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APPENDIX A. List of Types of Comparison Values

Comparison values represent media-specific contaminant concentrations that are used to select contaminants for further evaluation to determine the possibility of adverse public health effects. The conclusion that a contaminant exceeds the comparison value does not mean that it will cause adverse health effects.

Cancer Risk Evaluation Guides (CREGs)

CREGs are estimated contaminant concentrations that would be expected to cause no more than one excess cancer in a million (10-6) persons exposed over their lifetime. ATSDR’s CREGs are calculated from EPA’s cancer potency factors (CPFs).

Maximum Contaminant Level (MCL)

The MCL is the drinking water standard established by EPA. It is the maximum permissible level of a contaminant in water that is delivered to the free-flowing outlet. MCLs are considered protective of public health over a lifetime (70 years) for individuals consuming 2 liters of water per day.

Reference Media Evaluation Guides (RMEGs)

ATSDR derives RMEGs from EPA’s oral reference doses. The RMEG represents the concentration in water or soil at which daily human exposure is unlikely to result in adverse noncarcinogenic effects.

APPENDIX B. Glossary

Absorption: How a chemical enters a person’s blood after the chemical has been swallowed, has come into contact with the skin, or has been breathed in.

Acute Exposure: Contact with a chemical that happens once or only for a limited period of time. ATSDR defines acute exposures as those that might last up to 14 days.

Additive Effect: A response to a chemical mixture, or combination of substances, that might be expected if the known effects of individual chemicals, seen at specific doses, were added together.

Adverse Health Effect: A change in body function or the structures of cells that can lead to disease or health problems.

ATSDR: The Agency for Toxic Substances and Disease Registry. ATSDR is a federal health agency in Atlanta, Georgia that deals with hazardous substance and waste site issues. ATSDR gives people information about harmful chemicals in their environment and tells people how to protect themselves from coming into contact with chemicals.

Background Level: An average or expected amount of a chemical in a specific environment. Or, amounts of chemicals that occur naturally in a specific environment.

Biota: Used in public health, things that humans would eat – including animals, fish and plants.

Cancer: A group of diseases which occur when cells in the body become abnormal and grow, or multiply, out of control

Carcinogen: Any substance shown to cause tumors or cancer in experimental studies.

CERCLA: See Comprehensive Environmental Response, Compensation, and Liability Act.

Chronic Exposure: A contact with a substance or chemical that happens over a long period of time. ATSDR considers exposures of more than one year to be chronic.

Completed Exposure Pathway: See Exposure Pathway.

Comparison Value: (CVs) Concentrations or the amount of substances in air, water, food, and soil that are unlikely, upon exposure, to cause adverse health effects. Comparison values are used by health assessors to select which substances and environmental media (air, water, food and soil) need additional evaluation while health concerns or effects are investigated.

Comprehensive Environmental Response, Compensation, and LiabilityAct (CERCLA): CERCLA was put into place in 1980. It is also known as Superfund. This act concerns releases of hazardous substances into the environment, and the cleanup of these substances and hazardous waste sites. ATSDR was created by this act and is responsible for looking into the health issues related to hazardous waste sites.

Concern: A belief or worry that chemicals in the environment might cause harm to people.

Concentration: How much or the amount of a substance present in a certain amount of soil, water, air, or food.

Contaminant: See Environmental Contaminant.

Delayed Health Effect: A disease or injury that happens as a result of exposures that may have occurred far in the past.

Dermal Contact: A chemical getting onto your skin. (see Route of Exposure).

Dose: The amount of a substance to which a person may be exposed, usually on a daily basis. Dose is often explained as "amount of substance(s) per body weight per day".

Dose / Response: The relationship between the amount of exposure (dose) and the change in body function or health that result.

Duration: The amount of time (days, months, years) that a person is exposed to a chemical.

Environmental Contaminant: A substance (chemical) that gets into a system (person, animal, or the environment) in amounts higher than that found in Background Level, or what would be expected.

Environmental Media: Usually refers to the air, water, and soil in which chemicals of interest are found. Sometimes refers to the plants and animals that are eaten by humans. Environmental Media is the second part of an Exposure Pathway.

U.S. Environmental Protection Agency (EPA): The federal agency that develops and enforces environmental laws to protect the environment and the public’s health.

Epidemiology: The study of the different factors that determine how often, in how many people, and in which people will disease occur.

