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The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal public health agency with headquarters in Atlanta, Georgia, and 10 regional offices in the United States. ATSDRs mission is to serve the public by using the best science, taking responsive public health actions, and providing trusted health information to prevent harmful exposures and diseases related to toxic substances. ATSDR is not a regulatory agency, unlike the U.S. Environmental Protection Agency (EPA), which is the federal agency that develops and enforces environmental laws to protect the environment and human health.

This glossary defines words used by ATSDR in communications with the public. It is not a complete dictionary of environmental health terms. If you have questions or comments, call ATSDRs toll-free telephone number, 1-888-42-ATSDR (1-888-422-8737).

The process of taking in. For a person or animal, absorption is the process through which a substance gets into the body through the eyes, skin, stomach, intestines, or lungs.

The number of radioactive nuclear transformations occurring in a material per unit time. The term for activity per unit mass is specific activity.

Occurring over a short time [compare with chronic].

Acute exposure:
Contact with a substance that occurs once or for only a short time (up to 14 days) [compare with intermediate-duration exposure and chronic exposure].

Adverse health effect:
A change in body function or cell structure that might lead to disease or health problems.

Surrounding (for example, ambient air).

Analytic epidemiologic study:
A study that evaluates the association between exposure to hazardous substances and disease by testing scientific hypotheses.

Background level:
An average or expected amount of a substance or radioactive material in a specific environment, or typical amounts of substances that occur naturally in an environment.

Background radiation:
The amount of radiation to which a member of the general population is exposed from natural sources, such as terrestrial radiation from naturally occurring radionuclides in the soil, cosmic radiation originating from outer space, and naturally occurring radionuclides deposited in the human body.

Bedding planes:
The division of sediment or sedimentary rock into parallel layers (beds) that can be distinguished from each other by such features as chemical composition and grain size.

Plants and animals in an environment. Some of these plants and animals might be sources of food, clothing, or medicines for people.

Body burden:
The total amount of a substance in the body. Some substances build up in the body because they are stored in fat or bone or because they leave the body very slowly.

Any one of a group of diseases that occurs when cells in the body become abnormal and grow or multiply out of control.

Cancer risk:
A theoretical risk of getting cancer if exposed to a substance every day for 70 years (a lifetime exposure). The true risk might be lower.

A substance that causes cancer.

Case-control study:
A study that compares exposures of people who have a disease or condition (cases) with people who do not have the disease or condition (controls). Exposures that are more common among the cases may be considered as possible risk factors for the disease.

Central nervous system:
The part of the nervous system that consists of the brain and the spinal cord.

[See Comprehensive Environmental Response, Compensation, and Liability Act of 1980.]

Occurring over a long time (more than 1 year) [compare with acute].

Chronic exposure:
Contact with a substance that occurs over a long time (more than 1 year) [compare with acute exposure and intermediate-duration exposure].

Committed Effective Dose Equivalent (CEDE):
The sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent to the organs or tissues. The committed effective dose equivalent is used in radiation safety because it implicitly includes the relative carcinogenic sensitivity of the various tissues. The unit of dose for the CEDE is the rem (or, in SI units, the sievert—1 sievert equals 100 rem.)

Comparison value (CV):
Calculated concentration of a substance in air, water, food, or soil that is unlikely to cause harmful (adverse) health effects in exposed people. The CV is used as a screening level during the public health assessment process. Substances found in amounts greater than their CVs might be selected for further evaluation in the public health assessment process.

Completed exposure pathway:
[See exposure pathway.]

Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA):
CERCLA, also known as Superfund, is the federal law that concerns the removal or cleanup of hazardous substances in the environment and at hazardous waste sites. ATSDR, which was created by CERCLA, is responsible for assessing health issues and supporting public health activities related to hazardous waste sites or other environmental releases of hazardous substances.

The amount of a substance present in a certain amount of soil, water, air, food, blood, hair, urine, breath, or any other medium.

A substance that is either present in an environment where it does not belong or is present at levels that might cause harmful (adverse) health effects.

Curie (Ci):
A unit of radioactivity. One curie equals that quantity of radioactive material in which there are 3.7 × 1010 nuclear transformations per second. The activity of 1 gram of radium is approximately 1 Ci; the activity of 1.46 million grams of natural uranium is approximately 1 Ci.

Decay product/daughter product/progeny:
A new nuclide formed as a result of radioactive decay: from the radioactive transformation of a radionuclide, either directly or as the result of successive transformations in a radioactive series. A decay product can be either radioactive or stable.

Depleted uranium (DU):
Uranium having a percentage of U 235 smaller than the 0.7% found in natural uranium. It is obtained as a byproduct of U 235 enrichment.

Referring to the skin. For example, dermal absorption means passing through the skin.

Dermal contact:
Contact with (touching) the skin [see route of exposure].

Descriptive epidemiology:
The study of the amount and distribution of a disease in a specified population by person, place, and time.

Detection limit:
The lowest concentration of a chemical that can reliably be distinguished from a zero concentration.

Disease registry:
A system of ongoing registration of all cases of a particular disease or health condition in a defined population.

The United States Department of Energy.

Dose (for chemicals that are not radioactive) :
The amount of a substance to which a person is exposed over some time period. Dose is a measurement of exposure. Dose is often expressed as milligrams (a measure of quantity) per kilogram (a measure of body weight) per day (a measure of time) when people eat or drink contaminated water, food, or soil. In general, the greater the dose, the greater the likelihood of an effect. An "exposure dose" is how much of a substance is encountered in the environment. An "absorbed dose" is the amount of a substance that actually gets into the body through the eyes, skin, stomach, intestines, or lungs.

Dose (for radioactive chemicals):
The radiation dose is the amount of energy from radiation that is actually absorbed by the body. This is not the same as measurements of the amount of radiation in the environment.

Dose-response relationship:
The relationship between the amount of exposure [dose] to a substance and the resulting changes in body function or health (response).

Environmental Media Evaluation Guide, a media-specific comparison value that is used to select contaminants of concern. Levels below the EMEG are not expected to cause adverse noncarcinogenic health effects.

Enriched uranium:
Uranium in which the abundance of the U 235 isotope is increased above normal.

Environmental media:
Soil, water, air, biota (plants and animals), or any other parts of the environment that can contain contaminants.

Environmental media and transport mechanism:
Environmental media include water, air, soil, and biota (plants and animals). Transport mechanisms move contaminants from the source to points where human exposure can occur. The environmental media and transport mechanism is the second part of an exposure pathway.

The United States Environmental Protection Agency.

Epidemiologic surveillance:
The ongoing, systematic collection, analysis, and interpretation of health data. This activity also involves timely dissemination of the data and use for public health programs.

The study of the distribution and determinants of disease or health status in a population; the study of the occurrence and causes of health effects in humans.

Equilibrium, radioactive:
In a radioactive series, the state that prevails when the ratios between the activities of two or more successive members of the series remain constant.

Contact with a substance by swallowing, breathing, or touching the skin or eyes. Exposure can be short-term [see acute exposure], of intermediate duration [see intermediate-duration exposure], or long-term [see chronic exposure].

Exposure assessment:
The process of finding out how people come into contact with a hazardous substance, how often and for how long they are in contact with the substance, and how much of the substance they are in contact with.

Exposure-dose reconstruction:
A method of estimating the amount of people’s past exposure to hazardous substances. Computer and approximation methods are used when past information is limited, not available, or missing.

