John R. Crellin, Laura H. Barr, and Danika Holm
Use of GIS in the Murray Smelter Public Health Assessment
Abstract
The Agency for Toxic Substances and Disease Registry (ATSDR) has begun using geographic information systems (GIS) technology as an integral tool during the development of public health assessments (PHAs). GIS is particularly useful for identifying human exposure pathways and obtaining demographic information. Health assessors used GIS in the development of the Murray Smelter National Priorities List (NPL) PHA. The abandoned lead smelter facility operated in Murray, Utah, from 1902 through 1949 and contaminated the area with arsenic, cadmium, and lead. Assessors contoured data for soil lead concentrations in the Murray site area and used those concentration contours to identify areas contaminated with soil lead concentrations of 500 to more than 5,000 parts per million (ppm). Assessors identified the number of individuals living in areas where lead levels were of possible health concern by clipping census data into those areas with lead levels above 500 ppm. The results supported the need for an exposure investigation of residents living on the site. Assessors also compared soil lead concentrations with drinking water well concentrations to decide whether there was a need to test certain wells to determine whether soil contaminants had moved into groundwater. GIS also provided a map comparison that allowed assessors to determine whether the area contaminated by past smelter emissions had been identified and sampled appropriately. Use at sites such as Murray Smelter has helped ATSDR determine that GIS is a very useful tool for defining the spatial relationship between site contaminants and the people living near a site.
ATSDR
The Agency for Toxic Substances and Disease Registry (ATSDR) an agency of the Public Health Service, U.S. Department of Health and Human Services, addresses potential public health problems associated with exposure to hazardous materials in the environment. Congress created ATSDR through the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980 (Superfund) and amended its responsibilities through the Superfund Amendments and Reauthorization Act of 1986. ATSDR's mission is to prevent exposure, adverse human health effects, and diminished quality of life associated with exposure to hazardous substances from waste sites, unplanned releases, and other sources of pollution in the environment. ATSDR pursues this mission by conducting public health assessments, exposure investigations, and other appropriate investigations of hazardous waste sites and toxic substance releases.
ATSDR uses geographic information systems (GIS) and a variety of spatial analysis techniques in support of its mission. The agency uses GIS to characterize the population around hazardous waste sites; display and analyze contaminant, health outcome, and other site-related data; and conduct exposure-dose reconstruction studies.
Why We Used GIS
In a public health assessment, ATSDR evaluates the possibility of impact or the actual impact on public health of a hazardous waste site or a toxic substance release. Based on that evaluation, public health actions are taken or recommended to reduce, eliminate, communicate, or further evaluate the possibility of health impact. The evaluation of public health impact in a public health assessment is based on available environmental, demographic, and health outcome data and community health concerns.
We used GIS to help with the analysis and display of environmental and demographic data in the Murray Smelter Public Health Assessment. Specifically, we used it to develop figures that display general site information, demographic data, and results of soil sampling and air modeling. We also used GIS to help evaluate the spatial relationship between possible private drinking water wells and arsenic-contaminated groundwater.
Site Description and History
Murray Smelter is an abandoned lead smeltering facility that the American Smelting and Refining Company (ASARCO) operated from 1902 through 1949. The smelting process produced large amounts of a dark, rock-like waste material called slag that contains high concentrations of heavy metals, such as lead. During and after the operation of the smelter, the slag was used widely as railroad ballast, road base, parking lot gravel, and fill. About 80,000 tons of the slag remain at the site. When the Murray Smelter was operating, it also released metals and other materials to the air, resulting in contamination of the soil around the site. We do not know the extent of this soil contamination, and determining its specific origin is difficult because nearly 100 smelters operated in the area in the late 1800s and early 1900s.
Features of Murray Smelter Site Area
Knowledge of the locations of schools, parks, bodies of water, smelter sites, and drinking water wells around a site is important in identifying possible places for exposure to site-related contaminants. We used roads, bodies of water, and rail coverages created from Tiger Files; a public wells coverage provided by Utah; and a smelter sites coverage from the U.S. Environmental Protection Agency (EPA) and input area schools and parks to depict those locations for the Murray Smelter site. A simple figure like this represents a major advance in the presentation of this information in a public health assessment. In the past, the general features around a site were described verbally. If a figure was included, it came from another document, usually one that reported results of environmental sampling. This combination frequently led to a poor description of the relationship between the site and geographic features around it.
Who Lives Around the Murray Smelter Site
The demographics of the area around a site are important to evaluating who may be affected by the site. The racial, ethnic, and age characteristics of the site area is also key in communicating with the people living around the site.
The use of ArcInfo� to evaluate the demographics of an area has greatly improved the quality and detail of population analysis and simplified presentation of the analysis. In the past, ATSDR used published census data, house counts, and similar information in public health assessments. Frequently, census information could be obtained only for the city the site was in, rather than for a specific area around the site. With ArcInfo, ATSDR is able to perform detailed site specific demographic analyses.
For the Murray site, we used five separate maps and a table to describe the population characteristics within one mile of the site, the population density, and the distribution of children five years or years, individuals 60 years or older, and women 15 - 44.
Presentation of Soil Contaminant Data
Assessors contoured data for soil lead concentrations in the Murray site area. We used those concentration contours to identify areas contaminated with soil lead concentrations of 500 to more than 5,000 parts per million (ppm). Assessors identified the number of individuals living in areas where lead levels were of possible health concern by clipping census data into those areas with lead levels above 500 ppm. The results supported the need for an exposure investigation of residents living on the site.
Evaluating Past Air Emissions From Murray Smelter
A major source of the soil arsenic and lead contamination was the use of smelter waste (slag) as fill and in highway and rail roadbeds. Another source was air emissions from the smelter when it was operating. Assessors investigated this source by displaying the results of modeling of the smelter emissions. They determined that those areas contaminated by past smelter emissions had been identified and appropriately sampled.
Displaying Possible Drinking Water Well Locations
New data on contaminants in area groundwater became available during development of the Murray Smelter Public Health Assessment. The arsenic levels in shallow groundwater (about 25 feet deep) at several locations were as high as 48 ppm, which is about 1,000 times greater than EPA's drinking water standard. Those levels were much greater than [levels in] previous samples. While public drinking water is available to all residences and businesses in the area, it is possible that some residents still use their rights to groundwater for drinking, irrigation, or stock watering. The only information available to EPA on where these possible wells were located indicated township, range, and section of the possible wells, but not street address. The ATSDR assessors created a map of the possible well locations by identifying them on a United States Geological Survey Quadrangle map and then digitizing those locations into an existing public well coverage. By displaying the well depths, EPA and ATSDR were able to identify wells that needed additional follow-up.
Conclusions
GIS helped health assessors significantly in their evaluation and display of information about the people around the Murray Smelter site, including demographic breakdown, and the population's relationship with site contaminants and possible exposure pathways. ArcInfo helped them to improve the quality and detail of population analysis and simplify its presentation in the Murray Public Health Assessment. We also used GIS to evaluate the distribution of soil contaminants, the role of smelter air emissions as a source of contamination, and whether arsenic in area groundwater may represent a health risk.
John R. Crellin and Laura H. Barr
Environmental Health Scientists, Agency for Toxic Substances and Disease Registry
Danika Holm
Geographic Information Specialist, Orkand Corporation
1600 Clifton Road, Mail Stop E-32
Atlanta, GA 30333
Telephone: (404) 639-0635
Fax: (404) 639-4507