Tiered Approach to Corrective Action Objectives

Tiered Approach to Corrective Action Objectives (TACO) is a method for developing soil and groundwater remediation objectives that protect human health and take into account site conditions and land use. Before TACO, contaminated soil would be removed, or the soil and groundwater would be remediated to reduce the amount of chemicals as much as possible. This was a rather conservative approach that did not allow much flexibility or input from the site owners and could require more work than was necessary to make the site safe for future uses.

Under TACO, the site owner decides what approaches are best, and the remediation can be adjusted for the specific site. For example, the intended use of the land as industrial/commercial or residential determines the amount of remediation required. By taking into account site-specific information, the remediation can cost less, and the land may be used again sooner. The owner has more control and involvement in the process, and the remediation still protects human health.

Risk is the probability or likelihood of something undesirable happening. In environmental terms, risk is the probability of soil and groundwater contamination causing human injury or illness. There are three components to environmental risk. They are:

• Contaminants (chemicals from petroleum and hazardous materials)
• Exposure Routes (indoor inhalation; soil, dust, or groundwater ingestion)
• Receptors (humans)

All three of these components (contaminants, exposure routes and receptors) must be present for a health risk to exist. Controlling any one of these factors can either reduce or eliminate the risk. A goal of TACO is to reduce environmental risk to humans by managing one or more of these components.

If an exposure route can be limited or cut off, then the health risk from the contamination is also limited. In the TACO rules this is called pathway exclusion. A site owner using pathway exclusion needs to demonstrate that the exposure route will be properly blocked, and that the contaminants cannot move into new exposure routes. The primary means of pathway exclusion are institutional controls and engineered barriers.

Institutional controls are ways of regulating the use of a property. Contaminated properties intended for residential use (housing, child or health care, or outdoor recreational areas) require strict remediation objectives because sensitive populations, like children and the elderly, may be present and because the frequency and duration of human exposure are higher than at properties used for industrial/commercial purposes. When remediation objectives are based on an industrial/commercial land use, an institutional control prohibiting the property from residential use is imposed.

Institutional controls may also be used to prevent exposure to contaminated groundwater. If a property has contaminated groundwater, the owner does not necessarily need to clean the groundwater. Instead, the owner can obtain a deed restriction prohibiting the use of the groundwater as potable water (water for drinking, cooking, or bathing purposes). If the property is sold, the purchaser must either accept these restrictions as part of the deed transfer or clean up the groundwater.

Another option is the use of engineered barriers. A structure, such as a parking lot, could be used to cover contaminated soil. People will not come into contact with the contaminated soil beneath a parking lot, so they are as safe as if the contaminants were removed. Engineered barriers must be kept in good working order by site owners.

One more way to reduce risk is to reduce the amount of chemicals present to safe levels through removal or treatment. This is often the tactic used by site owners, and it is frequently combined with institutional controls and engineered barriers to make the risk acceptable.

Any work to remediate a contaminated site can be called a corrective action. Remediation objectives are the goals of corrective action. The final goal of any cleanup action is to protect human health and the environment. Before TACO can be used, site owners must investigate the site to find out 1) what chemicals caused the contamination, and 2) where the contamination is located. After identifying the extent and concentrations of the chemicals through soil and groundwater sampling, site owners use this information to develop remediation objectives using TACO.

Baseline remediation objectives, also called Tier 1 objectives, take into account the intended land use of the property, but do not consider other conditions specific to the site. Because of this, Tier 1 remediation objectives are calculated using the most conservative assumptions about the way the contamination might travel through the soil and groundwater and the amount of chemicals people might be exposed to.

Site owners can establish their own remediation objectives by conducting risk assessments. To accurately assess the health risk posed by the contamination, site owners must collect data and information on soil and groundwater conditions at the site and evaluate how long and how often people might be exposed to the chemicals. These site-specific remediation objectives, called Tier 2 and Tier 3, are usually less stringent than baseline remediation objectives but are just as protective of human health.

In deciding which remediation objectives to use, site owners consider the amount and extent of contamination, the future use of property, the cost of obtaining the information needed to develop Tier 2 and 3 objectives, and the cost of cleaning up to Tier 1 objectives. Once remediation objectives are established, the site owner may:

• Reduce contaminant concentrations to meet the remediation objectives through removal or treatment of the chemicals;
• Restrict exposure to contaminated soil or groundwater or both by using engineered barriers or institutional controls;
• Take no action, if contaminant concentrations present at the site do not exceed Tier 1 remediation objectives; or
• Use any combination of the options above.

Once a site owner satisfies the TACO and cleanup program requirements, the owner receives a No Further Remediation (NFR) letter. An NFR letter means no additional work is necessary to remediate a specific problem and it releases an owner from any responsibility to do more remediation, as long as the terms of the NFR letter are met.

The use of any institutional controls or engineered barriers at a site requires restrictions to be placed in the NFR letter. Common restrictions limit the land to industrial/commercial use or require the proper maintenance of an engineered barrier (e.g., asphalt pavement, concrete pavement, clean soil) to limit exposure to contamination. NFR letters are recorded with the County Recorder of Deeds so that future purchasers of the property will be aware of the terms and conditions of the NFR letter. If these conditions are violated, the NFR letter can be revoked.

The illustration to the right shows the major routes by which humans can be exposed to contamination. People can breathe in air containing chemical vapors or contaminated dust; ingest contaminated dust or dirt (a common behavior in small children); or drink, cook, or bathe in contaminated groundwater. TACO requires site owners to prevent contamination from reaching human receptors.

Sometimes contamination on a site has spread to adjacent property. This is called off-site contamination. When site owners investigate or remediate off-site contamination, they must do so with the full knowledge and consent of the off-site property owner. A site owner cannot use an institutional control or engineered barrier on off-site property if that property's owner does not want those methods used. Without the neighbor's consent, the Illinois EPA will not issue an NFR letter specifying off-site institutional controls. Site owners must either re-negotiate with the neighbor to gain consent or clean up the off-site contamination to residential remediation objectives. Site owners who cause or are responsible for contamination on neighboring properties are  subject to enforcement by the Illinois EPA and to third party lawsuits by people or businesses affected by the contamination.