Exposure investigation:
The collection and analysis of site-specific information and biological tests (when appropriate) to determine whether people have been exposed to hazardous substances.

Exposure pathway:
The route a substance takes from its source (where it began) to its end point (where it ends), and how people can come into contact with (or get exposed to) it. An exposure pathway has five parts: a source of contamination (such as an abandoned business); an environmental media and transport mechanism (such as movement through groundwater); a point of exposure (such as a private well); a route of exposure (eating, drinking, breathing, or touching), and a receptor population (people potentially or actually exposed). When all five parts are present, the exposure pathway is termed a completed exposure pathway.

Exposure registry:
A system of ongoing follow up of people who have had documented environmental exposures.

Feasibility study:
A study by EPA to determine the best way to clean up environmental contamination. A number of factors are considered, including health risk, costs, and what methods will work well.

Grand rounds:
Training sessions for physicians and other health care providers about health topics.

Water beneath the earth's surface in the spaces between soil particles and between rock surfaces [compare with surface water].

Half-life (t½):
The time it takes for half the original amount of a substance to disappear. In the environment, the half-life is the time it takes for half the original amount of a substance to disappear when it is changed to another chemical by bacteria, fungi, sunlight, or other chemical processes. In the human body, the half-life is the time it takes for half the original amount of the substance to disappear either by being changed to another substance or by leaving the body. In the case of radioactive material, the half-life is the amount of time necessary for one half the initial number of radioactive atoms to change or transform into other atoms (normally not radioactive). After two half-lives, 25% of the original number of radioactive atoms remain.

A source of potential harm from past, current, or future exposures.

Hazardous waste:
Potentially harmful substances that have been released or discarded into the environment.

Health consultation:
A review of available information or collection of new data to respond to a specific health question or request for information about a potential environmental hazard. Health consultations are focused on a specific exposure issue. They are therefore more limited than public health assessments, which review the exposure potential of each pathway and chemical [compare with public health assessment].

Health education:
Programs designed with a community to help it know about health risks and how to reduce these risks.

Health investigation:
The collection and evaluation of information about the health of community residents. This information is used to describe or count the occurrence of a disease, symptom, or clinical measure and to estimate the possible association between the occurrence and exposure to hazardous substances.

Health statistics review:
The analysis of existing health information (i.e., from death certificates, birth defects registries, and cancer registries) to determine if there is excess disease in a specific population, geographic area, and time period. A health statistics review is a descriptive epidemiologic study.

Indeterminate public health hazard:
The category used in ATSDR's public health assessment documents when a professional judgment about the level of health hazard cannot be made because information critical to such a decision is lacking.

The number of new cases of disease in a defined population over a specific time period [contrast with prevalence].

Incised Meander:
Incised meanders result from down-cutting along the deepest part of a river's channel. The down-cutting is so rapid, the river maintains a meandering pattern while deepening its valley. This erosion process creates exposed bedrock on its banks permitting the discharge of groundwater to surface streams.

The act of swallowing something through eating, drinking, or mouthing objects. A hazardous substance can enter the body this way [see route of exposure].

The act of breathing. A hazardous substance can enter the body this way [see route of exposure].

Intermediate-duration exposure:
Contact with a substance that occurs for more than 14 days and less than a year [compare with acute exposure and chronic exposure].

Ionizing radiation:
Any radiation capable of knocking electrons out of atoms and producing ions. Examples: alpha, beta, gamma and x rays, and neutrons.

Nuclides having the same number of protons in their nuclei, and hence the same atomic number, but differing in the number of neutrons, and therefore in the mass number. Identical chemical properties exist in isotopes of a particular element. The term should not be used as a synonym for "nuclide," because "isotopes" refers specifically to different nuclei of the same element.

Lowest-observed-adverse-effect level (LOAEL):
The lowest tested dose of a substance that has been reported to cause harmful (adverse) health effects in people or animals.

The conversion or breakdown of a substance from one form to another by a living organism.

Milligrams per kilogram.

Milligrams per cubic meter: a measure of the concentration of a chemical in a known volume (a cubic meter) of air, soil, or water.

Moving from one location to another.

Minimal risk level (MRL):
An ATSDR estimate of daily human exposure to a hazardous substance at or below which that substance is unlikely to pose a measurable risk of harmful (adverse), noncancerous effects. MRLs are calculated for a route of exposure (inhalation or oral) over a specified time period (acute, intermediate, or chronic). MRLs should not be used as predictors of harmful (adverse) health effects [see reference dose].

Death. Usually the cause (a specific disease, condition, or injury) is stated.

A substance that causes mutations (genetic damage).

A change (damage) to the DNA, genes, or chromosomes of living organisms.:
National Priorities List for Uncontrolled Hazardous Waste Sites (National Priorities List or NPL):
EPA’s list of the most serious uncontrolled or abandoned hazardous waste sites in the United States. The NPL is updated on a regular basis.

No apparent public health hazard:
A category used in ATSDR's public health assessments for sites where human exposure to contaminated media might be occurring, might have occurred in the past, or might occur in the future, but is not expected to cause any harmful health effects.

No-observed-adverse-effect level (NOAEL):
The highest tested dose of a substance that has been reported to have no harmful (adverse) health effects on people or animals.

No public health hazard:
A category used in ATSDR's public health assessment documents for sites where people have never and will never come into contact with harmful amounts of site-related substances.

[See National Priorities List for Uncontrolled Hazardous Waste Sites.]

A radionuclide which, upon disintegration, yields a new nuclide, either directly or as a later member of a radioactive series.

A volume of a substance that moves from its source to places farther away from the source. Plumes can be described by the volume of air or water they occupy and the direction in which they move. For example, a plume can be a column of smoke from a chimney or a substance moving with groundwater.

Point of exposure:
The place where someone can come into contact with a substance present in the environment [see exposure pathway].

A group or number of people living within a specified area or sharing similar characteristics (such as occupation or age).

Parts per billion.

Parts per million.

The number of existing disease cases in a defined population during a specific time period [contrast with incidence].

Actions that reduce exposure or other risks, keep people from getting sick, or keep disease from getting worse.

Public comment period:
An opportunity for the public to comment on agency findings or proposed activities contained in draft reports or documents. The public comment period is a limited time period during which comments will be accepted.

Public health action plan:
A list of steps to protect public health.

Public health advisory:
A statement made by ATSDR to EPA or a state regulatory agency that a release of hazardous substances poses an immediate threat to human health. The advisory includes recommended measures to reduce exposure and reduce the threat to human health.

Public health assessment (PHA):
An ATSDR document that examines hazardous substances, health outcomes, and community concerns at a hazardous waste site to determine whether people could be harmed by coming into contact with those substances. The PHA also lists actions that need to be taken to protect public health [compare with health consultation].

Public health hazard:
A category used in ATSDR's public health assessments for sites that pose a public health hazard because of long-term exposures (greater than 1 year) to sufficiently high levels of hazardous substances or radionuclides that could result in harmful health effects.

Public health hazard categories:
Statements about whether people could be harmed by conditions present at the site in the past, present, or future. One or more hazard categories might be appropriate for each site. The five public health hazard categories are no public health hazard, no apparent public health hazard, indeterminate public health hazard, public health hazard, and urgent public health hazard.

