Chapter 8 Assessment and Cleanup 8-

CHAPTER 8 

Assessment and Cleanup

This chapter outlines contamination cleanup procedures, including:

 Site investigations to determine the extent of contamination after an oil spill or 

release

 Risk assessments to determine possible risks, including exposure and toxicity

 Conceptual site models (CSMs) and remediation strategies to efficiently address 

cleanup

 Different treatment technologies for cleaning contaminated soil, groundwater, 

and remediation system off-gas

8.1 Regulatory Background

The U.S. Environmental Protection Agency (EPA) has several programs to

the cleanup of environmental contamination. The goal of each program is to

protect human health and the environment. If a spill has occurred, the environmental cleanup process begins as soon as emergency situations (such as fire, 

explosion, or vapor hazards) have been addressed and the proper agencies have 

been notified. See Chapter 2, Incident and Spill Reporting for a summary of these

initial actions.

The environmental cleanup process or corrective action process consists of

 Developing a 

 Conducting a site assessment or field investigation

 Updating the 

 Preparing a risk assessment and/or comparing investigation results to

cleanup or action levels

 Developing a remediation strategy and endpoint

 Evaluating feasible treatment technologies or remedial option

 Implementing the remedy or corrective action

This is the general approach to corrective action for all types of cleanup sites

For some releases into the environment, site assessments and cleanups may be 

relatively simple. It may be suitable to visually inspect a contaminated area and 

excavate the soil, followed by sampling to confirm the site is clean. However, a

large release or one that originates underground (for example, leaking buried 

pipeline or tank bottom) may require a long and costly multiphased investigation 

to determine the type and extent of damage. It also may require assessing and 

addressing potential impacts to human health and the environment. This investigation may be followed by a long-term cleanup operation

Because this guidance document is for LA Energy, most of expected s

cleanups will be associated with petroleum products. Therefore, although this

 Petroleum-contaminated 

soil cleaned up under an 

underground storage tank (UST) 

program is exempted as RCRA 

hazardous waste (40 CFR 261.4(b)

(10)).

 EPA does not set cleanup levels 

for soils and groundwater 

contaminated by petroleum 

products from leaking USTs (40 

CFR 280.66). Each individual state 

sets its own cleanup levels.

 EPA strongly encourages states to 

use risk-based decision-making 

to set the cleanup levels for any 

leaking UST site (Office of Solid 

Waste and Emergency Response 

Directive 9610.17 March 1, 1995).

 Remediation waste consists of all 

solid and hazardous waste, and 

all media (groundwater, surface 

water, soil, and sediment), and 

debris that are managed for 

implementing cleanup (40 CFR 

260.10).

The Law Says
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chapter touches on all aspects of remediation, the focus is on remediation of 

petroleum-contaminated sites.

8.1.1 Cleanup Programs

The main regulatory programs that address site cleanup include

 Leaking underground storage tank (LUST) remediation pro

 Hazardous waste site remediation for facilities permitted or formerly

permitted under the Resource Conservation and Recovery Act (calle

Corrective Action

 Superfund and state Superfund-type progra

 Brownfield programs

 Voluntary cleanup programs

Federal regulations for UST site assessments and corrective actions are cove

in 40 CFR 280 and are summarized in the flow chart in Appendix 8-1. Most states

territories, and many tribes and some local agencies have adopted their own 

regulations or are authorized to implement this program for EPA. These ot

requirements are similar to those summarized in Appendix 8-1; however, notification time frames and submittals may be different. Check with your state and local 

agencies. Appendix E provides state agency contact information.

The RCRA Corrective Action program is discussed in 40 CFR 264, which list

requirements for site monitoring, investigation, and remediation. Sites being

addressed in the RCRA Corrective Action program will generally be issue

Consent Order from PA or the authorized state agency under the authority 

RCRA Section 3008(a) or 3004(u). In many cases, states have adopted their st

Superfund regulations to implement remediation at RCRA Corrective Ac

sites. PA and the states have issued guidance documents that provide addition

direction.

The Comprehensive Environmental Response, Compensation, and Liability

of 1980 (CERCLA), also known as Superfund, addresses remediation of the m

highly contaminated sites in the U.S.; the federal regulations are found in 40 

300. Because the federal Superfund program addresses the worst sites, many

sites aren’t contaminated to high enough levels to be on the Superfund list but

still need to be addressed. As a result, most states have state Superfund-typ

regulations that address these other sites. PA and/or the state negotiate clean

agreements with potentially responsible parties. These agreements are in the

form of administrative orders on consent, administrative agreements, or judicial 

consent decrees. In the case of military installations, there is usually a Federal 

Facilities Agreement (FFA) that addresses Superfund requiremen

CERCLA specifically excludes petroleum from its definition of a hazard

substance (see Chapter 2, Incident and Spill Reporting). Therefore, if petroleum

is released to soil, CERCLA cannot be used as the regulatory basis for remed

action. However, petroleum-contaminated media may be subject to corrective

actions under other regulations, such as ST and state-specific abovegrou

storage tank (AST) remediation regulations, a RCRA Corrective Action p

if contaminated soil is located at a permitted RCRA facility, state Superfund-t
Chapter 8 Assessment and Cleanup 8-

programs, or the Clean Water Act if the petroleum was spilled into a water body

or wetland.

Brownfield is a term applied to a property where its reuse and redevelopment 

is hampered by contamination. Many state, county, and city governments offer

economic incentives (grants, liability protection, tax benefits) for cleanup, redevelopment, and revitalization of contaminated property and sometimes for 

abandoned, industrial, commercial, and military property. Some states combine

their Brownfield and voluntary cleanup programs. Voluntary cleanup or voluntary 

remediation of non-priority contaminated sites is conducted on a site-by-site, 

state-by-state basis, and cleanup and remedial actions are generally negotiated 

in memoranda of agreements between state regulators and responsible parties.

Remedial processes are similar for all site remediation programs in terms of the

end goals: to protect human health and the environment, to include the public 

in the remedial action decision-making process, and to clean up sites to regulated standards. Appendix 8-2 contains a comparison of the RCRA, CERCL

Brownfield environmental cleanup and remedial processes.

8.1.2 Permitting Requirements

Many remediation technologies involve activities that are regulated and may

require notification and/or permitting with a variety of agencies. For example, the 

soil vapor extraction technology described later in this chapter may require an air 

permit. It is important to investigate the federal and state regulations and permitting requirements regarding remediation technologies, including air emissions, 

water discharges, groundwater injection restrictions, air injection restrictions, 

land disposal requirements, and land application restrictions.

You may have heard of a Superfund exemption from permitting for some site

remediation activities where you instead comply with applicable or relevant 

and appropriate requirements (ARARs) in the regulations. Specifically, action

CERCLA sites must comply with substantive or technical aspects of AR

not the corresponding administrative requirements. That is, permit applications,

reporting, recordkeeping, and other administrative procedures such as administrative reviews are not considered ARARs for actions conducted entirely on-si

However, don’t count on always having the permit exemption at your Superfun

site; some states impose exclusive (that is, no federal counterpart) or more 

stringent requirements than EPA. For instance, New Jersey and New York req

the person conducting a remediation at a CERCLA site to submit most of 

permit application information and will issue permit equivalents to address the 

remedial actions. It takes as much time to get a permit equivalent as to obtain an 

actual permit.

8.2 Conceptual Site Model

A CSM is an organized set of ideas and a written or graphical representation of

site conditions. The development of a CSM is an integral part of site characterization effort. A preliminary CSM should be compiled as soon as the re

is discovered, using the information available at that time. As the work at the

site proceeds, the CSM should be updated and reconsidered A CSM serves 
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framework to understand how to plan and interpret underground investigations, 

as well as how to frame the value expected from additional investigations. The

CSM generally consists of these six major element

 Source component (the type of product released, what it contains, its physical

and chemical properties, the presence of light non-aqueous phase liquids 

[LNAPLs] or dense NAPLs [DNAPLs], where and how much

 Spatial dimensions (depth and lateral extent of contaminants in the ground

 Hydrogeological conditions (site geology, including types and depths of soil

and rock, depth to groundwater and flow direction)

 Potential receptors and exposure pathways (and possible migration routes,

such as utility corridors, surface water bodies, and basements)

 Mobility and stability of plume (whether non-aqueous phase liquid

groundwater, or soil vapor plumes are stable, diffusing, expanding, 

contracting, or migrating)

 Applicable regulatory standards (given the release, what end point can be

identified to guide remediation planning?)

