Public Health Risk Assessment, EPA Superfund Cleanup

(See PHRA excerpts below)

As part of the USEPA (US Environmental Protection Agency) agency Superfund Site process, WR Grace was required to conduct a Public Health Risk Assessment (PHRA) for the site. This quantitative risk assessment, conducted under EPA guidance, was undertaken to help determine the future level of cleanup required at the site. It assumes exposure to contaminated groundwater on the site, at concentrations present when the PHRA was conducted. It does not assess public health risks related to previous contamination levels in the drinking water or elsewhere. A July 1, 2005 Public Review Draft of the Public Health Risk Assessment was prepared for WR Grace by Menzie-Cura & Associates, Inc. and can be found in the public repository at the Acton Memorial Library. The risk assessment divided the site into six groundwater regions and found increased health risks in all six areas due to potential future exposures to groundwater contaminants. The assessed cancer risk in the six groundwater areas ranged from 2 in 1000 to 6 in 100 (PHRA Table ES-1).

Following are some excerpts from the Executive summary of the 2005 Public Health Risk Assessment submitted to EPA by WR Grace & Co.

Excerpts from Executive Summary:
Public Review Draft
Public Health Risk Assessment
W.R. Grace & Co. Operable Unit Three
Acton, Massachusetts
Prepared by: Menzie-Cura & Associates, Inc.
July 1, 2005

Summary of Findings:
“The USEPA cancer risk range identified in the National Contingency Plan (NCP) is 1 in 1,000,000 (expressed as 10 exp -6) to 1 in 10,000 (expressed as 10 exp -4) over the course of a 70-year lifetime. In this assessment, cancer risks are categorized as below the USEPA cancer risk range (equal to or less than 10 exp -6), within the USEPA cancer risk range (greater than 10 exp -6 but equal to or less than 10 exp -4), or exceeding the USEPA cancer risk range (greater than 10 exp -4). For non-cancer health effects, a total target organ-specific hazard index that exceeds 1 is considered a potential cause for concern. In this assessment, target organ-specific hazard indices are categorized as either below or above the USEPA non-cancer hazard index benchmark of 1.”

Conclusions:
“The PHRA indicates that future residential exposures to untreated groundwater from the two public water supply wellfields and the Powder Mill Plaza irrigation well do not result in exceedances of USEPA’s cancer risk range or target non-cancer risk. Future residential exposure to tap water from the School Street Wellfield results in a target organ-specific hazard index of 2 from both arsenic and manganese. However, arsenic is below the MCL, and although the maximum manganese concentration exceeds the Federal Health Advisory, it is below the maximum background groundwater concentration. In addition, current exposures to all Site surface water bodies and wetlands, and future exposures to all but Sinking Pond and the North Lagoon Wetland do not result in exceedances of these risk management criteria.

Exceedances of USEPA’s cancer risk range and target non-cancer hazard index for a future wader/swimmer in Sinking Pond and a future wader in the North Lagoon Wetland are from incidental ingestion of arsenic in accessible sediment.

For Site groundwater, exceedances of USEPA’s cancer risk range, target non-cancer hazard index, or both are from potential future residential exposure to VOCs (mostly vinyl chloride), arsenic, and manganese in tap water (all areas) and irrigation water (all areas but the Southwest Area) from potential future private wells.”

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