We've made some changes to EPA.gov. If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

Underground Storage Tanks (USTs)

Leaking Underground Storage Tanks Corrective Action Resources

Release Discovery and Confirmation

On this page:

Introduction

A typical leaking underground storage tank (LUST) scenario involves the release of a fuel product from an underground storage tank (UST) that can contaminate surrounding soil, groundwater, or surface waters, or affect indoor air spaces. Early detection of an UST release is important, as is determining the source of the release, the type of fuel released, the occurrence of imminently threatened receptors, and the appropriate initial response. The primary objective of the initial response is to determine the nature and extent of a release as soon as possible.

Warning signs of a release can be identified through inspection and monitoring, inventory control, and leak-detection technology. Once the release is confirmed, notification to the appropriate government agency must follow particular state or tribal requirements.

In some cases, emergency response actions must be taken immediately without waiting for government approval or oversight. Initial actions are all focused on protecting public health, safety, and the environment. Under most state regulations, the operator or owner has specific time frames to conduct initial response actions, submit reports, complete an initial site characterization, and conduct free product removal. It is important that LUST personnel reinforce these required targets in the event that an enforcement action becomes necessary.

Top of Page


Release Sources

Identifying the specific portion of the tank or tank system that has caused a subsurface release is a critical first step. Common vulnerable areas include the bottoms of USTs (particularly underneath the manhole where gauging sticks are or were formerly used), associated piping, UST fill manholes, dispensing pumps, and areas known likely to have installation issues. Piping failures are especially common at UST junction points and when ground settlement in the vicinity of an UST varies from one end of a tank to the other.

Many states have conducted studies on the sources and causes of releases. Links to some of these studies are provided below, but there may be additional information available from other sources.

Top of Page


Warning Signs of a Release

Releases are detected in various ways. Leak detection equipment may signal a release, or unexpected water may be detected in a tank. There may be a spill identified while delivering fuel into an UST or dispensing fuel at the point of sale. Releases may also be identified during tank upgrades or replacements as these activities are also known to be common causes of releases.

Often, inventory control can alert the UST operator of a release, which may be discovered as a discrepancy in the inventory of fuel delivered versus the fuel dispensed from the UST. Newer UST systems have automatic tank gauging systems that can immediately identify a discrepancy using electronic measurement sensors and sound an alarm.

If a tank or UST system is being upgraded or replaced, field screening and sampling by a qualified professional may help to quickly identify a release and its specific cause. Experienced field oversight can also help limit the impact of a release on public health, safety, and the environment. The benefits to an UST owner of an immediate discovery of a release are reduced downtime and costs.

Top of Page


Release Confirmation

Confirming that a release has occurred from an UST should be done systematically. A first step is to determine if the UST system and monitoring equipment are operating correctly. Sensors that monitor releases may need to be checked to ensure that they are functioning properly. Another step may involve checking fuel delivery receipts to examine inventory. Once the equipment and inventory have been checked, a release can be confirmed by testing the tightness of the UST system using government and industry acceptable methods. Tank tightness is an indication of leaks, including very small or slow leaks.

Top of Page


Regulatory Notification

Owners and operators of USTs are required to investigate, confirm, and notify the authorities of all suspected releases within 24 hours or other time period specified by the state or tribal agency. The amount of time permitted before providing notification as well as the reportable quantity threshold vary by implementing agency.

Documentation and reporting requirements are also unique to each state and tribe; inventory and maintenance records must be maintained at the facility according to these requirements to allow consultants and regulators access to information on the release.

Top of Page


Immediate Response Actions

Once a leak is confirmed, immediate response actions must be taken to minimize or eliminate the source of the release and to reduce potential harm to human health, safety, and the environment. Each state has unique requirements for initiating responses to a release, and it is up to the UST owner or operator to conduct actions in compliance with his/her local rules. State, local, and tribal contacts can help identify qualified professionals who will be able to provide quick assistance to help reduce costs and liability.

Immediate responses may include removing flammable or explosive materials from the release area and preventing discharges to stormwater utilities, wetlands, and surface waters. It may also be necessary to provide bottled water for individuals, families, or businesses that rely on groundwater for drinking, bathing, and food preparation. The intrusion of petroleum vapors into indoor building spaces has become an important concern and may require the active ventilation of indoor building spaces.

