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




The Iowa Department of Public Health (IDPH), Hazardous Waste Site Health Assessment Program, has prepared this public health consultation in response to a request from the Iowa Department of Natural Resources (IDNR). IDPH was asked to evaluate whether a petroleum spill from the Williams Pipeline Company site in Coralville, Iowa, and subsequent contamination of groundwater pose a threat to human health.


The Williams Pipeline Company Iowa City terminal stores various petroleum products and has been in operation since the early 1930's. It is located at the intersection of Interstate 80 and 1st Avenue in Coralville, Iowa. The facility consists of a number of above ground and underground storage tanks and several tank car and truck loading areas.

Land use around the site is both commercial and residential, with residential usage predominating south and west of the Williams Pipeline Company. The area immediately south of the site (down-gradient) is residential, and includes an elementary school. According to the 2000 Census, the number of persons living within one-quarter mile of the Williams site is about 3,000. Leakage of stored petroleum products was discovered in 1999, but the leak has been estimated to have started possibly six years prior to its discovery date. By November 2000, the contaminant plume had migrated approximately 4,500 feet south of the site, underneath the adjacent residential area. Monitoring well data indicate that mixtures of BTEX (benzene, toulene, ethylbenzene, xylene), and MTBE (methyl tert-butyl ether) are present in groundwater. The contaminant plume is of variable width but is generally less than 1,000 feet wide. An underground clay layer 10-40 feet thick overlies the contaminant plume throughout the residential area adjacent to the site (1).

There are no known private drinking water wells in this area. All homes are connected to the Coralville municipal water supply, and have been since at least the 1970's. The source of municipal water is located 1.5 miles north (up-gradient) from the Williams site and has not been impacted by the spill.

Depth to groundwater in the vicinity ranges from 20-80 feet. Highest concentrations of benzene, the most toxic of the BTEX compounds, were 1,000-2,000 µg/L (micrograms per liter) at a depth of approximately 50 feet. The Maximum Contaminant Level (MCL) for benzene in water is 5 µg/L. The highest MTBE concentration reported was 1,300 µg/L from a 40 foot deep monitoring well in the residential area (2). Its MCL is 3,000 µg/L. MCL's are considered to be safe levels for drinking water, levels at which persons may be exposed for many years without adverse health effects.

BTEX and MTBE are considered to be volatile organic compounds. It is possible for these compounds to evaporate from contaminated water and exist as a vapor. BTEX and MTBE vapors from contaminated groundwater can migrate through the soil and enter homes.

The site is now undergoing remediation. The Iowa Department of Natural Resources is providing quarterly monitoring of groundwater in the area.


There are no completed exposure pathways relating to ingestion of contaminated water at this site due to all residences being connected to the local municipal water supply. The municipal water supply has not been effected by petroleum contamination from the Williams site.

Although vapors from MTBE or the BTEX compounds in groundwater may enter homes through cracks in masonry or foundations, vapor migration is unlikely at the Williams site because of local geologic features and the depth of contamination (3). A thick clay layer underneath the site acts as a barrier to MTBE and BTEX vapors, and restricts these vapors within the contaminant plume some 20-80 feet underground. The U.S. Environmental Protection Agency (EPA)-approved Johnson-Ettinger model for indoor air quality has been used to estimate health risk from airborne exposure to MTBE and BTEX at the site. This model has shown that concentrations of MTBE and BTEX in air would be well below levels of health concern (3). Therefore, no ill health effects should be expected in the aftermath of the spill.


Children's unique physiology and behavior can influence the extent of their exposure and therefore their susceptibility to hazardous chemicals. Children and adults may differ in their capacity to repair damage from chemical assaults. Children also have a longer remaining lifetime in which to express damage from chemicals. Certain characteristics of the developing human may increase exposure or susceptibility. For example, children breathe more air per kilogram of body weight than do adults. And they are more likely than adults to misjudge possible environmental hazards and less likely to avoid these hazards.

Based on available evidence, it is unlikely that children have been or are now being exposed to contaminants from the Williams Pipeline Company site, either through ingestion or inhalation pathways.


  • BTEX and MTBE in groundwater in the vicinity of theWilliams Pipeline Company Iowa City Terminal poses no public health hazard.


  • Proceed with site remediation and quarterly groundwater monitoring.


  1. IDPH staff attended a community meeting in Coralville, Iowa (March 2001) hosted by the Iowa Department of Natural Resources. Issues discussed at the meeting included the nature and extent of groundwater contamination, and what, if any, effect this contamination might have on public health.

  2. At this time, there is no need for further community health education efforts at this site. However, quarterly groundwater monitoring data will be reviewed when available. After data review, further health education efforts may be undertaken if warranted.


  1. Leggette, Brashears & Graham, Inc. Supplemental Subsurface Investigation Report. Conducted for the Iowa Department of Natural Resources. St. Paul (MN); 2000 Jul-Nov.

  2. Leggette, Brashears & Graham, Inc. Supplemental Subsurface Investigation Report. Conducted for the Iowa Department of Natural Resources. St. Paul (MN); 2000 Mar-May.

  3. Environmental Strategies Corporation. Indoor Air Model Williams Iowa City Terminal. Conducted for the Iowa Department of Natural Resources. St. Paul (MN.); 2001 Mar.


Prepared by:

Hazardous Waste Site Health Assessment Program
Iowa Department of Public Health

Reviewed by:

Ben Puesta
ATSDR Regional Representative
Office of Regional Operations, Region VII
Office of the Assistant Administrator, ATSDR

Roberta Erlwein
ATSDR Technical Project Officer
Division of Health Assessment and Consultation
Superfund Site Assessment Branch


This health consultation for the Williams Pipeline Company site was prepared by the Iowa Department of Public Health, Hazardous Waste Site Health Assessment Program, 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 consultation began.

Roberta Erlwein
Technical Project Officer,

The Division of Health Assessment and Consultation, ATSDR, has reviewed this health consultation, and concurs with its findings.

Richard Gillig

Extent of Dissolved Plume in Groundwater, July through November 2000
Figure 1. Extent of Dissolved Plume in Groundwater, July through November 2000

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. #