Exposure: Coming into contact with a chemical substance.(For the three ways people can come in contact with substances, see Route of Exposure.)

Exposure Assessment: The process of finding the ways people come in contact with chemicals, how often and how long they come in contact with chemicals, and the amounts of chemicals with which they come in contact.

Exposure Pathway: A description of the way that a chemical moves from its source (where it began) to where and how people can come into contact with (or get exposed to) the chemical.

ATSDR defines an exposure pathway as having 5 parts:

  • Source of Contamination,
  • Environmental Media and Transport Mechanism,
  • Point of Exposure,
  • Route of Exposure, and
  • Receptor Population.

When all 5 parts of an exposure pathway are present, it is called a Completed Exposure Pathway. Each of these 5 terms is defined in this Glossary.

Frequency: How often a person is exposed to a chemical over time; for example, every day, once a week, twice a month.

Hazardous Waste: Substances that have been released or thrown away into the environment and, under certain conditions, could be harmful to people who come into contact with them.

Health Effect: ATSDR deals only with Adverse Health Effects (see definition in this Glossary).

Indeterminate Public Health Hazard: The category is used in Public Health Assessment documents for sites where important information is lacking (missing or has not yet been gathered) about site-related chemical exposures.

Ingestion: Swallowing something, as in eating or drinking. It is a way a chemical can enter your body (See Route of Exposure).

Inhalation: Breathing. It is a way a chemical can enter your body (See Route of Exposure).

LOAEL: Lowest Observed Adverse Effect Level. The lowest dose of a chemical in a study, or group of studies, that has caused harmful health effects in people or animals.

Malignancy: See Cancer.

MRL: Minimal Risk Level. An estimate of daily human exposure – by a specified route and length of time -- to a dose of chemical that is likely to be without a measurable risk of adverse, noncancerous effects. An MRL should not be used as a predictor of adverse health effects.

NPL: The National Priorities List. (Which is part of Superfund.) A list kept by the U.S. Environmental Protection Agency (EPA) of the most serious, uncontrolled or abandoned hazardous waste sites in the country. An NPL site needs to be cleaned up or is being looked at to see if people can be exposed to chemicals from the site.

NOAEL: No Observed Adverse Effect Level. The highest dose of a chemical in a study, or group of studies, that did not cause harmful health effects in people or animals.

No Apparent Public Health Hazard: The category is used in ATSDR’s Public Health Assessment documents for sites where exposure to site-related chemicals may have occurred in the past or is still occurring but the exposures are not at levels expected to cause adverse health effects.

No Public Health Hazard: The category is used in ATSDR’s Public Health Assessment documents for sites where there is evidence of an absence of exposure to site-related chemicals.

PHA: Public Health Assessment. A report or document that looks at chemicals at a hazardous waste site and tells if people could be harmed from coming into contact with those chemicals. The PHA also tells if possible further public health actions are needed.

Plume: A line or column of air or water containing chemicals moving from the source to areas further away. A plume can be a column or clouds of smoke from a chimney or contaminated underground water sources or contaminated surface water (such as lakes, ponds and streams).

Point of Exposure: The place where someone can come into contact with a contaminated environmental medium (air, water, food or soil). For examples: the area of a playground that has contaminated dirt, a contaminated spring used for drinking water, the location where fruits or vegetables are grown in contaminated soil, or the backyard area where someone might breathe contaminated air.

Population: A group of people living in a certain area; or the number of people in a certain area.

Public Health Assessment(s): See PHA.

Public Health Hazard: The category is used in PHAs for sites that have certain physical features or evidence of chronic, site-related chemical exposure that could result in adverse health effects.

Public Health Hazard Criteria: PHA categories given to a site which tell whether people could be harmed by conditions present at the site. Each are defined in the Glossary. The categories are:

          1. Urgent Public Health Hazard
          2. Public Health Hazard
          3. Indeterminate Public Health Hazard
          4. No Apparent Public Health Hazard
          5. No Public Health Hazard

Receptor Population: People who live or work in the path of one or more chemicals, and who could come into contact with them (See Exposure Pathway).

Reference Dose (RfD): An estimate, with safety factors (see safety factor) built in, of the daily, life-time exposure of human populations to a possible hazard that is not likely to cause harm to the person.

Route of Exposure: The way a chemical can get into a person’s body. There are three exposure routes:

  • breathing (also called inhalation),
  • eating or drinking (also called ingestion), and
  • or getting something on the skin (also called dermal contact).

