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TSSH Part 621

Soils and Cultural Resources

Background (621.00)

The NRCS policy for the consideration and protection of cultural resources during project and program planning and implementation is outlined in the General Manual, Title 420, Part 401Cultural ResourcesArchaeological and Historic Properties. This part applies to all NRCS financial and technical assistance activities and programs for which NRCS exercises control over the outcome, including actions that have the potential to affect historic properties (properties that are listed in or are eligible for listing in the National Register of Historic Places). This policy not only outlines responsibilities of NRCS regarding historic and cultural properties under the National Historic Preservation Act of 1966 (NHPA), implementing regulations for Section 106 of this law that provide step-by-step procedures, NRCS nationwide Programmatic Agreement, and other related authorities but also explains why Congress considered these resources important enough to pass the NHPA in 1966.

The nationwide Programmatic Agreement among the United States Department of Agriculture, Natural Resources Conservation Service, the Advisory Council on Historic Preservation, and the National Conference of State Historic Preservation Officers lists certain practice and program exemptions from compliance with Section 106, including basic soil survey.

The fundamental elements of the NRCS cultural resources policy involve protection and enhancement of cultural resources and historic properties in their original location to the fullest extent possible, avoidance of adverse effects when identified during program or practice planning, and mitigation of adverse effects that cannot be avoided.

NRCS operational procedures are provided in a companion directive to the General Manual policy chapter listed above. This directive, called the National Cultural Resources Procedures Handbook, is available in electronic directives at: Handbooks, Title 190, Part 601. This handbook provides procedural references and guidance regarding cultural resources compliance within NRCS. It provides direction on the roles and authorities of partners and consultants; the essential Federal responsibility of NRCS to conduct consultation with mandatory parties; and the steps to follow in order to successfully identify, evaluate, and protect cultural resources, including historic properties, in compliance with the National Historic Preservation Act (NHPA16 U.S.C. 470f, as amended through 2006 and several related authorities).

When addressing any issues related to identification, evaluation, avoidance, or treatment of cultural resources, always contact your NRCS State cultural resources specialist (CRS).

Issues specific to soil scientists (621.01)

National Cooperative Soil Survey program activities that involve no ground disturbance or are limited to small-scale field investigations, such as small shovel holes, auger holes, probe holes, and core holes, typically do not have the potential to impact cultural resources. Larger scale field investigations, however, such as soil investigation pits, may have the potential to affect historic properties.

NRCS soil scientists shall work with the NRCS cultural resources coordinators or specialists in their State to ensure that NRCS policy (including the exemptions in the nationwide Programmatic Agreement), Federal law, and regulations are followed in addressing potential impacts on historic and archeological properties. While soil scientists are well trained to identify historic properties in the field, particularly archeological remains, and often provide unique information on locations of such resources that they report to their State CRS or coordinator, the cultural resources specialists and coordinators are responsible for providing professional recommendations to State management and overseeing the cultural resources identification and consultation activities required by policy, regulation, and law.

The resource soil scientist can be helpful to the CRS when potential archeology sites are identified. The resource soil scientist should be able to identify signs of disturbance, such as buried surface layers and pedogenic discontinuities, that can indicate potential culturally important sites. In consultation with the archeologist or CRS, the resource soil scientist may also be able to help identify geologic or manmade features common to culturally important sites.

The resource soil scientist can work with the State CRS to create a map of soils that are not subject to or in need of investigation. For example, areas that are prone to ponding and/or flooding or are poorly or very poorly drained, including broad salt flats (except in the case of Hawaiian salt ponds), need not be investigated because they were seldom used for settlement. Examples of these areas include tidal marsh, areas of organic soils, and areas of very poorly drained mineral soils. These areas were typically used for hunting and fishing but not for settlement. The better drained adjacent areas were heavily used by Native Americans and Europeans.

The resource soil scientist can help the CRS in building a predictive map for locating potential archeological loci by applying soil-landscape relationships to predict settlement and land use. Such a map can be used to facilitate cultural resources compliance.

The resource soil scientist can also be of great assistance in determining whether a certain conservation activity would have an adverse impact on a cultural resource and, if so, what type of remedial action should be taken to limit the impact.

Geophysical tools for cultural resource assessments (621.02)

Geophysical methods can be used for cultural resource site identification and evaluation studies; they may also be used to detect archeological site intrusions or disturbance. NRCS staffs in several States and at the National Soil Survey Center (NSSC) have ground-penetrating radar (GPR) and electromagnetic induction (EMI) equipment, which can be used for high-intensity surveys of cultural resource sites. These geophysical methods have been used to identify areas of interest within sites, locate burials and forensic evidence, test hypotheses and confirm existing knowledge, and clear suspected cultural resource sites so that resources can be directed elsewhere. In many areas the efficacy of archeological investigations can be improved through the synergy of geophysical and traditional methods. Both EMI and GPR tools are available to NRCS staffs and can be used with little or no disturbance to sites. These tools are noninvasive and fast, and they produce large and very detailed datasets. As a consequence, these methods can be effectively used in sensitive areas, are cost effective, and provide comprehensive coverage of sites. The Soil Science Division can provide staff and equipment for this activity.