A CSM is sometimes represented as a two- or three-dimensional drawing. It 

developed from available analytical data, historical records, aerial photographs, 

and the risk assessment. The model establishes a hypothesis about possible

contaminant sources, transport, exposure pathways, and potential receptors. It 

can be used to present data supporting the implementation and monitoring of a 

selected remedy and for remedy evaluation and optimization.

8.3 Site Investigation

After discovery of a problem, the next step is usually the site investigation, sometimes referred to as remedial investigation, field investigation, site evaluation, or

hazard identification. Terms vary depending on what regulatory program you are

under.

The purpose of a site investigation is to determine or confirm

 Source of contaminatio

 Nature and extent of contamination (area, analytes present, concentrations,

and variation with depth) in soil, groundwater, surface water, sediment, or 

soil vapor

 Presence of free-phase non-aqueous phase liqui

 Impact of contamination on soil, surface water, groundwater, or any 

structures

The site investigation often consists of collecting samples (soil, soil gas, groundwater, surface water, sediment, ambient or indoor air, and biota, as appropriate)

for analysis either by field instruments or an off-site laboratory to determine the 

nature and extent of contamination. Collecting the samples sometimes requires 

the use of drill rigs with augers to collect split-spoon soil samples from soil 

borings. Drill rigs are also used to collect groundwater grab samples while drilling

or to install monitoring wells to collect groundwater samples.

You can dial 8-1-1 to reach the 

national “Call Before You Dig” 

hotline to arrange for subsurface 

utilities to be marked before you 

begin excavation or drilling.

Did You Know?
Chapter 8 Assessment and Cleanup 8-

As an alternative, direct push drill rigs are used to quickly gather grab samples

of soil vapor or groundwater, or to advance geophysical tools (such as laser-induced fluorescence). Direct push rigs have tools for probing and sampling that

are pushed or driven into the ground (without rotation) and do not generate 

contaminated soil cuttings. The speed and depth of penetration largely depends

on the soil type, the size of the sampler, and the weight and power of the rig. 

Direct push techniques are generally limited to shallow unconsolidated soil and

are of limited use for deep site contamination.

Groundwater and soil vapor monitoring can help document the extent and 

stability of the plume (area of soil vapor and groundwater contamination). Exhibit 

8−1 illustrates common terms used in soil and groundwater investigations. Note

also that vapors from the groundwater plume can travel upward through the soil 

and into buildings through cracks in the foundation or floor of basements. 

Prior to starting any underground investigation, a utility clearance needs to be

performed to identify the location of underground utilities. You can request 

utilities be marked in the investigation area prior to digging by calling 8-1-1, the 

national “call before you dig” hotline. It usually takes 2 to 3 days for the utilities 

to be marked, so plan accordingly. Note, however, that some one-call services

do not provide identification of utilities that are on private property or federal 

facilities. The facility public works department (or equivalent) should also be

contacted to identify site-specific utilities. It is not uncommon for a geophysical 

firm to be contracted to conduct non-invasive investigations using ground-penetrating radar, radio frequency utility-locating instruments, and electromagnetic 

metal detection methods to identify utilities and buried USTs in the propos

area of subsurface investigation. If there is remaining uncertainty, a drilling (or 

other contractor) can hand auger or air knife the first several feet in a borehole to 

identify buried utilities. 

EXHIBIT 8−1

Common Terms in Soil and Groundwater Investigations
8-6 Chapter 8 Assessment and Cleanu

8.3.1 Oxygenates and Lead Scavengers

Because of the increasing prevalence of fuel oxygenates, states have begun to 

establish investigation requirements and cleanup levels for methyl tert-butyl 

ether (MTBE) and other related compounds called oxygenates. Oxygenates a

oxygen-containing compounds that have been used for decades as gasoline 

additives to increase octane ratings and produce cleaner burning fuels. Tert-butyl

alcohol (TBA) can be both a degradation product of MTBE and a fuel addit

Other oxygenates are tert-amyl methyl ether (TAME), diisopropyl ether (

ethyl-tert-butyl ether (ETBE), ethanol, and methanol. You may need to modi

your investigation approach to look for oxygenates.

Oxygenates tend to migrate faster and farther in the groundwater. That is why at

sites with notable groundwater flow, it is important to recognize whether oxygenates may be a concern so that investigation sampling further downgradient 

can be planned to identify the extent of the groundwater plume. In addition, 

MTBE has a tendency to move deeper into an aquifer, so searching at depth 

vertically may be important, especially at the edge of the plume.

A recent transition has been made to replace a substantial portion of vehicle fuels

with biofuels, such as ethanol. As a water-soluble constituent, ethanol migrates

in the groundwater similarly to MTBE in that these constituents often migrate 

advance of the other fuel constituents, such as benzene, toluene, ethylbenzene, 

and xylene (BTEX). In addition, if the groundwater is naturally aerobic (contain

oxygen) and because of this fosters natural attenuation of the fuel constituents 

(see Section 8.9.5) ethanol can break down at the leading edge of the plume, 

using up oxygen that would have otherwise helped break down the fuel constituents (total petroleum hydrocarbons [TPH] or BTEX). This effect is called an o

shadow, and it can allow further migration of the PH and BTEX plume 

would have occurred had the fuel not contained ethanol. This affects investigation planning and may increase the cost of remediation

Lead scavengers were another category of gasoline additive used through the

end of the 1980s. Lead scavengers such as ethylene dibromide (EDB) and 1,2-dichloroethane (DCA) (also known as ethylene dichloride [EDC]) were used to prevent the buildup of lead deposits that can foul enines. EPA has found t

lead scavengers may persist in some groundwater environments. In addition, 

some aviation gasolines (AVGAS) continue to use leaded fuels. If the site histo

includes storage of gasoline prior to the late 1980s, or storage of AVGAS, the si

environmental media should be analyzed for these potential contaminants. 

8.3.2 Triad Approach

A comprehensive approach to the overall spill response and remedial action

implementation promoted by PA is the Triad Approach, which consists of t

three elements: systematic planning, dynamic work strategies, and real-time 

measurementtechnologies. It is also known as accelerated site characterization and uses existing tools and methods in an integrated approach to improve 

speed, quality, and effectiveness.

The goal of this approach is to manage decision uncertainty. As mentioned, it

principal elements are:
Chapter 8 Assessment and Cleanup 8-

 Systematic Planning – Systematic planning usually includes identification of

key decisions to be made (such as regulatory, scientific, toxicological, and 

engineering), the development of a CSM to support decision-making, and a

evaluation of the uncertainties in the CS

 Dynamic Work Strategies – During contaminated site characterization,

remediation, and monitoring, dynamic work strategies consist of being 

able to change or adapt based on information generated by real-time 

measurement technologies. Given the CSM, and the information about it a

it is being gathered, this element enables decisions to be made about what 

additional activities would best resolve remaining uncertainties and/or best 

meet cleanup goals. For instance, some dynamic decisions could be triggered 

while the work crew is in the field and could lead to specific preapproved 

actions as new information becomes available.

 Real-Time Measurement Technologies – These technologies return results

quickly enough to influence decisions about ongoing field efforts for data 

collection and site restoration. This could refer to rapid turnaround from a

fixed laboratory (using either quantitative or screening analytical methods) 

or field-based measurement technologies, such as field screening analytical 

instruments, geophysics, cone penetrometer testing, and computer mapping.

The Triad Approach focuses on data collection methods that can increase spati

coverage (larger area) without sacrificing sample representativeness or increasing 

total sampling program costs.  weight of evidence approach to decision-making

is used, where appropriate, based on collaborative data sets. Collaborative data 

sets can contain data from a number of sources, including quantitative and 

screening analytical methods.

In its essence, the Triad Approach is a planning approach that joins together th

work being done in the field with the decisions that will be made to accomplish 

the cleanup. Because of this, the stakeholders are usually involved in deciding the 

rules for field decisions if the Triad Approach is use

Whether a program fully adopts the elements of the Triad Approach or not, al

programs benefit from understanding its principles and applying what can be 

incorporated. While simple site contamination may not benefit as much from this 

as larger, more complex sites do, it is good to be aware of the Triad Approach an

its elements for increasing confidence and effectiveness during remedial design 

and implementation.

