A small community gets its water from wells that tap into an old, large aquifer. Recently, an environmental impact study found toxic contamination in the groundwater due to improperly disposed chemicals from a nearby manufacturing plant. Since this is the community’s only source of potable water and the health risk due to exposure to these chemicals is potentially large, the study recommends that the community reduce the overall risk to below a 1 in 10,000 cancer risk with 95% certainty (95th percentile less than 1E-4).
A task force narrowed down the number of appropriate treatment methods to three. It then requested bids from environmental remediation companies to reduce the level of contamination down to recommended standards, using one of these methods.
Your remediation company wants to bid on the project. The costs for the different cleanup methods vary according to the resources and time required for each (cleanup efficiency). With historical and site-specific data available, you want to find the best process and efficiency level that minimizes cost and still meets the study’s recommended standards with a 95% certainty.
Complicating the decision-making process:
You have estimates of the contamination levels of the various chemicals. Each contaminant’s concentration in the water is measured in micrograms per liter.
The cancer potency factor (CPF) for each chemical is uncertain. The CPF is the magnitude of the impact the chemical exhibits on humans; the higher the cancer potency factor, the more harmful the chemical is.
The population risk assessment must account for the variability of body weights and volume of water consumed by the individuals in the community per day.
All these factors lead to the following equation for population risk:
