Skip directly to search Skip directly to A to Z list Skip directly to site content




The criteria for listing a chemical as a contaminant of concern include: exceedance or lack of media specific health comparison values, community health concerns, and data quality. Also, any contaminant of concern detected in one medium will be by default listed in all other media in which it is detected.

Media-specific health comparison values are contaminant concentrations in specific media (i.e., soil, water and air) used to select contaminants of concern for further evaluation. If the concentration of a chemical exceeds the health comparison value, it does not mean that a public health threat exists but rather signifies that the chemical be further evaluated.

The health comparison values used in this public health assessment include environmental media evaluation guidelines (EMEGs), reference dose media evaluation guidelines (RMEGs), cancer risk evaluation guidelines (CREGs), and lifetime health advisories (LTHA). Ecology Model Toxic Control Act (MTCA) cleanup levels were also used when no other comparison values were available.20, 21 For metals in soil, Ecology natural background values are also used as comparison values since metals occur naturally in the environment.

EMEGs are media-specific health comparison values derived from minimal risk levels (MRLs) presented in ATSDR Toxicological Profiles. RMEGs are media-specific health comparison values derived from EPA's reference dose (RfD) that are used when EMEGs are not available. MRLs and RfDs are estimates of daily exposure of a human to a chemical that is likely to be without an appreciable non-cancer risk over a specified duration of exposure. CREGs are estimated media specific contaminant concentrations that are anticipated to result in one excess cancer risk in one million persons exposed over a lifetime. CREGs are derived from EPA's cancer slope factors (CSFs), also known as cancer potency factors. CSFs are cancer potency estimates derived for chemicals shown to be carcinogenic in animals or humans. LTHAs are guidelines derived for a lifetime ingestion exposure to a contaminant in drinking water. They are derived for non-carcinogenic compounds from Drinking Water Equivalent Levels (DWELs) which are based on oral RfDs. Ecology MTCA cleanup levels are derived for carcinogenic and non-carcinogenic compounds using CSFs and RfDs, respectively.


To obtain conservative daily exposure doses to evaluate non-cancer health effects and cancer risk associated with the ingestion and dermal contact with site soil contaminants, a site worker exposure was used. An ingestion and dermal exposure dose were calculated using the following formulae:

Ingestion Exposure Dose = C x CF x IR x EF x ED)/ BW x AT.

Dermal Exposure Dose = C x CF x A x ABS x EF x ED)/ BW x AT

C =

Concentration of tetrachloroethene in water (mg/l)


Conversion Factor (10 -6)

IR =

Ingestion Rate (liters per day)
Child (0 - 5 years): 1 liter per day
Young adult (6-15 years): 2 liters per day
Adult (>= 16 years): 2 liters per day

EF =

Exposure Frequency (day/year)
It was assumed that people were exposed 350 days per year.

ED =

Exposure Duration (years)
It was assumed that residents were exposed to contamination for 30 years. Thirty years represents the average time that a person spends at one residence.

BW =

Body Weight (kg)
Child (0 - 5 years): 16 kg
Young adult (6-15 years): 40 kg
Adult (>= 16 years): 70 kg

AT =

Averaging Time (days)
For exposure to carcinogens the averaging time is assumed to be 70 years x 365 days/year. For non-carcinogens, the averaging time is the actual length of the exposure period.

A =

Total Soil Adhered (mg)
The total soil adhering to the dermal surface is estimated as the product of the exposed dermal area and the soil adherence concentration.


Absorption Factor (unitless)
Absorption factors are used to reflect the desorption of the chemical from soil and the absorption of the chemical across the skin and into the bloodstream.


Evaluating Non-Cancer Adverse Health Effects

In order to evaluate the potential for non-cancer adverse health effects from exposure to contaminated media (i.e., soil, water, and air), a dose is estimated for each contaminant of concern. The doses are calculated for situations in which people might come into contact with the contaminated media. The estimated dose for each contaminant of concern under each situation is then compared to ATSDR's minimal risk level (MRL) or EPA's oral reference dose (RfD) to determine if there is a potential for non-cancer adverse health effects. MRLs and RfDs are derived from toxic effects levels obtained from human and animal laboratory studies. The toxic effects levels are expressed as either the lowest adverse effect level (LOAEL) or the no-observed adverse effect level (NOAEL). In human or animal studies, the LOAEL is the lowest dose at which an adverse effect is seen; the NOAEL is the highest dose that did not result in any adverse human health effect.