Top of Page

Site Characterization and Conceptual Site Model

On this page:

Introduction

Site characterization is the process by which site-specific information and data are gathered from a variety of sources to characterize the physical, biological, and chemical systems at a contaminated site. A conceptual site model (CSM) integrates all lines of evidence into a three- dimensional picture of site conditions that illustrates contaminant distributions, release mechanisms, migration routes, exposure pathways, and potential receptors. The CSM uses a combination of text and graphics to portray both known and hypothetical information. The CSM documents current site conditions and is supported by maps, cross-sections, and site diagrams that illustrate human and environmental exposure through contaminant release and migration to potential receptors. Frequently, a CSM may be presented as a site map and/or developed as a flow diagram which describes potential migration of contaminants to sit. The CSM synthesizes data acquired from historical research, site characterization, and remediation system operation.

Top of Page


Characterizing the Source Contaminants

The initial identification of the contaminants that are released from a leaking underground storage tank (LUST) requires an understanding of the specific properties of the fuel involved. Different types of fuels and additives present different problems at a site. For example, older gasoline releases contained lead, while newer releases contain oxygenates that promote clean air (such as methyl tertiary butyl ether, or MTBE). Recent federal mandates to add ethanol and other biofuels to gasoline and diesel fuel may require modified or additional investigation.

Different contaminants of concern have different chemical and physical properties and toxicological characteristics, causing them to behave differently underground and to present a variety of risks to human health and the environment. It is important to identify the applicable contaminants present to develop an accurate idea of how to remediate the site effectively.

Top of Page


Characterizing the Site

Site conditions play a critical role in the fate of a release and how contamination can best be mitigated. The known characteristics of a site, such as geology and hydrology, are used to create a conceptual site model (CSM), which is utilized to guide the collection of data and determine the type and amount of required cleanup. The location of the leak source and its extent, both horizontally and vertically, must be understood. Site conditions could affect response actions, so information is needed on the site’s proximity to receptors, such as drinking water supplies, sensitive wetlands or surface waters, schools, day-care facilities, hospitals, and residences that may complete exposure pathways.

Potential concerns associated with petroleum contamination may include, but are not limited to, threatened water supply sources, and impaired indoor air, also known as petroleum vapor intrusion, that can be an elevated threat to children and pregnant women, and exposure for construction workers and other potential sources of public exposures. In addition, storm drains and underground utilities can create preferential pathways that can alter and exacerbate the migration of pollutants.  Site assessment activities may include removing USTs and piping to collect soil or groundwater samples. As specific site information is gathered, the data are used to refine the CSM.

One of the first steps in the site characterization process is reviewing existing records and historical site information to create a baseline of information on the problem. Typically the owner would have this documentation on-site or be able to access it from his monitoring system. A CSM is also developed at this stage. The CSM describes the geological and physical setting of the release, possible migration pathways, and the potential threat to public health and the environment. Once the historic and current UST system information is understood and the CSM is established, the process of identifying the exact source, quantity, and timing of the release can be more productive. Existing inventory records or data from electronic inventory systems can be used to estimate the source of the piping, tank, or system failure and the quantity of fuel that may have been released. This information can then be used to productively guide the remedial design and help evaluate the effectiveness of the cleanup.

Under both the traditional and expedited assessment approaches, a sampling and analysis plan must be developed and samples collected as described below. Site assessment is an iterative process: as information is gathered about the site history and conditions, the CSM is modified and, in turn, the remedial action approach revised. Sample collection is also an ongoing process, and the analytical results from sampling help to inform the assessment and cleanup.

Top of Page


Sampling and Data Collection

During site sampling, care must be taken to ensure that samples are representative of site contamination conditions and are handled properly so that cross-contamination does not occur or integrity of the samples is not compromised. EPA employs a process to identify specific requirements for each sampling event and to guide project managers in designing a sampling program. A good sampling program will record detailed site information at the time of collection, such as soil types at various depths, ground water observations, weather conditions, equipment used, photographs, and field personnel qualifications. These notes can be important in making key decisions related to cleanup of the site.

  • Environmental Data Quality
    EPA's process to identify specific requirements for each sampling event and to guide project managers in designing a sampling program.