Safety Factor: Also called Uncertainty Factor. When scientists don't have enough information to decide if an exposure will cause harm to people, they use "safety factors" and formulas in place of the information that is not known. These factors and formulas can help determine the amount of a chemical that is not likely to cause harm to people.

SARA: The Superfund Amendments and Reauthorization Act in 1986 amended CERCLA and expanded the health-related responsibilities of ATSDR. CERCLA and SARA direct ATSDR to look into the health effects from chemical exposures at hazardous waste sites.

Source (of Contamination): The place where a chemical comes from, such as a landfill, pond, creek, incinerator, tank, or drum. Contaminant source is the first part of an Exposure Pathway.

Special Populations: People who may be more sensitive to chemical exposures because of certain factors such as age, a disease they already have, occupation, sex, or certain behaviors (like cigarette smoking). Children, pregnant women, and older people are often considered special populations.

Superfund Site: See NPL.

Synergistic effect: A health effect from an exposure to more than one chemical, where one of the chemicals worsens the effect of another chemical. The combined effect of the chemicals acting together are greater than the effects of the chemicals acting by themselves.

Toxic: Harmful. Any substance or chemical can be toxic at a certain dose (amount). The dose is what determines the potential harm of a chemical and whether it would cause someone to get sick.

Toxicology: The study of the harmful effects of chemicals on humans or animals.

Tumor: Abnormal growth of tissue or cells that have formed a lump or mass.

Uncertainty Factor: See Safety Factor.

Urgent Public Health Hazard: This category is used in ATSDR’s Public Health Assessment documents for sites that have certain physical features or evidence of short-term (less than 1 year), site-related chemical exposure that could result in adverse health effects and require quick intervention to stop people from being exposed.

APPENDIX C. Estimated Exposure and Health Effects

Estimates of Human Exposure Doses and Determination of Health Effects

Deriving Exposures Doses

ATSDR estimated the human exposure doses from ingestion of water from the wells located at the auto speedway downgradient from Fort Riley’s Marshall Army Airfield Fire Training Area, where VOCs were detected in the past. Deriving exposure doses requires evaluating contaminant concentrations to which people may have been exposed and how often and how long exposure to those contaminants occurred. Together, these factors help influence the individual's physiological response to chemical contaminant exposure and potential outcomes. In the absence of complete exposure-specific information, ATSDR applied several conservative exposure assumptions to define site-specific exposures as accurately as possible for visitors and workers.

Evaluating Potential Health Hazards

The estimated exposure doses are used to evaluate potential noncancer and cancer effects associated with chemicals of concern. When evaluating noncancer effects, ATSDR uses standard toxicity values, including ATSDR's minimal risk levels (MRLs) and EPA's reference doses (RfDs) to determine whether adverse effects will occur. The chronic MRLs and RfDs are estimates of daily human exposure to a substance that are unlikely to result in adverse noncancer effects over a specified duration. To be very protective of human health, MRLs and RfDs have built in "uncertainty" or "safety" factors that make them much lower than levels at which health effects have been observed. Therefore, if an exposure dose is much higher than the MRL or RfD, it does not necessarily follow that adverse health effects will occur.

When evaluating cancer effects, ATSDR sometimes uses cancer potency factors (CPFs) that define the relationship between oral exposure doses and the increased likelihood of developing cancer over a lifetime. The CPFs are developed using data from animal or human studies and often require extrapolation from high exposure doses administered in animal studies to the lower exposure levels typical of human exposure to environmental contaminants. CPFs represent the upper-bound estimate of the probability of developing cancer at a defined level of exposure; therefore, they tend to be very conservative (i.e., overestimate the actual risk) in order to account for a number of uncertainties in the data used in the extrapolation.

ATSDR estimated the potential for cancer to occur using the following equation. (The estimated exposure doses and CPF values for the contaminants of concern are incorporated into the equation):

Lifetime Cancer Risk = Estimated exposure dose (mg/kg/day) x CPF (mg/kg/day)-1

Although no risk of cancer is considered acceptable, it is impossible to achieve a zero cancer risk. Consequently, ATSDR often uses a range of 10-4 to 10-6 estimated lifetime cancer risk (or 1 new case in 10,000 to 1,000,000 exposed persons), based on conservative assumptions about exposure, to determine the likelihood of excess cancer resulting from this exposure.

