Team Gamma- Disadvantages/Limitations of Various Remediation Technologies

Limitations of slurry walls - Team Gamma, by George Schuler

The purpose of slurry walls is to reduce the movement of unconsolidated materials. Slurry walls are constructed by digging a trench with a backhoe; at the same time the trench is filled with a mixture of bentonite and soil or cement. This filling of the trench prevents the walls from collapsing. The walls then solidify and a barrier is created between contaminants and groundwater. Slurry walls are most effective when the wall contacts the bedrock beneath, so the possibility of contaminant migration is minimized. Slurry walls can be effective prevent the migration of LNAPL’s when bedrock is not near the ground surface. However if another contaminant is present it is possible for that contaminant the pass underneath the slurry wall. One disadvantage of slurry walls is that the composition of the contaminant or soil might not be compatible for this type of remediation technique. Slurry wall’s are very cost and labor intensive. If the bedrock is too far beneath the ground surface and the type of contaminant is resting on the bedrock, then a slurry wall would not be suitable choice. Slurry walls also require a large construction site in order to excavate soil and mix the slurry.
References
Opdyke, S. M., & Evans, J. C. (2005). Slag-cement-bentonite slurry walls. Journal of Geotechnical & Geoenvironmental Engineering, 131(6), 673-681.
Pichtel, John. (2007). Fundamentals of Site Remediation. Lanham, MD: The Scarecrow Press, Inc.

Bioreactors- Tracie Panzek

The most common bioreactors are used in the treatment of groundwater that has been pumped to the surface. Groundwater is transferred to a large vessel or basin where microorganisms breakdown organic matter into a sludge or slurry that can be disposed of or recycled.
Bioreactors are used mainly to treat VOC’s and fuel hydrocarbons in soil and groundwater. It is not very effective in treating pesticides. Not all of the contaminants in the groundwater are biodegradable and they will not completely degrade. Heavy metals are not treated by this method and they can be toxic to the microorganisms that are being used to treat the water. There are also concerns that some of the products may be more dangerous or toxic than the original contaminants.
Cost is another limitation due to the specific design and size of the system. The dilute nature of contaminated ground water often will not support an adequate microbial population density. Additional nutrients may need to be added. Low ambient temperatures significantly decrease biodegradation rates, resulting in longer cleanup times or increased costs for heating. Air pollution and other controls may need to be applied before the slurry or sludge is recycled due to some of the volatile compounds that are produced in the process.
References
Pichtel, John. (2007). Fundamentals of Site Remediation. Lanham, MD: The Scarecrow Press, Inc.
http://www.cpeo.org/techtree/ttdescript/biorec.htm
http://www.frtr.gov/matrix2/section4/4-42.html

Granular Activated Carbon Filtration Limitations – Team Gamma, by Robert Sandoval

Granular activated carbon filtration is used mainly as a tertiary treatment system, used behind the secondary wastewater treatment system. This method is used mainly for the removal of a wide range of organic compounds, inorganic compounds, and heavy metals by absorption (U.S. Environmental Protection Agency [EPA], 2000). Although it is an effective method to remove small quantities of these types of contaminates, the following disadvantages are inherent in utilizing GAC absorption (EPA, 2000):
1. Possibility of odor and corrosion issues as a result of hydrogen sulfide development due to bacteria activity.
2. Wet GAC can be abrasive and can also contribute to corrosion issues.
3. Non-regenerated GAC, containing absorbed contaminates, may contribute to disposal challenges.
4. Tertiary treatment of wastewater with GAC requires that the water: meet conditions of low suspended solids, fall within a designated pH range, fall within a certain temperature range, and have limits on flow rate.

In addition to the inherent disadvantages of using GAC absorption processes, several exist with regards to the regeneration process, removing the absorbed substances from the absorbent; these include (EPA, 2000):
1. Exhaust emissions contain the absorbed VOC’s, requiring secondary air cleaners
2. Excess noise originating from the regeneration furnace
3. The regeneration process usually requires 24-hour operation
4. The regeneration process is inclined to experience mechanical problems.

U.S. Environmental Protection Agency. Office of Water. Municipal Technology Branch. (, 0). Wastewater Technology Fact Sheet: Granular Activated Carbon Absorption and Regeneration (09/2000 ed.) (EPA 832-F-00-017). Washington, DC: U.S. Government Printing Office. Retrieved November 1, 2009 from the World Wide Web: http://www.epa.gov/owm/mtb/carbon_absorption.pdf.

Disadvantages of flushing metals from soils using chelating agents-Amanda Rasmussen

Soils contaminated with metals may be “treated” by flushing them with acids, chelating agents, or other solvents. This is one type of remediation technology among many. The efficiency of this type of treatment may be dependent on soil pH, particle size, and the presence of other compounds, for example. Some examples of chelating agents that may be used are ethylenedinitrilotetraacetic acid (EDTA) and diethylene triamine pentaacetic acid (DTPA).
While EDTA and DTPA may be good chemicals to flush contaminated soils of metals there are disadvantages to their use. These chemicals may leave trace amounts in the soils after flushing causing them to migrate into water sources. These two chemicals if released in natural waters can affect the natural aquatic environment, by being persistent compounds. Both EDTA and DTPA, are not suspected to toxic to aquatic organisms, though in combination with other compounds they may be acutely toxic. With this the release of EDTA and DTPA should be minimized when possible.
EDTA has become known as a persistent organic pollutant, meaning the chemical is resistant to environmental degradation. Traces of EDTA may be left in the soil after flushing and removal of the metals from the EDTA itself. These traces may be cause of widespread human exposure, depending on what the site will be used for after remediation. EDTA also has been shown to have a low acute toxicity to rats at an LD50 of 2-2.2 g/kg and also being cytotoxic and genotoxic. . Oral exposure has been shown to cause reproductive and developmental effects.
Fundamentals of Site Remediation, second edition, Pichtel, John
http://en.wikipedia.org/wiki/EDTA
http://www.ncbi.nlm.nih.gov/pubmed/9297986

