risk management

Maximum Contaminant Levels (MCLs) and individual State Cleanup Target Levels (CTLs), determined by the Environmental Protection Agency (EPA) and agencies such as the Florida Department of Environmental Protection (FDEP), respectively, are based upon average site conditions and assumptions on human and ecological exposure. Actual site conditions may be more favorable to reduction of site contaminant levels that the average site conditions. In this case an argument can be made for modification of the Cleanup Target Levels (CTLs) or setting of Alternative Cleanup Target Levels (ACTLs) for the site. If warranted, a full Risk Assessment could be conducted to determine the site specific exposure scenarios and risk to humans and ecological systems. The Risk Assessment could also result in modification or lowering of the standard Cleanup Target Levels (CTLs). Risk Assessments are often completed in phases with each level increasing in detail, scope and costs to the project.

Groundwater modeling may be conducted to evaluate site-specific fate and transport of contaminants as a screening for a Remedial Investigation/Cost Feasibility or Monitoring Only scenario. Based on the site conditions, the appropriate model will be selected taking into consideration the simulation of advection, dispersion, adsorption, and aerobic decay as well as anaerobic reactions. Simplifying assumptions may include:
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• Groundwater transport is one-dimensional along the centerline, between the source and the receptor;
• Dispersion is quantified in three-dimensions;
• The solution includes error functions that provide approximate solutions for groundwater transport equations across the site, over time;
• Source area concentrations are constant; and the
• Aquifer is initially clean.

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