Soil is often nothing more than the dirt we kick up from our feet, but the intricate ground medium is a dynamic natural body containing minerals, water, gases, organic matter, and microorganisms. Its sedimentary, effluent, gaseous, and biological parts find a worldly range of variability in terms of composition and characteristics. In fact, there are almost 20,000 soils in the United States alone.
Formed through an assortment of means, and depending on the specific conceptual model of soil genesis, soil components can be shaped continuously by the deposition of parent materials, alluvial origins, decomposing organisms, climatic forces, relief (the landscape position), and the passage of time. These sources of soil formation are part of the surrounding ecosystem, in which the soil plays an active role.
These processes function smoothly in the natural world. However, where nature and society converge (for soil, this is practically everywhere), there can be issues with comfortable integration between the two. Often, we see society dominate these conflicts, as things like environmental degradation persist.
However, with enclosed indoor environments like homes and buildings, soil gases and leak into dwellings and public places. These gases, invisible and odorless, can be severe health hazards, and they may even lead to death.
The Dangers of Radon Gas
The most pervasive and significant soil gas is radon. Uranium is found in almost all rocks, generally in the limited quantities of 1-3 parts per million (ppm). While uranium’s harm is relatively limited due to its solid state, radon—a daughter product formed through the radioactive decay of uranium—is gaseous, therefore having greater mobility. It can easily escape through fractures and opening in rocks.
Leaking radon can find its way into buildings and homes. Exposure to radon at any level may carry some kind of risk. The EPA has set an action level of 4 picocuries per liter (pCi/L), meaning that any higher concentration of radon should be reduced to limit one’s exposure to the gas.
Throughout the United States, radon concentrations persist at relatively alarming levels. In fact, according to this map of EPA Radon Zones, much of the U.S. has predicted average indoor radon screening levels greater than 4 pCi/L.
Correlating with these concentrations, radon is the second leading cause of lung cancer in the general population and the leading cause among nonsmokers. In all, it claims 21,000 U.S. lung cancer deaths each year.
Other Soil Gases
Additional soil gases include methane, nitrogen, carbon dioxide, and oxygen, as well as vapor-forming chemicals—volatile organic compounds (VOCs), semivolatile organic compounds (like naphthalene), elemental mercury, and some pesticides. While these are, for the most part, safe in small doses, overexposure can lead to detrimental health effects, and, in certain instances, near-term safety hazards, such as explosions.
Mitigation for Radon and Soil Gas
The solution for dealing with these gaseous home threats is mitigation. The U.S. government first pushed for reducing citizen risk of lung cancer deriving from indoor radon concentrations in 1988 with the Radon Abatement Act. In the 1990s, the EPA advised that all schools test for radon and set its 4 pCi/L action level.
The EPA also has an operating procedure for soil gas sampling, something that also is covered by ASTM D7648/D7648M-18 and other international standards for soil gas sampling.
ANSI/AARST CC-1000-2018: Soil Gas Control Systems in New Construction of Buildings holds a focus particular to radon and other soil gases in indoor environments, detailing prescriptive guidelines for the construction of buildings in order to reduce occupant exposure to radon and other hazardous soil gases.
ANSI/AARST CC-1000-2018 is multipurposed, as it assures that buildings are capable of mitigating soil gas entry, provides a means for qualified personnel to inspect and evaluate installed mitigation systems, and provides practices that may be recommended or adopted for use as requirements by a contract or local jurisdiction. It covers plenums, pressure field evaluations, soil gas exhaust vent pipes, exhaust locations, the completion of systems, and HVAC evaluations. It is not applicable for one or two family dwellings.
In the 2018 edition of ANSI/AARST CC-1000, Section 9 on Exhaust Locations was rewritten as part of harmonization efforts with recent AARST publications.
The American Association of Radon Scientists and Technologists (AARST) is an ANSI-accredited standards developing organization dedicated to radon measurement, radon mitigation, and the transfer of radon information that benefits its members, customers, and the general public.
Additional standards by AARST detail protocols for conducting radon measurement in various dwellings and public buildings, such as schools. In general, there are short-term tests, which stay in a home or building for 2 to 90 days, and long-term tests, which remain for longer than 90 days.
If radon is found, there are numerous mitigation methods, which are also addressed by the standards. Furthermore, ASTM E2121-21 covers radon mitigation systems in existing low-rise residential buildings. Common radon mitigation systems or methods consist of soil suction, sealing, room pressurization, heat recovery ventilators, and increasing natural ventilation.
Radon is a naturally occurring radioactive gas and comes from the natural breakdown (radioactive decay) of uranium