Samples are typically sent off-site to laboratories for analysis. To more quickly identify conditions in the field, portable analytical equipment may be brought on-site during field sampling. This equipment can be used to achieve a more real-time understanding and reduce the need for iterative laboratory sampling. A specified percentage of the collected samples are then submitted to an analytical laboratory to confirm and correlate the results of the field instrument screening. Complete on-site labs can be expensive, and often site sampling and assessment becomes an iterative process whereby samples are collected and sent to an off-site lab to be analyzed with results fed into an interim assessment report. This process must be repeated until the extent of the contamination is fully characterized. Fully assessing a site may take months to complete.

Prior to collecting samples or undertaking any subsurface work, contact utility companies to identify the location of any underground utilities. Likewise, field personnel must be careful not to operate large excavation equipment where there might be interference with overhead utility lines. Furthermore, if contamination extends beyond the source property boundaries, site access agreements need to be executed to make provisions for proper access onto adjacent properties.

New sampling technologies are available to help collect samples cost effectively and to provide better protection of samples prior to analysis. For example, some new technologies allow for soil sampling in a way that minimizes the loss of any potentially volatile chemicals prior to lab analysis. Other methods or preservation techniques maintain the integrity of the sample during transit between the site and the lab.

Finally, it is important that all sampling equipment be properly decontaminated between individual sampling points. Equipment decontamination is a critical practice to ensure the integrity of each sample by preventing cross-contamination.

Soil

Determining the nature and extent of a petroleum release generally begins with characterizing soil and rock permeability and conducting soil sampling, and this is typically an iterative process. Soil samples are collected to establish the full horizontal and vertical extent of the release in the soil. Samples are often screened for petroleum hydrocarbons in the field using a portable photo-ionization detector (PID), flame-ionization detector (FID), or an ultraviolet fluorescence (UVF) instrument to quickly establish where contamination is present. Continuous sampling of soil cores allows rapid visual observations of soil staining from releases, and technologies such as UVF screening can quickly identify the exact vertical extent of a release in the soil column. Using continuous screening of soils in this way, from the ground surface to the bottom of the borehole, allows a precise understanding of the vertical extent of contamination at each boring. Identifying soil strata is critical in development of the CSM and in design of the remediation strategy. Each implementing agency will have its own acceptable field screening methods and requirements for analytical testing.

Groundwater

Commonly a fuel release will be present as dissolved contaminants in the groundwater. Monitoring wells are usually constructed to establish the horizontal and vertical impact to the groundwater resource. Groundwater nearly always flows in a specific direction, although the direction can change during various times of the year or be artificially impacted by underground utilities or man-made changes. Monitoring wells are typically established around a release to understand the extent of contamination, together with background up-gradient and down-gradient conditions that existed before the release. The number and location of ground water monitoring wells are used to characterize the nature and extent of contamination. A minimum of three monitoring wells is necessary to establish the direction of groundwater flow. For sites with complex geologic conditions, man-made disturbances, or underground utilities within the groundwater, more wells will be necessary to fully understand groundwater flows.

Gauging groundwater depths periodically is important in understanding how a fuel release behaves underground throughout the year. Seasonal fluctuations in ground water levels may impact dissolved contaminants in the groundwater. To accurately characterize ground water contamination at a site, groundwater sampling should be conducted during different seasons to account for potential variations in dissolved contaminant levels.

When a large quantity of product has been released, pure gasoline or fuel is often found floating on the groundwater surface. This free-floating petroleum is referred to as Light Non-Aqueous Phase Liquid (LNAPL). The thickness of the LNAPL layer must be accurately gauged with an oil or water interface probe. Thickness of the LNAPL will vary considerably as the groundwater table rises and falls and the product either saturates or evacuates from the surrounding soil particles. To fully characterize LNAPL thicknesses, it is best to collect measurements at various times of the year to account for seasonal groundwater fluctuations in LNAPL depths. Before any remedial action is conducted to remove the LNAPL, it is important to quantify the mass or volume of the product, evaluate the LNAPL mobility, consider any vapors that may partition from the product, and evaluate the exposure pathways of the LNAPL. These are unique considerations regarding cleanup of sites impacted with LNAPL. Federal regulations require that any free product identified during the LNAPL assessment be removed from the ground and properly managed.