Public health statement:
The first chapter of an ATSDR toxicological profile. The public health statement is a summary written in words that are easy to understand. It explains how people might be exposed to a specific substance and describes the known health effects of that substance.

Public meeting:
A public forum with community members for communication about a site.

Quality factor (radiation weighting factor):
The linear-energy-transfer-dependent factor by which absorbed doses are multiplied to obtain (for radiation protection purposes) a quantity that expresses - on a common scale for all ionizing radiation - the approximate biological effectiveness of the absorbed dose.

The unit of absorbed dose equal to 100 ergs per gram, or 0.01 joules per kilogram (0.01 gray) in any medium [see dose].

The emission and propagation of energy through space or through a material medium in the form of waves (e.g., the emission and propagation of electromagnetic waves, or of sound and elastic waves). The term "radiation" (or "radiant energy"), when unqualified, usually refers to electromagnetic radiation. Such radiation commonly is classified according to frequency, as microwaves, infrared, visible (light), ultraviolet, and x and gamma rays and, by extension, corpuscular emission, such as alpha and beta radiation, neutrons, or rays of mixed or unknown type, such as cosmic radiation.

Radioactive material:
Material containing radioactive atoms.

Spontaneous nuclear transformations that result in the formation of new elements. These transformations are accomplished by emission of alpha or beta particles from the nucleus or by the capture of an orbital electron. Each of these reactions may or may not be accompanied by a gamma photon.

An unstable or radioactive isotope (form) of an element that can change into another element by giving off radiation.

Any radioactive isotope (form) of any element.

Risk-based Concentration, a contaminant concentration that is not expected to cause adverse health effects over long-term exposure.

[See Resource Conservation and Recovery Act (1976, 1984).]

Receptor population:
People who could come into contact with hazardous substances [see exposure pathway].

Reference dose (RfD):
An EPA estimate, with uncertainty or safety factors built in, of the daily lifetime dose of a substance that is unlikely to cause harm in humans.

A unit of dose equivalent that is used in the regulatory, administrative, and engineering design aspects of radiation safety practice. The dose equivalent in rem is numerically equal to the absorbed dose in rad multiplied by the quality factor (1 rem is equal to 0.01 sievert).

Remedial investigation:
The CERCLA process of determining the type and extent of hazardous material contamination at a site.

Resource Conservation and Recovery Act (1976, 1984) (RCRA):
This act regulates management and disposal of hazardous wastes currently generated, treated, stored, disposed of, or distributed.

[See reference dose.]

The probability that something will cause injury or harm.

Route of exposure:
The way people come into contact with a hazardous substance. Three routes of exposure are breathing [inhalation], eating or drinking [ingestion], and contact with the skin [dermal contact].

Safety factor:
[See uncertainty factor.]

A portion or piece of a whole; a selected subset of a population or subset of whatever is being studied. For example, in a study of people the sample is a number of people chosen from a larger population [see population]. An environmental sample (for example, a small amount of soil or water) might be collected to measure contamination in the environment at a specific location.

Sievert (Sv):
The SI unit of any of the quantities expressed as dose equivalent. The dose equivalent in sieverts is equal to the absorbed dose, in gray, multiplied by the quality factor (1 sievert equals 100 rem).

A liquid capable of dissolving or dispersing another substance (for example, acetone or mineral spirits).

Source of contamination:
The place where a hazardous substance comes from, such as a landfill, waste pond, incinerator, storage tank, or drum. A source of contamination is the first part of an exposure pathway.

Special populations:
People who might be more sensitive or susceptible to exposure to hazardous substances because of factors such as age, occupation, gender, or behaviors (for example, cigarette smoking). Children, pregnant women, and older people are often considered special populations.

Specific activity:
Radioactivity per unit mass of material containing a radionuclide, expressed, for example, as Ci/gram or Bq/gram.

A person, group, or community who has an interest in activities at a hazardous waste site.

A branch of mathematics that deals with collecting, reviewing, summarizing, and interpreting data or information. Statistics are used to determine whether differences between study groups are meaningful.

The horizontal line marking the intersection between the inclined plane of a solid geological structure and the Earth's surface.

A chemical.

Surface water:
Water on the surface of the earth, such as in lakes, rivers, streams, ponds, and springs [compare with groundwater].

[see epidemiologic surveillance]

A systematic collection of information or data. A survey can be conducted to collect information from a group of people or from the environment. Surveys of a group of people can be conducted by telephone, by mail, or in person. Some surveys are done by interviewing a group of people.

Toxicological profile:
An ATSDR document that examines, summarizes, and interprets information about a hazardous substance to determine harmful levels of exposure and associated health effects. A toxicological profile also identifies significant gaps in knowledge on the substance and describes areas where further research is needed.

The study of the harmful effects of substances on humans or animals.

Uncertainty factor:
A mathematical adjustment for reasons of safety when knowledge is incomplete—for example, a factor used in the calculation of doses that are not harmful (adverse) to people. These factors are applied to the lowest-observed-adverse-effect-level (LOAEL) or the no-observed-adverse-effect-level (NOAEL) to derive a minimal risk level (MRL). Uncertainty factors are used to account for variations in people's sensitivity, for differences between animals and humans, and for differences between a LOAEL and a NOAEL. Scientists use uncertainty factors when they have some, but not all, the information from animal or human studies to decide whether an exposure will cause harm to people [also sometimes called a safety factor].

Units, radiological:
Units Equivalents
Becquerel* (Bq) 1 disintegration per second = 2.7 × 10-11 Ci
Curie (Ci) 3.7 × 1010 disintegrations per second = 3.7 × 1010 Bq
Gray* (Gy) 1 J/kg = 100 rad
Rad (rad) 100 erg/g = 0.01 Gy
Rem (rem) 0.01 sievert
Sievert* (Sv) 100 rem

Urgent public health hazard:
A category used in ATSDR's public health assessments for sites where short-term exposures (less than 1 year) to hazardous substances or conditions could result in harmful health effects that require rapid intervention.

A watershed is a region of land that is crisscrossed by smaller waterways that drain into a larger body of water.

Water table:
The surface that lies between the unsaturated zone and the underlying saturated zone of the soil.

Other Glossaries and Dictionaries:
Environmental Protection Agency
National Center for Environmental Health (CDC)
National Library of Medicine


ORR is located in the East Tennessee Valley, which is part of the Valley and Ridge Province of the Appalachian Mountains. The East Tennessee Valley is bound to the west by the Cumberland Mountains of the Appalachian Plateau Province and to the east by the Smokey Mountains of the Blue Ridge Province. The defining characteristics of the Valley and Ridge Province are the southwest trending series of ridges and valleys caused by crustal folding and vaulting due to compressive tectonic forces as well as the differential weathering of the various formations underlying the area. There are ten geologic formations underlying parts of the ORR, all are of sedimentary origin. These formations range in age from early Cambrian (530 mya) to early Mississippian (354 mya). From youngest to oldest they are:

  1. Fort Payne Chert (Mfp)
  2. Chattanooga Shale (MDc)
  3. Rockwood Formation (Sr)
  4. Sequatchie Formation (Os)
  5. Reedsville Shale (Or)
  6. Chickamauga Group (Och)
  7. Knox Group (O€k)
  8. Conasuaga Group (€c)
  9. Maynardville Formation (€)
  10. Rome Formation (€r)

Each of these formations is described briefly in Table B-1. All of the formations consist mainly of shales, limestones and siltstones. The three major geologic formations are the Chickamauga Group, the Knox Group, and the Conasuaga Group. These formations are considered 'major' based on the location of the various plants (ETTP, ORNL, and Y-12), location of the contaminant plumes (see Figure 4), and proportion of ORR underlain by these three formations.

