Ongoing ISCO Projects Performance for 13 Sites

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.

>10,000 ^g/L to <50^g/L and has achieved MTBE concentration reductions >99%. Because the dataset included relatively few completed projects with performance data, Table 24.15 provides a summary of specific projects instead of a summary of minimum, median, and maximum concentrations. The median project duration for the 19 completed sites ranged from 9 to 18 months.

24.8.6 Costs of ISCO Treatment of MTBE

The total project cost was reported for one of the 21 ISCO projects identified above. The completed Former Service Station, Pennsylvania, project that used ISCO with SVE, reported a total project cost of USD146,000. This cost was broken down further into USD90,000 of capital cost and USD56,000 of operation and maintenance cost. Because the area, volume, or mass treated was not available for this project, no unit cost was calculated.

There is little additional information in the literature about the costs of using ISCO for the treatment of MTBE and other oxygenates, or for other contaminants. The cost per volume of subsurface treated was reported in one literature source as ranging from USD68 to USD405/m3 (USD52-USD310/yd3) in general.75 The cost of ISCO is generally considered to be the average of the costs for remediation technologies for treatment of contaminated groundwater.34

24.8.7 Factors That Affect the Performance and Cost of Oxygenate Treatment Using ISCO

When MTBE or other oxygenates are present and must be remediated at a site, ISCO, either alone or in combination with other technologies, may be a suitable remediation approach. Although both ether- and alcohol-based oxygenates are susceptible to chemical oxidation, the chemical, hydraulic, and geologic conditions of a given site will determine whether ISCO is a feasible option for treatment. For example, ISCO may not be economically feasible for sites with high concentrations of NOM or other constituents that may consume large amounts of oxidant. In addition, sites with low subsurface permeability may require more complex approaches, such as fracturing or soil mixing, to deliver the necessary oxidant to the treatment zone, potentially increasing costs. Other site characteristics, such as pH, alkalinity, and temperature will also affect system design and impact cost and performance. For example, for oxidants that have specific pH requirements, pretreatment of the aquifer with an acid solution to lower the pH is typically considered. In addition, off-gas generated by the chemical reactions in ISCO may require capture and treatment.76

In addition to the technology-specific factors described above, additional factors may also affect the performance and cost of an ISCO system. These factors include the concentration, mass, and distribution of contaminants in the groundwater; subsurface geology and hydrogeology; cleanup goals; and requirements for site cleanup. For example, heterogeneity within the subsurface may result in preferential pathways that prevent the injected oxidant from reaching the entire treatment area. Because of the above factors, the design of an ISCO system is typically based on pilot-scale testing rather than generic design equations.

24.8.8 Advantages and Limitations

The advantages of applying ISCO are as follows3440:

1. It has the potential to be used to target hot spots that may not be amenable to bioremediation.

2. It has the potential to achieve cleanup goals in a relatively short amount of time (several months to a year).

3. Depth of application is only limited to the delivery approach used.

The limitations to applying ISCO are as follows34,40:

1. Relatively large amounts of oxidant may be needed for treatment of large masses of contaminant (the oxidant does not target only the contaminants of concern).

2. ISCO may have low contact between the oxidant and the contaminant in heterogeneous media or in areas with low permeability.

3. Special precautions may need to be taken to protect worker health and safety during operation (because of the use of strongly oxidizing chemicals); also concentrated oxidant injection can result in violent subsurface reactions.

4. Chemical reactions may form toxic by-products (such as bromate during ozone oxidation) in the groundwater.

5. Off-gas may require capture and treatment.

24.8.9 Example Projects

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