Risk assessment and brownfields-determining exposure to site contaminants

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Courtesy of Atlantic Environmental, Inc.

The USEPA’s Brownfields Program was developed to facilitate the rehabilitation of contaminated property for re-development. EPA has set forth criteria that must be met for a revitalized property to be used for residential, commercial or industrial purposes. The main thrust of these criteria is the long-term protection of residents or visitors (including shoppers and business employees).

As Industrial Hygienists, we may be called upon to evaluate the health risks to construction workers actively engaged in the remediation project, and to recommend engineering controls and/or personal protective equipment sufficient to protect on-site workers and visitors from potential exposures to contaminants on, in or under the subject property. For the most part, remediation and re-development construction workers are primarily facing inhalation and dermal exposures. Ingestion of contaminated water, as well as dermal absorption of contaminants in water are unlikely. Consequently, this risk assessment protocol will deal with exposure potentials that might be experienced in any OSHA-regulated endeavor.

As part of any Brownfields project, preliminary soil and groundwater tests characterize the nature and amount of contaminants present. A history of potential contaminants arising from previous uses of the property will add to the characterization. Unless there are several peak areas of contamination whose origins are not known, most brownfield areas have fairly uniform levels of common contaminants throughout either the entire property or are present within a narrowly defined area, and is corroborated by the prior use history of the property. For example, a coal-gasification production facility may have occupied a “foot print” that was much smaller than the total property area. Finding high levels of semi-volatiles in and around the area that had been occupied by the facility itself would be expected. High levels in remote corners of the property would not.

One approach to initiating the risk assessment process is to isolate the geophysical area with the highest concentration of the contaminants of interest and assume that the highest level of each contaminant of interest found in the soil assays is uniformly present throughout the contaminated area. This assumption will allow us to calculate a “worst-case” exposure scenario for each of the contaminants of interest.

Further assumptions are as follows:

  • All remediation work will be done at the highest summertime temperatures.
  • Volatile contaminants adhering to soil particles will be completely released when the soil is exposed to atmospheric air.
  • The concentration of soil particles in air (dust) will average 3 milligrams per cubic Meter of air.
  • Contact with contaminated groundwater will not occur.
  • Exposures will occur over 8-hour workdays.

Assume a Brownfields project where prior use history shows an auto body repair shop had occupied the property for 35 years. The property had been undeveloped woodland before that. Soil sampling showed the presence of toluene, xylene, benzene and ethyl benzene, ranging from a low of 350 mg per kilogram of soil to a high of 1,600 mg benzene per kilogram of soil. For the purposes of illustration, only the high benzene level will be treated further.

Extrapolating the 1,600 mg/kg to be present throughout the property, we find a benzene concentration of 1,600 mg benzene per million mg soil; or, 0.0016 mg benzene per mg soil/dust. This can also be expressed as 1.6 micrograms benzene per mg soil/dust.

When excavation begins, the exposed soil will generate a dust level of 3 mg per cubic Meter of air. Since each mg of soil (now called dust) contains 1.6 micrograms of benzene, a dust concentration of 3 mg per cubic Meter will contain 4.8 mg benzene per cubic Meter of air. OSHA’s PEL for an 8-hour exposure to benzene is 1 part per million, Time-Weighted Average, 8 hours (1 ppm, TWA-8). A soil concentration of 1,600 mg per kg can be expected to produce a “worst-case” inhalation exposure of 4.8 mg/cuM or 1.5 ppm which clearly exceeds the OSHA PEL.

During the early construction/excavation phase of the project, appropriate respiratory protection should be provided to potentially exposed workers and breathing zone air samples collected to verify the actual exposure concentration. If several sets of test results are below 0.5 ppm benzene, the use of respirators can be discontinued.

This approach will provide protection to on-site workers without demanding expensive and uncomfortable respiratory protection when it may not be necessary.

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