To account for uncertainty, the toxic effect levels are divided by safety factors (10, 100, or 1,000) to provide the more protective MRL or RfD. If a dose exceeds the MRL or RfD, the potential exists for adverse health effects. Therefore, a dose only slightly exceeding the MRL or the RfD would fall well below the toxic effect level. The higher the estimated dose is above the MRL or RfD, the closer it will be to the toxic effect level.

Evaluating Cancer Risk

By calculating a dose similar to that described above and multiplying the dose by the EPA cancer slope factor, the increased cancer risk can be estimated. An exposure to a contaminant which results in an estimated increased cancer risk of one additional cancer in a population of one million people exposed, averaged over a 70 year lifetime, is considered an acceptable risk, and is used as the screening value. In a population of one million men in the U.S., 333,000 (one in three) are expected to develop cancer from all causes in the lifetime (through 79 years of age). For U.S. women, the figure is 200,000.22 The additional estimated cancer risk means that if those one million men are exposed for 30 years to this level of chemical, 333,001 would be expected to develop cancer. For the one million women exposed, 200,001 would be expected to develop cancer.


Comment 1: Page 2, paragraph 4. There is no mention of the surface soil on the BOC property. BOC has investigated their site and analyzed many surface soil samples as part of their site characterization efforts. No significant concentrations of organic compounds have been detected in the surface soil at BOC.

The data for site surface soil contamination are limited. Please refer to Section C, paragraph 2.

Comment 2: Page 3, last paragraph. The equivalent of a door-to-door survey was conducted several years ago when Ecology was the lead agency. This would include the efforts of Clark Public Utilities, Ecology, and Belle Fuchs at the Department of Health.

DOH has talked with utility and agency representatives regarding this informal door-to-door survey. Unfortunately, no documentation could be located on the methods, results, and conclusions of the survey.

Comments 3: Page 5, first paragraph, line 5. The dry well on the BOC property where water and sediment containing organic compounds was found was used for waste water and storm water infiltration.

Comment noted.

Comment 4: Page 5, first paragraph, line 6. Replace the word "most" with "some." Most of the dry well contents were removed in March 1994.

Comment noted.

Comment 5: Page 7, first bullet, line 6 and 7. Replace "whether" with "that" and insert "not" between "had migrated." The soil vapor survey did not find significant concentrations of VOCs on adjacent properties.

This paragraph merely states what was done in the way of environmental investigation. Results of the soil vapor survey are presented in Section C.

Comment 6: Page 14, last paragraph, last two lines. Replace "A portion" with "Most," replace "Surface sediments" with "Sediments remaining in the dry well."

Comment noted.

Comment 7: Page 15, first two lines. Replace "at the surface of the "with "in the." After the sediment removal was completed a sample of the residual sediment in the bottom of dry well was collected and analyzed. The sample was not at the surface of the dry well.

Comment noted.

Comment 8: Page 15, Conclusions, first line. Replace Boomsnub with BOC.

Comment noted.

Comment 9: Page 16, paragraph 3, line 3. After "4,400 feet in length and "add "up to."

The distances are already qualified with the word "approximately."

Comment 10: Page 16, paragraph 3, last line. After "plume extends" insert "to."

Comment noted.

Comment 11: Page 17, first full paragraph. Has DOH contacted the two residents they identified that may be using well water for household purposes? If not, please provide the names of the potential users to EPA.

The water well locations of the potential users have been provided to EPA.

Comment 12: Page 17, paragraph 2. There are no City of Vancouver wells identified on Figure 1. Identify the City well locations on Figure 1 or delete the reference to City wells.

Comment noted.

Comment 13: Page 18, Recommendation No. 2. Clark Public Utilities currently uses wells near the Site to meet peak water demand only. This practice should be continued.

Recommendations for this health assessment pertain to reducing or eliminated potential human exposures to environmental contaminants. DOH can not make any specific recommendation on how Clark Public Utilities should meet peak water demand.

Comment 14: Page 20, Actions Proposed No. 4. After "EPA" insert "and BOC."

EPA is the lead regulatory agency for the site. DOH will work directly with EPA on groundwater contamination issues as they relate to public health. BOC is welcome to be involved in these discussions.

Comment 15: Page 21, Actions Proposed. Add "BOC will reduce or eliminate groundwater and soil contamination on their property to levels protective of human health."

Please see response to Comment 14. EPA will be working with BOC gases to further define, contain, and reduce levels of groundwater contamination on the site.


An underground formation composed of materials such as sand, soil, or gravel that can store and/or supply groundwater to wells and springs.

Agency for Toxic Substances and Disease Registry (ATSDR):
The principal federal pubic health agency involved with hazardous waste issues, responsible for preventing or reducing the harmful effects of exposure to hazardous substances on human health and quality of life. ATSDR is part of the U.S. Department of Health and Human Services.