Petroleum Vapor Intrusion and Indoor Air

Petroleum contamination can partition from soil or groundwater and migrate into indoor air spaces where it can cause a health hazard to humans. The impact to indoor air may be affected by site conditions that increase the potential for vapor intrusion into buildings, such as direct contact between a contaminant source (groundwater or LNAPL) and a building foundation. Soil vapor can be sampled outside or underneath building slabs before it reaches indoor pathways. Alternatively, indoor air can be sampled directly for volatile organic compounds (VOCs). Care must be exercised in sampling indoor air spaces because many household and industrial products, such as paints, new carpet, or household cleaners, can lead to false positive readings.

Top of Page


Quality Assurance and Quality Control

Quality assurance (QA) addresses process management and refers to the establishment of a system to plan, carry out, and review data collection activities. Quality control (QC) focuses on operational aspects and refers to the process of taking appropriate scientific precautions, such as proper calibrations and duplications, to ensure data quality of the collected samples. During site assessments, QC samples are collected in the field to check whether the site characterization samples are representative of site conditions. The samples are used to evaluate the quality and usability of data collected from soil, groundwater, and air for accuracy, representativeness, comparability, and completeness. Government agencies may require that a QA project plan be approved before sampling or that a data usability assessment be conducted after samples are analyzed at a laboratory.

  • Environmental Data Quality
    EPA's process to identify specific requirements for each sampling event and to guide project managers in designing a sampling program.

Top of Page


Personal Protection and Safety

Fuel releases from LUSTs can present dangerous conditions to site workers and occupants of nearby buildings. Examples of these conditions include elevated concentrations of VOCs creating low levels of oxygen in confined spaces (i.e. suffocating conditions) or potentially explosive concentrations of vapors. Workers and other individuals who may be exposed to petroleum-contaminated soil or groundwater need to avoid direct contact with the material. Ingestion and inhalation exposures can be dangerous and hazardous to health.

In addition, excavation or trenching is sometimes conducted in association with a remedial action, and may pose a risk of collapse. Personnel involved in underground storage tank removals, site assessments, and remedial actions must complete Hazardous Waste Operations and Emergency Response Standard (HAZWOPER) training certified by the Occupational Safety and Health Administration (OSHA) of the U.S. Department of Labor. Local implementing agencies may require additional certifications for these individuals. OSHA has recently adopted stricter guidelines for trenching and excavation in response to a number of accidental deaths caused by excavation collapses during UST removal and installation projects. Worker health and safety should remain a continuing priority during all assessment and cleanup actions.

Top of Page


Documentation and Reporting

Field observations and results from all site assessment work should be documented in a written site assessment report. Report requirements can vary among implementing agencies; the relevant authority should be contacted for specific report requirements and guidance. In general, a site assessment report will document the environmental investigation work performed at the site and an evaluation of the findings. It may include maps and cross-sections that show the geologic and hydrogeologic conditions and the distribution of contaminants as well as recommendations for future assessment or mitigation of the contamination. Assessment actions generally need to be documented and filed with the appropriate government agency. Some agencies require that the scope of work of a proposed assessment action be reviewed and approved prior to implementation.

Top of Page

Corrective Action

On This Page:

Introduction

The conceptual site model (CSM) along with acceptable risk factors, cost, local policies, available technologies, and community input will all help dictate the appropriate cleanup method to apply to a leaking underground storage tank (LUST) site. Various remedial actions are reviewed for effectiveness, and a detailed corrective action plan (CAP) may be developed according to the requirements of the implementing agency. To ensure protection of public health, safety, and the environment, the site owner or his/her consultant may discuss the proposed immediate actions directly with the implementing agency to avoid delays and misunderstandings. Possible corrective action options, such as excavation and removal, pump and treat, or soil-vapor extraction, undergo a thorough analysis to select a reasonable approach from both a technical and cost perspective. An evaluation report that summarizes the benefits and drawbacks of each alternative is usually prepared for review by government agencies. A pilot test may be necessary to determine the effectiveness of the selected remedy prior to full scale application. Once the review of alternatives is completed, a specific corrective action or set of actions is selected and implemented.

The selected remedial action is described in detail in the CAP and may include preparation of written specifications and detailed engineering drawings. The plan may require that the action be performed by qualified contractors and may outline strategies to help the tank owner or operator control costs. The plan may also include specific cleanup goals, a project schedule, and project milestones.

