In Situ Flushing/In Situ Bioremediation Process variations & synonyms
Classifications
Physical/biological/chemical Soil, water In situ (saturated/vadose)
Risk Management Role
Pathway management Source management?
Outcome
Extraction or destruction or stabilisation
In situ soil washing In situ chemical treatment
7.2.4
Leaching
OUTLINE In situ flushing is a development of pump and treat (see Table 7.2.3). Flushing systems combine injection with recovery wells. The injected liquid flushes the subsurface. The liquid is often treated groundwater, but some applications use organic solvents. Treatment typically is for the saturated zone, but unsaturated zone applications also exist. Both water and soil are treated. Flushing may be designed to achieve one or more of the following: • solubilise or mobilise contaminants into a liquid phase (usually as an aqueous solution but may be dissolved in an organic solvent) • stimulate in situ biodegradation • stimulate in situ redox reactions (see Table 7.2.7) Solution recovered at the surface is treated to remove contaminants extracted from the subsurface and prevent system fouling. Depending on regulatory requirements, treated water may be also be returned to the aquifer, or discharged to sewer or be re-injected after conditioning. Conditioning injected water is used to control subsurface conditions to continue ongoing mobilisation, biodegradation or to stabilise contaminants (e.g. Cr VI to Cr III). Possible conditioning amendments include: surfactants, cosolvents, microbial nutrients, pH modifiers, redox agents, ozone, and aeration.
Air emissions control Flushing solution
Monitoring wells
Contaminated sludge for disposal Water treatment
Injection well Extraction well
Mounding of water table
Cone of depression
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7.2.4
The environmental impacts of any additive or treatment agent must be fully assessed before use. Accessibility to the treatment may be enhanced using fracturing techniques or horizontal drilling. In situ flushing is used both in pathway management and source management. Source removal is often incomplete, with 70% removals seen as a realistic upper limit. Some regulators may take the view that this source term removal is necessary. However, residual sources may have enhanced mobility, causing greater contaminant flux into groundwater over long periods. STRENGTHS
WEAKNESSES
• Minimal site disturbance
• Transfer of soil contaminants into solution may be slow
• Extraction of organic or inorganic contaminants which are soluble or can be brought into solution • Use of in situ biodegradation results in contaminant destruction rather than extraction • May also work if contaminants are physically suspended (e.g. emulsified) within liquid extracted from ground • Process may be designed to treat specific contaminants • Process may be designed to stabilise or extract inorganic contaminants • Combinations of in situ flushing with MNA may show enhanced costeffectiveness
• Potential changes to soil and geotechnical properties by surfactants or other amendments • Potential production of more toxic or mobile compounds • Treatment of process effluent may be required • Good understanding of geology and hydrogeology required to predict movement of flushing solution and design of well system • Often of limited effectiveness for source removal especially in the short term, and for NAPLs the process of flushing may also result in increased risk of dissolution of remaining NAPL into groundwater
• Can be highly effective as a pathway management strategy
?
Organic cyanides
?
Gravel >2mm Key:
Sand 0.06–2mm
Pesticides/herbicides Dioxins/furans Volatile metals
?
Non-volatile metals
?
Radionuclides
?
Silt 2–60 µm ?
Cyanides
?
Corrosives
?
Asbestos Misc
Organic corrosives
Inorganic
PCBs Organic
Halogenated volatile Halogenated semivolatile Non-halogenated volatile Non-halogenated semivolatile
Inorganic
Organic
APPLICABLE CONTAMINANTS AND MATERIALS – Outcome: extraction or destruction or stabilisation
Oxidisers
?
Reducers Clay <2 µm
? Peat
Usually applicable; Potentially applicable; ? May be applicable; not treatable; may worsen situation. See Tables 4.9.2 and 4.9.3 for contaminant classifications.
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7.2.4
Notes Treatability depends on choice of flushing approach Also possible for chalk, dependent on fissure flow High permeability is important to enable liquids to enter, move through and exit efficiently Heterogeneous ground conditions militate against soil flushing Sandy soils less likely to be adversely affected by treatment agents Difficult to treat certain mixtures of contaminants, e.g. metals and oils, as different flushing solutions are required PROCESS VARIATIONS In situ bioremediation
Injected water is conditioned with microbial nutrients and electron acceptors (e.g. dissolved oxygen by aeration or peroxide addition, nitrate) to stimulate aerobic biodegradation. Conversely, injected water may contain materials that effectively produce electron donors, such as lactic acid, where anaerobic biodegradation is being stimulated. The conditioning selected is dependent on the nature of the degradable contaminants, the nature of the aquifer (e.g. pH, redox potential, dissolved organic matter) and the biodegradation route most likely to be effective. Surfactants may be added to try and improve the availability of organic contaminants such as PAHs.
