capacity for MTBE or TBA.

More detailed information relevant to the application of aboveground treatment at sites contaminated with fuel oxygenates and in general is available in the literature.88-90

24.10.4 Types of Projects That Used Aboveground Treatment of Extracted Groundwater

From the 323 projects in the MTBE Treatment Profiles Website dataset, 85 projects were identified where MTBE in groundwater was remediated using pump-and-treat along with 15 additional projects that treated MTBE in drinking water (collectively referred to as pump-and-treat projects). Seventy of these projects reported the type of aboveground treatment used, as shown in Table 24.22. The projects in the dataset used adsorption most frequently, either alone or in combination with other technologies. Nine of the 39 projects that used adsorption reported information about the type of adsorption media that was used in the treatment system. Bituminous carbon was used for four projects; coconut shell carbon for two projects; and organoclay carbon, resin, or biologically enhanced GAC for one project each. Air stripping (21 projects) and oxidation (22 projects) were also used frequently. Three of the air stripping projects reported that catalytic oxidation was used for off-gas treatment. No other projects reported information about off-gas treatment. Two of the air stripping projects reported air-to-water ratios; they were 150:1 and 200:1. Most21 of the oxidation projects reported the type of oxidation that was employed. Hydrogen peroxide/ozone was used for 16 projects; hydrogen peroxide/UV was used for three projects; hydrogen peroxide alone and ultrasonic cavitation were used for one project each.

As an example of aboveground treatment, a site in Mission Viejo, California had an operating DPE system withdrawing soil vapor and groundwater for treatment with oxidation and bioreaction,

TABLE 24.22

Aboveground Treatment Technologies Used at 70 Groundwater Pump-and-Treat Remediation and Drinking Water Treatment Projects

Aboveground Treatment Number of Number of Drinking Total Number of

Technology Employed Pump-and-Treat Projects Water Treatment Projects Projects

TABLE 24.22

Aboveground Treatment Technologies Used at 70 Groundwater Pump-and-Treat Remediation and Drinking Water Treatment Projects

Aboveground Treatment Number of Number of Drinking Total Number of

Technology Employed Pump-and-Treat Projects Water Treatment Projects Projects

Air stripping only

8

3

11

Air stripping with adsorption

9

1

10

Adsorption only

18

8

26

Adsorption with oxidation

1

2

3

Oxidation only

19

0

19

Biotreatment only

1

0

1

Total

56

14

70

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04—009, United States Environmental Protection Agency, Washington, DC, May 2004.

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04—009, United States Environmental Protection Agency, Washington, DC, May 2004.

respectively. Initially, the major contaminant was TBA, with a lesser concern about MTBE. However, as the formation dried out and more porosity developed, the concentrations of BTEX were found to be increasing. Site consultants considered that if the BTEX exceeded the TBA/MTBE concentration for a long time period, then the biomass would prefer the BTEX and would lose its ability to consume TBA/MTBE. To address this concern, a "sacrificial" carbon canister containing 200 lb of coconut carbon was installed ahead of the bioreactor to remove the BTEX while allowing the TBA/ MTBE to pass through and be remediated in the bioreactor. While feeding approximately 5.7 L/min (1.5 gpm) of a stream containing approximately equal concentrations of TBA/MTBE and BTEX, the stream exiting the carbon canister showed breakthrough for TBA in 2 days, the first time a sample was taken. The TBA entering and leaving the carbon canister showed no decrease in concentration after the first week. The BTEX took about 45 days to breakthrough.99

24.10.5 Performance of Technologies in Aboveground Treatment of Oxygenates

Of the projects in the database, four completed projects using pump-and-treat provided performance data for initial and final MTBE concentrations. Median concentrations were 27,000 pg/L for before treatment and <1 pg/L for after treatment. The median project duration for these projects was 14 months. Note that these treatment performance figures are based on the data provided by project managers and others in the source materials used to prepare the treatment profiles website.

