U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS-015-03

March 2003 Printed on recycled paper

Printed on recycled paper

The most requested data from 

the U.S. Geological Survey’s (USGS) 

National Geochemical Database is a set 

of 1,323 soil samples. Why? Consider the 

following examples:

Example 1—Imagine for a moment

that you are employed by an environmental regulatory agency of either the Federal

or a State Government. Your assignment

is to establish a “remediation value” for

arsenic in soil at a contaminated site

where a wood preservative facility once

operated. Current arsenic values in soils

at the facility range from 15 to 95 ppm

and you must decide the concentration of

arsenic that is acceptable after remediation efforts are completed. Scientists refer

to the natural or native concentration of

an element in soils as the “background

concentration.” Given the fact that arsenic

occurs naturally in all soils, how would you determine the background

concentration of arsenic in soils for this particular area?

Example 2—Your environmental consulting firm has been assigned 

to work with a team of specialists conducting a risk-based assessment of 

land contaminated with lead, zinc, and cadmium from a metal foundry. 

The assessment would determine the likelihood of adverse health or 

ecological effects caused by the contaminants. Again, an important part 

of this determination is, “What is the background concentration of these 

elements in the soil?”

What data are available for persons responsible for making the 

determinations of background concentrations for soils contaminated with 

potentially toxic metals? The most-often-quoted data set for background 

concentrations of metals and other trace elements in soil of the conterminous United States consists of only 1,323 samples collected during the 

1960s and 1970s by the U.S. Geological Survey (Boerngen and Shacklette, 1981; Shacklette and Boerngen, 1984). (There is a similar data set 

for Alaska (Gough and others, 1984, 1988)). Samples for the “Shacklette 

data” were collected from a depth of about 1 ft, primarily from noncultivated fields having native vegetation, and samples were analyzed for 

more than 40 elements. Data in this study represent about one sample 

per 2,300 mi2, indicating that very few samples were collected in each 

State. For example, the State of Arizona is covered by only 47 samples, 

and Pennsylvania has only 16. Despite the low number of samples, this 

data set is still being used on a regular basis to determine background 

concentrations of metals in soil to aid in remediation or risk-based 

assessments of contaminated land.

The only other national-scale soil geochemical data set for the United 

States was generated by the Natural Resources Conservation Service 

(NRCS), formerly the Soil Conservation Service (Holmgren and others, 

1993). This data set consists of 3,045 samples of agricultural soil collected from major crop-producing areas of the conterminous United 

A Proposal for Upgrading the National-Scale Soil

Geochemical Database for the United States

States. The primary purpose of this study was to assess background levels of lead and cadmium in major food crops and in 

soils on which these crops grow. Thus, the samples were only analyzed for five metals—lead, cadmium, copper, zinc, and nickel.

The Shacklette data set allows us to produce geochemical 

maps for specific elements, such as that shown on figure 1 for 

arsenic (Gustavsson and others, 2001). A map produced from such 

sparse data points obviously carries a large degree of uncertainty 

with it and does not have the resolution needed to answer many of 

the questions raised by land-management and regulatory agencies, 

earth scientists, and soil scientists. An example of the poor data 

set resolution is illustrated for Pennsylvania (fig. 2). The State is 

divided into major soil taxonomic units referred to as Suborders 

(Soil Survey Staff, 1999). Suborders group similar soil types in 

any region. The dots represent the sample points from the Shacklette data set. The few sample points shown on figure 2 illustrate 

that this data set would be inadequate for someone who must 

define the arsenic content of a given soil. At this time, no data set 

exists that will allow us to make these kinds of determinations.

The USGS and NRCS are currently studying the feasibility 

of a national-scale soil geochemical survey that will increase the 

sample density of the Shacklette data set by at least a factor of 10. 

This project, called Geochemical Landscapes, began in October 

2002. The first 3 years will be devoted to determining how such a 

survey should be conducted. Therefore, we are actively soliciting 

input from potential customers of the new data. Interested members of the private sector, government, or academic communities 

Figure 1. Map of arsenic distribution in soils and other surficial materials 

of the conterminous United States based on 1,323 sample localities as 

represented by the black dots.
Pennsylvania are asked to provide input on a design for sampling the nation, establishing sampling and analytical protocols, and the types of products 

that will be most useful. For further information about this project or 

about available data sets, please contact any of the following:

David B. Smith

U.S. Geological Survey

Box 25046, Mail Stop 973

Denver Federal Center

Denver, CO 80225-0046

303-236-1849

dsmith@usgs.gov

Martin B. Goldhaber

U.S. Geological Survey

Box 25046, Mail Stop 973

Denver Federal Center

Denver, CO 80225-0046

303-236-1521

mgold@usgs.gov

Michael A. Wilson

Natural Resources Conservation Service

Federal Building, Room 152

Mail Stop 41

100 Centennial Mall North

Lincoln, NE 68508-3866

402-437-4134

mike.wilson@nssc.nrcs.usda.gov

Rebecca Burt

Natural Resources Conservation Service

Federal Building, Room 152

Mail Stop 41

100 Centennial Mall North

Lincoln, NE 68508-3866

402-437-5133

rebecca.burt@nssc.nrcs.usda.gov

References Cited

Boerngen, J.G., and Shacklette, H.T., 1981, Chemical analyses of soils 

and other surficial materials of the conterminous United States: 

U.S. Geological Survey Open-File Report 81-197, 143 p.

Gough, L.P., Peard, J.L., Severson, R.C., Shacklette, H.T., Tompkins, 

M.L., Stewart, K.C., and Briggs, P.H., 1984, Chemical analyses 

of soils and other surficial materials, Alaska: U.S. Geological 

Survey Open-File Report 84-423, 77 p.

Gough, L.P., Severson, R.C., and Shacklette, H.T., 1988, Element 

concentrations in soils and other surficial materials of Alaska: 

U.S. Geological Survey Professional Paper 1458, 53 p.

Gustavsson, N., Bølviken, B., Smith. D.B., and Severson, R.C., 

2001, Geochemical landscapes of the conterminous United 

States—New map presentations for 22 elements: U.S. 

Geological Survey Professional Paper 1648, 38 p. [http://

geology.cr.usgs.gov/pub/ppapers/p1648/].

Holmgren, G.G.S, Meyer, M.W., Chaney, R.L., and Daniels, R.B., 1993, 

Cadmium, lead, zinc, copper, and nickel in agricultural soils of 

the United States of America: Journal of Environmental Quality, 

v. 22, p. 335–348.

Shacklette, H.T., and Boerngen, J.G., 1984, Element concentrations in 

soils and other surficial materials of the conterminous United 

States: U.S. Geological Survey Professional Paper 1270, 105 p.

Soil Survey Staff, 1999, Soil taxonomy: A basic system of soil 

classification for making and interpreting soil surveys: 

Washington, D.C., U.S. Government Printing Office, U.S. 

Department of Agriculture–Soil Conservation Service 

Agriculture Handbook 436, 2nd ed. 

Figure 2. Map of Pennsylvania showing soil Suborders and sampling sites from Shacklette and

Boerngen (1984).