Sites that are suspected of being chemically contaminated are referred to ADEQ's Site Assessment Unit for preliminary assessment and inspection. Through this initial investigation, ADEQ determines the risk posed to human health and environmental quality and identifies sites that require more detailed investigation or emergency response action. As a result of this work, some sites may be placed on the EPA's National Priority List or the state's Water Quality Assurance Revolving Fund (WQARF) Registry.
A Risk-based Approach to Cleanups
As part of ADEQ's process for investigating and cleaning up contaminated sites, department scientists consider the risks associated with the presence and movement of chemicals in the environment. The purpose of this risk assessment is to evaluate the potential for adverse health effects from exposure to the chemicals. The assessment helps ensure that an appropriate remedy and level of cleanup is implemented.
Options for cleaning up soil and groundwater are based on levels that protect human health and the environment. An alternative cleanup standard that protects human health and environmental quality can be calculated using site-specific information gathered during site investigation. The site-specific standard may be a higher concentration than the pre-determined standard, and it may cost less to attain.
ADEQ risk assessment activities include:
- Administering an inter-agency service agreement with the Arizona Department of Health Services
- Processing risk assessment review requests for ADEQ's Superfund, Voluntary Remediation, hazardous waste, underground storage tank and other programs
- Evaluating chemicals that do not currently have regulatory cleanup standards
- Educating the public on the principles and use of risk assessment processes
Levels of Cleanup
Options for cleaning up soil and groundwater are based on standards that protect human health and the environment:
- Tier 1 standards are the most conservative and use predetermined assumptions (i.e., soil remediation levels or aquifer water quality standards) in the risk assessment calculations.
- Tier 2 standards use the same equations to calculate risk as Tier 1 but substitute site-specific information for the predetermined values. The site-specific standard may be a higher concentration than the pre-determined standard, but it also may cost less to attain.
- Tier 3 standards offer the most flexibility in assessing risk by allowing use of any methodology or set of equations that are valid and appropriate to the site conditions. A Tier 3 standard calculated at one site may differ considerably from one calculated at another site. More information is required to complete Tier 3 calculations, and this additional information must account for potential exposures outside the property boundaries to verify that human health and groundwater quality will continue to be protected.
Deciding Which Tier to Use
If contaminant concentrations at a site are less than the Tier 1 standards, the site is eligible for closure without further work. However, if contaminant concentrations exceed the Tier 1 standards, an owner may consider using site-specific values to calculate Tier 2 standards. Complying with the tiered corrective action standards demonstrates that the site meets the regulatory requirement that remaining concentrations adequately protect human health and the environment. Using one tier may be more efficient and cost-effective than using another tier.
This evaluation is done by estimating the Tier 2 standards, and the cost to achieve them. Indicators that Tier 2 standards may be useful may include:
- Site conditions that are significantly different than those assumed for Tier 1
- Small changes in the assumptions result in a large change to the calculated standard
- Site chemical concentrations are close to or less than the estimated Tier 2 standards
- Conducting the proper calculations for and cleaning up the site to Tier 2 concentrations costs less than cleaning up the site to Tier 1 concentrations
The same process is used to decide between Tier 2 and Tier 3 standards.