Risk Assessments
The Hanford Cumulative Impact Assessment effort assesses Hanford's impact on the groundwater,
the Columbia River, and the users of those resources. An integrated system of computer models
and databases enables users to model the movement of contaminants from all waste sites at the
Hanford Site through the vadose zone, groundwater, and the Columbia River and estimate the impact
of contaminants on human health, ecological, economic, and cultural systems. In the future,
transport of contaminants through the air will also be available so that contaminant impact
through all pathways can be assessed.
Cumulative impact assessments provide a sitewide context for the decisions that must be made
on individual waste sites. In addition, this capability allows users to explore the potential
impact of remediation alternatives, and, finally, it provides a way to visualize how the impact
from various waste types remaining at the Hanford Site will overlap across time.
Analyses to support cleanup decisions are performed at many levels at the Hanford Site.
Cumulative impact assessments are performed at the sitewide or area level. Performance
assessments for individual waste sites or groups of sites and calculations to support cover
design or to examine the detailed chemical and physical interactions between waste and soil
may be performed on the level of a few square meters. A Hanford Site assessment coordination
board assures the various programs and projects approach assessments in a consistent and
defendable manner. The board is a joint effort by the Office of River Protection and the
Richland Operations Office.
To bring consistency to the assessment approach, DOE and the regulators developed a framework
for how risk assessments will be performed and used on and around the Central Plateau. The
framework has seven tenants and will be applied to assessments that support cleanup decisions.
The Core Zone (200 Areas including B Pond [main pond] and S Ponds) will
have an industrial scenario for the foreseeable future. The Core Zone will be remediated and closed allowing for other uses
consistent with an industrial scenario (environmental industries) that will maintain active
human presence in this area, which in turn will enhance the ability to maintain the
institutional knowledge of the waste left in place for future generations. Exposure
scenarios used for this zone should include a reasonable maximum exposure to a worker/day
user, possible Native American users, and intruders. DOE will follow the required regulatory processes for groundwater
remediation (including public participation) to establish the points of compliance and
remedial action objectives. It is anticipated that groundwater contamination under the
Core Zone will preclude beneficial use for the foreseeable future, which is at least the
period of waste management and institutional controls (150 years). It is assumed that the
tritium and iodine-129 plumes beyond the Core Zone boundary will exceed the drinking water
standards for the period of the next 150 to 300 years (less for the tritium plume). It is
expected that other groundwater contaminates will remain below, or be restored to drinking
water levels outside the Core Zone. No drilling for water use or otherwise will be allowed in the Core Zone.
An intruder scenario will be calculated for in assessing the risk to human health and
environment. Waste sites outside the Core Zone but within the Central Plateau
(200 N, Gable Mountain Pond, BC Crib) will be remediated and closed based
on an evaluation of multiple land use scenarios to optimize land use, institutional control
cost, and long-term stewardship. An industrial land use scenario will set cleanup levels on the Central Plateau. Other scenarios (for example, residential, recreational) may be used for comparison purposes to support decision making especially for:
The post-institutional controls period (more than 150 years). Sites near the Core Zone perimeter to analyze opportunities to shrink the site. Early (precedent-setting) closure/remediation decisions.
This framework does not deal with the tank retrieval decision.
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