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The Big Cover-Up

By Carlson Environmental | Share

Engineered barriers have become the most common cleanup strategy used to obtain No Further Remediation (NFR) letters from the Illinois Environmental Protection Agency’s (IEPA’s) Site Remediation Program (SRP), and it is no wonder. Barriers are a flexible and economical alternative to removal or treatment as a means of protecting human health from contaminated soil and groundwater.  For an exposure (and therefore, a risk) to occur, three factors must be present:

  • Contaminants
  • An exposure route
  • A receptor

The purpose of an engineered barrier is to limit exposure by “cutting off” the exposure route. Barriers succeed because risk is at the point of human exposure and without exposure there is no risk. That being said, it is important to remember that simply paving over pollution is not enough; details matter when incorporating engineered barriers into your remediation and risk management strategies.

How Barriers Work

Under the SRP regulations, the source of contamination need not be eliminated if potential exposure to that contamination (i.e. risk) is successfully managed. Impacted soil, groundwater, and soil vapor can only threaten human health if there is a “pathway” by which contaminants can reach potential receptors. Block those pathways (also known as routes of exposure) and health risks posed by those contaminants are successfully managed. Another attractive feature of barriers is that the rules allow contaminated soil to be moved from different parts of the site and consolidated under a single barrier or a “soil management zone”. This can however, be a double edged sword because even though the flexibility inherent in the program can simplify up-front design decisions, these choices may limit site changes down the road.

What Constitutes a Barrier?

Engineered barriers take various forms. A barrier may be natural or human-made, but its effectiveness must be verified by engineering practices. A very common barrier is a permanent structure made of materials such as concrete or asphalt. Regulatory agencies commonly consider pavement in the form of roadways or parking lots as well as building foundations, to be acceptable barriers. That being said, a concrete slab and foundation walls may not be an adequate barrier if the contaminants of concern present a potential indoor inhalation hazard. Cracks need to be sealed as do penetrations for things like water and sewer pipes and electrical conduit. Sheet or spray-applied membrane vapor barriers can be readily incorporated in to new construction; however, installing vapor barriers on existing construction is typically much more challenging and alternate remediation approaches are commonly more feasible/economical.

Pavement and building foundations are the most common engineered barriers, but they are not the only ones. Layers of clean soil/material can also be acceptable barriers. In Illinois, clean cover consists of materials that have contaminant levels not exceeding the applicable Tier 1 residential remediation objectives. The requisite thickness of the soil barrier depends on the potential route of exposure. Illinois regulations require that contaminants posing risk through inhalation must be no closer than ten feet from the soil surface. Potential ingestion or direct contact risks can be managed by barriers of at least three feet of clean soil/material.

Other types of barriers may be attractive depending upon the circumstances. In some cases the IEPA will approve a composite barrier where a synthetic membrane is held in place by a layer of clean material. Creative approaches can be implemented in landscaped areas, but owners need to be aware that there will be a need for long-term maintenance.

Barriers are not limited to caps and permanent structures. Two barriers accepted under TACO to address the ingestion of groundwater route: slurry walls and hydraulic control of groundwater. A slurry wall is a vertical barrier constructed of a material that will prevent or impede the horizontal movement of soil or groundwater contamination. A slurry wall may be used in conjunction with a cap to prevent the migration of the contaminated groundwater. Hydraulic groundwater control is used to prevent groundwater from coming in contact with contaminated soil, and prevent contaminated groundwater from migrating.

Building most engineered barriers is straightforward; building them so they provide permanent protection is not as easy as it looks. The first challenge is design. The second is long-term maintenance to insure the structural integrity of the barrier. The third is a plan to avoid undue risk when a barrier must be breached.

Thoughtful, Coordinated Design

In years past, a site might be remediated through soil removal or treatment and then site development would proceed independently; close coordination of environmental cleanup work with the design process was not typically necessary. Now, because new construction can serve as barriers under SRP rules, the location of building foundations and parking lots and the design of landscaped areas often become critical elements of both the remediation program and the site development. Close coordination between the environmental consultants and the design professionals early in the conceptualization of a project is fundamental to long-term success. Environmental expertise must find space at a table that is already likely to be crowded with developers, architects, engineers and attorneys.

Maintenance Matters

An engineered barrier will only be approved by the IEPA as part of the final corrective action if the barrier is permanent. Although an engineered barrier may be permanently recorded in an IEPA NFR letter, in the real world, they break down, wear out, and unfortunately get forgotten.  Therefore, a remediation plan using engineered barriers must also include an institutional control, transferable with the property, and provides procedures to be followed if intrusive work (breaching of the barrier) is necessary. The intent of the institutional control is to guarantee the barrier will stay sound over time, even if tenants move or ownership of the site is transferred.

Over time, some breaches of engineered barriers are inevitable. Excavating to repair or install a sewer pipe in a contaminated area, for example, may both jeopardize the integrity of the engineered barrier and expose construction workers to contaminated soils.  As a result, the IEPA includes a requirement in its NFR letters that there be a plan in place to protect construction workers if barriers are disturbed.

Don’t be That Guy: The IEPA Does Not Forget

In 2002 the Illinois EPA began a program of follow-up inspections to determine if the conditions imposed by the first wave of NFR letters issued in 1997 were actually being met. As a result of the first 150 inspections, 14 sites required further evaluation and six NFR letters required some sort of follow-up action.  In several cases, engineered barriers were found to have been breached and not repaired, and in one case, residential construction was undertaken even though the NFR letter restricted the property to commercial or industrial site use.

The Good News

Because NFR letters are issued as the result of a voluntary program, such failures to comply with their terms do not carry the threat of civil or criminal enforcement proceedings by the government.

The Bad News

The Agency can void the NFR letter—not a good thing for the owner if development financing and leasing were contingent upon receiving the NFR letter in the first place. Non-compliance may also leave owners vulnerable to third party environmental claims.

What’s an Owner to Do?

Manage actively not passively:

  • Inspect your engineered barrier regularly;
  • Document the results of your inspections;
  • Maintain your barrier so that there is no question that it is doing its job;
  • If you must disrupt your barrier, provide proper notification to construction workers so that they can implement appropriate health and safety protocols, restore the barrier once work is done, and document that the barrier has been reestablished consistent with the requirements of your NFR letter.
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