In addition to estimating the likelihood of noncancer and cancer effects, ATSDR reviewed the toxicologic literature to evaluate possible health effects associated with exposure at the doses/concentrations estimated for the pathways described below.

Estimated Exposure Doses from Ingesting Drinking Water from the Auto Speedway

ATSDR determined that drinking water containing even the highest detected concentrations of VOCs is unlikely to have caused harmful effects in visitors to or workers at the auto speedway.

VOCs in the private wells (R-1, used for drinking water, and R-2, not used for drinking water) located at the auto speedway north of Fort Riley’s MAAF-FFTA exceeded EPA maximum contaminant levels for drinking water. To determine whether exposure to these contaminants in the well water is related to adverse health effects ATSDR estimated exposure doses for people consuming water containing the highest measured concentrations in the wells (either well R-1 or R-2). (Even though the R-2 well water is reportedly not used for human consumption, a higher value of TCE was detected in its well water. As a conservative measure, ATSDR uses the maximum concentration found in any of the speedway wells in this evaluation.) The estimated exposure doses were then used to estimate potential noncancer outcomes. In estimating to what extent people might be exposed to contaminants, ATSDR used "conservative" or safe assumptions about possible human exposure and any associated health effects. ATSDR assumed that a person drank the most contaminated well water. ATSDR also used conservative assumptions about how often people drink water and how much they drink. These assumptions allow ATSDR to estimate the highest possible exposure dose and determine the corresponding health effects. Although ATSDR expects that few individuals, if any, were exposed to the highest levels of contamination, the "conservative" estimates are used to protect public health.

Table C-1 summarizes the estimated exposure doses to VOCs in the well water and the following describes the equation and assumptions used to estimate the exposure dose:

Estimated exposure dose = Conc. x CF x IR x EF x ED
                                                         BW x AT


Conc.: Maximum concentration in the well water (ppb)
CF: Conversion factor to convert ppb to parts per million (1/1,000)IR: Ingestion rate: adult=2 liters per day; child=1 liter per day
EF: Exposure frequency or number of exposure events per year of exposure: 2 days/week x 20 weeks/year
ED: Exposure duration or the duration over which exposure occurs: adult=13 years; child=6 years
BW: Body weight: adult=70 kg (154 pounds); child=10 kg (22 pounds)
AT: Averaging time or the period over which cumulative exposures are averaged (6 or 13 years x 365 days/year for noncancer effects or 70 years for cancer)

Assumptions for Estimating Exposure Doses

  • ATSDR estimates that an adult drank 2 liters and a child drank 1 liter of water a day and that all drinking water came from the wells at the auto speedway. This assumption likely leads to an overestimate of the actual exposure dose because individuals most likely drank water from other sources.

  • The exposure frequency (EF), or number of exposure events per year, was assumed to be 40 days per year, based on a 2-day-a-week exposure over 20 weeks per year.

  • The duration of exposure (ED) is assumed to have occurred over a 13-year period for adults. Although we do not know when contamination first reached the wells, we use a 13-year period to account for the time period that the auto speedway R-1 well is believed to have been used as a water source for the concession stand. For a child, ATSDR used a 6-year exposure duration.

Noncancer: Using the equation to calculate exposure dose, ATSDR estimated exposure doses from ingestion of water from the auto speedway wells with 1,2-DCE (adult: 0.0009 mg/kg/day; child: 0.003 mg/kg/day), PCE (adult: 0.001 mg/kg/day; child: 0.004 mg/kg/day), and TCE (adult: 0.0003 mg/kg/day; child; 0.001 mg/kg/day (see Table C-1). The resulting exposure doses for 1,2-DCE and PCE are lower than their respective health guidelines of 0.02 mg/kg/day and 0.01 mg/kg/day. No chronic oral MRL or RfD is currently available for TCE. ATSDR recently withdrew the intermediate MRL and no chronic MRL or RfD exists for TCE. The study on which the intermediate MRL was based has been questioned because it contains certain flaws and limitations (e.g., the exact amount of TCE-contaminated water consumed by laboratory animals in the study is uncertain). For comparison, ATSDR reviewed the available toxicological literature to determine possible adverse effects associated with exposure at doses estimated for this pathway. On the basis of this review, the exposure doses estimated for TCE by ATSDR are several orders of magnitude lower than the lowest doses reported in the toxicological literature capable of producing noncancer effects in experimental animals administered oral doses of TCE (ATSDR, 1997). Therefore, drinking water containing the highest detected levels of 1,2-DCE, PCE, and TCE, reported in the wells before their closure, is not likely to result in adverse noncancer effect.

