Divisibility, Apportionment & Allocation

Contaminated sites are technically complex to investigate and remediate. Where multiple potentially responsible parties (PRPs) are involved, they also present unique challenges regarding the determination of the degree of responsibility of each PRP. Under CERCLA and many state-equivalent statutes, the courts have held that liability is both joint and several. However, joint and several does not mean that all PRPs have equal shares of liability. Sophisticated clients now rely on the use of many technical tools available to determine their share of liability — whether that relates to remediation costs, natural resource damages, or other liabilities where exposure to contamination is a main driver.

Apportionment of liability typically involves three components: demonstrating that contamination and its harm is divisible; applying generally accepted technical tools to apportion the harm; and then applying those tools to determine the allocation of costs.

To assess its liability, a PRP must first investigate and eventually demonstrate to an allocator or to the court that the environmental harm is divisible, and then show that there is a reasonable basis for apportioning the PRP’s contribution to the harm. Demonstration of divisibility among PRPs is based on site-specific factors, including a site’s physical setting, history and use(s), and the extent and types of the associated contaminants. Because of the joint and several liability imposed on PRPs, apportionment and allocation is of particular interest both to clients who may have greater liability and financial resources than other PRPs, and to PRPs who believe that they have a de minimis share but have been swept into the larger liability soup.

For more than 25 years, Exponent has supported clients in developing technically sound apportionment and allocation strategies, and in presenting our analyses for consideration by courts and in alternative dispute resolution settings.

Apportionment and allocation issues at a site typically involve multiple successive owners of involved properties, multiple operations that may change over time, commingled groundwater plumes or sediment impacts from multiple releases and sources, changes in industrial practices, technologies and associated waste streams, the degree of regulatory compliance, and care exercised in dealing with site-specific contaminants. Exponent’s scientists and engineers are expert in applying multiple allocation criteria and in evaluating and developing models based on factors including, but not limited to, the so-called Gore Factors, approaches included in many state statutes, and criteria contained in federal and state court decisions.

Exponent uses historical and technical information available for a particular site to develop specific defensible allocation factors to assist the allocator, or the court, in assigning relative responsibilities and costs to PRPs. These factors may include the relative timing and duration of ownership and operation, historical operations, the quantity of contaminants released to the environment, the estimated timing and duration of releases, the chemical fingerprints of the contaminants, the relative toxicity of the contaminants, and the distribution of the contaminants in soil, groundwater and sediment.

The data used to establish allocation factors may range from a relatively simple review of historical records to more complex considerations, such as chemical fingerprinting. Approaches also include statistical chemical source models to estimate source contributions. Exponent has an extensive understanding of industrial processes and the environmental behavior of the chemicals associated with those processes. We have a proven track record of applying this experience to assess the sources of releases and to differentiate environmental damages among multiple sources.

The range of capabilities that Exponent brings to apportionment and allocation issues includes: 


  • Industrial archeology
  • Historical release reconstruction
  • Advanced chemical fingerprinting
  • Multivariate statistics and data analytics
  • Receptor (multivariate) modeling
  • Chemical fate and transport
  • Toxicology 
  • Geospatial analysis
  • Environmental cost consulting

Where existing data are insufficient, we are experienced in designing and implementing site assessment programs. We work with our clients to integrate such information into a scientifically defensible approach for apportionment and cost allocation.

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