Radon concentration

Radon mitigation by SSD has been proven to be very effective, often decreasing indoor radon concentrations by 90% or more following mitigation. 

Builders should be aware that wells can be a potential problem. The only way to ensure that a well is not a potential radon source is to have the water tested after the well is drilled. It is not adequate to make a decision based on tests made in wells in the same area or even on adjoining building sites. A recent research project disclosed two homes with water radon concentrations of over 400,000 pCi/L, while the well used at a house between the two had waterborne radon concentrations of less than 1000 pCi/L.18 It should be understood that, when considering waterborne radon, the concentrations that concern us are much higher than when we are considering radon in the air. As a rule of thumb, between 8000 and 10,000 pCi/L of radon in the water will contribute 1 pCi/L of radon to the air. 

In theory, the application of radon barriers should be adequate to avoid elevated radon levels in houses. In practice, however, a backup radon mitigation system has been found essential for maintaining indoor radon concentrations below 4 pCi/L in most homes studied. In the recent radon-resistant residential construction projects conducted by U.S. EPA and/or private builders, several of the homes designed to be radon resistant have contained radon concentrations above 4 pCi/L. In each of those houses, a backup system consisting of an active (fan-assisted), or passive (wind-and-stack-effect-assisted), SSD system was installed at the time of construction. When mechanical barriers failed to adequately control radon, the soil depressurization methods were made operational. 

Of the study homes mentioned in the previous section, some passive systems seemed sufficient to lower the radon concentrations, while in all cases, active systems resulted in significantly lower concentrations. Table 31.1 summarizes the findings of these particular projects.9... 

As can be seen in Figure 31.13, active SSD systems consist chiefly of a pipe system and a fan. There are several other components that should be included in a good system, but are not necessary to make the system reduce radon concentrations. 

A passive system is much the same as an active system with the exception of the fan. A passive system relies only on stack and wind effects to produce the pressure field. As can be seen in Table 31.1, passive systems do not always reduce radon concentrations to acceptable levels, but careful design and installation may improve the effectiveness of a passive system. 

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 buildings with indoor radon concentrations greater than 4pCi/L, the majority of the radon is produced in the soil and enters the building through foundation openings. The radon gas found in soils is... 

Several studies have been attempted to make simple correlations between radon or radium concentrations in the soil and indoor radon concentrations.4344 No significant correlations were made between these variables. 

Florida Survey Soil Radon and Corresponding Indoor Radon Concentrations... 

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. 

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. 

The Clinton experience can be contrasted with radon observations in Boyertown, Pennsylvania, where buildings with radon concentrations over 500 times the U.S. EPA action level were found adjacent to buildings below the action level.48 Therefore, the presence of elevated-radon buildings in a neighborhood is at best only an indication that the probability of having a radon problem has increased. 

Radon dissolves into groundwater from rocks or soils. When the water is exposed to the atmosphere, some of the dissolved radon is released. As a rule of thumb, there is an increase of about 1 pCi/L in the air inside a house for every 10,000 pCi/L of radon in the household water.50 Higher radon levels have been observed in individual rooms when water is heated or agitated, such as during shower use.51 Builders should be aware that houses require groundwater as the house water supply could have a radon problem. The only way to be certain that the groundwater is not a potential radon source is to have the water from the well tested. Some states and private companies provide test kits for this purpose. It should also be noted that radon concentrations in water, like radon concentrations in the air, can vary significantly. 

A small percentage of the buildings in the United States with indoor radon concentrations in excess of 4 pCi/L can be attributed to building materials. Most of the building material problems have arisen from the use of known radium- or uranium-rich wastes such as aggregate in block or as backfill around houses. None of the houses studied in the U.S. EPA Radon Reduction Demonstration program have had any identifiable problem associated with radon from building materials. 

Traditionally, residential mechanical equipment has been treated as independent devices that have little or no impact on the rest of the building other than the obvious stated purpose. Bath fans, dryers, and kitchen ranges are assumed to exhaust moisture, lint, and cooking by-products, but to have no impact on the performance of chimneys. Instances have been reported that show that this is not the case in some houses where the fireplaces and other combustion appliances backdraft52 when one or more of the exhaust fans are in operation. Houses have been reported in which the operation of exhaust devices increases the radon concentration.53 Houses have been found in which pressure differences between different rooms of the house caused by HVAC distribution fans have increased energy costs,54 occupant discomfort,54,55 condensation of the building shell,55 and radon concentrations in parts of the houses.29,56 All of these effects are the result of air pressure relationships created by the interaction of equipment, indoor/outdoor temperature differences, wind velocity, and moisture and radon availability. 

Rugg, M., House Age, Substructure and heating system Relationships to indoor radon concentrations, in Proceedings of the 1988 Symposium on Radon and Radon Reduction Technology, Vol. 2, EPA-600/ 9-89-006b (NTIS PB89-167498), March 1989. 

Thus, Vanmarcke et al. (1987) shows that over the range of values they have measured, the dose is relatively constant per unit radon concentration according to the James-Birshall model (NEA, 1982). 

This inverse relationship between equilibrium factor and "unattached" fraction and their relationship to the resulting dose is important in considering how to most efficiently and effectively monitor for exposure. This inverse relationship suggests that it is sufficient to determine the radon concentration. However, it is not clear how precisely this relationship holds and if the dose models are sufficiently accurate to fully support the use of only radon measurements to estimate population exposure and dose. 

It is clear that some proper planning in the design phase of new houses can lead to less likelihood of indoor radon problems and make provision for lower cost modifications later to mitigate against such problems. The experience in Sweden is that houses with low radon concentrations can be constructed on high risk soils by proper design and construction practices. 

Shimo, M., T. Iida, and Y. Ikebe, Intercomparison of Different Instruments for Measurement of Radon Concentration in Air, this volume (1987). 

Yonehara, H., H. Kimura, M. Sakanoue, E. Iwata, S. Kobayashi, K. Fujimoto, T. Aoyama, and T. Sugahara, Improvement in the Measurement of Radon Concentrations by a Bare Track Detector, this volume (1987). 

Radon concentration in soil gas at depths well below the surface can be estimated from ... 

As noted in Table I, average surface radium concentrations appear to vary by about a factor of 20. This can also be seen from the distributions from the NARR data. Soil permeabilities, on the other hand, have much larger variations, and thus, in principle, may have a greater influence on the spatial variations in average indoor radon concentrations that have been observed. As with the case of surface radium concentrations, the spatial variability of air permeabilities of soils is an important element in developing a predictive capability. 

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