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

LOCATION: Nyanza Superfund Site, Ashland, MA

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.


  • 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

“CSTAG commends the site team for a thorough and systematic assessment of human health and ecological risks….one of the best assessments reviewed by CSTAG.”
— Steve Ells, Ph.D.
 – USEPA’s National Contaminated Sediment Technical Assistance Group (CSTAG)

Chickadee-eggs Winter-St-Dam


Avatar was contracted by EPA Region 1 to assess ecological and human health risks in the Sudbury River in eastern Massachusetts and the surrounding watershed associated with the Nyanza Superfund Site. This operable unit consists of approximately 30 miles of mercury-contaminated river that meanders through diverse urban and ecological communities, including the Great Meadows National Wildlife Refuge. Avatar’s scope of work included:

  • 1) Multi-media field investigations
  • 2) Human health risk assessment
  • 3) Comprehensive ecological risk assessment associated with mercury bioaccumulation in the Sudbury River watershed

Avatar performed field investigations including a detailed trophic-level profile of mercury contamination within the fish community, a multi-phased evaluation of mercury exposure and effects on insectivorous and piscivorous bird populations and piscivorous mammals to support a multi-media evaluation of mercury transport through the aquatic and terrestrial food chains, and included bioaccumulation modeling, sediment toxicity analysis, in-situ bivalve toxicity and accumulation studies, sediment coring and dating, and complex sediment transport modeling. Avatar developed and employed innovative biological monitoring techniques including tissue sampling from such species as mink, kingfishers, and bats. Avatar developed a site-specific GIS database that incorporated all Sudbury River data collected over the past 15 years and included photogrammetric data collected over the life of the project. Avatar used this database to identify appropriate sampling locations to fill data gaps and populate both the HHRA and ERA with spatially-referenced chemistry and biological data. This database was provided to EPA, MADEP and USFWS and is currently being used to evaluate remedial alternatives.

Avatar conducted risk assessments to enable integration of extensive site-specific data, including fish data, chronic toxicity testing, and detailed sediment fate and transport modeling to characterize the nature and extent of human and ecological risks throughout the river. We prepared a risk synthesis report summarizing the human health risk analysis and interpretations completed by many consultants and government agencies spanning a 15 year period. The synthesis report allowed EPA to focus future actions on fish bioaccumulation.