24.10.6 Costs of Pump-and-Treat for Treatment of MTBE

Project cost data were reported for 12 pump-and-treat projects in the dataset based on type of above-ground treatment used; these include data for both ongoing and completed projects. In most cases, the components that make up the project costs were not reported. However, it is likely that these costs incorporate different components, such as treatment, monitoring, design, oversight, and health and safety. Table 24.23 summarizes the cost information from these 12 projects, broken down according to the type of aboveground treatment technologies used.

Table 24.24 summarizes ranges of projected unit costs90 for the treatment of different flow rates—3.78, 37.8, and 378 L/s (60, 600, and 6000 gpm) of MTBE-contaminated water using air stripping, oxidation, and adsorption technologies. These results show that air stripping is less costly than either adsorption or oxidation, and that there are economies of scale with treatment of relatively larger quantities of water.

TABLE 24.23

Cost Summary for Pump-and-Treat by Aboveground Treatment Technologies (2000 USD)a

Total Cost Range (USD)

Median Total Reported Cost (USD)

545,000 339,000

Aboveground Treatment Technologies

Air stripping only Air stripping with adsorption Adsorption only Total

Number of Projects

3 12

Minimum

74,000 216,000

160,000 450,000

Maximum

1,200,000 1,180,000

624,000 3,000,000

180,000 1,060,000

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04-009, United

States Environmental Protection Agency, Washington, DC, May 2004. a 2009 USD = 1.22 x 2000 USD.

TABLE 24.24

Estimated Range of Unit Costs for Aboveground Treatment Technologies (2000 USD)a

Technology Category

Air stripping

Adsorption

Oxidation

USD/3.78 m3 Treated (3.78 L/s system)

Minimum

Maximum

USD/3.78 m3 Treated (37.8 L/s system)

Minimum

Maximum

USD/3.78 m3 Treated (378 L/s system)

Minimum

Maximum

Source: Adapted from U.S. EPA, Technologies for Treating MTBE and Other Fuel Oxygenates, EPA 542-R-04-009, United

States Environmental Protection Agency, Washington, DC, May 2004. a 2009 USD = 1.22 x 2000 USD.

24.10.7 Factors That Affect the Performance and Cost of Aboveground Treatment of Oxygenates

Once water contaminated with MTBE or other oxygenates has been extracted, the relative tendency to remain in the aqueous phase can make aboveground treatment more complicated than the treatment of other contaminants, such as BTEX. Key factors that may affect the cost and performance of aboveground treatment include

1. The concentrations of oxygenates and other contaminants.

2. Extracted groundwater flow rates.

3. Other groundwater chemistry parameters that may interfere with treatment, such as natural organic carbon, iron, manganese, hardness, alkalinity, and pH.

4. Effluent water and off-gas discharge standards.

These factors may influence the specific aboveground treatment technology that is selected, the possible need for multiple aboveground treatment processes (treatment trains), and the need for pretreatment of groundwater or posttreatment of off-gas. Also, as with the extraction component, the presence of an active source area may result in the need for long-term operation of aboveground treatment systems.

24.10.8 Treatability and Limitations

The treatability of MTBE and other oxygenates using aboveground treatment is as follows1:

1. In general, aboveground treatment systems can be more readily controlled and monitored to optimize the removal of MTBE and other oxygenates than in situ treatment systems.

2. Air stripping—Treatment of ether-based oxygenates may require greater air-to-water ratios than treating only BTEX; treatment of alcohol-based oxygenates may be impractical.

3. Adsorption—Ether-based oxygenates are less readily removed than BTEX using GAC and some alcohol-based oxygenates may not be adsorbable at all; synthetic resins that more selectively remove fuel oxygenates are available.

4. Chemical oxidation—Fuel oxygenates can be destroyed using hydroxyl radical oxidation; the oxidant dosage and contact time are based more on overall oxidant demand of extracted groundwater than on types of oxygenate contaminants.

