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More than one-third of the United States is estimated to have high geologic radon potential. A high radon potential area is defined as an area in which the average indoor radon screening measurement is expected to be 4 pCi/L or greater. Geologic terrains of the United States with high radon potential include:1. Uraniferous metamorphosed sediments, volcanics, and granite intrusives that are highly deformed and often sheared. Shear zones in these rocks cause the highest indoor radon problems in the United States.2. Glacial deposits derived from uranium-bearing rocks and sediments and glacial lake deposits. Clay-rich tills and lake clays have high radon emanation because of high specific surface area and high permeability due to desiccation cracking when dry.3. Marine black shales. The majority of black shales are moderately uraniferous and have high emanation coefficients and high fracture permeability. 4. Soils derived from carbonate, especially in karstic terrain. Although most carbonates are low in uranium, the soils derived from them are very high in uranium and radium.5. Uraniferous fluvial, deltaic, marine, and lacustrine deposits. Much of the nation's reserve uranium ores are contained within these sedimentary deposits, which dominate the stratigraphy of the western U.S.

As part of the special interest series, Public Issues in Earth Science, published by the U.S. Geological Survey (USGS), this Circular describes the importance of the earth sciences in the investigation of environmental problems. The report focuses on geochemistry-the study of the amounts, distribution, and cycling of chemical elements in the Earth and atmosphere-and how this science helps to evaluate critical issues that relate to our fragile environment. The mission of the USGS is to provide geologic, topographic, and hydrologic information that contributes to the wise management of the Nation's natural resources and promotes the health, safety, and well-being of our people. Part of this task includes characterizing the Nation's geochemical environment and understanding the dynamic processes responsible for change in that environment. One of our greatest assets at the USGS is our long tradition of excellence in unbiased earthscience research. Part of that legacy is our commitment to supply the geochemical information necessary to confront urgent environmental challenges. Geochemistry provides information on the distribution of chemical elements to help us define and understand environmental problems. This information then allows us to provide answers for their resolution and possible remediation. This Circular presents an overview of geochemistry and its application to various case studies that illustrate the use of geochemistry in examining environmental problems. Some new and exciting areas of environmental geochemistry are discussed, involving r(.)ck/water, soil / water, and plant/ soil investigations. These investigations focus on many of our natural resources including minerals, soil, water, air, and vegetation and examine environmental concerns-such as acid precipitation, mine drainage, and sources of contamination-from a "systems" or "holistic" approach. As the primary Federal earth-science agency, the USGS leads in the collection, interpretation, and dissemination of earth-science information. This report helps to define one area in which the USGS is an active participant-the application of geochemistry to environmental concerns.

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Soil‐gas radon concentrations are controlled seasonally by factors of climate and pedology. In a swelling soil of the semiarid Western United States, soil‐gas radon concentrations at 100 cm depth increase in winter and spring due to increased emanation with higher soil moisture and the capping effect of surface water or ice. Increased soil moisture results from a combination of higher winter and spring precipitation and decreased insolation in fall and winter, lowering soil temperatures so that water infiltrates deeper and evaporates more slowly. Radon concentrations in soil drop markedly through the summer and fall. The increased insolation of spring and summer warms and dries the soil, limiting the amount of water that reaches 100 cm. As the soil dries, radon emanation decreases, and deep soil cracks develop. These cracks aid convective transport of soil gas, increase radon's flux into the atmosphere, and lower its concentration in soil gas. Probable controls on the distribution of uranium within the soil column include its downward leaching, its precipitation or adsorption onto B‐horizon clays, concretions, or cement, and the uranium content and mineralogy of the soil's granitic and gneissic precursors.

Concentrations of radon-222 in soil gas measured over about 1 yr at a monitoring site in Denver, Colorado, vary by as much as an order of magnitude seasonally and as much as severalfold in response to changes in weather. The primary weather factors that influence soil-gas radon concentrations are precipitation and barometric pressure. Soil characteristics are important in determining the magnitude and extent of the soil's response to weather changes. The soil at the study site is clay rich and develops desiccation cracks upon drying that increase the soil's permeability and enhance gas transport and removal of radon from the soil. A capping effect caused by frozen or unfrozen soil moisture is a primary mechanism for preventing radon loss to the atmosphere.

During July of 1995 and June of 1996, thirteen oilfield production sites in the Big Sinking Creek and Schumaker Ridge areas of northern Lee County in eastern Kentucky were visited to determine if produced waters and produced water solids had impacted sites in this area. Salt-scarred areas at oilfield production sites in this area were found to be relatively restricted in size, not very deeply eroded compared to sites in the midwest and southwest, and to have revegetated fairly quickly, probably because of the high rainfall and rapid flushing of salts from the root zone of plants. Saline groundwater still remains in the shallow subsurface beneath small barren areas at some sites. Areas of barren or sparse vegetation at some sites were found to be underlain by oil-saturated soil at shallow depths suggesting that the oil inhibits plant growth. Seepage of brine at one site has raised stream conductivities about 35-45 percent higher than values just upstream. Five sites have slightly anomalous concentrations of copper, lead, and zinc in soils containing tank sludge. Two samples from one site have high levels of radium (1770-3390 pCi/g), copper (165-195 ppm), and lead (200-245 ppm). These two samples have high concentrations of barium and strontium and low concentrations of zirconium suggesting that they are composed mostly of solids from tank sludge and that barite is present in high concentrations. The lead levels in these two samples are below action levels used for Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and Resource Conservation and Recovery Act (RCRA) sites (400 ppm). Radiometric surveys and radiochemical analyses determined that 9 of 13 sites have high radioactivity and radium in equipment, soils, and wetland sediments. Moderate levels occur at 2 sites and low levels occur at 2 sites. Radium-rich tank sludge, soils, and sediments are widespread at one site at the northern end of Lake Zachariah. Sites with high radioactivity in equipment or high radium activity in soils would be Naturally Occurring Radioactive Material (NORM)-contaminant sites under the least conservative state regulations proposed or in place. The State of Kentucky does not presently have NORM regulations. Dispersion of radium is occurring in two ways: 1) by the movement of radium-bearing solids (mostly barite), and 2) movement of dissolved radium in water. Iron oxyhydroxide precipitates are forming in the seep zone in a small wetland downslope from a tank battery at one site. These precipitates are radioactive and the iron oxyhydroxides are probably adsorbing dissolved radium from the ground water. Elsewhere at this same site, radium-bearing barite is accumulating at the edge of and probably within the wetland at the toe of the slope below a large area of radiumenriched soils. Figure IB-Location map showing 13 oilfield production sites visited during this study in the Big Sinking Creek and Schumaker Ridge areas of northern Lee County. X-study sites (in the text the sites are designated LC95-1 to LC95-13). ...