Soil radon measurements

It is clear from Table 31.3 that soil radon measurements that varied over an order of magnitude produced significantly less than a factor of 2 difference in the indoor radon levels. Predictions of radon potential based on soil radon measurements would be highly suspect based on these data. 

The major drawback to using the Florida study to support the correlation between indoor and soil measurements was that the indoor measurements were obtained from 3-day closed-house charcoal measurements, and soil radon was obtained from 1-month alpha track measurements buried 1 ft beneath the soil surface. Comparisons of charcoal and alpha track data are generally not recommended since they are quite different measurement techniques, and represent radon levels over different time periods. However, the study was subjected to numerous quality control checks including deployment of alpha track detectors in 10% of the houses to obtain a check on indoor air measurements made by charcoal canisters. In spite of the measurement drawbacks, the study indicates that soil radon measurements taken alone are not a dependable predictor of potential indoor radon concentration. 

Using the permeability and soil radon measurements for the gravel soils in New York State to compare with the Swedish guidelines would result in a recommendation for radon-resistant techniques to be used in a large fraction of new houses in all the areas listed, except Long Island. 

The major difference between these data and the Florida survey data in Table 31.3 is that this portion of the NEWHEP data was collected from newly constructed houses where passive radon-resistant construction features were being tested. There are no data on control houses in the same area that did not have those built-in features, making it difficult to compare soil radon measurements with indoor radon concentrations. It appears, however, that passive-only building techniques do not consistently result in indoor radon levels below 4 pCi/L. 

Aside from the difficulty in correlating soil radon measurements with indoor radon measurements, various field studies have also shown that obtaining a representative soil gas measurement is difficult. Soil gas radon measurements were made with a permeameter in seven central Florida houses.42... 

Indoor Radon and Soil Radon Measurements in Colorado and Michigan... 

Radon measurements in the interstitial soil and bedrock pores. 

In addition to the house described above, air permeability of soils was measured at several other house sites in the Spokane, WA, vicinity as part of a study of remedial measures for radon (Turk fit al.1986). Soil probes 1-cm-diameter and ranging between 1 and 1.5 m long were placed in the soil at two locations... 

In an early study by Schery and Gaeddert (1982), an accumulator device was used to measure the effect of atmospheric pressure variations on the flux of Radon (222Rn), an inert radioactive element with a half-life of 3.8 days, from the soil. Fluxes measured by the accumulator were compared with predictions for flow-free diffusion from a model developed by Clements and Wilkening (1974), which applies Fick s law. A mean 222Rn-flux enhancement of about 10%, with a high value of 20%, due to cyclic atmospheric pressure variations was observed. However, the device s effectiveness was limited by back diffusion from the accumulator to the subsurface, leading the authors to view the flux values as semi-quantitative. 

As stated in Section 5.2.1, soil is the primary source of radon. As such, radon is not released to soil but is the result of radioactive decay of radium-226 within the soil. The radon concentration in the soil is a function of the radium concentration, the soil moisture content, the soil particle size, and the rate of exchange of air with the atmosphere (Hopke 1987). Hopke (1987) states that normal soil-gas radon measurements are in the range of 270 to 675 pCi radon-222/L of air (10,000 to 25,000 Bq/m However, levels exceeding 10,000 pCi radon-222/L of air (370,000 Bq/m ) have been documented. 

Only two soil-gas measurements for United States locations were found in the literature one from Spokane, Washington, with soil-gas radon from 189 to 1,000 pCi radon-222/L of air (7,000 to... 

Environmental Fate. Information is available on the environmental fate of radon in air and water and on the transport of radon in environmental media. Factors which affect the partitioning of radon from soil or water to air have been identified. Flowever, rates of flux from one media to another are rarely reported. The emanation rate of radon from soil is uncertain. Additional information on the behavior of radon at the soil-air interface, as well as soil-gas measurements, would facilitate a better understanding of the emanation rate of radon from soil. Movement of radon into and within homes and the influence of meteorological conditions on this movement should be investigated. Study of radon movement would enhance understanding of potential indoor exposures. Transformation of radon has been adequately characterized. There is limited information on the uptake of radon by plants. Additional research of this phenomenon is needed in order to determine the effects of exposures which might be incurred from ingestion of food. 

Indoor radon measurements obtained for homes in North Virginia, USA, revealed that existing high or low median indoor radon levels in each house persist through four seasons [59], however, attempts to compare between the soil radon outside and the soil... 

Radon Measurement in Water, Soil, and Other Solid Matrices... 

These measurements of soil radon by detectors in the ground are of interest when long-term... 

Although radon does enter. snow from frozen soil, it does not emanate appreciably from. solid rock. A scintillometer should be used to complement any radon-measuring technique and especially in areas of outcrop. Czarnecki and co-workers compared radon-measuring devices at 100 locations over a 1.5-km area in the Red Desert of. south-central Wyoming. A prototype microprocessor-controlled emanometer was found to be more reliable with a 13% coefficient of variation (standard deviation/mean) than an established emanometer with a coefficient of 31%. 

In alpha-track detectors the carbonate etch method was found to be 20 times more sensitive than the nitrate track etch. The instruments that measured instantaneous radon did not correlate well with the pos.sibly more reliable methods based on a 30-day sample time. All the radon-measuring techniques correlated poorly with the radiometric equivalent uranium in the soil, which led to the conclusion that the radon was coming from below the surface. 

In summary, it is worthwhile to continue the installation of a vapor barrier that serves as the added valid function of moisture barrier. More comprehensive installation measures and more expensive materials may be merited in areas where the radon source is strong because of either high radon concentrations or high soil gas how rates. 

In addition to the above measurements, indexes using soil concentrations in combination with permeability measurements have been suggested by some researchers.4142 As elaborated on later in this section, these methods have been successful in establishing relationships between some of the site measurements and indexes, and indoor radon concentrations for specific areas and regions. 

In U.S. EPA Office of Radiation Program s New House Evaluation Program (NEWHEP), two builders in the Denver area, two in Colorado Springs, and one in Southfield, Michigan, installed various radon-resistant features in houses during construction. A sampling of subsequent measurements of indoor radon, adjacent soil gas radon, and soil radium content is summarized in Table 31.6.36... 

Factors influencing the production and migration of radon in soils have been examined, and various sources of geographic data have been discussed. Two significant soil characteristics include air permeability and, less importantly, radium concentration. While there are, at present, few opportunities to compare the larger-scale data with on-site field measurements, those comparisons that have been made for both surface radium concentrations and air permeability of soils show a reasonable correspondence. Further comparisons between the aerial radiometric data and surface measurements are needed. Additional work and experience with SCS information on soils will improve the confidence in the permeability estimates, as will comparisons between the estimated permeabilities and actual air permeability measurements performed in the field. 

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