What is TACO?
TACO, an acronym that stands for Tiered Approach to Corrective
Action Objectives, is a method for deciding the amount of remediation a contaminated site
needs in order to protect human health. Before TACO, contaminated soil would be removed or
the soil and groundwater would be treated 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 really 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 — industrial/commercial or residential — influences the amount of
cleanup 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 cleanup process, and the remediation still protects human health.
- How does TACO limit risk?
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:
- 1. Contaminants (chemicals
from petroleum and hazardous materials)
- 2. Exposure Routes (vapor
inhalation; soil, dust, or groundwater ingestion)
- 3. 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.
How does TACO work?
TACO is a risk-based method for developing corrective action
objectives. Any work to remediate a contaminated site can be called a corrective action.
Objectives refers to the goals of that 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, site owners use
this information to develop remediation objectives using TACO.
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 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.
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.
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 on the NFR letter. Common restrictions limit the
land to industrial/commercial use, or require the proper maintenance of an engineered
barrier. NFR letters are recorded with the County Recorder of Deeds so that future
purchasers of the site will be aware of the terms and conditions of the letter. If these
conditions are violated, the letter can be revoked.
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