Geologic Map of the ORR and Groundwater Contaminant Plumes
Figure B-1. Geologic Map of the ORR and Groundwater Contaminant Plumes

Table B-1: Hydrogeology of the Formations Underlying the Oak Ridge Reservation (USGS 2004)

Geologic Feature Age Geology Description Conductivity (at ORR)
Fort Payne Chert (Mfp) Mississipian (early) Bluish-gray Limestone Thin outcrops at western edge of Valley and Ridge Province
Average thickness 100' – 250'
Contains water in secondary openings.
Yields from 0 to more than 300 gpm.
Chattanooga Shale (MDc) Mississipian (early), Devonian (late) Black, fissle shale About 25 ft thick
Very dark to black carbonaceous shale
Overlies Rockwood Formation
Underlies Fort Payne Chert
Low porosity and permeability.
Yields little or no water to wells.
Rockwood Formation (Sr) Silurian (early – middle) Greenish to Brownish Shale, Limestone Ranges in thickness from 150 – 1000 feet
Limited outcrop results in limited recharge
Some beds associated with iron ore (hematite) deposits
Underlies Chattanooga Shale
Overlies Sequatchie Formation
Not a good aquifer because of limited recharge.
Groundwater occurs in fractures.
Sequatchie Formation (Os) Ordovician Shale, Limestone Near ORR, thickness approx. 100ft.
Overlies Chickamauga Group
Poor aquifer
Groundwater occurs in fractures.
Reedsville Shale (Or) Ordovician (late) Shale Uppermost layer of the Chickamauga Group
Underlies the Sequatchie Formation
Near ORR, thickness ranges from 250 – 400 feet
Poor aquifer
Groundwater occurs in fractures.
Chickamauga Group (Och) Ordovician (middle) Limestone ORNL (Bethel Valley) and ETTP are built on this group
Approximately 2000' thick
Overlies the Knox Group
Underlies the Sequatchie Formation
AQUITARD - flow limiting strata
Groundwater occurs in fractures
Variable lithology results in varying conductivities
Knox Group (O€k) Ordovician (early, middle), Cambrian (late) Dolomite, Limestone Overlies Conasauga Group (Shale)
Massive calcareous unit that is the prominent formation in the Appalachian Valley ranging from 2000 – 4000 feet thick
Contains fossil fuels (oil, gas) in other regions
Most important aquifer in the ORR area
Groundwater occurs in joints and fractures
Large springs are common
Highly variable flow rates: from several gpm to several thousand gpm
Maynardville Formation Cambrian (late) Limestone, Dolomite Off-site contamination at Y-12 occurs in this formation.
Uppermost unit of the Conasauga Group
Historically included in the Knox Group
Relatively thin (thickness 60-250ft)
Generally yields several gpm up to 200 gpm
Conasauga Group (€c) Cambrian Shale, Limestone, Dolomite Y-12 complex is built on this group
Contains the largest waste management areas at ORR:
Bear Creek Valley
Melton Valley
Very limited migration of contaminant plumes
Most groundwater resurfaces to surface water
Limestone layers retard downward migration of groundwater
In some areas can be up to 2000' thick
AQUITARD – typically flow limiting strata
Contains the AQUIFER subunit Maynardville Formation (limestone), which contains the only off-site contaminant plume from Y-12.
Rome Formation (€r) Cambrian (early) Shale, Siltstone Underlies Conasauga Group
Approximately 1500 feet thick
Groundwater occurs in fractures
Upper zone is more permeable than lower zone
Springs are common
Wells can yield several gpm.

Since this health assessment is focused solely on groundwater in and around the ORR, it is necessary to first establish a basic understanding of general groundwater principles, particularly as they relate to the specific geology of the ORR. An important feature of the hydrology of the ORR is the interaction of groundwater with surface water. Depth to bedrock in the ORR is typically very shallow. In this physiographic region, groundwater flow tends to be localized (within a relatively small area such as a watershed), as opposed to regional (larger area such as the Oak Ridge Reservation or perhaps an even larger area), and flow-paths to surface water are short (USGS 1986b). So, a discussion on how groundwater and surface water interact is warranted.

In general, a stream can be described in three ways based upon it's interaction with groundwater. A stream can either be a gaining stream, a losing stream, (Figure 8) or a combination of both (Figure 14). In order to have a gaining stream system, the water table altitude must be higher than that of the stream (USGS 1998). The reverse is true for a losing stream system. Because the bedrock is very close to the ground surface in and around the ORR, and in many cases, occurs as outcrops, the streams are gaining. This is a very common situation in East Tennessee because of the topography of the area. The water table and the groundwater flow path typically mirror the undulations of the overlying land. Since surface water occurs at the low areas, groundwater often flows toward surface water. Therefore, the altitude of the water table is higher than that of the surface water. Recharge of groundwater around the ORR is spatially distributed (occurs over a large area as opposed to small outcrops or ridgelines), but discharge areas are at local springs, seeps as well as diffuse discharge into surface waters (MMES 1986, USGS 1986b, SAIC 2004). Indeed, groundwater constitutes much of the baseflow of many streams and tributaries in the area, including East Fork Poplar Creek (EFPC) (USGS 1989, SAIC2004).

Gaining (Left) and Losing (Right) Streams and Associated Groundwater Flow Direction
Figure B-2. Gaining (Left) and Losing (Right) Streams and Associated Groundwater Flow Direction

Groundwater System Involving the Hyporheic Zones (Alley et. al 2002)
Figure B-3: Groundwater System Involving the Hyporheic Zones (Alley et. al 2002)

In the Bear Creek Valley watershed there are both gaining and losing reaches of Bear Creek. This illustrates the third groundwater-surface water system where there groundwater enters and exits the surface water at different sections of the stream. In this case the concept of hyporheic flow becomes relevant (Figure B-3). Hyporheic flow, or the hyporheic zone, refers to the areas beneath and adjacent to the stream where surface water and groundwater mix. In systems such as this, surface water contamination can percolate through the sediments and contaminate the groundwater (Alley et al. 2002).

Groundwater flow in this area (ORR) is influenced largely on the extent of fractures in the bedrock which create preferential flow paths. In the regional aquifers of East Tennessee, including those underlying the ORR, fractures in bedrock are typically limited to the upper extents of the bedrock formations and significantly decrease with depth (MMES 1986, USGS 1986b, USGS 1988, USGS 1989, SAIC 2004). The karst geology of the ORR makes accurate predictions of groundwater flow rate and direction problematic, particularly in the carbonate formations such as the Knox Group and the Maynardville Limestone. Most groundwater flow in these carbonate formations occurs in the shallow interval (<100 feet) through fracture flow and through solution-enlarged cavities. For example, there are several large solution cavities beneath Bear Creek which (along certain reaches) serve as a hydraulic drain to the Maynardville Limestone (Lemiski 1994, SAIC 1996b). Groundwater will flow along bedding planes and along strike, especially in areas where carbonate units have well-developed conduit systems (ORNL 1982, USGS 1997). This is the case in the UEFPC Watershed where VOC contamination has migrated off-site from the Y-12 Complex and is migrating along strike in the Maynardville Limestone (ORNL 1982, SAIC 2004).

