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Appendix A - Figures

Appendix A, Figure 1

Location Map for the Eastern Michaud Flats Contamination National Priorities List Site, Pocatello, Bannock County, Idaho

Appendix A, Figure 2

Map Delineating the FMC Wastewater Discharge Point (Outfall) into the Portneuf River and the Areas Sampled in the Portneuf River for Site-Related Contaminants, Eastern Michaud Flats Contamination National Priorities List Site, Pocatello, Bannock County, Idaho

Appendix A, Figure 3

Map Delineating Land Ownership near the FMC and J.R. Simplot Company Facilities, Eastern Michaud Flats Contamination National Priorities List Site, Pocatello, Bannock County, Idaho


Appendix B - Comparison Values

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 (70 years) exposure, with an 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).

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.

Life Time Health Advisories (LTHAs) are developed by the EPA. LTHAs are lifetime exposure levels specific for drinking water (assuming 20 percent of an individual's exposure comes from drinking water) at which adverse, non-carcinogenic health effects would not be expected to occur.

Maximum Contaminant Level Goals (MCLGs) are drinking water health goals. MCLGs are set at a level at which, in the EPA Administrator's judgement, "no known or anticipated adverse effect on human health occurs and which allows an adequate margin of safety."

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.


Response to Comments Received during the Public Comment Period for the Eastern Michaud Flats Surface Water and Sediment Health Consultation

The Surface Water and Sediment Health Consultation for the Eastern Michaud Flats site was available for public review and comment from November 12 through December 19, 1997. We announced the Public Comment Period in The Idaho State Journal and the Sho-Ban News. ATSDR made copies of the health consult available at the Idaho State University Library and the Shoshone-Bannock Tribal Business Center. In addition, we sent the health consultation to 10 persons or organizations.

The comments and ATSDR's responses are summarized below.


The health consultation provides only a cursory review of the wealth of knowledge developed for the Eastern Michaud Flats (EMF) site and the characterization of potential exposure which might impact human health. Greater detail and analyses have been incorporated in previously prepared documents and presentations in conjunction with the Remedial Investigation and Feasibility Studies under EPA's oversight.


ATSDR agrees that the health consultation does not provide an in-depth review of all the data and information available. The purpose of the health consultation is not to give a complete history of how and when the various environmental samples were taken. The health consultation is ATSDR's public health review of the available environmental data and information regarding the information and data concerning the Eastern Michaud Flats Contamination site. People requiring more detailed information about the environmental sampling results should review the referenced documents.


The text of the health consultation indicates that the tables are a "summary" of the available sampling data. However, only maximum levels are reported in the table. In addition, the emphasis on maximum exposures overstates the possible risks.


The purpose of the tables are to select which contaminants may be at levels of health concern. The selected contaminants are then evaluated further
in the document. The text of the health consultation has been modified to clarify this issue.

An explanation of comparison values is included in the appendices of the health consultation. This explanation clearly states that comparison values are not intended to be used as clean-up levels or to be indicators of public health effects.

In the discussion section of the health consultation, ATSDR discusses the range of possible exposures that may have occurred. Mean concentrations of exposure were used to determine if people were chronically exposed to contaminants at levels of health concern. Maximum concentrations of exposure were not used to determine if people were exposed chronically to contaminants at levels of health concern.

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