Cancer Slope Factor:
A number assigned to a cancer causing chemical that is used to estimate it's ability to cause cancer in humans.

Any substance that can cause or contribute to the production of cancer.

Oral Reference Dose (RfD):
An amount of chemical ingested into the body (i.e., dose) below which health effects are not expected. RfDs are published by EPA.

Comparison Value:
A concentration of a chemical in soil, air or water that, if exceeded, requires further evaluation as a contaminant of potential health concern. The terms comparison value and screening level are often used synonymously.

Any chemical that exists in the environment or living organisms that is not normally found there.

Cancer Risk Evaluation Guide (CREG):
The concentration of a chemical in air, soil or water that is expected to cause no more than one excess cancer in a million persons exposed over a lifetime. The CREG is a comparison value used to select contaminants of potential health concern and is based on the cancer slope factor (CSF).

A dose is the amount of a substance that gets into the body through ingestion, skin absorption or inhalation. It is calculated per kilogram of body weight per day.

Environmental Media Evaluation Guide (EMEG):
A concentration in air, soil, or water below which adverse non-cancer health effects are not expected to occur. The EMEG is a comparison value used to select contaminants of potential health concern and is based on ATSDR's minimal risk level (MRL).

U.S. Environmental Protection Agency (EPA):
Established in 1970 to bring together parts of various government agencies involved with the control of pollution.

Contact with a chemical by swallowing, by breathing, or by direct contact (such as through the skin or eyes). Exposure may be short term (acute) or long term (chronic).

Water found underground that fills pores between materials such as sand, soil, or gravel. In aquifers, groundwater often occurs in quantities where it can be used for drinking water, irrigation, and other purposes.

Hazardous Substance:
Any material that poses a threat to public health and/or the environment. Typical hazardous substances are materials that are toxic, corrosive, ignitable, explosive, or chemically reactive.

Compounds composed of mineral materials, including elemental salts and metals such as iron, aluminum, mercury, and zinc.

Ingestion Rate
The amount of an environmental medium which could be ingested typically on a daily basis. Units for IR are usually liter/day for water, and mg/day for soil.

Lowest Observed Adverse Effect Level (LOAEL):
LOAEL's have been classified into "less serious" or "serious" effects. In dose-response experiments, the lowest exposure level at which there are statistically or biologically significant increases in the frequency or severity of adverse effects between the exposed population and its appropriate control.

Soil, water, air, plants, animals, or any other part of the environment that can contain contaminants.

Monitoring Wells:
Special wells drilled at locations on or off a hazardous waste site so water can be sampled at selected depths and studied to determine the movement of groundwater and the amount, distribution, and type of contaminant.

Minimal Risk Level (MRL):
An amount of chemical that gets into the body (i.e. dose) below which health effects are not expected. MRLs are derived by ATSDR for acute, intermediate, and chronic duration exposures by the inhalation and oral routes.

Model Toxics Control Act (MTCA):
The hazardous waste cleanup law for Washington State.

No Apparent Public Health Hazard:
Sites where human exposure to contaminated media is occurring or has occurred in the past, but the exposure is below a level of health hazard.

No Observed Adverse Effect Level (NOAEL):
The dose of a chemical at which there were no statistically or biologically significant increases in frequency or severity of adverse effects seen between the exposed population and its appropriate control. Effects may be observed at this dose but were judged not to be "adverse".

Compounds composed of carbon, including materials such as solvents, oils, and pesticides which are not easily dissolved in water.

An area of contaminants in a specific media such as groundwater.

Remedial Investigation:
A study designed to collect the data necessary to determine the nature and extent of contamination at a site.

The probability that something will cause injury, linked with the potential severity of that injury. Risk is usually indicated by how many extra cancers may appear in a group of people who are exposed to a particular substance at a given concentration, in a particular pathway, and for a specified period of time. For example, a 1%, or 1 in 100 risk indicates that for 100 people who may be exposed, 1 person may experience cancer as a result of the exposure.

Reference Dose Media Evaluation Guide (RMEG):
A concentration in air, soil, or water below which adverse non-cancer health effects are not expected to occur. The EMEG is a comparison value used to select contaminants of potential health concern and is based on EPA's oral reference dose (RfD).

Route of Exposure:
The way in which a person my contact a chemical substance that includes ingestion, skin contact and breathing.


This Public Health Assessment was prepared by the Washington State Department of Health under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health assessment was begun.

Debra Gable
Technical Project Officer,

The Division of Health Assessment and Consultation, ATSDR, has reviewed this Public Health Assessment and concurs with the findings.


Richard Gillig
Branch Chief,

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #