In the new and improved June 2014 version of the Massachusetts Contingency PlanEnvironmental regulations like the MCP(MCP), the Massachusetts Department of Environmental Protection (MassDEP) revised the definition of “background”. Background is now defined as “those levels of oil and hazardous material that would exist in the absence of the disposal site of concern, including both Natural Background and Anthropogenic Background.”

But what does this really mean and why is it significant?

First – A Few More Regulatory Definitions

The revised MCP introduces the following new terms: Natural Background, Anthropogenic Background and Historic Fill.

Natural Background means “those levels of oil and hazardous material that would exist in the absence of the disposal site of concern, are ubiquitous and consistently present in the environment at and in the vicinity of the disposal site of concern, and are attributable to geologic or ecological conditions.”

Anthropogenic Background means “those levels of oil and hazardous material that would exist in the absence of the disposal site of concern and which are:

  1. attributable to atmospheric deposition of industrial process or engine emissions and are ubiquitous and consistently present in the environment at and in the vicinity of the disposal site of concern;
  2. attributable to Historic Fill;
  3. associated with sources specifically exempt from the definitions of disposal site or release as those terms are defined in MGL c. 21E and 310 CMR 40.0006;
  4. releases to groundwater from a public water supply system; or
  5. petroleum residues that are incidental to the normal operation of motor vehicles.”

Historic Fill means “Fill Material that based on the weight of evidence and consistent with the Conceptual Site Model:

  1. was emplaced before January 1, 1983;
  2. may contain, but is not primarily composed of, construction and demolition debris, reworked soils, dredge spoils, coal ash, wood ash or other solid waste material;
  3. was contaminated with metals, hydrocarbons, and/or polycyclic aromatic hydrocarbons prior to emplacement, at concentrations consistent with the pervasive use and release of such materials prior to 1983;
  4. does not contain oil or hazardous materials originating from operations or activities at the location of emplacement;
  5. is not and does not contain a generated hazardous waste, other than Oil or Waste Oil;
  6. does not contain chemical production waste, manufacturing waste, or waste from processing of metal or mineral ores, residues, slag or tailings; and
  7. does not contain waste material disposed in a municipal solid waste dump, burning dump, landfill, waste lagoon or other waste disposal location.”

Why Should I Care About Background?

Every hazardous waste site has some “background” concentrations of oil or hazardous materials, be they naturally occurring (Natural Background) or the result of human activities (Anthropogenic Background). The type and amount will vary depending on the site but at the very least, every site has concentrations of metals which meet the definition of Natural Background.  Sites in urban areas tend have a wider range of contaminants at higher concentrations which meet the definition of Anthropogenic Background.

Under the MCP, if site contaminants meet the above definition for either Natural Background or Anthropogenic Background based on documented lines of evidence, then those contaminants do not need to be included in the risk characterization for the site. As a result, the calculated risk to human health will be lower which, in turn, increases the likelihood of achieving a Permanent Solution for the environmental case. In short, documenting elevated background concentrations can make it significantly easier to achieve closure of the environmental case.

An Example of Using Background

Installing soil borings, looking for background

Sampling for background

An automobile salvage facility was a listed disposal site under the MCP as a result of elevated concentrations of petroleum. A soil sample collected to characterize excavated petroleum-contaminated soil for off-site disposal contained an arsenic concentration above its associated Reportable Concentration which, as a consequence, required additional response actions under the MCP.  Subsequent soil sampling found elevated arsenic concentrations in soil were ubiquitous and consistently present both horizontally and vertically across the site.  Samples of bedrock, which was located near the ground surface at the site, also found elevated concentrations of arsenic were ubiquitous and consistently present in bedrock across the site.

Based on multiple lines of evidence, the arsenic was determined to represent Natural Background. The arsenic would have represented a significant risk to human health if it was included in the risk characterization.  Because the arsenic met the definition of Natural Background and no longer had to be included in the risk characterization, the calculated risk to human health was reduced to a point where the environmental case could be closed.

Need more info?

If you need more information about how the new background definition might affect your site, please contact Omni Environmental Group’s Licensed Site Professional (LSP) at 978-256-6766 or

“An LSP’s Opinion” is an occasional feature here in the Omni Environmental Group blog where we talk about the Massachusetts Contingency Plan along with the roles and responsibilities of Licensed Site Professionals.