Disadvantages of the Groundwater Pumping Method of Site Remediation-Steve Peckerman

Groundwater pumping has been used as a remediation technique with for many years. Despite the successes it had had there are still significant drawbacks to this method of site remediation.
One of the largest factors in this process is the cost. In addition to the cost of the well the removed water must be treated and either reinjected or discharged elsewhere. The cost of a pump and treat operation may run anywhere from $50,000 to $5 million (Moyers, 1997) A relatively new technique of directional drilling can be even more costly, as high as $850,000 per well. (Miller, 1996)
Another drawback to groundwater pumping is time. A pump and treat plan may last many years. This length of time serves to increase the cost due to upkeep of equipment, create a negative public sentiment and may result in a need to redesign the pump plan due to changes in geology and groundwater flow.
Results of the groundwater pumping plan are significantly affected by subsurface geology, more so than many other techniques. This can result in well designed plan not being as effective as hoped. A contamination plume that splits may not be a able to be contained with the original plan and may require a redesign. If the plume goes under property that is inaccessible there may be a need for directional drilling. As mentioned above this can be even more costly than conventional drilling and is subject to limitations on depth and vulnerability to fluctuations in the water table and subsurface geography.
The efficiency of pump and treat operations is fairly low typically removing only 1/3 of NAPLs. Using enhanced pumping systems this can be increased to the 50%-80%range. (Moyers, 1997)
Reducing contamination to levels where groundwater consumption is safe is often beyond the capabilities of pump and treat operations .
Contaminated Sites Management Working Group. (2003, September 7). Site Remediation Technologies: A Reference Manual. Retrieved November 1, 2009, from Contaminated Sites Management Working Group: https://www.ec.gc.ca/etad/csmwg/pub/site_mem/en/c5_e.htm#521
Miller, R. R. (1996). Horizontal Wells. Pittsburgh: Ground-Water Remediation Technologies Analysis Center.
Moyers, J. ,. (1997). Disadvantages of Pump and Treat Remediation.
SGC Industries. (2004). A review of Remediation Techniques. Retrieved November 1, 2009, from www.scgindustries.com: http://www.scgindustries.com/techniques.html

Soil vaporization-Michael Rice

Soil vapor extraction is an effective technique used to remove volatile organic compounds from soil. Although it is effective in most circumstances, there are some limitations that environmental managers must be aware of before selecting this technique for remediation. The type of chemical being remediated is one consideration of soil vaporization extraction’s effectiveness. Soil vaporization extraction is limited to volatile organic compounds. The removal of heavier VOCs is one limitation since soil vaporization is mostly effective on lighter VOCs. The effectiveness of soil vaporization depends upon the rate at which the contamints can volatilize. Volatilization allows contaminats to be removed through vapor diffusion to the surface. Therefore, limitation of this method is that more volatile compounds can be more effectively remediated than less volatile compounds. The site of where this technique is to be used is another consideration. The water content of soil is a site consideration needed to determine the effectiveness of soil vaporization extraction. Dry soil has a grater rate of volatilization than wet soil so wetter soil is a limitation of this technique. Soil vapor extraction is only effective in the vadose zone. It does not work on groundwater. It does not work or not as effective to surfaces near groundwater or in areas that have groundwater fluctuations. Soil content is another factor. Soil evaporation is successful in lighter and porous materials like sand and gravel rather than heavy and impermeable materials like clay. Other considerations for this technique are its impacts on air pollution due to the release of vapors. Air permits are required as well as additional air pollution treatments.
References:
1) Soil Vapor Extraction (SVE) General Principles and Site Applications Former Marine CorpsAir Station El Toro (May, 25, 2005). [Online]. Available: http://www.bracpmo.navy.mil/base_docs/eltoro/documents/enviro_docs/SVE_Presentation_052505.pdf [2009, Nov. 1]
2) Pichtel, John. (2007).Fundamentals of Site Remediation. Government Institutes, Lanham

Disadvantages of Construction Wetlands-Amanda Mann

One of the major disadvantages of construction wetlands is the large amount of land required for this system. In areas where land is expensive it would not be cost effective. Another issue is that additional technologies may be needed for the wetlands to function properly. Solid wastes may need to be filtered in order to avoid a buildup of sediment which can decrease the efficiency of the construction wetlands overtime. A variable water flow rate can be a problem and may require a flow equalization basin. With certain types and high concentrations of waste pretreatment may be necessary. Some pollutants are not capable of being broken down in a construction wetlands and would require other means of treatment. The time that is needed to start up the system is also an issue. Plants require time to grow and become established before the wetlands can work efficiently.

Brookhaven National Laboratory. Technology Fact Sheet Peconic River Remedial Alternatives Wetland Restoration/Construction. Retrieved October 30, 2009, from www.bnl.gov
Federal Ministry of Economical Cooperation and Development. Facts and Frequently Ask Constructed Wetlands: A Sustainable Option for Wastewater Treatment in the Philippines. Retrieved October 30, 2009, from www.watsansolid.org.ph
Wetlands Pacific. Questions and Answers about Construction Wetlands. Retrieved October 30, 2009, from www.wetlandspacific.com