This section of the LUST Corrective Action Resources offers an overview of the corrective action process as well as the operation, maintenance, and monitoring requirements that will likely be an integral part of the process.

Top of Page


Corrective Action Plan

A corrective action plan (CAP) is a comprehensive plan that describes how a LUST will be cleaned up and justifies why this remedial method has been chosen. The CAP typically needs to be approved by the local implementing agency. Any confirmed release that requires a CAP also requires notifications to local municipal or county officials, notices in the local newspaper, and public hearings to provide a forum for parties who may be impacted by a specific response or corrective action. Additional measures may also be proposed to protect people from harm, such as supplying drinking water to nearby residences or venting indoor air spaces.

Risk-based decision-making is used in some states to determine the appropriate levels of action and oversight based upon the risk to human health and environmental receptors. One state example is offered in the links below. ASTM's E1739 standard is an example of a framework for implementing a risk-based corrective action strategy. With this process, implementing agencies can make sound, quick, consistent management decisions for a variety of sites using a three-tiered approach to data collection and site review.

Top of Page


Remediation Methodologies

Corrective Action Plans (CAPs) typically include an overview and evaluation of the proposed remediation methodologies. Each alternative is analyzed to address its effectiveness, efficiency, and cost as well as environmental sustainability, and, increasingly, the impact on greenhouse gas emissions. The selection of a remedial solution is optimized to consider the oil and hazardous materials present, the media that is contaminated, the feasibility of achieving cleanup, the potential greenhouse impacts, the cost-benefit of various solutions, and the unique subsurface characteristics at the release site.  Remedial action alternatives are identified by screening various cleanup options to determine which alternative will meet the performance goals of the reviewing agency.  The thorough evaluation of alternatives ensures that the optimal remedial solution is reliable, effective, energy-efficient, and protective of human health and the environment.

Remediation methods for liquids or vapors include free-product recovery as well as passive and active single-phase and multi-phase recovery. Depending on site conditions, it may be possible to collect free product passively, as opposed to using active methods that rely on electricity or pneumatic devices. Passive product collection may be just as effective as active remediation while having significantly lower operational costs and electrical demands and producing lower greenhouse gas emissions. Examples of passive remediation methods may include skimmers, absorbent socks, or floating oil/water separators. Examples of active remediation systems may include soil vapor extraction or ground water pumping with activated carbon treatment. For soil, some treatment methods require excavation of the soil (ex situ treatment) while others allow soil to remain in place (in situ treatment) for procedures such as in situ oxidation or bioremediation. Excavated soil may even be reused in the making of asphalt.

Top of Page


Light Non-Aqueous Phase Liquid Recovery

When pure gasoline or fuel is floating on the groundwater surface, the product needs to be recovered as quickly and efficiently as possible. The longer it stays in the ground, the greater the chance of migration into utilities, drinking water wells, or indoor spaces. Free-floating petroleum is often referred to as Light Non-Aqueous Phase Liquid (LNAPL). The thickness of LNAPL varies considerably as the water table rises and falls. When groundwater subsides, LNAPL thickness tends to be greatest. LNAPL can be removed through excavation, withdrawn by active or passive collection equipment, or chemically oxidized in situ.

Top of Page


Performance Monitoring

The selected corrective action must be monitored and evaluated for both cost control and achievement of objectives throughout implementation. Performance monitoring approaches will vary depending on the situation. If surface water has been impacted, periodic monitoring of aquatic organisms, plants, or sediments may be undertaken. In the case of groundwater, many government agencies require semi-annual or quarterly reporting to document the performance of the selected action because of variation in groundwater contamination levels at different times of the year. Indoor air monitoring may be conducted more frequently in the wintertime because of the stack effect that occurs in buildings when they are closed during cold weather resulting in less air flow. If a particular action does not appear to be effective, an alternative corrective action may be proposed by the tank owner or operator.

Top of Page


Institutional and Engineering Controls

Institutional controls (ICs) are non-engineered instruments, such as administrative and legal controls, that help minimize the potential for human exposure to contamination and/or protect the integrity of the remedy. Although it is EPA's expectation that treatment or engineering controls will be used to address principal threat wastes and that ground water will be returned to its beneficial use whenever practicable, ICs play an important role in site remedies because they reduce exposure to contamination by limiting land or resource use and guide human behavior at a site. For instance, zoning restrictions prevent site land uses, like residential uses, that are not consistent with the level of cleanup.

