U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006–3094

July 2006 Printed on recycled paper

Navajo Coal and Air Quality in Shiprock, New Mexico

Among the Navajo people, high levels of respiratory disease, such as 

asthma, exist in a population with low rates of cigarette smoking. Air quality outdoors and indoors affects respiratory health. Many Navajo Nation 

residents burn locally mined coal in their homes for heat, as coal is the 

most economical energy source. The U.S. Geological Survey (USGS) and 

Diné College, in cooperation with the Navajo Division of Health, are conducting a study in the Shiprock, New Mexico, area to determine if indoor 

use of this coal might be contributing to some of the respiratory health 

problems experienced by the residents. Researchers in this study will (1) 

examine respiratory health data, (2) identify stove type and use, (3) analyze 

samples of coal that are used locally, and (4) measure and characterize air 

quality inside selected homes. Interim results are summarized below.

Inversions.—In the Shiprock area of the San Juan basin, people are 

exposed to poor air quality outdoors when atmospheric thermal inversions 

trap combustion products from two nearby large-capacity coal-fired powerplants (fig. 1). The number of respiratory incidents in the Shiprock area 

increases in winter (when inversions are more common) and decreases in 

summer. This increase may be related to inversions and to burning coal, 

wood, and other materials indoors for heating during the winter.

Respiratory health data.—Our study indicates that people living 

in Shiprock are more than five times as likely to be seen at the Northern Navajo Medical Center (NNMC) Indian Health Service facility for 

respiratory complaints as are residents of other nearby communities that 

are less affected by inversions. Another notable finding is that Shiprock 

residents under the age of 5 and over 56 are more than twice as likely to 

be treated at NNMC for respiratory issues as would be expected of the 

entire Shiprock population. The very young and the elderly spend more 

time indoors during winter when coal may be used for home heating, and 

people in these age groups may have immune systems that are compromised relative to the systems of people between 5 and 56.

Stove type and use.—The use of a properly operated and maintained stove designed to burn coal should not significantly lower air 

quality indoors. The research team surveyed 137 households that used 

coal-burning stoves in 2004 and found that one-quarter of them were 

burning coal in stoves that were designed to operate at lower temperatures for burning wood and that many of the stoves had visible cracks 

or were poorly vented to the outside (fig. 2).

According to the results of this study, people can reduce their risk 

of respiratory disease by doing the following:

Cleaning and properly maintaining coal-burning stoves

Properly venting those stoves

Using a stove designed for the appropriate fuel

Safely handling coal and ash

Coal analyses.—Most of the coal used by our survey participants came from the Navajo mine at the Four Corners Power Plant. 

Samples of coal from Shiprock area homes, as well as from the mines 

and powerplants, have been analyzed for their chemical composition. 

No significant differences were found in the quality of coal from those 

various sources, and no dangerous levels of trace elements, such as 

mercury, were detected.

Particulate matter.—When coal is burned, numerous potentially 

harmful materials are released into the air. Of particular concern are 

small particles known as PM2.5 (particulate matter 2.5 micrometers or 

less in diameter). These particles, less than 1/30th the diameter of a 

human hair, are small enough that they can travel deep into the lungs 

and can directly enter the bloodstream. PM2.5 can then be transported 

to any organ in the body, and they have been implicated as a cause of 

heart disease among other ailments. From a human health standpoint, 

the composition of the particles may be even more important than their 

size. USGS scientists are currently measuring the amount of PM2.5

indoors and outdoors and analyzing that material in the laboratory to 

determine what chemical elements and compounds make up or are 

stuck to the particles.

Results.—This collaborative study of USGS scientists with 

Navajo students, residents, and health officials is providing valuable 

training for Navajo students in geographic information science (GIS), 

public health research methods, and geochemistry. Final results of 

the study will be provided to Tribal leaders, who can use the data in 

developing community practices that improve the public health effects 

of coal used for home heating in the Navajo Nation.

For more information, please contact:

Joseph E. Bunnell Linda V. Garcia

U.S. Geological Survey Diné College, Uranium Education Program

956 National Center 1228 Yucca Street, P.O. Box 580

12201 Sunrise Valley Drive Shiprock, New Mexico 87420

Reston, Virginia 20192 Navajo Nation

Telephone: (703) 648–6497 Telephone: (505) 368–3516

E-mail: jbunnell@usgs.gov E-mail: lvgarcia@dinecollege.edu

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Figure 1.  Typical emission plume from a powerplant near Shiprock, New Mexico, is horizontal during an inversion October 26, 2003; inversions are more common in

winter than summer. Photograph copyright (2003) Diane J. Schmidt, all rights reserved; used with permission.

Figure 2.  Representative

of stoves used in 25

percent of homes

surveyed, this stove

was not designed

to burn coal safely.

Photograph by Veronica

Francisco-Lapahie, Diné

College, 2004; used with

permission.