8.4 Risk-based Decision-making and Risk 

Assessments

EPA encourages the use of risk-based decision-making in the corrective acti

process. For large or complex spills and releases, complete removal of the contamination may be technically impossible, cost prohibitive, and not necessary 

from a health standpoint. Risk-based decision-making helps you develop necessary and appropriate actions that are based on the relative risks to human health

and the environment.
8-8 Chapter 8 Assessment and Cleanu

The American Society for Testing and Materials (ASTM) developed a 

based on the risk-based decision-making process entitled Guide for Risk-Based 

Corrective Action Applied at Petroleum Release Sites [E−1739−95 (reapproved

2015)]. This process developed byASTM is known as risk-based correc

action (RBCA). The formal definition of RBCA is as follo

A streamlined approach in which exposure and risk assessment practices are 

integrated with traditional components of the corrective action process to ensure 

that appropriate and cost-effective remedies are selected and that limited resources are properly allocated.

EPA has advised state agencies that te ASTM standard may be a good st

point for developing a risk-based process tailored to applicable state and local 

laws and regulatory practices. Most states have adopted some form of risk-based

cleanup standards and many use the tiered approach outlined in the STM standard. Tier 1 uses a look-up table of screening level contaminant concentrat

to determine if site conditions will allow a quick regulatory closeout or if a more 

detailed risk analysis needs to be completed. Some states have online tools that

can assist in the determination of risk-based standards.

Because sites vary greatly in physical and chemical characteristics and the risks 

they pose, you may need to complete a risk assessment to make a site-specific, 

risk-based decision.  risk assessment usually consists of a toxicity assessment,

exposure assessment, and risk characterization.

8.4.1 Toxicity Assessment

In a toxicity assessment, you (or your contracted environmental consultant) 

identify the contaminants of concern and the types of hazards or health effects 

associated with exposure to those chemicals. Both the National Institute for

Occupational Safety and Health (NIOSH) and the Occupational Safety and 

Administration (OSHA) have published the physical, chemical, and toxicologi

properties of many chemicals (including chemicals found in fuels), which are 

available in several electronic databases. An example of a toxicological property

is the estimated dose of a chemical that is considered “safe” or does not cause any 

ill effects. Chemicals can sometime cause acute (short-term) or chronic (longterm) toxicity or both.

8.4.2 Exposure Assessment

In an exposure assessment, you identify if an exposure pathway exists. An

exposure pathway is a route that a chemical might travel from the contaminated 

area to people, animals, or aquatic life. An exposure pathway has four parts

 Contaminant source (that is, area of contamination)

 Mechanism for contaminant release and transport (for example, dissolved,

resuspension, volatilization, infiltration, percolation)

 Potential receptors (that is, people and environments

 Feasible exposure routes (that is, inhalation, ingestion, and dermal 

absorption)
Chapter 8 Assessment and Cleanup 8-

Exposure cannot occur unless each element of the pathway exists or is reasonably

expected to exist. More specifically, an exposure pathway is complete if a chemical

is released from a source area and is transported in an environmental media (such 

as by the wind, through groundwater, or via soil vapor intrusion) until there is a 

way for the receptor to take it in through ingestion, inhalation, or dermal absorption (skin contact). Exhibit 8−2 illustrates potential exposure pathways.

EXHIBIT 8−2

Potential Exposure Pathways

8.4.3 Risk Characterization

In a risk characterization, you or an environmental consultant combine the 

results of the toxicity assessment and exposure assessment to estimate potential 

contaminant concentrations that receptors might be exposed to. If there’s not 

enough site-specific data, you could estimate risk-based thresholds or levels that 

should be avoided to prevent adverse health effects. These target risk levels are

sometimes used as cleanup levels or risk-based action levels. PA has sever

guidance documents on the specific calculations and assumptions required in a 

risk characterization and can be found at their website.

With this information, you can propose cleanup levels to the state agencies or 

perhaps justify having a no further action or monitoring-only decision by the 

implementing regulatory agency. Based on your results, as well as other criteria, 

the state determines the cleanup level your site must achieve. You will then have 

to begin remediation to achieve this level, or be directed to simply monitor a site.

8.5 Cleanup Levels

Cleanup standards in soil, soil gas, and groundwater generally vary by state. 

Several associations and websites present state cleanup standards, including

petroleum-hydrocarbon-contaminated soil and groundwater. Cleanup levels 

compiled by associations should be viewed with caution and confirmed with 

the appropriate state regulatory agency prior to use. Many states also provide
8-10 Chapter 8 Assessment and Cleanu

the option to develop site-specific risk-based cleanup levels as described in 

Section 8.4.

EPA has established Regional Screening Levels (RSLs) to determine

levels of contamination found at the site may warrant further investigation or 

site cleanup, or whether no further investigation or action may be required. RS

are chemical-specific concentrations for individual contaminants in air, drinking 

water, and soil under a residential or industrial exposure scenario. Section 8.12, 

For More Information has a link to EPA’s list of

The RSLs contained in e EPA RSL table are generic; they are calculate

site-specific information. It should be emphasized that RSLs are not de fa

cleanup standards. They may be used as initial cleanup goals, and exceeding an

RSL may suggest that further evaluation of the potential risks by site contaminants is appropriate. RSLs can be incorporated into the CSM and help

the analysis of different remedial alternatives. However, the selection of final

cleanup goals will need to take into consideration site-specific conditions, 

exposure routes, receptors, and exposure durations and accommodate relevant 

and appropriate regulations and land use. PA provides an onlie RSL calcu

format where default parameters can be changed to reflect site-specific risks (see 

Section 8.12, For More Information).

It should be noted that the A RSL tables are based on human health ris

do not address potential ecological risk. Some sites in sensitive ecological settings may need to be evaluated using an ecological risk assessment. Also

tables, which are purely risk-based, may yield RSLs lower than naturally occurri

background concentrations of some contaminants in some areas. Generally, 

and state agencies do not require cleanup below natural background levels. 

Arsenic, aluminum, iron, and manganese are common elements in soils and have

background levels that may exceed risk-based RS

Other possible groundwater cleanup goals might include the maximum contaminant levels (MCLs) and secondary drinking water standards for over 9

contaminants in EPA’s Safe Drinking Water Act regulations published in

141 and 143.

8.6 Remedial Strategies

Based on the CSM, the data collected during the site investigation and an assessment of risk and cleanup levels, the next step is to identify and implement th

appropriate remedial strategy.

The remedial strategy consists of establishing specific, measurable, attainable,

relevant, and time-bound (SMART) remedial action objectives (RAOs)

identifying remedial or treatment technologies to meet the objectives. It might 

include a rationale for coupling two or more treatment technologies, applied 

simultaneously or sequentially. The remedial strategy might include smaller

pilot-scale tests to determine if technologies that appear to be likely candidates 

for treatment are effective at achieving the RAOs for the site. For groundwate

remediation, the RAOs should clearly state if the objective is restoration of th

groundwater, containment of the plume, or both. 
Chapter 8 Assessment and Cleanup 8-1

The remedial strategy can involve passive or active measures, and may (or may

not) achieve complete restoration (especially in cases of highly weathered, 

immobile, and inaccessible hydrocarbons). Between each remedial alternative 

there will be trade-offs of time, certainty, regulatory acceptance, cost, and effectiveness. In some cases, the future land use can influence the remedial strategy. 

For example, on a site that currently has an industrial use, with a long-term 

commitment to that use, the preferred remedial strategy might be an approach 

that focuses on containing the contamination at the property line, and imposing 

land use restrictions within it. Further, technologies that could be invasive or 

disruptive may not be compatible with the current land use.

Some other considerations for the overall remedial strategy for a site include

 Removing free product from the groundwater

 Understanding if the release contains oxygenate additives (if so, the potential

exists that these compounds will migrate more quickly and further and may 

require differing methods for treatment).

 Reducing groundwater concentrations in the source (release) area through

an active remedy. These concentrations will drive the total extent of the

dissolvedgroundwater plume; reducing source area concentrations quickly 

will reduce the eventual impact of the groundwater plume.

 Understanding whether the site has the potential to naturally attenuate the

contaminants (degrade or reduce concentrations), and if so, build the overall 

remedy around this natural attenuation capability.

 Employing an active plume management strategy if natural attenuation is

not adequate.

