Human Health and Ecological Risk / Environmental Investigation Support- Nyanza OU 4, Sudbury River Mercury Contamination

U.S. Environmental Protection Agency, Region I, under contract to Nobis Engineering, Inc.

Overview:

• Conducted state-of-the-art human health and ecological risk assessments of mercury contamination throughout 30-miles of the Sudbury River
• Designed and executed a variety of extensive field investigations
• Developed a site-wide geospatial mercury database
• Integrated fish data, chronic toxicity testing, and fate and transport modeling into comprehensive risk assessments
• Provided risk assessment/ecological evaluation support in the development of remedial strategies for mitigation of exposure and risk to mercury
• Coordinated and integrated more than 15 stakeholder agencies/contractors in the development of technical approaches

Description:


Under subcontract to Nobis Engineering, Bluestone staff members were the primary authors of the supplemental human health risk assessment technical memorandum to evaluate potential construction worker exposures to shallow groundwater and vapors during excavation work – for the Nyanza Chemical Waste Dump Superfund Site Operable Unit II – Off-Site Property Groundwater. The Off-Site Property Groundwater investigation is one of four operable units (OU) associated with the Nyanza Superfund Site. A baseline HHRA and ROD for OU II, as well as an indoor air study, have been completed previously. Remedial actions, including extraction of contaminated dense non-aqueous phase liquids (DNAPL) and operation of vapor mitigation systems and continued groundwater monitoring activities, are on-going. Nyanza, Inc. and its predecessors manufactured a wide variety of dyes and intermediates from 1917 to 1978. Primary contaminants in the groundwater plume are chlorinated volatile organic compounds (VOCs). An approximately 75-acre area of groundwater contamination underlies homes and businesses to the east and northeast of the original Nyanza, Inc. facility. The supplemental HHRA for OU II addresses contaminant identification, exposure assessment, toxicity assessment, and risk characterization. Bluestone evaluated potential construction worker exposures to shallow groundwater and vapors via incidental ingestion and dermal contact and inhalation of associated vapors. To estimate the exposure point concentration (EPC) for air in a construction trench, Bluestone used an approach suggested by the Virginia Department of Environmental Quality (VDEQ) within the Virginia Unified Risk Assessment Model – VURAM 2.0 User’s Guide (VDEQ, 2018), which is based on a combination of a vadose zone model (to estimate volatilization of gases from contaminated groundwater into a trench) and a box model (to estimate dispersion of the contaminants from the air inside the trench into the above-ground atmosphere).