5. Biotreatment—Fuel oxygenates can be biodegraded given adequate retention time in a bioreactor with a sufficient mass of conditioned microbes.

The limitations to applying aboveground treatment are as follows3440:

1. The cost of constructing, operating, and maintaining treatment systems is considered to be relatively high.

2. Biofouling or mineral precipitation in extraction wells or treatment processes can reduce system performance.

24.10.9 Example Projects

The following two project descriptions relate to demonstrations of innovative ex situ treatment systems for groundwater contaminated with MTBE and other oxygenates.

24.10.9.1 Biodegradation of MTBE in a High Biomass Retention Reactor

Demonstration study at Pascoag, Rhode Island: a pilot-scale specialized Biomass Concentrator Reactor (BCR), an activated sludge-type bioreactor that uses a membrane-based biomass separation system, was tested for the aerobic biodegradation of MTBE. The BCR design encompasses an aeration chamber housing a high surface area porous polyethylene membrane system that retains all of the biomass within the aeration chamber. Its simple operation and low maintenance requirements may render it economically more feasible than other water treatment technologies. The water flux through the membrane relies completely on gravity. The system includes 30 membrane compartments, with each one removable for cleaning.

The BCR was used in a demonstration at a Pascoag, Rhode Island abandoned gasoline station where substantial amounts of gasoline had leaked into the groundwater, contaminating it with MTBE, TBA, TAME, TAA, DIPE, TBF, acetone, methanol, ethanol, and BTEX. The objective of the study was to demonstrate the effectiveness of the BCR in treating MTBE, other oxygenates, and BTEX to near or below detectable limits. The BCR was operated at the Pascoag site for nearly 6.5 months up to 18.9 L/min (5 gpm). Average influent concentrations of VOCs were MTBE, 6500 pg/L; TBA, 69 pg/L; TAME, 1130 pg/L; TAA, 130 pg/L; DIPE, 36 pg/L; TBF, 29 pg/L; acetone, 480 pg/L; methanol, 300 mg/L; and the sum of BTEX, 3700 mg/L. Effluent concentrations were very low despite continual flow interruptions from the source wells. Over the entire project, including flow interruptions and non-steady-state flow conditions, MTBE in the effluent averaged near 9 pg/L (<5 pg/L during 5 gpm steady-state flow conditions without flow interruptions); TBA, 0.5 pg/L; TAME, 1.4 pg/L; TAA, 0.06 pg/L; DIPE, 0.05 pg/L; TBF, 0.02 pg/L; acetone, 6.6 pg/L; methanol, 2 pg/L; and sum of BTEX, 1.3 pg/L. Nonpurgeable organic carbon (NPOC) was reduced by close to 50%.100

24.10.9.2 Demonstration of the HiPOx Oxidation Technology for the Treatment of MTBE-Contaminated Groundwater

The HiPOx technology is an advanced oxidation process that incorporates high-precision delivery of ozone and hydrogen peroxide to chemically destroy organic contaminants while minimizing bromate formation. The MTBE-contaminated groundwater (initial MTBE concentration of 748 pg/L) from the Ventura County Naval Base in Port Hueneme, California was used to evaluate this technology. Due to extremely high concentrations of bromide in the feed water (1.3 mg/L) and the desire to limit bromate formation, a pilot-scale system was operated with 630 ozone injector ports in series, as part of U.S. EPA's Superfund Innovative Technology Evaluation (SITE) program.

The HiPOx process achieved >99.9% reduction in MTBE concentration and easily met the treatment goal of reducing the concentration of MTBE to below 5 pg/L. However, significant concentrations of MTBE degradation intermediates and oxidation by-products were present in the final effluent. TBA was produced early during the chemical oxidation process. Its concentration was diminished by further oxidation, reaching below its regulatory limit of 12 pg/L in two of the three runs. Acetone was generated and a sizable percentage was left unoxidized in the final effluent (>100 pg/L). Bromate concentrations in the effluent exceeded the drinking water standard of 10 pg/L for all three runs.

