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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 Locations of the Monitoring Wells, the Drinking Water Wells, the Production Wells, and Springs at and near the 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 (0.05 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 unacceptable excess lifetime cancer risk of one case per one million exposed people. 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.

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).

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."

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 nontransient 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.


Response to Comments Received during the Public Comment Period for the Eastern Michaud Flats Groundwater Health Consultation

The Groundwater 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.


The consultation mistakenly refers to the dairy near the site as Gold Medal. The correct name of the dairy is Meadow Gold.


The name of the dairy has been corrected in the consultation.


Recently the spring used by the Meadow Gold Dairy was sampled and checked for site-related contaminants. The analytical results of this sampling event indicate that the spring water has not been impacted by the site.


ATSDR appreciates the quick response taken to collect this important piece of information. It has been incorporated into this health consultation.


The consultation fails to provide any adequate description of the knowledge of the regional groundwater flow. Analysis of conducted for the responsible parties and reviewed by the U.S. Environmental Protection Agency indicates that site-related contaminants can not migrate towards the spring used by the Meadow Gold Dairy.


Although the information developed during the Remedial Investigation indicates that it is unlikely that site-related contaminants would migrate towards the spring used by the Meadow Gold Dairy, the computer simulations can not predict all possible situations (i.e., the models will always have a degree of error associated with them). Therefore, ATSDR believes that it is appropriate to conclude that "it may be possible for site-related contaminants to enter the spring being used by the Meadow Gold Dairy." Given that the spring used by the dairy is near the contaminant plume and the spring water is sold to the public, it is in the best interest of public health to, at a minimum, monitor the movement of the plume to assure that the spring is not impacted by the migration of the site-related contaminant plume. For these reasons, ATSDR recommends:

"Appropriate remedial actions should be instituted or continued to prevent future migration of site-related groundwater contaminants into any drinking water sources (e.g., the Meadow Gold Dairy spring). Appropriate monitoring of the groundwater should be conducted to assure that site-related contaminants do not impact drinking water sources (e.g., quarterly monitoring of monitoring wells 524 and 525)."


In evaluating the hazards, the consultation fails to place the potential risks in proper perspective. The consultation presents only the maximum concentrations as a summary of the years of site characterization and does not report the natural regional background concentrations. Specifically, the consultation does not indicate that the arsenic levels detected in the Batiste and Swanson Road Springs reflect only natural arsenic concentrations.


In the discussion of the Batiste Spring, the average concentration of arsenic is used. That discussion clearly indicates that the average amount of arsenic detected in the Batiste Spring is not at levels that have been shown to cause adverse health effects in humans. In the conclusions, ATSDR states that the only possible health concerns associated with the Batiste Spring is nitrate/nitrite exposes and the possible development of acute acquired methemoglobinemia.

As stated on page 3 of the health consultation, the Swanson Road Spring has never been used as a drinking water source for human consumption. Therefore, no human health risk exists.


The presentation of the historical exposures from the Old Pilot House Well and potential health concerns overstate the risks and should be so noted with greater clarity. The consultation assumes that people used the well for their primary water supply, which is highly unlikely.


In the Discussion Section, "The Pilot Cafe", of the Health Consultation, the potential for exposure to site-related contaminants are clearly discussed. Maximum concentrations were not used to determine whether people were exposed chronically to contaminants at levels of health concern. The average concentration of arsenic was used in ATSDR's evaluation of the potential chronic exposures. In addition, ATSDR clearly states its assumptions. To conclude that it is "highly unlikely" that the Old Pilot House Well was the primary water supply for this family run business is debatable. In order to err on the side of public health, ATSDR assumed that the well could have been used as the primary drinking water source. This assumption is clearly stated in the discussion section and is also stated in the conclusion section of the health consultation: "If the employees drank a significant amount of water at work, they may have a higher risk of developing skin, liver, bladder, and kidney cancers."


The risk with respect to nitrates are overstated in that the risk are no longer current.


The very first conclusion of the health consultation states the no one is currently exposed to site-related contaminants.

In conclusion number three, ATSDR clearly indicates that people were exposed in the past and that the past exposures would have increased an infants risk of developing acute acquired methemoglobinemia. ATSDR's health consultation provides information not only about current and future health risks, but also health risks that may have occurred in the past.


The health consultation should point out that the population upon which the health-based value was derived was a non-U.S. population who were generally poor and not well nourished. The nutritional status of the population used to derive the health-based arsenic value has been a major issue; the relationship between nutritional status and health effects is undergoing great scrutiny.


As this comment indicates, there is some debate as whether the nutritional status of an individual has an impact on the ability of arsenic to produce adverse human health impacts. However, it is important to realize that the Old Pilot House Well has been shown to contain arsenic at levels that could have resulted in exposure doses as high as 0.25 milligrams of arsenic per kilogram body weight per day (mg/kg/day) with an average exposure dose of 0.02 mg/kg/day. The toxic effects of arsenic have been observed in humans starting at 0.009 mg/kg/day (this is not a theoretical cancer risk calculation but actual observations of a human population). Therefore, the known exposures as a result of the arsenic contamination in the Old Pilot House Well are above those levels observed to cause adverse health effects (two to 27 times higher). This is only for the time period that analytical sampling results are available (1972 forward). The concentration of arsenic in the Old Pilot House Well may have been even higher in the past. Therefore, ATSDR believes that it is appropriate to conclude that:

"If the employees drank a significant amount of water at work, they may have a higher risk of developing skin, liver, bladder, and kidney cancers."


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