The numerous springs and seeps in the area support the notion of a very active shallow groundwater system in the ORR. Open cavities at bedrock outcrops in the ORR area range in size from small drains to easily enterable caves. These areas serve as rapid recharge areas and result in rapid flow rates through the interconnected fractures and solution cavities and can contribute to significant hydraulic head pressure changes during heavy rainfall events (SAIC 1996, Lemiszki 1994). The intermediate interval (100 feet – 300 feet) of the Maynardville Limestone is known to have high flow rates but does not receive the dilution effect that is seen in the shallow interval (SAIC 1996b), and therefore, is seen as an important interval with respect to contaminant transport. While fracture flow remains the dominant mode of groundwater movement at depth (below 300 feet), solution cavities and fractures are limited and decrease significantly beyond 300 feet.

An incised meander is formed when a stream's ancestral floodplain is uplifted causing intense downward erosion by the current stream. In East Tennessee, this uplifting caused the formation of many of the ridges in the area such as Black Oak Ridge, Pine Ridge, Chestnut Ridge, and Haw Ridge. The incised meander of the Clinch River cuts through these uplifted ridges creating "gaps". This deep, relatively rapid erosion of the bedrock creates exposed bedrock on the river banks. Groundwater is discharged to surface water where bedrock is exposed. Because of this deep erosion through bedrock, the Clinch River serves as an effective barrier to groundwater flow.

While mapping springs and seeps in the ORR area, Lemiszki (1994) noted that most occurred along the banks of the Clinch River. For most of the year, these seeps and springs were underwater, but winter is when the Clinch River is in low stage and these karst features can be seen. There was a wide variety in flow rates observed. Some springs were mere trickles of water from bedrock outcrops while others were large volume springs (up to 25 gal/min) actively filling potholes along the river flats. This observation supports the notion that the incised meander (see Appendix A) of the Clinch River serves as an effective hydraulic barrier for groundwater flow.

Groundwater flow in predominantly aquitard formations occurs mostly in the shallow interval (<100 feet) at the bedrock/residuum interface or in other preferential flow paths, such as fractures. In times of heavy precipitation, the elevation of the water table typically rises rapidly and discharge to streams increases. Groundwater flow through porous media in predominantly aquitard formations near the ORR is minimal.

Karst groundwater systems form through the chemical weathering of predominantly carbonate formations (Prothero and Schwab 1996). In the vicinity of the ORR, calcium carbonate (CaCO3) limestones and calcium magnesium carbonate [CaMg(CO3) 2] dolomites are eroded as rainwater (H2O) combines with carbon dioxide (CO2) to form carbonic acid (H2CO2). This weak acid solution dissolves limestone and dolomite according to the following reaction:

CaCO3 (limestone) + H2CO3 (carbonic acid) arrow Ca2+ (dissolved calcium) + 2HCO3- (dissolved bicarbonate)

SAIC (1996b) cites studies that show distinct groundwater geochemical facies in the Bear Creek Valley. In the shallow zone (<100 ft), the geochemical profile is similar to that of the equation above. This facies type indicates that there is a shallow water table and a short residence time, meaning that groundwater is quickly replaces by recharge as it is discharged to surface water. There is a gradual, but noticeable change in groundwater composition from Ca/Mg HCO3 to a sodium bicarbonate (Na-HCO3) at depth. This implies longer residence times at depth where groundwater mixes with older, less active brines. However, because of the interconnected karst networks in the area, Ca/Mg HCO3 type groundwater occurs at many depths, but in the deepest wells Na-Cl groundwater dominates (SAIC 1996b).

Depending on the geology of the area, flow times from points of recharge to points of discharge can range from days to millennia (Figure 15). As is the case at the ORR, shallow surface water has short flow paths with relatively quick travel times. However, the limestones and dolomites of the Valley and Ridge Province often contain cracks, fissures, fractures, and solution cavities that can make groundwater flow direction and speed unpredictable (USGS 1997).

Groundwater Flow Times
Figure B-4: Groundwater Flow Times

It is unlikely that contaminated groundwater at the ORR will flow beneath, and continue to flow away from, streams and rivers that surround the site. The vast majority of information available concerning the geology and hydrogeology of the site indicates that groundwater occurs as shallow flow with short flow paths to surface water (ORNL 1982, MMES 1986, USGS 1986b, USGS 1988, USGS 1989, SAIC 2004). The fractures and solution cavities present in the bedrock occur in shallow (0'-100' deep) bedrock and significantly decrease at depth. There is also evidence that beneath the alluvium at the bottom of the stream beds there is a silty-clay glei horizon that likely further impedes downward groundwater movement (USGS 1989). The incised meander (see Appendix A) of the Clinch River in bedrock represents a major topographic feature that prevents groundwater from passing beneath the river (ORNL 1982). The extensive interconnection between groundwater and surface water coupled with the fact that groundwater contamination sources at the ORR are in the shallow subsurface (with the exception of deep-well injection conducted at ORNL, which will be discussed in the Melton Valley Watershed section of this document), leads ATSDR scientist to conclude that on-site contaminated groundwater does not likely migrate beneath and away from streams and rivers either as slug-flow or in fractures, solution channels, or other conduits in the bedrock.

It is important for the reader to understand that ATSDR scientists acknowledge the fact that karst systems are notoriously difficult to fully characterize with respect to groundwater flow direction and rate. We have based our conclusions on currently available data concerning groundwater flow and specific contaminant fate and transport from well monitoring data. There are large solution cavities beneath ORR and the surrounding area which are often interconnected and have high flow rates. Some have been encountered in various well drilling activities or by casual observation, and some have yet to be discovered. It is our intention to assess the currently available data, and to arrive at a conclusion of whether the community has had (or is currently having) an exposure to contaminants in off-site groundwater.


ATSDR received comments on the Evaluation of Potential Exposures to Contaminated Off-Site Groundwater from the ORR Public Health Assessment, Public Comment Release (August 19, 2005), from peer reviewers, individuals, organizations, and agencies. We have also received additional comments at various public meetings. We thank all of those who took the time to comment. This appendix includes a listing of the public, peer review, and agency comments and our responses to them. Some grammatical and editing comments, such as typos and undefined acronyms, have been corrected in this document but not included in this appendix.

1. Reliability of data used in this PHA

Reviewer Comments:

"The nature and extent of contamination are described by something that I would compare to liar's poker – the reader needs to have faith that the data are correctly and fully reported. These data may be included in many of the numerous documents cited, but this report itself concentrates on the maximum concentration reported in respect to the Comparison Values (CVs) sometimes as much as a decade ago. What are missing are any reports of data quality, variability of measurements (site, background and reference) over time and the date of the last measurement"

"When added, discussions of the historical monitoring data should also address the consistency and adequacy of the data sets for PHA purposes."

ATSDR Response:

In preparing this PHA, ATSDR reviewed and evaluated environmental data provided to ATSDR scientists directly from the Department of Energy or in various reports prepared by the Environmental Protection Agency Region IV, the Tennessee Department of Environment and Conservation (TDEC) DOE Oversight Division, or their contractors. ATSDRs evaluation included the identification of inconsistencies and data gaps. The validity of analyses and conclusions drawn in this PHA are based on the reliability of the information referenced in reports related to the Oak Ridge Reservation (ORR). In our assessment, the quality of environmental data available in these documents is sufficient for public health decisions. A statement similar to this one has been added to the "Evaluation of Environmental Contamination and Potential Exposure Pathways" section of this document.