A model calculation showed that the HiPOx system may have been fully successful in limiting bromate formation under the chosen oxidant doses if the influent bromide concentration was 0.56 mg/L or less. Since a bromide concentration of 0.56 mg/L is still extremely high for a drinking water source, the HiPOx system appears to hold promise for destroying MTBE and its oxida-tive by-product TBA while controlling bromate formation, even in waters that have high bromide concentrations.101

24.10.9.3 Application of High-Energy E-Beam to the Treatment of MTBE-Contaminated Groundwater

A demonstration of the high-energy electron beam (E-beam) technology applied to groundwater contaminated with MTBE and with BTEX was conducted at the Naval Base Ventura County, Port Hueneme, California, as part of U.S. EPA's SITE program. The E-beam technology destroys organic contaminants in groundwater through irradiation with a beam of high-energy electrons; the oxidizing radicals that are generated by the E-beam react with and destroy organic contaminants, including MTBE and its breakdown products.

Results of two weeks of steady-state operation at an E-beam dose of 1200krads indicated that MTBE and BTEX concentrations in the effluent were reduced by >99.9% from influent concentrations that averaged over 1700 pg/L MTBE and 2800 pg/L BTEX. Further, the treatment goals for the demonstration, which were based on drinking water regulatory criteria, were met for all contaminants except TBA, a degradation product of MTBE. Dose experiments indicated that TBA was not consistently reduced to below the treatment goal of 12 pg/L although the results indicated that TBA by-product formation decreased as the dose increased. Acetone and formaldehyde were the two most prevalent organic by-products that were formed by E-beam treatment, with mean effluent concentrations during the two-week steady-state testing of 160 and 125 pg/L, respectively. Bromate was not formed during E-beam treatment.

An economic analysis of the E-beam treatment system indicated that the primary costs are for the E-beam equipment and for electrical energy. The estimated cost ranged from over USD10.6/m3 (USD40/1000 gallons) fora small-scaleremedial application to aboutUSD0.26/m3 (USD1/1000 gallons) for a larger-scale drinking water application.102

24.11 PHYTOREMEDIATION, PRBs, AND THERMAL TREATMENT 24.11.1 Other Technologies Used in Treatment of MTBE and Other Oxygenates

In addition to the technologies discussed earlier in this chapter, three additional technologies (phyto-remediation, PRBs, and thermal treatment) have also been used to treat MTBE and other oxygenates in soil and groundwater. Phytoremediation is a category of treatment technologies that employs plants (or in some cases fungi) to conduct remediation. Treatment during phytoremediation can be accomplished through one or more natural processes, including enhanced bioremediation in the rhizosphere (plant root zone), phytostabilization of contaminants by organic plant material, plant uptake, plant metabolism, and phytovolatilization (volatilization through plant leaves).103 PRBs are subsurface barriers that remediate groundwater as it passes through an engineered treatment zone. For the treatment of MTBE and other oxygenates, treatment zones that use bioremediation processes are most common.104 Thermal treatment is a generic term that applies to technologies that use heat to mobilize, extract, or destroy contaminants either in situ or ex situ. While these technologies were applied less frequently, they may represent viable treatment options at some sites contaminated with MTBE and other oxygenates.