Institutional controls are meant to be used in conjunction with treatment or engineering controls such as containment. Engineering controls are the physical structures that limit or restrict exposure to contamination in the short term or for extended future use. Typically they are well-engineered barriers, such as a reinforced concrete slab constructed in the ground to prevent access to contamination and reduce the exposure pathway.

Top of Page


Documentation and Reporting

Reporting requirements for corrective actions can vary among implementing agencies. Corrective actions generally must be documented and filed with the appropriate government agency. Some agencies require that the performance of an implemented action be periodically reviewed and evaluated to justify continuing the action. Field documentation is conducted to meet this requirement through field notes, photographs, and performance monitoring. It is also important to develop and review a health and safety plan to protect workers who are involved in the action.

Top of Page


Case Studies

Case studies of various corrective actions are often provided by government agencies and industry associations to assist responsible parties and their consultants in selecting the most efficient and cost-effective action for a particular release. EPA maintains a comprehensive website to evaluate innovative corrective actions at Clu-In.

Top of Page

Site Closure

On this page:

Introduction

Site closure is a milestone achieved when the remaining contamination in the soil, surface water, groundwater, or air meets a risk or cleanup threshold determined not to pose a threat to human health or the environment. Determining the end point of a corrective action at a leaking underground storage tank (LUST) site may involve reaching a targeted concentration for certain contaminants or reducing the risk of contamination to a specific threshold. Risk-based decision-making (RBDM) criteria are applied more and more frequently to enable tank owners and operators to achieve a quicker and more cost-effective site closure. RBDM allows cleanup to be performed to a risk level that reflects the future use of the site rather than a generic, potentially more stringent cleanup level that is difficult to justify in the context of certain site uses.

Top of Page


Risk Characterization and Closure

Depending on the jurisdiction overseeing the remedial activity, completion of corrective action at a LUST site may be based on the remaining and foreseeable risk to human health and the environment. Risk assessors or toxicologists are often engaged to evaluate human risks based on the potential inhalation, skin, or ingestion exposures from the contamination. These risk characterizations often analyze the potential carcinogenic threats of petroleum constituents to pregnant women and small children. Environmental risks are evaluated based on the impact to vertebrates and invertebrates, plants, and their respective habitats. Once a characterization adequately evaluates the risk of all contaminants of concern and their potential exposures, a risk-based decision can be made regarding closure of a LUST site.

In cases when site closure is not based on risk, there are conservative thresholds established by government agencies that must be met for site closure. These thresholds are calculated levels based on generally accepted safety standards.

Top of Page


Maintenance and Abandonment of Sampling Points

Groundwater and vapor intrusion sampling points are often maintained after site closure to allow owners, operators, or implementing agencies an opportunity to confirm and re-evaluate the decision to close a LUST site. Ground water monitoring wells must be properly maintained at the ground surface to ensure that surface petroleum releases or contaminated stormwater do not flow into the well boring and contaminate a clean groundwater resource.

Top of Page


Documentation and Reporting

Site closure requirements vary significantly among implementing agencies. Final closure actions generally must be documented and filed with the appropriate government agency. Documentation typically includes narrative descriptions of the release, a full summary of assessment, and corrective actions, maps, plans, summaries of field and laboratory data, a data quality assessment, and a risk characterization. Closure reports are public records that remain open for inspection. Some jurisdictions require legal notices in the local newspaper or certified notifications to adjoining property owners when the cleanup process has been completed.

Top of Page


Closure Records

Once the implementing agency approves the final documentation and reporting from a cleanup, a final approval may be certified in writing. This written approval documents a liability endpoint that can be used for lending or conveyancing purposes.

Increasingly, many implementing agencies are relying on qualified professionals to certify that a permanent closure has been achieved. These individuals are usually licensed, and their certification of closure states that the cleanup endpoints, which are either established by the implementing agency or carefully evaluated based upon risk to public health or the environment (i.e., RBDM) have been met. This certification may be subject to screening and audit at the discretion of the implementing agency.

Top of Page