Monitored Natural Attenuation and Risk-Based Corrective Action at Underground Storage Tanks Sites Mike Trombetta Department of Environmental Quality Environmental Quality Counsel Petroleum Tank Release Fund Subcommittee Meeting June 4, 2008
Monitored Natural Attenuation and Risk-Based Corrective Action at Underground Storage Tanks Sites
Jan 01, 2016
Monitored Natural Attenuation and Risk-Based Corrective Action at Underground Storage Tanks Sites. Mike Trombetta Department of Environmental Quality Environmental Quality Counsel Petroleum Tank Release Fund Subcommittee Meeting June 4, 2008. Agenda. Science of a Petroleum Cleanup - PowerPoint PPT Presentation
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Monitored Natural Attenuationand
Risk-Based Corrective Actionat
Underground Storage Tanks Sites
Mike Trombetta
Department of Environmental Quality
Environmental Quality CounselPetroleum Tank Release Fund Subcommittee
MeetingJune 4, 2008
Agenda
• Science of a Petroleum Cleanup
• Monitored Natural Attenuation
– Science Behind MNA
– Implementation Issues
• Risk - Based Corrective Action
• Long-Term Monitoring
Science Behind
Petroleum
Release Cleanup
GROUNDWATER
PRODUCT SMEAR ZONEDISSOLVED
CONTAMINATION
EXPANDING PLUME
FLOATING FREE PRODUCT
GROUNDWATER
CONCENTRATIONSBELOW DEQ-7STANDARDS
CONCENTRATIONSEXCEED DEQ-7
STANDARDS
0
505
500200
1,000
mg/kg(parts per million)
µg/liter(parts per billion)
GROUNDWATER
PRODUCT SMEAR ZONEDISSOLVED
CONTAMINATION
CLEAN FILL
TANK SYSTEM
REMOVED
FLOATING FREE PRODUCT
GROUNDWATER
PRODUCT SMEAR ZONEDISSOLVED
CONTAMINATION
CLEAN FILL
STEADY STATE
STABLE OR SHRINKING
TANK SYSTEM
REMOVED
FLOATING FREE PRODUCT
CONTAMINATED SOIL CONTINUES TO LEACH INTO GROUNDWATER
GROUNDWATER
PRODUCT SMEAR ZONEDISSOLVED
CONTAMINATION
CLEAN FILL
STEADY STATE
STABLE OR SHRINKING
TANK SYSTEM
REMOVED
• Sorption• Diffusion• Dispersion• Volatilization• Bio-degradation
Natural Attenuation Mechanisms
GROUNDWATER
PRODUCT SMEAR ZONEDISSOLVED
CONTAMINATION
CLEAN FILL
STEADY STATE
STABLE OR SHRINKING
TANK SYSTEM
REMOVED
FLOATING FREE PRODUCT
GROUNDWATER
PRODUCT SMEAR ZONEDISSOLVED
CONTAMINATION
CLEAN FILL
SOURCEREMOVAL
(EXCAVATION)
PLUME
SHRINKS
BACK
FLOATING FREE PRODUCT
GROUNDWATER
PRODUCT SMEAR ZONEDISSOLVED
CONTAMINATION
CLEAN FILL
SOURCEREMOVAL
(EXCAVATION)
NEW “STEADY STATE”
(SLOW SHRINK BACK)
FLOATING FREE PRODUCT
GROUNDWATER
PRODUCT SMEAR ZONE
DISSOLVED CONTAMINATION
BELOW DEQ-7STANDARDS
CLEAN FILL
SOURCEREMOVAL
(EXCAVATION)
GROUNDWATER
PRODUCT SMEAR ZONE
DISSOLVED CONTAMINATION
BELOW DEQ-7STANDARDS
CLEAN FILL
SOURCEREMOVAL
(EXCAVATION)
SITE
CLOSED
Natural AttenuationNatural Attenuation
A reduction in the
concentration and mass of a
substance in groundwater, due
to naturally occurring physical,
chemical, and biological
processes without human
intervention or enhancement.
Monitored Natural Monitored Natural Attenuation Attenuation (MNA)
The reliance on natural
attenuation 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
other more active methods.