Note that various site remediation programs may list specific criteria that need

to be addressed in this evaluation of remedial alternatives. These criteria can

include how established the technology of the proposed remedy is, time to 

complete cleanup, public acceptance, cost, and other regulatory-specific criteria. 

Check the regulations associated with your cleanup to determine what needs to 

be addressed.

8.6.1 Green and Sustainable Remediation

The Office of the Under Secretary of Defense released the first green and sustainable remediation memorandum in August 2009. The memorandum was 

incorporated into a U.S. Department of Defense (DoD) Manual that s

is committed to conducting its environmental program in a sustainable manner 

and stresses the need to decrease the energy demand of existing and future 

remedial systems to minimize their environmental impact. DoD offers the following definitio

“Green and sustainable remediation expands upon the Department’s current 

environmental practices and employs strategies for environmental restoration 

that use natural resources and energy efficiently, reduce negative impacts on the 

environment, minimize or eliminate pollution at its source, and reduce waste to 

the greatest extent possible. Green and sustainable remediation uses strategies 

that consider all environmental effects of remedy implementation and operation 
8-12 Chapter 8 Assessment and Cleanu

and incorporates options to maximize the overall environmental benefit of 

response actions.”

Fortunately, there are online tools that allow project team members to compare 

alternatives and their carbon equivalents of construction, operation, and vehicle 

use (see Section 8.12, For More Information).

8.6.2 Source and Barrier Treatment Strategies

Other strategic components to consider include the need to reduce elevated concentrations in a defined source area and the need to contain the contaminants.

In source area treatment, contaminants are addressed directly, at their location. 

At most spill locations, elevated concentrations at the source area will contribute

over a long period of time to the downgradient groundwater plume, causing 

concentrations in the groundwater to increase and the overall groundwater 

plume to expand. In general, the larger extent of the groundwater plume, the 

more the future costs of remediation will increase. That is why treatment of elevated concentrations at the source, especially soon after the spill, is considered a

cost-effective action.

Barrier treatment, in contrast to source area treatment, provides a form of containment-based treatment at the edge of the source area, or at the downgradient 

limit of elevated concentrations, or sometimes near a property line. With this 

approach, the groundwater is permitted to flow through the treatment zone, but 

the contaminants in the groundwater are treated and not allowed to flow past 

this zone. The flow-through treatment zone typically consists of a trench backfilled with permeable or reactive materials. In areas with coarse gravel or sandy

soil, the most effective barriermay be a series of injection wells near one another. 

Because contaminants are treated as they migrate through this barrier, the effect 

on concentrations further downgradient is comparable to direct source treatment. Because a barrier or perimeter approach requires the source area contaminants to migrate to the treatment zone to be treated, this approach, if used alone, 

leaves the source area at higher concentrations for a longer time.

Most of the active treatment technologies described later in this chapter, except

for excavation and the thermal methods, can be deployed in either source or 

barrier treatment. The design of a source area treatment tends to balance the

treatment with the area, volume, and contamination load that is present. In 

the case of the barrier treatment, the design focuses on the area, volume, and 

contamination load that would flow through the treatment zone at any one time. 

For this reason, barrier systems tend to be more effective when installed early in 

the life of a plume, when most of the mass is still near the source area, and not 

already far downgradient.

One special barrier application is known as a permeable reactive barrier. When 

used for fuel spills, these take the form of a trench backfilled with pervious material (that is, gravel) and usually contain piping with screened sections to allow 

pumping in of treatment fluids or air (enabling oxidation or bioremediation).
Chapter 8 Assessment and Cleanup 8-1

Other types of barriers are passive (no active recharging or operation). One type 

that has been used for petroleum contamination consists of oleophilic clay, also 

known as organoclays, which attract petroleum oils but not water.

Source and barrier approaches can be used alone or in combination with each

other. Barrier approaches, alone, can work well when the direction of groundwater flow is known with great certainty; when there is no overriding reason (for 

example, operational or regulatory) to accelerate the source area cleanup; and 

when time to closure is not important (barrier systems will need to continue to 

operate as long as there is contamination that could flow through them).

8.7 Free Product Management

In some remedial strategies, the most important aspect of releases to the subsurface is removal of the source area. This often addresses the presence of freephase hydrocarbons in liquid form, usually called free product or NPL.

often identified as one of two forms: NAPL or DNAPL. Some e

include jet fuel (JP−4, JP−5, JP−8), kerosene, and gasoline. These are conside

LNAPL because they are less dense than water and tend to stay above or floa

top of the water table.

Other compounds, typically heavier oils, bunker fuel, or chlorinated solvents, can 

form DNAPL, which is usually found within and at the bottom of the groundwater-bearing zone. Each tye of NAPL requires different remedial st

strategies should consider:

 Free product may represent a source of explosive vapors in nearby vaults, 

sewers, or other spaces.

 Free product represents a large concentration of mass that will spread into 

the groundwater for years to come, if not recovered.

 Until free product is no longer present on or above the water table, nearby

groundwater will not be likely to meet cleanup standards.

8.7.1 Near-term Product Recovery

Immediately after a release, the appropriate response is to contain the released 

material as much as possible. Refer to Chapter 1, Environmental and Emergency

Response Planning for spill prevention and planning measures. If the spill infiltrates through soil and into the groundwater, the approach is to install collection 

sumps, trenches, or wells that gather the free product; pump the collected 

product to a safe, contained storage; and recycle or otherwise safely dispose of 

the recovered product. Temporary or short-term recovery programs typically

use vacuum trucks (pumping both fuel and water) or skimmer pumps (pumping 

only fuel). Refer to Chapter 2, Incident and Spill Reporting for agency notification

requirements when a spill occurs.

8.7.2 Long-term Product Recovery

For sites that are recovering fuel that has been in the ground a long time or that 

have soils that are silty or clayey in nature, free product recovery may need to 

continue for months or years. In these situations, it’s usually best to automate the 

product recovery until most of the product has been removed and then follow 
8-14 Chapter 8 Assessment and Cleanu

the final stages with periodic, manually operated recovery to extract the product 

and minimize the groundwater uptake and management as the free product or 

oil layer thins.

Many skimmer systems for recovering free product in the short term can be

adapted for longer-term application. If more aggressive recovery is needed, a 

recovery system to be used at your facility can be designed on the basis of the hydrologic and geologic conditions of the site. Dual-phase extraction (also known 

as multiphase extraction, vacuum-enhanced extraction, or bioslurping) can be 

used successfully when the petroleum product floats on the water table (that is, 

LNAPL). In these systems, one pump draws down the water table and creat

cone of depression into which the free product floats.  skimmer pump transfers

the free product to the surface for recovery (see Exhibit 8−3).

EXHIBIT 8−3

Free Product Recovery

The down-hole skimmer or product pump in this application only pumps fuel,

with little or no groundwater. These types of pumps are becoming more widely

used, as the removed fuel is typically pure enough to not require further treatment with an oil/water separator, and it can usually be reused.

8.8 Soil Remedation Technologies

Numerous soil remediation technologies are available. Often a combination

of soil remediation technologies (and groundwater treatment technologies 

discussed later) may be the most effective remedial strategy. Soil can be treated

while still in the ground (in situ) or after excavation (ex situ). The volume of

soil needing treatment, the location of contamination, and other site-specific 

conditions as described in the CSM will influence the choice of technologies. I

addition, consideration of equipment and operation and maintenance (O&M)

costs for some technologies may be justified only for large volumes of soil.
Chapter 8 Assessment and Cleanup 8-1

In situ treatment methods include soil vapor extraction, bioventing, and enhanced bioremediation.

If land and time are available, there may be several on-site ex situ treatment 

options:

 Biopiles or biomounding, in which the soil is treated in piles with nutrients 

and water

 Phytoremediation, in which the soil is spread, amended, and planted to be

gradually treated by the roots of the grasses and plants

 Landfarming, in which the soil is spread, fertilized, irrigated, and heated by

the sun to encourage biological treatment of the contaminants

 Portable low-temperature thermal units that can process limited quantities of

soil, often more quickly and with more certainty 

 Excavation and off-site disposal, generally for small volumes of contaminated

soil.

The following sections discuss the above options; other treatment options may

be available.