Cancer: TCE and PCE have been shown to cause cancer in laboratory animals given large doses. The link between TCE or PCE and cancer in humans drinking water is controversial, however. Available studies are inconclusive and the data are inadequate to establish a link. EPA is currently reviewing the scientific literature pertaining to the carcinogenicity of TCE and PCE to determine its cancer classification. As a conservative measure, ATSDR used the previously derived CPFs for TCE and PCE to estimate the excess lifetime cancer cases resulting from exposure to water containing the maximum concentration of TCE (96 ppb) and PCE (330 ppb). ATSDR estimated 6 new cancer cases per 10,000,000 persons and 1 new case in 100,000 persons could be expected if people were exposed to the maximum level of TCE and PCE, respectively (see Table C-2). On the basis of these results, ATSDR concludes that ingestion of either TCE or PCE at the levels detected in the well water is not expected to result in an increased likelihood of developing cancer.


Estimated Exposure Doses—Noncancer Effects Ingestion of Water at the Auto Speedway


Maximum Detected Contaminant Concentration (ppb)

Estimated Exposure Dose (mg/kg/day)a

Health Guideline (mg/kg/day)

Basis for Health Guideline



1,2-Dichloroethylene (1,2-DCE)





chronic oral RfD
(for trans 1,2,-DCE)

Tetrachloroethylene (PCE)





chronic oral RfD






not available

acute oral MRL

a Estimated Exposure Dose= Conc. x CF x IR x EF x ED
                                           BW x AT

Conc.= Maximum contaminant concentration in the wells at the auto speedway, before closure (ppb)
IR = Ingestion rate: adult = 2 liters per day; child = 1 liter per day
EF= Exposure frequency or the number of exposure events (2 days x 20 weeks or 40 days per year)
ED = Exposure duration or the duration over which exposure occurs: adults = 13 years; child = 6 years
BW= Body weight (kg): adult = 70 kg (154 pounds); child = 10 kg (22 pounds)
AT= Average time or the period over which cumulative exposures are averaged (6 or 13 years x 365 days)

Key: ppb = parts per billion; mg/kg/day=milligrams contaminant per kilogram body weight per day; MRL = ATSDR’s minimal risk level; RfD= EPA’s reference dose.

Table C-2.

Estimated Exposure Doses—Cancer Effects Ingestion of Water at the Auto Speedway
Contaminant Maximum Contaminant Concentration (ppb) Estimated Exposure Dose-Cancer (mg/kg/day) a Cancer Potency Factor Lifetime Cancer Risk c

Tetrachloroethylene (PCE)




1 x 10-5

Trichloroethylene (TCE) 96


0.011b 6 x 10-7

a Estimated Exposure Dose-Cancer = Conc. x IR x EF x ED
                                                        BW x AT

Conc.= Maximum contaminant concentration in the wells at the auto speedway, before closure (ppb)
CF= Conversion factor to convert ppb to ppm (1/1000)
IR = Ingestion rate: 2 liters per day
EF= Exposure frequency, or the number of exposure events (2 days x 20 weeks or 40 days per year)
ED = Exposure duration, or the duration over which exposure occurs = 13 years
BW= Body weight (kg): 70 kg (154 pounds)
AT= Average time or the time over which cumulative exposures are averaged (70 years x 365 days)

b EPA is currently reviewing CPFs for trichlorethylene and tetrachloroethylene. ATSDR has used these previously derived values for screening purposes.


1. The owner of the speedway reports that bottled water was used at the concession stand since the 1980s, however, it is unclear whether or to what extent water from the R-1 wells was used. People probably have not consumed water from the R-1 well since 1993 when contamination was detected and signs were then posted at the speedway to advise visitors against drinking tap water (Fort Riley, 1999c).

2 During routine monitoring, halogenated methanes associated with the chlorination process have been detected in Fort Riley water supply wells, but at levels below MCLs.

3 Lead was analyzed by X-Ray Fluorescence (XRF). Unlike laboratory methods that measure total lead, XRF is a screening analytical tool that measures surface lead in soil and therefore excludes measurements of large lead particulates such as bullet fragments (Louis Berger & Associates, Inc., 1993a, 1993b).

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