Combined Typically used to support in situ bioremediation, with in situ flushing approaches with supplying microbial growth factors (such as nitrate) and sparging being used sparging to supply electron acceptors (dissolved oxygen) Chemical destruction
Most commonly achieved by the addition of redox reagents (see Table 7.2.7), but customised approaches may be used to target specific contaminants
Acid leaching approaches
Acidification used to leach metals from the subsurface, as many metallic species show greater solubility at reduced pH; the reduced pH also assists in promoting desorption of these metals from soil
Use of surfactants and complexing agents
Surfactants may be used to assist the mobilisation of organic contaminants, in particular DNAPLs and PAHs. Complexing agents such as EDTA may be used to increase the mobility of metallic contaminants
Solvent flushing Flushing with water-miscible solvents such as alcohol or cyclodextrin (modified sugars) used to increase mobilisation of NAPL contaminants In situ treatment Use of in situ flushing in managed zones or curtains across an aquifer to zones and achieve more controlled risk management (see Table 6.1.11) control planes Linkage to MNA Treatments may be designed to achieve initial contaminant reductions, with MNA used as a ‘polishing’ step over time, for example downstream of a treatment area Application of fracturing
Fracturing can be used to create zones of enhanced permeability within the subsurface. This has been applied to increasing the influence of injection and recovery wells in low-permeability materials, and may also be used to create in situ treatment zones
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7.2.4
OPERATIONAL PARAMETERS Typical equipment
Civil engineering plant, injection and extraction wells, pumping water treatment and conditioning. Note installation and maintenance costs are usually high in comparison to design costs, so third-party peer review of suggested designs may be prudent
Operation and maintenance
Repair and maintenance, e.g. pump, treatment systems, sampling and testing to check treated water
Monitoring progress
Groundwater monitoring is likely to be a strict regulatory requirement, including wider effects on water quality (e.g. dissolved non-aqueous phase, chemical agents such as surfactants, as well as contaminant and daughter compound concentrations)
Site requirements
Plant access, access to subsurface
Footprint
Well locations, above-ground treatment and conditioning plant
Potential environmental impacts
Environmental impacts from the addition of chemicals to the subsurface, indirect impacts on aquifer quality from in situ processes, e.g. on aquifer pH, redox conditions, nitrate concentration and dissolved organic matter
Health and safety issues
Risks from contact with treatment solutions and extracted water Risks of possible release of noxious gases from chemical reactions in ground (e.g. hydrogen cyanide, hydrogen sulphide, arsine)
Practical depth of 20m or more depth limited by hydrogeological controls and cost of deep treatment drilling/pumping
Time
In ideal conditions, pathway management goals may be reached in months; source removal applications may last many years
Availability in UK
Widely available
REFERENCES Learning Alvarez, P.J. and Illman, W.A. (2005) Bioremediation and Natural Attenuation: Process Fundamentals and Mathematical Models. Wiley ISBN 0471650439. www.wiley.com American Petroleum Institute (2003) Answers to Frequently Asked Questions about Managing Risks at LNAPL Sites. API Soil and Groundwater Res. Bull. No 18. May 2003. www.api.org Environment Agency (1996) Evaluation of Remedial Actions for Groundwater Pollution by Organic Solvents. R&D Tech. Report P9, Bristol. ISBN 1857050525. http://publications.environment-agency.gov.uk/epages/eapublications.storefront/ Evans, D., Jefferis, S.A., Thomas, A.O. and Cui, S. (2001) Remedial Processes for Contaminated Land: Principles and Practice. C549 CIRIA, London. ISBN 0 86017 549 9. www.ciria.org.uk GWRTAC (2002) Fracturing Technologies to Enhance Remediation â&#x20AC;&#x201C; Shuring, J.R. GWRTAC Technology Evaluation Report TE-02-02. Groundwater Remediation Technologies Analysis Center, Pittsburgh. www.gwrtac.org
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GWRTAC (2003) Treatment Trains for the Remediation of Soil and Groundwater â&#x20AC;&#x201C; Roote, D.S. GWRTAC Technology Status Report TS-03-01. Groundwater Remediation Technologies Analysis Center, Pittsburgh, USA. www.gwrtac.org Interstate Technology and Regulatory Council (2004) Strategies for Monitoring the Performance of DNAPL Source Zone Remedies. Interstate Technology and Regulatory Council, Washington DC, USA. www.itrcweb.org Interstate Technology and Regulatory Council (2004) Remediation Process Optimization: Identifying Opportunities for Enhanced and More Efficient Site Remediation. Interstate Technology & Regulatory Council, USA. http://www.itrcweb.org/RPO-1.pdf MacDonald, J.A. and Rittmann, B.E. (1993) Performance