8.8.1 Soil Vapor Extraction

Soil vapor extraction (SVE) is an in situ treatment that physically separates 

contaminants from the soil. It uses wells screened above the water table (soil 

above the water table is called the vadose zone), with a vacuum applied by a 

blower system at the ground surface. The vacuum creates a flow of soil vapor to

the well. The air drawn from the soil is made up by air that originally comes into

the soil from the atmosphere, so this usually has two effects on the constituents 

in the vadose zone:

 The air flowing through the soil takes up vapors from theLNAPL a

evaporates; these are carried to the well to be recovered

 The oxygen in the air adds to the dissolved oxygen in the soil moisture, which

helps soil bacteria consume dissolved vapors

SVE systems are designed to remove contaminants that have a tendency t

volatilize (evaporate easily). The extracted air, especially if it contains high concentrations of petroleum vapors, may initially be combustible or even explosive

when it is brought to the surface to be treated. Care must be taken in handling 

these vapors, especially in the early stages of recovery; this typically involves the 

use of explosion-proof equipment and grounded, spark-arrested components. 

Often these systems must be permitted before operation, often with local fire 

departments, building departments, or state or local air quality agencies.

The basic components of an SVE system include an air/water separator, an inli

filter, a blower (matched to the soil permeability), and an air treatment system 

(see Section 8.10, Off-gas or Air Treatment Technologies).

Exhibit 8−4 shows a typical SVE system. Some configurations use horizont

extraction wells placed in trenches instead of vertical wells. The only limit on
8-16 Chapter 8 Assessment and Cleanu

depth for these wells is the depth of the water table; SVE is effective only in soi

above the water table.

SVE may be enhanced by the addition of heat or steam. The heat is transferred 

the soil and the volatile constituents tend to evaporate for collection by a heat-resistant SVE system. Some temperatures may rise above the melting temperatu

for plastic well materials; therefore, all wells and piezometers need to be made of 

stainless steel to maintain their function through and after a thermal treatment.

EXHIBIT 8−4

Soil Vapor Extraction

8.8.2 Bioventing

In situ bioventing involves delivery of oxygen to contaminated unsaturated soils 

by forced air movement (either extraction or injection of air) to increase oxygen 

concentrations and stimulate biodegradation. It may use most of the same components as SVE, but it applies a smaller vacuum to produce a lower flow. Duri

extraction, the blower discharge may require air treatment or may be discharged 

directly through a tall stack depending on concentrations and site location. In 

some situations, air or oxygen is injected into the soil at a slow rate, stimulating 

the bacteria in the soil to use contaminants as food. Bioventing can be used 

to treat aerobically biodegradable constituents. Bioventing has been proven 

effective in remediating releases of gasoline, jet fuels, kerosene, and diesel fuels.

Bioventing is typically used after the highest concentration source removal is 

completed. Bioventing is appropriate for the lower concentration phases of the 

remediation.
Chapter 8 Assessment and Cleanup 8-1

8.8.3 Enhanced Bioremediation

Bioremediation is a treatment process that uses naturally occurring microorganisms (such as, yeast, fungi, bacteria) to degrade (break down) hazardous 

substances into less toxic or non-toxic substances. Microorganisms eat and

digest organic substances for nutrients and energy. (In chemical terms, organic 

substances are those that contain carbon and hydrogen atoms.) Certain microorganisms can digest organic substances, such as fuels or solvents, that are hazardous to humans. The microorganisms break down the organic contaminants

into harmless products—mainly carbon dioxide and water. Although successful

in situ biodegradation has been demonstrated in cold weather climates, low 

temperatures slow the microbial degradation rate. For contaminated sites with 

low soil temperature, heat blankets may be used to cover the soil surface to 

increase the soil temperature and the degradation rate.

Enhanced bioremediation or biodegradation is a broad, general term that simply means adding something into the soil with the purpose of stimulating the

bacteria to use the contamination as food. The term “enhanced biodegradation”

or bio-stimulation for soil remediation usually involves adding nutrients to the 

soil in situ.

Nutrients are usually added to the soil by percolating or injecting water mixed

with nutrients through the soil. An infiltration gallery or spray irrigation is typically used for shallow contaminated soils, and injection wells are used for deeper

contaminated soils. When enhanced biodegradation involves the addition of 

supplementary microorganisms, the technology is termed bioaugmentation.

8.8.4 Biopiles or Biomounding

Soil biopiles or biomounding involves excavation and piling contaminated soil 

in heaps over a system of perforated piping. Air is supplied to the piping using

blowers or is drawn through the pile using vacuum pumps. Microorganisms in the

soil degrade the organic compounds in the contaminated soil. Moisture and nutrients are added to maximize bioremediation. Volatile contaminants are controlled

easily if a vacuum is being used to pull air through the pile (see Exhibit 8−5).

EXHIBIT 8−5

Typical Biopile System

Biopiles have been proven effective in reducing concentrations of petroleum-related constituents. Depending on the state’s regulations for air emissions of
8-18 Chapter 8 Assessment and Cleanu

volatile organic compounds (VOCs), vapor controls may be required before 

venting exhaust to the atmosphere.

8.8.5 Phytoremediation

Phytoremediation is a process that uses plants (such as grasses or willow and 

poplar trees) to remove, transfer, stabilize, and destroy contaminants in soil and 

sediment. The mechanisms of phytoremediation include enhanced rhizosphere

biodegradation, phytoextraction (also called phytoaccumulation), phytodegradation, and phytostabilization. Phytoremediation generally works best for

contamination that is widespread, shallow, and low to medium levels of contamination. Phytoremediation can be used to clean up certain metals, pesticides,

crude oil, and components of gasoline, diesel, and jet fuel. Different plants are

selected for each application. Phytoremediation is a slow process but can be used

where other technologies are not practical or are undesirable. This technology

has the distinct advantage of being aesthetically pleasing, and beneficial to the 

environment.

8.8.6 Landfarming

Landfarming or land treatment is a relatively simple treatment method. 

Contaminated soils are excavated and spread on a pad or liner with a built-in 

drainage system to collect any leachate (contaminated liquids that seep out of 

contaminant-soaked soil) (see Exhibit 8−6). The soils are periodically turned over

or tilled to mix air into the waste. Moisture and nutrients are added to enhance

bioremediation. Biodegradation (broken down by bacteria) accounts for most of 

the remediation, but volatilization (release of vapors) and photodegradation

(broken down by light) can also enhance cleanup.

Landfarming, like biopiles, has been proven to be effective in reducing concentrations of petroleum-related constituents

EXHIBIT 8−6

Landfarming Schematic
Chapter 8 Assessment and Cleanup 8-1

8.8.7 Low-temperature Thermal Stripping

Low-temperature thermal stripping is also known as low-temperature thermal 

desorption, thermal volatilization, and soil roasting (see Exhibit 8−7). The process

involves feeding contaminated soil into a feed hopper, which falls into a thermal 

processor. Thermal processors are designed to heat soils to sufficient temperatures

(200 ̊F−1,000 ̊F/93 ̊C−538 ̊C) to cause constituents to volatilize and desorb (physically separate) from the soils. Air pollution control equipment (such as an afterburner, catalytic oxidation chamber, scrubber, or carbon adsorption unit) is usually

required to treat exhaust gases (vaporized hydrocarbons) prior to discharge.

EXHIBIT 8−7

Low-temperature Thermal Stripping

After leaving the desorber, soils are cooled, remoistened to control dust, and

stabilized (if necessary) to prepare them for disposal or reuse. Treated soil may be

redeposited on-site, used as cover in landfills, or incorporated into asphalt.

Low-temperature thermal desorption has been proven effective in reducing

concentrations of petroleum products including gasoline, jet fuels, kerosene, 

diesel fuel, heating oils, and lubricating oils.

8.8.8 Excavation and Off-site Disposal or Recycling

Soil removal is an appropriate strategy if the area is small and shallow, and a

quickly implemented cleanup is important. Excavation of contaminated soil is

generally possible to a depth of 25 feet or more, depending on the equipment 

available and the water table depth. When contaminated soil is excavated, it must 

be either treated on-site or transported for off-site treatment or disposal.

You can landfill soil off-site if it’s not heavily contaminated with petroleum and 

has no free liquids. Many municipal or solid waste landfills will accept this waste

if it is non-hazardous. PA exempts petroleum-contaminated soil and debris fr

the hazardous waste toxicity characteristic (D018 through D043) if it is bein

cleaned up under the ST regulations in 40 CFR 280. Check to see if state requirements also provide this exception. Other contaminants may need additio

treatment before landfilling, depending on the landfill’s permit. The landfill may

be able to treat the soil at its facility prior to land disposal and include this cost in 

the disposal price.
8-20 Chapter 8 Assessment and Cleanu

Petroleum-contaminated soil can be incorporated into marketable products.