2. Narrow focus of this PHA on groundwater

Reviewer Comments:

"[T]he document concentrates single-mindedly on groundwater itself and no pathways other than residential drinking water."

"I am firmly convinced that isolated health assessments of the type attempted here (ignoring all other pathways and media) do a disservice to the public and do not assist ATSDR in its mission."

"You only talk about off-site groundwater."

ATSDR Response:

It may be unclear to the reviewer that there are 8 other PHAs being conducted for ORR. These PHAs address all other contaminants of concern and related pathways of exposure. This document was intended to be specific and narrowly focused on contaminated groundwater and associated off-site exposure pathways.

3. Adequacy and completeness of off-site groundwater sampling

Reviewer Comments:

"In some instances contaminated sources are not re-sampled!"

"The nature and frequency of the off-site sampling program is not well-described in the report and may be inadequate. Monitoring programs based on snapshots in time every few years or even on an annual basis often lead to false conclusions concerning public health safety and the effectiveness of remediation programs."

"Based on my reading of the report, the off-site monitoring program appears to be random and infrequent, particularly as it relates to residential wells."

ATSDR Response:

ATSDR used all available data in this assessment. We recognized the sporadic and inconsistent nature of the off-site residential sampling data and have noted this as a data gap in the document (p. 7). However, this sampling was conducted by TDEC and was never intended to be comprehensive or to fully characterize off-site contamination from ORR. TDEC does not have the resources or funding to complete a comprehensive sampling program. A recommendation has been added to this document that a regular monitoring of off-site residential wells should be included in DOE's groundwater monitoring program.

4. Health outcome data

Reviewer Comments:

"Based on their assumptions and views of the data, the authors reach conclusions for which their explanations are appropriate, and therefore they communicate the proposition that there are no adverse health effects expected, and if there are any in the area (not checked or evaluated) they are unrelated to site-based exposure via groundwater because of the absence of complete pathways."

"Sites such as the subject area often have the attention of activists and others creating a counter-balance to any tendency to whitewash a potentially dangerous situation. Frequently they seize upon some statistical aberration or local cancer cluster as their cause celebre, thereby inflaming public and agency reaction (and over-reaction). Although I know there have been issues in the area, especially regarding mercury, apparently they have not motivated anyone to get very excited about potential threats. Hence, I was surprised that the authors did not present some population-based statistics to validate their assertions that there was no threat. Even census tract data on longevity or disease incidence from the cancer registry would add confirming support for the conclusions which, to me, seemed stretched."

ATSDR Response:

ATSDR scientists generally consider health outcome data to evaluate the possible health effects in a population known to have been exposed to enough environmental contamination to experience health effects. In this pubic health assessment on off-site groundwater at ORR, ATSDR scientists determined that people were not and are not using private groundwater wells and were not exposed to ORR related contaminants from groundwater exposure. For these reasons, health outcome data were not evaluated in this public health assessment.

5. Include more maps

Reviewer Comments:

"The significant ETTP monitoring points should be clearly shown on a map. This same comment applies to data locations for the other sites/watersheds."

"Potentiometric maps and geologic cross-sections are appropriate and needed to adequately evaluate potential hazards to public health."

"The report does not include maps of the contaminant plumes emanating from the Y-12 complex. Such maps are also appropriate and needed to adequately evaluate potential hazards to public health."

"In the discussion of contamination in Bethel Valley and Melton Valley, creeks are mentioned by name, such as White Oak Creek, Raccoon Creek, First Creek, and the Northwest Tributary, but there is no figure to show the reader the locations and the configurations of these creeks. This problem is actually generic to the whole report. There are figures in the draft PHA for releases to White Oak Creek, especially Figure 10, that show these creeks, although sometimes not too distinctly. A good figure showing the surface water drainage pattern for the ORR is considered a necessity for this report, because the message of this report is as much or more graphical and qualitative than it is quantitative."

"Figure B-1 does not include the Maynardville Formation, which is described in Table B-1 as a significant aquifer and is also mentioned several times in the text."

"Figure B-1 is an incomplete representation of the geologic and hydrogeologic relationships that exist on and around the ORR. Vertical profiles or cross-sections are needed to show the interrelationships of the various formations, aquifers, and flow paths. Depictions of flow gradient and conductivity calculations or models would also be helpful."

ATSDR Response:

Several maps and figures have been added to the document to address the issues raised by the reviewers. Figure 2 shows the monitoring locations near ETTP. Geologic cross-sections are provided in several maps including Figures 3, 6, 9, 11, and 12. The contaminant plume emanating from Y-12 and extending off-site into Union Valley is depicted in Figure 13 and Figure B-1. White Oak Creek, Raccoon Creek, First Creek, and the Northwest Tributary are represented in Figure 5.

The Maynardville Formation is a sub-group of the Conasauga Group. This is indicated in the text of the document as well as in Table B-1. Figure B-1 is intended to show the major geologic formations of the ORR

6. Vapor intrusion

Reviewer Comments:

"Absent are any consideration of vapor intrusion for VOCs and semi-VOCs, including some forms of mercury..."

"One potential pathway of human exposure that is not addressed in the report is the volatilization of contaminants from the groundwater system to the soil system and subsequent inhalation by residents in underground structures (i.e., basements or houses partially located below grade) or in buildings with cracked foundations."

ATSDR Response:

A thorough discussion of vapor intrusion as it relates to the EEVOC plume extending off-site from the Y-12 Complex has been added to the "Evaluation of Environmental Contamination and Potential Exposure Pathways" section of the document.

7. Adequacy of institutional controls and pump-and-treat technology in Union Valley

Reviewer Comments:

"The document should detail which institutional controls are in place in Union Valley. It is our understanding that these include deed restrictions on groundwater use."

"The idea of institutional controls being adequate to exclude [hunting and fishing], of course, runs counter to the local culture."

"The administrative controls are not adequately described. Technical details of the plume, remediation system, and performance metrics are also lacking. The general tone of the section (ATSDR's Conclusion for Bear Creek Valley and UEFPC Watersheds) suggests that the pump-and-treat will be sufficient when it is well-known that this remediation technology is rarely effective in reaching site-specific remedial action objectives."

"The recommendation to solely rely on institutional controls set forth in the Interim Record of Decision is flawed given that the pump-and-treat remediation technology is ineffective in reducing contamination to safe levels."

"Most of the pathways seem to be well-defined. However, the Union Springs pathway seems ambiguous. It is unclear why an area zoned as industrial can be assumed to have unlikely human contacts. What about humans that exercise in this area during break periods at facilities? Also, workers involved in infrastructure maintenance may contact these seeps."

ATSDR Response:

The institutional controls are outlined under "UEFPC Watershed' in the "Contamination at Bear Creek Valley and UEFPC Watersheds" section.

The issues of hunting and fishing are addressed in other PHAs for the ORR, including: White Oak Creek, Current Chemical Exposures and Mercury PHAs.

