Closure is generally defined as the point of the project where no additional investigation or remediation activities are required and the regulatory agency has provided a letter to that effect.  It is the point in the project that all responsible parties want to achieve, and in most cases, must achieve, preferably sooner than later. 

Spills or other releases to the environment can include emergency responses, such as  fuel releases  to surface water, a release of petroleum from an underground storage tank (UST), a release associated with a hazardous waste storage area at an industrial facility, or releases associated from an unidentified, historical sources.  Regardless of the nature of the release, once a release has been identified, and before the Site can be “closed”, the responsible party must take actions to prevent further release(s), investigate the nature and extent of impacts, and if warranted, conduct remediation and ongoing monitoring.  Once these activities are completed, then Site closure could be achieved. 

For most states and the U.S EPA, there is more than one way to achieve Site closure, and there is inherent flexibility in the process.  If a responsible party wants to achieve the most stringent, risk-based criteria (usually for residential land use), then the closure letter from the regulatory body will have few or no restrictions.  However, if contamination is left behind, then closure could still be obtained, but there will be long-term obligation (with accompanying costs and liability) for the responsible party.  We will review closure approaches for a couple states below, followed by the U.S. EPA approach under the Resources Conservation & Recovery Act (RCRA).

Under RCRA, the term “closure” refers to a series of formal procedures required to minimize the need for maintenance and control, minimize or eliminate post-closure releases of hazardous waste, hazardous constituents, leachate, contaminated run-off, or hazardous waste decomposition products to the environment (IDEM RCG).  Like Indiana’s Conditional and Unconditional Closure, when closing a facility or a unit (e.g., landfill, waste pile, tank, containment, etc.), the EPA has two approaches:

• Clean Closure – all wastes are removed and the facility or unit and surrounding soils (or other impacted media) is decontaminated. 
• Closure with Waste In-Place – this is used for landfills or other units when responsible parties cannot remove all waste and contamination.  Similar to the approaches in the states identified above, sites that are closing with residual waste left in place will require additional long-term controls or restrictions to ensure there is no risk to human health and the environment.