Contaminated soil may be accepted by certain asphalt processing, cement 

production, and brick-making facilities.

8.9 Groundwater Remediation Technologies

At many sites, the focus of long-term remedial actions centers on the groundwater and restoring water quality. Some common groundwater treatment technologies include groundwater extraction and treatment (called pump and treat) o

in situ methods, such as air sparging, chemical oxidation, thermal treatment, and 

monitored natural attenuation.

8.9.1 Pump and Treat

A pump and treat system is a common method for treating contaminated

groundwater. With this technique, a system of extraction wells or trenches and 

pumps brings contaminated groundwater to the surface. The water is collected

and sent through an aboveground treatment system, such as an oil/water 

separator, air stripper, biological treatment system, or granular activated carbon 

(GAC) system. There are regulatory considerations and possible permits fo

discharge of treated groundwater.

There are various kinds of extraction wells and pumps for groundwater recovery

systems. An experienced hydrogeologist will establish the best locations and

spacing of the wells. Belowground drains or interceptor trenches (sometimes 

called French drains) to collect contaminated groundwater are an alternative to 

extraction wells.

There is considerableEPA and state concern that pump and treat does not produce required cleanup levels in a reasonable time and that it is costly. Alth

often used in the past, it may not be your best long-term solution because the 

long-term costs can be significant. However, pump and treat does have an advantage of capturing or arresting the migration of a plume that could be threatening

a downgradient receptor.

8.9.2 Air Sparging

Air sparging is also known as in 

situ air stripping, groundwater 

sparging, and in situ volatilization. 

Air sparging is an in situ remedial

technology that reduces concentrations of volatile constituents 

that are adsorbed to soils and 

dissolved in groundwater. This

technology involves injecting 

pressurized air into the saturated 

zone (below the water table) via 

an injection well, called a sparging 

well. The air bubbling up allows

volatile compounds dissolved in 

EXHIBIT 8−8

Air Sparging
Chapter 8 Assessment and Cleanup 8-2

the groundwater to migrate up into the unsaturated soil as a vapor (see Exhibit 

8−8). In addition to its air stripping capability, air sparging enhances biodegradation by supplying oxygen to groundwater, which helps microorganisms digest 

organic substances. Air sparging using low air flow rates and the addition of

nutrients is sometimes called biosparging.

Air sparging is often used together with SVE. When air sparging is combined wi

SVE, the SVE system mechanically extracts vapors that the sparging system 

freed from the groundwater and prevents the dispersion of these vapors to any 

sensitive or potentially explosive surface receptors. Air sparging is effective in

reducing concentrations of VOCs. Air sparging is generally more applicable to the

lighter gasoline constituents (such as BTEX) because they readily transform fro

liquids into gases. Air sparging is less applicable to diesel fuel and kerosene

For treatment of elevated concentrations in source areas, sparging requires soils 

that are sand-sized or greater (otherwise, the air cannot bubble up through the 

groundwater). Both vertical wells and horizontal wells are used to deliver the air, 

with horizontal wells having advantages in coverage and versatility. Horizontal

wells can often be installed beneath structures or piping systems, where vertical 

wells might not have easy access.

8.9.3 In situ Chemical Oxidation

In situ chemical oxidation (ISCO) involves the introduction of a chemical oxidant

for the purpose of reacting and transforming or breaking down groundwater 

contaminants into less toxic compounds that are more stable, less mobile, or 

inert. There are several different forms of oxidants that have been used for ISCO

The four most commonly used oxidants are permanganate (MnO4−), persulfat

(S2O8), hydrogen peroxide (H2O2), and ozone (O3). Chemical oxidation is primaril

used to treat contaminants in the source area saturated zones and capillary 

fringe. Chemical oxidants are typically delivered via injection wells, infiltration 

galleries, and temporary injection points.  good chemist can assist with selecting the oxidant that works best against specific contaminants

There are potential hazards using chemical oxidants because most are corrosive

and highly reactive, with the potential to be explosive. Heat may be generated by

the chemical reactions and excessive heat production may need to be addressed 

(it may damage or melt polyvinyl chloride or plastic wells). Proper worker protection is needed when handling these chemicals

In addition, there are several regulatory requirements pertaining to chemical 

oxidation including approval of an oxidant injection permit from federal or state 

environmental agencies under their underground injection control programs. 

Chemical storage may trigger Emergency Planning and Community Right-toKnow Act (EPCRA) requirements (see Chapter 12, Routine Rep

8.9.3.1 Permanganate and Persulfate Oxidation

Potassium permanganate (KMnO4), is the most common oxidant of the four an

is available in a solid that must be mixed with water before injection. Another

form is sodium permanganate (NaMnO4), which is more stable and supplied as 

liquid. Activated sodium persulfate (Na2S2O8) is a relatively new form of oxidan
8-22 Chapter 8 Assessment and Cleanu

These are strong oxidizers and typically only used in high concentration cases.

It’s not safe to apply these compounds if free product is present unless the risk 

of uncontrolled oxidation is eliminated. Often the most successful use of these 

oxidants is in otherwise difficult to treat settings, such as low permeability soils, 

heavier fuels, or hard to access locations.

8.9.3.2 Hydrogen Peroxide Infiltration

Hydrogen peroxide, injected or infiltrated into the saturated zone, serves as a

source of oxygen to enhance bioremediation of organic-contaminated areas, 

includingpetroleum-impacted areas. Hydrogen peroxide is often delivered via

extracted groundwater that is re-injected or re-infiltrated back into the subsurface. Subsurface persistence has been cited as a concern in some cases, but the

liquid delivery adds an advantage in that its delivery can be incorporated into an 

existing water pumping system. Hydrogen peroxide is particularly effective when

catalyzed by iron. The subsequent reaction between hydrogen peroxide and

ferrous iron produces what is called Fenton’s reagent.

8.9.3.3 Ozone Injection

Ozone is another powerful oxidant and may be injected into the ground in a 

dissolved phase or in a gaseous phase through the use of sparging wells. The instability of ozone requires that it be generated on-site. This can be accomplishe

using a simple process where electrical energy breaks apart oxygen molecules 

present in the air to react and make ozone. In situ decomposition of the ozone 

can lead to beneficial oxygenation and biodegradation of contaminants in 

addition to the oxidation reactions.

Vapor control equipment, such as an SVE system, may be needed if ozone injection rates are sufficient to emit fugitive ozone emissions into the unsaturate

zone and atmosphere.

8.9.4 In Situ Thermal Treatment

Different in situ techniques can be used to apply heat to contaminated groundwater and soil. The heat can destroy or volatilize organic chemicals. As the contaminants change into gases, their mobility increases, and the gases can be extract

via SVE wells, which may require off-gas treatment depending on the state regulations and the site location. Alternatively, thermal treatment areas may be cover

with an impermeable surface cover (such as concrete, asphalt, or a heavy-duty 

tarp) to keep the heat and steam underground. Such covers also help prevent the

release of chemical vapors into the air. Thermal methods can be particularly useful

for LNAPLs, especially less volatile oils. Heat can be introduced belowgrou

injecting steam and hot water or through electricity using electrical resistance 

heating and thermal conduction heating. Selecting the most appropriate heating

technology is a site-specific decision that is influenced by subsurface permeability, 

contaminant properties, and the contaminant distribution.

In situ heating with steam couples subsurface injection of steam (or hot water) 

with multiphase extraction of soil vapor and groundwater. In practice, steam will 

also displace APL from a treatment area, which makes this heating appro

the most effective for NAPLs with low volatility. Overall, the method is well-sui
Chapter 8 Assessment and Cleanup 8-2

for large sites with moderate to high permeability because heating is strongly 

controlled by the lateral distribution of steam in the treatment area. Treatment

temperatures are pressure-dependent, but conditions over 212 ̊F/100 ̊C are 

feasible with this technology.

Electrical resistance heating (ERH) delivers an electrical current between an ar

of metal rods called “electrodes” installed underground. The heat generated as

movement of the current meets resistance from soil converts groundwater into 

steam, vaporizing contaminants. Given the nature of this heating mechanism, 

ERH treatment temperatures are limited to the boiling point of water at loc

pressure conditions. The heating technology excels in fine-grained soils with low

to moderate permeability.