The efficacy of pump and treat technologies is certainly a debatable point; however, the purpose of this health assessment is not to recommend treatment technologies which would reduce contamination, nor is it our objective to evaluate whether the selected remediation tactics can reach site-specific remedial action objectives. It is our goal to evaluate whether exposure to contaminated groundwater is occurring, has occurred in the past, or will likely occur in the future. If a completed exposure route has been identified, we would then evaluate the health impacts, if any, from that level of exposure. The institutional controls that are in place were not intended to reduce the EEVOC plume's toxicity, mobility of volume of contamination. They were merely intended to 1) ensure that the public's health is protected by mitigating exposure, 2) to prohibit future activities that could lead to exposure, and 3) prohibit activities that can make the plume migrate faster or increase in extent.

The exposure scenario that is mentioned here is the possibility of someone coming in contact with contaminated groundwater in this area. Because of the zoning for this area as industrial, we do not anticipate any contact by people with groundwater. While it is entirely possible that maintenance workers could somehow come in contact with springs or seeps in the area, we feel that an exposure (especially one of any health consequence) of this nature is an unlikely scenario.

8. Description of contaminant sources and provision of additional data

Reviewer Comments:

"Deficiencies in the report with respect to the description of groundwater contamination include: (a) description of contaminant sources in the aquifer; (b) disconnect between the description and discussion of contaminants found in off-site monitoring points and the activities of the various facilities; (c) incomplete presentation of the positioning of off-site monitoring and residential wells (i.e., depths and hydrogeologic units) in relation to groundwater flow paths; (d) inadequate description of biogeochemistry of the groundwater system."

"The contamination discussion is too brief. Only selected contaminants are discussed without giving any sense of the data sets that were available to the PHA preparers. Were radionuclides and non-VOCs not a potential groundwater issue at ETTP? Summary tables of pertinent data sets should be provided so the reader can clearly see why, for example, only VOCs are discussed for ETTP groundwater. Otherwise it's left open to question whether or not data exists or was examined for other possible contaminants. This same comment applies to the discussion of selected analytes/contaminants for the other sites, watersheds, or media."

"The PHA fails to give the reader the general perspective of what the potential groundwater contamination sources and constituents are, how much data is available, and why only certain contaminants are discussed. Consequently, the PHA discussions of only a few contaminants come across as selective and incomplete."

"The source data on area hydrogeology and groundwater monitoring are included only as reference citations. Sufficient portions of that data need to be presented in the PHA text and as tables and figures to support and justify ATSDR's conclusions. Without the supporting information, the lay reader does not get the sense that the historical data have been reviewed critically and that any potential data gaps have been looked for."

ATSDR Response:

We believe that the document contains adequate descriptions of relevant contaminant sources in each watershed. Each respective section has a subsection devoted to the contaminant sources as well as a section discussing relevant data from monitoring wells, residential wells, and seep/spring data. (Monitoring well depth and biogeochemistry issues are discussed below)

The primary contaminants of concern in groundwater at ETTP are VOCs. The primary contaminants in sediments at ETTP are inorganic elements, radionuclides, and polychlorinated biphenyls (PCBs). In soils, the contaminants of concern include inorganic elements, radionuclides, semi-volatile organic compounds (SVOCs), polyaromatic hydrocarbons (PAHs), and VOCs. As is the case with other watersheds discussed in the PHA, the contaminants that are discussed are the primary contaminants of concern in groundwater. A statement similar to this one has been added to the "Contamination at ETTP" section for clarity.

The vastness of the data sets that exist concerning the hydrogeology of the ORR precludes their inclusion, even as summary tables, in this document. We feel that summarizing these studies in text is sufficient to convey the concepts of the hydrology of the area. These concepts are well-supported and are not of a generally contentious nature. Relevant data from off-site groundwater monitoring and from residential well sampling are included in summary form in the relevant sections. If the reader would like to review the raw data, we will be happy to provide them.

9. Well (monitoring and residential) depths and sampling depths

Reviewer Comments:

"...there is no information provided in the report that explains whether off-site wells are sampling groundwater from the shallow aquifer system or deeper formations."

"[Appendix B] indicates fractures and solution cavities occurring from 100' to 300' deep in bedrock, which seems to contradict the earlier statement ... that they occur mostly from 0 – 100' deep. How deep is the Clinch River bottom on average? How deep is the hyporheic zone beneath the Clinch? How deep are typical groundwater drinking wells in the area?"

ATSDR Response:

Specific well depths were not available with the data received by ATSDR. However, from all reports reviewed by ATSDR, it appears that many of the samples were taken using multi-port sampling devices from wells that extend deep into bedrock (>500 feet). The Clinch River varies in depth but is typically around 100 feet deep.

Residential well depths were not reported along with the data. However, the depth of residential wells can vary greatly. Variables that affect well depth include: type of well, location of well with respect to surface water, composition of bedrock and location of the water table. Because of the cost of drilling and the likelihood of finding usable amounts of groundwater at depth, most private wells in this area are less than 200 feet deep.

The text mentioned in Appendix B contained a typo – an apparent remnant from earlier edits. This sentence has been corrected to read that fractures and solution cavities occur predominantly in the shallow zone (0' – 100' deep) and decrease significantly at depth.

10. Geochemistry of groundwater around ORR

Reviewer Comments:

"Deficiencies in the report include... inadequate description of biogeochemistry of the groundwater system."

ATSDR Response:

A general discussion about the geochemistry for the relevant formations underlying the ORR has been included in Appendix B.

11. More in-depth discussion of Karst

Reviewer Comments:

"Karst zones do not appear in Figs. B-2, -3, or –4, or in the text of Appendix B, although an exposition on this subject would be a useful addition to this Appendix."

"Also discussed in ORNL-5870 is the fact that the more calcareous formations underlying Bear Creek Valley often contain large solution-weathered cavities that are conduits for groundwater. This fact probably needs some additional explicit discussion in the PHA because the existence of this type of condition tends to fuel speculation by concerned citizens."

"Portions of the geology discussion are incorrect. Many of the streams on the Oak Ridge Reservation are now known to gain or lose water through their beds. This is especially true of Bear Creek. Acknowledgement of the presence of karst and the understanding of it's effects on groundwater flow and contaminant migration has changed substantially since the 1980s. Karst features are important conduits for groundwater in the Upper East Fork Poplar Creek watershed, Union Valley, Bear Creek Valley, at East Tennessee Technology Park and in Bethel Valley. It was the primary reason that X-10 waste disposal activities were moved from Bethel Valley to Melton Valley, which is underlain by shale bedrock. Additionally, groundwater flow in the industrial areas is strongly influenced by the presence of pipes, building formations, buried utilities, and backfill."

ATSDR Response:

A more thorough discussion of the karst geology beneath the ORR has been added to Appendix B. Also, a discussion of the presence of karst geology as well as buried pipelines and other structures below ground and their impact on groundwater flow, has been added to the "UEFPC Watershed' section of the document.

Appendix B addresses the fact that Bear Creek has both gaining and losing reaches. The presence of karst systems and their effect on groundwater movement in the Oak Ridge area is addressed repeatedly in the document; however, because of the variability and unpredictability that the presence of karst conduits introduce to a groundwater system, the topic has been expounded upon further in Appendix B.

12. Explanation of "incised meander"

Reviewer Comment:

"The important term "incised meander", occurring on page B-7, should be explained."

ATSDR Response:

The term "incised meander" has been defined in Appendix A and explained further in Appendix B.

