Hazardous Waste Disposal Sites
We have evaluated potential hazards associated with contaminants of soil and groundwater at many sites to satisfy regulatory requirements of the federal Superfund program and analogous state programs. Our human health and ecological risk assessments have considered numerous metals and organic chemicals (both volatile and semi-volatile) present in various environmental media. Since the context and setting of each site is unique, our risk assessments are tailored to meet both regulatory and client needs. In most cases, both present and foreseeable risks are evaluated, respectively considering current site conditions and plausible development (including potential use restrictions).
Risk assessment under the aegis of the federal Superfund program has long been a business focus. Our involvement has included development of baseline risk assessments for CERCLA sites, technical assistance to citizens' groups, critical evaluation of risk assessments and their use in regulatory decision-making, and risk-based allocation of remedial action costs. The influence of Superfund risk assessment guidance is manifest in many state regulatory programs, and we have conducted risk characterizations within the Massachusetts Contingency Plan (MCP) for as long as that program has been in existence. We work with clients and Licensed Site Professionals (or their equivalents in other states) to develop appropriate evaluations of sites to manage and mitigate risks (e.g., in conjunction with Activity and Use Limitations or equivalents). We have also been active participants in committees organized by the Massachusetts Department of Environmental Protection to develop and revise MCP risk assessment procedures.
We take pride in our abilities to deal with complex sites and issues. Our skills in fate and transport modeling and toxicology enable us to enhance our risk assessments to account for site-specific conditions and uncertainties. We have, for example, been including vapor intrusion (VI) pathways in human health risk assessments since the early 1990s. VI, which typically refers to the penetration (or risk of penetration) of vapors from volatile contaminants present in soil and/or groundwater underneath homes or other buildings, demands prudent data collection. Soil-gas and indoor air must often be sampled to evaluate multiple lines of evidence to differentiate VI impacts from background air contaminants. Many VI assessments involve chlorinated solvents (and their breakdown products), for which remedial and occupational perspectives on toxicology differ markedly.
Health risk assessment of lead contamination at a former lead foundry
We developed a baseline Superfund risk assessment for a former foundry in Portsmouth, VA that for many years cast bronze bearings with lead-containing inserts. Site investigation revealed soils with high concentrations of various heavy metals, especially lead. The site is near other sources of lead, including naval shipyards and an old downtown area (implicating lead paint as a potential source of contamination), and preliminary work entailed modeling the spatial variation of different metal concentrations in the soils to delineate site-related contaminated areas that required refined sampling. Following site delineation, we prepared an endangerment assessment, including estimates of risk to human health and the environment, according to EPA's Risk Assessment Guidance for Superfund and involved one of the first applications of EPA's Biokinetic Uptake Model that was developed to assess human exposure to lead.
Paint manufacturing facility
We performed a Method 3 MCP Risk Characterization for an active paint manufacturing facility. Various spills of petroleum-based solvents from above-ground storage tanks led to soil and groundwater contamination. Testing of soil and soil-gas helped define a source release area, limited to the property but of considerable extent. Evaluation of vapor intrusion was complicated by use of the same chemicals in ongoing paint production. Modeling was used to evaluate potential vapor migration under future use scenarios under the assumption that background air quality dominates present exposure potential. Another issue of interest was the transition of analytical methods to evaluate petroleum hydrocarbon contamination. Early data were quantified using methods for Total Petroleum Hydrocarbons (TPH), but subsequent evolution of methods for Extractable and Volatile Petroleum Hydrocarbons (EPH/VPH) introduced questions regarding the applicability and utility of the more extensive TPH data. The decision was made to limit the use of TPH data to determination of the extent of contamination and to utilize the more limited (but sufficiently comprehensive) EPH/VPH dataset to develop quantitative risk estimates.
BTEX plumes at refineries
We assessed indoor air risks in homes located atop extensive groundwater contamination plumes that migrated from oil refineries in Indiana and Virginia. Publicly supplied water eliminated concerns over groundwater use as a source of domestic water, and indirect exposure to contaminants via vapor intrusion served as the only complete exposure pathway. Transport of petroleum-related BTEX compounds (benzene, toluene, ethylbenzene, and xylene) was modeled in unsaturated soils using Farmer's algorithms and the pattern of predictions used to distinguish the contribution of vapor intrusion to measured indoor air concentrations. Statistical analysis was also used to differentiate vapor intrusion impacts from background.
Risk-based cost allocation of a Superfund cleanup
EPA required stakeholders at the Old Southington Landfill Superfund Site to develop a risk-based cost-sharing algorithm. We designed an appropriate algorithm based on the risk estimates provided in the baseline risk assessment, accounting for both the volumes and the relative risks of each waste stream. The scheme equitably accounted for both cancer and non-cancer risks, and its consideration of relative toxicity correctly accounted for all site-specific factors. The algorithm was adopted by EPA in the settlement negotiations with stakeholders.