standards for in situ bioremediation. Environ. Sci. Technol., 27 (10), 1974-1979. http://pubs.acs.org/journals/esthag/ NATO Committee on the Challenges of Modern Society (2002) Performance Verification of In Situ Remediation Technologies. Report 251, EPA 542-R-02-002. www.clu-in.org Otten, A., Alphenaar, A., Pijls, C., Spuij, F. and de Wit, H. (1997) In Situ Soil Remediation. Soil and Environment Volume 6. Kluwer Acad. Pub., Dordrecht, The Netherlands. ISBN 0792346351. www.springerlink.com Suthersan, S.S. (1999) Remediation Engineering Design Concepts. CRC Press, Boca Raton, Florida (CD ROM). ISBN 0849321689. www.crcpress.com/ Suthersan, S.S. and Payne, F. (2004) In Situ Remediation Engineering CRC Press ISBN 156670653X. www.crcpress.com/ Teutsch et al. (2001) Source remediation vs. plume management: factors affecting costefficiency. Land Contamination and Reclamation, 8 (4), 128-139. www.clarinet.at and www.epppublications.com United States Department of Defence (2004) Cyclodextrin-Enhanced In Situ Removal of Organic Contaminants from Groundwater at Department of Defense Sites. Environmental Security Technology Certification Program ESTCP Report. CU-0113. www.estcp.org/documents/techdocs/cu-0113.pdf United States Department of Energy (2000) Remediation of DNAPLs in Low Permeability Soils Subsurface Contaminants Focus Area. US DOE Office of Science and Technology OST/TMS ID 163 DOE/EM-0550. http://apps.em.doe.gov/ost/pubs/itsrs/itsr163.pdf United States Environmental Protection Agency (1993) Hydraulic Fracturing Technology. Applications Analysis and Technology Evaluation Report. EPA/540-R-93-505. www.epa.gov/ORD/SITE/reports/540r93505/ United States Environmental Protection Agency (2004) Technologies for Treating MtBE and Other Fuel Oxygenates. Report: EPA 542-R-04-009. http://clu-in.org/techpubs.htm United States Environmental Protection Agency (2004) The DNAPL Remediation Challenge: Is There a Case for Source Depletion. US EPA Report: EPA/600/R-03/143. www.epa.gov/ada/download/reports/600R03143/600R03143.pdf United States Environmental Protection Agency (2006) Evaluation of the Role of Dehalococcoides Organisms in the Natural Attenuation of Chlorinated Ethylenes in Ground Water. EPA/600/R-06/029. www.epa.gov/ada/download/reports/600R06029/600R06029.pdf United States Environmental Protection Agency (2006) Microfracture Surface Characterizations: Implications for In Situ Remedial Methods in Fractured Rock. EPA/600/R05/121. www.epa.gov/ada/download/reports/600R05121/600R05121.pdf
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United States Naval Facilities Engineering Command (2003) Surfactant-Enhanced Aquifer Remediation (SEAR) Implementation Manual. April 2003 NFESC Technical Report TR-2219ENV.US NFESC Washington DC 20374-5065. http://clu-in.org/techpubs.htm CLU-IN In Situ Flushing web page www.cluin.org/products/isf CLU-IN Fractured Bedrock web page: www.cluin.org/fracrock/ Handbooks Interstate Technology and Regulatory Council (2003) Technical and Regulatory Guidance for Surfactant/Cosolvent Flushing of DNAPL Zones. April 2003. Available from www.itrcweb.org NOBIS (1996) Design and Maintenance of Infiltration and Extraction Systems. Report 96-3-06. CUR/NOBIS, Gouda, The Netherlands. www.skbodem.nl/ United States Air Force (2004) Principles and Practices of Enhanced Anaerobic Bioremediation of Chlorinated Solvents. Report of the Environmental Security Technology Certification Program (ESTCP). www.afcee.brooks.af.mil/products/techtrans/ Bioremediation/default.asp United States Department of Energy (2002) Guidance for Optimizing Ground Water Response Actions at Department of Energy Sites Contaminants US Department of Energy, Office of Environmental Management. http://web.em.doe.gov/er/May2002gwguide1_508.pdf United States Environmental Protection Agency (2000) Engineered Approaches to In Situ Bioremediation of Chlorinated Solvents: Fundamentals and Field Applications. EPA 542-R-00008. www.clu-in.org Case studies and demonstrations GWRTAC (1998) In Situ Flushing – Roote, D.S. Technology Status Report TS-98-01 Groundwater Remediation Technologies Analysis Center, Pittsburgh, USA. www.gwrtac.org Interstate Technology & Regulatory Council (2007) In Situ Bioremediation of Chlorinated Ethene DNAPL Source Zones: Case Studies. April 2007. IRTC 444 North Capitol Street, NW, Suite 445, Washington, DC 20001. www.itrcweb.org/Documents/bioDNPL_Docs/BioDNAPL2.pdf NATO Committee on the Challenges of Modern Society (2002) Demonstration of Remedial Action Technologies for Contaminated Land and Groundwater. Pilot Study Reports 1985 to 2002 (CD ROM) EPA/542-C-01-002. www.clu-in.org US Environmental Protection Agency (2004) FRTR Cost and Performance Remediation Case Studies and Related Information. CD ROM. EPA 542-C-04-004. www.frtr.gov (has a comprehensive listing of case studies). www.clu-in.org US Federal Remediation Technologies Roundtable (FRTR) Cost and performance web page: www.frtr.gov/costperf.htm
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