24.11.2 Phytoremediation Treatment of Oxygenates

Phytoremediation, as it applies to MTBE and other oxygenates, is a relatively new remedial approach and many of the removal and degradation pathways are currently being studied. However, it is known that phytoremediation relies on multiple processes to accomplish the removal of contaminants from shallow groundwater. Each of these processes is affected by different chemical properties as well as site-specific conditions. The biodegradability of oxygenates affects their treatment in the rhizosphere, where the conditions support an abundance of metabolically active bacteria and fungi that may enhance contaminant degradation. The relatively high solubility and low organic partition coefficients of oxygenates generally limits significant removal through phytostabilization, but facilitates removal through root uptake. In addition, volatility and Henry's constants may affect the removal through phytovolatilization.105

The manner in which phytoremediation can be applied to treat MTBE and other fuel oxygenates is highly variable, based on the site conditions, specific contaminants to be treated, cleanup goals, and other factors. Information relevant to the application of phytoremediation at sites contaminated with MTBE and other oxygenates is available in the literature.105-109

From the 323 MTBE treatment profiles, eight projects were identified where MTBE was treated using phytoremediation. These projects used various approaches, including hybrid poplar trees, Monterey pine, oak, eucalyptus, and engineered wetlands.

24.11.3 PRB Treatment of Oxygenates

A PRB is a treatment system configuration with treatment zones that can employ any of a number of treatment technologies, such as in situ bioremediation or ISCO. Depending on which treatment technology is employed, the properties of MTBE and other oxygenates as they apply to that specific technology will affect the treatment differently.

Information relevant to the application of PRBs at sites contaminated with MTBE and other oxygenates is available in Refs. [110-114].

Although no projects in the dataset were identified explicitly to be using PRBs, several projects discussed under other technologies involved these types of components. For example, several biore-mediation projects, such as at Port Hueneme, were performed using a PRB configuration.

No total project cost data were reported for any of the projects in the dataset that employed PRB treatment technology. However, additional information in the literature indicates the application of PRBs for the treatment of other contaminants. A U.S. EPA case study in 2000 showed a range of total costs for 16 PRB projects ranging from USD43,000 to USD1,900,000 with a median total cost of USD680,000.50

24.11.4 In Situ Thermal Treatment of Oxygenates

Thermal treatment can be used to mobilize or destroy MTBE and other oxygenates from soil either in situ or ex situ, similar to other petroleum contaminants. Volatilization from soil is affected by vapor pressure, with a higher vapor pressure making volatilization occur more readily. In general, alcohol-based oxygenates have lower vapor pressures than ether-based oxygenates, but the vapor pressures of both are comparable with or greater than other petroleum contaminants such as benzene. Similar to other organic contaminants, MTBE and other oxygenates may also be susceptible to thermal destruction at high temperatures.

Information relevant to the application of in situ thermal treatment at sites contaminated with MTBE and other oxygenates is available in a U.S. EPA report.115

While no projects in the dataset were identified explicitly as using in situ thermal treatment, several projects discussed under other technologies involved these types of components. For example, one site in Texas discussed under bioremediation (Rural Area Disposal Area, Liberty, Texas) used a combination of technologies that included an in situ thermal treatment component.

24.11.5 Advantages and Limitations

The advantages of applying other treatment technologies are as follows1:

1. Phytoremediation or PRBs may be a cost-effective alternative for remediating or containing relatively low-concentration, shallow, and widespread groundwater plumes.

2. Thermal treatment technologies tend to remove oxygenates along with other petroleum contaminants (such as petroleum hydrocarbons) that are more typically treated using this technology.

The limitations to applying other treatment technologies are as follows1:

1. The processes that effectively treat MTBE and other oxygenates during phytoremediation are still being studied.

2. Phytoremediation may be less applicable to higher concentration or deeper groundwater plumes.

24.12 NONTREATMENT REMEDIES

Nontreatment remedies that address oxygenates include excavation, free product recovery, MNA, and ICs. Nontreatment remedies may be appropriate for use either alone or in conjunction with one or more of the other remedies discussed in this chapter.