13. Historical groundwater use and over-pumping of wells

Reviewer Comments:

"The PHA lacks any meaningful discussion on historical groundwater usage in the area. Other than the figures depicting offsite well locations near the ORR boundaries, there is no inventory or discussion of well usage in the area and how pumping may or may not have influenced localized flow of groundwater emanating from the ORR."

"There is a need in the conclusions section of the report to add a statement about the potential (or lack of potential) for induced infiltration of water through well pumping as an off-site groundwater exposure pathway (i.e., the potential that part of the discharge from a well near contaminated surface water could be water drawn from the contaminated surface water)."

ATSDR Response:

The figures depicting off-site well locations include residential wells from which we have sampling data. While it is true that most residences near the ORR receive their drinking water from municipal sources, we are aware that there are many more residential wells than are depicted on these maps. For the areas near ETTP and ORNL, there are a significant number of monitoring wells near the ORR border. We have evaluated these data and have concluded that contamination from the ORR has not migrated beyond the ORR boundaries in groundwater. This conclusion is based upon the limited data currently available. Should any new data become available that could change our assessment, the issue will be reevaluated.

It is true that heavy well pumping can create a negative hydraulic gradient and cause groundwater to flow toward the well in all directions. Also, the theoretical potential exists for contaminated water to be drawn from surface water sources. Based on available data, we do not believe this is occurring in residential wells surrounding the reservation. This discussion appears in the "Conclusion" section of the PHA as a consideration.

14. Melton Valley contamination

Reviewer Comment:

"Page 21, lines 5 – 14 seem to discuss only strontium 90. What happened to the tritium and cesium 137 mentioned in the preceding paragraph? What about other contaminants (rad and chemical) that have been detected in wells throughout Melton Valley?"

ATSDR Response:

The contaminants mentioned are indeed contaminants of concern in Melton Valley; however, because of the close interaction between groundwater in the aquitard formations of Melton Valley and surface water, these contaminants migrate via surface water. Consequently, most of the monitoring that is performed in Melton Valley concerns surface water with emphasis on the WOD. Surface water contamination in this area is addressed in the White Oak Creek Public Health Assessment. Contaminant data from off-site wells near Melton Valley are discussed in the relevant section of this document.

15. Significance of "integration points"

Reviewer Comment:

Please explain the meaning and significance of an "integration point."

ATSDR Response:

Integration points are important in defining and integrating conditions at the watershed level and are key sites for assessing long-term water quality improvement as various remedial actions in the watershed are completed (SAIC 2005).

16. Significance of Comparison Values

Reviewer Comment:

"Although hazard identification as such is adequate, toxicological data themselves are not really brought into play, since the authors have determined that there are no completed pathways and therefore no subject population at risk to evaluate toxicologically. The significance (or lack thereof) of CVs as toxicologic benchmarks is not discussed."

ATSDR Response:

Comparison Values (CVs) are used to assess voluminous data sets in an efficient and consistent manner during the screening analysis. They enable you to identify substances that are not expected to result in adverse heath effects (i.e., substances detected below comparison values) and substances requiring further evaluation (i.e., substances detected above comparison values).

Comparison Values are not thresholds of toxicity. Comparison values should not be used to predict adverse health effects. These values serve only as guidelines to provide an initial screen of human exposure to substances. Although concentrations at or below the relevant comparison value may reasonably be considered safe, it does not automatically follow that any environmental concentration that exceeds a comparison value would be expected to produce adverse health effects.

A text box on page 12 reflects the above information and directs readers to Appendix A where there is a more thorough explanation of comparison values.

17. Presence of other springs in the area

Reviewer Comment:

"Bacon Springs where Oliver Springs get all there water from. Key Springs is one more. And right where the Oak Ridge outdoor swimming pool there is a spring that is where they get the water to fill the swimming pool up. All along the Black Oak Ridge there is springs and water coming out from that ridge line. All too much water to come from one mountain chain."

ATSDR Response:

Because of the karst nature of the geology in the Oak Ridge area there are many springs and seeps. ATSDR has reviewed all available data from seeps and springs that have been identified in the vicinity of the Oak Ridge Reservation. A summary and discussion of these data is provided in respective sections for each watershed.

18. Contamination in the Lower EFPC floodplain

Reviewer Comment:

"On page 23, under the heading Monitoring Wells, the sentence beginning "As previously mentioned...' needs to be followed by a sentence that states how the contamination in the EFPC floodplain ground water arrived at the off-site monitoring locations, in not through "...a direct result of groundwater contamination emanating from the Y-12 complex.'"

ATSDR Response:

The groundwater contamination in the EFPC Floodplain results from contaminated surface water (EFPC) infiltrating into the groundwater. In 1993, ATSDR conducted a Health Consultation for this area and concluded that there is a possible health threat to people consuming groundwater in this area; however, based on available data, all residences in the area were using water from the municipal water system. This statement has been added in the document.

19. Contamination leaving the ORR via surface water

Reviewer Comment:

"The document needs to reiterate that while only one site has off-site migration of groundwater (i.e., EEVOC – not defined in the acronym list), the short groundwater pathway for subsurface contamination to surface creeks and streams does not imply that surface waters leaving the site are safe. There is a significant amount of groundwater contamination being diluted within the surface creeks and streams."

ATSDR Response:

Indeed, groundwater contamination is contributing to surface water contamination. This point is mentioned in the document and has been reiterated in the appropriate sections. However, this document is solely focused on human exposure to off-site groundwater. Exposure to contamination in surface water and other media is addressed in other ATSDR public health assessments including: Current & Future Chemical Exposure Evaluation (1990-2003), White Oak Creek Radionuclide Releases, and Y-12 Mercury Releases PHA's.

20. Figures are too general in Appendix B

Reviewer Comment:

"Pages B-5 and B-7. The discussion and two figures are very general and conceptual in nature. Need to provide specific local data to support what's depicted in the figures."

ATSDR Response:

Figures B-2, -3, and -4 are intended to be demonstrative of general surface water/groundwater interactions and not necessarily specific to the geology of the ORR area. Information presented in Appendix B is supported by cited sources throughout the text. These sources contain site-specific data to confirm concepts expressed in Appendix B. These concepts are well-supported and are not of a generally contentious nature. We feel that it is unnecessary and beyond the scope of this document to include these data.

21. Inadequacy of ATSDR response to Community Concern #4 (p. 51)

Reviewer Comment:

"Page 40, comment # 4. ATSDR's response is inadequate. The overall summary level discussion in the PHA does not reflect "a thorough investigation of the underlying geology." Previous geologic reports are cited in the PHA, but salient data from these reports are not presented to support or justify ATSDR's conclusions. Also, the response refers the reader to Appendix B for "specific information regarding the geology and hydrogeology of the ORR." However, the information in Appendix B seems to be highly general, presenting textbook concepts without the support of localized, site-specific data."

ATSDR Response:

We believe that the comment itself is of such a general nature that it expresses the sentiment that drives the preparation of this PHA. This citizen is concerned that contaminated groundwater may be reaching private residents through karst conduits or other pathways. The entire PHA is designed to address this issue. In our response to this comment, we are expressing our recognition of these concerns and the fact that they are addressed throughout this PHA. We also hope that additions made to this PHA as a result of some of the excellent comments received through the public comment process has increased the thoroughness and specificity of the document.

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