GROUNDWATER
CLEAN FILL
MONITORING MONITORING WELLSWELLS
MNA
Implementation
Issues
U.S. Environmental Projection AgencyU.S. Environmental Projection Agency
Office of Solid Waste and Office of Solid Waste and Emergency ResponseEmergency Response
Guidance 9200.4-17P, April 21, 1999
Use of Monitored Natural Attenuation Use of Monitored Natural Attenuation at Superfund, RCRA Corrective at Superfund, RCRA Corrective
Action, and Action, and Underground Storage Underground Storage Tank SitesTank Sites
• Not a Presumptive Remedy
• Thorough Site Characterization
• Source Control
• Remove Free Product
• Performance Monitoring
• Contingency Remedies
• Reasonable Timeframe Compared to other methods
• Institutional Controls
Implementation Issues
Other Issues
• Vapor Intrusion
• Utility Impacts
• Risks to Construction Workers
VAPORS VAPORS EMINATING FROM EMINATING FROM DISSOLVED AND DISSOLVED AND FREE PRODUCTFREE PRODUCT
BURIED WATER LINEBURIED WATER LINE
• PERMEATION OF PIPEPERMEATION OF PIPE
• MIGRATION ALONG TRENCHMIGRATION ALONG TRENCH
CONSTRUCTION CONSTRUCTION WORKER WORKER
VAPOR VAPOR
INTRUSIONINTRUSION
MNA Wrap-Up• MNA is not applicable where
human receptors are at risk.
• Source removal is critical.
• Long-term monitoring will likely be required after source removal.
• Source area soils cannot always be fully removed.
• Closure requires DEQ-7 Standards.
Minimal Source Removal
Very long cleanup time
up to 100 years or more…
in tight clay-type soils.
Significant Source Removal
Reduced cleanup time
down to 10 years …
in tight clay-type soils.
Low – PermeabilityClay Soil
Low – PermeabilityClay Soil
NATURAL ATTENUATION PROCESSES EXIST AT ALL SITES
MNA can be used as a stand-alone cleanup strategy, but is typically combined with other technologies
(source removal).
MNAQuestions?
(RISK - BASED CORRECTIVE ACTION DISCUSSION -- NEXT)
Risk-Based
Corrective
Action (RBCA)
GROUNDWATER
BURRIED WATER LINEBURRIED WATER LINE
DRINKING WATER
POTENTIAL HUMAN POTENTIAL HUMAN RECEPTORSRECEPTORS
VAPORS
GROUNDWATER IS AN GROUNDWATER IS AN ENVIRONMENTAL RECEPTORENVIRONMENTAL RECEPTOR
GROUNDWATER
DISSOLVED CONTAMINATION
BELOW DEQ-7STANDARDS
MONTANA RBCA ADDRESSES
GROUNDWATER AS A RECEPTOR
Long-Term Monitoring
A method of managing release sites remaining above cleanup standards for a long period of time.
LTM generally follows MNA protocols
Long-Term Monitoring
A site-specific monitoring schedule selected by DEQ where groundwater is sampled on a frequency of 1 to 3 years, that ensures the plume is stable and shrinking and there is minimal risk to potential receptors.
Long-Term Monitoring
• Typically implemented following active cleanup
• Dissolved groundwater plume fully defined
• Low risk to all Current and Potential Receptors
• Establish Attenuation Curve (shrinking plume)
• Reduce Monitoring (least expensive option)
GROUNDWATER
CLEAN FILL
MONITORING MONITORING WELLSWELLS
Long-Term Monitoring 4414 Total Release Sites 2708 Release Sites Closed1706 Releases Sites Open
134 Release Sites Still in LTM
89 Annual Schedule24 Every 2 years3 Every 3 years18 Other Schedule
14 Monitoring 1 well14 Monitoring 2 wells
CONCLUSIONS• Source removal is critical.
• Source area soils cannot always be removed.
• Closure requires DEQ-7 Standards.
• Long-term monitoring will likely be required at sites with tight soil, even after source removal.
• Reduced monitoring protects human health and the public while limiting ongoing costs.
Questions?
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