Compared with EMI, GPR provides higher levels of resolution; however, the effective use of GPR is highly site specific, and the reliability is directly affected by the chemistry and type of soils. Although EMI provides lower resolution than GPR, it can be used across a broader spectrum of soils and spatial scales. Experienced NRCS soil scientists and cultural resources specialists have developed instructions on optimum conditions for the effective use of GPR and EMI for cultural resources identification and evaluation studies. The following paragraphs provide more information.

Ground-penetrating radar involves the rapid, noninvasive detection of subsurface anomalies, which, based on additional supporting evidence and disturbance signatures, are identified as potential burials, archeological structures, or artifacts. The efficacy of GPR is highly site specific, and success is dependent on favorable soil and site conditions. Results vary according to the soils and soil properties. Soils having high electrical conductivity rapidly attenuate radar energy, restrict penetration depths, and severely limit the effectiveness of GPR. The electrical conductivity of soils increases as the content of water, clay, and soluble salts increases. In many soils, high rates of signal attenuation severely restrict penetration depths, reduce the resolution of subsurface features, and limit the suitability of GPR for archeological investigations. Ground-penetrating radar is highly suited to most applications in dry sands, but a thin, conductive soil horizon or layer can cause high rates of signal attenuation, which severely limit the suitability of GPR for a large number of cultural resource studies. In saline and sodic soils, where penetration depths are typically less than 10 inches, GPR is an inappropriate tool. In wet clays, where penetration depths are typically less than 3 feet, GPR has a very low potential for many cultural resource investigations.

Knowledge of soils and soil properties is important for the effective use of GPR. Most potential users of GPR are unable to foretell the relative suitability of soils for GPR at cultural resource sites. Knowledge of the suitability of soils helps to assess the appropriateness of using GPR and the likelihood of achieving acceptable penetration depths. Ground-penetrating radar soil suitability maps have been prepared based on soil attribute data contained in the USDA-NRCS Soil Survey Geographic (SSURGO) database. These maps are available here. These maps should be consulted before requesting GPR field assistance.

Electromagnetic induction measures the bulk apparent conductivity (ECa) of soil materials. Advantages of EMI include its portability, speed of operation, flexible observation depths, and moderate resolution of subsurface features. Electromagnetic induction provides, in a relatively short time, very large numbers of observations so that sites can be comprehensively covered. Maps prepared from properly interpreted EMI data provide the basis for assessing site conditions.

Electromagnetic induction uses electromagnetic energy to measure the apparent conductivity (ECa) of earthen materials. Apparent conductivity is the weighted, average conductivity for a column of earthen materials. Variations in ECa are produced by changes in the electrical conductivity of earthen materials. Electrical conductivity is influenced by the volumetric water content, type and concentration of ions in solution, temperature and phase of the soil water, and amount and type of clays in the soil matrix. In general, the ECa of earthen materials will increase with increases in content of soluble salt, water, and/or clay. In any soil-landscape, variations in one or more of these factors will dominate the EMI response.

Electromagnetic induction measures vertical and lateral variations in ECa. Values of ECa are seldom diagnostic in themselves; however, lateral and vertical variations in ECa can be used to infer changes in soils and the presence of buried cultural features. Interpretations are based on the identification of spatial patterns within datasets. Computer simulations are normally used to assist in making interpretations.

Electromagnetic induction has been used as a fast, easy reconnaissance tool in cultural resource investigations. This tool has been used to map buried tombs, walls, structures, chambers, borrow pits, middens, and mounds. In these field investigations, anomalous spatial ECa patterns were associated with and used to identify potential cultural resource features.

In some instances, through a hierarchical approach, EMI and GPR methods have been combined to support cultural resource investigations. In this approach, EMI provides a rapid, lower resolution overview of a larger area. This step allows the use of the higher resolution GPR to be focused onto smaller target areas. As complementary methods, these geophysical tools can provide a more complete evaluation of potential buried cultural resource features.

Both EMI and GPR tools are available to NRCS staffs. NRCS staffs in several States have GPR and/or EMI instruments and operators. In States where these geophysical tools are not available, requests can be made to the National Soil Survey Center for geophysical assistance.

Additional information (621.03)

More information on cultural resources is available here.

For training information, go here