When using ERH, the electrical current is prevented from traveling outside 

the treatment area or to aboveground structures by using common electrical 

grounding techniques.

Thermal conduction heating (TCH), also referred to as in situ thermal desorptio

supplies heat to the soil through electric heating elements encased in steel wells 

that are sealed from groundwater entry.  recent variation of TCH has coupl

propane or natural gas combustion for in situ heating. Like ERH, multiple heat

are installed within the treatment area; similarly, TCH also works well in finegrained soils with low to moderate permeability. Unlike ERH, the TCH pro

capable of in situ treatment temperatures in excess of 212 ̊F/100 ̊C. In practice, as 

the contaminated area is heated, the contaminants are destroyed in situ, evaporated, or extracted and treated aboveground.

8.9.5 Monitored Natural Attenuation

Natural attenuation is a passive remedial approach that depends on natural 

processes to reduce contaminant levels in groundwater, and in soil to a lesser 

degree. This approach is often called monitored natural attenuation (MNA).

most important natural processes are aerobic biodegradation and volatilization. 

Other processes that can contribute are oxidation and/or reduction, sorption, 

dispersion, dilution, and radioactive decay. These processes tend to occur naturally without human intervention. Natural attenuation is also known as passiv

or intrinsic bioremediation.

MNA is usually not implemented as the main remedy untl LNAPL (free p

has been removed to the maximum extent practicable. For ST releases, fr

product removal must be conducted per 40 CFR 280.64. As discussed previously

the removal of free product carries other practical benefits, such as shortening the 

expected time of remediation and minimizing cost. Likewise, understanding the

CSM an MNA potential will lead to the optimization of the groundwater p

strategy (for example, an oxygen limitation might favor an oxidation approach).

Because petroleum hydrocarbons are readily broken down by aerobic bacteria 

and most groundwater sites are naturally replenished with oxygen, intrinsic 

bioremediation can be an important aspect of groundwater plume management 

for these types of releases. Naturally occurring degradation often exceeds, on a

mass basis, the amount being degraded by sparging, or ISCO, or similar active

remedies for large spills.
8-24 Chapter 8 Assessment and Cleanu

The major exceptions to this condition of naturally aerobic groundwater should

be expected around shorelines or bays, or in heavily industrialized zones. At these

locations, the natural replenishment of atmospheric oxygen may be suppressed, 

or the decaying organic matter in the soil may steadily consume the oxygen 

naturally present, leaving little if any for MNA. Under these conditions, ot

processes take on a greater importance. In addition to sorption, dispersion, and 

dilution, there are also other oxidation processes that can occur when oxygen 

is absent, involving nitrate (consumed), iron (made soluble, appearing), sulfate 

(consumed), and methane (produced). In the absence of oxygen, these processes 

are typically important to consider for NA effectivene

Natural attenuation of groundwater requires routine monitoring to confirm that

natural processes are reducing contaminant levels.

8.10 Off-gas or Air Treatment Technologies

Certain remedial technologies for soil and groundwater transfer the contaminants from those media to the atmosphere. In most areas of the U.S. and fo

most sites, some form of treatment will be required before these vapors can be 

discharged. In some cases, permits will be required for the air treatment systems. 

For example, air treatment systems typically represent at least 50% of the life 

cycle cost of most remediation projects and can consume over 75% of the energy 

used. For these reasons, the air treatment system selected and deployed should 

be understood and managed carefully.

Air treatment systems are based on three principles: adsorption, thermal oxidation (controlled burning), and condensation. Each has an optimum applicatio

based on concentration range and contaminant loading. The following sections

discuss these general treatment types.

The primary remediation systems that will require air treatment are SVE (wi

or without air sparging) and air stripping of groundwater. The concentration

ranges to be expected from each of these systems are the key to understanding 

the optimum air treatment system to use, or whether to start with one and plan 

to transition to another when concentrations have fallen. Planning this sort

of staged treatment before installation of the initial system can make a future 

switchover relatively simple.

8.10.1 Air Treatment by Adsorption

Vapor-phase granular activated carbon (VGAC) is a common system used to purify waste gases from site remediation systems. VGAC is easy to operate, has lo

energy costs, and can be used over a wide range of concentrations.  VGAC system consists of containers of activated carbon (from 55-gallon drums to 10,000 l

tanks) that are typically connected as the final treatment step of a system. VGAC

adsorption works most effectively when the incoming vapor stream is warm 

(100 ̊F/40 ̊C to 140 ̊F/60 ̊C) and of medium humidity. This is one of the reasons

VGACs are placed downstream of blowers, as blowers tend to heat up and dry out

the vapors they collect from the ground or from the discharge of an air stripper. 

Another reason is the air is near atmospheric pressure coming into and exiting

the VGAC vessels, so collecting samples to verify compliance is simpler
Chapter 8 Assessment and Cleanup 8-2

VGAC usually adsorbs hydrocarbon vapors at a rate of about 10 percent by

weight (for example, it takes 500 lb of VGAC to adsorb 50 lb of hydrocarbons).

wide variety of contaminants, not just fuel components, can be adsorbed by the 

carbon.

8.10.2 Air Treatment by Thermal Oxidation

Hydrocarbons are readily oxidized, so burning vapors is a common method of air

treatment for remediation systems. The two most common methods used are

 Thermal oxidizers (THERMOX) are flares that burn the incoming vap

fuel and frequently have a natural gas feed line to make up energy when 

the incoming concentrations decrease. They are simpler to operate than a

catalytic oxidizer but more expensive at lower concentrations (because of 

supplemental fuel).

 Catalytic oxidizers (CATOX) use a heated catalyst to efficiently treat the fue

vapors, with either electricity or natural gas used to preheat the catalyst. 

These systems typically have higher capital costs than THERMOX units

can cost-effectively treat to lower concentrations.

Both of these units require an external power supply and permitting prior to 

operation, but are highly efficient for relatively high concentration vapor streams. 

These also represent a well-understood technology, which can lead to expedited

regulatory approval. Units are typically available on short notice

If a mixed contamination source is to be treated, thermal options tend to be 

effective for oxygenated fuels, but sensitive otherwise. Any halogenated compounds (chlorinated, fluorinated), such as Freon or solvents, can be problematic;

side-effects could include the formation of acids in the discharge or poisoning of 

the CATOX unit’s catalys

8.10.3 Air Treatment by Condensation

For high vapor concentrations, condensation using a refrigeration cycle in which 

the incoming vapor is chilled to the point that the hydrocarbons form a liquid. 

The liquid can then be separated and then recycled or incinerated.A VGAC unit 

typically used for the remaining vapor stream.

These units require a significant energy supply and are typically available on a

leased basis for 6 or 12 months. They can be complex to run but include telemetry and remote operation options. Overall they work best during the initial stages

at large spill sites, when the concentrations will stay high (greater than 5,000 

parts per million by volume TPH) for many months. Condensation units are t

most robust technology for mixed-compound air streams.
8-26 Chapter 8 Assessment and Cleanu

8.11 State Requirements

State petroleum assessment and cleanup programs, regulations, policy and

guidance can evolve, so always check with your state agency for its remediation 

program requirements. 

 Most states have developed their own programs for LUSTs, and some 

programs for ST releases. The requirements vary widely between states 

often are site-specific. These programs indicate what parameters to test for,

what levels need corrective action, and what the cleanup level should be. 

Many programs also require that individuals performing the assessment be

certified by the state agency. Appendix E lists state environmental agency 

contacts. Be aware that in a few states, the registration, testing and closeout 

of USTs are handled by the state Fire Marshal’s Office or other department

state government. 

 Most states have voluntary cleanup programs. Frequently these are coupled

with the state Brownfields programs to encourage redevelopment of 

contaminated property. 

 Most states have risk-based approaches based either on theAS

standard, or their own risk-based process, for ST cleanups. This means 

level of cleanup is based on many factors, and not necessarily one given 

value for all sites. 

 Most states have cleanup levels for MTBE in groundwater. The remai

states are waiting for PA to establish a national primary drinking wat

regulation or MCL for 

 States such as Missouri, Delaware, Maine, Michigan, New Jersey, and se

others have begun establishing cleanup levels for other oxygenates in 

addition to MTBE. For instance, California and New Jersey have establis

drinking water and groundwater action levels for the oxygenate TBA, whic

is an intermediate of MTBE biodegradation and was used as a gasoli

blending component circa 1975−85.