24.12.1 Excavation

Excavation is the removal of contaminated soil or sludge from a site by using mechanical equipment. It is often used at sites where significant volumes of petroleum products are present in the soils located near the surface and which are likely to be a continuing source of contaminant migration. Commonly, excavation is performed prior to or while implementing other remedies such as groundwater treatment technologies. Similar to free product recovery, excavation is used to remove/ control the source of contamination, so that MTBE will not continue to migrate to the vadose zone and groundwater.34

Site-specific characteristics, such as the presence of aboveground and belowground obstructions, largely dictate the implementation of excavation. Locations where underground utilities or storage facilities exist may require extensive and time-consuming exploratory excavation and hand-digging. Excavation around or near buildings may require the use of underpinning or sheet piling to stabilize the structure and rerouting of utility lines. Shoring or sloping may be required in sandy soil to maintain trench wall stability. Monitoring for air quality may be required during excavation. When fugitive air emissions exceed air quality standards, there may be limitations imposed on the quantity of soil that can be excavated per day.

Excavation equipment ranges from hand tools, such as pick axes and shovels, to backhoes, frontend loaders, clamshells, and draglines, depending on the amount of soil to be excavated, the total depth of the excavation, moisture content of the soil, and the space allowed at the site for staging of excavated material. Backhoes and front-end loaders are the most commonly used equipment for excavation of relatively shallow (<4.58 m (15 ft) below the ground surface) soils. Excavation rates for these types of units with 0.76 m3 (1yd3) bucket capacities are typically 57.3 m3/h (75yd3/h). Larger bucket capacities can increase this rate to up to 122.3 m3/h (160yd3/h).116 The maximum excavation rate using hand tools is approximately 0.76m3/h/laborer (1 yd3/h/laborer).

Factors that affect the costs for excavation include the depth of contamination, depth of ground-water (requiring dewatering), and extent of underground infrastructure and/or nearby structures that require shoring. The cost for excavation tends to be higher for areas with deeper contamination, shallower groundwater, and more infrastructures and nearby structures.

24.12.2 Free Product Recovery

Free product recovery is the extraction of separate phase material (primarily petroleum liquids) that is located in the subsurface (in the case of petroleum liquids, at the top of the water table). It is often used at sites where significant volumes of petroleum products have reached the water table, and which are likely to be a continuing source of contaminants migrating to the vadose zone or dissolving in groundwater. Commonly, free product recovery is performed prior to or during implementation of remedies such as groundwater treatment. Similar to excavation, free product recovery is used to remove/control the source of contamination, so that the source will not continue to migrate to the vadose zone or the groundwater.

Note that free product removal is a federal regulatory requirement, under 40 CFR. It requires owners and operators to remove free product to the maximum extent practicable, while continuing other remedial actions.

Technologies typically used to recover free product include skimming equipment in wells, trenches, or excavation pits, and pumping of free product. These approaches have been used with and without depressing the water table to enhance migration of free product to a well or drain. The design of a free product recovery system requires an understanding of the site hydrogeology and characteristics, the types, extent, and distribution of free product in the subsurface, and the engineering aspects of the equipment and installation. Free product recovery is sometimes combined with other technologies to enhance removal of contaminants from the vadose zone or that are dissolved in the groundwater.

U.S. EPA published a guide117 for state regulators about how to effectively recover free product at leaking USTs. In the guide, U.S. EPA provided scientific and engineering considerations for evaluating technologies for the recovery of free product from the subsurface. The guide discussed the behavior of hydrocarbons in the subsurface, methods for evaluating the recoverability of subsurface hydrocarbons, and recovery systems and equipment.

24.12.3 Monitored Natural Attenuation

U.S. EPA defines MNA as "the reliance on natural processes, within the context of a carefully controlled and monitored site cleanup approach, to achieve site-specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. The natural processes include biodegradation, dispersion, dilution, sorption, volatilization, stabilization, and transformation. These processes reduce site risk by transforming contaminants to less toxic forms, reducing contaminant concentrations, and reducing contaminant mobility and bioavailability." Other terms for natural attenuation in the literature include "intrinsic remediation," "intrinsic bio-remediation," "passive bioremediation," "natural recovery," and "natural assimilation."30

While offering the potential to clean up sites at lower cost, MNA typically would require a longer period of time to achieve remediation objectives, compared with active remediation measures. In addition, it generally requires extensive long-term monitoring data. Other potential limitations of MNA include the potential that the toxicity and/or mobility of transformation products may be greater than for the parent compound (e.g., TBA as a degradation product of MTBE); hydrologic and geochemical conditions amenable to natural attenuation may change over time and could result in renewed mobility of previously stabilized contaminants; and more extensive education and outreach efforts may be required to gain public acceptance of MNA. Information about research on field use of MNA is provided in Ref. [118].

