House Enrollment Act (HEA) 1162 requires the Indiana Department of Environmental Management (IDEM) to consider risk-based solutions while evaluating environmental closures. Risk-based closures can include several approaches for example:

• Applying pre-approved closure levels
• Determining site-specific closure levels
• Considering risk of exposure

IDEM has established default closure levels that can be used at most sites in Indiana. These closure levels are calculated using conservative parameters so they can be applied to a wide variety of sites. This process includes multiple layers of conservativeness to allow this broad use. The default closure level calculation is based on an equation including numerous inputs related to exposure, toxicity and site setting. In most instances, the actual default closure level for soil is a concentration of the contaminant considered protective of groundwater considering the closure level for the contaminant in groundwater.

This same equation can be used to calculate Site Specific Closure Levels (SSCLs) by changing some of the parameters to more accurately reflect actual site conditions. IDEM does not allow modification of some established parameters, but others can be modified. The most common parameter to modify is fraction of organic carbon. Fraction of organic carbon data can be collected from a particular site and have a significant impact on the closure level when utilized in the risk equation.  

Another way of demonstrating closure is to evaluate exposure pathways related to the site conditions. This evaluation involves a number of facts related to the site and surrounding use, site features and layout, geologic setting and contaminant(s). IDEM needs a clear understanding of these various factors while evaluating risks related to a site. A responsible party and its environmental team can evaluate and compile these factors and present them to IDEM for the purposes of obtaining closure. This approach can limit the amount of cleanup needed and can result in significant cost savings.

These factors are best presented in the form of "multiple lines of evidence." If presented accurately and clearly, multiple lines of evidence can be a very important part of obtaining closure at a site. In fact, using the multiple lines of evidence approach is necessary for all closures not considered "default" by IDEM.

Strong closure justification beyond a default closure should address considerations related all potential exposure pathways. Additionally, the lines of evidence should address not only current situations, but potential future situations as well. For example, a risk-based closure using multiple lines of evidence will likely include site use restrictions documented in an Environmental Restrictive Covenant (ERC) or Environmental Restrictive Ordinances (EROs) that might be in place already. Additionally, the lines of evidence should address surrounding site use considerations and the closure might ultimately include conditions related to surrounding site use.