 California, Colorado, Illinois, Massachusetts, Minnesota, New York, Orego

and Wisconsin have green remediation programs.

 Many states have their own state Superfund, which may include othe

contaminants that are not included under the federal Superfund. For

example, in Hawaii, petroleum oils are included in the state Superfun

 Many states have issued their own state cleanup standards. These standard

are called by many different names and can be found in guidance documents 

or in regulations.

 Some states, such as New Jersey, New York, Pennsylvania, and Misso

may require permit equivalents for CERCLA projects, despite th

exemption from permitting for remedial actions.

State Requirements
Chapter 8 Assessment and Cleanup 8-2

8.12 For More Information

For Information On... See...

Assessment and Cleanup Related Agencies

EPA Federal Facilities Restorat

and Reuse Office www.epa.gov/fedfa

EPA Office of Underground Sto

Tanks www.epa.gov/US

EPA Superfund Website www.epa.gov/super

EPA Vapor Intrusion www.epa.gov/oswer/vaporintrus

EPA Site Characterizat

Assessmen

www.epa.gov/land-research/site-characterization-and-monitoring-technical-support-center-scmtsc

EPA Brownfields Program www.epa.gov/brownfi

Triad Resource Center www.triadcentral.o

DoD Strategic Environmen

Research and Developmen

Program (SERDP

Environmental Security Technolo

Certification Program (E

http://serdp−estcp.org/Program−Areas

Utility marking prior to digging National “Call Before You Dig” Phone Number Dial 8

www.call811.com

Documents and References

Cleanup Level

Use of Risk−Based Decision−Making in UST Corrective

Action Programs. PA OSWER Directive 9

March 1, 1995. Available fr

www.epa.gov/sites/production/files/2014-02/documents/d9610.17.pdf

Guide for Risk−Based Corrective Action Applied 

at Petroleum Release Sites. STM Stan

E−1739−95(2005). American Society for Testin

Materials (ASTM). Philadelphia, Pennsylvania.

299−5585.

EPA Regional Screening 

EA RSL Calc

www.epa.gov/reg3hwmd/risk/human/ rb−concentration_table/Generic_Tables/index.htm

https://epa-prgs.ornl.gov/cgi-bin/chemicals/csl_search

EPA Contaminated Site Clea

Information (CLU−IN) a

Software (extent, flux, cost

www.clu−in.org

www.clu−in.org/software

EPA Green Remedia

https://clu-in.org/greenremediation/

and 

www.epa.gov/greenercleanups/

epa-principles-greener-cleanups

SiteWise tool (jointly developed by the U.S. Army Co

of Engineers and U.S. Navy,

collaboration with Battelle).

www.clu−in.org/products/tins/ tinsone.

cfm?num=33952490

Sustainable Remediation Too

(developed by U.S. Air Force Civ

Engineer Center for use by the U.

Air Force

www.clu−in.org/products/tins/ tinsone.

cfm?num=66247610

For More Information
8-28 Chapter 8 Assessment and Cleanu

8.13 Action Items

Item

Date 

Started

Date 

Completed N/A Comment(s)

Notify regulatory agencies in the 

event that an environmental 

release is identified at your facility.



Hire a qualified and capable consulting firm to initiate response 

actions, including the preparation 

of an investigation work plan 

and initial negotiations with your 

environmental agency.



Charter the selected consulting 

firm to jointly confirm program 

values, project objectives, 

time-critical actions, performance 

criteria, lines of communication, 

initial CSM, and range of probabl

remedial actions.



Determine the cause and extent of 

site contamination through field 

investigation and prepare a site 

investigation report for submittal 

to your environmental agency.



Obtain permits for investigation 

and cleanup in sensitive areas 

such as wetlands, floodplains, and 

wildlife habitats, and for air and 

wastewater discharges.



Conduct human health and 

ecological risk assessments to 

understand which receptors and 

pathways are important and how 

much cleanup is necessary.



Prepare a proposed cleanup plan 

for submittal to your environmental agency, and negotiate 

the details prior to initiation of 

cleanup actions.



Choose and implement a cleanup 

method that provides the optimum balance between effectiveness and life cycle cost.



Manage site investigation and 

remediation wastes as hazardous 

waste, if appropriate.



Maintain detailed records of all 

site investigation and remedial 

actions.



Install, operate, and maintain 

pollution control and remediation 

systems for many years.



Action Items
Chapter 8 Assessment and Cleanup 8-2

Appendix 8−1 Regulatory Flow Chart for UST Release Reporting, 

 Investigation, Response, and Corrective Action

Appendix 8−2 General Comparison of Environmental Cleanup 

 Process Under Three Regulatory Programs

CHAPTER 8 

Appendices
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Chapter 8 Assessment and Cleanup 8-3

Appendix 8-1: Regulatory Flow Chart for UST Release Reporting, 

Investigation, Response, and Corrective Action

Yes

No

Uncontained spill

overflow?

40 CFR 280.53

Take immediate abatement and cleanup action

and notify agency within 

24 hours*

Report activities/results within 45 day

Notify agency of

suspected release within 

24 hours*

No further action

needed

Confirm suspected release 

within 7 days

• Perform system test

• Perform site chec

40 CFR 280.52

Take actio

• Notify agency of actual

release within 24 hours

• Prevent further releas

• Mitigate hazar

40 CFR 280.61

Report abatement and initial sampling results within 20 days

of confirmed release

40 CFR 280.62

Perform free product

removal

40 CFR 280.64

Perform initial site

characterization

40 CFR 280.63

Perform further

investigations and 

report 

Implement corrective action and report

40 CFR 280.66

Suspect a release

40 CFR 280.50

Release confirmed

Implementing 

agency can require 

corrective action 

plan

*NOT: A release of a hazardous substance ≥ its reporta

quantity under 40 CFR 302 and 355 requires immediate

notification (rather than 24 hours)
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Chapter 8 Assessment and Cleanup 8-3

Appendix 8-2: General Comparison of Environmental Cleanup 

Process Under Three Regulatory Programs

Elements of Program RCRA Corrective Action CERCLA (Superfund) Brownfields

Responsible Agency RCRA−authorized tate EPA Region or federal ag

as D

EPA, state or local governm

Initiation of the

Investigation Proces

Required by a RCRA 

B Treatment, Storage

Disposal Facility permit or

under an RCRA enforceme

order

A hazardous substance may be

released to the environment or a 

release or a threat of a release of 

a hazardous substance, pollutant, 

or contaminant into the environment that may be presenting an 

imminent threat to public health 

and welfare

Desire to redevelop propert

Records Search RCRA Facility Assessment Preliminary Assessment Due-diligence 

Confirmatory Sampling (Optional)A Phase 

Facility Investigation or a 

Release Assessment may 

conducted to determine if 

interim measures (conducted at the discretion of the

implementing agency) are

necessary

Site Inspection Due-diligence Assessme

through a Phase I Environmenta

Site Assessment and Phase II 

needed

Interim Action (can occur

during any point in the

remedial process)

Interim or stabilization 

measures

Removal Action Not Applic

Site Scoring Not applicable Hazardous Ranking System scoring for National Priorities

determination

Not Applicab

Nature and Exten

Determinatio

RCRA Facility Investigation Remedial Investigation Due-diligence Asses

through a Phase II

Environmental Site Assessm

Alternatives Evaluation Corrective Measures Study Feasibility Study Predevelopment, incl

identifying and refining development idea by assessing

potential reuse and identifying 

sources of financing

Proposed Action Fact Sheet or Statement

Basis

Proposed Plan Securing the Deal, includ

negotiating contract terms, 

securing financing, and deciding 

how to manage environmental 

liability

Remedy Selectio

Decision Docume

RCRA Permit Modifica

or Agreed Orde

Record of Decision Remedial Action

Action Implementation Corrective Measure

Implementation

Remedial Design/Remedial Action Remedial action and construction or land reuse develo

Long-term O&M RCRA Permit Modifi

Including Closure and 

Post-closure Care or Agree

Order

Long-Term Response Acti

(LTRA); Operation 

Maintenance; Institutional

Controls; Five-year Reviews

Remedy Optimizatio

Long-term sustainable reuse

remedial system maintenance, 

and institutional controls may 

be negotiated with property 

owners as part of a deed of sale
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