U.S. EPA published a guide about the steps needed to understand the rate and extent to which natural processes are reducing contaminant concentrations.56 Although this guide is directed at sites contaminated by chlorinated solvents, some of the steps would also have relevance for sites contaminated by oxygenates like MTBE. The guide identifies parameters that are useful in the evaluation of natural attenuation and provides recommendations on how to analyze and interpret the data collected from the site characterization process. It also provides suggestions for integrating MNA into an integrated approach to remediation that includes an active remedy.

Recently, U.S. EPA published a report119 that provides guidance about the types of monitoring used during MNA remedies.

24.12.4 Institutional Controls

ICs are nonengineered instruments such as administrative and/or legal controls that minimize the potential for human exposure to contamination by limiting land or resource use, and generally are used in conjunction with engineering measures such as treatment or containment. ICs are used during all stages of a cleanup and often involve multiple activities ("layered IC") implemented in parallel or in series. Examples of ICs are120

1. Easements

2. Covenants

3. Well drilling prohibitions

4. Zoning restrictions

5. Special building permit requirements (sometimes referred to as deed restrictions).

Often, ICs are considered within the context of long-term plume management and MNA. Typically, after the source of contamination has been addressed (such as through removal or destruction), ICs are used to limit the long-term use of a site and the potential for exposure of residual contaminants to human or environmental receptors. When deciding about appropriate types of ICs, site managers look at the life cycle strengths, weaknesses, and costs for implementation, monitoring, and enforcement, and coordination with state and local governments that have responsibilities for ICs. Additional information about ICs is available in a U.S. EPA guide.120

ACRONYMS

BTEX

DIPE

ETBE

Aboveground storage tank

Biomass concentrator reactor

Benzene, toluene, ethylbenzene, and xylene

Diisopropyl ether

Detection limit

Dual-phase extraction

Chemical oxygen demand

Ethyl tert-butyl ether

Granular activated carbon

Horse power

Institutional control

In situ chemical oxidation

Light nonaqueous phase liquid

Monitored natural attenuation

Multiphase extraction

Methyl tert-butyl ether

Nonaqueous phase liquid

Nondetect

Natural organic matter Nonpurgeable organic carbon Parts per million by volume Permeable reactive barriers Polyvinyl chloride

ISCO

LNAPL

MTBE

NAPL

NPOC

ppmv

RCRA

Superfund and Resource Conservation and Recovery Act

RFG

Reformulated gasoline

ROI

Radius of influence

scfm

Standard ft3/min

SITE

Superfund Innovative Technology Evaluation

SSTL

Site-specific target level

SVE

Soil Vapor extraction

TAA

tert-Amyl alcohol

TAEE

tert-Amyl ethyl ether

TAME

tert-Amyl methyl ether

TBA

tert-Butyl alcohol

TPE

Two-phase extraction

US

United States

U.S. EPA

United States Environmental Protection Agency

UST

Underground storage tank

VE/GE

Vapor extraction/groundwater extraction

VOC

Volatile organic compound

ZOI

Zone of influence

APPENDIX

U.S. Army Corps of Engineers Civil Works Construction Yearly Average Cost Index for Utilities3

Year

Index

Year

Index

1967

100

1989

383.14

1968

104.83

1990

386.75

1969

112.17

1991

392.35

1970

119.75

1992

399.07

1971

131.73

1993

410.63

1972

141.94

1994

424.91

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