Abs: 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.
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.
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, flushing,bioremediation. Excavated soil may even be reused in the making of asphalt.
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.
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.
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.
