Guidance for Conducting Risk Assessments and Related Risk ...

fail the screening. If the chemicals present at a site pass this screening, it is simply an indication that
further assessment should be conducted to determine the need for continued investigation.
5.2 INTEGRATION POINT ASSESSMENTS
For the ORR sites, the majority of any off-site public exposure to chemicals of potential concern
results from exposure to contaminants in surface water because surface water is the primary receiving
medium in and around the reservation. Other potential receiving media, such as agricultural products, air,
and groundwater, are currently not primary exposure media. The integration point assessment, which
supports watershed actions, is designed to actively use monitoring, surveillance, compliance, and
Remedial Investigation (RI) data to evaluate off-site risk from a variety of sources that input into the
surface water integrator. The data will be used to:
• establish a baseline for evaluating the risk at different points within the integrators;
• identify and prioritize sites within the context of the integrator; and
• estimate the potential risk reduction resulting from an action to control contaminant sources.
Note: The integration point assessment provides critical information to the baseline human health risk
assessment because of frequent updates (as data become available). As the integration point assessment is
updated, the results are used to provide current estimates of potential risk/hazard at the surface water or
watershed level.
The integration point assessment is a flux-based screening assessment. Flux is defined as the mass
of chemical that migrates through a cross-sectional area in a given time. Flux is important because of the
number of actual and potential sources of chemicals that exist on the ORR. In addition, there is
considerable variability in flow rates of the different surface water systems that transport these chemicals
to the surface water integrator sites and eventually to the Clinch River (near the ORR). Controlling
sources of contamination at areas with high fluxes of integrator chemical of concern (COCs) is the
quickest means of reducing contaminant concentrations in off-site areas to target levels.
One of the more important objectives during early phases of an integrator site investigation is to
assimilate available information from existing programs to estimate fluxes and mass balances of
chemicals within the integrator system. The information is then used to assess fluxes within the
watershed and compare them to fluxes that input into public access areas in order to differentiate between
various contaminant sources at the ORR. Mass balance information is important for describing the
accumulation and discharge of chemicals within a system where inputs and outputs are known. The
integration point assessment allows communication of this information in terms of risk to the public and
risk managers. It also provides an important link between the risk posed by contamination at source
locations and risk posed by contamination in surface water integrators so that the impact of actions to
control contaminant fluxes at sources can be evaluated at the integrator or watershed level. Appendix I
provides a detailed description of the integration point assessment methods.
32