Assessment, Remediation, and Monitoring (ARM) is the process of determining the extent to which a Site has been impacted (assessment), identifying and implementing appropriate remediation measures based upon the assessment findings (remediation) and monitoring the effectiveness of the implemented remedy (monitoring). ARM services are generally called for once a hazardous substance has been released to the environment, or the potential for a release to have occurred has been identified, often following completion of a phase I environmental site assessment.
The ARM Project Lifecycle
When a release or threat of a release to the environment is identified, the ARM process begins by assessing the nature and extent of the contamination present. In many cases the need for remediation or additional assessment can be reduced or eliminated through a well-planned site characterization strategy that determines the levels of contaminants at a site is de minimus or below levels of concern. In other cases, the presence of hazardous substances warrants remediation. In these cases, candidate remediation approaches are evaluated based upon expected effectiveness, cost, and acceptability among other criteria. Once selected, the remedy is implemented and the process of monitoring the effectiveness of the chosen remedy begins. Monitoring provides the data needed to evaluate remediation effectiveness, adjust the remediation strategy and to ultimately demonstrate compliance with regulatory agencies overseeing and approving the work.
Step 1: Assessment
Specific Site assessment methods and procedures are specific to the Site being investigated and the contaminants that are potentially present. This requires a detailed understanding of contaminant fate and transport – that is understanding how chemicals behave and move in the environment once released. Chemical properties including volatility, solubility, density, and many others influence chemical behavior in the environment as does the nature of the soil and/or groundwater into which they have been released. A understanding of current and potential uses for the Site is also critically important to ensure that the levels of contaminants, and their associated risks, are appropriate for the intended land use. As an example, child day care centers are a more sensitive land use than parking lots, and the acceptable levels for a particular contaminant are derived based upon these differing land use scenarios.
The assessment step of an ARM project typically involves the collection of samples of environmental media (e.g., soil, groundwater, soil gas) for chemicals suspected to be present based upon the findings of a Phase I ESA or in response to a known release. While methods vary significantly site to site, typically the assessment stage involves collection of soil samples - either through subsurface drilling or direct sampling of surface soil, groundwater sampling - through the installation of sampling points or monitor wells, and increasingly in recent years collection of soil gas samples – through installation of subsurface soil gas monitoring points.
Site assessment is usually an iterative process with the initial data collection effort informing the subsequent investigation steps until a clear picture of the environmental system and the presence of the contaminants within that system are sufficiently understood.
Technology screening includes sampling suspected soil, rocks, groundwater, sediment, and air to determine the specific types of present contaminants. Multiple rounds of investigation allow experts to fill data gaps on the site to create a greater understanding of the issues at hand. Geologic and hydrologic samples are collected at this stage to assess where migration has occurred. At this point, site characterization will confirm whether further action is needed to carry out the remediation process and solution.
Step 2: Remidiation
If the assessment identifies contaminants at levels of concern, remediation is often the answer. The remediation process begins with selection of the remedy, through a feasibility or corrective measures study. Once the best plan of action has been established, a remediation plan is created and implemented.
Active remediation solutions include those that can be applied quickly to resolve contamination, such as soil excavation and treatment or disposal. These types of actions are typically used when a significant threat to the environment and need for remediation is identified. In other cases, more active remediation methods are selected due to timing (e.g., prior to redevelopment). Other forms of active remediation include groundwater extraction and treatment, soil vapor extraction, or chemical treatment.
Passive remediation approaches include those that are designed to treat contaminated media over a longer time frame. These approaches are generally less resource intensive and rely upon the environmental systems natural ability to degrade contaminants or retard their movement in the environment. Passive remediation approaches include monitored natural attenuation, whereby no active measures are employed, and impacted soil or groundwater is simply monitored to demonstrate the effectiveness of the environmental system at containing or removing the contaminant. Bioaugmentation involves the introduction of specific contaminant degrading microorganisms and creating conditions suitable for them to thrive. Soil vapor intrusion can be passively remediated through installation of vapor intrusion mitigation systems that prevent contaminants from entering a building where occupants can be exposed. Cameron-Coles Targeted Microbial Applications (TMA) practice is an example of a passive remediation approach that has been used widely to remediate a variety of organic contaminants with minimal resource consumption relative to other active remediation methods.
Step 3: Monitoring
Monitoring is critical for tracking progress and effectiveness of the remediation stage. Long-term trends in the chemistry of the soil, groundwater, and air quality are evaluated. The site will also be assessed for additional threats that may or may not have been identified. A properly designed monitoring program will provide sufficient data to verify the effectiveness of a remediation approach such that adjustments to the cleanup program can be made for the greatest overall effect of the chose remediation approach. Monitoring is also performed to ensure that passive remedies are appropriate for a particular site, by demonstrating stable or improving aquifer conditions.
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