SURFACE SOIL CONTAMINATION
EASTERN MICHAUD FLATS CONTAMINATION
POCATELLO, BANNOCK COUNTY, IDAHO
Figure 3 - Location Map of the Surface Soil Sampling Sites not at the FMC or J.R. Simplot Facilities, Eastern Michaud Flats Contamination National Priorities List Site, Pocatello, Bannock County, Idaho
Comparison values for the Agency for Toxic Substances and Disease Registry (ATSDR) public health assessments and health consultations are contaminant concentrations that are found in specific media (air, soil, and water) and that are used to select contaminants for further evaluation. Comparison values are designed to be conservative and non-site specific, and therefore protective for all probable exposures. Their intended use is only to screen out contaminants which do not need further evaluation. They are not intended to be used as clean-up levels or to be indicators of public health effects. They are derived from toxicological information, using assumptions regarding body weights, ingestion rates, and exposure frequency and duration. Generally, the assumption used are very conservative (i.e., worst case). For example, soil health comparison values are developed for children who exhibit pica behavior. Soil ingestion in pica children (5 to 10 grams per day) greatly exceeds the soil ingestion rate for the normal population (0.1 grams per day).
There are two different types of comparison values, those based on carcinogenic (cancer-causing) effects, and those based on non-carcinogenic effects. Cancer-based comparison values are calculated from the U.S. Environmental Protection Agency's (EPA's) oral cancer slope factor or inhalation unit risk. They are calculated for a lifetime exposure (70 years), with an unacceptable excess lifetime cancer risk of one case per million persons exposed. Non-cancer comparison values are calculated from ATSDR's Minimal Risk Levels, or EPA's Reference Doses or Reference Concentrations. These values are calculated for adults, children, and small children who may eat large amounts of soil.
The comparison values used in the health consultation are listed and described below.
Cancer Risk Evaluation Guides (CREGs) are estimated concentrations that would be expected to cause no more than one excess cancer in a million persons exposed over a lifetime. CREGs are calculated from EPA's cancer slope factors.
Environmental Media Evaluation Guides (EMEGs) are based on ATSDR's minimal risk levels (MRLs) and factor in body weight and ingestion or inhalation rates. Separate EMEGs are developed for specific durations of exposure (acute, 1-14 days; intermediate, 15-364 days, and chronic, 365 days and longer).
EPA Screen are developed by EPA Superfund Office to be used to determine if any soil contamination at or near Superfund sites warrant further investigation.
Maximum Contaminant Levels (MCLs) are enforceable drinking water regulations that are protective of public health to the "extent feasible." National primary drinking water regulations apply to all public water systems including community water systems and transient and non-transient noncommunity water systems. EPA promulgates MCLs.
For radiological contaminants, ATSDR uses information on radiation exposure and its effects related to environmental levels prepared by federal agencies, including EPA, DOE, and the Nuclear Regulatory Commission. The agency also uses other publicly available data sources and recommendations on radiation dose limits. The National Council on Radiation Protection and Measurements (NCRP), the International Commission on Radiological Protection (ICRP), and the United Nations Scientific Committee on the Effects of Atomic Radiation and others develop these sources.