Remediation techniques designed to clean-up
contaminated soil and groundwater have evolved since promulgation
of regulations associated with the Resource Conservation and Recovery Act
(RCRA) and the Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA) in the 1970s and 1980s. There are now so many choices to
consider when determining the “right” way to address contamination, and the
“best” way depends on several important factors.
that go into the decision of how to best address contamination include:
(chance for success)
involvement and program
the beginning of the remedial evolution, the common approach was “you
contaminated it – you clean it up to pre-incident conditions”. These earliest techniques were essentially
“removal actions” that involved excavation of grossly impacted soils and
placement of those soils in an off-site landfill or incinerator and pumping
groundwater and treating it in an above-grade treatment system. The removal cleanups progressed to a
“how clean is clean enough” approach and were targeting a specific cleanup
level such as the US Environmental Protection Agency Maximum Contaminant Levels.
As remediation experts soon discovered, removal of
100% (or close to depending on site factors) of the contamination was generally
not possible, particularly in groundwater. Groundwater pump and treat systems
would operate five (5) to even 20 years or more and there would still be
appreciable contamination left behind.
Although pump and treat systems hydraulically controlled the groundwater
contaminant plume, residual soil and groundwater impacts were left behind at
levels that were substantially higher than the concentrations deemed “safe” at
the time. As a result, additional
remediation technologies were evaluated and refined.
As the state of the science evolved in the 1990s
and early 2000s, there was increased focus on utilizing a combination of risk
assessment techniques to establish site-specific clean-up criteria, and newer in
situ and ex situ techniques for soil and groundwater cleanup. Newer ex situ treatment for soils
included technologies like thermal desorption and multi-phase or dual-phase
extraction, while a number of in situ techniques became increasingly
common and relied upon, such as soil vapor extraction (SVE) and air sparging
(AS), chemical oxidation, groundwater circulation wells, permeable reactive
barriers, and bioremediation.
From the mid-2000s to present, there has been a
fundamental focus in remediation techniques toward in situ approaches
such as various chemical oxidants and reductants, zero valent iron blends, and
thermal remediation. These approaches are now commonly coupled with evaluating exposure potential and the
use of exposure prevention measures to protect human health and the
environment. Exposure prevention measures include the use of risk assessment, multiple lines of evidence, and use
of deed restrictions, institutional controls, and engineering controls such as
vapor intrusion mitigation systems.
to the shift in risk-based thinking to achieve remediation objectives, you must
consider whether or not the source should be treated and the effects the source
area will have on the contaminant plume over time. Risk based decisions alone
are not typically viable over long periods of time if the environmental
conditions continue to change because of factors such as contaminant migration,
leaching and/or additional contaminant contributions, among other things. Source areas can continue to dissipate
contamination as it spreads from highly contaminated areas to less contaminated
areas. Eventually the process will stabilize but depending on the contaminant
and geologic setting it can take many years or decades. Source area cleanup is
almost always an important part of the remediation and closure process.
wide variety of cleanup techniques are available for reducing contaminant
concentrations in the source area. The appropriate technique depends on a
number of factors similar to those presented above as well as the source area
location, geologic setting, type of contaminant, and remedial objectives. In
determining how much source area cleanup is warranted, consideration must be
given to long-term costs and obligations related to contamination that is left
in place. These include:
and maintenance of remedial systems and engineered controls
(indoor air, groundwater)
of future land use options
In addition, there are potential ongoing legal liabilities, such as third party claims, associated with contamination which is left in place.
For more information on remediation techniques used to address soil and groundwater contamination, sign up to attend the webinar on May, 13 2020.